(proeng_mohamed) #1

[LEFT]Thin film technology is a large branch of the generic technology that has to do
surface modifications and coatings. In the surface modification process the
properties of the surface of the substrate material is changed, as exemplified by
the hardening of steel surface by introducing carbon or nitrogen to the surface
or as in the doping of semiconductors to change its electrical conductivity. In
the process that involves the application of a coating, the substrate material and
the coating may be quite different, as exemplified by the deposition of aluminum
or chromium on polymer surfaces or deposition of a hard coating of
titanium nitride on tool bits. There are a number of questions that one immediately
encounters in studying this subject. What types of
phases form on the
surface and what is the science that underlies their formation? For example,
how does one form the polytype 6H or 4H in SiC that has over 150 polytypes?
Which face, either Ga or N, is the top face when GaN is grown epitaxially
perpendicular to its
c-axis? How does one grow the low temperature polymorph
diamond cubic structure of tin at room temperature? What features of the[/left]
[LEFT]processes are important to form the desired modifications of the surface? One
has to consider the role of background pressure, concentration of impurities in
the vapor phase, kinetic energy of the incident particles, deposition rate, nature
of substrate material, temperature of the substrate and its surface cleanliness,
orientation and microstructure. All of these have an effect on the type of
microstructure of the film that is formed. The microstructure that forms can
also be influenced by external agencies, such as photon, electron and ion
bombardment. What is the relationship of the variables in processing to the[/left]
[LEFT]characteristics [FONT=AdvP4B6849][SIZE=3]of the microstructure of films? The ability to control intervoid
networks in the growing polycrystalline film, the control of point defects,
dislocations and grain boundaries in films are all dependent on the control of
process parameters and in some cases are possible only with certain deposition