US20090038382A1

US20090038382A1 - Probe and cantilever

Info

Publication number: US20090038382A1
Application number: US12/089,349
Authority: US
Inventors: Kouji Koyama; Toshiro Kotaki; Kazuhiko Sunagawa
Original assignee: Namiki Precision Jewel Co Ltd
Current assignee: Namiki Precision Jewel Co Ltd
Priority date: 2005-10-06
Filing date: 2006-10-06
Publication date: 2009-02-12
Also published as: JP4403585B2; WO2007040283A1; US8104332B2; US20100293675A1; JPWO2007040283A1; EP1950551A1; EP1950551A4

Abstract

[Object of the Invention] To provide a probe 1 for use in a cantilever 2 of an scanning probe microscope (SPM) manufacturable in a simple manufacturing process and usable while allowing full use of the properties of single-crystalline material and a cantilever 2 using that probe.

[Solution] A probe 1 disposed at the tip of beam part 2 a of a cantilever 2 used for an SPM, wherein the probe 1 comprises a needle-like part 1 a having a length of not less than 10 μm or and a flat plate part 1 b having a face contacting a beam part of the cantilever, the needle-like part 1 a and the flat plate part 1 b are integrally formed with a single-crystalline material, and at least one side face of the flat plate part 1b contains a flat surface 1c in order to indicate the crystal orientation of the single-crystalline material.

Description

FIELD OF THE INVENTION

The present invention relates to a probe for use in a scanning probe microscope comprising a single-crystalline material having various properties and a cantilever onto which the probe is disposed.

DESCRIPTION OF RELATED ART

Scanning probe microscopes (hereafter SPM) are widely used as instruments for observing material surfaces in nanoscale resolution. An SPM obtains images using atomic forces and other interactions that occur between the probe tip and a sample surface.
A probe constituting the key part of an SPM is required to have an atomically sharp point. Generally, when manufactured using a single-crystalline material, a probe can easily be formed to have a sharp point. As measurement and observation needs for sample materials with high aspect ratios have been rising, in particular, over the recent years, there is increasingly high demand for probes with a long needle part. Accordingly, single-crystalline materials are increasing the importance of their role.
Previously known conventional methods to fix a probe made of a single-crystalline material, such as single crystal diamond, onto abeam part of a cantilever include the following:
(1) a method of manufacturing a cantilever for atomic force microscope comprising

a process of forming a photoresist on a one side surface of a silicon wafer,
a process of patterning the photoresist,
a process of etching the silicon wafer using the patterned photoresist as a mask,
a process of removing the photoresist after completion of etching,
a process of scratching the surface opposite to the etched surface of the silicon wafer,
a process of growing a diamond to be a probe on the scratched region,
a process of forming an oxide film on the silicon wafer surface after the growth of the diamond,
a process of forming a nitride film on the oxide film surface,
a process of forming a patterned photoresist mask for etching for removing nitride films from the diamond probe and the back side of the silicon wafer,
a process of removing the photoresist,
a process of additionally etching an etched region of the silicon wafer until exposing an oxide film on the diamond probe-formed side of the silicon wafer,
and a process of forming a thin metal film on the etched region of the silicon wafer after completion of etching (Patent Document 1)

(2) a method wherein a rough diamond is fixed in a round stylus holder comprising a magnetic material in order to grind the diamond into a stylus, magnetize the magnetic material of the stylus holder, spread an glue on the beam part of a cantilever, fix the stylus holder on the glue spread surface of the beam part, and separate the magnet from the beam part after solidification of the glue so that the magnetic material of the stylus holder will be demagnetized (Patent Document 2).
[Patent Document 1] JP-A-H05-203444
[Patent Document 2] JP-A-H04-106852

DISCLOSURE OF THE INVENTION

[Problems to be Solved by the Invention]

The method according to the method of Patent Document 1, wherein a probe comprising diamond is formed on the beam part of a cantilever, however, involves many compulsory steps, such as resist and nitride film formation and removal, and therefore has a complicated process.
Moreover, the method according to the method of Patent Document 1, wherein a probe made of diamond is formed on the beam part of a cantilever, requires that the diamond grow inside a hole disposed through the surrounding silicon. The crystalline lattice constant of a diamond growing in there differs significantly from that of the silicon of the beam part. Consequently, the grown crystal of the probe can often be defective and have a drawback of reducing the mechanical strength of the probe.
In addition, in the method according to Patent Document 2, a stylus holder is fixed by using the glue on a cantilever, and a stylus (probe) comprising diamond is fixed on the stylus holder. Thus, this method involves two interfaces between the stylus and the cantilever, and consequently has a high possibility of a shift of the crystal orientation of the diamond on each interface and hence a drawback of being unable to manufacture a probe that makes fall use of the properties of the material.
In view of the aforementioned drawbacks, it is an object of the present invention to provide a probe for use in a cantilever of an SPM manufacturable in a simple manufacturing process and usable while allowing full use of the properties of a single-crystalline material and a cantilever using that probe.

[Means for Solving the Problems]

The inventors have completed the present invention based on their finding that the properties of a probe can be taken full advantage of when a probe having an optimally selected crystal orientation is formed independently of a beam part of a cantilever and mounted on the beam part by means of a flat plate part formed on the base of the probe.
In other words, an aspect of the present invention according to claim 1 is a probe disposed at the tip of a cantilever used for an SPM, the probe comprising a needle-like part having a length of not less than 10 μm and a flat plate part having a face contacting the beam part of the cantilever, the needle-like part and the flat plate part are integrally formed with a single-crystalline material, and at least one side face of the flat plate part containing a flat surface in order to indicate the crystal orientation of the single-crystalline material.
Meanwhile, an aspect of the present invention according to claim 2 is a probe characterized by a structure according to claim 1 and further characterized by the flat surface comprising both side faces of the flat plate part parallel to each other.
Then, two mutually parallel flat surfaces will facilitate the holding of the probe when mounting the probe on the beam part of the cantilever.
Additionally, an aspect of the present invention according to claim 3 is a probe characterized by a structure according to claims 1 and 2 and further characterized by the single-crystalline material made of a single crystal diamond.
A single crystal diamond is known to be the hardest material and is characterized by very high wear resistance as the property of the single-crystalline material. Then, if the scanning direction of a probe can be set parallel to the direction <110> of a {100} plane, which is relatively easy to form, the wear of the probe can be preferably prevented.
An aspect of the present invention according to claim 4 is a cantilever with a probe according to claims 2 and 3, wherein both side faces of the beam part in the cantilever parallel to each other, the probe is disposed on the main surface of the beam part so that both side faces of the flat plate part and those of the beam part are parallel to each other, the distance between both side faces of the flat plate part has a length 0.9 to 1.1 times of that of both side faces between the beam part, and the probe is bonded using a liquid adhesive onto the main surface of the beam part as disposed thereon.
Then, the aforementioned positional configuration of a probe and a beam part allows both side faces of the flat plate part of the probe and that of the beam part to be in alignment with a nearly same plane.

[Effect of the Invention]

According to an embodiment of a probe for use in an SPM in accordance with the present invention, even if manufactured using a single-crystalline material having distinctive properties, an SPM probe will allow a high precision adjustment of crystal orientation as mounted on the beam part of a cantilever. Accordingly, an advantage will be obtained that allows for providing a cantilever making full use of the properties of the single-crystalline material.
According to an embodiment of a cantilever manufacturing method in accordance with claim 4 of the present invention, when both side faces of the flat plate part of a probe and that of the beam part of a cantilever are on an approximately same plane and bonded using a liquid adhesive, a surface tension will act on the surface of the liquid adhesive and push both side faces of the beam part and those of the flat plate part. Consequently, an advantage will be obtained that allows for automatic adjustment of the crystal orientation of a probe to an optimal direction.

PREFERABLE EMBODIMENTS OF THE INVENTION

Explanations are provided below regarding preferable embodiments of the present invention:
A probe 1 according to a preferable embodiment of the present invention consists of a needle-like part 1 a and a flat plate part 1 b, which are integrally formed as illustrated in FIG. 1, and is used as the tip of a cantilever 2 of an SPM.

A single-crystalline material 4 having distinctive properties can be used as a material for a probe 1 according to a preferable embodiment of the present invention. More specifically, use of a single crystal diamond, which is a material having a high wear resistance, is preferable, but a single crystal sapphire or silicon nitride can be used instead.
In measurement or observation using an SPM, a probe 1 and a sample surface are either in an extreme proximity, where interactions such as atomic force can occur, or in a full contact. Then, use of a material having high wear resistance as a single-crystalline material 4 is preferable because the wear of the probe 1 can be prevented in measurement or observation by scanning with a cantilever 2 having the probe 1; consequently, the measuring resolution of the SPM can be long maintained.
The needle-like part 1 a of a probe 1 is given a length of not less than 10 μm, while the point of the needle-like part 1 a has a diameter of several nanometers to several tens of nanometers. Elongation of the needle-like part 1 a facilitates applicability to a high aspect ratio structure. Here, the needle-like part 1 a can be given a length of 1,000 μm so that it can be used for deep etched sample. Alternatively, the needle-like part 1 a can be given a length of less than 500 μm to make the probe 1 less prone to breakage when colliding a sample material.
Meanwhile, the flat plate part 1 b of the probe 1 is given a bottom width of 20 to 500 μm, a depth of 20 to 500 μm, and a thickness of 5 to 500 μm, or preferably 5 to 20 μm. Here, the flat plate part 1 b can have a bottom thickness of less than 20 μm so that a reduced weight of the probe 1 will prevent the lowering of the resonance frequency of a cantilever 2 and consequently increase the resolution of an SPM. Alternatively, the flat plate part 1 b can be not less than 20 μm thick to make the flat plate part 1 b less prone to breakage. On the other hand, the probe 1 should preferably have a bottom area exceeding 400 μm²so that a sufficient contact area between the bottom face and the beam part 2 a of the cantilever 2 can prevent disengagement of the probe 1 from the cantilever 2.
Then, a side face of the flat plate part 1 b of the probe 1 should be provided with at least one flat surface 1 c in order to indicate the crystal orientation of the single-crystalline material 4. The crystal orientation of this flat surface 1 c should preferably be selected to be parallel to a side face of a cantilever 2 when the scanning direction of the cantilever 2 coincides with the most wear-resistant crystal orientation of the single-crystalline material 4. This is because the crystal orientation of the flat surface 1 c, if so selected, can be easily adjusted with high precision when mounting the probe 1 on the beam part 2 a of the cantilever 2.
Moreover, the flat surfaces 1 c on the side faces of the flat plate part 1 b should preferably be formed parallel to each other. In particular, when the probe 1 has a point-symmetric shape, whichever flat surface 1 c can be used for crystal orientation adjustment when mounting the probe 1 on the beam part 2 a of a cantilever 2. Another desirable advantage is the ease of retaining of the probe 1 when mounting the probe 1 on the beam part 2 a of the cantilever 2.
Finally, the needle-like part 1 a and the flat plate part 1 b should be integrally formed using a same single-crystalline material 4. Detailed explanations are given below regarding methods of forming a probe 1.

A single-crystalline material 4 used as the material of a probe 1 described above is cut out to have a bottom face shaped similarly to that of the flat plate part 1 b of the probe 1 and a thickness equivalent to the sum of the length of the needle-like part 1 a of the probe 1 and the thickness of the flat plate part 1 b. Thus, the entire single-crystalline material 4 is polished by publicly known polishing means such as fixed- or slurry-abrasive particles or by scaife polishing for in particular single crystal diamond.
A side face of the single-crystalline material 4 thus cut out should contain at least one flat surface 1 c in order to indicate the crystal orientation of the single-crystalline material 4. The crystal orientation of the flat surface 1 c should preferably be selected to be parallel to a side face of the beam part 2 a of a cantilever 2 when the scanning direction of the cantilever 2 coincides with the most wear-resistant crystal orientation. This is because the crystal orientation of the flat surface 1 c, if so selected, can be easily adjusted with high precision when mounting the probe 1 on the beam part 2 a of the cantilever 2.
The polished single-crystalline material 4 should have a face provided with a needle-like part 1 a, which is formed by ablating the surface of the face except a region corresponding to the needle-like part 1 a. Available ablation techniques include laser ablation, plasma etching, focused ion beam-(FIB) processing, and thermochemical processing among others. Alternatively, means such as a chemical vapor deposition (CVD) method can be employed to form such a needle-like part 1 a on a flat plate part 1 b consisting of the polished single-crystalline material 4.
For example, when a laser ablation technique is used to form a needle-like part 1 a, any of the first through third techniques below, for example, can be used to folio a modified region 5 on the surface of a single-crystalline material 4 excluding a region where the needle-like part 1 a is formed. Then, the modified region 5 is ablated by means of, for example, etching to form such a needle-like part 1 a on the single-crystalline material 4.
The first technique uses a laser 3 that exhibits intrinsic absorption for a single-crystalline material 4 and moves a focus 3 c of the collected light relatively to the single-crystalline material 4.
This technique uses, for example, YAG laser and harmonics thereof, CO₂laser, or excimer laser as the laser 3. Then, the single-crystalline material 4 is placed, for example, as shown in FIG. 2 (a), on a stage 10 having an XYZ movable stage, where the laser 3 emitted from a laser source 3 a is collected by a lens 3 b into the focus 3 c on the surface of the single-crystalline material 4. Then, the XYZ movable stage (not illustrated) is operated to move the single-crystalline material 4 relatively to the focus 3 c and form a modified region 5 in proximity of the focus 3 c.
The second technique uses a laser 3 that exhibits intrinsic absorption for a single-crystalline material 4, in which a masking 11 is pre-formed, to irradiate the laser 3 on a predetermined irradiation area and form a modified region 5 thereon.
This technique uses, for example, YAG laser and harmonics thereof, CO₂laser, or excimer laser as the laser 3. In a region of the surface of the single-crystalline material 4, where a probe 1 is to be pre-formed, the pattern of a masking 11 is pre-formed and the single-crystalline material 4 is placed, as shown in FIG. 2 (b), on a stage 10, where the beam of the laser 3 is narrowed down as necessary by means of a lens 3 b to irradiate a desired area on the single-crystalline material 4 and form a modified region 5 on the region uncovered by the masking 11.
The third technique uses a laser 3 that exhibits multi-photon absorption for a single-crystalline material 4 and moves a focus 3 c of the collected light relatively to the single-crystalline material 4.
This technique uses, for example, Ti-sapphire laser as the laser 3. Then, the single-crystalline material 4 is placed, for example, as shown in FIG. 2 (c), on a stage 10 having an XYZ movable stage so that at least its one side mirror-polished face will be oriented to a laser source 3 a. Following that, the laser 3 emitted from the laser source 3 a is collected by means of a lens 3 b into the focus 3 c and the XYZ movable stage (not illustrated) is operated to move the single-crystalline material 4 relatively to the focus 3 c and form a modified region 5. Then, the laser 3 exhibits multi-photon absorption and provides activation energy required for phase change to form the modified region 5 inside the single-crystalline material 4. The forming of the modified region 5 should preferably start from the farthest to the nearest face from the laser source 3 a in order of distance until the surface of the single-crystalline material 4 is eventually reached.
On the other hand, when a thermochemical ablation technique is used to form a needle-like part 1 a, a single crystal diamond (FIG. 3 (a)) is used as a single-crystalline material 4. After planarization of an ablated surface of the single crystal diamond by means such as mirror-polishing technique to less than Ra=1 nm, a thin film 6 of a carbon-soluble metal such as nickel, rhodium, palladium, platinum, iridium, tungsten, molybdenum, manganese, iron, titanium, chromium, or an alloy consisting thereof is formed with a uniform thickness of not less than 0.1 μm on the ablated surface of the single crystal diamond (FIG. 3 (b)). The thin metal film 6 can be formed using a film formation technique such as sputtering method, molecular beam epitaxy (MBE) method, vacuum evaporation method, ion plating method. Here, the thin metal film 6 can be given a thickness of at least 0.1 μm to make the thin metal film less prone to aggregation in the heat-treatment process described below.
A thin metal film 6 is partially ablated by means such as mechanical processing, laser ablation, photolithography, and focused ion beam (FIB) processing among others according to the shape of a needle-like part 1 a in order to form a single crystal diamond exposing portion 7 (FIG. 3 (c)). Then, a single crystal diamond containing the partially ablated thin metal film 6 is heat-treated to cause absorption of carbon atoms of the single crystal diamond into the thin metal film 6. Then, the thin metal film 6 will be embedded into the single crystal diamond while leaving the single crystal diamond exposing portion 7 behind (FIG. 3 (d)). Consequently, the single crystal diamond exposing portion 7 is left untreated. The residual of the thin metal film 6 on the surface of the single crystal diamond can be removed as necessary by means such as acid treatment (FIG. 3 (e)). Thus, the process described above can be used to form the needle-like part 1 a on the single crystal diamond with high precision.

A probe 1 thus formed is mounted on the tip of the beam part 2 a of a cantilever 2. The beam part 2 a used here is such that has at least one side containing a flat surface 2 c when the face on which the probe 1 is mounted is specified as the top face.
Here, it is desirable that, as shown in FIG. 4, both side faces be formed as flat surfaces 2 c parallel to each other at least in the vicinity of a probe 1—mounting position of a beam part 2 a of a cantilever 2. Moreover, it is also preferable that a probe 1 be formed to have flat surfaces 1 c, of which both surfaces are parallel to each other.
The probe 1 is mounted on the top face of the beam part 2 a of the cantilever 2 in such a manner that a fiat surface 1 c formed on the probe 1 will be mutually parallel to (and preferably on a same plane as) a flat surface 2 c formed on the beam part 2 a. This parallel alignment provides a condition where the crystal orientation of the probe 1 on the cantilever 2 allows full use of the properties of the probe 1.
Here, it is preferable that the flat plate part 1 b and the cantilever 2 be configured so that the distance ratio between each of their respective side faces will be 0.9 to 1.1. It is additionally preferable that the probe 1 and the beam part 2 a be bonded together using a liquid adhesive 8, because, in such a case, the surface tension of the liquid automates the angle adjustment process. As a preferable example of liquid adhesive 8, an epoxy-based adhesive liquefied at ambient temperature or a thermally fusible brazing material can be used.

EXAMPLE

A rectangular parallelepiped single crystal diamond was prepared which had a {100} plane in its top face, a bottom of 50 μm square, and a thickness of 100 μm. The crystal orientation of the single crystal diamond was defined by the top face with {100} plane and the directions of both side faces with {110}. After polishing each face of the single crystal diamond, a thin nickel film 1 μm thick was formed on its top face. Then, an opening with a diameter of approximately 10 nm was cut in the thin nickel film by means of electron beam lithography. When all set, thermochemical processing was carried out to fuse a 50 μm thick layer around the single crystal diamond except the opening into the thin nickel film and form a needle-like part thereon. As the result, a probe made of a single crystal diamond was formed with a needle-like part having a length of 50 μm long and a point diameter of 10 nm, and a bottom diameter of approximately 10 μm around the boundary with the flat plate part.
Then, a cantilever beam part with both side faces parallel to each other with a distance of 50 μm in between was prepared. After a small quantity of an epoxy-based adhesive was applied on the bonding face of the beam part to the probe, the probe was placed on and bonded to the bonding face. Then, an angle between the direction <110>, which was the most wear-resistant crystal orientation of the diamond probe, and the direction perpendicular to the side face of the beam part prepared as the scanning direction of the cantilever was limited to within approximately 5° without any angle adjustment performed.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a probe and a cantilever according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a process for forming a needle-like part of a probe using a laser ablation processing according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a process for forming a needle-like part of a probe using a thermochemical processing technique according to an embodiment of the present invention.

FIG. 4 is a plan view illustrating a preferably formed cantilever beam part according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating a preferable process for bonding a probe and a cantilever beam part according to an embodiment of the present invention.

EXPLANATION OF LETTERS OR NUMERALS

1 Probe
1 a Needle-like part
1 b Flat plate part
2 Cantilever
2 a Beam
1 c, 2 c Flat surface
3 Laser
3 a Laser source
3 b Lens
3 c Focus
4 Single-crystalline material
5 Modified region
6 Thin metal film
7 Single crystal diamond exposing portion
8 Adhesive
9 Cantilever support
10 Stage
11 Masking

Claims

1. A probe disposed at a tip of a cantilever for use in a scanning probe microscope, the probe comprising:

a needle-like part having a length of not less than 10 μm, and

a flat plate part having a face contacting a beam part of the cantilever,

wherein the needle-like part and the flat plate part are integrally formed with a single crystalline material, and a flat surface in order to indicate a crystal orientation of the single-crystalline material is provided on at least one side face of the flat plate part.

2. A probe according to claim 1, wherein the flat surface comprising both side faces of the flat plate part are parallel to each other.

3. A probe according to claim 1, wherein the single-crystalline material is made of a single crystal diamond.

4. A cantilever having a probe according to claim 1,

wherein both side faces of the beam part in the cantilever are parallel to each other,

wherein the probe is disposed on a main surface of the beam part so that both side faces of the flat plate part and those of the beam part are parallel to each other,

a distance between both side faces of the flat plate part has a length 0.9 to 1.1 times that of both side faces of the beam part, and

the probe is bonded using a liquid adhesive onto a main surface of the beam part.

5. A probe according to claim 2, wherein the single-crystalline material is made of a single crystal diamond.

6. A cantilever having a probe according to claim 2, wherein both side faces of the beam part in the cantilever are parallel to each other,

a distance between both side faces of the flat plate part has a length 0.9 to 1.1 times of that of both side faces of the beam part, and

7. A cantilever comprising:

a beam part having a main surface for supporting a probe, said probe comprising:

a needle-like part having a length of not less than 10 μm, and

a flat plate part having a face contacting a beam part of the cantilever,

wherein the needle-like part and the flat plate part of the probe are integrally formed with a single crystalline material with at least one side face of the flat plate part having a flat surface in order to indicate a crystal orientation of the single-crystalline material;

wherein the probe is disposed on the main surface of the beam part so that both side faces of the flat plate part and those of the beam part are parallel to each other, a distance between both side faces of the flat plate part has a length 0.9 to 1.1 times of that of both side faces of the beam part, and the probe is bonded using a liquid adhesive onto a main surface of the beam part.

8. The cantilever according to claim 7, wherein the flat surface comprising both side faces of the flat plate part are parallel to each other.

9. The cantilever according to claim 8, wherein the single-crystalline material is made of a single crystal diamond.