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.
Nonuniform residual stresses may develop during anodic bonding due to variations in wafer curvature prior to bonding or due to nanotopography interactions between the bonding surfaces. In this work, we discuss the significance of nonuniform residual stress in anodically bonded wafer pairs and present a method for measuring local stress variations even in cases when the bonded wafers are apparently defect free based on conventional inspection tools. These residual stresses can vary significantly between two different wafers processed identically, depending on the local interactions, but they are present in all standard bonding methodologies. In some instances, these local residual stresses can significantly alter the resulting wafer curvature in apparently defect free substrates. Currently, anodically bonded devices or substrate wafers are considered "defect free" if no large debonds are found after bonding; however the residual stress state of the wafers cannot be determined using the same conventional techniques.
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