| 摘要 |
PURPOSE:To obtain the optimum contrast and S/N ratio by adjusting a light screening range by a light screening member by corresponding a signal level of detection pattern to a signal level by roughness of a substance surface in a photoelectric detector used for relative alignment and etc. CONSTITUTION:A laser light from a laser light source 1 enters in a rotating polyhedral mirror 3 through a condenser 1 lens 2 and the reflected light from the mirror 3 is projected on a mask present on a wafer 13 through an objective 11 comprising a relay lens 4, a beam splitter 5, a field lens 6, a beam splitter 7, a relay lens 8, a beam splitter 9 and an incident aperture 10 thereby performing alignment of the wafer 13 and the mask 12. In this constitution, the reflected light from the splitter 5 enters in a photoditector 18 through an image forming lens 14 and a filter 15 and a light screening range of the system is adjusted there. Consequently, the light accepting plane of detector 18 is divided into concentric light accepting planes 18a-18d so as to synthesize there planes according to expansion of the scattered light from the surface of detected substance. |
