Automated atomic force microscope and the operation thereof

• US 9,921,242 B2
• Filed: 07/05/2016
• Issued: 03/20/2018
• Est. Priority Date: 04/21/2014
• Status: Active Grant

• Current Assignee: Oxford Instruments Asylum Research Inc (Oxford Instruments PLC)
• Original Assignee: Oxford Instruments Asylum Research Inc (Oxford Instruments PLC)
• Inventors: Proksch, Roger, Callahan, Roger C., Stetter, Frank, Limpoco, Ted, Hohlbauch, Sophia, Bemis, Jason, Cleveland, Jason, Geiss, Nicholas
• Primary Examiner(s): Stoffa, Wyatt
• Assistant Examiner(s): Chang, Hanway
• Application Number:
  US15/202,445
• Publication Number:
  US 20160313369A1
• Time in Patent Office: 623 Days
• Field of Search: 850 5, 850 6, 850 7, 850 21, 850 33
• CPC Class Codes: G01Q 10/065 Feedback mechanisms, i.e. wherein the signal for driving the probe is modified by a signal coming from the probe itself
• CPC Class Codes: G01Q 40/00 Calibration, e.g. of probes
• CPC Class Codes: G01Q 60/24 AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
• CPC Class Codes: G01Q 60/32 AC mode
• CPC Class Codes: G01Q 70/08 Probe characteristics

Abstract

Improvements for rapidly calibrating and automatically operating a scanning probe microscope are disclosed. A central component of the SPM is the force transducer, typically a consumable cantilever element. By automatically calibrating transducer characteristics along with other instrumental parameters, scanning parameters can be rapidly and easily optimized, resulting in high-throughput, repeatable and accurate measurements. In contrast to dynamic optimization schemes, this can be accomplished before the surface is contacted, avoiding tip or sample damage from the beginning of the measurement process.

Claims

1. A cantilever based measuring instrument apparatus, comprising:

a cantilever based instrument that has a cantilever, where the cantilever is driven by a driving signal to measure a surface, and the instrument uses a feedback loop with a signal from the cantilever, said feedback loop having a controllable gain;

a computer based controller, operating to measure and produce sensitivity information about the cantilever without touching the surface, where said sensitivity information is a function of said gain in the feedback loop; and

said controller accepting a setting of desired gain, and based on said setting of desired gain, estimating parameters to drive the cantilever based instrument to measure said surface using said sensitivity information and said amount of desired gain, by using a tip of the cantilever to measure characteristics of the surface.

2. The apparatus as in claim 1, wherein said computer based controller operates to find said sensitivity information in a dynamic environment where the sensitivity depends on distance to a sample, and determining a dynamic optical lever sensitivity based on an inverse optical lever sensitivity, herein invOLS, of said cantilever.

3. The apparatus as in claim 1, wherein said computer based controller determines a relationship between optical lever sensitivity and gain to produce said sensitivity information.

4. The apparatus as in claim 3, wherein said computer based controller obtains a frequency spectrum of Brownian movement, and uses said frequency spectrum to determine said sensitivity.

5. The apparatus as in claim 1, wherein said computer based controller measures said characteristics of the sample by adjusting a gain of the feedback loop, to control a separation between a tip and the sample based on an error signal that is based on at least one gain parameter that is estimated from the measured sensitivity.

6. The apparatus as in claim 1, wherein said computer based controller determines a relationship by estimating a first spring constant of the cantilever using one technique that depends on detection sensitivity and estimating a second spring constant with a second technique different than the first technique, and estimating a sensitivity of the cantilever detection by comparing the first spring constant against the second spring constant.

7. The apparatus as in claim 1, wherein said cantilever based instrument is an Atomic Force Microscope.

8. The apparatus as in claim 1, wherein said computer based controller calculates and outputs cantilever excitation parameters, including drive amplitude, frequency and phase;

and controls a gain of the feedback loop, based on the sensitivity information and the setting of desired gain.

9. A method of operating a cantilever based measuring instrument, comprising:

using a computer for obtaining a relationship between an optical lever sensitivity of a cantilever of the cantilever based instrument, where the sensitivity depends on distances to a sample, and where said relationship is measured without touching the sample;

using said relationship to determine an optical lever sensitivity value, invOLS of said cantilever; and

measuring characteristics of a surface of the sample, said invOLS value, by using a tip of the cantilever to measure characteristics of the surface and by estimating parameters of gain in the measurement based on the invOLS value for the cantilever used to measure.

10. The method as in claim 9, further comprising receiving a user setting of gain amount, which selects between a first gain that has high level of risk of instability, and a second gain that has lower level of risk of instability, and using said user setting to produce outputs representing said parameters of gain based on the invOLS value and the user setting.

11. The method as in claim 9, wherein said obtaining a relationship comprises obtaining a frequency spectrum of Brownian movement, and using said frequency spectrum to determine said sensitivity.

12. The method as in claim 9, wherein said obtaining a relationship comprises obtaining a frequency spectrum based on a driven cantilever, and using said frequency spectrum to determine said sensitivity.

13. The method as in claim 9, further comprising determining a spring constant of the cantilever to determine said relationship, by estimating a first spring constant of the cantilever using one technique that depends on detection sensitivity and estimating a second spring constant with a second technique different than the first technique, and estimating a sensitivity of the cantilever detection by comparing the first spring constant against the second spring constant.

14. The method as in claim 9, further comprising using said computer to calculate and output cantilever excitation parameters, including drive amplitude, frequency and phase;

and controlling a gain of a feedback loop used in said measuring, based on the sensitivity information and the setting of desired gain.

15. A cantilever based measuring instrument apparatus, comprising:

a cantilever based instrument that has a cantilever, where the cantilever is driven by a driving signal to measure a surface, and the instrument uses a feedback loop with a signal from the cantilever, said feedback loop having a controllable gain;

a computer based controller for the cantilever based instrument, said controller producing outputs that control cantilever excitation parameters, and control a gain of said feedback loop used for measuring said surface,

said controller operating to measure and produce sensitivity information about the cantilever,

said controller accepting a setting of desired gain, including a first value that indicates a high level of risk for instability in the feedback loop, and a second value that indicates a lower level of risk for instability in the feedback loop, and said controller using said setting of desired gain and said sensitivity information to produce said cantilever excitation parameters and a gain value, and receiving values by using a tip of the cantilever to measure characteristics of the surface to measure characteristics of the surface.

16. The apparatus as in claim 15, wherein said computer based controller calculates and outputs said cantilever excitation parameters, including drive amplitude, frequency and phase;

and controls a gain of the feedback loop, based on the sensitivity information and the setting of desired gain.

17. The apparatus as in claim 16, wherein said computer based controller operates to find said sensitivity information in a dynamic environment where the sensitivity depends on distances to a sample, and using said relationship to determine a dynamic optical lever sensitivity based on an inverse optical lever sensitivity, herein invOLS, of said cantilever.

18. The apparatus as in claim 16, wherein said computer based controller estimates a first spring constant of the cantilever using one technique that depends on detection sensitivity and estimates a second spring constant with a second technique different than the first technique, and uses said first and second spring constants using both techniques being the same as part of determining the sensitivity information.

19. The apparatus as in claim 16, wherein said cantilever based instrument is an Atomic Force Microscope.