The Application Of Polarized Confocal Microscopy For The Size Measurement Of Resist Structures

Abstract

The accurate and precise measurement of the critical dimensions of submicron structures is a fundamental aspect of modern integrated circuit fabrication. The limit of optical resolution of classical microscopy has been reached and new, improved methods are needed. Confocal laser scanning microscopy can provide measurement repeatability of well below 10 nm. However, the gathered image is not always a true image of the real structure. The image depends very much on the intricate interaction of the structure with the optical field in the focal region. In particular for the case of semi-transparent structures, such as photoresist, accurate measurement of the size proves to be more difficult. In this case the structure reflects only a fraction of the incoming light and the signal is mainly determined by the underlying layer. If this is a metal layer (e.g. aluminium) which reflects more than 90 % of the incoming light, the influence of this layer is observable even in a region of more than 1.5 micron outside the geometrical focus. Therefore the light reflected by the substrate interferes coherently with the light reflected by the resist structures and both signals cannot be separated. The real shape of the resist edge is not correctly imaged and an accurate measurement is difficult. The purpose of this paper is to analyse this effect in detail and present an optical arrangement in which the reflection of the substrate is suppressed with respect to the reflection from the air-resist interface.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.