The characterization of photoresist for accurate simulation beyond Gaussian diffusion

Abstract

With the continued shrink of integrated circuit fabrication groundrules, the achievement of good critical dimension (CD) control becomes more and more dependent on optical proximity correction (OPC). Current simulation capabilities involve a first principle aerial image simulation algorithm, such as the transmission cross coefficient (TCC) algorithm, and a resist model, which captures the dynamics of the chemical amplification and the developing process. In the past few years, it has been found that the key photolithographic parameters, such as, the exposure latitude (EL) and the mask error factor (MEF) for the dense features can be very accurately simulated by the algorithm in which the latent image are made by simple Gaussian diffusion of the aerial image. However, more detailed comparison between the simulation and experiment in isolated features, or two-dimensional features indicates that the current modeling algorithm is still not good enough. This may have resulted in the fact that even advanced model based OPC may require hundreds, even more than a thousand experimental data points for model building. In addition, the model made with such endeavor does not usually extend well beyond the minimum groundrule, which can cause sub-groundrule test structures to fail. We have studied one process parameter of the photoresists, the MEF, and we found that a single Gaussian can not explain well the CD behavior and it seems that such difference varies with different resists. The effective diffusion length of some resists are found to vary with line to space ratio within a dense pitch.