16. Contact-Type Micro Thermal Sensor for Surface Defect Detection

Surface defect detection, which is carried out in advance of defect review process during surface defect inspection of products having smoothly finished surfaces such as bare semiconductor wafers, magnetic disks, and optical components, is important process to assure the quality of products. In this chapter, a surface defect detection method, in which defect detection is carried out in such a way that the existence of a surface defect on a target of interest is verified by detecting frictional heat induced by a collision between a micro thermal sensor and a surface defect, is described. Although the frictional heat to be generated by a collision between the micro thermal sensor and a surface defect is expected to be small since surface defects required to be verified during the inspection are quite small, the micro thermal sensor designed to have a micrometric sensor element is expected to carry out highly sensitive detection of the frictional heat and thus realize high-resolution surface defect detection. A principle of the surface defect detection method based on the micro thermal sensor is at first described. After that, design and fabrication of the micro thermal sensor based on photolithography process are presented. In addition, by using the developed micro thermal sensor, some experiments have been carried out to demonstrate the feasibility of the defect detection method. An example of the application of micro thermal sensor for surface defect detection in the hard disk drive industry is also introduced.