An alternative polymeric protection mask for bulk KOH etching of silicon

The utilization of a newly developed photosensitive polymeric coating, ProTEK PSB plays a significant role in realizing simple process steps in the fabrication of MEMS devices using bulk micromachining technology. The photosensitive coating serves as an alternative to the conventional silicon nitride mask of bulk KOH etching in devising MEMS devices, particularly suspended microcantilever structure. Although the coating is an excellent outer protective layer from any pinhole issues, the lateral etching in KOH solution is prominent, which results in an undercut issue. Therefore, the combination of ProTEK PSB and thermal oxide layer was studied for its possibility in obtaining minimum undercut-etch depth ratio of the polymeric coating in KOH (45%wt, 80°C). The combination of ProTEK PSB patterned on thermal oxide results in an effective etching condition attributed by minimum undercut ratio with respect to the etch depth.