NOVELTY - The method comprises introducing a first auxiliary reactant in vapor phase into a reaction chamber under conditions allowing the first reactant to adsorb onto a substrate surface, where a substrate is provided in a reaction chamber, introducing a second reactant in vapor phase into the reaction chamber while the first reactant is adsorbed on the substrate surface, where the second reactant is introduced without first sweeping the first reactant out of the reaction chamber, and introducing a third reactant into the reaction chamber under conditions.    USE - The method is useful for depositing a dielectric film on a substrate surface, where the dielectric film is: a conformal structure for forming shallow trench isolation, a through silicon via liner, an interlayer dielectric, a gate spacer and an intermetal dielectric; an anti-reflective layer; a low-k dielectric layer (all claimed); useful for manufacturing integrated semiconductor device; in the solar energy field such as photovoltaic devices; in the electrochromics field; intermetal dielectric applications; pre-metal dielectric applications; dielectric liners for through-silicon via applications; resistive random access memory applications; and/or stacked capacitor fabrication in dynamic random access memory applications.    ADVANTAGE - The method is capable of uniformly depositing the dielectric film on the substrate surface with improved physical, chemical or electrical characteristics, increased deposition rate and good adhesion thus providing excellent device performance to the semiconductor device.    DETAILED DESCRIPTION - The method comprises introducing a first auxiliary reactant in vapor phase into a reaction chamber under conditions allowing the first reactant to adsorb onto a substrate surface, where a substrate is provided in a reaction chamber, introducing a second reactant in vapor phase into the reaction chamber while the first reactant is adsorbed on the substrate surface, where the second reactant is introduced without first sweeping the first reactant out of the reaction chamber, introducing a third reactant into the reaction chamber under conditions allowing the third reactant to adsorb onto the substrate surface, where the plasma drives a reaction between the first, second, and third reactants, exposing the substrate surface to plasma to drive a reaction between the first and second reactants on the substrate surface to form the film, depositing additional film directly on the portion of the film by chemical vapor deposition, selectively etching the film at an entrance of the recessed feature, and depositing an additional portion of the film on the etched film. Plasma is ignited while one of the reactants is present in a gas phase and is exposed to the substrate. The amount of the film is limited by the amounts of the first and second reactants adsorbed on the substrate surface. The second reactant flows to the substrate surface at a non-constant flow rate during the step of introduction of second reactant. A sweep phase sweeps out the second reactant in vapor phase before the exposure of the substrate surface. The substrate surface is exposed to the second reactant after the sweep phase and before exposure of the substrate surface. The first and second reactants co-exist in vapor phase. The first reactant flows continuously at a non-constant rate and a reduced flow rate during the intermittent delivery of the second reactant. The film is plasma treated to modify a property of the film. The plasma treating is conducted under plasma conditions that are different from the plasma conditions employed to drive the reaction between the first and second reactants on the substrate surface. The property of the deposited film modified by the plasma treating consists of internal film stress, etch resistance, density, hardness, an optical property, dielectric constant, carbon content, and an electrical property. The treatment of deposited film changes the composition of the film, removes a contaminant from the film. The reaction chamber sweeps after the exposing and before etching steps. The method further comprises applying photoresist to the substrate, exposing the photoresist to light, patterning the resist and transferring the pattern to the substrate, and selectively removing the photoresist from the substrate. INDEPENDENT CLAIMS are included for:    (1) an apparatus for depositing films on a substrate; and    (2) a system comprising the apparatus.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a conformal film deposition process.    Deposition cycles (110A, 110B)    Exposure phases (120A, 120B)    Post-saturation exposure time (130, 150)    Plasma post-saturation exposure time (190)    Plasma activation phase. (180A)