Error reducing method in heterodyne interferometry

摘要

A shape of a surface (111a) is measured using a measurement signal (Isig(x, y, t)) based on an interfering light of reference light of first light reflected by a reference surface (108a) and test light of second light reflected by the surface to be measured. The method includes detecting the measurement signal and a reference signal (Iref(t)) based on interfering light of the first light not incident on the reference surface and the second light not incident on the surface to be measured, obtaining a sine multiplied signal and a cosine multiplied signal of the measurement signal, correcting the sine multiplied signal and the cosine multiplied signal by a sine signal and a cosine signal of the error component; obtaining a phase by calculating an arctangent of the corrected sine multiplied signal and the corrected cosine multiplied signal and obtaining the shape based on the phase.