JP2000199048A - Substrate having zinc oxide film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zinc oxide film satisfying both piezoelectric characteristics and film stress in an angular velocity sensor film-formed on the surface of a silicon substrate and having the zinc oxide film as a piezoelectric element. SOLUTION: An angular velocity sensor 100 has a vibrator 2 formed by subjecting a silicon substrate 1 to etching or the like, a zinc oxide film 3 formed on the vibrator 2 as a piezoelectric element for driving and detecting the vibrator 2 and an electrode part 4 formed on the zinc oxide film 3 as a driving and detecting electrode, where the zinc oxide film 3 is composed of two layers continuously film-formed under different film forming conditions, i.e., of a seath layer 3a positioning at the base and for securing orientation properties and an upper layer 3b having film stress smaller than that of the seath layer 3a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate having a zinc oxide film as a piezoelectric element used as a G sensor for measuring acceleration, an angular velocity sensor for measuring angular velocity, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a zinc oxide (ZnO) thin film has been used as a piezoelectric element suitable for an acceleration sensor, an angular velocity sensor and the like. Usually, the zinc oxide thin film is formed on a substrate such as a silicon wafer by a vacuum deposition method, an ion plating method, a sputtering method, or the like. Further, an Al electrode or a Cr electrode is formed on the zinc oxide thin film as an electrode by an electron beam evaporation method, a sputtering method, or the like. Al
Electrodes and Cr electrodes are selected because they can be used as wirings because they are easy to pattern and have low resistivity.

The ideal properties of a zinc oxide film as a piezoelectric element are desirably good orientation, high resistance, and low stress. It is said that zinc oxide has piezoelectricity because there is no center of symmetry in its crystal structure, but good orientation is important to use the piezoelectricity efficiently. Further, it is necessary to increase the resistance so that a sufficient electric field is applied to the zinc oxide film when a voltage is applied. on the other hand,
If the stress of the film is high, it may cause warpage of the substrate or peeling of the film.

Normally, measures are taken to optimize the film forming conditions of the zinc oxide film in order to obtain the above film quality. For example, when the sputtering method is used, the optimal conditions are determined by controlling the substrate temperature, sputtering power, gas pressure, gas flow rate, and the like.

[0005]

However, as described above, when a film is formed by sputtering or the like, even if optimization is performed by changing various film forming conditions, the orientation and the piezoelectricity are excellent. Both properties had a trade-off relationship with each other, with the film tending to have high stress. Therefore,
Conventionally, a compromise between piezoelectric characteristics and film stress has been found, and the conditions have been optimized.

[0006] However, in practice, although there are film forming conditions with better characteristics in terms of both the piezoelectric characteristics and the film stress, the conditions are not satisfied at the same time. As a result of compromising the characteristics, the sensitivity of the sensor must be sacrificed.On the other hand, when priority is given to the piezoelectric characteristics, if the film thickness is increased, the film will crack, causing problems such as failure. there were.

In view of the above problems, it is an object of the present invention to realize a zinc oxide film which satisfies both piezoelectric characteristics and film stress on a substrate having a zinc oxide film as a piezoelectric element formed on one surface. .

[0008]

According to the first aspect of the present invention, a zinc oxide film (3) formed on one surface of a substrate (1) is continuously formed under different film forming conditions. A first layer (3) which is formed of at least two layers formed and is located on one surface side of the substrate to secure orientation.
a) and a second layer (3b) located above the first layer and having a smaller film stress than the first layer.

According to the present invention, in a zinc oxide film, a first layer (3a) located on one surface side of a substrate for ensuring orientation.
That the second layer (3b) as the upper layer is a film having a low stress even if the upper layer is a low-stress film. This is based on the findings experimentally found by the present inventors. A zinc oxide film having a laminated structure of these two layers can realize a film having high piezoelectric characteristics and low film stress. When a substrate using this zinc oxide film as a piezoelectric element is used for a G sensor or the like, a conventional film is used. Good sensor sensitivity can be obtained as compared with single layer film formation.

[0010] The invention according to claim 3 relates to a method of manufacturing a substrate (1) having a zinc oxide film (3) as a piezoelectric element formed on one surface thereof. A first layer (3a) and a second layer (3b) are sequentially formed on one surface of the substrate by sputtering using a zinc oxide target.
Is formed under the condition that the gas pressure or the substrate temperature is lower than that of the second layer.

The present manufacturing method can provide a manufacturing method for appropriately manufacturing a substrate having a zinc oxide film according to the first aspect. Further, the invention according to claim 4 and claim 5
The present invention provides specific film forming conditions in the method for manufacturing a substrate having a zinc oxide film according to claim 3, and the film forming conditions have been obtained by the study of the present inventors.

Note that the reference numerals in parentheses above are examples showing the correspondence with specific means described in the embodiment described later.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. In this embodiment, a substrate having a zinc oxide film is described as being applied to an angular velocity sensor using a zinc oxide film as a piezoelectric element. FIG. 1 shows a schematic sectional configuration of an angular velocity sensor 100 according to an embodiment of the present invention.

The angular velocity sensor 100 is formed by subjecting a silicon substrate 1 to a known micromachining process using a semiconductor manufacturing technique, and is provided in a horizontal plane of the substrate 1 so as to be movable with the substrate 1 cantilevered. A vibrator (for example, a two-leg tuning fork shape) 2 is formed as a part. The angular velocity sensor 100 is used, for example, as an angular velocity sensor mounted on a vehicle and applied to attitude control.
The substrate 1 is mounted with the horizontal direction (z-axis direction in the figure) as the vertical direction. The basic operation is that the vibrator 2 is driven and vibrated in a predetermined direction (x-axis direction in the figure) in the horizontal plane of the substrate 1 and is vibrated by Coriolis force generated when an angular velocity Ω around the z-axis is input. The child 2 vibrates in the y-axis direction (detection vibration), and the magnitude of the detection vibration is electrically detected to detect the angular velocity.

Next, based on FIG.
Is described below. In FIG. 1, in the silicon substrate (substrate according to the present invention) 1, the upper surface is referred to as a front surface (one surface of the substrate), and the lower surface is referred to as a back surface. Vibrator 2
Is formed by dividing a diaphragm formed by etching a predetermined region on the back surface side of the silicon substrate 1 into a predetermined shape by a groove 1a. Although not shown, the vibrator 2 has a planar shape (a shape as viewed from above in FIG. 1), for example, a two-leg tuning fork shape generally used as a vibrator, and has one end opposite to the two-leg portion. 1b
Are cantilevered by the body of the silicon substrate 1.

Oscillator 2 on the front side of silicon substrate 1
In a predetermined area, a zinc oxide film 3 is formed as a piezoelectric element for driving and detecting (a detecting portion for detection is shown in the illustrated example). As shown in FIG. 1, the zinc oxide film 3 is located on the surface side of the silicon substrate 1 and has a seed layer (first layer) 3a for ensuring orientation, and is located on the seed layer 3a. It has a two-layer structure of an upper layer (second layer) 3b having a smaller film stress than the sheath 3a, and satisfies both piezoelectric characteristics and film stress.

On the zinc oxide film 3, an electrode portion 4 as a drive electrode for inputting / outputting a signal to / from the zinc oxide film 3 and a detection electrode is formed. This electrode part 4
Is composed of a barrier metal made of TiW or TiN on the surface side of the silicon substrate 1 and an aluminum (Al) film thereon. The electrode section 4 in FIG. 1 constitutes a detection electrode for extracting a signal due to detection vibration from the zinc oxide film 3 as a detection piezoelectric element.

A silicon oxide film 5 is formed in a region where the zinc oxide film 3 of the vibrator 2 is not formed on the surface side of the silicon substrate 1, and the electrode portion 4 is formed thereon.
And a wiring portion 4a electrically connected to. The wiring portion 4a is formed integrally with the electrode portion 4 using the same material as the electrode portion 4 and is electrically connected to an external circuit (not shown).

The angular velocity sensor 100 having such a configuration
Is an electrode part 4 as a drive electrode by the external circuit.
And a vibrator 2 is driven and vibrated in a direction parallel to the x-axis direction by a zinc oxide film 3 as a driving piezoelectric element in that portion. Under this driving vibration, z
The vibrator 2 vibrates in the direction parallel to the y-axis direction (detection vibration) due to the Coriolis force generated when the angular velocity Ω around the axis is input, and the magnitude of this detection vibration is oxidized as the detection piezoelectric element. The angular velocity is output from the electrode section 4 as a detection electrode to the external circuit via the zinc film 3.

Next, a method of manufacturing the angular velocity sensor 100 will be described with reference to a process chart shown in FIG. In addition,
2A to 2F show cross sections in the course of the manufacturing process corresponding to the cross section shown in FIG. As shown in FIGS. 2A and 2B, a silicon oxide film 5 having a thickness of about 5000 Å is formed on the surface of the silicon substrate 1 by thermal oxidation, and the silicon oxide film 5 is patterned and driven. Oxide film 3 as piezoelectric element for detection and detection
The window 5A is opened at a portion where the (driving unit and detecting unit) are formed,
The silicon substrate 1 is exposed in the window 5A.

Next, as shown in FIG. 2C, a zinc oxide film 3 is formed on the surface of the silicon substrate 1 by a sputtering method using a zinc oxide target.
The upper layer 3b is continuously formed. At this time, the seed layer 3a
Is formed under the condition that the gas pressure or the substrate temperature is lower than that of the upper layer 3b. In other words, by forming a thin film having good orientation under low gas pressure and low temperature conditions as the seed layer 3a, the amount of warpage of the silicon substrate 1 is suppressed, and the upper layer 3b is formed thereon under high gas pressure and high temperature conditions. To form a low stress film.

Accordingly, in the conventional single-layer film formation, the film having a condition that the piezoelectric constant is not so high because the orientation is slightly inferior to the condition of low temperature and low gas pressure can be oriented according to the orientation of the seed layer of the base. A film can be formed with good properties. Specifically, the substrate temperature is set to 300 ° C. and the gas pressure is set to 1.5 mTorr by a sputtering method using, for example, a zinc oxide target to which 2 mol% of Ni is added for increasing the resistance.
r, a seed layer 3a having a thickness of about 1000 Å is formed, and a substrate temperature of 300 ° C. is formed thereon.
The upper layer 3b having a thickness of about 9000 angstroms is formed under a film forming condition of a gas pressure of 5 mTorr, and the total thickness is 1 μm.
Then, a zinc oxide film having a two-layered structure is formed so that

According to the study by the present inventors, the range of the film forming conditions at this time is as follows: the seed layer 3a has a substrate temperature of room temperature to 300 ° C. and a gas pressure of 1.5 mTorr to 5 mT.
The upper layer 3b is formed thereon at a substrate temperature of 100 ° C. to 300 ° C. and a gas pressure of 5 mTorr to 10 mT.
It is desirable to form a film under the condition of orr. Next, FIG.
As shown in FIG. 5D, the silicon oxide film 3 is patterned to cover the silicon substrate 1 in the window 5A and to cover the window 5A.
A zinc oxide film (a driving piezoelectric element and a detecting piezoelectric element) 3 extending to the peripheral silicon oxide film 5 is formed.

Next, as shown in FIG. 2 (e), a 500 angstrom thick T
An iW or TiN film and an Al film having a thickness of 1000 to 2000 angstroms are formed thereon and patterned together by ion milling, dry etching or the like to form an electrode portion 4 as a drive and detection electrode and a silicon oxide film 2. The upper wiring portion 4a is formed integrally.

Next, as shown in FIG. 2F, the back surface of the silicon substrate 1 in the region where the zinc oxide film 3 as the driving piezoelectric element and the detecting piezoelectric element is formed is treated with an alkali (for example, KOH aqueous solution). The diaphragm 6 is formed by etching. Finally, a resist (not shown) having a pattern defining the shape of the vibrator 2 is formed on the diaphragm 6 on the surface of the silicon substrate 1, and dry etching or the like is performed from the surface side to form a groove 1.
The vibrator 2 partitioned by a is formed. Thus, the sectional configuration shown in FIG. 1 is completed.

By the way, according to the present embodiment, the zinc oxide film 3 has the seed layer 3a located on the surface side of the substrate 1 for ensuring the orientation, so that the upper layer 3b is a low stress film. However, the upper layer 3b can be a highly oriented film following the orientation of the underlying seed layer 3a. And, the zinc oxide film 3 having such a laminated structure can realize a film having high piezoelectric characteristics and low film stress, and can obtain better sensor sensitivity than the conventional single-layer film formation.

Here, the above-mentioned effect of the present embodiment will be shown in a specific example in comparison with a conventional angular velocity sensor having a single-layered film-forming structure as a prototype manufactured by the present inventors. FIG. 3 shows a prototype of the conventional structure. In the angular velocity sensor 100 shown in FIG. 1, only a single layer of a zinc oxide film J3 as a piezoelectric element is formed, and the other parts are the same ( In FIG. 3, the same reference numerals are used as in the present embodiment).

FIG. 4 is a graph showing the relationship between the piezoelectric constant and the amount of warpage of the silicon substrate 1 in the laminated film structure (this embodiment) shown in FIG. 1 and the single-layer film structure (comparative example) shown in FIG. It is written. In the figure, white circles represent the piezoelectric constant (× 10 ⁻¹² m / V) shown on the left vertical axis, and black circles show the warpage amount (μm) shown on the right vertical axis. In the horizontal axis of FIG.
Is the substrate temperature: room temperature (RT), and the gas pressure is 1.5 mTorr.
Comparative Example 2 has a zinc oxide film J3 formed as a single layer under the conditions of a substrate temperature of 300 ° C. and a gas pressure of 5 mTorr.

Further, in the embodiment on the horizontal axis of FIG. 4, the seed layer 3 having a thickness of about 1000 angstroms formed under the conditions of a substrate temperature: room temperature and a gas pressure: 1.5 mTorr.
a, and a zinc oxide film 3 having a laminated structure of an upper layer 3b having a thickness of about 9000 angstroms formed under the conditions of a substrate temperature of 300 ° C. and a gas pressure of 5 mTorr.

As can be seen from FIG. 4, in a single-layer film formation as a comparative example, there is a trade-off relationship between the piezoelectric constant and the amount of warpage, and it is not easy to find a film formation condition with a high piezoelectric constant and low stress. . Comparative Example 1 has high piezoelectric characteristics but a large amount of warpage (large film stress), and Comparative Example 2 has a small amount of warpage (small film stress) but low piezoelectric characteristics. On the other hand, in the multilayer film formation of the present embodiment, it is possible to satisfy the better characteristic level of each comparative example, that is, satisfy both the high piezoelectric constant and the low stress.

(Other Embodiments) In the above embodiment, an example of an angular velocity sensor has been described. However, the present invention can be applied to an acceleration sensor (G sensor). For example, as the acceleration sensor, in the above structure, when an acceleration is applied in the y-axis direction, the vibrator 2 is also displaced in the y-axis direction, and the displacement is detected by a zinc oxide film as a piezoelectric element. Can be.

Further, since the main part of the present invention is a zinc oxide film, it goes without saying that the structure of the substrate, the electrode portion and the like may be appropriately changed in design. In addition, the present invention can be applied to a substrate having a zinc oxide film as a piezoelectric element formed on one surface so as to realize a zinc oxide film that satisfies both piezoelectric characteristics and film stress.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a cross-sectional configuration of an angular velocity sensor according to an embodiment of the present invention.

FIG. 2 is a process chart showing a method for manufacturing the angular velocity sensor shown in FIG.

FIG. 3 is a diagram showing a conventional angular velocity sensor prototyped by the present inventors.

FIG. 4 is a diagram showing specific effects of the present invention.

[Explanation of symbols]

Reference numeral 1: silicon substrate, 3: zinc oxide film, 3a: seed layer,
3b: Upper layer.

Continued on the front page (72) Inventor Muneo Yorinaga 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Kenichi Ao 1-1 1-1 Showacho, Kariya-shi, Aichi Pref. F term in DENSO Corporation (reference) 4K029 AA06 AA24 BA49 BB02 CA05 DC05 EA03 EA08

Claims (5)

[Claims] 1. A substrate (1) having a zinc oxide film (3) as a piezoelectric element formed on one surface, wherein the zinc oxide film is formed by at least two films continuously formed under different film forming conditions. A first layer for ensuring orientation while being located on one surface side of the substrate.
A substrate having a zinc oxide film, comprising: a first layer (3a); and a second layer (3b) located on the first layer and having a smaller film stress than the first layer. 2. The substrate having a zinc oxide film according to claim 1, wherein said substrate (1) is made of silicon (Si). 3. A method of manufacturing a substrate (1) having a zinc oxide film (3) as a piezoelectric element formed on one surface thereof, wherein the zinc oxide film is formed by a sputtering method using a zinc oxide target. A first layer (3a) and a second layer (3b) are successively formed on one surface of the substrate in sequence, wherein the first layer is formed more than the second layer. A method for manufacturing a substrate having a zinc oxide film, wherein the substrate is formed under conditions of a low gas pressure or a low substrate temperature. 4. A gas pressure for forming the first layer (3a) is 1.5 mTorr to 5 mTorr, and the gas pressure for forming the second layer (3a) is 1.5 mTorr to 5 mTorr.
b) forming a gas pressure of 5 mTorr to 10 mTorr
4. The method for manufacturing a substrate having a zinc oxide film according to claim 3, wherein: 5. The substrate temperature when forming the first layer (3a) is from room temperature to 300 ° C., and the substrate temperature when forming the second layer (3b) is from 100 ° C. to 300 ° C. ,
5. The method for manufacturing a substrate having a zinc oxide film according to claim 3, wherein the first layer is formed at a substrate temperature lower than that of the second layer in the temperature range. 6.