Scanning probe microscope and method for obtaining topographic image, surface potential image, and electrostatic capacitance distribution image

• US 5,742,172 A
• Filed: 10/11/1996
• Issued: 04/21/1998
• Est. Priority Date: 05/23/1994
• Status: Expired due to Fees

• Current Assignee: SII NanoTechnology Inc. (Hitachi High- Tech Corporation)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Yasutake, Masatoshi
• Primary Examiner(s): Nguyen, Vinh P.
• Application Number:
  US08/728,942
• Time in Patent Office: 557 Days
• Field of Search: 324/73.1, 324/158.1, 324/754, 324/758, 324/767, 324/662, 324/750, 250/306, 250/307, 250/423 F, 250/443.1, 73/105
• US Class Current: 324/750.22
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01B 7/34 for measuring roughness or irregularity of surfaces
• CPC Class Codes: G01N 27/24 Investigating the presence of flaws
• CPC Class Codes: G01Q 60/30 Scanning potential microscopy
• CPC Class Codes: G01Q 60/40 Conductive probes
• CPC Class Codes: G01Q 60/48 Probes, their manufacture, or their related instrumentation, e.g. holders
• CPC Class Codes: G01R 29/12 Measuring electrostatic fields or voltage-potential
• CPC Class Codes: Y10S 977/851 Particular movement or positioning of scanning tip
• CPC Class Codes: Y10S 977/852 for detection of specific nanostructure sample or nanostructure-related property

Abstract

A scanning probe microscope used for obtaining a surface topographical image, a surface potential image and an electrostatic capacitance distribution includes a probe having a tip attached to a lever, an oscillator for oscillating the probe in close proximity to a specimen, a displacement detector for detecting the probe oscillations and outputting a displacement signal in accordance therewith, a positioning device for relative positioning of the probe tip with respect to the specimen in the X and Y directions and for controlling the distance between the probe tip and the specimen in the Z direction, an AC voltage source for applying an AC voltage between the probe to oscillate the probe at a composite frequency having components at ω and 2ω, a DC voltage source for applying a DC voltage between the probe and the specimen to maintain the ω amplitude component of the probe oscillation at zero to enable the calculation of a surface potential of the specimen in accordance with the DC voltage and to enable the calculation of an electrostatic capacitance between the specimen and the probe in accordance with the 2ω amplitude component of the probe oscillation, and a display device responsive to the phase difference between an output of the oscillator and the displacement signal for indicating when the probe collides with the surface of the specimen.

Claims

1. A scanning probe microscope comprising:

a probe extending in a Z direction attached to an electroconductive lever;

oscillator means for producing a resonance signal to oscillate the probe at a resonance frequency ω

r thereof in close proximity to a specimen;

displacement detecting means for detecting the lever vibration and producing a corresponding displacement signal according to a change in a resonant amplitude and phase around the resonance frequency ω

r of the lever;

positioning means responsive to the displacement signal for scanning one of the probe and the specimen in X and Y directions and extending and retracting one of the probe and the specimen in the Z-direction so as to control the relative distance between the probe and the specimen;

means for vibrating the lever at an applied angular frequency ω and

at a doubled angular frequency 2ω

by use of electrostatic coupling between the probe and the specimen;

means for applying a DC voltage between the specimen and the probe so as to maintain the average amplitude of an ω

-component of the probe vibration at zero to permit detection of a surface potential of the specimen in accordance with the DC voltage and to permit detection of an electrostatic capacitance of the specimen;

displacement phase detecting means for detecting the respective amplitude components of said lever vibration and a phase difference between an ω

r component of said lever vibration and that of an output of said oscillator means, and for multiplying the phase difference component and the amplitude of the ω

r component, the multiplied value being input to said positioning means for controlling the Z-direction distance between the probe and the specimen in order to keep the multiplied value constant, so that the collision of the probe and a surface of the specimen can be detected since such a collision results in the positioning means separating the probe and the specimen rapidly due to a large phase delay in response to the collision.

2. A scanning probe microscope according to claim 1;

wherein the positioning means includes means for scanning the probe across the surface of the specimen in the X and Y directions and adjusting the distance between the specimen and the probe in the Z-direction to set a different distance depending upon whether a measured characteristic is a surface topography or one of a surface potential and an electrostatic capacitance in order to obtain a surface configuration image, a surface potential image and an electrostatic capacitance distribution image having an optimized resolution.

3. A scanning probe microscope according to claim 1;

further comprising an electric voltage supply; and

means for selectively activating and deactivating the electric voltage supply in cooperation with the positioning means for applying a potential distribution across the specimen for each pixel or each line scanned by the positioning means in the X and Y directions so as to measure an electric response of the specimen and to remove a contact potential caused by a difference in materials of the probe and the specimen.

4. A scanning probe microscope comprising:

a probe having a lever and a probe tip, the probe tip being disposable proximate a surface of a specimen;

an oscillator for oscillating the probe at a resonant frequency ω

_r of the probe;

AC signal generating means for applying an AC voltage between the probe tip and the specimen to generate an alternating electrostatic force to oscillate the probe at a composite frequency having an amplitude component at a first frequency ω and

an amplitude component at a second frequency 2ω

;

displacement detecting means for detecting an amplitude and a frequency of oscillation of the probe;

displacement phase detecting means receptive of outputs from the displacement detecting means, the oscillator, and the AC signal generating means for detecting the respective amplitude components at frequencies ω

_r, ω and

2ω

of the probe oscillation and for determining a phase difference between the amplitude component at ω

_r and an output signal of the oscillator;

positioning means responsive to the phase difference for rapidly separating the probe and the sample when the probe tip comes in contact with the sample;

such that a surface potential image of the specimen may be produced in accordance with the ω

amplitude component of the probe oscillation, an electrostatic capacitance distribution image of the specimen may be produced in accordance with the 2ω

component of the probe oscillation, and a topographical surface profile image of the specimen may be produced in accordance with the ω

_r component of the probe oscillation.

5. A scanning probe microscope according to claim 4;

further comprising DC voltage generating means for applying a DC voltage between the specimen and the probe so as to maintain the ω

amplitude component of the probe vibration at zero; and

means for determining a surface potential of the specimen in accordance with an output of the DC voltage generating means.

6. A scanning probe microscope according to claim 4;

further comprising calibration means including a DC voltage supply for applying a DC voltage between the specimen and the probe tip to obtain the surface potential of the specimen.

7. A scanning probe microscope according to claim 4;

wherein the AC signal generating means includes means for applying a different AC signal between the probe tip and the specimen depending upon whether a measured characteristic is a surface topography, a surface potential, or an electrostatic capacitance, so as to produce a topographical image, a surface potential image, and an electrostatic capacitance distribution image at an optimized resolution.

8. A scanning probe microscope according to claim 7;

further comprising means for applying a potential distribution across the specimen to test the electrical response of the specimen.

9. A scanning probe microscope according to claim 8;

further comprising DC voltage generating means for applying a DC voltage between the specimen and the probe so as to maintain the ω

amplitude component of the probe vibration at zero; and

means for determining a surface potential of the specimen in accordance with an output of the DC voltage generating means.

10. A scanning probe microscope according to claim 9;

wherein the means for applying a potential distribution comprises a voltage supply having a pair of contacts electrically connectable to the specimen, one of the contacts being further connected to a ground terminal of the DC voltage generating means.

11. A scanning probe microscope comprising:

a probe having a probe tip attached to an electroconductive lever;

oscillator means for oscillating the probe in close proximity to a specimen;

displacement detecting means for detecting the probe oscillation and outputting a displacement signal in accordance with a change of a resonant amplitude of the probe and a phase of the probe oscillation around a resonance frequency of the lever;

positioning means for relative positioning of the probe tip with respect to the specimen in X and Y directions and for controlling the distance between the probe tip and the specimen in a Z direction;

means for applying an AC voltage between the probe and the specimen to generate an alternating electrostatic force to oscillate the probe at a first amplitude component having a first frequency ω and

a second amplitude component having a second frequency 2ω

;

means for applying a DC voltage between the probe and the specimen so as to maintain the average value of an ω

amplitude component of the probe oscillation at zero to enable the calculation of a surface potential of the specimen in accordance with the DC voltage and to enable the calculation of an electrostatic capacitance of;

wherein the positioning means is responsive to a phase difference between an output of the oscillator means and the displacement signal for rapidly separating the probe and the specimen due to a large phase delay when the probe collides with a surface of the specimen to thereby enable detection that a measured value at that point is inaccurate and to enable the setting of a correct control parameter to control the distance between the probe and the sample in the Z direction in order to avoid a variation in the measured surface potential of the specimen due to the collision.

12. A scanning probe microscope according to claim 11;

wherein the means for supplying an AC voltage between the probe and the specimen includes means for setting a different AC voltage depending upon whether a measured characteristic is a surface topography, a surface potential, or an electrostatic capacitance, so as to produce topographical image, a surface potential image, and an electrostatic capacitance distribution image at an optimized resolution.

13. A scanning probe microscope according to claim 11;

wherein the positioning means includes means for setting the distance between the probe and the specimen in the Z-direction to a different value depending upon whether a measured characteristic is a surface topography, or one of a surface potential and an electrostatic capacitance in order to obtain a topographical image, a surface potential image, and an electrostatic capacitance image at an optimized resolution.

14. A scanning probe microscope according to claim 11;

wherein an electrostatic coupling force between the probe and the specimen is defined by the following equation;

##EQU9## wherein F_es denotes the electrostatic coupling force, C denotes an electrostatic capacitance between the probe and the specimen, V_S denotes a surface potential of the specimen to be measured, V_off denotes a DC voltage applied by the means for applying a DC voltage between the probe and the specimen and V_AC sin ω

t denotes an AC voltage applied between the probe and the specimen by the means for vibrating the probe.

15. A scanning probe microscope according to claim 11;

wherein the change in resonant amplitude of the probe is defined by the following equation;

##EQU10## wherein Δ

A denotes the change in resonant amplitude caused by Van der Waals forces between the probe and the specimen, A₀ denotes a constant resonant amplitude of probe vibration, Q is a Q value of the lever, K denotes an elastic constant of the lever and F_vdw denotes a Van der Waals force between the probe and the specimen.

16. A scanning probe microscope according to claim 15;

wherein the positioning means includes means for controlling a Z-direction distance between the probe and the specimen so as to keep the average value of Δ

A constant while scanning one of the probe and the specimen in the X and Y directions to carry out an image scanning to obtain a topographic image under constant Van der Walls forces and constant electrostatic forces.

17. A scanning probe microscope according to claim 15;

wherein the means for applying a DC voltage between the specimen and the probe includes means for controlling the DC potential between the specimen and the probe such that V_S =-V_OFF such that an amplitude component at frequency ω

is maintained at zero to thereby enable calculation of the surface potential of the specimen.

18. A scanning probe microscope according to claim 11;

wherein the positioning means comprises a three-directional scanner for controlling a Z-direction gap between the specimen and the probe and relatively scanning in the X and Y directions between the specimen and the probe, Z-direction servo control means for controlling the Z-direction movement of the three-directional scanner, and X and Y scan control means for controlling the X and Y movement of the three-directional scanner.

19. A scanning probe microscope according to claim 18;

wherein the displacement phase detecting means includes means for multiplying an output of the oscillator means and the displacement signal and producing a multiplied output signal, filter means for filtering out a high frequency component of the multiplied output signal and producing a filtered output signal.

20. A scanning probe microscope according to claim 18;

wherein the Z-direction servo control means includes means for controlling the three-directional scanner to maintain the filtered output signal constant.

21. A method for obtaining a surface topographical profile, a surface potential distribution and an electrostatic capacitance distribution of a specimen using a scanning probe microscope having a probe comprising an electroconductive lever and a probe tip, the probe tip being disposable proximate a surface of the specimen, the method comprising the steps of:

applying a resonance signal having a frequency ω

_r to oscillate the probe at a resonance frequency thereof in close proximity to a surface of a specimen;

applying an AC voltage between the probe and the specimen to generate an alternating electrostatic force to oscillate the probe at a composite frequency having an amplitude component at a first frequency ω and

an amplitude component at a second frequency 2ω

;

detecting the respective amplitude components at frequencies ω

_r, ω and

2ω

of the probe oscillation;

determining a phase difference between the frequency component at ω

_r and the resonance signal;

detecting inaccurate data when the probe comes into contact with the specimen in accordance with the phase difference between the amplitude component at ω

_r and the resonance signal;

producing a surface potential distribution of the specimen in accordance with the ω

component of the probe oscillation by scanning the probe with respect to the .specimen while measuring the surface potential of the specimen;

producing an electrostatic capacitance distribution of the specimen in accordance with the 2ω

component of the probe oscillation by scanning the probe with respect to the specimen while measuring the electrostatic capacitance of the specimen; and

producing a topographical surface profile of the specimen in accordance with the ω

_r component of the probe oscillation by scanning the probe with respect to the specimen.

22. A method according to claim 21;

further comprising the steps of preventing the specimen and the probe from being contaminated by moisture and dust, measuring a surface potential of a standard specimen coated with the same conductive material as the probe, measuring the surface potential of the specimen, and subtracting therefrom the potential of the standard specimen to determine an absolute surface potential of the specimen.

23. A method according to claim 21;

further comprising the steps of measuring a first surface potential of the specimen while applying a voltage potential across the specimen, measuring a second surface potential of the specimen without a voltage potential applied thereacross, and subtracting the second surface potential from the first surface potential to thereby determine the electrical response of the specimen.

24. A method according to claim 21;

further comprising the step of varying a distance between the probe and the specimen depending upon whether a measured characteristic is a surface topography, or one of a surface potential and an electrostatic capacitance, in order to obtain a topographical image, a surface potential image, and an electrostatic capacitance distribution image at optimized resolutions.