Growth mechanism of silicon for solar cell in thin film zone melting Crystallization

We have developed thin film zone melting crystallization (ZMC) to fabricate high quality Si thin films for solar cells. We prepared the three-layer structure of SiO₂/Si/SiO₂ using chemical vapor deposition and RF sputtering. The Si thin films in the three-layer structure were crystallized by using the ZMC. The Si ZMC film can be separated from the Si wafer by removing the bottom layer of SiO₂, and the expensive Si wafer can be reused. We had reported that the defect density measured by electron spin resonance decreased drastically by changing the initial Si film from the poly crystal Si to the amorphous Si. In this paper, we will show the very high quality of ZMC films and will also discuss the mechanism for crystal orientation in Si-ZMC using the crystal orientation map measured by orientation image microscopy (OIM). The different kinds of Si-ZMC films were fabricated (1. normal ZMC films with scanning upper lamp heater, 2. ZMC films melted once and cooled down without scanning, and 3. quenched ZMC films during scanning). By comparing the OIM images of these ZMC films, we concluded that the crystal orientations seem to be uniformed by the stability at the interface of Si/SiO₂ and by the scan of the melting zone