Scanning near field optical microscope

• US 5,894,122 A
• Filed: 03/12/1997
• Issued: 04/13/1999
• Est. Priority Date: 03/13/1996
• Status: Expired due to Fees

• Current Assignee: SII NanoTechnology Inc. (Hitachi, Ltd.)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Tomita, Eisuke
• Primary Examiner(s): Allen, Stephone B.
• Application Number:
  US08/815,816
• Time in Patent Office: 762 Days
• Field of Search: 250/234, 250/216, 250/306, 250/461.1, 359/368
• US Class Current: 250/234
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01Q 60/20 Fluorescence
• CPC Class Codes: Y10S 977/862 Near-field probe

Abstract

A high resolution observation apparatus capable of resolving details smaller than the wavelength of a laser beam used for detection includes a probe for scattering evanescent light projected from a sample in response to the incident laser light. The scattered evanescent light is detected by a photodetector located proximate the probe tip. During measurements, the position of the probe is controlled in the Z axis by a fine movement mechanism while being scanned in the XY plane to conduct measurements. The distance between the probe and the sample is maintained constant by use of a Z-axis servo circuit responsive to an output signal of the photodetector for producing a control signal to control the fine movement mechanism to maintain the detected evanescent light constant. A three-dimensional display of an output of the servo circuit is provided.

Claims

1. A scanning near field optical microscope comprising:

an optical waveguide probe having a sharpened tip portion provided with a small aperture at the tip portion;

light emitting means for emitting a light to irradiate a sample so that an evanescent light is projected by the sample and scattered by the probe tip, the light emitting means comprising a laser light source, a lens, and a prism;

coarse displacement means for moving one of the optical waveguide probe and the sample to bring the optical waveguide probe close to a surface of the sample;

evanescent light detecting means comprising a lens for collecting the evanescent light projected by the sample and scattered by the probe tip, and a photodetector for detecting the collected evanescent light and producing a corresponding output signal;

means for controlling a distance between the sample and the probe tip comprising a Z axis fine displacement element for moving one of the probe and the sample in response to a control signal, and a Z servo-circuit for receiving the output signal of the photodetector and generating the control signal to control the Z axis fine displacement element so as to control the distance between the probe tip and the sample to maintain the intensity of the detected evanescent light constant;

scanning means for causing relative scanning motion between the probe and the sample in two dimensions, comprising an XY fine displacement element and an XY scanning circuit; and

data processing means for providing an image of a measured characteristic of the sample in three dimensions on the basis of outputs of at least the Z servo-circuit and the XY scanning circuit.

2. A scanning near field optical microscope according to claim 1;

wherein the optical waveguide probe comprises a single mode optical fiber coated with a metal at the sharpened tip portion thereof except at the aperture, and the diameter of the aperture is smaller than a wavelength of the light emitted by the light emitting means.

3. A scanning near field optical microscope according to claim 1;

wherein the laser light source comprises an infrared laser, and the photodetector comprises an infrared light detecting element.

4. A scanning near field optical microscope according to claim 1;

further comprising means for modulating a laser light periodically and a lock-in detecting means.

5. A scanning near field optical microscope according to claim 1;

further comprising light detecting means for detecting a light projected by the sample and picked up by the optical waveguide probe.

6. A scanning near field optical microscope according to claim 1;

further comprising a second laser light source for producing a second laser light which is guided in the optical waveguide probe and which irradiates the sample.

7. A scanning near field optical microscope according to claim 6;

further comprising light detecting means for detecting light reflected by the sample in response to light irradiated onto the sample from the tip of the optical waveguide probe.

8. A scanning near field optical microscope according to claim 6;

further comprising light detecting means for detecting luminescence emitted from the sample in response to the light irradiated onto the sample from the tip of the optical waveguide probe.

9. A scanning near field optical microscope according to claim 8;

further comprising means for analyzing the spectrum of luminescence emission from the sample.

10. A high resolution observation apparatus comprising:

a light emitting source for emitting an incident light to be incident on a sample so that an evanescent light is projected from the sample in response to the incident light;

a probe disposed proximate a surface of the sample and having a narrow tip for scattering the evanescent light projected by the sample;

an evanescent light detector disposed proximate the probe tip for detecting the evanescent light scattered by the probe tip and outputting a corresponding signal;

a position control system responsive to a control signal for supporting and moving at least one of the probe and the sample in a first direction to control the distance therebetween in the first direction and for causing relative scanning movement therebetween in a plane perpendicular to the first direction; and

a servo circuit responsive to the output signal of the light detector for producing the control signal to control the position control system to maintain the detected evanescent light constant.

11. A high resolution observation apparatus according to claim 10;

wherein the incident light has a predetermined wavelength and is incident on the sample at a total reflection angle.

12. A high resolution observation apparatus according to claim 10;

further comprising an optical device on which the sample is disposed.

13. A high resolution observation apparatus according to claim 12;

wherein the optical device is an optical prism made of a transparent material and having a flat first surface on which the sample is disposed.

14. A high resolution observation apparatus according to claim 13;

wherein the incident light is a laser light and is incident on a second surface of the prism at a total reflection angle.

15. A high resolution observation apparatus according to claim 10;

wherein the probe tip is formed with an aperture portion having a diameter smaller than a wavelength of the incident light.

16. A high resolution observation apparatus according to claim 10;

wherein the probe comprises an optical waveguide probe made of an optical fiber having a sharpened tip coated with a metal and having an aperture at the tip portion at which no metal is coated, the aperture having a diameter smaller than a wavelength of the incident light.

17. A high resolution observation apparatus according to claim 10;

wherein the position control system comprises a coarse position adjustment mechanism for moving one of the probe and the sample in the first direction to bring the probe close to the sample so that the evanescent light is scattered by the probe tip, a fine movement element comprising a piezoelectric element capable of extending and retracting one of the probe and the sample in the first direction in response to the control signal generated by the servo circuit so as to control the distance between the probe tip and the sample in the first direction to maintain the detected evanescent light constant.

18. A high resolution observation apparatus according to claim 10;

further comprising data processing means for producing a three-dimensional image of a measured characteristic of the sample based on outputs of the servo circuit and the position control system when the probe is scanned relative to the sample.

19. A high resolution observation apparatus according to claim 10;

wherein the light emitting source comprises a laser source for projecting a laser light, and a lens onto which the laser light is projected for directing the laser light onto the sample.

20. A high resolution observation apparatus according to claim 19;

wherein the laser is one of an argon laser, a semiconductor laser, and an infrared laser.

21. A high resolution observation apparatus according to claim 19;

further comprising a prism having a flat first surface on which the sample is disposed, a second surface onto which the parallel light is irradiated at a total reflection angle, and wherein the probe is disposed proximate a first surface of the sample opposite to a second surface of the sample which is in contact with the prism.

22. A high resolution observation apparatus according to claim 21;

wherein the probe is an optical waveguide probe.

23. A high resolution observation apparatus according to claim 22;

wherein the probe is formed of an optical fiber having a sharpened tip coated with a metal except at an aperture portion thereof, the aperture portion having a diameter smaller than a wavelength of the laser light.

24. A high resolution observation apparatus according to claim 23;

wherein the optical fiber is a single mode optical fiber.

25. A high resolution observation apparatus according to claim 23;

wherein the optical fiber is a multimode optical fiber.

26. A high resolution observation apparatus according to claim 23;

wherein the evanescent light detector comprises a lens for collecting the evanescent light, and a photodetector for receiving the light collected by the lens and outputting the corresponding signal.

27. A high resolution observation apparatus according to claim 26;

further comprising data processing means including a display for producing a three-dimensional image of a detected characteristic of the sample based on outputs of the servo circuit and position control system.

28. A high resolution observation apparatus according to claim 27;

further comprising a second light emitting source for irradiating a second incident light through the probe to be incident on the sample, and a light detector for detecting light reflected from the sample in response to the second incident light.

29. A high resolution observation apparatus according to claims 28;

wherein the data processing means further comprises means for producing another three-dimensional image of another characteristic of the sample based on an output of the light detector.

30. A high resolution observation apparatus according to claim 29;

further comprising a modulator for modulating the incident light and a lock-in amplifier.

31. A high resolution observation apparatus comprising:

an optical device having a surface on which a sample to be observed is disposed;

an optical source for generating an incident light of a predetermined wavelength to be incident to the sample through the optical device at a total reflection angle;

a probe having a sharpened tip for scattering a sample light projected from the sample surface in response to the incident light;

an optical detecting system for detecting the sample light scattered by the probe;

a position control unit for moving one of the probe and the sample in the XY plane to scan the sample over a two-dimensional area to be observed; and

a Z-axis control unit for positioning the probe at a distance from the sample surface in the Z direction close enough to locally scatter sample light projected from a minute region of the sample and for controlling the Z-direction distance between the probe and the sample surface so as to keep a positioning signal detected by the optical detecting system constant during a course of scanning the sample surface over the two-dimensional area to be observed.

32. A high resolution observation apparatus according to claim 31;

wherein the optical device is an optical prism made of a transparent material and having a flat surface on which the sample is mounted.

33. A high resolution observation apparatus according to claim 31;

wherein the probe is an optical detecting probe comprising an optical fiber having a sharpened tip portion coated with a metal for scattering the sample light and having an aperture at the tip portion at which no metal is coated.

34. A high resolution observation apparatus according to claim 33;

wherein the aperture at the tip portion of the probe is smaller in size than a wavelength of the incident light.

35. A high resolution observation apparatus according to claim 31;

wherein the incident light is a laser light.

36. A high resolution observation apparatus according to claim 35;

wherein the laser light is selected from the group consisting of an argon laser, a semiconductor laser, and an infrared laser.

37. A high resolution observation apparatus according to claim 31;

wherein the probe comprises a single mode optical fiber having a sharpened tip coated with metal at the tip thereof except for an aperture portion located at the tip.

38. A high resolution observation apparatus according to claim 31;

wherein the incident light comprises an infrared laser, and the optical detecting system comprises a lens for collecting sample light an infrared light detecting element.

39. A high resolution observation apparatus according to claim 31;

further comprising means for modulating the incident light periodically and lock-in detecting means.

40. A high resolution observation apparatus according to claim 31;

further comprising light detecting means for detecting sample light transmitted through the probe.

41. A high resolution observation apparatus according to claim 31;

further comprising a laser light source for transmitting a laser light through the probe tip to irradiate the sample.

42. A high resolution observation apparatus according to claim 41;

further comprising light detecting means for detecting light reflected by the sample in response to irradiation by the laser light through the probe tip.

43. A high resolution observation apparatus according to claim 41;

further comprising light detecting means for detecting luminescence emitted by the sample in response to irradiation by the laser light through the probe tip.

44. A high resolution observation apparatus according to claim 43;

further comprising means for analyzing the spectrum of luminescence emission from the sample.