Optical stress generator and detector

• US 20010028460A1
• Filed: 05/03/2001
• Published: 10/11/2001
• Est. Priority Date: 01/23/1996
• Status: Active Grant

• Current Assignee: Humphrey J. Maris, Robert J. Stoner
• Original Assignee: Humphrey J. Maris, Robert J. Stoner
• Inventors: Maris, Humphrey J., Stoner, Robert J.
• Granted Patent: US 6,400,449 B2
• Time in Patent Office: Days
• US Class Current: 356/432
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 2291/02881 Temperature
• CPC Class Codes: G01N 2291/0426 Bulk waves, e.g. quartz crystal microbalance, torsional waves
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• 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: Y10S 977/834 Optical properties of nanomaterial, e.g. specified transparency, opacity, or index of refraction
• CPC Class Codes: Y10S 977/90 having step or means utilizing mechanical or thermal property, e.g. pressure, heat
• CPC Class Codes: Y10S 977/901 having step or means utilizing electromagnetic property, e.g. optical, x-ray, electron beamm
• CPC Class Codes: Y10S 977/955 Of thermal property
• CPC Class Codes: Y10S 977/956 Of mechanical property

Abstract

Disclosed is a system for the characterization of thin films and interfaces between thin films through measurements of their mechanical and thermal properties. In the system light is absorbed in a thin film or in a structure made up of several thin films, and the change in optical transmission or reflection is measured and analyzed. The change in reflection or transmission is used to give information about the ultrasonic waves that are produced in the structure. The information that is obtained from the use of the measurement methods and apparatus of this invention can include: (a) a determination of the thickness of thin films with a speed and accuracy that is improved compared to earlier methods; (b) a determination of the thermal, elastic, and optical properties of thin films; (c) a determination of the stress in thin films; and (d) a characterization of the properties of interfaces, including the presence of roughness and defects.

Claims

1. A method for characterizing a structure, comprising the steps of:

applying first electromagnetic radiation to the structure for creating propagating stress pulses within the structure;

applying second electromagnetic radiation to the structure at a plurality of different incidence angles so as to intercept the propagating stress pulses;

sensing a reflection or transmission of the second electromagnetic radiation from the structure at the plurality of incidence angles;

associating a change in the reflection of the second electromagnetic radiation over time with a value of an optical characteristic of the structure, and determining in accordance with the value of the optical characteristic the velocities of the propagating stress pulses; and

optionally determining the elastic modulus of the structure in accordance with the determined velocities of the propagating stress pulses.

2. A method for characterizing a three dimensional sample comprised of a substrate and possibly one or more films deposited on said substrate together with at least one structure that is disposed upon or embedded within the substrate or one or more of the films, comprising the steps of:

simulating a mechanical response of the sample, at a plurality of discrete time steps, to the application of pulses of first electromagnetic radiation;

applying pulses of the first electromagnetic radiation to the sample for creating propagating stress pulses within the sample;

applying second electromagnetic radiation to the sample so as to intercept the propagating stress pulses;

sensing from a reflection of the second electromagnetic radiation from the sample at least one of a time-varying change in intensity, position, direction, polarization state, and optical phase of the second electromagnetic radiation; and

associating the sensed time-varying change with a property of interest of the sample in accordance with the simulated response of the sample.

3. A method as set forth in

claim 2

, wherein the property of interest includes a dimension that is other than a thickness of the at least one film.

4. A method for characterizing a structure, comprising the steps of:

simulating at predetermined time step increments, in accordance with one or more characteristics of the structure, a mechanical response of a simulated structure over an interval of time to an application of a first pulse of optical radiation by at least the steps of,

determining an initial stress distribution within the simulated structure,

determining a change over the interval of time in the stress and strain distribution in the simulated structure following an application of the first pulse of optical radiation, and

determining the transient optical response of the simulated structure by application of a second pulse of optical radiation within the interval of time;

applying the first pulse of optical radiation to the structure;

applying, during the interval of time, the second pulse of optical radiation to the structure;

comparing a measured transient response of the structure to the determined transient response for the simulated structure;

adjusting a value of the one or more characteristics of the simulated structure so as to bring the determined transient response into agreement with the measured transient response; and

associating the adjusted value of the one or more characteristics with a value of one or more actual characteristics of the structure.

5. A method as set forth in

claim 4

, wherein the structure further comprises at least one layer disposed over a substrate, and wherein the step of determining an initial stress distribution within the simulated structure includes the steps of:

from optical constants and a thickness of the at least one layer, calculating an electric field, due to the first optical pulse, in the simulated structure in terms of an amplitude, angle of incidence, and polarization of the first pulse on a surface of the structure;

from the calculated electric field distribution, calculating an amount of energy absorbed in the simulated structure as a function of position;

determining an effect of thermal diffusion on the absorbed energy distribution;

calculating a temperature rise as a function of position within the simulated structure; and

calculating a stress within the simulated structure from the calculated temperature rise.

6. A method as set forth in

claim 4

, wherein the step of determining a change in stress and strain in the simulated structure includes the steps of:

selecting a time step τ

;

for each layer of the simulated structure, calculating a bin size b equal to the time step τ

multiplied by the sound velocity in the layer; and

dividing each layer into bins of the calculated bin size or bins smaller than the calculated bin size.

7. A method as set forth in

claim 6

, wherein the step of determining a change in stress and strain in the simulated structure further includes the steps of:

decomposing the stress in each bin into two components, one component initially propagating towards a free surface of the simulated structure and one component propagating away from the free surface of the simulated structure;

within each layer, stepping the two components forward from bin to bin in the appropriate direction, wherein for a bin adjacent to a boundary between two layers the stress propagating towards the boundary is stepped partly into the first bin on the other side of the boundary;

repeating the foregoing steps for a sufficient number of time steps τ

to determine the stress distribution for a period at least equal the interval of time; and

calculating the strain from the determined stress by division by an appropriate elastic coefficient.

8. A method as set forth in

claim 4

, wherein the structure further comprises at least one layer disposed over a substrate, and wherein the step of determining a transient response of the simulated structure to an application of a second pulse of optical radiation within the interval of time includes the steps of:

calculating changes Δ

n and Δ

κ

in optical constants of each layer from calculated strain distribution as a function of depth into the simulated structure; and

from the calculated changes Δ

n and Δ

κ

in the optical constants as a function of depth, and from unperturbed optical constants of the at least one layer, calculating at least one of the quantities Δ

R, Δ

T, Δ

P, Δ

φ and

Δ

δ

.

9. A method as set forth in

claim 8

, wherein the step of comparing a measured transient response of the structure to the determined transient response compares the at least one of the calculated quantities Δ

R, Δ

T, Δ

P, Δ

φ and

Δ

δ

with a measured result.

10. A method as set forth in

claim 4

, wherein said plurality of discrete time steps are selected to be small compared to a time required for an acoustic wave to propagate through a thinnest layer that comprises the structure.

11. A non-destructive system for characterizing a sample, comprising:

means for generating an optical pump pulse and for focussing the pump pulse relative to a surface of the sample;

means for generating an optical probe pulse and for focussing the probe pulse relative to the surface of the sample;

means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a reflected or transmitted portion of the probe pulse; and

detector means for automatically adjusting the focus of at least one of the pump and probe pulses in response to reflected portions of at least one of the pump and probe pulses.

12. A non-destructive system for characterizing a sample as set forth in

claim 11

, wherein said means for generating an optical pump pulse generates a train of pump pulses which are applied to a single location on the surface of the sample.

13. A non-destructive system for characterizing a sample as set forth in

claim 11

, wherein the pump pulse induces a stress pulse in the sample that propagates normal to the surface.

14. A non-destructive system for characterizing a sample, comprising:

means for generating an optical pump pulse and for directing the pump pulse to an area of the surface of the sample;

means for generating an optical probe pulse and for directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse;

means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a reflected or transmitted portion of the probe pulse; and

means for determining an electrical resistivity of at least a portion of the sample in accordance with the measured transient response.

15. A non-destructive system for characterizing a sample, comprising:

means for generating an optical pump pulse and for directing the pump pulse to an area of the surface of the sample;

means for generating an optical probe pulse and for directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse;

means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a characteristic of a reflected or transmitted portion of the probe pulse;

means for varying a temperature of at least a portion of the structure during the operation of the measuring means; and

means for determining, from the measured transient response, a derivative of a velocity of an acoustic wave within the structure with respect to temperature, and for associating the determined derivative of the velocity with a static stress within the structure.

16. A method for operating a non-destructive system for characterizing a sample, comprising the steps of:

generating an optical pump pulse and directing the pump pulse to an area of the surface of the sample;

generating an optical probe pulse and directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse;

measuring at least one transient response of the structure to the pump pulse by detecting a change in a characteristic of a reflected or transmitted portion of the probe pulse; and

determining an electrical resistivity of a portion of the sample in accordance with the measured transient response.

17. A method for operating a non-destructive system for characterizing a sample, comprising the steps of:

generating an optical pump pulse and directing the pump pulse to an area of the surface of the sample;

generating an optical probe pulse and directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse;

measuring at least one transient response of the structure to the pump pulse by detecting a change in a characteristic of a reflected or transmitted portion of the probe pulse;

varying a temperature of at least a portion of the structure during the step of measuring; and

determining, from the measured transient response, a derivative of a velocity of an acoustic wave within the structure with respect to temperature, and associating the determined derivative of the velocity with a static stress within the structure.

18. A non-destructive system for characterizing a sample, comprising:

means for a generating a sequence of optical pump pulses at a frequency f₁ and for directing the sequence of pump pulses to an area of the surface of the sample;

means for generating a sequence of optical probe pulses at a frequency f₂ and for directing the sequence of probe pulses to a same or different area of the surface of the sample, wherein f₁ is not equal to f₂ for continuously varying a delay between the generation of a pump pulse and the generation of a probe pulse; and

means for measuring, at a rate given by one of (f₁−

f₂) or (f₁+f₂), at least one transient response of the structure to the sequence of pump pulses by detecting a change in a characteristic of a reflected or transmitted portion of the sequence of probe pulses.

19. A non-destructive system for characterizing a sample, comprising:

means for a generating a sequence of optical pump pulses and for directing the sequence of pump pulses to an area of the surface of the sample;

means for generating a sequence of optical probe pulses, wherein a delay between individual ones of the probe pulses, with respect to an individual one of the pump pulses, is modulated at a frequency f and for directing the sequence of probe pulses to a same or different area of the surface of the sample; and

means for measuring, at a rate given by f, at least one transient response of the structure to the sequence of pump pulses by detecting a change in a characteristic of a reflected or transmitted portion of the sequence of probe pulses.

20. A non-destructive system for characterizing a sample, comprising:

means for a generating a sequence of optical pump pulses that are intensity modulated at a frequency f₁ and for directing the sequence of pump pulses to an area of the surface of the sample;

means for generating a sequence of optical probe pulses, wherein a delay between individual ones of the probe pulses, with respect to an individual one of the pump pulses, is modulated at a frequency f₂, and for directing the sequence of probe pulses to a same or different area of the surface of the sample, wherein f is not equal to f₂; and

means for measuring, at a rate given by one of (f₁−

f₂) or (f₁+f₂), at least one transient response of the structure to the sequence of pump pulses by detecting a change in a characteristic of a reflected or transmitted portion of the sequence of probe pulses.

21. A non-destructive system for characterizing a sample, comprising:

means for generating an optical pump pulse having a first wavelength and for directing the pump pulse to an area of the surface of the sample;

means for generating an optical probe pulse from the optical pump pulse and for directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse, the optical probe pulse being generated to have a second wavelength that is a harmonic of the first wavelength; and

means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a characteristic of the reflected or transmitted portion of the probe pulse.

22. A non-destructive system for characterizing a sample, comprising:

means for generating an optical pump pulse and an optical probe pulse from an input pulse having a first wavelength, wherein the pump pulse has a wavelength that is a harmonic of the first wavelength and the probe pulse has a wavelength that is equal to the first wavelength;

means for directing the pump pulse to an area of the surface of the sample and for directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse; and

means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a characteristic of the reflected or transmitted portion of the probe pulse.

23. A method for operating a non-destructive system for characterizing a sample, comprising the steps of:

generating an optical pump pulse and directing the pump pulse to an area of the surface of the sample;

generating an optical probe pulse and directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse;

measuring at least one transient response of the structure to the pump pulse by detecting a change in a reflected portion of the probe pulse; and

detecting at least one acoustic echo in the reflected portion of the probe pulse, the step of detecting including a step of determining a time of arrival of the acoustic echo by convolving the detected acoustic echo with a predetermined function.

24. A method for operating a non-destructive system for characterizing a sample, comprising the steps of:

generating an optical pump pulse and directing the pump pulse to an area of the surface of the sample;

for each generated optical pump pulse, generating an optical probe pulse and directing the probe pulse to the surface of the sample so as to arrive after the pump pulse, wherein some of the probe pulses are directed to the surface at a first angle relative to the surface, and others of the probe pulses are directed to the surface at a second angle relative to the surface; and

measuring at least one transient response of the structure to the pump pulses by detecting a change in a reflected portion of the probe pulses at each of the first and second angles.

25. A method for characterizing a structure comprised of a substrate and at least one layer that is an intentionally or a non-intentionally formed layer that is disposed over the substrate, comprising the steps of:

generating a reference data set of a transient optical response of the structure to an optical pump pulse, the reference data set being generated from at least one of (a) at least one reference sample or (b) a simulation of a mechanical motion of a simulated structure at predetermined time step increments selected to have a duration of less than one half of a time required for an acoustic pulse to propagate through a thinnest layer of the structure;

applying a sequence of optical pump pulses and optical probe pulses to the structure;

comparing a measured transient response of the structure to the reference data set;

adjusting a value of the one or more characteristics of the structure so as to bring the reference data set into agreement with the measured transient response; and

associating the adjusted value of the one or more characteristics with a value of one or more actual characteristics of the structure.

26. A non-destructive system for characterizing a sample, comprising:

means for generating an optical pump pulse and for directing the pump pulse to an area of the surface of the sample;

means for generating an optical probe pulse and for directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse, wherein the pump pulse has the same wavelength as the probe pulse or a wavelength that is different than the wavelength of the probe pulse;

means for automatically controlling a focusing of the pump and probe pulses on the surface of the sample;

means for measuring at least one transient response of the structure to the pump pulse, the measured transient response comprising a measurement of at least one of a modulated change Δ

R in an intensity of a reflected portion of the probe pulse, a change Δ

T in an intensity of a transmitted portion of the probe pulse, a change Δ

P in a polarization of the reflected probe pulse, a change Δ

φ

in an optical phase of the reflected probe pulse, and a change in an angle of reflection Δ

δ

of the probe pulse;

means for calibrating the measurement system for a determination of an amplitude of the transient optical response of the sample; and

means for associating an output of said means for measuring with at least one characteristic of interest of the structure.

27. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for measuring a derivative of the transient response as a function of at least one of an incident angle of the pump or probe pulses and as a function of a wavelength of at least one of the pump and probe pulses.

28. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for measuring at least one static response of the sample to the pump pulse, the static response measurement comprising at least one of a measurement of the optical reflectivity in accordance with an incident and a reflected average intensity of at least one of the pump and probe pulses, an average phase change of at least one of the pump and probe pulses upon reflection from the structure;

and an average polarization and optical phase of at least one of the incident and reflected pump and probe pulses.

29. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said characteristic of interest includes a thickness of at least one layer of the sample, a mechanical property of the at least one layer, and a characteristic of an interface between the at least one layer and at least one of another layer or the substrate.

30. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for varying a location of said sample relative to at least one of said pump and probe pulses.

31. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for varying a temperature of said sample during an operation of said measuring means, and for measuring a derivative of a velocity of an acoustic wave in said sample with respect to temperature, and for correlating the measured derivative with a static stress within said sample.

32. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said pump and probe pulses are applied along parallel optical paths to a focussing objective that is disposed for focussing said pump and probe pulses on said sample.

33. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said pump and probe pulses are applied along parallel optical paths to a focussing objective that is disposed for focussing said pump and probe pulses on said sample, and are applied with one of a normal or oblique incidence angle to said sample.

34. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein one of said pump and probe pulses is applied to said surface of said sample with a normal incidence angle, and wherein the other one of said pump and probe pulses is applied to said surface of said sample with an oblique incidence angle.

35. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said pump and probe pulses are derived from a single laser pulse.

36. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said pump and probe pulses are each derived from a separate laser pulse.

37. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said pump and probe pulses are derived from a single laser pulse, and further comprising means for converting a wavelength of said single laser pulse to a harmonic of the wavelength such that one of the pump and probe pulses has a wavelength that differs from the wavelength of the other pulse.

38. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for impressing an intensity modulation on at least one of said pump and probe pulses.

39. A non-destructive system for characterizing a sample as set forth in

claim 38

, wherein said means for impressing is synchronized to a pulse repetition rate of a laser that generates said pump or probe pulses.

40. A non-destructive system for characterizing a sample as set forth in

claim 38

, wherein said means for impressing impresses a first intensity modulation frequency on said pump pulse and a second, different intensity modulation frequency on said probe pulse.

41. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising:

a continuous wave laser source for illuminating a portion of a surface of said sample with cw light; and

means, responsive to reflected cw light, for performing an ellipsometric measurement of said sample.

42. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising:

a light source for illuminating a portion of a surface of said sample; and

means for imaging said illuminated portion and for providing the image to one of an operator or a pattern recognition software.

43. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising a thermal source for illuminating a portion of a surface of said sample with thermal radiation for controllably varying a temperature of said sample during the operation of the system.

44. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said measuring means directly measures a derivative of said at least one transient response of the sample with respect to a time delay between said pump pulse and said probe pulse.

45. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein one of the pump and probe pulses has a wavelength that differs from the wavelength of the other pulse, and further comprising a wavelength selective filter in an optical path of the probe pulse for passing the probe pulse while blocking any scattered portion of the pump pulse.

46. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for changing a spatial relationship between a location where the probe pulse is incident on the sample to a location wherein the pump pulse is incident on the sample.

47. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said pump and probe pulses are derived from first and second pulsed laser sources, respectively, and wherein a pulse repetition rate of said first laser source differs from a pulse repetition rate of said second laser source.

48. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for automatically varying a ratio of pump pulse energy to probe pulse energy.

49. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for automatically maintaining a substantially constant location, shape and size of the probe pulse on the sample for a range of temporal offsets between the probe pulse and the pump pulse.

50. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for focussing and translating said probe pulse on a surface of said sample independent of said pump pulse.

51. A non-destructive system for characterizing a sample as set forth in

claim 50

, wherein said focussing and translating means is comprised of a fiber optic having a tapered end diameter for performing near field focussing of said probe pulse, and means for translating said tapered end of said fiber optic relative to a focal spot of said pump pulse.

52. A non-destructive system for characterizing a sample as set forth in

claim 50

, wherein said focussing and translating means is comprised of a fiber optic having an end disposed for collecting reflected probe light, and means for translating said fiber optic relative to a surface of said sample.

53. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising a plurality of fiber optics each having an end disposed relative to a surface of said sample for directing said pump and probe pulses to said sample.

54. A non-destructive system for characterizing a sample as set forth in

claim 53

, and further comprising a further fiber optic having an end disposed relative to the surface for collecting reflected probe light.

55. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said sample is comprised of a plurality of patterned sub-structures having dimensions less than a focal spot diameter of either said pump or probe pulses, and wherein a plurality of said sub-structures are simultaneously illuminated by said pump and probe pulses.

56. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said sample is comprised of a plurality of sub-structures that are arranged periodically, and further comprising means for determining at least one characteristic of said sub-structures by comparing an optical response of said sub-structures to simulations of a vibrational response of said sub-structures to the pump pulse.

57. A non-destructive system for characterizing a sample as set forth in

claim 26

, and further comprising means for detecting a presence of at least one acoustic echo in the reflected portion of the probe pulse.

58. A non-destructive system for characterizing a sample as set forth in

claim 57

, wherein said detecting means determines a time of arrival of the acoustic echo by detecting a location in time of a feature of interest of the acoustic echo.

59. A non-destructive system for characterizing a sample as set forth in

claim 57

, wherein said detecting means determines a time of arrival of the acoustic echo by convolving the detected acoustic echo with a predetermined function.

60. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said measuring means measures the transient response at at least two different angles of incidence of said probe pulse.

61. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said sample is further comprised of one of a transparent layer and a partially absorbing layer.

62. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said sample is further comprised of at least one first layer disposed beneath at least one second layer, and wherein at least said probe pulse passes through said at least one second layer to reach said at least one first layer.

63. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said associating means comprises means for comparing an output of said measuring means with at least one of a simulation of the sample to an application of the pump and probe pulses or to a result of an application of the pump and probe pulses to a reference sample.

64. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said pump pulse is applied at a first location on a surface of the sample, wherein said probe pulse is applied at a second location on the same or a different surface of the sample, and wherein said associating means determines a characteristic of interest for a portion of the sample that lies between the first and second locations.

65. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said sample is patterned into at least one three-dimensional multilayered sub-structure, and wherein said associating means comprises means for comparing an output of said measuring means with a three-dimensional simulation of the at least one multilayered sub-structure to an application of the pump and probe pulses.

66. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said characteristic of interest includes a characteristic of an interlayer between at least one layer and at least one of another layer or the substrate.

67. A non-destructive system for characterizing a sample as set forth in

claim 66

, wherein said characteristic of the interlayer includes at least one of a thickness of the interlayer, a structural phase of the interlayer, and a chemical species that is located within the interlayer.

68. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said characteristic of interest includes an adhesion property of at least, one layer to another adjacent layer or to the substrate.

69. A non-destructive system for characterizing a sample as set forth in

claim 26

, wherein said characteristic of interest includes at least one of a derivative of an index of refraction or a derivative of an extinction coefficient with respect to stress or strain induced by the pump pulse.

70. A method for characterizing a structure comprised of a substrate and at least one layer disposed on the substrate, comprising the steps of:

simulating a response of a model of the structure to an application of a first pulse of optical radiation followed by a transient response of the structure to an application of a second pulse of optical radiation within an interval of time;

applying the first pulse of optical radiation to the structure;

applying, during the interval of time, the second pulse of optical radiation to the structure;

comparing a measured transient response of the structure to the determined transient response;

adjusting one or more characteristics of the model of the structure so as to bring the determined transient response into agreement with the measured transient response; and

associating the adjusted one or more characteristics with one or more actual characteristics of the structure, wherein

the step of adjusting adjusts at least one of a crystal orientation within the at least one layer, an interface roughness between the at least one layer and another layer or the substrate, a thermal diffusivity within the at least one layer, an electronic diffusivity within the at least one layer, optical constants within the at least one layer, derivatives of optical constants with respect to stress or strain within the at least one layer, and a surface roughness of the sample.

71. A method as set forth in

claim 70

, wherein the step of adjusting further adjusts a static stress within the at least one layer.

72. A method as set forth in

claim 70

, wherein the step of adjusting further adjusts a presence of or a thickness of a region of intermixing between two layers or a layer and the substrate.

73. A method for characterizing a structure comprised of a substrate and at least one layer disposed on the substrate, comprising the steps of:

simulating a mechanical response of a model of the structure to an application of a first pulse of optical radiation by the steps of determining an initial stress distribution within the structure in response to the first pulse of optical radiation, calculating acoustical normal modes of the structure, decomposing the determined initial stress distribution into a sum over the calculated normal modes, and determining a change in a transient optical response of the structure, at a time of interest, to a second pulse of optical radiation by summing, for each calculated normal mode, a change in the transient optical response due to a spatial stress pattern associated with each normal mode;

applying the first pulse of optical radiation to the structure;

applying, at the time of interest, the second pulse of optical radiation to the structure;

comparing a measured transient optical response of the structure to the determined transient optical response;

adjusting one or more characteristics of the structure so as to bring the determined transient optical response into agreement with the measured transient optical response; and

associating the adjusted one or more characteristics with one or more actual characteristics of the structure.

74. A method for characterizing a structure comprised of a substrate and at least one layer disposed on the substrate, comprising the steps of:

simulating a vibrational response of the at least one layer to an application of a first pulse of optical radiation, the response being simulated in accordance with a spring constant parameter per unit area at an interface between the at least one layer and another layer or the substrate;

measuring the actual response of the at least one layer by applying the first pulse of optical radiation followed by an application of a second pulse of optical radiation, and sensing a vibration of the at least one layer by a change in a reflected portion of the second pulse of optical radiation;

comparing the measured response with the simulated response;

adjusting the spring constant parameter to bring the simulated response into agreement with the measured response; and

characterizing a strength of the interface from the adjusted spring constant parameter.

75. A method as set forth in

claim 74

, wherein the simulated vibrational response is a simulated damping rate.

76. A non-destructive method for characterizing a sample, comprising the steps of:

generating an optical pump pulse and directing the pump pulse to an area of the surface of the sample;

for each generated optical pump pulse, generating an optical probe pulse and directing the probe pulse to the surface of the sample so as to arrive after the pump pulse;

automatically focusing the pump and probe pulses to achieve predetermined focusing conditions;

measuring at least one transient response of the structure to the pump pulse, the measured transient responses comprising a measurement of at least one of a modulated change Δ

R in an intensity of a reflected portion of the probe pulse, a change Δ

T in an intensity of a transmitted portion of the probe pulse, a change Δ

P in a polarization of the reflected probe pulse, a change Δ

φ

in an optical phase of the reflected probe pulse, and a change in an angle of reflection Δ

δ

of the probe pulse;

applying at least one calibration factor to the at least one transient response;

associating an output of said means for measuring with at least one characteristic of interest of the structure;

adjusting a value of the one or more characteristics of the structure so as to bring a reference data set into agreement with the measured transient response; and

associating the adjusted value of the one or more characteristics with a value of one or more actual characteristics of the structure.

77. A method for characterizing a structure, comprising the steps of:

applying first electromagnetic radiation to the structure for creating propagating stress pulses within the structure;

applying second electromagnetic radiation to the structure at a predetermined incidence angle so as to intercept the propagating stress pulses;

sensing a reflection or transmission of the second electromagnetic radiation from the structure;

associating a change in the reflection of the second electromagnetic radiation over time with a value of an optical characteristic of the structure for

determining a transient response of the structure;

determining an index of refraction of the structure using an ellipsometric technique; and

determining a velocity of sound in the structure in accordance with the predetermined angle and the determined transient response and index of refraction.