Circular apertures for contact hole patterning in 193nm immersion lithography

Abstract

A novel concept of contact holes patterning for 193 nm immersion lithography is demonstrated in this study. Conventional contact holes patterning involve targeting a square printed feature on the wafer and applying optical proximity correction (OPC) such as corner serifs addition and dimensional biasing. As dimension of contact holes reduces, the resolution enhancement provided by conventional OPC methods has become limited. This is because at smaller dimension, more light is diffracted towards higher order and is not captured in the pupil plane. As a result, the corners of the printed features are rounded and features appear circular as dimension reduces. Hence, the efforts made to generate OPC assist features using a square target are inefficient. In this paper, the patterning of contact hole using circular target is demonstrated. The imaging performance of isolated and regular contact holes array is reported. Comparison with conventional approach is made. The effects of the proposed method on critical dimension (CD), depth of focus (DOF), and image contrast is investigated. © 2010 SPIE.