| As the integrated circuit(IC)process node enters the sub-10 nm era,the requirements for lithography resolution are further improved,especially for the resolution of lithography mask manufacturing.The manufacture of high-precision lithography masks is mainly realized by direct-writing electron beam lithography(EBL)technology.Due to the influence of secondary effects such as electron beam scattering in solids,the resolution of EBL is seriously reduced.Therefore,performing secondary effect correction(SEC)is a key link in the nanoscale EBL process.Currently,due to the further reduction of the critical dimensions(CD)of the lithography layout and the continuous expansion of the layout scale,the electron beam simulation not only requires the calculation accuracy of the SEC algorithm,but also requires the calculation efficiency to be further improved to meet actual engineering needs.At present,the electronic design automation(EDA)software for EBL simulation and optimization is mainly monopolized by several European and American companies.In the Wassenaar Agreement and the US Import and Export Control Regulations,the computational lithography EDA software is included in the embargo list for China,which is a typical “strangled” technique.China’s research in the field of EBL calculation and simulation is relatively weak.In China’s “14th Five-Year Plan”and the 2035 long-term goal outline,it is clearly pointed out that we should make up for the shortcomings in this technology field.In order to break through the international blockade,this project mainly studies the optimization algorithm of electron beam secondary effects,and focuses on the development of “independent and controllable” high-performance EBL EDA software HNU-EBL.The core code of the software exceeds 50,000 lines.There are nine Chinese invention patents(three of which have been authorized),and five software copyrights have been authorized.The software is free and open to major research institutions(link: http://www.ebeam.com.cn/),and has been adopted by Huawei Technologies Co.,Ltd.,the research institutions of the Chinese Academy of Sciences,Tsinghua University,Fudan University and other research institutions.The specific innovation points of this dissertation are:(1)This dissertation proposes a fast multipole method(FMM)with unequally spaced grid(calculation time complexity is O(N))to accelerate the SEC of EBL based on dose correction.Compared with the algorithm based on fast Fourier transform(FFT)(calculation time complexity is O(Nlog N))adopted by international mainstream EDA tools,it can achieve a substantial speedup.The actual measurement shows that when the layout density is lower than 80%,the FMM correction calculation speed exceeds the FFT algorithm;when the layout density is lower than 40%,the FMM correction calculation speed can be increased by more than 1.0 times.At the same time,this dissertation proposes a lithography layout compression method based on non-uniform quadtree grid shearing,which is used to compress the layout after SEC of EBL based on dose correction.The actual measurement shows that,compared with the mainstream uniform pixel grid method,through three polygon cases with different characteristics,the compression accuracy of the algorithm is within a controllable range,and its compression ratio exceeds 10 times.(2)This dissertation proposes a SEC algorithm based on pattern edge shape adjustment(PESA)method.Compared with the two mainstream PID algorithm and L-BFGS-B algorithm based on shape correction,the iterative convergence of proposed method is faster,and it has higher stability and robustness under different CDs and layout sizes.The actual measurement shows that compared on the advanced IC process nodes(40 nm,28 nm and 14 nm),the calculation efficiency of the PESA algorithm is 3 to 10 times higher than that of the two mainstream algorithms under the condition of the same calculation accuracy,which can greatly improve the calculation efficiency of algorithms based on shape correction.(3)This dissertation proposes a SEC algorithm for EBL based on multilayer perceptron(MLP)neural network(NN).The trained NN directly predicts the exposure dose after the SEC,which greatly reduces the calculation time.The actual measurement shows that the calculation speed of proposed method for different periodic gratings is 7 to 10 times faster than the iterative dose correction method,and the correction error is at the same level as the iterative dose correction method,which can significantly improve the SEC computing efficiency based on dose correction method.(4)This dissertation develops the high-performance EBL “autonomously controllable” EDA software HNU-EBL.According to the process flow of EBL,the software designs “pipeline” EBL simulation and optimization functions,including:calculation of electron beam scattering process based on Monte Carlo method,and point spread function(PSF)based on multi-Gaussian model fitting,SEC calculation,development simulation and edge placement error accuracy verification,etc.The actual measurement shows that,compared with the commercial software Nano PECS developed by Raith,under the premise of ensuring the calculation accuracy,the calculation efficiency of SEC is increased by about 1 order of magnitude.(5)This dissertation implements two high-performance parallel computing optimization schemes:(a)is the Monte Carlo method for simulating the scattering process of electron beams in solids based on the graphics processing unit(GPU)parallel acceleration.Compared with the serial calculation results based on the central processing unit(CPU),the discrete energy deposition density distribution is completely consistent,and the acceleration ratio of parallel computing based on GPU is more than 50 times.(b)is the SEC method based on the message passing interface(MPI)distributed parallel computing.Compared with the CPU-based serial computing results,when the MPI computing nodes are 2,4,and 6 nodes,the speedup ratios of proposed method are 2.28,5.29,and 8.31,which greatly improves the efficiency of parallel computing. |
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