| 摘要 |
PURPOSE:To enhance the relative aligning accuracy and efficiency of a mask and a wafer by always superposing two diffracted beams at a predetermined position by correcting the light path lengths of diffracted beams between a guide means and a beam mixing means. CONSTITUTION:Laser beams having frequencies f1, f2 are respectively diffracted by mask aligning marks 4, 5 and condensed to a wafer aligning mark 6 through a projection lens 3. The heterodyne signal obtained from the diffracted beam having the position data of a wafer 1 and a mask 2 among reflected diffracted beams is sent to a phase detector. At the same time, the diffracted beams L1, L2 are guided to the beam synthesizing point on a half mirror 10 to be superposed one upon another and the obtained beat signal component is detected by a reference signal detector 13 to be sent to a phase detector as a beam heterodyne reference signal and the alignment of both of them is performed on the basis of phase difference. At this time, the shift of the light path length of L1 is corrected through a prism 14 and the light path length difference l' of L1, L2 can be held to a predetermined value. |
