JPH0293304A - Microscopic device - Google Patents

Abstract

PURPOSE:To simplify the device to be compact in size by incorporating into a scanning- type tunnel microscope a scanning-type capacity microscope whereby a position to be observed by said scanning-type tunnel microscope is determined by said scanning- type capacity microscope and observing the surface of a specimen at said position. CONSTITUTION:When the distance between a probe 21 and a specimen 13 and the position of the specimen 13 are to be determined, both the probe 21 and the specimen 13 are connected to an electrostatic capacity detector circuit 45, a driving element 12 is connected to an X-Y scanner 46 and a driving element 23 is connected to a Z servo 44. In this state, the probe 21 is positioned while being monitored by an optical microscope 15 as a general scanning-type capacity microscope. Then, switches 31-35 are switched for minute observation by a scanning-type tunnel microscope. At this time, the probe 21 and specimen 13 are connected to a tunnel current detector circuit 43 and the driving element 22 is connected both to the Z servo 44 and to X-Y scanner 46, so that the surface of the specimen 13 is observed in the structure of a general STM. Therefore, only by adding a detecting circuit to detect the electrostatic capacity between the specimen and probe essential to the scanning-type tunnel microscope, the device can be made compact and simple.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a microscope device for inspecting the surface condition of a sample, and particularly relates to a scanning tunneling microscope (hereinafter abbreviated as STM). type capacitance microscope m (hereinafter abbreviated as SCaM)
The present invention relates to a microscope device incorporating a microscope.

(Prior art) In recent years, ST has been used to observe sample surfaces on an atomic scale.
M has been developed and is attracting attention. The fourth principle of STM is
This will be briefly explained with reference to FIGS. 6 to 6. As shown in FIG. 4, when the distance between the conductive probe and the sample is reduced to about 10 people, the electron clouds seeping from the surface overlap, allowing electrons to pass between them. At this time, when a slight voltage is applied between the probe and the sample, a tunnel current flows between them. This tunnel current is the probe −
Since the tunneling current value changes sensitively depending on the distance between the samples, the probe is scanned along the sample surface while moving the probe up and down as shown in FIG. 5 to keep the tunneling current value constant. Then, by electrically reading the behavior of the probe as shown in FIG. 6, information on the unevenness of the sample surface can be obtained.

An example of the basic configuration of a conventional STM is shown in FIG. A micrometer or the like is used as the coarse movement mechanism 3 for bringing the probe 1 closer to the sample 2, and a piezoelectric element or the like is used as the fine movement mechanism 4 for finely moving the probe 1 in three axial directions on the surface of the sample 2. In addition, a vibration isolation table 5 is provided to eliminate the influence of disturbances such as vibrations transmitted from the floor surface.

Using STM with this principle and configuration, we can analyze the atomic arrangement and atomic steps on the clean surfaces of semiconductors and metals.
A lot of research is being carried out to inspect surface roughness and shape on a slightly more macroscopic scale than the atomic scale, as well as the surface and surface defects of sputtered metals.

By the way, in view of the principle of operation of STM, it is necessary to maintain the position of the probe at extremely high resolution. In order to increase the positional resolution of the probe, it is necessary to reduce the displacement with respect to the supplied voltage by increasing the rigidity of the piezoelectric element as the fine movement element. In this case, the movement stroke of the fine movement element is sacrificed, and the scanning range of the STM probe in the X-Y direction is generally narrow (approximately 1000 people x 1000 people). Therefore, if the specific phenomenon to be observed is localized in a limited area on the sample surface (for example,
(interface of a compound semiconductor), it is extremely difficult to drive the STM probe into the region to be observed.

The solution to this problem is to use a combination of STM and a scanning capacitance microscope (hereinafter abbreviated as SEM) to observe a relatively large area with SEM and align the STM probe to the target location. After that, it is possible to conduct detailed observation using STM. However, the SEM is a large-scale device and is extremely expensive. Therefore, ST
In a configuration that uses both M and S E M, the device configuration is complicated.
It is large-sized and disadvantageous in terms of cost.

(Problem to be solved by the invention) As described above, the conventional STM has a limit in the scanning range of the probe, and in order to overcome this, combining STM and SEM will lead to a complicated and larger device configuration. There was a problem.

The present invention was made in consideration of the above circumstances, and its purpose is to simultaneously observe a relatively wide area on the sample surface at a stage when the probe and the sample are not yet sufficiently close to each other. The object of the present invention is to provide a microscope device that can locate the observation target position of STM, align the srMm probe to the observation target position, and simplify and downsize the device configuration.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to incorporate a scanning volumetric microscope (hereinafter referred to as STM) into an STM.
(abbreviated as CaM), and after aligning the STM probe with SCaM, fine observation is performed with STM.

That is, in the present invention, a probe is brought close to the surface of a sample to be inspected, a predetermined voltage is applied between the sample and the probe, and the sample or the probe is moved in the X-Y direction parallel to the sample surface. , a scanning tunneling microscope that observes the surface of the sample based on the tunnel current flowing between them, and a scanning tunneling microscope that detects the capacitance between the sample and the probe, and connects the sample or the probe from the time of the tunnel current detection. This microscope device is equipped with a scanning capacitance microscope that observes the sample surface from changes in capacitance when moving in the X-Y direction over a wide range, and the scanning tunneling microscope is used to locate the position to be observed using the scanning tunneling microscope. This is determined using a scanning tunneling microscope, and the sample surface is observed at this position using the scanning tunneling microscope.

(Function) SCaM detects the capacitance between the probe and the sample, and observes the sample surface from the change in capacitance when the sample or probe is moved in the X-Y direction. , the detection accuracy is rougher than STM, but the detection range is sufficiently wide. In addition to the STM configuration, a circuit is installed to detect the capacitance between the tip and the sample.
The distance between the probe and the sample is set to an appropriate distance that is sufficiently farther than when detecting the tunnel region, and the sample or probe is coarsely scanned (covering an area wider than the movement range of the first driving element when detecting the tunnel current). By performing X-Y scanning at coarse intervals), it becomes possible to detect changes in capacitance between the probe and test t4 that occur in response to changes in the distance between the two. For example, a bimorph element or the like is used for the rough scanning mechanism (third drive element), and the scanning area of STM (1000 people x to
(for example, an area of 150×150 μm for an applied voltage of ±75 V).

When scanning such a large area, there may be inclinations and irregularities that are larger than the set distance between the tip and the sample, so the initial set distance between the tip and the sample is maintained. A voltage is supplied to the piezoelectric element (second driving element) through a servo circuit to keep the initial capacitance constant, and the probe or sample integrated with this piezoelectric element moves up and down. Use a feedback system. By electrically reading the behavior of the piezoelectric element and the scanning distance at this time, information corresponding to the shape of the sample surface can be obtained, and STM
The position of the observation target can be fixed.

By adding these SCaM functions to STM, it is possible to align the probe to the desired location on the sample surface. In this case, SCaM, unlike SEM, does not require the addition of complicated configurations such as an electron optical column, and instead adds a circuit that detects the capacitance between the probe and the sample, which is originally provided in STM. Therefore, it is possible to simplify and downsize the entire configuration.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic configuration diagram showing a microscope apparatus according to an embodiment of the present invention, and this apparatus is constructed using a combination of STM and SCaM. In the figure, reference numeral 11 denotes an X-Y stage movable in the X-Y direction.
2. A drive element (third drive element) 12 that is moved in the X-Y direction by a bimorph element is fixed on the stage 11, and a specimen N13 to be inspected is placed a on this drive element 12. Here, the drive element 12 is SC
When detecting the capacitance by aM, the sample 13 is X-Y scanned (for example, the scanning range is 140 μm x 150 μm).
μm). A light source 14 that irradiates light onto the sample 13 and an optical microscope 15 that detects reflected light from the sample 13 are installed diagonally above the sample 13, and these light II+! 14
The surface of the sample 13 is then observed using an optical microscope 15.

The conductive probe 21 is held at the lower end of a drive element (first drive element) 22 made of a piezoelectric element that expands and contracts in the three axes directions of x, y, and z. The upper end of the drive element 22 is connected to the lower end of a drive element (second drive element) 23 made of a piezoelectric element that expands and contracts in the Z direction over a wider range than the drive element 22, and the upper end of the drive element 23 is connected to a micrometer head. 24. Here, the tip of the probe 21 is formed to have an acute angle (for example, a radius of curvature of 500 mm) by electropolishing or the like. The drive element 22 moves the probe 21 minutely during tunnel current detection (for example, scanning range 1000 people x 1000 people), and this drive element 22 has high rigidity and a small stroke relative to the supplied voltage. For example, a tube-type piezoelectric element is used because a piezoelectric element can provide higher resolution. Further, since the drive element 23 requires a larger stroke than the drive element 22, for example, a laminated piezoelectric element is used.

The drive element 12 is connected to X via a changeover switch 34.
- A predetermined voltage is applied by the Y scanner 46. The sample 13 is selectively connected to a tunnel current detection circuit 43 or a capacitance detection circuit 45 via a changeover switch 31. Similarly, the probe 21 is selectively connected to a tunnel current detection circuit 43 or a capacitance detection circuit 45 via a changeover switch 32. Here, tunnel current detection circuit 4
A bias power supply 47 for applying a predetermined voltage between the probe and the sample is connected between the changeover switch 32 and the changeover switch 32 . In addition, the capacitance detection circuit 45 is connected to this circuit and the probe 2.
In order to reduce the influence of capacitance due to the wiring connecting 1 and 1,
It is attached at a position close to the probe 21, for example, at drive elements 22, 23, etc. The drive element 22 includes a changeover switch 3
2 driving voltage is applied from the Z servo circuit 44 through the switch 34, and the X-Y scanner 4 is applied through the changeover switch 34.
6, an X-Y drive voltage is applied. A predetermined voltage is applied to the drive element 23 from the Z servo circuit 44 via the changeover switch 33, and the power supply 3 is applied via the switch 35.
5 to which a predetermined voltage is applied.

The outputs of the tunnel current detection circuit 43 and the capacitance detection circuit 45 are supplied to the two-server circuit 44 together with the microcomputer 41 . In addition, Z in the Z servo circuit 44
The driving voltage is supplied to the oscilloscope 53 together with the microcomputer 41. Then, the microcomputer 41 obtains an SCaM image 51 based on the moving position of the driving element 13 and the static capacitance between the probe and the sample. Drive element 2
S T M l based on the moving position of 1 and the tunnel current
It is supposed to get 52 elephants. Further, the SCaMl image and the STM image are also displayed on an oscilloscope 53 into which the outputs of the Z servo circuit 44 and the X-Y scanner 46 are input.

The operation of this device configured in this way will be explained.

In FIG. 1, the switch 31. ~． 35 is SCaM
This indicates the position during operation. In this state, the second
As shown in Figure (a), the probe 21 and the sample 13 are connected to a capacitance detection circuit 45, the driving element 12 is connected to an X-Y scanner 46, and the driving element 23 is connected to a Z servo circuit 44.
The configuration is similar to that of a general SCaM.

The distance between the probe 21 and the sample 13 is set up to a sensitive detection range of the capacitance detection circuit 45 using, for example, a micrometer 24. The approximate position of sample 13 is
The stage 11 is set to move based on a command from the Y drive circuit 42 . Here, the capacitance detection circuit 45 has a sensitivity of about 250 to a change of 1 rF when the probe-sample distance is 0.2 μm, and about 120 people/“P” when the probe-sample distance is 0.1 μm. Therefore, by reading a change on the order of 0.01 rP, the displacement in the height direction can be determined with the resolution of several people from a distance sufficiently far away from the tunnel current detection area.

Note that since the above-mentioned probe-sample distance setting and sample position setting are performed while observing with the optical microscope 15, the capacitance detection circuit 45 can be operated without causing the probe 21 and the sample 13 to collide. The probe 21 can be easily brought close to the detection range. In addition, for capacitance detection, the probe 2
1 and the capacitance detection circuit 45, the sample 13 side is raster scanned in the X-Y direction.

STM microscopic observation uses tube-type piezoelectric elements that provide high resolution and performance, but as mentioned above, in the case of SCaM, which uses a capacitance detection method, images of individual atoms on the sample surface can be obtained. This is not necessary, and it is sufficient to confirm a location on the sample surface that has a specific phenomenon that is desired to be observed. Therefore, the drive element 12 of the SCaM is required to be capable of raster scanning with a relatively large stroke. If a mechanism incorporating a bimorph element is used as the drive element 12, the resonant frequency will be as low as IKIIz or less, but it can be stably resonant with a relatively high resolution of 150 μm x 150 μm (±
(when 75V is applied) can be scanned. FIG. 3 shows the relationship between the surface of the sample 13 and the scanning area 13a, and the relationship between the scanning area 13a and an STM scanning area 13b, which will be described later.

During actual scanning, the inclination and waviness of the sample 13
Considering that the distance between the samples may be larger than the set distance, the Z servo circuit is set so that the output voltage from the capacitance detection circuit 45 that detects the capacitance between the probe and the sample is constant. A feedback circuit for expanding and contracting the laminated piezoelectric element 23 is provided via 44. Z servo circuit 44 and X-Y
The SCaM image 51 can be obtained by processing the signal output from the scanner 46 with the microcomputer 41 or directly observing it with an oscilloscope 53.

When a place to be minutely observed is confirmed in the S Ca M image 51, the positioning of the probe 21 is performed using, for example, X-Y
Considering the case where a voltage of ±75V is supplied from the scanner 46 to the drive element 12 to scan the sample 13 in the X-Y direction, the probe position C1 at Ov is at the center of the screen, so the above-mentioned This is accomplished by sending a bias voltage from the X-Y scanner 46 to the drive rope 12 so that the desired location is centered on the screen.

After positioning the probe 21 in this way, the switch 31. ~． 35 and proceed to the step of microscopic observation using STM. In this state, as shown in FIG. 2(b), the probe 21 and the sample 13 are connected to the tunnel current detection circuit 43, the driving element 22 is connected to the Z servo circuit 44 and the X-Y scanner 46, and the general The configuration is similar to STM. Further, a Z drive voltage is applied to the drive element 23 from a power source 48 .

The probe 21 is moved in the Z direction and approaches the surface of the sample 13 by varying (for example, increasing) the power source 48. Then, by controlling the power supply 48, the probe 21 can be brought close to the tunnel current detection area of about 10 people from the sample 13. When the probe-sample enters the tunnel current detection region and a slight voltage is supplied from the bias power supply 47, the tunnel current is detected by the tunnel current detection circuit 43, and the I
/■ The converted value is sent to the two-servo circuit 44.

Since the tunnel current value to be controlled is preset in the Z servo circuit 44, when the value manually inputted from the tunnel current detection circuit 43 reaches the set value, the two servo circuits are activated so that the value becomes constant. 44 works to supply voltage to the three-dimensional drive element 22 and move the probe 21 up and down. at this point
The probe 21 is three-dimensionally driven on the sample surface by fixing the voltage supplied to the drive rod 24 and raster scanning the probe 21 in the X-Y direction using the X-Y scanner 46.

When the inclinations and irregularities of minute regions observed by STM are at the atomic level, the X-Y scanner 46
The output signal from the tunnel current detection circuit 43 is processed by the microcomputer 41 to obtain STMa52. When this constant high mode is used, it is possible to increase the scanning period of the probe 21 to the limit of the device, and it is possible to eliminate the effects of temperature drift and the like.

If the above conditions are violated, the Z servo circuit 44 is operated and the output signal of the X-Y scanner 46 and the Z servo circuit 44 are
The microcomputer 41 receives an output signal for driving the drive element 22 and obtains an STM image 52.

Thus, according to this embodiment, a relatively wide area on the sample surface can be observed all at once using SCaM, the STM observation target position can be found, and the STM probe can be aligned to this observation target position. .

By performing this alignment, even if the unique phenomenon to be observed is localized in a limited area on the sample surface, the STM probe can be reliably tracked to the area to be observed. Using STM, it is possible to easily and reliably observe the required locations on the surface of a sample.

In this case, SCaM differs from SEM in that it does not require the addition of complicated structures such as an electron optical column, and it uses the circuit that detects the capacitance between the probe and the sample that is originally provided in STM. Just add it. Therefore, it is possible to simplify and downsize the overall configuration. Also, SE
The observation position by M and the observation position by STM do not necessarily match completely, and there is a possibility that a shift may occur in these detection positions. On the other hand, since SCaM uses the same probe as STM, there is no deviation between the observation position by SCaM and the observation position by STM, and therefore the probes can be properly aligned. Furthermore, since the SCaM and the STM share the Z servo circuit, the X-Y scanner, etc., the increase in the number of components due to the addition of the SCaM can be minimized.

Note that the present invention is not limited to the embodiments described above. For example, the first driving element is not limited to a tube-type piezoelectric element, but may be any element that can provide sufficient resolution when detecting tunnel current in STM. In addition, the second driving element is not limited to a laminated piezoelectric element, but may be any element that can obtain a sufficiently larger stroke in the Z direction than the first driving element, and is furthermore installed on the sample side rather than on the probe side. You may. In addition, the third drive element is not limited to one using a bimorph element, and has sufficient resolution (may be coarser than STM) and sufficient stroke (more than the first drive element) when detecting capacitance in SCaM. Any type that provides a large stroke is fine. others,
Various modifications can be made without departing from the spirit of the invention.

[Effects of the Invention] As detailed above, according to the present invention, SCaM is added to STM.
After incorporating the STM probe and aligning the STM probe with S Ca M, fine observation with STM is performed.
At the stage when the probe and the sample are not yet close enough, a relatively wide area on the sample surface is observed all at once to find the STM observation target position, and the STM river probe is used to accurately locate the STM observation target position. It can be well aligned. Moreover, STM
Since the S Ca M is configured using a mechanism inherent in the device, it is possible to simplify and downsize the device configuration.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a microscope apparatus according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing a state in which the switch is switched to the SCaMlL side -, -, - switch is switched to the STM side , FIG. 3 to FIG. 6 are schematic diagrams for explaining the basic principle of STM, and FIG. 7 is a perspective view showing the basic configuration of a conventional STM. DESCRIPTION OF SYMBOLS 11... X-Y stage, 12... Third drive element, 13... Sample to be inspected, 14... Light source, 15...
Optical microscope, 21... probe, 22... first drive element, 23... second drive element, 24... micrometer, 31, -. 35... Switch, 41... Microcomputer, 42... X-Y drive circuit, 43...
...Tunnel current detection circuit, 44...Z servo circuit,
45...Capacitance detection circuit, 46...X-Y scanner 47.48- source, 51-S Ca M image, 52
,,. STM image, 53...Oscilloscope. Applicant's agent Patent attorney Takehiko Suzue Figures 1 and 2 Figure 3

Claims (6)

[Claims] (1) Bring the probe close to the surface of the sample to be inspected, apply a predetermined voltage between the sample and the probe, move the sample or the probe in the X-Y direction parallel to the sample surface, and a scanning tunneling microscope that observes the surface of a sample based on changes in tunneling current flowing during the detection; and a scanning tunneling microscope that detects the capacitance between the sample and the probe, and X-Y in a wide range
a scanning capacitance microscope that observes a sample surface based on changes in capacitance when moving in a direction, the scanning capacitance microscope determines a position to be observed with the scanning tunneling microscope, A microscope apparatus characterized in that a surface of a sample is observed using the scanning tunneling microscope at a certain position. (2) The scanning tunneling microscope moves the probe in the X-Y direction.
and a second driving element that moves the sample or the probe in the Z direction over a wider range than the driving element, The probe is moved slightly in the X-Y direction and the probe is moved in the Z direction by the first driving element so that the tunneling current remains constant, and the irregularities on the sample surface are observed from changes in the position of the probe in the Z direction. 2. The microscope apparatus according to claim 1, wherein the microscope apparatus comprises: (3) The scanning tunneling microscope moves the probe in an X-Y direction.
and a second driving element that moves the sample or the probe in the Z direction over a wider range than the driving element, Claim 1: The unevenness of the sample surface is observed from the change in tunnel current when the sample is moved minutely in the X-Y direction.
The microscopic apparatus described. (4) The scanning capacitance microscope includes a third drive element that moves the sample or probe in the X-Y direction over a wider range than the first drive element, and a third drive element that is common to the scanning tunneling microscope. 2. The device further comprises a second driving element, and the unevenness of the sample surface is observed from changes in capacitance when the sample or the probe is moved in the X-Y direction by the third driving element.
Or the microscope device according to 3. (5) The scanning capacitance microscope includes a third driving element that moves the sample or probe in the X-Y direction over a wider range than the first driving element, and a third driving element that is common to the scanning tunneling microscope. The sample or the probe is moved in the X-Y direction by the third drive element, and the probe is moved in the Z direction by the second drive element so that the capacitance is constant.
4. The microscope apparatus according to claim 2, wherein the probe moves in the Z direction and the unevenness of the sample surface is observed from changes in the position of the probe in the Z direction. (6) means for applying a predetermined voltage between the sample to be inspected and the probe; means for detecting a tunnel current flowing between the sample and the probe; a first drive element that moves minutely in the Z direction perpendicular to A scanning tunneling microscope that moves the probe minutely in the Y direction and in the Z direction using a first driving element so that the tunneling current remains constant, and observes the sample surface from changes in the position of the probe in the Z direction. a means for detecting capacitance between the sample and the probe; and a third drive element that moves the sample or the probe in the X-Y direction over a wider range than the first drive element. , comprising a second driving element common to the scanning tunneling microscope, and observing the sample surface from changes in capacitance when the sample or probe is moved in the X-Y direction by the third driving element. a scanning capacitance microscope, the scanning capacitance microscope determines a position to be observed using the scanning tunneling microscope, and the sample surface is observed using the scanning tunneling microscope at this position. microscope equipment.