JP2848116B2 - Quartz blank processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of processing a quartz crystal plate, and more particularly to a method of processing a quartz crystal plate used for a crystal resonator having a structure in which a quartz crystal plate is bonded on a semiconductor substrate.

[0002]

2. Description of the Related Art Quartz resonators have high stability
It is used as an important device indispensable for information communication. In recent years, with the development of satellite communications, mobile phones, etc., high performance has been one of the major goals,
Quartz resonators are no exception.

[0003] In recent years, various new processing methods have been proposed as attempts to reduce the size and hybridize the quartz oscillator. Hereinafter, a processing method using a direct bonding of a crystal unit, which has been recently proposed, will be briefly described.

[0004] Direct bonding is a technique in which silicon substrates or silicon and glass substrates are directly bonded to each other without an adhesive agent interposed therebetween. Surface-treated silicon or glass substrates are brought into contact in a clean atmosphere. ,
Heat treatment is performed to obtain strong adhesion.

[0005] The above direct bonding technique is applied to a quartz crystal plate, and the quartz crystal plate and the semiconductor substrate are appropriately processed and processed.
A processing method of directly bonding and processing the quartz crystal plate into a desired shape by applying a semiconductor processing technique to obtain a small and hybrid crystal resonator has been newly developed.
A conventional processing method of this kind will be described with reference to FIG.

In the figure, reference numeral 21 denotes a quartz crystal plate, 22a, 2
2b is an upper excitation electrode and a lower excitation electrode, respectively.
Is a space, and 24 is a semiconductor substrate. The crystal plate 21 and the semiconductor substrate 24 are subjected to a surface treatment for direct bonding, and then brought into contact in a clean atmosphere and subjected to a heat treatment. The space 23 is opened in the semiconductor substrate 24 for the vibration of the quartz crystal plate 21. This method can process the quartz crystal plate 21 into an arbitrary shape and size by using a semiconductor processing technique such as photolithography or etching, and is a processing method excellent in high performance, miniaturization, and mass productivity. . Further, by incorporating an active circuit for driving the quartz crystal plate 21 into the semiconductor substrate 24 to which the quartz crystal plate 21 is adhered, a hybrid crystal oscillator in which an oscillation circuit and a vibrating part are integrated is provided. It is also possible to get.

[0007]

However, in the above-mentioned conventional processing method, even if an attempt is made to perform a heat treatment necessary for improving the bonding strength after the direct bonding between the quartz crystal plate 21 and the semiconductor substrate 24, The quartz crystal plate 21 or the semiconductor substrate 2 depends on the difference in thermal expansion coefficient between quartz and semiconductor.
4 may be destroyed due to thermal stress, and there is a problem that conditions are restricted. For example, an AT-cut quartz plate having a thickness of 80 μm and a size of 8φ is used as the quartz plate 21, and a size of 10 mm ×
When a silicon single crystal substrate with a thickness of 10 mm, a thickness of 350 μm, and a plane orientation (100) is used, the thermal expansion coefficient of quartz (AT cut) is 13 × 10 ⁻⁶ / ° C., and that of silicon is 2.5 × 10 ⁻⁶ / ° C.
Therefore, when the heat treatment temperature is set to 300 ° C. or higher, the quartz crystal plate 21 and the semiconductor substrate 24 may be broken due to thermal stress. Therefore, there is a problem in mass productivity in order to obtain sufficient adhesive strength.

If the thickness of the crystal plate 21 is small,
Since damage due to thermal stress is unlikely to occur, if the quartz plate 21 is polished to 20 μm or less before direct bonding and then bonded, for example, even if a heat treatment at 500 ° C. or more is performed, damage due to thermal stress is unlikely to occur. However, in that case, the crystal blank 2
Since the handling of No. 1 became very difficult, there was a problem in workability.

Further, as the frequency band used for mobile communication increases to the GHz band, the oscillation frequency of the quartz oscillator also needs to increase. Since the oscillation frequency of the crystal unit is inversely proportional to the thickness of the quartz plate 21, the quartz plate 21 needs to be thinned in order to increase the oscillation frequency. However, with the current processing method, it is very difficult to realize when the thickness of the quartz plate 21 is 40 μm or less, and it is very difficult to handle such a thin quartz plate 21. Therefore, the upper limit of the oscillation frequency of the mass-produced quartz oscillator obtained by the fundamental wave oscillation is 40
At about MHz, to further increase the frequency, techniques such as wet etching and dry etching are used, but if the etching rate is kept low to improve the controllability of the thickness, the amount of crystal to be etched and removed is large For this reason, there has been a problem that it takes a very long time for the crystal element plate 21 to have a desired thickness.

The present invention solves the above-mentioned problems, and a quartz crystal plate can be easily polished thin and thin, a high frequency of a quartz oscillator can be easily achieved, an adhesive strength with a semiconductor substrate can be improved, and mass production can be easily performed. An object of the present invention is to provide a method for processing a plate.

[0011]

According to the present invention, there is provided a method for processing a quartz crystal plate, comprising: directly bonding a semiconductor substrate having a hydrophilized surface to a quartz crystal plate having a thickness of 50 μm or more and 80 μm or less to achieve the above object. After that, a heat treatment of 350 ° C. or more and 400 ° C. or less is performed, the quartz plate is processed to a thickness of 50 μm or less, and the quartz plate and the semiconductor substrate are subjected to a heat treatment of 400 ° C. or more and 573 ° C. or less. Processing method.

[0012]

According to the present invention, by the above-described processing method, the quartz plate or the semiconductor substrate is hardly cracked, and a heat treatment for obtaining a sufficient adhesive strength can be performed, so that mass productivity is improved.

Further, since the quartz crystal plate can be thinned by polishing or etching while being adhered to the semiconductor substrate, it is easy to handle even if the thickness of the quartz crystal plate becomes thin. Higher frequency becomes easier.

Further, since the thickness of the quartz crystal plate can be very thinly polished, the amount of quartz to be removed by etching can be reduced, and the resonance frequency of the quartz resonator can be easily increased. It will be.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail. The relationship between the thickness of the quartz crystal plate and the maximum heat treatment temperature at which the failure rate of cracking or peeling after the heat treatment after direct bonding is 20% or less is determined by the following equation.
As a result of an experiment in which the heat treatment temperature was changed from room temperature to 500 ° C. for five types of 60 μm, 80 μm, 55 μm, 40 μm, and 20 μm, the results shown in Table 1 were obtained.

[0016]

[Table 1]

In this case, the size of the quartz plate used for direct bonding is 8φ, and the size of the semiconductor substrate is 11 × 11 m.
m, a thickness of 400 μm, and a (100) plane single-crystal silicon substrate. Further, the quartz crystal plate and the semiconductor substrate are heated in air by an electric furnace, and the temperature rise rate is 100 ° C.
/ 1 hour, the temperature drop rate is about 300 ° C./2 hours, and the sample in which the quartz plate and the semiconductor substrate are directly bonded is
Twenty pieces were prepared for each thickness of the quartz plate.

The heat treatment temperature after the direct bonding is 35.
If the temperature is 0 ° C. or higher, it is known that the bonding strength between the quartz crystal plate and the semiconductor substrate is at least such that there is no problem in mechanically polishing the quartz crystal plate while holding the semiconductor substrate. However, it can be seen from Table 1 that the heat treatment at 350 ° C. cannot be performed unless the thickness of the quartz crystal plate is at least 80 μm or less. In addition, it is not easy to polish the thickness of the quartz plate to 50 μm or less, and it is difficult to handle a thinner quartz plate. Therefore, the thickness of the quartz plate before directly bonding is 50 μm or more and 80 μm or less. do it. Therefore, in the present embodiment, the thickness of the quartz plate used for direct bonding is set to about 60 μm. The semiconductor substrate to which the quartz plate is bonded is a silicon single crystal substrate having a size of 11 × 11 mm, a thickness of 400 μm, and a plane orientation of (100). Both sides of the quartz plate and the silicon substrate are provided. It is mirror finished.

After the quartz crystal plate and the semiconductor substrate were hydrated, they were washed in running water and brought into contact in a clean atmosphere. Thereafter, the crystal plate and the semiconductor substrate were sufficiently slowly heated to 350 ° C. in air in an electric furnace to perform a first heat treatment.

After the first heat treatment, the semiconductor substrate side of the quartz crystal plate and the semiconductor substrate cooled sufficiently slowly to room temperature is fixed to a surface plate of a polishing machine using electron wax, and the quartz crystal plate is cooled. Was thinned by polishing. Although the thinner quartz crystal plate can be heated at a higher temperature and can respond to higher frequency when the thickness of the quartz crystal plate is reduced, it is possible to precisely polish by mechanical polishing at least 10 μm. In the case of the above, the thickness of the quartz plate was 15 μm.

Thereafter, the crystal plate and the semiconductor substrate were again heated sufficiently slowly in an electric furnace to 500 ° C. in air, and a second heat treatment was performed.

A vibrating portion is formed by applying a semiconductor processing technique to the quartz crystal plate directly adhered on the semiconductor substrate as described above, to obtain a quartz oscillator. FIG. 1 shows an external view of a crystal unit directly bonded on a semiconductor substrate obtained according to this embodiment. In FIG. 1, 1 is a crystal blank, 2
Is a vibrating section, 3 is a semiconductor substrate, 4 is an excitation electrode, the vibrating section 2 is a rectangle having a width of 0.8 mm and a length of 5 mm, and the excitation electrode 4 is a rectangle having a width of 0.5 mm and a length of 2 mm. The vibrating part 2 was formed by hollowing out the quartz crystal plate 1 by wet etching. The crystal blank 1 is processed to a thickness of about 2 μm by wet etching and dry etching while being directly adhered to the semiconductor substrate 3, and the obtained crystal resonator has a resonance frequency of 167 μm.
MHz. Since the thickness of the quartz crystal plate 1 is very thin, 15 μm, even if the etching rate is kept low in order to improve the controllability of the thickness in each etching, the quartz crystal plate 1 is kept at a desired thickness. Less time is needed.

As described above, since the quartz crystal plate 1 is firmly and directly adhered to the semiconductor substrate 3, it is possible to precisely machine the quartz crystal plate 1 by applying a semiconductor processing technique. In addition, since it is easy to process the crystal blank 1 very thinly, it is easy to process a crystal resonator having a resonance frequency of 100 MHz or more, which has been difficult to obtain until now.

In the present embodiment, the first heat treatment temperature is set to 350 ° C., but is not limited to this.
It is clear that the first heat treatment temperature may be 350 ° C. or more, since it is sufficient to obtain an adhesive strength that enables polishing while the crystal plate 1 is directly adhered to the semiconductor substrate 3. Further, the quartz crystal plate 1 before the first heat treatment is performed.
Is set to 60 μm, but is not limited to this, and may be any thickness as long as it can be heated to the first heat treatment temperature.

Further, the quartz crystal plate 1 before the second heat treatment is performed.
Is 15 μm, but is not limited to this. Any thickness may be used as long as it can be heated to the second heat treatment temperature. For example, if the second heat treatment temperature is 450 ° C., the crystal The thickness of the plate 1 may be 40 μm.
In the present embodiment, the second heat treatment temperature is set to 500 ° C., but the present invention is not limited to this.
And the semiconductor substrate 3 are not likely to be cracked or peeled off, and may be any temperature that is lower than or equal to the α-β transition temperature (573 ° C.) of quartz.

[0026]

As described above, according to the present invention, the heat treatment temperature after directly bonding the quartz crystal plate and the semiconductor substrate and the thickness of the quartz crystal plate are defined, whereby the semiconductor substrate and the quartz crystal are defined. Even when heated to a heat treatment temperature at which the bonding strength with the base plate is sufficient, the quartz plate and the semiconductor substrate are less likely to be cracked or peeled.

Further, since the quartz plate is bonded to the semiconductor substrate, it is easy to handle even if the thickness of the quartz plate is thin, and the workability is good.

In addition, since the quartz crystal plate can be easily made very thin by mechanical polishing while being adhered to the semiconductor substrate, the amount of the quartz crystal plate to be removed by etching or the like can be reduced. It is possible to provide a method for processing a quartz crystal plate that facilitates increasing the resonance frequency of the crystal element.

[Brief description of the drawings]

FIG. 1 is a perspective view of a crystal resonator obtained by a processing method of the present invention.

FIG. 2A is a perspective view of a crystal resonator obtained by a conventional processing method; FIG. 2B is a cross-sectional view of the crystal resonator obtained by the processing method;

[Explanation of symbols]

 Reference Signs List 1 crystal blank 3 semiconductor substrate

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuo Eda 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) H03H 3/00 -3/10 H03H 9/00-9/76 H01L 41/00-41/26

Claims (2)

(57) [Claims] 1. After directly bonding a semiconductor substrate having a hydrophilized surface to a quartz plate having a thickness of not less than 50 μm and not more than 80 μm, a heat treatment is performed at not less than 350 ° C. and not more than 400 ° C. And processing the quartz crystal plate and the semiconductor substrate by heating at 400 ° C. or more and 573 ° C. or less. 2. The method according to claim 1, wherein a silicon substrate is used as the semiconductor substrate.