Crystallinity Control of Silicon Thin Films for High-Efficiency Solar Cells by Two-Step Growth Method

为了控制硅薄膜的结晶度，采用氢自由基化学气相沉积方法制备了微晶硅薄膜，并对其结构和性能进行了表征。特别是，为了阐明非晶态初始层和晶体生长过程的影响，对薄膜的结晶度和电学性能进行了详细的估计。比较了玻璃衬底和铝衬底对薄膜结构的影响。此外，通过改变气相反应与衬底位置进行了两步生长。结果表明，在200℃下制备的微晶薄膜具有(111)择优取向，X-射线衍射仪估算的微晶薄膜的最大粒径为30 nm。而原子力显微镜测得的平均晶粒尺寸从90 nm变为270 nm，同时表面粗糙度增加。这些结果表明，微晶颗粒生长、碰撞和共聚。垂直方向的电导率与横向方向相比很小，与非晶态薄膜的电导率相当。这一结果说明了非晶态初始层的影响。当衬底温度从2 0 0℃升高到35 0 min时，非晶态初始层的厚度减小。两步生长实验表明，通过调节SiH4流量，可以提高生长速度，控制薄膜的结晶度。

To control crystallinity of silicon thin films, microcrystalline silicon thin films were prepared by hydrogen radical CVD method and their structure and properties were evaluated. Especially, to clarify effect of amorphous initial layer and crystalline growth process, crystallinity and electrical properties of thin films were estimated in detail. Substrate dependence of film structure was compared by using glass and Al substrates. Moreover, two-step growth was done by changing gas phase reaction with substrate position. As a result, the following matters were clarified.The microcrystalline films prepared at 200℃ showed (111) preferential orientation and the grain size estimated from XRD was 30nm in maximum. However, the average grain size obtained from AFM was changed from 90nm to 270nm and simultaneously the surface roughness was increased. These results suggest that microcrystalline grains grow, collide and coaggregate. The vertical electrical conductivity was very small compared to the lateral one and nearly equal to the values of amorphous films. This result shows the effect of amorphous initial layer. By raising the substrate temperature from 200 to 350℃, the thickness of amorphous initial layer was decreased. The experiments of two-step growth showed that, by regulating SiH4 flow rate, growth rate can be increased and crystallinity of films can be controlled.