JPH0735539A - Cantilever incorporated film type displacement sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a cantilever incorporating a film type displacement sensor, which has a stable performance with no restriction to the manufacture thereof, by providing a buffer layer between a flexible plate and a lover electrode. CONSTITUTION:A silicon nitride layer having a thickness of about 0.3mum is formed on a silicon substrate with the use of a CVD process. Next, a part of the silicon nitride layer is removed by reactive dry-etching so as to form a hole where a part which will be turned into a stylus (needle-like chip) after anisotropic etching with the use of potassium hydroxide. Further, silicon nitride is deposited with the use of a CVD process so as to increase the film thickness up to 0.5mum. Further, an aluminum oxide layer is formed over the silicon nitride layer. Then, a lower electrode pattern is formed by photolithography and sputtering. Further, with the use of the same process, a resist pattern is formed, and then, a part of the silicon nitride layer, other than those from which a lever and a substrate are formed, is removed by reactive dry etching. Further, a silicon part is removed so that the lever is formed. A PZT film having a thickness of 1.0mum is formed over the lever by sputtering, and finally, a platinum upper electrode (g) is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cantilevers, and more particularly to cantilevers used in atomic force microscopes and the like.

[0002]

2. Description of the Related Art An atomic force microscope (AFM), which is one of scanning microscopes, forms a secondary observation image of a surface by a force acting between substances. AFM is expected to have a wide range of applications because it can observe material surfaces without electrical conductivity and organic molecules on the nanometer scale (Yamada, Applied Physics Vol. 59, Vol. 2).
No. P191-192).

FIG. 11 shows a conceptual diagram of the principle of a conventional AFM. The AFM is composed of a cantilever composed of a needle-shaped tip having a small tip radius of curvature and a flexible plate, and a displacement detection system for measuring the deflection (bending) of the flexible plate. Next, the measuring method of AFM is described. Bring the needle-like tip at the tip of the cantilever close to the sample (about 10 nm)
Then, static electricity, magnetism, van der Waals force, etc. act between the sample atom and the needle tip to bend the flexible plate. The measurement is performed by detecting the displacement amount of this deflection by a displacement detection system.

Then, by scanning the sample, two-dimensional information on the force on the sample surface can be obtained. Further, the microscopic shape of the surface can be known by scanning the sample while controlling the position of the sample so as to keep the deflection of the flexible plate constant. For example, JP-A-3-218998
Describes a cantilever composed of a silicon substrate and a sharp silicon chip integrated therewith, or a cantilever composed of a silicon nitride substrate and a sharp silicon chip.

In addition to the above cantilever, Japanese Patent Laid-Open No. 1-262403 discloses a cantilever having a structure in which a plate made of silicon rotates. A tunnel detection method, a light wave interference method, and an optical lever method have been used as a displacement detection system for detecting the displacement caused by the force received from the sample atoms of these cantilevers.

In either method, since the movement of the needle-shaped tip is measured by the relative displacement between the cantilever and the displacement detection system, the displacement reading error becomes large unless the displacement detection system is fixed to the cantilever. for that reason,
Conventionally, the cantilever and the displacement detection system are fixed and the sample is scanned. However, in this method, it is necessary to process the sample thin and small because the mechanical characteristics deteriorate as the sample becomes larger. Therefore, we want to scan the cantilever when observing a large sample, but with the conventional AFM,
As described above, it is necessary to scan the cantilever and the heavy displacement detection system as one body, and this cannot be avoided because the characteristics are deteriorated.

Further, the AFM has a field of view of up to 100 μm, and in that range, it takes one frame for several minutes,
It does not have a smooth viewfinder function like an optical microscope or an electron microscope. Also, because of the large displacement detection system, it is not possible to align the cantilever and the sample with an optical microscope with a large NA from above, 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 lead-based ferroelectric thin film displacement sensor is used as a displacement detection system that utilizes the piezoelectric and electrostrictive effects, and a thin film displacement sensor is provided on a flexible plate of the cantilever, and a cantilever is being researched (special feature Wishhei 4-18078
6).

[0009]

SUMMARY OF THE INVENTION
In the AFM in which the electrostrictive thin film type sensor is provided on the flexible plate of the cantilever, in order to prevent the chemical reaction between the flexible plate material such as silicon nitride, silicon oxide and silicon and the lead-based ferroelectric material, the flexible plate is used. It is necessary to cover the entire upper surface (on which the sensor is provided) with platinum that is the lower electrode. Then, the upper electrode is patterned on the lead-based ferroelectric thin film in order to stabilize the performance of the cantilever such as avoiding a short circuit with the lower electrode when reading the induced charge at the root portion.

In the manufacturing process of such a thin film type cantilever with a sensor, patterning of the upper electrode is performed as follows.
It is performed after the lever shape is formed by the etching process. However, after the etching process, there is a restriction on the manufacturing process such that a resist for patterning cannot be formed. In view of such conventional problems, it is an object of the present invention to provide a thin film type displacement sensor-equipped cantilever with stable performance without any restrictions in the manufacturing process.

[0011]

SUMMARY OF THE INVENTION The present inventors firstly found that the reactivity of a lead-based ferroelectric material on the flexible plate is extremely high in order to prevent the reaction between the flexible plate and the lead-based ferroelectric thin film. It was conceived to provide a low buffer layer made of a material such as aluminum oxide or magnesium oxide. This allows
It is not necessary to cover the entire surface of the flexible plate with the lower electrode.

Therefore, as a result of further research, by patterning the lower electrode in an arbitrary shape on the buffer layer in an arbitrary shape, the upper electrode can be formed as a full-scale electrode without patterning. It came to completion. Therefore, the present invention provides a flexible plate, a needle-shaped tip fixed near the tip thereof, a lower electrode provided on the flexible plate, a lead-based ferroelectric intermediate layer having piezoelectric or electrostrictive characteristics. A cantilever having a thin film displacement sensor including an upper electrode, wherein a buffer layer is provided between the flexible plate and the lower electrode.

[0013]

The cantilever of the present invention is characterized in that a buffer layer having extremely low reactivity with the lead-based ferroelectric material is provided between the flexible plate and the lower electrode of the thin film displacement sensor provided thereon. To do. In the cantilever of the present invention, the thin film displacement sensor can be provided on the flexible plate regardless of the material of the flexible plate. For example, silicon dioxide, silicon nitride, silicate glass, and other metals are used as the flexible plate material.

Examples of the material of the buffer layer having a low reactivity with the lead-based ferroelectric material include oxides such as aluminum oxide, magnesium oxide, magnesium aluminate, and chromium oxide. The material of the lower electrode and the upper electrode is not particularly limited, but it is desirable that the lower electrode be made of platinum as a main raw material in consideration of withstanding the heat treatment at the time of forming a thin film and strongly binding to the buffer layer material. Further, it is particularly desirable to use titanium or tantalum together with platinum in order to further improve these characteristics.

Forming a buffer layer on the flexible plate,
When the lower electrode is patterned on this and a lead-based ferroelectric intermediate layer is further formed thereon, the buffer material and the lead-based ferroelectric material are in direct contact with each other in the portion where the lower electrode is not formed.
However, since the mutual reactivity of these materials is extremely low, the lead-based ferroelectric material can take a perovskite crystal phase and obtain desired piezoelectric / electrostrictive characteristics.

On the other hand, when there is no buffer layer, the lead-based ferroelectric material is in direct contact with the flexible plate material,
Since these materials easily react with each other, the desired perovskite crystal phase cannot be obtained, and therefore the piezoelectric /
It cannot be a sensor that uses electrostrictive characteristics. For example, when lead zirconate titanate (PZT) having a phase boundary composition is used as the ferroelectric material, when the flexible plate is silicon nitride, the pyrochlore crystal phase having no piezoelectric property is
In the case of silicon oxide, an amorphous phase is formed, and in the case of silicon, many silicon compounds are formed.

In the present invention, the AFM and the scanning tunneling microscope (Scanning Tunneling Microscope) are used.
The thin film displacement sensor / actuator of the present invention can be used as a displacement sensor or actuator in other micro systems such as micromachines. It is possible.

[0018]

Embodiment 1 FIGS. 1 to 10 show an example of a method for manufacturing a cantilever according to the present invention. First, 0.3 on the silicon substrate
Silicon nitride having a thickness of about μm is formed by the CVD method (FIG. 1). Next, a part of the silicon nitride film is removed by reactive dry etching (FIG. 2). From this hole, a portion to be a stylus (needle-shaped tip) is formed by anisotropic etching using potassium hydroxide (FIG. 3). Further CVD
Method is used to deposit silicon nitride to a thickness of 0.5 μm (FIG. 4). An aluminum oxide film of 0.3 μm is formed on this (FIG. 5). Then, a lower electrode pattern is formed by the usual photolithography and sputtering method (FIG. 6). Further, a resist pattern is formed by photolithography, and the silicon nitride film other than the portion serving as the lever main body and its base is removed by reactive dry etching (FIG. 7). Ethylenediamine-pyrocatechol-water-based anisotropic etching removes the silicon portion to produce a lever body (FIG. 8). A PZT film is formed thereon by sputtering to a thickness of 1.0 μm (FIG. 9). Finally, a platinum upper electrode is formed on the entire surface (FIG. 10).

[0019]

As described above, according to the present invention, since the buffer layer having extremely low reactivity with the lead-based ferroelectric material is provided, the flexible plate reacts with the lead-based ferroelectric material. It is possible to obtain a cantilever with stable performance without lowering the piezoelectric / electrostrictive characteristics.

Further, since the upper electrode can be formed on the entire surface by patterning the lower electrode layer, there is no restriction on the manufacturing process.

[Brief description of drawings]

FIG. 1 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 2 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 3 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 4 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 5 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 6 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 7 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 8 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 9 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 10 is an example of a method for manufacturing a cantilever according to the present invention.

FIG. 11 is a conceptual diagram of the principle of a conventional AFM.

[Explanation of symbols]

 a Silicon substrate b Silicon nitride film (flexible plate) c Silicon nitride film (flexible plate) d Aluminum oxide film (buffer layer) e Platinum lower electrode f PZT piezoelectric Membrane (Lead-based ferroelectric intermediate layer) g ・ ・ ・ Platinum upper electrode

Claims (2)

[Claims] 1. A flexible plate, a needle-shaped tip fixed near the tip thereof, a lower electrode provided on the flexible plate, a lead-based ferroelectric intermediate layer having piezoelectric or electrostrictive characteristics. A cantilever having a thin film displacement sensor including an upper electrode, wherein a buffer layer is provided between the flexible plate and the lower electrode. 2. A flexible plate, a needle-shaped tip fixed near the tip thereof, a lower electrode provided on the flexible plate, a lead-based ferroelectric intermediate layer having piezoelectric or electrostrictive characteristics. A method of manufacturing a cantilever having a thin film displacement sensor including an upper electrode, wherein a buffer layer is provided between the flexible plate and the lower electrode, and the lower electrode is patterned on the buffer layer. A method for manufacturing a cantilever with a thin-film displacement sensor, which is a feature.