The Role of a Photoresist Film on Reverse Gas Plasma Etching of Chromium Films

Abstract

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.

Plasma Processing of Thin Chromium Films for Photomasks

“…The following possible chemical reactions should be considered SiI-I4(g) + 2 02(g) 0 ) SiO2(s) + 2H~O(~) [1] k, SiH4(~) + Os(g) ) SiOcs) + 2H~O(~) [2] ks ) SiOs(,) + 2Hs(~) [3] Key words: belt, transfer, CVD. 1 Not ',to be confused with chemical transport reactions in which deposition results from transport (usually by diffusion) between zones of different temperature in a reversible equilibrium (4).…”

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“…Such masks are capable of transferring patterns with dimensions at least as small as 0.15 ~m; these structures may be defined in the chromium by either optical or electron beam patterning procedures, Up to the present time, pattern transfer of a structure defined in resist that is coated upon the chromium has been accomplished largely by wet etching techniques. There are a number of reports in the literature in which chromium photomasks are prepared by plasma etching using carbon tetrachloride or chlorine mixed with oxygen (2)(3)(4)(5) or carbon tetrafluoride mixed with oxygen (6). This report describes the application of plasma processing to the etching of chromium photomasks.…”