Measuring and testing – Surface and cutting edge testing – Roughness
Patent
1996-10-03
1998-09-08
Noland, Thomas P.
Measuring and testing
Surface and cutting edge testing
Roughness
250306, G01B 734
Patent
active
058047093
DESCRIPTION:
BRIEF SUMMARY
This invention relates generally to to means for measuring the forces and/or deflections of cantilever type elements, as encountered for example in the field of Atomic Force Microscopy (AFM). The invention further relates to a method and apparatus for determining material properties. In particular, it relates to a dopant profiler based on a scanning probe microscope involving the generation and detection of higher harmonics of an applied electromagnetic field.
BACKGROUND OF THE INVENTION
The Atomic Force Microscope as first known from the U.S. Pat. No. 4,724,318 and further described by G. Binnig, C. F. Quate and Ch. Gerber in Phys. Rev. Letters, Vol.56, No.9, March 1986, pp.930-933, employs a sharply pointed tip attached (to a spring-like cantilever beam to scan the profile of a surface to be investigated. At the distances involved, minute forces occur between the atoms at the apex of the tip and those at the surface, resulting in a tiny deflection of the cantilever. In U.S. Pat. No. 4,724,318, this deflection is measured by means of a tunneling microscope, i.e., an electrically conductive tunnel tip is placed within tunneling distance from the back of the cantilever beam made also conductive, and the variations of the tunneling current are used to determine the deflection. With known characteristics of the cantilever beam, the forces occurring between the AFM tip and the surface under investigation can be determined.
The forces occurring between a pointed tip and a surface are usually described as van-der-Waals, covalent, ionic, or repulsive core interaction forces.
An important aspect of AFM is to accurately determine the deflection of the cantilever. One group of these defection measuring methods is based on coupling the cantilever to another distance sensitive microscope. A combination of the cantilever with a scanning tunneling microscope is described, for example, in the above mentioned patent U.S. Pat. No. 4,724,318. Another approach using an evanescent wave coupling sensor, also known as scanning near-field optical microscope (SNOM) or scanning tunneling optical microscope (STOM), is described by Diaspro and Aguilar in: Ultramicroscopy 42-44 (1992), pp. 1668-1670.
Another group of detecting methods is based on the well known piezoelectric or piezoresistive effect. An example is described in: M. Tortonese et al., Appl. Phys. Lett. 62(8), 1993, pp.834-836. These methods provide detection schemes in which the deflection detector is integrated in the cantilever.
Yet another feasible way of detecting the displacement of the cantilever relies on capacitance sensing and is known, for example, from Joyce et al., Rev. Sci. Instr. 62(1991), p. 710, and Goddenhenrich et al., J. Vac. Sci. Technol. A8(1990), p. 383, and the European patent application EP-A-0 290 648.
By this application as well as from U.S. Pat. No. 4,851,671 methods are known use the changes in the resonance frequencies of the flexible element and higher harmonics thereof to measure its bending. The frequencies are detected either by a quartz oscillator or by a capacitance additionally attached to the cantilever.
The displacement of the flexible element can also be measured by applying optical methods, such as beam deflection or interferometry. The beam deflection method makes use of the length of the lever. Usually, a light beam, preferably produced by a laser diode or guided through an optical fiber, is directed onto the lever. A small deflection of the lever causes a reasonable change in the reflecting angle and, therefore, results in a deflection of the reflected light beam that is measured with bicell or other suitable photo detectors. The beam deflection method is simple and reliable. It is described, for example, by Myer and Amer in Appl. Phys. Lett. 53 (1988), pp.1045-1047. Interferometric methods are described, for example, by Martin et al., J. Appl. Phys. 61(1987), p.4723, by Sarid et al., Opt.Lett. 12(1988), p.1057, and by Oshio et al., Ultramicroscopy 42-44(1992), pp.310-314. As the sensitivity of the SPM can be increased by bu
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Bourgoin Jean-Philippe M.
Johnson Matthew B.
Michel Bruno
International Business Machines - Corporation
Noland Thomas P.
Strunck Stephen S.
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