特种化学气相沉积法制备大面积纳米硅薄膜的微结构和电学性能研究

Microstructures and Electrical Properties of Large-area Nanocrystalline Silicon Films Grown by Specially Designed Chemical Vapor Deposition System

采用可与Si平面工艺兼容的特殊设计的化学气相沉积系统在玻璃衬底上制备了大面积的纳米Si薄膜。高分辨率电子显微镜和选区电子衍射分析表明 ,成膜温度对薄膜微结构有关键影响 ,衬底温度的升高促进了薄膜晶态率的提高和Si晶粒的长大。 6 6 0℃成膜时非晶Si薄膜基体中镶嵌了尺寸为 8～ 12nm ,晶态率为 5 0 %的纳米Si晶粒 ,具有明显的纳米Si薄膜微结构特征。用变温薄膜暗电导率测试系统研究表明 ,随成膜温度的升高 ,薄膜的晶态率提高、室温暗电导率提高而相应的电导激活能降低 ,用热激活隧道击穿机制解释了纳米Si薄膜微结构与特殊电学性能的关系。研究了原位后续热处理对薄膜微结构和电学性能的影响 ,发现延长热处理时间以及采用低温成膜、高温后续退火的热处理方法能有效提高纳米Si薄膜的晶态率 。

A specially designed chemical vapor deposition (CVD) system,which is compatible to the well developed silicon technology,was constructed to grow large area,nanocrystalline Si films on glass substrate.The films were studied with high resolution electronic microscopy (HREM) and area selected electronic diffraction.The results show that the deposition temperature strongly affects the crystallization ratio and the average sizes of Si crystallites.The temperature increase enhances the crystallization ratio and promotes the growth of Si crystallite.The nanocrystalline silicon embedded in amorphous silicon films was obtained at 660 ℃ with a crystallization ratio of 50% and an average silicon crystallite size of 8～12 nm,which exhibits the obvious structural characteristics of nanocrystalline silicon films.Deposition temperature increase results in an increase of room temperature dark conductivity and a decrease of the conductivity activation energy.The microstructures and the special electrical properties of the film can be accounted for with the mechanism of thermally assisted tunneling.Influence of post annealing on the microstructures and electrical properties of the films was also studied.We found that long time post annealing or low temperature growth followed by high temperature annealing improves the crystalline ratio and increases the room temperature dark conductivity of the film.