Analysis and simulation of diffractive imaging field in thick film photoresist by using angular spectrum theory

The thick film photoresist lithography is a much more complicated process compared to the thin film photoresist lithography. In this paper, we have developed a new model for lithography of thick film photoresist by using the angular spectrum theory. The thick film photoresist is divided into many homogeneous layers, and the diffractive optical imaging distribution in photoresist is regarded as superposition of different spectrum plane waves. Propagation of each plane wave is determined by the optical transfer function, and the propagation direction, amplitude and phase are dominated by reflection and transmission between each interface of the sub-layers. The fast Fourier transform (FFT) has been converted into a convolution calculation to keep the computation accurate and reduce computation cost. Numerical calculation results show that optical intensity in cross-sect of thick film resist is strongly affected by reflection, transmission on interface and variation of dielectric permittivity along direction of depth, and therefore these factors should be considered while analyzing diffractive imaging field in thick film photoresist.