The Divergence of Image and Resist Process Metrics

摘要

It is common for computational lithography optimization to be performed using the metrics of the simulated aerial image (AI). Using the AI, the wafer-level CD can be estimated in a number of ways, such as thresholding with or without convolution of the AI with a point-spread function. The assumption of such an approach is that the relationship between the AI CD and the resist CD response is linear. However, the properties of resist reaction-diffusion-development yield a process which is highly non-linear. For example, it is well-known that different photoresists produce a different lithographic response to the same aerial image; isofocality, depth-of-focus, exposure latitude, MEF etc. all vary from one resist to another for the same projection optics and mask. Several publications have demonstrated that a well-calibrated physical resist model can be extrapolated to accurately predict the CD and profile response of the resist process over a wide range of optical and process conditions1"4. In this work, the divergence in performance between resist processes and the projected image-in-the resist is explored through simulation.