Measurement method and measurement apparatus

A measurement apparatus of measuring a shape or a position of a surface to be measured using a measurement signal based on an interfering light of reference light of first light reflected by a reference surface and test light of second light reflected by the surface to be measured by emitting the first light and the second light having different frequencies from a light source,

• the measurement signal including an error component which does not depend on an optical path length difference between the test light and the reference light,
• said measurement apparatus comprising:
• a first detector configured to detect a reference signal based on interfering light of the first light which is not incident on the reference surface and the second light which is not incident on the surface to be measured, and the measurement signal;
• a second detector configured to detect the measurement signal;
• and
• a processing unit configured to obtain the shape or the position of the surface to be measured based on the reference signal and the measurement signal,
• wherein said processing unit generates a sine signal and a cosine signal, which are in synchronization with the reference signal, and obtains a sine multiplied signal and a cosine multiplied signal of the measurement signal by multiplying the measurement signal by the generated sine signal and the generated cosine signal,
• said processing unit corrects the sine multiplied signal and the cosine multiplied signal by a sine signal and a cosine signal of the error component,
• said processing unit obtains a phase corresponding to the optical path length difference by calculating an arctangent of the corrected sine multiplied signal and the corrected cosine multiplied signal, and
• said processing unit obtains the shape or the position of the surface to be measured based on the phase.