Chemistry Reference
In-Depth Information
is distinguished from physical processes by chemical reactions that change the
chemical state of the surface. Pure physical processes such as sputtering or ion
implantation are beyond the scope of this chapter. A systematic compilation of the
treated plasma surface chemical processes is given in Table 8.4 together with material
transfer from or on the target surface as well as some applications of the selected
processes. Deposition and etching transfer weighable materials. In activation pro-
cesses, the material transport is negligible; sometimes only the chemistry is changed.
The coating and deposition processes that are discussed here are known as plasma-
assisted chemical vapor deposition (PACVD). The chapter is organized as follows.
The first part deals with plasma etching, especially for the formation of micro- and
nanostructures in the microelectronic industry. Biological decontamination and ster-
ilization are covered in the next part. Surface modifications of polymers, textiles,
and biomedical applications and plasma medicine are treated in further sections.
The following treats various fields of plasma enhanced chemical vapor deposition
(PECVD) of organic thin films, including diamond, a-C:H films, plasma polymers,
and inorganic films. Electrical discharges in liquids and nano- and microparticles are
further topics.
8.2.1 P
LASMA
E
TCHING
8.2.1.1 Plasma Etching, Micro- and Nanostructures
A standard technique for the removal of material from a surface is etching Figure 8.20.
Wet etching is a long-established technique that uses aggressive chemical liquids
such as acids, bases, or other chemical compounds also in mixtures according to the
chemical properties of the treated substance. Wet etching is very species selective but
isotropic.
Plasma etching is a key process step, e.g., in microelectronic production, in
the nanoelectronic industry, and for micromachining of materials [75,76]. It is a dry
etching procedure that is characterized by the application of plasmas for the activation
of primary nonreactive gases by dissociation or ionization. The plasma generates
energetic ions reacting with surfaces by physical and/or chemical processes. Using
the electric field near the surfaces, ion-induced anisotropic etching gets possible.
The dry etching process is species selective by the generation of volatile products in
reactions of activated species with the substrate.
8.2.1.1.1 Application of Plasma Etching in Micro- and Nanoelectronics
The demands on etching technology are growing rapidly according to the increasing
number of transistors on a processor chip. Moore's law is based on the observation
of a doubling of the transistors per chip every 2 years. This is necessarily coupled
with a decrease of the structure width, typically the width of the current lines or
of a dielectric region [77]. In the 1970s, the structure width was about 10 μm and
2
10
3
transistors were integrated on a chip. Nowadays, using extreme ultraviolet
lithography, structure widths of 35 nm and 2
·
10
9
transistors per chip can be achieved
(Intel) Figure 8.21. This development is connected with an increase of, e.g., the
maximal memory capacity and the upper limit frequency, but also with a drastic
miniaturization.
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