Wafer alignment using form birefringence of targets or product
An alignment method includes directing an illumination beam with a first polarization state to form a diffracted beam with a second polarization state from an alignment target, and passing the diffracted beam through a polarization analyzer. The alignment method further includes measuring a polarization state of the diffracted beam and determining a location of the alignment target from the measured polarization state relative to its initial polarization state. The alignment target includes a plurality of diffraction gratings with a single pitch and two or more duty cycles, wherein the pitch is smaller than a wavelength of the illumination beam, and the location of the alignment target corresponds to the duty cycle of the diffraction grating.
1. A method comprising:
directing an illumination beam with a first polarization state to form a zeroth order diffracted beam with a second polarization state from an alignment target;
splitting the diffracted beam into first and second polarization sub-beams in a non-interfering manner;
measuring a polarization state of the first and second polarization sub-beams; and
determining a location of the alignment target from the measured polarization state.
2. The method of claim 1 , wherein:
the alignment target comprises a plurality of diffraction grating periods with a single pitch and two or more duty cycles;
the pitch is smaller than a wavelength of the illumination beam; and
the location of the alignment target corresponds to a duty cycle of a diffraction grating of the plurality of diffraction gratings.
3. The method of claim 2 , wherein the diffraction gratings comprise a rectangular shape.
4. The method of claim 2 , wherein the diffraction gratings comprise asymmetric shapes with a top-tilt, a bottom tilt or a sidewall angle.
5. The method of claim 2 , wherein the diffraction gratings comprise a sinusoidal shape.
6. The method of claim 2 , wherein:
the illumination beam is linearly polarized; and
an electric field of the illumination beam forms an angle between 0 degrees and 90 degrees with respect to grating lines.
7. The method of claim 1 , wherein the illumination beam is circularly or elliptically polarized.
8. A system, comprising:
first and second optical systems, wherein:
the first optical system is non-interfering and configured to direct an illumination beam with a first polarization state towards an alignment target and direct a diffracted beam including a zeroth order with a second polarization state from the alignment target to the second optical system; and
the second optical system is configured to split the diffracted beam into first and second polarization sub-beams;
first and second detectors configured to measure a polarization state from the first and second polarization sub-beams; and
a processor configured to determine a location of the alignment target from the measured polarization state.
9. The system of claim 8 , wherein the first and second optical systems are monolithically integrated together on a photonics circuit and coupled to the alignment target on a substrate.
10. The system of claim 9 , wherein:
the substrate comprises silicon; and
the first and second optical systems comprise silicon photonics.
11. The system of claim 8 , wherein the first and second detectors are monolithically integrated to filters and beam shaping optics in an integrated photonics package.
12. The system of claim 8 , further comprising optical links using fiber optics for the first and second optical systems.
13. The system of claim 8 , wherein the alignment target comprises a plurality of diffraction gratings with a single pitch and two or more duty cycles, the pitch being smaller than a wavelength of the illumination beam.
14. The system of claim 13 , wherein the diffraction grating comprise a rectangular shape.
15. The alignment system of claim 13 , wherein the diffraction gratings comprise asymmetric shapes with a top tilt, a bottom tilt or a sidewall angle.
16. The alignment system of claim 13 , wherein the diffraction gratings comprise a sinusoidal shape.