Relations between Photomask and Photoresist Patterns

As the semiconductor industry continues to progress, photoetching techniques must be improved to meet a new demand which is to engrave complicated patterns less than 2 μm in line-width on thin films. An etched pattern is affected by the photoresist pattern which in turn depends on the density distribution on the photomask. So the relations between the photomask patterns and the sectional shapes of photoresist films are discussed through Γ-characteristic and modulation transfer function in this paper, and the photomask for resolving fine patterns is examined. Consequently, the results obtained are as follows : (1) The thickness of the KPR (Kodak Photoresist) film dissolved by developing is related to the exposure by a linear function on a log scale.(2) The modulation transfer function of the KPR film including an exposing system is obtained experimentally. For example, the modulation at 250 c/mm is about 0.2.(3) The minimum density of photomask determined by line width is required in order to resolve a fine pattern on a photoresist film.