RESISTANCE MEASUREMENTS OF PLATINUM-TITANIA THIN-FILM GAS DETECTORS IN ULTRA-HIGH-VACUUM (UHV) AND REACTIVE ION ETCHER (RIE) SYSTEMS

The application of a conductometric Pt-TiOx thin film gas detector for monitoring oxygen and hydrogen impurities in vacuum and in semiconduc tor process gases is described. The gas detector exhibits reversible r esistance responses to gases such as O-2 and H-2 in the 10(-5)-10(-3) Pa range, but does not register a response to inert gases such as CF4. The gas detector utilizes an evaporated 65 Angstrom Ti-35 Angstrom Pt film deposited on a micromachined dielectric window of the silicon ba sed structure. Additional features of the gas detector structure inclu de Ti-Ir electrodes arranged on the sensing film in a four point probe configuration and a boron-doped silicon heater beneath the dielectric window which is capable of varying the temperature of the sensing fil m from ambient to 750 degrees C. The gas detector is activated for sen sing with oxidation in 1.3 x 10(-4) Pa O-2 at 750 degrees C followed b y reduction in 1.3 x 10(-4) Pa H-2 at 400 degrees C. This series of ac tivation steps converts the 65 Angstrom Ti-35 Angstrom Pt film into a discontinuous network structure of discrete Pt-TiOx islands. Gas detec tor responses to oxygen and hydrogen in vacuum, both under isothermal and temperature-programmed operation, are reported and mechanistically discussed. The utility of the Pt-TiOx gas detector to detect small le aks and to track in-situ the effluent dynamics during operation of an Applied Materials hexode reactive ion etcher (RIE)is demonstrated. (C) 1997 Elsevier Science S.A.