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Simulations and Experiments on O Density and Distribution in Ashing Process Using Surface Plasma Excited by Microwave

Simulation methods for the density and spatial distribution of O atoms have been developed to analyze high-density plasma (1011 cm-3) excited by two microwave sources. The density of O atoms, that react with photoresist, was calculated in a gas mixture of CF4 and O2, and the density has a maximum value at 10% CF4 partial pressure. For the distribution simulation, the rate of reaction between O atoms and photoresist was measured in a small cell, and the sticking coefficient was estimated to be 0.002. The O atom distribution on a glass substrate was calculated by the simulator, where the sticking coefficient was input, focusing on the density under a beam that connected the microwave sources and had no plasma source. The results of both the simulations are in good agreement with the experimental results. The simulations were applied to optimize the chamber configuration and process conditions. As a result, a high ashing rate of over 1430 nm with a uniformity of ±9.3% was obtained.