Measurement method and measurement apparatus

A measurement apparatus that illuminates a surface to be tested having an aspheric surface using light beams that form spherical waves to measure a figure of the surface to be tested, comprising:

• a detection unit configured to detect interference patterns between light beams from the surface to be tested and light beams from a reference surface, and
• a controller configured to control processing for obtaining a figure of the surface to be tested based on the interference patterns detected by the detection unit,
• wherein the controller executes:
• a first detection step of positioning the surface to be tested at multiple positions in order by driving the surface to be tested in a direction of an aspheric surface axis of the aspheric surface in a state in which a center of curvature of the spherical waves is on the aspheric surface axis, and detecting the interference patterns between light beams from the surface to be tested and light beams from the reference surface at each of the multiple positions,
• a second detection step of positioning the surface to be tested at multiple shift positions at which the surface to be tested has been shifted from the multiple positions respectively by a known amount in the direction of the aspheric surface axis, and detecting the interference patterns between light beams from the surface to be tested and light beams from the reference surface at each of the multiple shift positions,
• a first calculation step of calculating a length between a center of curvature of the spherical waves and positions on the surface to be tested at which the light beams are perpendicularly incident based on the interference patterns detected in the first detection step and the second detection step in regard to each of the multiple positions and each of the multiple shift positions,
• a second calculation step of calculating change in the length based on a calculation result calculated in the first calculation step in regard to when positioning of the surface to be tested was performed at the multiple positions and when the positioning was performed at the multiple shift positions, and
• a third calculation step of determining positions on the surface to be tested based on the change in the lengths calculated in the second calculation step, and of calculating figure error, which is a difference between a length obtained from a design value at that position of the surface to be tested and the length calculated in the first calculation step when positioning of the surface to be tested was performed at the multiple positions.

A measurement method of illuminating a surface to be tested having an aspheric surface using light beams that form spherical waves, and measuring a figure of the surface to be tested, comprising:

• a first detection step of positioning the surface to be tested at multiple positions in order by driving the surface to be tested in a direction of an aspheric surface axis of the aspheric surface in a state in which a center of curvature of the spherical waves is on the aspheric surface axis, and detecting interference patterns between light beams from the surface to be tested and light beams from a reference surface at each of the multiple positions,
• a second detection step of positioning the surface to be tested at multiple shift positions at which the surface to be tested has been shifted from the multiple positions respectively by a known amount in a direction perpendicular to the aspheric surface axis, and detecting interference patterns between light beams from the surface to be tested and light beams from the reference surface at each of the multiple shift positions,
• a first calculation step of calculating a length between a center of curvature of the spherical waves and positions on the surface to be tested at which the light beams are perpendicularly incident based on the interference patterns detected in the first detection step and the second detection step in regard to each of the multiple positions and each of the multiple shift positions,
• a second calculation step of calculating change in the length based on a calculation result calculated in the first calculation step in regard to when positioning of the surface to be tested was performed at the multiple positions and when the positioning was performed at the multiple shift positions, and
• a third calculation step of determining positions on the surface to be tested based on the change in the lengths calculated in the second calculation step, and of calculating figure error, which is a difference between a length obtained from a design value at that position of the surface to be tested and the length calculated in the first calculation step when positioning of the surface to be tested was performed at the multiple positions.

A measurement apparatus that illuminates a surface to be tested having an aspheric surface using light beams that form spherical waves to measure a figure of the surface to be tested, comprising:

• a detection unit configured to detect interference patterns between light beams from the surface to be tested and light beams from a reference surface, and
• a controller configured to control processing for obtaining a figure of the surface to be tested based on the interference patterns detected by the detection unit,
• wherein the controller executes:
• a first detection step of positioning the surface to be tested at multiple positions in order by driving the surface to be tested in a direction of an aspheric surface axis of the aspheric surface in a state in which a center of curvature of the spherical waves is on the aspheric surface axis, and detecting the interference patterns between light beams from the surface to be tested and light beams from the reference surface at each of the multiple positions,
• a second detection step of positioning the surface to be tested at multiple shift positions at which the surface to be tested has been shifted from the multiple positions respectively by a known amount in a direction perpendicular to the aspheric surface axis, and detecting the interference patterns between light beams from the surface to be tested and light beams from the reference surface at each of the multiple shift positions,
• a first calculation step of calculating a length between a center of curvature of the spherical waves and positions on the surface to be tested at which the light beams are perpendicularly incident based on the interference patterns detected in the first detection step and the second detection step in regard to each of the multiple positions and each of the multiple shift positions,
• a second calculation step of calculating change in the length based on a calculation result calculated in the first calculation step in regard to when positioning of the surface to be tested was performed at the multiple positions and when the positioning was performed at the multiple shift positions, and
• a third calculation step of determining positions on the surface to be tested based on the change in the lengths calculated in the second calculation step, and of calculating figure error, which is a difference between a length obtained from a design value at that position of the surface to be tested and the length calculated in the first calculation step when positioning of the surface to be tested was performed at the multiple positions.