Ion Implantation

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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

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A report on Ion Implantation

Transcript of Ion Implantation

Page 1: 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

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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)

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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.

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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

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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

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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.

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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).

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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

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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

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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

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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

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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

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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

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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

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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

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Figure 10: Basic Ion source

5.2 Different type of Ion sources

Figure 11: Microwave Ion source Figure 12: RF Ion source

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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.

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References

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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.