Etching of Germanium with Water Vapor

The gas phase etching of germanium with the water vapor is studied. Germanium reacts with the water vapor in the temperature range of 700∼880°C according to the reaction, Ge(s)+H2O(g)=GeO(g)+H2(g). The water vapor is superior as an etchant in such respects as the purity, uncorrosiveness and uniformity in mask etching. The etching rate is found to depend strongly on the atmosphere of hydrogen or the inert gas. The difference in etch rate is qualitatively discussed in terms of the chemical kinetics. The structure of hexagonal pits, which are observed to grow under a particular etching condition, is clarified.