Manufacture of aluminium micromirror arrays using a dual damascene process

Liquid crystal over silicon (LCoS) is an established technology for reflective spatial light modulators (SLM's) and microdisplays. While most of the manufacturing methods used are mature, there exist a number of unresolved issues associated with the mass production of high quality devices. Existing manufacturing technology leaves the final mirror elements raised from the surface of the surrounding dielectric causing problems with the filling of the liquid crystal (LC). The flow front during filling is influential on the final alignment qualities, so it is essential that this flow front follows the ideal linear shape. We report on a method to remove this mirror step height by the use of an aluminum dual damascene technique. This process produces mirrors which are embedded within the dielectric insulating layer thereby removing most of the LC flow front aberrations, caused by the surface topography, during LC filling. We discuss the novel methods developed to overcome the damascene induced problems of dishing and erosion. The results will be discussed with particular bias towards their use in the manufacture of reflective micro-displays.