Patent ID: 6982793
Filing Date: 2006-01-03
Classification: G03F,H01L

Abstract:
1. A method of determining the alignment 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 a first overlay pattern, a second overlay pattern, and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said first overlay pattern having a first designed in offset between the periodic pattern on said first and second elements, said first designed in offset having a first magnitude, said third overlay pattern having a third designed in offset between the periodic pattern of said first and second elements, said third designed in offset having a magnitude that is different than said first magnitude; illuminating said first overlay pattern, said second overlay pattern, and said third overlay pattern on said alignment target with incident radiation that reacts with said alignment target; detecting the radiation that is diffracted from said first overlay pattern, said second overlay pattern, and said third overlay pattern; and calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said second overlay pattern to produce a first measured difference; calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said third overlay pattern to produce a second measured difference, and determining the approximate alignment error based on said first measured difference and said second measured difference.