| 摘要 |
<p>PURPOSE:To measure the film thickness of phase shifter in a phase shift mask highly accurately. CONSTITUTION:Two light beams having slightly different frequencies are split by a beam splitter 15. One beam is received, as a reference beam, by a first light receiver 17 to produce a first electric signal representative of a beat line whereas the other beam is projected to a phase shift mask 20 and the transmitted beam is received by a second light receiver 22 to produce a second electric signal representative of beat component. A phase comparator 24 detects the phase difference between the first and second electric signals thus measuring the amount of phase shift of phase shifter.</p> |
