after the inactivation step regions 15 of layer 11 are etched or removed this is done by allowing the etchant to permeate through the remaining portions of layer 12 to come into contact with regions 15 of layer 11 and hence the name permeation etching in the preferred embodiment wherein layer 11 is comprised of silicon dioxide anhydrous hydrogen fluoride at a pressure of about 20 torr is used at a temperature of about 175 u00b0 c to etch regions 15 of layer 11 different temperatures and pressures may be used to obtain a desired etch rate it is contemplated that the etch reaction products migrate away from the substrate and cause to form a depression or groove in the layer 11 allowing for the movement of the remaining portions of the layer 12 towards the semiconductor substrate after the etching is completed the remaining portions of layer 12 fit into the depression so formed as shown in fig3 it is contemplated that etchants other than hydrogen fluoride may be used so long as they permeate through the masking layer 12 and are suitable to etch the material of layer 11 the higher impurity concentration base regions are formed by ion implanting impurities through the layer 11 into regions 14 of the semiconductor substrate shown in fig2 these regions.