A spin coating process produces a constant film thickness across a planar substrate by placing a frame around the substrate boundary to act as an auxiliary surface to allow a continuous film of the fluid to be spin coated. The auxiliary surface is elevated with respect to the plane of the substrate ...http://www.google.com.au/patents/US4068019?utm_source=gb-gplus-sharePatent US4068019 - Spin coating process for prevention of edge buildup
