A method and apparatus for sputter depositing an insulation layer onto a surface of a cavity formed in a substrate and having a high aspect ratio. A target formed from a material to be included in the insulation layer and the substrate are provided in a substantially enclosed chamber defined by a housing. A plasma is ignited within the substantially enclosed chamber and a magnetic field is provided adjacent to a surface of the target to contain the plasma adjacent to the surface of the target. A voltage is rapidly increased to repeatedly establish high-power electric pulses between a cathode and an anode. An average power of the electric pulses is at least 0.1 kW, and can be much greater. An operational parameter of the sputter deposition is controlled to promote sputter depositing of the insulation layer in a transition mode between a metallic mode and a reactive mode.