Mechanical Behavior of Diamond-Sawn Multi-Crystalline Silicon Wafers and its Improvement

Abstract

Poor mechanical property is identified as a potential barrier to commercial development of diamond wire sawn multi-crystalline silicon wafers. 3-point bending tests of the diamond-sawn multi-crystalline silicon wafer samples, along with those of mono-crystalline silicon and of the slurry-sawn wafers for references, were carried out. The bending in two orthogonal orientations relative to the cutting marks was tested respectively. Critical strain at breakage is chosen to indicate the wafer’s strength against breakage in bending. Effective elastic moduli of the different wafer samples in bending were also measured. The results show that, compared to slurry-sawn silicon wafers, diamond-sawn silicon wafers, either of mono-crystalline or multi-crystalline, are stronger in the direction parallel to the cutting marks, and weaker in the direction vertical to the cutting marks; more importantly, for diamond-sawn multi-crystalline silicon wafers, a very low critical strain level, ∼57 % of the slurry-sawn multi-crystalline silicon wafers, is identified, in their direction vertical to the cutting marks. In view of the relevance of the critical strain to the breakage rate for the main stream slurry-sawn wafers, this would cause an unacceptably high breakage rate in industrial production and application of the diamond-sawn multi-crystalline silicon wafers. Annealing was found to significantly raise the critical strains of various wafers, and encouragingly, annealing at temperature as low as 400 °C can raise the critical strain of the diamond-sawn multi-crystalline silicon wafers to a level similar to that of the slurry-sawn multi-crystalline silicon wafers.