An automated image-shearing microscope for measuring the lengths of the gaps in magnetic recording heads is discussed. A model, developed for a manual measurement system, is used to identify sources of measurement error. The architecture of an automated measurement system is described in detail. Algorithms for automating the measurement process are presented, and the model is extended to analyze their performance. These algorithms include a method of finding a clean site, of automatic focusing, and of automatic measurement based on image shearing. The effects of system parameters such as illumination bandwidth, focus error, and transducer resolution are investigated, and it is shown that gap lengths as narrow as 0.5 µm may be measured reliably. Performance tests show that the system can measure gap lengths to better than 0.01 µm (lo) reproducibility in less than 4 s.
Chris P. Kirk, Chris P. Kirk,
"Design Of An Automated Optical Microscope For Measuring The Critical Dimensions Of Magnetic Recording Heads," Optical Engineering 26(6), 266507 (1 June 1987). https://doi.org/10.1117/12.7974106