JPH1019574A - Manufacture of piezoelectric vibration angular velocity meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately manufacture a vibrator base body and form a piezoelectric thin film without deteriorating electric characteristics, by forming the vibrator base body of a silicon single crystal by photolithography and anisotropic etching, forming the piezoelectric thin film on a lower electrode and it is subjected to a heat treatment. SOLUTION: A photoresist 210 is applied to the lower face of a wafer 10. The photoresist at a position where a vibrator is formed is removed by photolithography. An Si3 N4 film 202 without the photoresist is removed by reactive ion etching, thereby to expose silicon. Then, a photoresist 220 is applied to an upper face of the wafer to form a resist pattern of a lever part. Moreover, the Si3 N4 film is removed. A PZT (lead titanate zirconate) film 20 is formed with the use of a metal mask by RF sputtering. Subsequently, the PZT film is subjected to a heat treatment to be crystallized. Finally, an Al film is formed on the PZT thin film 20 as three split upper electrodes 30, 31, 40 by a lift-off method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an gyro for use in navigation systems of aircraft, ships, automobiles, etc., attitude control of these systems, and sensing of camera shake and vibration of steel cameras, video cameras, etc. The present invention relates to a piezoelectric vibration angular velocity meter using a piezoelectric material.

[0002]

2. Description of the Related Art A piezoelectric vibrating gyro is a type of gyroscope utilizing a mechanical phenomenon in which when a rotating angular velocity is given to a vibrating object, a Coriolis force is generated in a direction perpendicular to the direction of vibration. 8 and 9 show an example of a vibrator used in a conventional piezoelectric vibration gyro.
(A) is a perspective view, and (B) is a cross-sectional view as viewed from the length direction.

The base of the vibrator 300 shown in FIG. 8 is a quadrangular prism 310 having a square cross section, and is made of an Elinvar alloy whose elastic constant has a small temperature change. On each side of the substrate, a piezoelectric material having silver paste electrodes formed on both sides, for example, PZT
(Lead zirconate titanate) plates 311, 312, 31
3, 314 are pasted. PZT plates 311 and 312
When the voltage for vibration is applied to the PZT plate, the PZT plate vibrates due to the inverse piezoelectric effect, and the metal base 310 vibrates in a simple manner so as to have an amplitude in the vertical direction of FIG. At this time, the metal base 310
When a rotation having a certain angular velocity occurs around an axis parallel to the length direction of (B), Coriolis force is generated in the left and right direction of (B), and the metal base 310 has irregularities in the left and right direction of (B). Vibrates.

[0004] The PZT plates 313 and 314 for detection generate the vibration in the left and right directions as a voltage at the electrodes by the positive piezoelectric effect, and take a differential of the voltage, thereby causing the Coriolis force, that is, the angular velocity. Signal can be obtained. As another conventional example, there is a triangular or cylindrical vibrator in which a base itself is formed of a piezoelectric material.
FIG. 9 shows an example of a triangular prism-shaped vibrator. In the vibrator 400, a base 410 of the vibrator is formed of a PZT piezoelectric material, and electrodes 411, 412 of silver paste are directly provided on each side surface thereof.
413 are formed. When the base 410 is rotated at an angle around an axis parallel to the longitudinal direction during the vibration of the base 410 so as to generate unevenness in the vertical direction of the electrode 413, the base 4
A vibration caused by the Coriolis force occurs in a direction perpendicular to the vibration direction of 10, and a voltage is generated at the electrodes 411 and 412, and a signal caused by the Coriolis force can be obtained by taking a difference between the outputs of the two. .

[0005]

However, the vibrator of the conventional piezoelectric vibrating gyro has the following problems since it is manufactured by processing the bulk of metal or piezoelectric material as described above. Was. In the case of a metal-based vibrator, the commonly used Elinvar alloy is poor in workability and difficult to process with high accuracy. In addition, a piezoelectric material must be accurately attached to the side surface, and the number of steps is large. It becomes something.

In the case of a vibrator made of a piezoelectric material base, it is necessary to process a ceramic piezoelectric material, which is difficult to process, into a triangular prism or a cylindrical shape with high accuracy, and further, to form electrodes on the side surface with high precision by a method such as screen printing. Must be formed. In the vibrator, an error in setting the area and position of the electrode becomes an error in vibration as it is. For this reason, it has been difficult to accurately measure the angular velocity with a vibrator made of a metal substrate or a piezoelectric material substrate. Furthermore, it is difficult to make the device small enough to enable micro-mechanical navigation and attitude control.

An object of the present invention is to solve these problems and to provide a vibrator which can be miniaturized.

[0008]

Means for Solving the Problems In a conventional vibrator,
The reason that the miniaturization could not be realized is that a bulk material, which is difficult to process, whether a metal or a piezoelectric material, was used as the base material. Therefore, the present inventors first,
The use of a material that can be easily processed, for example, a semiconductor material, was studied as the base material of the vibrator.

It has been found that a semiconductor material typified by silicon can produce a single crystal wafer, and that ultra-miniaturization can be realized by etching utilizing crystal anisotropy. Furthermore, in order to vibrate a vibrator obtained by micromachining of a semiconductor material, a piezoelectric material is formed on the vibrator by vacuum thin film forming technology, and the microvibrator is obtained by exciting the film. I thought and studied diligently.

As a result, the present invention is achieved by forming a pattern of a vibrator by performing pattern formation and etching on a wafer, and then adopting a thin film forming method which does not deteriorate electrical characteristics such as piezoelectric characteristics. Reached. The present invention provides a method for manufacturing a piezoelectric vibration gyro comprising a lower electrode, a piezoelectric thin film, and an upper electrode formed on a vibrator base in this order, wherein the vibrator base is formed by photolithography and anisotropic etching. Wherein the piezoelectric thin film is a piezoelectric crystal formed by forming a film on the lower electrode and then heat-treating the piezoelectric thin film. It is.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Lead-based piezoelectric materials are used for various applications because of their excellent piezoelectric properties. However, when a lead-based piezoelectric thin film is formed on a silicon wafer, the temperature of the wafer may be reduced to 6 regardless of physical or chemical vapor phase synthesis.
At a high temperature of 00 ° C. or higher, a perovskite single structure is obtained, but at a lower temperature, a mixed phase of perovskite and pyrochlore is formed. For this reason, when the film was formed at a temperature of 600 ° C. or less, a sufficient piezoelectric crystal layer could not be obtained, and the piezoelectric characteristics were significantly inferior to those of the bulk. On the other hand, when forming a film at a high temperature in a vacuum chamber at 600 ° C. or higher, it is particularly difficult to control the composition of the lead component, and a composition having a stoichiometric ratio cannot be obtained. Therefore, a thin film forming method in which a thin film is formed at a low temperature and subsequently heat-treated and crystallized to form a film is used.

It is not clear why a thin film is formed at a low temperature and subsequently heat-treated and crystallized to improve the electrical characteristics such as the piezoelectric characteristics. However,
Experimental facts prove it. Probably, this is because the re-evaporation of the lead component in the vacuum chamber is suppressed by forming the thin film at a low temperature. Therefore, as a film forming method,
Regardless of the physical or chemical vapor phase synthesis method, a vacuum thin film forming technique such as sputtering, metal organic chemical vapor deposition, vacuum deposition, and ion plating can be used.

Further, by forming a buffer layer between the wafer and the piezoelectric thin film, decomposition and reaction due to mutual diffusion of the components of the wafer and the piezoelectric thin film are further prevented, and a dense piezoelectric thin film having a stable composition can be obtained. This was also confirmed by experiments. In the present invention, the wafer temperature is preferably from 300 ° C. to 500 ° C. At a temperature lower than this, the densification or oxidation reaction of the film does not completely proceed, and at a temperature higher than this, re-evaporation of the lead component seems to be accelerated. Heat treatment temperature from 600 ° C to 700
C. is preferred. At lower temperatures, the generation of the piezoelectric crystal layer does not completely proceed, and at higher temperatures, the lead oxide vaporizes remarkably.

As the lower electrode, noble metals, Pt, Rh,
Re may be used. Piezoelectric thin film in oxidizing atmosphere, 600
When crystallized at a high temperature of over ℃, the lower electrode and the piezoelectric material interdiffuse, especially highly reactive lead diffuses into the lower electrode,
By using a noble metal having low reactivity, electrical characteristics such as piezoelectric characteristics can be improved. The lower electrode is formed by sputtering or vacuum evaporation. However, it is preferable to form the film after forming a titanium or tantalum film in order to enhance the adhesion to the wafer.

Further, the particle size of the piezoelectric thin film is further reduced,
In order to increase the density, a piezoelectric material containing lanthanum oxide is preferably used. Further, when performing heat treatment for crystallization, good results can be obtained by performing the heat treatment in an atmosphere having an oxygen concentration of 50% or more. The shape of a vibrator base used in a piezoelectric vibrating gyro is formed on a wafer using photolithography technology and an etching method, and a piezoelectric thin film is formed on the vibrator base using the thin film forming method to form a micro vibrator. Can be produced.

Hereinafter, the present invention will be described in detail with reference to examples.

[0017]

FIG. 1 and FIG.
1 shows a perspective view of a vibrator of two piezoelectric vibrator speedometers. Each
10 or 100 in these figures indicates that silicon nitride (S
i _ThreeN_Four) A silicon single crystal substrate on which a film (not shown) is formed
The vibrators 11, 101 according to the crystal orientation.
The shape of the tip becomes different. Vibrator base 11 or 1
Reference numeral 01 denotes a cantilever structure protruding from a silicon wafer.
And lower electrodes 50 and 150 on the upper surface, respectively.
PZT (zircon titanate) as a piezoelectric thin film
Lead oxide) films 20 and 120 are formed to sandwich PZT.
The excitation electrodes 40 and 140 are provided at substantially the center of the piezoelectric thin film.
On both sides, signal detection electrodes 30, 31 or 130, 13
1 is formed, and the piezoelectric vibration angular velocity as a whole is formed.
It becomes a vibrator for the degree meter.

Hereinafter, a method of manufacturing these vibrators will be described with reference to FIGS. 3 and 4
5 is a top view, and the lower figure is a cross-sectional view as viewed from the side. However, 3
From -2 to 4-1 is a bottom view for explaining the lower surface.

3 inch silicon wafer (thickness 0.38)
Si by CVD on both sides over the entire surface of mm) ₃ N ₄ film 20
Films 1 and 202 are each formed with a thickness of 100 nm. 28 vibrators are formed parallel to a line that forms an angle of 35 degrees with the orientation flat of the wafer 10. The rectangle on the wafer 10 indicates a tentative one for manufacturing a vibrator from this part. Finally, the vibrator is cut by a dicing saw along the solid line, and is completed as a chip (3-1). Hereinafter, a manufacturing method will be described using one chip on the wafer 10 as an example.

First, a photoresist 210 is applied to the lower surface of the wafer 10, and the photoresist at the position where the vibrator is to be formed is removed by photolithography (see FIG.
2). Next, the Si ₃ N ₄ film 202 in a portion where there is no photoresist is removed by etching by a reactive ion etching (RIE) method to expose silicon. On this occasion,
Care should be taken to remove the Si ₃ N ₄ film without leaving any residue (3-3). Further, silicon is anisotropically etched in a potassium hydroxide (KOH) solution at 40 ° C. and 90 ° C. for about 200 minutes. As a result, silicon is reduced to about 0.33.
mm. After that, the photoresist 210
Is peeled off (4-1).

Next, a photoresist 220 is applied on the upper surface of the wafer, and a resist pattern for the lever portion is formed by the same processing as described above (4-2). Further, similarly to the above, the Si ₃ N ₄ film is removed by the RIE method. At this time, care should be taken that there is no residue (4-3). Further, anisotropic etching is performed in a KOH aqueous solution (40 wt%, 90 ° C.) for about 30 minutes to form a lever portion, and thereafter, the photoresist 220 is peeled off (4-4).

The upper and lower electrodes and the piezoelectric thin film are described below.
The formation method is shown in the order of steps. With silicon as an electrode base
A Pt film is formed in addition to the Ta film for improving the adhesion.
Pattern formation is lift-off using photoresist
And the film is formed by sputtering (5-
1). The PZT thin film 20 is made of a metal mask (SUS304).
Formed by an RF sputtering method. Success
The film condition is Ar gas 9 × 10 ^-3Torr, O_TwoGas 1 × 10
^-3Torr, RF power 3W / cm^Two, Substrate temperature 400 ° C,
The target used is Pb_1.1(Zr_0.5Ti_0.5) O_ThreeIn
The film thickness is 1 μm at a long speed of 15 nm / min. Deposited
The X-ray diffraction pattern of the film is shown in FIG. This figure shows
As shown, the PZT film is amorphous
It was state. Subsequently, the PZT film in this state is subjected to an oxygen partial pressure of 5%.
Heat treatment is performed at 650 ° C. for 1 hour in an atmosphere of 0% or more. heat
The X-ray diffraction pattern after the treatment is shown in FIG. This figure
As shown in the figure, the amorphous PZT film
Confirmed to have a tetragonal perovskite structure
(5-2).

The electrical characteristics of the PZT film thus obtained are as follows: relative dielectric constant: 400, remanent polarization: 30 μC / cm ² ,
The coercive electric field was 150 kV / cm, which was equivalent to that of a bulk material having the same composition. The dielectric breakdown strength was 500 kV / cm or more. FIG. 7 shows an applied electric field-polarization curve (hysteresis loop) measurement result when an electric field of 500 kV / cm was applied by the Sawyer tower circuit.

Finally, the upper electrodes 30, 31, 4 divided into three parts
As 0, an Al film is formed on the PZT thin film 20 by lift-off (5-3). The base of the vibrator is cut with a dicing saw so that the frame 110 can be cut and removed at the base in a later step. The frame serves to protect the vibrator by holding it until immediately before use.

As described above, a vibrator used for a piezoelectric vibrating gyro can be manufactured with high accuracy without deteriorating the electrical characteristics of the piezoelectric thin film.

[0026]

According to the present invention, a vibrator base can be accurately manufactured on a single crystal wafer of a semiconductor material which is easy to process by using photolithography technology and etching method. It is possible to form a piezoelectric thin film on a vibrator base without deteriorating electrical characteristics by using the method.

[Brief description of the drawings]

FIG. 1 is a perspective view of an example of a vibrator manufactured according to the present invention.

FIG. 2 is a perspective view of an example of a vibrator manufactured according to the present invention.

FIG. 3 is a diagram showing a manufacturing process of the vibrator according to one embodiment of the present invention.

FIG. 4 is a diagram showing a manufacturing process of the vibrator according to one embodiment of the present invention.

FIG. 5 is a diagram showing a manufacturing process of the vibrator according to one embodiment of the present invention.

FIG. 6 is an X-ray diffraction pattern of a PZT thin film formed by the thin film forming method according to one embodiment of the present invention. (A) is before heat treatment, and (b) is after heat treatment.

FIG. 7 is a hysteresis loop of a PZT thin film formed by a thin film forming method according to one embodiment of the present invention.

FIG. 8 is a diagram of a vibrator used in a conventional piezoelectric vibration angular velocity meter. (A) is a perspective view, and (B) is a cross-sectional view as viewed from the length direction.

FIG. 9 is a diagram of a vibrator used in a conventional piezoelectric vibration angular velocity meter. (A) is a perspective view, and (B) is a cross-sectional view as viewed from the length direction.

[Explanation of symbols]

10, 100 Silicon wafer 11, 101 Transducer base 110 Frame 20, 120 PZT thin film 30, 31, 130, 131 Signal detection electrode 40, 140 Excitation electrode 50, 150 Lower electrode 201, 202 Si ₃ N ₄ film 210, 220 Photo Resist 300, 400 Transducer 310, 410 Transducer base

Claims (6)

[Claims] A lower electrode, a piezoelectric thin film,
And a method of manufacturing a piezoelectric vibration gyro comprising an upper electrode, wherein the vibrator base is a silicon single crystal formed by photolithography and anisotropic etching, and the piezoelectric thin film is formed on the lower electrode. A method for manufacturing a piezoelectric vibration angular velocity meter, comprising a piezoelectric crystal formed by heat treatment after forming a film. 2. A method for manufacturing a piezoelectric vibrating gyro according to claim 1, wherein said upper electrode is formed on said vibrator base body in two lengthwise parallel directions, and said two detection electrodes are formed in parallel. A method for manufacturing a piezoelectric vibrating angular velocity meter, wherein the piezoelectric vibrating angular velocity meter is an excitation electrode formed between the electrodes. 3. A method for manufacturing a piezoelectric vibration gyro according to claim 1, wherein said substrate is formed by forming a silicon nitride film on a silicon single crystal wafer by a CVD method, and then forming said silicon nitride film by photolithography and reactive ion etching. A method for manufacturing a piezoelectric vibration gyro, characterized by being a silicon single crystal formed by removing a silicon nitride film in the shape of (1) and etching silicon by anisotropic etching. 4. The method of manufacturing a piezoelectric vibration gyro according to claim 1, wherein said piezoelectric thin film is formed on said lower electrode by 30 minutes.
A method for manufacturing a piezoelectric vibration angular velocity meter, comprising a piezoelectric crystal formed by forming a film at a temperature of 0 to 500 ° C. and then performing a heat treatment at a temperature of 600 to 700 ° C. 5. The method for manufacturing a piezoelectric vibration gyro according to claim 4, wherein said piezoelectric thin film is formed on said lower electrode by sputtering, metal organic chemical vapor deposition, vacuum vapor deposition, or ion plating. From 300 to
A method for manufacturing a piezoelectric vibration angular velocity meter, wherein the piezoelectric crystal is made of lead zirconate titanate formed by forming a film at a temperature of 500 ° C. and then performing a heat treatment at a temperature of 600 to 700 ° C. 6. A method of manufacturing a piezoelectric vibration gyro according to claim 1, wherein a lower electrode is formed after forming a layer made of a titanium film or a tantalum film on said base by sputtering or vacuum evaporation. A method for manufacturing a piezoelectric vibrating angular velocity meter, comprising: