NOVEL POSTEXPOSURE BAKE SIMULATOR - FIRST RESULTS

We have designed and implemented a simulator that models the physics o f the chemically amplified photoresist process postexposure bake (FEB) step, based on a general mathematical formulation. The photoacid loss due to kinetic reaction and the photoacid diffusion are simulated usi ng experimentally determined model parameters. The FEB simulator, whic h can be used in conjunction with any lithographic image modeling soft ware, has been integrated into the CXrL ToolSet, a comprehensive model ing system for x-ray lithography. The FEB simulator converts the depos ited dose into an initial concentration of photoacid, and then compute s its evolution and the corresponding evolution of the protected sites , for a given bake time and temperature. System dynamics are defined b y coupled partial differential equations containing acid loss and diff usion terms. As the two phenomena take place at the same time during F EB, the numerical algorithm does not separate the terms in the calcula tion. An alternating direction implicit and explicit numerical differe ntiation technique for solving a multidimensional partial differential equation in x and z has been employed, resulting in a system which re duces computational complexity without loss of accuracy or speed. Line width can be extracted from the final profile of the protected sites, or, alternatively, the concentration of the protected sites can be con verted into a dissolution rate and fed to other dissolution modeling t ools to generate a developed resist profile. Process latitude simulati ons can be performed to study linewidth variation with respect to dose , gap or focus, bake temperature, and time. An initial evaluation has been performed by comparing simulation results with data from an x-ray lithography experimental study. (C) 1995 American Vacuum Society.