Improved optical performance of silicon backplane spatial light modulators using chemical-mechanical polishing

The optical performance of current electrically addressed spatial light modulators is impaired because of the low optical quality of the metal mirrors. The distortion in the metal film is accounted for by hillock formation during the sintering phase of the metallization stage [1]. There have been several techniques developed to reduce or eliminate hillock formation [2,3,4] all of which increase the complexity of the processing sequence. From an electrical point of view the hillocks are only problematic in multi-level metallization schemes where they can cause shorts between levels, therefore, the added work to eliminate hillock formation is only applied to lower level metal. The top level metal which is always used to provide the mirrors has no hillock reduction applied since electrically this is not necessary which results in low quality mirrors. Silicon fabrication foundries will not alter the fabrication sequence to suit one application which leaves only one way to improve the mirrors and that is by post-processing completed wafers and adding another level of metal.