Method for rapid determination of ion gauge sensitivity factors

In ultrahigh vacuum thin film growth processes using gas phase growth precursors, the pressure of the gas at or near the substrate is a critical parameter since it is directly related to the collision frequency of the precursor with the substrate and ultimately to the growth rate. These pressures are usually measured using a nude Bayrd-Alpert-type ion gauges, which are generally calibrated for nitrogen. Consequently, it is necessary to know the ion gauge sensitivity factor that relates the measured pressure to the actual pressure of the growth precursor. The purpose of this article is to describe a simple method to obtain such sensitivity factors. This method uses a simple gas manifold comprised of equipment commonly found in laboratory settings where ultrahigh vacuum work is performed. Results are reported for dimethyl silane, monomethyl silane, methane, and hydrogen. The gauge sensitivity factors for the latter two gases are known and, therefore, provide a basis for validating the method.