Mechanisms of etch hillock formation

We have studied the formation of etch hillock defects during anisotropic etching of (100) silicon in KOH. Defect density is correlated with low etchant concentration and high etch temperature. Cathodic etch experiments indicate that hillocks form under conditions of decreased OH^- ion concentration. The activation energy for defect formation is 1.2 eV, considerably higher than the energy associated with silicon removal. We propose a mechanism to explain hillock formation that involves nucleation by silicon redeposited from the etch solution. The incidence of hillocks in this model is the result of a competition between the forward and reverse etch reactions. Examination of defects by electron microscopy suggests that growth occurs preferentially on slow-etching planes, in agreement with the model predictions