Anomalies in modeling of anisotropic etching of silicon: Facet boundary effects

Beginning with an idealized model of anisotropic etching of silicon in which the etch behavior depends only on the crystal features presented to the etchant, this article extends the model to address certain anomalies observed in the data. The idealized model is based on profiles of underetched surfaces and underetch behavior as a function of mask-edge deviation in wagon-wheel experiments on Si{110} and Si{100} at different TMAH concentrations. Underetched surfaces are found to follow a cohesive system composed of planes defined by two types of crystal features: periodic bond chains and rows of kinks. But it is also found that the same crystal planes in the same etchant often exhibit different etch rates. These anomalies are outlined, and interactions at the boundaries between adjacent facets are proposed to explain them.