Hp45 lithography in consideration of the mask 3D effect

Abstract

In the exposure using ArF immersion exposure tool, under the conditions in which the mask pattern pitch is smaller than a several times of the exposure wavelength, diffraction light distribution cannot be predicted correctly by the Kirchhoff approximation mask model, and therefore, rigorous Electromagnetic Field (EMF) analysis is required. In particular, in the dense L&S formation using oblique illumination and an attenuated phase shift mask (att-PSM), the intensity of 0th and 1st diffraction lights changes as pitch shrinks. In high density L&S formation, it is necessary to reduce a mask error enhancement factor (MEF) and to obtain sufficient exposure latitude. We consider the following two contrast control knobs: (1) optimizing the transmittance of attenuated mask material, (2) optimizing mask bias. The important image characteristics are normalized image log slope (NILS) and dose-MEF. Dose-MEF means a dose to size change per mask critical dimension (CD) change. We performed a simple optimization for exposure-defocus window of dense L&S pattern reflecting consideration of the mask EMF model for half pitch 45nm L&S imaging using att-PSM and oblique illumination. We explain the characteristics of the contrast control knobs and their effectiveness. An optimized combination of contrast control knobs depends on the capability of mask CD process as a smallest limit of mask CD and mask CD uniformity.