Grain Enhancement of Thin Silicon Layers Using Optical Processing
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FILMS
WITH
OPTICAL
When a small-grain (or an amorphous) silicon film deposited on a glass substrate is subjected to a thermal anneal at temperatures above 600 'C for an extended period of time, an increase in the 419
Mat. Res. Soc. Symp. Proc. Vol. 470 01997 Materials Research Society
grain size is observed. The grain enhancement results from a movement of grain boundaries activated by temperature. An increase in the time or temperature or both can further promote the grain growth. As described in the next section, the rate of grain growth may be increased by other mechanisms that can facilitate the movement of grain boundaries. These include addition of dopants or generation of free carriers, injection of point defects, and lowering the grain boundary barriers by optical illumination. The next section briefly discusses the influence of these parameters in a semi-quantitative manner. This section describes the procedure we have used to enhance the grain growth by combining these concepts. Thin silicon films were sputtered from a silicon target on to quartz substrates coated with a thin layer of Al (about 1 gm thick). Figure 1 illustrates the composite structure of the samples. The resultant films had very fine grains and adhered well to the substrates. The expected boron concentration was
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