| 摘要 |
<p>PURPOSE:To eliminate the need for an optical system, and to simplify a device and reduce cost thereof by applying laser beams from the two directions in place of the scanning of laser beams by using two lenses and a vibrating mirror and the acquisition of a positional displacement signal, obtaining the difference of the intensity of each reflected diffracted light and acquiring the positional displacement signal. CONSTITUTION:Laser beams 7 applied to an LFZP 3 on a mask 1 at an incident angle theta are condensed onto a wafer 2 positioned where separate only by a gap (s) from the mask 1, and a spot is formed. Likewise, laser beams 8 applied to the LFZP 3 at an incident angle conjugate with laser beams 7 shape an imaging spot on the wafer 2. A distance between both imaging spots is represented by 2Ssintheta. An output from a detector 9 and an output from a detector 10 are amplified up to signal strength required by an amplifier. Accordingly, a servo system is constituted by using a normalized positional displacement signal acquired, thus preventing the change of servo gains due to the fluctuation of signal strength, then forming a stable servo system.</p> |
