Cylindrical Magnetron Sputtering of Antireflection Coatings on Three Dimensional Substrates

Precision optical coatings having excellent thickness uniformity are needed on substrates with a variety of shapes. That typically requires a combination of complex motion and shadow masks. Unbalanced cylindrical magnetron sputtering, in which the source of sputtered material is the inside surface of a cylinder, is able to produce coatings with excellent uniformity on both planar and non-planar substrates without masks. This is achieved using simple two axis planetary motion and proper positioning of the substrates along the cathode axis. Single layer and multi-layer coatings have been deposited onto both flat and curved surfaces in a production scale system incorporating two 400 mm diameter magnetrons. In one case, individual layers deposited onto convex lenses with a diameter of 50.8 mm and radius of curvature of 50 mm have a coating thickness uniformity of ±0.3% from center to edge. Normal incidence reflectance measurements made at several points from the center to the edge of an identical lens having a narrow band AR coating resulted in a minimum in the reflectance at a wavelength of 555 ±2.3 nm. This is in good agreement with the uniformity seen for individual layers.