Ph.D. Proposal Presentation by Shijiang He
Monday, December 6, 2004

(Dr. Steven Danyluk, Chair)

"Near Infrared Photoelasticity of Polycrystalline Silicon and it's Relation to In-Plane Residual Stresses"


The goal of this research is to investigate an experimental infrared transmission technique and associated analysis tools to extract the in-plane residual stresses in thin single and poly-crystalline silicon sheet and try to relate the residual stresses to physical parameters associated with silicon growth and cell processing.

Previous research has suggested this concept, but many engineering and analytical details had not been addressed. In this research, a system has been designed and built and the sensitivity of the system is in the process of being determined. The equivalent anisotropic stress-optic coefficients are being developed to convert the photoelastic parameters to principal residual stresses, which are further separated using least-square method. The anisotropic coefficients and the fringe multiplier are being calibrated by a four-point bending fixture.

The polariscope together with other techniques will be applied to silicon wafers going through various processing steps in the manufacture of photovoltaic cells. It is intended to relate the residual stresses to minority lifetime at each step of cell processing. The object is to understand and perhaps optimize the interaction between the residual stresses, the lifetime and the cell efficiency.