Fundamental investigations of surface and subsurface damage, and wear in diamond wire sawing of silicon

Abstract

An impediment to widespread adoption of photovoltaics is the high cost of solar cells, which use mono- or multi-crystalline silicon wafers as substrates. The wafers are cut from silicon ingots using the wire sawing process, which is an expensive step in the manufacturing process. To reduce the cost of solar cells, low-cost, thin silicon wafers of superior surface quality and strength are needed. Recent industry trends indicate a shift from the loose abrasive slurry (LAS) to fixed abrasive diamond wire sawing (DWS) process for slicing silicon wafers. DWS offers several advantages including smaller kerf loss, reduced costs and environmental impact over the LAS process. However, fundamental research to advance the scientific understanding of DWS is lacking. An open problem in DWS is how the abrasive grits fixed to the core wire can be engineered to produce favorable surface and subsurface properties, which would reduce processing time and resources in addition to enhancing the mechanical strength of the substrate. Moreover, cutting multi-crystalline silicon by DWS has known limitations of higher wire consumption. Multi-crystalline silicon is less expensive than mono-crystalline silicon and is therefore expected to enhance the affordability of solar energy. In spite of the advantages of DWS and the low cost of multi-crystalline silicon, lack of fundamental knowledge of the DWS process is a limiting factor for widespread practical application. The goal of this research is to advance the scientific understanding of diamond wire sawing of silicon through fundamental studies of the effects of grit shape, silicon microstructure, abrasive wear, and cutting fluid on the resulting surface and subsurface damage. It is expected that the proposed research will provide the knowledge required to guide future development and optimization of the DWS process to cut brittle materials, including multi-crystalline silicon for photovoltaic applications.