The role of a photoresist film on reverse gas plasma etching of chromium photomask plates has been studied. The variation of etching profiles has been observed using SEM techniques. It is speculated that a WO3 layer on the chromium film forms a masking layer to the etching and that the WO3 layer can be removed by decomposition of the photoresist film in the plasma. A study of the relation between photoresist thickness and etching time has shown that there is an optimum photoresist thickness for each WO3 concentration in the chromium film.
The mechanism of the reaction in the reversal gas plasma etching of anti-reflective chromium photomasks was studied. Auger spectrometer and x-ray photoelectron spectrometer studies of the film revealed that WO3 is incorporated in the surface of the chromium oxide layer of the anti-reflective photomasks for the samples showing reversal etching. WO3 forms a kind of masking layer for the etching. Decomposed species of the photoresist film are found to be responsible for the etching of WOs, and carbon monoxide is proposed as the reactive species for etching the WO~ masking layer. This reversal etching was applied to the fabrication of the photomasks for MOS LSI.
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