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In Situ Measurements of the Resist Etch Rate for Submicron Patterns

A resist film is etched by oxygen-based plasmas, and fine grating patterns of the resist are fabricated. During etching, a laser beam is irradiated onto the sample and the reflection intensity from the sample is measured in order to determine the etching depth. The reflection intensities are calculated by solving the Maxwell equations for electromagnetic wave propagation. The dependence of the reflection intensity on the etching depth varies greatly with the ratio of the space width to the grating period. The absolute etch rate can be obtained by comparison between the experimental and simulated reflection intensities. The fabricated gratings are 0.5 µm in period and the ratios of the space width to the grating period are between 0.4 and 0.7. The reflection intensities obtained from the experiments agree very well with those from the simulations. The etch rate decreases as the etching depth increases, but it is almost independent of the aspect ratio of the fabricated patterns. The etch rate decrease is not caused by an increase in the aspect ratio of the etched pattern, but may be induced by the time variation of plasma conditions.