Temperature influence in confocal techniques for a silicon wafer testing

The paper discusses problems of Silicon wafer measurements accuracy in context of the scanning helium atom microscope, which is a new technique currently under development. In the microscope the helium atom beam is used as a probe. The overall microscope resolution depends on a deflecting element, which shapes the beam and focuses it onto a sample's surface. The most promising focusing component appears to be an ultra thin silicon wafer that is deformed under a precise electric field. Thus its quality is decisive for the project success. Flatness and thickness uniformity of the wafer must be measured in order to select the best plate to be used in the microscope. A scanning measurement system consists of two coaxially positioned confocal heads. Recent studies have revealed that the system is very sensitive to temperature variation. The compensation algorithms and further measures designed to suppress the temperature effect are presented and discussed.