Optical Metrology With Reduced Focus Error Sensitivity

摘要

Methods and systems for performing broadband spectroscopic metrology with reduced sensitivity to focus errors are presented herein. Significant reductions in sensitivity to focus position error are achieved by imaging the measurement spot onto the detector such that the direction aligned with the plane of incidence on the wafer surface is oriented perpendicular to the direction of wavelength dispersion on the detector surface. This reduction in focus error sensitivity enables reduced focus accuracy and repeatability requirements, faster focus times, and reduced sensitivity to wavelength errors without compromising measurement accuracy. In a further aspect, the dimension of illumination field projected on the wafer plane in the direction perpendicular to the plane of incidence is adjusted to optimize the resulting measurement accuracy and speed based on the nature of target under measurement.

主权项

1. A metrology system comprising:
an illumination source configured to generate an amount of illumination light; an illumination optics subsystem configured to direct the amount of illumination light from the illumination source to a measurement spot on a surface of a specimen under measurement at one or more angles of incidence within a plane of incidence; a detector having a planar, two-dimensional surface sensitive to incident light, wherein the detector is configured to generate a plurality of output signals indicative of a response of the specimen to the amount of illumination light; and a collection optics subsystem configured to collect an amount of collected light from the measurement spot on the surface of the specimen and direct the amount of collected light to the surface of the detector, wherein the collection optics subsystem images the measurement spot onto the surface of the detector such that a direction aligned with the plane of incidence on the wafer surface is oriented perpendicular to a direction of wavelength dispersion on the detector surface.