US 7,321,432 B2
Measurement and compensation of errors in interferometers
Henry A. Hill, Tucson, Ariz. (US)
Assigned to Zygo Corporation, Middlefield, Conn. (US)
Filed on Sep. 09, 2003, as Appl. No. 10/659,103.
Claims priority of provisional application 60/409285, filed on Sep. 09, 2002.
Prior Publication US 2004/0085546 A1, May 06, 2004
Int. Cl. G01B 11/14 (2006.01)
U.S. Cl. 356—500 59 Claims
OG exemplary drawing
 
1. A method for determining the location of an alignment mark on a stage, the method comprising:
measuring a location, x1, of a stage along a first measurement axis using an interferometer;
measuring a location, x2, of the stage along a second measurement axis substantially parallel to the first measurement axis; and
determining a location of the alignment mark along a third axis substantially parallel to the first measurement axis based on x1, x2, and a correction term, ψ3,
wherein the interferometer comprises interferometer optics configured to direct a measurement beam to reflect from a mirror where the interferometer optics or the mirror are attached to the stage, and ψ3 is calculated from predetermined information comprising information characterizing imperfections in the interferometer optics.