Development of etch hillocks on different Si(h k l) planes in silicon anisotropic etching

The connection between the way of development and appearance of mesa structures and typical hillocks developing during anisotropic etching of monocrystalline silicon in 5 M KOH saturated with isopropanol has been studied both theoretically and experimentally. A simple geometrical model of mesa formation was presented. Then, the process of hillock growth in result of mesa transformation caused by etch mask underetching was analyzed. At the second part of the paper, the model of hillocks formation was verified experimentally. For this purpose, a series of experiments with etching of mini-mesas through the masks with various patterns in the conditions favoring hillock formation was carried out. It was shown that at the final stage of the etching process the mesas transform into hillocks, bounded by the planes close to {1 1 1}. Probably at the first stage of hillocks formation, mini-mesas develop. Such stable mini-mesas, produced in the presence of random micro-masks, may transform into typical hillocks in effect of successive releasing of {1 1 1} mini-faces. It seems that the process of hillock formation is similar to mesa etching. apes of hillocks produced on the substrates with different from (0 0 1) crystallographic orientations have been also analyzed. The similarities of the hillocks and intentionally prepared mesas were underlined. It was stated that the morphologies of hillocks are strictly connected with crystallographic orientation of etched substrate. Different shapes of hillocks developing on the substrates with different crystallographic orientations, reflect the arrangement and inclination of {1 1 1} planes on considered substrate.