JP3597613B2 - Scanning probe microscope - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a scanning probe microscope, and more particularly to a scanning probe microscope used for measuring and analyzing the surface shape and surface properties of semiconductors, liquid crystals, optical disks, and the like.
[0002]
[Prior art]
Scanning probe microscopes have a measurement resolution on the order of atoms, and are used in various fields such as surface shape measurement. The scanning probe microscope includes a scanning tunneling microscope (STM), an atomic force microscope (AFM), a magnetic force microscope (MFM), and the like according to the physical quantity of a detection target. Among them, the atomic force microscope is suitable for detecting the shape of the sample surface with high resolution, and is used for measuring the surface shape of a semiconductor, an optical disk, or the like.
[0003]
FIG. 3 shows a configuration example of an AFM, which is a kind of a scanning probe microscope. This AFM is an AFM combined with an optical microscope. An XY stage 12 is arranged on a base 11, and a sample 14 to be measured is placed on a sample table 13 on the XY stage 12. The XY stage 12 has a function of arbitrarily moving the sample table 13 within an XY plane defined by orthogonal X-axis and Y-axis directions. The XY plane is a plane that is horizontal in FIG. 3 and perpendicular to the paper surface. The sample 14 placed on the sample table 13 is moved in an arbitrary direction on the XY plane as the sample table 13 moves. A mounting frame 15 is provided on the base 11, and the optical microscope 16, the Z coarse movement stage 17, and the cantilever displacement detector 23 are mounted on the mounting frame 15. In the optical microscope 16, the objective lens 18 faces downward and faces the sample 14. The Z coarse movement stage 17 is a moving mechanism that enables coarse movement in the Z-axis direction perpendicular to the XY plane. An xyz scanner 20 is mounted below the Z coarse movement stage 17 via a mounting block 19. A cantilever 21 is attached to the lower surface of the xyz scanner 20. The xyz scanner 20 is a fine movement device having a function of finely moving the cantilever 21 in each of the X, Y, and Z axis directions. A probe 22 facing the surface of the sample 14 is provided at the tip of the cantilever 21. Note that a “probe” is usually also called a “probe”, and therefore is individually referred to as a “probe” unlike the device name (“scanning probe microscope”). The cantilever displacement detector 23 is a device for detecting the displacement of the probe 22 at the tip of the cantilever 21. The cantilever displacement detector 23 uses, for example, a detection optical system including a laser light source and a photodetector. .
[0004]
The Z coarse movement stage 17, the xyz scanner 20, the cantilever 21, the probe 22, and the cantilever displacement detector 23 form an AFM mechanism portion 24.
[0005]
The operation of the XY stage 12 is performed under the control of the XY stage control circuit 25, and the amount of operation of the XY stage 12 is detected by the stage displacement meter 26. The XY stage control circuit 25 receives data on the control amount from the computer 27, and the stage displacement meter 26 sends the data on the detected operation amount to the computer 27. The operation of the Z coarse movement stage 17 is controlled by a Z coarse movement stage control circuit 28, and the operation of the xyz scanner 20 is controlled by an xyz scanner control circuit 29. In the position control of the probe 22 in the Z-axis direction based on the Z coarse movement stage control circuit 28 and the xyz scanner control circuit 29, the atomic force acting between the probe 22 and the surface of the sample 14 is kept constant. Thus, the displacement detection data detected by the cantilever displacement detector 23 is taken out, and the displacement detection data and the force set value relating to the interatomic force are taken out by the force setting device 30. Control data such that the interatomic force acting between the probe and the sample surface always coincides with the force setting value, is transmitted from the force setting device 30 to the Z coarse movement stage control circuit 28 and the xyz scanner control circuit 29. Given. The computer 27 gives a force setting value to the force setting device 30, and is connected to the Z coarse movement stage control circuit 28 and the xyz scanner control circuit 29, and exchanges data with these circuits. The computer 27 has a monitor 31, on which an image of the sample surface obtained by the measurement is displayed.
[0006]
The operation and operation of the AFM having the above configuration are as follows. The sample 14 is placed on the sample table 13 on the XY stage 12, and the observation position of the sample 14 is searched using the optical microscope 16 while moving the sample 14 in the XY plane using the XY stage 12. Next, the probe 22 of the cantilever 21 is adjusted to that position. When the position of the probe 22 is adjusted to the observation position of the sample 14, the probe is moved by the distance d1 shown in FIG. The probe 22 positioned at the observation position of the sample 14 is brought close to the surface of the sample 14 by the Z coarse movement stage 17 until it reaches a position where an atomic force acts. Next, while using the Z-direction drive unit of the xyz scanner 20 to control the probe 22 of the cantilever 21 to receive a constant force from the sample surface, simultaneously using the XY-direction drive unit of the xyz scanner 20 The probe 22 is scanned. The computer 27 creates an image of the observation surface of the sample 14 based on the drive signal of the xyz scanner 20 at this time, and displays the image on the monitor 31. Thus, an atomic level image of the observation surface of the sample 14 can be observed.
[0007]
According to the AFM having the above configuration, for example, the optical microscope 16 with a magnification of 100 enlarges the range of 88 × 66 μm with an accuracy of 0.25 μm in the horizontal direction and 0.5 μm in the vertical direction, and about 10 × 10 μm in the AFM 24. The range can be measured with a resolution of 0.1 nm horizontally and 0.01 nm vertically.
[0008]
FIG. 4 shows an example of the structure of the xyz scanner 20. The xyz scanner 20 has a cylindrical shape as a whole, and is formed of a piezoelectric element such as lead zirconate titanate PZT, for example. The dimensions of the cylindrical portion are, for example, an outer diameter of about 15 mm, an inner diameter of about 14 mm, and a height of about 40 mm. A ground electrode is provided on substantially the entire inner surface of the cylindrical piezoelectric element, and a Z-axis drive electrode 32, an X-axis drive electrode 33, and a Y-axis drive electrode 34 are provided on the outer surface. The upper end of the xyz scanner 20 is fixed as shown in FIG. 3, and the lower end is a free end to perform a scanning operation. In order to displace (expand or contract) in the Z-axis direction, a necessary voltage is applied to the electrode 32. In order to displace in the X-axis direction, a required voltage is applied to each of the two electrodes 33 disposed opposite to each other at positions opposite to the outer surface on the upper and lower sides in accordance with the displacement direction, and in the Y-axis direction. In order to perform the displacement, a required voltage is applied to each of the two upper and lower electrodes 34 which are disposed oppositely at the upper and lower positions, respectively, according to the displacement direction. Further, the amount of displacement can be changed by adjusting the magnitude of the applied voltage. According to the xyz scanner having the above-described dimensions, for example, a maximum displacement of ± 10 μm occurs in the X-axis direction.
[0009]
However, in the cylindrical piezoelectric element (PZT) forming the xyz scanner 20, about 10% of the hysteresis occurs in the stroke. Therefore, in order to generate an accurate displacement by the xyz scanner, a strain gauge 35 is appropriately affixed to each of the electrodes 32, 33, and 34, and a capacitance-type calibration displacement meter (see FIG. (Not shown), and it is necessary to first determine the relationship between the output of the strain gauge and the output of the displacement gauge with respect to the voltage applied to the xyz scanner 20. In the subsequent scanning operation, the output of the strain gauge itself is treated as the displacement of the xyz scanner.
[0010]
[Problems to be solved by the invention]
When the measurement is performed using the conventional scanning probe microscope having the above configuration, the following problem occurs. For example, it is assumed that the measurement is performed by scanning the sample 14 having the uneven surface as shown in FIG. The uneven surface of the sample 14 is assumed to be spread in a plane. As shown in FIG. 5, it is assumed that distances a ₁ , a ₂ , and a ₃ are determined on the uneven surface of the sample. Here, if the _{a 1} 10 [mu] m, and the _{a 2} and _{a 3} are 0.3 [mu] m. Consider a case in which measurement is performed with a resolution of 1 nm in a rectangular area having a side of 0.3 μm, for example.
[0011]
In the measurement by the conventional apparatus configuration, it is relatively easy to identify a rectangular area with a side of 10 μm by using the optical microscope 16, but a part of the rectangular area with a side of 0.3 μm is identified. It is difficult. Therefore, in the conventional apparatus, first, a rectangular area having a side of 10 μm is measured using the AFM, and the distance is obtained based on the result. The display resolution at this time is obtained at 10 μm / 256, which is approximately 40 nm. Here, 256 is the number of divisions corresponding to the display resolution. If the distance a ₂ is determined specifically, the AFM can be moved exactly to the rectangular area of the side 0.3μm is a _3, the rectangular area can be measured by AFM. The display resolution at that time is given by 0.3 μm / 256, which is approximately 1 nm. According this way the structure of the conventional scanning probe microscope, a rectangular area of the distance a ₁ measured by AFM, to confirm the rectangular area determined by the distance a ₃ on the basis of subsequent measurement data, finer the region The measurement is performed at the resolution, and the display is performed at the resolution.
[0012]
According to the above-described measuring method based on the conventional apparatus configuration, the efficiency required for the measurement, that is, the throughput becomes a significant problem. For example, it takes about 80 seconds to measure the 0.3 μm rectangular area using an AFM. Therefore, as described above, if a coarse measurement and a fine measurement are performed using the AFM, a time corresponding to two AFM measurements is required, and the measurement time becomes longer as a whole, thereby increasing the measurement throughput. Raise the issue of inability to do so.
[0013]
An object of the present invention is to provide a scanning probe microscope such as an AFM with improved throughput in measuring the surface shape and surface properties of a sample.
[0014]
Means and action for solving the problem
In order to achieve the above object, a scanning probe microscope according to a first aspect of the present invention (corresponding to claim 1) has a fine movement mechanism (a fine movement mechanism for changing a relative position of a probe facing a sample and a sample and the probe). xyz scanner), control means for controlling the operation of the fine movement mechanism, and detection means for detecting a change in the position of the probe, wherein the control means and the fine movement mechanism change the relative positional relationship between the sample and the probe. The scanning type scans the surface of the sample with the probe, detects the change in the position of the probe based on the physical quantity acting between the sample and the probe with the detection means (cantilever displacement detector), and measures the surface of the sample. In a probe microscope, setting means (distance setting circuit) for setting a constant distance from a reference surface of a sample , and a probe so that a distance between the probe and the reference surface of the sample does not become less than the set constant distance. to the height direction And drive means for work (set distance driving circuit) configured to measure a state of the sample surface exists in the distance or more regions.
[0015]
According to the first aspect of the present invention, the surface of the sample can be scanned without the probe approaching the surface of the sample more than the distance set by the setting means, so that a relatively wide range of the sample surface can be roughened in a short time. Can be measured. As a result, it is possible to efficiently search for a portion that is originally desired to be measured.
[0016]
In a scanning probe microscope according to a second aspect of the present invention (corresponding to claim 2), in the configuration of the first aspect, the probe is provided at a tip of a cantilever attached to a fine movement mechanism, and the physical quantity is It is an atomic force.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[0018]
FIG. 1 shows an embodiment of a scanning probe microscope according to the present invention. Since the configuration shown in FIG. 1 is basically the same as the configuration shown in FIG. 3 (AFM with optical microscope), the same elements as those shown in FIG. 3 are denoted by the same reference numerals.
[0019]
In FIG. 1, 11 is a base, 12 is an XY stage, 13 is a sample table, 14 is a sample, 15 is a mounting frame, 16 is an optical microscope, 17 is a Z coarse movement stage, 20 is an xyz scanner, 21 Is a cantilever, 22 is a probe, and 23 is a cantilever displacement detector. The mounting structure, configuration, and function of each component described above are as described with reference to FIG.
[0020]
In the control circuit section, an XY stage control circuit 25 and a stage displacement meter 26 are provided for the XY stage 12, a Z coarse movement stage control circuit 28 is provided for the Z coarse movement stage 17, and an xyz scanner is provided. An xyz scanner control circuit 29 is provided for 20. The Z coarse movement stage control circuit 28 and the xyz scanner control circuit 29 receive, from the force setting device 30, control data for ensuring that the interatomic force acting between the probe and the sample surface always coincides with the force set value. Given. A computer 27 having a monitor 31 is provided for the circuits 25, 28, 29, the force setting device 30, and the like. The mounting structure, configuration, and function of each component described above are as described with reference to FIG.
[0021]
As for the control circuit portion, a probe-sample distance setting circuit 41 and a set distance drive circuit 42 are additionally provided.
[0022]
Distance a ₄ shown in distance setting circuit 41 For example, in FIG. 2 (b) is set. The distance a ₄ is equivalent to the height from the reference surface 14a of the sample 14. This distance _{a 4,} in a case where the reference surface 14a, for example of three different height protrusions 51, 52 and 53 of the sample 14, for example, is formed with a periodicity, than the height of the protrusions 51 and 52 Is set to be smaller than the height of the projection 53. Since the height of each convex portion is known in advance, it is easy to set the distance a _4. In FIG. 2, the distances a ₁ , a ₂ , and a ₃ are the same as the distances described in FIG. Setting the distance a ₄ at a distance setting unit 41 is performed based on the command given from the computer 27.
[0023]
When scanning the surface of the sample 14 with the probe 22 based on the control operations of the Z coarse movement stage control circuit 28 and the xyz scanner control circuit 29, the set distance driving circuit 42 This is a circuit for driving the operation of the probe 14 in the height direction (Z-axis direction) so that the distance does not become smaller than the distance set by the distance setting circuit 41. The probe drive by the set distance drive circuit 42 is performed via the Z coarse movement stage control circuit 28 and the xyz scanner control circuit 29.
[0024]
Next, the operation and operation of the AFM with an optical microscope having the above configuration will be described. As described above, the basic operation and operation are as follows. First, the sample 14 is placed on the sample table 13 on the XY stage 12, and the optical microscope is moved while moving the sample 14 in the XY plane using the XY stage 12. Using 16, a portion of the sample 14 to be observed and measured is searched for. Next, the probe 22 of the cantilever 21 is moved to the measurement position of the sample 14 by moving the XY stage 12 by the distance d1 shown in FIG. The probe 22 positioned at the measurement point of the sample 14 is brought close to the surface of the sample 14 by the Z coarse movement stage 17 until the position where the atomic force acts, and then the probe 22 of the cantilever 21 is moved to the sample. The probe 22 is scanned using the XY-direction drive unit of the xyz scanner 20 while controlling using the Z-direction drive unit of the xyz scanner 20 so that the force received from the surface is constant. The computer 27 creates an image of the observation surface of the sample 14 based on the data on the drive signal of the xyz scanner 20 at this time, and displays the image on the monitor 31.
[0025]
Next, in the case where, for example, one rectangular area is set at a distance a ₃ and the measurement region will be described the operation and operation for locating the rectangular area. It is difficult for the optical microscope 16 to find a certain rectangular area having one side of a ₃ (= 0.3 μm). Therefore, first, for example, a rectangular area having one side of a ₁ (= 10 μm) is searched using the optical microscope 16. This search is possible with the optical microscope 16. If such a rectangular area is found by the optical microscope 16, then the rectangular area is roughly measured by AFM.
[0026]
Rough measurement by the AFM for a rectangular area having one side of the distance a ₁ (= 10 μm) is performed as follows.
[0027]
On the measurement surface of the sample 14, it is assumed that, for example, convex portions 51, 52, and 53 having different heights as shown in FIG. The value of the height of each projection is known. The coarse measurement with the above AFM, height a ₄ described above in consideration of the height of each protrusion is set.
[0028]
Setting the distance a ₄ is performed by inputting to the computer 27 through input device (not shown) by the operator. When the distance a ₄ is input to the calculator 27, the calculator 27 sets the distance a ₄ in the distance setting circuit 41. If the distance a ₄ to distance setting circuit 41 is set, when controlling the position of the probe 22 relative to the reference surface 14a of the sample 14, the set distance driving circuit 42 according to the Z coarse moving stage control circuit 28 Z Regarding the position control of the probe in the coarse movement stage 17 in the height direction and the position control of the probe in the xyz scanner 20 by the xyz scanner control circuit 29 with respect to the reference surface 14a of the sample 14, 22 to perform the operation control so as not to approach than the distance a _4. When a rectangular area of one side a ₁ sets the distance a ₄ when measured by AFM, since the probe 22 may not perform exactly scanning along the irregularities formed on the measurement surface of the sample 14, the coarse measurement It can be performed. The greater the distance a _4, it is possible to perform rough measurement. Although measurement itself is roughened by setting the distance a ₄ described above to the distance setting circuit 41, the time required for measurement is shortened. This can increase the measurement throughput.
[0029]
In practice, the distance a ₄ that how much to set the value is determined based on the size relationship between the target and the surrounding parts to attempts to locate. In the present embodiment, in the sample surface with topographical features shown in FIG. 2 (a), since the rectangular area the distance a ₃ and one side is a measurement target, allows issues Heading this area (less than the height of the convex portions 51 and 52, larger than the height of the convex portion 53) the condition that the distance a ₄ satisfying is set.
[0030]
When a specific distance is not set in the distance setting circuit 41, the Z coarse movement stage 17 and the xyz scanner 20 are operated to move the probe 22 toward the reference surface 14a of the sample 14. Reference numeral 22 contacts the reference surface (bottom surface) 14a. Whether the probe 22 has touched the reference surface of the sample can be known from the change in the bending direction of the cantilever 21. When the probe 22 approaches the sample 14, a suction force acts and the probe 22 bends so as to be drawn into the sample 14. When the probe 22 approaches the sample at a distance of 1 nm or less where an atomic force acts, a repulsive force acts to change the cantilever 21 in the opposite direction. This change point is treated as a point at which the probe 22 is in contact with the sample 14, and is regarded as the bottom surface of the sample.
[0031]
When measurement is performed by the AFM including the set distance driving circuit 42 and the like in a state where the distance a ₄ is set in the distance setting circuit 41, the xyz scanner 20 is operated to move the probe 22 from the reference surface 14a of the sample 14. a ₄ away. Scanning is performed in each of the X-axis and Y-axis directions with the height position as the origin (point 0) in the Z-axis direction (height direction). During the scanning, the displacement of the cantilever 21 is detected through the cantilever displacement detector 23, and the displacement of the cantilever 21 in the height direction of the probe 22 is adjusted so that the detected displacement value matches the force setting value set by the force setting device 30. The position is controlled. If Z-axis direction position of the probe 22 becomes equal to or less than the distance a ₄ described above, need not match the force setting value, the probe 22 is moved in the XY direction as that detected the origin. As a result, shown so in FIG. 2 (b), XY area of the distance a ₄ or more sample surface, will have been measured based on select force setting value. This measurement is a coarse measurement, and is a measurement for efficiently searching for a portion to be originally measured, thereby improving the throughput of the scanning probe microscope. Based on the result of the rough measurement, determine the distance a _2, it is possible to find the rectangular region of one side a ₃ to be measured, as shown in FIG. 2 (c), to measure the area with a resolution of 1nm be able to. However when measuring a rectangular area of one side a _3, it is necessary to perform precise measurement, the distance set in the distance setting circuit 41 (a ₄₎ is set to 0.
[0032]
By using the measurement shown in FIG. 2B, the measurement can be performed in about 1/5 of the time of the conventional measurement method, the measurement can be speeded up, and the measurement throughput can be increased.
[0033]
In the above-described embodiment, the example of the AFM is described as the scanning probe microscope. However, it is needless to say that the present invention can be applied to other types of scanning probe microscopes such as STM and MFM.
[0034]
【The invention's effect】
As is apparent from the above description, according to the present invention, when the probe scans the sample surface, the distance between the probe and the sample, that is, the height on the sample surface, is set, and the shape or the like of the height or more is set. Since it is configured to perform measurement, it is possible to find a portion where high-resolution measurement is to be performed in a short time by performing a coarse measurement using an AFM or the like. Thereby, the throughput of the measurement by the scanning probe microscope can be improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing one embodiment of a scanning probe microscope according to the present invention.
FIG. 2 is an explanatory diagram showing a scanning mode according to the present invention.
FIG. 3 is a configuration diagram showing an example of a conventional scanning probe microscope.
FIG. 4 is a front view showing an example of a fine movement mechanism.
FIG. 5 is an explanatory diagram showing a conventional scanning mode.
[Explanation of symbols]
12 XY stage 13 Sample table 14 Sample 16 Optical microscope 17 Z coarse movement stage 20 Xyz stage 21 Cantilever 22 Probe 23 Cantilever displacement detector 27 Computer 41 Distance setting circuit 42 Setting distance drive circuit

Claims (2)

A probe facing the sample, a fine movement mechanism for changing the relative positional relationship between the sample and the probe, control means for controlling the operation of the fine movement mechanism, and detection means for detecting a change in the position of the probe. By changing the relative positional relationship between the sample and the probe with the control means and the fine movement mechanism, the probe scans the surface of the sample and acts between the sample and the probe. In the scanning probe microscope which detects a change in the position of the probe based on a physical quantity by the detection means and measures the surface of the sample,
Setting means for setting a constant distance from the reference surface of the sample, and operating the probe in the height direction so that the distance between the probe and the reference surface of the sample does not become less than the set constant distance . A scanning probe microscope, comprising: driving means for measuring a state of a surface of a sample existing in an area longer than the distance. The scanning probe microscope according to claim 1, wherein the probe is provided at a tip of a cantilever attached to the fine movement mechanism, and the physical quantity is an atomic force.

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