Nothing survives during KOH etching?? It is impossible. I used Si3N4 to be the mask that can resist KOH etching until the wafer is etched through(300um, 4~5 hours). The nitride (0.3um) is still there. You can use oxied also but it has to be thicker . Lung-hao Hu Graduate Student Dept.of Mechanical Engineering Univ.of Colorado Boulder