Patent ID: 7724375
Filing Date: 2010-05-25
Classification: G01B

Abstract:
1. A method for performing measurements on a test sample with a metrology or inspection tool, comprising: moving at least one of the test sample and the tool with respect to one another from a first position to a second position, wherein, at the second position, the tool is aligned for measurement of a measurement target on the sample; and while moving from the first position to the second position, adjusting a focus of the tool on the test sample; wherein adjusting the focus of the tool includes adjusting the focus based on a signal from a scanning interferometer located proximate the tool; wherein adjusting the focus based on a signal from a scanning interferometer includes splitting collimated light into a test beam and a reference beam; transmitting three or more different portions of the reference beam through three or more corresponding optical path delays; reflecting the test beam from the test sample; and combining each of the three or more different portions with the test beam at three or more corresponding sensors.