JPH0537275A - Production of surface acoustic wave element - Google Patents

Abstract

PURPOSE:To form a minute electrode pattern with a good reproducibility and a high precision in a simple process. CONSTITUTION:Front and rear sides of a transparent substrate 1 for surface acoustic wave propagation coated with a resist 2 are irradiated with ultraviolet rays to form a resist pattern whose section is an inverted trapezoid. Thereafter. a metallic film 5 for electrode is formed on the resist 2 and the substrate 1 by sticking, and the resist 2 is removed from the substrate 1 to form an electrode. Thus, the minute electrode is formed with a high precision and a good re-producibility in the simple process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a surface acoustic wave device in which an electrode pattern is formed by a lift-off process.

[0002]

2. Description of the Related Art At present, single crystals such as LiNbO ₃ and LiTaO ₃ are widely used as piezoelectric materials for SAW filters applied to TV / VTR / mobile communication. Since the material does not satisfy both the insertion loss and temperature characteristics of the filter,
Li ₂ B ₄ having a large mechanical coupling constant and a zero temperature coefficient
O ₇ single crystals have recently been receiving attention.

However, the Li ₂ B ₄ O ₇ single crystal is easily attacked by acid, and the SAW using the Li ₂ B ₄ O ₇ single crystal as a substrate.
When manufacturing a filter, it is impossible to form an electrode by patterning with an acidic etching solution.

Therefore, a method of patterning by a lift-off process that does not require chemical etching using acid has been proposed (for example, M. Hatzakis et.al, IBM.
J.RES.DEVELOP VOL.24, NO.4, JULY 1980 p452-460).

However, in the conventional lift-off process described above, a resist is deposited on a substrate, patterned, a metal film is deposited on the patterned resist and the substrate, and then the resist is erased. Although it is to form an electrode, it is common to form an altered layer by dipping the resist in monochromebenzene to form an overhang shape when patterning the resist, and the process is complicated. In addition, there is a problem that it is difficult to control the immersion time and the liquid temperature, and reproducibility is poor particularly when a fine electrode pattern is formed.

[0006]

It is therefore an object of the present invention to solve the above problems and provide a method of manufacturing a surface acoustic wave device capable of forming a fine electrode pattern with high reproducibility and high accuracy in a simple process. ..

[0007]

In order to achieve the above object, a method of manufacturing a surface acoustic wave device according to the present invention is characterized in that a transparent substrate for surface acoustic wave propagation coated with a resist is irradiated with ultraviolet rays. To form a resist pattern having an inverted trapezoidal cross-sectional shape by carrying out from both front and back sides, and then depositing a metal film for electrodes on the resist and the substrate, and then removing the resist from the substrate. It is characterized in that an electrode is formed.

[0008]

Embodiments of the present invention will be described in detail. First, a process of forming a fine pattern of metal electrodes on the substrate 1 as shown in FIG. 1 will be described. A transparent substrate 1 of Li ₂ B ₄ O ₇ single crystal with a thickness of about 500 μm is prepared and ultrasonically cleaned with pure water, acetone, etc. (Fig. 1
(A)).

Next, a resist of novolac resin (HPR-1182 Fuji Hunt) is applied to the substrate 1 by spin coating to form a single layer resist 2 having a thickness of about 1.5 μm (FIG. 1 (b)). ).

Next, as shown in FIG. 2, the substrate 1 is placed on an exposure sample stage 4 having a high reflectance formed of cork or the like, and a glass mask (thickness: 2-3 mm, 5 mm) having a predetermined opening. Ultraviolet light with a wavelength of about 405 nm is irradiated from above resist 2 coated with 860 Å-thick chrome (3) on soda-lime glass of inch square (Fig. 1 (c)). Here, the exposure sample stage 4 was made of alumina powder that was roughened to # 240. The exposure sample stage 4 does not need to be roughened, but in such a case, the back side of the substrate 1 is roughened. That is, the exposure sample stage 4 and the substrate 1
At least one of these is formed on a rough surface,
It is important to use a highly reflective material such as cork for the exposure sample stage 4.

Since the ultraviolet light is diffusely reflected by the rough surface 4a of the exposure sample stage 4, the back surface side of the resist is also exposed. Therefore, as shown in FIG. 2, the exposure time is 30
Resist 2 as the length increases from seconds to 60 seconds to 90 seconds to 120 seconds
Is patterned in the order of →→→. By the above exposure, a resist 2a having an inverted trapezoidal cross section is formed (FIG. 1D). Here, if the overhang amount of this resist 2a is defined by (T−B) / 2, the amount is about 1.
It becomes 5 μm.

Next, the resist 2a having an inverted trapezoidal cross section and the substrate 1 are covered with a metal film 5 of Al to be an electrode to a thickness of about 0.5 μm by a vacuum deposition method (FIG. 1 (e)).

Next, the resist 2a is dissolved with acetone, and the metal film 5 coated thereon is peeled off (FIG. 1).
(F)).

As described above, a comb-shaped electrode having an electrode width of about 7.27 μm could be accurately formed over a length of 1.5 to 2.0 mm. After exposure by ultraviolet irradiation, baking was performed at about 110 ° C. for about 8 minutes to further improve the pattern accuracy of the metal film 5. That is, by performing this, it is believed that by rearranging the photosensitizer after exposure, fluctuations that occur in the film thickness direction are prevented, and the pattern accuracy is further improved in addition to the electrode accuracy improvement by the lift-off method. Be done.

The method of irradiating ultraviolet rays from both sides of the resist is not limited to the method of utilizing the reflection of the exposure sample stage 4 as described above. For example, the substrate 1 is placed on a transparent table. For example, the ultraviolet rays may be irradiated from two directions on the front and back of the substrate 1, and may be appropriately changed and implemented within a range not departing from the gist.

[0016]

As described above, according to the method of manufacturing a surface acoustic wave device of the present invention, for example, a substrate is placed on a table having a high reflectance and the cross-sectional shape of the resist is utilized by utilizing the reflection of the table. Can be formed into an inverted trapezoid, and fine electrodes can be formed with high precision by a simple process. Further, even if lift-off of a thick metal film is performed, a resist having a desired taper shape can be formed by exposure from the back surface side of the resist, and the disappearance of the resist can be further facilitated to form a fine electrode. Can be performed easily.

[Brief description of drawings]

1A to 1F are views showing a lift-off process of an embodiment according to the present invention.

FIG. 2 is a cross-sectional view illustrating patterning of a resist.

[Explanation of symbols]

S ... Surface acoustic wave device 1 ... Substrate 2 ... Resist 3 ... Glass mask 4 ... Exposure sample stage 5 ... Metal film

Claims (1)

Claim: What is claimed is: 1. A transparent substrate for surface acoustic wave propagation coated with a resist is irradiated with ultraviolet rays from both sides of the resist to form a resist pattern having an inverted trapezoidal cross section. After that, a metal film for an electrode is deposited on the resist and the substrate, and then the resist is removed from the substrate to form an electrode, which is a method for manufacturing a surface acoustic wave device.