Patent ID: 11940264
Assignee: ASML NETHERLANDS B.V.
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 18:
19. A method for measuring a position of an object using an interferometer system including a first interferometer and a second interferometer, the first interferometer being a multi-pass interferometer having a first optical system and a first mirror, wherein the first optical system is configured to direct a first measurement beam towards the first mirror such that the first measurement beam is incident to the first mirror at at least two distinct measurement locations, wherein the first mirror is arranged on the object and mainly extends in a Y-direction to allow the first interferometer to measure a position of the object in an X-direction perpendicular to the Y-direction, the second interferometer being a multi-pass interferometer having a second optical system and a second mirror, wherein the second optical system is configured to direct a second measurement beam towards the second mirror such that the second measurement beam is incident to the second mirror at at least two distinct measurement locations, wherein the second mirror is arranged on the object at a side opposite to the first mirror and mainly extends in the Y-direction to allow the second interferometer to measure a position of the object in the X-direction, wherein the method makes use of a mirror map including data representative for the shape of the first mirror in the Y-direction, and wherein the method comprises:
a. measuring a position of the object in the Y-direction using one or more sensors;
b. measuring a rotational position of the object about an axis extending parallel to a Z-direction using the one or more sensors, which Z-direction is perpendicular to both the X-direction and the Y-direction;
c. using the measured position in the Y-direction and the measured rotational position about the axis parallel to the Z-direction to determine the position of the at least two distinct measurement locations of the first measurement beam on the first mirror in the Y-direction;
d. measuring a position of the object in the X-direction using the interferometer system; and
e. using the mirror map and the determined positions of the at least two distinct measurement locations to adjust the measured position of the object in the X-direction for the shape of the first mirror.