Resolution enhanced optical metrology

• US 20040239954A1
• Filed: 05/28/2003
• Published: 12/02/2004
• Est. Priority Date: 05/28/2003
• Status: Active Grant

• Current Assignee: Tokyo Electron Limited
• Original Assignee: Timbre Technologies Incorporated (Tokyo Electron Limited)
• Inventors: Bischoff, Joerg
• Granted Patent: US 7,274,472 B2
• Time in Patent Office: Days
• US Class Current: 356/635
• CPC Class Codes: G01B 11/303 using photoelectric detection means

Abstract

A resolution enhanced optical metrology system to examine a structure formed on a semiconductor wafer includes a source configured to direct an incident beam at the structure through a coupling element. The coupling element is disposed between the source and the structure with a gap having a gap height defined between the coupling element and the structure.

Claims

1. A resolution enhanced optical metrology system to examine a structure formed on a semiconductor wafer, the system comprising:

a source configured to direct an incident beam at the structure,

wherein the incident beam has a wavelength; and

a coupling element disposed between the source and the structure,

wherein a gap having a gap height is defined between the coupling element and the structure, and

wherein the wavelength of the incident beam is greater than the gap height.

2. The system of claim 1, wherein the coupling element is a coupling lens.

3. The system of claim 1, wherein the coupling element is a coupling prism.

4. The system of claim 1, wherein the structure has a top surface and a base, wherein the gap is defined between a bottom surface of the coupling element and the base of the structure, and wherein the coupling element can contact the top surface of the structure.

5. The system of claim 1, wherein the gap is filled with a liquid medium.

6. The system of claim 5, wherein the liquid medium and the coupling element have reflection indexes that are approximately the same.

7. The system of claim 1, wherein the gap is filled with a gas medium.

8. The system of claim 7, wherein the gas medium and the coupling element have reflection indexes that are approximately the same.

9. The system of claim 1, wherein the coupling element comprises:

a diffractive element configured to disperse the incident beam.

10. The system of claim 9, wherein the diffractive element has a pitch, wherein the structure has a pitch, and wherein the pitch of the diffractive element is adapted to the pitch of the structure.

11. The system of claim 10, wherein the pitch of the diffractive element is approximately the same as the pitch of the structure.

12. The system of claim 10, wherein a ratio between the pitch of the diffractive element and the pitch of the structure is approximately an integer.

13. The system of claim 10 further comprising:

an assembly having two or more diffractive elements,

wherein a first diffractive element has a first pitch, and

wherein a second diffractive element has a second pitch different than the first pitch.

14. The system of claim 1 further comprising:

an alignment structure formed adjacent to the structure having a height,

wherein the height of the alignment structure corresponds to the gap height.

15. The system of claim 1 further comprising:

an unpatterned area adjacent to the structure,

wherein the gap height is determined using the unpatterned area.

16. The system of claim 1 further comprising:

a detector configured to receive a diffracted beam from the structure,

wherein the diffracted beam results from the incident beam diffracting from the structure, and

wherein a measured diffraction signal is generated based on the diffracted beam.

17. The system of claim 16,

wherein the measured diffraction signal is compared to a simulated diffraction signal to determine a profile of the structure, and

wherein the simulated diffraction signal is generated for a hypothetical profile of the structure being illuminated by the incident beam through the coupling element.

18. The system of claim 17 further comprising:

a library of simulated diffraction signals,

wherein a first simulated diffraction signal in the library corresponds to a first hypothetical profile, and

wherein a second simulated diffraction signal in the library corresponds to a second hypothetical profile different than the first hypothetical profile.

19. The system of claim 17, wherein if the measured diffraction signal and the simulated diffraction signal do not match within a matching criterion, a different simulated diffraction signal is generated for a different hypothetical profile of the structure.

20. A resolution enhanced optical metrology system to examine a structure formed on a semiconductor wafer, the system comprising:

a source configured to direct an incident beam at the structure;

a coupling element disposed between the source and the structure,

wherein a gap is defined between the coupling element and the structure;

a detector configured to receive a diffracted beam resulting from the incident beam diffracting from the structure; and

a processor configured to process the received diffracted beam to determine a profile of the structure.

21. The system of claim 20, wherein the gap is filled with a liquid medium.

22. The system of claim 21, wherein the liquid medium and the coupling element have reflection indexes that are approximately the same.

23. The system of claim 20, wherein the gap is filled with a gas medium.

24. The system of claim 23, wherein the gas medium and the coupling element have reflection indexes that are approximately the same.

25. The system of claim 20, wherein the coupling element comprises:

a diffractive element configured to disperse the incident beam.

26. The system of claim 25, wherein the diffractive element has a pitch, wherein the structure has a pitch, and wherein the pitch of the diffractive element is adapted to the pitch of the structure.

27. The system of claim 26, wherein the pitch of the diffractive element is approximately the same as the pitch of the structure.

28. The system of claim 26, wherein a ratio between the pitch of the diffractive element and the pitch of the structure is approximately an integer.

29. The system of claim 26 further comprising:

an assembly having two or more diffractive elements,

wherein a first diffractive element has a first pitch, and

wherein a second diffractive element has a second pitch different than the first pitch.

30. The system of claim 20, wherein the gap has a gap height, and wherein the incident beam has a wavelength greater than the gap height.

31. The system of claim 30 further comprising:

an alignment structure formed adjacent to the structure having a height,

wherein the height of the alignment structure corresponds to the gap height.

32. The system of claim 30 further comprising:

an unpatterned area adjacent to the structure,

wherein the gap height is determined using the unpatterned area.

33. The system of claim 20,

wherein the processor is configured to obtain a measured diffraction signal based on the received diffracted beam and to compare the measured diffraction signal to a simulated diffraction signal to determine the profile of the structure, and

wherein the simulated diffraction signal is generated for a hypothetical profile of the structure being illuminated by the incident beam through the coupling element.

34. The system of claim 33 further comprising:

a library of simulated diffraction signals,

wherein a first simulated diffraction signal in the library corresponds to a first hypothetical profile, and

wherein a second simulated diffraction signal in the library corresponds to a second hypothetical profile different than the first hypothetical profile.

35. The system of claim 33, wherein if the measured diffraction signal and the simulated diffraction signal do not match within a matching criterion, the processor generates a different simulated diffraction signal for a different hypothetical profile of the structure.

36. A method of examining a structure formed on a semiconductor wafer using a resolution enhanced optical metrology system, the method comprising:

directing an incident beam at the structure through a coupling element,

wherein the coupling element is disposed adjacent to the structure, and

wherein a gap is defined between the coupling element and the structure;

receiving a diffracted beam resulting from the incident beam diffracting from the structure; and

processing the received diffracted beam to determine a profile of the structure.

37. The method of claim 36, wherein the gap is filled with a liquid medium.

38. The method of claim 37, wherein the liquid medium and the coupling element have reflection indexes that are approximately the same.

39. The method of claim 36, wherein the gap is filled with a gas medium.

40. The method of claim 39, wherein the gas medium and the coupling element have reflection indexes that are approximately the same.

41. The method of claim 36, wherein the coupling element comprises:

a diffractive element configured to disperse the incident beam.

42. The method of claim 41, wherein the diffractive element has a pitch, wherein the structure has a pitch, and wherein the pitch of the diffractive element is adapted to the pitch of the structure.

43. The method of claim 42, wherein the pitch of the diffractive element is approximately the same as the pitch of the structure.

44. The method of claim 42, wherein a ratio between the pitch of the diffractive element and the pitch of the structure is approximately an integer.

45. The method of claim 42 further comprising:

selecting the diffractive element from an assembly having two or more diffractive elements,

wherein a first diffractive element on the assembly has a first pitch, and

wherein a second diffractive element on the assembly has a second pitch different than the first pitch.

46. The method of claim 36, wherein the gap has a gap height, and wherein the incident beam has a wavelength greater than the gap height.

47. The method of claim 46 further comprising:

before directing the incident beam at the structure, positioning the coupling element on an alignment structure formed adjacent to the structure having a height, wherein the height of the alignment structure corresponds to the gap height.

48. The method of claim 46 further comprising:

before directing the incident beam at the structure, determining the gap height using an unpatterned area adjacent to the structure.

49. The method of claim 36, wherein processing comprises:

obtaining a measured diffraction signal based on the received diffracted beam;

comparing the measured diffraction signal to a simulated diffraction signal to determine the profile of the structure,

wherein the simulated diffraction signal is generated for a hypothetical profile of the structure being illuminated by the incident beam through the coupling element.

50. The method of claim 49,

wherein the simulated diffraction signal is obtained from a library of simulated diffraction signals,

wherein a first simulated diffraction signal in the library corresponds to a first hypothetical profile, and

wherein a second simulated diffraction signal in the library corresponds to a second hypothetical profile different than the first hypothetical profile.

51. The method of claim 49, wherein if the measured diffraction signal and the simulated diffraction signal do not match within a matching criterion, generating a different simulated diffraction signal for a different hypothetical profile of the structure.