Investigation of mask deformation by oxygen-radical irradiation during resist trimming

The mechanism of resist-mask distortion during a resist trimming process was investigated experimentally. It was found that oxygen-radical irradiation creates a degraded layer on the resist surface and causes compressive stress. Non-uniform spatial distribution of oxygen radicals, therefore, causes asymmetrical irradiation of the radicals and makes an unbalanced or asymmetrical stress field on the resistmask surface. Such an asymmetrical stress field results in the distortion of a resist mask.