Surface and subsurface detection sensor

• US 20060215175A1
• Filed: 05/18/2006
• Published: 09/28/2006
• Est. Priority Date: 07/28/2004
• Status: Active Grant

• Current Assignee: LER Technologies, Inc.
• Original Assignee: LER Technologies, Inc.
• Inventors: Yacoubian, Araz
• Granted Patent: US 7,397,596 B2
• Time in Patent Office: Days
• US Class Current: 356/502
• CPC Class Codes: G01N 21/1717 with a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance
• 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 21/9505 Wafer internal defects, e.g. microcracks
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10

Abstract

A sensor comprises an optical modulator that generates a modulation signal, an interferometer that mixes an acoustic signal evoked by a pulsed laser with the modulation signal to down-convert the acoustic signal to lower frequencies, and a photodetector that detects the down-converted signal.

Claims

1. A sensor comprising:

an optical modulator that generates a modulation signal;

an interferometer that mixes the modulation signal with an acoustic signal evoked by a pulsed laser to down-convert the acoustic signal to lower frequencies; and

a multiple-dimensional photodetector that detects the down-converted signal.

2. The sensor according to claim 1 further:

a camera operative as the multiple-dimensional photodetector.

3. The sensor according to claim 1 further comprising:

an acoustic excitation source configured to supply the acoustic signal.

4. The sensor according to claim 1 further comprising:

the acoustic excitation source selected from a group consisting of a laser, a pulsed laser, a flash-lamp, an arc-lamp, and a thermal source.

5. The sensor according to claim 1 further comprising:

controllable optics coupled to the interferometer and the optical modulator configured to detect surface and subsurface sample structures.

6. The sensor according to claim 1 further comprising:

controllable optics coupled to the interferometer and the optical modulator configured to reflect elastic waves from interfaces, subsurface structures and defects in a sample; and

a controller adapted to scan modulator frequency within a selected range, acquire measurements of a spatially-varying acoustic spectrum of the sample, and analyze the measurements for subsurface features and defects.

7. The sensor according to claim 1 further comprising:

a continuous wave laser configured to generate laser light that is passed through the optical modulator forming a modulated continuous wave laser beam;

the interferometer that receives and passes a pulsed laser beam and the continuous wave laser beam through a beam-splitter and an objective lens to a sample, and passes reflections from the sample back through the objective lens to the multiple-dimensional photodetector and to a reference mirror that reflects the continuous wave laser beam and sample reflections back to the multiple-dimensional photodetector; and

processing electronics coupled to the camera and configured to perform bandpass filtering, image subtraction, and image processing.

8. The sensor according to claim 1 further comprising:

the interferometer selected from a group consisting of a Mach-Zehnder interferometer, and a Michelson interferometer.

9. The sensor according to claim 1 further comprising:

the interferometer comprising an all-glass beam splitter/reflector interferometer including a glass block of selected length for optical delay.

10. The sensor according to claim 1 further comprising:

the interferometer comprising a reference mirror selected from a group consisting of a planar mirror, a curved mirror with curvature configured to produce linear fringes at the multiple-dimensional photodetector, a beam-splitter, and a reference mirror positioned between an objective lens and a sample.

11. The sensor according to claim 1 further comprising:

a diffractive or holographic optical element positioned between a pulsed laser source and the interferometer and passing a pulsed laser beam in a configuration that generates a plurality of pulsed laser spots for acoustical excitation.

12. The sensor according to claim 1 further comprising:

a diffractive optical element, a holographic optical element, or a cylindrical lens positioned between a pulsed laser source and the interferometer and passing a pulsed laser beam in a configuration that generates a line focus.

13. The sensor according to claim 1 further comprising:

a diffractive optical element, a holographic optical element, or a cylindrical lens positioned between a pulsed laser source and the interferometer and passing a pulsed laser beam in a configuration that produces directional sensitivity and detects anisotropy using a line focus.

14. The sensor according to claim 1 further comprising:

the interferometer configured to produce two-dimensional data that indicates surface and subsurface structures and defects.

15. The sensor according to claim 1 further comprising:

the optical modulator and the interferometer configured to simultaneously image multiple segments of a sample.

16. The sensor according to claim 1 further comprising:

a 1×

N fiber coupler configured to receive light from the optical modulator;

a plurality of beam splitters coupled to receive light via the coupler;

a plurality of objective lenses that pass light from the beam splitter plurality to a sample; and

a plurality of photodetectors configured to receive light reflected from the sample and simultaneously acquire multiple image sample segments.

17. The sensor according to claim 1 further comprising:

a plurality of integrated waveguide modulators configured to receive light from the optical modulator;

a plurality of beam splitters coupled to receive light via the integrated waveguide modulator plurality;

a plurality of objective lenses that pass light from the beam splitter plurality to a sample; and

a plurality of photodetectors configured to receive light reflected from the sample and simultaneously acquire multiple image sample segments.

18. The sensor according to claim 1 further comprising:

a 1×

N fiber coupler configured to receive light from the optical modulator;

a plurality of beam splitters coupled to receive light via the coupler;

a plurality of objective lenses that pass light from the beam splitter plurality to a sample; and

a plurality of photodetectors configured to receive light reflected from the sample and simultaneously acquire multiple image sample segments.

19. The sensor according to claim 1 further comprising:

the sensor configuration that increases detection resolution above the interferometer optical limit.

20. The sensor according to claim 1 further comprising:

a stepper and/or scanner configured for sub-wavelength movement of a sample or the interferometer whereby detection resolution is increased above the interferometer optical limit.

21. The sensor according to claim 1 further comprising:

a stepper and/or scanner configured for measuring and comparing spectra from a sample segment and neighbor segments of the sample segment whereby detection resolution is increased above the interferometer optical limit.

22. The sensor according to claim 1 further comprising:

a plurality of optical fibers configured to receive light from the optical modulator and produce multiple fringe sets whereby detection resolution is increased above the interferometer optical limit.

23. The sensor according to claim 1 further comprising:

processing electronics coupled to the camera and configured to execute an acoustic spectrum analysis that measures sample critical dimensions.

24. The sensor according to claim 1 further comprising:

processing electronics coupled to the camera and configured to execute an acoustic spectrum analysis that detects line slope as a function of spectral response breadth.

25. The sensor according to claim 1 further comprising:

processing electronics coupled to the camera and configured to execute an acoustic spectrum analysis that detects an undercut line as a function of spectral shape.

26. The sensor according to claim 1 further comprising:

processing electronics coupled to the camera and configured to execute an acoustic spectrum analysis that detects line edge roughness as a function of spectral shape and spectral line broadening.

27. The sensor according to claim 1 further comprising:

processing electronics coupled to the camera and configured to execute an acoustic spectrum analysis that measures variation of thickness, slope, roughness, and undercut across a sample wafer.

28. The sensor according to claim 1 further comprising:

processing electronics coupled to the camera and configured to execute a convolution and/or correlation function to obtain shape and size of sample features.

29. The sensor according to claim 28 further comprising:

processing electronics coupled to the camera and configured to execute a Fourier transform operation that performs the correlation function in inverse spatial domain.

30. The sensor according to claim 1 further comprising:

an acoustic excitation device configured to thermally agitate electrons in a sample, the acoustic excitation device selected from a group consisting of pulsed laser, flash-lamp, arc-lamp, thermal pulse heating, and thermal excitation using thermal pulse.

31. The sensor according to claim 1 further comprising:

an acoustic excitation device configured to heat the sample, thereby increasing thermal noise that is converted to acoustic resonance.

32. The sensor according to claim 1 further comprising:

polarization optics coupled between the optical modulator and the interferometer in a configuration that improves signal-to-noise ratio and light control.

33. The sensor according to claim 1 further comprising:

polarization optics coupled between the optical modulator and the interferometer in a configuration that detects surface acoustic waves.

34. The sensor according to claim 1 further comprising:

polarization optics coupled between the optical modulator and the interferometer in a configuration that detects elastic wave induced birefringence in a sample.

35. The sensor according to claim 1 further comprising:

a controller adapted to control the sensor and check alignment of multiple layers of a patterned wafer.

36. The sensor according to claim 1 further comprising:

a lithography tool configured for patterning a wafer and aligning the lithography mask to at least one surface and/or subsurface layers.

37. The sensor according to claim 1 further comprising:

a mount configured to mount the sensor inside a process chamber or in a location enabling access to a sample through a window inside a process chamber.

39. A method of acquiring subsurface structural information comprising:

illuminating a sample under test with a pulsed laser signal that propagates a shock wave through the sample; and

measuring a surface vibration signature of a micro or nano structure of the sample induced by the pulsed laser signal; and

analyzing an acoustic spectrum to determine sample critical dimensions.

40. The method according to claim 39 further comprising:

illuminating a multiple-layer sample under test with a pulsed laser signal that excites elastic waves propagating normal to a sample surface, reflecting from multiple-layer surfaces back to the surface; and

measuring changes in refractive index near a surface of the sample under test induced by the pulsed laser signal.

41. The method according to claim 39 further comprising:

analyzing the acoustic spectrum to perform a function selected from a group consisting of;

detecting line slope as a function of spectral response breadth;

detecting an undercut line as a function of spectral shape;

detecting line edge roughness as a function of spectral shape and spectral line broadening; and

measuring variation of thickness, slope, roughness, and undercut across a sample wafer.

42. The method according to claim 39 further comprising:

checking alignment of multiple layers of a patterned wafer.

43. The method according to claim 39 further comprising:

detecting phenomena selected from a group consisting of defects and integrity of subsurface structures, line edge roughness, line slope, real-time phenomena;

performing multiple processing steps while maintaining a sample in position in a process chamber.

44. A sensor comprising:

an optical modulator that generates a modulation signal;

an interferometer that mixes the modulation signal with an acoustic signal evoked by a pulsed laser to down-convert the acoustic signal to lower frequencies;

a photodetector that detects the down-converted signal; and

processing electronics coupled to the photodetector and configured to perform phase sensitive measurement of elastic waves.

38. The sensor according to claim 44 further comprising:

the sensor mounted to the process chamber whereby the sensor is configured to detect phenomena selected from a group consisting of defects and integrity of subsurface structures, line edge roughness, line slope, real-time phenomena in multiple processing steps while maintaining a sample in position in the process chamber.

45. The sensor according to claim 44 further comprising:

the photodetector selected from a group consisting of a camera, a two-dimensional photodetector, a single element detector, and a linear array detector.

46. The sensor according to claim 44 further comprising:

the processing electronics configured to perform a phase sensitive measurement that detects depth and location of a feature in the surface or subsurface of a sample.

47. The sensor according to claim 44 further comprising:

the processing electronics configured to perform a phase sensitive measurement that determines elastic wave path.

48. The sensor according to claim 44 further comprising:

the processing electronics configured to perform a phase sensitive measurement that increases optical resolution above the interferometer optical limit.

49. The sensor according to claim 44 further comprising:

an acoustic excitation device configured to thermally agitate electrons in a sample, the acoustic excitation device selected from a group consisting of an external pulses laser, a pulsed laser, flash-lamp, arc-lamp, thermal pulse heating, and thermal excitation using thermal pulse.

50. The sensor according to claim 44 further comprising:

a controller adapted to control the sensor and check alignment of multiple layers of a patterned wafer; and

a lithography tool configured for patterning a wafer and aligning the lithography mask to at least one surface and/or subsurface layers.

51. The sensor according to claim 44 further comprising:

a mount configured to mount the sensor inside a process chamber or in a location enabling access to a sample through a window inside a process chamber; and

the sensor mounted to the process chamber whereby the sensor is configured to detect phenomena selected from a group consisting of defects and integrity of subsurface structures, line edge roughness, line slope, real-time phenomena in multiple processing steps while maintaining a sample in position in the process chamber.

52. A sensor comprising:

an optical modulator that generates a modulation signal;

an interferometer that mixes the modulation signal with an acoustic signal evoked by a pump laser beam to down-convert the acoustic signal to lower frequencies;

a photodetector that detects the down-converted signal; and

a direct modulated light coupled to the interferometer and operative as an acoustic excitation source.

53. The sensor according to claim 52 further comprising:

the photodetector selected from a group consisting of a camera, a two-dimensional photodetector, a single element detector, and a linear array detector.

54. The sensor according to claim 52 further comprising:

cascaded interferometers adapted to use modulated laser beams as the acoustic excitation source.

55. The sensor according to claim 52 further comprising:

a pulsed optical modulator configured for direct light modulation as the acoustic excitation source.

56. The sensor according to claim 52 further comprising:

an acoustic excitation device configured to thermally agitate electrons in a sample, the acoustic excitation device selected from a group consisting of an acousto-optic modulator, an electro-optic modulator, an electro-absorptive modulator, a direct modulated laser, and a light modulator.

57. The sensor according to claim 52 further comprising:

a controller adapted to control the sensor and check alignment of multiple layers of a patterned wafer; and

a lithography tool configured for patterning a wafer and aligning the lithography mask to at least one surface and/or subsurface layers.

58. The sensor according to claim 53 further comprising:

a mount configured to mount the sensor inside a process chamber or in a location enabling access to a sample through a window inside a process chamber; and

the sensor mounted to the process chamber whereby the sensor is configured to detect phenomena selected from a group consisting of defects and integrity of subsurface structures, line edge roughness, line slope, real-time phenomena in multiple processing steps while maintaining a sample in position in the process chamber.

59. A sensor comprising:

an optical modulator that generates a modulation signal;

a plurality of interferometers that mix the modulation signal with an acoustic signal evoked by a pulsed laser to down-convert the acoustic signal to lower frequencies, the interferometer plurality configured to generate frequency modulation higher than attained for a singular modulator; and

a photodetector that detects the down-converted signal.

60. The sensor according to claim 59 further comprising:

the interferometer plurality are a plurality of cascaded interferometers.

61. The sensor according to claim 59 further comprising:

the interferometer plurality are a plurality of parallel amplitude modulators and a mutually coherent light source.

62. The sensor according to claim 59 further comprising:

the interferometer plurality are a plurality of parallel amplitude modulators and a plurality of mutually incoherent light sources.

63. The sensor according to claim 59 further comprising:

the interferometer plurality are a plurality of direct modulated lasers and a plurality of mutually incoherent light sources.

64. The sensor according to claim 59 further comprising:

the interferometer plurality are a plurality of parallel phase modulators and a mutually coherent light source.

65. The sensor according to claim 59 further comprising:

the interferometer plurality configured to perform acoustic excitation and detection.

66. The sensor according to claim 59 further comprising:

the photodetector selected from a group consisting of a camera, a two-dimensional photodetector, a single element detector, and a linear array detector.