| 摘要 |
PURPOSE:To improve the foreign matter detection accuracy by providing a cylindrical lens on the light path of laser light. CONSTITUTION:A cylindrical lens 13 is provided on the light path of laser light 30 between a laser oscillator 20 and a foreign matter detecting points on a wafer 1. By this arrangement, when laser light 30 from the laser oscillator 20 is irradiated on the wafer 1, laser light can be throttled without varying its width, and the laser light irradiated surface 15 on the wafer 1 is extremely narrowed. Accordingly, even when an angle formed by the wafer 1 and laser light 30 is small, the quantity of light per unit area of the laser light irradiated surface 15, is increased, the detected quantity obtained by photoelectrically converting reflected light rays from the foreign matters and patterns is increased, thus enabling the use of a low-pass filter of a high cutoff frequency and achieving a desired object. |
