Reflective waveplates for pupil polarization filtering
AssigneeKLA Corporation
InventorsChong Shen, Guoheng Zhao, Bret Whiteside
Life of this patent
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Abstract
An optical inspection system includes one or more gratings to convert the polarization of light scattered from a target from an elliptical polarization that varies spatially across a collection pupil to a linear polarization that is uniformly oriented across the collection pupil. The one or more gratings have phase retardation that varies spatially across the collection pupil in accordance with the elliptical polarization. The one or more gratings include at least one grating on a reflective substrate. The optical inspection system also includes a linear polarizer to filter out the linearly polarized light.
Claims21
An optical inspection system, comprising:
- one or more gratings to convert a polarization of light scattered from a target from an elliptical polarization that varies spatially across a collection pupil to a linear polarization that is uniformly oriented across the collection pupil, wherein:
- the one or more gratings have phase retardation that varies spatially across the collection pupil in accordance with the elliptical polarization, and
- the one or more gratings comprise at least one grating on a reflective substrate;
- and
- a linear polarizer to filter out the light having the linear polarization.
A method, comprising:
- illuminating a target;
- collecting light scattered from the illuminated target, wherein the collected light scattered from the illuminated target has an elliptical polarization that varies spatially across a collection pupil;
- using one or more gratings, converting the polarization of the collected light from the elliptical polarization that varies spatially across the collection pupil to a linear polarization that is uniformly oriented across the collection pupil, wherein:
- the one or more gratings have phase retardation that varies spatially across the collection pupil in accordance with the elliptical polarization, and
- the one or more gratings comprise at least one grating on a reflective substrate;
- and
- using a linear polarizer, filtering out the light having the linear polarization that is uniformly oriented across the collection pupil.
Dependencies are inferred from the claim text.