Thermal stability and hydrogen induced abstraction of silyl groups on Si(100) surfaces

The formation and the thermal stability of silyl (SiH3) groups on Si(1 0 0) surfaces was investigated by mass spectrometry. Silyl groups were prepared either by adsorption and decomposition of disilane (Si2H6) on clean Si(1 0 0), or by using thermal hydrogen atoms to generate silicon hydride groups. The silyl coverage decreases with increasing temperature during disilane or H atom exposure. Maximum silyl coverages of 0.15 and 0.12 ML, respectively, were obtained after disilane or H atom saturation exposures at 110 K. On saturated Si(1 0 0) surfaces, i.e., in absence of dangling bonds, silyl groups are stable up to 500 K; above 500 K the formation of silane (SiH4) via disproportionation, -SiH3(a) + SiH2(a) --> SiH4(g) + SiH(a), was observed. In the presence of dangling bonds, silyl groups decompose toward SiH, and SiH groups, even at 110 K. The abstraction of adsorbed silyl by impinging hydrogen atoms, -SiH3(a) + H(g) --> SiH4(g), was investigated in the temperature range from 110 to 800 K by in situ mass spectrometry. Silane was the sole product observed. The silyl abstraction probability increases by a factor of 6 with increasing substrate temperature between 110 and 500 K, indicating an apparent activation energy of 12.5 kJ mol(-1), which can be discussed in terms of an increased reaction probability of vibrationally excited silyl groups. The regeneration of silyl groups by impinging hydrogen atoms was identified as the rate limiting step of the hydrogen induced etching of silicon under steady-state conditions. (C) 2001 Elsevier Science B.V. All rights reserved.