Chemistry Reference
In-Depth Information
The F radicals react with the Si and generate SiF, then stepwise SiF
2
,SiF
3
, and
finallythevolatileSiF
4
.LossprocessesforFatomsarerecombinationreactionssuchas
SF
x
+
+
−→
SF
(
x
+
1
)
+
F
M
M.
(8.53)
The admixture of O
2
avoids the deposition of sulfur by generation of SO
2
.
8.2.1.6 Conclusions
Plasma etching is an advanced method for material processing not only in microelec-
tronics but also in micromachining. Until now, the requirements for miniaturization
have been fulfilled down to structure widths of about 50 nm. Future tasks will be
the etching of new metals and complex oxides. Further developments of polymer
electronics may be connected with the introduction of microstructuring of polymers
by plasma etching. Improvements of the established procedures should reduce the
consumption of etching gases with their high global warming potential.
8.2.2 B
IOLOGICAL
D
ECONTAMINATION UP TO THE
L
EVEL OF
S
TERILIZATION
8.2.2.1 Plasmas as New Prospects for Hygiene and Life Science
In nonthermal plasmas, the neutral background gas enthalpy is usually not signifi-
cantly increased. This enables the treatment of heat-sensitive materials and biological
tissues. In many studies, the inactivation or removal of biological contaminants such
as pathogens has been demonstrated and opens up new fields of applications. For
sensitive goods, e.g., medical instruments and implants that cannot be treated by clas-
sical thermal or chemical methods,
∗
nonthermal plasmas introduce an alternative for
sterilization. Plasma-based sterilization and disinfection technologies for packaging
will lead to safer products with longer shelf life in food and pharmaceutic industry.
Electrical discharge-driven ozone generators are used for water treatment for about
100 years; new activities consider the generation of plasmas inside liquids as well.
The use of plasmas for the decontamination of exhaust gases and room ventilation
air (e.g., in hospitals, laboratories, and cabines) has been demonstrated and is on
the way to comercialization. The therapeutic application of plasmas in medicine for
electrosurgery (e.g., coagulation for wound sealing and nonspecific removal or cut-
ting of tissue) is already known, and the new arising interdisciplinary area of plasma
medicine addresses the disinfection of chronic wounds, the generation of sublethal
effects (e.g., affection of metabolic cell functions) for healing stimulation, and the
removal of tissue without unwanted inflammatory reactions [98,99].
The American inventor Smith granted a patent on a process for destroying insect
life and microorganism based on spark and corona discharges [100] already in 1920.
The first report on plasma as a sterilizing agent was by Menashi in 1968 [101]. By
means of pulsed RF-driven corona-type discharges in argon at atmospheric pressure,
the inner surface of vials in times of less than 1 s was sterilized. The biocidal effect
∗
Classical sterilization processes uses wet (autoclaves) or dry heat. The most widely used steri-
lants in chemical processes for heat-sensitive products are ethylene oxide, hydrogen peroxide, and
glutaraldehyde.
