Raman Scattering Study of Order and Disorder in Tungsten Silicide and Amorphous Hydrogenated Carbon Films
Abstract
Raman spectroscopy has been used to study order and disorder in tungsten silicide and amorphous hydrogenated carbon (a: C-H) films. Tungsten silicide films were formed by first sputter depositing 200 A^{cdot} of tungsten on Si wafers. These films were then annealed, by both rapid thermal annealing and laser annealing, to form the silicide. During annealing Si diffuses into tungsten to form tungsten silicide (WSi_2 ). At low annealing temperatures i.e., from 600 C to 800 C, an intermediate compound WSi_ {rm x} is formed, but at temperatures greater than 900 C the tetragonal silicide is formed. Raman spectra were obtained from all of the above samples and indicate that the rapid thermally annealed samples form uniform tetragonal silicides, whereas laser annealed samples form an intermediate compound in addition to the tetragonal silicide. Raman data were correlated with scanning electron micrographs and four point probe measurements. X-ray diffraction was performed on some of these samples. Both X-ray diffraction and Raman data indicate the formation of tetragonal tungsten silicide. At higher annealing temperatures, an intense rise in Raman intensity from silicon, indicates possible outdiffusion of Si. The increase in the sheet resistance at very high annealing temperatures is attributed to this outdiffusion. This thesis also reports the study of Raman scattering from amorphous hydrogenated carbon films or diamond-like carbon films. Many of amorphous carbon films have been termed as diamond-like because of their hardness and large optical gap (0.5 to 2.5 eV). The as-deposited a: C-H thin films were implanted with the ions H^+, C^+ , N^+ and Kr^+ in order to study the structural modification in the films. The as-deposited films were also rapid thermally annealed and compared with the implanted samples. Some of the as-deposited samples were irradiated by using pulsed lasers. RBS measurements were done on all of these samples as well and were correlated with Raman data. As the hydrogen effuses, the longitudinal optical phonon peak at 1550 cm ^{-1} would shifts towards 1580 cm^{-1} and the shoulder at 1355 cm^{-1} grows, which indicates the transformation from less tetragonal to trigonal bonding. Thus the amorphous hydrogenated carbon films are more graphitie-like than diamond-like. (Abstract shortened with permission of author.).
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1991
- Bibcode:
- 1991PhDT........52V
- Keywords:
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- CARBON FILMS;
- Physics: Condensed Matter; Physics: Optics