摘要
Photoacoustic imaging of subsurface microcracks in silicon wafers and modulation frequency response of photoacoustic signals detected at the cracks are described. 30 nm wide cracks 12 μΐη below the surface of a wafer have been successfully detected. The results indicate that amplitude images obtained from different frequencies represent the distribution of the thermal impedance which is increased by cracks at a depth corresponding to the thermal diffusion length. Cracks can be clearly detected by a phase image which represents the distribution of the phase delay sensitive to the thermal discontinuity at the cracks. © 1992 The Japan Society of Applied Physics.