FILM QUALITY IN RELATION TO DEPOSITION CONDITIONS OF A-SI-H FILMS DEPOSITED BY THE HOT-WIRE METHOD USING HIGHLY DILUTED SILANE

The deposition parameter space has been extensively explored using the hot wire technique with 1% SiH4 in He as a source gas. To achieve rea sonable deposition rates despite the high dilution, the filament was p ositioned at 1-2 cm from the substrate. This short distance introduced a large nonuniformity across the substrate in deposition rate as well as in film properties. These spatial variations were used to analyze which factors in the deposition determine film quality. Radiation from the filament as well as deposition rate cannot explain the large vari ation in film properties, leaving gas-phase reactions of Si and H from the hot filament as the primary cause. It is clear that radicals evap orated from the filament must undergo gas-phase reactions with SiH4 be fore deposition in order to produce high-quality material. Thus, condi tions such as increasing the chamber pressure or going to a heavier ca rrier gas increase the fraction of radicals that can react before reac hing the substrate and, therefore, improve the film quality. However, such conditions also enhance multiple radical reactions before such ra dicals reach the substrate and this can have a negative effect on film quality: this is attributed to gas-phase nucleation with incorporatio n of conglomerates. The gas-phase chemistry is quite different from th at of plasma-enhanced decomposition in that no disilane or trisilane i s formed in significant quantities. This, and the dependence on pressu re, indicates that the pathway for formation of these heavier particle s is radical-radical reactions. (C) 1996 American Institute of Physics .