Patent ID: 7573580
Filing Date: 2009-08-11
Classification: G01B

Abstract:
1. A position determining system that measures a position of an alignment mark on a substrate, comprising: a superluminescent device (SLD) that transmits a light beam having a longitudinal coherence length based on at least one optical parameter associated with one or more optical elements of the position determining system, wherein the longitudinal coherence length substantially eliminates ghost or spurious reflections from the one or more optical elements present during exposure of a pattern in a lithography tool; a lens system that directs the light beam to be diffracted from the alignment mark on a wafer, the diffracted light causing the ghost or spurious reflections through its interaction with the lens system, an interferometer configured to use the diffracted light to determine a position of the alignment mark to produce a control signal related to the determined position, wherein the interferometer is configured to determine the position of the alignment mark using an interference pattern; and a positioning system configured to align the substrate to receive the subsequent pattern based on the control signal, wherein the positioning system is configured to use the control signal to substantially reduce the ghost or spurious reflections during receipt of the subsequent pattern by the substrate.