EFFECT OF CRUCIBLE PURITY AND INTERFACE CHARACTERISTICS ON MULTICRYSTALLINE SILICON INGOT QUALITY

摘要

Impurities diffusing from crucible/coating into the silicon during melting and crystallization degrade the silicon quality by reducing the minority carrier lifetime. This work was undertaken to test how the lifetime is affected by the purity of fused silica crucibles and silicon nitride used as coating. Also a crucible coated with high purity silica was tested to investigate if this layer functioned as a diffusion barrier by inhibiting impurities diffusing from the crucible into the melt/solidified silicon. It was found that reducing impurity content in the silicon nitride is important to achieve high minority carrier lifetime. A lifetime of 95 μs was measured on silicon from the high purity crucible coated with purified silicon nitride. The silica coated crucible showed a small improvement in minority carrier lifetime compared to the reference crucible, although the lifetime was considerably lower than for the high purity crucible. Investigation of the silica coating after the experiment revealed that the coating was not sufficiently thick. The high purity crucible showed different thermal behavior resulting in shorter melting time.