in mils are graphically represented respectively by curves 11 and 21 in fig1 and 2 respectively as shown therein as the ionic concentration increases the lateral etch rate decreases while the etch depth increases dramatically in the range of 1 000 2 000 ppm and reaches an approximate saturation level in the neighborhood of 3 000 ppm for the barium cation species ba 2 from an initial etch depth of 0 07 mils without the addition of the barium ions the etch depth can be increased to a value on the order of 0 25 mils for a koh solution having a ba 2 ion concentration on the order of 5 000 ppm lanthanum chloride lacl 3 u00b7 7h 2 o was dissolved in a 45 0 w w alcoholic potassium hydroxide solution and successive samples of the solution were applied to the 100 crystal face of a silicon substrate with the etching bath being maintained at a constant temperature in a range of 65 u00b0 95 u00b0 c as in example i described above the lateral etch rate and the etch depth in the silicon versus the ion concentration of the la 3 cations species are plotted in curves 12 and 22 in fig1 and 2 respectively as shown therein an even more dramatic effect in terms of maintaining desired moat geometry and increased etched depth than that obtained with the barium cation of example i was observed it should be noted that the salt cation species given in examples i and ii above are not to be considered limitative of the invention cation species and their salts other than those.