Trends in Wafer Cleaning Technology

Abstract

Every wafer-processing step is a potential source of contamination, not only from particles but also from a variety of contaminants, as described in Part I. Keeping wafer surfaces scrupulously clean throughout the wafer processing cycles is essential for obtaining high yields in the fabrication of VLSI devices. In order to remove these contaminants, cleaning steps appear repetitively within the semiconductor process flow, occupying 30–40% of all the process steps. However, cleaning processes, in relation to other processes, have been relegated to a subordinate role as pre- and post-treatments. And, because a simple, convenient and highly sensitive method of measuring the cleanliness of the wafer surface has not been produced, for many years we have ceased to move forward, merely using cleaning solutions developed decades ago and relying on intuition and experience. It was only seven or eight years ago that the debate at symposiums about cleaning mechanisms became lively and encouraged serious reconsideration of cleaning technology.