Silicon hydride etch products from the reaction of atomic hydrogen with Si(100)

Abstract

The formation of silane, SiH4, on the Si(100) surface following atomic hydrogen chemisorption has been investigated using temperature programmed desorption (TPD) mass spectrometry and static secondary ion mass spectrometry (SSIMS). The yield of SiH3+ ions in SSIMS is correlated with trends observed in the SiH4 TPD yield, as the hydrogen surface coverage (θH) and the surface temperature during hydrogen exposure are varied. A mixture of silicon hydrides is formed on the Si(100)-(2×1) surface by adsorption of H atoms, including SiH3(a) which yields SiH4(g) during the temperature program. The peak temperature (Tp) for SiH4 in TPD occurs at 375 °C, which is 50 °C below the H2 β2 desorption peak. The maximum yield of SiH4 is observed at θH = 1.5 monolayers, with roughly 4% of all the surface hydrogen desorbing as SiH4, resulting in removal of about 1% of a monolayer of silicon atoms. The minimum hydrogen coverage needed for detectable SiH4 formation is 0.25-0.3 monolayers. The SiH4 TPD yield and the SiH3+ intensity in SSIMS are proportional to θH between θH = 0.25 and 0.5. As θH is increased beyond 0.5, the SiH4 TPD yield gradually saturates at the maximum value. Desorption of polysilicon hydrides, SixHy (x = 2,3,4) is also observed. These higher silicon hydride species desorb in TPD with Tp coincident with the β2 desorption peak for H2 at 425 °C. Molecular species Si2H6, Si3H8 and Si4H10 desorb. and mass spectrometry fragmentation patterns indicate that hydrogen deficient radical species such as Si2H2, Si2H, or Si2 are thermally desorbed. The silicon surface temperature during hydrogen adsorption dramatically affects the yields of all the silicon hydride products. © 1989.