Apparatus and methods related to forming films on sidewalls of memory cell stacks in memory and logic devices. In one approach, a silicon wafer is held in a chamber of an atomic layer deposition (ALD) reactor. A temperature in the reactor is controlled to a first temperature (e.g., room temperature or below) where a first gas reactant that is provided into the chamber condenses and is adsorbed on the target wafer or substrate. The first reactant or precursor is partly vaporized at a second temperature in the reactor that is greater than the first temperature. A second gas reactant is provided into the chamber. The second gas reactant reacts with the adsorbed portion of the first gas reactant in its activated state. The reaction product is a film on the sidewall of a memory cell stack or logic devices. The foregoing steps are repeated to form a desired thickness of the film.

A method of processing a substrate having a gap includes loading the substrate onto a substrate support unit, supplying an oligomeric silicon precursor and a nitrogen-containing gas to the substrate through a gas supply unit on the substrate support unit, and generating a direct plasma in a reaction space by applying a voltage to at least one of the substrate support unit and the gas supply unit, wherein a plurality of sub-steps are performed during the supplying of the oligomeric silicon precursor and the nitrogen-containing gas and the generating a direct plasma, and different plasma duty ratios are applied during the plurality of sub-steps.