Method and apparatus for the ultrasonic actuation of the cantilever of a probe-based instrument

• US 6,694,817 B2
• Filed: 03/12/2002
• Issued: 02/24/2004
• Est. Priority Date: 08/21/2001
• Status: Expired due to Term

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia), Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Degertekin, F. Levent, Onaran, Abidin Guclu, Hadimioglu, Babur B.
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US10/096,367
• Publication Number:
  US 20030041669A1
• Time in Patent Office: 714 Days
• Field of Search: 736/52, 736/49, 735/79, 731/05, 736/61, 438/52
• US Class Current: 73/661
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• 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 29/2456 Focusing probes focusing arrangements G01N29/221
• CPC Class Codes: G01N 29/346 with amplitude characteristics, e.g. modulated signal
• CPC Class Codes: G01Q 30/14 Liquid environment
• CPC Class Codes: G01Q 60/32 AC mode
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: Y10S 977/872 Positioner

Abstract

The cantilever of a probe-based metrology instrument such as an AFM is deflected by directing a beam of ultrasonic energy at the cantilever to apply ultrasonically generated acoustic radiation pressure to the cantilever. The energy is generated by an ultrasonic actuator such as a ZnO transducer driven by a power source such an RF signal generator. The transmitted beam preferably is shaped by focusing, collimation, or the like so that it impinges at least primarily on a region of interest of the cantilever such as the free end. The ultrasonic actuator produces a much better controlled force on the cantilever than can be achieved through the use of a traditional piezoelectric actuator and, accordingly, produces a response free of spurious effects (at least when the cantilever is operating in liquid). It also has a frequency bandwidth in the MHz range.

Claims

1. A metrology instrument comprising:

(A) a probe including a cantilever; and

(B) an ultrasonic actuator configured to direct a beam of ultrasonic energy at the cantilever that imposes a force on the cantilever that drives the cantilever to oscillate.

2. The instrument as recited in claim 1, wherein the ultrasonic actuator is configured to drive the cantilever to oscillate substantially at the resonant frequency of the cantilever or a harmonic thereof.

3. The instrument as recited in claim 2, wherein at least a free end portion of the cantilever is configured to be submerged in a liquid.

4. The instrument as recited in claim 1, wherein the instrument is configured to transmit an RF oscillation signal to the ultrasonic actuator, and wherein the amplitude of the RF oscillation signal is adjustable to provide an adjustable force to the cantilever.

5. The instrument as recited in claim 4, wherein the ultrasonic transducer has a modulation frequency bandwidth of at least 1 MHz.

6. The instrument as recited in claim 5, wherein the ultrasonic transducer has a modulation frequency bandwidth of at least 5 MHz.

7. The instrument as recited in claim 4, wherein the ultrasonic transducer has a modulation frequency bandwidth of at least 50 kHz.

8. The instrument as recited in claim 4, further comprising a second actuator configured to drive the cantilever to oscillate, and wherein the instrument is switchable between a first state in which an oscillating drive voltage is supplied to modulate the RF excitation to the ultrasonic actuator and a second state in which an oscillating drive voltage is supplied to the second actuator.

9. The instrument as recited in claim 1, further comprising a detector that is configured to detect cantilever deflection.

10. The instrument as recited in claim 9, wherein the cantilever and the detector are positioned on a common side of the cantilever disposed opposite a sample holder, and wherein the ultrasonic actuator comprises a first ultrasonic actuator, and further comprising a second ultrasonic actuator configured to direct a beam of ultrasonic energy at the cantilever, wherein the first and second ultrasonic actuators flank a longitudinal centerline of the cantilever.

11. The instrument as recited in claim 9, wherein the detector comprises a photodetector configured to detect a light beam reflected from the cantilever.

12. The instrument as recited in claim 1, wherein the cantilever comprises one of an array of cantilevers, and wherein multiple ultrasonic actuators are provided for directing beams of ultrasonic energy at multiple cantilevers of the array.

13. The instrument as recited in claim 1, wherein the cantilever comprises one of an array of cantilevers, and wherein a single ultrasonic actuator is provided for directing a beam of ultrasonic energy at one or more cantilevers of the array.

15. The instrument as recited in claim 13, wherein the modulated RF signal has a bandwidth of at least 50 kHz.

14. A metrology instrument comprising:

(A) a cantilever;

(B) an ultrasonic actuator configured to direct a beam of ultrasonic energy at the cantilever so as to drive the cantilever to oscillate;

(C) an RF excitation signal; and

(D) a modulation signal generator configured to generate a modulation signal that modulates the amplitude of the RF excitation signal to produce a modulated RF signal that is transmitted to the ultrasonic actuator.

16. The instrument as recited in claim 14, wherein the modulated RF signal has a bandwidth of at least 1 MHz.

17. A scanning probe microscope (SPM) comprising:

(A) a probe including a cantilever;

(B) an ultrasonic actuator coupled to the probe so as to drive the cantilever in a selected mode of SPM operation, wherein, when driving the cantilever, the frequency response of the cantilever has amplitude peaks at substantially only the fundamental resonance of the cantilever and harmonics of the fundamental resonance.

22. The method as recited in claim 17, wherein at least a free end of the cantilever is immersed in a liquid during the transmitting step, and further comprising reconfiguring the cantilever so that it is not immersed in a liquid and driving the cantilever to oscillate using a second actuator.

23. The method as recited in claim 17, further comprising detecting cantilever deflection.

24. The method as recited in claim 22, further comprising taking elasticity measurements using data collected as a result of the detecting step.

18. A method comprising:

(A) generating a beam of ultrasonic energy using an ultrasonic actuator;

(B) transmitting the beam onto a cantilever of a probe of a metrology instrument to impose a force on the cantilever so as to drive the cantilever to oscillate.

19. The method as recited in claim 18, wherein the cantilever is driven to oscillate at the resonant frequency of the cantilever or a harmonic thereof.

20. The method as recited in claim 18, further comprising adjusting a drive frequency supplied to the ultrasonic actuator through a range at least 50 kHz.

21. The method as recited in claim 19, further comprising focusing the beam onto a region of the cantilever so as to produce peak deflection when the cantilever is oscillated in a second or higher order resonance mode.