Method and apparatus for surface diagnostics

• US 4,733,073 A
• Filed: 05/16/1986
• Issued: 03/22/1988
• Est. Priority Date: 12/23/1983
• Status: Expired due to Term

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Gillen, Keith T., Buttrill, Sidney E. Jr., Becker, Christopher H.
• Primary Examiner(s): Church, Craig E.
• Assistant Examiner(s): Berman, Jack I.
• Application Number:
  US06/865,580
• Time in Patent Office: 676 Days
• Field of Search: 250/282, 250/287, 250/288, 250/423 P, 250/281
• US Class Current: 250/288
• CPC Class Codes: H01L 21/67242 Apparatus for monitoring, sorting or marking testing or measuring during manufacture H01L22/00, marks per se H01L23/544; testing individual semiconductor devices G01R31/26
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring

Abstract

Method and apparatus for mass spectral analysis of unknown species of matter present on a surface even in extremely low concentrations. A probe beam such as an ion beam, electron beam or laser is directed to the surface under examination to remove a sample of material. An untuned, high-intensity laser is directed to a spatial region proximate to the surface. The laser has sufficient intensity to induce a high degree of nonresonant, and hence non-selective, photoionization of the sample of material within the laser beam. The non-selectively ionized sample is then subjected to mass spectral analysis to determine the nature of the unknown species.

Claims

1. A method of analyzing a surface including unknown species of matter comprising the steps of:

directing a probe beam at the surface to cause a sample of material to be removed therefrom;

directing a non-resonant ionizing beam of radiation at the removed sample proximate the surface, said ionizing beam having an intensity sufficient to induce non-resonant photo-ionization of said sample, whereby species of matter included in said sample will be non-selectively ionized; and

subjecting the ionized sample to mass-spectrometric analysis to determine the nature of said species.

2. The method of claim 1 wherein said ionized sample is subjected to time-of-flight mass spectrometric analysis and said analysis includes the step of time focusing said ionized sample so as to compensate for a spread in velocities of ions in said sample, thereby enhancing the resolution of said analysis.

3. The method of claim 2, further comprising the step of adjusting the intensity of said probe beam so as to remove only minute amounts of material from said surface, whereby minimal damage is done to said surface.

4. The method of claim 2 wherein said time focusing step comprises the step of electrostatically reflecting said ionized sample.

5. The method of claim 1 wherein said ionized sample is subjected to time of flight mass spectrometric analysis and said analysis includes the step of energetically discriminating against secondary ions from the surface, thereby reducing unwanted background.

6. The method of claim 5, further comprising the step of adjusting the intensity of said probe beam so as to remove only minute amounts of material from said surface, whereby minimal damage is done to said surface.

8. The method of claim 2 wherein said ionized sample is subjected to time-of-flight mass spectrometric analysis and said analysis includes the step of time focusing said ionized sample so as to compensate for a spread in initial velocities of ions in said sample, thereby enhancing the resolution of said analysis.

9. The method of claim 8 further comprising the step of adjusting the intensity of said probe beam so as to remove only minute amounts of material from said surface, whereby minimal damage is done to said surface.

10. The method of claim 8 wherein said time focusing step comprises the step of electrostatically reflecting said ionized sample.

11. The method of claim 2 wherein said ionized sample is subjected to time-of-flight mass spectrometric analysis and said analysis includes the step of energetically discriminating against secondary ions from the surface, thereby reducing unwanted background.

12. The method of claim 11, further comprising the step of adjusting the intensity of said probe beam so as to remove only minute amounts of material from said surface, whereby minimal damage is done to said surface.

18. The apparatus of claim 5 wherein said time-of-flight mass spectrometer includes means for discriminating against secondary ions from the surface under examination.

19. The apparatus of claim 18 wherein said means for discriminating comprises ion reflector means.

20. The apparatus of claim 5 wherein said time-of-flight mass spectrometer includes means for time focusing said ionized sample so as to compensate for a spread in initial velocities of ions in said sample, thereby enhancing the resolution of said analysis.

21. The apparatus of claim 20 wherein said means for time focusing comprises ion reflector means.

7. A method of analyzing a surface including unknown species of matter comprising the steps of:

directing a probe beam at the surface to cause a sample of material to be removed therefrom;

directing a non-resonant ionizing beam of radiation at the removed sample proximate the surface, said ionizing beam having an intensity sufficient to induce non-resonant multi-photon ionization of said sample, whereby species of matter included in said sample will be non-selectively ionized; and

subjecting the ionized sample to mass-spectrometric analysis to determine the nature of said species.

13. A method of analyzing a surface with comparatively little damage thereto wherein a probe beam is directed at said surface to cause a sample of material to be removed therefrom for subsequent analysis, said method comprising the steps of:

adjusting the intensity of said probe beam so as to remove only minute amounts of material from said surface, whereby minimal damage is done to said surface;

directing a non-resonant ionizing beam of radiation at the removed sample in a spatial region proximate said surface, said ionizing beam having an intensity sufficient to induce non-resonant photoionization of said sample, whereby species of matter in said sample will be non-selectively ionized; and

subjecting the ionized sample to mass spectral analysis to determine the nature of said unknown species.

14. Apparatus for use in analyzing a surface including unknown species of matter comprising:

probe beam means providing a probe beam directed at the surface under examination to cause a sample of material to be removed therefrom;

ionizing beam means providing a non-resonant ionizing beam of radiation directed at a spatial region proximate said surface, and having an intensity sufficient to induce non-resonant photoionization of said sample in said spatial region, whereby species of matter included in said sample will be non-selectively ionized; and

a mass spectrometer disposed with respect to said spatial region for analyzing the ionized sample.

15. The apparatus of claim 14, wherein said mass spectrometer is provided by a time-of-flight mass spectrometer.

16. The apparatus of claim 15, further including means for pulsing said probe beam, thereby reducing damage to said surface.

17. The apparatus of claim 16, further including means for pulsing said ionizing beam in time correlation with said probe beam.

22. Apparatus for use in analyzing a surface of a specimen including unknown species of matter comprising:

an evacuation chamber;

mounting means disposed within said chamber for holding said specimen;

probe beam means providing a probe beam directed at a surface of said specimen to cause a sample of material to be removed therefrom;

ionizing beam means providing a non-resonant ionizing beam of radiation directed at a spatial region proximate said surface, said ionizing beam having an intensity sufficient to induce non-resonant photoionization of said sample in said spatial region, whereby species of matter included in said sample will be non-selectively ionized;

wherein said evacuation chamber includes a field-free ion drift region;

acceleration means disposed within said evacuation chamber for propelling the ionized sample across said drift region; and

detector means disposed within said chamber for detecting the ionized sample exiting from said drift region, said above-named means being operatively connected for conducting time-of-flight mass spectral analysis of the ionized sample.

23. The apparatus of claim 22, further comprising ion reflector means disposed in operative association with said ion drift region so as to reflect said ionized sample toward said detector means.

24. Apparatus for use in analyzing a surface including unknown species of matter comprising:

probe beam means providing a probe beam directed at the surface under examination to cause a sample of matreial to be removed therefrom;

ionizing beam means providing non-resonant ionizin beam of radiation directed at a spatial region proximate said surface, and having an intensity sufficient to induce non-resonant multiphoton ionization of said sample in said spatial region, whereby species of matter included in said sample will be non-selectively ionized; and

a mass spectrometer disposed with respect to said spatial region for analyzing the ionized sample.

25. The apparatus of claim 24 wherein said mass spectrometer is provided by a time-of-flight mass spectrometer.

26. The apparatus of claim 25 said time-of-flight mass spectrometer includes means for discriminating against secondary ions from the surface under examination.

27. The apparatus of claim 26 wherein said means for discriminating comprises ion reflector means.

28. The apparatus of claim 25 wherein said time-of-flight mass spectrometer includes means for time focusing sid ionized sample so as to compensate for a spread in inital velocities of ions in said sample, thereby enhancing the resolution of said analysis.

29. The apparatus of claim 28 wherein said means for time focusing comprises ion reflector means.

30. Apparatus for use in analyzing a surface of a specimen including unknown species of matter comprising:

an evacuation chamber;

mounting means disposed within said chamber for holding said specimen;

probe beam means providing a probe beam directed at a surface of said specimen to cause a sample of material to be removed therefrom;

ionizing beam means providing a non-resonant ionizing beam of radiation directed at a spatial region proximate said surface, said ionizing beam having an intensity sufficient to induce non-resonant multiphoton ionization of said sample in said spatial region, whereby species of matter included in said sample will be nonselectively ionized;

wherein said evacuation chamber includes a field-free ion drift region;

acceleration means disposed within said evacuation chamber for propelling the ionized sample across said drift region;

ion reflector means disposed in operative association with said ion drift region so as to reflect said ionized sample toward said detector means; and

detector means disposed within said chamber for detecting the ionized sample exiting from said drift region, said above-named means being operatively connected for conducting time-of-flight mass spectral analysis of the ionized sample.

31. A method of analyzing a surface including unknown species of matter comprising the steps of:

directing a probe beam at the surface to cause a sample of material to be removed therefrom;

directing a non-resonant ionizing beam of radiation at the removed sample in an ionizing region proximate the surface, said ionizing beam having an intensity sufficient to induce saturated non-resonant multi-photon ionization of said sample in said ionizing region, whereby species of matter included in said sample will be non-selectively ionized; and

subjecting the ionized sample to mass spectrometric analysis to determine the nature of said species.

32. The method of claim 31 wherein said ionized sample is subjected to time-of-flight mass spectrometric analysis and said analysis includes the step of time focusing said ionized sample so as to compensate for a spread in initial velocities of ions in said sample, thereby enhancing the resolution of said analysis.

33. The method of claim 32 further comprising the step of adjusting the intensity of said probe beam so as to remove only minute amounts of material from said surface, whereby minimal damage is done to said surface,

34. The method of claim 32 wherein said time focusing step comprises the step of electrostatically reflecting said ionized sample.

35. The method of claim 31 wherein said ionized sample is subjected to time-of-flight mass spectrometric analysis and said analysis includes the step of energetically discriminating against secondary ions from the surface, thereby reducing unwanted background.

36. The method of claim 35, further comprising the step of adjusting the intensity of said probe beam so as to remove only minute amounts of material from said surface, whereby minimal damage is done to said surface.