Spray coating - a solution for resist film deposition across severe topography

There are situations when it is beneficial to generate lithographic patterns in, on, over or near sever topographical features >10 microns and often up to 300 microns in vertical height or depth from the wafer surface. Current spin coating approaches create unusable films with striations, streaks, pinholes and other anomalies. Dry laminated films have been used but are limited in the achievable resolution to the range of their thickness. Electroplated resists have also been considered, but are costly to deposit and limited to conductive surfaces. Finally, ordinary spray coating approaches have been attempted but seem to lack a suitable process window for production use. This paper explores a novel spray coating technology and its capability to deposit high resolution resist films on different 3D microstructures. The 3D microstructures represent the type commonly found in the field of microelectromechanical systems (MEMS), optical microelectromechanical systems (MOEMS) and backend processes (advanced packaging). In this paper the edge coverage on various structures and materials will be shown as well as the achievable uniformity on plane wafer with spray coating.