Fracture Strength of Polycrystalline Silicon Wafers for the Photovoltaic Industry

Abstract

The fracture strength of polycrystalline silicon wafers has been investigated by means of twist and four‐point bending tests. Under a twisting configuration, which generates high tensile stresses within the middle of the wafers, a unimodal distribution in strength is obtained. The characteristic strength and Weibull modulus are 131.0 MPa, and 14.4, respectively. Under a four‐point bending configuration, which generates high stresses both at the surface and at the edges, an additive bimodal distribution is obtained. The first mode of the distribution has a characteristic strength of 76.0 MPa and a Weibull modulus of 1.6; the second mode has a characteristic strength of 161.2 MPa and a Weibull modulus of 11.5. Fractographic observations confirm that the first mode (lower strength) corresponds to wafers which failed from large edge chips (sizes up to 90 μm). Weibull analysis suggests that the second mode (higher strength) corresponds to wafers which failed from smaller surface chips (sizes up to 50 μm). The results obtained point to large edge chips as the most dangerous defects degrading the fracture strength of the wafers. This is of great relevance for the photovoltaic industry, as fracture of silicon wafers limits both the performance and lifetime of the solar cells, and production yields.

Investigation of Partial Discharge and Fracture Strength in Piezoelectric Ceramics

“…If edge chips or surface flaws arising from inadequate machining are the main factor to affect the strength, one may expect to see a deviation from the two-parameter Weibull distribution. 34 However, in our study, no significant deviation can be observed. Therefore, it is reasonable to assume that the extrinsic flaws introduced by machining are not the operative flaws controlling the strength.…”

“…Moreover, the fact that the strength data can be fitted well using the two‐parameter Weibull distribution also indicates that machining flaws are unlikely to be the major reason to influence the strength. If edge chips or surface flaws arising from inadequate machining are the main factor to affect the strength, one may expect to see a deviation from the two‐parameter Weibull distribution . However, in our study, no significant deviation can be observed.…”

Improved fracture strength of multicrystalline silicon by germanium doping

“…Consequently, it is essential to understand the fracture behavior of thin silicon wafers and to develop ways for their strength improvement. At room temperature, silicon is a brittle material and neither plastic deformation nor dislocation generation is observed when the applied stress exceeds a certain limit [3]. Its fracture strength is limited by the structural defects, which can serve as stress concentrators [4][5][6].…”

“…Therefore, most studies focused their efforts on the impact of surface or edge damage, i.e., biaxial flexure test [7] is used to investigate the quality of the wafers surface, and four-point bending test [3] is applied to probe both surface and edges of the wafers. Moreover, fracture of brittle material exhibits statistical behavior and the Weibull analysis is applied to demonstrate the statistical fracture data [3,7,8].…”

Fracture Strength of Photovoltaic Silicon Wafers Evaluated Using a Controlled Flaw Method

“…[3,4] Those wafer sawing processes, which can be regarded as a series of overlapping micro-indentations by sharp, abrasive particles, yield distinct damage pattern reaching tens of micrometers deep into the silicon surface, which are not completely removed by damage etching steps. [9][10][11] In the future, as the thickness of PV silicon wafer is reduced to 100 mm or less, wafer breakage issue due to the presence of micro-scale flaws will become even more detrimental. [9][10][11] In the future, as the thickness of PV silicon wafer is reduced to 100 mm or less, wafer breakage issue due to the presence of micro-scale flaws will become even more detrimental.…”