The use of interferometry and image analysis techniques for metrology of MST devices

The manufacture and fabrication of MST/MEMS devices is now a hugely expanding technology with new applications being developed almost daily. The issue of geometrical metrology and surface metrology of such devices remains a major technological hurdle and could eventually hold back future developments. Both optical interferometric and scanning probe instruments have been employed to measure the surfaces with varying degrees of success. The difficulties of the metrology lies around the ability to separate and quantify zones of multiple features of differing planer geometry and then analyse the metrology of the zones individually as well as being able to successfully characterise the geometrical relationships between the device's structural elements. Complicated multi featured surfaces pose particular difficulties in terms of establishing measurement datums and levelling zones of important surface data. These problems are further accentuated by the limited size of the data sets available form the current metrology tools. The present paper deals with attempts to overcome some of the above difficulties by using areal pattern recognition where zones of differing planer height are separated efficiently and robustly.These techniques are then combined with digital image analysis to from a coherent analysis methodology The paper makes use of these combined analysis techniques to establish demonstrate device characterisation. The methods developed show promise towards improving the metrology and examples are given throughout the paper.