On the mechanical strength of monocrystalline, multicrystalline and quasi‐monocrystalline silicon wafers: a four‐line bending test study

Abstract

Quasi-monocrystalline silicon wafers have appeared as a critical innovation in the PV industry, joining the most favorable characteristics of the conventional substrates: the higher solar cell efficiencies of monocrystalline Czochralski-Si (Cz-Si) wafers and the lower cost and the full square-shape of the multicrystalline ones. However, the quasi-monocrystalline ingot growth can lead to a different defect structure than the typical Cz-Si process. Thus, the properties of the brand new quasimonocrystalline wafers, based on low and high crystal defect densities, have been for the first time studied from a mechanical point of view, comparing their strength with that of both Cz-Si monocrystalline and typical multicrystalline materials. The study has been carried out employing the four line bending test and simulating them by means of FE models. For the analysis, failure stresses were fitted to a three-parameter Weibull distribution. High mechanical strength was found in all the cases. However, the quasi-monocrystalline wafers characterized by large density of bulk defects, due to the noticeable density of extended defects, showed lower fracture tensions.

Polycyclic Aromatic Hydrocarbons as Sublimable Adhesives

“…Previous research on wafer thinning has focused on two aspects: (i) improving existing equipment and techniques for processing, 12,13,18,19 and (ii) studying the mechanics of crack propagation to avoid fracturing. 18−21 While these efforts have led to improvements, the typical method for processing silicon wafers has remained relatively constant for the past six decades.…”

Effect of Small‐Angle Grain Boundary on the Mechanical Properties in Direct Silicon Bonded Wafer

“…It was reported that quasi‐mono silicon has higher averaged residual stress than multi‐crystalline silicon, and the strength of the former is weaker than the latter especially when appearance of locally high density defects . To our surprise, the statistical fracture strengths of multi‐crystalline silicon wafers are comparable with or even higher than those of CZ silicon wafers by Weibull distribution. The influence of GBs on the mechanical properties and the weak point in multi‐crystalline silicon wafer are not well understood yet.…”

“…The stress fields around GBs are critical in terms of the mechanical stability of the wafer, as they can act as sources for crack formation if additional force is applied . It was reported that quasi‐mono silicon has higher averaged residual stress than multi‐crystalline silicon, and the strength of the former is weaker than the latter especially when appearance of locally high density defects . To our surprise, the statistical fracture strengths of multi‐crystalline silicon wafers are comparable with or even higher than those of CZ silicon wafers by Weibull distribution.…”

About the origin of low wafer performance and crystal defect generation on seed-cast growth of industrial mono-like silicon ingots

“…Therefore, an increase in the macroscopic breakage yield during the industrial handling can be expected. It has been verified that there were direct effects of such a high density of defects (Figure 9(a)) in the fracture tension limits of the wafers, as determined by a systematic four-line bending test (FLBT) analysis [10]. By FLBT fitted to the corresponding Weibull distribution analysis, a batch of 50 highly dislocated mono-like wafers exhibited up to ca.…”