JPH11189500A - Production of oxide single crystal substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject single crystal substrate used in e.g. elastic surface wave devices through specular polishing thereof without bringing about any handling problem during and after its polishing so as to ensure polishing accuracy such as high flatness and high parallel degree to be afforded in high reproducibility. SOLUTION: This oxide single crystal substrate is obtained through such specular polishing operation that the roughened reverse surface of an oxide single crystal substrate 5 is brought into contact with an attractive plate 6 of porous ceramic with a liquid such as water included therein and attractively held; in this state, one side or both sides of the substrate is subjected to specular polishing operation; when a double sided polishing is to be applied, two oxide single crystal substrates are held by the aid of an attractive plate interposed between these substrates, and in this posture, disposed between a pair of upper and lower grinders to subject the respective outside surfaces of the two oxide single crystal substrates to specular polishing operation.

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 an oxide single crystal substrate having a mirror polishing process for an oxide single crystal substrate.

[0002]

2. Description of the Related Art In recent years, many surface acoustic wave devices have been used for various elements such as filters, delay lines, and transmitters of electronic devices using radio waves. In particular, a surface acoustic wave filter that is small and lightweight and has a high sharp cutoff property as a filter has been frequently used as an RF stage and an IF stage filter for a television receiver or a portable terminal device in the field of mobile communication. Therefore, it is required to improve the characteristics and the productivity as well.

A surface acoustic wave device is made of LiTa exhibiting piezoelectricity.
It is configured by using an O ₃ single crystal wafer or a LiNbO ₃ single crystal wafer as a substrate, and providing an interdigital (comb-shaped) transducer (electrode) on one main surface of such a substrate. In such a configuration, since the surface acoustic waves are excited and received by the transducer, the transducer formation surface of the single crystal wafer needs to be mirror-polished. If the back surface of the single crystal wafer has a similar mirror surface, unnecessary waves (disturbance waves) such as bulk waves are also excited and received at the same time as excitation and reception of surface acoustic waves, causing spurious interference in frequency characteristics. Therefore, in a single crystal wafer for a surface wave device,
The back side is roughened by polishing with a rough abrasive or honing.

Conventionally, the above-mentioned mirror polishing of a single crystal wafer for a surface acoustic wave device is performed by heating a wax-coated ceramic plate to bond the single crystal wafer to a wax, or by adsorbing a resin system called a template. The single crystal wafer is adsorbed on the material with water and is mainly polished on one side.

[0005] Among these conventional methods for holding a single crystal wafer, the method of bonding and holding a single crystal wafer with wax is excellent in processing accuracy such as parallelism and flatness, but requires techniques for bonding and is used for bonding. It is necessary to carry out a step of cleaning the wax, which makes handling difficult, and in particular, if the wax attached to the roughened back side cannot be completely removed, it may cause electrode peeling and the like. There was a problem. Furthermore, since the ceramic plate is heated and bonded, there has been a problem that the single crystal wafer is liable to crack or the like in the heating step.

On the other hand, the method of holding a single crystal wafer by suction using a template is not particularly problematic in the post-process, but the deformation of the template made of resin causes a problem.
There are problems that the accuracy of parallelism, flatness, and the like are easily reduced, and that the outer periphery is apt to be drooped.

[0007] Further, it has been studied to apply double-side polishing, which can easily improve the flatness and the like, to the mirror polishing of a single crystal wafer for a surface acoustic wave device. It is necessary to perform the surface roughening process, which requires time and effort to protect the mirror surface on the front side, and even if the surface side is protected and roughened, the surface side mirror surface is easily scratched. There was such a problem.

[0008]

As described above, in a mirror polishing process of an oxide single crystal wafer used in a conventional surface acoustic wave device or the like, a method of bonding and holding an oxide single crystal wafer using wax. In this case, a wax cleaning step is required, which makes handling complicated and causes wax to remain on the roughened back surface, causing electrode peeling, etc., and furthermore, an oxide single crystal wafer in the heating step during bonding. There is a problem that cracks and the like are apt to occur. On the other hand, the method of adsorbing and holding a single crystal wafer using a template made of a resin material has a problem that it is difficult to obtain high parallelism, high flatness, and the like due to deformation of the template.

When double-side polishing is applied, it is necessary to roughen the back surface of the oxide single crystal wafer after mirror polishing, so that the mirror surface on the front surface is likely to have scratches or the like. was there.

For this reason, in the mirror polishing of an oxide single crystal substrate used for a surface acoustic wave device or the like, a high flatness can be obtained without causing a problem in handleability at the time of polishing and after the polishing step. Excellent processing accuracy such as degree of parallelism and high parallelism, especially for 3 inch oxide single crystal wafers.
It is an issue to obtain a flatness of μm or less with good reproducibility. In addition, it is required to be able to apply double-side polishing that can easily obtain high-precision flatness or the like after roughening the rear surface.

SUMMARY OF THE INVENTION The present invention has been made to address such a problem, and has improved the workability and the like of holding an oxide single crystal substrate during mirror polishing to improve workability and the like. It is an object of the present invention to provide a method for manufacturing an oxide single crystal substrate, which can improve processing accuracy such as degree and parallelism.

[0012]

According to a first aspect of the present invention, there is provided a method for manufacturing an oxide single crystal substrate, comprising the step of mirror-polishing the surface of an oxide single crystal substrate. In the manufacturing method, the oxide single crystal substrate,
The mirror polishing is performed by holding the liquid by using a suction plate made of porous ceramics containing a liquid.

The method for producing an oxide single crystal substrate according to the present invention comprises:
It can be applied to both single-side polishing and double-side polishing. For example, as described in claim 2, two oxide single crystal substrates are held by the adsorption plate interposed therebetween, and Placed between a pair of upper and lower polishing disks in the state, the said
The outer surface of each of the two oxide single crystal substrates is mirror-polished.

In the method of manufacturing an oxide single crystal substrate according to the present invention, the mirror polishing step is preferably performed after roughening the back surface of the oxide single crystal substrate. The back surface side of the roughened oxide single crystal substrate is held in contact with the suction plate.

In the method for manufacturing an oxide single crystal substrate according to the present invention, the oxide single crystal substrate is, for example, water-adsorbed by an adsorption plate made of porous ceramics. Since this adsorbing plate has much higher hardness than a conventional template made of a resin material, there is no possibility that the adsorbing plate itself will be deformed during mirror polishing, thereby improving the flatness and parallelism of the oxide single crystal substrate. It can be processed with high precision. In addition, even if the back surface of the oxide single crystal substrate is roughened and mirror-polished, and the roughened back surface is held in contact with the adsorption plate, the reduction in the back surface roughness is within a sufficient limit. Can be suppressed.

On the other hand, the adsorption holding of the oxide single crystal substrate itself is performed by, for example, water adsorption as in the case of using the conventional template, as described above. In addition, it is possible to improve the working efficiency, and furthermore, there is very little possibility that the adhered matter remains on the roughened rear surface side. Therefore, it is possible to prevent electrode peeling or the like due to the residual adhered matter.

In the method of manufacturing an oxide single crystal substrate according to the present invention, when the two oxide single crystal substrates are held by an adsorption plate interposed therebetween and the double-side polishing is applied, the adsorption plate itself may be used. Since there is no risk of deformation, the outer surfaces of the two oxide single crystal substrates after the back surface roughening can be mirror-polished in the same manner as in normal double-side polishing. Therefore, thickness variation does not easily occur in the oxide single crystal substrate, and the accuracy of the lapping process can be more easily maintained. Furthermore, despite the double-side polishing method, the polishing time per one oxide single crystal substrate can be shortened, and since the flatness is good, the processing amount can be reduced. It is possible to efficiently produce an oxide single crystal substrate having the same.

[0018]

Embodiments of the present invention will be described below.

FIG. 1 is a diagram showing a configuration example of a single-side polishing apparatus used in the first embodiment of the method for manufacturing an oxide single crystal substrate according to the present invention. In FIG. 1, reference numeral 1 denotes a polishing machine. A polishing cloth 2 is affixed to the surface of the polishing board 1.
It provides a polished surface. A drive shaft 3 is fixed to the lower side of the polishing platen 1, and a driving system (for example, a motor) (not shown) is connected to the polishing shaft 1 via the drive shaft 3.
Are driven to rotate at a predetermined rotation speed.

An oxide single crystal wafer 5 held on a pressure plate 4 made of, for example, a ceramic plate is set on the polishing board 1 (actually on the polishing cloth 2) as described above. The set of the oxide single crystal wafer 5 on the pressure plate 4
The suction plate 6 made of porous ceramics is embedded in the concave portion 4a serving as the wafer holding position, and the suction plate 6 is made to contain a liquid such as water, and the suction is performed by the suction force of the liquid. That is, the oxide single crystal wafer 5 is adsorbed (for example, water adsorbed) by the liquid such as water contained in the adsorption plate 6 made of porous ceramics.

Here, in the single-side polishing apparatus shown in FIG. 1, the suction plate 6 made of porous ceramics is
Since it is embedded in the inside, there is no possibility that the suction plate 6 comes into contact with the polishing plate 1. Accordingly, it is possible to prevent the suction plate 6 from being damaged, and further prevent the occurrence of defective mirror polishing due to the damage to the suction plate 6.

The porous ceramic used as the adsorbing plate 6 is not particularly limited to its material. For example, various materials such as alumina (Al ₂ O ₃ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), etc. Ceramic materials can be used. In addition, a porous ceramic plate is used for the adsorption plate 6 to contain a liquid such as water. The porosity of the ceramic plate may be, for example, a pore diameter in a range of 0.5 to 150 μm. preferable. The amount of porosity in porous ceramics is 5 to 30% by volume.
It is preferred that it is about.

If the pore diameter of the porous ceramics is less than 0.5 μm, there is a possibility that a sufficient attraction force cannot be obtained.
Also, if the porosity is less than 5% by volume or exceeds 30% by volume, there is a possibility that a sufficient adsorption force may not be obtained. On the other hand, if the pore diameter exceeds 150 μm, the surface roughness of the porous ceramics, which increases simultaneously, may reduce the roughness of the back surface of the oxide single crystal wafer 5 or cause scratches.

Further, the contact surface of the oxide single crystal wafer 5 is to be processed flat so that the oxide single crystal wafer 5 directly contacts the adsorption plate 6 made of porous ceramics. . If the flatness of the suction plate 6 is low,
The processing accuracy of the oxide single crystal wafer 5 decreases.

The pressure plate 4 on which the oxide single crystal wafer 5 is held by suction is driven to rotate by a drive system (not shown) via a rotary shaft 7. A polishing liquid, such as a mixed slurry of abrasive particles and a polishing liquid, is supplied onto the polishing cloth 2 from a polishing liquid supply device (not shown). The polishing platen 1 is rotated while the polishing liquid is supplied, and the pressure plate 4 is moved in the opposite direction to the polishing platen 1 while the oxide single crystal wafer 5 is pressed against the polishing pad 2 by the pressure plate 4. Rotate to. In this way, the surface of the oxide single crystal wafer 5 (the surface in contact with the polishing pad 2) is mirror-polished.

Next, a first method using the above-described single-side polishing apparatus is described.
The manufacturing process of the oxide single crystal wafer according to the embodiment will be described. That is, first, an oxide single crystal ball is sliced into a predetermined thickness to form a wafer, and both surfaces of the oxide single crystal wafer are lapped. The slicing and lapping may be performed in the same manner as in the related art. Also,
Examples of the oxide single crystal to be processed include a LiTaO ₃ single crystal and a LiNbO ₃ single crystal used for a surface acoustic wave device and the like.

Next, the back surface of the lap-processed oxide single crystal wafer is polished with relatively coarse free abrasive grains or directly sprayed with free abrasive grains, for example, to the center defined in JIS B 0601. Line average roughness _Ra is 2.0μ
The surface is roughened so that the surface roughness becomes not less than m.

Here, the oxide single crystal wafer having the back surface roughened may be directly sent to the next mirror polishing step. However, the oxide single crystal wafer having undergone the lapping process and the back surface roughening process may be used. Since a crystal wafer has many fine cracks on its outer peripheral surface, it is preferable to perform a mirror polishing process after performing a beveling process to make the outer peripheral surface of the wafer into a C-chamfered shape, an R shape, or the like. The beveling process may be performed after the lapping process or after the mirror polishing process.However, if the beveling process is performed after the lapping process, cracks may occur again during the back surface roughening process, and when the beveling process is performed after the mirror polishing process. Is likely to adversely affect mirror polishing.

After thoroughly cleaning the above-described oxide single crystal wafer whose back surface has been roughened and further, the oxide single crystal wafer whose outer peripheral surface has been beveled, it is mirror-polished using the single-side polishing apparatus shown in FIG. Perform processing. In this mirror polishing step, first, a liquid such as water is contained in an adsorbing plate 6 made of porous ceramics, and the back surface of the roughened oxide single crystal wafer 5 is applied to the adsorbing plate 6 containing the water or the like. Contact and hold by suction.

Next, the pressure plate 4 holding the oxide single crystal wafer 5 by suction is slowly lowered onto the polishing plate 1 and set. By rotating the pressure plate 4 and the polishing plate 1 while supplying the polishing liquid onto the polishing plate 1, the surface of the oxide single crystal wafer 5 (the surface opposite to the surface subjected to the roughening process) is changed. Mirror polishing. In the mirror polishing described above, the oxide single crystal wafer 5
Is adsorbed on the adsorbing plate 6 made of porous ceramics, for example, and the adsorbing plate 6 is made of porous ceramics having much higher hardness than a template made of a conventional resin material. There is no risk of deformation during mirror polishing. Therefore, processing accuracy of the oxide single crystal wafer 5, for example, parallelism, flatness, and the like can be improved. Specifically, for example, the surface acoustic wave device 30
Flatness of less than 8μm required for high frequency band substrate of 0MHz or more (eg, 3 inch diameter oxide single crystal wafer)
In addition, it becomes possible to mirror-process the oxide single crystal wafer 5 with good reproducibility.

Further, since the oxide single crystal wafer 5 is held by suction, for example, by water adsorption as in the case of using the conventional template, the handleability after mirror polishing is excellent, and the conventional wax bonding is performed. As described above, since advanced cleaning or the like is not required, a decrease in work efficiency can be prevented. Furthermore, since there is very little risk of deposits remaining on the roughened rear surface side, peeling of electrodes due to the remaining deposits can be prevented, and the yield of surface acoustic wave devices and the like can be improved. .

As described above, according to the first embodiment of the method for manufacturing an oxide single crystal wafer described above, it is possible to obtain processing accuracy such as high flatness suitable for a substrate for a high frequency band and the like, and to obtain such processing accuracy. It is possible to improve the workability of mirror polishing of an oxide single crystal wafer and the workability of a post-process. Therefore, it greatly contributes to the improvement of the yield and the working efficiency of the surface acoustic wave device using the oxide single crystal wafer.

Next, a second embodiment of the method for manufacturing an oxide single crystal substrate according to the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing a configuration example of a double-side polishing apparatus used in the second embodiment. In FIG.
Denotes a lower polishing machine, and above the lower polishing machine 11,
The upper polishing machine 12 is disposed to face the upper polishing machine 12. These polishing machines 1
A polishing cloth 13 is attached to each of the opposing surfaces of 1 and 12. These polishing plates 11 and 12 are driven to rotate in the same direction or in opposite directions at a predetermined rotation speed by a drive system (not shown) (not shown) via drive shafts 14 and 15, respectively.

Between the pair of upper and lower polishing disks 11 and 12, two oxide single crystal wafers 17 and 18 are set in a carrier 16 so that the back surfaces thereof are overlapped. As shown in an enlarged manner in FIG. 3, the insertion portion 1 which is a wafer holding position of the carrier 16 is provided in the carrier 16.
6a, through the adsorbing plate 6 made of the same porous ceramics as in the first embodiment described above, the back surface side of each of the two oxide single crystal wafers 17 and 18 is roughened to the adsorbing plate 6. It is set in a state of being abutted and laminated.

The adsorbing plate 6 made of porous ceramics used here is processed so that the contact surfaces with the oxide single crystal wafers 17 and 18 are flat and parallel, respectively. If the flatness and parallelism of the suction plate 6 are low, the processing accuracy of the oxide single crystal wafers 17 and 18 will be reduced. The material and pore diameter of the porous ceramics are the same as in the first embodiment.

The above-mentioned two oxide single crystal wafers 1
Numerals 7 and 18 are adsorbed (for example, water adsorbed) by a liquid such as water contained in an adsorbing plate 6 made of porous ceramics.
a. That is, the two oxide single crystal wafers 17 and 18 stacked via the suction plate 6 function in the same manner as one wafer in normal double-side polishing,
Each surface is simultaneously mirror-polished.

The carrier 16 on which the two oxide single crystal wafers 17 and 18 held by suction on the suction plate 6 are arranged,
Like a normal double-sided polishing apparatus, it has a planetary gear meshing with the sun gear of the drive shaft 19 at the center and the internal gear of the outer peripheral portion 20. It is configured to make a planetary motion around it. In addition, a polishing liquid composed of a mixed slurry of abrasive particles and a polishing liquid or the like is supplied between a pair of upper and lower polishing disks 11 and 12 from a polishing liquid supply device (not shown).

Then, two oxide single crystal wafers 1
A predetermined pressure is applied to a pair of upper and lower polishing plates 11 and 12 with respect to 7 and 18, and in this state, the lower polishing plate 11 and the upper polishing plate 12 are rotated while supplying the polishing liquid, The carrier 16 on which the oxide single crystal wafers 17 and 18 are arranged is caused to perform planetary motion. In this manner, the mirror polishing of the respective surfaces (the surfaces in contact with the polishing pad 2) of the two oxide single crystal wafers 17 and 18 is performed.

Next, the second using the double-side polishing apparatus described above
The manufacturing process of the oxide single crystal wafer according to the embodiment will be described. First, as in the first embodiment described above,
After thoroughly cleaning the two oxide single-crystal wafers whose back surfaces have been roughened and the two oxide single-crystal wafers whose outer peripheral surfaces have been beveled, they are mirror-polished using a double-side polishing apparatus shown in FIG. Polishing is performed. In the mirror polishing step, first, the adsorption plate 6 made of porous ceramics is used.
Contains a liquid such as water, and the adsorbing plate 6 containing the water or the like.
The two rough surfaces of the oxide single crystal wafers 17 and 18 are brought into contact with each other, and these oxide single crystal wafers 17 and 18 are sucked and held on the suction plate 6.

Next, the two oxide single crystal wafers 17 and 18 respectively held by suction on the suction plate 6 are placed in a carrier 16 set on the lower polishing plate 11 in this state. The upper polishing plate 12 is slowly lowered and set. By rotating the lower and upper polishing disks 11 and 12 and the carrier 16 while supplying the polishing liquid between the polishing disks 11 and 12, the respective surfaces of the two oxide single crystal wafers 17 and 18 ( The surface opposite to the roughened surface) is mirror-polished.

In the above-mentioned double-sided mirror polishing, two single-crystal oxide wafers 17 and 18 are attached to a suction plate 6 made of porous ceramics and interposed therebetween.
Water, for example, and a pair of upper and lower polishing
It is arranged between 1 and 12. As described above, since the adsorbing plate 6 itself does not deform during the mirror polishing process, each of the two oxide single crystal wafers 17 and 18 after the back surface roughening is performed in the same manner as the normal double-side polishing. Mirror surface can be satisfactorily polished.

Accordingly, as in the case of ordinary double-side polishing, the occurrence of thickness variation of the oxide single crystal substrate can be suppressed, and the accuracy of lapping can be more easily maintained. The processing accuracy of 17, 18 such as parallelism and flatness can be further improved. More specifically, the surfaces of the oxide single crystal wafers 17 and 18 can be mirror-processed to a flatness of, for example, 5 μm or less (eg, an oxide single crystal wafer having a diameter of 3 inches) with good reproducibility.

Further, in spite of the double-side polishing method, the polishing time per one of the oxide single crystal wafers 17 and 18 can be shortened, and since the flatness is good, the processing amount can be reduced. Oxide single crystal wafers 17 and 18 having good flatness and the like can be efficiently manufactured. The workability during the mirror polishing of the oxide single crystal wafers 17 and 18 and the workability in the post-process can be improved in the same manner as in the above-described first embodiment.

[0044]

Next, specific examples of the present invention will be described.

Example 1 First, a LiTaO ₃ single crystal ball was sliced into a wafer, and both sides of the wafer were wrapped. Next, the wafer was roughened using fused alumina abrasive grains having a particle size of 60 to 120 μm so that the rear surface of the wafer became _Ra = 2.2 μm. This back surface is roughened to a thickness of 0.39
The outer surface of the LiTaO ₃ mm wafer was chamfered (using an R-shaped grindstone (radius: 0.125 mm, taper angle: 22 °, # 800)).

Thereafter, mirror polishing was performed using a single-side polishing apparatus as shown in FIG. Specifically, the roughened rear side of the LiTaO ₃ wafer is brought into contact with an adsorption plate 6 made of porous alumina (# 400) embedded in a ceramic pressure plate 4 to adsorb water. 4 was slowly lowered onto the polishing machine 1 and set. Then, gradually pressurized while flowing colloidal silica, after slowly rotating, the rotation speed 30 rp
m, a predetermined pressure was applied, and mirror polishing was performed for 2 hours. After this mirror polishing, the substrate was washed with an acid, an alkali and water, further washed with a brush, and dried.

This process was carried out on 100 LiTaO ₃ wafers, and the flatness and the back surface roughness were measured and evaluated.
(Otalthickness value) was in the range of 1 to 5 μm, and the back surface roughness was also in the range of _Ra = 2.2 to 2.7 μm.

The porous plate (# 1000) is used for the adsorption plate 6.
Also in the case where porous alumina (# 1400) was used, similarly good mirror polishing could be performed.

Comparative Example 1 The procedure of Example 1 was repeated except that the water absorption of the LiTaO ₃ wafer was performed using a resin template attached to a ceramic pressure plate.
Mirror polishing of the LiTaO ₃ wafers was performed.
When the flatness and the back surface roughness were measured and evaluated, the back surface roughness was in the range of _Ra = 2.2 to 2.7 μm.
The flatness was in the range of 8 to 20 μm in TTV, and a flatness of 5 μm or less could not be realized.

Example 2 First, a 3 inch diameter LiNbO ₃ single crystal ball was sliced into a wafer shape, and both sides of the 3 inch × 0.63 mmt wafer were wrapped with a GC (# 2000) slurry to form a wafer. After finishing to 0.52mmt, the back side is Alundum (# 18
In 0), honing was performed so that _Ra = 5 μm, and the surface was roughened. Then, LiNbO ₃ whose back surface is roughened
The outer periphery of the wafer was chamfered (using an R-type grindstone (radius 0.125 mm, taper angle 22 °, # 800)).

Thereafter, the LiNbO ₃ wafer was thoroughly washed and mirror-polished using a double-side polishing apparatus as shown in FIG. Specifically, water-containing thickness 1.0mm
Plate 6 made of porous SiC (average pore diameter: 5 μm)
Then, the roughened back surfaces of the two LiNbO ₃ wafers are brought into contact with each other to adsorb water, and in this state, the lower polishing plate 11
It was arranged in the carrier 16 set above. Next, the upper polishing plate 12 was slowly lowered and set, and gradually pressurized while flowing colloidal silica. After rotating slowly, a predetermined pressure was applied at a rotation speed of 20 rpm, and mirror polishing was performed for 1 hour. . After this mirror polishing, the substrate was washed with an acid, an alkali and water, further washed with a brush, and dried.

The two mirror-polished LiNs
Measure bO ₃ wafer flatness, thickness variation, appearance
As a result of the evaluation, no scratches or chips were found, and the thickness variation was within ± 1 μm in each case. When the flatness was measured with a flatness meter made of Fujinon while adsorbing one side, the PV value was 2 μm or less in all cases. Using such a LiNbO ₃ wafer, an 800MHz band surface acoustic wave device was prototyped by stepper exposure.Electrode peeling and line width variation hardly occurred due to uneven exposure, and a 98% stable device yield was obtained. Was.

Example 3 A 3 inch diameter LiTaO ₃ single crystal ball was sliced into a wafer, and both sides of this 3 inch × 0.50 mmt wafer were wrapped with a slurry of GC (# 2000) to a thickness of 0.39 mm. After finishing to mmt, the back side is rounded with Alundum (# 180)
Honing was performed so that _a = 5 µm, and the surface was roughened.
Next, the outer surface of the LiTaO ₃ wafer whose surface was roughened was chamfered (using an R-shaped grindstone (radius: 0.125 mm, taper angle: 22 °, # 800)).

Thereafter, the LiTaO ₃ wafer was thoroughly washed, and mirror-polished using a double-side polishing apparatus as shown in FIG. Specifically, 0.15 mm thick containing water
Plate 6 made of porous alumina (average pore diameter: 5 μm)
Then, the roughened rear surfaces of the two LiTaO ₃ wafers are brought into contact with each other to adsorb water, and in this state, the lower polishing plate 11
It was arranged in the carrier 16 set above. Next, the upper polishing plate 12 was slowly lowered and set, and gradually pressurized while flowing colloidal silica. After rotating slowly, a predetermined pressure was applied at a rotation speed of 20 rpm, and mirror polishing was performed for 1 hour. . After this mirror polishing, the substrate was washed with an acid, an alkali and water, further washed with a brush, and dried.

The two mirror-polished LiTs
Measure flatness, thickness variation and appearance of aO ₃ wafer,
As a result of evaluation, no scratches or chips were found, and the thickness variation was within ± 2 μm in all cases. When the flatness was measured with a flatness meter made of Fujinon while adsorbing one side, the PV value was 3 μm in all cases. Such L
Using an iTaO ₃ wafer, a surface acoustic wave device in the 800 MHz band was prototyped by stepper exposure, and there was almost no electrode peeling or line width variation due to exposure unevenness.
A stable device yield of 8% was obtained.

Comparative Example 2 In the same manner as in Example 2, LiN which had been subjected to slicing, lapping, backside honing and outer peripheral chamfering was performed.
After thoroughly cleaning the bO ₃ wafer, the roughened rear surface of the LiNbO ₃ wafer is brought into contact with a 0.20 mm thick organic fiber adsorption pad (template) adhered to an alumina plate to adsorb water, and a single-side polishing machine is used. Set to Next, the alumina plate was slowly lowered and set, and gradually pressurized while flowing colloidal silica. After slowly rotating, the rotation speed was set to 20 rpm and a predetermined pressure was applied, and mirror polishing was performed for 1 hour. After this mirror polishing, the substrate was washed with an acid, an alkali and water, further washed with a brush, and dried.

LiNbO ₃ mirror-polished in this way
When the flatness, thickness variation and appearance of the wafer were measured and evaluated, no flaws or chips were found, but the thickness variation was ± 9 μm. When one side was adsorbed and the flatness was measured with a Fujinon flatness meter, the P-
Only a flatness of 12 μm was obtained in V value. Using such a LiNbO ₃ wafer, a surface acoustic wave device in the 800 MHz band was prototyped by stepper exposure. As a result, electrode peeling and line width variation occurred due to exposure unevenness, resulting in a poor device yield of 70%.

Comparative Example 3 LiN subjected to slicing, lapping, backside honing and outer peripheral chamfering in the same manner as in Example 2.
After thoroughly cleaning the bO ₃ wafer, the roughened back surface of the LiNbO ₃ wafer was bonded to an alumina plate with wax and set in a single-side polishing machine. Next, the alumina plate is slowly lowered and set, and gradually pressurized while flowing colloidal silica. After slowly rotating, the rotation speed is set to 20 rpm and a predetermined pressure is applied.
Time mirror polishing was performed. After the processing, the alumina plate was heated and peeled off, the wax was washed with an organic solvent, and further washed with an acid, an alkali and water, and with a brush for drying.

Thus, the mirror-polished LiNbO
_{(3) When} the flatness, thickness variation, and appearance of the wafer were measured and evaluated, no cracks or chips were found, but cracks occurred during peeling, the yield was 80%, and the thickness variation was ± 9 μm. Was. When one side was adsorbed and the flatness was measured with a Fujinon flatness meter, P
A flatness of only 12 μm was obtained in -V value. Using such a LiNbO ₃ wafer, a surface acoustic wave device in the 800 MHz band was prototyped by stepper exposure. As a result, electrode peeling and line width variation due to exposure unevenness occurred, and the device yield was 78%, which was poor.

Comparative Example 4 In the same manner as in Example 3, LiT subjected to slicing, lapping, backside honing and outer peripheral chamfering
After thoroughly cleaning the aO ₃ wafer, the roughened back surface of the LiTaO ₃ wafer is brought into contact with a 0.20 mm thick organic fiber suction pad (template) adhered to an alumina plate to adsorb water, and a single-side polishing machine is used. Set to Next, the alumina plate was slowly lowered and set, and gradually pressurized while flowing colloidal silica. After slowly rotating, the rotation speed was set to 20 rpm and a predetermined pressure was applied, and mirror polishing was performed for 1 hour. After this mirror polishing, the substrate was washed with an acid, an alkali and water, further washed with a brush, and dried.

The mirror-polished LiTaO ₃
When the flatness, thickness variation, and appearance of the wafer were measured and evaluated, no flaws or chips were found, but the thickness variation was ± 7 μm. When one side was adsorbed and the flatness was measured with a Fujinon flatness meter, the P-
Only a flatness of 12 μm was obtained in V value. Using such a LiTaO ₃ wafer, a surface acoustic wave device in the 800 MHz band was prototyped by stepper exposure. As a result, electrode peeling and line width variation occurred due to exposure unevenness, resulting in a poor device yield of 80%.

Comparative Example 5 LiT subjected to slicing, lapping, backside honing, and outer peripheral chamfering in the same manner as in Example 3.
After thoroughly cleaning the aO ₃ wafer, the roughened rear surface of the LiTaO ₃ wafer was bonded to an alumina plate with wax and set in a single-side polishing machine. Next, the alumina plate is slowly lowered and set, and gradually pressurized while flowing colloidal silica. After slowly rotating, the rotation speed is set to 20 rpm and a predetermined pressure is applied.
Time mirror polishing was performed. After the processing, the alumina plate was heated and peeled off, the wax was washed with an organic solvent, further washed with an acid, an alkali and water, and brush-washed, and dried.

The mirror-polished LiTaO ₃
When the flatness, thickness variation and appearance of the wafer were measured and evaluated, no flaws or chips were found, but the thickness variation was ± 9 μm. When one side was adsorbed and the flatness was measured with a Fujinon flatness meter, the P-
Only a flatness of 9 μm was obtained in V value. Using such a LiTaO ₃ wafer, a surface acoustic wave device in the 800 MHz band was prototyped by stepper exposure. As a result, electrode peeling and line width variation occurred due to exposure unevenness, and the device yield was poor at 75%.

[0064]

As described above, according to the method for manufacturing an oxide single crystal substrate of the present invention, the workability at the time of mirror polishing and the post-process is improved, and the flatness and the parallelism are improved. Processing accuracy can be improved. By using such an oxide single crystal substrate, it is possible to improve the yield in the subsequent device formation process.

[Brief description of the drawings]

FIG. 1 shows a first method for producing an oxide single crystal substrate according to the present invention.
FIG. 4 is a diagram showing a configuration of a single-side polishing apparatus used in the embodiment.

FIG. 2 shows a second example of the method for manufacturing an oxide single crystal substrate according to the present invention.
FIG. 3 is a diagram showing a configuration of a double-side polishing apparatus used in the embodiment.

FIG. 3 is a diagram showing a configuration of a main part of the double-side polishing apparatus shown in FIG. 2;

[Description of Signs] 1... Polishing surface plate 4... Pressure plate 5, 17, 18... Oxide single crystal wafer 6... Upper polishing machine 16 Carrier

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiharu Yokoi 4231 Sakura Hamaoka-cho, Ogasa-gun, Shizuoka Prefecture Inside (72) Inventor Hideki Kawaharazaki 4231 Sakura, Hamaoka-cho, Ogasa-gun, Shizuoka Prefecture Hamaoka Toshiba Electronics Corporation Inside

Claims (4)

[Claims] 1. A method for manufacturing an oxide single-crystal substrate, comprising a step of mirror-polishing the surface of an oxide single-crystal substrate, wherein the oxide single-crystal substrate is formed by an adsorption plate made of a porous ceramic containing a liquid. A method for manufacturing an oxide single crystal substrate, wherein the mirror polishing is performed while holding the substrate. 2. The method for manufacturing an oxide single crystal substrate according to claim 1, wherein the two oxide single crystal substrates are held by the adsorption plate interposed therebetween, and in this state, a pair of upper and lower oxide single crystal substrates is held. A method for producing an oxide single-crystal substrate, wherein the outer surfaces of each of the two oxide single-crystal substrates are mirror-polished by being arranged between polishing plates. 3. The method for manufacturing an oxide single crystal substrate according to claim 1, wherein the mirror polishing step is performed after roughening a back surface of the oxide single crystal substrate. A method for manufacturing an oxide single crystal substrate, characterized in that the back surface side of the formed oxide single crystal substrate is held in contact with the suction plate. 4. The method for producing an oxide single crystal substrate according to claim 1, wherein the adsorbing plate is made of a porous ceramic having a pore diameter in a range of 0.5 to 150 μm. A method for manufacturing a single crystal substrate.