Quantitative Infrared Photoelasticity of Silicon Photovoltaic Wafers Using a Discrete Dislocation Model

Abstract

Residual stress and crystalline defects in silicon wafers can affect solar cell reliability and performance. Infrared photoelastic measurements are performed for stress mapping in monocrystalline silicon photovoltaic (PV) wafers and compared to photoluminescence (PL) measurements. The wafer stresses are then quantified using a discrete dislocationbased numerical modeling approach, which leads to simulated photoelastic images. The model accounts for wafer stress relaxation due to dislocation structures. The wafer strain energy is then analyzed with respect to the orientation of the dislocation structures. The simulation shows that particular locations on the wafer have only limited slip systems that reduce the wafer strain energy. Experimentally observed dislocation structures are consistent with these observations from the analysis, forming the basis for a more quanti tative infrared photoelasticity-based inspection method.

Polarized light emission from grain boundaries in photovoltaic silicon

“…The strain-induced retardation varies significantly around location 'Q' relative to location 'P', where the retardation remains relatively uniform in the defect-free grain. The non-uniform strain field is a signature associated with crystal defects found in silicon wafers [18].…”

Stress evaluation of Through-Silicon Vias using micro-infrared photoelasticity and finite element analysis

“…Our basic strategy was to build virtual fringe patterns based on the FEA results and the principle of photoelasticity [15], and then to compare the virtual fringe patterns with the experimental pattern. In the stress investigation using FEA, different "equivalent" stress free temperatures were used so that each TSV would have different virtual fringe patterns, but only the pattern that most resembled the real pattern and its corresponding stress was adopted.…”

“…The total birefringence of IR light when it passed through the silicon was then calculated as the sum of the birefringence of each layer, where the stress variation along the thickness was negligible and the birefringence was calculated using the stress-optic law [15]. The total birefringence of IR light in terms of phase delay Δðx; yÞis expressed as Δðx; yÞ ¼ ðf π=λÞ…”