| 摘要 |
PURPOSE:To perform high-precision positioning in atmosphere by arranging a diffraction grating on a sample nearly in parallel to interference fringes obtained by the interference between two pieces of luminous flux, and photodetecting plural diffracted light beams as return light by a photodetecting element. CONSTITUTION:Coherent light R from a laser generator 10 is guided to a pinhole 14 arranged near the focus position of a diffusion optical system 13, and the light passed through the pinhole 14 is passed through the hole (e) of the photodetecting element 18 and then split by amplitude through a two-luminous-flux splitting optical system 17 into reflected light beams R1 and R2, which are allowed to interfere with each other on the sample W such as a semiconductor wafer through reflecting mirrors M1 and M2, forming interference fringes. The diffraction grating G is arranged on the surface of the sample W nearly in parallel to the interference fringes, and plural diffracted light beams from the diffraction grating G are returned through said optical system and detected as return light by a photodetection part provided at the circumference of the hole (e) of the photodetection element 18 to generate an electric signal, thereby making an adjustment so that the pitch of the diffraction grating G on the sample W is nearly equal to the pitch of the interference fringes. |
