Transmission Of Ultra-deep Sub-micron Ic Lithography Process Imaging Studies

Optical proximity correction (OPC) is emerging as an important tool in design and manufacturing of next generation integrated circuits. The basic idea behind OPC is to intentionally and systematically distort the mask in such a way as to compensate for optical diffraction limit and process non-idealities. OPC is considered to be useful in two ways: first it enables smaller features with closer proximities to be printed on the same area; second, it increases the process latitude, decreases the variations of linewidth across a chip and could potentially enhance yield. To predict lithographic results well for OPC purpose, a fast, practical and efficient lithographic model, which is suitable for OPC processing of complicated 1C layouts, is becoming an important research topic.The basics of lithography process, as well as the basic structure of lithographic system and the basic theory of partially coherent imaging are introduced in this paper. A bi-linear model of optical imaging is also presented. Based on these theories, the simulation process of CSPLAT is particularly analyzed, especially the computation of TCCs (Transmission Cross Coefficient) under different illuminations and the processing of primary lens aberrations inside TCC computation process. For practical OPC applications, CSPLAT is not suitable for intensity calculation on huge amount of sparse aerial points, hence a fast algorithm of sparse aerial image intensity calculation for lithography simulation is derived in this paper based on the theory of principal waves. According to this derivation, a bi-linear optical system could be decomposed into a set of convolution kernels, which could then be convoluted with input pattern, and the resulting set of convolution fields could be superimposed to yield an intensity field. Aerial image can be computed fairly fast by this method compared with the rigorous solution of the Hopkins equation, especially for the situation of many sparse aerial points which is often met in OPC application.