| 摘要 |
PROBLEM TO BE SOLVED: To prevent noise from being transmitted to a photo-diode and improve measuring accuracy by holding the photo-diode from a body frame side through an insulating body. SOLUTION: A PD(photo-diode) fitting part 47 is provided with a PD stage fitting plate 52 fitted to a X-axis stage 45, a lens 53 fitted to the PD stage fitting plate 52, and a PD holder 54 for fitting a photo-diode 48 to the position corresponding to the lens 53. The PD stage fitting plate 52 is a member of U-shaped section, and it is formed so as to be fitted with the lens 53. The PD stage fitting plate 52 and the PD holder 54 are formed out of ceramics as an insulating body. Hereby, it is prevented the change of the electromagnetic field in an IC wafer, or the change of the electromagnetic field around an elecro- optical sampling probe is transmitted to the photo-diode 48 to be detected as noise.
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