Imaging dissolution rate monitor: Mapping the photoresist response

A 2048 channel linear charge coupled device array dissolution rate monitor (DRM) has been constructed and tested for the characterization of x-ray photoresists during development to measure and quantify: exposure uniformity, onset and magnitude of surface roughening, and resist contrast and sensitivity for various processing conditions. DRM measurements were made on Shipley XP-90104C photoresist, and a simple empirical model of surface roughening was proposed based on scanning electron and atomic force microscope images of the resist surface. In addition, resist contrast, sensitivity, time to clear, and normalized remaining thickness curves were all calculated from a single wafer and used to characterize the photoresist. The DRM has been used to measure the inhomogeneity of various x-ray exposure window materials used to isolate the ultrahigh vacuum environment. These can cause variations in the intensity of the beam and consequently yield exposure inhomogeneity. The Be window had significantly more exposure field variation (±5%) than the poly-Si window (±1%). Vibrating the Be window during exposure reduces the exposure variation to ±1%.