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

Abstract

The formation of silane, SiH 4, 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 SiH 3 + ions in SSIMS is correlated with trends observed in the SiH 4 TPD yield, as the hydrogen surface coverage (θ H) 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 SiH 3(a) which yields SiH 4(g) during the temperature program. The peak temperature ( T p) for SiH 4 in TPD occurs at 375 °C, which is 50 °C below the H 2 β 2 desorption peak. The maximum yield of SiH 4 is observed at θ H = 1.5 monolayers, with roughly 4% of all the surface hydrogen desorbing as SiH 4, resulting in removal of about 1% of a monolayer of silicon atoms. The minimum hydrogen coverage needed for detectable SiH 4 formation is 0.25–0.3 monolayers. The SiH 4 TPD yield and the SiH 3 + intensity in SSIMS are proportional to θ H between θ H = 0.25 and 0.5. As θ H is increased beyond 0.5, the SiH 4 TPD yield gradually saturates at the maximum value. Desorption of polysilicon hydrides, Si x H y ( x = 2,3,4) is also observed. These higher silicon hydride species desorb in TPD with T p coincident with the β 2 desorption peak for H 2 at 425 °C. Molecular species Si 2H 6, Si 3H 8 and Si 4H 10 desorb. and mass spectrometry fragmentation patterns indicate that hydrogen deficient radical species such as Si 2H 2, Si 2H, or Si 2 are thermally desorbed. The silicon surface temperature during hydrogen adsorption dramatically affects the yields of all the silicon hydride products.