Different Crystal Growth Mechanisms of Si(001)-(2 × 1):H during Plasma-Enhanced Chemical Vapor Deposition of SiH3 and SiH2 Radicals: Tight-Binding Quantum Chemical Molecular Dynamics Simulations

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We use tight-binding quantum chemical molecular dynamics to investigate the crystal growth mechanisms of H-terminated Si(001)-(2 × 1) during plasma-enhanced chemical vapor deposition of SiH 3 and SiH 2 radicals. We find that crystal growth by SiH 3 radical deposition consists of two stages: (1) the first SiH 3 radical abstracts a surface-terminating H atom and produces a dangling bond, and (2) a second SiH 3 radical is adsorbed on the dangling bond. Thus, at least two SiH 3 radicals are required for generating a new Si–Si bond. Interestingly, during SiH 2 deposition, a SiH 2 radical can be directly adsorbed onto a H-terminated site without H abstraction by another SiH 2 radical. Thus, one SiH 2 radical is sufficient for generating a new Si–Si bond. This SiH 2 radical crystal growth mechanism is different from the SiH 3 radical mechanism. The direct adsorption process consists of a two-step chemical reaction: (1) the SiH 2 radical abstracts a surface-terminating H atom and produces a dangling bond and a SiH 3 radical, and (2) the SiH 3 radical is adsorbed on the dangling bond. In addition, the crystal growth rate for SiH 2 radicals is higher than that for SiH 3 radicals, because generating one new Si–Si bond requires either a single SiH 2 radical or two SiH 3 radicals. However, our simulations reveal that SiH 2 deposition produces defective Si thin films because many dangling bonds are formed during crystal growth. Compared with SiH 2 deposition, SiH 3 deposition should therefore produce Si thin films of higher quality.