Application of an inverse Mack model for negative tone development simulation

A negative tone development (NTD) process benefits from the superior imaging performance obtained with light field (LF) masks to print metal and contact layers, resulting in improved process window. In this paper, we introduce an inverse Mack development model to simulate the NTD process and validate its process advantage. Based on this model, a NTD resist model calibration has been carried out and the model results are presented. Various NTD application cases have been studied and the prediction capabilities of simulations are demonstrated: 1) LF+NTD process helps to achieve a broader pitch range and smaller feature size compared to the traditional dark field (DF) with positive tone development (PTD) process. NTD brings a significant improvement in exposure latitude (EL) and MEEF for both line-and-space (L/S) and contact hole (CH) patterns through pitch. 2) The NTD process has been explored for double exposure lithography with extreme off-axis illumination using L/S patterns with horizontal and vertical orientation, respectively, which creates dense contact hole arrays down to a 80 nm pitch. 3) Simulation can also be used to explore new NTD process variances. We have demonstrated the simulations of the NTD model in applications such as printing specific CH or Metal patterns, a dual-tone development process and a combination of source mask optimization (SMO) and NTD to print SRAM patterns at smaller sizes.