Surface roughness hillock formation

Crystallographic Characters and Formation of Hillocks. The surface roughness of silicon single crystals has clear crystallographic characteristics as illustrated in... 

The extent of hillock formation in alkaline solutions depends strongly on solution composition and operating conditions. Formation of hillocks in KOH solutions occurs in certain concentration ranges. ° Solution stirring and higher solution temperature reduce the hillock-associated surface roughness. The density of hillocks is... 

In particular, the hillocks formed on (100) surface are crystallographic structures bounded by four (111) planes resulting from the anisotropic etching and their formation directly contributes to the roughness of the surfaces [127]. Hillocks may, under certain conditions, form in HF-based solutions [158], but most commonly in alkaline etchants [88, 109, 127]. 

In TMAH solutions a smooth etched surface is obtained at concentrations above 22% TMAH. Addition of l-4g/liter pyrazine to 25% TMAH solution increases slightly the etch rate and improves the surface smoothness. Dissolved silicon in the etchant results in higher roughness as shown in Fig. 7.51. In the ternary etching system of hydrazine, IPA, and water,the etched surfaces vary from being highly faceted to very flat. The faceted surfaces are made up of square pyramidal hillocks whereas flat surfaces are marked by a cellular structure. In ethanolamine-based etchants, the roughness of etched surface appears to be associated with the formation of precipitates. ... 

Roughness developed in a cleaning or etching solution is a result of uneven dissolution across the crystal surface. Many factors in an etching process may cause the uneven distribution of the dissolution rate at both micro and macro scales. One particular example is the roughness associated with the formation of hillocks. In general, any process that causes temporary or permanent surface inhomogeneity will result in preferential dissolution of some areas relative to other areas. 

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