In Situ Ellipsometry in Microelectronics

Abstract

Ellipsometry has been used in microelectronics since the early 1960s when it became necessary to measure the thickness of transparent films on reflective substrates. Ellipsometry is an old technique but with the increasing technological importance of thin films, particularly in microelectronics, and with the availability of faster computers for calculations, ellipsometry is in a renaissance. In principle it is a simple technique (don't confuse simple with easy!) that relies primarily on the physical optics of stratified media. Excellent treatments of ellipsometry exist (e.g., a book, recent reviews), and it is not the intent here to try to improve upon them. Rather, this article is intended to briefly discuss the essential ideas and then to show a few examples of in situ ellipsometry applied to modern materials-research problems. The emphasis here is on in situ ellipsometry, because it is one of the few techniques that can accurately monitor thin-film processes while they occur, yielding both fundamental properties and process information about the system under measurement. In addition it is now possible to use feedback to affect control of thickness, composition, and temperature, for example.We first consider some basic questions: What is ellipsometry, what does it measure, and how well? Next, we discuss hardware for in situ ellipsometry, and finally we show a few examples.