JPS6278906A - Manufacture of surface acoustic wave device - Google Patents

Abstract

PURPOSE:To eliminate the need for positioning and to improve productivity by forming patterns of different conductive material films by using only one photomask for the electrode pattern of a surface acoustic wave device. CONSTITUTION:A thin gold film 6' and photoresist 10' are formed on a crystal substrate 1 successively. The thin gold film 6' is etched away except at a reflector part by using a photomask 8 for a window and left only at the reflector part. The substrate is coated with photoresist 10' and the whole pattern is developed after being exposed by using the photomask 11 corresponding to the negative pattern of an Al electrode, thus forming a resist pattern 10. The thin gold film 6' is removed by etching where the resist is not present and a surface acoustic wave reflecting strips 6 are formed below the resist. Then, Al7' is formed from above the resist pattern. The Al7' on the resist pattern is lifted off and the resist is removed lastly to form the reflector composed of Al strips 7 and gold strips 6 and the pattern 9 of an inter-digital converter composed of only Al stripes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface acoustic wave device, and more particularly to a method for manufacturing a surface acoustic wave device using surface acoustic waves.

[Technical background of the invention and its problems] Surface acoustic wave devices For example, the basic structure of a surface acoustic wave resonator that has been widely known is the Clinton-Sylvester
・Invention by Hartman et al. (Special Publication No. 5B-16289)
It is based on That is, as shown in FIG. 3, a large number of surface acoustic wave reflecting strips 2 having a width λ/4 are arranged on a piezoelectric substrate 1, where λ is the wavelength of the surface acoustic wave propagating on the substrate 1. The interdigital converter 5 is provided with a grating inverse Q'J device 4 arranged in a periodic manner and an interdigital converter 5 consisting of electrode fingers 3 having a width of λ/4. Since the characteristics of such a surface acoustic wave resonator are mainly determined by the grating reflector, improving the characteristics of the grating reflector is an extremely important issue. Generally strips, ridges,
When the reflectance ε of one electrode finger (hereinafter referred to as a reflector) for surface acoustic waves such as a group is large, the number of reflectors may be small, but as ε becomes smaller, a larger number of reflectors are required. Become.

Therefore, if it is taken into consideration that two or more grating reflectors are generally used in a resonator, there is a problem in that the entire resonator becomes extremely large. on the other hand,
As the strip thickness, ridge height, and group depth are increased to increase ε per reflector, the mode conversion from surface acoustic waves to bulk waves increases accordingly. The conversion loss reduces the Q of the resonator by 18<.

As a means to solve these problems, we developed a grating reflective grating in which two types of reflectors, each having a width of λ/8 with respect to the surface wave wavelength λ of the used frequency and opposite reflection coefficients, are arranged alternately at a period of λ/4. There is a Technical Research Report of the Institute of Electronics and Communications Engineers of Japan (Reference: Institute of Telecommunications Engineers Technical Report US 84-30, September 1984) at the Ultrasonic Study Group of the Telecommunications Monthly Meeting, which proposed the device. In the grating reflector shown in this technical research report, the reflected wave from the reflector with a positive reflection coefficient and the reflected wave from the reflector with a negative reflection coefficient are added, so that Compared to a conventional grating reflector in which gratings are arranged at a period of λ/2, the amount of reflection per unit length increases nearly twice.

On the other hand, the mode conversion loss to bulk waves only increases by about 1.4 times. Therefore, if compared with the conventional one with the same amount of reflection, mode conversion loss to bulk waves will be reduced.

As a specific method for realizing such a reflector, as shown in FIG. When the wavelength of is λ, the line width is λ/8 and the film thickness is λ/200 (1
00H1fz, the first surface acoustic wave reflective strip 6 is made of a gold film (equivalent to 1,600 people), and aluminum FyJW/A is made of aluminum FyJW/A with a line width of λ/8 and a film thickness of λ150 (equivalent to 6,400 people in the case of 100 rivers 11). The second surface acoustic wave reflecting strips 7 and the second surface acoustic wave reflecting strips 7 include surface acoustic wave resonators arranged alternately at a period of λ/4. In this surface acoustic wave resonator, the reflectance of the surface acoustic wave reflective strip made of the thin gold film and thin aluminum film formed on the quartz substrate is negative for the reflective strip made of the thin gold film, and positive for the reflective strip made of the thin aluminum film, which are opposite to each other. , and its film thickness dependence is such that the reflectance of a surface acoustic wave reflecting strip made of a thin gold film is four times greater than the reflectance of a surface acoustic wave reflecting strip made of a thin aluminum film. Therefore, in order to have the same reflectance in absolute value, the thickness of the gold thin film may be 174 times the thickness of the aluminum thin film.

With such a structure, the reflectance of surface acoustic waves per unit length of the grading reflector 4 becomes high, thereby making it possible to reduce the size. Conventionally, in manufacturing the surface acoustic wave resonator shown in Fig. 4, a process is used in which photoric roughy is performed twice using two types of photomasks corresponding to reflective strip patterns of different conductive materials. . This manufacturing process will be explained using FIG. 5. First, as shown in FIG. 5(a), a thin gold film 6- is deposited on the entire surface of the crystal substrate 1 by vapor deposition or sputtering. In addition, for the purpose of improving this adhesion, a thin gold film 6'
In some cases, a base layer (not shown) consisting of a very thin layer of chromium or titanium is added below. Next, resist is applied and exposed using a photomask that corresponds to the electrode pattern of the gold thin film.

As shown in FIG. 5(b), the line width λ/8° period λ/
A first surface acoustic wave reflecting strip 6 made of a thin gold film of No. 2 is formed. If there is an underlying layer, it is also removed by etching at the same time as the gold thin film.

Next, as shown in FIG. 5C, an aluminum thin film 7- is deposited over the entire surface to a thickness approximately four times that of the gold thin film 6' by vapor deposition or sputtering. Then, as shown in FIG. 5(d), a mask with a line width λ/82 period λ/
The second surface acoustic wave reflective strip 7 made of an aluminum thin film of No. 2 is connected to the first surface acoustic wave reflection strip 6 made of a gold thin film.
It is formed so that it is located approximately in the middle of the In this case, when the aluminum thin film 7- is formed, the first surface acoustic wave reflecting strip 6 made of the gold thin film underneath becomes invisible. For this reason, in order to perform photomask alignment in the step of FIG. 5(d), a mark 8 for mask alignment is formed outside the region where the crating reflector is formed in the step of FIG. 5(b). Furthermore, in the step of the same figure (C), the crystal substrate 1
It is necessary that at least the upper region where the mark 8 is formed is not covered with the aluminum thin film.

However, when manufacturing a surface acoustic wave resonator using such a process, two photomasks are required: one corresponding to the gold thin film pattern and the other photomask corresponding to the aluminum thin film pattern.
Different types of masks must be used. Furthermore, when aligning masks in one photolithography step when forming a pattern with an aluminum thin film, the pattern of the aluminum film is strictly formed between the surface acoustic wave reflecting strips of the gold thin film. Must be aligned.

In particular, as the frequency increases, the line width of the surface acoustic wave reflective strip becomes narrower, and higher alignment accuracy is required. For example, in the case of a surface acoustic wave resonator with a frequency of 79QMHz, λ is approximately 4 μm, and the line width λ/8 of the surface acoustic wave reflective strip is approximately 0.5 μm, ±
To achieve position accuracy within 5%, ±0.025
Positional deviation must be suppressed to within μm, and very strict positional accuracy is required.

In this way, when manufacturing a surface acoustic wave device, which is constructed by arranging surface acoustic wave reflectors made of thin films of different conductive materials and having positive and negative reflection coefficients, using the conventional method, two types of photomasks are also required. Therefore, one photolithography process is also two steps.
Since the mask must be rotated and the mask positioning requires very strict accuracy, the recircularity of a surface acoustic wave device, such as the surface acoustic wave resonator shown in FIG. 4, becomes extremely low. Therefore, mass production in factories was extremely difficult.

[Object of the invention] The present invention has been made in view of the above-mentioned problems, and
The purpose of this method is to provide a method for manufacturing a surface acoustic wave device with extremely high productivity using a simple method.The method for manufacturing a surface acoustic wave device is to provide a method for manufacturing a surface acoustic wave device using a simple method. forming a resist pattern having an overhang structure on the first conductive material film, and removing a part of the first conductive material film through the resist pattern. At least a step of forming the first electrode finger group and a second conductive material film made of a different material from the first conductive material film and constituting the second electrode finger group are formed on the resist pattern. The method is characterized by comprising at least the steps of forming at least a second group of electrode fingers on the piezoelectric substrate in the gap, and removing the resist pattern. As a result, patterns of different conductive material films can be formed simply by using a single photomask for the electrode pattern of the surface acoustic wave device, and strict alignment is not required.

[Embodiments of the Invention] Hereinafter, embodiments of the surface acoustic wave device of the present invention will be described with reference to the drawings. In addition, in describing the embodiments of the present invention,
This will be explained using a surface acoustic wave device as an example.

FIG. 1 shows a method of manufacturing a surface acoustic wave resonator according to an embodiment of the present invention. In FIG. 1, as shown in FIG. 1 (a), an elastic surface that propagates on the substrate 1 is formed by vapor deposition or sputtering on the entire surface of a crystal substrate 1 consisting of a 32° rotated Y plate as a piezoelectric substrate. When the wavelength of the wave is λ, the film thickness is λ/200 (100HIIZ, 1
After depositing a gold thin film 6' (equivalent to 600 people), a photoresist 10- is applied on this gold thin film 6-. Then,
As shown in FIG. 1(b), using a simple photomask 8 for a window corresponding to the area where the reflector is to be formed, by ordinary photolithography, as shown in FIG. 1(c), the area other than the reflector area is is removed by etching, leaving a thin gold film 6' only on the reflector portion. In addition, a thin gold film 6' was added for the purpose of improving adhesion.
In some cases, an underlayer (not shown) consisting of a very thin layer of chromium or titanium is added under the gold film, and this is also removed by etching at the same time as the gold thin film.

Next, as shown in FIG. 1(d), photoresist 10' is applied to the substrate again, and a negative pattern (photoresist 10- is applied only to the areas irradiated with light) of the aluminum electrodes (reflector and interdigital converter) is applied. is removed.

) The entire pattern is exposed to light using a photomask 11 corresponding to the pattern. Then, the substrate was subjected to rapid development by immersing it in chlorobenzene for several minutes or more, and the substrate 1 shown in FIG.
A resist pattern 10 having an overhang structure having a narrow cross-sectional shape on the side is formed. At this time, the gap between the resist patterns 10 and 10 is set to λ/
8, the base of the resist pattern 10 is λ/8, and the tip is 3λ/8. To achieve this, the thickness of the photoresist 10'' is 1 foot, the mask width of the photomask 11 is 3λ/8, the spacing is λ/8, and the chlorobenzene (
99% purity) for 10 minutes.

Next, the thin gold film 6' where there is no resist is removed by etching, and a surface acoustic wave reflecting strip 6 made of the thin gold film 6' is formed under the resist as shown in FIG. As shown in FIG.
double the film thickness (the wavelength of the surface acoustic wave propagating on the substrate 1 is λ)
As, for film thickness λ150 (100)i112, 6
(equivalent to 400 people)) by vapor deposition or sputtering. Next, aluminum 7 on the resist pattern
' Lift off and remove the resist to the utmost. As a result, as shown in FIG. 1(h), a reflector consisting of the aluminum strip 7 and the gold strip 6 and an interdigital transducer pattern 9 consisting only of the aluminum strip are formed. If this manufacturing method is used, only one type of glass mask is required that corresponds to the electrode pattern of the surface acoustic wave reflection resonator, and unlike the conventional manufacturing method, a reflective strip made of an aluminum thin film and a reflective strip made of a thin gold film are required. There is no need for a process to precisely align the relative positions of the two by photomask alignment.

In this embodiment, the gold thin film 6 of the reflector part shown in FIG.
- was formed using photolithography,
The present invention is not limited to this, and a process for attaching a gold thin film to a piezoelectric substrate by vapor deposition or sputtering may be performed using a mask having a window in a portion corresponding to the reflector portion.

FIG. 2 shows a method of manufacturing a surface acoustic wave resonator according to another embodiment of the present invention. Other embodiments will be described below.

As shown in FIG. 2(a), a photoresist 10'' is deposited on the entire surface of the piezoelectric substrate 1 by vapor deposition or sputtering, followed by a thin aluminum film 7.Next, as shown in FIG. 2(b), As shown in , a pattern is formed using a photomask 12 corresponding to a positive pattern (the photoresist 10' is removed only in the areas that are not irradiated with light) of aluminum electrodes (reflectors and interdigital converters). The entire substrate is exposed to light.Then, the substrate is immersed in chlorobenzene for several minutes or more and then developed to form a resist pattern 10 with an overhang structure as shown in FIG. The portion of the aluminum thin film 7' was removed by etching, as shown in Fig. 2(d).
), a reflector strip 7 and an interdigital converter 9 are formed of a resist 10'' aluminum film.

Next, as shown in FIG. 2(0), a thin gold film 6' is formed on the reflector part by vapor deposition or sputtering using a mask 13 with a window opened only in the reflector part, and then a resist pattern is formed. The gold thin film 6- is lifted off. @later,
The resist is removed, and finally, as shown in FIG. 2(f), a pattern is formed of a reflector consisting of an aluminum strip 7 and a gold strip 6, and an interdigital transducer 9 consisting only of an aluminum strip. In the case of this manufacturing method, as in the embodiment shown in FIG. You can increase your sexuality.

In addition to the embodiments described above, the present invention can be implemented with various modifications as follows.

For example, although it has been explained that a 32° rotated Y plate is used as the piezoelectric substrate, it is not necessarily limited to this angle, and a crystal substrate with other cutting angles may also be used.
i A TaO3 substrate may also be used.

Furthermore, when surface acoustic waves are referred to, they generally refer to Rayleigh waves, but are not necessarily limited to this vibration mode; for example, surface acoustic waves propagating at right angles to the X axis on a -50.5° rotated Y plate of a quartz crystal substrate. pseudo surface acoustic waves, 105°±10' rotation Y
It can also be applied to a surface acoustic wave resonator using a plate or a pseudo surface acoustic wave of X-axis propagation.

In addition, the gold thin film and aluminum thin film used in the examples were
There is no problem even if a trace amount of additives, not more than a few percent, are included.In particular, if aluminum is doped with 0.1 to 4% by weight of copper or silicon, metal migration can be suppressed.
It can contribute to improving the power resistance characteristics (excitation resistance strength U) of the surface acoustic wave resonator.

Furthermore, in the embodiment, a case has been described in which strips of gold thin film and aluminum thin film are arranged only in the reflector part, but strips of gold thin film and aluminum thin film are arranged in the interdigital converter part as well. The same manufacturing process can be used for those with the same structure by simply changing the part where the gold thin film is formed. That is, the same effect can be obtained even if the manufacturing method of the present invention is applied to only one electrode, for example, a reflector on one side or an interdigital converter.

Furthermore, the line width of the strip used for the surface acoustic wave reflector and the electrode finger, or the width of the group, should be determined by λ/
It is not necessary to specify exactly 8, and generally the amount of reflection of surface acoustic waves is 10 for these line widths or group widths.
% deviation changes the reflection amount by 8%, so the number 10
Deviations in width up to the order of % are permissible. That is, even if the shape of the resist pattern having the overhang structure is not necessarily exactly formed in the above shape, a surface acoustic wave device having characteristics sufficient for practical use can be obtained.

In addition, in the embodiment shown in FIGS. 1 and 2,
Although the present invention has been explained using a surface acoustic wave resonator, it goes without saying that the present invention is not limited to this, and can be used in a manufacturing method of a general surface acoustic wave device such as a surface acoustic wave filter.

[Effects of the Invention] The method for manufacturing a surface acoustic wave device of the present invention having the above-mentioned configuration uses only a single photomask for patterns such as electrodes and reflectors of a surface acoustic wave device, and allows the production of thin films of different conductive materials. Since surface acoustic wave reflectors with strips having positive and negative reflection coefficients can be formed, there is no need for a step of strictly aligning the relative positions of the respective reflectors, resulting in extremely high productivity.

[Brief explanation of drawings]

FIG. 1(a) to FIG. 1(h) are simplified process diagrams showing one embodiment of the method for manufacturing a surface acoustic wave device of the present invention. Fig. 2(a) to Fig. 2) are simplified process diagrams showing another embodiment of the method for manufacturing a surface acoustic wave device of the present invention, and Fig. 3 shows the basic configuration of a conventional surface acoustic wave resonator. FIG. 4 is a perspective view showing the basic configuration of a surface acoustic wave resonator for explaining the present invention, and FIGS. 5(a) to 5(d) show a conventional manufacturing method of a surface acoustic wave device. FIG. 1......Crystal substrate 6...Gold strip 6'...Gold thin film 7...Aluminum strip 7'...
...Aluminum 8...Photomask 9...Interdigital converter 10...
...Resist pattern 10 - ... Photoresist 11 ... Photomask representative Patent attorney Nori Chika Yudo Norio Ogo (cL) <b) (Figure 1 (f) Figure 1 (a) (b) O (d) (e)

Claims (8)

[Claims] (1) Forming a first conductive material film constituting a first electrode finger group on a piezoelectric substrate; and forming a resist pattern having an overhang structure on the first conductive material film. a step of removing a portion of the first conductive material film through the resist pattern to form at least the first electrode finger group; and forming at least a second electrode finger group by forming a second conductive material film constituting a second electrode finger group on the piezoelectric substrate in a gap between the resist patterns; 1. A method of manufacturing a surface acoustic wave device, comprising at least a step of removing. (2) The step of removing a part of the first conductive material film through the resist turn to form at least the first electrode finger group includes removing another electrode at the same time as removing the first electrode finger group. 2. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the method is a step of forming a surface acoustic wave device. (3) Forming at least a second electrode finger group by forming a second conductive material film constituting the second electrode finger group on the piezoelectric substrate in the gap between the resist patterns; 2. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the step is to form another electrode at the same time as the second electrode finger group. (4) The step of forming at least a second electrode finger group by forming a second conductive material film constituting the second electrode finger group on the piezoelectric substrate in the gap between the resist patterns includes Compared to the surface acoustic waves propagating on the substrate, the first
The second conductive material film having a reflection coefficient different from that of the electrode finger group is formed in the gap between the resist patterns to form at least the second electrode finger group. A method for manufacturing a surface acoustic wave device according to item 1. (5) The step of removing the resist pattern is performed by removing the resist pattern so that substantially 1/4 of the wavelength of the surface acoustic wave propagating on the piezoelectric substrate alternately with the first electrode finger. 2. The method of manufacturing a surface acoustic wave device according to claim 1, further comprising forming at least the second group of electrode fingers so as to be arranged with a period of . (6) Claim 1, wherein the piezoelectric substrate is either a crystal or a LiTaO_3 substrate.
A method for manufacturing a surface acoustic wave device as described in 2. (7) One of the first conductive material film and the second conductive material film is a conductive material film mainly composed of aluminum, and the other is a conductive material film mainly composed of gold. 2. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is a flexible material film. (8) The method for manufacturing a surface acoustic wave device according to claim 7, wherein the conductive material film containing aluminum as a main component is a film doped with at least one of copper and silicon.