HETERODYNING OPTICAL PHASE MEASURING DEVICE FOR DIFFRACTION BASED OVERLAY

Abstract

Methods and systems are provided for diffraction-based overlay (DBO) metrology of a multilayered sample. In one example, a method may include generating spatially structured light via a light source and an optical modulator, transmitting the spatially structured light onto the multilayered sample, detecting diffracted spatially structured light at one or more of a plurality of sensors, and estimating an overlay error of the multilayered sample based on the diffracted spatially structured light detected at the one or more of the plurality of sensors.

Description

Claims

1. A method, comprising: generating spatially structured light from a light source by projecting light emitted from the light source through an optical modulator;transmitting the spatially structured light from the optical modulator onto a multilayered periodic sample;detecting diffracted spatially structured light from the multilayered periodic sample at one or more of a plurality of sensors, the plurality of sensors communicatively coupled to a computing system; andestimating an overlay error of the multilayered periodic sample based on signals received at the computing system of the diffracted spatially structured light detected at the one or more of the plurality of sensors.

2. The method of claim 1, wherein the one or more of the plurality of sensors is selected from a group including: a CMOS sensor, a photodetector, a photomultiplier tube (PMT), and a charged coupled device (CCD).

3. The method of claim 2, wherein the light source includes at least one selected from a group including: a light emitting diode (LED), a laser, a plasma source, and a filament source.

4. The method of claim 3, wherein the optical modulator generates spatially structured light with a given spatial period.

5. The method of claim 4, wherein the spatial period of the spatially structured light can be modulated through amplitude modulation, frequency modulation, or a combination of both.

6. The method of claim 5, wherein estimating the overlay error includes regressing over at least one of the spatial period of the spatially structured light or a wavelength of the light source.

7. The method of claim 6, further comprising a plurality of lens elements, with a first lens element of the plurality of lens elements placed in between the optical modulator and the multilayered periodic sample, and each lens element of a remainder of the plurality of lens elements placed in between the multilayered periodic sample and the one or more of the plurality of sensors, and wherein the diffracted spatially structured light detected at the one or more of the plurality of sensors is compared to a reference signal.

8. The method of claim 7, wherein estimating the overlay error is based on estimating an asymmetry in an electric field of the diffracted spatially structured light as a function of time.

9. The method of claim 7, wherein each of the one or more of the plurality of sensors are CCDs, and wherein a phase difference between the diffracted spatially structured light and the reference signal is estimated by comparing the diffracted spatially structured light and the reference signal as a function of time and as a function of pixel positions on each of the CCDs.

10. The method of claim 7, wherein estimating the overlay error includes estimating a phase difference between the diffracted spatially structured light and the reference signal via lock-in amplification of the diffracted spatially structured light with respect to the reference signal.

11. The method of claim 6, further comprising an objective lens placed between the multilayered periodic sample and the one or more of the plurality of sensors, the objective lens projecting a spatial Fourier-transform of the diffracted spatially structured light into a pupil plane of the objective lens to be detected at the one or more of the plurality of sensors, and wherein estimating the overlay error includes applying an inverse Fourier transform to the spatial Fourier-transform of the diffracted spatially structured light detected at the one or more of the plurality of sensors.

12. The method of claim 6, wherein the spatially structured light transmitted from the optical modulator includes a two-dimensional (2D) spatial variation projected onto a plane of the multilayered periodic sample, and wherein estimating the overlay error includes estimating a vector displacement of the overlay error based on the 2D spatial variation of the diffracted spatially structured light detected at the one or more of the plurality of sensors.

13. The method of claim 7, wherein estimating the overlay error includes estimating a phase difference of the diffracted spatially structured light with respect to the reference signal, the reference signal generated by the computing system.

14. A system for estimating overlay errors in a multilayered periodic sample, the system comprising: an axis;an optical modulator coupled with the axis;a lens element;a light source configured to shine light through the optical modulator to project spatially structured light along the axis onto the multilayered periodic sample through the lens element;a plurality of sensors configured to detect diffracted spatially structured light from the multilayered periodic sample; anda computing system including: a synchronization module configured to apply lock-in amplification of light detected at one or more of the plurality of sensors with respect to a reference signal; andan analysis module configured to compute a phase difference between the reference signal and the diffracted spatially structured light detected at the one or more of the plurality of sensors, the phase difference being a function of one or more of: a wavelength of the light source, and a spatial period of the spatially structured light.

15. The system of claim 14, wherein the one or more of the plurality of sensors is selected from a group including: a CMOS sensor, a photodetector, a photomultiplier tube (PMT), and a charged coupled device (CCD).

16. The system of claim 15, wherein the light source includes at least one selected from a group including: a light emitting diode (LED), a laser, a plasma source, and a filament source.

17. The system of claim 16, wherein the plurality of sensors includes a first sensor configured to detect diffracted spatially structured light from the multilayered periodic sample, and a second sensor configured to detect the reference signal of the spatially structured light from the optical modulator.

18. The system of claim 16, wherein the reference signal is generated by the computing system.

19. The system of claim 17, wherein the diffracted spatially structured light detected at the first sensor is a first order diffraction signal.

20. An optical system for diffraction based overlay (DBO) metrology of a multilayered periodic sample, the optical system comprising: an axis;an optical modulator coupled to the axis;a lens element;a light source configured to shine light through the optical modulator to project spatially structured light along the axis;a beam splitter positioned between the optical modulator and the multilayered periodic sample, the beam splitter configured to reflect a first portion of the spatially structured light in a direction perpendicular to the axis, and transmit a second portion of the spatially structured light along the axis and onto the multilayered periodic sample;a reference surface configured to receive the first portion of light, and reflect the first portion of light as a reference signal to be detected at a first sensor;a second sensor configured to detect diffracted spatially structured light from the multilayered periodic sample; anda computing system including: a synchronization module configured to apply lock-in amplification of the diffracted spatially structured light at the second sensor with respect to the reference signal detected at the first sensor; andan analysis module configured to compute a phase difference between the diffracted spatially structured light detected at the second sensor with respect to the reference signal detected at the first sensor, the phase difference being a function of one or more of: a wavelength of the light source, and a spatial period of the spatially structured light.