Prediction of the critical dimensions by using a threshold energy resist model

Abstract

In lithography, the variable threshold resist model (VTRM), an aerial-image-based simulation, is a useful tool for acquiring a resist process margin. The VTRM is used to compensate for the optical proximity effect (OPE) and to optimize the optical system while a full simulation method requires all the process parameters. However, The VTRM has shown some problems. The exposure dose and the focus should be fixed in one special condition to improve the prediction accuracy for the pattern size and for various pattern types and cannot be combined together in one equation. In this paper, we suggest a new simulation method that gives more accuracy and has wider applicability than the VTRM method. The new simulation method can represent the photolithography process with a simple formula. The parameters of this formula are composed of the exposure dose and the defocus as input components, and the critical dimension as the output component. Also, the formula for the resist process is kept constant to be consistent with other resist processes. The first technical improvement of this, equation is that the equation adopts a process-matched aerial image because the aerial image at the top of the resist surface cannot represent the bulk resist energy distribution. The second one is the introduction of the new concept of the threshold energy resist model (TERM). The threshold energy level is used, instead of the aerial image's threshold intensity level, to predict the critical dimensions. The threshold energy levels can be found by using a simple equation and an experiment.