Phase-shifting mask topography effects on lithographic image quality

The impact of phase-shifting mask topography on wafer exposure was studied via simulations and experimentation using phase-shifting masks fabricated by etching the quartz to define the shifted areas. The influence of the refractive index of the chromium layer and of the profile of the chromium patterns was shown to be minimal. On the other hand, the quartz profiles have a large impact on the wafer results. For vertical quartz profiles, the intensity of the light going through the etched portion of the mask is lower than that going through the unetched portion of the mask and varies with feature size. This problem can be addressed either by optimizing the quartz profiles or by biasing the size of the features depending on the type of pattern.<>