Atomic force microscope and driving method therefor

Details Atomic force microscope and driving method therefor Atomic force microscope and driving method therefor

2001-12-05

2004-03-23

Raevis, Robert (Department: 2856)

Measuring and testing

Surface and cutting edge testing

Roughness

Reexamination Certificate

active

06708556

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to an atomic force microscope and a driving method therefor; and, more particularly, to an atomic force microscope equipped with plural scanning probes capable of observing the topography of a sample at high speed with a high resolution under the atmospheric pressure and to a driving method therefor.
DESCRIPTION OF THE PRIOR ART
A variety of techniques have been utilized to observe the topography of a surface, such as the surface of a semiconductor device. A scanning probe microscope such as an atomic force microscope (AFM) is a microscope capable of observing a surface with a high resolution in nanometer or sub-nanometer range without damaging the surface observed by scanning the surface using, as a feedback signal, a signal generated by the inter-atomic force between the surface observed and a tip provided on a scanning probe, while keeping a constant interval between the surface observed and the tip.
U.S. Pat. No. 5,338,932 entitled “METHOD AND APPARATUS FOR MEASURING THE TOPOGRAPHY OF A SEMICONDUCTOR DEVICE” issued to Theodore et al. discloses an apparatus and method for performing a combination of atomic force microscopy and scanning tunneling microscopy measurements to provide an accurate representation of a surface's topography and a material composition. A variable flexibility probe of the apparatus includes a reference element, a variable stiffness element, a support member, a conductive tip and a force element. A first end of the reference element and a first end of the variable stiffness element are attached to the support member so that the reference and the variable stiffness element form two parallel cantilever arms that project from the support member.
The force element is attached to both the reference and the variable stiffness element. The force element applies a variable force to the variable stiffness element in order to vary the stiffness or spring-constant of the variable stiffness element. Although the variable flexibility probe can perform a combination of atomic force microscopy and scanning tunneling microscopy measurements, it would be difficult to downscale the dimension of the variable flexibility probe in order to construct a system employing a plurality of the variable flexibility probes, since the variable flexibility probe is made of two parallel cantilever arms separated from each other with a small gap and including the force element therebetween.
U.S. Pat. No. 5,468,959 entitled “SCANNING PROBE MICROSCOPE AND METHOD FOR MEASURING SURFACES BY USING THIS MICROSCOPE” issued to Tohda et al. discloses a scanning probe microscope of advanced functions combining atomic force microscopy and scanning tunneling microscopy equipped with an active cantilever and a method for observing surfaces by using this microscope. This microscope may be operated at the atmospheric pressure, however, it will be preferable to place this microscope in a super-high vacuum if a measurement for obtaining detailed information of a clean sample surface is required. While this microscope has an advantage capable of being operated under the atmospheric pressure, it would be difficult to downscale the dimension of a scanning probe employed in the microscope since the scanning probe has a large structure for varying a stiffness or spring-constant of the scanning probe as similar to the one by Theodore et al.
U.S. Pat. No. 5,723,775, entitled “ATOMIC FORCE MICROSCOPE UNDER HIGH SPEED FEEDBACK CONTROL” issued to Watanabe et al. discloses an atomic force microscope (AFM) capable of performing a high-speed feedback control achieved by decreasing the mass of a cantilever including an axial driving actuator while eliminating drawbacks caused by the decrease in mass. The AFM scans the structure of a sample to be observed while keeping the constant interval between the surface of the sample and a tip provided on a scanning probe. However, an image representing the topography of the sample surface will be degraded when the tip is contaminated by impurities, e.g., dusts, drops of water and the like which may exist on the surface of the sample observed under the atmospheric pressure.
As described above, none of the aforementioned patents teach a system with plural scanning probes and a driving method therefor capable of observing the topography of a sample surface. When a system employing plural scanning probes is constructed by employing one of techniques described in the aforementioned patents, it will end up to be an expensive and bulky system. Therefore, it is desirable to provide a system, which is inexpensive and of a compact size, with plural scanning probes and a driving method therefor in order to observe the topography of a sample surface at high speed with a high resolution under the atmospheric pressure.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an atomic force microscope capable of observing the topography of a sample at high speed with a high resolution under the atmospheric pressure and a driving method therefor.
In accordance with one aspect of the present invention, there is provided an atomic force microscope (AFM) capable of observing the topography of a sample surface at high speed with a high resolution under the atmospheric pressure, comprising: a plurality of scanning probes for measuring the sample surface, wherein each of the scanning probes includes a cantilever having a tip and a first and a second actuator; means for detecting a light beam reflected from said each of the scanning probes to convert same into a first signal depending on a second signal; and means for driving the scanning probes by generating a third and a fourth signal and detecting information regarding the topography of the sample surface, wherein the first actuator performs a tapping operation in response to the third signal, the second actuator performs a positioning operation in response to the fourth signal and the frequency of the third signal is higher than that of the fourth signal.
In accordance with another aspect of the present invention, there is provided an atomic force microscope capable of observing the topography of a sample surface at high speed with a high resolution under the atmospheric pressure, comprising: a scanning probe matrix having N×M scanning probes thereon for measuring the sample surface, wherein each of the scanning probes includes a cantilever having a tip and a first and a second actuator, N and M being positive integers greater than 1, respectively; means for detecting a light beam reflected from said each of the scanning probe's to convert same into an electrical signal; and means for driving the scanning probes by generating a reference and a servo signal and detecting information regarding the topography of the sample surface, wherein the first actuator performs a tapping operation in response to the reference signal, the second actuator performs a positioning operation in response to the servo signal and the frequency of the reference signal is higher than that of the servo signal.
In accordance with still another aspect of the present invention, there is provided a method for driving an atomic force microscope (AFM) with plural scanning probes capable of observing the topography of a sample surface at high speed with a high resolution under the atmospheric pressure, comprising the steps of: a) vibrating, responsive to a reference signal, a first actuator provided on each of the scanning probes; b) detecting a deflection amount of a cantilever provided with a tip at its free end; and c) transmitting a servo signal to a second actuator based on the deflection amount of the cantilever, wherein the cantilever provided on said each of the scanning probes and the first and second actuator are provided on the cantilever opposite to the free end where the tip is provided.


REFERENCES:
patent: 5723775 (1998-03-01), Watanabe et al.
patent: 5902928 (1999-05-01), Chen et al.
patent: 5986262 (1999-11-01), Volcker
patent: 6094972 (2000-08-01),

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