Nanocrystalline silicon films prepared from silane plasma in RF-PECVD, using helium dilution without hydrogen: structural and optical characterization
Nanocrystalline silicon films prepared from silane plasma in RF-PECVD, using helium dilution without hydrogen: structural and optical characterization
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DOI：
10.1088/0957-4484/18/41/415704
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发表时间：
2007-10
期刊：
影响因子：
3.5
通讯作者：
Koyel Bhattacharya;D. Das
中科院分区：
文献类型：
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作者：
Koyel Bhattacharya;D. Das
在衬底温度为200 °C、气体压力为0.5 Torr的条件下，采用硅烷作为源气体，氦气作为稀释剂，不使用氢气，通过PECVD研究了射频功率对Si：H网络纳米晶化的影响。通过紫外-可见光谱对薄膜进行了光学表征。通过红外吸收、X-射线衍射、显微拉曼光谱和电子显微镜（HRTEM和FESEM）进行了结构表征。在一般情况下，从非晶到纳米晶相的结构转换完成的亚稳态氦原子在等离子体中已被确定在80 W的低RF功率。随着所施加的RF功率增加至高达150 W，结晶度的系统性改善已经被示出，如通过增加的结晶体积分数（约77%）、较小的晶粒尺寸（约77 nm）、降低的键合氢含量（约8at.%）、在高沉积速率（107 μ min-1）下获得的网络中增强的聚合和光学带隙（1.86 eV）的逐渐加宽，使用1 sccm的硅烷作为源气体和氦气作为唯一的稀释剂。稀释SiH 4等离子体是一种行之有效的提高生长速率的方法。然而，具有高晶体体积分数和良好排列的晶体晶格分布的纳米晶网络，在Si：H中从低功率RF等离子体在低至200 °C的生长温度下获得，并且从纯He稀释获得，而不使用H2，是首次报道。显著的特点包括nc-Si：H薄膜的结晶体积分数增加，减少键合氢含量和更宽的光学带隙产生的同时增加沉积速率，这值得广泛的技术影响。
The effect of RF power on the nanocrystallization of a Si:H network has been studied by PECVD at a substrate temperature of 200 °C and a gas pressure of 0.5 Torr, using silane as the source gas and helium as diluent, without using hydrogen. Optical characterization of the films has been done by UV–vis spectroscopy. Structural characterization has been performed by infrared absorption, x-ray diffraction, micro-Raman studies and electron microscopy by HRTEM and FESEM. In general, a structural transformation from the amorphous to nanocrystalline phase accomplished by metastable helium atoms in the plasma has been identified at a low RF power of 80 W. With an increase in the applied RF power up to 150 W, systematic improvement in crystallinity has been shown as depicted by increased crystalline volume fraction (∼77%), smaller grain size (∼7 nm) reduced bonded hydrogen content (∼8 at.%), enhanced polymerization in the network and gradual widening in the optical gap (∼1.86 eV) obtained at a high deposition rate (107 Å min−1), using 1 sccm of silane as the source gas and helium as the only diluent. He dilution of the SiH4 plasma is a well-proven approach to increase the growth rate. However, a nanocrystalline network with high crystalline volume fraction and well-aligned crystallographic lattice distribution, attained in Si:H from a low-power RF plasma at a growth temperature as low as 200 °C, and that obtained from purely He dilution, without using H2, is being reported for the first time. The striking feature comprises that nc-Si:H films of increasing crystalline volume fraction, reduced bonded hydrogen content and wider optical gap are produced with simultaneously increasing deposition rates, which deserves extensive technological impact.