Non-destructive Observations of Internal Microstructures of Materials by Scanning Electron-induced Acoustic Microscopy
Yoji SHIBUTANI, Atsuhiro KOYAMA and Takeshi SHIOTA
Abstract:The scanning electron-induced acoustic microscopy (SEAM) has been developed as a new tool for non-destructive observations of the internal microstructures of materials. It consists of the electric chopper to pulse the high current electron beam and the detector of the longitudinal acoustic waves, being attached to the commercial scanning electron microscopy (SEM). The SEAM gives the best performance for observing the internal defects like the local delamination of the interface in the sub-surface of the semiconductor, because it senses the local difference of thermal properties in the sample. The acoustic waves transmitted from the thermal waves generated near to the surface, in principle, carry the information on such internal defects. In the present paper, the outline of our improvements to the system for getting higher resolution is first stated with emphasis on electric chopper way, sample holder design and image data processing method. Some typical samples of a soldered copper piece, Fe-3%Si and TRIP steels are supplied to ascertain the detectability of the internal microstructures. And then, the effects of the pulsing frequency of the electron beam and the accelerating voltage to the resolution of the electron acoustic images are investigated. The higher resolution can be achieved as the higher pulsing frequency, as suggested by the phenomenological considerations. Key Words:Scanning electron-induced acoustic microscopy (SEAM), Non-destructive observation, Thermal wave, SEM, Internal microstructure