Study Of Mask Diffraction Modeling And Its Impact On Imaging In Extreme-ultraviolet Lithography

Lithography is the one of the key technologies of integrated circuit manufacturing.Extreme ultra-violet(EUV)lithography technology is currently the most advanced lithography technology.High-volume manufacturing(HVM)of 7nm technology node chips has been achieved by using EUV lithography.Lithography simulation is used to reduce costs and shorten the development cycle.Mask diffraction field simulation is one of the important components of EUV lithography simulation.Due to the thick mask effects of EUV mask,the traditional Kirchhoff thin mask model is no longer suitable for EUV lithography simulation.Although the rigorous simulation method of mask diffraction field has high simulation accuracy,it consumes a lot of calculation time and memory resources.The fast simulation method generally sacrifices a certain simulation accuracy in order to increase the simulation speed.In order to quickly calculate the mask diffraction field with high simulation accuracy,an improved structure decomposition model is established using interpolation in this thesis,which utilizes the cubic spline interpolation to calculate the reflection coefficients of the multilayer.Simulation and analysis of the impact of diffraction field on lithography imaging are carried out.The main content includes the following aspects:(1)A fast model of EUV mask diffraction spectrum based on interpolation is proposed.The mask is decomposed into the absorber and the multilayer.The diffraction spectrum of the absorber is calculated by edge point pulses model(EPPM),and the reflection coefficients of the multilayer are calculated by the cubic spline interpolation method.Simulations are carried out with 15 nm line-space pattern as an example.Compared with the rigorous simulation results,the root mean square error(RMSE)of the proposed model for the mask diffraction spectrum calculation is less than 0.005,and the calculation error of the aerial image critical dimension(CD)is less than 0.3nm.The proposed model shows better performance than the traditional structure decomposition model.(2)On the basis of the Hopkins imaging formula,the influence of diffraction spectrum amplitude sensitivity on lithography imaging is studied.It is deduced that the relationship between aerial image CD error and diffraction spectrum amplitude noise,which is defined as amplitude noise sensitivity,is linear.The lower the diffraction order,the larger the noise sensitivity.The relationship between the amplitude noise sensitivity and the mask period is studied,of which the results are consistent with that of the rigorous simulations.The influence of the amplitude noise of the diffraction spectrum on the aerial image CD is studied.The results are consistent with that of the rigorous simulations.(3)Graphical user interface of forward imaging simulation for Si Litho lithography simulation software is designed and developed.Graphical user interface functions include mask parameters setting and drawing,illumination source setting and drawing,projection objective parameters setting,diffraction spectrum parameters setting and drawing,and aerial image drawing.