JPH1090287A - Probe for interatomic force microscope and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probe which can observe a sample even though it is a sample having a steep uneven surface, in the probe of an AFM (interatomic force microscope) furnishing a piezoelectric sheet type displacement sensor to the cantilever, and to provide its manufacturing method. SOLUTION: A probe 3 provided at the tip of a cantilever 2 is made of a silicon with the length more than 1μm, and a triangular pyramid form, and the aspect ratio at the part from the tip of the probe 3 to 1μm is made 5 or more. In the manufacturing method of this AFM probe, a cantilever 2 is produced by applying an anisotropic etching to a single crystal silicon wafer, and the oxydization and the anisotropic etching are repeated alternative to the same silicon wafer, so as to manufacture the probe 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe having a piezoelectric thin film displacement sensor, and more particularly to a probe used for an atomic force microscope or the like.

[0002]

2. Description of the Related Art Atomic force microscope (AFM), which is one of the scanning microscopes.
Is to form a secondary observation image of the sample surface by using a force acting between substances. AFM can observe a material surface or an organic molecule having no electrical conductivity on a nanometer scale, so that it is expected to be widely applied (Yamada, Applied Physics Vol. 59, No. 2, pp. 191 to 192).

[0003] In the sample observation by the AFM, a "contact mode" in which the probe is brought into contact with the sample surface, a "non-contact mode" in which the probe is not in contact, and a so-called "tapping mode" in which the contact and non-contact of the probe are periodically repeated. There is. FIG. 4 is a conceptual diagram of a conventional tapping mode AFM. The AFM has a probe 101, a tube-type actuator 106, a displacement detection system including a laser light source 107 and a photodiode 108, and an electric processing circuit as main components.

[0004] A conventional probe 101 has a cantilever 1.
02, a probe 103, a vibrator 104, and an electrode 105. The cantilever 102 is a flexible plate, and a needle-like probe 1 having a small tip radius of curvature near its tip.
And a vibrator 104 for vibrating the cantilever on an upper surface or a lower surface thereof. Cantilever 102
Vibrates the cantilever near the resonance frequency of
When 3 is brought closer to the sample (about 10 nm), in the case of AFM, the van der Waals force acts between the probe 103 and the sample 100, the resonance frequency of the cantilever 102 changes, and the amplitude changes accordingly. The change in the amplitude is detected by a displacement detection system, and the data is processed to obtain the probe 10.
The distance between the tip of No. 3 and the sample 100 can be measured.

[0005] In the case of AFM observation, a tube-type actuator 106 is usually mounted on an XY stage (not shown), and scans the sample in the X and Y directions, thereby causing atoms on the sample surface and the tip of the probe to be scanned. Van der Waals force acting between the atoms of the atom can be obtained as two-dimensional information.
Further, by scanning the sample while controlling the position of the sample in the Z direction (height direction) using the tube type actuator 106 so as to keep the amplitude of the cantilever 102 constant, the sample surface is directly microscopically scanned. You can know the shape.

Conventionally, a tunnel detection system, an optical interference system, and an optical lever system have been used as a method for detecting a change in the amplitude of the cantilever due to the van der Waals force.
However, any of these methods requires precise alignment between the cantilever and the displacement detection system, and particularly when performing AFM observation in a vacuum or in water, the operation is very complicated.

In addition, the AFM has a visual field of a maximum of about 100 μm, and it takes several minutes to obtain an image of one frame within the range. The AFM does not have a smooth finder function unlike an optical microscope or an electron microscope. To compensate for this, an AFM is used together with a high-magnification optical microscope to obtain a wide field of view. However, even when attempting to align the cantilever and the sample from above using an optical microscope, the AFM's displacement detection system hinders the alignment, which also deteriorates the operability of the AFM.

Therefore, attempts have been made to integrate the displacement detection system and the cantilever. One of the effective methods is a displacement detection system using the piezoelectric effect. For example, an AFM probe in which a lead-based ferroelectric thin film displacement sensor is provided on a cantilever and integrated is being studied (Japanese Patent Application No. 4-180786). As for a cantilever provided with a piezoelectric thin film type displacement sensor, a quadrangular pyramid-shaped silicon nitride probe manufactured in the process of anisotropic etching of a single crystal silicon substrate and formation of a nitride film has been developed (Japanese Patent Application No. Hei. 5-180532).

[0009]

In order to represent the shape of the probe, the ratio between the length and the thickness of the probe (aspect ratio)
Is often used. In general, the probe has a so-called cone shape with a sharp tip, and the aspect ratio is the ratio of the total length of the probe to the thickness of the root. However, since the probe actually manufactured is not a perfect cone, it is more appropriate to use the “tip aspect ratio” defined below. In the present invention, the tip aspect ratio is defined as the aspect ratio in a portion from the tip of the probe to 1 μm. That is, the ratio of the length of 1 μm to the diameter at a position 1 μm away from the tip is the tip aspect ratio.

The above-mentioned quadrangular pyramid-shaped silicon nitride probe has a tip aspect ratio as small as about 2, and is unsuitable for observing a sample whose surface has a larger aspect ratio. The silicon nitride probe employs a technique in which a single crystal silicon substrate is formed by forming a film of silicon nitride in a square pyramid-shaped hole formed by anisotropic etching. Therefore, it has been very difficult to increase the aspect ratio of the probe.

Therefore, the present invention provides an AFM probe in which a cantilever is provided with a piezoelectric thin film type displacement sensor.
It is an object of the present invention to provide a probe capable of observing a steep uneven surface.

[0012]

In order to accurately observe or measure a sample having a large step with respect to the pitch of the surface unevenness, that is, a so-called large aspect ratio, the tip aspect ratio of the probe must be adjusted to the aspect ratio of the sample. Must be greater than the ratio. In the AFM probe of the present invention, the probe is made of silicon having a triangular pyramid shape, and the tip aspect ratio of the probe is increased. That is, in the AFM probe of the present invention, the tip aspect ratio of the probe is 5 or more, and the shape of the probe is triangular pyramid.

The method for manufacturing an AFM probe according to the present invention comprises:
A (100) single crystal silicon wafer was anisotropically etched to produce a cantilever, and a probe was fabricated by alternately repeating oxidation and anisotropic etching on the same silicon wafer. Further, the AFM probe of the present invention has a probe provided at the tip of the lower surface of the cantilever, and a piezoelectric thin film displacement sensor provided at the upper surface of the cantilever.

[0014]

FIG. 1 is a perspective view showing a part of an AFM probe having a probe and a piezoelectric thin film displacement sensor according to the present invention. The probe 1 is configured by providing a probe 3, a piezoelectric thin film 4, a lower electrode (not shown), and an upper electrode 5 on a cantilever 2 of a cantilever projecting from a silicon substrate 6. The probe 3 has a triangular pyramid shape with a tip aspect ratio of 10, and the conical surface is a (111) plane.

It is desirable that the tip of the AFM has a high tip aspect ratio and a small tip radius of curvature. For this purpose, a triangular pyramid is more geometrically suitable than a quadrangular pyramid. On the other hand, the piezoelectric thin film 4 is a thin film having a thickness of 1μm lead zirconate titanate (PZT), is sandwiched between the upper electrode 5 of the lower electrode and the gold platinum, together form d ₃₁ piezoelectric effect To construct a piezoelectric thin film displacement sensor. A buffer layer such as a titanium film or a tantalum film may be provided below the lower electrode, that is, between the lower electrode and the cantilever 2. The piezoelectric thin film displacement sensor of the present invention is arranged on the side opposite to the probe 3 with respect to the cantilever 2. Therefore, there is an advantage that a film can be formed independently of the probe 3 in the manufacturing process.

The upper and lower surfaces of the cantilever 2 correspond to the (100) plane of the silicon single crystal, the dimensions are 0.6 mm in length, 0.15 mm in width and 0.02 mm in thickness, and the resonance frequency is 90 kHz. The spring constant is 250 N / m. FIG. 2 and FIG.
A with a probe and a piezoelectric thin film displacement sensor according to the present invention
It is the schematic for demonstrating an example of the manufacturing method of the FM probe. In actual manufacturing, a large number of probes are collectively formed on one silicon wafer. However, this drawing shows a manufacturing process of one probe. The numbers in parentheses below correspond to the numbers in parentheses in FIGS. 2 and 3 and indicate the order of steps.

(1) 0.3 μm on both surfaces of a silicon substrate 6 which is a part of a (100) single crystal silicon wafer by CVD.
Then, a back etching pattern is formed on the back surface of the silicon substrate 6, and a portion of the silicon nitride film 7 is removed by reactive ion etching to expose silicon. (2) Anisotropic etching of exposed silicon is performed with a potassium hydroxide solution.

(3) Again, CVs are applied to both surfaces of the silicon substrate 6
A silicon nitride film 7 is formed by the method D. (4) A cantilever pattern is formed on both surfaces of the silicon substrate 6 by being aligned and etched until the silicon substrate 6 is penetrated by reactive ion etching to complete the shape of the cantilever 2.

(5) In an oxidation furnace, a silicon oxide film 8 is formed on portions where silicon is exposed, that is, on side surfaces etched by reactive ion etching. (6) Only the silicon nitride film on the back surface is removed by reactive ion etching. (7) When anisotropic etching is performed on an exposed portion of silicon with a potassium hydroxide solution, only the tip of the cantilever where the silicon oxide film 8 is formed on the side surface has a small etching amount, so that the projection 9 remains.

(8) After dissolving and removing the silicon oxide film with a mixed solution of hydrofluoric acid and ammonium fluoride, a silicon oxide film is formed again on the surface of the projection in an oxidation furnace. The silicon oxide film is removed again with a mixed solution of hydrofluoric acid and ammonium fluoride. By repeating the above steps alternately,
The aspect ratio of the projection 9 gradually increases, and the triangular pyramid-shaped probe 3 is completed.

(9) After a tantalum film, a platinum film, and a lead zirconate titanate film are sequentially formed on the upper surface, that is, on the entire surface opposite to the probe by a sputtering method, a portion is formed only on the upper surface of the cantilever using a metal mask. A gold film is formed by an evaporation method. Through the above steps, the AFM probe of the present invention was completed. The gist of the present invention is to increase the aspect ratio of the projection by the step (8). As a result, a triangular pyramid-shaped probe having a tip aspect ratio as large as 10 can be obtained. As a result, the use of this probe enables the AFM to observe even a sample having a large aspect ratio of surface irregularities.

In the case of a conventional quadrangular pyramid-shaped probe, it is extremely difficult to obtain a probe having a large overall length because of the limitations of the manufacturing method.
By repeating the step (8) many times, the length of the projection can be increased, and a probe with a large overall length can be obtained. As a result, it is possible to cope with the case where a sample having a large unevenness on the surface is observed by AFM.

Furthermore, since a tip having a smaller radius of curvature than a conventional quadrangular pyramid-shaped probe can be easily obtained, the resolution of an AFM observation image is improved.

[0024]

According to the AFM probe of the present invention, since a triangular pyramid-shaped silicon probe having a high tip aspect ratio is provided, even if the surface of the observation sample has a steep uneven surface, Alternatively, measurement becomes possible. The AF of the present invention
Since the probe for M can produce a probe having a large overall length, it can be used for a sample having severe surface irregularities.

In addition, the AFM probe of the present invention is provided with a piezoelectric thin film displacement sensor and the detection system is compact, so that the operation of aligning the cantilever with the sample can be easily performed, and the optical microscope of a high magnification can be used. AFM observation is possible below.

[Brief description of the drawings]

FIG. 1 is a partial perspective view of an AFM probe including a probe and a piezoelectric thin film displacement sensor according to the present invention.

FIG. 2 is a schematic view illustrating an example of a method for manufacturing an AFM probe including a probe and a piezoelectric thin film displacement sensor according to the present invention.

FIG. 3 is a schematic view showing an example of a method for manufacturing an AFM probe including a probe and a piezoelectric thin film displacement sensor according to the present invention.

FIG. 4 is a conceptual diagram of a conventional tapping mode AFM.

[Explanation of symbols]

 1 ... Probe 2 ... Cantilever 3 ... Probe 4 ... Piezoelectric thin film 5 ... Upper electrode 6 ... ······ Silicon substrate 7 ···· Silicon nitride film 8 ··· Silicon oxide film 9 ··· Projection 101 ··· Probe 102 ··· ··· Cantilever 103 ··· Probe 104 ····· Transducer 105 ··· Electrode 106 ··· Tube actuator 107 ··· Laser light source 108 ····· Photo diode

Claims (4)

[Claims] 1. A probe for an atomic force microscope comprising: a cantilever; a probe provided at a tip of a lower surface of the cantilever; and a piezoelectric thin film displacement sensor provided on an upper surface of the cantilever. Is manufactured from the same silicon wafer as the cantilever, has a length of 1 μm or more and has a triangular pyramid shape,
An atomic force microscope probe, wherein the aspect ratio in a portion from the tip of the probe to 1 μm is 5 or more. 2. An upper surface and a lower surface of the cantilever,
(100) parallel to the surface of the single crystal silicon wafer,
The probe for an atomic force microscope according to claim 1, wherein the conical surface of the probe is parallel to the (111) plane of the silicon wafer. Wherein the piezoelectric thin film displacement sensor includes a lead zirconate titanate thin-film, atomic force microscope probe according to claim 1, characterized in that the displacement detected by the d ₃₁ piezoelectric effect. 4. A method of manufacturing a probe for an atomic force microscope, comprising: a cantilever; a probe provided at a tip of a lower surface of the cantilever; and a piezoelectric thin film displacement sensor provided on an upper surface of the cantilever. The method for manufacturing the cantilever includes the step of anisotropically etching the (100) single crystal silicon wafer, and the method for manufacturing the probe includes the step of oxidizing the (100) single crystal silicon wafer and the step of anisotropically etching the (100) single crystal silicon wafer. A method for manufacturing a probe for an atomic force microscope, comprising a step of alternately repeating a step of etching.