NOVELTY - The method involves depositing layer on substrate (207), during which combustible processing by-products are produced in foreline portion(277) of the deposition chamber (200). The oxygen-containing gas is flown into the foreline to oxidize portion of the combustible processing by-products. The gas flow between the deposition chamber and foreline is shut before the oxygen-containing gas is flown. The product of reaction of the combustible processing by-products and oxygen-containing gas is caught in a catch pot (276) connected to the foreline upstream from a vacuum pump.    USE - Method of processing solar cell substrate in deposition chamber e.g. plasma enhanced chemical vapor deposition (PECVD) chamber.    ADVANTAGE - The method of processing substrate in deposition chamber, prevents explosion of explosive material in vacuum foreline of chemical vapor deposition systems, by introducing purges of oxygen-containing gas into the vacuum foreline in between or during deposition cycles, so that explosive silicon particulates interact and react with the supplied oxygen to form unreactive silicon dioxide. The oxygen purges avoid reaction of large quantities of explosive silicon particulates and generation of too much heat, while reducing contamination of the upstream process chamber. The oxygen gas is ionized using the radio frequency plasma source, so that the efficiency of reaction of reactive materials in foreline and oxygen-containing gas is improved. Since the chamber foreline valve controls the amount of fluid communication between the chamber and foreline, the chamber is prevented from contamination due to entry of oxygen or other materials. The vapor phase exhaust is delivered from the collection vessel to the abatement unit to eliminate residual by-product.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for system for processing substrate.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the plasma enhanced chemical vapor deposition (PECVD) chamber.    Plasma enhanced chemical vapor deposition chamber (200)    Substrate (207)    Catch pot (276)    Foreline portion (277)    Foreline valve (289)