The Impact of Microroughness on the Generation of Watermarks on Etched Silicon Surfaces

We found that watermarks caused haze in a polycrystalline silicon film grown on an etched silicon surface by the chemical vapor deposition process. The film, called a “poly-backseal”, traps metallic impurities inside itself. We investigated the possible cause of these watermarks, and found that the microroughness of the wafer surface plays a role in their generation. This suggested the microroughness had to be controlled to the order ≤8.0 nm for a large range (20×20 µm 2 ) and to the order ≤0.2 nm for a small range (0.1×0.1 µm 2 ) in order to reduce the occurrence of watermarks per unit area <1.0%. Minute particles with diameters of 0.1 to 0.3 µm were observed on the wafer surface where watermarks had generated. An analysis of the particles suggested the main component of the watermarks was silica, as indicated in previous studies.