JP3335543B2 - Surface acoustic wave functional device and method of manufacturing substrate for surface acoustic wave functional device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, a substrate used for the device, and a method of manufacturing the substrate.
More specifically, a device in which a functional device including a surface acoustic wave element such as a filter and a resonator and a semiconductor circuit element such as an amplifier is formed on a single substrate (hereinafter, abbreviated as a surface acoustic wave functional device), And a manufacturing method.

[0002]

2. Description of the Related Art In the construction of portable radio communication terminal devices such as portable telephones, miniaturization of the devices is strongly required. LS
I. The use of surface acoustic wave devices has considerably reduced the size of equipment, but it is necessary to further reduce the size of equipment. Conventionally, a surface acoustic wave device is formed by forming comb-shaped fingers of a metal thin film on a piezoelectric substrate such as a quartz substrate, a lithium tantalate substrate, or a lithium niobate substrate, and is actually hermetically sealed as a single component. Used. For example, IEICE Transactions, Jay 76-A Vol. 2, No. 23
8 February 1993 (Transactions of the Institute of Electronics, Information and Communication Engineers, Vol.
As shown in J75-A No.2 p2381993 / 2), the surface acoustic wave front-end module prints a copper thick film circuit on a dielectric substrate such as an alumina substrate, a glass epoxy substrate, etc.
A single component of a surface acoustic wave element such as a surface acoustic wave filter and a mixer is mounted together with a circuit element such as a low noise amplifier.

[0003]

As described above, there is a strong demand for further miniaturization and weight reduction of small wireless communication devices and the like, and it is necessary to develop devices that are significantly smaller than the current ones. However, in the conventional configuration of communication equipment, the components of the surface acoustic wave element and the main components of the device such as the amplifier and mixer are packaged independently, and they are individually mounted on a dielectric substrate on which connection lines are printed. Since it is mounted and configured, it requires a certain space, and there is a limit to miniaturization of the device. In addition, a mounting process is required, which is an obstacle to reducing the manufacturing cost.

Accordingly, the present invention solves the above problems,
A surface acoustic wave device capable of dramatically reducing its size, including various components conventionally mounted on a dielectric substrate, making full use of the advantages of a surface acoustic wave device, whose main feature is miniaturization, and its use. It is an object to realize a method for manufacturing a substrate.

[0005]

To achieve the above object, the present invention provides a surface acoustic wave functional device substrate having an epitaxial Si substrate layer formed on at least a part of a piezoelectric substrate that propagates a surface acoustic wave. Then, a semiconductor circuit element is formed directly on the epitaxial Si substrate layer of the surface acoustic wave functional plate, and a surface acoustic wave is directly formed on the piezoelectric substrate, thereby producing a surface acoustic wave functional device.

Therefore, in the method of manufacturing a substrate for a surface acoustic wave function device according to the present invention, the substrate is manufactured in the following steps. (1) forming a Si0 ₂ layer on a piezoelectric substrate. (2) An Si substrate having an epitaxial Si layer on one surface is formed. (3) The Si0 ₂ layer and the epitaxial Si layer is bonded to the aforementioned piezoelectric substrate and the Si layer to adhere. (4) The bonded Si substrate layer is deleted so that the epitaxial Si layer is exposed.

Further, the surface acoustic wave function device of the present invention is characterized in that an epitaxial S
A circuit element and a surface acoustic wave element are formed on the i-layer by the same semiconductor process as before. The surface acoustic wave device is formed by patterning electrode fingers on the exposed piezoelectric substrate except for the epitaxial Si layer so that the piezoelectric substrate is exposed in a region where the surface acoustic wave device is formed on the substrate.

In the method of manufacturing a substrate for a surface acoustic wave function device, the porous Si oxide film formed under the single-crystal Si epitaxial growth film can form a single-crystal Si epitaxial layer of good quality even when bonding is applied. can get. In addition, a substrate having few crystal defects and optimal for the configuration of a circuit element can be obtained.

The surface acoustic wave function device of the present invention can perform the same process as a normal semiconductor process and the manufacture of a surface acoustic wave element on a single substrate, and can be performed on a conventional substrate of alumina, glass epoxy or the like. The space for mounting various packaged components can be eliminated, and the size of the surface acoustic wave function device can be reduced. Further, the semiconductor process and the packaging of the surface acoustic wave element become unnecessary, and the manufacturing process can be shortened.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described. FIG. 1 is a perspective view showing an embodiment in the middle of the manufacturing process of the surface acoustic wave device according to the present invention.
The piezoelectric substrates that generate surface acoustic waves include lithium tantalate (LiTaO ₃ ) and lithium niobate (LiN
The substrate 1 is made of bO ₃ ), lithium tetraborate (Li ₂ B ₄ O ₇ ), quartz (Quartz), or the like. An epitaxially grown Si film 2 is formed on a substrate 1 as a Si substrate layer for forming a semiconductor circuit element such as a low noise amplifier and a mixer and a transmission line (wiring). By forming as shown in the figure, a surface acoustic wave element is formed on a portion of the substrate where the piezoelectric substrate 1 is exposed, and a semiconductor circuit element is formed on the epitaxially grown Si film 2. Among them, the connection between the surface acoustic wave element and the semiconductor circuit element is performed simultaneously.

FIG. 2 is a manufacturing process diagram for explaining an embodiment of a method of manufacturing a substrate used in a surface acoustic wave device according to the present invention. The drawings show only a part of the substrate for simplicity of explanation.

(A) A porous Si oxide film 4 is formed on a Si substrate 3, and a single crystal Si epitaxial growth film 2 is formed thereon. In the process of forming the Si epitaxial growth film 2, first, a porous Si film having a thickness of about 10 μm is formed on the surface of the Si substrate 3.
An oxide film 4 is formed by anodic oxidation.
A single crystal Si film 2 is epitaxially grown on the surface of the substrate.
Here, in order to reduce defects in the single crystal Si epitaxial growth film 2, H ₂ heat treatment for removing a natural oxide film on the surface, which is also performed during normal homoepitaxial growth, is performed at a temperature of 1000 ° C. or more. Porous Si
The holes on the surface of the oxide film 4 disappear, and the surface becomes flat. When epitaxial growth is performed on the surface of the porous Si oxide film 4 in which holes are left open, an enormous amount of defects are generated, but the defects are drastically reduced on the surface of the porous Si oxide film 4 in which the holes have been eliminated by the H ₂ heat treatment. Can be. Further, in order to reduce the number of defects, it is effective to carry out the HF treatment time immediately before entering the epitaxial growth apparatus for 3 minutes or more.

In addition to the formation of the single-crystal Si epitaxial growth film 2 shown in FIGS.
A SiO ₂ film 5 of about Å is formed by a normal method such as a sputtering method or a CVD method. Here, by forming the SiO ₂ film 5 on the piezoelectric substrate 1, it is possible to suppress the generation of void defects which are a problem when the substrates are bonded to each other and bonded by a dehydration condensation reaction by heating. This is S
This is because the iO ₂ film absorbs water or OH groups generated by heating.

(C) Single crystal Si of Si substrate 3 in (a)
Si on the epitaxial growth film 2 side and the piezoelectric substrate 1 of (b)
The O ₂ film 5 side is bonded, heated, and bonded by a dehydration condensation reaction. By suppressing the heating temperature at this time to 400 ° C. or less, the occurrence of defects due to the difference in thermal expansion coefficient is suppressed, and the warpage of the substrate is suppressed. (D) Next, the Si substrate 3 is ground until the entire surface of the porous Si oxide film 4 is exposed from the back surface on the Si substrate 3 side.

(E) Further, the porous Si oxide film 4 is dissolved by selective chemical etching to expose the single crystal Si epitaxial growth film 2. What is important here is that a porous S film is formed between the Si substrate 3 and the single crystal Si epitaxial growth film 2.
That is, the i-oxide film 4 is used. As a result, a practical etchant that can obtain a large etching selectivity in the selective chemical etching of the single crystal Si epitaxial growth film 2 and the porous Si oxide film 4 can be used. The etchant used here is a mixture of HF and a weak oxidant, H ₂ O ₂ . At this time, the etching rate of the porous Si oxide film 4 is as fast as 2 μm / min or more, and the etching selectivity of the porous Si oxide film 4 / single crystal Si epitaxial growth film 2 is 1
A very large value of about 0 ⁵ can be realized. In the selective chemical etching, it is considered that the etchant penetrates into the inside of the pores of the porous Si oxide film 4 by capillary action, and the diameter of the pores is increased, whereby the Si pillars are narrowed and collapse from inside starts. As a result, the etching proceeds, the porous Si disappears, and a single crystal Si epitaxial growth film 2 is obtained. Since porous Si collapses from the inside, it is not affected by particles on the surface of the substrate that cause a change in film thickness, or particles that float or deposit during etching.

Therefore, it is possible to suppress the variation in film thickness to several nm for the single crystal Si epitaxial growth film 2 having a thickness of several hundred nm.
The single-crystal Si epitaxial growth film 2 having a thin film thickness of about 0.1 μm is also formed without causing a problem in thickness variation.

FIG. 3 is a sectional view showing a part of a step of forming a semiconductor circuit element on a substrate for a surface acoustic wave function device according to the present invention. The substrate obtained by the method described with reference to FIG. 2 is coated with a resist pattern 6 only on a portion of the single crystal Si epitaxial growth film 2 for forming circuit elements such as a low noise amplifier and a mixer by a normal photoresist process, and then hydrofluoric acid. The Si substrate layer is removed by a normal etching process such as selective chemical etching using an etching solution such as an etching gas or reactive ion etching using an etching gas such as SF ₆ or CF ₄ . As a result, it is possible to arbitrarily select a region where a circuit element constituting the surface acoustic wave function device is to be formed, and to form the single crystal Si epitaxial growth film 2 on the piezoelectric substrate 1 via the SiO ₂ film 5. Are obtained.

FIG. 4 is a perspective view showing an embodiment of a surface acoustic wave function device according to the present invention. The surface acoustic wave function device of the present embodiment constitutes a receiver for spread spectrum communication. The received signal from the antenna 12 is turned by the surface acoustic wave filter 9-1 to the low noise amplifier 7.
It is added to -1. The output of the amplifier 7-1 becomes one input of the mixer 8 via the second surface acoustic wave filter 9-2.
The amplifier 7-2 and the surface acoustic wave resonator 10 constitute a transmitter, and a part of the transmitter becomes another input of the mixer 8 via the surface acoustic wave filter 9-3. The PN signal applied from the input terminal 15 is applied to the surface acoustic wave resonator 13.
The signal of the resonator 13 is applied to the surface acoustic wave convolver 11, decoded, and output from the output terminal 14.

The production of the above surface acoustic wave function device is performed as follows. Single crystal S of surface acoustic wave functional device substrate obtained by the method described with reference to FIGS.
The amplifiers 7-1 and 7-2 on the i-epitaxial growth film 2
A semiconductor circuit element (Si device) such as the mixer 8 is formed by a conventionally known semiconductor process. In this semiconductor process, the portion where the piezoelectric substrate 1 is exposed is always coated with a resist film to proceed with the manufacturing process.
Should not be adversely affected.

After the semiconductor circuit elements are formed, surface acoustic wave devices such as surface acoustic wave filters 9-1, 9-2, 9-3, surface acoustic wave resonator 10, surface acoustic wave convolver 11, and surface acoustic wave resonator 13. Is formed on the piezoelectric substrate 1. In this case, connection wiring between the semiconductor circuit element and the surface acoustic wave element is performed at the same time. Here, as in the previous step, the portion where the semiconductor element is formed is always protected by coating with a resist pattern. As described above, the semiconductor element portion and the surface acoustic wave element portion are each protected by the resist pattern and the manufacturing process is advanced, so that a surface acoustic wave functional device can be manufactured by the same method as a normal device manufacturing process. Here, in the above embodiment, the semiconductor circuit element is formed first, but it goes without saying that the surface acoustic wave element may be formed first.

When a lithium tantalate or lithium niobate substrate is used as a piezoelectric substrate for generating a surface acoustic wave, the electromechanical coupling coefficient is large.
It can be realized by the AW process.

[0022]

According to the present invention, a single-crystal Si epitaxial growth film having very few crystal defects can be formed on a piezoelectric substrate such as a quartz substrate, a lithium tantalate substrate, or a lithium niobate substrate. Devices such as low-noise amplifiers and mixers, and surface acoustic wave devices such as surface acoustic wave filters and surface acoustic wave resonators on piezoelectric substrates can be formed with good performance, and RF circuits can be realized with one chip. became. An RF circuit conventionally implemented by mounting individual components on an alumina or glass epoxy substrate can be created as a one-chip device. A sufficient effect can be obtained for miniaturization of the element and, consequently, miniaturization of the terminal.

Further, by selecting a board to be combined, there is a possibility that a variety of functional devices can be integrated into one chip, and in a future portable information terminal or the like, an indispensable device in terms of miniaturization can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a surface acoustic wave functional device according to the present invention during its production.

FIG. 2 is a manufacturing process diagram for explaining an embodiment of a method of manufacturing a substrate used for a surface acoustic wave device according to the present invention.

FIG. 3 is a cross-sectional view showing a part of a process of forming a semiconductor circuit element on a surface acoustic wave function device substrate according to the present invention.

FIG. 4 is a perspective view of one embodiment of a surface acoustic wave function device according to the present invention.

[Explanation of symbols]

1. Piezoelectric substrate, 2. Single crystal Si epitaxial growth film,
3 ... Si substrate, 4 ... porous Si oxide film, 5 ... SiO
₂ film, 6: resist pattern, 7: low noise amplifier,
8 mixer, 9 surface acoustic wave filter, 10 surface acoustic wave resonator, 11 surface acoustic wave convolver, 12 antenna, 13 surface acoustic wave resonator, 14 output terminal, 1
5. Input terminal.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-211876 (JP, A) JP-A-5-6883 (JP, A) JP-A-51-12780 (JP, A) JP-A-54-1979 14137 (JP, A) JP-A-61-256714 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 9/25 H03H 3/08

Claims (7)

(57) [Claims] A first surface of the piezoelectric substrate having a first surface;
A first step of forming one SiO ₂ layer, and a Si-based layer having a second surface and a third surface which is a back surface of the second surface.
Anodizing the second surface of the plate to form a _second SiO ₂ layer
And a second step formed on the second surface in the second step.
Single crystal S on the SiO ₂ layer of
Through the third step of forming an i-layer and the first step, the first SiO ₂ layer is formed.
Through the first surface of the piezoelectric substrate,
The second surface on which the crystalline Si layer is formed
A fourth step of bonding by heating at a temperature, and exposing the single-crystal Si layer and the first surface of the piezoelectric substrate.
The surface of the single crystal Si layer and the first surface of the piezoelectric substrate.
Forming a semiconductor circuit element and a surface acoustic wave element, respectively,
The connection wiring between the semiconductor circuit element and the surface acoustic wave element is performed.
Method for manufacturing a surface acoustic wave functional device having a fifth step
Law. 2. The manufacturing method according to claim 1, wherein
5 steps are the Si substrate of the substrate bonded in the 4th step
Until the second SiO ₂ layer is exposed from the third surface.
Polishing the surface acoustic wave functional device, comprising:
Production method. 3. The manufacturing method according to claim 2, wherein
The fifth step is to remove the second SiO ₂ layer until the single crystal Si layer is exposed.
Dissolve or polish by selective chemical etching
Method for manufacturing surface acoustic wave functional device having seventh step
Law. 4. The method according to claim 3, wherein
The fifth step is that at least the single-crystal Si layer exposed in the seventh step is
Partially etched to expose the first surface of the piezoelectric substrate
Manufacture of a surface acoustic wave functional device comprising an eighth step of
Method. 5. The manufacturing method according to claim 4, wherein
The fifth step is a step in which the surface of the single crystal Si layer of the substrate obtained in the eighth step is pressed.
A semiconductor circuit element and an elastic member are respectively provided on the first surface of the circuit board.
Forming a surface acoustic wave element, the semiconductor circuit element and the elastic table
A ninth step of performing connection wiring with the surface wave element.
Manufacturing method of surface wave functional device. 6. The pre-processing step of the third step according to claim 1.
Performing a H ₂ heat treatment and then performing an HF treatment.
Of manufacturing a surface acoustic wave functional device. 7. A piezoelectric substrate having a first surface, the first surface of which is provided on the first surface.
A first step of forming one SiO ₂ layer, and a Si-based layer having a second surface and a third surface which is a back surface of the second surface.
Anodizing the second surface of the plate to form a _second SiO ₂ layer
And a second step formed on the second surface in the second step.
Single crystal S on the SiO ₂ layer of
Through the third step of forming an i-layer and the first step, the first SiO ₂ layer is formed.
Through the first surface of the piezoelectric substrate,
A temperature of 40 ° C. or less is applied to the second surface on which the crystalline Si layer is formed.
A fourth step of bonding by heating at a temperature, and the Si substrate of the substrate bonded by the fourth step
Until the second SiO ₂ layer is exposed from the third surface side.
And polishing the second SiO ₂ layer until the single crystal Si layer is exposed.
Dissolve or polish by selective chemical etching
Manufacturing of a substrate for a surface acoustic wave function device having a sixth step
Construction method.