| 摘要 |
PURPOSE:To reduce detecting errors in the number and particle size of foreign matters adhered to the surface of a wafer by measuring the thickness and refractive index of said wafer before checking foreign matters, and on the basis of the result of said measurement, measuring the sensitivity and threshold value of a photoelectric converter most suitable for the checking. CONSTITUTION:An optical system which emits laser beams 10 is a first optical system. A second optical system is comprised of a laser source 1, a shutter 3 for shutting laser beams from the light source 1 and a photoelectric converter 5 which receives a reflecting light of the laser beams from a wafer 16. An electric signal from the photoelectric converter 5 of the second optical system is fed to a processing circuit 7, where a control value to set the sensitivity and threshold value of a photoelectric converter 20 of the first optical system 1 is calculated. The control value is sent to the photoelectric converter 20. In other words, the film thickness and refractive index of the wafer 16 are measured prior to checking of foreign matters. Accordingly, the detecting errors in the number and particle size of the foreign matter can be remarkably reduced. |
