JPH05327383A - Working method for crystal element board - Google Patents

Abstract

PURPOSE:To provide a working method for crystal element board for easily and thinly grinding a crystal element board, facilitating oscillation in higher frequency for a crystal oscillator improving adhesive strength with a semiconductor substrate and improving mass productivity concerning the constitution of a crystal oscillator adhering the crystal element board on the semiconductor substrate. CONSTITUTION:A semiconductor substrate 3 performing hydrophilic processing for the surface and a crystal element board 1 having thickness thicker than 40mum and thinner than 80mum are directly adhered, thereafter, heating processing of higher than 350 deg.C and lower than 400 deg.C is performed, the crystal element board 1 is worked into the thickness thinner than 40mum, and heating processing of higher than 400 deg.C and lower than 573 deg.C is performed for the crystal element board 1 and the semiconductor substrate 3.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Crystal oscillators have high stability,
It is used as an important device indispensable for information communication. In recent years, with the development of satellite communications and mobile phones, it has become a major goal to improve their performance.
The crystal unit is no exception.

In recent years, various new processing methods have been proposed for crystal oscillators in an attempt to reduce their size and make them hybrid. Hereinafter, a recently proposed processing method to which the direct bonding of the crystal unit is applied will be briefly described.

The direct adhesion is a technique of directly adhering silicon substrates or silicon and glass substrates without an adhesive agent, and bringing the surface-treated silicon or glass substrate into contact in a clean atmosphere. ,
Heat treatment is performed to obtain strong adhesion.

After applying the above-mentioned direct bonding technique to a crystal blank and subjecting the crystal blank and the semiconductor substrate to appropriate treatment and processing,
A processing method has been newly developed in which a quartz crystal plate is directly bonded and processed into a desired shape by applying a semiconductor processing technology to obtain a small-sized hybridized crystal resonator.
A conventional processing method of this type will be described with reference to FIG.

In the figure, reference numeral 21 is a quartz crystal plate, and 22a, 2
2b is an upper excitation electrode and a lower excitation electrode, 23
Is a space and 24 is a semiconductor substrate. Then, the crystal blank 21 and the semiconductor substrate 24 are subjected to a surface treatment for direct bonding, and then brought into contact with each other in a clean atmosphere to be heat-treated. Further, the space 23 is opened in the semiconductor substrate 24 due to the vibration of the quartz crystal plate 21. This method is a processing method capable of processing the crystal blank 21 into an arbitrary shape and size by using a semiconductor processing technique such as photolithography or etching, and having excellent performance, miniaturization and mass productivity. .. Further, by incorporating an active circuit for driving the crystal element plate 21 in the semiconductor substrate 24 to which the crystal element plate 21 is adhered, a hybrid type crystal oscillator in which an oscillation circuit and a vibrating portion are integrated is provided. It is also possible to obtain.

[0007]

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

If the crystal blank 21 is thin,
Since destruction due to thermal stress is unlikely to occur, for example, if the crystal element plate 21 is ground to 20 μm or less before being directly adhered and then adhered, even if heat treatment is performed at 500 ° C. or more, destruction due to thermal stress is unlikely to occur. However, in that case, the crystal blank 2
Since handling of No. 1 becomes very difficult, there was a problem in workability.

Further, as the frequency band used for mobile communication is increased to the GHz band, the oscillation frequency of the crystal oscillator is also required to be increased. Since the oscillation frequency of the crystal unit is inversely proportional to the thickness of the crystal element plate 21, the crystal element 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 crystal blank 21 is 40 μm or less, and it is very difficult to handle such a thin crystal blank 21. Therefore, the upper limit of the oscillation frequency of a crystal oscillator that can be mass-produced by fundamental wave oscillation is 40
At frequencies of about MHz, methods such as wet etching and dry etching are used for further increasing the frequency, but if the etching rate is kept low to improve the controllability of the thickness, the amount of crystal removed by etching is large. Therefore, there is a problem that it takes a very long time until the crystal blank 21 has a desired thickness.

The present invention solves the above-mentioned problems. The crystal element plate can be easily polished thinly, the frequency of the crystal oscillator can be easily increased, the adhesive strength with the semiconductor substrate is improved, and the crystal element is excellent in mass productivity. An object is to provide a method for processing a plate.

[0011]

In order to achieve the above-mentioned object, a method for processing a quartz crystal plate according to the present invention directly adheres a semiconductor substrate having a surface hydrophilized to a quartz crystal plate having a thickness of 50 μm or more and 80 μm or less. After that, heat treatment at 350 ° C. or more and 400 ° C. or less is performed, the quartz crystal plate is processed to have a thickness of 50 μm or less, and heat treatment at 400 ° C. or more and 573 ° C. or less is performed on the quartz crystal plate and the semiconductor substrate. The processing method.

[0012]

According to the present invention, by the above-described processing method, the quartz crystal plate and the semiconductor substrate are less likely to be cracked, and the heat treatment that can obtain a sufficient adhesive strength can be performed, so that the mass productivity is improved.

Further, since the crystal blank can be thinned by polishing or etching while it is adhered to the semiconductor substrate, it is easy to handle even if the thickness of the crystal blank is thin, and therefore, the crystal blank can be easily processed. High frequency becomes easy.

Further, since it becomes easy to polish the crystal blank to a very thin thickness, the amount of crystal to be removed by etching processing can be small, and the resonance frequency of the crystal resonator can be easily increased. It will be.

[0015]

EXAMPLES An example of the present invention will be described in detail below. For the relationship between the thickness of the crystal blank and the maximum heat treatment temperature at which the defective rate of cracking or peeling after heat treatment after direct bonding is 20% or less,
The results shown in (Table 1) were obtained as a result of an experiment in which five kinds of 60 μm, 80 μm, 55 μm, 40 μm, and 20 μm were examined by changing the heat treatment temperature from room temperature to 500 ° C.

[0016]

[Table 1]

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

The heat treatment temperature after direct bonding is 35
It is known that if the temperature is 0 ° C. or higher, the adhesive strength between the crystal blank and the semiconductor substrate is such that there is no problem in mechanically polishing the crystal blank while holding at least 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. Further, it is not easy to polish the thickness of the crystal blank to 50 μm or less, and it becomes difficult to handle a thinner crystal blank. Therefore, the thickness of the crystal blank before directly bonding should be 50 μm or more and 80 μm or less. do it. Therefore, in this embodiment, the thickness of the crystal blank used for direct bonding is set to about 60 μm. The semiconductor substrate to which the crystal blank is bonded is a silicon single crystal substrate having a size of 11 × 11 mm, a thickness of 400 μm, and a plane orientation (100), and both the crystal blank and the silicon substrate have both surfaces. It is mirror-finished.

After the crystal blank and the semiconductor substrate were hydrated, they were washed in running water and brought into contact in a clean atmosphere. Then, the quartz 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 crystal substrate and the semiconductor substrate that have been cooled to room temperature sufficiently slowly is fixed on the surface plate of the polishing machine with electron wax, and the crystal substrate is Was thinned by polishing. The thinner the quartz crystal plate is, the higher the heat treatment is possible, and the higher the frequency can be dealt with. However, the mechanical polishing can be performed with a precision of 10 μm or more. In this case, the thickness of the crystal blank was 15 μm.

After that, the quartz crystal plate and the semiconductor substrate were again heated in an electric furnace to 500 ° C. in air slowly enough to perform a second heat treatment.

As described above, the quartz crystal plate directly bonded onto the semiconductor substrate was applied with a semiconductor processing technique to form a vibrating portion to obtain a quartz oscillator. FIG. 1 shows an external view of a crystal unit directly bonded onto a semiconductor substrate obtained in this example. In FIG. 1, 1 is a quartz crystal plate, 2
Is a vibrating part, 3 is a semiconductor substrate, 4 is an excitation electrode, the vibrating part 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 portion 2 was formed by hollowing out the quartz crystal plate 1 by wet etching. Further, the crystal blank 1 is processed to have a thickness of approximately 2 μm by wet etching and dry etching while being directly bonded to the semiconductor substrate 3, and the resonance frequency of the obtained crystal resonator is 167.
Became MHz. Since the thickness of the quartz crystal plate 1 is as thin as 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 has a desired thickness. The time will be less.

As described above, the crystal blank 1 is firmly bonded directly to the semiconductor substrate 3, so that the crystal blank 1 can be precisely processed by applying a semiconductor processing technique. Further, since it becomes easy to process the crystal blank 1 very thinly, it becomes easy to process a crystal resonator having a resonance frequency of 100 MHz or more, which has been difficult to obtain so far.

Although the first heat treatment temperature is 350 ° C. in this embodiment, the temperature is not limited to this.
It is clear that the first heat treatment temperature may be 350 ° C. or higher as long as the bonding strength is such that polishing can be performed while the crystal blank 1 is directly bonded to the semiconductor substrate 3. Further, the crystal blank 1 before the first heat treatment
The thickness is 60 μm, but the thickness is not limited to this, and may be any thickness equal to or smaller than the thickness capable of heating up to the first heat treatment temperature.

Furthermore, the crystal blank 1 before the second heat treatment
The thickness is 15 μm, but the thickness is not limited to this and may be any thickness 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 thickness of the plate 1 may be 40 μm.
Further, although the second heat treatment temperature is set to 500 ° C. in the present embodiment, the present invention is not limited to this, and the crystal blank 1
The semiconductor substrate 3 is less likely to be cracked or peeled off, and the temperature may be the α-β transition temperature (573 ° C.) of the crystal or lower.

[0026]

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

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

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

[Brief description of drawings]

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

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

[Explanation of symbols]

 1 Crystal blank 3 Semiconductor substrate

Continued Front Page (72) Inventor Kazuo Eda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A semiconductor substrate whose surface has been hydrophilized and a crystal element plate having a thickness of 50 μm or more and 80 μm or less are directly adhered to each other, and then heat treatment is performed at 350 ° C. or more and 400 ° C. or less to make the crystal element plate 50 μm or less. A method of processing a crystal blank, which is processed to a thickness of 4 ° C. and heat-processes the crystal blank and the semiconductor substrate at 400 ° C. or higher and 573 ° C. or lower. 2. The method for processing a quartz crystal plate according to claim 1, wherein a silicon substrate is used as the semiconductor substrate.