Development of in-sutu observation system for internal stress fields due to lattice defects using the infrared photoelastic method

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In order to develop high quality silicon wafer with large diameter, it is essential to control lattice defects such as dislocations in those wafers. Polycrystalline silicon has also received much attention recently, but it is inevitable to improve its mechanical property for developing their practical use. In order to investigate such mechanical property and lattice defects of silicon crystals, it is very useful to make direct observation of internal stress fields caused by those crystal defects in crystals.The essential point in the present research project is to develop the in-sutu observation system for internal stress fields due to lattice defects by using the infrared photoelastic method. By using this system, we made in-situ obaervation of crack tip stress fields developed around a crack tip in compact tension specimen of silicon crystals. The simulation of photoelastic images has been also made, and we have obtained a good agreement with those experimentally observed. In addition, in this research project, we observed the detailed configurations of dislocations generated around a crack tip in silicon thin crystals, which is essential not only to understand the toughness of silicon wafer, but also to study the physical meaning of the photoelastic images obtained by the present system.