A process for removing moisture from metal surfaces and inhibiting water from readsorbing using organosilanes

Abstract

Summary form only given. The storage of ultra-high purity (UHP) gases is a critical issue to the electronics industry. To prepare a storage vessel or delivery manifold for ultra-high purity gas service, all the atmospheric contaminants must be thoroughly removed from the system. Of these contaminants, atmospheric moisture is the most difficult to remove. It readily condenses on metal surfaces in multiple layers with a large heat adsorption. Typically, moisture is removed by purging or evacuation for long periods of time. In some cases it takes several weeks to adequately remove moisture from a delivery system. This is an expensive, time consuming process. Sometimes systems are heated to high temperature to reduce the time required to remove moisture. However, heating is not always practical, and it does nothing to prevent re-adsorption of water if the system is again exposed to ambient atmosphere. In many cases, moisture is the critical contaminant in the gas delivery system. This is especially true when the ultra-high purity gas is corrosive. Gases such as hydrogen chloride, hydrogen bromide, fluorine, tungsten hexafluoride and other halogen containing gases will severely corrode many metals if moisture is present. Corrosion of the storage vessel or delivery manifold can result in introduction of particle or gas-phase impurities into the ultra-high purity gas, or in extreme cases, result in failure of the system. Components such as valves, regulators, and mass now controllers are very susceptible to failure due to corrosion and frequently need to be replaced. This paper describes a new method for rapidly removing moisture from metal surfaces used in the packaging and delivery of high purity bulk and corrosive-speciality gases. Furthermore, the process passivates the metal by forming a hydrophobic surface that prevents water from readsorbing. Reagents of the type RsiXYZ where R is an alkyl group and at least one of X, Y, or Z is a hydrolyzable group are shown to enhance the removal of surface adsorbed moisture and gaseous product (HX). The HX by-product and unreacted RsiXYZ are rapidly and completely purged from the system. Since water is removed from the surface by chemical reaction rather than by simple purging, the initial dry down is faster. In addition to removing adsorbed water, the treatment incorporates a stable organosilicon group into the surface which greatly reduces the polar character associated with the OH terminated surface. The treated surface is hydrophobic inhibiting water from re-adsorbing during a subsequent moisture exposure. Stainless steel surfaces passivated in this manner are shown to have improved corrosion resistance compared to unpassivated stainless steel.