Pattern transfer processes

The etching resistance of a resist is simply a function of how well the material withstands the pattern transfer processes used in device manufacturing. Its resistance must be sufficiently high to allow precise transfer of the resist image into the underlying substrate with < 10% linewidth change. This is not an easy... 

Etchant Resistance. Etchant resistance refers to the ability of the resist to withstand the etching environment during the pattern transfer process. The most common method of pattern transfer is wet chemical etching which places emphasis on the adhesion and chemical stability of the resist. Etchant solutions may be either acidic or basic, depending on the type of substrate to be etched. For example, buffered hydrofluoric acid is used to etch Si02. However, lateral penetration of the chemical etchant is significant for thick substrate films and... 

It has been found, however, that the etch rate of PBS can be reasonably controlled in both oxygen and CF4/O2 plasmas if the substrate temperature is kept below room temperature (9). This fact has been utilized to reduce the defect density in the manufacture of chrome photomasks by exposing the developed PBS pattern to a low-temperature oxygen plasma (descum) prior to wet-etching the chrome. We have now found that the plasma-etch resistance of PBS in a CF4/O2 plasma can be markedly enhanced at room temperature simply by exposing the resist to a short oxygen plasma pretreatment prior to exposure to the fluorinated plasma. This effect can be used in a variety of pattern transfer processes to controllably generate submicron features on wafers and masks. This paper examines the parameters associated with this effect, proposes a mechanism to account for the results and delineates some possible pattern transfer processes. 

The spacer technique is unique in that with one lithographic exposure, the pitch can be reduced by a factor of two indefinitely, just with the application of a succession of spacer-formation and pattern-transfer processes. Furthermore, because spacer materials are mostly drawn from HM materials, their postetch pattern quality tends to be superior, especially in terms of line edge roughness and CD control, when compared to corresponding resist profiles after etch. It is also not sensitive to interlayer alignment. 

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