1982 Volume 48 Issue 12 Pages 1573-1577
In this paper a differential laser interferometer is described which has been developed for the purpose of measuring the pitch and width of a micropattern like LSI. In order to make sensitivity optically high, the interferometer has two pairs of prism devices to extend optical path difference five times by each device. The method extending optical path difference is to arrange multipass beam with two rows at the limited incident area of each prism device. As the result it is possible to make the prism device small until 1/2.5 in the ratio of prism diameter compared with the usual arrangement of a row multipass beam. The interferometer, moreover, can detect differentially double the small displacement of a micro positioning table. As the result the interferometer optically increases 10 times in sensitivity and has the measurement unit of λ/40 together with the signal procedure of a photodetector. The stability of all the interferometer to be assembled is 0.02 μm in fluctuation over half an hour.
