NOVELTY - The process comprises: depositing a layer having a density of 1500 kg/m3 and a silicon compound containing 5-66% of carbon atoms (calculated as the proportion of carbon atoms in a deposited layer to total atoms excluding hydrogen) on a silicon wafer substrate (25); and thermally treating the deposited layer of silicon compound in an oxygen containing atmosphere at a temperature of 700 degrees C for 1-60 seconds. A percentage of carbon atoms in the deposited layer is less than 65%. The layer of silicon compound is deposited from a non-local thermal equilibrium atmospheric pressure plasma.    USE - The process is useful for producing a silicon wafer coated with a passivation layer of a silicon oxide for producing a photovoltaic cell (all claimed).    ADVANTAGE - The process is capable of stably enhancing the passivation of the silicon wafer thus enhancing conversion efficiency of the photovoltaic cell, and producing the silicon wafer with high yield and performance.    DETAILED DESCRIPTION - The process comprises: depositing a layer having a density of 1500 kg/m3 and a silicon compound containing 5-66% of carbon atoms (calculated as the proportion of carbon atoms in a deposited layer to total atoms excluding hydrogen) on a silicon wafer substrate (25); and thermally treating the deposited layer of silicon compound in an oxygen containing atmosphere at a temperature of 700 degrees C for 1-60 seconds. A percentage of carbon atoms in the deposited layer is less than 65%. The layer of silicon compound is deposited from a non-local thermal equilibrium atmospheric pressure plasma containing an organosilicon compound. The process further comprises: applying a radio frequency high voltage to a needle electrode (11) positioned within a dielectric housing (14) having an inlet and an outlet, while causing a process gas to flow from the inlet through a channel (16) past the electrode to the outlet, for generating the non-local thermal equilibrium atmospheric pressure plasma; incorporating the organosilicon compound in the non-local thermal equilibrium atmospheric pressure plasma so that the organosilicon compound interacts with the non-local thermal equilibrium atmospheric pressure plasma to generate activated organosilicon compound species and organosilicon compound fragments; and positioning the silicon wafer substrate adjacent to the outlet of the dielectric housing so that the surface of the silicon wafer substrate is present in contact with activated organosilicon compound species and organosilicon compound fragments generated by plasmaorganosilicon compound interaction. The non-local thermal equilibrium atmospheric pressure plasma extends to the outlet of the dielectric housing so that the surface of the silicon wafer substrate is present in contact with the plasma. The organosilicon compound is introduced into the non-local thermal equilibrium atmospheric pressure plasma via an atomizer (21) positioned within the dielectric housing. A gas is used to atomize a surface treatment agent in the atomizer. The organosilicon compound is introduced into the non-local thermal equilibrium atmospheric pressure plasma at 2-14 l/minute. The process gas is fed to the inlet of the dielectric housing at 1-15 l/minute. The deposited layer of silicon compound contains no carbon as measured by X-ray photoelectron spectroscopy after thermal treatment. An INDEPENDENT CLAIM is included for a process for producing a photovoltaic cell.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross sectional view of an apparatus for generating a non-equilibrium atmospheric pressure plasma incorporating an atomized organosilicon compound.    Needle electrode (11)    Dielectric housing (14)    Channel (16)    Atomizer (21)    Silicon wafer substrate. (25)