Radiant energy – Inspection of solids or liquids by charged particles
Reexamination Certificate
1998-10-06
2001-08-21
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
C250S442110
Reexamination Certificate
active
06278113
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scanning probe microscope, and more particularly to a scanning probe microscope capable of selectively carrying out high-resolution measurement based on scanning operation in a fine range and low-resolution measurement based on scanning operation in a wide range, and further being easily combined with other measuring probes.
2. Description of Related Art
A scanning probe microscope (SPM) has high measurement resolution equal to a size of atoms (no more than a nanometer (nm) scale). The scanning probe microscope has been generally used for measuring a surface shape of fine objects and is further being utilized in various fields. The scanning probe microscopes are classified into a scanning tunnel microscope (STM), an atomic force microscope (AFM), and a magnetic force microscope (MFM), etc. depending on a physical amount used for detecting operation, and therefore application domains are being increased. Especially, the AFM is suitable for detecting an even shape of sample surfaces in high resolution, and is achieving satisfactory results in the fields of semiconductor devices and disks. Hereinafter, an example of an AMF will be explained.
FIG. 6
shows one example of a conventional AMF. A sample stage
101
a
on which a sample
102
to be observed is placed is formed in a lower section of a frame
101
. The sample
102
is kept to be static and its position is not changed. A probe tip approaching mechanism (coarse movement mechanism)
103
is fixed to the upper section of the frame
101
and further an XYZ fine movement mechanism
104
is fixed to the lower side of the probe tip approaching mechanism
103
.
A cantilever
105
is disposed at an upper position above the sample
102
. A probe tip
106
arranged at the tip of the cantilever
105
is directed to a surface of the sample
102
. When measuring the surface of the sample
102
, the probe tip
106
is placed close to the sample
102
so that the atomic force can be created between the probe tip and the sample. A basic end of the cantilever
105
is fixed to the lower end of the XYZ fine movement mechanism
104
. The cantilever
105
has a necessary flexibility and therefore has such a characteristic that flexual deformation is produced depending on a change of the atomic force in relation to a change of the distance between the probe tip and the sample.
The configuration shown in
FIG. 6
shows a system in which the side of the cantilever
105
is movable. The probe tip approaching mechanism
103
causes the probe tip
106
to approach the sample
102
quickly before carrying out the measurement and thus is used for the movement of a comparatively larger distance (coarse movement). The XYZ fine movement mechanism
104
is a tripod type fine movement mechanism or a tube type fine movement mechanism, which is configured by utilizing piezoelectric elements. The tripod type fine movement mechanism is provided with X, Y and Z actuators for producing a fine movement in X, Y and Z directions respectively. In case of using the tripod type fine movement mechanism as the XYZ fine movement mechanism
104
, when carrying out the measurement, the X and Y actuators included in the XYZ fine movement mechanism
104
cause the cantilever
105
to scan the sample surface, while the Z actuator included in the mechanism
104
adjusts the distance between the probe tip
106
and the sample
102
.
A displacement detector
107
is arranged for detecting displacement of the cantilever
105
. As the displacement detector
107
, an optical-lever-type detection optical system or a detector utilizing an interference method is used, for example. The optical-lever-type detection optical system comprises a laser source for emitting a laser beam and a photodetector for receiving the laser beam emitted from the laser source. The laser beam emitted from the laser source is reflected on a rear surface of the cantilever and afterward is incident on the photodetector. The incident position of the laser beam on the photodetector changes in response to the amount of the flexural deformation of the cantilever, the change as to the distance between the probe tip and the sample can be detected on the incident position of the laser beam in the photodetector.
When the operation of the probe tip approaching mechanism
103
causes the probe tip
106
to approach the sample at a fine distance of about 1 nm, the atomic force generated between the probe tip and the sample acts the cantilever
105
to produce the flexural deformation. The displacement detector
107
detects a flexural angle in the cantilever
105
. A detecting signal outputted from the displacement detector
107
is inputted into an adder
108
. The adder
108
compares the detecting signal with a standard value V
ref
and outputs a difference (deviation) signal Vd between the detecting signal and the standard value. The difference signal Vd is inputted into a control section
109
. This control section
109
generally carries out proportional and integral compensation (PI control) and an output signal (Vz) from the control section
109
is supplied to the Z actuator of the XYZ fine movement mechanism
104
so as to change the distance between the probe tip
106
and the sample
102
to become a set value. The distance between the probe tip
106
and the sample
102
is always kept to be a predetermined constant distance based on the standard value V
ref
.
The above-mentioned configuration controls the distance between the probe tip
106
and the sample
102
so that the distance is always kept to be constant. An XY scanning circuit
110
provides two output signals (Vx, Vy) to the X and Y actuators of the XYZ fine movement mechanism
104
, respectively. The scanning signals (Vx, Vy) outputted from the XY scanning circuit
110
are used for causing the probe tip
106
to scan the surface of the sample
102
in the directions of the X-axis and the Y-axis. While the scanning operation is carried out, as mentioned above, the distance between the probe tip
106
and the sample
102
is maintained to be identical with the constant value set in advance.
Data Vz corresponding to the movement amount due to the Z actuator and data (Vx, Vy) as to output signals of the XY scanning circuit
110
are stored in a memory (not shown in the figure). As the result of carrying out necessary processing to these data, images as to the sample surface obtained by the measurement are displayed on a screen of a display unit
111
. The shape of the surface in the sample
102
can be observed on the basis of the images. The atomic force microscope performing the measurement as mentioned above has very high measurement resolution, and in this microscope, further, when performing the measurement, a range for the measurement can be easily switched from a few nanometers scale to a few hundred micrometer scale.
In the aforementioned conventional AFM, the measurable range thereof is limited by that of the XYZ fine movement mechanism
104
. It is essential for the XYZ fine movement mechanism
104
to use solid actuators formed by piezoelectric elements in order to make sure of the resolution of the atomic size level, as mentioned above. Consequently, the movable range of the conventional XYZ fine movement mechanism
104
sets a limit to about 100 &mgr;m. Even if a stroke in the XYZ fine movement mechanism
104
is expanded in order to expand the movable range, its resolution is lowered. Therefore, it was general for the conventional AFM to set its scanning range as a fine range of about 10 &mgr;m in view of a practical aspect.
On the other hand, in recent years, a request to measure a surface shape in a wide range, such as undulation on the surface of silicon wafers, by using a microscope with high measurement resolution no more than a nanometer level, like the AFM, is gradually increased. If the measurable range of the SPM having the high measurement resolution can be expanded in response to circumstances, value in use as the microscopes will be e
Kuroda Hiroshi
Morimoto Takafumi
Murayama Ken
Nishigaki Tsuyoshi
Onozato Harumasa
Hitachi Construction Machinery Co, Ltd.
Mattingly, Stanger & Malur
Nguyen Kiet T.
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