JPH04254930A - Probe unit and information processing device and scanning tunnel microscope using the unit - Google Patents

Abstract

PURPOSE:To make the unit rapidly responsive, to stabilize the follow-up to the command and to precisely control displacement by forming a flexible part to close the cavity of a substrate and reducing the part connecting the cavity and the outside. CONSTITUTION:Metallic electrodes 9, 10 and 11 and a ZnO dielectric are alternately laminated on a silicon substrate 1 through a silicon nitride film 2 to constitute a cantilever of specified size, and a probe 4 is formed on the free end of the cantilever. The cantilever is set on the cavity 7 of the substrate 1, a covering sheet 14 previously provided with a protrusion is adhered to the rear of the substrate 1, and a hole extending to the rear from the opening of the substrate 1 through the cavity 7 is closed. Consequently, an antiseismic mechanism is omitted or simplified, and the device to be provided with the probe unit is miniaturized.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a probe unit for detecting tunneling current used in a scanning tunneling microscope or an information processing device that performs high-density recording, reproduction, and erasing of information applying the principle thereof, and a probe unit using the same. This relates to the above-mentioned device, etc.

0002

[Prior Art] In recent years, scanning tunneling microscopes (hereinafter referred to as ST), which can directly observe the electronic structure of surface atoms of conductors, have been
(abbreviated as M) was developed (G. Binning et
al. , Phys. Rev. Lett. 49 (198
2) 57) It has become possible to measure real space images of both single crystal and amorphous materials with extremely high resolution (nanometers or less).

[0003] Such STM uses a metal probe.
This method utilizes the fact that when a voltage is applied between a conductive material and a conductive material and the material is brought close to a distance of about 1 nm, a tunnel current flows between the two. This current is very sensitive to changes in the distance between the two and changes exponentially, so by scanning the probe while keeping the tunnel current constant, it is possible to observe the surface structure in real space with atomic-order resolution. can.

Analysis using this STM is limited to conductive materials, but it has also begun to be applied to structural analysis of thin insulating films formed on the surfaces of conductive materials. Furthermore, the above-mentioned device/
Since the method uses a method of detecting minute currents, it has the advantage of not damaging the medium and allowing observation with low power. Furthermore, since it is possible to operate in the atmosphere, STM is expected to have a wide range of applications.

[0005] In particular, Japanese Patent Application Laid-Open No. 63-161552,
As proposed in Japanese Unexamined Patent Application Publication No. 63-161553, the practical use of high-density recording and reproducing devices is being actively promoted. This uses a probe similar to STM to perform recording by changing the voltage applied between the probe and the recording medium, and the recording medium exhibits switching characteristics with memory characteristics in voltage-current characteristics. A thin film layer of a material such as a chalcogenide or a π-electron based organic compound is used. On the other hand, reproduction is performed by changing the tunnel resistance between the recorded area and the unrecorded area. Recording and reproduction can be performed on a recording medium using this recording method, even if the surface shape of the recording medium changes depending on the voltage applied to the probe.

Conventionally, as a method for forming probes, semiconductor manufacturing process technology is used to create a fine structure on a single substrate (K.E. Peterson, "Silicon").
con as a mechanical M
material”,Proceedings of
The STM constructed using the IEEE, Vol. 70, p. 420, 1982) was published in Japanese Unexamined Patent Application Publication No. 61-2061.
This is proposed in Publication No. 48. This uses single-crystal silicon as a substrate, and uses microfabrication to produce this in the direction parallel to the substrate surface (X
A parallel spring that can be moved slightly in the Y direction is formed, and a cantilever structure tongue-like part in which a probe is formed is provided on the movable part, and an electric field is applied between the tongue-like part and the bottom part to generate static electricity. It is configured to be displaced in a direction perpendicular to the substrate plane (Z direction) by electric power.

[0007] Furthermore, Japanese Patent Laid-Open No. 62-281138 discloses a storage device equipped with a transducer array having a multi-array of tongue-shaped portions similar to that disclosed in Japanese Patent Laid-Open No. 61-206148. has been done.

[0008]

[Problems to be Solved by the Invention] However, the conventional cantilever structure is easily affected by vibrations, etc., and it is extremely difficult to perform precise displacement control with good reproducibility. Therefore, a vibration isolation mechanism to remove vibrations from outside the system is essential, which results in a complicated structure and makes it difficult to downsize the entire device.

[0009] In addition to vibrations from outside the device, parasitic vibrations are likely to occur when the flexible part itself undergoes sudden displacement, and as a result, when controlling the position between the probe and the medium, Another problem was that large discrepancies occurred. If the control is not performed satisfactorily, the probe may come into contact with the scanned medium.
This is a very important problem in that the probe and the medium may be damaged.

[0010] As a specific means for suppressing steep displacements to prevent such parasitic vibrations from occurring, it is possible to ensure control stability by cutting off the high-frequency characteristics of the control signal frequency characteristics. However, on the other hand, this results in sacrificing the responsiveness of probe displacement.

[0011] Originally, such a micro-drive mechanism represented by a cantilever is expected to have high speed in spite of its small movable range, but as mentioned above, it is difficult to achieve high-speed response due to the limitation of vibration. there were.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to overcome the above-mentioned drawbacks of the conventional example, and to enable precise displacement control that enables high-speed response and stable target value tracking even in the presence of disturbances. An object of the present invention is to provide a probe unit, an information processing device using the same, and a scanning tunneling microscope.

[0013]

[Means and actions for solving the problem] The above purpose is to
This is achieved by the invention having the following configuration.

[0014] A probe unit having a beam-shaped flexible portion formed on a substrate and a probe at an end of the flexible portion, the probe unit comprising a driving means for displacing the probe at least in a direction perpendicular to the substrate surface, and This is achieved by a probe unit with a damper mechanism against displacement.

[0015] Here, the beam-shaped flexible portion refers to a beam structure in which one end of the flexible portion is fixed to a substrate, that is, a cantilever structure. The cantilever is formed with at least a driving mechanism and wiring, and a wiring area for applying voltage to the probe. At this time, the shape of the cantilever is arbitrary.

In addition, as means for displacing the cantilever, means such as piezoelectric effect and electrostatic force are generally known, but in view of the maximum displacement amount and the linearity of the displacement amount with respect to the driving voltage, it is preferable to use a piezoelectric bimorph. Displacement means are used. The production of such a piezoelectric bimorph is known. For example, a bimorph structure is formed on the surface of a semiconductor substrate by repeating sputtering or vapor deposition, photolithography, and etching steps, and then the semiconductor substrate is etched to form a cantilevered bimorph structure. It is intended to be supported in a similar manner. Of course, it is also possible to form a bimorph structure by forming a cantilever structure on a semiconductor substrate in advance and then layering a desired material on the cantilever by means such as mask evaporation or mask sputtering. The method of manufacturing the flexible portion does not limit the present invention in any way. Further, the effect of the damper mechanism is not affected by the method of driving the flexible portion, and the present invention does not limit the selectivity of the driving method.

Furthermore, in the above probe unit, the damper mechanism is realized by filling the cantilever lower cavity 7 formed on the substrate with another medium. That is, parasitic vibrations of the cantilever 3 are suppressed by filling the gap with gas (for example, air) and by its damping effect, or by the effect of shifting the natural frequency of the cantilever to a higher frequency range by the gas acting as a spring. It is something to do.

At this time, by narrowing the portion communicating the gap 7 with the outside, gas can be confined in the gap and the resistance of the velocity component can be increased. Furthermore, Japanese Patent Application Publication No. 2-2829
As shown in Publication No. 45, it is easy to house the probe unit itself in a closed system, and at this time, the damper characteristics can be controlled by filling the closed system, including the voids, with a gas other than air or a liquid. It is also possible to do so.

[0019] Conventionally, the reason why the probe unit has exhibited a characteristic of being sensitive to vibrations and the like is mainly due to the fact that the cantilever 3 is formed in a minute size. That is,
In practice, the length of the beam in the longitudinal direction is several tens of μm to several hundred μm.
Since the Q value for that vibration is about 10 to 100
It had an extremely high value, indicating that parasitic vibration was caused by external vibration or the behavior of the cantilever itself. The present invention provides a probe unit with high controllability by suppressing unnecessary displacement by providing a damper mechanism in the cantilever portion.

Furthermore, conventionally known semiconductor manufacturing techniques can be applied to the production of the piezoelectric bimorph structure forming the cavity 7 and the cantilever, and a highly reproducible shape and desired characteristics can be easily obtained. It is possible.

[0021] Also, one or more probes facing the medium are independently driven to write information to the medium, erase written information, read information from the medium, or write information to the medium. The above object can be achieved by using an information processing apparatus that has a damper mechanism as described above as a probe unit in each information processing apparatus that performs writing, reading, and erasing.

Furthermore, in a scanning tunneling microscope in which a sample is inspected by independently driving one or more probes facing the sample, scanning using a probe unit having a damper mechanism as described above is possible. The above objective can be achieved by using a type tunneling microscope.

[0023]

EXAMPLES The probe unit and damper mechanism described above will be explained in detail below using examples.

Example 1 This example will be explained with reference to the drawings. FIG. 1 is a perspective view of the external appearance of the probe unit of this embodiment. This probe unit has a piezoelectric bimorph structure in which metal electrodes and ZnO dielectric are alternately laminated, and has a width of 100 μm and a length of 500 μm.
It consists of a cantilever 3 with a diameter of μm and a probe electrode 4 provided at the free end of the cantilever 3. If such a probe unit is used, the cantilever 3 can be moved in a direction perpendicular to the substrate surface (Z direction) by applying a voltage to the piezoelectric body.
It is possible to flex the probe and displace the probe position in the Z direction. Furthermore, the cantilever 3 is formed on the cavity 7 of the substrate, and in this embodiment, this cavity is filled with air. The steps for forming the bimorph and damper mechanism will be explained below using FIG. 2.

First, a silicon nitride film 2 having a thickness of 500 nm was formed as an insulating film on the surface of a silicon semiconductor substrate 1 by high-frequency sputtering (FIG. 2(a)). Next, after forming an opening 8 (width 1 μm) in the nitride film through a photolithography process,
A piezoelectric bimorph consisting of a laminated structure of a metal electrode and a piezoelectric material was formed on a nitride film (FIGS. 2(b) to 2(e)). As electrode materials, Au with Cr subbing was used for the base electrode 9, and Al was used for the intermediate electrode 10 and the upper electrode 11. Further, for the piezoelectric layer 12, ZnO (film thickness: 1.2 μm) deposited by high frequency sputtering was used. Furthermore, after the entire bimorph device fabricated as described above is covered with a protective layer 13 made of a silicon nitride film deposited by sputtering, a probe 4 having a conical protrusion made of vapor-deposited Au is formed. Ta. Further, anisotropic etching was performed from the bottom of the substrate using a KOH aqueous solution as an etchant to form a void 7 in the opening 8 (FIG. 2(f)). Thereafter, a covering plate 14 made of a silicon wafer was adhered to the back surface of the substrate to close the back side of the hole penetrating from the front surface to the back surface of the substrate, thereby obtaining a probe unit whose cross section is schematically shown in FIG. 3. Incidentally, in order to realize a desired void volume, a protrusion was provided in advance on the cover plate 14 which was adhered from the back side. Here, to describe the dimensions of the void 7, the void volume (V) 5 x 10-13 m3 to 2 x 10-12 m3, the opening area (a) 1 x 10-9 m2 to 8 x 10-9 m2, the void Base area (A) 5 x 10-8 m2 ~ 5 x 10-7 m2
It is. In addition, the vibration mass of the cantilever at this time is 2×
It is 10-9 kg.

The probe unit manufactured as described above was installed in an information processing device having the functions of recording, reproducing and erasing information as shown in FIG.
Publication No. 3-161552 and JP-A-63-161553
Recording, reproducing, and erasing experiments were conducted using a polyimide LB film (two-layer film) laminated on an Au electrode as disclosed in the publication. In this device, reference numerals 17 and 18 are a driving section and a displacement mechanism section that perform coarse movement in the Z direction, and fine movement is performed by the flexible range of the cantilever. Regarding drive in the XY directions, 20 acts as a coarse movement mechanism, and 23 acts as a fine movement mechanism. The Z-direction displacement is servo-controlled, and a bias power supply 25 applies a DC bias voltage between the sample 26 and the probe 4, and the microcomputer 15 calculates an error signal between the current value flowing through the probe and the target value, and the drive circuit 2
4 to displace the cantilever 3. While scanning the probe in the X and Y directions in such a device,
Bias voltage (0.1V) and peak value -6V and +1.5
Electrical information was written by applying a voltage with a continuous pulse wave of V superimposed between the sample and the probe. Furthermore, as a result of reading recorded information from the obtained STM image, it was confirmed that the recorded information and reproduced information matched with good reproducibility. In addition, when the probe approached the recorded area on the sample, a pulse voltage with a peak value of 3V was superimposed on the bias voltage, and the reproduced STM
It has been confirmed that the information recorded from the statue has been erased.

Furthermore, with scanning in the X and Y directions stopped, the probe was brought close to the sample until a tunnel current of about 100 pA flowed, and then the displacement amount of the probe unit was controlled to examine stability. Specifically, while servo control of the probe position (probe/sample distance) is being performed, the tunnel current target value is periodically changed between 100 pA and 1 nA, and at this time, the tunnel current target value is changed in advance in series with the servo system. A programmable filter with a variable cutoff frequency inserted into the
By changing the cutoff frequency of a low-pass filter (-12 dB/oct), we observed the frequency at which the servo system becomes unstable, in other words, the actual measured value of the tunnel current starts to cause damped oscillation or oscillation. As a result, the cutoff frequency is 3 to 5.
It was confirmed that stable displacement control is possible even in the range reaching KHz. However, this frequency is the mechanical natural frequency of the entire device including the sample support stand (approximately 8 to 10
KHz), and it is thought that the response frequency of the single probe unit of this embodiment is even higher.

In this embodiment, the probe unit is installed in an information processing device, but it can be applied as a probe unit for a scanning tunnel current detection device such as an STM without any modification.

Example 2 A probe unit was manufactured in the same manner as in Example 1 except for the damper mechanism. However, at this time, anisotropic etching with KOH was performed from the upper part of the substrate, and by controlling the etching time, a cavity 7 that did not penetrate to the back surface was formed, and a probe unit whose cross section is schematically shown in FIG. 5 was obtained. Here, the depth of the cavity 7 is 12 μm, the volume of the cavity (V) 7 × 10-13 m3, and the area of the opening (a) 4 ×
It was 10-9 m2.

Using the probe unit manufactured as described above, the stability of displacement control was examined in the same manner as in Example 1 when it was installed in an information processing device. As a result, it is still 1~
It was confirmed that stable servo control can be performed even in the 5KHz P frequency band. Regarding the method of forming the damper mechanism, it can be seen that although the method shown in this example has simplified steps compared to Example 1, the same degree of effect on damper characteristics was obtained.

Comparative Example A probe unit without a damper mechanism was manufactured and evaluated (FIG. 6). The probe manufacturing process was the same as in Example 2, but the width of the nitride film opening was 20 μm and the gap between the substrate and the flexible portion was made sufficiently large, resulting in a probe unit with a significantly small damper effect. The evaluation was conducted in the same way as in Example 2, after confirming that recording and reproducing could be performed stably using the fabricated probe unit, the stability of the control system was examined by changing the target value of the servo system.

As a result, the tunnel current target value was set to 100p.
When changing periodically between A and 1 nA, the cutoff frequency of the low-pass filter must be 10 in order for the system to operate stably.
It needed to be ~30Hz or less. If the tunnel current target value to be changed is limited to the range of 100 pA and 300 pA, the cutoff frequency at which stable operation is observed can be increased, but it is about 100 Hz, and stable operation on the KHz order was not realized.

[0033]

[Effects of the Invention] According to the present invention, by adding an extremely simple manufacturing process, it is possible to perform precise displacement control that enables high-speed response and stably follows the target value even in the presence of disturbances. A probe unit can be provided. Further, since the probe unit of the present invention is stable against external vibrations, a vibration isolation mechanism can be omitted or simplified, and the probe unit is suitable for downsizing the entire device in which the probe unit is installed. As a result, economic effects are expected due to the simplification of the vibration isolation mechanism.

[Brief explanation of the drawing]

FIG. 1 shows a perspective view of the external appearance of a probe unit according to a first embodiment of the present invention.

FIG. 2 shows a cross-sectional view of the probe unit showing the main steps of forming the cantilever and damper mechanism.

FIG. 3 shows a schematic cross-sectional view of a probe unit according to a first embodiment of the present invention.

FIG. 4 is a schematic diagram showing the configuration of an information processing device.

FIG. 5 shows a schematic cross-sectional view of a probe unit according to a second embodiment of the present invention.

FIG. 6 is a perspective view of the appearance of a conventional probe unit.

[Explanation of symbols]

1 Silicon substrate 2 Silicon nitride film 3 Cantilever 4 Probe 5 Cantilever probe 7 Cavity 8 Opening 9 Base electrode 10 Intermediate electrode 11 Upper electrode 12 Piezoelectric layer 13 Protective layer 14 Cover plate 15 Microcomputer 16 Display device 17 Z direction roughness Dynamic drive circuit 18 Z direction coarse movement mechanism 19 XY direction coarse movement drive circuit 20 XY direction coarse movement mechanism 21 XY stage 22 Scan drive circuit 23 XY direction fine movement scanning mechanism 24 Servo circuit and probe drive circuit 25 Bias voltage source and probe current amplifier 26 Sample

Claims (6)

[Claims] 1. A beam-shaped flexible section formed on a substrate, a probe on a free end side of the flexible section, and a drive means for displacing the probe at least in a direction perpendicular to the substrate surface. A probe unit characterized in that the flexible portion is formed to close a gap formed on a substrate, and a portion communicating with the gap to the outside is narrowed. 2. The probe unit according to claim 1, wherein the cavity is filled with gas. 3. An information processing apparatus that writes information to the medium and erases written information by independently driving one or more probes facing the medium, as a probe unit, according to claim 1 or An information processing device comprising the probe unit according to item 2. 4. In an information processing device that reads information from a medium by independently driving one or more probes facing the medium, as a probe unit:
An information processing device comprising the probe unit according to claim 1 or 2. 5. An information processing device that writes, reads, and erases information on a medium by independently driving one or more probes facing the medium, as a probe unit according to claim 1 or 2. An information processing device comprising: a probe unit. 6. A scanning tunneling microscope that inspects a sample by independently driving one or more probes facing the sample, comprising the probe unit according to claim 1 or 2 as a probe unit. A scanning tunneling microscope characterized by: