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Transcript of Ion Implantation
A
REPORT
ON
Ion Implantation
Submitted by
Abhishek Goyal
2009UEC302
DEPARTMENT OF ELECTRONICS AND COMM. ENGINEERING
MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY JAIPUR
MARCH 2013
Under the guidance of
Dr. Srinivasa Rao Nelamarri
Assistant Professor
DEPARTMENT OF PHYSICS
MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY JAIPUR
MARCH 2013
ACKNOWLEDGEMENT
I take this opportunity to express my deep sense of gratitude and respect
towards Dr. Srinivasa Rao Nelamarri (Assistant Professor, Dept. of
Physics, Malaviya National Institute of Technology Jaipur). I am
very much indebted to him for the generosity, expertise and guidance I
have received from him while working on this report and throughout
my studies related to Nano Materials.
Abhishek Goyal
(2009UEC302)
I Report on Ion Implantation by Abhishek Goyal
Abstract
In this report, a detailed introduction of Ion Implantation is given and various
techniques to implement the same are being discussed. Various advantages of the
Ion Implantation over the diffusion has also been discussed in this report.
Ion implantation is a materials engineering process by which ions of a material
are accelerated in an electrical field and impacted into a solid. We have also
discussed what could be the various sources for ion generation like RF,
Microwave, plasma source etc. Various applications of Ion Implantation are also
discussed in this report.
The various stopping mechanisms and the channelling effect is also discussed in
this report so as to have an in depth information about the penetration of Ion.
Moreover, shadowing effect is also discussed in this report and how it is useful
for the Ion Implanter.
The last section discusses about the various safety measures that are to be
followed during the process.
I Report on Ion Implantation by Abhishek Goyal
CONTENTS
CHAPTER PAGE NUMBER
Chapter 1: INTRODUCTION
1.1 What is Semiconductor? 1
1.2 Why semiconductor need to be doped? 1
1.3 What is n-type and p-type dopant? 2
Chapter 2: Doping Techniques
2.1 Diffusion 3
2.2 Ion implantation 4
2.3 Comparison between both techniques 5
Chapter 3: Stopping Mechanism
3.1 Nuclear stopping 6
3.2 Electronic stopping 6
3.3 Stopping mechanism 7
Chapter 4: Channelling, Shadowing and Post Implementation Annealing
4.1 Channelling 8
4.2 Shadowing 9
4.3 Post Implementation Annealing 9
Chapter 5: Ion Implanter
5.1 Ion source 10
5.2 Different type of Ion sources 11
5.3 Safety Measures 12
References 13
II Report on Ion Implantation by Abhishek Goyal
INDEX OF FIGURES PAGE NUMBER
Figure 1: Diffusion Process 3
Figure 2: Ion Implantation 4
Figure 3: Comparison between Diffusion and Ion Implantation 5
Figure 4: Stopping Mechanism 7
Figure 5: Ion Trajectory and Projected range 7
Figure 6: Channelling Effect 8
Figure 7: Shadowing Effect 9
Figure 8: Effect of Annealing 9
Figure 9: Ion Implanter 10
Figure 10: Basic Ion source 11
Figure 11: Microwave Ion source 11
Figure 12: RF Ion source 11
Figure 13: Plasma Flooding system 12
INDEX OF TABLES PAGE NUMBER
Table 1: Comparison between Diffusion and Ion Implantation 5
1 Report on Ion Implantation by Abhishek Goyal
Chapter 1: Introduction
1.1 What is Semiconductor?
A semiconductor is a material which has electrical conductivity between that of a conductor
such as copper and an insulator such as glass. The conductivity of a semiconductor increases
with increasing temperature, behaviour opposite to that of a metal. Semiconductors can display
a range of useful properties such as passing current more easily in one direction than the other.
Because the conductive properties of a semiconductor can be modified by controlled addition
of impurities or by the application of electrical fields or light, semiconductors are very useful
devices for amplification of signals, switching, and energy conversion. Understanding the
properties of semiconductors relies on quantum physics to explain the motions of electrons
through a lattice of atoms.
1.2 Why semiconductor need to be doped?
In semiconductor production, doping intentionally introduces impurities into an extremely pure
(also referred to as intrinsic) semiconductor for the purpose of modulating its electrical
properties. The impurities are dependent upon the type of semiconductor. Lightly and
moderately doped semiconductors are referred to as extrinsic. A semiconductor doped to such
high levels that it acts more like a conductor than a semiconductor is referred to as degenerate.
Doping a semiconductor crystal introduces allowed energy states within the band gap but very
close to the energy band that corresponds to the dopant type. In other words, donor impurities
create states near the conduction band while acceptors create states near the valence band.
Dopants also have the important effect of shifting the material's Fermi level towards the energy
band that corresponds with the dopant with the greatest concentration.
2 Report on Ion Implantation by Abhishek Goyal
1.3 What is n-type and p-type dopant?
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance
(in very low concentrations) in order to alter the electrical properties or the optical properties
of the substance. The addition of a dopant to a semiconductor, known as doping, has the effect
of shifting the Fermi levels within the material. This results in a material with predominantly
negative (n-type) or positive (p-type) charge carriers depending on the dopant variety. Pure
semiconductors that have been altered by the presence of dopants are known as extrinsic
semiconductors. When a doped semiconductor contains excess holes it is called "p-type"(B),
and when it contains excess free electrons it is known as "n-type"(P, As, Sb).
3 Report on Ion Implantation by Abhishek Goyal
Chapter 2: Doping Techniques
2.1 Diffusion
Diffusion is one of several transport phenomena that occur in nature. A distinguishing feature
of diffusion is that it results in mixing or mass transport, without requiring bulk motion. In the
phenomenological approach, according to Fick's laws, the diffusion flux is proportional to the
negative gradient of concentrations. It goes from regions of higher concentration to regions of
lower concentration. The procedure is as follows:
Figure1: Diffusion Process
4 Report on Ion Implantation by Abhishek Goyal
2.2 Ion implantation
Ion implantation is a materials engineering process by which ions of a material are accelerated
in an electrical field and impacted into a solid. This process is used to change the physical,
chemical, or electrical properties of the solid. They also cause much chemical and physical
change in the target by transferring their energy and momentum to the electrons and atomic
nuclei of the target material. This causes a structural change, in that the crystal structure of the
target can be damaged or even destroyed by the energetic collision cascades. Because the ions
have masses comparable to those of the target atoms, they knock the target atoms out of place
more than electron beams do.
Typical ion energies are in the range of 10 to 500 keV (1,600 to 80,000 aJ). Energies in the
range 1 to 10 keV (160 to 1,600 aJ) can be used, but result in a penetration of only a few
nanometers or less. Energies lower than this result in very little damage to the target, and fall
under the designation ion beam deposition. Higher energies can also be used: accelerators
capable of 5 MeV (800,000 aJ) are common. However, there is often great structural damage
to the target, and because the depth distribution is broad (Bragg peak), the net composition
change at any point in the target will be small.
Figure 2: Ion Implantation
5 Report on Ion Implantation by Abhishek Goyal
2.2 Comparison between both techniques
Table 1: Comparison between Diffusion and Ion Implantation
Diffusion Ion Implantation
High temperature, hard mask Low temperature, photoresist mask
Isotropic dopant profile Anisotropic dopant profile
Cannot independently control of the dopant
concentration and junction depth
Can independently control of the dopant
concentration and junction depth
Batch process Both Batch and single wafer process
Figure 3: Comparison between Diffusion and Ion Implantation
6 Report on Ion Implantation by Abhishek Goyal
Chapter 3: Stopping mechanism
The procedure followed is as follows:
• Ions penetrate into substrate
• Collide with lattice atoms
• Gradually lose their energy and stop
• Two stop mechanisms
3.1 Nuclear stopping
It occurs due to
• Collision with nuclei of the lattice atoms
• Scattered significantly
• Causes crystal structure damage.
3.2 Electronic stopping
It occurs due to
• Collision with electrons of the lattice atoms
• Incident ion path is almost unchanged
• Energy transfer is very small
• Crystal structure damage is negligible
7 Report on Ion Implantation by Abhishek Goyal
3.3 Stopping mechanism
• The total stopping power
Stotal = Sn + Se
• Sn: nuclear stopping, Se: electronic stopping
• Low E, high A ion implantation: mainly nuclear stopping
• High E, low A ion implantation, electronic stopping mechanism is more important
Figure 4: Stopping Mechanism
Figure 5: Ion Trajectory and Projected range
8 Report on Ion Implantation by Abhishek Goyal
Chapter 4: Channelling, Shadowing and Post
Implementation Annealing
4.1 Channelling
• If the incident angle is right, ion can travel long distance without collision with lattice
atoms
• It causes uncontrollable dopant profile
Figure 6: Channeling Effect
• Ways to avoid channeling effect
– Tilt wafer, 7° is most commonly used
– Screen oxide
– Pre-amorphous implantation, Germanium
• Shadowing effect
– Ion blocked by structures
• Rotate wafer and post-implantation diffusion
9 Report on Ion Implantation by Abhishek Goyal
4.2 Shadowing
Figure 7: Shadowing Effect
4.3 Post Implementation Annealing
Ion collides with lattice atoms and knock them out of lattice grid. Implant area on substrate
becomes amorphous structure. Dopant atom must in single crystal structure and bond with four
silicon atoms to be activated as donor (N-type) or acceptor (P-type). Thermal energy from high
temperature helps amorphous atoms to recover single crystal structure.
Figure 8: Effect of Annealing
10 Report on Ion Implantation by Abhishek Goyal
Chapter 5: Ion Implanter
Ion Implantation: Basic requirements
• Ion energies above 200 keV and up to 10 MeV
• Argon is used for purge and beam calibration
• Pressure of 10-5 to 10-7 Torr
• Turbo pump and Cryo pump
Figure 9: Ion Implanter
5.1 Ion source
• Hot tungsten filament emits thermal electron
• Electrons collide with source gas molecules to dissociate and ionize
• Ions are extracted out of source chamber and accelerated to the beamline
• RF and microwave power can also be used to ionize source gas
11 Report on Ion Implantation by Abhishek Goyal
Figure 10: Basic Ion source
5.2 Different type of Ion sources
Figure 11: Microwave Ion source Figure 12: RF Ion source
12 Report on Ion Implantation by Abhishek Goyal
Figure 13: Plasma flooding system
5.3 Safety Measures
In the ion implantation semiconductor fabrication process of wafers, it is important for the
workers to minimize their exposure to the toxic materials are used in the ion implanter process.
Such hazardous elements, solid source and gasses are used, such as arsine and phosphine. For
this reason, the semiconductor fabrication facilities are highly automated, and may feature
negative pressure gas bottles safe delivery system (SDS). Other elements may include
antimony, arsenic, phosphorus, and boron. Residue of these elements show up when the
machine is opened to atmosphere, and can also be accumulated and found concentrated in the
vacuum pumps hardware. It is important not to expose yourself to these carcinogenic,
corrosive, flammable, and toxic elements. Many overlapping safety protocols must be used
when handling these deadly compounds. Use safety, and read MSDSs.
High voltage power supplies in ion implantation equipment can pose a risk of electrocution. In
addition, high-energy atomic collisions can generate X-rays and, in some cases, other ionizing
radiation and radionuclides. Operators and maintenance personnel should learn and follow the
safety advice of the manufacturer and/or the institution responsible for the equipment. Prior to
entry to high voltage area, terminal components must be grounded using a grounding stick.
Next, power supplies should be locked in the off state and tagged to prevent unauthorized
energizing.
Other types of particle accelerator, such as radio frequency linear particle accelerators and laser
wake field plasma accelerators have their own hazards.
13 Report on Ion Implantation by Abhishek Goyal
References
[1] Y Hamm, Robert W.; Hamm, Marianne E. (2012). Industrial Accelerators and Their Applications.
World Scientific. ISBN 978-981-4307-04-8.
[2] A. J. Armini, S. N. Bunker and M. B. Spitzer, "Non-mass-analyzed Ion Implantation Equipment for
high Volume Solar Cell Production," Proc. 16th IEEE Photovoltaic Specialists Conference, 27-30 Sep
1982, San Diego California, pp. 895-899.
[3] G. Landis et al., "Apparatus and Technique for Pulsed Electron Beam Annealing for Solar Cell
Production," Proc. 15th IEEE Photovoltaic Specialists Conf., Orlando FL; 976-980 (1981).
[4] B.G. Yacobi, Semiconductor Materials: An Introduction to Basic Principles, Springer 2003 ISBN
0306473615, pp. 1-3
[5] http://www.nit.eu/czasopisma/JTIT/2010/1/3.pdf Lidia Łukasiak and Andrzej Jakubowski, History
of Semiconductors in Journal of Telecommunication and Information Technology1/2010
[6] Peter Robin Morris: A History of the World Semiconductor Industry, IET 1990, ISBN 0863412270,
pp.11-25
[7] Smart, L. et al. (2005). State Chemistry: An Introduction. pp. 165–171. ISSN 0-7487-7516-1.
[8] Miessler, G. et al. (1965). Inorganic Chemistry (3rd Ed.). pp. 237–240. ISSN 0-7487-7516-1.
[9] Robert L. Sproull, Modern Physics:The quantum physics of atoms, solids and and nuclei, Second
Edition, John Wiley and Sons, 1963 ISBN 0-471- 8145-3 Chapter 8
[10] Muller, Richard S.; Theodore I. Kamins (1986). Device Electronics for Integrated Circuits (2d
Ed.). New York: Wiley. p. 427. ISBN 0-471-88758-7.
[11] Jones, B. et al (2007). "Tuning Orbital Energetics in Arylene Diimide Semiconductors". Prog J.
Am. Chem. Soc. 129: 15259–15278. Doi: 10.1021/ja075242e.
[12] Facchetti, A. (2007). "Semiconductors for organic transistors". Materials Today 10 (3): 29–37.
ISSN 7021 1369 7021.
[13] Newman, C. et al (2004). "Introduction to Organic Thin Film Transistors". Chem. Mater 16: 4436–
4451. Doi: 10.1021/cm049391x.
[14] J. W. Allen (1960). "Gallium Arsenide as a semi-insulator". Nature 187 (4735): 403–405. Bibcode
1960Natur.187.403A. Doi: 10.1038/187403b0.