1. Final Project: Low Pressure CCP Etcher
ENGR 4390-003 Plasma Engineering
Advisor: Dr. Magesh
Submitted by: Shawn Robinson
Date: 5/14/14

2. Abstract
Plasma and plasma design configurations are a new frontier is science due to their unique
physical and chemical properties, especially when it comes to their interaction with other
material surfaces. Due to recent advances in technology such as electrical component
innovations, sensor and detector designs, and better understanding in relevant physics concepts,
we can better create and diagnose different plasmas, and test theories as to their application
results. Plasma is an excited gas mixture, that has received enough energy, whether mechanical,
thermal, or electrical, to reach gas breakdown. This process ionizes a small portion of the gas,
meaning that electrons have been stripped from otherwise inert atoms of gas, and have become
ions. This mixture consists of Ions, excited electrons, released photons, reactive species, and
neutral atoms. For this project we use plasma for the purposes of etching, where layers of
materials will be taken away by the plasma mixture. This project will consist of design,
construction, diagnostics, and testing/optimization of plasma etch chamber.

3. Objective
Plasma etching is a relatively new method for used for the manufacturing of integrated circuits.
In the 70’s plasma was used to strip resistors but in the 80’s further study into plasma resulted in
the ability to add layers which gave way to better chip manufacturing and the modern day
integrated circuit. . First a semiconductor material, usually Si based, is grown with perfect
crystalline structure, into a column. This is then cut into disk with thicknesses ranging from 500-
900um depending on the diameter which come in sizes; 150mm, 200mm, 300mm, and 450mm.
This disk is then carefully transferred to a sealed container between two electrodes. These
electrodes usually have a dialectic barrier on them to help the plasma form uniformly and protect
the electrode. The chamber is then pumped down to < 10.Torr for processing, or < 0.1mTorr for
industry grade processing. Then the gas of choice is pumped into the chamber. The gas is chosen
by its electronegativity, because that the DC voltage is very dependent on this property if using
DC power supply. For plasma etching Gases with low electronegativity, such as O2, N2 are
used, but for more precise industrial processing gasses containing Fluorine, chlorine and bromine
are used because atoms of group VII are very prone to absorb any free electron which passes
nearby. This reduces the electron density an increases the reactive ion density. The reactive ions
“eat” away at the disk in specified patterns. This process of etching is known as reactive ion
etching or dry etching. The objective of this project is to design a plasma etch source that holds
vacuum, and creates a stable plasma that contains etch species.

4. Initial Design
For my initial design I went with simplified
version of the basic CCP etch reactor. Today
capacitive coupled RF plasmas are still the
most common plasmas used in dry etching.
In most cases RF power (13.56MHz) is
supplied to the top, bottom or both
electrodes. RF is used because between 1 and
100MHz, free electrons are easily influenced
in the direction of the applied electric fields.
In the initial design the top electrode was
going to be made of perforated graphite, but
was changed to an aluminum electrode. The
bottom electrode was going to be titanium
alloy but was changed to graphite disc
electrode instead. The chamber itself is made
of steel and the window is made from Lucite.
Final Design
The final design didn’t change much from
the initial other than the electrode materials
due to cost. The bottom electrode is now a
graphite electrode encased in Lucite housing.
The top electrode is now an aluminum
electrode encased in Lucite. There is
no longer a stage, but a manual screw
to adjust the gap distance. There is an
insulated stand to raise the bottom
electrode.
The final design was able to withhold
a 10 tor vacuum pressure. The
operation voltage was 12KV and the
gas used was atmospheric air.

5. Construction
For the majority of this semester, we have spent our time building our plasma devices. This
process has tested and developed some of my hands on skills as a mechanical engineer. I have
learned the process of how to take an idea from thought, design it on paper, then in AutoCAD,
and then finally fabricate. During this I’ve learned that not all designs go according to first plan,
and that it’s ok to make little changes along the way, as long as it doesn’t affect the overall
quality. I’ve gotten a lot of practical skills and independent problem solving practice. In addition
to these experiences I’ve gotten hands on use with power tools and engineering equipment. Here
is a list of some of the main equipment used
-Lathe: Used to machine parts from bulk material
Parts made on lathe: Vacuum nipple (8+hrs), Top electrode (6hrs)
-Mill: Used mill to machine high tolerance features on parts
Parts made on mill: Bottom electrode assembly and housing (5hrs)
-Drill press: Used drill press to machine high tolerance holes
Parts: Bottom electrode assembly, top electrode housing, tap threads

6. -Soldering Iron: Used to connect electrical circuit parts to High voltage wire
Parts: bottom electrode, top electrode
-Band saw: used to cut bulk material to precise measurements for machining
Parts: glass window, top electrode housing, bottom electrode housing
General skills
Vacuum checking
Weld inspection
Correct caliper use
Troubleshooting
Parts list Steel chamber 12”x 9”
1- 3” aluminum disk electrode
2- 3” graphite electrode
9.5” Lucite window
6- 1” flange bolts
9.5” rubber gasket
3- 1” rubber plugs
Diagnostics
OES diagnostics techniques will be used to
diagnose the plasma. If the chamber is a stainless
steel chamber, then OES can be done through a
quartz window using a laser or fiber optics. If it is
Lucite container then sensor wafers or probes are
available to perform OES. Things to look for in
etch plasma are low electron density, low gas
temperature, high gas density, and low high
electron temperature. To the right is what is an
expected spectrum of an oxygen-nitrogen etch
plasma.

7. Species Wavelength Lower transition Upper transition
O IV 588.245 2p2(3P)3p 2D° 5/2 2p2(3P)3d 2P 3/2
O II 765.6779 2s22p2(3P)3d 4D 1/2 2s22p2(3P)4p 4D° 1/2
O II 398.27141 2s22p2(3P)3s 2P 3/2 2s22p2(3P)3p 2P°
O II 404.82163 2s22p2(3P)3d 4F 7/2 2s22p2(3P)4f F 2[3]°
O IV 426.047 2s2p(1P°)3p 2D 3/2 2s2p(1P°)3d 2F° 5/2
Ar II 532.96992 3s23p4(3P2)4f 2[5]° 11/2 3s23p4(3P2)7g 2[6] 13/2
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PlasmaSpectrum
Wavelength(nm)
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Spectrum300-400nm Spectrum400-500nm

8. Optimization/ Troubleshooting:
During the first demonstration, the plasma was unstable. This was due to leaks in the vacuum.
The gasket had to be resized and the ports needed to be resealed with threaded nylon fittings.
This improved the quality of the vacuum and was able to pump down to 10tor instead of the
previous 30tor. Also the plasma would arc to the walls of the chamber, so to avoid this extra
insulator was added to the top and bottom electrodes and the gap distance was adjusted. This
kept the chamber grounded and the circuitry electrically isolated and safe.
Summary/ Future work
During the course, I learned the basics of non-thermal plasma, plasma generation techniques, and
got a good handle on Optical emission spectroscopy. The final design worked well and it’s
something I’m proud of. I got a lot of other diagnostic and trouble shooting skills that will be
able to transfer over into other experiences. Future work would include creating a bolt on flange
window, experimenting with different gasses, and playing with electromagnets to change plume
shape and size. I would also like to try changing targets to find other species in the plasma.
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Spectrum700-800nm
Spectrum500-600nm Spectrum600-700nm

9. References
http://www.nist.gov/pml/data/asd.cfm
Wafer Net Inc. Worldwide Silicon & Semiconductor provider
Sillicon Valley Microelectronics, Inc
Parallel Synthesis Technologies, Inc.
The National Institute of Standards and Technology (NIST)
Verdonck, “Dry Etching for Integrated Circuit Fabrication”, in Processos de Microeletrônica, editor
Baranauskas,1990
DC PLASMA POTENTIAL PATTERN IN LOW-PRESSURE RF DISCHARGE; Lbvaky V.A., KraranilPov O.V.
Kharkov University, Department of Physics and Techndogy,Scientific Center of Ph* and Technology
M. Kogelschatz, G. Cunge, O. Joubert, L. Vallier, and N. Sadeghi, Contrib.
Plasma Phys. 44, 413 _2004_.
GaN etch enhancement in inductively coupled BCl3 plasma with the addition of N2 and SF6 gas Chang
Seok Oh, Tai Hong Kim, Kee Young Lim and Jeon Wook Yang
Impact of Etcher Chamber Design on Plasma Induced Device Damage for Advanced Oxide Etching