Enhanced ultra-high resolution acoustic microscope

• US 8,302,480 B2
• Filed: 02/05/2008
• Issued: 11/06/2012
• Est. Priority Date: 02/05/2007
• Status: Expired due to Fees

• Current Assignee: Brown University
• Original Assignee: Brown University
• Inventors: Maris, Humphrey J., Nurmikko, Arto V.
• Primary Examiner(s): Macchiarolo, Peter
• Assistant Examiner(s): Shah, Samir M
• Application Number:
  US12/449,415
• Publication Number:
  US 20110036171A1
• Time in Patent Office: 1,736 Days
• Field of Search: 736/06, 736/42, 736/43, 735/87, 735/99
• US Class Current: 73/643
• CPC Class Codes: G01N 29/0681 by acoustic microscopy, e.g. scanning acoustic microscopy
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046
• CPC Class Codes: G01S 15/8965 using acousto-optical or acousto-electronic conversion techniques
• CPC Class Codes: G10K 15/046 using optical excitation, e.g. laser bundle

Abstract

An optical-acoustic transducer structure includes at least one metal or semiconducting film in which a part of a pump light pulse is absorbed to generate a sound pulse; and at least one dielectric film. The thicknesses and optical properties of the at least one metal or semiconducting film and the at least one dielectric film are selected so that a returning sound pulse results in a measurable change in the optical reflectivity and/or some other optical characteristic of the transducer structure. The transducer structure includes a resonant cavity, and an output surface that is shaped so as to provide no significant focusing of generated sound waves when the sound waves are launched towards a surface of the sample.

Claims

1. An opto-acoustic transducer structure, comprising:

at least one metal or semiconducting film in which a part of a pump light pulse is absorbed to generate a sound wave;

a surface through which the generated sound wave exits the transducer structure and is launched towards a sample, and further through which a sound wave returning from the sample is collected and enters the transducer structure; and

at least one dielectric film;

wherein thicknesses and optical properties of the at least one metal or semiconducting film and the at least one dielectric film are selected so that the returning sound wave results in a measurable change in an optical reflectivity and/or some other optical characteristic of the transducer structure; and

further wherein the sound wave that is launched towards the sample through the surface has a substantially planar wave front.

2. An opto-acoustic transducer assembly comprising:

a substrate having a top surface, for receiving a pump light and a probe light, and a bottom surface; and

a transducer structure coupled to the bottom surface,

said transducer structure comprising an optical cavity and configured to generate sound waves in response to the pump light,

said transducer structure having an output surface configured to direct the generated sound waves towards a sample and to collect sound waves returning from the sample, and

said output surface being shaped so as to provide no significant focusing of the generated sound waves when the sound waves are launched towards a surface of the sample.

3. The transducer assembly of claim 2, wherein said output surface is shaped to direct a substantially planar sound wave towards the sample.

4. The transducer assembly as in claim 2, wherein said transducer structure is comprised of a layer of dielectric material that is interposed between two non-dielectric layers, and wherein a thickness of said layer of dielectric material is selected to have a value that is related to a wavelength of the probe light and is modifiable by the collected sound waves to cause a detectable change in the probe light.

5. The transducer assembly according to claim 2, wherein said transducer structure is comprised of an optical micro-cavity layer that is interposed between a metal-containing layer and a multi-layered dielectric stack, and wherein a thickness of said optical micro-cavity layer is selected to have a value that is related to a wavelength of the probe light and is modifiable by the collected sound waves to cause a detectable change in the probe light.

6. The transducer assembly as in claim 2, wherein the output surface is patterned.

7. The transducer assembly as in claim 2, wherein said output surface is patterned to generate a detection signal that indicates a registration between the transducer assembly and the surface of the sample.

8. The transducer assembly as in claim 2, having an output coupled to means for adjusting input parameters to a simulator based on acoustic signals detected from the sample to obtain best fit parameters indicative of the sample.

9. The transducer assembly as in claim 2, having an output coupled to means for comparing acoustic signals detected from the sample to a library of simulation results, said comparing means indicating a best fit between acoustic signals detected from the sample and at least one simulation result found in the library.

10. The transducer assembly as in claim 2, embodied as a part of an equipment used to process a semiconductor wafer.

11. The transducer assembly as in claim 2, embodied as a part of a system that performs a chemical mechanical polish process on a semiconductor wafer, said transducer assembly operable for detecting at least one of wafer-scale and chip-scale process non-uniformities that may result from the chemical mechanical polish process.

12. The transducer assembly as in claim 2, embodied as a part of an equipment used to process the sample and operable to detect and enable characterization of surface features having dimensions less than about 50 nm.

13. The transducer assembly as in claim 2, wherein said transducer structure includes at least one film in which a part of the pump light is absorbed to generate the sound waves, and further wherein the at least one film has at least one aperture made therein enabling a surface of the sample to be viewed through the transducer structure.

14. The transducer assembly as in claim 2, wherein said transducer structure includes at least one film in which a part of the pump light is absorbed to generate the sound waves, and further wherein the at least one film is comprised of a material that is at least partially transmissive to light of certain wavelengths for enabling the surface of the sample to be viewed, using the certain wavelengths, through the at least one film.

15. The transducer assembly as in claim 2, wherein said optical cavity is bounded by first and second metal-containing films, and futher wherein a metal in the first metal-containing film differs from a metal in the second metal-containing film.

16. The transducer assembly as in claim 2, further comprising means for tuning said optical cavity.

17. The transducer assembly of claim 16, wherein said optical cavity is comprised of one of a whispering gallery resonator and an optical ring resonator.

18. The transducer assembly as in claim 2, wherein said optical cavity comprises an air gap.

19. The transducer assembly as in claim 18, further comprising means for electrostatically changing a width of said air gap.

20. The transducer assembly as in claim 2, wherein multiple pump pulses arriving at different angles are received by said top surface such that the intensity of pump light spatially varies within the transducer assembly resulting in a spatial variation in amplitude of the generated sound waves that are directed towards the sample.

21. The transducer assembly as in claim 2, wherein said transducer assembly forms part of a first measurement system and is configured to generate a first detection signal that is used with a second detection signal generated from the sample by at least one second measurement system.

22. The transducer assembly as in claim 2, wherein said substrate is comprised of diamond.

23. The transducer assembly as in claim 2, coupled to an end of an optical fiber through which the pump light and the probe light are delivered.

24. An opto-acoustic transducer assembly comprising:

a substrate having a top surface, for receiving a pump light and a probe light, and a bottom surface; and

a transducer structure coupled to the bottom surface,

said transducer structure comprising an optical cavity and configured to generate sound waves in response to the pump light,

said transducer structure having an output surface configured to direct the generated sound waves towards a sample and to collect sound waves returning from the sample, and

said output surface being shaped so as to provide no significant focusing of the generated sound waves when the sound waves are launched towards a surface of the sample,

wherein the surface of the sample is characterized by a presence of at least one feature disposed at some vertical distance above or below a surface of at least one other feature,

and further wherein said transducer assembly is configured to generate a detection signal that indicates the vertical distance.

25. The transducer assembly as in claim 24, wherein said at least one feature has a feature surface, wherein said transducer assembly is configured to generate a detection signal that indicates a radius of curvature of the feature surface.

26. A processing system, comprising:

a process controller;

a plurality of process stations implementing a process flow on a structure under direction of the process controller; and

at least one opto-acoustic microscope system coupled to the process controller and operable for determining at least one characteristic of a surface of the structure,

said opto-acoustic microscope comprising a transducer assembly that comprises a substrate having a top surface, for receiving a pump light and a probe light, and a bottom surface; and

a transducer body coupled to the bottom surface,

said transducer body comprising an optical cavity and configured to generate sound waves in response to the pump light,

said transducer body having an output surface configured to direct the generated sound waves towards the surface of the structure and to collect sound waves returning from the surface of the structure, and

said output surface shaped so as to provide no significant focusing of the generated sound waves when the sound waves are launched towards the surface of the structure.

27. The processing system of claim 26, wherein said output surface is shaped to direct a substantially planar sound wave towards the surface of the structure.

28. The processing system as in claim 26, wherein said transducer assembly is comprised of a layer of dielectric material that is interposed between two non-dielectric layers, and further wherein a thickness of said layer of dielectric material is selected to have a value that is related to a wavelength of the probe light and is modifiable by the collected sound waves to cause a detectable change in the probe light.

29. The processing system as in claim 26, wherein said transducer assembly is comprised of an optical micro-cavity layer that is interposed between a metal-containing layer and a multi-layered dielectric stack, and further wherein a thickness of said optical micro-cavity layer is selected to have a value that is related to a wavelength of the probe light and is modifiable by the collected sound waves to cause a detectable change in the probe light.

30. The processing system as in claim 26, wherein the output surface is patterned.

31. The processing system as in claim 26, wherein the surface of the structure is characterized by a presence of at least one feature disposed at some vertical distance above or below a surface of at least one other feature, and further wherein said transducer assembly is configured to generate a detection signal that indicates the vertical distance.

32. The processing system as in claim 26, wherein the surface of the structure is characterized by a presence of at least one feature disposed at some vertical distance above or below a surface of at least one other feature, and further wherein said output surface is patterned to generate a detection signal that indicates a registration between the transducer assembly and the surface of the structure.

33. The processing system as in claim 26, wherein the surface of the structure is characterized by a presence of at least one feature disposed at some vertical distance above or below a surface of at least one other feature, said at least one feature having a feature surface, and further wherein said transducer assembly is configured to generate a detection signal that is indicative of a radius of curvature of the feature surface.

34. The processing system as in claim 26, wherein said process controller is responsive to an output of said opto-acoustic microscope system to adjust at least one input parameter to a simulator based on acoustic signals detected from the surface of the structure to obtain best fit parameters.

35. The processing system as in claim 26, wherein said process controller is responsive to the output of said opto-acoustic microscope system to compare acoustic signals detected from the surface of the structure to a library of simulation results to obtain a best fit between acoustic signals detected from the surface of the structure and at least one simulation result found in the library.

36. The processing system as in claim 26, wherein the structure is comprised of a semiconductor wafer.

37. The processing system as in claim 36, wherein at least one of the process stations performs a chemical mechanical polish process on the surface of a semiconductor wafer, and further wherein said opto-acoustic microscope system is operated to detect at least one of wafer-scale and chip-scale process nonuniformities that may result from the chemical mechanical polish process.

38. The processing system as in claim 36, wherein said opto-acoustic microscope system is operable to detect and enable characterization of wafer surface features having dimensions less than about 50 nm.

39. A method comprising:

applying a pulse of a pump light to an opto-acoustic transducer structure comprising an optical cavity;

generating a pulse of acoustic energy within the transducer structure in response to the pulse of the pump light;

directing the pulse of acoustic energy from the transducer structure towards a surface of a sample, the directed pulse having a substantially planar wave front;

receiving, in the transducer structure, at least a portion of acoustic energy returning back from the surface;

applying a pulse of a probe light to the transducer structure;

detecting, in cooperation with the optical cavity, the received acoustic energy through a change in at least one characteristic of the probe light; and

in response to the detecting, determining at least one characteristic of the surface of the sample.

40. The method of claim 39, wherein the pulse of pump light and the pulse of probe light are obtained from one of first and second laser sources or from one laser source.

41. The method of claim 39, wherein the detected at least one characteristic comprises at least one of intensity, phase, polarization and angle.

42. The method as in claim 39, wherein the determined at least one characteristic comprises a presence or an absence of at least one surface feature.

43. The method as in claim 39, wherein the determined at least one characteristic comprises at least one of a height or a depth of at least one surface feature, and an amount of curvature of at least one surface feature.

44. The method as in claim 39, wherein the determined at least one characteristic comprises a thickness of at least one film disposed on the surface of the sample.

45. The method as in claim 39, wherein the determined at least one characteristic indicates a registration between the transducer structure and the surface of the sample.

46. The method as in claim 39, wherein the determined at least one characteristic is obtained by adjusting input parameters to a simulation to obtain best fit parameters indicative of the at least one characteristic of the sample.

47. The method as in claim 39, wherein the determined at least one characteristic is obtained by comparison to a library comprised of results obtained by at least one of simulations and measurements made from at least one reference sample.

48. The method as in claim 39, executed during processing of a semiconductor wafer.

49. The method of claim 48, executed during a polishing process performed on the semiconductor wafer, wherein the determined at least one characteristic is indicative of at least one of wafer-scale and chip-scale process nonuniformities that may result from performance of the polishing process.

50. The method as in claim 39, operable to characterize a surface feature having dimensions less than about 50 nm.

51. The method of claim 50, further comprising viewing a portion of the sample surface through a film that comprises part of the transducer structure using wavelengths of light to which the film is at least partially transmissive.

52. The method as in claim 39, further comprising viewing a portion of the sample surface through an aperture made through a film that comprises part of the transducer structure.

53. The method as in claim 39, further comprising tuning said optical cavity.

54. The method of claim 53, wherein said optical cavity comprises an air gap, and further wherein the tuning comprises changing a width of said air gap in response to application of an electrical signal.

55. The method as in claim 39, wherein the substantially planar wave front has one of a substantially constant amplitude or a spatially varying amplitude when it impinges on the surface of the sample.

56. The method as in claim 39, executed as part of a first measurement method, wherein determining at least one characteristic of the surface of the sample is performed in conjunction with a result of a measurement made by at least one second measurement method.

57. The method as in claim 39, wherein the pump light and the probe light are delivered to the transducer structure through an optical fiber.

58. The method as in claim 39, wherein the directing and the receiving occur through a coupling medium interposed between a surface of the transducer structure and the surface of the sample.

59. The method of claim 58, further comprising varying a temperature of the coupling medium during execution of the method.

60. A computer-readable medium storing computer program instructions, the execution of which results in a performance of the method as in claim 39.