Analysis Of Nearfield For Photomask Based On Extended Fourier Diffraction Theory And Rigorous Coupled-Wave Method

In order to improve the resolution of photolithographic system, many resolution enhance technology were used which were phase-shifting mask, offaxis illumination, optical proximity correction, and so on. So the hyper numerical aperture small current dimension and thick mask were needed. And then, normal scalar diffraction theory was not exact any more. Extended scalar diffraction theory and rigorous electromagnetic method were used to simulate the nearfields for different mask model. Two methods were used in this paper to get the diffraction efficiencies and the nearfields, one method was called extended fourier diffraction theory, another was called rigorous coupled-wave analysis.However, analysis of transfer function with Fourier diffraction theory will be inadequate, and shadowing effects must be considered for oblique illumination. Therefore, a new approximation model for alternating phase shift mask considering shadowing effects was proposed in this paper,. Extended Fourier diffraction theory was used, and a relation of function depended on incident angle. Diffraction efficiencies and interference fields were simulated using approximation model. Rigorous coupled-wave analysis is a method which solving Maxwell equation to get the nearfield of the mask. For this method doesn't use any approximation in solving Maxwell equation, it is a rigorous method. We got the diffraction efficiencies and the nearfields. In this paper, our mask was considered infinitely in the y direction, so Maxwell equation was simplified to be a two-dimensional problem, and we can save time. TE polarization and TM polarization incident light diffraction efficiencies change with incident angle and mask pitch were both calculated. And the results of two methods were compared at last. The rigorous electromagnetic method was more exact than the extended fourier diffraction theory.