| 摘要 |
PURPOSE:To accurately measure the surface and internal information of a sample by constituting a condensing means and optical interference detection means as a confocal optical system. CONSTITUTION:A modulated laser radiation optical system 300 and a Michelson interferometer 310 are constituted as the confocal optical system. Namely, a beam from a laser 31 reflected on a sample 170 is splitted by beam splitters 56 and 42 and the splitted beams are condensed by lenses 43 and 46. Photoelectric conversion elements 45 and 48 and pinholes 44 and 47 are provided in and just before respective optical paths respectively. The element 45 is arranged behind the rear focusing position of the lens 43 and the element 48 is arranged ahead of the rear focusing position of the lens 46. Output currents from the elements 45 and 48 are compared in a comparison circuit 54 and a Z stage 30 is controlled to perform feedback so that the front focusing position 131 of an objective lens 28 always coincides with the surface of the sample 170. Thus, the laser beam can be always stably condensed on the surface of the sample even if there is unevenness on the surface of the sample like a semiconductor wafer where a circuit pattern is formed. |
