High sensitivity deflection sensing device

• US 6,455,838 B2
• Filed: 10/06/1998
• Issued: 09/24/2002
• Est. Priority Date: 10/06/1998
• Status: Expired due to Fees

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Hansma, Paul K., Schäffer, Tilman
• Primary Examiner(s): Le, Que T.
• Assistant Examiner(s): Luu, Thanh X.
• Application Number:
  US09/166,979
• Publication Number:
  US 20020000511A1
• Time in Patent Office: 1,449 Days
• Field of Search: 250/216, 250/306, 250/307, 250/234, 250/237.R, 250/203.1, 250/203.2, 731/05
• US Class Current: 250/216
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01Q 20/02 by optical means
• CPC Class Codes: G01Q 70/06 Probe tip arrays
• CPC Class Codes: Y10S 977/863 Atomic force probe
• CPC Class Codes: Y10S 977/869 Optical microscope
• CPC Class Codes: Y10S 977/87 Optical lever arm for reflecting light

Abstract

A high sensitivity beam deflection sensing optical device, such as an atomic force microscope, including one or more of the following: specified means in the path of the incident beam for adjusting the size and/or power of the incident beam spot, means for moving the incident beam spot with movement of the object whereby to maintain the position of the spot on the object, and means for increasing the signal to noise ratio of the optical detector in which adjusted gains are applied to different segments of the optical detector.

Claims

1. In an atomic force microscope containing an optical beam deflection sensing device, having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected reflective object and an optical detector for receiving the beam when reflected from the reflective object, said detector generating a signal against background noise, the improvement whereby the sensitivity of the optical beam deflection sensing device is increased, comprising providing at least one of the following features:

(a) a plurality of movable, removable, or interchangeable lenses in the path of the incident beam for adjusting the size of the incident beam spot, whereby to produce different size focused spots for a selected reflective object;

(b) control means in the path of the incident beam for adjusting the power, size or shape of the incident beam spot including a mask inserted in the path of the incident beam having adjacent regions through which the beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes;

(c) means for viewing the spot and the reflective object, means for moving the reflective object, and spot position control means based on imaging the reflective object and the spot through the viewing means for moving the incident beam spot with movement of the reflective object whereby to maintain the position of the spot on the reflective object; and

(d) control means for increasing the signal to noise ratio of the optical detector, in which the optical detector has an array of three or more segments generating signals with gains adjusted based on evaluation of one or more segment signals, and summing means for adding the signals from said three or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments.

2. The improvement of claim 1 comprising said spot position control means, and means for determining a change in position of the reflective object, comparing it to the position of the spot, and adjusting the position of the spot until it corresponds to the position of the reflective object.

3. The improvement of claim 1 comprising said control means for increasing the signal to noise ratio of the optical detector, the gain of the signal from each segment being adjusted to optimize the signal to noise ratio.

4. The improvement of claim 3 including a plurality of pre-amplifiers associated with respective segments and summing means to receive the pre-amplified outputs thereof.

5. The improvement of claim 4 wherein said different gains are applied to the respective pre-amplifiers.

6. The improvement of claim 3 wherein said different gains are applied to the summing means.

7. The improvement of claim 1 comprising thermal drift limiting means for regulating the temperature of the environment closely about said optical beam deflection sensing device and reflective object.

8. The improvement of claim 7 in which said thermal drift limiting means comprises a housing closely about said optical beam deflection sensing device having a glove extending from said housing interiorly to reach said optical beam deflection sensing device.

9. In an optical beam deflection sensing device, having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a reflective object and an optical detector for receiving the beam when reflected from the reflective object, said detector generating a signal against background noise, the improvement whereby the sensitivity of the optical device is increased, comprising providing control means in the path of the incident beam for adjusting the power or shape of the incident beam spot including a mask inserted in the path of the incident beam having adjacent regions through which the beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes, said reflective object comprising a cantilever disposed in a predetermined plane and means for forming an image plane, with respect to the plane of the cantilever, in the path of the incident beam, said mask being inserted in said image plane whereby to produce a desired spot shape.

10. In an optical beam deflection sensing device, having a light source providing tin incident beam, a lens for focusing the incident beam to a spot on a reflective object and an optical detector for receiving the beam when reflected from the reflective object, said detector generating a signal against background noise, the improvement whereby the sensitivity of the optical device is increased, comprising providing control means in the path of the incident beam for adjusting the power or shape of the incident beam spot including a mask inserted in the path of the incident beam having adjacent regions through which the beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes, said mask being patterned whereby to produce a desired spot irradiance distribution on the cantilever.

11. In an optical beam deflection sensing device having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected one of one or more reflective objects, and an optical detector for receiving the beam when reflected from the selected reflective object, said detector generating a signal against background noise, the improvement whereby the sensitivity of the optical beam deflection sensing device is increased, comprising providing:

(a) a plurality of moveable, removable or interchangeable lenses in the path of the incident beam for adjusting the size of the incident beam spot, whereby to produce different size focused spots for respective selected reflective objects; and

(b) means for viewing the spot and the reflective objects and spot position control means based on imaging the reflective object and the spot through the viewing means for moving the incident beam spot with movement of the reflective object whereby to maintain the position of the spot on the respective reflective object; and

(c) control means for increasing the signal to noise ratio of the optical detector, in which the optical detector has an array of three or more segments generating signals with gains adjusted based on evaluation of one or more segment signals, and means for adding the signals from said three or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments.

12. A method for improving the sensitivity of an atomic force microscope containing an optical beam deflection sensing device having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected one of one or more reflective objects, and an optical detector having an array of three or more segments for receiving the beam when reflected from the selected reflective object, comprising at least one of the following steps:

(a) modifying the incident beam to adjust the size of the incident beam spot, comprising the step of discretely adjusting the size of the incident beam spot by adjusting or placing one or more lenses in the path of the incident beam whereby to produce different size focused spots for respective selected reflective objects;

(b) adjusting the power, size or shape of the incident beam spot by inserting a mask in the path of the incident beam said mask having adjacent regions through which the beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes;

(c) determining the position of the reflective object, determining the position of the incident beam spot, and determining any difference in said positions then, if there is a difference in said positions, moving the incident beam spot whereby to maintain the position of the spot on the selected reflective object; and

(d) evaluating one or more segment signals, weighting and adding the signals from said three or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments, whereby to increase the signal to noise ratio of the optical detector.

13. The method of claim 12 adjusting the power of the incident beam by inserting said mask in its path, and determining a change in position of the reflective object, comparing it to the position of the spot, and adjusting the position of the spot until it corresponds to the position of the reflective object.

14. The method of claim 12 in which the array of segments generates signals, including the step of applying different gains to different segments to amplify the signals from respective segments, the signal from each segment being amplified by adjusting it to optimize the signal to noise ratio of the optical detector.

15. The method of claim 14 in which said optical detector includes a plurality of pre-amplifiers associated with respective segments and summing means to receive the pre-amplified outputs thereof, comprising the step of applying said different gains to the respective pre-amplifiers.

16. The method of claim 14 in which said optical detector includes a plurality of pre-amplifiers associated with respective segments and summing means to receive the pre-amplified outputs thereof, comprising the step of applying said different gains to the summing means.

17. The method of claim 12 comprising regulating the temperature of the environment closely about said optical beam deflection sensing device and reflective object to limit thermal drift.

18. The method claim 17 in which the regulating step comprises enclosing said optical beam deflection sensing device in a housing closely thereabout, said housing having a glove extending interiorly to reach said housing optical beam deflection sensing device.

19. A method for improving the sensitivity of an optical beam deflection sensing device having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected one of one or more reflective objects, and an optical detector having an array of three or more segments for receiving the beam when reflected from the selected reflective object, comprising adjusting the power, size or shape of the incident beam spot by inserting a mask in the path of the incident beam said mask having adjacent regions through which the beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes, said beam deflection sensing device including, as one or more of said reflective objects, a cantilever disposed in a predetermined plane and including means for forming an image plane, with respect to the plane of the cantilever, in the path of the incident beam, comprising the step of inserting said mask in said image plane whereby to produce a desired spot shape.

20. The method of claim 19 in which said mask is patterned, and controlling said incident beam whereby to produce a desired spot irradiance distribution on the cantilever.

21. A method for improving the sensitivity of an optical beam deflection sensing optical device having a light source providing an incident beam, a lens for focusing the incident beam to a spot on selected one of one or more reflective objects, and an optical detector having an array of segments for receiving the beam when reflected from the reflective object, comprising:

(a) modifying the incident beam to adjust the size of the incident beam spot, comprising the step of discretely adjusting the size of the incident beam spot whereby to produce different size focused spots for respective elected reflective objects;

(b) adjusting the power size or shape of the incident beam spot by inserting a mask in the path of the incident beam, said mask having adjacent regions in direction perpendicular to the incident beam path through which the incident beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes;

(c) moving the incident beam spot with movement of the reflective object whereby to maintain the position of the spot on the respective reflective object; and

(d) adjusting the gains of different segments of the optical detector based on an evaluation of one or more segment signals and adding the signals from said one or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments, whereby to increase the signal to noise ratio of the optical detector.

22. In an optical beam deflection sensing device, having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected reflective object and an optical detector for receiving the beam when reflected from the reflective object, said detector generating a signal against background noise, the improvement whereby the sensitivity of the optical beam deflection sensing device is increased, comprising a confocal viewing system formed of a plurality of movable, removable, or interchangeable lenses comprising an adjustable beam expander or zoom optics in the path of the incident beam for adjusting the size of the incident beam spot and arranged to focus the incident beam on the reflective object, whereby to produce different size focused spots for a selected reflective object, said beam expander or zoom optics being also in the path of said confocal viewing system, and providing at least one of the following features:

(a) control means in the path of the incident beam for adjusting the power, size or shape of the incident beam spot including a mask inserted in the path of the incident beam having adjacent regions through which the beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes;

(b) means for viewing the spot and the reflective object, and spot position control means based on imaging the reflective object and the spot through the viewing means for moving the incident beam spot with movement of the reflective object whereby to maintain the position of the spot on the reflective object; and

(c) control means for increasing the signal to noise ratio of the optical detector, in which the optical detector has an array of three or more segments generating signals with gains adjusted based on evaluation of one or more segment signals, and summing means for adding the signals from said three or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments.

23. The improvement of claim 22 in which said reflective object is a cantilever, and including a plurality of other cantilevers selectively placeable in the path of said incident beam, and including a plurality of cylindrical lenses or prisms, each cylindrical lens or prism associated with a cantilever.

24. In an atomic force microscope having one or more cantilevers, a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected cantilever and an optical detector for receiving the beam when reflected from the selected cantilever, said detector generating a signal against background noise, the improvement comprising a confocal viewing system formed of a plurality of movable, removable, or interchangeable lenses comprising an adjustable beam expander or zoom optics in the path of the incident beam for adjusting the size of the incident beam spot and arranged to focus the incident beam on the selected cantilever, whereby to produce different size focused spots for a selected cantilever, said beam expander or zoom optics being also in the path of said confocal viewing system.

25. The improvement of claim 24 including a plurality of cantilevers selectively placeable in the path of said incident beam, and including a plurality of cylindrical lenses or prisms, each cylindrical lens or prism associated with a cantilever.

26. A method for improving the sensitivity of an optical beam deflection sensing device having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected one of one or more reflective objects, and an optical detector having an array of three or more segments for receiving the beam when reflected from the selected reflective object, comprising:

adjusting the size of the incident beam spot by adjusting or placing one or more lenses in the path of the incident beam whereby to diverge or converge said beam and then focusing said diverged or converged light beam, and comprising at least one of the following steps;

(a) adjusting the power, size or shape of the incident beam spot by inserting a mask in the path of the incident beam said mask having adjacent regions through which the beam is transmitted, said adjacent regions having either different optical transmission characteristics or different shapes;

(b) moving the incident beam spot with movement of the reflective object whereby to maintain the position of the spot on the selected reflective object; and

(c) evaluating one or more segment signals, weighting and adding the signals from said three or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments, whereby to increase the signal to noise ratio of the optical detector.

27. A method for improving the sensitivity of an optical beam deflection sensing device in an atomic force microscope having one or more cantilevers, a light source providing an incident beam, and a lens for focusing the incident beam to a spot on a selected one of said one or more cantilevers, comprising:

discretely adjusting the size of the incident beam spot by adjusting or placing one or more lenses in the path of the incident beam whereby to diverge or converge said beam, and then focusing said diverged or converged light beam.

28. In an optical beam deflection sensing device, having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected reflective object and an optical detector for receiving the beam when reflected from the reflective object, said detector generating a signal against background noise, the improvement whereby the sensitivity of the optical beam deflection sensing device is increased, comprising providing control means for increasing the signal to noise ratio of the optical detector, in which the optical detector has an array of three or more segments generating signals with gains adjusted based on evaluation of one or more segment signals, and summing means for adding the signals from said three or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments.

29. A method for operating an optical beam deflection sensing device having a light source providing an incident beam, a lens for focusing the incident beam to a spot on a selected one of one or more reflective objects, and an optical detector having an array of three or more segments for receiving the beam when reflected from the selected reflective object, the array of segments generating signals, comprising increasing the signal to noise ratio of the device by the steps of applying different gains to signals from different segments, adjusting said gains based on evaluation of one or more segment signals, and adding the adjusted signals from said three or more segments to detect a change of position or shape of the spot as the reflected beam traverses said three or more segments.