JPH04326538A - Manufacture of fine probe and manufacture and manufacture of cantilever type probe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing microprobes and cantilever probes used in scanning tunneling microscopes or high-density recording/reproducing devices applying the principles thereof.

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
M) was developed (G. Binnig et al.
．． , Phys. Rev. Lett. 49 (1982) 5
7) It has become possible to measure real space images of both single crystal and amorphous materials with extremely high resolution (nanometers or less). STM utilizes the fact that a tunnel current flows when a voltage is applied between a metal probe and a conductive substance and the probe is brought close to a distance of about 1 nm. This current is very sensitive to changes in the distance between the two and changes exponentially, so by scanning the probe while keeping the tunneling current constant, it is possible to observe the surface structure in real space with atomic resolution. . Analysis using STM is limited to conductive materials, but
It is also beginning to be applied to structural analysis of thin insulating films formed on the surface of conductive materials. Furthermore, since such devices and means use a method of detecting minute currents, they also have the advantage of being able to perform observations without damaging the medium and with low power. Also,
Operation in the atmosphere is also possible.

It is said that the resolution of this STM is higher as the radius of curvature of the tip of the probe facing the sample surface is smaller. Ideally, it is desired that the tip be as sharp as one atom. Furthermore, one of the applications of this STM is an ultra-high density recording/reproducing device, and of course, in order to achieve high recording density, the radius of curvature of the tip is required to be small. At the same time, from the perspective of improving the functionality of recording/reproducing systems, especially speeding up, it was proposed to drive a large number of probes simultaneously (probe multiplication). Probes are required.

[0004] Conventionally, as a method for forming the above-mentioned microprobes, microprobes arranged in a multi-layered manner by anisotropic etching of silicon using semiconductor manufacturing process technology have been described (Japanese Unexamined Patent Publication No. 61-206148). ). Furthermore, a method for forming a microprobe using a lift-off method has been proposed.

A method for manufacturing a microprobe using this method is shown in FIG. 2 below. First, a composite thin film having a layered structure consisting of a probe extraction electrode 2, a lift-off layer 3, and a mask layer 4 having a circular or polygonal mask opening 6 is prepared on a support 1.

Next, as shown in FIG. 2(a), the support 1
While the probe material 8 is being rotated, a desired probe material 8 is vapor-deposited onto the composite thin film on the support 1 from an oblique direction toward the opening. At this time, the probe material 8 is deposited on the mask layer 4 and also at the end of the opening of the mask layer 4, so as the deposition progresses, the mask opening 6 is covered and the opening area is reduced. decreases (Figure 2(b)). As a result, minute protrusions of the deposited material are formed under the mask layer 4 in the shape of a cone or pyramid with a pointed tip.

Thereafter, by removing the lift-off layer 3 by chemical treatment or the like, a microprobe 9 on the support can be obtained (FIG. 2(c)).

On the other hand, the work function of the surface of the recording medium is changed by applying a voltage from a converter consisting of a tunneling current generating probe located on a driving means whose distance from the recording medium can be finely adjusted, thereby performing recording and writing. Further, a recording/reproducing device has been proposed that reads information by detecting changes in tunnel current due to changes in work function and has a minimum recording area of 10 nm square.

[0009] In such an apparatus, the sample is probed by a number n
It is necessary to scan in the range of m to several μm, and a piezoelectric element (bimorph) is used as the movement mechanism at that time. Examples of this include a tripod type in which three piezoelectric elements are combined perpendicularly to each other along the x, y, and z directions, and a probe is placed at the intersection, and a cylindrical piezoelectric element on the outer peripheral surface. There are types such as a cylindrical type in which the electrode is divided, one end is fixed, a probe is attached to the other end, and the cylinder is deformed and scanned in accordance with each divided electrode.

Furthermore, a cantilever type probe using a piezoelectric bimorph has been proposed (USP No. 4).
, 912, 822). The method for manufacturing this cantilever probe will be described below with reference to FIG.

First, an opening is formed in a part of the back surface of the protective layer 22 formed on the silicon substrate 21, and then KOH
A silicon membrane 23 is formed by anisotropic etching using an aqueous solution (FIG. 5(a)). Next, metal electrode 2
A piezoelectric bimorph consisting of a laminated structure of 4, 26, 28 and piezoelectric bodies 25, 27 is formed on the protective layer 22 (FIG. 5(b)
)). Next, a lift-off layer 29 is formed on the substrate including the piezoelectric bimorph, and then an opening is formed on the piezoelectric bimorph. Subsequently, a probe material 30 is formed by vapor deposition (FIG. 5(c)). Next, the probe 31 is obtained by dissolving the lift-off layer 29 and removing the unnecessary probe material 30. Subsequently, a protective film 32 is formed on the surface (FIG. 5(d)). Next, plasma etching is performed from the back surface direction to remove the silicon membrane 3, and then the protective layer 32 is removed to manufacture a cantilever probe (FIG. 5(e)).

The cantilever probe manufactured in this manner has the following characteristics: (1) Since the probe is formed on the piezoelectric displacement element, the probe position can be moved three-dimensionally in X, Y, and Z directions. ■ Since it is formed using semiconductor manufacturing process technology, miniaturization and multiplication are easy, and mass production is also possible. There are advantages such as:

[0013]

However, in the conventional probe manufacturing method shown in FIG. 2, an organic material such as photoresist or Al2O3 is used for the lift-off layer, and the method for processing the lift-off layer under the mask opening is isotropic. It is processed by natural etching to create an undercut. However, with this method, it is difficult to control undercuts due to uneven etching, and especially when using a photoresist for the lift-off layer and processing with acetone, the processing time is only a few seconds, making it difficult to control undercuts. there were. For this reason, if the undercut is small when forming the probe, resist will remain under the probe and the probe will be removed during lift-off, and if the undercut is large, the mask layer will be curved and the height position of the opening will change. Therefore, there was a problem that the height and shape of the probe varied.

On the other hand, in the conventional method for manufacturing a cantilever type probe shown in FIG. 5, the order of the manufacturing steps is important. This is because when forming a probe after removing the silicon membrane and forming a cantilever made of piezoelectric bimorph, the cantilever has a cantilever shape with a thickness of at most 1 to 2 μm, so the tip of the cantilever is This is because it is extremely difficult to form an opening for the probe in the. Therefore, as in the conventional example, a cantilever type probe is manufactured by removing the silicon membrane after forming the probe. However, this case had the following problems. (2) Since the probe was protected using a relatively soft material such as an organic material, the probe could be damaged or deformed during the plasma etching process that is a subsequent process. This occurred because the surface on which the probe was formed was placed on the cathode electrode of the etching device during plasma etching. ■ Since the protective film is formed directly on the probe, it is difficult to completely remove the protective film when removing it later, resulting in contamination of the probe and deterioration of its characteristics.

[0015] The object of the present invention was made in view of the problems of the prior art described above, and is to manufacture a microprobe that can be formed with good reproducibility and that allows probes with uniform shapes to be obtained when multi-probes are used. The purpose is to provide a method.

An object of the present invention is to provide a method for manufacturing a cantilever probe that can reduce damage to the probe and improve its characteristics.

[0017]

[Means and effects for solving the problems] According to the microprobe manufacturing method of the present invention, a positive photoresist is used for the lift-off layer, and the opening of the lift-off layer is formed into an inverted tapered shape by photolithography using oblique exposure. It is to be formed. Here, since the mask layer serving as a photomask is formed on the lift-off layer, oblique exposure can be easily performed at any angle. Furthermore, by using photolithography, the shape of the opening in the lift-off layer can be easily controlled.

That is, the present invention is characterized by using a positive photoresist as a lift-off layer and a mask having an opening on the lift-off layer in a method for manufacturing a microprobe formed by vapor deposition and lift-off. In this method of manufacturing a microprobe, after forming a layer, the lift-off layer under the opening of the mask layer is exposed to light by oblique exposure, and then a reverse taper pattern is formed under the opening by development.

Further, according to the method for manufacturing a cantilever probe of the present invention, the probe material on the lift-off layer formed after the deposition of the probe material is used as a protective film for the probe in a subsequent process, so that the probe material can be directly attached to the probe. This allows the probe to be protected without forming a protective film.

In other words, the present invention is characterized by the production of a cantilever probe consisting of a substrate, a beam-shaped piezoelectric displacement element formed on the substrate, and a probe provided on the free end side of the piezoelectric displacement element. In the method, a first step is to form a piezoelectric bimorph made of a laminated layer of a metal electrode and a piezoelectric material on a substrate, and a lift-off layer is formed on the entire surface of the substrate on which the piezoelectric bimorph is located after completing the first step. a second step, a third step of forming an opening in the lift-off layer on the piezoelectric bimorph that has completed the second step;
a fourth step of depositing a probe material on the lift-off layer after completing the third step; a fifth step of etching away the substrate under the piezoelectric bimorph of the substrate after completing the fourth step to form a beam shape; The method for manufacturing a cantilever probe includes a sixth step of removing the lift-off layer of the substrate after the fifth step.

Next, the present invention will be explained using the drawings. FIG. 1 is a diagram showing the manufacturing process of the microprobe of the present invention.

In FIG. 1(a), first, a support 1 is prepared. The support 1 is preferably made of a material with small surface irregularities;
For example, #7059 fusion, fused quartz, #7059 with a polished surface, quartz, silicon wafer, etc. can be used. Also, a substrate having a drive mechanism, such as P
An LZT piezoelectric body, a piezoelectric element formed on a substrate, a cantilever using electrostatic force, a double-supported beam, etc. can be used. Next, a probe extraction electrode 2 is formed on the support 1. Since the probe extraction electrode 2 is a wiring for extracting tunnel current, it only needs to have high conductivity. Next, a lift-off layer 3 is formed on the probe extraction electrode 2. It is necessary to use a positive photoresist as the lift-off layer 3 and to perform baking under conditions that do not cause loss of photosensitivity. Next, a mask layer 4 is formed on the lift-off layer 3. Since the mask layer 4 serves as a photomask in a subsequent process, it is preferably made of a metal material that does not transmit ultraviolet rays. Next, a resist layer 5 is formed on the mask layer 4. The baking conditions for the resist layer 5 are preferably lower than the baking temperature for the lift-off layer.

Next, in FIG. 1(b), the resist layer 5
is patterned using photolithography, and the exposed mask layer 4 is removed by etching. Thereafter, the support is tilted with respect to the exposure light source, and the entire surface is exposed while being rotated, thereby exposing the area under the mask opening. In this case, the exposure is performed while rotating the support, but the same effect can be obtained even if the exposure is performed from multiple directions.

Subsequently, in FIG. 1(c), by developing the photosensitive portion, an inversely tapered opening corresponding to the incident angle of exposure is obtained. Further, the resist layer 5 is also removed in the same manner. Note that although an inverted tapered shape is obtained here by oblique exposure and development, if the exposure incident angle becomes deep (an angle close to parallel to the substrate surface), the area directly under the opening may not be exposed. It is better to expose and expose the substrate once from a direction perpendicular to the substrate surface.

Subsequently, in FIG. 1(d), the probe material 8 is formed by oblique vapor deposition while rotating the support. Although a conventionally known thin film forming technique is sufficient as the forming method, since the probe is formed by a lift-off method, a method with high directionality during vapor deposition is preferable. Examples include vacuum evaporation, ion beam sputtering, and the like. Furthermore, the probe material 8 is preferably a highly conductive material that is resistant to oxidation, such as platinum, gold, palladium, and the like. More preferably, hard materials such as WC and TiC are used.

Subsequently, in FIG. 1(e), the lift-off layer 3 is removed using an organic solvent or the like to form the probe 9.

The method for manufacturing a cantilever probe according to the present invention will be explained below with reference to the drawings. FIG. 3 is a cross-sectional view of each manufacturing process of the present invention.

First, in FIG. 3(a), the silicon substrate 21
A protective layer 22 is formed thereon, and then an opening is formed in the protective layer 22 by photo-etching, and then the exposed silicon is processed halfway through anisotropic etching to form a silicon membrane. The protective layer 22 may be made of a material that can be selectively etched with the silicon substrate 21, such as silicon nitride or silicon oxide. Further, as an etching solution for anisotropic etching, a solution whose etching rate differs depending on the crystal orientation of the substrate, such as a potassium hydroxide aqueous solution, ammonia water, hydrazine, an aqueous solution of ethylenediamine and pyrocatechol, etc. can be used.

Next, in FIG. 3(b), after forming a lower electrode 24 on the protective layer 22, a piezoelectric body 25, a middle electrode 26, a piezoelectric body 27, and an upper electrode 28 are sequentially formed to form a piezoelectric bimorph. do. The upper, middle, and lower electrodes are piezoelectric drive electrodes, and are formed by depositing metals such as Al, Au, and Cr. The piezoelectric bodies 5 and 7 are made of a piezoelectric material such as ZnO or AlN, and a C-axis oriented film is formed by magnetron sputtering or the like.

Next, in FIG. 3(c), the lift-off layer 2
9 is formed on a substrate containing the piezoelectric bimorph, and then an opening is formed on the piezoelectric bimorph. The lift-off layer 29 is made of RD-2000, which is a photoresist material.
The opening is formed by an inverted tapered shape such as N (manufactured by Hitachi Chemical) or a two-layer structure of an inorganic material formed on an organic material, or by undercutting the lower layer. Subsequently, the lift-off layer 2
A probe material is formed on 9 by vapor deposition or the like. At this time, since the diameter of the opening gradually decreases as the vapor deposition progresses, a conical protrusion is formed under the opening, which is utilized. This method is a conventionally known technique. Further, as the probe material, noble metals, noble metal alloys, or metal carbides such as WC and TiC can be used.

Next, in FIG. 3(d), the silicon membrane 23 is etched from the back side.
A cantilever type probe is manufactured by removing 3 and further removing the lift-off layer 29 (FIG. 3(e))
. The thin film manufacturing method for the above manufacturing process uses conventionally known techniques, such as thin film manufacturing techniques such as vacuum evaporation, sputtering, and chemical vapor deposition, which are generally used in the semiconductor industry, as well as photolithography and etching techniques. The manufacturing method thereof does not limit the present invention.

[0032]

[Examples] The present invention will be explained in more detail below using Examples.

Example 1 A microprobe was manufactured. The manufacturing process is shown in Figure 1.

First, as shown in FIG. 1(a), a 100 nm thick gold vapor deposited film is patterned on a support 1 to form a probe lead-out electrode 2. Subsequently, a positive photoresist AZ4620 (manufactured by Hoechst) was applied using a spinner, and further prebaked at 100° C. for 30 minutes to form a lift-off layer 3. Spinner rotation speed is 5000 rpm
m, and the resist film thickness obtained at this time was 6.0 μm. Subsequently, a 300 nm thick aluminum vapor deposition film was formed on the lift-off layer 3 to form a mask layer 4. Subsequently, a positive photoresist AZ1370 (manufactured by Hoechst) was coated on the mask layer 4 using a spinner, and further heated at 80°C for 1
Prebaking was performed for 5 minutes to form a resist layer 5 with a thickness of 1.3 μm.

Next, as shown in FIG. 1(b), an area where a microprobe is to be formed is irradiated with ultraviolet light, the resist layer 5 is exposed, and the exposed portions of the resist are removed by development. At this time, the developer used was MIF-312 (manufactured by Hoechst) diluted to half with water, and the development time was 30 seconds. Furthermore, the exposed Al was etched with a phosphoric acid-based etchant to form a mask opening 6. Subsequently, the substrate surface was tilted at 15 degrees with respect to the ultraviolet light source, and the entire surface was irradiated with ultraviolet light 7 while rotating the substrate. At this time, MA-10 (manufactured by Mikasa) was used as an exposure device, and the exposure time was 40 seconds.

Next, as shown in FIG. 1(c), a development process was performed to form an inverted tapered opening in the lift-off layer 3. At this time, AZ developer (manufactured by Hoechst) was used as the developer, and the development time was 60 seconds.

Next, as shown in FIG. 1(d), gold was deposited as a probe material 8 on the structure having such a shape. Vapor deposition was performed from an oblique direction (15 degrees with respect to the vertical direction of the substrate) while the substrate was being rotated. Through the vapor deposition, the probe material 8 grew on the substrate 1 under the mask opening 6 and also on the mask layer 4 at the same time, and the area of the mask opening 6 decreased as the vapor deposition progressed.

Further, as shown in FIG. 1(e), unnecessary portions were removed by lift-off to obtain a probe 9 with a sharp tip. At this time, acetone was used for lift-off, and the lift-off layer 3 was dissolved by ultrasonic cleaning.

Next, when the microprobe prepared by the above method was observed with an SEM (scanning electron microscope), it was found that
A probe with a sharp tip was confirmed. The probe shape had a bottom diameter of 6 μm, a height of 6.5 μm, and a tip radius of curvature of 0.06 μm.

Example 2 A probe was produced in the same manner as in Example 1 except that the probe was made of a multi-layered probe and the probe material was changed to TiC. Note that ion beam sputtering was used to form the TiC film. The number of probes was 25, arranged in a matrix. The pitch between the probes is 20 μm, and the aperture diameter is 4 μm.
And so. When the probe thus formed was observed with an SEM, the probe shape was found to be 6 μm ± 0.2 μm in diameter at the bottom.
, height 6.4μm±0.1μm, tip curvature radius 0.0
The variation was within 5 μm±0.02 μm, and it was found that probes with a uniform shape could be obtained when multi-layered.

Example 3 A cantilever type probe was manufactured. The manufacturing process is shown in Figure 3.

First, a protective layer 2 is formed on a silicon semiconductor substrate 21.
2, a silicon nitride film with a thickness of 200 nm was LP-CV
After forming an opening in the protective layer 22 by the D method and subsequently forming an opening in the protective layer 22 by a photoetching method, the exposed silicon is processed by anisotropic etching using an aqueous potassium hydroxide solution to form a silicon membrane 23 with a thickness of 30 μm. was formed (Fig. 3(a)).

Next, after forming a lower electrode 24 on the protective layer 22, a piezoelectric body 25, a middle electrode 26, a piezoelectric body 27, and an upper electrode 28 were successively formed to form a piezoelectric bimorph. Here, gold with a thickness of 100 nm was used for the electrode by vapor deposition. In addition, the piezoelectric body is coated with a Z layer with a thickness of 300 nm by magnetron sputtering.
nO was used (Figure 3(b)).

Next, RD-200 was used as the lift-off layer 29.
0N photoresist (manufactured by Hitachi Chemical) was applied to the entire surface to a thickness of 2.0 μm, and an opening with a diameter of 2 μm was formed by photolithography. Subsequently, palladium was deposited as a probe material to a thickness of 3 μm on the lift-off layer 29 by vapor deposition. At this time, a probe 31 was formed in the opening (Fig. 3
(c)).

Next, after processing the silicon membrane 23 by plasma etching, the lift-off layer 29 was removed with acetone to produce a cantilever type probe (FIGS. 3(d) and (e)).

When the cantilever probe prepared as described above was observed using a scanning electron microscope (SEM), the probe had a height of 3 μm and a bottom diameter of 2.8 μm.
It had a conical shape. Moreover, no deformation of the probe tip occurred. Furthermore, the cantilever type probe was incorporated into an STM device and evaluated. FIG. 4 is a block diagram of the STM device, in which 201 is a power supply for bias application, 202
203 is a cantilever driving driver; 204 is a cantilever; 205 is a probe;
206 is a sample. Here, a tunnel current It flowing between the probe 205 and the sample 206 is detected,
Feedback is applied so that It is constant, the cantilever is driven, and the distance between the probe 205 and the sample 206 is kept constant. Click here for the sample
Using G substrate, bias current 1nA, scan area 1
When observed at 00 Å x 100 Å, a good atomic image could be obtained with good reproducibility. This confirmed that the probe was not contaminated by resist residue or the like.

Example 4 A cantilever probe was formed using the same manufacturing method as in Example 3 except for the lift-off layer 29. At this time, the lift-off layer 29 is a positive photoresist AZ4620 (
Hoechst Co., Ltd.) was coated to a thickness of 5 μm, aluminum was formed to a thickness of 300 nm, an opening was formed in the aluminum by photo-etching, and the exposed AZ4620 was isotropically processed. Further, palladium with a thickness of 6 μm was used as the probe material, and acetone was used for lift-off.

[0048] When the cantilever type probe prepared as described above was observed with an SEM, the height of the probe was 5.5 μm.
m, and the bottom diameter was 4 μm, and no deformation occurred at the tip. Furthermore, when it was incorporated into STM and evaluated in the same manner as in Example 3, the same results as in Example 3 were obtained.

[0049]

[Effects of the Invention] As explained above, according to the microprobe manufacturing method of the present invention, since the opening in the lift-off layer is formed by photolithography using oblique exposure, the shape of the opening can be controlled with good reproducibility. became. This has the effect that microprobes can be formed with good reproducibility, and probes with uniform shapes can be obtained when multi-layered.

Furthermore, in the method for manufacturing a cantilever type probe of the present invention, the following effects can be obtained by using the probe material of the lift-off layer formed after the deposition of the probe material as a protective film. ■ Since the probe is protected by the probe material, it is less likely to be damaged or deformed in post-processing, which improves yield. (2) Since a protective layer is not directly formed on the probe, the probe surface is not contaminated and the characteristics are improved when used in an STM probe. ■ There is no need to form a new protective film, so
The manufacturing process can be shortened.

[Brief explanation of drawings]

FIG. 1 shows a manufacturing process diagram of a microprobe of the present invention.

FIG. 2 shows a manufacturing process diagram of a conventional microprobe.

FIG. 3 shows a manufacturing process diagram of the cantilever probe of the present invention.

FIG. 4 shows a block diagram of an STM device.

FIG. 5 shows a manufacturing process diagram of a conventional cantilever probe.

[Explanation of symbols]

1 Support 2 Probe extraction electrode 3 Lift-off layer 4 Mask layer 5 Resist layer 6 Mask opening 7 Ultraviolet rays 8 Probe material 9 Probe 21 Substrate 22 Protective layer 23 Silicon membrane 24 Lower electrode 25 Piezoelectric body 26 Middle electrode 27 Piezoelectric body 28 Upper electrode 29 Lift-off layer 30 Probe material 31 Probe 32 Protective film 201 Bias application power supply 202 Tunnel current amplification circuit 203 Cantilever driving driver 204 Cantilever 205 Probe 206 Sample

Claims (2)

[Claims] 1. A method for manufacturing a microprobe formed by vapor deposition and a lift-off method, wherein a positive photoresist is used as a lift-off layer used in the lift-off method, and a mask layer having an opening is formed on the lift-off layer. Thereafter, a lift-off layer under the opening in the mask layer is exposed to light by oblique exposure, and then a reverse taper pattern is formed under the opening by development. 2. A method for manufacturing a cantilever probe consisting of a substrate, a beam-shaped piezoelectric displacement element formed on the substrate, and a probe provided on the free end side of the piezoelectric displacement element. A first step of forming a piezoelectric bimorph made of a laminated layer of a metal electrode and a piezoelectric body, a second step of forming a lift-off layer on the entire surface of the substrate on which the piezoelectric bimorph is located after completing the first step, and the second step. a third step of forming an opening in the lift-off layer on the piezoelectric bimorph that has been completed; a fourth step of depositing a probe material on the lift-off layer that has completed the third step;
a fifth step of removing the substrate under the piezoelectric bimorph of the completed substrate by etching to form a beam shape;
A sixth step of removing the lift-off layer of the substrate after completing the process.
1. A method for manufacturing a cantilever probe, comprising a series of steps.