PHASE CHARACTERIZATION OF TARGETS

• US 20140111791A1
• Filed: 10/18/2013
• Published: 04/24/2014
• Est. Priority Date: 10/19/2012
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation (KLA Corporation)
• Original Assignee: KLA-Tencor Corporation (KLA Corporation)
• Inventors: Manassen, Amnon, Bachar, Ohad, Negri, Daria, Golovanevsky, Boris, Kandel, Daniel, Sapiens, Noam, Svizher, Alexander, Aloni, Meir, Bringoltz, Barak, Feler, Yoel, Irina, Paykin, Dov, Guy Ben, Shalmoni, Hadar, Levinski, Vladimir
• Granted Patent: US 9,581,430 B2
• Time in Patent Office: Days
• US Class Current: 356/51
• CPC Class Codes: G01B 9/02027 Two or more interferometric channels or interferometers
• CPC Class Codes: G01B 9/02043 Imaging of the Fourier or pupil or back focal plane, i.e. angle resolved imaging
• CPC Class Codes: G01B 9/02087 Combining two or more images of the same region
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods

Abstract

Systems and methods are provided which derive target characteristics from interferometry images taken at multiple phase differences between target beams and reference beams yielding the interferometry images. The illumination of the target and the reference has a coherence length of less than 30 microns to enable scanning the phase through the coherence length of the illumination. The interferometry images are taken at the pupil plane and/or in the field plane to combine angular and spectroscopic scatterometry data that characterize and correct target topography and enhance the performance of metrology systems.

Claims

1. A system comprising:

an illumination source arranged to produce electromagnetic radiation having a coherence length of less than 30 microns;

a reference optical element;

a phase controlled interferometer arranged to;

receive the radiation from the illumination source;

split the radiation between a target and the reference optical element, wherein the interferometer is arranged to controllably introduce a phase between radiation directed to the target and to the reference optical element, and,

generate, from reflected radiation from the target and from the reference optical element, an interference beam;

an imaging unit arranged to receive the interference beam and generate a plurality of interferometry images corresponding to different introduced phases at at least one of a pupil plane and a field plane, and

an analysis unit arranged to derive from the interferometry images at least one target characteristic.

2. The system of claim 1, wherein the illumination source is arranged to produce radiation having at least one band within a wavelength range of 170-900 micron.

3. The system of claim 1, wherein the reference optical element comprises a reference objective which is identical to a target objective and a mirror.

4. The system of claim 1, wherein the reference optical element comprises a mirror.

5. The system of claim 1, wherein the phase controlled interferometer comprises a beam splitter which is mechanically adjustable to control the introduced phase.

6. The system of claim 5, wherein the phase controlled interferometer is arranged to scan the phase through the coherence length of the radiation.

7. The system of claim 1, wherein the imaging unit is arranged to generate the interferometry images at the pupil plane and the analysis unit is arranged to characterize the target from angular information obtained at the pupil plane.

8. The system of claim 1, wherein the imaging unit is arranged to generate the interferometry images at the field plane and the analysis unit is arranged to characterize and correct target imperfections identified from the phase controlled interferometry images.

9. The system of claim 1, wherein the imaging unit is arranged to generate corresponding interferometry images at both pupil and field planes, and the analysis unit is arranged to derive and relate angular and spectroscopic information from the respective plane.

10. The system of claim 1, wherein the imaging unit comprises a beam splitter arranged split the interferometry images between a pupil camera and a field camera.

11. The system of claim 1, wherein the at least one target characteristic comprises at least one of:

target topography, target side wall angles (SWA), a target asymmetry merit, film thickness, film optical parameters and exposed layer quality before layer development.

12. The system of claim 1, wherein the analysis unit is arranged to carry out, according to the at least one derived target characteristic, at least one of:

detect edges of unresolved features, correct target measurements and enhance metrology measurements.

13. The system of claim 1, further arranged to refine focusing by introducing a phase difference derived from the interferometry images.

14. A method comprising deriving at least one target characteristic from a plurality of interferometry images taken at a respective plurality of phase differences between target beams and reference beams yielding the interferometry images, wherein an illumination of the target and the reference has a coherence length of less than 30 microns and wherein the interferometry images are taken at at least one of a pupil and a field plane.

15. The method of claim 14, further comprising scanning the phase through the coherence length.

16. The method of claim 14, further comprising calculating a spectral response of each pixel using interferometry images at a field plane.

17. The method of claim 14, further comprising generating the interferometry images in both pupil and field planes simultaneously.

18. The method of claim 14, further comprising maintaining a same optical path for the target and reference beams.

19. The method of claim 18, further comprising using an objective for the reference beams which is identical to a target objective.

20. The method of claim 14, further comprising deriving target topography from generated wavelength specific phase maps.

21. The method of claim 20, further comprising analyzing target side wall angles (SWA) from the derived target topography.

22. The method of claim 14, further comprising evaluating an asymmetry merit from the analyzed interferometry images.

23. The method of claim 14, further comprising characterizing and correcting target imperfections as derived from the target characteristics.

24. The method of claim 14, further comprising deriving thickness and optical parameters of deposited films as the target characteristics.

25. The method of claim 14, further comprising measuring exposed layer quality before layer development using a refractive index sensitivity of the interferometry images with respect to the phase differences.

26. The method of claim 14, further comprising refining focus signal calculation by introducing a phase difference derived from the interferometry images.

27. The method of claim 14, further comprising detecting edges of unresolved features from spectral changes at different phase differences in the unresolved features.

28. The method of claim 14, further comprising controlling input and output polarization to refine the deriving.

29. The method of claim 14, further comprising applying a training stage to characterize typical target asymmetries and identifying the characterized typical target asymmetries during runs.