Patent ID: 6958819
Filing Date: 2005-10-25
Classification: G01D

Abstract:
1. A method of determining the position of a first element with respect to a second element, said method comprising: providing an alignment target on said first element and said second element, the alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, the at least one periodic pattern on said first element overlying the at least one periodic pattern on the second element, the at least one periodic pattern on said first element and the at least one periodic pattern on said second element having the same pitch, said alignment target, when aligned, has a first location with the periodic pattern on the first element offset from the periodic pattern on the second element by a first amount and having a second location with the periodic pattern on the first element offset from the periodic pattern on the second element by a second amount; moving at least one of said first element and said second element with respect to the other; illuminating said first and second locations on said alignment target with incident radiation; detecting the radiation from said first and second locations of said alignment target after interacting with said periodic pattern on said first element and said periodic pattern on said second element; and using said detected radiation to determine the position of said first element with respect to said second element by comparing the detected radiation from said first and second locations to determine when the alignment target is aligned.