JPH06300515A - Scanning probe microscope probe and fine machining device - Google Patents

Abstract

PURPOSE:To perform fine pit machining in nanometer scale by applying an appropriate current between a probe of an atomic force microscope and a conductor sample surface. CONSTITUTION:In a surface of a conductive probe 1 provided at a tip of a cantilever 2, an insulating coating film 3 of appropriate thickness of, for example, about 10nm-1mum is formed. A surface where the probe 1 is not fitted is coated with an Au thin film 4 in order to find deflection of the cantilever 2 by means of an optical lever method, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe for a scanning probe microscope used in a scanning probe microscope typified by an atomic force microscope and a fine processing apparatus.

[0002]

2. Description of the Related Art Conventionally, a scanning tunneling microscope (hereinafter referred to as STM) has been used as an apparatus capable of observing a solid surface in an atomic order.
Is proposed. STM is not only for observation, but the height between the sample tips is several V and the width is ms with the distance between the sample tips kept at about 1 nm.
It is possible to form pits and mounds with a diameter of several nanometers on the sample surface by applying a pulse voltage of ec or less [Applied Physics Letter 55, Vol. 17, pp. 1727 to 1729 (1989). (Appl.Ph
ys.Lett.55 (17) 1727-1729 (1989))], and is expected to be applied to ultra-high density probe recording technology. However, in STM, a tunnel current is used to control the distance between probe samples. A current other than the tunnel current flows when the pulse voltage is applied, and the tunnel current is not stable for a while after the application. Therefore, when applying a pulse voltage at a plurality of places, the movement of the places must wait until the tunnel current stabilizes.

In addition to STM, atomic force microscope (hereinafter AFM)
Called) is being developed. The STM detects the tunnel current, but the AFM detects the interatomic force acting between the tip of the probe and the sample surface, and controls the distance between the sample probes by keeping this constant. Therefore, when processing is performed by applying a pulse voltage between the sample tips, stable distance control is possible. Therefore, it is considered possible to process a plurality of locations in a shorter time than STM. In recent years, fine processing has been performed in which the AFM probe is covered with a conductive film and a voltage is applied between the sample probes. For example, Koyanagi et al. Apply Au to the surface of a SiO ₂ cantilever and apply a pulse voltage of -5V for 0.3 seconds between the sample probes while pressing the sample against the sample and maintaining a repulsive force of 10 ^-8 N. By doing so, pits are formed on the graphite surface [Proceedings of the 53rd JSAP Academic Lecture Meeting 4
56 (1992)].

[0004]

[Problems to be Solved by the Invention] However, the above A
In the case of a conductive sample processed by FM, a pulse voltage is applied while the conductive probe is in direct contact with the sample, so an excessive current flows compared with STM processing and pits of less than 25 nm are formed. Is extremely difficult.

In order to solve the above conventional problems, the present invention suppresses the current flowing when a pulse voltage is applied to an appropriate value,
An object of the present invention is to provide a probe for a scanning probe microscope and a microfabrication device capable of forming pits or mounds of less than 25 nm on the surface of a sample.

[0006]

In order to achieve the above object, the probe for a scanning probe microscope of the present invention comprises a cantilever having a probe in which the surface of a sharpened metal or semiconductor is coated with an insulator. It has a configuration.

In the above structure, the thickness of the insulator is 10
It is preferably nm or less. Further, in the above structure, the insulator is preferably a nitride.

Further, the microfabrication apparatus of the present invention comprises the probe for a scanning probe microscope, means for scanning the probe or sample in a three-dimensional direction, means for measuring the amount of deflection of the cantilever, and amount of deflection of the cantilever. And a means for applying a voltage between the sample and the probe.

[0009]

According to the above-described structure of the present invention, since the surface of the conductive probe is covered with the insulating film, the conductive portion of the probe does not come into direct contact with the sample. However, if the insulating film is appropriately thinned, a tunnel current, a field emission current, a displacement current, etc. can flow between the conductive portion of the probe and the sample when the pulse voltage is applied. These currents can be suppressed to several hundred μA or less by changing the height and width of the pulse voltage and adjusting the rising and falling slopes. Therefore, the pits formed on the sample surface are
Can be smaller.

[0010]

EXAMPLES Examples of the present invention will be specifically described below.
FIG. 1 shows a sectional view of a probe according to an embodiment of the present invention.
This probe was prepared by the following method as shown in FIG. A silicon substrate 21 having a resistivity of 0.1 Ω · cm was processed to form a cantilever having a thickness of 20 μm and a length of 100 μm. A nitride film is formed on the surface and the diameter is 5 by photolithography.
A mask 22 having a circle of μm was formed on the surface of the tip of the cantilever (FIG. 2A). After that, the cantilever was isotropically etched with a KOH aqueous solution. Although the lower part of the mask is not etched from the surface, it is etched from the side, so that a protrusion is formed as shown in FIG. 2B. After removing the mask of the nitride film (FIG. 2C), the following treatment was performed in order to further reduce the radius of curvature of the tip portion. The surface of the silicon protrusion was dry-oxidized with dry oxygen at 950 ° C. to form a thermal oxide film 23 (FIG. 2 (d)). During this oxidation process, the silicon at the tips of the protrusions receives stress due to volume expansion during oxidation, and the oxidation rate becomes slower than at other portions, and the radius of curvature of the silicon tips at the bottom of the oxide film is smaller than that before oxidation. Become. If the thickness of the oxide film becomes thicker, the oxidation rate becomes slower, and the relaxation rate of the generated stress becomes faster, so that the above-mentioned action cannot be obtained. Therefore, the thickness of the oxide film in this step is 100
It is desirable that the thickness is between Angstrom (10 nm) and 1 μm. In this example, a 100 nm oxide film was formed. Next, the thermal oxide film 23 is formed into a buffer etch solution (HF: NH ₄ F =
By removing with a mixed solution of 1: 6 (volume ratio), a silicon protrusion having a tip portion with a very small radius of curvature was obtained (FIG. 2 (e)). After removing the thermal oxide film, it was put in a quartz tube, and the surface thereof was nitrided by the following method to form a silicon nitride film 24 (FIG. 2 (f)). 0.1T for quartz tube
Nitrogen gas of orr was introduced, and AC power with a frequency of 400 kHz and 500 kW was applied to the coil installed so as to surround the quartz tube. In this state, the temperature was raised to about 1100 ° C. and kept for 10 hours. After that, when the tip of the probe was observed with a transmission electron microscope, a layer of irregular atomic arrangement with a thickness of about 4 nm was observed on the surface of the cone with regular atomic arrangement. This surface layer is considered to be a nitride film. A 200 nm-thick Au thin film 25 was vapor-deposited on the surface of the cantilever having no probe (FIG. 2 (g)).

As shown in FIG. 3, the probe 31 is attached to the AFM body 33 with a leaf spring 32. At this time, the strength of the leaf spring 32 was adjusted so that it could be electrically connected to the conductive portion inside the probe. The AFM body 33 is made of stainless steel and has a ground potential. The sample 34 is fixed to a three-dimensional fine movement mechanism 36 via an insulating spacer 35. The sample 34 is electrically connected to the pulse generator 37. Fine processing was performed using HOPG as a sample. First, with the probe and sample at ground potential, 1 × 10 ^-9
HOPG (highly oriented graphite) in N repulsive force mode
Area of 50 nm × 50 nm was observed by AFM. In this region, the surface roughness was very small and was 1 nm or less. After the observation, the probe was moved to the center of the visual field, and with the probe at the ground potential, a square wave pulse of 4.0 V and 20 μsec was applied to the sample side. After that, when the sample was returned to the ground potential and subjected to AFM observation again, it was confirmed that a pit having a diameter of 5 nm and a depth of 0.6 nm was formed in the center of the visual field. 50 nm this way
16 pits were formed at a pitch of 10 nm in a region of × 50 nm, but the time required was less than 1 second, which was 1/10 that of STM.
I was able to do the following: Also, it is not a pit, but a few nm
The following mounds were sometimes formed.

Similar results were obtained with a probe having an oxide film formed on its surface by thermal oxidation or plasma oxidation. Similar results were obtained with a probe in which a silicon nitride thin film or a silicon oxide thin film was formed on the probe surface by the CVD method. However, when the oxide film was formed, the reproducibility of the pit formation was lower than that of the probe formed with the nitride film because the film thickness was difficult to control due to natural oxidation in the air.

When the thickness of the nitride film was set to 20 nm, pits could not be formed even if a pulse voltage was applied. This is probably because the distance between the tip of the conductive part of the probe and the surface of the sample was too large, and tunnel current or field emission current did not flow. When the thickness of the nitride film was 4 nm, when a constant voltage of 2 V was applied to the sample with the probe and the sample in contact with each other, it was confirmed that a tunnel current of about 0.1 nA was flowing between the sample probes.

Although low resistance silicon of 0.1 Ω · cm was used in this embodiment, a cantilever and a probe were made of high resistance silicon having a resistivity of 10 Ω · cm or more, and after removing the thermal oxide film. , Cr, Fe, Ni, W, Mo, A
l, Pt, etc. are deposited on the surface of the probe and cantilever,
Even if a probe having a silicon nitride thin film or a silicon oxide thin film deposited thereon by a CVD method was used, pits could be similarly formed on the sample surface. Also, Au
Similar processing was possible when a thin film or a chalcogenide substance such as MoS ₂ or NbSe _{2 was used} as a sample.

[0015]

As described above, according to the present invention, the STM
It became possible to form a fine pit structure with a diameter of less than 25 nm on the surface of a sample made of a conductive material in the fine processing by AFM which can be performed at a higher speed than the above.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross section of a probe according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a method of manufacturing a probe according to an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a microfabrication device according to an embodiment of the present invention.

[Explanation of symbols]

 1 Conductive probe 2 Cantilever 3 Insulating film 4 Au thin film 21 Low resistance silicon substrate 22 Circular mask 23 Thermally oxidized silicon film 24 Silicon nitride film 25 Au thin film 31 Probe 32 Leaf spring 33 AFM body 34 Sample 35 Insulating spacer 36 3D Fine movement mechanism 37 Pulse generator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Yamamoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A probe for a scanning probe microscope comprising a cantilever having a probe in which the surface of a sharpened metal or semiconductor is covered with an insulator. 2. The probe for a scanning probe microscope according to claim 1, wherein the insulator has a thickness of 10 nm or less. 3. The insulator according to claim 1, wherein the insulator is a nitride.
A probe for a scanning probe microscope as described above. 4. The probe according to claim 1, claim 2 or claim 3, means for scanning the probe or sample in a three-dimensional direction, means for measuring the amount of deflection of the cantilever, and amount of deflection of the cantilever. A microfabrication apparatus comprising a control means for keeping the temperature constant and a means for applying a voltage between the sample and the probe.