Mask 3D effect on 45-nm imaging using attenuated PSM

In the exposure using ArF immersion exposure tool, under the conditions in which the mask pattern pitch is smaller than several times the exposure wavelength, diffraction light distribution cannot be predicted correctly by the Kirchhoff approximation mask model, and therefore, rigorous electromagnetic field analysis, or 3D mask model, is required. In particular, in the dense line and space (L/S) formation using oblique illumination and an attenuated phase shifting mask (att-PSM), the intensity of 0th and 1st diffraction lights changes as pitch shrinks. In dense L/S formation, it is necessary to reduce a mask error enhancement factor (MEF) and to obtain sufficient exposure latitude. We consider the following three contrast control "knobs" (CCKs): (1) Mask bias, (2) Transmittance of attenuating mask material (absorber), (3) Thickness of absorber. We also considered the effect of illumination angle of incidence on 3D mask. We performed a simple optimization for exposure latitude of dense L/S pattern, reflecting consideration of the mask 3D model for half pitch (hp) 45nm L&S imaging using att-PSM and oblique illumination. The important image characteristics are normalized image log slope (NILS) and dose-MEF for obtaining sufficient exposure latitude. We carried out an experiment of attenuated PSM exposure using hyper-NA exposure tools and compared the results with the 3D mask simulation. The degree of agreement between the and the 3D mask simulation, and the practical effectiveness of the CCKs are discussed in this paper. Keywords: 3D mask model, hyper NA, attenuated PSM, MEF, dose-MEF, contrast control knob.