JP3306284B2 - Scanning tunnel microscope equipped with Auger electron detection means - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a scanning tunneling electron microscope for observing a sample by utilizing the principle of the tunnel effect, and in particular, an Auger capable of detecting Auger electrons emitted from the sample. It belongs to the technical field of a scanning tunnel microscope provided with an electron detecting means.

[0002]

2. Description of the Related Art The principle of the so-called tunnel effect, in which when a metal probe having a sharpened tip is brought close to a sample and a small bias voltage is applied during this time, electrons move through a vacuum gap between the probe and the sample. 2. Description of the Related Art A scanning tunneling electron microscope (hereinafter, also referred to as "STM") that has been used has been conventionally developed. This STM is equipped with an excellent surface observation technology with atomic and molecular resolution on the sample surface, and scans the probe or sample two-dimensionally using a piezoelectric element while keeping the distance between the probe and sample constant. By doing so, an uneven image of the sample surface can be obtained at the atomic level. Moreover, recently, it has been found that this STM has a revolutionary method such as a function of scanning each atom.

FIG. 6 is a diagram schematically showing a configuration of a signal processing system in an example of such a conventional STM. In the figure, 1 is an STM, 2 is a sample, 3 is a probe, 4 is a scanner comprising piezoelectric elements 4a, 4b, 4c of X, Y, Z axes, 5 is X
Axis piezoelectric element driving circuit, 6 is a Y axis piezoelectric element driving circuit, 7 is a Z axis piezoelectric element driving circuit, 8 is a scan generator, 9
Denotes a CPU monitor, 10 denotes a bias circuit, 11 denotes a tunnel current I / V amplifier, 12 denotes a logarithmic conversion circuit, 13 denotes a comparison circuit, and 14 denotes an integration circuit.

In the STM 1, the Z-axis piezoelectric element 4c is driven by the Z-axis height adjustment signal, and the probe 3 is brought closer to the sample 7 by an initial set distance d (nm). In this state, the scan generator 8 generates each X- and Y-axis scanning signal according to the control signal. The X and Y axis piezoelectric elements 4a and 4b are driven by these scanning signals, respectively, and the probe 3 scans the surface of the sample 7 in the X and Y axis directions.

At the same time, a bias voltage _VT is applied between the sample 2 and the probe 3 by the bias circuit 13. This bias voltage causes a tunnel current from the probe 3 to the sample 2.
I _T flows. In that case, when the probe 3 scans the surface of the sample 7 X, the Y-axis direction, the distance between the sample 2 and the probe 3 for unevenness of the surface of the sample 7 is changed, the tunneling current I _T
Will also change. Therefore, the distance between the sample 2 and the probe 3 is controlled such that the tunnel current _IT is constant even when scanning in the X and Y-axis directions by the probe 3 is performed.

More specifically, this control will be described. The tunnel current I _T is converted into a voltage by the tunnel current I / V amplifier 11 and amplified and sent to the logarithmic conversion circuit 12.
The logarithmic conversion circuit 12 performs signal conversion, that is, linearizes the output signal of the tunnel current I / V amplifier 11 so as to linearly correspond to the distance between the sample 2 and the probe 3. Next, the output signal of the logarithmic conversion circuit 12 is sent to the comparison circuit 13, and the comparison circuit 13 compares the output value of the logarithmic conversion circuit 12 with a reference value corresponding to a preset tunnel current setting value. . The comparison circuit 13 outputs a difference value between the output value of the logarithmic conversion circuit 12 and the reference value to the integration circuit 14, and the integration circuit 14 integrates the output value of the comparison circuit 13. The Z-axis piezoelectric element 4 c
Is driven and the distance between the sample 2 and the probe 3 is controlled so that the tunnel current _IT is constant.

The output of the integrating circuit 14 is also sent to the CPU monitor 9, and a signal corresponding to the control information of the height of the probe 3 is output as a video signal together with the scan signal of the scan generator 8 sent to the CPU monitor 9. By displaying, an uneven image of the surface of the sample 2 is displayed at the atomic level.

However, such an STM1 has a problem that it is not possible to identify what kind of atoms each atom is made of, that is, to analyze the composition of a sample. In order to solve this problem, various developments such as the STS method for measuring the local electronic state of the surface and the CITS method for two-dimensionally measuring the distribution of atoms have been energetically attempted. The solution has not been established technically in terms of resolution or interpretation.

[0009] On the other hand, as devices become finer and thinner,
In recent years, it has become important to control these elements at the atomic and molecular level to make them finer and thinner. When a thin film controlled at the atomic level or a quantum minute structure is formed, it is important to identify atoms in individual crystal structures in order to produce a stable material. For these reasons, it is increasingly required that STM1 be provided with an analysis function.

One of the ways in which the STM1 is provided with an analysis function is to use Auger electrons emitted from a sample as S
Analysis of a sample surface by capturing and measuring captured Auger electrons by TM1, that is, an STM combined with an Auger function has been proposed, for example, in US Pat. No. 5,099,117. In this U.S. patent, Auger electrons emitted from a sample by a current flowing between a probe and the sample are passed through a cylindrical mirror analyzer by a voltage between an inner tube and an outer tube of the sample, and are passed to the detector. To be detected by this detector.

On the other hand, there has been a considerable demand for mounting a hemispherical analyzer (HSA) on the STM as a high resolution and high sensitivity type.

[0012]

However, in the STM having the Auger function of the above-mentioned U.S. Patent, units such as a probe and a scanner of the STM are built in the space of the detector. It is difficult to bring the detector close to the sample. For this reason, it is difficult to obtain sufficient detection sensitivity with the STM of this US patent.

[0013] In addition, when HSA is mounted on the STM, it is impossible to mount HSA near the sample because of the limitation of the size of the tip of the detector. For this reason,
A sufficient solid angle cannot be secured, and as a result, sufficient detection sensitivity cannot be obtained as in the case of the above-mentioned United States.

The present invention has been made in view of such circumstances, and an object of the present invention is to combine an STM with an Auger function and to detect Auger electrons emitted from a sample with a sufficient detection sensitivity. An object of the present invention is to provide a scanning tunnel microscope provided with an Auger electron detecting means.

[0015]

According to a first aspect of the present invention, there is provided a probe arranged to face a surface of a sample, comprising: a probe holding the probe; A scanner for controlling a relative position with respect to the sample surface, a bias voltage applying unit for applying a voltage between the probe and the sample, and an Auger electron detecting unit for detecting Auger electrons emitted from the sample. When a voltage is applied between the probe and the sample by the bias voltage applying unit, the sample surface is observed by controlling a tunnel current flowing between the probe and the sample, and In a scanning tunnel microscope provided with Auger electron detecting means adapted to detect Auger electrons emitted from the sample by Auger electron detecting means, Auger electron detection means is attached to an end of the scanner facing the sample, and includes at least a screen for capturing the Auger electrons and a grid for energy selection of the Auger electrons, and Auger electrons emitted from the sample. Is captured by the screen.

The invention according to a second aspect is characterized in that the grid and the screen are attached to a probe holder fixed to the scanner and holding the probe.

Further, according to a third aspect of the present invention, the grid is formed from a mesh made of fine conductive wires in a circular shape having an outer peripheral circle and a cross section curved in an arc shape, and a through hole is formed in the center thereof. And the probe is provided so as to pass through the through hole.

Further, according to a fourth aspect of the present invention, the grid comprises:
A predetermined number, and are arranged at predetermined intervals in the axial direction of the probe around the axis of the probe, and the screen is coaxial with the grid and axially from the grid farthest from the sample. The probe is provided at a predetermined interval, and the probe penetrates at least the through hole of the grid facing the sample among the predetermined number of grids.

Further, according to a fifth aspect of the present invention, the outer diameter of each of the predetermined number of grids is set such that the diameter of the grid closest to the sample is the smallest, and the diameter of the grid increases as the distance from the sample increases. It is characterized by having.

According to a sixth aspect of the present invention, in the predetermined number of grids, a grid closest to the sample and a grid farthest from the sample are grounded, and individual variable voltages are applied to other intermediate grids. It is characterized in that the voltage of each grid is set in such a manner.

[0021]

The scanning tunneling microscope provided with the Auger electron detecting means of the present invention having the above-described structure has the following features.
M also has an analysis function by capturing Auger electrons emitted from the sample by a screen, in addition to an observation function by a tunnel current flowing between the probe and the sample. In that case, since the grid and screen are attached to the end of the scan facing the sample,
The grid becomes closer to the sample. As a result, the efficiency of capturing Auger electrons from the sample becomes extremely high. Therefore, the detection sensitivity of the Auger electron detection means increases, and more accurate analysis can be performed.

In addition, since the grid can be positioned very close to the sample, it is possible to set a large solid angle of the grid for capturing Auger electrons. Therefore, even when the number of Auger electrons is small or the peak direction of the emission of Auger electrons emitted from the sample is in any direction, Auger electrons are efficiently captured.

The Auger electron detecting means has a structure in which a probe protrudes from the center of the grid. Therefore, the influence of the electric field generated from the probe holder or the scanner is reduced as much as possible, and Auger electrons can be more efficiently captured.

Further, by changing each voltage of the grid to which the variable voltage is applied, Auger electrons having desired energy are selected, and the selected Auger electrons are captured by the grid farthest from the sample. As a result, energy scanning becomes possible, and Auger electrons having various energies are individually detected.

Further, since Auger electrons are emitted from the sample by the tunnel current, it is possible to analyze atoms individually. In that case, since the applied voltage is low, the surface of the sample is not broken.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an STM used as an example of an embodiment of a light detection system in a minute area according to the present invention.
FIG. 2 is a diagram showing an overall configuration of the embodiment. Note that the above-mentioned conventional STM
The same components as those in the light detection method are denoted by the same reference numerals, and a detailed description thereof will be omitted.

As shown in FIG. 1, in the STM 1 of this embodiment, a scanner 4 for holding a probe 3, a sample holder 17, and an XY stage 18 for moving the sample 2 in the XY plane are all disposed via a flange 19 having a predetermined thickness. It is installed in an ultra-high vacuum chamber.

As shown in FIG. 2, the probe 3 is a probe holder 2
The probe holder 20 has a grid and a screen 21 attached thereto. As shown in detail in FIGS. 3 and 4, the grids include first to fourth grids arranged at predetermined intervals along the longitudinal direction of the probe holder 20.
The screen 21e is composed of grids 21a, 21b, 21c and 21d, and the screen is arranged at a predetermined distance from the fourth grid 21d farthest from the sample 2 along the longitudinal direction of the probe holder 20. Consists of

The first grid 21a is formed from a mesh composed of very fine conductive wires in a circular shape with an outer peripheral circle and in a bowl shape with a cross section curved in an arc shape. A through hole 22 is formed. The first grid 21 a is attached to the probe holder 20 via the first insulator 23 so that the probe 3 is fitted into the through hole 22. Also, the second to fourth grids 21b, 21c, 21d are also the first grid 2 respectively.
1a is formed of the same material and in the same shape,
A through-hole through which the probe holder 20 penetrates is formed at the center of these. Then, the second to fourth grids 21b,
21c and 21d allow the probe holder 20 to be fitted into the through holes, and the second to fourth insulators 2c and 21d respectively.
It is attached to the probe holder 20 via 4, 25, 26.

Further, the first to fourth grids 21a, 21
The diameters of the outer peripheral ends of 1b, 21c, and 21d are larger in this order so that a solid angle α formed by two straight lines facing each other with respect to the center is formed by connecting the outer peripheral ends through the center of the grid. Is set. The outer peripheral ends of the first to fourth grids 21a, 21b, 21c, 21d are supported by an outer peripheral end support insulator 27.

The first to fourth grids 21a, 21b, 2
1c and 21d are connected to voltage application control means 25, respectively, and the screen 21e is connected to a detector 26. A variable voltage is applied to the second and third grids 21b and 21c by the voltage application control means 25, and the first and fourth grids 21a and 21d are applied.
Is to be grounded. By controlling the voltage applied to the second and third grids 21b and 21c to scan the energy of Auger electrons, Auger electrons having energy corresponding to those voltages move the second and third grids 21b and 21c. Each passes and reaches the screen 21e. Thereby, the screen 2
By detecting the current flowing in 1e as the Auger current by the detector 26, the analysis of the sample surface by measuring the Auger electrons is performed. In this manner, the scanner 4, the probe holder 20, the grid and the screen 21, and the detector 26 constitute the Auger electron detection means of the present invention.

In the STM1 of the present embodiment configured as described above, when STM1 is used as an observation function,
As with the above-described conventional STM, the probe 4
Is moved in the Z-axis direction to approach the sample 2 on the order of nm, and then a bias voltage is applied between the probe 3 and the sample 2 by the bias circuit 10. As a result, a tunnel current flows between the probe 3 and the sample 2. In this state, by scanning the probe 3 in the X and Y axis directions by the scan 4,
An uneven image of the surface of the sample 2 is observed.

When the STM 1 is used as an analysis function, similarly, after the probe 3 approaches the sample 2, a voltage is applied between the probe 3 and the sample 2 to generate a tunnel current. . At this time, the first grid 21a is located very close to the sample 2. When the energy of the tunnel current is injected into the sample 2, Auger electrons are emitted from the sample 2. By controlling the voltages of the second and third grids 21b and 21c by the voltage application control means 25, Auger electrons having energy corresponding to those voltages are generated by the first to fourth grids 21.
a, 21b, 21c, 21d sequentially pass through the screen 2
1e. As a result, the Auger current corresponding to the energy of the Auger electrons flowing through the screen 21e is detected by the detector 26, and the surface of the sample 2 is analyzed. Further, Auger electrons having various energies are detected by variously changing the voltage of at least one of the second and third grids 21b and 21c.

In this analysis function, since the voltage applied by the bias circuit 10 is relatively low, the sample 2
The number of Auger electrons emitted from is not so large.
As shown in FIG. 5, when an electron beam is incident on the sample 2, Auger electrons emitted from the sample 2 have a radiation peak in the same reflection angle direction as the incident angle of the incident electron beam. Therefore, the number of Auger electrons to be detected may be extremely small depending on the incident angle of the incident electron beam. However, in the STM1 of this example, since the solid angle α formed by the first to fourth grids 21a, 21b, 21c, 21d is set to be large, even if the number of Auger electrons is small or the peak of Auger electron emission. In any direction, Auger electrons can be efficiently captured. As a result, more Auger electrons are detected, and the analysis of the sample 2 becomes more accurate.

Further, as shown in FIG. 4, the structure in which the probe 3 protrudes from the center of the first grid 21a minimizes the influence of the electric field generated from the probe holder 20, thereby further reducing Auger electrons. It will be caught efficiently.

As described above, according to STM1 of this embodiment, ST
M1 can be provided with an analysis function in addition to the observation function. In that case, the detection efficiency of Auger electrons emitted from the sample 2 is extremely high, so that more accurate analysis can be performed. Moreover, the operation of the analysis function is
Since the operation for generating the tunnel current in the observation function only requires changing the voltages of the second and third grids 21b and 21c, the operation is extremely simple and S
At least one of the observation function and the analysis function can be easily and quickly set in the TM1.

The second and third grids 21b, 2b
Since the energy scan can be performed by variously changing the voltage of 1c, Auger electrons having various energies can be detected. Further, by superimposing the modulation on this voltage, the sensitivity can be improved.

Further, the first to fourth grids 21a, 21
Since only 1b, 21c and 21d are directly attached to the probe holder 20 fixed to the tip of the scanner 4, the Auger electron detecting means can be made very compact.

Further, since the grid can be brought very close to the sample 2, the solid angle of the grid for capturing Auger electrons can be set large. Therefore, even if the number of Auger electrons is small, Auger electrons can be efficiently captured.

Further, by adopting a structure in which the probe 3 protrudes from the center of the grid, the influence of the electric field generated from the probe holder 20 can be reduced as much as possible, and the Auger electrons can be captured more efficiently. Can be. Furthermore,
A cooling magnetic field can be applied to the sample 2 which can detect energy with high sensitivity.

Further, since the applied voltage is low, Auger electrons can be reliably detected and the sample 2 can be analyzed without causing the surface destruction of the sample 2. Further, since the Auger electrons are emitted from the sample by the tunnel current, it is possible to analyze atoms individually.

In the above-described example, a tunnel current flowing between the sample 2 and the probe 3 is used as a means for emitting Auger electrons from the sample 2. It is also possible to use an excitation source for an electron beam such as an electron beam or a laser beam provided in the above. In this case, as shown in FIG. 5, since the direction of incidence of the electron beam on the sample 2 is different from the direction of the probe 3, the direction of the peak of the emission of Auger electrons emitted from the sample 2 is also different. By four grids 21a, 21b, 21c, 21d,
Auger electrons can be efficiently captured.

In the above-described example, three grids for changing the voltage are provided. However, the present invention is not limited to this, and one or more grids may be provided. However, considering the controllability of the energy scan and the compactness of the detection means, it is desirable that the number of grids is three or four. By changing the number of grids for changing the voltage, the number of types of energy of Auger electrons that can be captured can be changed.

[0044]

As is clear from the above description, according to the scanning tunneling microscope provided with the Auger electron detecting means of the present invention, the STM can be provided with an analysis function in addition to an observation function. . In this case, since the capture efficiency of Auger electrons emitted from the sample is extremely high, the detection sensitivity of the Auger electron detection means can be increased, and more accurate analysis can be performed.

In addition, since the Auger electrons are emitted from the sample using the tunnel current in the observation function, the operation of the analysis function can be performed only by changing the grid voltage in addition to the operation of the observation function. The operation is extremely simple. Thereby, at least one of the observation function and the analysis function can be easily and quickly set in the STM.

Further, since a grid for selecting Auger electrons having desired energy by changing a voltage and a screen for capturing Auger electrons are provided, Auger electrons having desired energy can be captured. In particular,
Since a predetermined number of grids for changing the voltage are provided and the voltages of these grids are changed variously, energy scanning becomes possible. Therefore, Auger electrons having various energies can be individually detected.

Further, since the Auger electron detecting means has a structure in which the probe protrudes from the center of the grid, the influence of the electric field generated from the probe holder can be reduced as much as possible, and the Auger electron can be more efficiently emitted. Can be captured.

Further, since the grid is attached to the sample facing end of the scanner, the Auger electron detecting means becomes very compact.

Further, since the grid can be located very close to the sample, the solid angle of the grid for capturing Auger electrons can be set large. Therefore,
Even if the number of Auger electrons is small or the direction of the peak of the emission of Auger electrons emitted from the sample is in any direction, Auger electrons can be efficiently captured.

Further, a cooling magnetic field can be applied to a sample capable of detecting energy with high sensitivity. Furthermore, since the applied voltage is low, Auger electrons can be reliably detected and the sample can be analyzed without destruction of the surface of the sample. Further, since the Auger electrons are emitted from the sample by the tunnel current, it is possible to analyze atoms individually.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a scanning tunnel microscope provided with an Auger electron detecting means according to the present invention.

FIG. 2 is a conceptual diagram of the Auger electron detection means of the present example.

FIG. 3 is an enlarged sectional view showing a scanner to which the first to fourth grids of the present example are attached.

FIG. 4 is a diagram illustrating a relationship between a probe and a grid according to the present embodiment.

FIG. 5 is a diagram illustrating a relationship between an incident direction of an electron beam and a direction of a peak of Auger electron emission.

FIG. 6 is a diagram schematically showing a configuration of a signal processing system in an example of a conventional STM.

[Explanation of symbols]

1 .... Tunneling electron microscope (STM), 2 .... sample,
3 probe, 4 scanner, 4a X-axis piezoelectric element, 4b
Y-axis piezoelectric element, 4c: Z-axis piezoelectric element, 5: X-axis piezoelectric element drive circuit, 6: Y-axis piezoelectric element drive circuit, 7: Z-axis piezoelectric element drive circuit, 8: scan generator, 9: CPU monitor, 10 ... Bias circuit, 11 ... Tunnel current I / V
Amplifier, 12: logarithmic conversion circuit, 13: comparison circuit, 14 ...
Integration circuit, 17: sample holder, 18: X, Y stage,
19: flange, 20: probe holder, 21: grid,
21a: first grid, 21b: second grid, 21c
... 3rd grid, 21d ... 4th grid, 21e ... Screen, 22 ... Through hole, 23 ... First insulator, 24 ... Second
Insulator, 25 ... Third insulator, 26 ... Fourth insulator, 27 ...
Outer edge support insulator

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01N 13/10-13/24 G01N 23/227 H01J 40/00-49/48 JICST file (JOIS)

Claims (6)

(57) [Claims] A probe disposed opposite to a sample surface;
A scanner that holds the probe and controls a relative position of the probe with respect to the sample surface, a bias voltage applying unit that applies a voltage between the probe and the sample,
And at least an Auger electron detecting means for detecting Auger electrons emitted from the sample, wherein when a voltage is applied between the probe and the sample by the bias voltage applying means, a voltage is applied between the probe and the sample. Scanning tunnel microscope provided with Auger electron detecting means for observing the sample surface by controlling a tunnel current flowing through the sample and detecting Auger electrons emitted from the sample by the Auger electron detecting means. In the Auger electron detection means, the scanner is provided at an end of the scanner facing the sample, and includes at least a screen for capturing the Auger electrons and a grid for energy selection of the Auger electrons, and is emitted from the sample. Captured Auger electrons by the screen. Scanning tunneling microscope equipped with an Auger electron detection means. 2. The scanning tunnel according to claim 1, wherein the grid and the screen are mounted on a probe holder fixed to the scanner and holding the probe. microscope. 3. The grid is formed from a mesh made of fine conductive wires in a circular shape having an outer peripheral circle and a cross section curved in an arc shape, and a through hole is formed at the center thereof. 3. A scanning tunnel microscope provided with Auger electron detection means according to claim 1 or 2, wherein a needle is provided through said through hole. 4. The grid according to claim 1, wherein a predetermined number of the grids are arranged around the axis of the probe and at predetermined intervals in an axial direction of the probe, and the screen is coaxial with the grid. The probe is disposed at a predetermined interval in the axial direction from the grid farthest from the sample, and among the predetermined number of grids, the probe penetrates at least the through hole of the grid facing the sample. A scanning tunnel microscope provided with the Auger electron detection means according to claim 3. 5. The diameter of each of the predetermined number of grids is set such that the diameter of the grid closest to the sample is the smallest, and the diameter of the grid is set larger as the distance from the sample increases. A scanning tunnel microscope provided with the Auger electron detecting means according to claim 4. 6. A grid closest to the sample and a grid farthest from the sample among the predetermined number of grids, and each of the other intermediate grids is applied with a variable voltage individually. 6. A scanning tunnel microscope provided with the Auger electron detecting means according to claim 4, wherein a voltage is set.