Half circle chrome loss by electrochemical effects

For certain designs, we observe a rather peculiar defect during phase-shift mask production. At distinct positions on the mask, the chrome disappears within the second level process in almost perfect half circles. This effect can even be observed if no etching is applied at all. The root cause of this defect is electrochemical dissolving of chrome in DI water during the development rinse process, which appears at locations where the chrome is in contact to the developer rinse medium. In this publication we describe the experimental set-up to investigate the root cause mechanism and propose solutions to overcome the effect.