Efficient solution to selective wet etching of ultra-thick copper sacrificial layer with high selective etching ratio

In this paper, developed is an effective solution to selective etching of ultra-thick copper sacrificial layer for the realization of 3-D suspended metal microstructures, in which the thickness of sacrificial Cu laminations can reach more than 100 microns. The proposed effective etching solution is based on an additive complex in the ammonia liquor with the assistance of oxidant. The primary purposes of the additive complex catalyst account for strengthening the complexing capabilities of the etching liquor as well as increasing the selective etching ratio of Cu. The effects of process conditions on etching rate and surface morphology were investigated. Therefore, the complex-based etching solution to ultra-thick Cu SL possesses unique features in high selective etching ratio, low-cost, high efficiency, time-saving, and compatible with MEMS process. The novel etching solution has a potential application in fabricating the complicated 3-D MEMS devices with movable suspensions.