JPH11284469A - Production of surface acoustic wave substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the defect rate in a substrate production process and device manufacturing process, after sufficiently eliminating a fault caused by a bulk wave in the production process of a surface acoustic wave(SAW) substrate, using a piezoelectric monocrystal wafer. SOLUTION: After wrap working is performed to both the sides of a piezoelectric monocrystal wafer (102), its rear side is made coarse by performing horning work or the like (103). Flatness of the piezoelectric monocrystal wafer having the coarse rear surface is controlled within the range from +60 μm to -20 μm in respect to the coarse rear surface (104), and then, the end face of the piezoelectric monocrystal wafer is worked. The end face is worked over two stages. while using coarse-grading grindstone and fine-grading grindstone. By polishing the front side of the piezoelectric monocrystal wafer (106) with its end face worked, a target SAW substrate can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a surface acoustic wave substrate.

[0002]

2. Description of the Related Art A surface acoustic wave device is generally made of LiTaO _3.
Single crystal wafer, LiNbO ₃ single crystal wafer, Li ₂
A substrate having piezoelectricity such as a B ₄ O ₇ single crystal wafer is used, and an interdigital transducer is provided on one principal surface of such a piezoelectric wafer. 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. Bulk waves and the like cause spurious interference in frequency characteristics. Therefore, measures against bulk waves such as roughening the back surface of the piezoelectric single crystal wafer by honing are being implemented.

Conventionally, a piezoelectric single crystal wafer has been sliced from a single crystal ball to form a wafer. After lapping both sides of the wafer, the above-described roughening of the back side is performed, and furthermore, mirror finishing of the front side is performed. Is generally performed. In addition, cracks are generated on the end surface (outer peripheral surface) of the piezoelectric single crystal wafer by a slicing process, a lapping process, and the like, and thermal distortion remains, which causes a wafer crack in a subsequent manufacturing process. Later, processing such as chamfering is performed on the end face of the piezoelectric single crystal wafer.

Although the above-described roughening of the back surface of the piezoelectric single crystal wafer is effective in suppressing unnecessary waves such as bulk waves, it is difficult to form large irregularities on the back surface by mechanically. Therefore, there is a problem that the yield of the wafer is lowered and the yield of the device process is lowered as a result. In particular, in recent years, a high degree of device accuracy has been demanded because automation of a device process by using a stepper has been advanced. Since such a requirement is based on the premise that the wafer has high flatness, high accuracy is required even when large irregularities are formed on the back surface of the piezoelectric single crystal wafer.

[0005] For this reason, double-side polishing using two wafers has been attempted. However, cracks and chippings are present as damage to the wafer due to the roughening of the rear surface. There are problems such as generation of cracks and scratches accompanying chipping. Due to these, a good processing yield cannot be obtained, and it has not yet been put to practical use.

Further, after roughening the back side of the piezoelectric single crystal wafer wrapped on both sides, the end face of the wafer is processed,
Measures such as removing the damage associated with the surface roughening process in the end face processing process have also been proposed, but this alone has not necessarily achieved sufficient effects with piezoelectric single crystal wafers that are being made thinner and larger in diameter. . In particular, in a piezoelectric single crystal wafer having a reduced thickness and a larger diameter, there is a problem that the damage and deformation associated with the roughening of the rear surface side are large, and the occurrence rate of defects in edge processing is increased.

[0007]

As described above, in the conventional manufacturing process of a piezoelectric single crystal wafer, particularly in the manufacturing process of a thinned or large-diameter piezoelectric single crystal wafer, the back surface is roughened. The occurrence rate of defects due to the occurrence of cracks and deformation is increasing, and the occurrence of defects is also increasing at the time of processing an end face or the like.

SUMMARY OF THE INVENTION The present invention has been made to address such a problem, and has been made to sufficiently eliminate obstacles caused by bulk waves and to reduce a defect rate in a substrate manufacturing process or a device manufacturing process. It is an object of the present invention to provide a method of manufacturing a wave substrate.

[0009]

According to a first aspect of the present invention, there is provided a method for manufacturing a surface acoustic wave substrate, comprising the steps of: lapping both surfaces of a piezoelectric single crystal wafer; Roughening the back surface side of the piezoelectric single crystal wafer, and flatness of the back surface roughened piezoelectric single crystal wafer by +60 μm with respect to the roughened back surface side.
m ~ -20μm in the range of adjusting, and the step of processing the end surface of the piezoelectric single crystal wafer is adjusted flatness,
Polishing the front surface side of the piezoelectric single crystal wafer after the end face processing.

In the first method of manufacturing a surface acoustic wave substrate, the step of adjusting the flatness of the piezoelectric single crystal wafer is performed, for example, by etching the piezoelectric single crystal wafer.

According to a second aspect of the present invention, there is provided a method for manufacturing a surface acoustic wave substrate, comprising the steps of: lapping both surfaces of a piezoelectric single crystal wafer; A step of roughening the back side, a step of processing the end face of the piezoelectric single crystal wafer having the back side roughened in two stages using a coarse-grain stone and a fine-grain stone, Polishing the surface side of the single crystal wafer.

In the second method of manufacturing a surface acoustic wave substrate, the step of processing the end face of the piezoelectric single crystal wafer is preferably performed.
As described in the above, while using a diamond grindstone of # 100 ~ # 800 as the coarse grain whetstone, # as the fine grain whetstone
It is preferable to use a 1000 to # 3000 diamond grindstone.

In the method of manufacturing a surface acoustic wave substrate according to the present invention, the flatness adjusting step of the piezoelectric single crystal wafer is carried out, and the method using the coarse grain grinding wheel and the fine grain grinding stone is performed. It is preferable to carry out the step of processing the end face of the piezoelectric single crystal wafer at the stage.

In the first method of manufacturing a surface acoustic wave substrate according to the present invention, the back surface of the piezoelectric single crystal wafer is roughened, and then the end surface is processed. Flatness is + 60μm ~
Adjusted to the range of -20μm. In this way, by adjusting the flatness of the piezoelectric single crystal wafer and performing the end face processing, for example, even if the piezoelectric single crystal wafer is thinned and the diameter is increased, cracks during the end face processing are greatly reduced. Can be suppressed. In addition, by processing the end surface after the surface roughening, it is possible to remove damage caused in the surface roughening process, particularly cracks and chipping near the end surface, thereby suppressing occurrence of defects in a subsequent polishing process. Becomes

In the second method of manufacturing a surface acoustic wave substrate according to the present invention, the end face is processed after the back surface of the piezoelectric single crystal wafer is roughened. Furthermore, cracks and chipping, which are damages caused in the surface roughening step, can be removed. Furthermore, by performing the end face processing of the piezoelectric single crystal wafer in two stages using a coarse-graining whetstone and a fine-graining whetstone, for example, a thinned or large-diameter piezoelectric single-crystal wafer can be processed at the end face processing. Cracks and the like can be greatly suppressed, and micro cracks and minute chippings that adversely affect the subsequent steps can be removed satisfactorily. Become.

According to the method for manufacturing a surface acoustic wave substrate of the present invention, the processing yield of a piezoelectric single crystal wafer, particularly the processing yield of a thinned and large-diameter piezoelectric single crystal wafer, is greatly improved. It is also possible to minimize the occurrence rate of defects in a device process using the same.

[0017]

Embodiments of the present invention will be described below.

FIG. 1 is a view showing a manufacturing process according to an embodiment of a method for manufacturing a surface acoustic wave substrate of the present invention. In the manufacturing method of the present invention, first, a piezoelectric single crystal ball is sliced into a predetermined thickness (FIG. 1-101) to form a wafer.
As the piezoelectric single crystal, LiTaO ₃ single crystal, LiNbO
₃ single crystal, Li ₂ B ₄ O ₇ single crystal and the like are used. Both sides of such a piezoelectric single crystal wafer are wrapped (see FIG. 1).
-102). These slicing and lapping can be performed in the same manner as in the related art.

Next, the back side of the double-sided lap-processed piezoelectric single crystal wafer is roughened (FIG. 1-103). The roughening process on the back surface side is performed by a honing process or the like. The degree of surface roughening on the back side of the piezoelectric single crystal wafer is appropriately set according to requirements for prevention of bulk wave disturbance, for example, the surface roughening is performed so that the center line average roughness _Ra is 2.0 μm or more. Perform processing.

The piezoelectric single crystal wafer whose back surface has been roughened is then subjected to edge processing (beveling). Before this edge processing, the warpage of the piezoelectric single crystal wafer is confirmed.
That is, if the warpage of the piezoelectric single crystal wafer after the surface roughening is large, cracks and the like frequently occur in the subsequent steps, and the production yield of the surface acoustic wave substrate is greatly reduced. Therefore, in the present invention, the flatness of the roughened piezoelectric single crystal wafer is adjusted in the range of +60 μm to −20 μm with respect to the roughened rear surface side (FIG. 1-104).

Even if the flatness of the roughened piezoelectric single crystal wafer exceeds +60 μm with respect to the back surface side or exceeds -20 μm with respect to the back surface side, in any case, the above-described cracks and the like Increase the incidence of In other words, when the piezoelectric single crystal wafer is convex on the back side, the maximum value is 60 μm or less, and when the piezoelectric single crystal wafer is concave on the back side, the maximum value is 20 μm or less. The occurrence rate of the above-mentioned cracks and the like can be significantly reduced.

The roughened piezoelectric single crystal wafer can be subjected to end face processing as long as the degree of warpage (flatness) is within the above range, but the degree of warpage (flatness) is not limited to the above range. If it exceeds the range, the flatness of the piezoelectric single crystal wafer after roughening is +60 μm Adjust to -20μm range. The flatness of the piezoelectric single crystal wafer can be adjusted to a desired range by controlling the immersion time in hydrofluoric acid and the like according to the degree of the initial warpage.

The etched piezoelectric single crystal wafer is subjected to end face processing (beveling processing) after passing through respective steps such as water washing, alkali washing, ultrasonic washing, water washing, and drying (FIG. 1-). 105). At this time, the piezoelectric single crystal wafer after the lapping process is subjected to processing damage during rounding, slicing, and lapping of the outer periphery of the single crystal ball, and a number of small cracks are generated on the outer peripheral surface thereof. Further, even when the back surface is roughened by honing or the like, the piezoelectric single crystal wafer is damaged by the abrasive grains, and a large number of cracks are generated particularly on the outer peripheral surface and the back side corners. Therefore, the end face processing of the piezoelectric single crystal wafer is performed after the roughening step.

By subjecting the end face of the piezoelectric single crystal wafer to roughening and chamfering after roughening, cracks and cracks on the outer circumferential face of the wafer and corners on the back side where many cracks and the like are generated are removed. Can be. The shape of the chamfering is not particularly limited, and an R shape, a C chamfered shape, or the like is applied. As described above, by eliminating the influence of the roughening processing that causes a large damage, a piezoelectric single crystal wafer with few cracks, cracks, and deformations of the chamfered shape can be obtained. According to such a piezoelectric single crystal wafer, it is possible to reduce the rate of occurrence of defects in a polishing step in a later step and further in a device forming step performed thereafter. Conversely, if the back surface roughening is performed after the wafer end face processing, cracks and the like accompanying the roughening processing remain as they are, and the defect occurrence rate increases in the polishing step and the device forming step. Further, it is desirable that the end face processing of the piezoelectric single crystal wafer is performed in two stages using a coarse-grain grindstone and a fine-grain grindstone (FIG. 1-105). As described above, by processing the end face of the roughened piezoelectric single crystal wafer with a coarse-grain grindstone first, large cracks and scratches are removed. After that, finish processing with fine grain whetstone,
By removing fine cracks and the like that affect the subsequent steps, it is possible to greatly reduce the rate of occurrence of defects in the polishing step and the subsequent device formation step.

It is preferable to use a diamond wheel of # 100 to # 800 as a coarse grain whetstone in the above-described two-stage end face processing, and it is preferable to use a diamond wheel of # 1000 to # 3000 as a fine grain whetstone. If the roughness (mesh) of the diamond of the coarse-graining stone exceeds # 800, large cracks and scratches generated in the surface roughening process may not be sufficiently removed, while if it is less than # 100. The possibility that cracks, scratches, etc. are newly generated increases. In addition, if the roughness (mesh) of the diamond of the fine-grain grinding stone exceeds # 3000, the efficiency of removing fine cracks and scratches that cannot be removed by the first stage using the coarse-grain grinding stone decreases, while less than # 1000 If so, good end face properties may not be obtained.

Further, in the end face processing using a diamond grindstone, it is preferable that the grinding fluid used at the time of the processing be changed after about 5,000 or less. By adopting such a condition, clogging of the diamond grindstone (particularly, clogging of the fine-grain grindstone) can be suppressed, and damage during end face processing can be reduced.

Thereafter, the surface of the piezoelectric single crystal wafer having been subjected to the two-stage end face processing described above is subjected to polishing processing (FIG. 1-106), whereby a target surface acoustic wave substrate is obtained. The polishing process on the front side is performed by a template method or the like.

According to the above-described piezoelectric single crystal wafer processing step, that is, the surface acoustic wave substrate manufacturing step, the damage in the back surface roughening step and the end face processing step is removed.
Or it can be made smaller, so it is possible to greatly suppress the occurrence of cracks and the like during the end face processing and the occurrence of defects in the polishing process, and for example, it is possible to reduce the thickness and the diameter of a piezoelectric single crystal wafer. Even if there is, the occurrence of defects can be suppressed. Therefore, the processing yield of a piezoelectric single crystal wafer, particularly the processing yield of a thinned and large-diameter piezoelectric single crystal wafer, can be significantly improved, and furthermore, the defect occurrence rate in a device forming process using the same can be minimized. It can be suppressed to the minimum.

[0029]

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

Comparative Example 1 A LiTaO ₃ single crystal ball was sliced into a wafer having a diameter of 4 inches.
Lapping was performed to a thickness of about 0.3 mm. Then, the back side of the wafer is subjected to honing to roughen the surface,
The wafers whose back side was roughened were immersed in a tank of hydrofluoric nitric acid as 25 sheets per cassette. Water washing, alkali ultrasonic cleaning and water washing were sequentially performed on the wafer immersed in hydrofluoric acid, and after drying, the warpage of the wafer was measured. As a result, the degree of warpage of each wafer was convex on the roughened rear side, and the maximum value was about 70 μm.

When the above-mentioned 103 wafers were beveled, cracks occurred in the suction portion and the like, and the yield was 71.8%. Bebeling uses # 600 diamond whetstone,
Performed in one stage. Next, the surface side of the 74 wafers after the beveling was polished using a template. In this polishing process, a large number of wafers jumped out of the template, and only 16 wafers completed the polishing process properly.

Thus, in Comparative Example 1, LiTaO
The total processing yield of ₃ single crystal wafers was as low as 15.5%.

Example 1 A LiTaO ₃ single crystal ball was sliced to form a wafer having a diameter of 4 inches.
Lapping was performed to a thickness of about 0.3 mm. Then, the back side of the wafer is subjected to honing to roughen the surface,
The wafers whose back side was roughened were immersed in a tank of hydrofluoric nitric acid as 25 sheets per cassette. The degree of warpage of each wafer was adjusted by controlling the time of immersion in hydrofluoric acid. The warpage of each of the wafers which had been washed with water, alkali ultrasonic cleaning, water washing and drying was measured. As a result, the wafer was convex on the roughened rear side, and the maximum value was about 50 μm.

When the above 101 wafers were beveled, no cracks or the like were generated, and the yield was 100%. The beveling was performed in one step using a # 600 diamond grindstone. Next, the surface side of 101 wafers after beveling was polished using a template. In this polishing process, some wafers were scratched, chipped, cracked, etc., resulting in 19 defective wafers. Nevertheless, according to Example 1, LiTa
The total processing yield of the O ₃ single crystal wafer was as good as 81.2%.

COMPARATIVE EXAMPLE 2 In the above-mentioned Example 1, the etching process to the polishing process were performed on 105 wafers under the same conditions as in Example 1 except that the immersion time of the wafer in hydrofluoric acid was changed. .

The warpage of each wafer according to Comparative Example 2 was as follows:
It was concave on the roughened back side, and its maximum value was about 25 μm (-25 μm with respect to the roughened back side). For such a wafer, cracking and the like occurred at the adsorption part during beveling, and the yield during beveling was 88.6%. Also,
Cracks occurred during polishing, and the processing yield by polishing was 85.3% (81 non-defective products). In Comparative Example 2, the total processing yield of the LiTaO ³ single crystal wafer was 77.1%.

Example 2 In Example 1, the flatness (warpage) of 105 wafers was measured under the same conditions as in Example 1 except that the end face of the wafer was processed using a # 800 diamond grindstone. ) Adjustment to polishing.

As a result, the yield during beveling is 99.0%
And the yield during polishing is 81.2% (85 non-defective products).
Sheets). According to Example 2, the total processing yield of the LiTaO ₃ single crystal wafer was as good as 81.0%.

Example 3 The flatness (warpage) of 102 wafers was the same as in Example 1 except that the end face of the wafer was processed using a # 1000 diamond grindstone. ) Adjustment to polishing. The degree of wafer warpage is the same as in the first embodiment.

As a result, the yield during beveling was 88.0%
And the yield during polishing is 97.8% (good 88
Sheets). According to Example 3, the total processing yield of the LiTaO ₃ single crystal wafer was as good as 86.3%.

Example 4 The same procedure as in Example 1 was applied to 100 wafers, except that the end face processing of the wafer in Example 1 was performed in two steps using a # 600 diamond wheel and a # 1000 diamond wheel. Under the conditions, the process from the adjustment of the flatness (the degree of warpage) to the polishing was performed.

As a result, the yield during beveling is 100%
And the yield during polishing is 98% (98
Sheets) and was good. As described above, according to Example 4, the total processing yield of the LiTaO ₃ single crystal wafer was as extremely good as 98%. Further, the above-described Li
Using a TaO ₃ single crystal wafer (surface acoustic wave substrate)
A TV IF filter was fabricated, and the yield in this device fabrication process was examined. The yield was 96%, which was good.

Example 5 The same procedure as in Example 1 was applied to 110 wafers, except that the end face processing of the wafer in Example 1 was performed in two steps using a # 600 diamond wheel and a # 1500 diamond wheel. Under the conditions, the process from the adjustment of the flatness (the degree of warpage) to the polishing was performed.

As a result, the yield during beveling is 100%
And 99.1% yield during polishing (non-defective product 109
Sheets) and was good. As described above, according to Example 4, the total processing yield of the LiTaO ₃ single crystal wafer was as extremely good as 99.1%.

Further, using the LiTaO ₃ single crystal wafer (surface acoustic wave substrate) described above, an IF filter for a television was manufactured, and the yield in this device forming process was examined. The result was 97%, which was good.

Example 6 In Example 1 described above, the wafer end face was processed using a # 600 diamond wheel and a # 2000 diamond wheel.
Except for the step processing, 107 wafers were subjected to the same conditions as in Example 1 from the adjustment of the flatness (the degree of warpage) to the polishing processing.

As a result, the yield at the time of beveling was 98.1%.
And 100% yield during polishing (non-defective 105
Sheets) and was good. Thus, according to Example 4, the total processing yield of the LiTaO ₃ single crystal wafer was extremely good at 98.1%.

Further, an IF filter for a television was manufactured using the above-described LiTaO ₃ single crystal wafer (surface acoustic wave substrate), and the yield in this device-making step was examined.

Example 7 In Example 4, except for changing the immersion time of the wafers in hydrofluoric acid, from the etching step to the polishing process were performed on 100 wafers under the same conditions as in Example 1. .

The warpage of each wafer according to the seventh embodiment is as follows:
It was convex on the roughened back side, and its maximum value was about 5 μm. The yield during beveling of such a wafer is
100%, 99% yield during polishing (99 non-defective products)
And was good. Thus, according to the seventh embodiment,
The total processing yield of LiTaO ₃ single crystal wafer is
It was extremely good at 99%.

Further, an IF filter for television was manufactured using the above-mentioned LiTaO ₃ single crystal wafer (surface acoustic wave substrate), and the yield in this device-forming step was examined. As a result, it was as good as 97%.

In each of the above embodiments, LiTaO _{3 was used.}
A single crystal wafer was used, but instead of a LiTaO ₃ single crystal wafer, a LiNbO ₃ single crystal wafer and Li ₂ B
Similar effects were obtained when a ₄ O ₇ single crystal wafer was used.

[0053]

As described above, according to the method for manufacturing a surface acoustic wave substrate of the present invention, the processing yield of a piezoelectric single crystal wafer, particularly the processing yield of a thinned and large-diameter piezoelectric single crystal wafer, is improved. It can be greatly improved. In addition, it is possible to suppress the occurrence rate of defects in the subsequent device formation process.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a process of manufacturing a surface acoustic wave substrate (a process of processing a piezoelectric single crystal wafer) according to the present invention.

Claims (5)

[Claims] 1. A step of lapping both sides of a piezoelectric single crystal wafer, a step of roughening the back side of the wrapped piezoelectric single crystal wafer, and a step of roughening the back side of the piezoelectric single crystal wafer. The flatness of the roughened rear surface side + 60μm ~ -20μ
m, a step of processing an end face of the piezoelectric single crystal wafer whose flatness has been adjusted, and a step of polishing the front side of the piezoelectric single crystal wafer after the end face processing. A method for manufacturing a surface acoustic wave substrate. 2. The method of manufacturing a surface acoustic wave substrate according to claim 1, wherein a step of etching the piezoelectric single crystal wafer is performed as the flatness adjusting step of the piezoelectric single crystal wafer. Method of manufacturing a wave substrate. 3. The method for manufacturing a surface acoustic wave substrate according to claim 1, wherein the step of processing the end face of the piezoelectric single crystal wafer is performed in two stages using a coarse-grain grindstone and a fine-grain grindstone. A method for manufacturing a surface acoustic wave substrate. 4. A step of lapping both surfaces of the piezoelectric single crystal wafer, a step of roughening the back side of the wrapped piezoelectric single crystal wafer, and a step of roughening the back side of the piezoelectric single crystal wafer. A surface acoustic wave, comprising: a step of processing the end face of the piezoelectric single crystal wafer in two stages using a coarse-grain stone and a fine-grain stone; and a step of polishing the front side of the piezoelectric single crystal wafer after the end face processing. Substrate manufacturing method. 5. The method for manufacturing a surface acoustic wave substrate according to claim 4, wherein a diamond grindstone of # 100 to # 800 is used as the coarse grain grindstone and a diamond grindstone of # 1000 to # 3000 is used as the fine grain grindstone. A method for manufacturing a surface acoustic wave substrate, comprising: