A chemical gas phase deposition process comprises steps of providing a high vacuum chamber, and inside the high vacuum chamber: positioning a substrate surface; positioning a mask parallel to the substrate surface, whereby the mask comprises one or more openings; adjusting a gap of determined dimension between the substrate surface and the mask; and orienting a plurality of chemical precursor beams of at least one precursor species towards the mask with line of sight propagation, each of the plurality of chemical precursor beams being emitted from an independent punctual source, and molecules of the chemical precursor pass through the one or more mask openings to impinge onto the substrate surface for deposition thereon. At least a part of the chemical precursor molecules decompose on the substrate surface at a decomposition temperature. The process further comprises adjusting a temperature of the substrate surface greater or equal to the chemical precursor molecule decomposition temperature, thereby remaining greater than a mask temperature, and maintaining the mask temperature below the decomposition temperature, thereby causing a decomposition of the chemical precursor and a growth of a film on the substrate surface, but not on the mask; and heating the substrate surface using a heating device.