![]() ![]() If this stress exceeds the wafer strength, the wafer will break. As the wafers move under the light source, each wafer undergoes a dynamic temperature profile that produces a preset elastic stress. The wafers are carried on a belt through a chamber that illuminates the wafer with an intense light of a predetermined intensity distribution that can be varied by changing the power to the light source. ![]() Based on this, we have developed a high throughput, noncontact method for applying a predetermined stress to a wafer. ![]() If a wafer survives this stress, it has a high probability of surviving without breakage during cell/module fabrication. We believe that the best way to isolate the wafers with fatal microcracks is to apply a stress to wafers-a stress that mimics the highest stress during cell/module processing. Furthermore, even if such detection is successful, it is not straightforward to relate them to wafer breakage. Unfortunately, it is very difficult to detect microcracks that are embedded within the roughness/texture of the wafers. Some attempts have been made to develop optical techniques to detect microcracks. To eliminate the cost of processing the wafers that break, it is best to remove them prior to cell fabrication. ![]() Additional propensity for breakage is caused by texture etching and incomplete edge grinding. The major cause of this excessive wafer breakage is that these wafers have residual microcracks-microcracks that were not completely etched. Wafer breakage is a serious problem in the photovoltaic industry because a large fraction of wafers (between 5 and 10%) break during solar cell/module fabrication. Wafer screening device and methods for wafer screening ![]()
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