JP2000124758A - Manufacture of surface acoustic wave substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the formation accuracy of a recess for a bulk wave measure after sufficiently dissolving a fault due to bulk waves in the manufacture process of a surface acoustic wave substrate. SOLUTION: In this manufacturing method, after washing a piezoelectric single crystal wafer for the surface acoustic wave substrate with weak acid liquid whose pH is in the range of 4.0-6.5, it is cleaned with pure water whose pH is in the range of 6.0-8.0 (pre-processing process). Then, an ultraviolet ray setting resin layer is arranged on a surface on the opposite side of the electrode formation surface of the cleaned piezoelectric single crystal wafer, an exposure and development processing is executed to the ultraviolet ray setting resin layer and a hole pattern corresponding to a desired recess is formed. The ultraviolet ray setting resin layer where the hole pattern is formed is turned to a mask, the piezoelectric single crystal wafer is honed through the mask and the desired recess for the bulk wave measure is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a surface acoustic wave substrate used for manufacturing a surface acoustic wave filter or the like.

[0002]

2. Description of the Related Art In general, a surface acoustic wave device comprises a substrate made of a LiTaO ₃ single crystal wafer or a LiNbO ₃ single crystal wafer exhibiting piezoelectricity, and an interdigital transducer provided on one principal surface of such a substrate. Is done. In such a configuration, the surface acoustic wave is excited and received by the transducer, but at the same time, an unnecessary wave (disturbance wave) such as a bulk wave is also excited and received.

[0003] The above-mentioned bulk waves cause spurious interference in frequency characteristics. Therefore, in order to remove the spurious interference, grooves and recesses are formed on the back surface of the piezoelectric single crystal wafer for the surface acoustic wave device by dicer cutting or mask honing, or the entire back surface is randomly roughened (for example, the front surface). Bulk wave countermeasures such as _a roughness _Ra of 2 μm or more are being implemented.

[0004] However, although the above-described bulk wave countermeasures can provide a certain effect, in a surface acoustic wave filter or the like that requires strict characteristics, it is not possible to sufficiently eliminate the obstacle caused by the bulk wave. The problem remains.

That is, in the case of the surface acoustic wave filter, since the obstacle caused by the simultaneously excited bulk wave is large and it is difficult to cope with the design, the bulk wave obstacle is eliminated by the back surface shape of the piezoelectric single crystal wafer. However, forming large irregularities on the back surface of the wafer causes a decrease in mechanical strength, and consequently lowers the yield of the wafer or the yield of the device process.

In particular, recently, there has been a demand for automation and a high degree of device accuracy accompanying the use of a stepper in a device process, and such a requirement is premised on a high flatness of a wafer. For this reason, high precision is also required in a processing method for forming large irregularities on the back surface of the wafer.

For this reason, after forming a predetermined hole pattern in the ultraviolet-curable resin layer using an ultraviolet-curable resin as a mask, a honing process is performed to form a concave portion on the back surface of the piezoelectric single crystal wafer. Have been tried.
According to the UV-curable resin layer, the accuracy of the hole pattern can be improved. Therefore, honing using the UV-curable resin layer as a mask is expected as a back surface processing method capable of maintaining a high flatness of the wafer.

[0008]

However, the conventional process for manufacturing a piezoelectric single crystal wafer for a surface acoustic wave device involves the following steps.
When the honing process using the UV-curable resin layer as a mask is simply applied, the adhesion between the piezoelectric single crystal wafer and the UV-curable resin layer may be insufficient, or the hole pattern may be precisely formed on the UV-curable resin layer. However, it has not been put to practical use because of the problem that it cannot be formed.

SUMMARY OF THE INVENTION The present invention has been made to address such a problem, and a surface acoustic wave capable of improving the accuracy of forming a concave portion for bulk wave countermeasures while sufficiently eliminating an obstacle due to a bulk wave. An object of the present invention is to provide a method for manufacturing a substrate.

[0010]

The inventor of the present invention has made intensive studies on the cause of the decrease in the hole pattern accuracy of the ultraviolet-curable resin layer. It has been found that it reacts with the ultraviolet curable resin or reduces the adhesiveness of the ultraviolet curable resin layer. In other words, since the alkaline polishing liquid cannot be sufficiently removed only by pure water cleaning, the hole accuracy of the UV-curable resin layer as a mask in the conventional mask formation and honing process decreases, and the bulk wave It has been found that a concave portion on the back surface of a piezoelectric single crystal wafer for preventing a failure cannot be formed with high accuracy.

The present invention has been made based on such knowledge, and a method of manufacturing a surface acoustic wave substrate according to the present invention is directed to a method of manufacturing a piezoelectric single crystal wafer for a surface acoustic wave substrate, which comprises the steps of: After washing with a weak acid solution in the range of 4.0 to 6.5, a pretreatment step of washing with pure water having a pH in the range of 6.0 to 8.0, and a surface opposite to the electrode forming surface of the piezoelectric single crystal wafer after the washing. The step of disposing an ultraviolet-curable resin layer, and exposing and developing the ultraviolet-curable resin layer,
A step of forming a hole pattern corresponding to a desired recess, and using the ultraviolet-curable resin layer on which the hole pattern is formed as a mask, and honing the piezoelectric single crystal wafer through the mask to form a desired recess. And a step of forming

According to the cleaning using a weak acid solution having a pH in the range of 4.5 to 6.0 as compared with the pure water cleaning, an alkaline liquid such as an alkaline polishing liquid can be removed favorably and stably. In the method of manufacturing a surface acoustic wave substrate according to the present invention, as a pre-process of forming a concave portion for preventing bulk wave disturbance on the back surface of the piezoelectric single crystal wafer, cleaning with a weak acid solution having a pH in the range of 4.0 to 6.5 and pH. Has performed cleaning with pure water in the range of 6.0 to 8.0. Therefore, after sufficiently removing the alkaline liquid that causes the formation failure and the adhesion failure of the ultraviolet-curable resin layer, the formation of the ultraviolet-curable resin layer, the exposure and development of the ultraviolet-curable resin layer, and the mask as the mask. Since the honing process can be performed, the concave portion for bulk wave countermeasures can be formed with high accuracy by utilizing the original characteristics of the ultraviolet curable resin layer.

In the method of manufacturing a surface acoustic wave substrate according to the present invention, the cleaning as a pretreatment step is immediately performed without drying the double-sided lap-processed piezoelectric single crystal wafer. It is preferred to carry out. If the piezoelectric single crystal wafer is dried after double-sided lapping, the alkaline polishing liquid will dry and solidify, and it will take time to remove even by washing with a weak acid solution, or the removal itself will not be possible. This can be difficult. By immediately washing the piezoelectric single crystal wafer after the double-sided lap processing without drying, an alkaline liquid such as an alkaline polishing liquid can be reliably removed in a short time.

The ultraviolet-curable resin layer used as a mask during honing can be peeled off using, for example, an alkaline solution. Therefore, the method for manufacturing a surface acoustic wave substrate according to the present invention preferably further includes a step of peeling the ultraviolet-curable resin layer using an alkaline solution, as described in claim 3.

[0015]

Embodiments of the present invention will be described below.

In the method of manufacturing a surface acoustic wave substrate according to the present invention, first, a piezoelectric single crystal wafer for forming a concave portion for bulk wave countermeasures is prepared. Here, the pre-process of the concave portion forming process is usually a double-sided lapping process. Therefore, a cleaning step is performed on the double-sided lap-processed piezoelectric single crystal wafer as a pretreatment step of the concave part forming step. Note that typical examples of the piezoelectric single crystal wafer include LiTaO ₃ single crystal and LiNb.
An O ₃ single crystal may be used, but the method for manufacturing a surface acoustic wave substrate of the present invention is not limited to these, and can be applied to various piezoelectric single crystal wafers.

In the cleaning step as a pretreatment step, for example, a double-sided lap-processed piezoelectric single crystal wafer is adjusted to a pH of 4.0 to 4.0.
A first cleaning step of cleaning with a weak acid solution in the range of 6.5, and a pH of the piezoelectric single crystal wafer having been subjected to the first cleaning step is adjusted to pH.
A second washing step of washing with pure water in a range of 6.0 to 8.0.

In the first washing step using a weak acid solution,
The alkaline liquid mainly attached to the surface of the piezoelectric single crystal wafer, for example, the alkaline polishing liquid used in the double-sided lapping step is removed. With a weak acid solution having a pH in the range of 4.0 to 6.5, an alkaline solution such as an alkaline polishing solution can be removed more favorably and more stably than pure water washing.
The object to be cleaned with the slightly acidic cleaning liquid is not limited to the alkaline polishing liquid, but can be applied to the removal of various alkaline liquids.

Here, if the pH of the cleaning liquid used in the first cleaning step exceeds 6.5, the alkaline liquid cannot be removed satisfactorily. On the other hand, if the pH of the cleaning liquid is less than 4.0, the piezoelectric single crystal wafer cannot be removed. It will have an adverse effect. In particular, it is preferable that the pH of the cleaning liquid is 5.0 or more in order to maintain the characteristics of the piezoelectric single crystal wafer. Such a weakly acidic washing solution can be adjusted by dissolving a carbonate in pure water. In some cases, city water can be used directly.

If the preceding step of the above-mentioned cleaning step is a double-sided lapping step, the double-sided wrapped piezoelectric single crystal wafer is immediately washed with a slightly acidic cleaning liquid without drying (first cleaning step). Is preferred. More specifically, the double-sided lap-processed piezoelectric single crystal wafer is immediately immersed in a slightly acidic cleaning solution or sprayed with a slightly acidic cleaning solution without drying.

If the piezoelectric single crystal wafer is dried after the double-sided lapping process, the alkaline polishing liquid is dried and solidified, and it takes a long time to remove or remove even by cleaning using a weak acid solution. This may be difficult. By immediately washing the piezoelectric single crystal wafer after the double-sided lapping process with a slightly acidic washing solution without drying, an alkaline solution such as an alkaline polishing solution can be reliably removed in a short time.

The piezoelectric single crystal wafer that has been subjected to the first cleaning step is then cleaned with substantially pure water having a pH in the range of 6.0 to 8.0 (second cleaning step). In the second cleaning step, replacement and cleaning of the cleaning liquid used in the first cleaning step are performed. That is, only in the first cleaning step, the weakly acidic cleaning liquid has an adverse effect on the formation of the ultraviolet-curable resin layer. Therefore, the surface of the piezoelectric single crystal wafer is cleaned by washing the piezoelectric single crystal wafer with water having a pH in the range of 6.0 to 8.0.

Even if the pH of the water (cleaning liquid) used in the second cleaning step is less than 6.0 or more than 8.0, formation of the ultraviolet curable resin layer and exposure / development are performed in any case. Adversely affect More preferably, the pH of the water used in the second washing step is in the range of 6.5 to 7.5.

Next, an ultraviolet curable resin layer functioning as a mask is disposed on the surface of the piezoelectric single crystal wafer, which has been subjected to the pre-cleaning step, on the side opposite to the electrode forming surface. The arrangement of the ultraviolet-curable resin layer is performed, for example, by thermocompression bonding an ultraviolet-curable resin film to a piezoelectric single crystal wafer.

The UV-curable resin used as a mask is preferably a urethane-based UV-curable resin (such as a film).
It is preferred to use The urethane-based UV-curable resin has an advantage that it can be laminated on the surface of a wafer and a free form of a fixed form or an irregular form can be expressed by a mask.

Next, the ultraviolet curable resin layer is exposed and developed to form a hole pattern corresponding to a desired concave portion for bulk wave countermeasures. Here, in the piezoelectric single crystal wafer forming the mask, an alkaline liquid (eg, an alkaline polishing liquid) which causes a formation failure and an adhesion failure of the ultraviolet curable resin layer has been sufficiently removed in the above-described cleaning step. The ultraviolet curable resin layer can be satisfactorily adhered. Also,
The exposure accuracy of the ultraviolet curable resin layer can be stabilized. Therefore, it becomes possible to form a hole pattern with high precision on the ultraviolet-curable resin layer as a mask.

Thereafter, the piezoelectric single crystal wafer is honed through the mask using the ultraviolet curable resin layer having the hole pattern formed thereon as a mask. By this honing process, a concave portion for preventing bulk wave interference is formed on the back surface side of the piezoelectric single crystal wafer. According to this honing process, the concave portion can be formed with high accuracy by utilizing the original characteristics of the ultraviolet curable resin layer, and the back surface process having a required flatness can be stably and easily realized.

The ultraviolet-curable resin layer used as a mask in the honing process is peeled off using, for example, an alkaline solution. That is, the method for manufacturing a surface acoustic wave substrate according to the present invention includes, as a step subsequent to the step of forming a concave portion, a step of peeling the ultraviolet curable resin layer using an alkaline solution.

[0029]

Next, specific examples of the present invention and evaluation results thereof will be described.

Example 1 First, 128 ° Y having a thickness of 0.52 mm and wrapped on both sides
The LiNbO ₃ single crystal wafer was taken out of the double-sided lapping apparatus, inserted into 20 wafer carriers per batch, and immediately immersed in a cleaning solution having a pH of 6.0 so as not to be dried. City water was used for the pH 6.0 washing solution.

Next, both sides of the wafer are washed with city water,
Further, it was immersed in water (second cleaning liquid) having a pH of 6.5 for 10 minutes to replace the water. After the wafer having been washed with water was dried with hot air, an ultraviolet-curable urethane resin film (mask material) was adhered (bonded) to the back surface by thermocompression bonding.

Next, the ultraviolet-curable urethane resin film adhered to the back side of the wafer is selectively exposed to ultraviolet light for several minutes, and then developed with an alkali solution to 500 μm
Hole patterns with a diameter of 250 μm were formed at the pitch. Note that L
The surface of the iNbO ₃ single crystal wafer in contact with the ultraviolet-curable urethane resin film had a diameter of 180 μm.

Thereafter, using the ultraviolet-curable urethane resin film having the hole pattern as a mask, LiNbO ₃
Honing was performed by spraying Alundum (No240) on the single crystal wafer for about 20 minutes. After the honing, it was immersed in a stripping solution. The UV-curable urethane resin film completely peeled off in about 5 minutes.

Observation of the back surface of the wafer after the honing process described above confirmed that the concave portion was formed uniformly with a diameter of 190 μm and a depth of 90 μm.

Example 2 First, 128 ° Y having a thickness of 0.52 mm and wrapped on both sides
The LiNbO ₃ single crystal wafer was taken out of the double-sided lapping apparatus, inserted into 20 wafer carriers per batch, and immediately immersed in a cleaning solution having a pH of 6.0 so as not to be dried. City water was used for the pH 6.0 washing solution.

Next, both sides of the wafer are washed with city water,
Further, it was immersed in water (second cleaning liquid) having a pH of 6.5 for 10 minutes to replace the water. After the wafer having been washed with water was dried with hot air, an ultraviolet-curable urethane resin film (mask material) was adhered (bonded) to the back surface by thermocompression bonding.

Next, the ultraviolet-curable urethane resin film adhered to the back side of the wafer is selectively exposed to ultraviolet light for several minutes, and then developed with an alkaline solution to 500 μm
Hole patterns with a diameter of 250 μm were formed at the pitch. Note that L
The surface of the iNbO ₃ single crystal wafer in contact with the ultraviolet-curable urethane resin film had a diameter of 240 μm.

Thereafter, using the ultraviolet-curable urethane resin film having the hole pattern as a mask, LiNbO ₃
Honing was performed by spraying Alundum (No240) on the single crystal wafer for about 20 minutes. After the honing, it was immersed in a stripping solution. The UV-curable urethane resin film completely peeled off in about 5 minutes.

When the back surface of the wafer after the above honing was observed, it was confirmed that a concave portion having a diameter of 250 μm and a depth of 90 μm was uniformly formed. The accuracy of forming the concave portion was extremely high, and the flatness of the back surface of the wafer having the concave portion was excellent.

Example 3 First, 128 ° Y having a thickness of 0.52 mm and wrapped on both sides
The LiNbO ₃ single crystal wafer was taken out of the double-sided lapping apparatus, inserted into 20 wafer carriers per batch, and immediately immersed in a cleaning solution having a pH of 5.5 so as not to be dried. An aqueous carbonate solution was used for the pH 5.5 washing solution.

Next, the both surfaces of the wafer are washed with the same cleaning solution, and furthermore, the wafer is washed with water having a pH of 7.0 (second cleaning solution).
Replaced by immersion for minutes. After the wafer after the pure water cleaning was dried with hot air, an ultraviolet-curable urethane resin film (mask material) was adhered (bonded) to the back surface by thermocompression bonding.

Next, the ultraviolet-curable urethane resin film adhered to the back side of the wafer is selectively exposed to ultraviolet light for several minutes, and then developed with an alkaline solution to 500 μm
Hole patterns with a diameter of 250 μm were formed at the pitch. Note that L
The surface of the UV curable urethane resin film in contact with the iNbO ₃ single crystal wafer had a diameter of 250 μm.

Thereafter, using the ultraviolet-curable urethane resin film having the hole pattern as a mask, LiNbO ₃
Honing was performed by spraying Alundum (No240) on the single crystal wafer for about 20 minutes. After the honing, it was immersed in a stripping solution. The UV-curable urethane resin film completely peeled off in about 5 minutes.

Observation of the back surface of the wafer after the above-mentioned honing processing confirmed that concave portions having a diameter of 260 μm and a depth of 90 μm were uniformly formed. The accuracy of forming the concave portion was extremely high, and the flatness of the back surface of the wafer having the concave portion was excellent.

Example 4 First, 128 ° Y having a thickness of 0.52 mm and wrapped on both sides
The LiNbO ₃ single crystal wafer was taken out of the double-sided lapping apparatus, inserted into 20 wafer carriers per batch, and immediately immersed in a cleaning solution having a pH of 6.0 so as not to be dried. City water was used for the pH 6.0 washing solution.

Next, both sides of the wafer are washed with city water,
Further, the substrate was immersed in water having a pH of 7.5 (second cleaning solution) for 10 minutes to perform replacement. After the wafer having been washed with water was dried with hot air, an ultraviolet-curable urethane resin film (mask material) was adhered (bonded) to the back surface by thermocompression bonding.

Next, the ultraviolet-curable urethane resin film adhered to the back surface of the wafer is selectively exposed to ultraviolet light for several minutes, and then developed with an alkaline solution to 500 μm
Hole patterns with a diameter of 250 μm were formed at the pitch. Note that L
The surface of the iNbO ₃ single crystal wafer in contact with the ultraviolet-curable urethane resin film had a diameter of 260 μm.

Thereafter, using the ultraviolet-curable urethane resin film having the hole pattern as a mask, LiNbO ₃
Honing was performed by spraying Alundum (No240) on the single crystal wafer for about 20 minutes. After the honing, it was immersed in a stripping solution. The UV-curable urethane resin film completely peeled off in about 5 minutes.

Observation of the back surface of the wafer after the honing process described above confirmed that the concave portion was uniformly formed with a diameter of 270 μm and a depth of 90 μm. The accuracy of forming the concave portion was extremely high, and the flatness of the back surface of the wafer having the concave portion was excellent.

Example 5 First, 128 ° Y having a thickness of 0.52 mm and wrapped on both sides
The LiNbO ₃ single crystal wafer was taken out of the double-sided lapping apparatus, inserted into 20 wafer carriers per batch, and immediately immersed in a cleaning solution having a pH of 4.0 so as not to be dried. A mixed solution of pure water and carbonic acid was used as the pH 4.0 washing solution.

Next, both surfaces of the wafer were washed with the same cleaning solution, and further immersed in water having a pH of 8.0 (second cleaning solution) for 10 minutes to replace the wafer. After the wafer having been washed with water was dried with hot air, an ultraviolet-curable urethane resin film (mask material) was adhered (bonded) to the back surface by thermocompression bonding.

Next, the ultraviolet-curable urethane resin film adhered to the back surface of the wafer is selectively exposed to ultraviolet light for several minutes, and then developed with an alkaline solution to 500 μm
A hole pattern having a diameter of 320 μm was formed at a pitch. Note that L
The surface of the iNbO ₃ single crystal wafer in contact with the ultraviolet-curable urethane resin film had a diameter of 330 μm.

Thereafter, using the ultraviolet-curable urethane resin film having the hole pattern as a mask, LiNbO ₃
Honing was performed by spraying Alundum (No240) on the single crystal wafer for about 20 minutes. After the honing, it was immersed in a stripping solution. The UV-curable urethane resin film completely peeled off in about 5 minutes.

Observation of the back surface of the wafer after the honing process described above confirmed that the concave portion was formed uniformly with a diameter of 340 μm and a depth of 90 μm. The accuracy of forming the concave portion was extremely high, and the flatness of the back surface of the wafer having the concave portion was excellent.

Comparative Example 1 First, 128 ° Y having a thickness of 0.52 mm and wrapped on both sides
The LiNbO ₃ single crystal wafer was taken out of the double-sided lapping apparatus and inserted into 20 batch wafer carriers. After the wafer was dried with hot air without washing, an ultraviolet-curable urethane resin film (mask material) was adhered (bonded) to the back surface by thermocompression bonding.

Next, the ultraviolet-curable urethane resin film adhered to the back side of the wafer was selectively exposed to ultraviolet light for several minutes, and then developed with an alkaline solution to obtain a film having a thickness of 500 μm.
Hole patterns with a diameter of 250 μm were formed at the pitch. Note that L
The surface where the ultraviolet curable urethane resin film was in contact with the iNbO ₃ single crystal wafer had a blinding phenomenon.

Thereafter, honing was performed by spraying Alundum (No. 240) onto the LiNbO ₃ single crystal wafer for about 20 minutes through the above-mentioned UV-curable urethane resin film.
After the honing, it was immersed in a stripping solution. The UV-curable urethane resin film completely peeled off in about 5 minutes.

Observation of the back surface of the wafer after the honing process described above revealed that almost no concave portion was formed.

Example 6 First, 36 ° Y L having a thickness of 0.37 mm, which was wrapped on both sides.
The iTaO ₃ single crystal wafer is taken out of the double-sided lapping apparatus, and inserted into a batch of 20 wafer carriers.
This was immediately immersed in a washing solution having a pH of 6.5 so as not to be dried. A pure water diluted with hydrochloric acid was used as the pH 6.5 washing solution.

Next, both surfaces of the wafer are washed with the same cleaning solution, and furthermore, 10% water is added to pure water having a pH of 7.0 (second cleaning solution).
Replaced by immersion for minutes. After the wafer after the pure water cleaning was dried with hot air, an ultraviolet-curable urethane resin film (mask material) was adhered (bonded) to the back surface by thermocompression bonding.

The ultraviolet-curable urethane resin film adhered to the back surface of the wafer was selectively exposed to ultraviolet light for several minutes, and then developed with an alkaline solution to form a hole pattern having a pitch of 500 μm and a diameter of 250 μm. Thereafter, as a mask with ultraviolet curable urethane resin film having a hole pattern, A randomly LiNbO ₃ single crystal wafer (N
o240) was sprayed for about 20 minutes to perform honing. After the honing, it was immersed in a stripping solution. Observation of the back surface of the wafer after honing showed a diameter of 250 μm and a depth of 90 μm.
It was confirmed that the concave portions were formed uniformly.

[0062]

As described above, according to the method for manufacturing a surface acoustic wave substrate of the present invention, it is possible to sufficiently eliminate the obstacle caused by the bulk wave and to sufficiently enhance the formation accuracy of the concave portion for the countermeasure against the bulk wave. Can be. Therefore, it is possible to provide a surface acoustic wave substrate having a high degree of flatness, which can cope with, for example, a stepper in device manufacturing and a high degree of device accuracy, and further, it is possible to improve device characteristics and a yield.

[0063]

Claims (4)

[Claims] After washing a piezoelectric single crystal wafer for a surface acoustic wave substrate with a weak acid solution having a pH in the range of 4.0 to 6.5,
A pretreatment step of cleaning with pure water in a range of 6.0 to 8.0; a step of disposing an ultraviolet-curable resin layer on a surface opposite to an electrode forming surface of the piezoelectric single crystal wafer after the cleaning; and Exposing and developing the mold resin layer to form a hole pattern corresponding to a desired concave portion; and using the ultraviolet-curable resin layer on which the hole pattern is formed as a mask, the piezoelectric unit through the mask. Honing the crystal wafer to form a desired concave portion. 2. The method for manufacturing a surface acoustic wave substrate according to claim 1, wherein the piezoelectric single crystal wafer subjected to the double-sided lapping process is immediately washed as the pretreatment step without drying. A method for manufacturing a surface acoustic wave substrate. 3. The method for manufacturing a surface acoustic wave substrate according to claim 1, further comprising a step of peeling off the ultraviolet-curable resin layer using an alkaline solution. . 4. The method for manufacturing a surface acoustic wave substrate according to claim 1, wherein the ultraviolet-curable resin layer is made of a urethane-based ultraviolet-curable resin.