Electron-cyclotron-resonance (ECR) plasma etching was applied to gas pressure sintered Si3N4, β′-SiAlON and α′/β′ composite SiAlON. The etching was successfully performed within about 15min, and the shapes of Si3N4 and SiAlON grains were clearly observed. Also the grains of α′-SiAlON were distinguishable from β′-SiAlON grains and grain boundaries. The volume ratio of α′ phase to β′ phase obtained from the area of the etched surface was almost consistent with the value obtained from X-ray diffraction. However, the grain boundary area observed from the etched surface did not correspond to that obtained from back scattered electron image.
