In the sub-100-nm mass production of semiconductor devices, thin-film resists dispersing acid generator molecules, referred to as chemically amplified resists, have been used. Feature sizes in lithography are approaching the molecular scale with the rapid progress in miniaturization. With reductions in lateral dimensions, a decrease in resist thickness is inevitable and the effects of interfaces become significant. A requirement for ultrafine fabrication is the uniformity of resist components. In this work, the depth profile of the acid generator distribution was investigated by X-ray reflectivity measurement at SPring-8. The depth profile in thin resist films was clarified. It was found that the depth profile varies with acid generator concentration.
The acid generator distribution in resist films is an important issue for fine patterning based on chemical amplification. In particular, extreme ultraviolet (EUV) resists require a high acid generator concentration compared with conventional chemically amplified photoresists. In this study, the depth density profiles in partially protected poly(4-hydroxystyrene) films containing dispersed triphenylsulfonium salts were investigated by X-ray reflectivity measurements to clarify the depth profile of acid generator distribution. It was found that the depth profile depends on the molecular structure of acid generators. The hydrogen bonding between polymers and acid generators affected the depth profile of acid generator distribution.
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