JP2005083852A - Scanning probe microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conform an assigned scanning area with an actual scanning area to allow accurate measurement reduced in an error, by measuring an electrostatic capacity due to temperature variation, and by correcting scanner sensitivity based on the electrostatic capacity, in a temperature-varied scanning probe microscope. <P>SOLUTION: This scanning probe microscope for detecting interatomic force acting between a probe and a sample or a tunnel current therein is provided with a piezoelectric scanning body for scanning the probe relatively with respect to the sample, an electrostatic capacity measuring means for measuring the electrostatic capacity of the piezoelectric scanning body, and a scan voltage generation means for supplying a voltage for the scanning by the piezoelectric scanning body in response to the electrostatic capacity measured by the electrostatic capacity measuring means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a scanning probe microscope, which is a general term for a scanning tunnel microscope, an atomic force microscope, a magnetic force microscope, a friction force microscope, a micro viscoelastic microscope, a surface potential difference microscope, and similar devices.

  A scanning tunneling microscope is a so-called tunnel current in which electrons move through a vacuum gap between a probe and a sample when a distance between the sample and a metal probe is kept at 1 nm or less and a bias voltage is applied between them. In this case, the tunnel current is sensitive to the distance between the sample and the probe, so that the tunnel current is constant over the sample surface so that the tunnel current is constant. By scanning regularly, the unevenness of the sample surface can be observed at the atomic level.

  FIG. 1 shows an embodiment in the prior art. A probe 6 is attached to the piezoelectric element 2 and faces a sample (not shown). Electrodes 3, 4, and 5 that scan the probe 6 in the XYZ directions are attached to the piezoelectric element 2, and high-voltage amplifiers 7 and 8 and scan waveform generation sources 9 and 10 are connected to each electrode. By applying a voltage to the electrodes 3, 4, and 5, the probe 6 scans in the XYZ directions. The sample is installed in a sample holder (not shown). In the case of cooling, cooling is performed not only with the sample holder but also with the SPM head such as a probe, a probe holder, and a scanner. The scanning probe microscope performs scanning by designating a scanner area by software operating on the computer 1.

  For example, when measuring silicon, in order to observe silicon with a well-organized structure, the sample may be annealed by heating to a high temperature of 600 to 1000 degrees. Since silicon is easily oxidized, it is observed in a vacuum.

  However, when the sample is heated or cooled, the peripheral parts of the sample are also affected by the temperature. Since the scanner is arranged to face the sample through the probe 6, even if heat insulation is performed on the sample, the influence of heat conduction, radiation, and convection cannot be completely blocked. Since the sensitivity of the piezoelectric element 2 used in the scanner (the amount of displacement with respect to the applied voltage) varies with temperature, the scanning range of the scanner also varies with temperature. The sample holder or the like uses a material with good heat conduction (copper, aluminum, etc.), but the scanner is composed of the piezoelectric element 2 and the heat conductivity is very poor. The time constant is large and it takes a very long time to be the same as the sample temperature. That is, even if the sample temperature is set to a certain temperature, the temperature of the scanner differs depending on how much time has passed. Even if the sample temperature is changed to a certain temperature, the temperature of the scanner varies greatly depending on whether the temperature reaches a higher temperature or a lower temperature. Even when the entire SPM head is cooled, it may take several hours for the sample temperature and the scanner to reach the same temperature.

  From the above, in the scanning probe microscope that changes the temperature of the sample, there is a possibility that the designated scanning area is different from the actual scanning area. This can be confirmed by changing the temperature and measuring a known sample with a scanning probe microscope. Since not only scanning in the XY direction but also displacement in the Z direction, which is the depth direction of the sample, is performed using the piezoelectric element 2, the measurement of unevenness also lacks accuracy.

  Conventionally, the piezoelectric sensitivity is measured at room temperature, and the scanning area is defined based on this measurement. Therefore, the designated area differs from the actual scanning area when the temperature changes.

  As a conventional technique, there is a Z displacement detection mechanism using a capacitance sensor (for example, Patent Document 1).

JP-A-9-133690

  The problem to be solved by the present invention is to perform accurate measurement by correcting the sensitivity of the scanner due to temperature change when performing measurement with a scanning probe microscope in which the temperature of the sample is variable.

  According to a first aspect of the present invention, there is provided a scanning probe microscope that detects a physical quantity acting between a probe and a sample, a piezoelectric scanning body that relatively scans the probe and the sample, and a capacitance of the piezoelectric scanning body. Capacitance measuring means for measuring, and scanning voltage generating means for supplying a voltage for scanning by the piezoelectric scanning body according to the capacitance measured by the capacitance measuring means are provided.

  A second invention is the scanning probe microscope described in the first invention, characterized in that the scanning voltage generating means has a correction circuit for correcting the voltage by the capacitance.

  A third invention is the scanning probe microscope described in the first invention, characterized in that the scanning voltage generating means has a calculating means for calculating a scanning voltage corresponding to the capacitance.

  A fourth aspect of the invention is the scanning probe microscope described in the first to third aspects of the invention, wherein the cylindrical piezoelectric body is in one direction in the diametrical direction and in the other direction perpendicular to the one direction. A scanning electrode for displacing, wherein the capacitance measuring means measures a capacitance of the scanning electrode portion, and the scanning voltage generating means independently applies a voltage to each scanning electrode. Features.

  A fifth invention is the scanning probe microscope described in the fourth invention, wherein the scanning voltage generating means includes a voltage amplifying means and a scanning waveform generating means.

A sixth invention is a scanning probe microscope according to any one of the first to fifth inventions, wherein the sample observation chamber provided in an airtight manner and a gas for discharging the gas in the sample observation chamber Discharging means; and sample temperature variable means for heating or cooling the sample;
It is characterized by providing.

  By measuring the electrostatic capacitance due to the temperature change in the scanning probe microscope in which the temperature changes, and correcting the scanner sensitivity with this electrostatic capacitance, the designated scanning area and the actual scanning area can be matched. For this reason, accurate measurement with few errors can be performed.

  The capacitance of the piezoelectric scanning body that relatively scans the probe and the sample is measured, and a voltage corresponding to the capacitance is supplied.

  First, the configuration of the first embodiment will be described with reference to FIGS. FIG. 6 is an external view of a scanning probe microscope according to the present invention. The observation chamber 21 in which the inside is kept airtight is installed via a vibration isolation table 24. A vacuum pump 25 is connected to the observation chamber 21 so that the inside can be brought into an ultrahigh vacuum. A gas cylinder 20 is connected to the observation chamber 21, and a gas such as nitrogen can be enclosed. In addition, a vacuum flange 22 is installed in the observation chamber 21, and a scanning electron microscope or the like can be connected to perform observation with a scanning electron microscope. The scanning probe microscope is under the control of the computer 26.

  FIG. 7 is a cross section of the observation chamber 21 in FIG. Hereinafter, the same number is attached to the part of the same name in the figure. A sample holder 27 holding a sample 28 is installed in the observation chamber 21. A heater 30 is built in the sample holder 27. Instead of the heater 30, liquid nitrogen (not shown) or the like may be connected via a heat conductor (not shown) to be cooled. A probe 6 is disposed opposite to the sample 28, and a scanner 29 is attached to the probe 6.

  FIG. 4 is a detailed view of the scanner 29 in FIG. The piezoelectric element 2 is formed by sintering a ferroelectric material such as a piezoelectric ceramic element, and has a cylindrical shape. A common ground electrode is formed on the entire inner surface of the piezoelectric element 2, and an X electrode 3, a Y electrode 4, and a Z electrode 5 are metallized on the outer surface. The characteristic of the piezoelectric element 2 is that it expands when a positive voltage is applied to the outer electrode with respect to the common ground electrode and contracts when a negative voltage is applied. Therefore, when one end of the piezoelectric element 2 is held and a voltage having a reverse characteristic is applied to one and the other of the facing X electrodes 3, the piezoelectric element 2 is bent. In this way, two-dimensional scanning is possible by applying scanning signals to the X electrode 3 and the Y electrode 4. Similarly, by applying a voltage to the Z electrode 5 and controlling it, the distance between the sample 28 and the probe 6 can be maintained at 1 nm or less. A conductive probe 6 is installed at one end. A scan waveform generation source 9 for applying an arbitrary voltage, an X high voltage amplifier 7 and an X voltage corrector 15 are electrically connected to the X electrode 3 and are under the control of the computer 1. The computer 1 is the same as the computer 26 of FIG. Further, an X electrostatic capacity measuring device 13 is connected to the X electrode 3, and the X electrostatic capacity measuring device 13 is also connected to an X voltage corrector 15. The X capacitance measuring device 13 is a tester and may display a numerical value. By measuring the capacitance between the common ground electrode and the X electrode inside the piezoelectric element 2, the capacitance of the portion covered with the electrode can be measured. The X scan waveform generation source 9, the X high-voltage amplifier 7, the X piezoelectric corrector 15, and the X capacitance measuring device 13 are configured as a unit including a circuit board and the like. The Y direction is similarly connected. Although not shown, the Z direction may be similarly connected.

  FIG. 3 is a view A in FIG. One direction in the diameter direction of the piezoelectric element 2 is defined as an X direction, a direction orthogonal to the X direction is defined as a Y direction, and a height direction is defined as a Z direction. The electrodes in the X and Y directions are connected to the facing electrodes, respectively. A temperature sensor 31 is attached inside the scanner.

  Next, the operation of the first embodiment will be described. 4 and 7, the observation chamber 21 is kept in a high vacuum, the distance between the sample 28 and the probe 6 is kept at 1 nm or less, and a tunnel current flows. The sample 28 is fixed, and scanning is performed by applying a voltage to the XY electrodes of the scanner 29 and displacing the scanner 29. By applying a voltage to the scanner Z electrode and displacing the scanner 29 and controlling the computer so that the tunnel current is constant, the applied voltage can be converted into a displacement amount, and an uneven image can be observed at the atomic level. .

  When the sample 28 is heated by the heater 30, heat is also transmitted to the scanner 29 by radiation, conduction or the like. Since the scanner 29 has poor thermal conductivity as described above, the temperature of the sample 28 measured by a thermometer (not shown) is difficult to reach. The sensitivity of the piezoelectric element 2 differs depending on the temperature, and the scan area designated in the computer 1 may be different from the area actually scanned. From the experimental results, it was found that the capacitance of the piezoelectric element 2 with respect to the temperature changes substantially linearly at the temperature at which the scanning probe microscope of 5 to 350 [K] is measured, and the piezoelectric element 2 with respect to the capacitance. A similar characteristic curve is obtained for the sensitivity. FIG. 2 shows a change in capacitance with respect to a change in temperature of the piezoelectric element 2. As an example, a scanner that changes approximately linearly at 5 to 350 [K] is used. FIG. 9 shows a change in displacement with respect to the change in capacitance of the piezoelectric element 2, and changes substantially linearly as indicated by a solid line at a normal temperature. By utilizing this fact, the sensitivity of the piezoelectric element 2 can be corrected from the change in capacitance by measuring the capacitance of the piezoelectric element 2 due to temperature change.

For example, when the room temperature is 300 [K], the following values are used.
X direction piezoelectric element sensitivity: KX (300) [nm / V]
Capacitance of the portion corresponding to the X direction: CX (300) [nF]
Further, when the observed scanner temperature is T [K], the following values are used.
X direction piezoelectric element sensitivity: KX (T) [nm / V]
Capacitance of the portion corresponding to the X direction: CX (T) [nF]
By measuring CX (T), KX (T) can be obtained from the following equation.
KX (T) = KX (300) / CX (300) × CX (T)
Since the voltage VX (T) [V] corresponding to the instructed piezoelectric element 2 sensitivity is known, the actual X-direction scan distance VX (T) × KX (T) can be obtained.

  The X voltage corrector 15 includes a circuit that performs the above correction. Therefore, when scanning the designated scan area on the PC, a voltage corresponding to the designated waveform can be applied after correcting the piezoelectric element sensitivity at the temperature at that time. Similar corrections can be made for the Y and Z directions.

  As described above, it is possible to match the designated scanning area with the actual scanning area by measuring the electrostatic capacity due to the temperature change and correcting the piezoelectric element sensitivity with this electrostatic capacity. For this reason, accurate measurement with few errors can be performed.

  Figures 5, 6, 7 and 8 are alternative embodiments. 6 and 7 are the same as those in the first embodiment.

  FIG. 5 is a detailed view of the scanner 29 in FIG. The difference from the first embodiment is that the scanning voltage calculated on the computer 1 is corrected by the voltage correctors 15 and 16 in the first embodiment, whereas the second embodiment is corrected by software operating on the computer 1. This is the point at which the scanning voltage is calculated. One end of the X capacitance measuring device 13 is connected to the X electrode 3, and the other end is connected to the computer 1. The computer 1 is connected to an X scan waveform generation source 9 and an X high voltage amplifier 7. The same applies to the Y direction and the Z direction.

  FIG. 8 is a flowchart of a program that operates on the computer 1 that controls the scanner 29. A program operating on the computer 1 executes the following steps. A known X-direction piezoelectric element sensitivity KX (300) at a temperature of 300 [K] and a capacitance CX (300) at this time are set. The capacitance CX (T) of the piezoelectric element 2 at the temperature T is measured. As described above, the piezoelectric element sensitivity at the temperature T can be obtained by KX (T) = KX (300) × CX (T) / CX (300). The actual scanning distance in the X direction is VX (T) × KX (T), and a voltage is applied to the piezoelectric element 2 of the scanner 29 under the control of the computer 1. The Y direction and the Z direction are similarly calculated, and a voltage is applied to the piezoelectric element 2 of the scanner 29 under the control of the computer 1.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, a piezoelectric element may be installed on the sample holder and the sample side may be scanned. Moreover, you may apply to the scanning probe microscope in atmospheric pressure measurement. Further, in the embodiment, the correction is shown as the piezoelectric element sensitivity is KX (T) = KX (300) × CX (T) / CX (300). However, the software on the computer displays the piezoelectric element sensitivity data for each capacitance. So that the correction may be performed.

  Further, the SPM head may be cooled by a cooling tank as shown in FIG.

It is a detailed view of a conventional scanner. It is a related figure of the temperature change of a piezoelectric element, and an electrostatic capacitance. It is an arrow A figure in FIG. FIG. 4 is a detailed view of a scanner that performs piezoelectric element sensitivity correction after scan waveform generation in the present invention. FIG. 4 is a detailed view of a scanner that performs piezoelectric element sensitivity correction when a scan waveform is generated in the present invention. It is a scanning probe microscope external view. It is observation chamber sectional drawing in FIG. It is a flowchart of the piezoelectric element sensitivity correction program which operate | moves on the computer in FIG. It is observation chamber sectional drawing at the time of cooling an SPM head with a cooling tank.

Explanation of symbols

1 Computer 2 Piezoelectric Element 3 X Electrode 4 Y Electrode 5 Z Electrode 6 Probe 7 X High Voltage Amplifier 8 Y High Voltage Amplifier 9 X Scan Waveform Source 10 Y Scan Waveform Source 11 X Capacitance Measurement Wiring 12 Y Capacitance Measurement Wiring 13 X capacitance measuring device 14 Y capacitance measuring device 15 X voltage correcting device 16 Y voltage correcting device 17 Z capacitance measuring 18 Z high voltage amplifier 19 Z scan waveform generating source 20 gas cylinder 21 observation chamber 22 vacuum flange 23 Observation window 24 Anti-vibration table 25 Vacuum pump 26 Computer 27 Sample holder 28 Sample 29 Scanner 30 Heater 31 Temperature sensor 32 SPM head 33 Cooling tank

Claims (6)

In a scanning probe microscope that detects a physical quantity acting between a probe and a sample,
A piezoelectric scanning body that relatively scans the probe and the sample;
A capacitance measuring means for measuring a capacitance of the piezoelectric scanning body;
A scanning probe microscope comprising scanning voltage generating means for supplying a voltage for scanning by the piezoelectric scanning body according to the capacitance measured by the capacitance measuring means. A scanning probe microscope according to claim 1, wherein
The scanning probe microscope characterized in that the scanning voltage generating means has a correction circuit for correcting the voltage by the capacitance.   The scanning probe microscope according to claim 1, wherein the scanning voltage generation unit includes a calculation unit that calculates a scanning voltage according to the capacitance.   4. The scanning probe microscope according to claim 1, wherein the cylindrical piezoelectric body has a scanning electrode for displacing in one direction in the diameter direction and in another direction orthogonal to the one direction. The scanning probe microscope is characterized in that the capacitance measuring means measures the capacitance of the scanning electrode portion, and the scanning voltage generating means independently applies a voltage to each scanning electrode.   5. The scanning probe microscope according to claim 4, wherein the scanning voltage generating means includes a voltage amplifying means and a scanning waveform generating means for each scanning electrode. A scanning probe microscope according to any one of claims 1 to 5,
An airtight sample observation room,
Gas discharging means for discharging the gas in the sample observation chamber;
Sample temperature variable means for heating or cooling the sample;
A scanning probe microscope comprising:

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