Optimization of the optical phase shift in attenuated phase-shifting masks and application to quarter-micrometer deep-UV lithography for logics

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Abstract
New developments in the field of embedded shifter materials look very promising for defect free phase shifting mask (PSM) manufacturing. Nevertheless, a good control of the shifter parameters (phase shift and absorber transmittance) remains of utmost importance. In this paper, a lithography sensitivity analysis to shifter deviations has been carried out. It was found that dark field masks require different tolerances than light fields. Because of a growing need for an accurate measurement method of the phase shift, an optical technique, based on measurement of the zero diffraction order of diffraction gratings, is investigated. Using this technique, an attenuated PSM manufacturing process has been optimized for deep-UV, in order to demonstrate the possibilities of quarter micron PSM lithography. As a result, 0.3 micrometers contact windows could be printed with sufficient process latitudes. Using modified illumination techniques in combination with the attenuated PSM, considerable gain in process latitudes was found for quarter micron gates as well, although proximity effects are still a concern.

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