Interactions between radical growth precursors on plasma-deposited silicon thin-film surfaces.
Interactions between radical growth precursors on plasma-deposited silicon thin-film surfaces.
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等离子体沉积硅薄膜表面上自由基生长前体之间的相互作用。
DOI：
10.1063/1.2672799
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发表时间：
2007
影响因子：
4.4
通讯作者：
D. Maroudas
中科院分区：
文献类型：
--
作者：
T. Bakos;M. S. Valipa;D. Maroudas
我们详细分析了生长前驱体SiH3自由基在硅薄膜表面的相互作用。该分析是基于氢终止的Si(001)-(2x1)表面的密度泛函理论计算和分子动力学(MD)对分子动力学(MD)产生的氢化非晶硅(a-Si：H)薄膜表面生长的分子动力学(MD)模拟的协同结合。特别是，作者发现，两个相互作用的生长前体可能形成二硅烷(Si2H6)并从表面解吸，或者不成比例地形成表面二氢化合物(吸附的SiH2物种)和气相硅烷(SiH4)。研究发现，形成二硅烷的反应势垒强烈地依赖于硅表面的局部化学环境，如果相互作用的两个前体中的一个或两个处于“快速扩散状态”，即附着在五个配位的表面硅原子上，则反应势垒减小(或消失)。最后，得到了两个化学吸附(即键合在一个四配位表面硅原子上)的SiH3自由基的激活能垒大于1 eV。歧化反应的活化势垒遵循相同的趋势，尽管在大多数情况下，与从相同初始构型开始的二硅烷生成反应相比，获得了更高的势垒。MD模拟证实，在a-Si：H生长表面上也会发生二硅烷的形成和歧化反应，优先在至少一个SiH3自由基处于“扩散状态”的情况下发生。我们的结果与实验观测和等离子体过程模拟器的结果一致，表明在低功率等离子体中，二硅烷的主要来源可能是衬底表面。
We present a detailed analysis of the interactions between growth precursors, SiH3 radicals, on surfaces of silicon thin films. The analysis is based on a synergistic combination of density functional theory calculations on the hydrogen-terminated Si(001)-(2x1) surface and molecular-dynamics (MD) simulations of film growth on surfaces of MD-generated hydrogenated amorphous silicon (a-Si:H) thin films. In particular, the authors find that two interacting growth precursors may either form disilane (Si2H6) and desorb from the surface, or disproportionate, resulting in the formation of a surface dihydride (adsorbed SiH2 species) and gas-phase silane (SiH4). The reaction barrier for disilane formation is found to be strongly dependent on the local chemical environment on the silicon surface and reduces (or vanishes) if one/both of the interacting precursors is/are in a "fast diffusing state," i.e., attached to fivefold coordinated surface Si atoms. Finally, activation energy barriers in excess of 1 eV are obtained for two chemisorbed (i.e., bonded to a fourfold coordinated surface Si atom) SiH3 radicals. Activation energy barriers for disproportionation follow the same tendency, though, in most cases, higher barriers are obtained compared to disilane formation reactions starting from the same initial configuration. MD simulations confirm that disilane formation and disproportionation reactions also occur on a-Si:H growth surfaces, preferentially in configurations where at least one of the SiH3 radicals is in a "diffusive state." Our results are in agreement with experimental observations and results of plasma process simulators showing that the primary source for disilane in low-power plasmas may be the substrate surface.