Pattern Displacement Error Under Off-Axis Illumination

Pattern displacement errors under off axis illumination (OAI) are investigated using multiple OAI settings and patterns which simulate a dynamic random access memory (DRAM) device situation. Pattern displacement errors of various systems were observed and aberration effects were simulated. The difficulty in correlating between pattern displacement errors and line width asymmetries is observed from measurement and analyzed with simulation. In order to avoid this problem, use of a larger pole size and grouping of machines which have similar pattern displacement errors are suggested.