Method and apparatus for accurate calibration of VUV reflectometer

• US 20070181793A1
• Filed: 08/31/2004
• Published: 08/09/2007
• Est. Priority Date: 08/11/2004
• Status: Active Grant

• Current Assignee: Bruker Technologies Ltd. (Bruker Corporation)
• Original Assignee: Jordan Valley Semiconductors Ltd. (Bruker Corporation)
• Inventors: Harrison, Dale
• Granted Patent: US 7,804,059 B2
• Time in Patent Office: Days
• US Class Current: 250/252.100
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/55 Specular reflectivity

Abstract

A calibration technique is provided that utilizes a standard sample that allows for calibration in the wavelengths of interest even when the standard sample may exhibit significant reflectance variations at those wavelengths for subtle variations in the properties of the standard sample. A second sample, a reference sample may have a relatively featureless reflectance spectrum over the same spectral region and is used in combination with the calibration sample to achieve the calibration. In one embodiment the spectral region may include the VUV spectral region.

Claims

1. A method of calibrating a system that obtains reflectance data, comprising:

collecting reflectance data from a standard sample, wherein exact properties of the standard sample vary from assumed properties of the standard sample; and

utilizing, in the wavelength region for which calibration is desired, the presence of reflectance variations from the standard sample that result from variations between actual and assumed properties of the standard sample to assist in calibrating the system.

2. The method of claim 1 wherein the utilizing step further comprises utilizing a ratio.

3. The method of claim 2 wherein the ratio is a ratio of an assumed reflectance spectrum of the standard sample and an actual reflectance spectrum of the standard sample.

4. The method of claim 3 wherein a calibration error function is utilized to assist in calibrating the system.

5. The method of claim 4 wherein the calibration error function represents an error that exceeds 0.2% for at least some wavelengths in the wavelength region for which calibration is desired.

6. The method of claim 4 wherein the utilizing step further comprises obtaining a product of the calibration error function and a reflectance of a reference sample.

7. The method of claim 5 wherein the utilizing step further comprises obtaining a derivative of the product of the calibration error function and a reflectance of a reference sample.

39. The method of claim 4 wherein the calibration error function represents an error that exceeds 10% for at least some wavelengths in the wavelength region for which calibration is desired.

40. The method of claim 4 wherein the calibration error function represents an error that exceeds at least 30% for at least some wavelengths in the wavelength region for which calibration is desired.

8. A method of calibrating a reflectometer, comprising:

assuming the presence of a calibration error function in a standard sample; and

calibrating the reflectometer by utilizing the calibration error function of the standard sample.

9. The method of claim 8 wherein the calibration error function utilized to calibrate the reflectometer represents an error that exceeds 0.2% for at least some wavelengths in a wavelength region for which calibration is desired.

10. The method of claim 8 wherein physical changes of the magnitude expected in the standard sample create changes in a reflected signal of the standard sample and a large calibration error function contribution.

11. The method of claim 8 further comprising determining the reflectance of a reference sample.

12. The method of claim 11 wherein the reference sample has a reflectance spectrum that has less features, in the wavelengths of at least the calibration, than the standard sample.

13. The method of claim 12 wherein physical changes in the standard sample create changes in a reflected signal of the standard sample and a calibration error function contribution.

14. The method of claim 13 wherein the reflectometer is first calibrated utilizing assumed properties of the standard sample, the reflectance spectrum of the reference sample is obtained and processed utilizing the first calibration, the actual properties of the standard sample are determined utilizing the reflectance spectrum of the reference sample, and then the reflectometer is re-calibrated utilizing the determined actual properties of the standard sample.

41. The method of claim 8 wherein the calibration error function utilized to calibrate the reflectometer represents an error that exceeds 10% for at least some wavelengths in a wavelength region for which calibration is desired.

42. The method of claim 8 wherein the calibration error function utilized to calibrate the reflectometer represents an error that exceeds at least 30% for at least some wavelengths in a wavelength region for which calibration is desired.

43. The method of claim 10 wherein the calibration error function represents an error that exceeds 0.2% for at least some wavelengths in a wavelength region for which calibration is desired.

44. The method of claim 10 wherein the calibration error function represents an error that exceeds 10% for at least some wavelengths in a wavelength region for which calibration is desired.

45. The method of claim 10 wherein the calibration error function represents an error that exceeds at least 30% for at least some wavelengths in a wavelength region for which calibration is desired.

46. The method of claim 13 wherein the calibration error function represents an error that exceeds 0.2% for at least some wavelengths in a wavelength region for which calibration is desired.

47. The method of claim 13 wherein the calibration error function represents and error that exceeds 10% for at least some wavelengths in a wavelength region for which calibration is desired.

48. The method of claim 13 wherein the calibration error function represents an error that exceeds at least 30% for at least some wavelengths in a wavelength region for which calibration is desired.

15. A method for providing a calibration routine for calibrating a reflectometer, comprising:

configuring the calibration routine to utilize a standard sample calibration being desired in at least a portion of a first wavelength region;

configuring the calibration routine to utilize a first set of reflectance data from the standard sample and to provide a first calibration of the reflectometer based at least in part upon the first set of reflectance data;

configuring the calibration routine to utilize a reference sample that spectrally has less features in at least the first wavelength region, than the standard sample;

configuring the calibration routine to utilize a second set of reflectance data from the reference sample; and

configuring the calibration routine to utilize the first and second set of reflectance data to further calibrate the reflectometer.

16. The method of claim 15, wherein the calibration routine utilizes a calibration error function.

17. The method of claim 16 wherein the calibration error function is indicative of a ratio of an assumed reflectance spectrum of the standard sample and an actual reflectance spectrum of the standard sample.

18. The method of claim 17 wherein a product of the calibration error function and the reflectance spectrum of the reference standard is obtained for use in the calibration routine for calibrating a reflectometer.

19. The method of claim 18 wherein a derivative is obtained of the product of the calibration error function and the reflectance spectrum of the reference, for use in the calibration routine for calibrating a reflectometer.

20. The method of claim 19 wherein an integral of the absolute value of the derivative is utilized.

49. The method of claim 16 wherein the calibration error function represents an error that exceeds 0.2% for at least some wavelengths in the first wavelength region.

50. The method of claim 16 wherein the calibration error function represents an error that exceeds 10% for at least some wavelengths in the wavelength region.

51. The method of claim 16 wherein the calibration error function represents an error that exceeds at least 30% for at least some wavelengths in the wavelength region.

21. A method of calibrating a reflectometer, comprising:

collecting a first set of reflectance data from a standard sample that has a calibration error function in a first wavelength region in which calibration is desired;

collecting a second set of reflectance data from a reference sample that has less spectral features as compared to the standard sample in the first wavelength region; and

utilizing the first and second sets of reflectance data to calibrate the reflectometer.

22. The method of claim 21 wherein the first wavelength region comprises at least a portion of the VUV wavelength region.

23. The method of claim 22 wherein the calibration error function represents an error that exceeds 0.2% for at least some wavelengths in the VUV region.

24. The method of claim 23, further comprising:

performing a first calibration of the reflectometer by utilizing assumed properties of the standard sample and measured reflectance data of the standard sample;

obtaining a reflectance spectrum of the reference sample utilizing reflectometer measurements from the reference sample and data from the first calibration;

utilizing the obtained reflectance spectrum of the reference sample to determine actual properties of the standard sample; and

re-calibrating the reflectometer utilizing the determined actual properties of the standard sample.

25. The method of claim 24 wherein the actual property of the standard sample is a material thickness.

26. The method of claim 24 further comprising utilizing a ratio of an assumed standard sample reflectance spectrum and an actual standard sample reflectance spectrum.

52. The method of claim 22 wherein the calibration error function represents an error that exceeds 10% for at least some wavelengths in the VUV region.

53. The method of claim 22 wherein the calibration error function represents an error that exceeds at least 30% for at least some wavelengths in the VUV region.

27-38. -38. (canceled)