Because the mechanisms of 200 mm and 300 mm tools are similar, comparable numbers of particles tend to fall on wafers of either size. The absolute number of particles will be about the same for both, but thanks to the 300 mm wafer's larger area, the defect density will be about 2.2x better for the 12-inch wafers. In terms of the number of good die produced, the yield and productivity of 300 mm wafers should be much better than that of 200 mm wafers. When all of these elements are considered, there remains a distinct productivity advantage with 300 mm. Another factor in the 300 mm decision is, of course, cost.
Higher productivity is good.
Both the tool costs and the materials costs impact this evaluation. Currently the capital cost for all 300 mm tools combined falls somewhere between 1.2x to 2.0x that of the 200 mm tools. Given the 2.25x size ratio of the wafers, there is a measurable cost advantage for 300 mm lines. At present, the price of a 300 mm wafer is about 7x to 8x that of a 200 mm wafer, far exceeding the 2.25x multiplier. Still, normal market dynamics will bring prices down as the demand for 300 mm wafers increases.