Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
2002-04-16
2004-02-24
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
C250S306000
Reexamination Certificate
active
06694805
ABSTRACT:
This application claims benefit of Japanese Application No. 2001-119174 filed in Japan on Apr. 18, 2001, the contents of which are incorporated this reference.
BACKGROUND OF THE INVENTION
The present invention relates to a cantilever for use in Scanning Probe Microscopes (SPM), such as Atomic Force Microscopy (AFM).
Scanning Probe Microscopes (SPM) are the apparatus having a resolution of atomic order in measurement and are widely used for example to measure sample surface irregularities. In SPM, a physical quantity, such as tunnel currents or interatomic force, occurring between a probe and a sample is detected and measured. While retaining the probe and the sample at a predetermined distance from each other so as to make constant such measured quantities, the two are scanned relative to each other in the XY direction to measure a fine surface configuration of the sample. A cantilever having the probe at its terminal end is used in such measurement.
Cantilevers for such application are disclosed in Japanese patent laid-open application Hei-1-262403.
FIGS. 1A
to
1
C are each a perspective view showing a certain part of the cantilever disclosed in the publication. Referring to
FIGS. 1A
to
1
C, numerals
101
,
103
, and
105
denote a lever portion and numerals
102
,
104
, and
106
denote a probe portion. The cantilevers shown in
FIGS. 1A and 1B
have the probe portion
102
in the shape of a quadrangular pyramid or the probe portion
104
in the shape of a circular cone in the vicinity of the free end of the lever portions
101
and
103
, respectively. In these cantilevers, neither of the probes
102
,
104
is formed on the free end of the lever portions
101
,
103
. Both are formed in the vicinity of the free end. The cantilever shown in
FIG. 1C
, on the other hand, has the plane-like probe portion
106
at the free end of the lever portion
105
.
Further, the above publication discloses an embodiment where a silicon oxide film or silicon nitride film is used as the material for the lever and probe portions. In the technique disclosed as a fabricating method of the cantilever having the quadrangular pyramid-shaped probe portion
102
, gas shown in
FIG. 1A
, a pit is formed on a silicon substrate; a silicon oxide film or silicon nitride film to become the lever and probe portions is formed on the silicon substrate and in the pit thereof; a support portion consisting of glass is then bonded to the rear of the fixing end of the lever portion, and the silicon substrate is etched away. This method is the so-called microcast method.
Further, a cantilever disclosed in U.S. Pat. No. 5,021,364 is shown in
FIG. 1D
as a typical example of a cantilever having a probe portion formed by an etching process of silicon. While, as shown in
FIG. 1D
, a probe portion
108
is formed on the free end of a lever portion
107
, the probe portion
108
is not of a film. It is provided as a bulk-like probe portion formed of a piece of silicon block.
The above described conventional cantilevers, however, have the following problems: First, of the cantilevers such as those shown in
FIGS. 1A and 1B
where the probe portion
102
,
104
is not formed on the terminal end of the free end of the lever portion
101
,
103
, the probe portion is covered by the lever portion. The probe portion is thus hidden and cannot be seen from the upper side of the cantilever. Accordingly, when these cantilevers are used in SPM, the terminal end of the probe and the measurement point of the object to be measured cannot be simultaneously observed from an optical microscope for use in aligning the sample and the probe portion. Positioning alignment at the micrometer level of the point to be measured thus becomes difficult when the cantilever is set to the SPM apparatus.
Further, since the probe position is not ascertainable, it is not always possible to start the measurement from a desired region on the sample. Since it is manipulated so as to shift the measurement position by a small extent each time, it takes time before the measurement of such a desired region can be made. As a result, a longer time is necessary until the completion of the measurement. Also in some cases, the resolution may be degraded during the scanning for alignment due to the adhering of dust or the like or to the thickening of the probe portion by abrasion with the sample.
In this regard, the probe portion of those cantilevers as shown in
FIGS. 1C and 1D
is located at the terminal end of free end of the lever portion; and the probe portion can be easily brought near to a region to be observed on the sample. In short, it is easy to use. Both of these constructions, however have problems to be mitigated. In particular, since acuteness of the terminal end of the probe of the cantilevers shown in
FIG. 1C
cannot go beyond the resolution of photolithography, it is difficult to achieve a sharp terminal end of the probe which is important in SPM measurement at high resolution. Specifically, it is not easy to achieve a radius of curvature of 50 nm or less for the terminal end of the probe. Further, since the probe portion is in the shape of a triangular flat plate, the probe portion lacks rigidity. When a large force is placed between the sample and the probe portion, deformation occurs not only in the lever portion, but also at the triangular flat plate of the probe portion whereby measurement becomes unstable. If such a cantilever is used in the type of SPM measurement method where the cantilever is kept oscillated, a peak due to a separate oscillation mode occurs in a frequency region relatively near the fundamental frequency. The measurement becomes unstable or is degraded in sensitivity.
Further, the probe portion
108
of the cantilever shown in
FIG. 1D
is a bulk probe portion consisting of silicon. When compared with the other cantilevers shown in
FIGS. 1A
to
1
C, the probe portion becomes heavier for the same probe height. This causes a difficulty in making a cantilever of which the cantilever length is short and the resonance frequency is high. In particular, its terminal end becomes structurally heavier so that the cantilever having a high resonant frequency becomes difficult to be designed.
Further, in SPM measurement, the probe portion of a cantilever is required to have an extremely acute tip to perform high resolution measurement. In this regard, of the probe portion
102
in the shape of a quadrangular pyramid shown in
FIG. 1A
, the tip is difficult to be terminated at a point theoretically because of its structure. It has a problem concerning acuteness of the probe portion. This is because the quadrangular pyramid has four ridgelines extending toward the terminal end of the probe and the four line segments do not theoretically cross each other at a point. Further, for the probe portion in the shape of a circular cone shown in
FIG. 1B
, it is also rather difficult to make the probe portion terminating at a point for a similar reason as the above, if a cone-shaped probe is regarded as resulting from the transition of a quadrangular pyramidal probe to a polygonal pyramidal probe
Furthermore, while SPM was used originally for the observation of a crystal sample surface or a deposited film surface, there has been an increasing need for SPM in recent years to measure the surface configuration of a sample (such as semiconductor IC device) having a larger irregularity for example of 100 nm to several &mgr;m. There is a demand thus for further slenderness not only of the probe tip but also of the thickness of the probe portion away from the probe tip toward the lever side. In short, a probe portion having a high aspect ratio is demanded. This, however, is difficult to be achieved by the conventional cantilevers.
SUMMARY OF THE INVENTION
To eliminate the above problems, it is an object of the present invention to provide a cantilever for Scanning Probe Microscopy by which it is easy, before SPM measurement (scanning), to position the probe portion in alignment with the region to be observed on a sample and a SPM measuremen
Kitazawa Masashi
Sato Kenji
Shiotani Koichi
Toda Akitoshi
Larkin Daniel S.
Olympus Optical Co,. Ltd.
Westerman Hattori Daniels & Adrian LLP
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