JP2890268B2 - Probe unit, information processing apparatus using the same, and scanning tunnel microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe unit for detecting a tunnel current used in a scanning tunneling microscope or an information processing apparatus for performing high-density recording, reproduction and erasure of information by applying the principle thereof, and a probe unit using the same. The present invention relates to the device and the like.

[0002]

2. Description of the Related Art In recent years, a scanning tunneling microscope (hereinafter referred to as ST) capable of directly observing the electronic structure of surface atoms of a conductor.
M) (G. Binning et a)
l. Phys. Rev .. Lett. 49 (1982)
57), real space images can be measured with remarkably high resolution (not more than nanometers) irrespective of single crystal or amorphous.

[0003] Such an STM is a metal probe.
When a voltage is applied between the conductive material and the conductive material to approach a distance of about 1 nm, a tunnel current flows during that time. Since this current is very sensitive to the change in distance between them and changes exponentially, it is possible to observe the surface structure in real space with atomic-order resolution by scanning the probe so that the tunnel current is kept constant. it can.

Although the analysis using the STM is limited to conductive materials, it has begun to be applied to the structural analysis of an insulating film formed thinly on the surface of the conductive material. Furthermore, the above-described device
Since the means uses a method for detecting a minute current, there is also an advantage that the medium can be observed with low power without damaging the medium. Further, since operation in the atmosphere is possible, a wide range of applications of STM is expected.

[0005] In particular, JP-A-63-161552,
As proposed in JP-A-63-161553 and the like, practical application as a high-density recording / reproducing apparatus has been actively promoted. In this method, recording is performed by changing the voltage applied between the probe and the recording medium using a probe similar to the STM, and the recording medium exhibits a switching characteristic having a memory property in a voltage-current characteristic. A thin film layer of a material, for example, a chalcogenide or a π-electron organic compound is used. On the other hand, reproduction is performed based on a change in tunnel resistance between a recorded area and a non-recorded area. As a recording medium using this recording method, recording and reproduction can be performed even if the surface shape of the recording medium changes according to the voltage applied to the probe.

Conventionally, as a method of forming a probe, a processing technique for forming a fine structure on one substrate using a semiconductor manufacturing process technique (KE Peterson, "Sili"
con as a Mechanical Mater
ial ”, Proceedings of the I
An STM constructed using EEE, vol. 70, p. 420, 1982) has been proposed in JP-A-61-206148. This is based on single crystal silicon
A parallel spring that can finely move in a direction parallel to the substrate surface (XY directions) is formed by micromachining, and a tongue of a cantilever (cantilever) structure having a probe formed on its movable part is provided. It is configured so that an electric field is applied between the substrate and the bottom surface and the surface is displaced in a direction (Z direction) perpendicular to the substrate plane by electrostatic force.

Japanese Patent Application Laid-Open No. Sho 62-281138 discloses a storage device having a converter array in which tongue-shaped portions are arranged in multiples, similar to that disclosed in Japanese Patent Application Laid-Open No. 61-206148. Have been.

[0008]

However, the conventional cantilever structure is susceptible to vibration and the like, and it is extremely difficult to perform precise displacement control with good reproducibility.
Therefore, an anti-vibration mechanism for removing vibration from outside the system is indispensable, and as a result, the structure becomes complicated, and it has been difficult to reduce the size of the entire device.

In addition, not only the vibration from the outside of the device, but also the parasitic vibration easily occurs when the flexible portion itself is suddenly displaced. As a result, in the position control between the probe and the medium, the target value is deviated from the target value. Is also a problem. If the control is not performed satisfactorily, the probe may come into contact with the medium to be scanned,
It is also a very important problem that the probe and the medium are damaged.

As a specific means for suppressing the steep displacement so as not to cause such parasitic vibration, it is possible to secure control stability by cutting off the high frequency characteristics in the frequency characteristics of the control signal. However, on the other hand, the response of probe displacement is sacrificed.

Originally, a minute drive mechanism represented by such a cantilever is expected to have a high speed instead of a small movable range. However, it is difficult to realize a high-speed response because the vibration is limited as described above. there were.

Accordingly, an object of the present invention is to overcome the drawbacks of the conventional example described above, and to enable precise displacement control that enables high-speed response and stably follows a target value in the presence of disturbance. The object of the present invention is to provide a probe unit, a data processing apparatus and a scanning tunnel microscope using the same.

[0013]

The above object is achieved by
This is achieved by the invention having the following configuration.

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

Here, the beam-shaped flexible portion refers to a beam structure having one end fixed at one end of the flexible portion on a substrate, that is, a cantilever structure. The cantilever has at least a driving mechanism and wiring, and a wiring area for applying a voltage to the probe. At this time, the shape of the cantilever is arbitrary.

As means for displacing the cantilever, means such as a piezoelectric effect and an electrostatic force are generally known. However, from the viewpoint of the maximum displacement and the linearity of the displacement with respect to the driving voltage, a piezoelectric bimorph is preferably used. Displacement means is 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 an etching process, and then the semiconductor substrate is etched to change the bimorph structure to a cantilever. It is to be supported in a shape. Of course, after forming the cantilever structure on the semiconductor substrate in advance, it is also possible to form a bimorph structure by laminating 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 at all. Further, the effect of the damper mechanism is not affected by the driving method of the flexible portion, and the present invention does not limit the selectivity of the driving method.

In the above probe unit, the damper mechanism is realized by closing the cantilever lower gap 7 formed on the substrate with another medium. That is, the cavity is filled with gas (for example, air), and the damping action of the gas or the effect of shifting the natural frequency of the cantilever to a higher range by the gas acting as a spring suppresses the parasitic vibration of the cantilever 3. Is what you do.

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

Conventionally, the probe unit has exhibited a characteristic sensitive to vibrations and the like mainly because the cantilever 3 is formed in a minute size. That is,
Practically, the length in the longitudinal direction of the beam is several tens μm to several hundred μm.
The Q value for the vibration is 10 to 100
And the parasitic vibration was caused by the external vibration or the behavior of the cantilever itself. An object of the present invention is to provide a probe unit having high controllability by providing a damper mechanism in a cantilever portion, thereby suppressing a displacement which is originally unnecessary.

Furthermore, a conventionally known semiconductor manufacturing technique can be applied to the fabrication of the piezoelectric bimorph structure forming the gap 7 and the cantilever, and a shape with high reproducibility and desired characteristics can be easily obtained. It is possible.

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

Further, in a scanning tunneling microscope for inspecting a sample by independently driving one or a plurality of probes facing the sample, scanning using a probe unit having the above-described damper mechanism as a probe unit. The above object can be achieved by using a tunneling microscope.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The probe unit and the damper mechanism will be described in detail below using embodiments.

Embodiment 1 This embodiment will be described with reference to the drawings. FIG. 1 is a perspective view of the appearance of the probe unit of the present embodiment. The probe unit has a piezoelectric bimorph structure in which metal electrodes and ZnO dielectrics are alternately stacked, and has a width of 100 μm and a length of 500 μm.
It comprises a μm cantilever 3 and a probe electrode 4 provided at a free end of the cantilever 3. If such a probe unit is used, a voltage is applied to the piezoelectric body to move the cantilever 3 in a direction perpendicular to the substrate surface (Z direction).
And the probe position can be displaced in the Z direction. Further, the cantilever 3 is formed on the gap 7 of the substrate, and in this embodiment, the gap is filled with the atmosphere. The procedure for forming the bimorph and damper mechanism will be described below with reference to FIG.

First, a 500 nm-thick silicon nitride film 2 was formed as an insulating film on the surface of a silicon semiconductor substrate 1 by high frequency sputtering (FIG. 2A). Next, after an opening 8 (1 μm width) is provided in the nitride film through a photolithography process,
A piezoelectric bimorph having a laminated structure of a metal electrode and a piezoelectric body was formed on the nitride film (FIGS. 2B to 2E). As an electrode material, Au was used for the base electrode 9 and Cr was applied to the lower electrode, and Al was used for the intermediate electrode 10 and the upper electrode 11. The piezoelectric layer 12 was made of ZnO (1.2 μm thick) deposited by high frequency sputtering. Further, after covering the entire bimorph element fabricated as described above with a protective layer 13 made of a silicon nitride film deposited by a sputtering method, a probe 4 having a conical projection made of vapor-deposited Au is formed. Was. Further, anisotropic etching using a KOH aqueous solution as an etchant was performed from the lower part of the substrate, and a void 7 was provided in the opening 8 (FIG. 2 (f)). Thereafter, the cover plate 14 made of a silicon wafer is
Was adhered and the back surface side of the hole penetrating from the substrate surface to the back surface was closed to obtain a probe unit having a schematic cross section in FIG. In order to realize a desired void volume, a projection is provided in advance on the cover plate 14 bonded from the back surface. Here, the dimensions of the gap 7 will be described. The gap volume (V) is 5 × 10 ⁻¹³ m ³ to 2 × 10 ⁻¹² m ³ , and the opening area (a) is 1 × 10 ⁻⁹ m ² to 8 ×. 10 ⁻⁹ m ² , and the void bottom area (A) is 5 × 10 ⁻⁸ m ^{2 to} 5 × 10 ⁻⁷ m ² . The vibration mass of the cantilever at this time is 2 × 10 ⁻⁹ kg.

The probe unit manufactured as described above is installed in an information processing apparatus having the functions of recording, reproducing and erasing information shown in FIG. 4 as a recording medium.
JP-A-3-161552 and JP-A-63-161553
Experiments of recording, reproduction and erasure were performed using a laminate of a polyimide LB film (two-layer film) on an Au electrode disclosed in Japanese Unexamined Patent Publication (Kokai) No. H11-15095. In such an apparatus, reference numerals 17 and 18 denote a drive section and a displacement mechanism section for performing coarse movement in the Z direction, and fine movement is performed by the flexible range of the cantilever. As for driving in the XY directions, 20 functions as a coarse movement mechanism and 23 functions as a fine movement mechanism. The Z-direction displacement is servo-controlled, a DC bias voltage is applied between the sample 26 and the probe 4 by the bias power supply 25, the microcomputer 15 calculates an error signal between a current value flowing through the probe and a target value, and a driving circuit 2
4, the cantilever 3 is displaced. While scanning the probe in the XY directions in such an apparatus,
Peak value -6V and +1.5 to bias voltage (0.1V)
Electrical information was written by applying a voltage superimposed with a continuous V pulse wave between the sample and the probe.
Furthermore, as a result of reading the recorded information from the obtained STM image, it was confirmed that the recorded information and the reproduced information matched with good reproducibility. When the probe approached the area where recording was performed on the sample, an operation of superimposing a pulse voltage having a peak value of 3 V on the bias voltage was performed.
It was confirmed that the recorded information was erased from the image.

Further, after stopping the scanning in the X and Y directions, the probe was brought close to the sample until a tunnel current of about 100 pA flowed, and then the displacement of the probe unit was controlled to examine the stability. Specifically, the target value of the tunnel current is periodically changed between 100 pA and 1 nA while the servo control of the probe position (probe / sample distance) is being performed, and at this time, a serial connection is made in advance with the servo system. The cutoff frequency of a programmable filter (low-pass filter, -12 dB / oct) having a variable cutoff frequency is changed, and the servo system becomes unstable. In other words, the measured value of the tunnel current starts to cause damped oscillation or oscillation. An observation of the frequency was made. As a result, the cutoff frequency becomes 3 to
It was confirmed that stable displacement control was possible even in the region reaching 5 KHz. However, such a frequency is the mechanical natural frequency (about 8 to 1) of the entire apparatus including the sample support.
0 KHz), and the response frequency of the probe unit alone in this embodiment is considered to be even higher.

In this embodiment, the probe unit is installed in the information processing apparatus. However, the probe unit can be applied as a probe unit for a scanning type tunneling current detecting device such as an STM without any change.

Example 2 A probe unit was produced in exactly 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 portion of the substrate, and a gap portion 7 not penetrating to the back surface was formed by controlling the etching time, thereby obtaining a probe unit schematically shown in cross section in FIG. Here, the depth of the void 7 is 12 μm, the void volume (V) is 7 × 10 ⁻¹³ m ³ , and the opening area (a) is 4 × 10
^-9 m ² .

Using the probe unit manufactured as described above, the stability of displacement control was examined in the same manner as in Example 1 while being installed in the information processing apparatus. As a result,
It has been confirmed that stable servo control can be performed even in the 5 kHz P frequency band. Regarding the method of forming the damper mechanism, the method shown in the present embodiment has simplified the process as compared with the first embodiment, but it can be seen that the same effect was obtained as the damper characteristics.

Comparative Example A probe unit having no damper mechanism was manufactured and evaluated (FIG. 6). The probe fabrication process was the same as in Example 2, except that the width of the opening of the nitride film was set to 20 μm and the gap between the substrate and the flexible portion was sufficiently large, so that a probe unit having a significantly small damper effect was obtained. In the evaluation, as in Example 2, after confirming that recording and reproduction could be performed stably using the manufactured 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 is set to 100 p
When the frequency is periodically changed between A and 1 nA, the cut-off frequency of the low-pass filter is 10 in order for the system to operate stably.
Ｈｚ30 Hz or less was required. When the target value of the tunnel current to be changed is limited to the range of 100 pA and 300 pA, the cutoff frequency at which the stable operation is observed can be increased, but the stable operation on the order of KHz was not realized because it was about 100 Hz.

[0033]

According to the present invention, by adding a very simple manufacturing process, high-speed response is possible, and precise displacement control in which the target value is followed stably in the presence of disturbance can be realized. The probe unit can be provided. Further, since the probe unit of the present invention is stable against external vibrations, the vibration elimination mechanism can be omitted or simplified, and the probe unit is suitable for miniaturization of the entire equipment on which the probe unit is installed. As a result, it is expected that the simplified seismic isolation mechanism will have an economic effect.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a probe unit showing main steps of forming a cantilever and a damper mechanism.

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

FIG. 4 is a schematic diagram illustrating a configuration of an information processing apparatus.

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon substrate 2 silicon nitride film 3 cantilever 4 probe 5 cantilever probe 7 void 8 opening 9 base electrode 10 intermediate electrode 11 upper electrode 12 piezoelectric layer 13 protective layer 14 covering plate 15 microcomputer 16 display device 17 coarse in Z direction Dynamic drive circuit 18 Z direction coarse movement mechanism 19 XY direction coarse movement mechanism 20 XY direction coarse movement mechanism 21 XY stage 22 Scan drive circuit 23 XY direction fine movement scan mechanism 24 Servo circuit and probe drive circuit 25 Bias voltage source and probe current amplifier 26 samples

────────────────────────────────────────────────── ─── Continuation of the front page (72) Osamu Takamatsu, inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-4-78037 (JP, A) JP-A-4 -143943 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 9/00 G01N 37/00 G11B 9/04 H01J 37/28 G01B 7/34 G01B 21/30

Claims (6)

(57) [Claims] 1. A system comprising a beam-shaped flexible portion formed on a substrate, a probe on a free end side of the flexible portion, and driving means for displacing the probe at least in a direction perpendicular to the substrate surface. A probe unit according to claim 1, wherein the flexible portion is formed so as to close a gap formed on the substrate, and a portion communicating the gap with the outside is narrowed. 2. The probe unit according to claim 1, wherein the gap is filled with a gas. 3. An information processing apparatus for independently driving one or more probes facing a medium to write information on the medium and erasing the written information, wherein the probe unit is used as a probe unit. An information processing apparatus comprising the probe unit according to item 2. 4. The probe unit according to claim 1, wherein the information processing apparatus reads one or more information from the medium by independently driving one or more probes facing the medium. An information processing apparatus comprising: 5. The information processing apparatus according to claim 1, wherein one or more probes facing the medium are independently driven to write, read, and erase information on the medium. An information processing apparatus comprising: a probe unit. 6. A scanning tunneling microscope for inspecting a sample by independently driving one or more probes facing the sample, wherein the probe unit is used as a probe unit.
Or a scanning tunnel microscope provided with the probe unit according to 2.