By Halvor Dalaker, Research Scientist, SINTEF Materials and Chemistry; Shawn Wilson, Senior Engineer in the Metallurgy Department, SINTEF Materials and Chemistry
In slurry-based wafering of silicon bricks using multi-wire saws, the slurry is subject to significant evolution with time as the grits become worn and the silicon kerf accumulates. A good understanding of this evolution would allow wafer producers to make better-informed decisions on when and how to replenish slurry during wafering. This paper summarizes certain important slurry properties and presents some experimental results regarding their evolution. Sampling the slurry at the front and rear of silicon bricks during wafering has allowed the effect of a single pass through the sawing channel to be studied. The wear on the slurry grit is interpreted in terms of identifying what portion of the particle-size distribution plays the most critical role in wafering, and how this critical region changes as the slurry ages. It is found that in a relatively fresh slurry, the particles around the median size and slightly larger are the most active, while particles more than a few μm below the median play only a small part. As the slurry ages, the active region of the particle-size distribution becomes narrower, and shifts towards larger particles even though there are fewer such particles available. This leads to less slurry–brick interaction and poorer material removal properties.