Phase-shifting lithographic masks having phase-shifting layers of differing compositions

摘要

A phase-shifting lithographic mask (500 or 600), for use in conjunction with optical radiation of wavelength lambda , has a transparent substrate (10) upon which are successively located a bottom (2m+1) pi radian phase-shifting layer (11) and a patterned top (2n+1) pi radian phase-shifting layer (12) each having at least approximately the same refractive index at the wavelength lambda as that of the substrate. A more finely patterned, opaque chromium layer (13) is located on the patterned top phase-shifting layer. The bottom phase-shifting layer is chemically different from both the substrate and the top layer, in order to provide either etch-stopping or end-point etch detection during subsequent dry ion beam millings--as with gallium ions--of either or both of the layers, for the purpose of mask repair. For example, the substrate is quartz (silicon dioxide), the bottom phase-shifting layer is calcium fluoride, and the top phase-shifting layer is silicon dioxide. Remnants of the gallium then can be removed, if need by, from both the exposed portions of the substrate and of the bottom layer--such as by forming indentation regions (52; 51) by means of successive etchings, for example, with HF and HCl, respectively, for respective prescribed time intervals having a ratio such that the relative phase shifts of the substrate and both phase-shifting layers are not disturbed by the respective etchings.