JPH07111435A - Method for manufacturing crystal piezoelectric device - Google Patents

Abstract

(57) [Abstract] [Purpose] A crystal piezoelectric device having a long-term stability, in which a crystal plate and a substrate holding the crystal plate can be directly bonded without an adhesive, and the excitation part of the crystal plate has no phase transition. A step of mirror-polishing one end surface of the quartz plate 8 and the substrate 14 which is a mutual bonding surface to form a mirror surface, and a through hole 10 in which a supporting portion 9 is left in a region surrounding the excitation portion 16 of the quartz plate 8. And the step of providing the depressed portion 15 on the mirror surface of at least one of the crystal plate 8 and the substrate 14 over a wider area than the excitation portion 16, and the cleaned crystal plate 8 and the substrate 14 are butted against each other on their mirror surfaces. And heating to a temperature of 100 ° C. or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a quartz crystal piezoelectric device used as a high frequency vibrator, a filter or the like in a mobile communication device, a mobile phone or the like.

[0002]

2. Description of the Related Art With the miniaturization and higher frequency of mobile communication devices, mobile phones, etc., there is a demand for miniaturization and higher frequency of quartz crystal piezoelectric devices used therein.

The crystal plate used for the crystal piezoelectric device is
An AT-cut crystal plate having excellent temperature characteristics is used for a high-frequency crystal piezoelectric device, which is obtained by subjecting a raw stone cut at a predetermined cut angle to rough polishing and precision double-sided polishing. Since it is the thickness vibration mode, the resonance frequency is determined by the thickness, and the smaller the thickness, the higher the resonance frequency.

A small crystal piezoelectric device is mounted in a flat package as shown in FIG. The crystal plate 1 is fixed on the insulating base 2 by the conductive adhesive layers 3a and 3b, and the excitation electrode 4a provided on the upper surface of the crystal plate 1 is fixed.
Is one of the lead terminals 5a through the conductive adhesive layer 3a.
And an excitation electrode 4b provided on the lower surface of the crystal plate 1
Is the other lead terminal 5b through the conductive adhesive layer 3b.
It is connected to the.

Since the excitation part of the crystal plate 1 must be free, a recess 2a is provided on the upper surface of the insulating base 2. The crystal plate 1 is fixed on the insulating base 2 at its peripheral portion, and the lid 6 forming a package together with the insulating base 2 is hermetically sealed to the insulating base 2 by the adhesive layer 7 provided on the peripheral portion. It is sealed.

[0006]

In the quartz crystal piezoelectric device having the above-described structure, if the thickness of the quartz crystal plate is reduced to reduce the size and increase the frequency, the following problems occur.

The crystal plate of the crystal piezoelectric device having a resonance frequency of about 30 MHz has a plate thickness of about 50 μm. If the crystal plate is thinner than this, the mechanical strength of the crystal plate is extremely lowered. For this reason, the processability in the process of applying the conductive adhesive or mounting the package on the package becomes poor, and the risk of damaging the crystal plate during handling increases. In addition, the work efficiency is generally low because the crystal plates are handled one by one.

Since various substances are contained and adsorbed in the conductive adhesive and the package sealing adhesive, the resonance frequency shifts when these substances are desorbed and adsorbed on the crystal plate. There is danger. In particular, the phenomenon of frequency shift remarkably appears in a high resonance frequency using a thin quartz plate.

Therefore, an object of the present invention is to realize a quartz crystal piezoelectric device which does not use an adhesive at all and is capable of handling and processing a large number of quartz plates at a time and which is excellent in workability. To provide a method.

[0010]

In order to achieve the above-mentioned object, the present invention provides a step of forming a mirror surface by mirror-polishing one end surface which is a mutual bonding surface of a crystal plate and a substrate, and an excitation of the crystal plate. A step of providing a through hole leaving a supporting part in a region surrounding the part, and a mirror surface of at least one of the crystal plate and the substrate,
A step of providing a depressed portion over a wider area than the excitation portion,
A method of manufacturing a quartz crystal piezoelectric device, comprising the steps of bringing a cleaned quartz plate and a substrate into contact with each other on their mirror surfaces and heating them to a temperature of 100 ° C. or higher.

[0011]

According to the present invention, the mirror surfaces formed on the respective end faces of the quartz plate and the substrate are butted against each other and heated to a temperature of 100 ° C. or more. After that, both can be handled as one part.

In the case of a glass substrate or a silicon substrate, if a mirror surface is formed on one end surface of each of them, dirt on the mirror surface, an adsorption layer and particles are removed and the mirror surfaces are butted against each other, intermolecular force between the substrates causes mutual interference. The phenomenon of adhesion is known. Also,
It is also known that when both are heated to a temperature of 100 ° C. or higher, a direct bonding effect of Si—O—Si at the atomic level between the substrates can be obtained due to intermolecular force and hydrogen bond of —OH group on the surface. However, it was only between silicon and silicon compound substrates such as glass and quartz.

The present inventors have found that a good direct bonding effect can be obtained even between the mirror surfaces of silicon or a silicon compound and quartz. It has also been confirmed that the same good bonding effect as described above can be obtained even when a buffer layer containing silicon such as silicon oxide or silicon nitride is interposed therebetween.

In the present invention, since the thin crystal plate is held on the substrate by utilizing the direct bonding effect of silicon or a silicon compound and the crystal, it becomes possible to handle both as one component, and the workability is remarkably improved. Can be improved.
Further, since the substrate and the crystal plate can be directly bonded in the state of a large wafer, it becomes possible to manufacture a large number of crystal piezoelectric devices at once. Moreover, since the adhesive layer does not intervene in the direct bonding portion, it is possible to eliminate the risk of degrading the crystal plate or the substrate by the gas generated from the adhesive layer.

Furthermore, according to the present invention, since the concave portion is provided on the mirror surface of at least one of the quartz plate and the substrate over a wider area than the excitation portion, and the quartz plate is supported only by the supporting portion, the quartz plate during the heat treatment. Since the exciting part does not come into direct contact with the substrate, that is, no thermal stress is applied to the exciting part, there is no phase transition of the quartz plate and desired resonance characteristics can be obtained. Therefore, it is possible to set the difference between the coefficient of thermal expansion of the AT-cut quartz plate in the X direction and the coefficient of thermal expansion of the substrate to 20 × 10 ⁻⁷ / ° C. or more.

If the heat treatment is performed with the quartz plate and the substrate in close contact with each other over the entire surface, thermal stress is generated due to the difference in coefficient of thermal expansion, and the quartz plate undergoes a phase transition. When excessive processing strain is applied to the crystal plate, twin crystals of the right crystal and the left crystal occur.
For example, when a + 35 ° AT cut (right crystal) 30 MHz blank is joined to a substrate having a different coefficient of thermal expansion, a phase change as shown in Table 1 occurs. Since the cut angle of the phase-changed left crystal is apparently -35 ° BT, the resonance frequency is about 1.5 times 40 MHz. It should be noted that it is possible to know whether the surface is AT-cut, BT-cut, or twin-crystal by etching the quartz plate with an aqueous solution of ammonium fluoride and by the pattern of the etch pits appearing on the surface. Compared to AT cut, BT cut has many extra spurious components and has poor temperature stability. If it becomes a twin crystal, even basic resonance characteristics cannot be obtained.

[0017]

[Table 1]

The coefficient of thermal expansion of quartz has anisotropy and is 140 × 10 ⁻⁷ / ° C. in the AT direction in the X direction, while
It is 95 × 10 ⁻⁷ / ° C. in the Z ′ direction. Under high thermal stress conditions, the stress causes self-destruction. In addition, since the coefficient of thermal expansion of quartz is anisotropic, the coefficient of thermal expansion cannot be perfectly matched with that of the substrate.
As shown in, the phase transition occurs in either the left crystal or the twin crystal.

[0019]

Embodiments of the present invention will now be described with reference to the drawings.

A first embodiment of the present invention is shown in FIG. Figure 1
The (4) quartz plate 8 shown in (a) is obtained by cutting a rough stone by AT cutting and polishing it to a plate thickness of about 10 μm, and mirror-polishing one end surface to be a joint surface to finish it into a mirror surface. . On the plate surface of the crystal plate 8, there is a through hole 10 provided in a region surrounding the excitation part, leaving the support part 9 left. The through hole 10 is formed by blasting using a photoresist as a mask so as to have a cantilever structure. Crystal plate 8
An upper electrode 11 is provided on the upper surface and a lower electrode 12 is provided on the lower surface. The lower electrode 12 is drawn out to the upper surface side through the through hole 13 formed during the blasting.

The four substrates 14 shown in FIG. 1 (b) are made of silicon (silicon), and one end surface to be a joint surface with the crystal plate 8 is mirror-finished by mirror polishing.
A part of the mirror surface has a recess 15 formed by etching. The recess 15 is, as shown in FIG. 1C, the excitation part 16 and the lower electrode of the crystal plate 8 abutted against the substrate 14. It is formed over a range wider than 12. Therefore, the butting does not cause the substrate 14 to come into contact with the excitation part 16 or the lower electrode 12 of the crystal plate 8.

Prior to the butting, the quartz plate 8 and the substrate 14 are cleaned. This cleaning is performed by so-called semiconductor precision cleaning, which uses both organic cleaning and ammonia water / hydrogen peroxide water cleaning, and spin drying is performed after the cleaning.

After the cleaned quartz plate 8 and the substrate 14 are abutted against each other at their mirror surfaces, heat treatment is performed. The temperature of this heat treatment was 100 ° C, 200 ° C and 3 ° C.
When tested at each of 00 ° C., a desired resonance frequency of about 170 MHz was obtained in each case. When the heat treatment temperature exceeds 400 ° C., cracks are likely to occur at the joint, and the yield is reduced.

Although not shown in the figure, since a series of operations from thinning and polishing the crystal plate 8 to forming electrodes are performed while being fixed to another thick work substrate, the period until the bonding with the substrate 14 is performed. Even in the inside, four thin crystal plates 8 are processed together.

As described above, according to this embodiment, the crystal plate 8
Since the mirror surfaces of the holding substrate 14 and the holding substrate 14 are butted against each other, a large number of devices can be processed at one time, and the handling property is significantly improved. In addition, the crystal plate 8 and the substrate 14
Since and are directly bonded, no adhesive layer serving as a gas generation source is interposed between the two, and even if heat treatment for bonding is performed, the excitation part 16 of the crystal plate 8 does not undergo phase transition, A crystal piezoelectric device having stable characteristics can be obtained.

FIG. 2 shows a second embodiment of the present invention. Figure 2
The crystal plate 8 shown in (a) has a through hole 10 as in the first embodiment, and has an upper electrode 11 on the upper surface. On the other hand, as shown in FIG. 2B, the substrate 14 made of silicon has a buffer layer 17 made of a silicon oxide film on its upper surface.
have. The buffer layer 17 has a recess 18 formed by etching, and the lower electrode 12 is provided in the recess 18.

In this case, the mirror-polished mirror surface of the crystal plate 8 is butted on the buffer layer 17 as shown in FIG. 2 (c), and heat-treated at a temperature of 100 ° C. or higher. As a result, the effect of direct bonding between the buffer layer 17 and the crystal plate 8 can be obtained.

The buffer layer 17 may be a thin film of silicon nitride. If the substrate 14 is made of glass and a thin film containing silicon such as a silicon thin film is provided as the buffer layer 17 on the surface of the substrate 14, a direct bonding effect with the crystal plate 8 can be obtained. Further, even if a gap is formed between the crystal plate 8 and the lower electrode 12, as long as the gap is minute, it does not hinder the excitation operation. Therefore, the lower electrode 12 can be used also as another electrode on the circuit board.

Another embodiment of the present invention is shown in FIG. The substrate 18 shown in FIG. 3A is made of glass and has a hole 19 formed by etching. The crystal plate 8 used in this embodiment is the same as that shown in FIG. As shown in FIG. 3B, the crystal plate 8 and the substrate 18 have their mirror-polished mirror surfaces butted against each other.
Heat treatment is performed at a temperature of 00 ° C. or higher. As a result, a direct bonding effect can be obtained between the crystal plate 8 and the substrate 18, and then the lower electrode 12 is provided on the lower surface of the crystal plate 8.
In this case, the recess 19 for freeing the excitation part of the crystal plate 8 is formed by the hole 19.

Another embodiment of the present invention is shown in FIG. The crystal plate 20 shown in FIG. 4 (a) has a mirror-finished surface A
It is T-cut, and the recesses 21, 21 provided on both sides are formed by etching. Also.
As in the above-described embodiment, a through hole 22 is provided for making the crystal plate 20 into a cantilever structure. Then, the upper electrode 11 and the lower electrode 12 are placed in the recesses 21, 21.
And are provided respectively.

The substrate 23 shown in FIG. 4B is made of glass and has through holes 24 for leading out electrodes. As shown in FIG. 4C, the substrates 23 are directly bonded to both surfaces of the crystal plate 20, and the conductor 25 press-fitted into the through hole 24 serves as an electrode lead terminal and is hermetically sealed. It has stopped.

In this embodiment, the concave portions 2 are formed on both sides of the crystal plate 20.
Since Nos. 1 and 21 are provided, the work-affected layer generated when the crystal plate 20 is polished is removed during the etching process. Therefore, good resonance characteristics could be obtained in most of the samples. Further, when the substrates 23 having the same thickness and made of the same material are bonded to both surfaces of the crystal plate 20, warpage of the crystal plate 20 due to thermal stress can be suppressed, so that the yield can be increased. Moreover, since airtight sealing can be obtained by direct bonding, an adhesive layer is not required, and there is no gas generated from the adhesive layer, and a sealing effect with excellent airtightness can be obtained.

In short, if the excitation part of the crystal plate is not joined to the substrate holding the crystal plate, there is no phase transition of the crystal plate, and therefore the place and means for providing the recess can be variously modified. Also, the substrate is not limited to silicon or glass.

[0034]

As described above, according to the present invention, the crystal plate can be directly bonded to the substrate without interposing the adhesive layer without impairing the resonance characteristics of the crystal plate, so that a large number of devices can be collectively processed. Therefore, it is possible to manufacture a quartz crystal piezoelectric device that is easy to handle and has excellent long-term stability of resonance characteristics.

[Brief description of drawings]

FIG. 1 is a plan view and a side sectional view of a component / joint body in a manufacturing process according to an embodiment of the present invention.

FIG. 2 is a side sectional view of a component / joint body in a manufacturing process of another embodiment of the present invention.

FIG. 3 is a side sectional view of a component / joint body in a manufacturing process of another embodiment of the present invention.

FIG. 4 is a side sectional view of a component / joint body in a manufacturing process of another embodiment of the present invention.

FIG. 5 is a side sectional view of a conventional crystal piezoelectric device.

[Explanation of Codes] 8 Quartz Plate 10 Through Hole 11 Upper Electrode 12 Lower Electrode 14 Substrate 15 Cavity 16 Excitation Part 17 Buffer Layer 18 Substrate 19 Hole 20 Quartz Plate 21a, 21b Recess 22 Through Hole 23 Substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Eda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A step of forming a mirror surface by mirror-polishing one end surface that is a mutual bonding surface of a crystal plate and a substrate, and a step of providing a through hole in a region surrounding an excitation part of the crystal plate while leaving a supporting portion. , A step of forming a depression on a mirror surface of at least one of the crystal plate and the substrate over a wider area than the excitation part, and a step of bringing the cleaned crystal plate and the substrate into contact with each other and heating them to a temperature of 100 ° C or higher. A method of manufacturing a quartz crystal piezoelectric device, comprising: 2. The method for manufacturing a quartz crystal piezoelectric device according to claim 1, wherein the substrate is made of silicon or glass. 3. The method for manufacturing a quartz crystal piezoelectric device according to claim 1, wherein the substrate has a thin film layer made of silicon or a silicon compound, and a depression is provided in the thin film layer. 4. The method of manufacturing a quartz crystal piezoelectric device according to claim 1, wherein the depression is a hole penetrating the substrate.