PLASMA CHEMISTRY IN DISILANE DISCHARGES

We have measured the initial silane and polysilane product yields from disilane decomposition in rf and dc discharges, at 25 and 250-degrees-C and 20 Pa (0.15 Torr) pressure as typically used for a-Si:H film deposition. From analyses of these yields we conclude that the initial Si2H6 fragmentation pattern is SiH3 + SiH2 + H (91 +/- 9%) and H3SiSiH + 2H (9 +/- 9%), that the primary product of the H + Si2H6 reaction is SiH4 + SiH3, and that SiH3 is the dominant radical causing film growth. We have measured a radical-surface reaction probability of 0.34 +/- 0.03, very similar to that observed for SiH3 in SiH4 discharges. We report a spatial distribution of emission indicative of a gamma-regime discharge. From deposition on glass fibers strung between the electrodes, we find that highly strained a-Si:H film is produced everywhere except on or near the electrodes, suggesting that energetic ion impact is necessary to yield useful films in disilane discharges.