Atomistic calculation of the SiH3 surface reactivity during plasma deposition of amorphous silicon thin films

摘要

We report a direct, statistically significant calculation of the surface reactivity of the SiH3 radical on hydrogenated amorphous silicon (a-Si:H) using molecular-dynamics simulations of repeated impingement of SiH3 radicals on growth surfaces of smooth a-Si:H films over the temperature range 475-800K. SiH3 can either incorporate into the film by adsorbing onto a surface Si dangling bond or inserting into Si-Si bonds (sticking), or abstract surface H through Eley-Rideal (ER) or Langmuir-Hinshelwood (LH) pathways to produce SiH4 gas, or react with another surface SiH3 to desorb as Si2H6 (recombination), or leave the film by reflection or desorption. The overall surface reaction probability, beta, includes both radical sticking and recombination. In agreement with experimental measurements, beta is almost constant over the temperature range studied, as are the probabilities for sticking and recombination, s and gamma, respectively; the calculated mean value of beta is 0.47 +/- 0.03. Energetic analysis of the various surface reactions shows that radical adsorption, radical insertion, and ER abstraction are barrierless processes, which explains the measured temperature independence of beta. LH abstraction is activated, but competes with disilane formation, yielding a temperature-independent gamma. Also, LH abstraction leads to H elimination from a-Si:H during growth and can partly explain the experimentally measured temperature dependence of the H content in the a-Si:H film. (C) 2004 Elsevier B.V. All rights reserved.