New Evaluation Approach of Alignment Signal from Resist-Coated Patterns

Abstract

A new evaluation approach of alignment signals from resist-coated patterns using a linear Fresnel zone plate alignment method is described. In most alignment methods, signals are greatly influenced by resist topography on the target pattern. For calculations of alignment signals, Fraunhofer diffraction from the target pattern and optical path change through the resist materials are considered. In order to determine resist topography on the pattern, a mass transport method is introduced. Based on these results, a target pattern of shallow step depth (0.09 µm) is selected as the best target for alignment, and an alignment accuracy of 0.09 µm (3σ) is obtained.