Handbook of Silicon Based MEMS Materials and Technologies

16.4.4. Contamination and Surface Quality

Automated Surface Inspection

Instead of being perfectly flat and clean, the wafer surface tends to contain imperfections consisting of roughness, defects, and contaminants. All of these may affect critical fabrication processes, for instance lithography, thin film deposition, etching, and—particularly in MEMS processing—wafer bonding. Surface roughness, as well as defects and particles on the wafer surface, are all detected and measured with optical methods. Large surface defects and particles can be detected with visual inspection and identified with microscopy. These labor-intensive techniques are of limited use in a production environment, however, and automated inspection has to be used. Scattering ...