Study on growth kinetics of Si clusters in silane plasmas

虽然a-Si：氢基太阳能电池是一种很有前途的太阳能电源电池，高速沉积的a-Si：H薄膜的光致退化是近20年来研究的热点问题。最近，在硅烷射频（rf）放电中形成的几个纳米以下的尺寸的集群已被指出是使用放电沉积的a-Si：H膜的光致降解的可能原因。这项研究已经进行，以澄清硅团簇在硅烷射频放电中的生长动力学，使用两种新的原位方法测量团簇的尺寸和密度，并揭示生长抑制团簇和沉积膜的质量之间的相关性。主要研究结果如下：1）即使在器件质量的沉积条件下，放电中也存在大量团簇; 2）利用热泳力、气体粘性力、脉冲调制放电和氢气稀释可以有效抑制团簇数量; 3）研制了团簇抑制型等离子体CVD反应器。利用该反应器，可以在0.2nm/s的速率下沉积出微结构参数小于0.02、肖特基电池填充因子大于0.53的a-Si：H薄膜。这些结果表明，抑制团簇的形成使沉积超高质量的a-Si：H薄膜成为可能。作为未来的工作，这是重要的是建立在更高的速率沉积超高质量的a-Si：H薄膜的太阳能电池的技术，通过上述结果的发展。

Although a-Si : H-based solar cells are promissing as solar cells for electrical power source, the light-induced degradation of a-Si : H films deposited at a high rate has been the most important issue over twenty years. Recently, clusters below a few nanometers in size formed in silane radio frequency (rf) discharges have been pointed out to be a possible cause of light-induced degradation of a-Si : H films deposited using the discharges. This research has been carried out in order to clarify growth kinetics of Si clusters in silane rf discharges using two novel in-situ methods for measurements of size and density of clusters, and also to reveal correlation between growth suppression of clusters and quality of deposited films. Main results obtain in this research are as follows :1) Large amount of clusters exist in the discharges even under the device-quality deposition conditions.2) Cluster amount can be significantly suppressed using the thermophoretic force, gas viscous force, pulse modulation of discharges, and hydrogen dilution.3) A cluster-suppressed plasma CVD reactor is developed. By using this reactor, a-Si : H films of microstructure parameter below 0.02 and fill factors of Schottky cell after light degradation above 0.53 can be deposited at a rate of 0.2 nm/s. These results show that suppression of clusters makes it possible to deposite ultra-high quality a-Si : H films. As the future work, it is important to establish techniques for depositing ultra-high quality a-Si : H films for solar cells at higher rate by developing results mentioned above.