Study Of Polarization Aberration Induced By 3D Mask Effects For Immersion Lithography System

To fit Moore's law,the critical dimension(CD)shrinks continually,and the imaging precision of integrated circuit lithography technology improves quickly.To enhance the resolution,it' a good method in immersion lithography to increase the numerical aperture and import polarization illumination.Therefore,the vector character of incident light have to be considered.With the continuously shrinking of critical dimension,imaging model using Kirchhoff's approximation of mask will not predict lithography image formation precisely.It's essential to consider the mask thickness,which result in 3D mask effects under polarization illumination.In immersion lithography of 45 nm node,the size of mask line width is close to illumination wavelength,the interaction between them is strong.In the Kirchhoff's approximation,it would make a larger imaging error to think the mask layout as infinite thin,and could not meet lithography imaging requirements.The mask diffraction field need to be calculated by rigorous electromagnetic field simulation.As the mask have 3D structure,the amplitude,phase and polarization state of incident light will probably change after transmitting through the mask.The change of light field mentioned above is defined as 3D mask effects.The 3D mask effects are related to the mask materials,the thickness of absorber layer,the mask layout,mask sidewall angle,the polarization direction of illumination light and so on.With the polarization illumination in immersion lithography system,the 3D mask effects affect the amplitude transmittance,the phase shift and the polarization direction of incident light,which are similar to the polarization aberration induced by the objective lens.Based on polarization aberration theory and vector imaging model,we propose a novel approach to represent the 3D mask effects exactly,which is the diffraction frequency spectrum difference between the rigorous electromagnetic field model and the Kirchhoff model and can be expressed as Jones pupil.In addition,the Jones pupil representing the3 D mask effects could be decomposed through Pauli decomposition and the physical decomposition to obtain physical properties.The 3D mask effects under different effective source points,different mask layouts and different technology nodes(45-14nm)are studied.The 3D mask effects are quantitatively analyzed thoroughly and precisely.The results show that,as the technology node moves down,the 3D mask effects will have stronger influence on the incident light's polarization and the polarization aberration induced by 3D mask effects becomes more notable.