REMAINING DAMAGE MEASURING METHOD OF WAFER EDGE PART AND ITS APPARATUS

PROBLEM TO BE SOLVED: To effectively use a non-contact and non-destructive optoacoustic measuring method of high accuracy, and measure remaining damages on a wafer edge part with high efficiency, by irradiating a laser beam pumping part with probe light for measurement, and measuring thermal response due to pumping light, by a laser interference method. SOLUTION: An edge part 31 of a semiconductor wafer is divided into 3 part positions, i.e., an upper slant surface, a lower slant surface and a circular arc end portion. To the respective surfaces, a laser beam pumping part 13 is irradiated with probe light 10 for measurement. Thermal response to an exciting light 22 is measured by a laser interference method. Crystal damages are estimated by the above optoacuostic measuring method. For example, an He-Ne laser light is used as the probe light, and divided into 2 frequency lights different in frequency by an acoustooptic modulator 11. With one of the lights, the laser light pumping part 13 is irradiated by a semitransparent mirror 12, and a reflected light beam 20 is obtained. A reference mirror 14 is irradiated with the other light, and a reflected light beam 21 is obtained. From the reflected beam lights 20 and 21, an interference signal 23 is obtained by a photoelectric transducer 15.