micro hole drlling by industrial co2 laser
TRANSCRIPT
MICRO HOLE DRLLING BY INDUSTRIAL CO2 LASER
MOHD KAMAL BIN MOHD KASIM
B051010151
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
2014
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
This report submitted in accordance with requirement of the Universiti Teknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Manufacturing Process) (Hons.)
by
MOHD KAMAL BIN MOHD KASIM
B051010151
910428-06-5079
FACULTY OF MANUFACTURING ENGINEERING
2014
MICRO HOLE DRLLING BY INDUSTRIAL CO2 LASER
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA
TAJUK: Micro Hole Drilling by Industrial CO2 Laser
SESI PENGAJIAN: 2013/14 Semester 2
Saya MOHD KAMAL BIN MOHD KASIM
mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti
Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan
pertukaran antara institusi pengajian tinggi.
4. **Sila tandakan ( )
SULIT
TERHAD
TIDAK TERHAD
(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia sebagaimana yang termaktub dalam AKTA RAHSIA RASMI 1972). (Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi/badan di mana penyelidikan dijalankan)
Alamat:
J13 Felda Kampung Awah,
28030 Temerloh
Pahang Darul Makmur
Tarikh: ________________________
Disahkan oleh:
Cop Rasmi:
Tarikh: _______________________
** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai
SULIT atau TERHAD.
DECLARATION
I hereby, declared this report entitled “Micro Hole Drilling by Industrial CO2
Laser" is the results of my own research except as cited in references.
Signature : ………………………………………….
Author’s Name : Mohd Kamal Bin Mohd Kasim
Date : …………………………………………
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a
partial fulfillment of the requirements for the degree of Bachelor of Manufacturing
Engineering (Manufacturing Process) (Hons). The member of the supervisory is as
follow:
……………………………..
(Project Supervisor)
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1. ABSTRAK
Pemesinan Laser adalah salah satu kemajuan pemesinan yang paling popular di dunia
ini. Pada masa kini, pemesinan micro laser digunakan dalam pengeluaran MEMS
untuk mengambil alih kaedah tradisional seperti proses punaran yang memerlukan
tempoh masa untuk menyelesaikan proses tersebut. Objektif kajian ini adalah untuk
menyiasat keupayaan penggerudian laser industri, laser CO2, dalam pemprodedan
silikon wafer. Dalam karya ini, lubang-lubang digerudi pada wafer silikon jenis-P
dengan ketebalan 525 μm dan 100 mm diameter. Lubang-lubang diperhatikan dengan
menggunakan mikroskop optik. Ciri geometri lubang yang terhasil iaitu diameter
pintu masuk lubang yang bergantung kepada parameter laser telah disiasat dan
dianalisis. (RSM) telah digunakan untuk menganalisis keputusan dan model yang
sesuai telah dihasilkan untuk laser penggerudian pemprosesan. Parameter laser yang
terlibat ialah kekuasaan laser, frekuansi laser dan kitar tugas. Keputusan eksperimen
menunjukkan diameter pintu masuk lubang penggerudian telah meningkat apabila
kuasa laser dan kitar tugas meningkat tetapi diameter pintu masuk akan berkurangan
apabila frekuensi laser turut berkurangan.
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2. ABSTRACT
Laser machining is one of the most popular advance machining in this world.
Nowadays, laser micromachining is currently used in the MEMS production to take
over the traditional method such as etching process that needs a period of time to
finish the process. The objective of this study is to investigate the drilling capability
of industrial laser, CO2 laser, in silicon wafer processing. In this work, the holes were
drilled on P-type silicon wafer with thickness 525 µm and 100 mm diameter. The
holes were observed by using an optical microscope. Geometrical characteristic of
holes produce, which is diameter entrance that depends on laser parameter were
investigated and analyzed. Response Surface Methodology (RSM) was used to
analyze the result and generated an appropriate model for the laser drilling
processing. The laser parameters involve were laser power, pulse frequency and duty
cycle. The experiment result showed the entrance diameter of drilling holes increased
when the laser power and duty cycle increased, but the entrance diameter decreased
as the pulse frequency decreased.
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DEDICATION
To my beloved father and mother
Mr. Mohd Kasim Bin Ahmad
Mdm. Mismawati Binti Kadis
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3. ACKNOWLEDGEMENT
Alhamdulillah, all my praise to Allah S.W.T for the bless that been given to complete
Project Sarjana Muda 1 (PSM 1) and Project Sarjana Muda 2 (PSM 2) successfully.
In this good opportunity, I would like to thank you to all people that involved directly
or indirectly in completing this technical report. Firstly, I would like to thank to my
supervisor, Profesor Madya Ir. Dr. Sivarao a/l Subramonian, for his guidance,
advices, ideas and support all of the way through the execution of this project. Not
forgotten, my appreciation also goes to all technicians from the Faculty of
Manufacturing Engineering (FKP) for all the supports, contribution and cooperation
during my investigation and completing my project. Finally, I would like to thanks to
my family, especially to my parent and siblings for their love and support from
behind. Not forget to all of my colleagues and members that help and give their
opinions for completing this project and report either directly or indirectly.
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TABLE OF CONTENT
Abstrak i
Abstract ii
Acknowledgement iv
Table of Content v
List of Figures viii
List of Tables x
List of Symbols xi
CHAPTER 1: INTRODUCTION 1
1.1 Introduction 1
1.2 Background of Study 1
1.3 Problem Statement 2
1.4 Objectives of the Research 3
1.5 Scope of the Study 3
CHAPTER 2 : LITERATURE REVIEW 4
2.1 Introduction 4
2.2 Micro Electro Mechanical System (MEMS) 4
2.2.1 Application of MEMS 5
2.2.2 Fabrication of MEMS 6
2.3 Laser Micromachining 7
2.4 Fundamental Principle of Laser 8
2.5 Laser Drilling 12
2.6 Types of Laser 15
2.6.1 Carbon Dioxide (CO2) Laser 16
2.7 Laser Cutting Machine 19
2.8 Silicon Wafer 20
2.9 Process Parameters 23
2.10 Selection of Parameters 23
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2.11 Laser Parameter 25
2.11.1 Laser Power 26
2.11.2 Pulse Frequency 26
2.11.3 Duty Cycle 27
2.12 Entrance Diameter (dentrance) 27
2.13 Silicon Surface Preparation 28
CHAPTER 3 : METHODOLOGY 30
3.1 Introduction 30
3.2 Research Flow Chart 30
3.3 Preliminary Investigation 32
3.4 Design Parameters 32
3.5 Design of Experiment (DoE) 33
3.5.1 Response Surface Methodology 34
3.5.2 Box-Behnken Design 35
3.5.3 Level 36
3.5.4 Variables 36
3.5.5 Design Expert 36
3.6 Material Selection 38
3.7 Laser Cutting Machine (Helius 2513) 39
3.8 Experimental Setup 40
3.8.1 Silicon Solvent Cleaning 41
3.8.2 Hole Drawing 42
3.9 Data Observation 44
3.9.1 Entrance Diameter (dentrance) of Drilling Hole 44
3.11 Modelling 45
3.12 Conclusion 46
CHAPTER 4 : RESULT AND DISCUSSION 47
4.1 Introduction 47
4.2 Investigation of Entrance Diameter of Drilling Holes 48
4.3 Experimental Result of Laser Drilling Process 48
4.4 Laser Drilling of Silicon Wafer Model Analysis 51
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4.4.1 Optimization 56
4.5 The Spatter Deposition Area of Laser Drilling Hole 58
CHAPTER 5 : CONCLUSION 61
5.1 Conclusion 61
5.2 Recommendation 62
6. APPENDIX A 70
7. APPENDIX B 73
8. APPENDIX C 75
viii
4. LIST OF FIGURES
2.0: Micromotor as one of the MEMS product 5
2.1: Basic formation of laser 9
2.2: Electromagnetic spectrum wavelength for several laser types 9
2.3: Absorption mechanism 10
2.4: Spontaneous emission process 11
2.5: Stimulated emission mechanism 11
2.6: Various techniques in laser drilling 13
2.7: Laser drilling process diagram 13
2.8: Silicon wafer 20
2.9: Percentage of silicon reflectivity versus laser wavelength 21
2.10: Difference number of cycle that produce in one second 26
2.11: Laser pulse 27
2.12: Measuring process of hole diameter on silicon wafer 28
3.0: Research flow chart 31
3.1: Central composite design 35
3.2: Box-behnken design for three factors 35
3.3: Experimental parameters setup 37
3.4: Experiment response setup 37
3.5: Table of run for experiment 38
3.6: Laser cutting machine (Helius 2513) 39
3.7: The experimental setup flow chart 40
3.8: AUTOCAD drawing for the laser drilling process 42
3.9: Schematic diagram of CO2 laser micromachining setup 43
3.10: Laser beam nozzle 43
3.11: X and Y direction of drilling hole 45
3.12: Meiji Techno Microscope 45
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4.0: Drilled hole on a silicon wafer 47
4.1: The experimental value and predicted value of dentrance 52
4.2: Effects of Laser power to the dentrance of drilling holes 53
4.3: Effects of pulse frequency to the dentrance of drilling holes 54
4.4: Effects of duty cycle on the dentrance of drilled hole 55
4.5: Interaction of laser power and pulse frequency to the dentrance 56
4.6: Suggested parameter value of laser drilling process 57
4.7: Predicted entrance diameter of drilling hole 58
4.8: Spatter deposition area for different silicon wafer side 59
x
5. LIST OF TABLES
2.0: Types of laser with wavelength and average power range. 16
2.1: Typical carbon dioxide (CO2) laser parameters. 18
2.2: Standard on silicon wafer sizes and thickness. 21
2.3 (a): Mechanical properties of silicon. 22
2.3 (b): Thermal properties of silicon 22
2.4: Laser input and output parameters 23
2.5: Frequency for laser input and output parameters 24
2.6: Descend order of input and output laser parameters 24
2.7: Summary of laser input and output parameters 25
3.0: Parameter used for experiment 33
3.1: Basic specification of laser machine Helius - 2531 39
4.0: Experiment run and test result for laser drilling process 49
4.1: Experiment result after run eliminating process 50
4.2: Table of ANOVA for dentrance holes 51
4.3: Optimization solution proposed by Design Expert 57
xi
6. LIST OF SYMBOLS
mm - Millimetre
nm - nanometer
In - Inch
W - Watt
KW - Kilowatt
oC - Celcius
µ - Micron, 1 x 10-6
Hz - Hertz
% - Percent
N - Nitrogen
O2 - Oxygen
CO2 - Carbon Dioxide
He - Helium
1
1. CHAPTER 1
INTRODUCTION
1.1 Introduction
This chapter explains about several sections which include the background of study,
problem statements, research objectives, research scope and completed by
limitations of research.
1.2 Background of Study
In the world today, the manufacturing industries need advanced machining
techniques to follow the rigorous design requirement and to machine the hard-to-
machine material such as titanium, steel, super alloy materials, composite and
ceramics. Laser machining is one of the most popular advances machining in this
world. Lasers are broadly applied in industry as cutting tools due to ultra-flexibility
of the cutting conditions, quick set up, obtaining a high quality end product, the
small size of the heat affected zone, and non-mechanical contact between the
workpiece and the tool (Yilbas, 2004).
There are a lot of laser resource types that commonly used in manufacturing
industries and the current types of laser used are CO2 and Nd: YAG laser. Nearly 90
percent of all industrial laser material processing used both types of lasers. Basically,
both types of laser have different capabilities cut or drill a piece of materials by
depending on the thickness and properties of that material. Today, laser micro-
drilling is increasingly being used in the fabrication of small components for
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electronics, aerospace, biomedical, MEMS, and other applications because it
provides rapid, precise, clean, flexible, and efficient process (Han et al, 2004).
Micro-electromechanical system (MEMS) is a technology used to create small
integrated devices or systems that merges mechanical and electrical components.
This technology has abilities to sense, control and actuate on the micro scale, and
generate effects on the macro scale. There are four types of MEMS component
which is micro sensors, micro actuators, microelectronics and microstructure. The
primary material used in MEMS is Silicon (Jiang et al, 2009). MEMS application
includes the process control and automation, automotive industry, scientific and
medical instrumentation, and telecommunication.
1.3 Problem Statement
In recent year, majority of MEMS manufacturing companies likes to use Nd: YAG
laser for drilling micro hole on the silicon wafer. By applying Nd: YAG lasers which
produce short pulses and the UV wavelength, this permit a reduction of thermal
effects like heat affected zones (HAZ) and deposition of molten material at the
cutting edge (Klozbach.U et al, 2011).
The wavelength of a CO2 laser is 10.64 μm and not absorbed by silicon material
(Chung et al, 2006). Silicon is not an active optical material. This material is only
effective in detecting light and the emission of light is difficult to achieve. So, this is
difficult to apply the drilling technique by using CO2 laser because this laser
provides a long pulse and wavelength that cannot absorb by silicon material.
CO2 laser is typically used to drill holes larger than 100 μm in diameter and cannot
drill holes smaller than 75 μm (Luziusa et al, 2013). Furthermore, there is still less
research done regarding the laser drilling process on a silicon wafer by using CO2
laser. Although there are several related journals and report done regarding the usage
of CO2 lasers for drilling hole on the other materials such as fiberglass and stainless
steel. The parameter on those researches cannot be used directly because different
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material will have different properties that allowed the laser move throughout the
material.
This project is about the experimental studies of the micro laser drilling of silicon
wafers by using CO2 laser. Laser parameters such as laser power, pulse frequency,
and duty cycle will be set up to drill holes on 525 µm thickness of silicon wafers.
Entrance diameter of drilling holes will be analyzed. This project results will provide
a common advice in generating micro holes on the MEMS structure on silicon
wafers using CO2 laser.
1.4 Objectives of the Research
The objectives of this research are to:
i. Investigate the drilling capability of CO2 laser in silicon wafer processing.
ii. Model the laser processing of silicon wafer.
iii. Optimize the develop model.
1.5 Scope of the Study
This research will be conducted by using Helius 2513 Laser Cutting Machine with
rated power of 3000 watts. P-types silicon wafer with 525 µm thickness and 100 mm
diameter will be used for the laser drilling process. Then, the entrance diameter of
drilling holes will be analyzed. Design Expert software will be used as a tool to
design the experiment and analyze the result.
4
2. CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
In this chapter, the research review is focused on several main sections such as the
Micro Electro Mechanical System (MEMS), types of machine and material, and the
methods used to design an experiment. This information is useful so that appropriate
parameters of laser machining can be chosen based on previous research, in order to
drill silicon wafer.
2.2 Micro Electro Mechanical System (MEMS)
Micro-electromechanical system or known as MEMS is one of the process
technology applied to produce smaller devices or systems that bring together the
electrical and mechanical components. In the United States, the technology is known
as micro-electromechanical system (MEMS) but in Europe, it is known as
microsystem technology (MST) (Nadim Maluf, 2004). According to Hsu (2002),
MEMS also can be defined as a small and integrated device, which combine
electronics, electrical and mechanical elements to meet the control related functional
requirement (see Figure 2.0).
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Figure 2.0: Micromotor as one of the MEMS product (Hsu 2002).
This technology basically made up using integrated circuit (IC) and can be in several
of sizes from a few micrometres to millimeters. MEMS contains components of sizes
in ranges of 1 micrometer to 1 milimeter (Nadim Maluf, 2004). MEMS are a
developing technology which applies integrated circuit (IC) fabrication methods to
create integrated microsensor, microactuators, and microelectronics to make micron
size devices which can sense and act on the local environment (Simon, 2010). There
were several types of MEMS components which consisting of mechanical
microstructures, microsensors, microactuators and microelectronics. All of this form
was integrated onto the same silicon chip.
2.2.1 Application of MEMS
Nowadays, MEMS is an unknown and famous technology used in the world.
Smartphone industries are not neglecting to apply MEMS in producing new models
of Smartphone. Smart phones were generally provided with tri-axis magnetometer
and tri-axis MEMS accelerometer such as the start adding tri-axis MEMS gyroscope,
which is iPhone 4 from Apple Inc (Niu et al, 2012).
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MEMS technology also has been used in the automotive sectors in term of sensors.
There were above 100 sensors used involving gyroscopes for higher fuel efficiency,
MEMS Tire Pressure Monitoring System (TPMS) and other purposes (Chun et al,
2012). For the Electronic Stability Program (ESP) or vehicle dynamic system
(VDC), this system was the most effective active safety systems in the automotive
domain, supporting the driver to retain the vehicle on the intended path, thus helping
to avoid accidents (Marek, 2011). The MEMS technology also can help in the
vehicle fuel consumption. The vehicle based pressure sensors such as manifold
pressure sensor are used to determine the air intake of the engine. With the help of a
barometric pressure sensor, combustion algorithms can be adjusted in correlation
with the ambient air pressure (Finkbeiner, 2007).
For the medical sectors, accelerometers and pressure sensors remain the largest two
market segments for MEMS products and technology. These components can be
applied to determine the human blood pressure accurately only in several second
time. For the efficiency of computer using in medical application, MEMS
accelerometers and fiber optic sensors have produced as an interface between a user
and a computer. The movement of user's body can be measured directly by wearing
these types of sensors. In the biomedical application, optical MEMS also have been
applying in multifunctional endoscope that used for advanced diagnosis and
endoscopic surgery (Miyajima, 2002).
2.2.2 Fabrication of MEMS
Laser micromachining of dielectrics and metals is a multipurpose fabrication and
repair tool for applications in MEMS, microelectronics, and micro-fluidics,
(Fedosejevs et al, 2003). There are three types of micromachining techniques used
by current industry in MEMS production, which is bulk micromachining, surface
micromachining and LIGA process (Hsu, 2002).
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Bulk micromachining is a process of removal of material from the bulk substrates to
form the desired three dimensional geometry of the microstructure. This is
sometimes done to “undercut” structures that compulsory to physically move which
is to produce membranes on one side of a wafer and to make a mixture of trenches,
holes, or other structures. These types of micromachining basically consist of several
techniques which is wet etchant and dry etchant.
Then in the surface micromachining technique, the material is removed by physical
or chemical means and the micromachining surface will build microstructure by
adding material layer by layer on top of the substrate. Surface micromachining
technique many benefits which a low-cost technique, batch-manufacturing process,
and can achieve much higher alignment accuracy than is possible by conventional
passive-alignment techniques.
In the LIGA process, this process begins with deep x-ray lithography that sets the
desired pattern of a thick film of photoresist. After the substrates and photoresists
material have been chosen, the electroplating process will be done. In many
micromachining technologies, photolithography techniques are used to transfer the
desired pattern from a mask to the structural material. As one of the cheapest and
most capable surface-micromachining processes, LIGA has concerned much
attention for millimeter-wave and microwave device (Yun et al, 2002).
2.3 Laser Micromachining
Laser micromachining is based on the local supports of energy to materials on the
surface where the laser light is transformed into heat (Meijer, 2001). Nowadays, laser
micromachining was currently used in the MEMS production to take over the
traditional method such as etching process that needs a period of time to finish the
process. Laser micromachining is one of the economically and rapidly process to get
a high aspect ratio through hole diameter to hole length, which interrelates in the die
or multichip modules (MCM) substrate for the 3-D application.
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Different issues when used laser micromachining to replace the traditional etching
process that result will be faster, accurate and high production rate. The application
areas of laser micro machining involved of manufacturing methods like cutting,
drilling, welding as well as ablation and material surface texturing, whereby it is
possible to get a very fine surface structure ranging in the micrometer domain
(Klozbach. U et al, 2011). The established laser micromachining method has
minimized normal problems in laser micromachining such as the laser polarization
effect, material recast (microcracks to the sidewall of structures), and Heat Affected
Zone (HAZ), (Zhu et al, 2002).
There were many types of lasers used in the laser micromachining process. There are
from microsecond pulsed infrared CO2 gas laser at a wavelength between 9.3-11µm
to nanosecond pulsed excimer gas laser in the 157-353 µm UV wavelength range. In
silicon etching process, CO2 laser with wavelength 10.64 μm have been used with
glass attached to the Si backside because the pure silicon cannot absorb the laser
wavelength (Chung et al, 2006).
The increasing of the laser pulse is continuing from Femto-second to nanosecond
pulsed solid state laser between wavelengths of 266 - 1060 NM. A micro-structuring
of SiO2 thin film on Si have been applied by using Femto-second laser pulse with
150 femtosecond pulse duration and a maximum energy up to 3mJ/pulse. Actually,
all of the laser types are used depending on the types of material to be processed.
2.4 Fundamental principle of Laser
The word" laser" is an acronym and stand for: (L) light (A) amplification by (S)
stimulated (E) emission of (R) radiation (Silfvast, 2004). Each type of lasers is
optical amplifiers which operate by pumping (exciting) an active medium placed
between two mirrors (see Figure 2.1). In fact, the active medium was a collection of
specially selected atoms, molecules or ions which can be in a gas, liquid or solid
form and which will form laser.