Methods Of Mask Pattern Optimization For Optical Lithography With Partially Coherent Illumination

With ever decreasing critical dimension in optical lithography, the functions ofintegrated circuit may be greatly affected by the optical proximity effect caused by opticaldiffraction. In order to eliminate this effect, the mask optimization technique whichcorrects the design pattern to improve the fidelity of the output patterns and the targetpatterns is widely utilized. In this thesis, the theories and methods of the forward modelingof optical lithography and inverse mask optimization are developed and discussed, andsimulations are performed to verify the developed theories and methods.A Fast Fourier Transform (FFT) based algorithm is introduced for fast calculation ofTransmission Cross Coefficient (TCC), and the theory of Sum of Coherent System (SOCS)is introduced for fast computation of aerial image. Simulation results demonstrate thistheory can be used for fast aerial image simulation, and its accuracy is satisfactorycompared with the widely used commercial software PROLITH.A fast aerial image calculation algorithm based on one basis mask pattern is proposedfor optical proximity correction, namely the polygon based mask optimization algorithm.The convolutions of the partially coherent kernels with the one basis pattern is calculatedin advance and saved in a table, and then the convolutions of any polygon based maskpatterns with the kernels can be obtained from the table is a fast speed. Simulation resultsdemonstrate that this method is quite suitable for fast aerial image calculation, and isapplicable for optical proximity correction.The pixel based mask optimization technique, namely the inverse lithographytechnique is developed by using the steepest descent algorithm, and the regularizationmethod is introduced to improve the manufacturability of the optimized mask patterns.Simulation results of mask optimization demonstrated this method can be used for maskoptimization for both incoherent and partially coherent systems, and the quadratic andtotal variation penalty are helpful for improving the mask manufacturability.The theories and methods discussed above will be applicable for mask optimizationin lithography systems, and can also be extended to applications such as source maskoptimization, aberration metrology and CD characterization.