Measurement of Sub-Surface Microstructures Based on a Developed Ultrasonic Atomic Force Microscopy

Abstract

Accurate and non-destructive technology for detection of subsurface defect has become a key requirement with the emergence of various ultra-precision machining technologies and the application of ultra-precision components. The combination of acoustic technique for sub-surface detection and atomic force microscopy (AFM) for measurement with high resolution is a potential method for studying the subsurface structure of workpiece. For this purpose, contact-resonance AFM (CR-AFM) is a typical technique. In this paper, a CR-AFM system with a different principle from commercially available instruments is set up and used for the detection of sub-surface Si sam-ples with grating structures and covered by different thickness of highly oriented pyrolytic graphite (HOPG). The influence of subsurface burial depth on the detection capability is studied by simula-tions and experiments. The thickest HOPG film allowing for sub-surface measurement by the proposed method is verified to be about 30 μm, which is much larger than the feature size of the sub-surface microstructure. The manuscript introduces the difference between this subsurface topogra-phy measurement principle and the commercially available AFM measurement principle, and ana-lyzes its advantages and disadvantages. The experimental results demonstrates that the technique has the capability to reveal sub-surface microstructures with relatively large buried depth and is potential for engineering application in ultra-precision technologies.