Decomposition of silane on Si(111)-(7×7) and Si(100)-(2×1) surfaces below 500 °C

Abstract

Using static secondary ion mass spectrometry (SIMS) to observe the silicon hydride species formed by silane adsorption on atomically clean single crystal silicon surfaces, two distinct adsorption mechanisms are identified. Dissociation to SiH3 plus H occurs on the Si(100)-(2×1) surface, which contains pairs of dangling bonds located on Si dimers (with Si–Si distance ≊2.4 Å). In contrast, SiH2 formation in the adsorption step is indicated on the Si(111)-(7×7) surface, where adjacent dangling bonds are separated by more than 7 Å. Lower limits on the silane reactive sticking coefficient (SR) are evaluated using hydrogen coverage (ΘH) measurements after calibrated SiH4 exposures, and this limit is ≊10−5 for 25 °C gas and 100–500 °C surface temperatures. Within experimental error, SR is the same for both mechanisms on the two clean surfaces (ΘH near zero). Dependence of SR on ΘH is reported at 400 °C for both surfaces, and differences appear as ΘH exceeds 0.1 H/Si. Silane adsorption is weakly activated on Si(111)-(7×7), as evidenced by enhanced adsorption as TS is increased between 50 and 400 °C.