Principles of hydrocarbon detection in ultra high vacuum: Optimizing sensitivity and selectivity towards harmful species

The performance in regard to sensitivity and selectivity of a simple, reproducible hydrocarbon sensor based on a platinum film interfaced with yttria-stabilized zirconia has been characterized with respect to a range of hydrocarbons under high vacuum conditions that are pertinent to the intended application. Sensing and in situ X-ray photoelectron spectroscopy (XPS) data acquired under open circuit conditions permitted identification of the active oxygen species present at the sensing electrode as a function of sensor temperature. This fundamental information provides the basis for a plausible hypothesis for the mode of sensing action under conditions that are directly relevant to the intended application and remote from those under which YSZ-based sensors are normally operated. For unsaturates, which are damaging species, sensitivity is a strong function of the C:H ratio of the impinging molecule, increasing as this quantity increases, and a plausible explanation for this effect is proposed. Additionally, we show that the relative sensitivity (selectivity) towards different analytes may be strongly altered by choice of operating temperature, thus providing a means of tuning device performance. The device requires no power supply and is therefore well suited to large-scale application involving multiple locations, for example within next-generation extreme ultra-violet lithography (EUV) semiconductor chip fabrication plants.