MEMS Wet-Etch Processes and Procedures

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Abstract

Wet chemical etching through openings in photoresist or hard masks underlies many process sequences for MEMS device fabrication. This chapter presents more than 800 wet-etch recipes for over 400 varieties and combinations of substrates and deposited thin films, with emphasis on processes that use laboratory chemicals often found in university and industrial cleanrooms. Over 600 citations serve as additional resources for selecting or developing etchants suitable for processing MEMS devices. Nearly 40 tables, organized internally by material then by etch components, allow quick location and comparisons among recipes. Abbreviations for target materials and etch components are standardized to aid in comparisons. Etch rates and etch selectivities over other materials are given where available. While emphasizing silicon and other popular materials in the MEMS field, III-V compounds and more exotic materials are also presented.

Topics addressed include wet-etch principles and procedures; process architectures that incorporate wet-etch sequences; evaluation and development of wet-etch procedures and equipment with emphasis on safety and an anticipation of foundry transfer; oxide, nitride, silicon, polysilicon, and germanium isotropic etching; standard metal etching; nonstandard dielectric, semiconductor and metal etching; photoresist removal and wafer cleaning sequences; silicide etching; plastic and polymer etching; anisotropic silicon etching; bulk silicon and silicon–germanium etch stops; electrochemical etching and etch stops; photoassisted etching and etch stops; thin-film etch stops; sacrificial layer removal; porous silicon formation; layer delineation for failure analysis; and defect determination. Practical examples offer some of the finer nuances in the processes and procedures related to wet chemical etching. This chapter provides a practical and valuable guide for device designers and process developers to select or develop an etch for many types of MEMS and integrated MEMS devices.