JP2001044526A - Piezoelectric element and processing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To process more thinly than the thickness of manufacturing limit by a method, wherein after a polished quartz plate is wet-etched from one face to remove a prescribed thickness, it is dry-etched and again polished by a both-face processing machine. SOLUTION: A polished quartz plate is chemically wet-etched from one face, or etched with reactive ions, to remove about a few tens of μm. After that, it is chemically dry-etched and is again polished by a both-face polishing machine or a one-side polishing machine, or by other polishing means. Thus, a quartz oscillator can be made thin, a quartz resonator, or the like with high accuracy, and to manufacture readily as a policy the quartz oscillator and the quartz resonator which can oscillate at a few tends of GHz or highes by fundamental waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to barium titanate, quartz, lithium niobate or potassium niobate used for an acceleration sensor or an angular velocity sensor.
Processing tools for processing other single crystals or piezoelectric elements such as piezoelectric ceramics or other ceramics, or silicon, gallium arsenide, or other electronic materials, optical lenses or other substances, and the processing thereof About the method.

[0002]

2. Description of the Related Art A quartz oscillator, which is a kind of piezoelectric element,
Oscillator of reference frequency of communication equipment and measurement equipment,
Microcomputers for general-purpose computers, office automation equipment, and home electric appliances have a wide variety of uses, such as clock generation, but the thickness of the vibrator has been reduced by improving the performance of information processing and transmission. It is required to increase the natural vibration frequency. In order to obtain a high-quality vibrator, it has been proposed to finish it into a lens shape, and it has achieved results in the relatively low frequency range. A crystal unit is an electronic device that is indispensable to digital devices such as a communication device and a computer. To improve the performance of information processing and transmission, the thickness of the vibrator was reduced,
It is required to raise the natural vibration frequency. In addition, mobile communication devices are required to have higher fundamental frequencies in order to reduce the size and power consumption. As a method of manufacturing a quartz oscillator, generally, mechanical polishing and chemical wet etching are used. The former is excellent in processing surface properties, but 3
The thickness cannot be reduced to 0 μm or less. The latter is a method suitable for exfoliation without a process-affected layer in principle. However, this method also has a limit in exfoliation due to the occurrence of Etch channels. On the other hand, Reactive Ion Etchin which is reactive ion etching
In g (RIE) or plasma etching (abbreviated as chemical, dry etching), ion damage is introduced, but thinning without deterioration of surface roughness is possible. As a method of manufacturing a high-frequency crystal unit,
By effectively utilizing the advantages of these processing methods, a processing method that can be mass-produced could be developed.

[0003] However, as a problem when the thickness of the vibrator is reduced, the production method using a double-sided lapping machine currently has a production limit of 30.0 μm (= 55.6 MHz). Also, when the vibrator is finished in a lens shape,
Creating a curved surface on a slice is very difficult,
Until now, there was no processing means capable of mass production at low cost.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electronic material, a piezoelectric element, and a method for processing the same, which are thinner than the conventional manufacturing difficulties. It is.

[0005]

Means for Solving the Problems A method for manufacturing a high-frequency crystal resonator developed to solve the above problems is as follows. The mechanical polishing method is excellent in processing surface properties, but cannot process a vibrator having a thickness of 30 μm or less due to insufficient strength of a carrier, which is a processing aid. Chemical wet etching is a processing method which is basically suitable for thinning without generating a work-affected layer. However, deep etching causes deterioration in surface roughness and Etch channels. RI
E indicates that the surface roughness is deteriorated and that the Etch Channel
s can be generated without s generation, but Ion sputtering damage due to ion bombardment is
It is known that the electric characteristics of the crystal unit are harmful. As described above, each processing method has advantages and disadvantages, and in order to utilize these advantages of the processing method, the final surface must be mechanically polished or C
It may be formed by chemical etching. Therefore, a Single I having a thickness of 30 μm or more, manufactured by Chemical Etching, was used.
The inverted mesa type blank,
As the processed material, Mechanical polis
The limitations of the wing processing method can be exceeded.
To further reduce the thickness, the flat side is removed by RIE. This is a mechanical polish
By using g, thinning with excellent quality can be achieved.
At this time, a convex lens shape (Plano-Convex Type) is formed without the thin vibrating portion being damaged. For mass production, Q of 70 μm or more
It is effective to use uartz wafer.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Chemical Etchin
g, Reactive Ion Etching, Plasma Etching, Mechanical Poli
We have devised a method of manufacturing a high-frequency crystal unit that effectively utilizes the advantages of the SHING. As a result, Single
Quarter of Inverted Mesa Type
By using tz Blank as a processing material, Plano-Conv is a widely used double-sided lapping machine.
A high-frequency crystal resonator of ex Type was manufactured.

FIG. 1A shows RIE, ion milling, or plasma etching (abbreviated as Dr).
2 shows an example of the reactance frequency characteristic of the crystal unit made by y Etching. Harmful peaks occur near the peak, which indicates the natural vibration frequency. This is considered to be due to ion damage of RIE. When the RIE-processed surface was manually polished, the surface changed as shown in FIG. 1B, and the harmful peak was eliminated to improve the characteristics. For this reason, the ion damage layer of RIE is extremely thin, 0.3 μm or less, and is characterized by a mechanical polish.
ng was found to be removable.

FIG. 2 shows Chemical
Single Invert by Etching
Quartz Bla from ed Mesa Type
Considering the production of nk and mass production, Quartz Wafe
r is masked, Chemical Etc
The one produced by hin was used. The shape is shown in FIG. 73.4 μm Quartz Wa
The fer had a thickness of 32.68 μm by virtue of Chemical Etching.
The depth of the ching is a critical depth that maintains good surface roughness. Reactance-f of this material
frequency Characteristic
Is shown in FIG. 2 (b). The characteristics are similar to those of the RIE shown in FIG.

FIG. 3 shows the use of RIE for thinning, and for high frequency, RIE. However, in the next step, Me using a double-sided lapping machine
In the case of mechanical polishing, the RIE treated surface is Singl to remove the ion damage layer.
e Inverted Mesa Type, Qua
The plane side of rtz Blank. The RIE processing was performed under normal conditions. It is possible to reduce ion damage by lowering RFpower and increasing Pressure. However, Et
leading to lowering the Ching Rate,
In the first RIE, the processing was performed under the condition of high efficiency, and in the third RIE, the processing was performed under the condition of less damage and three conditions. The removal amount was adjusted in the first RIE processing time. Through this series of processing, the reaction-frequency chara of the processed material obtained is obtained.
Ceristic is shown in FIG. As a result, C
Only by chemical etching, 1
A total of four types of processed materials were produced, including three types and three types obtained by processing the same by the RIE processing means.

[0010] FIG.
g Conditions and Mechanical
Single Inverted as a processing material obtained by the above-mentioned processing method as a result of Polishing
Quartz Blank of Mesa Type
To Dual-face Lapping Machi
Polishing is performed with ne. At this time, the polishing was performed under general processing conditions. However, in order to investigate the damage to the thin vibrating part and its effect on the shape,
Two types of Upper Lapping Plates, iron and aluminum, were used. Iron Upper L
When an applying plate is used, the load applied to the crystal is 1.8 times that of aluminum.

[0011] Using a double-side polishing machine,
As a result of the execution of the polishing process, the first point, that is, the breakage of the thin vibrating portion, did not occur at all, and the polishing was possible. The second point, the formation of a shape, was also very successful. FIG. 4 shows the results. FIG. 4 shows a Single Inverted MesaT.
The shape of a vibrating portion on the plane side of Quartz Blank of ype is measured by an interference microscope. From this, it can be seen that the vibrating portion is formed in a convex lens shape. It has a very beautiful spherical shape, and the other side is basically kept flat. From this, Du for forming a plane is used.
Even if it is al-face Lapping Machine, Single Inverted Mesa
If Quartz Blank of Type is used as the processing material, Plano-Convex Type of Qu
It can be said that artz Oseillator can be manufactured. The principle of this shape formation is as follows. Single Inv has a thin structure only in the vibrating part
The erted Mesa Type receives a polishing pressure, so that it is bent in the direction of the hollow portion, and the processing proceeds without being polished much. When the processing is completed and the polishing pressure is removed, the shape is restored to the opposite direction, and the shape becomes a protruding convex lens.

FIG. 5 shows that the polishing was performed with four types of processing materials and two types of processing pressures.
eactance-frequency Charac
The tactic is shown in FIG. Compared to before polishing, electrical characteristics have been dramatically improved, and higher frequencies have been achieved. Before polishing, SpuriousR
Esonance is eliminated by the polishing process, and Sha
rp Resonance Curve.
However, when the thickness is reduced or the polishing pressure is increased, the sharpness of the resonance curve is maintained, but the spurious resonance is maintained.
Will occur. Appropriate polishing pressure and caliber /
There is a thickness ratio.

FIG. 6, FIG. 7 and FIG. 8 show that the thickness of the vibrating part is equal to Form and Surface Rou.
The effect on ghness, the thickness of the vibrating part,
FIG. 6 shows a result of examining a change in peak to valley (PV) in a range of 1.44 × 1.31 mm at the center of the vibrating portion. FIG. 7 shows the change in the reciprocal of the radius of curvature of the formed convex lens shape. In the case of using an aluminum surface plate, the changes are the same in both figures.However, in the case of an iron surface plate, the change is different. It seems to be oval. On the other hand, Single Inverte
On the Concave side of the d Mesa Type, the degree of the concave surface increased due to the change in thickness. this is,
This is considered to indicate the degree of processing distortion when the convex lens shape is formed on the plane side. It is thought that improvement can be achieved by selecting optimal polishing conditions, heat treatment, etc.
We expect that it will lead to improvement of electrical characteristics. C
FIG. 8 shows a change in surface roughness of the central portion on the oncave side. The free abrasive grains also act on the portion of the polishing pad that is not in contact with the polishing pad, thereby changing the surface roughness. In the case of Chemical Etching, Ra was 2.6 nm.
Stripe-like irregularities unique to electronic etching become apparent and deteriorate to Ra 7 nm. Surface roughness is not deteriorated, Concave by RIE (Singl
e Inverted MesaType or Dou
ble Inverted Mesa Type), and then, from about 0.3 μm to about 0.4 μm,
This improvement can be attained by removing the ion damage layer by al Etching. Note that, based on the results shown in FIG.
Double Inverted Mesa Type
But Single Inverted Mesa T
As with ype, it has been proved that the properties can be improved using a double-side polishing machine. From these results, the ratio of the thickness to the diameter (d / t) was 10 to 350.
It has been found that by setting the optimum ratio to about 30 to 80, it is possible to manufacture a high-frequency crystal resonator of 334 MHz or more which has excellent electrical characteristics.

[0014]

Advantages of the Invention Single Inverted
By using Quartz Blank of Mesa Type as a processing material, using a widely used double-side polishing machine (double-sided lapping machine), single-side polishing machine, or float polishing machine, or other polishing means. As a result, it has become possible to produce a high-frequency crystal resonator having excellent electrical characteristics. 2. In this developed processing method, Single In
verted MesaType to Plano-co
The shape of nvexType could be formed.
Also, Double Inverted Mesa Ty
The electrical characteristics of pe are also Single Invert
As in the case of ed Mesa Type, the electrical characteristics were improved. 3. It has been found that by setting the aperture ratio to about 80, a crystal resonator of 334 MHz or more can be manufactured.

Up to the present time, chemical, dry etching, such as RIE processing or plasma etching,
Although the processing means of the ng processing is a wonderful processing technique, the reason that the processing means of the RIE processing was not used in the electronic material and the piezoelectric material industry, particularly the crystal industry, which is the piezoelectric industry, is, for example, a crystal processing means. When RIE processing is performed on a plate, the ion particles cannot be accelerated to a speed close to the speed of light, but the ion particles used in RIE processing usually have a voltage of about 600 V between the electrodes. A process in which a current of about 240 W to 300 W is applied as current, and ion particles are accelerated at a speed of several tens of km to several hundred km per second to accelerate fluorine- or chlorine-based ion particles and collide with the surface of the quartz plate. Because it is a means, on the very thin, surface of the quartz plate where the ion particles collide,
At the moment when the ion particles collide, they are generated by the kinetic energy of the ion particles and reach several thousand degrees Celsius (for example, a high temperature of about 1,500 degrees Celsius to 3,000 degrees Celsius. Incidentally, quartz and quartz dissolve. Melting temperature is 1,14
0 ° C.), on the surface of the quartz plate under the influence of heat, which melts on the surface of the quartz plate, and is very thin on the surface of the quartz plate. A film of silicon (eg, about 0.2 μm to 1.0 μm) formed of amorphous (not crystalline, amorphous quartz or fluorine ions are generated by causing a chemical reaction with oxygen of quartz) The formation of a damaged layer in the area of (a) causes a phenomenon in which the electrical characteristics inherent in the crystal are extremely reduced, and the frequency and the shape of the oscillation waveform are deteriorated. Furthermore, the processing-affected layer (amorphous portion) generated when the quartz plate is processed using the RIE process is slightly proportional to the processed thickness of the quartz plate, but hardly proportional thereto. Then, for example, 60
The thickness of the affected layer is between 0.2 μm and several μm, even when it is shaved, 10 μm, or several μm. I do. However, initially, the fine scratches created when mechanical polishing was performed, and the irregularities formed by enlarging impurities, became larger in proportion to the thickness to be scraped, the ratio of which was determined by using RIE processing. When shaving off 10 μm, irregularities of about 0.1 μm to 1.0 μm are formed, but the area is about 5% of the area, so it can be ignored. Also, RIE processing The thickness of the irregularities (deformed layer) generated when processing the quartz plate using the means is as follows: the speed at which the ion particles are accelerated and collided with the quartz plate is several kilometers per second; Number 1
In the case of 0 km and the case of 100 km / s, the thickness at which the irregularities are generated is different from each other. Therefore, when it is desired to increase the surface accuracy (to reduce the work-affected layer), the acceleration of the ion particles is reduced. It is good to make ion particles collide with a quartz plate. However, the collision of the ion particles is still the same, so that the size of the ion particles becomes larger or smaller, and irregularities (work-affected layers) occur. As means for solving the above, R
Amorphous (processed layer) formed on the surface of the quartz plate, which is generated by the IE processing or the chemical wet etching processing means, is removed using a mechanical polishing processing means. It was found that the electrical characteristics inherent to quartz can be exhibited by this, which means that high-precision processing such as thinning of future quartz oscillators and quartz resonators will be performed. In addition to the development of processing technology to perform, the impact on the industry of processing electronic materials and piezoelectric materials is incalculable, the development of processing technology, and eventually, in the future communication and electronics industry,
The fact that it has been found that it is possible to easily manufacture a crystal resonator and a crystal resonator capable of oscillating at several tens of GHZ or more with a fundamental wave is a source of a revolutionary and industrial revolution that will occur in the future. It is a processing technology that will have an effect.

The dry etching process, RI
E processing, ion milling and plasma etching processing means, such as Dry Etching processing means, or chemical, Wet Etching processing means, or other chemical, Etching processing means,
As a means for removing a processing-degraded layer (amorphous or oxide film or compound layer) generated on the surface of the quartz plate, any machine used as a mechanical polishing processing means may be used. Or the thickness of the quartz plate is 0.1
Since it is only necessary to remove about 0.5 μm from μm, it is cut into small pieces. For example, when the thickness is 10 μm, the diameter is 1.
Cutting into 2 mm or 2 mm round or square shapes, or using ultrasonic vibration or barrel polishing while maintaining a 1-inch or 2-inch base, or human manual work However, it is an operation that can sufficiently remove the affected layer. In addition, even if other processing means using loose abrasives are used, it is an operation that can easily remove the damaged layer, but it will fully exhibit the original electrical characteristics of quartz. It is better to remove the affected layer using mechanical polishing processing means.
Better electrical characteristics.

The above processing means is Single Inve.
rted Mesa Type (one side is concave lens shape) or Double Inverted Me
The present invention can be applied to saType (both surfaces having concave lens shapes), a flat plate shape, and any other shape of quartz plate. Alternatively, the work-affected layer is an amorphous, fluorine compound layer or a film made of another oxide. Therefore, the work-affected layer is an electrically insulating layer. This insulating layer is on both sides of the quartz plate,
Because it is made on the surface, by forming electrodes, it is the same as the state where capacitors are made on both sides of the quartz plate, so a damaged layer is formed on the surface of the quartz plate If it is present, the electrical characteristics of the quartz plate are extremely reduced, the waveform of the oscillation is deteriorated, and the Q value is reduced. By removing the work-affected layer (for example, about 0.06 μm), the crystal or the original quartz plate can be removed.
It has been found that the electrical characteristics are extremely improved, the oscillation waveform of the reactance frequency characteristics is improved, and the Q value is increased.

As described above, according to the present invention, it is possible to provide a piezoelectric element which is thinner than the conventionally difficult thickness, and a method of processing the same, thereby providing a vibrator having less auxiliary vibration. can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing the reactance frequency characteristics of a quartz resonator having a thick AT-cut surface material.

FIG. 2 is a diagram showing a reactance frequency characteristic diagram of a quartz crystal unit having a thick AT-cut surface material and a thick crystal unit,
ingle Inverted MesaType,
3A and 3B are a top view and a vertical cross-sectional view of a crystal resonator.

FIG. 3 is a diagram showing a reactance frequency characteristic of a thin quartz resonator having an AT cut and a thin material.

FIG. 4 is a shape measurement diagram obtained by measuring the shape of the crystal unit using an interference microscope.

FIG. 5 is a diagram showing a reactance frequency characteristic of a quartz crystal unit having a thin AT-cut surface material.

FIG. 6 is a graph showing a change in Peak to Valley (PV).

FIG. 7: Single Inverted Mesa
Type of convex lens, radius of curvature,
It is a graph which showed the change of the reciprocal.

FIG. 8: Single Inverted Mesa
4 is a graph showing a change in surface roughness of a central portion of Type on the Concave side.

Claims (6)

[Claims] 1. A quartz plate is polished using a double-side polishing machine, a single-side polishing machine, or another polishing machine.
Polished quartz plate (for example, the thickness of the quartz plate is 80 μm
RIE (Reactive Ion Et) from one side or both sides
Ching) processing or chemical wet etching processing is performed, and several tens μm is set (for example, 60 μm).
, After removal, chemical, DRY Etching
Processing (hereinafter referred to as RIE or plasma etching)
Alternatively, the irregularities of several μm generated by the chemical wet etching process (for example, when 60 μm is removed by the RIE process, a damaged layer, a damaged layer, or a deformed layer or irregularities of about 0.2 μm to 3 μm is generated). A piezoelectric element characterized by processing a piezoelectric material such as a quartz plate or an electronic material such as silicon, which is polished again by a double-side polishing machine, or a single-side polishing machine, or other polishing means. Processing method. 2. A mask is applied to the object to be polished with a mask using a mask, and only the central portion is made of, for example, CF ₄ , C ₂ F
Chemical, DryEt using, for example, ₆ or CHF ₃
Using a processing means of RIE processing, ion milling, or plasma etching, or other chemical wet etching processing, such as ching, a flat plate, Bi-
After processing into a Convex type shape or a concave lens shape (inverted MESA shape), etching is performed by using a double-side polishing machine, a single-side polishing machine, a float polishing machine or other polishing processing means as a subsequent processing means. And mechanically polishing the processed surface or the processed surface on the back surface of the piezoelectric element. 3. One or both sides are concave lens shape, Con
Cavo-Convex type shape or Bi-Conve
A method of polishing a piezoelectric element, wherein a quartz plate processed into an x-shape is simultaneously polished from above and below using a double-side polishing machine to process an extremely thin piezoelectric element. 4. After processing the quartz plate into a flat plate shape, a concave lens shape, or another shape by RIE processing or other chemical wet etching processing means, a flat plate shape or a concave lens shape is formed. Several tens of μm are shaved off by RIE, plasma etching, or other chemical etching means from the back surface of the surface being formed,
The back surface of the flat plate shape or concave lens type shape is several tens μm,
By RIE processing or other etching means, the unevenness of 1 μm to several μm formed on the machined surface that has been shaved off is polished by machining to about 0.2 μm to several μm to obtain a flat plate shape. Or, the back surface forming the concave lens type shape, in order to polish to the mirror surface, the flat surface, or the surface of the concave lens type shape, and the back surface, single-side polishing machine, float polishing machine, or double-side polishing machine, Or other polishing means, from 0.2μm to several μm
m, a method for processing a piezoelectric element, which performs polishing and mirror finishing. 5. When a piezoelectric material such as quartz is processed by RIE, if a mixed gas of a fluorine-based gas such as CF ₄ , CHF ₃ or C ₂ F ₆ and an argon gas is used, the surface accuracy of the quartz or the like can be improved. A method for processing a piezoelectric element, characterized in that the processing accuracy of the piezoelectric element is good. 6. Polishing a quartz plate having a concave lens shape on one or both sides by using a double-side polishing machine from the top and bottom simultaneously to process a very thin piezoelectric element. Processing method.