Control of Corrosion on Aluminum MEMS Structures after Post Etch Clean

During the fabrication of aluminum MEMS (Microelectromechanical Systems) structures for display applications, surface corrosion or pitting appeared intermittently on the aluminum structures after aluminum (Al) plasma etch and post etch cleaning. Such surface corrosion severely limited the light reflecting capabilities of the planar aluminum micromirrors. The formulated organic solvent cleaners or post etch residue removers used after aluminum plasma etch such as NE14 from Air Products (AP) and ST250 from Advanced Technologies and Materials Incorporated (ATMI) were suspected to be the main culprits of the Al corrosion but without conclusive evidences. In order to better understand the causes of the post etch aluminum corrosion, extensive work has been carried out to look at the factors that may lead to Al corrosion after plasma etch and post etch clean. In particular, we have evaluated the surfaces of Al structures after NE14 and ST250 post etch cleaning using tools such as SEM and AFM. We focused on the three main aspects that may affect the Al corrosion: The Al plasma etch process, the extended cleaning in the organic solvent chemistries, and the Al corrosion as a result of water dilution in the organic solvent cleaners.