Assessing Requirements for Wafer Environment Control

A methodology for assessing wafer environment control (WEC) needs based on process specific defect density (D₀) goals, actual process and airborne particle levels, particle deposition velocity and wafer exposure time, as well as risks associated with changes in these factors is presented. The motivation is to ultimately determine cost-effective wafer isolation technology (WIT) strategies needed to achieve the required levels of particulate contamination at the wafer surface. The means of extending the methodology to other potentially yield-limiting nonparticulate airborne contaminants is also discussed.