Photoresist Characteristics and Their Reaction Mechanism for Crystalline Peroxopolytungstic Acid

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Abstract
Crystalline peroxopolytungstic acid, , is found to produce a homogeneous thin film which is ultraviolet (UV)‐sensitive. Although the original film is difficult to dissolve in solutions, the irradiated XW film becomes even more insoluble in an aqueous solution (negative‐type resist characteristic). On the other hand, it becomes soluble in methanol when the UV dose is small (positive‐type resist characteristic). In situ gas measurements, TPD, IR, and XRD studies lead us to conclude that, generally, with irradiation, peroxo groups decompose to produce oxygen, and XW becomes amorphous in a way that the portion of edge sharing of octahedra and pseudo‐octahedra increases. In the region showing the positive‐type resist characteristic, aside from the general reaction described above, corner linking of the polyhedra breaks though the XW phase is still present with hydrogen‐bonded OH. In then negative‐type resist characteristic region, in addition to the general reaction described above, the broken molecules polymerize mainly by edge sharing, and XW and hydrogen‐bonded OH disappear. These changes due to irradiation are compared with thermal changes.

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