Faculty of Engineering, Architecture and Information Technology

THE UNIVERSITY OF QUEENSLAND

Precision grinding of semiconductor materials

Student Name: Juien Yi Ng

Course Code: MECH4501

Supervisor: Professor Han Huang

Submission date: 8 June 2020

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Acknowledgement

I would not be able to complete this thesis without the support and help of the individua ls.

I show my appreciation and deeply thankful for the guidance of my supervisor, Professor Han

Huang who have involved me in the area of grinding technology and the knowledge and experience

shared by him are invaluable.

Many thanks to Xuliang Li for his assistance in the experiments throughout the whole

process of finishing my thesis. I am really thankful to have my parents and siblings to show their

warm encouragement and positive mind set given to me throughout the whole process of finishing

the thesis. In addition, I would like to show appreciation to my friends who have always been

giving me moral support and wise counsel I value and appreciate immeasurably: Chok Jia Qi, Toh

Jie Guang, Too Lik Jun, Wong Juin Liang, and Tui Yik Wei who unconditionally gave me support

throughout the whole process of thesis.

To every one of you, I thank you. This thesis would not been complete without the help of

all of your presence and contributions.

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Abstract

Nowadays, the semiconductor materials such as Silicon (Si) and Gallium Arsenide (GaAs) are

widely used in electronic device. Most of the semiconductor materials are difficult to machine

owing to their hard hardness and brittleness, and therefore, many efforts were made to develop to

machining technics especially the grinding process. The aim of this project is to use the high speed

grinding machine to grind the semiconductor materials to obtain a good surface quality and to

promote ductile flow without brittle fracture. High speed grinding are well known as increasing the

wheel speed to achieve a good surface finish. In this experiment the effects of wheel speed, depth

of cut, feed rate, and types of wheel were conducted to measure the grinding force and surface

roughness of the material. By using the resin bond diamond wheel with different grit size of SD

800 and SD 3000, it shows that the grinding force performed by SD 800 with larger grit size have

larger force compared to the wheel type of SD 3000. In contrast, wheel type of SD 3000 performed

a better surface roughness compared to wheel type of SD 800. With the increase of wheel speed,

the results of the surface roughness and surface quality improved and the grinding force was

decreased. From this experiment, it is concluded that the high speed grinding performance would

be better to achieve a good surface quality and result in the ductile removal mode. Last but not

least, the final results will be observed from the confocal microscope to determine the surface

morphology.

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Table of Content

Acknowledgement i

Abstract ii

1.0 Introduction 1

1.1 Objectives 2

2.0 Literature Review 2

2.1 Semiconductor 2

2.2 History of grinding 5

2.2.1 Types of grinding 5

2.3 Grinding wheel characteristics 7

2.3.1 Wear of grinding wheel 9

2.3.2 Dressing in grinding wheel 10

2.4 Material removal mechanism in grinding 12

2.4.1 Ductile and brittle transition 14

2.4.2 Maximum undeformed chip thickness 15

2.4.3 High speed grinding 17

2.5 Summary of literature review 20

3.0 Methodology 22

4.0 Results and discussions 28

4.1 Effect of depth of cut 28

4.2 Effect of feed rate 29

4.3 Effect of wheel speed 31

4.4 Effect of types of wheel 33

4.5 Effect of materials 35

4.6 Surface morphology 37

4.7 Calculations of maximum chip thickness and critical depth of cut 40

5.0 Conclusion 41

6.0 Future Work 43

7.0 References 44

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List of Figure Figure 1: Machining process of semiconductor 4

Figure 2-1: Different types of grinding 6

Figure 2-2: Stationary tools dressing 11

Figure 2-3: Rotary tools dressing 11

Figure 2-4: Material removal process 13

Figure 2-5: Ductile and brittle grinding 15

Figure 2-6: Theoretical cutting path of an individual grain 16

Figure 2-7: Results of grinding force to depth of cut and feed rates 18

Figure 2-8:Graph of forces and the maximum undeformed chip thickness 18

Figure 2-9: Results of surface roughness to depth of cut and feed rate 19

Figure 3-1: CNC Ultra Precision form grinding machine 22

Figure 3-2: Wheel types of (a) and (b) are SD 800 and SD 3000 respectively 23

Figure 3-3: Diamond Pen 23

Figure 3-4: Balancing kit 25

Figure 3-5: Vertical rotary wheel dresser 26

Figure 3-6: Dynamometer 27

Figure 3-7: Confocal Microscope 27

Figure 4-1: Effect of depth of cut on grinding force on silicon. Grinding was performed with the wheel speed of 40m/s, wheel type of SD 800, feed rate of 500mm/min, and different depth of cuts of 5um, 10um, and 15um.

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Figure 4-2: Effect of feed rate on grinding force on silicon. Grinding was performed with the wheel speed of 60m/s, wheel type of SD 3000, depth of cut of 10um, with different

feed rates of 250mm/min, 500mm/min, and 1000mm/min.

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Figure 4-3: Effect of feed rates on surface roughness on silicon. Grinding was performed with the wheel speed of 60m/s, wheel type of SD 3000, depth of cut of 10um, with

different feed rates of 250mm/min, 500mm/min, and 1000mm/min.

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Figure 4-4: Effect of wheel speed on grinding force on silicon. Grinding was performed

with the wheel type of SD 800, feed rate of 500mm/min, depth of cut of 10um, with different wheel speed of 40m/s, 60m/s, and 80m/s.

31

v

Figure 4-5: Effect of wheel speed on surface roughness on silicon. Grinding was performed with the wheel type of SD 800, feed rate of 500mm/min, with different depth of cuts of 5um, 10um, and 15um, and different wheel speed of 40m/s, 60m/s, and 80m/s.

32

Figure 4-6: Effect of different types of wheel on grinding force on silicon. Grinding was performed with the wheel speed of 60m/s, feed rate of 500mm/min, depth of cut of 10um,

and wheel types of SD 800 and SD 3000.

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Figure 4-7: Effect of depth of cut on surface roughness of silicon. Grinding was performed with the wheel speed of 60m/s, feed rate of 500mm/min, wheel types of SD

800 and SD 3000, and with different depth of cuts of 5um, 10um, and 15um.

34

Figure 4-8: Effect of depth of cut on grinding force on silicon. Grinding was performed

with the wheel speed of 60m/s, wheel type of SD 3000, feed rate of 500mm/min, with different depth of cuts of 5um, 10um, and 15um.

35

Figure 4-9: Effect of depth of cut on grinding force on Gallium Arsenide. Grinding was

performed with the wheel speed of 60m/s, wheel type of SD 3000, feed rate of 500mm/min, with different depth of cuts of 5um, 10um, and 15um.

35

Figure 4-10: Effect of depth of cut on surface roughness on silicon and gallium arsenide. Grinding was performed with the wheel speed of 60m/s, wheel type of SD 3000, feed rate of 500mm/min, with different depth of cuts of 5um, 10um, and 15um.

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Figure 4-11: Surface morphology – Effect of wheel speed on silicon. Grinding was performed with wheel type of SD 800, feed rate of 500mm/min, depth of cut of 15um,

with different wheel speed (a), (b), and (c) of 40m/s, 60m/s, and 80m/s respectively.

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Figure 4-12: Surface morphology – Effect of types of wheel on silicon. Grinding was performed with the wheel speed of 60m/s, feed rate of 500mm/min, depth of cut of 15um,

with the different wheel types (a) and (b) of SD 800 and SD 3000 respectively.

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Figure 4-13: Surface morphology – Effect of feed rate on silicon. Grinding was performed

with wheel type of SD 3000, wheel speed of 60m/s, depth of cut of 10um, with different feed rates (a), (b), and (c) of 250mm/min, 500mm/min, and 1000mm/min respectively.

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List of table Table 1: Experiment parameter 22

Table 2: Characteristics of grinding machine 23

Table 3: Calculation of critical depth of cut 40

Table 4: Calculation of maximum undeformed chip thickness 40

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1.0 Introduction

Semiconductor have been a very useful material for electrical industries and it is widely

used in the world as an electrical component. Both of the semiconductor silicon substrates (Si) and

gallium arsenide (GaAs) are one of the best semiconductor used to operate the electrical component.

The semiconductor have to gone through a machining process to achieve the final product of the

processes semiconductor material. The semiconductor are expected to achieve ductile removal

mode to able to obtain a good surface quality. However, Silicon has a relatively hard brittle material

unless they are machine in ductile mode on precision grinding machine.

There are several grinding machine types and each types of grinder has their own

characteristics. The grinding machine consist of a few important mechanism in order to operate the

grinding machine. Grinding wheel is one of the most essential mechanism in the grinding machine ,

the material of the grinding wheel is very important which it will affect the surface quality of the

material. The grinding wheel must be dressed before conducting the grinding operations. The

purpose of dressing the grinding wheel is to prevent the wheel from wear and it would affect the

grinding results. Furthermore, the material removal mechanism play an important role in the

grinding process. In the material removal process, the depth of cut, chip thickness, and the materials

transitions might occur.

In the process of grinding, there are three stages of process which are the sliding, ploughing,

and cutting that are involved in the material removal mechanism. This three processes are used to

achieve ductile removal mode and a good surface quality. Moreover, by depending on the grinding

force, the depth of cut and feed rates could be determined. Last but not least, the whole grinding

machine mechanism are very essential and each of the mechanism have done a huge contributed

to the grinding process.

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1.1 Objectives

The objective of this thesis project is to familiarise with the grinding machine and to examine the

data collected by grinding semiconductors. The objectives of this thesis project are evaluated as

below:

To utilise high speed grinding to achieve ductile removal mode and high surface finish from

the semiconductor materials.

To understanding the material removal mechanism of the semiconductor in grinding though

the surface analysis.

To understand the effect of depth of cuts, wheel speed, types of wheel, and feed rate towards

the semiconductors.

2.0 Literature review

2.1 Semiconductor

Semiconductors are widely used in the electrical industries, people often used it as a

conductor or an insulator in the electrical device. In a semiconductor the mobility of the carriers is

affected by the temperature and the presence of charge impurities. At lower temperature the

mobility of carriers is weaken which results in carrier interaction with charge impurities, and it

react as an insulator(Green, 2019). At higher temperature the mobility of carriers is increase due to

electron escaping from the covalent bond. This results in higher amount of free electron flowing in

the semiconductor which increases the conduction in semiconductors, which this act as a conductor.

Semiconductors weren’t as great as metals, as the temperature rises the resistance got weaker which

the metal act opposite of it. A wafers with good reproduction quality will automatically leads to

produce a good yielding component and achieve a better device performance (Landry & Barron,

1993). Nowadays, semiconductor are overly used as an electrical component such as radio, mobile

phones, and etc.

There are several types of semiconductors, Silicon (Si) and gallium arsenide (GaAs) are the

two most essential semiconductors (Sze, 2007). Silicon is an indispensable conductors where it has

a relatively low defects, and it has become the most valuable component for the electronic devices.

According to (Shu, 2015), the advantages of silicon are: (i) The silicate and silica were made use

of 90% of the earth’s crust, as this is an essential product to produce silicon wafer, which happen

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to produce the silicon wafer in a low cost. (ii) Rigidity and thermal conductivity are excellent. (iii)

A massive and highly purified wafer were easily grown and obtained.

Nowadays silicon has been widely used in the electronic industry not only because of its

good electronic properties but also the great mechanical properties (Petersen, 1982). When the

strain increases, the stress associated with the strain increases first mostly due to elastic

deformation, then approaches a limit called the upper yield stress and gradually decreases to the

lower yield stress. Eventually, the stress associated with the strain increases again fairly gradually

due to the enhancement of internal stresses induced, in fact, by the dislocation field (Petukhov,

2004). It was proven from (H. Zhang, López‐Honorato, Javed, Shapiro, & Xiao, 2012) that the

micro-crack with stress induction tends to introduce the fracture behavior which likely to have high

fracture toughness to the coating on silicon. In fact, silicon is well known to be strongly dependent

to the size of the material at the scale of micrometer and nanometer. From the statement above

shows that fracture toughness are not affected by the size despite in the scale of nanometer, while

on the other hand the silicon’s tensile strength are strongly affected by it (Sumigawa, Ashida,

Tanaka, Sanada, & Kitamura, 2015).

However, as both of the silicon and gallium arsenide are brittle material and not only by the

condition of a clean, reduced surface defect and the devise geometries being reduced, it must also

go through a complex process to produce a material with damage free, flat, and clean surfaces

(Landry & Barron, 1993). As compared to silicon, gallium arsenide have a great electron mobility

and high saturated electron. Due to the wide band gap of gallium arsenide, it doesn’t not get

sensitive with heat. Besides that, exclusively at a higher frequency the devices create lesser noise

compared to silicon(Atlantic Euipment Engineers, 2013). Gallium arsenide wafers will have a

better concentration of the remaining electrically operating impurities than silicon due to the poor

technology to purified gallium and arsenide as compete to the available method of silicon

(Buschow, Flemings, & Cahn, 2001).

Silicon substrate is a hard and brittle solid, but it has a relatively hard brittle material unless

they are machine in ductile mode on precision grinding machine. Semiconductor shows a sharp

decreasing in hardness, where by increasing the temperature of the material silicon and gallium

arsenide with degree Celsius of 500 and 200 respectively will starts to result in macroscopic

dislocation motion and also the plastic deformation. The element of the semiconductor with the

structure of diamond or sphalerite like silicon and gallium arsenide have the potential of stress-

strain reaction followed by an exceptional reduce of stress after the process of yield along with a

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slight increase in stress with strain owing to the work hardening in the plastic deformation process,

and the deformation mostly happened in a low temperature. Generally the strain rate and

temperature sensitively affect the stress-strain element in the semiconductor. An increase in the

strain rate actually have the same effects with the decrease in temperature (Michler, Wasmer, Meier,

Östlund, & Leifer, 2007). The fabrication method for the wafer of silicon and gallium arsenide

generally the same because both of the materials are brittle (Landry & Barron, 1993).

Figure 3: Machining process of semiconductor (Pei, Fisher, & Liu, 2008)

To convert a single-crystal silicon ingot (IG) into wafers that have to passed a few stages

of processing to obtained the final result. An arrangement of machining processes shown in the

figure 1 above. First process is the slicing, it could be performed by wire saw slicing or double disc

grinding in this process. After the process of slicing follow by the flattening process, the flattening

process can be done by using surface grinding to flatten both sides of the silicon. The third process

is the etching, etching is a process where the material is covered with a surface of wax which is

resistant to acid. The following process are the polishing process, this process ensure the surface

roughness of the material. Finally, cleaning process is the process where it takes places in cleaning

up the whole material and make sure it is clean and clear (Pei et al., 2008). Besides that, the reaction

of the abrasives machining of materials are usually analyze by the toughness and hardness. In fact,

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the crack extensions are affected by the toughness of silicon with microstructures which contribute

in elongated grains. In the studies of (Xu, Jahanmir, Ives, Job, & Ritchie, 1996), it is proved that

the damage tolerance and toughness are strongly affected by the elongated grains in silicon.

2.2 History of grinding

In the early stage of grinding, the abrasive stone were used as a grinding tools to sharpen

knives, and weapons. The abrasive have been useful in the early life as a tools to produce a well-

shaped rocks and stone for construction of building, for example the pyramid (W. Brian Rowe,

2014). At a later stage, eating utensils were found out that it could be made by grinding out stones

by using abrasive. Other than using grinding to sharpen objects, grinding may be one of the earliest

inventions in machine operation to be able to produce a desired shapes. To build the Pyramids of

Egypt, big stone blocks were cut into desired size by sawing with a specific indecent model of

grinding machine, and the sandstone surfaces were smooth. Metal grinding first initiated around

2000 BC in ancient Egypt, which lead to the origins of metallurgy(Grinding Technology, 2008).

In the period of 800 and 600 BC it was believed that the India have invented the diamond

mining, and this was the only invention of diamonds until the century of nineteenth. Belgium was

one of the earliest country to utilise the abrasive which is made out of diamond powder in the

fifteenth century, it was then use to cut diamond and to produce soft finishing to manufacture watch.

In the beginning of metallurgy the grinding wheel have been invented in time of ancient Egypt, the

earliest invention of grinding wheel are made out of sandstone and manufacture with the method

of grind grain by using the crude mill. The earliest abrasive wheels were being manufactured in

India in the nineteenth century, and it was used for grinding gems. In 1860s, Brown & Sharpe

Company invented the first new grinding machine for sewing machine parts. In 1870s, Norton

Company invented the most welcome product of the grinding wheel which is the vitrified bond

grinding wheel. With the technology of grinding machine, grinding wheel plays an important tools

in the grinding machine to fully utilise the machine(Grinding Technology, 2008). Nowadays,

grinding played an important role in machining process and lots of grinding methods have been

invented for different demands on materials and specifications.

2.2.1 Types of grinding

The shape of the grinding wheel and the relationship between the wheel head and the

workpiece are based on many types of grinding processes (S. Chen, 2018). The types of grinding

are as follow: (i) Surface grinder. (ii) Cylindrical grinder. (iii) Internal grinder. (iv) Centerless

grinder. (v) Special grinding process. Different types of grinding has their characteristics and uses

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towards different material and methods. Different types of grinding are as shown in the figure 2-1

below:

Figure 4-1: Different types of grinding (S. Chen, 2018)

Among all the types of grinding the most commonly used grinding operations are the

surface grinder. The surface grinder are normally used to achieve irregular, flat, smooth, and

angular shapes (S. Chen, 2018). While rotating the wheel and object the material are being hold by

a chuck to produce a smooth finish surface. This results in good surface finish together with the

capability to grind to excessively high tolerances.

The cylindrical grinder do has a same trait as the surface grinder which is both of the grinder

have the exact same level of tolerances which is attainable with the surface finish. The only

difference between the two methods is, on cylindrical grinder both workpiece can be hold by the

chuck or between centers and let the wheel rotate(Samar, 2011). Cylindrical grinder is a machine

that can shape the outer face of the object as long as it has central axis of rotation (S. Liang & Shih,

2016).

Other than that, a centerless grinder is similar like the cylindrical grinder as it uses two

spinning wheel to support the workpiece firmly in place (S. Chen, 2018) . The rate of material

removal is define by the speed of rotation of the wheel (S. Chen, 2018). One of the most difficult

grinding types is the internal grinding. Internal grinding can develop a tapered, straight or formed

holes to produce an exclusive surface finish or similar tolerance (S. Chen, 2018). The grinding

wheel is rotated by a different motor head in the same way as the workpiece (S. Kumar &

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Dhanabalan, 2018). Therefore, the grinding wheel can be modified accordingly for the depth of

cut(Schneider, 2011).

Lastly, the special grinding process designed for different types of work and methods. In

special grinding processes there are several grinders such as tool and cutter grinder, jig grinder,

and thread grinder. The tool and cutter grinder is mainly used to sharpen milling cutters and other

cutting mechanisms. It is commonly used for providing the tools to the metal and wood cutting

industries. Besides that, the tools and cutter grinder has a very high versatility and it can be used

to perform several grinding operations. Moreover, the jig grinder is designed to detect and precisely

grind holes and complex shapes. It is attached to a high speed air spindle to hold and drive the

grinding wheel. Thread grinding is normally perform on a grinding machine by using dressed

grinding wheel depending on the shape of the threads. It must be equip with a precision screw to

achieve the desire pitch on the threaded section (S. Chen, 2018).

2.3 Grinding wheel characteristics

Grinding wheels are created from several grain types in a large range of sizes in

combination with some bond materials and compositions(Grinding Technology, 2008). In

conventional abrasive wheels there are aluminum oxide and silicon carbide abrasives and are

produced with vitrified or resinoid bonds. While the superabrasives wheel contains diamond and

cubic boron nitride (CBN) and are made of with resin, metal bonds, and vitrified. For conventiona l

abrasive wheels it is generally covering the whole bonded abrasives, while the superabrasives

wheels is defined to a thinner rim to lessen the amount of costly CBN and diamond. Nowadays, all

the grinding wheels of conventional abrasives are basically aluminum oxide (A12O3) or silicon

carbine (SiC)(Grinding Technology, 2008); W.B.Rowe, 2010).

The maximum wheel speed of the cubic boron nitride (CBN) wheel is 200m/s, while the

maximum speed of the diamond wheel is only 80m/s, the diamond wheel has low heat resistant as

if it occurred a high temperature it will leads to diamond carbonization(B. Li, Ni, Yang, & Liang,

2014). The process of hard aluminum oxide is alumina with a hexagonal crystal similar to that of

natural abrasives of aluminum oxide which occur in different pureness and crystalliza t ion

degrees(Grinding Technology, 2008). Aluminum oxides consist of different concentrations of other

metal oxides either internationally introduced or as impurities(Grinding Technology, 2008). Many

types of abrasives aluminum oxide and a defined number of forms of silicon carbides are widely

used, which each has a special chemical composition and a collection of basic characteristics which

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influence granular properties and grinding process which is helpful for specific task(Grinding

Technology, 2008).

Knoop or Vickers hardness test was used to determine the abrasives hardness in conjunction

of the static indentation hardness. Dynamic strength and toughness are very critical to the abrasives

property(Grinding Technology, 2008). When the abrasives grain employ or collide with the

workpiece, it is less expected to tear or fragment if it is very tough. Abrasives wear resistance are

depending on all these properties (W. B. Rowe, 2010). Generally the finer grits with the equivalent

material are less friable than expected as they are normally formed by crushing the coarser

material(Grinding Technology, 2008). All silicon carbide forms are significantly harder than

alumina and are equivalent to the toughest abrasives of alumina, and this sequence of physical

properties would say that alumina oxide might not be as good as silicon carbide for fine grinding

operation(Grinding Technology, 2008). Grinding wheel that are superabrasives consist of diamond

and cubic boron nitride (CBN). Normally grinding wheel with high wheel speed are made out from

superabrasives (W. B. Rowe, 2010). The profit gain from the potential of highly increasing the

wear life and redress life of the grinding is due to the cost of the abrasives (W. B. Rowe, 2010).

Both diamond and cubic boron nitride (CBN) are well known as hard materials and they

are very useful in cutting hard brittle(S. Chen, 2018; Grinding Technology, 2008; W. B. Rowe,

2010). Due to its significant high hardness and wear resistance, the CBN is able to commit to a

broad range of materials (W. B. Rowe, 2010). To grind hard ceramics a harder abrasives like

diamond is preferred (W. B. Rowe, 2010). Conventional abrasives are not designed to grind hard

ceramics because the material they are made out of are hard and brittle and that will cause an

extremely high wear rates (W. B. Rowe, 2010). In between both of the superabrasives grinding

wheel, the thermal stability in CBN is greater than diamond(Grinding Technology, 2008). In the

temperature of 800 degree Celsius, diamond is thermally stable in the natural atmosphere(Grinding

Technology, 2008). In a higher temperature, CBN wheels with vitrified bonds can perform better

than the diamond in a much broader range of vitrified bond during the manufac ture

process(Grinding Technology, 2008). Due to the graphitization and carbon diffusion, diamond is

not suggested to grind most of the rigid materials (S. Chen, 2018; Grinding Technology, 2008; W.

B. Rowe, 2010)

To grind hard and difficult materials, diamond is the most desire choice to choose because

of its wear resistance and excessively hardness that will not easily wear the wheels (S. Chen, 2018).

Besides that, diamond has become the most effectively dressing tool material to sharpen all types

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of abrasives wheel (S. Chen, 2018). The grit and the grits number is linked with the grain size are

determined by a series of standard sieves during the production of the grinding wheel (S. Chen,

2018). However, the heat conductivity level for resin bond material are generally low, thus heat

produce during the grinding process will not simply transferred to the wheel. Other than that, when

a higher grit size was performed, to fit the abrasives tightly the resin bond have to be thicker (Z.

Zhang, Huo, Wu, & Huang, 2011). As according to (S. Chen, 2018), a specific shape of the grinding

wheel is chosen based on: (i) The workpiece material that are going to be grind. (ii) The standard

of surface finish and the accuracy of grinding. (iii) Parameters of grinding. (iv)The condition of the

grinding.

2.3.1 Wear of grinding wheel

Grinding wheel performance can be effectively affected by the wheel surface and wheel

wear (W. Brian Rowe, 2014). During the grinding process, wheel wear influences the form of the

cutting edges and it can cause difference contact in the kinematics zone. Different types of wheel

used in different manufacturing process determine the rate of wheel wear (S. Chen, 2018; Singleton,

2012). The wear in grinding wheel affect the quality and efficiency of the workpiece (Singleton,

2012).

In order to examine the wheel wear condition, the wheel radius reduction was measured

(Singleton, 2012). Regardless the wear type, the components dimensional tolerance is critical and

it can negatively influence the surface integrity (Singleton, 2012). While the wear involved with a

standard abrasive grinding wheel are much lower compared to high-speed steel or carbide milling

and turning operations, the production of tool wear is comparable (Singleton, 2012).

The mechanism of wear in the steady stage was represented as attritious wear when it do

not involve dressing and truing. Due to the increasing number of material removed it is strongly

affected by the increment of grits introducing the wear flats area. As the same concept, the grinding

force will generate a higher force when the rate of attritious wear is high, as this will contribute to

damage the workpiece. The definition of attritious wear is when wear mechanism occurred at a flat

surfaces (Liao, Li, & McSpadden, 2000). It is also proven by (Zeng, Li, Pei, & Treadwell, 2005)

that the increase of grinding force are affected by the increment of the wear flats owing to the

attritious wear. The grinding wheel life highly dependent on the attritious wear, but the attritious

wear slightly benefited to the reduction of wheel volume (Z. Liang et al., 2012). According to

(Singleton, 2012), the wheel will face failure if the wheel is not redressed. Due to the extreme

attrition of the grains contributed from the power and force, the wheel experienced a grain and

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bond fracture (Singleton, 2012). This can results to an impressive loss to the wheel radius, and also

has the response of refreshing the surface of the wheel and cause the force and power to be reduce

(Singleton, 2012). It was concluded in the experiment of (Han Huang, 2003) that the wheel wear

rate was significantly decrease and the surface finish was having a small improvement due to the

increase of depth of cut. The surface roughness was badly affected with the increase of depth of

cut and feed rate. In the situation where increasing the depth of cut and feed rate, it will cause

additional force acting on each abrasive and it will produce a high temperature during the grinding

process which will result in damaging the wear of abrasive (Tao, Yaoyao, Laakso, & Jinming,

2017).

2.3.2 Dressing in grinding wheel

Before the grinding process, the grinding wheel must be dress. In the manufacture of

component grinding is mostly the last machining procedure and it have a great demand on

constructing surface quality and accuracy (Jackson & Davim, 2011). Before conducting the

grinding process, the bonded and vitrified wheels are dressed. A straightness or specified model is

use to exclude the deviations by using truing (Opoz, 2012). Cutting desire can be improve by

removing the unwanted abrasive grains, and this is one of the reason of dressing the grinding wheels

(S. Chen, 2018). A uniform random distributed cutting edge is perform by dressing to obtain a good

cutting surface (S. Liang & Shih, 2016).

Superabrasives wheels specified built for grinding in a long term period with a minimum

redressing. Dressing is an operation that manages to remove unwanted material around the

abrasives grains to produce a wide wheel surface, and this is essential for the vitrified and resin

bonded superabrasives wheels. Carbide or alumina abrasive sticks may be used as a tools for

dressing sometimes. With frequently use of the abrasives sticks, the abrasives wheels will wears

and lessen the redress life. Another approach of the dressing is to improve the removal rate of

grinding process when the grinding wheel has a clear surface. After the wheel were used to perform

a few grinding operations, the grinding wheel are to be dressed to add new grains to the process of

cutting and to maintain its initial shape (Opoz, 2012). The carbide wheel are seldom used as a

dressing tools for the metal bond multi- layer superabrasives wheels. Sometimes, a carbide wheel

were used to dress the metal-bond multi- layer superabrasives.

Basically, the two mostly used dressing tools are the stationary tools and the rotary tools.

Conventional abrasives are normally dressed using the stationary dressing tools which contain

single-point diamond (SD) and impregnated diamond (ID). Form dressing tools come in a few

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variety of shapes that consists of round sharp-shaped tools. To not get involved of wear in rapid

dressing tools, the rotary dressing tools are usually used to dress the diamond wheels, vitrified

cubic boron nitride (CBN), and resin bonded CBN. The rotary dressing tools might be structure in

a limit spaced disc with a surface covered by diamond perform surrounding the periphery or a cup

with a surface covered by diamond somewhere near the edge. By bringing the width of the roll

together with the grinding wheel, it is proven that this is the best rotary dressing tools with the use

of motor. The dressing process normally operates when the grinding wheel is running in a regular

speed, this limit the errors of the wheel from a little unbalance phase to a minimum phase (Opoz,

2012). It is also important to perform the wheel balancing carefully during the dressing process (W.

Brian Rowe, 2014). It is justify that coarse dressing method identify to have a minimum grinding

force and grinding power but a surface roughness with a huge work material (Opoz, 2012). The

figure below shows the examples of stationary dressing tools and rotary dressing tools.

Figure 2-2: Stationary tools dressing (Jackson & Davim, 2011)

Figure 2-3: Rotary tools dressing(Jackson & Davim, 2011)

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2.4 Material removal mechanism in grinding

The wheel wear and material removal object must be taken into account for material

removing process when undergoing the process of machining with grinding wheels (Opoz, 2012).

Other than the grinding geometry, the material properties also strongly contributed to the effect of

surface quality and removal process mechanism in high speed grinding process (Yin & Huang,

2004).

To fully utilise the potential of the removal rate without affecting the surface quality, the

grinding parameter have to be concise to achieve the most effective grinding process for the

ceramics with great material properties. By having the process of damaging the workpiece owing

to the crack causing by the grinding process are usually applied to achieve removal rate with faster

process and this process is cost saving. Thus, it is important to understand and be familiar with the

properties of the material removal process and to be concise with the grinding parameter that are

going to process as an outcome. Material removal mechanism was strongly affected by the

dislodgement of the grain or the boundaries of the grain having a lateral crack (Agarwal &

Venkateswara Rao, 2010; Yin, Huang, Ramesh, & Huang, 2005).

By acknowledging the ground surface quality and knowing the topography of the grinding

wheel in combining with the performance of the grinding operations and material removal essential,

the grinding performance is determined by the topography of the grinding wheel and it is also one

of the most common factor to it (Opoz, 2012). Several cuts that performed from an amount of

individual grain work material interacted act as a grinding material removal process (Singleton,

2012). From the studies (Agarwal & Venkateswara Rao, 2010) it is stated that the surface finish

and the surface morphology are totally not being affected by the increment in material removal rate.

With constantly dressing and improving the grinding wheel surface it is likely to achieve high

removal rate (Jahanmir, Ramulu, & Koshy, 1999).

In the material removing process at an individual grit scale have to undergo three process,

which is, rubbing, ploughing, and cutting as shown in the figure 5 below. The three process starting

off with the grit work material interactions, where the grit move across the workpiece within the

material’s elastic limit before the plastic deformation occur, and this process is called sliding, which

have not done any important improvement to the grinding in material removing process. After the

sliding process it is follow on by the ploughing process, the material can be plastically deformed

but there is no chip formation taking place in this process. During the ploughing process, the

material expand on one and the other of the grit along with the material accumulated directly from

13

the grit till the material removal happen with the chip formation (Opoz, 2012). The process from

sliding to ploughing and from ploughing to cutting it all depends on depth of grit that are going to

go through the work material (Rowe, 2009). Even though the process of sliding and ploughing does

not made a huge effect to the material removal, but they can be negatively affect the grinding

process by adding an extreme rate of wheel wear and surface misrepresentation cause by the rising

specific energy and friction, with a relatively rising in temperature (Opoz, 2012).

(Takenaka & Sasaya, 1966) says that the ploughing process was greatly relying on the

shape of the grit. The abrasives grain that are primarily sliding, occur a different wear of grains that

happened in heavy chip removing process (W. Brian Rowe, 2014). In the process of high speed

grinding, the material removal mechanism will be affected by the grinding wheel speed which

mainly controlling the hardness of the strain and thermal softening (Tian, Fu, Xu, Li, & Ding,

2015). To achieve a high removal rate, usually a relatively huge depth of cut is considered (H.

Huang & Liu, 2003). With the effective process of rough composition is to increase the wheel

speed and the feed rate, and result in enlarging the material removal process rate with not making

any contribution to the wheel wear (Jahanmir et al., 1999). In this case, the material removal

process are in brittle transition. Chip removal happen in the starting of the interactions of the

individual grain occur in down-cut grinding. During the conventional in the down-cut grinding, the

force applied will be relatively low, and the surface roughness become useful and the wheel wear

was also decreased. In the process of up-cut grinding, the individual grain have an interaction

against the workpiece, and after the process the chip removal is obtained (W. Brian Rowe, 2014).

Figure 2-4: Material removal process(Winter, 2016)

14

2.4.1 Ductile and brittle transition

According to (Bifano, Dow, & Scattergood, 1991; S. Liang & Shih, 2016), the following

guidelines are widely applicable for the selection of a suitable grinding wheel: (i) To choose a hard

surface wheel to cause the soft material to slower down the wear and a soft surface wheel to cause

the hard material to ease self-sharpening. (ii) To choose a hard wheel to grind the ductile material

and choose a soft wheel to grind the brittle material. (iii) To choose a softer wheel to acquire a

good surface finish and a harder wheel to maximize the material removal rate. Today, through the

enhancement of the ultraprecision machine tools which leads to minimum error motion and greater

stiffness, brittle materials that are going through a machining process of ductile mode is now a

popular technique used by many to achieve higher precision, improved surface finish and lesser

costs (Shimada, Inamura, & Ikawa, 1997).

It is notable fact that there exists brittle and ductile materials transition in material removal

mechanism. The brittle to ductile transition occur when the critical value is more than the depth of

cut which are important for the workpiece to be machined (Bifano et al., 1991; Shimada et al.,

1997). Therefore, plastic deformation is superior to brittle fracture when the critical value is larger

than the depth of cut in terms of energy consumption (Bifano et al., 1991; S. Liang & Shih, 2016).

During the brittle material undergoing a plastic deformation process, surface finishes are the same

to those accomplished polishing or lapping are achieved (Bifano et al., 1991). In brittle transition,

the material removal process is conducted by propagation and intersection of cracks, while for the

ductile transition it creates material behavior of a plastic in a state of extremely sheared machining

chips (Bifano et al., 1991).

In the studies of (Young, Liao, & Huang, 2007) it is proven that with the critical depth of

cut larger than the maximum undeformed chip thickness then it will achieve ductile transition

grinding. As shown in the figure 2-5(a) below, through the ductile regime grinding process, it

shows that there weren’t any sign of cracks on the surface but the process are undergoing the elastic

deformation, plastic ploughing, and micro crack removal. Then, in figure 2-5(b), in the ductile-

brittle grinding process, with the increment to maximum, the micro crack starting to occur on the

surface of work material and produces some cracking results in the process of chip formation.

Finally, in figure 2-5(c), the brittle grinding process, by increasing it to the maximum, it is shown

on the figure that the material are completely eliminated by the brittle fracture and resulting a

massive crack on the surface. Brittle regime is the term used to define this method of material

removal mode (Dai et al., 2018).

15

Figure 2-5: Ductile and brittle grinding(Dai et al., 2018)

The model acquired from the formula describes the critical depth of a fracture occur during the

indentation of brittle materials (Lawn, Jensen, & Arora, 1976). Referring to the Griffith fracture

propagation criterion, the formula indicates a critical depth of indentation,

𝑑𝑐 =𝐸𝑅

𝐻…………………………………………… (1)

and the dc shown in the formula appear to be the critical indentation depth, where E is well known

as the elastic modulus, R appear to be the material’s fracture energy, and H indicates the hardness

of the material. Due to the material that shows a plastic area around the crack tip, the R from the

formula above can be found in Griffith’s classical crack propagation analysis. One way to define

small scales of the fracture energy is by substituting it with a dimensionally equivalent

measurement of the energy needed to propagate cracks are,

𝑅 =𝐾𝑐

2

𝐻….…….…..….…………….……………. (2)

For the indentation, the formula 𝑘𝑐

2

𝐻 has been subjected to an effective way to indicate the brittleness

(Marshall and Lawn, 1986). This quantity can be substituting in with critical depth model of

equation that are shown above to achieve,

𝑑𝑐 ∝ (𝐸

𝐻) (

𝐾𝑐

𝐻)

2

……….……. …………………….. (3)

and this shows a formula to measure the brittle transition depth of cut (Bifano et al., 1991). With

the application of the maximum undeformed chip thickness lesser than the critical depth of cut,

hm< dc, the surface are being examined as ductile transition mode. While when hm >dc, then the

surface will be examined as brittle transition mode which the surface involve crack propagation

during machining process (S. Chen, 2018).

2.4.2 Maximum undeformed chip thickness

By comparing the milling process and making assumptions on equally spaced cut points

near the wheel periphery was used in the earliest stage of chip thickness in grinding process

16

(Singleton, 2012). By using the abrasives grains the equivalent chip thickness is normally used to

measure the depth of material removal and it is nearly the same to the harshness of force applied

on the grains than in depth of cut (W. Brian Rowe, 2014). In a research of grinding process, it is

essential to significant process the undeformed chip thickness, exclusively in the section of

machining hard materials (S. Chen, 2018). During the operations of chip generation and surface

information, the wheel model and spec highly contributed in this process (S. Chen, 2018).

It is proven by (Yin & Huang, 2004) that when the grinding speed increases, an

improvement of surface finish will occur when the maximum undeformed chip thickness is reduce.

Other than the force applied and chip thickness, the process of edge shape cutting strongly affected

to the chip forming performance (Jahanmir et al., 1999). In terms of building a theoretical model

to determine the chip thickness, the grinding force is performed from the relationship between the

chip condition and surface quality (S. Chen, 2018). The chip geometry can be achieve when the

grinding wheel depth of cut and the amount of active abrasives grain were determined (S. Chen,

2018).

When an individual grain occur a maximum depth of cut during cutting it is indicated as

the maximum undeformed chip thickness, hm (Singleton, 2012).

Figure 2-6: Theoretical cutting path of an individual grain (Singleton, 2012)

From the figure 2-6 above, the parameter is related to the feed per tooth parameter used in milling,

𝑠 = 𝑣𝑤 ∙ 𝑡𝑟𝑒𝑠…….….………………….………….. (4)

The hm is calculated from dealing with the distance:

ℎ𝑚 = 𝑂′𝐶 − 𝑂′𝐴 =𝑑𝑠

2− 𝑂′𝐴………….………………….. (5)

By using the mathematical trigonometry and substituting the parameter S above, the equation are

ℎ𝑚 = 2 ∙ 𝑆 𝑎𝑒

𝑑𝑠

1

2 = 2 ∙ 𝑆𝑎𝑒

𝑑𝑒

1

2 = 2 ∙ 𝐿𝑣𝑤

𝑣𝑠 𝑎𝑒

𝑑𝑠

1

2………...…………… (6)

17

Where L indicates the distance between the cutting edges in unit (mm). The amount of cutting

points near any line of the wheel periphery K is calculated by,

𝐾 = 𝐶 𝜋 ∙ 𝑑𝑒 ∙ 𝑏𝑐 =𝜋∙𝑑𝑠

𝐿 ……………………………….. (7)

Where C indicates the amount of cutting points as per unit area of the wheel(1

𝑚𝑚2 ), where the 𝑏𝑐

indicate in the formula as the chip width. By dealing with L and calculate the chip width with the

maximum chip thickness, hm is then determined as

ℎ𝑚 =4

𝐶∙𝑟

𝑣𝑤

𝑣𝑠

𝑎

𝑑𝑠

1

2

1

2

……………………………………. (8)

where r indicates the ratio of the chip width to the thickness (Singleton, 2012). The advantages of

a smaller maximum undeformed chip thickness are, the layers that are being damage during the

grinding process are lesser and the surface roughness will be smoother, but it require more energy

to produce the material removal process (Zhou, Guo, & Wang, 2017).

2.4.3 High speed grinding

High speed grinding are freshly introduced as an effective grinding process and contained

a high capability of achieving a good surface quality with great productivity as compared to the

normal grinding (J. Chen, Shen, Huang, & Xu, 2010). High speed grinding highly performed for a

good surface quality with a relatively high efficiency (Klocke et al., 1997). By reducing the grinding

force, the high wheel speed can reduced the undeformed chip thickness (J. Chen et al., 2010; Han

Huang, Yin, & Zhou, 2003). Other than that it is proven from (J. Chen et al., 2010) that using the

brazed diamond wheel in high speed grinding will achieve a great performance (J. Chen et al.,

2010).

(Han Huang et al., 2003) carried out a report show that the studies of the high speed grinding

performance on a material removal mechanism of using the resin bond diamond wheels. The report

show an investigation on the surface quality that can caused by the wheel speed and the grinding

parameters. The two different grit sizes resin bond diamond wheel with related to the material

removal mechanism is showed. As per figure 8 below, the figure on the left was plotting the

grinding force against the depth of cut. As proven from (Han Huang et al., 2003) when the depth

of cut increases, the force applied on the material increases. And it is also proven that when using

a larger depth of cut the outcome of the wheel speed acted on the grinding force will be more

specified. As for the figure on the right in figure 2-7, it shows that the grinding forces plotted

against the feed rates. By increasing the feed rate, the grinding force increases constantly respective

18

with the feed rates. As when the feed rates are performed in a higher speed, the force applied on

the material are getting more linear towards the end.

Figure 2-7: Results of grinding force to depth of cut and feed rates(Han Huang et al., 2003)

Figure2-8:Graph of forces and the maximum undeformed chip thickness(Han Huang et al., 2003)

From the figure 2-8 above, (Han Huang et al., 2003) have proven that maximum undeformed chip

thickness will occur in the larger grit wheel. From the experiment results of (J. Li, Fang, Zhang, &

Liu, 2015) it is proven that by using a higher grinding wheel speed to machine a brittle material

such as silicon will result in having a larger chip thickness and produce a high temperature which

will bring lesser subsurface damage to the material.

According to the grinding speed division standard that have been said by (Dornfeld & Lee,

2008; B. Li et al., 2014), the standard of high speed grinding are from 45m/s to 150m/s, where the

standard for the ultra-high speed grinding are expected to be 150m/s and higher. To prevent

grinding procedure from damaging the ceramics, high speed grinding has been introduce as a

finishing process. By increasing the wheel speed leads to a better surface quality when the grinding

process was conducted at the area where the ductile flow was concentrated on the material will

helped to prevent brittle fracture transition. With a different wheel speed of 80m/s and 120m/s, the

brittle material can be defined by the different wheel speed.

19

For brittle material ductile transition it is strongly affected by the maximum undeformed

chip thickness value, which by increasing the wheel speed effectively affect the results of the

maximum undeformed chip thickness as well. It is proven in the experiment that by diamond

grinding wheel with speed of 120m/s will effectively improve the grinding quality. Brittle material

will not achieved brittle transition when the material are being grinded with higher wheel speed

during the high speed grinding process (B. Li et al., 2014). Due to the circumstances of surface

finish, grinding wheel, and wheel speed, the performance of the grinding could be improve with

conducting at a higher speed and it will reduce the maximum undeformed chip thickness. For a

different wheel speed of high speed grinding could affect the surface contact between the abrasive

grit and the material, as it will significantly enlarged the depth of each grit that will pass through

the material without having fracture crack generation. It was studied from (Yin & Huang, 2004)

that with increasing the wheel speed will result the grinding force to be decrease and also increase

the toughness and hardness of the material.

High speed grinding was introduced as a process which was considered as a tool to optimize

cost and achieve high efficiency during machining process.(Han Huang, 2003). From the studies

of (Agarwal & Venkateswara Rao, 2010) it is stated that in the comparison of high speed grinding

and conventional grinding there were not much changes in the form of surface morphology and the

roughness of the surface as well. The ceramics properties will not have any reduction in fracture

strength which affected by the high removal process rate by performing the high speed grinding

(H. Huang & Liu, 2003). High speed grinding was introduced to optimize cost for grinding process

where polishing process are very expensive, as both of the process aims to achieve a better surface

quality, therefore high speed grinding was performed to shorten the possible time for polishing

process to optimize the cost production of grinding process (N, Hung, Tung, & Long, 2016)

Figure 2-9: Results of surface roughness to depth of cut and feed rate (Han Huang et al., 2003)

20

As per figure 2-9 above the left graph represent the surface roughness which performed under

different wheel speed and in terms of different depth of cut. It have been shown clearly in the

experiment of (Han Huang et al., 2003), with the decrease of depth of cuts owing to the increase

of wheel speed, the surface roughness decreases which means that the surface roughness improved

and achieving a better surface. Nonetheless, as observed from the figure above by increasing the

wheel speed the surface roughness are slightly increasing as well. However, from the right graph

in figure 10 shows the relation of surface roughness and wheel speed with different feed rates. It is

shown that when the feed rates increases from 500mm/min to 1000mm/min the surface roughness

have a huge improvement, and the surface roughness slightly increases when the feed rates

increases from 200mm/min to 500mm/min. It is proven from (Han Huang et al., 2003) that with

the increase of feed rates and depth of cut it will damages the surface of the material and increases

the surface roughness. During the grinding process of the ceramics, by increasing the depth of cut

will usually contribute to a larger grinding force but also produce a negative effect to the surface

finish. By maintaining the grinding parameters being constant, with increasing the depth of cut

would strongly affect the coolant to not being able to have much contact between the ground of

grinding, therefore the effect of cooling were being reduce (H. Huang & Liu, 2003).

2.5 Summary of literature review

Semiconductor materials like silicon and gallium arsenide have hard hardness and

brittleness, as both of the materials have to go through a machining process before conducting the

grinding experiment. There are several types of grinding, but the most common type of grinding

are surface grinding which were performed in this thesis experiment. Moreover, the characterist ics

of grinding wheel are essential as different types of grinding wheel have different effect on

materials. For instance, grinding wheel with different grit size may result in different grinding force

and surface roughness. Other than that, grinding wear occurred in every grinding process as wheel

wear affect the form of cutting edges and it could cause difference contact in kinematics zone. On

top of that, wheel wear could affect the quality and efficient of the experiment. Dressing process

are crucial before conducting the grinding experiment, as the dressing procedure aims to remove

the abrasives particle on the wheel and reduce the vibration during the grinding process. As for the

material removal process it consists of three stages which are the sliding, ploughing, and cutting.

In the three process each performed an essential role in machining and grinding the workpiece to

achieve a better surface quality. Semiconductors like silicon and gallium arsenide have hard

hardness and brittleness, as both of the materials could achieve brittle fracture to ductile transition

21

with levelling the wheel speed. It is proven that when the critical depth of cut is larger than the

maximum undeformed chip thickness then the material could achieve ductile transition. High speed

grinding was introduced as an effective grinding process where it could provide a better surface

quality and surface roughness by increasing the wheel speed. With different grinding parameter

used, it could improve the surface roughness, surface quality, and reduce the grinding force. High

speed grinding are cost effective process and it could provide a better surface finish with higher

speed.

22

3.0 Methodology

This thesis experiments were conducted using the CNC Ultra Precision Form Grinding

Machine (Okamoto UPZ315Li). Due to the topic of precision grinding of semiconductor, this is a

suitable machine to conduct this experiment as the machine can operate in high speed grinding

which met the requirement of this experiment. In this experiment, the both semiconductors material

that are going to be examine are Silicon (Si) and Gallium Arsenide (GaAs). The parameters that

are used to conduct the experiment are, wheel type of SD 800 and SD 3000 which are the resin

bond wheel, depth of cut of 5um, 10um, and 15um, feed rates of 250 mm/min, 500 mm/min, and

1000mm/min, lastly the wheel speed of 40m/s, 60m/s, and 80m/s. The experiment parameter are

tabulated in the table below:

Table 5: Experiment parameter

Experiment details Parameter

Material Silicon (Si), Gallium Arsenide (GaAs)

Wheel speed 40m/s, 60m/s, and 80m/s

Types of wheel SD 800 and SD 3000

Feed rate 250mm/min, 500mm/min, 1000mm/min

Depth of cut 5𝜇𝑚, 10 𝜇𝑚, and 15 𝜇𝑚

The goals of this experiment are to determine the force applied to the material during grinding

process, and by using the confocal microscope to examine the surface roughness of the material.

Each measurement will be repeated twice to obtain a more precise force results as taking the

average forces between the two experiments as the final force results for the measurement.

Figure 3-1: CNC Ultra Precision form grinding machine (Okamoto UPZ315Li)

23

Table 6: Characteristics of grinding machine

X-axis (Table horizontal movement)

Y-axis (Wheel vertical movement)

Z-axis (Wheel cross movement)

Motor 2 sets * 1200W 750W 500W

Feed Speed 0-100m/min 1000mm/min 1000mm/min

Jog Speed - 1-1000mm/min 1-1000mm/min

Minimum setting unit 0.1𝜇𝑚 0.1𝜇𝑚 0.1𝜇𝑚

Figure 3-2: Wheel types of (a) and (b) are SD 800 and SD 3000 respectively

Firstly, the preparation before grinding are the samples of silicon and gallium arsenide are

cut into a square dimension of 1cm2. The both material are to be cut by a special pen called diamond

pen, the diamond pen are made out of natural diamond material and it is specialized to cut

semiconductor materials.

Figure 3-3: Diamond Pen

The samples have to be stick on a stage by applying a layer of wax on it, the melting point of wax

are around 60 to 80 degree Celsius. After the wax have melted, the samples will automatically stick

on the stage by itself. By using a cotton tip simply press lightly on the edge of the samples to make

it hold a better grip on the stage as it will not move easily while conducting the experiment. If there

are wax stained on the samples, use a cotton tip with a little drip of ethanol on it and wipe the

a)

24

samples in one direction to remove the stain. The purpose of wiping off the wax stained is to

improve the accuracy of grinding without having any extra thickness contributing on the samples.

One stage could fit up to four samples with tightly spaced between one and another, and the

arrangement of the samples are placed in a vertical position which aligned with the stage.

In the process of setting up the precision grinding machine (Okamoto UPZ315Li), there

involve plenty of steps to switch on the machine. The steps of switching on the machine are taught

by my supervisor and are advised to operate with care. After the machine is switched on, the next

step is to be sure that the correct wheel are fitted on the machine otherwise it should be change.

The wheel must be in a completely stopped position to be able to start changing the wheel. It have

a specialize equipment that are designed to fit perfectly to the wheel to be unscrew and change to

the desire wheel.

Moreover, the following steps of preparation before the grinding process are balancing.

This is a procedure where it is important when conducting a high speed grinding experiment, as

the faster the wheel spin the more the wheel vibrate. The outcome of the final results will be

strongly affected by the unbalance wheel, therefore this procedure must be taken precisely in order

to achieve a better final results. There is a balancing kit that are used to balance the wheel, and the

procedure of operating the balancing kit were taught by my supervisor. There is a laser stand that

are connected to the balancing kit and the laser stand were being adjusted to a 45 degree angle to

accurately point the laser sensor directly to the wheel spindle. For a normal grinding wheel speed

of less than 80m/s are expected to reach 0.1 offset of wheel balance, and a minimum of 0.02 offset

for high speed grinding which is the wheel speed of 80m/s or higher. It is relatively easy for the

normal grinding wheel speed to achieve the requirement of 0.1 offset as the wheel has less vibration

when it is not operating in high speed grinding. As to achieve a minimum requirement of 0.02

offset for the high speed grinding, it is harder as the higher the wheel speed the more the unbalance

the wheel and vibration.

Besides that, when the wheel does not meet the offset requirement, a list of procedure to

balance the wheel were introduced. On the grinding wheel, there are 23 holes and the holes were

labelled with number on it as an indication of position for wheel balancing purpose. In the

procedure list, it was asked to insert a tiny screw that weigh around 0.190g into the grinding wheel

position 1. After allowing the wheel to be run for a few minutes, it is observe from the balancing

kit display screen that the value of mass should be added into which position of the wheel. After

the wheel has completely stop, retrieve the tiny screw that are inserted into position 1 and replace

25

the desire mass into the position stated on the balancing kit. Sometimes, it is hard to find the

relatively accurate value of mass to be replace into the wheel and there is a new method introduced

to overcome this problem. For the position that could not find the desired value of mass to be

replaced, it could be solve by taking the difference between the current position and the

corresponding opposite position’s screws mass to find a new desired value of mass to be replace

into the wheel. Therefore, there will be two sets of mass to be added into the wheel, and the heavier

mass will be replace into the position indicated on the balancing kit and the lighter mass will be

put back into the corresponding opposite position.

Figure 3-4: Balancing kit

The last preparation before starting the grinding process are wheel dressing. Moreover, the

purpose of dressing is to remove the abrasives particles from the wheel surface by truing the

grinding wheel and makes the wheel more concentrical. By dressing it helps to minimize the

vibration of the wheel and also made contribution to improve on the surface finish. Dressing is a

crucial procedure to be done before the experiment as it will affect the grinding results. The

dressing equipment that is used in this experiment is vertical rotary wheel dresser. For vertical

rotary wheel dresser, the wheel spin in horizontal direction while the grinding wheel interact with

the wheel dresser from above with the wheel spinning the opposite direction from the wheel dresser.

During the truing process, the water based coolant was sprayed towards the wheel spindle as the

coolant will dripped into the middle of the vertical rotary wheel dresser. As this shows that both

wheels are moving in the opposite direction, therefore the grinding wheel is being dressed to

achieve a better grinding results with good surface finish.

26

Figure 3-5: Vertical rotary wheel dresser

Aside from making the necessary preparations, there are certain measures to be taken which

are crucial to achieve accurate results prior to conducting the grinding experiments. It is important

to adjust the grinding wheel to a specific wheel speed as this allows it to maintain a constant and

balanced wheel speed. To ease the process, a list of varying wheel speeds and RPM (revolution per

minutes) was prepared. After pre-heating the grinding wheel, the stage was carefully positioned in

the grinding machine. The four samples placed on the stage were ground in the order starting from

the furthest to the nearest for efficiency. First, by aligning the grinding wheel to the center of the

sample and make sure the grinding wheel doesn’t have any contact with the sample in this process

because it will damage the surface of the sample and the results will be affected. After aligning the

grinding wheel to the sample, the grinding wheel were carefully move vertically downward nearer

to the sample. In the meantime, a small piece of paper was used to measures the distance between

the grinding wheel and the sample, as when the grinding wheel touched the paper it means that the

approximately distance between the grinding wheel and the sample are 100 micrometer. By

knowing the approximately distance of the wheel and the sample, it is much easier to determine

the distance for the grinding wheel to exactly contact with the sample. Moreover, the grinding

wheel were lifted 2 micrometer when the grinding wheel slightly contacted with the sample.

The process of grinding a flat surface of the sample were then occurred after a slightly

interaction between the grinding wheel and the sample. In the process of grinding, the grinding

wheel were conducted along the x-axis direction as the grinding wheel move back and forth while

the stage remain stagnant. Throughout the grinding process, the grinding wheel will constantly

move downwards by 2 micrometer until the sample were to have a flat surface. When going through

the grinding process, a constant wheel speed of 40m/s were used. During the grinding process, the

water based coolant was sprayed to the direction of the wheel where it interacted with the sample.

27

According to (Yin & Huang, 2004) experiment process, it is stated that six passes of grinding were

made to create steady condition before conducting the force measurement. The force measurement

was taken using the piezoelectric dynamometer and the results were analyzed using the software

DEWSOFT. The force measurement were taken twice in order to obtain a precise results.

Figure 3-6: Dynamometer

After the grinding process, the surface of the samples were to be cleaned with ethanol. As

this procedure is crucial before the surface roughness being examine. The surface roughness and

the surface morphology of the samples were assessed by using a confocal microscope. When the

samples are being analyzed, the surface roughness results were taken perpendicularly of the

grinding direction. Each measurement of the surface roughness were conducted three times on the

same sample and the average and standard deviations of the surface roughness were then calculated

in the excel sheet. After the surface roughness measurement, the samples were being examined for

the surface morphology and the image of the surface were taken and being discussed.

Figure 3-7: Confocal Microscope

28

4.0 Results and discussions

4.1 Effect of depth of cut

The following results were obtained during the experiment and the results were being analyzed

using the software DEWSOFT. After the results being analyzed, the data was tabulated in an excel

sheet and plotted on a graph. The section below discuss the results of force applied on the material

during grinding process, the surface roughness of the material, and the surface morphology

obtained from the confocal microscope.

Figure 4-1: Effect of depth of cut on grinding force on silicon. Grinding was performed with the wheel speed of 40m/s, wheel type of SD 800, feed rate of 500mm/min, and different depth of cuts

of 5um, 10um, and 15um.

This is a graph that showed the effect of depth of cuts to the grinding force applied on the material.

From the graph above it is shown that as the depth of cut increases, the grinding force increases. It

was concluded that the maximum undeformed chip thickness and the material removal rate are the

factors that lead to this result. It was proven that the experiments results from (Grinding Force of

Cylindrical and Creep Feed Grinding Modelling, 2018; Han Huang et al., 2003; Sivaraman,

Sankaran, & Vijayaraghavan, 2012; L. C. Zhang & Yasunaga, 1997) conclude that a larger grinding

force was produce when the depth of cut increases.

29

4.2 Effect of feed rate

Figure 4-2: Effect of feed rate on grinding force on silicon. Grinding was performed with the wheel speed of 60m/s, wheel type of SD 3000, depth of cut of 10um, with different feed rates of

250mm/min, 500mm/min, and 1000mm/min.

From the graph above it shows the grinding force as a function of feed rate with the material silicon.

The results show that with the increasing in feed rates, the grinding force increases as well. As

observed from the increasing of feed rate from 500mm/min to 1000mm/min, the grinding force

slightly increases compared to the feed rate from 250mm/min to 500mm/min. It can be concluded

that by performing a higher table speed, the surface contact between the wheel and the material is

lesser, therefore the grinding force is increasing slowly from feed rates of 500mm/min to

1000mm/min. It is also proven from the experiment results from (Grinding Force of Cylindrical

and Creep Feed Grinding Modelling, 2018; Han Huang et al., 2003; A. Kumar, Ghosh, &

Aravindan, 2017; Sivaraman et al., 2012) that the grinding force increased double when the feed

rates increased from 200mm/min to 1000mm/min compared to 500mm/min to 1000mm/min. By

performing a higher feed rate result in decreasing the grinding force owing to the wheel of speed

increases (Han Huang et al., 2003).

30

Figure 4-3: Effect of feed rates on surface roughness on silicon. Grinding was performed with the wheel speed of 60m/s, wheel type of SD 3000, depth of cut of 10um, with different feed rates of

250mm/min, 500mm/min, and 1000mm/min.

From the graph above it shows that a silicon with a depth of cut of 10um plotting against different

feed rates and surface roughness. As observed from the increasing of feed rate from 250mm/min

to 1000mm/min, the surface roughness increases linearly. The surface roughness generally getting

worse with each increase of feed rates. It can be concluded that by performing a higher table speed,

the surface roughness will get worst. From the experiment results of (Tao et al., 2017) has shown

that in increasing of feed rates will result in having bad outcome on the surface roughness. It is

because by increasing feed rates, it might add loads to each abrasives cut. From the studies of (Han

Huang et al., 2003) it is proven that there is a large elevation for the surface roughness by reducing

the feed rate from 1000mm/min to 500mm/min, where there is only a small changes of surface

roughness when reducing the feed rates from 500mm/min to 200mm/min.

31

4.3 Effect of wheel speed

Figure 4-4: Effect of wheel speed on grinding force on silicon. Grinding was performed with the wheel type of SD 800, feed rate of 500mm/min, depth of cut of 10um, with different wheel speed

of 40m/s, 60m/s, and 80m/s.

The graph above shown the silicon plotted against the grinding force and different wheel speeds.

It is shown in the graph that the grinding force decreases when the wheel speed increases. This

scenario is related to the maximum undeformed chip thickness and the material removal rate. It

can be explain that when the maximum undeformed chip thickness is smaller than the critical depth

of cut then the material will occur ductile transition. As proven from the experiments from

(Grinding Force of Cylindrical and Creep Feed Grinding Modelling, 2018; Han Huang et al., 2003;

A. Kumar et al., 2017; Singleton, 2012; Sivaraman et al., 2012; Zhu, Yan, & Li, 2014) that a small

undeformed chip thickness will achieved with increasing the wheel speed, and it will result to

achieve a smaller grinding force.

32

Figure 4-5: Effect of wheel speed on surface roughness on silicon. Grinding was performed with

the wheel type of SD 800, feed rate of 500mm/min, with different depth of cuts of 5um, 10um, and 15um, and different wheel speed of 40m/s, 60m/s, and 80m/s.

The graph above shows the surface roughness as a function of wheel speed with different depth of

cuts. From the results shown in the graph above that the surface roughness increases when the

wheel speed increases. As the result achieved from this experiment does not satisfy the theory of

high speed grinding. The surface roughness will become finer with the increase of wheel speed,

but as shown in the graph above that with the highest wheel speed which have achieve high speed

grinding, the surface roughness increases which means that the surface turns bad. As proven from

the experiment of (Zhu et al., 2014) that by increasing the wheel speed will result in enlarging the

material removal rate and the surface roughness will improve owing to the increase of wheel speed.

The error results performed in the graph above could address to the factor of not dressing the

grinding wheel properly as the abrasive are not completely removed from the grinding wheel which

contributed in increasing the surface roughness. Another factor that could lead to this result is

vibration of the wheel, vibration caused by wheel imbalance at higher speed could worsen the

surface quality as well. To mitigate this problem, in future work research the wheel must be dressed

properly with a longer time and the grinding wheel must be balance according to the actual speed.

33

4.4 Effect of types of wheel

Figure 4-6: Effect of different types of wheel on grinding force on silicon. Grinding was

performed with the wheel speed of 60m/s, feed rate of 500mm/min, depth of cut of 10um, and wheel types of SD 800 and SD 3000.

The graph above shows the relations of grinding force and different types of wheel. As observed,

the wheel of SD 3000 achieve a higher force than the wheel of SD 800. It is proven from this graph

that smaller grit wheel will have a smaller force compare to the larger grit wheel, and it is concluded

that higher grit wheel will have higher grit wear. From the experiment of ("The Effect of Grinding

on grinding Wheel Condition," 2006; L. C. Zhang & Yasunaga, 1997) it can strongly support that

the conclusion that have been made towards this graph is reasonable. Besides that, it is proven from

the("The Effect of Grinding on grinding Wheel Condition," 2006), with smaller grit wheel the

cutting grit rates will drop with time which affected by a large number of grit being wear off.

34

Figure 4-7: Effect of depth of cut on surface roughness of silicon. Grinding was performed with the wheel speed of 60m/s, feed rate of 500mm/min, wheel types of SD 800 and SD 3000, and

with different depth of cuts of 5um, 10um, and 15um.

The graph above aims to compare the surface roughness with different types of grinding wheel

applied in the experiment. Ra was performed as an output measurement for surface roughness, as

it is commonly used in an aerospace sector. From the experiment outcome that have been concluded

by (Z. Zhang et al., 2011) that there was a small variation in surface roughness between the

sample’s chip thickness. It is clearly shown in the graph that the surface roughness obtained from

SD 800 are larger than SD 3000. From this experiment it is proven that with rougher grit wheel

will result in removing more materials and produce a rougher surface finish, while with a finer grit

wheel will result in removing lesser material and produce a smoother finish. Therefore, it is shown

that by using the wheel of SD 3000 improves the surface roughness compare to the wheel of SD

800. The effect of grain size will strongly influence the surface roughness of the material, as the

smaller grain size wheel it improve the surface roughness of the material compared to the larger

grain size wheel (Wang & etc, 1999). It is safe to assume that the surface roughness slightly

increases owning to the increase of depth of cuts in each wheel.

35

4.5 Effect of materials

Figure 4-8: Effect of depth of cut on grinding force on silicon. Grinding was performed with the wheel speed of 60m/s, wheel type of SD 3000, feed rate of 500mm/min, with different depth of

cuts of 5um, 10um, and 15um.

Figure 4-9: Effect of depth of cut on grinding force on Gallium Arsenide. Grinding was

performed with the wheel speed of 60m/s, wheel type of SD 3000, feed rate of 500mm/min, with different depth of cuts of 5um, 10um, and 15um.

The graph above shows the grinding force as a function of depth of cuts with two different materials

which is the silicon and gallium arsenide. By comparing both of the graphs above, the results does

not vary much as the grinding force obtained for both of the experiment are almost similar. This

could be conclude that both of the materials have the same properties of hard and brittle surface,

therefore both of the material have the same grinding force resistance.

36

Figure 4-10: Effect of depth of cut on surface roughness on silicon and gallium arsenide.

Grinding was performed with the wheel speed of 60m/s, wheel type of SD 3000, feed rate of 500mm/min, with different depth of cuts of 5um, 10um, and 15um.

The graph above aims to show the effect of surface roughness to the function of depth of cuts. As

presented in the graph above it shows that by increasing the depth of cut, the surface roughness of

both of the semiconductor material increases as well. As for the silicon surface roughness is slightly

higher than gallium arsenide is due to the material properties of silicon which is hard and brittle

solid with a better fracture toughness and yielding stress, therefore by comparing both of this

material the surface roughness of silicon is slightly higher. From the studies of (Han Huang et al.,

2003) it is stated that by reducing the depth of cut of the wheel, the surface roughness improved.

From the research of (Tao et al., 2017) it is stated the surface roughness will get worst owing to the

increase of depth of cuts, because by increasing the depth of cuts it might add loads to each abrasive

cut.

.

37

4.6 Surface morphology

The following results of the surface morphology were obtained from the confocal microscope

during the experiment. In this section, the surface quality of the material were being discussed with

different grinding parameter applied.

Figure 4-11: Surface morphology – Effect of wheel speed on silicon. Grinding was performed

with wheel type of SD 800, feed rate of 500mm/min, depth of cut of 15um, with different wheel speed (a), (b), and (c) of 40m/s, 60m/s, and 80m/s respectively.

From the three samples of different wheel speed shown above, the sample (a) with a lower wheel

speed has the worst surface quality. As observed from the samples above, with the increase of

wheel speed the surface quality gets better. It is shown in the surface morphology above that when

the wheel speed of 40m/s applied, there consists of brittle fracture, ploughing area and ductile

transition. Due to the increase of wheel speed the surface quality improved and it consist of lesser

brittle fracture and it involved more ductile transition. It is proven from the experiment of (J. Chen

38

et al., 2010; Han Huang et al., 2003) (Tian et al., 2015) saying that in changes of the wheel speed

from low to high, the removal mechanism for the surface quality will changes its form from brittle

transition to ductile transition. From the studies of (Tian et al., 2015) it is concluded that the

material and chip formation are strongly affected by the wheel speed. It is stated in the experiment

from (Z. Zhang et al., 2011) saying that when the depth of cut decreases and the wheel speed

increase will result in achieving a better surface finish. The material removal rate of the extremity

of deformation will increase by lessen the depth of cut, thus it will increase the grinding heat as

well.(Z. Zhang et al., 2011)

Figure 4-12: Surface morphology – Effect of types of wheel on silicon. Grinding was performed with the wheel speed of 60m/s, feed rate of 500mm/min, depth of cut of 15um, with the different

wheel types (a) and (b) of SD 800 and SD 3000 respectively.

From both of the samples above shows the surface quality of two different grinding wheel applied .

As observed from both of the surface morphology above that the surface quality had a huge

improvement when the different grinding wheel is applied. It is proven that the smaller grit size

wheel which is indicated as (b) produce a smoother finish than the larger grit size wheel. From the

studies of (Kimura & Horio, 2007), the diamond wheel SD 800 effectively remove the material on

silicon but damages the surface of the material. While the diamond wheel SD 3000 produce a good

surface quality and minimize the damage of the material.

39

Figure 4-13: Surface morphology – Effect of feed rate on silicon. Grinding was performed with wheel type of SD 3000, wheel speed of 60m/s, depth of cut of 10um, with different feed rates (a),

(b), and (c) of 250mm/min, 500mm/min, and 1000mm/min respectively.

From the three samples of different feed rates shown above, the feed rate with 250mm/min as

shown in sample (a) has the smoother surface as the ploughing area is lesser. As concluded from

the surface quality above with the increase in feed rate the surface roughness increases as well, the

fracture area occur mostly at the feed rate of 1000mm/min which is shown in (c). From the studies

of (Han Huang et al., 2003; Zhou et al., 2017) it is proven that smaller feed rate can produce a

smoother surface quality than using a larger feed rate.

40

4.7 Calculations of maximum chip thickness and critical depth of cut

The following section shows the calculation of maximum undeformed chip thickness and the

critical depth of cut by using the equation 3 and 8 derived above.

Table 7: Calculation of critical depth of cut

Material Elastic

Modulus (Gpa)

Fracture

Toughness (Mpa m1/2)

Hardness of

material (Gpa)

Critical depth of

cut (nm)

Silicon 169 0.7 12 5

Gallium Arsenide 85.5 0.4 6.8 4.4

Table 3 shows the calculated critical depth of cut by using the equation 1 shown above. The fracture

toughness and hardness of the material were taken from (Michler et al., 2007) and the elastic

modulus of the silicon and gallium arsenide were taken as 169 GPA and 85.5 GPA respectively.

Table 8: Calculation of maximum undeformed chip thickness

Types of wheel C r Vw (mm/min) Vs (m/s) a (um) ds (um)

hm (nm)

SD 3000 10.12 10 250 60 5 5 0.66

10 0.79

15 0.87

500 5 0.94

10 1.12

15 1.24

1000 5 1.33

10 1.58

15 1.75

SD 800 6.58 500 80 5 20 0.48

10 0.57

15 0.63

60 5 0.58

10 0.59

15 0.77

40 5 0.67

10 0.8

15 0.89

From table 4 above it shows the calculated maximum undeformed chip thickness by using the

equation 8 derived. The cutting of point C, were used for the different types of wheel of SD 800

and SD 3000 are 6.58 and 10.12 respectively and the ratio of the width and thickness r was 10. The

different wheel speed, feed rates, and depth of cut were used accordingly as the experiment made,

the wheel diameter was obtained from (Diamond, 2016) with according to the wheel size of 800

and 3000 which is 20um and 5um respectively.

41

5.0 Conclusion

Semiconductor materials like silicon and gallium arsenide have a material properties of

hard hardness and brittleness, most of the semiconductor materials will achieve brittle fracture

transition unless they are undergoing the machining technics especially grinding process. In

conclusion, the studies of precision grinding of semiconductor shows various possible outcomes to

the grinding process. It is concluded that high speed grinding have taken advantages in the grinding

process. From the experiment results shown in the discussion, semiconductors like silicon and

gallium arsenide with a material properties of hard hardness and brittleness, by performing high

speed grinding on the semiconductors it can achieve ductile transition. High speed grinding helps

to improve the surface roughness, surface quality, and decreases the grinding force when the

grinding wheel speed were increased. It can be concluded that the grinding force and surface

roughness increased with the increase of depth of cut and feed rate. Other than that, the surface

roughness will achieve smoother surface when the wheel speed reaches a higher speed. Besides

that, the grinding force decreases when the wheel speed increases. This could be explain by the

maximum undeformed chip thickness, with the increases of wheel speed the maximum undeformed

chip thickness will be smaller, therefore the grinding force will be lesser as well. In the application

of maximum undeformed chip thickness lesser than the critical depth of cut, then the surface quality

will occur ductile transition. While the maximum undeformed chip thickness is larger than the

critical depth of cut, the surface quality will occur brittle fracture transition. Moreover, two

different types of wheel were performed in the experiment which are the wheel type of SD 800 and

SD 3000. With two different types of wheel conducted in the experiment, it is concluded that the

rougher grit size wheel will remove more material and result in a rougher surface finish, while the

finer grit size wheel will remove lesser material but will provide a smoother finish. From the results

discussed, SD 800 with a larger grit wheel size will produce larger force while the SD 3000 with

smaller grit wheel size will have a smaller force. As observed from the surface morphology, with

the wheel speed of 40m/s the surface quality consist of brittle and ductile transition, and when the

wheel speed approached high speed grinding the surface quality improved and achieve ductile

transition. However, wheel type of SD 3000 produce a better surface quality compared to wheel

type of SD 800, as the surface quality of SD 3000 are more to ductile transition and smoother

surface. Next, it is shown in the surface morphology that the surface quality are getting rougher

when the feed rate increases. It is concluded that, by increasing the feed rate and depth of cut the

surface quality will become rougher, while with the increase of wheel speed the surface quality

42

achieve a smoother surface. On top of that, it is concluded that the grinding force are effective ly

influenced by the depth of cut follow by the wheel speed and then the feed rates. Overall, it is

concluded that high speed grinding are a very effective grinding process and it optimize cost for

the machining and grinding process as well.

43

6.0 Future work

During the experiment, there are several experiment errors occurred and due to the

insufficient time limitation to complete the experiment progress. There are a few possible ways

that could improve the efficiency and achieving a precise results in the future work. In the future

work, by conducting more experiments with different parameters could achieve a more precise and

accurate data. In one of the experiment result shown above, the results was being affected owing

to the insufficient time of dressing the wheel and it leads to an inaccurate results, and therefore, in

the future work the wheel must be dressed desirably in order to achieve a better surface finish and

surface quality. Lastly, the surface morphology obtained by using the wheel type of SD 3000 were

not clearly shown much difference in comparison of feed rates. In the future work, with using a

finer grit wheel in comparison with the wheel type of SD 3000 would possibly provide a better

surface quality and surface finish in the surface morphology.

44

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