Wafer inspection using short-pulsed continuous broadband illumination

• US 7,659,973 B2
• Filed: 03/09/2007
• Issued: 02/09/2010
• Est. Priority Date: 05/26/2006
• Status: Active Grant

• Current Assignee: Applied Materials South East Asia Pte Limited (Applied Materials Incorporated)
• Original Assignee: Applied Materials South East Asia Pte Limited (Applied Materials Incorporated)
• Inventors: Silberstein, Shai, Furman, Dov
• Primary Examiner(s): Toatley, Jr.; Gregory J
• Assistant Examiner(s): BRYANT, REBECCA CAROLE
• Application Number:
  US11/684,191
• Publication Number:
  US 20070273945A1
• Time in Patent Office: 1,068 Days
• Field of Search: 3562372-2376, 25055941-55948
• US Class Current: 356/237.2
• CPC Class Codes: G01N 2021/479 Speckle
• CPC Class Codes: G01N 2021/8825 Separate detection of dark field and bright field
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/95607 using a comparative method
• CPC Class Codes: G01N 21/95623 using a spatial filtering method per se G02B
• CPC Class Codes: G01N 2201/0697 Pulsed lasers
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14

Abstract

An inspection system may be configured to inspect objects, such as semiconductor wafers, using narrow-pulse broadband illumination. The illumination may be obtained in some embodiments using a laser configured to emit light into a material having a spectral broadening effect. The inspection system can include various filters which may be selectively placed in the illumination and/or imaging path in order to tune the spectrum of light impinging on the wafer and the light that is detected. The filters may include selectable filters, fixed filters, and filters whose characteristics can be adjusted in-place. In some embodiments, filters may be used to match the illumination/detection spectra of different tools. Additionally, the broadband illumination may be tuned between inspections and/or during inspections for best results. The system may support Fourier filtering whereby light, related to repetitive features of the object and in one or more wavelength sub-bands of the illumination, may be filtered.

Claims

1. A wafer inspection system comprising:

a. an imager operative to image at least one wafer while the wafer is illuminated and to determine a plurality of spectra for a plurality of regions of the wafer based on data including a degree of color variation in first and second regions of the wafer, the imager including at least one detector;

b. an illumination source comprising a laser and a non-linear optical component having a spectral broadening effect on light from the laser, so that the illumination source is configured to illuminate the at least one wafer with a pulse of illumination no longer than 1 ps in time and having a continuous spectral range of at least 20 nm; and

c. tuning means disposed in an optical path between the illumination source and the imager, the tuning means operative to tune a spectrum of the wafer inspection system to a desired spectrum by adjusting the spectrum to at least a first spectrum for inspection of the first region of the wafer and adjusting the spectrum to a second spectrum for inspection of the second region of the wafer.

2. The inspection system as set forth in claim 1, wherein the illumination source comprises a pulsed laser configured to emit illumination having a spectral range falling within a range of 180 to 450 nm.

3. The inspection system as set forth in claim 1, wherein the non-linear optical component comprises one or more photonic crystal fibers.

4. The inspection system as set forth in claim 1, wherein the non-linear optical component comprises one or more fused silica fibers.

5. The inspection system as set forth in claim 3, wherein the non-linear optical component comprises a bundle of photonic crystal fibers, at least some of the fibers in the bundle having differing optical lengths from one another.

6. The inspection system as set forth in claim 1, wherein the tuning means comprises at least one filter;

a. wherein the filter is configured to pass one or more specified ranges of wavelengths;

b. wherein the at least one filter is placed in the imaging path between the wafer and the at least one detector so as to filter light traveling from the wafer before said light reaches the detector.

7. The inspection system as set forth in claim 1, wherein the tuning means comprises at least one filter;

a. wherein the filter is configured to pass one or more specified ranges of wavelengths;

b. wherein the at least one filter is placed in the illumination path between the illumination source and the wafer so as to filter light traveling from the illumination source before said light reaches the wafer.

8. The inspection system as set forth in claim 1, further comprising:

a. at least one optical element positioned to form an image of the wafer, the optical element having a Fourier plane; and

b. at least one filter mask placed in the Fourier plane;

c. wherein the at least one mask is configured to block light corresponding to repetitive features of the wafer under inspection, the light falling in a continuous wavelength band.

9. The inspection system as set forth in claim 8,

a. wherein at least one filter mask comprises a plurality of blocking areas;

and

b. wherein at least some of the blocking areas block light in different wavelength sub-bands within the continuous wavelength band than the other blocking areas.

10. The system as set forth in claim 8,

a. wherein the system comprises a plurality of filter masks;

and

b. wherein at least some of the masks are configured to block light in different wavelength sub-bands within the continuous wavelength band than the other masks.

11. The inspection system set forth in claim 1, further comprising at least one optical element configured to focus at least one wavelength band of the illumination source at a different point above or below a focus point of another wavelength band relative to a surface of the wafer.

12. The inspection system as set forth in claim 11, wherein the system includes a plurality of optical elements configured to be selectively inserted into the optical path to adjust the dependency of the focus on wavelength.

20. The system set forth in claim 1, wherein the pulse of illumination has a length of at least 1 ns in time.

21. The system set forth in claim 1, wherein the pulse of illumination has a continuous spectral range of at least 50 nm.

13. A method of inspecting a wafer in an optical inspection system, the method comprising:

a. emitting a pulse of light, the pulse no longer than 1 ps in time;

b. directing the emitted pulse into a nonlinear optical element to obtain broadband illumination having a continuous spectral range of at least 20 nm;

c. directing the broadband illumination toward the wafer;

d. capturing at least one image of at least a portion of the wafer using an imager comprising at least one detector;

e. determining a plurality of spectra for a plurality of regions of the wafer based on data including a degree of color variation in first and second regions of the wafer; and

f. tuning a spectrum of the inspection system to a desired spectrum by adjusting the spectrum to at least a first spectrum for inspection of the first region of the wafer and adjusting the spectrum to a second spectrum for inspection of the second region of the wafer in order to reduce the color variation in images of the first and second regions.

14. The method as set forth in claim 13, wherein the nonlinear optical element comprises a bundle of photonic crystal fibers.

15. The method as set forth in claim 14, wherein at least some of the fibers in the bundle have differing optical lengths from one another.

16. The method as set forth in claim 13, wherein directing the broadband illumination includes focusing an illuminating beam such that at least one wavelength band of the beam is focused at a different location above or below a focus point of another wavelength band of the beam relative to a surface of the wafer.

17. The method as set forth in claim 13, wherein tuning includes filtering light by placing at least one filter in an optical path between the nonlinear optical element and the wafer.

18. The method as set forth in claim 13, wherein tuning includes filtering light by placing at least one filter in an optical path between the wafer and at least one detector included in the imager.

22. The method set forth in claim 18, wherein the pulse of illumination has a length of at least 1 ns in time.

23. The method set forth in claim 13, wherein the pulse of illumination has a continuous spectral range of at least 50 nm.

19. A method comprising:

a. illuminating a wafer with broadband illumination, wherein the wafer includes at least some repetitive structural features;

b. collecting illumination returned from the wafer by using at least one optical element having a Fourier plane and splitting the illumination returned from the wafer into a plurality of wavelength sub-bands, each wavelength sub-band having a separate optical path;

c. placing at least one filter mask at the Fourier plane in each optical path, wherein the at least one filter mask in each optical path is configured to block light containing information related to the repetitive features at a plurality of the respective optical path'"'"'s wavelength sub-band;

d. tuning a spectrum of the broadband illumination to a desired spectrum for each of a plurality of regions of the wafer by adjusting the spectrum according to color variations between images of the plurality of regions of the wafer.

25. The method set forth in claim 19, further comprising:

combining the illumination at each of the plurality of wavelength sub-bands into a single image after the blocking performed by each at least one filter mask.

26. The method as set forth in claim 19, wherein said step of illuminating a wafer with broadband illumination comprises illuminating a wafer with illumination having a continuous spectral range falling within a range from 180 nm to 450 nm.

27. The method as set forth in claim 19, wherein each of the plurality of wavelength sub-bands has a continuous spectral range of at least 50 nm.

24. A wafer inspection system comprising:

a. an imager operative to image at least one wafer while the wafer is illuminated and to determine a plurality of spectra for a plurality of regions of the wafer based on data including a degree of color variation in first and second regions of the wafer, the imager including at least one detector;

b. an illumination source comprising a laser and a non-linear optical component having a spectral broadening effect on light from the laser, so that the illumination source is configured to illuminate the at least one wafer with a pulse of illumination of at least 1 ns, but no longer than 1 ps, in time and having a continuous spectral range of at least 20 nm; and

c. a control system configured to adjust a spectrum of light illuminating the wafer in order to reduce the color variation in images of the wafer by controlling tuning means disposed in an optical path between the illumination source and the imager, the spectrum being adjusted to at least a first spectrum for inspection of the first region of the wafer and to a second spectrum for inspection of the second region of the wafer.