INTERNATIONAL AND NATIONWIDE LOW TEMPERATURE
PLASMA STUDIES AND APPLICATIONS: A BRIEF REVIEW
XIAOGANG WANG
STATE KEY LAB OF MARTERIAL MODIFICATIONS BY BEAMS
DALIAN UNIVERSITY OF TECHNOLOGY, DALIAN, CHINA 116024
Abstract
This is a brief review for recent developments in low temperature plasmas
science and technology. The relationship of low temperature plasma studies with
high-tech industry is also discussed to provide a reference for future policy making.
The major applications of low temperature plasma technology with emphasize on
plasma sources and pulsed power techniques as well as further discussions of the
dusty plasma application to plasma processing and biophysical applications are also
presented.
I.
INTRODUCTION
Low temperature plasma science and technology provide a strong base for
high-tech industries such as computer chip manufacturing, material modifications and
other plasma processing industries, as well as traditional industries such as the steel
and electrical industries, and recently developed industries such as environment and
space-aero industries, etc. The progresses of the area in the 80s and early 90s had
been summarized by US National Research Council Panel on Plasma Processing of
Materials [1]. We are here trying to review those new developments briefly.
In this brief review, we first discuss the relationship of low temperature plasma
studies with high-tech industry, in particularly the current situation in China in
comparison with that in developed countries. Then we give a glance to the major
applications of low temperature plasma technology with emphasize on plasma sources
and pulsed power techniques. The further discussions of the applications are focused
on the dusty plasma application to plasma processing and biophysical applications of
low temperature plasma science and engineering. The review is concluded by a
summary and further introduction to low temperature plasma research facilities in US
universities.
II.
RELATIONSHIP WITH INDUSTRY
The basic structure of the relationship in US and other developed countries has
three components: government supported basic researches, private sector research and
developments (R&D), and industry applications, such as plasma sources and beams,
processing, films, electronics, computer chips, etc. Those three components relate,
support and interact with each other. The funding for low temperature plasma
researches is then partially from the private sector R&D and partially from the
government. In China however, there are only government supported basic researches
and few industry applications. The bridge between the basic researches and
manufacturers: the industry R&D component either doesn’t exist or has little resource.
This is the major reason that the industry sector in China has no motivation to support
the research.
Nevertheless, the basics research in China itself has some shortcomes.
The basic research sector in developed countries includes following areas:
Pure scientific researches such as “What is going to happen in 20 years?” and
basics physical chemical and biological processes in the field;
“Basic” applied researches for new sources, new ways and new materials such as
helicons (in 90s), sources and beams for “big sciences”, PSII (in 80s), pulsed
technology, atmosphere pressure glow discharge (OAPUGD), etc., and the computer
code development.
However, few above areas are covered by basic researches in China.
The industry R&D in US have some overlaps with the basics researches,
particularly the R&D for new sources, new ways and new materials as well as
computer code development, but more specific and more profit-oriented. It also
focuses on new processes such as chemical and biological processes. This part is the
weakest link for plasma assisted manufacturing research in China. Without a strong
industry R&D component, our research achievements would be hardly applied to the
“real” world.
Finally, we come to the last and the dominant component: industry itself.
The plasma related industries in US are high-tech leaders. To keep their leading
status, they have to do basic researches to find new sources, new ways to accelerate
their business extension. Even the countries not as a leader, such as Japan, they are at
least a major manufacturer and have to do some process improvement research to
catch up. China is neither a high-tech leader nor a major high-tech manufacturer. Then
the companies can largely rely on imports: technology and devices. This is the fatal
circle for China: since we are not a leader in the field, either technically or
manufacturally, there is then no rush for basic researches; since we are not motivated
to do basic research, we will never be a leader in the field. Our policy has to consider
this point.
Even the government sectors in China are unwilling to support the basic
researches. In US, a large slice of funding is from government sector industry such as
aero-space industry and environment industry. We need to explore the opportunities in
similar areas. The “big sciences” such as space science and fusion science also are
major “users” of low temperature plasma technology, particularly plasma and beam
source technology. We need also to find opportunities in those fields.
III.
MAJOR APPLICATIONS
Low temperature plasma technology can be applied to following areas [2]:
Surface treatment, including ion implantation, surface hardening, welding, cutting,
drilling, and film deposition, etc;
Volume processing, such as flue gas treatment, metal recovery, waste treatment,
water purification, as well as plasma spraying etc;Light Sources, such as high
intensity sources, discharge lamps, low pressure lamps, specialty sources, lasers,
field-emitter arrays, plasma displays etc;
Switches, such as electric power switches, pulsed power etc;
Energy converters: MHD generators, thermionic energy converters, beam sources
etc;
Radiation processing: ceramic powders, plant growth, etc;
Medicine: surface treatment, instrument sterilization, etc;
……
The major applications of low temperature plasma researches include plasma
sources, beams, pulsed power technology, atmospheric pressure discharges, plasma
etching, etc. The plasma etching is reported in another talk, here we concentrate on
other major applications.
The widely used plasma sources are helicons, ECRs, ICPs, Magnetrons,
Gyrotrons, Thrusters, as well as GEC reference reactors. We here give a brief view of
a standard research and application plasma source GEC reference reactors [3].
The GEC reference reactor was proposed by leading experimentalists in gaseous
electronics area as a standard reference device for lab experiments and industry
applications. GEC stands for “Gaseous Electronics Conference”, a sub-division of
American Physical Society. This reactor is now widely used in university labs and
industry R&D centers all over the developed countries. The device is a capacitive
coupled plasmas source, using RF discharges (with a standard RF frequency of 13.56
MHz, and a work voltage of ~100 V). The detailed computer simulation code
developed by Boeuf and Pitchford [4] can give temporal profiles of important
parameters at any moment, which is a very convenient way of “numerical diagnosis”.
It provides a good example for us to do research in a “standard” way. The basic
parameters and some important parameter profiles are presented in Refs. [3 & 4].
Beams include laser beams, ion beams, electron beams, and other energetic
particle beams. The applications of beams are very extensive. We do not have time
and space to cover all of them. We here only give an example of beam application to
nano-structured micro-electronics [5]. In this Ge/Si quantum dot growth experiment, a
molecular beam is used to grow the sample, electron beam evaporators are used for Si
and Ge deposition, and furthermore, and the growth is enhanced by a build-in 1 keV
As ion implanter. It gives a good example of combination of multiple applications of
beam and ion implantation technologies in advanced microelectronics experiments.
Pulsed power technology is another important area of recent R&D. It includes
two methods in general: a pulsed power treatment can be realized by either a pulsed
voltage on electrodes or a pulsed beam on the surface. The research is carrying on
extensively in Dalian, at State Key Lab of Materials Modification by Beams of Dalian
University of Technology [6]. In the experiments, C is painted on Al surface which is
lately bombarded by pulsed electron beams. The regular deposition thickness is of
order of ms. However, after a single pulse, the thickness can be as deep as 1mm.
Multi-pulses give better results. What is the cause of the enhanced, or anomalous
diffusion effect? A combined experimental-numerical-theoretical research is on its
way at the State Key Lab. We have indicated that the enhanced diffusion is a
correlated effect of thermo-stress waves and an pulse induced defect-hole transport in
the micro level.
Atmosphere pressure discharges are most promised applications to industry, since
it can operate under atmosphere condition without a vacuum chamber. In general,
atmosphere pressure discharges include arc, corona and glow discharges. Arc
discharges are widely applied to electrical power industry such as circuit breakers, as
well as steel, auto, and environment industries such as plasma guns and furnaces. The
arc discharge can also be applied to surface physical simulation of re-entry. The
corona discharges are mostly applied to environment industry. Related research is
done in Dalian also. The glow discharges including filament discharges and OAUGD
have more and more applications in various fields ranged from paper industry to
textile modification. Those areas are going to be covered by other speakers. We then
here only brief the recent development in Dalian in the re-entry simulation research.
Re-entry simulations, both physically and numerically, are very important for
aero-space industry. The surface physical simulation has been done in Beijing. We are
developing a numerical simulation code for the experiment. We are using a fluid
model (electrostatic MHD developed by our research group [7]) to study kink
instabilities and two-stream instabilities. A detailed simulation code is under further
development.
IV.
DUSTY PLASMA APPLICATIONS
Dusty plasma studies are recently attracting more and more attentions in the field.
However, some people misunderstand the major focus of researches in this area.
Although lots of recent papers are for basic physical processes in dusty (or complex)
plasmas [8], particularly after the finding of plasma crystals in 1994 [9], a large
majority of dusty plasma researchers in technology and industry areas concentrates
their efforts on the front of dusty plasma industry applications [10].
In the recent decade, the researches of dusty plasma applications are focusing on
following areas: dust particles in reactors, removal of dust particle and “good” particle
applications.
Dust particles are observed in all types of plasma sources [11,12], and different
processes. In surface processes such as etching and sputtering, dust particles can be
created due to the particle emission and nucleation [13]. In PECVD (plasma enhanced
chemical vacuum deposition) processes dust particle sources are mostly walls and
chemical polymers. Reports on such observations and studies can be traced back to as
early as 80s [13,14]. The creation and growth of dust particles can be studied in
different phases: the cluster formation phase, the nucleation and cluster growth phase,
the coagulation phase, and the particle growth phase [12]. The presence of dust
particles can cause surface contamination and affect on the sheath efficiency and the
electron density. To clean the particles to avoid those “negative” effects, a few ways
have been tried: plasma wall cleaning [15], “square wave modulation” [16], fast
transport devices [17], and E  B drift removal [18,19].
Recent studies have also shown that the existence of dust particles in processing
plasmas has some “positive” effects. One of the effects is the application of dust
energetics, such as heavy particle deposition and dust-enhanced PECVD [20].
Furthermore, the development of particle size control technique [21] makes the
application to nano-structured thin films possible [22]. The future progress of this
technology may provide new ways in nano-science researches.
Research of dusty plasma applications to plasma processing in China just starts.
We need to further support in this area.
V.
BIOPHYSICAL APPLICATIONS
Biophysical applications of low temperature plasma technology are also very
extensive. We here list a few of them: electroporation, surface sterilization, and
medical surface modification etc.
Electroporation is a way to use electrical pulses to form “pore” stage, enhance
ionic and molecular transports. It can be applied to drug delivery and gene therapy
[23]. It may also have some impact to seed modifications by ion and plasma beams
[24].
Surface sterilization has be widely used, particularly medical and other industry
applications. A very important application however is anti-bioterrorism application.
Two tools have be developed [25]: Montec steam plasma torch and TTU arc-jet
thruster for bioterrorism agents such as anthrax cleaning.Other applications such as to
DNA and other biological systems are also making significant progresses.
VI.
SUMMARY AND DISCUSSIONS
We briefly reviewed the relationship between low temperature plasma studies and
industry applications. It is pointed out that the crucial sector for the relationship is
industry R&D which is typically the weakest link. To bridge industry and the basic
research, there are lots of work to do.
We in this presentation cover certain major areas of plasma applications.
Particular focuses are also on dusty plasma applications and biophysical applications
where researches are just starting in this country. However, some important areas such
as plasma chemistry, plasma etching etc are not discussed, where plasma chemistry is
particularly important. It should be paid attention to.
ACKNOWLEDGMENT
The work related to this review was supported by NSFC Grants #19875006 and
#10160420799.
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