New Method for Grain Size Characterization of a Multi-Crystalline Silicon Ingot

In order to estimate the quality of the crystallisation process of multi-crystalline Silicon ingots, we have developed a new optical method for the determination of grain sizes on as-cut wafers that were taken from different height positions of the ingot. This fast method is based on image analysis and allows in a simple way to get numerical data which represent the crystallographic quality of silicon wafers. The obtained data were used to calculate a grain size distribution over the analysed wafer area as well as an average grain size by using two different algorithms. It was thus possible to represent the average grain size as a function of ingot height, which indicates ingot regions of lower crystalline quality, for example regions of equiaxed growth of very small grains (?grit?). This technique was used for the characterisation of different multi-crystalline Silicon ingots, using Silicon feedstock of different quality (electronic, upgraded metallurgical or solar grade), and also to monitor the impact of modifications of the crystallisa-tion process parameters on the grain sizes distribution. It was found that this method is able to give a first qualitative impression of the multi-crystalline ingots and wafers which in the end are used to produce solar cells.