Atomic hydrogen-assisted chemical vapor deposition and etching of silicon thin films.

Abstract

In this study, the potential of a novel hot-wire technique for silicon thin film deposition and etching has been investigated. For silicon thin film deposition, molecular hydrogen was passed over a heated tungsten filament and catalytically dissociated into atomic hydrogen; source gas disilane was fed into the reactor bypassing the filament to form film forming species by reacting with atomic hydrogen. By using this method, good quality amorphous, microcrystalline, polycrystalline, and epitaxial silicon thin films have been deposited at low substrate temperatures and relatively high deposition rates. Particularly, polycrystalline silicon with a crystalline volume fraction of 98% has been deposited at a substrate temperature of 310$\sp\circ$C and a deposition rate of 110 A/min. Hydrogenated amorphous silicon has been deposited at a high growth rate of $\sim$1500 A/min. In addition, polycrystalline silicon has been selectively deposited on molybdenum or silicon over silicon dioxide, silicon nitride or Corning 7059 glass, or on silicon over molybdenum and these substrates at a substrate temperature of 300$\sp\circ$C and a deposition rate of $\sim$100 A/min with excellent selectivity on features of size as small as 1 $\mu$m. These results are attributed to a high concentration of atomic hydrogen present in the process and suggest that catalytic dissociation of molecular hydrogen by a heated filament is an efficient method to produce atomic hydrogen. A major function that atomic hydrogen has in achieving these results is etching of silicon during deposition. In this study, it has been found that a-Si:H can be etched at $\sim$60A/sec by atomic hydrogen. In addition, it has been found that etching rate increases with the increase in filament temperature, hydrogen pressure, and flow rate, and decreases with the increase in substrate temperature. Etching rate is sensitive to oxygen contamination on silicon surface, which may also cause surface roughening during etching. There are etching selectivities between intrinsic and boron-doped amorphous silicon, and poly-Si.