Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
1999-03-19
2002-07-09
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
C250S306000, C216S002000, C216S011000
Reexamination Certificate
active
06415653
ABSTRACT:
BACKGROUND OF THE INVENTION
A scanning probe microscope (SPM) is an apparatus for performing three-dimensional mapping of an interaction (atomic force, contact force, etc.) between a probe and a sample surface by scanning the probe or the sample in the XY or XYZ directions, while detecting the interaction between the probe and the sample surface, when they are in close proximity or contact to each other. SPM is the general term for a scanning tunneling microscope (STM), an atomic force microscope (AFM), a magnetic force microscope (MFM), and a scanning near-field optical microscope (SNOM). In particular, the AFM is most widely used of all the SPMs as an apparatus for obtaining information on configuration on a sample surface.
The AFM comprises a cantilever including a lever portion, a free end of which has a sharp projection (a probe having a sharp point), and the other end of which is fixed. The cantilever is brought into close proximity to a sample, such that the tip of the probe faces the surface of the sample. While the sample or the cantilever is scanned in the XY directions, the amount of displacement of the probe and the amount of elastic deformation (flexibility) of the lever portion, which vary due to an interaction (atomic force, contact force, etc.) between atoms at the tip of the probe and on the surface of the sample, are electrically or optically detected and measured. Thus, information on the sample, e.g., configuration, is detected three-dimensionally by relatively changing the positional relationship between the probe of the cantilever and the sample.
A method for detecting an amount of elastic deformation (flexibility) of the lever portion of an SPM is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publications Nos. 5-340718 and 9-15250, the contents of which are incorporated herein by reference. The detection of the amount of flexibility of the lever portion, disclosed in these references, is performed by means of a known “displacement detecting sensor of an optical lever system”. In connection with the detection of the amount of flexibility of the lever portion, “a method for detecting defocus by means of a critical angle prism”, “a displacement detecting sensor utilizing an optical interferometer”, etc. are also known.
The SPM measurement by means of the displacement detecting sensor is performed as follows. A probe is scanned over a measurement region of a sample in the XY directions. The amount of flexibility of the lever portion in the measurement region is detected by the displacement detecting sensor whenever necessary. The detected amount of flexibility is imaged at resolution of an atomic level as sample information, such as configuration or magnetic power of the surface of the sample, and displayed on a monitor.
Cantilevers used in such an SPM have been mainly produced by an applied semiconductor IC manufacturing process, since the process was proposed, as disclosed in Thomas R. Albrecht and Calvin F. Quate, “Atomic Resolution Imaging of a Nonconductor by Atomic Force Microscopy”, J. Appl. Phys. 62 (1987), page 2599. This is because the process allows a cantilever to be produced with high accuracy in the order of microns at low cost by using a batch process.
The cantilevers on the market now include the following two types: cantilevers made of silicon nitride; and cantilevers made of silicon. The mainstream of the silicon nitride cantilevers is described in Thomas R. Albrecht et al., “Microfabrication of Cantilever Styli for the Atomic Force Microscope”, J. Vac. Sci. Technol. A8, 3386 (1990). A detailed method for fabricating this type of cantilever is disclosed in U.S. Pat. No. 5,399,232, the contents of which are incorporated herein by reference. The mainstream of the silicon cantilevers is described in O. Wolter et al., “Micromachined Silicon Sensors for Scanning Force Microscopy”, J. Vac. Sci. Technol. B9, 1353 (1991). A detailed method for fabricating this type of cantilever is disclosed in U.S. Pat. No. 5,051,379, the contents of which are incorporated herein by reference.
[Problem 1A]
To fabricate a silicon nitride cantilever, first, a lever base material of silicon nitride and a supporting portion to be attached to an apparatus are produced separately, and then the two parts are adhered by anode adhesion or the like. The portion of the lever base material, which is not adhered to the supporting portion, functions as a lever portion.
Therefore, the length of the lever portion varies depending on accuracy of the adhesion between the lever base material and the supporting portion. The anode adhesion causes variance of about 10-30 &mgr;m in length of the portion where the lever base material adheres to the supporting portion. Accordingly, variance in length of the lever portion is about 10-30 &mgr;m in the silicon nitride cantilever.
To fabricate a silicon cantilever, a lever portion is formed by dry etching from one side of a silicon wafer, and a supporting portion made of silicon is formed by wet anisotropic etching from the other side on which the lever portion is not formed.
The length of the lever portion depends on the thickness of the silicon wafer, and displacement of a lever portion forming mask and a supporting portion forming mask formed on both sides of the silicon wafer. In general, variance in thickness of silicon wafers available on the market is at least 10 &mgr;m. Further, the displacement of the aforementioned masks formed on both sides of a silicon wafer is about 10 to 20 &mgr;m. Consequently, variance in length of the lever portion is about 10 to 30 &mgr;m in the silicon cantilever.
Moreover, in the silicon cantilever, variance in thickness of each of the silicon wafers is directly reflected in the thickness of the lever portion. Therefore, in the silicon cantilever, variance in thickness of the lever portion is about 1 &mgr;m.
In the cantilevers used in the SPM measurement, it is necessary that the spring constant of the lever portion be known. Further, in the cantilevers used in the SPM measurement in an oscillation mode for oscillating the cantilever, it is necessary that the resonance frequency, as well as the spring constant, of the lever portion be known. To obtain an accurate result of SPM measurement, it is desirable that variance in both the spring constant and the resonance frequency be little.
The frequency resonance of the lever portion of the cantilever is inversely proportional to the square of the length of the lever portion and proportional to the thickness thereof. The spring constant is inversely proportional to the cube of the length and proportional to the thickness. Therefore, to obtain a cantilever of little variance in the spring constant and the resonance frequency, it is necessary that the length and thickness of the lever portion be deviated as little as possible from the design values. In other words, a technique for forming a lever portion with high accuracy, in respect of the length and thickness, is required.
[Problem 1B]
Recently, an SPM, wherein the sample is raster-scanned at high speed of more than one screen per second, has been widely used by trial for observing microscopic movement of, for example, a biological sample. Further, the SPM technique has been also put to trial for high-density recording. Under these situations, there is a demand for a probe device shaped like a cantilever having a high resonance frequency in order to increase the input and output speeds.
The cantilever used for the SPM measurement at high-speed scanning is required to have a resonance frequency in the order of MHz or higher to increase the scanning speed. Further, the spring constant is required to be 40-50 N/m or smaller to prevent breakage of the probe or the sample in a case of contact therebetween.
In the conventional cantilever generally used in the SPM measurement, a resonance frequency is about 300 kHz, a spring constant is about 20-50 N/m, and a length of the lever portion is 100-200 &mgr;m. Therefore, such a cantilever is not suitable for the resent SPM measurement using high-s
Frishauf Holtz Goodman & Chick P.C.
Larkin Daniel S.
Olympus Optical Co,. Ltd.
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