A method of forming a film on a substrate by PEALD includes deposition cycles, each including (i) feeding a precursor in a pulse to a reaction space to adsorb a precursor on a surface of a substrate; (ii) after step (i), applying RF power to a second electrode to generate in the reaction space a plasma to which the precursor-adsorbed surface is exposed, thereby forming a sublayer on the surface; and (iii) applying a bias voltage to the second electrode while applying RF power in step (ii), which bias voltage is negative with reference to a potential on a surface of the first electrode, wherein the cycle is repeated to deposit multiple sublayers until a film constituted by the sublayers has a desired thickness.