Model-based OPC for phase-shifter edge lithography

Abstract

Phase shifter edge lithography (double-exposure method) provides improved image contrast and lithographic resolution. However, it is subject to the problems of optical proximity effects. Therefore, to make this technique practical for use in device manufacturing, it is necessary to understand the characteristics of optical proximity effects and through such understanding establish a practical OPC (Optical Proximity Correction) method to correct them. Since the size of both the phase shift mask (PSM) and the trim mask (a mask used to form a rough gate pattern) significantly affect the wafer CD (critical dimension), an OPC tool which takes the layout of the two masks into account is required. Due to the difficulty in describing a rule-table for both masks, a model-based approach is a suitable means to develop such a tool. A PSM and a trim mask are used to calculate aerial images. In a double-exposure approach, however, mask shape does not define the desired shape. Therefore, an additional layer which defines the desired shape has been introduced. The desired shape is also used to consider the etching effect, which is described in a rule-table and applied to the original layout. With this approach, the desired shape defines the resist shape. To improve computing time, we apply model-based OPC only to specified areas, and rule-based OPC outside of those areas. Because of the large amount of data that must be processed, the designed layout is divided into fractions and compute on a multi-processor system. Previously, we reported improvements in pattern-matching methods to reduce the simulation time. In this paper, we report full-chip- correction performance and results of OPC technology.