Inspection apparatus for lithography

• US 8,792,096 B2
• Filed: 03/24/2009
• Issued: 07/29/2014
• Est. Priority Date: 03/24/2008
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Straaijer, Alexander
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): AKANBI, ISIAKA O
• Application Number:
  US12/922,587
• Publication Number:
  US 20110102793A1
• Time in Patent Office: 1,953 Days
• Field of Search: 356/369, 356/492, 356/496
• US Class Current: 356/369
• CPC Class Codes: G01B 11/0641 with measurement of polarization
• CPC Class Codes: G01J 4/04 Polarimeters using electric detection means G01J4/02 takes precedence
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G03F 7/70608 Monitoring the unpatterned workpiece, e.g. measuring thickness, reflectivity or effects of immersion liquid on resist

Abstract

Four separately polarized beams are simultaneously measured upon diffraction from a substrate (W) to determine properties of the substrate. Linearly, circularly or elliptically polarized radiation is transmitted through a first beam splitter (N-PBS) and split into two polarized beams. These two beams are further split into two further beams using two further beam splitters, the further beam splitters (32,34) being rotated by 45° with respect to each other. The plurality of polarizing beam splitters enables the measurement of the intensity of all four beams and thus the measurement of the phase modulation and amplitude of the combined beams to give the features of the substrate. Algorithms are used to compare the four intensities of each of the polarized angles to give rise to the phase difference between the polarization directions and the ratio between the two main polarization direction amplitudes of the original polarized beam.

Claims

1. An inspection apparatus comprising:

a radiation source configured to supply a radiation beam;

an optical element configured to focus the radiation beam onto a substrate;

a beam splitter system configured to split the radiation once reflected from the substrate into at least four components having different polarization orientations;

a focusing system configured to focus the four components at different positions on a detector, the detector configured to detect simultaneously angle-resolved spectra of the four components of the radiation beam;

a processor configured to use the angle-resolved spectra of the four components to determine a phase difference between polarization directions and a ratio between polarization direction amplitudes of the reflected radiation beam; and

an iterative loop device configured to determine a refractive index, an absorption index, and a thickness of a resist layer on the substrate based on a difference between the determined phase difference and a modeled phase difference and based on a difference between the determined ratio and a modeled ratio.

2. The inspection apparatus according to claim 1, wherein the beam splitter system comprises:

a beam splitter configured to separate the radiation beam once reflected from the surface of the substrate into first and second sub-beams;

a first polarizing beam splitter configured to split the first sub-beam into two respectively orthogonally polarized components; and

a second polarizing beam splitter configured to split the second sub-beam into two further respectively orthogonally polarized components.

3. The inspection apparatus according to claim 2, wherein the first and second polarizing beam splitters comprise polarizing prisms.

4. The inspection apparatus according to claim 1, wherein the processor is configured to create an image made up of arrays of pixels, a relative value (F1, F2) of each pixel having been calculated using one of the following fractions:

5. The inspection apparatus according to claim 1, wherein the beam splitter system comprises:

a beam splitter configured to separate the radiation beam once reflected from the surface of the substrate into first and second elliptically polarized sub-beams;

a first polarizing beam splitter configured to split the first sub-beam into first and second components with about 0 and 90 degree polarization respectively; and

a second polarizing beam splitter rotated by about 45 degrees with respect to the first polarizing beam splitter and configured to split the second sub-beam into third and fourth components with about 45 and 135 degree polarization respectively.

6. The inspection apparatus according to claim 2, wherein the first and second polarizing beam splitters comprise Wollaston prisms.

7. The inspection apparatus according to claim 1, wherein the processor is configured to determine the phase difference (Δ

) between polarization directions and the ratio (tan Ψ

) between the polarized radiation direction amplitudes of the reflected radiation beam from measured intensities (I₁, I₂, I₃, I₄) of first, second, third and fourth components using the following equations;

8. The inspection apparatus according to claim 1, wherein the optical element is configured to focus the radiation beam onto the substrate at a range of azimuthal angles (A) from 0 to 360°

.

9. The inspection apparatus according to claim 1, wherein the radiation beam focused on the substrate is elliptically polarized.

10. The inspection apparatus according to claim 1, further comprising a polarizer and a retarder to circularly polarize the radiation beam to be focused on the substrate.

11. The inspection apparatus according to claim 1, wherein the focusing system comprises an optical wedge configured to focus the components onto the detector.

12. The inspection apparatus according to claim 11, wherein the optical wedge is placed in an image plane of the focusing system.

13. The inspection apparatus according to claim 1, wherein the focusing system comprises a deflector configured to deflect the components onto the detector.

14. The inspection apparatus according to claim 1, wherein the sub-beams comprise a TE-beam and a TM-beam.

15. A method comprising:

reflecting an elliptically polarized radiation beam off a surface of a substrate;

splitting the reflected radiation beam into first and second elliptically polarized sub-beams;

splitting the first sub-beam into first and second components with polarization orientations of about 0 and 90 degrees respectively;

splitting the second sub-beam into third and fourth components with polarization orientations of about 45 and 135 degrees respectively;

focusing the first, second, third, and fourth components at different position on a detector;

simultaneously detecting the first, second, third and fourth components using the detector;

using angle-resolved spectra of the four polarization orientations to determine a phase difference between polarization directions and a ratio between polarization direction amplitudes of the reflected radiation beam; and

iteratively determining a refractive index, an absorption index, and a thickness of a resist layer on the substrate using a difference between the determined phase difference and a modeled phase difference and using a difference between the determined ratio and a modeled ratio.

16. The method according to claim 15, further comprising creating an image made up of arrays of pixels, a relative value (F1, F2) of the pixels having been calculated using intensity values (I₁, I₂, I₃, I₄) of the detected radiation components at that pixel location on the detector according to one of the following fractions:

17. The method according to claim 15, further comprising determining the phase difference (Δ

) between the polarized radiation directions and the ratio (tan Ψ

) between the polarized radiation direction amplitudes of the reflected radiation beam from measured intensities (I₁, I₂, I₃, I₄) of the first, second, third and fourth components using the following equations;

18. The method according to claim 15, further comprising focusing the radiation beam onto the substrate at a range of azimuthal angles (A) from 0 to 360°

.

19. The method according to claim 18, further comprising creating an image made up of arrays of pixels, a relative value of the pixels being associated with the ratio (tan Ψ

) between polarization direction amplitudes of the reflected radiation beam, and the relative positions of the pixels being associated with the different azimuthal angles (A).

20. The method according to claim 18, further comprising creating an image made up of arrays of pixels, a relative value of the pixels being associated with the phase difference (Δ

) between the polarization direction of the reflected radiation beam, and the relative positions of the pixels being associated with the different azimuthal angles (A) of the radiation beam.

21. The method according to claim 15, wherein the splitting of the second sub-beam is carried out using a beam splitter rotated by about 45 degrees with respect to a beam splitter used for splitting the first sub-beam.

22. A lithographic apparatus comprising:

a radiation source configured to supply a radiation beam;

an optical element configured to focus the radiation beam onto a substrate;

a beam splitter configured to split the radiation beam once reflected from the substrate into at least four components having different polarization orientations;

a focusing system configured to focus the four components at different positions on a detector, the detector configured to detect simultaneously angle-resolved spectra of the four components of the radiation beam;

a processor configured to use the angle-resolved spectra of the four components to determine a phase difference between the polarized radiation directions and a ratio between polarization direction amplitudes of the reflected radiation beam; and

an iterative loop device configured to determine a refractive index, an absorption index, and a thickness of a resist layer on the substrate based on a difference between the determined phase difference and a modeled phase difference and based on a difference between the determined ratio and a modeled ratio.

23. A lithographic cell comprising:

a radiation source configured to supply a radiation beam;

an optical element configured to focus the radiation beam onto a substrate;

a beam splitter configured to split the radiation beam once reflected from the substrate into at least four components having different polarization orientations;

a focusing system configured to focus the four components at different positions on a detector, the detector configured to detect simultaneously angle-resolved spectra of the four components of the radiation beam;

a processor configured to determine a phase difference between the polarized radiation directions and a ratio between polarization direction amplitudes of the reflected radiation beam; and

an iterative loop device configured to determine a refractive index, an absorption index, and a thickness of a resist layer on the substrate based on a difference between the determined phase difference and a modeled phase difference and based on a difference between the determined ratio and a modeled ratio.