The invention is an apparatus and method for depositing a coating onto a substrate. The apparatus includes a vacuum chamber with an inlet for supplying a precursor gas to the chamber. The chamber includes a carrier for locating the substrate in the chamber, a first anode having an aperture in which plasma can be formed, and a magnetic field source. The substrate, when located in the carrier, constitutes a first cathode. When a substantially linear magnetic field between the anode and the cathode is formed, the direction of the magnetic field is substantially orthogonal to the surface to be coated and plasma production and deposition takes place substantially within the linear magnetic field.