Photolytic tungsten chemical vapor deposition by an ArF excimer laser from a WF6/H2/Ar gas mixture is a very complicated process with reactions occurring both in series and in parallel. In this article different reaction pathways were modeled and compared with experimental deposition rate data. The absorption cross section for WF6 was measured to 1.7 X10-18cm2 at the ArF excimer laser wavelength of 193 nm. From a rate equation model, it was concluded that the direct photolytic contribution to the deposition rate was negligible. Moreover, reduction of tungsten subfluorides by hydrogen atoms, formed in reactions between photolytically released fluorine atoms and molecular hydrogen, was also found to be negligible. However, photolysis in combination with various radical reactions generate a relatively high concentration of tungsten subfluorides (WF3, WF4, and WF5). Thermochemical calculations indicate that H2 reduction of tungsten subfluotides to solid tungsten, forming clusters in the vapor, is highly probable. Among the different cluster nucleation mechanisms polymerization of tungsten subfluorides seems to be an important step. This also explains the influence of WF6 partial pressure on the deposition rate.
|Number of pages||7|
|Journal||Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films|
|Publication status||Published - Nov 1993|
ASJC Scopus subject areas
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films