Method and apparatus for determining surface layer thickness using continuous multi-wavelength surface scanning

• US 20050018183A1
• Filed: 01/09/2004
• Published: 01/27/2005
• Est. Priority Date: 07/23/2003
• Status: Active Grant

• Current Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Shortt, David W.
• Granted Patent: US 7,271,921 B2
• Time in Patent Office: Days
• US Class Current: 356/239.100
• CPC Class Codes: G01B 11/0633 using one or more discrete wavelengths

Abstract

An inspection tool includes an illumination element for directing light beams onto a workpiece at differing wavelengths or at differing angles of incidence or combinations thereof. Such beams producing reflected light and scattered light optical signals. A scanning element and optical detector elements are provided. The optical detector elements receive reflected light signals and scattered light signals. Circuitry for receiving the reflected light signals and scattered light signals are used to determine thickness values for partially transmissive layers formed on the workpiece and correct for the effects of the thickness of the partially transmissive layer so that said signals can be used to identify and characterize defects of the workpiece. Moreover, the invention includes descriptions of methods for accomplishing such inspections.

Claims

1. A surface inspection apparatus comprising:

an illumination element for directing at least two light beams onto a surface to generate a reflected light signal and a scattered light signal for each of the at least two light beams, the at least two light beams having one of;

at least two different wavelengths or at least two different angles of incidence from the surface;

optical detectors configured to receive the reflected light signals; and

circuitry for analyzing the reflected light signals to determine thickness values for the partially transmissive layer.

2. A surface inspection apparatus as in claim 1 wherein the optical detectors are configured to detect reflected light signals at different wavelengths.

3. A surface inspection apparatus as in claim 1 wherein the optical detectors are configured to detect reflected light signals at different polarities.

4. A surface inspection apparatus as in claim 1 wherein the optical detectors are configured to detect reflected light signals at different light collection angles.

5. A surface inspection apparatus as in claim 1 wherein the optical detectors are configured to detect the scattered light signals and the reflected light signals;

and

wherein the circuitry analyzes the reflected light signals to determine thickness values for the partially transmissive layer and analyzes the scattered light signal incorporating the thickness values to detect defects in the surface.

6. A surface inspection apparatus as in claim 5 further including a scanning element for providing relative motion of the at least two light beams across the surface so that the entire surface can be inspected by the apparatus.

7. A surface inspection apparatus comprising:

an illumination element for directing at least two light beams, including a first beam and a second beam, onto a portion of the workpiece having a partially transmissive layer formed thereon to generate a reflected light signal and a scattered light signal for each of the at least two light beams;

a scanning element configured to provide relative motion of the at least two light beams across the surface of the workpiece;

a first optical detector element arranged to receive first reflected light signals produced by the first beam as it is scanned over the workpiece and measuring optical parameter values associated with the first reflected light signals and translating the optical parameter values into an associated first electrical signal;

a second optical detector element arranged to receive second reflected light signals produced by the second beam as it is scanned over the workpiece and measuring optical parameter values associated with the second reflected light signals and translating the optical parameter values into an associated second electrical signal;

circuitry for receiving the associated first and second electrical signals and using said signals to determine thickness values for the partially transmissive layer;

a third optical detector element arranged to receive the scattered light signal as the at least two beams are scanned over the workpiece and translating the scattered light signal into an associated third electrical signal; and

circuitry for receiving third electrical signals and thickness values for the partially transmissive layer and correcting for the effects of the thickness of the partially transmissive layer so that said third electrical signals can be used to identify and characterize defects of the workpiece.

8. The apparatus of claim 7 wherein the scanning element enables continuous relative motion of the at least two light beams across the surface of the workpiece to facilitate scans of the entire surface of the wafer.

9. The apparatus of claim 8 wherein the first beam is directed onto the surface of the workpiece at a different angle than the second beam.

10. The apparatus of claim 8 wherein the first beam and the second beam each comprise light having a different wavelength.

11. The apparatus of claim 10 wherein the first beam is directed onto the surface of the workpiece at a different angle than the second beam.

12. The apparatus of claim 8 wherein the first optical detector element measures an optical parameter value associated with the first reflected light signal selected from among light intensity values, light polarization values, angle of the reflected light signal, and phase values associated with said first reflected light signals;

and

wherein the second optical detector element measures an optical parameter value associated with the second reflected light signals selected from among light intensity values, light polarization values, angle of the reflected light signal, and phase values associated with said second reflected light signals.

13. The apparatus of claim 7 wherein the illumination element comprises at least three light beams including a third light beam that is directed onto said portion of the workpiece to generate a third reflected light signal and another scattered light signal;

further including a fourth optical detector element arranged to receive the third reflected light signal produced by the third beam as it is scanned over the workpiece and measuring optical parameter values associated with the third reflected light signal and translating the optical parameter values into an associated fourth electrical signal;

and

wherein the circuitry further receives the fourth electrical signal and uses said fourth signal to further determine the thickness of the partially transmissive layer.

14. A surface inspection apparatus as in claim 7,

wherein a third optical detector element includes a first optical detector sub-element arranged to receive the scattered light signal from the first beam and a second optical detector sub-element arranged to receive the scattered light signal from the second beam as the at least two beams are scanned over the workpiece and translating the first and second scattered light signals into a associated electrical signals;

and

wherein the circuitry further receives the electrical signals associated with the first and the second scattered light signals and thickness values for the partially transmissive layer and correcting for the effects of the thickness of the partially transmissive layer so that the electrical signals associated with the first and the second scattered light signals can be used to identify and characterize defects of the workpiece.

15. A method for conducting surface inspections comprising:

providing a workpiece having a surface;

continuously scanning the surface of the workpiece with at least two light beams to generate at least two reflected light signals;

detecting the reflected light signals; and

processing the reflected light signals to characterize the surface of the workpiece.

16. The method of claim 15 wherein providing the workpiece includes providing a workpiece having at least one partially transmissive layer formed on a surface thereof;

and

wherein processing the reflected light signals to characterize the surface of the workpiece includes processing the reflected light signals to determine the thickness of the at least one partially transmissive layer formed on the workpiece.

17. The method of claim 15 wherein processing the reflected light signals to characterize the surface of the workpiece includes processing the reflected light signals to generate a map of the workpiece that includes a spatial distribution of reflected light signal values as distributed over the surface of the workpiece.

18. The method of claim 17 wherein detecting the reflected light signals includes measuring optical parameter values of the reflected light signals wherein the optical parameter values for the reflected light signals are selected from among light intensity values, light polarization values, angle values, and phase values associated with said reflected light signals;

and wherein processing the reflected light signals to characterize the surface of the workpiece includes processing the measured optical parameter values of the reflected light signals to generate a map of the workpiece that includes a spatial distribution of the measured optical parameter values for the reflected light signal as distributed over the surface of the workpiece.

19. The method of claim 16 wherein

continuously scanning the workpiece includes scanning with at least two monochromatic light beams having at least two different wavelengths including a first beam at a first wavelength and a second beam at a second wavelength to produce a reflected signal that includes a first reflected light signal at the first wavelength and a second reflected light signal at the second wavelength;

wherein said detecting the reflected light signals includes detecting the first reflected light signal and the second reflected light signal; and

wherein said processing includes analyzing the first reflected light signal together with the second reflected light signal determine the thickness of the at least one partially transmissive layer.

20. The method of claim 19 wherein processing includes using the thicknesses of the at least one partially transmissive layer to generate a map of the workpiece that includes a spatial distribution of the thickness of the at least one partially transmissive layer over the surface of the workpiece.

21. The method of claim 19 wherein processing includes analyzing an optical parameter of the first reflected light signal together with an optical parameter of the second reflected light signal to determine the thickness of the at least one partially transmissive layer wherein the optical parameter is selected from among light intensity, light polarity, angle, and light change.

22. The method of claim 15 wherein

continuously scanning the workpiece includes scanning with at least two light beams including a first beam and a second beam configured such that each beam impinges the surface of the workpiece at a different angle to produce reflected signals that include a first reflected light signal at a first angle and a second reflected light signal at a second angle;

and

wherein said detecting the reflected light signals includes detecting the first reflected light signal and the second reflected light signal.

23. The method of claim 22 wherein continuously scanning the workpiece includes scanning with at least two light beams such that the first beam and the second beam each have different wavelengths of light.

24. The method of claim 16 wherein

scanning the workpiece with at least two light beams generates both a scattered light signal and the reflected light signal;

wherein detecting includes detecting the scattered light signal and the reflected light signal; and

wherein said processing includes processing the reflected light signal to determine the thickness of the at least one partially transmissive layer and includes using such thickness information together with the scattered light signal to detect and characterize defects in the workpiece.

25. The method of claim 24 wherein

scanning the workpiece with at least two light beams includes scanning with at least two monochromatic light beams at least two different wavelengths including a first beam at a first wavelength and a second beam at a second wavelength to produce a reflected signal that includes a first reflected light signal at the first wavelength and a second reflected light signal at the second wavelength;

wherein said detecting the reflected light signal includes detecting the first reflected light signal and the second reflected light signal; and

wherein said processing includes analyzing the first reflected light signal together with the second reflected light signal determine the thickness of the at least one partially transmissive layer.

26. The method of claim 25:

wherein detecting includes detecting optical parameter values associated with the first reflected light signal and optical parameter values associated with the second reflected light signal; and

wherein said processing includes analyzing the optical parameter values for the first reflected light signal together with the optical parameter values for the second reflected light signal determine the thickness of the at least one partially transmissive layer.

27. The method of claim 26:

wherein detecting optical parameter values associated with the first and second reflected light signals includes detecting optical parameter values selected from among light intensity values, light polarization values, angle, and phase values associated with said reflected light signals.

28. The method of claim 25 wherein the scanning further includes scanning the workpiece with the first beam and the second beam such that the first beam and the second beam are incident on a surface of the workpiece at different angles;

wherein detecting includes detecting optical parameter values associated with the first reflected light signal and optical parameter values associated with the second reflected light signal; and

wherein said processing includes analyzing the optical parameter values for the first reflected light signal together with the optical parameter values for the second reflected light signal determine the thickness of the at least one partially transmissive layer.

29. The method of claim 28 wherein detecting optical parameter values associated with the first and second reflected light signals includes detecting optical parameter values selected from among light intensity, light polarization, angle, and phase values associated with said reflected light signals.

30. The method of claim 24 wherein scanning the workpiece comprises scanning with at least two monochromatic light beams that impinge on a surface of the workpiece at least two different angles thereby generating a first reflected light signal and a second reflected light signal each at different angles from each other;

wherein detecting includes detecting the scattered light signal and the two reflected light signals; and

wherein said processing of the reflected light signal includes processing the two reflected light signals to determine the thickness of the at least one partially transmissive layer.

31. The method of claim 16 wherein

continuously scanning the workpiece includes scanning the entire surface of the workpiece with at least two light beams to generate a reflected light signal includes generating at least two reflected light signals, one associated with each light beam;

wherein detecting the reflected light signal includes measuring optical parameter values for each of the at least two reflected light signals;

wherein processing the reflected light signal to characterize the surface of the workpiece includes determining a thickness for the at least one partially transmissive layer by;

accessing a parametric curve associating thickness for the at least one partially transmissive layer with the measured optical parameter values for the reflected light signals generated by the at least two light beams; and

identifying a thickness value uniquely associated with the measured optical parameter values for the reflected light signals and thereby determining a thickness for the at least one partially transmissive layer for the entire surface of the workpiece.

32. The method of claim 31 wherein accessing a parametric curve includes accessing a parametric curve having at least two axes.

33. The method of claim 31 wherein continuously scanning the entire surface of the workpiece is accomplished with at least two light beams with each light beam having a different wavelength of light.

34. The method of claim 31 wherein continuously scanning the entire surface of the workpiece is accomplished with at least two light beams with each light beam being directed onto the workpiece at a different angle.

35. The method of claim 33 wherein the at least two light beams, each having different wavelengths of light, are also each being directed onto the workpiece at a different angle.

36. The method of claim 31 wherein measuring optical parameter values for each of the at least two reflected light signals includes measuring optical parameter values selected from among light intensity values, light polarization values, angle, and phase values associated with said reflected light signals.

37. A method for conducting surface inspection comprising:

providing a workpiece having a plurality of test patterns formed on a surface thereof;

scanning the surface of the workpiece with polychromatic light to illuminate the test patterns of the workpiece to generate a reflected light spectrum;

detecting the reflected light spectrum; and

comparing the polychromatic light beam with the reflected light spectrum to characterize attributes of the workpiece surface.

38. A method as in claim 37 wherein comparing the polychromatic light beam with the reflected light spectrum to characterize attributes of the workpiece surface includes determining the alignment between two layers formed on the surface of the work piece.

39. A method as in claim 37 wherein comparing the polychromatic light beam with the reflected light spectrum to characterize attributes of the workpiece surface includes determining whether features formed on the surface of the work piece are in compliance with a desired specification for critical dimension.

40. A method as in claim 37

wherein providing a workpiece includes providing a patterned workpiece and wherein the test patterns comprise diffraction gratings having a pre-specified regular pitch;

and

wherein comparing the polychromatic light beam with the reflected light spectrum to characterize attributes of the workpiece surface comprises comparing the polychromatic light beam with the reflected light spectrum reflected by the test pattern to characterize attributes of the workpiece surface.

41. A method as in claim 40 wherein the workpiece comprises a patterned wafer.

42. A method as in claim 37

wherein the provided workpiece comprises an un-patterned wafer and wherein the test patterns comprise diffraction gratings having a pre-specified regular pitch;

and

wherein comparing the polychromatic light beam with the reflected light spectrum to characterize attributes of the workpiece surface comprises comparing the polychromatic light beam with the reflected light spectrum reflected by the test pattern to characterize attributes of the workpiece surface.

43. A method as in claim 37 wherein scanning the surface of the workpiece with polychromatic light beam comprises scanning the majority of the surface illuminating the test patterns of the workpiece to generate reflected light spectra associated with each test pattern;

wherein detecting the reflected light spectrum includes selectively detecting only the reflected light spectra associated with the test patterns; and

wherein comparing the polychromatic light beam with the reflected light spectrum comprises comparing the polychromatic light beam with the reflected light spectra associated with the test patterns to characterize attributes of the workpiece surface.