JP2589634B2 - Electroacoustic integrated circuit and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroacoustic integrated circuit in which a semiconductor device and an electroacoustic device such as a surface acoustic wave device and a bulk type vibrating device are integrated, and a method of manufacturing the same. It is intended to reduce the size, weight, performance, and ease of manufacture of high-frequency devices such as oscillators.

[0002]

2. Description of the Related Art Conventionally, an electroacoustic element such as lithium niobate (LiNbO ₃ ) or lithium tantalate (LiTaO) has been used.
₃ ) Surface acoustic wave device (filter, resonator, etc.)
Or, an electronic circuit using a bulk type vibrating element such as crystal, for example, a voltage controlled oscillator (VCO) or a high frequency receiving device,
It is composed of a transistor as an active element for oscillation and amplification, a surface acoustic wave element and a bulk type vibration element for oscillating or resonating at a desired frequency, and some electric components such as a capacitor and a resistor.

[0003] The surface acoustic wave element or bulk type vibration element used here has a predetermined value as its vibration or resonance frequency, and is sealed in a container such as a metal container so that its performance is stable for a long period of time. Have been. As a result, the shape and dimensions of surface acoustic wave elements and bulk-type vibrating elements are several times larger than the size of the vibration or resonance part itself. It is a very important issue.

In order to reduce the size, it is desirable to integrate a semiconductor element having a transistor and the like and an electroacoustic element. As such an example, it is reported that, for example, an aluminum nitride (AlN) film, which is a piezoelectric material, is epitaxially grown on a Si substrate, and a surface acoustic wave (SAW) device is formed thereon. In order to obtain good vibration or resonance characteristics, epitaxial growth or a film oriented in a specific crystal axis direction is required. However, films that can be epitaxially grown and oriented include AlN and zinc oxide (Z
nO) and other materials.

In the case of a bulk-type vibrating element, for example, a quartz vibrator is used for a mobile phone, a cellular phone, or the like.
In order to obtain a high-frequency vibrator that can be used in the quasi-microwave band such as 0 MHz to 1.9 GHz, it is necessary to reduce the thickness of the quartz vibrator by polishing or etching. For example, it has been reported that quartz was polished to a thickness of about 10 μm by a precision polishing technique and oscillated at several hundred MHz.

However, it is extremely difficult to process a thin quartz crystal plate having a thickness of 10 μm or less and use it as a vibrator due to the problem of mechanical strength in holding and handling, when considering mass production. Therefore, it has been extremely difficult to obtain a high-frequency voltage-controlled oscillator exceeding 500 MHz using substantially the fundamental oscillation mode of the crystal oscillator. When a higher-order vibration mode is used, the Q of resonance is reduced, so that it is still difficult to obtain a high-performance and stable oscillator.

As one method for simultaneously achieving the reduction in size and weight of a voltage-controlled oscillator and the increase in the oscillation frequency, for example, Grundkowski et al., “Fundamental-mode VHF /
UHFMinature Acoustic Resonators and Filters on Sil
icon Applied PhysicsLetters Vol.37 (11) (1980) pp.99
3-995 reports a method of forming a ZnO thin film resonator on a silicon substrate to form a quasi-microwave band resonator. In this case, since a resonator having a thickness of several μm can be easily formed, a resonator in a quasi-microwave band can be obtained. However, the ZnO thin film vibrating element is not sufficient in performance because the temperature dependence of the resonance frequency and the resonance Q are inferior to those of a bulk type vibrating element such as quartz.

As a method for solving these problems, a semiconductor substrate is bonded to lithium niobate or lithium tantalate exhibiting excellent properties as a surface acoustic wave resonance element, or quartz crystal exhibiting excellent properties as a bulk type vibrating element. There is a method of achieving integration, thinning and mass production of a piezoelectric body by processing such as etching. However, since lithium niobate, lithium tantalate, and quartz are chemically quite stable substances, the types of substances that can be etched are very limited. Specifically, a strongly acidic etchant containing hydrofluoric acid as a main component is used.

Further, since the etching rate is low even when a hydrofluoric acid-based etching solution is used, when the depth to be etched is deep, several hours are required as the etching time. Since the hydrofluoric acid-based etchant erodes the semiconductor substrate very easily, it is necessary to cover a predetermined portion of the semiconductor substrate with a protective film during etching. However, there is no hydrofluoric acid-based etchant which is stable for a long time and is not effective as a protective film capable of microfabrication, and the etching of the piezoelectric body is particularly difficult when a precise shape processing is to be performed. There is a problem that the production is not easy from the aspect of.

[0010]

As described above, a high-frequency device constructed by a method of individually connecting a transistor and related components to a surface acoustic wave device or a bulk type vibrating device housed in a container, and a transistor and related components is large and heavy. Therefore, it is not preferable for a device such as a mobile phone or a mobile phone in which small and light weight is the most important factor. In the case of bonding lithium niobate, lithium tantalate, or quartz having excellent piezoelectric properties to a substrate and performing shape processing by etching, the material is chemically stable, which limits the selection of the substrate material. There have been various manufacturing problems such as difficulty in forming a protective film at the time of etching, time required for etching, and difficulty in fine processing with high precision.

An object of the present invention is to solve the above-mentioned conventional problems, and in particular, to reduce the size and weight of a high-frequency device such as a voltage-controlled oscillator and to facilitate the manufacture thereof.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to directly or directly apply a surface acoustic wave element or a bulk type vibration element made of a lithium borate single crystal piezoelectric substrate to a semiconductor substrate. And an electroacoustic integrated circuit is integrally formed on the semiconductor substrate, and the shape processing of the lithium borate single crystal piezoelectric substrate is performed with a weakly acidic etching solution.

[0013]

By using the configuration and the manufacturing method as described above, an electroacoustic integrated circuit which is small, lightweight, high-performance, extremely easy to etch, and easy to manufacture can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electroacoustic integrated circuit according to each embodiment of the present invention,
In particular, a configuration when applied to a voltage controlled oscillator and a manufacturing method thereof will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic sectional view showing a configuration of a voltage controlled oscillator according to a first embodiment of the present invention.
Wherein 1 is a semiconductor substrate, in this case silicon (Si)
It is composed of a substrate. Reference numeral 2 denotes a lithium borate single crystal piezoelectric substrate (hereinafter simply referred to as a lithium borate substrate) bonded on the Si substrate 1 and having a surface acoustic wave element on its surface. In this case, a surface acoustic wave resonator is formed. I have. 3 is a Si substrate 1
The field effect transistor (FET) formed above, 4 is a variable capacitance diode chip whose capacitance changes according to voltage, 5 is a passive chip component such as a capacitor, an inductor and a resistor, and 6 is an electrode of a surface acoustic wave resonator. Although not shown in the drawing, each component on the Si substrate 1 and the electrode of the surface acoustic wave resonator are connected by wiring so as to be a voltage controlled oscillator.

The lithium borate substrate 2 and the Si substrate 1 are directly bonded. Further, the voltage-controlled oscillator integrated as above is housed in a sealed container. An oscillator is composed of a field effect transistor 3, a variable capacitance diode 4, various passive chip components 5, and a surface acoustic wave resonator (lithium borate substrate 2). By changing a voltage applied to the variable capacitance diode chip 4, the capacitance is changed. Can change the oscillation frequency.

With this configuration, since the oscillation circuit and the surface acoustic wave resonator are integrated into a single body, the size can be significantly reduced as compared with the related art. In addition, it is easier to reduce the volume to about 1/10 and the weight to about 1/5 as compared with the case where the surface acoustic wave resonator is sealed in a container and individually attached.

In this embodiment, the variable capacitance diode 4 and the various passive chip components 5 are individually mounted on the Si substrate 1, but they can be simultaneously formed on the semiconductor substrate.

When the bonding between the semiconductor substrate and the electroacoustic element is performed by using an adhesive such as a general resin, from the viewpoint of heat resistance,
After that, there are problems such as the inability to perform the semiconductor process and the use up to high temperatures.
The substrate 1 and the lithium borate substrate 2 are directly bonded. Therefore, no other substance is interposed at the interface, and such a problem is greatly improved.

If an adhesive such as a resin is used for bonding, the parallelism between the Si substrate 1 and the lithium borate substrate 2 adhered thereon becomes poor, and then the surface formed on the lithium borate substrate by photolithography. The dimensional accuracy of the comb-shaped electrode for the acoustic wave device is deteriorated. For example, when the resonance frequency becomes about 1 GHz, the electrode size becomes a line and space width of about 1 μm. Therefore, if the parallelism is poor, a quasi-microwave band surface acoustic wave resonator cannot be formed. However, in the method of the present embodiment, since direct bonding is performed, the accuracy is determined by the accuracy of the surface shape of each substrate. However, since these are all single crystals, they can be processed with extremely high precision. This effect is particularly large at high frequencies.

Further, when a resin adhesive is used, there is a problem that the resin is weak to heat, and the thermal expansion coefficient is greatly different between an organic resin and an inorganic Si substrate or a lithium borate substrate. However, such a problem can be solved by bonding with an inorganic material as in the present embodiment.

Since the etching of the lithium borate substrate can be performed with a weakly acidic etching solution, the production is extremely easy.

Lithium borate has a condition that the electromechanical coupling coefficient is larger than that of quartz, the temperature dependency is almost as good as quartz, and there is a condition that the temperature dependency is almost zero around room temperature. In this case, it shows extremely excellent performance.
Therefore, it shows better performance as a resonator and an oscillator than those integrated with a thin film.

(Embodiment 2) FIG. 2 is a schematic diagram showing the configuration of a voltage controlled oscillator according to a second embodiment of the present invention. In FIG. 2, the same components 1 to 6 as those in FIG. Reference numerals are used, and the functions are the same as those in the first embodiment. Reference numeral 7 denotes a silicon compound film such as silicon or silicon oxide used for bonding the Si substrate 1 and the lithium borate substrate 2, whereby the Si substrate 1 and the lithium borate substrate 2 are directly bonded. The other configuration is the same as that of the first embodiment, and the effect of reducing the size and weight when the voltage controlled oscillator is formed is also the same.

In the present embodiment, the Si substrate 1 and the lithium borate substrate 2 are joined by the silicon compound film 7 such as silicon or silicon oxide. Is an inorganic substance, and is thermally stable up to a high temperature, so that the same effect as in the first embodiment can be obtained.
In addition, the problem of the parallelism for processing the substrate can be solved similarly to the first embodiment because the formation of the silicon compound film 7 such as silicon or silicon oxide can be generally controlled in the order of nm. Since a lithium borate substrate is used, the ease of fine processing of the shape by etching is also the same as in the first embodiment.

(Embodiment 3) A first embodiment of the method of manufacturing the voltage controlled oscillator of the present invention shown in FIG. 1 will be described below.

First, after the surfaces of the Si substrate 1 and the lithium borate substrate 2 which are the semiconductor substrates shown in FIG. 1 are extremely cleaned, the respective surfaces are subjected to a hydrophilic treatment. Specifically, the surface of the Si substrate is lightly etched with a hydrofluoric acid-based etchant, and the surface of the lithium borate substrate is lightly etched with a very diluted buffered hydrofluoric acid-based etchant.

Next, when the substrate is sufficiently washed with pure water and immediately superposed uniformly, direct bonding can be easily obtained by the constituents of water adsorbed on the respective substrate surfaces, for example, hydroxyl groups. In this state, heat treatment is performed at a low temperature of 100 to 300 ° C. This low-temperature heat treatment increases the bonding strength.

Next, using a weakly acidic etching solution, for example, an etching solution obtained by diluting acetic acid with pure water, a lithium borate substrate 2
Necessary part, that is, the part forming the surface acoustic wave resonator
Other parts are etched away except for (right side in the drawing). Since lithium borate is very easily etched with a weakly acidic solution, it can be etched very easily even if the thickness of the lithium borate substrate 2 is a standard thickness of a normal wafer, for example, about 400 μm. For example, the etching rate when using an etching solution diluted with acetic acid is about 10 μm / h at about pH 4.5 and about 100 μm / h at about pH 3, which is a sufficient rate. Further, since the surface of the Si substrate is hardly etched by a weak acid etching solution such as acetic acid, the surface of the Si substrate is not damaged. Thereby, the lithium borate substrate 2 is formed into an island shape, for example, 2
Process into a rectangle of 1.5mm square.

Next, in this state, if necessary, a heat treatment is performed at a temperature higher than the initial heat treatment temperature to further strengthen the bonding. When the heat treatment temperature is high, there is a difference in the coefficient of thermal expansion between the Si substrate 1 and the lithium borate substrate 2, so that the shape,
Some restrictions are imposed on dimensions and the like. Therefore, high-temperature heat treatment is difficult for a large wafer, but heat treatment at a high temperature can be easily performed by shaping into a small island shape as in this embodiment, and both bonding strength and heat resistance are improved. High temperature processing becomes possible.

Also, unevenness in bonding and the like are less likely to occur in a small area, thereby improving the manufacturing yield. Thereafter, various processes required for forming the field-effect transistor 3 and the like and various electrodes required for wiring are performed, and the voltage-controlled oscillator having the element configuration described in the first embodiment (FIG. 1) is obtained.

The electrode 6 is made of gold or the like on the basis of aluminum or chromium. The effect of the heat treatment for strengthening the bonding is, for example, that the bonding strength is increased several times even when the temperature is maintained at 200 ° C. for about one hour, and a strength of several tens kg / cm ² is obtained.
Practically effective above 100 ° C. When the temperature is raised to 800 ° C. or higher, lithium is released from the surface of the lithium borate substrate, so that surface characteristics are greatly deteriorated and performance as a surface acoustic wave resonator is deteriorated. Therefore, the bonding heat treatment temperature is preferably 800 ° C. or lower.

The mechanism of direct bonding is that initial bonding occurs due to van der Waals' force of a hydroxyl group or the like adsorbed on the surface of each substrate, and then heat treatment is performed to remove hydrogen, which is a constituent component of water, from the bonding interface. It is considered that silicon on the surface of the Si substrate and oxygen in the lithium borate substrate are bonded together to increase the bonding strength. It is also possible to lower the junction temperature by applying a voltage to the junction.

Since lithium borate can be etched at a high speed even when a weak acid such as acetic acid is used for etching, it is very convenient for manufacturing the device having the structure of this embodiment. Quartz, lithium niobate, and lithium tantalate use a 100% strong acid such as hydrofluoric acid or hydrofluoric nitric acid, but the etching rate is extremely slow, on the order of μm per hour, and
There is a problem that there is no good protective film that can withstand this, or the semiconductor substrate is eroded first during etching, but if etching with a weak acid such as acetic acid used in this example, Such problems are solved at once.

(Embodiment 4) A second embodiment of the method of manufacturing the voltage controlled oscillator of the present invention shown in FIG. 2 will be described below.

First, chemical vapor deposition (C) is performed on the substrate surfaces of the Si substrate 1 and the lithium borate substrate 2 which are the semiconductor substrates.
VD) or the like to form a silicon compound film (silicon oxide film) 7. The thickness is about 0.1 to 3 μm, and it is easy to realize the thickness and control the uniformity by using a manufacturing method such as CVD. Of course, sputtering or vacuum deposition is also possible. Then, after hydrophilic treatment of the silicon compound film surface,
If the substrate is washed with pure water and immediately superimposed uniformly, direct bonding can be easily obtained by a component of water adsorbed on the surface, for example, a hydroxyl group. In this state, heat treatment is performed at a low temperature of 100 to 300 ° C. This low-temperature heat treatment increases the bonding strength. Thereafter, in the same manner as in the third embodiment (first embodiment of the manufacturing method), the etching shape processing using a weakly acidic etching solution, the subsequent heat treatment as necessary, and various process treatments are performed. A voltage controlled oscillator having the configuration of the element described in FIG. 2 is obtained. Thus, the third embodiment
Various effects similar to those described above, in particular, the effect of ease of manufacture can be obtained.

The mechanism of the direct bonding is almost the same as that of the third embodiment, and the initial bonding occurs due to van der Waalska of the hydroxyl group adsorbed on the surface of the silicon compound film (silicon oxide).
After that, by heat treatment, hydroxyl group
Hydrogen, which is a constituent component, escapes and the remaining oxygen and oxidation
It is considered that the constituent elements of the silicon and lithium borate substrates combine to increase the bonding strength. Therefore, in this case, direct bonding is possible even when a silicon oxide film is formed only on the surface of one substrate, for example, a lithium borate substrate, or only on the surface of a Si substrate. It is also possible to lower the junction temperature by applying a voltage to the junction.

(Embodiment 5) A third embodiment of the method of manufacturing the voltage controlled oscillator of the present invention shown in FIG. 2 will be described below.

In the same manner as in the fourth embodiment (second embodiment of the manufacturing method), the silicon compound film 7 of amorphous silicon is formed on the surfaces of the Si substrate 1 and the lithium borate substrate 2 as the semiconductor substrates.
Is formed by plasma CVD or the like. The film thickness of the silicon compound of the amorphous silicon to be formed is approximately 0.1 to 3 μm, almost similarly to the case of the fourth embodiment. Thereafter, similarly to Example 4, the surface of the silicon compound film of amorphous silicon was extremely cleaned,
By sufficiently washing with pure water and immediately superimposing uniformly, direct bonding can be easily obtained by a component of water adsorbed on the surface, for example, a hydroxyl group. 100 to 300 in this state
Heat treatment is performed at a low temperature of ° C. This low-temperature heat treatment increases the bonding strength. Thereafter, in the same manner as in Example 3 (the first example of the manufacturing method), an etching shape processing using a weakly acidic etching solution, a subsequent heat treatment as necessary, and various process treatments are performed to obtain Example 2 (FIG. A voltage controlled oscillator having the element configuration described in 2) is obtained. As a result, various effects similar to those described in the third embodiment, in particular, the effect of easy manufacturing can be obtained. Also in this embodiment, it is possible to lower the junction temperature by applying a voltage to the junction.

The mechanism of the direct bonding is almost the same as that of the third embodiment. The initial bonding occurs due to van der Waalska of the hydroxyl group adsorbed on the surface of the silicon compound film of amorphous silicon.
After that, by heat treatment, hydroxyl group
Constituent hydrogen escapes, leaving oxygen and amorphous
The constituent elements of the porous silicon and lithium borate substrates combine,
It is considered that the joining strength is increased. Therefore, in this case as well as in Example 4, the amorphous state was formed only on the surface of one substrate, for example, only on the surface of the lithium borate substrate, or only on the surface of the Si substrate.
Even when a silicon film is formed, direct bonding is possible. It is also possible to lower the junction temperature by applying a voltage to the junction.

(Embodiment 6) FIG. 3 is a schematic sectional view of a third embodiment showing the configuration of the voltage controlled oscillator of the present invention. FIG.
1, 1 is a Si substrate which is a semiconductor substrate, 11 is a lithium borate bulk type vibrating element bonded on the Si substrate 1, and other components 3 to 5 which are the same as those in FIG.
Its function is the same as that of the first embodiment. 12 is the upper electrode of the lithium borate bulk type vibrating element, 13 is the lower electrode,
13 and the wiring on the Si substrate 1 are not shown in the figure, but are formed by via holes (through holes are provided in the substrate, the inside thereof is covered with a conductor, and the upper and lower sides of the substrate are electrically connected) and the like. It is connected.

Further, although not shown in the figure, each component on the Si substrate 1 and the upper and lower electrodes 12 and 13 of the lithium borate bulk type vibrating element 11 are connected by wiring so as to become a voltage controlled oscillator. The Si substrate 1 and the lithium borate bulk type vibration element 11 are directly joined. Further, the voltage-controlled oscillator integrated as above is housed in a sealed container. Field effect transistor 3 and variable capacitance diode 4
An oscillator is composed of the passive chip components 5 and the lithium borate bulk type vibration element 11.

Here, by changing the voltage applied to the variable capacitance diode 4, the capacitance can be changed and the oscillation frequency can be changed. With such a structure, the oscillation circuit unit and the crystal unit are integrated into a single body, so that the size can be significantly reduced as compared with the related art. Also,
Compared to the case where the lithium borate bulk type vibrating element 11 is individually sealed in a container, the volume is about 1/10 and the weight is about 1 /
5 is easy to do.

In this embodiment, the bonding is performed by direct bonding between the Si substrate and the lithium borate substrate, and the heat resistance, the environmental resistance,
The same effects as described in the first embodiment can be obtained in all aspects such as fine workability.

Further, since lithium borate has a larger electromechanical coupling coefficient than quartz and has a temperature dependency as good as quartz, it is far superior to a bulk type vibrating element formed of a thin film. Performance is obtained.

(Embodiment 7) FIG. 4 is a schematic sectional view of a fourth embodiment showing the configuration of the voltage controlled oscillator of the present invention. FIG.
In this example, the constituent elements 1 to 5 and 11 to 13 except for 7 are the same as those in the sixth embodiment shown in FIG. Reference numeral 7 denotes a silicon compound film such as silicon or silicon oxide used for bonding the Si substrate 1 and the bulk type vibration element 11 provided on the lithium borate substrate, whereby the Si substrate 1 and the lithium borate bulk type vibration element 11 are directly bonded. ing. The other configuration is the same as that of the sixth embodiment (FIG. 3).
The same applies to the effect of reducing the size and weight when the voltage controlled oscillator is formed.

In this embodiment, the Si substrate and the lithium borate bulk type vibrator 11 are joined by the silicon compound film 7 such as silicon or silicon oxide. Since the silicon compound is an inorganic substance and is thermally stable up to a high temperature, the same effects as in Example 1 (FIG. 1) can be obtained. Also, the problem of parallelism for substrate processing,
The formation of a silicon compound film such as silicon or silicon oxide is generally performed in nm
Therefore, the problem can be solved as in the first embodiment.
Since a lithium borate substrate is used, the ease of fine processing of the shape by etching is also the same as in the first embodiment.

(Embodiment 8) A fourth embodiment of the method of manufacturing the voltage controlled oscillator according to the present invention shown in FIG. 3 will be described below.

A through portion 1a is formed in advance on the Si substrate 1, which is the semiconductor substrate where the lithium borate bulk type vibration element 11 is to be formed. Next, the surface of the bulk type vibration element 11 composed of the Si substrate 1 and the lithium borate substrate is extremely cleaned, and each surface is subjected to a hydrophilic treatment. Specifically, the surface of the Si substrate is lightly etched with a hydrofluoric acid-based etchant, and the surface of the lithium borate substrate (lithium borate bulk type vibration element 11) is lightly etched with a very diluted buffered hydrofluoric acid-based etchant. .

Next, when the substrate is sufficiently washed with pure water and immediately superposed uniformly, direct bonding can be easily obtained by the constituents of water adsorbed on the respective substrate surfaces, for example, hydroxyl groups.
In this state, heat treatment is performed at a low temperature of 100 to 300 ° C. This low-temperature heat treatment increases the bonding strength. Next, using a weakly acidic etching solution, for example, an etching solution obtained by diluting acetic acid with pure water, a necessary portion of the lithium borate substrate, that is, a portion where the bulk type vibration element 11 is formed, is provided with a through portion 1a in advance on the Si substrate. The remaining portions are etched away except for the necessary portions.

Since lithium borate is very easily etched with a weakly acidic solution, it can be etched very easily even if the thickness of the lithium borate substrate is about 500 μm, which is the thickness of a normal wafer. Moreover, since the Si substrate surface is hardly etched by such an etching solution, the Si substrate is not damaged. Thus, the lithium borate substrate is processed into an island shape, for example, a rectangle of 1.5 × 1 mm square. In this state, if necessary, a heat treatment is performed at a temperature higher than the initial heat treatment temperature to further strengthen the bonding. When the heat treatment temperature is high, there is a difference in the coefficient of thermal expansion between the Si substrate and the lithium borate substrate, so that some restrictions are imposed on the shape and dimensions.

For this reason, it is difficult to perform high-temperature heat treatment on a large wafer. However, if a small island is formed as in this embodiment, high-temperature heat treatment can be easily performed, and both bonding strength and heat resistance can be improved. Then, high-temperature processing can be performed thereafter. In addition, unevenness in bonding and the like are less likely to occur in a small area, so that the production yield is improved.

Thereafter, the lithium borate substrate left in a rectangular shape is subjected to a thinning treatment. As the etching solution, the aforementioned weakly acidic etching solution is used. S for weakly acidic etchant
Since the surface of the i-substrate is hardly damaged, it is not particularly necessary to form a protective film on the Si substrate. Further, since the etching rate is sufficiently high, it is easy to perform the etching processing to a thickness of 5 μm or less. This makes the lithium borate substrate thinner. Thereafter, various processes required for forming transistors and the like, various electrodes necessary for wiring, and the like are performed.

Electrodes 12 and 13 are formed above and below the bulk type vibration element 11. Since this portion is formed in the Si substrate penetrating portion 1a, bulk vibration becomes possible. In order to effectively generate vibrations, an energy trapping structure using electrodes is used, or only the vibrating part is further processed by etching to form a trapped energy, and the joint at the Si substrate is stressed as much as possible. By doing so, a process that does not adversely affect the bulk vibration is performed. The lower electrode 13 is guided and electrically connected to the upper surface of the semiconductor substrate by a via hole or the like. As a result, a voltage controlled oscillator having the element configuration described in the sixth embodiment (FIG. 3) is obtained.

The electrodes 12 and 13 are made of gold or the like with aluminum or chromium as a base. The effect of the heat treatment for strengthening the bonding is, for example, that the bonding strength is increased several times even when the temperature is maintained at 200 ° C. for about one hour, and a strength of several tens kg / cm ² is obtained. Practically effective above 100 ° C. When the temperature is increased to 800 ° C. or higher, lithium is released from the surface of the lithium borate substrate, so that the surface characteristics are greatly deteriorated and the performance as a vibrator is deteriorated. Therefore, the bonding heat treatment temperature is preferably 800 ° C. or lower.

The mechanism of direct bonding is described in Example 1 (FIG. 1).
The same effect can be obtained. In the case of the present embodiment, there is also obtained a manufacturing effect that a bulk type vibration element having a thickness of 5 μm or less can be easily formed. This makes it possible to obtain a super-high frequency vibration element in the GHz band.

(Embodiment 9) A fifth embodiment of the method of manufacturing the voltage controlled oscillator according to the present invention shown in FIG. 2 will be described below.

In the same manner as in Example 4 (the second embodiment of the manufacturing method), a silicon oxide film is formed on the surface of a Si substrate as a semiconductor substrate and on the surface of a lithium borate substrate by CVD or the like. Forming a bonding film between the substrate and the lithium borate substrate; Thereafter, in the same manner as in Example 8 (fourth embodiment of the manufacturing method), the voltage of the configuration shown in FIG. 2 of Example 4 in which a thin lithium borate bulk type vibrating element was bonded on a Si substrate with silicon oxide. Obtain a controlled oscillator. As a result, various effects similar to those described in the eighth embodiment, in particular, the effect of easy manufacturing can be obtained.

(Embodiment 10) A sixth embodiment of the method of manufacturing the voltage controlled oscillator according to the present invention shown in FIG. 2 will be described below.

In the same manner as in Example 5 (third embodiment of the manufacturing method), a silicon compound film 7 of amorphous silicon was formed on the surface of a Si substrate as a semiconductor substrate and on the surface of a lithium borate substrate by plasma CVD or the like. Formed by amorphous silicon
Forming a bonding film between the substrate and the lithium borate substrate; afterwards,
As in Example 8 (fourth embodiment of the manufacturing method), Si
Embodiment 4 A voltage-controlled oscillator having the configuration shown in FIG. 2 of Embodiment 4 in which a thin lithium borate bulk type vibration element 11 is bonded on a substrate 1 with amorphous silicon. As a result, various effects similar to those described in the eighth embodiment, in particular, the effect of easy manufacturing can be obtained.

(Embodiment 11) FIG. 5 is a schematic sectional view of a fifth embodiment showing the configuration of the voltage controlled oscillator of the present invention. FIG.
In the above, reference numeral 14 denotes GaAs which is a III-V compound semiconductor substrate.
The substrate 2 is a lithium borate substrate bonded on the GaAs substrate 14 and has a surface acoustic wave element. In this case, a surface acoustic wave resonator is formed. The other components 3 to 6 except for 7 are the same as those in the first embodiment (FIG. 1). Reference numeral 7 denotes a silicon or silicon compound film that joins the GaAs substrate 14 and the lithium borate substrate 2. The circuit configuration is the same as that of the first embodiment, and wiring is connected so as to be a voltage controlled oscillator.
By storing the integrated voltage-controlled oscillator in a sealed container as described above, the same effects as in the first embodiment can be obtained in terms of size and weight as in the first embodiment.

In this embodiment, the bonding between the GaAs substrate and the lithium borate substrate is performed by a silicon or silicon compound film, and the same effects as those described in the first embodiment, such as heat resistance, environmental resistance, and fine workability, can be obtained. Things.

III-V of GaAs, InP, InGaAs, etc.
Compound semiconductors generally have a higher electron mobility than Si. Ga
In the case of As, the electron mobility is about six times larger than that of Si. Therefore, when a III-V compound semiconductor is used, generally, a high-speed transistor can be formed. It is easy to make a transistor that operates at several tens of Hz as a transistor, and it is possible to operate at a higher frequency than a transistor integrated on a Si substrate.

(Embodiment 12) FIG. 6 is a schematic sectional view of a sixth embodiment showing the configuration of the voltage controlled oscillator of the present invention. FIG.
Are the same as in the seventh embodiment (FIG. 4) and the eleventh embodiment (FIG. 5). That is, this configuration is different from the seventh embodiment only in that a GaAs substrate 14, which is a III-V compound semiconductor, is used instead of the Si substrate 1 in the seventh embodiment. It is almost the same as That is, it is more suitable for operation at a higher frequency than the seventh embodiment.

(Embodiment 13) A seventh embodiment of the method of manufacturing the voltage controlled oscillator according to the present invention shown in FIG. 5 will be described below.

A GaAs substrate 1 as a III-V compound semiconductor substrate was manufactured in the same manner as in Example 4 (second embodiment of the manufacturing method).
4 and a silicon compound film on each surface of the lithium borate substrate 2
A (silicon oxide film) 7 is formed by CVD or the like, and a bonding film of the GaAs substrate 14 and the lithium borate substrate 2 is formed by silicon oxide. Thereafter, in the same manner as in the fourth embodiment, a voltage controlled oscillator having the configuration of the eleventh embodiment (FIG. 5) in which a lithium borate surface acoustic wave device is bonded on a GaAs substrate by silicon oxide is obtained. As a result, various effects similar to those described in the fourth embodiment, in particular, the effect of easy manufacturing can be obtained.

The mechanism of the direct bonding is almost the same as that of the fourth embodiment. Therefore, even if the silicon oxide film is formed on both substrate surfaces or the silicon oxide film is formed only on the GaAs substrate surface, the direct bonding is performed. Is possible.

(Embodiment 14) An eighth embodiment of the method of manufacturing the voltage controlled oscillator according to the present invention shown in FIG. 5 will be described below.

In the same manner as in Example 13, a silicon compound film 7 of amorphous silicon is formed on the surfaces of a GaAs substrate 14 and a lithium borate substrate 2 as III-V compound semiconductor substrates by plasma CVD or the like. GaAs by amorphous silicon
Forming a bonding film between the substrate and the lithium borate substrate; afterwards,
In the same manner as in Example 5 (third embodiment of the manufacturing method), Ga
A voltage controlled oscillator having the configuration of Example 11 (FIG. 5) in which a lithium borate surface acoustic wave device is bonded on an As substrate by amorphous silicon is obtained. As a result, various effects similar to those described in the fifth embodiment, in particular, the effect of easy manufacturing can be obtained.

The mechanism of direct bonding is almost the same as that of the fifth embodiment. Therefore, when an amorphous silicon film is formed on both substrate surfaces, or when an amorphous silicon film is formed only on the GaAs substrate surface. However, direct bonding is possible.

(Embodiment 15) A ninth embodiment of the method of manufacturing the voltage controlled oscillator according to the present invention shown in FIG. 6 will be described below.

In the same manner as in Example 4 (the second and fifth embodiments of the manufacturing method), a silicon oxide film 7 was formed on the surfaces of a GaAs substrate 14 and a lithium borate substrate 2 as III-V compound semiconductor substrates. A bonding film of a silicon oxide and a GaAs substrate and a lithium borate substrate is formed by CVD or the like. After that, in the same manner as in the ninth embodiment, the lithium borate bulk type vibration element was bonded to the GaAs substrate using silicon oxide.
A voltage-controlled oscillator having the configuration of FIG. 12 (FIG. 6) is obtained. As a result, various effects similar to those described in the ninth embodiment, in particular, the effect of easy manufacturing can be obtained.

The mechanism of the direct bonding is almost the same as that of the fourth embodiment. Therefore, even if a silicon oxide film is formed on both substrate surfaces or a silicon oxide film is formed only on the GaAs substrate surface, the direct bonding is performed. Is possible.

(Embodiment 16) A tenth embodiment of the method of manufacturing the voltage controlled oscillator according to the present invention shown in FIG. 6 will be described below.

In the same manner as in Examples 5 and 9 (the third and fifth embodiments of the manufacturing method), the respective surfaces of the GaAs substrate 14 and the lithium borate substrate 2 as III-V compound semiconductor substrates were A GaAs substrate made of amorphous silicon by forming a silicon compound film of amorphous silicon by plasma CVD or the like.
A bonding film between the substrate 14 and the lithium borate substrate 2 is formed. afterwards,
Example 12 In the same manner as in Example 9, a lithium borate bulk type vibration element was bonded on a GaAs substrate by using amorphous silicon.
A voltage controlled oscillator having the configuration shown in FIG. 6 is obtained. As a result, various effects similar to those described in the ninth embodiment, in particular, the effect of easy manufacturing can be obtained.

The mechanism of direct bonding is almost the same as that of the fifth embodiment. Therefore, even when an amorphous silicon film is formed on both substrate surfaces or an amorphous silicon film is formed only on a GaAs substrate surface. , Direct bonding is possible.

In this embodiment, as the silicon compound, silicon oxide is used, but the silicon oxide formed by CVD or the like has a slightly different oxygen content depending on conditions. It may also contain nitrogen. In either case, a direct bond is obtained. The possibility of direct bonding depends on the nature of the bonding of the substance, and it is considered that similar effects can be obtained if the material has a covalent bonding property such as silicon or silicon oxide.

In each of the embodiments described above, a circuit example of a voltage controlled oscillator has been described. However, it is apparent that the present invention can be widely applied to a general electroacoustic integrated circuit including an electroacoustic element and a semiconductor element. .

[0079]

The above-described electroacoustic integrated circuit of the present invention and the method of manufacturing the same have the following effects.

In any of the embodiments, first of all,
Transistors, which are the basic components that cause oscillation and amplification, and electroacoustic elements such as lithium borate surface acoustic wave elements and bulk-type vibrating elements are integrated into a single unit. The weight can be reduced, and both the volume and the weight can be significantly reduced as compared with the case where a surface acoustic wave element or a bulk type vibration element housed in a conventional container is used.

In the bonding method of this embodiment, since the semiconductor substrate and the electroacoustic element are bonded directly or by using a silicon-based inorganic material having a controlled film thickness, the flatness is very good, and it is necessary to set the vibration frequency. In addition to enabling submicron photolithography, the reliability against heat, vibration, and the like is greatly improved.

In this embodiment, the configuration of the voltage controlled oscillator is shown. However, basically, an electroacoustic element and an active element such as a transistor can be integrated integrally. The present invention can be widely applied to electroacoustic integrated circuits in general, such as a high-frequency receiver integrated with the above.

Further, as shown in Examples 3 and 8, etc., since the lithium borate substrate can be etched and formed with a weakly acidic liquid such as acetic acid, the bonding and low-temperature heat treatment-lithium borate shown in this example were performed. By adopting the manufacturing method of the etching separation-high temperature heat treatment method of the substrate, it is possible to reduce the bonding unevenness and to manufacture using a larger semiconductor substrate. Therefore, the effect on the production side such as the improvement of the manufacturing yield is great.

Further, since fine processing such as forming a thin plate of 5 μm or less can be easily performed, a high-frequency device using a fundamental wave vibration in a quasi-microwave band (several hundred MHz to several GHz), which has been difficult in the past, is used. Manufacturing becomes easy. This enables high performance and low cost.

When integrated on a GaAs substrate, which is a III-V compound semiconductor, the high frequency characteristics of the transistor are several times better than when integrated with a silicon transistor, and operation at higher frequencies is possible. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of a voltage controlled oscillator according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a configuration of a voltage controlled oscillator according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view showing a configuration of a voltage controlled oscillator according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view showing a configuration of a voltage controlled oscillator according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view showing a configuration of a voltage controlled oscillator according to a fifth embodiment of the present invention.

FIG. 6 is a schematic sectional view showing a configuration of a voltage controlled oscillator according to a sixth embodiment of the present invention.

[Explanation of symbols]

1. Semiconductor (Si) substrate 2. Lithium borate single crystal piezoelectric substrate (surface acoustic wave device) 3. Field effect transistor (F
ET), 4: Variable capacitance diode chip, 5: Passive chip component, 6: Electrode of surface acoustic wave device, 7: Silicon compound film such as silicon or silicon oxide, 11: Lithium borate bulk type vibration device, 12: Upper electrode , 13 ... lower electrode,
14 ... III-V compound semiconductor (GaAs) substrate.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location H03H 9/25 H01L 41/22 Z (72) Inventor Tetsuyoshi Kotate 1006 Odakadoma, Kazuma, Kazuma, Osaka Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-56-79487 (JP, A) JP-A-61-101200 (JP, A) JP-A-3-296316 (JP, A) JP-A 61-794 232661 (JP, A) JP-A-61-183940 (JP, A)

Claims (15)

(57) [Claims] 1. A lithium-borate single-crystal piezoelectric substrate is directly bonded to a semiconductor substrate by a hydroxyl group or oxygen on the surface of a substrate bonding portion , and the lithium-borate single-crystal piezoelectric substrate has a surface acoustic wave element. Electroacoustic integrated circuits. 2. A lithium borate single crystal piezoelectric substrate is directly bonded to a semiconductor substrate by a hydroxyl group or oxygen on the surface of a substrate bonding portion , and the lithium borate single crystal piezoelectric substrate has a bulk type vibration element. Electroacoustic integrated circuits. 3. A semiconductor substrate having a silicon film or a silicon compound film , wherein a lithium borate single crystal piezoelectric substrate is provided on the silicon film or the silicon film.
An electroacoustic integrated circuit which is directly bonded by a hydroxyl group or oxygen on the surface of a silicon compound film and has a surface acoustic wave element on the lithium borate single crystal piezoelectric substrate. 4. A silicon film or lithium borate single crystal piezoelectric substrate in semiconductor <br/> body substrate having a silicon compound film, the silicon Makuma
An electroacoustic integrated circuit which is directly bonded by a hydroxyl group or oxygen on the surface of a silicon compound film and has a bulk-type vibration element on the lithium borate single crystal piezoelectric substrate. 5. The electroacoustic integrated circuit according to claim 3, wherein the semiconductor substrate is a silicon (Si) substrate. 6. The electroacoustic integrated circuit according to claim 3, wherein the semiconductor substrate is a III-V compound semiconductor substrate. 7. The electroacoustic integrated circuit according to claim 6, wherein GaAs is used as the III-V compound semiconductor. 8. The electroacoustic integrated circuit according to claim 1, wherein the electroacoustic integrated circuit is a voltage controlled oscillator. 9. The electroacoustic integrated circuit according to claim 3, wherein the silicon film is amorphous. 10. A semiconductor substrate and a lithium borate single crystal piezoelectric element.
A step of cleaning the surface of each joint, and hydrophilizing the substrate.
Process and the process of superimposing and directly joining
A method for manufacturing an electroacoustic integrated circuit . 11. A semiconductor device comprising : a silicon substrate;
Is a step of providing a silicon compound film ;
Cleans compound film and lithium borate single crystal piezoelectric substrate surface
Performing a step of making the semiconductor substrate hydrophilic,
The hydrophilic surfaces of the lithium borate single crystal piezoelectric substrate
A method for manufacturing an electroacoustic integrated circuit, comprising a step of joining and direct bonding . 12. After 100 ° C., the temperature is reduced from 100 ° C.
Having a step of performing heat treatment in a temperature range of 800 ° C.
An electroacoustic integrated circuit according to claim 10 or 11, wherein:
Road manufacturing method . 13. After the step of direct bonding, a weakly acidic liquid
Lithium borate single crystal piezoelectric substrate by etching
To separate islands into islands, followed by direct bonding
Even higher than the temperature in the heat treatment step performed later
2. The method according to claim 1, further comprising the step of:
3. The method for manufacturing an electroacoustic integrated circuit according to item 2 . 14. A method for manufacturing a semiconductor device, comprising:
Having a step of forming an electronic element in advance.
An electroacoustic integrated circuit according to claim 10 or 11, wherein:
Road manufacturing method . 15. After the step of direct bonding, lithium borate
Forming an electroacoustic element on a single-crystal piezoelectric substrate;
Having a step of forming wiring with electronic elements on the body substrate.
The electronic sound collection according to claim 10 or 11, wherein
Manufacturing method of integrated circuit .