Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
2000-11-21
2003-01-21
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
Reexamination Certificate
active
06508110
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to microscopes, and more particularly to an atomic force microscope that uses a probe tip to detect the surface of a test sample by the displacement of a laser beam.
2. Description of Prior Art
The relationship of distance and relative force between the probe tip of an atomic force microscope or a scanning atomic force microscope (AFM) and the surface of a test sample to be scanned by the probe is depicted in FIG.
1
. As shown, the abscissa represents the distance between the probe tip and the surface of the test sample, while the positive ordinate represents the repulsive force between the probe tip and the surface of the test sample and the negative ordinate represents the attractive force between the probe tip and the surface of the test sample. Consequently, there are two types of atomic force microscopes: one applied to an operation zone assigned with reference numeral A′ shown in
FIG. 1
which is subject to the contact mode under repulsive force and the other one applied to an operation zone assigned with reference numeral B′ shown in
FIG. 1
which is subject to the tapping mode under repulsive force and attraction force.
The contact mode AFM uses a repulsive force between a probe tip and the surface of the scanned test sample. If the distance between the probe tip and the surface of the scanned test sample obtaining from scanning a probe is larger than 0 and less than d
1
, the scanning probe will be separated from the atom on the surface of the scanned test sample due to the repulsive force. For a tapping mode atomic force microscope, a repulsive force occurs when the distance between the probe tip and the surface of the scanned test sample is between 0 and d
1
. When the distance between the probe tip and the surface of the scanned test sample is larger than d
1
and less than d
2
, the probe tip and the surface of the scanned test sample will attract each other to keep them in oscillation in a distance between 0 and d
2
(like tapping).
The structure of a contact mode atomic force microscope is illustrated in FIG.
2
. The probe tip
1
a
of the scanning probe
1
scans the surface of the test sample (not shown in the figure). The discontinuous signal generator
3
produces a discontinuous signal that will be sent to the modulating laser diode
4
to output a discontinuous laser beam. The laser beam reflects from the back side of the probe
1
to a photo detector
5
and it will then output a current signal corresponding to the intensity of the laser beam by a photoelectron conversion effect. The output current signal will be then converted into a voltage signal by a current/voltage converter
6
and calculated by a differential amplifier
7
to obtain a voltage value corresponding to the deformation of the probe
1
. After entering this voltage value to a Z-axis servo controller on the piezoelectricity platform (only the seat is shown), a corresponding control command will be obtained on the basis of the control calculation principle (for example, proportional integral differential, PID) to make the piezoelectricity platform seat
2
move up and down and keep the deformation value of the probe
1
be constant. If the position of Z-axis is recorded at a specific time point and all the data are collected, the surface profile of the test sample can be obtained. Because the laser beam is a kind of pulse signal, the voltage value of the deformation of probe
1
or the position of Z-axis may be discontinuous. To obtain a smoother servo controlled and scanning image, an interpolation operation
8
is employed to compensate the signals or data where no laser beam is used. The resulting data are stored in a scanning image data storage device
9
and incorporated into a collected data point to display on a display
19
after processing by an image-processing device
18
. Because the structure of a contact mode atomic force microscope uses a discontinuous laser beam, it can effectively reduce the heat deformation problem resulting from the laser beam. But it must use interpolation operation and cannot filter the interference caused, for example, by the coaxial light radiated from the charge coupling device (CCD) at the scanning probe or from a miscellaneous light source. All these are disadvantages thereof.
Details of the above-mentioned contact mode atomic force microscope may refer to the application for U.S. Pat. No. 5,567,872 with a title of “Scanning Atomic Force Microscope” submitted by Kyogaku et al., filed on Mar. 7, 1995.
The structure of a known tapping mode atomic force microscope is shown in FIG.
3
. The probe tip
1
a
of the scanning probe
1
scans the surface of the test sample (not shown in the figure). A sinusoidal wave signal generator
10
produces a sinusoidal wave signal that will be sent to a piezoelectricity oscillator
12
to make it vibrate in a manner similar to the sinusoidal wave. This further causes the probe
1
also to move in manner similar to the sinusoidal wave through the transmission of the mechanism. The laser diode
4
outputs a laser beam. The laser beam reflects from the back side of the probe to a photo detector
5
and it will then output a current signal corresponding to the intensity of the laser beam by photoelectric conversion effect. The output current signal will be then converted into a voltage signal by a current/voltage converter
6
and calculated by a differential amplifier
7
to obtain a voltage value corresponding to the amplitude of the probe
1
after the calculation of a digitized signal processor or an analog mean square root signal processing circuit
11
. After entering the voltage value to the Z-axis servo controller on the piezoelectricity platform (only the seat is shown), a corresponding control command will be obtained on the basis of the control calculation principle (for example, proportional integral differential, PID) to make the piezoelectricity platform seat
2
move up and down and keep the amplitude of the probe
1
be constant. If the position of Z-axis is recorded at a specific time point and all the data are collected and stored in a scanning image data storing device
9
, the surface profile of the test sample can be obtained and displayed on a displayer
19
after being processed by an image data processing device
18
. Because the probe tip
1
a
of the scanning probe contacts only for a considerable short time with the surface of the test sample (not shown in the figure), there is no friction during the scan, which further reduces the surface tension caused by the water molecule on the test sample and the influence of static electricity. Besides, the interference resulting from the vibration of the mechanism itself can be effectively isolated. However, the above-mentioned tapping mode atomic force microscope must have a digitized signal processor or analog mean square root signal processing circuit
11
to obtain the amplitude of AC signals, and the heat deformation caused by continuous laser beams will twist the scanned image. All these are disadvantageous.
Details of the above-mentioned tapping mode atomic force microscope may refer to U.S. Pat. No. 5,412,980 with a title of “Tapping Atomic Force Microscope” submitted by Elings et al., filed on Aug. 7, 1992.
SUMMARY OF THE INVENTION
In the present invention, under the consideration of the fact that the above-mentioned contact mode atomic force microscope must use an interpolation calculation and, therefore, cannot filter the interference caused, for example, by the coaxial light radiated from the current coupling device (CCD) at the scanning probe or the miscellaneous light source, and another, tapping mode atomic force microscope must use a digital signal processor or analog mean square root signal processing circuit to obtain the amplitude of AC signals, and the scanned image will be twisted due to the heat deformation caused by continuous laser beams. It can improve the disadvantages of the above-mentioned contact and tapping modes.
Accordin
Lin Hsi-Hsiang
Lo Shih-Che
Industrial Technology Research Institute
Larkin Daniel S.
Shoemaker and Mattare
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