Extreme ultraviolet mask defect simulation

Abstract

This article investigates the printability of defects embedded inside multilayer mirrors used for masks in extreme ultraviolet lithography. Models for buried defects of various shapes and sizes and their subsequent distorting of the deposited films are developed and used to assess the effect on both the fields at the mask and the aerial image at the wafer. Because most of the reflection occurs in the top 10–20 layers and thus it is hypothesized that simulating with a truncated multilayer will still yield insight into the printability of the defects. The relationship between point defects and line defects of the same height is explored. The intensity minimum in the aerial image for defects is found to vary periodically with only a quarter wave change in the height of the defect due to phase considerations. Defocus can enhance a defect’s printability and an isolated line with only 2 nm height and one quarter of a feature width may print. Nonprinting isolated defects are shown to become killer defects when feature interactions are considered.