JP2005034926A - Polishing method of wafer substrate, and wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method of wafer substrate, and a wafer provided thereby, superior in high flatness, and manufacturable with excellent reproducibility of work accuracy, without using a wax sticking method, in a mirror surface polishing work method of a piezoelectric oxide monocrystal wafer substrate such as for an elastic surface wave device. <P>SOLUTION: The roughened reverse surface of the piezoelectric oxide monocrystal wafer substrate 5 is directly held by a plate 4 via a liquid such as water, and a mirror surface polishing work is performed in this state by one surface polishing. In this case, rotation is prevented, by using a template drawn in the same pattern shape (with orientation flat (OF)) as the wafer substrate, so that an abrasion is not caused on the wafer substrate reverse, when the piezoelectric oxide monocrystal wafer substrate freely rotates in a recessed part becoming a wafer holding position of the plate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a method of mirror-polishing only one surface of a wafer, particularly a lithium tantalate single crystal wafer substrate used for a surface acoustic wave filter or the like, and a wafer obtained thereby.
[0002]
[Prior art]
In the mobile communication field such as PHS and mobile phones, piezoelectric oxide single crystal wafers such as lithium tantalate, lithium niobate, quartz, lithium tetraborate, or langasite are used as substrates for surface acoustic wave elements. .
[0003]
The surface acoustic wave element is configured by providing an interdigital (comb-shaped) transducer (electrode) on one main surface of an oxide single crystal wafer exhibiting piezoelectricity. In such a configuration, since the surface acoustic wave is excited and received by the transducer, the transducer forming surface of the single crystal wafer needs to be mirror-polished. Further, if the back surface side of the single crystal wafer has a similar mirror surface, unnecessary waves (failure waves) such as bulk waves are excited and received simultaneously with the excitation and reception of the surface acoustic waves, which causes spurious interference in the frequency characteristics. Therefore, in the single crystal wafer for the surface wave device, the back surface is roughened by polishing (lapping) with a rough abrasive or honing.
[0004]
Conventionally, these wafers are manufactured as follows. That is, a plane (orientation flat) is formed in a designated direction with respect to a single crystal ingot obtained by the Czochralski method, etc., and is cut using a slicer for an inner peripheral blade or a wire saw, It is obtained by wrapping both surfaces of the obtained wafer to a predetermined thickness, then mirror-polishing only one surface with a polishing apparatus, and cleaning after polishing.
The following items are important in the characteristics of the piezoelectric oxide single crystal wafer used for such a surface acoustic wave filter.
[0005]
In the application of the surface acoustic wave filter, it is necessary to form a metal electrode on the piezoelectric oxide single crystal wafer.For example, when forming a pattern on the wafer surface by photolithography, the wafer surface shape is irregularly wavy, A metal electrode conforming to the pattern is not formed. Therefore, in order to form a metal electrode on a piezoelectric oxide single crystal wafer according to the designed electrode pattern, a wafer having a small undulation, that is, good flatness must be provided with respect to the wafer surface shape.
[0006]
Conventionally, the mirror polishing of a piezoelectric oxide single crystal wafer for a surface acoustic wave element has been conventionally performed by heating a piezoelectric oxide single crystal wafer having a back surface coated with wax and bonding the wax to a ceramic plate (patent) Document 1: Japanese Utility Model Laid-Open No. 58-129658), and a ceramic plate single-crystal wafer is vacuum-adsorbed by providing innumerable adsorption holes in the portion of the ceramic plate holding the wafer (Patent Document 2: Japanese Patent Laid-Open No. Hei 2). No. -98926), a piezoelectric oxide single crystal wafer is water-adsorbed with an adsorbent made of foamed polyurethane or the like called a backing material (back pad) (Patent Document 3: Japanese Patent Laid-Open No. 62-297064, Patent Document 4). : JP-A-63-93562), which is carried out by single-side polishing.
[0007]
Of these conventional methods for holding piezoelectric oxide single crystal wafers, the method of bonding and holding a wafer with wax is excellent in processing accuracy such as flatness, but requires a technique for bonding, and the wax used for bonding is washed. Therefore, there is a problem in that the handling becomes complicated, and in particular, if the wax adhering to the roughened back surface cannot be completely removed, the electrode may be peeled off. In addition, since the piezoelectric oxide single crystal wafer is heated and bonded, there is a problem that the single crystal wafer is easily cracked in the heating process.
[0008]
The method of vacuum-holding the wafer on the ceramic plate is also excellent in processing accuracy such as flatness, but if there is a foreign object between the wafer and the plate, there is a risk that the part will be extremely polished and cause dents. High nature. Accordingly, it is necessary to prevent foreign matter from being mixed in, and it is necessary to thoroughly manage the degree of cleanliness and to promote automation without human intervention as much as possible, which requires enormous capital investment.
[0009]
On the other hand, the method of adsorbing and holding a wafer using a backing material does not have the above-mentioned problems and there is no particular problem with respect to the subsequent process, but due to the thickness variation of the adsorbent made of polyurethane foam, etc. There are problems that the processing accuracy such as the flatness of the crystal wafer is liable to be lowered, and that the wafer outer periphery is liable to occur.
[0010]
In addition, it is also considered to apply a double-side polishing method that facilitates high accuracy of flatness and the like for mirror polishing of a piezoelectric oxide single crystal wafer for surface acoustic wave elements. Roughening has to be performed, and it takes time and effort to protect the surface side mirror surface. Even if the surface side is protected and roughened, scratches etc. are generated on the surface side mirror surface. There was a problem that it was easy (Patent Document 5: JP 2000-124758 A, Patent Document 6: JP 2001-192296 A).
[0011]
In a mirror polishing process of a piezoelectric oxide single crystal wafer used for a conventional surface acoustic wave element or the like, the method of bonding and holding the piezoelectric oxide single crystal wafer using wax requires a wax cleaning step. For this reason, the handling becomes complicated, and at the same time, if wax remains on the roughened back surface, it may cause electrode peeling, and further, the piezoelectric oxide single crystal wafer is likely to be cracked in the heating process during bonding. The remaining. In the method of vacuum-holding a piezoelectric oxide single crystal wafer on a ceramic plate, the management of cleanliness is important, and there remains a problem that enormous capital investment is required. On the other hand, the method of adsorbing and holding a piezoelectric oxide single crystal wafer using a backing material still has a problem that high flatness and the like are difficult to obtain due to variations in the adsorbent thickness.
In addition, when the double-side polishing method is applied, it is necessary to roughen the back surface of the piezoelectric oxide single crystal wafer after mirror polishing, and thus there remains a problem that the mirror surface on the front side is likely to be scratched. It was.
[0012]
Furthermore, there is also proposed a method in which two wafers are bonded so that the surface to be mirrored becomes the outer surface and processed by a double-sided mirror polishing machine (Patent Document 7: JP-A-11-309665). There have been problems such as generation of scratches on the back surface of the wafer due to rubbing of the wafers and troublesome bonding operations.
[0013]
[Patent Document 1]
Japanese Utility Model Publication No. 58-129658
[Patent Document 2]
Japanese Patent Laid-Open No. 2-98926
[Patent Document 3]
JP-A-62-297064
[Patent Document 4]
JP-A-63-93562
[Patent Document 5]
JP 2000-124758 A
[Patent Document 6]
JP 2001-192296 A
[Patent Document 7]
JP-A-11-309665
[0014]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances. In a single-sided mirror polishing process of a wafer, particularly a piezoelectric oxide single crystal wafer substrate used for a surface acoustic wave device or the like, handling properties during polishing and after the polishing step, etc. Wafer substrate capable of manufacturing a single-sided mirror wafer having excellent processing accuracy such as high flatness with high reproducibility, without increasing the workability, and without requiring a huge investment in equipment. An object of the present invention is to provide a polishing method and a wafer obtained thereby.
[0015]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have found the following knowledge by devising a wafer substrate holding method in a polishing process in which one side of a wafer substrate is mirror-finished. This has led to the invention.
[0016]
That is, the present invention provides the following wafer substrate polishing method and wafer.
Claim 1:
By interposing a wafer substrate between a polishing cloth and a plate disposed on the polishing surface plate and rotating the polishing surface plate and the plate, respectively, the surface on the polishing cloth side of the wafer substrate is mirrored by the polishing cloth. A method for polishing a wafer substrate, comprising performing mirror polishing in a state in which the plate side surface of the wafer substrate is directly held on the plate by a liquid adsorption force through the liquid.
Claim 2:
A template in which an orientation flat is formed on the wafer substrate and a die hole having the same shape as that of the wafer substrate having the orientation flat is fixed to the plate, and the wafer substrate is fitted into the template die hole. The polishing method according to claim 1, wherein the plates are directly held via a liquid in a combined state.
Claim 3:
The polishing method according to claim 1, wherein the wafer substrate holding surface of the plate is formed so as to gradually protrude toward the wafer substrate side from the peripheral portion toward the central portion.
Claim 4:
The polishing method according to claim 3, wherein the wafer substrate holding surface of the plate is formed on a convex surface having a curvature radius R of 5.0 km or more.
Claim 5:
The polishing method according to claim 1, wherein the wafer substrate is a piezoelectric oxide single crystal substrate.
Claim 6:
The polishing method according to claim 5, wherein the piezoelectric oxide single crystal substrate is a lithium tantalate single crystal substrate.
Claim 7:
A wafer obtained by mirror polishing one side by the polishing method according to claim 1.
[0017]
In the wafer substrate polishing method of the present invention, the mirror polishing step is performed after the back surface of the wafer substrate of the piezoelectric oxide single crystal or the like is roughened, and the wafer of the roughened piezoelectric oxide single crystal or the like is obtained. The back surface side of the substrate is directly held on the plate through the liquid.
[0018]
In this case, since the wafer substrate polishing method of the present invention directly holds the back side of the wafer substrate on the plate via the liquid, the plate shape accuracy has a great influence on the wafer processing accuracy. It is preferable to form a convex shape having a curvature radius R of the wafer substrate holding surface of 5.0 km or more, preferably 9.0 km or more.
[0019]
Here, the radius of curvature means the radius of a circle in contact with the curve, and in this case, as the radius of a circle forming an arc passing through both ends of the plate facing each other around the center of the plate and the center of the plate. Can be easily calculated. For example, in the case of a plate having a diameter of φ485 mm, the radius of curvature R = 5.88 km corresponds to a height difference of 5.0 μm between the edge portions of the plate and the center portion of the plate. Therefore, specifically, when a plate having a diameter of 485 mm is used, it is preferable that the curvature radius R of the plate is a convex shape of 5.0 km or more, particularly 9.0 km or more (that is, as the plate accuracy, the plate is held on the wafer substrate). The protrusion height h at the center of the surface is preferably a convex surface of 0 μm ≦ h ≦ 5 μm, particularly preferably a convex surface of 0 μm ≦ h ≦ 3 μm). The plate may be completely flat (that is, the protruding height of the central portion of the wafer substrate holding surface of the plate is 0 μm), but it is preferable that the central portion protrudes in consideration of controllability of polishing conditions.
[0020]
In this way, when the wafer substrate holding surface of the plate has a convex shape for plate accuracy, the plate itself rotates on the polishing cloth, resulting in a difference in peripheral speed from the peripheral edge of the plate to the central portion. A difference in the polishing rate is generated therein, and the portion corresponding to the central portion of the plate tends to have a low polishing rate, and the portion corresponding to the peripheral portion of the plate tends to increase in the polishing rate. In addition, it is preferable that the shape of the plate is formed so that the surface opposite to the wafer substrate holding surface has the same shape, that is, gradually protrudes toward the rotating shaft as it goes from the peripheral portion toward the central portion.
In addition, although the thickness of a plate is selected suitably, it is preferable normally that it is 10-30 mm.
[0021]
In addition, the wafer substrate polishing method of the present invention is different from the method of bonding and holding a wafer using wax and the method of vacuum-holding and holding a piezoelectric oxide single crystal wafer on a ceramic plate. Therefore, it is preferable that a wafer substrate such as a piezoelectric oxide single crystal is freely rotated at the wafer holding position of the plate during mirror polishing so that the rear surface of the wafer is not rubbed and scratched. Therefore, in order to prevent the wafer substrate from freely rotating at the wafer holding position of the plate, an orientation flat (OF) is formed on the wafer substrate, and the template is punched in the same shape as the wafer substrate with OF. Is preferably used.
[0022]
For templates that have been punched into the same shape as this wafer substrate (with orientation flat (OF)), the orientation flat portion or the peripheral edge portion of the wafer substrate is used so that the wafer substrate can be easily recovered during the wafer substrate recovery operation immediately after the polishing process. It is more preferable to provide a notch about the size of a finger in a part of this.
[0023]
Furthermore, the position where the orientation flat portion is provided is also arranged in the length direction in order to more effectively suppress the wafer substrate from freely rotating in the template punching hole which becomes the wafer substrate holding position of the plate. More preferably, it is formed so that (the linear direction in the figure) substantially faces the rotation direction of the plate. For example, as shown in FIG. 2, it may be provided so as to be opposed to the central portion of the plate. However, in order to extend the use time of the template, the orientation flat portion is almost the same as the rotation direction of the plate as shown in FIG. More preferably, it is formed to face.
[0024]
In the method for polishing a wafer substrate of the present invention, the wafer substrate is directly held on the plate via a liquid such as water. Therefore, since the conventionally used backing material is not interposed, the flatness of the wafer substrate such as a piezoelectric oxide single crystal can be processed with high accuracy. Even if the back surface of a wafer substrate such as a piezoelectric oxide single crystal is roughened and then mirror polishing is performed, and the rough surface of the back surface is directly held by a plate, the wafer substrate is still a plate wafer substrate. By giving a device that does not rotate freely at the holding position, it is possible to suppress the change in the roughness of the back surface within the limit sufficiently effectively.
[0025]
On the other hand, as described above, the wafer substrate adsorption holding itself is performed by, for example, water adsorption, as in the case of using a conventional backing material, so that it is excellent in handleability during mirror polishing and after processing, and work efficiency. In addition, since there is very little possibility that deposits remain on the roughened back surface side, electrode peeling due to the remaining deposits can be prevented.
In addition, there are no major changes in equipment compared to conventional polishing methods using a backing material, and there is no need to invest in incidental equipment.
[0026]
In the present invention, the wafer substrate may be either a round shape or a square shape having at least one plane portion (for example, an orientation flat), and the size is not particularly limited, but the thickness is preferably 5 mm or less. In the present invention, the wafer substrate is preferably a piezoelectric oxide single crystal substrate, and particularly preferably a lithium tantalate single crystal substrate.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a mode for carrying out the present invention will be described taking as an example a case where a piezoelectric oxide single crystal wafer substrate is used as a wafer substrate.
FIG. 1 is a diagram showing a configuration example of a single-side polishing apparatus for explaining a method for manufacturing a piezoelectric oxide single crystal wafer of the present invention. In the figure, reference numeral 1 denotes a polishing surface plate. A polishing cloth 2 is attached to the surface (upper surface) of the polishing surface plate 1 to provide a polishing surface. A drive shaft 3 is fixed to the lower side of the polishing platen 1 and is not shown via the drive shaft 3. However, the polishing platen 1 is rotated at an arbitrary rotational speed by a drive system (for example, a motor). Driven by rotation.
[0028]
A piezoelectric oxide single crystal wafer substrate 5 held on a plate 4 made of, for example, a ceramic plate is set on the polishing surface plate 1 (actually on the polishing cloth 2) as described above. Prior to setting the piezoelectric oxide single crystal wafer substrate 5 on the plate 4, a template 6 (corresponding to FIGS. 2 and 3) having a die-cutting hole 6 a made of, for example, an epoxy glass material is adhered to the plate 4 in advance. Adhering via a tape, the plate 4 is provided with a recess (die-cut hole 6a) that serves as a wafer holding position. The piezoelectric oxide single crystal wafer substrate 5 can be held in the recess by an adsorbing force of the liquid via a liquid such as water. In addition, an orientation flat (OF) 6b is formed on the substrate 5 so that the piezoelectric oxide single crystal wafer substrate 5 does not rotate freely in the recess that is the wafer holding position of the plate 4 during the mirror polishing process. The template 6 is provided with a punching hole 6a having the same shape as that of this wafer (with an orientation flat (OF)).
[0029]
With respect to a template that has been punched into the same shape as this wafer (with orientation flat (OF)), the orientation flat portion or the peripheral portion of the wafer substrate can be easily recovered during the wafer substrate recovery operation immediately after the polishing process. It is more preferable to provide a notch 6c about the size of a finger in part.
[0030]
Further, it is more preferable that the orientation flat portion is provided so as to face the rotation direction of the plate in order to prevent the wafer from freely rotating in the concave portion serving as the wafer holding position of the plate. That is, the position as shown in FIG. 2 may be used, but the position as shown in FIG. 3 is more preferable in order to extend the use time of the template.
[0031]
The plate 4 on which the piezoelectric oxide single crystal wafer substrate 5 is adsorbed and held is rotated by another drive system (not shown) via the rotating shaft 7. Moreover, although illustration is abbreviate | omitted on the polishing cloth 2, an abrasive | polishing agent is supplied from an abrasive | polishing agent supply apparatus. Then, the polishing platen 1 is rotated while supplying the abrasive, and the plate 4 is opposite to the polishing platen 1 while the piezoelectric oxide single crystal wafer substrate 5 is pressed against the polishing cloth 2 by the plate 4. Rotate in the direction. In this way, mirror polishing of the surface of the piezoelectric oxide single crystal wafer substrate 5 (sliding contact surface with the polishing pad 2) is performed.
[0032]
FIG. 4 shows a configuration example of a single-side polishing apparatus in the case where a conventional backing material is used. Compared to the present invention, a backing material 8 is interposed between the plate 4 and the piezoelectric oxide single crystal wafer substrate 5. The polishing mechanism itself is the same as that of the present invention. The piezoelectric oxide single crystal wafer substrate 5 is adsorbed (for example, water adsorbed) to the backing material 8 via a liquid such as water. Since the backing material 8 is an adsorbent made of foamed polyurethane or the like, the piezoelectric oxide single crystal wafer substrate 5 is firmly fixed to the backing material 8. Therefore, the template 9 (corresponding to FIGS. 5 and 6) used in the polishing method can be sufficiently dealt with by punching a circle having substantially the same diameter as the piezoelectric oxide single crystal wafer substrate 5. In addition, 9a is a circular die-cut hole.
[0033]
Next, a manufacturing process of the piezoelectric oxide single crystal wafer according to the embodiment using the above-described single-side polishing apparatus will be described. That is, an oxide single crystal is first grown by, for example, the Czochralski method to obtain an ingot, a plane (orientation flat) is formed in a specified direction, and then this is sliced to a predetermined thickness to obtain a plate. A wafer substrate is obtained. The slice wafer substrate is polished to a desired thickness by double-sided lapping. This slicing and lapping may be performed in the same manner as in the past.
[0034]
The piezoelectric oxide single crystal wafer substrate 5 lapped (roughening the front and back surfaces) as described above is subjected to mirror polishing using the single-side polishing apparatus shown in FIG. In this mirror polishing step, first, the back side of the roughened piezoelectric oxide single crystal wafer substrate 5 is placed in the concave portion of the plate 4 (the die-cut hole 6a of the template 6 fixed to the plate 4), for example, It is adsorbed and held through a liquid such as water.
[0035]
Next, the plate 4 holding the piezoelectric oxide single crystal wafer substrate 5 by suction is set on the polishing surface plate 1 so that the surface to be polished is in contact with the polishing cloth 2. Then, the rotating shaft 7 is slowly lowered from directly above the plate 4 and brought into contact with the plate 4. The plate 4 and the polishing platen 1 are driven to rotate while supplying the abrasive onto the polishing platen 1. The surface of the single crystal wafer substrate 5 (the surface opposite to the roughened surface) is mirror-polished. In the mirror polishing described above, the piezoelectric oxide single crystal wafer substrate 5 is directly held by the plate 4 through a liquid such as water, and the conventionally used backing material 8 is not interposed. Therefore, the processing accuracy of the piezoelectric oxide single crystal wafer substrate 5, for example, the flatness can be increased. Specifically, a 4 inch diameter piezoelectric oxide single crystal wafer substrate TTV (Total Thickness Variation) is 3 μm or less and an LTV at 5 mm × 5 mmsite. _max (Local Thickness Variation) can be mirror polished with a reproducibility with a flatness of 0.5 μm or less.
[0036]
The flatness according to the present invention is determined by TTV (Total Thickness Variation), LTV by optical oblique incidence laser interference method. _max (Local Thickness Variation) can be used as an index. Here, TTV means a difference between the maximum value and the minimum value with respect to the back surface, with the wafer back surface being a reference plane in a state where the wafer is clamped.
[0037]
On the other hand, LTV _max Like the TTV, the height of the maximum value and the minimum value with respect to the back surface in a region where the wafer back surface is clamped and the wafer back surface is divided into squares (5 mm × 5 mm in the present invention). Is the maximum value of the difference.
[0038]
In addition, the adsorption holding of the piezoelectric oxide single crystal wafer substrate 5 is performed by, for example, water adsorption as in the case of using the conventional backing material 8, so that the handleability after mirror polishing is excellent, Since sophisticated cleaning or the like is not required unlike wax bonding, it is possible to prevent a reduction in work efficiency. Furthermore, since there is very little possibility of deposits remaining on the roughened back side, electrode peeling due to the deposits can be prevented, and the yield of surface acoustic wave elements and the like can be improved.
In addition, there is no significant change in equipment compared to the conventional polishing method using the backing material 8, and there is no need to invest in incidental equipment.
[0039]
Thus, according to the embodiment of the method for manufacturing a piezoelectric oxide single crystal wafer described above, by changing the polishing method using the conventional backing material without making any capital investment, the high flatness, etc. Thus, it is possible to improve the workability of the mirror polishing of the piezoelectric oxide single crystal wafer substrate and the workability of the subsequent process. Therefore, it greatly contributes to the improvement of the yield and work efficiency of the surface acoustic wave device using the piezoelectric oxide single crystal wafer.
[0040]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.
[0041]
[Example 1]
As a sample, lithium tantalate (LiTaO) having a diameter of 4 inches was used. ₃ ) A single crystal wafer substrate was used. This single crystal manufactured by the Czochralski (CZ) method is sliced with a wire saw after OF processing, and using an appropriate abrasive (free abrasive) so that the front and back surfaces are in a specified roughness state. The slice wafer substrate was polished to a desired thickness by double-sided lapping.
Thereafter, for the wafer lapped (roughening the front and back surfaces) as described above, a plate having a plate shape with a wafer substrate holding surface having a radius of curvature R = 9.8 km (projection height of 3 μm at the center) is used. Then, mirror polishing was performed using a single-side polishing apparatus as shown in FIG. Specifically, the roughened back surface side of the wafer substrate is brought into contact with water in the recess of the ceramic plate 4 (in the die-cut hole 6a of the template 6), and the plate 4 is polished in this state. 1 was set so that the surface to be polished was in contact with the polishing cloth 2. Next, the rotary shaft 7 is slowly lowered from directly above the plate 4 and brought into contact with the plate 4. While supplying the abrasive made of colloidal silica onto the polishing cloth 2, the pressure is gradually increased, and after rotating slowly, the specified rotational speed is maintained. While applying a predetermined pressure, mirror polishing was performed. In order to remove the abrasive and particles of colloidal silica adhering to the wafer surface after this mirror polishing, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution.
[0042]
When such a process was performed on 100 wafer substrates and the flatness was measured, the LTV was 0.78 to 2.89 μm by TTV and 5 mm × 5 mmsite. _max It was 0.21-0.48 micrometer.
Further, when the back surface of the wafer substrate was observed under a fluorescent lamp, no scratch was found.
[0043]
[Comparative Example 1]
Using a single-side polishing apparatus as shown in FIG. 4, a curvature radius R = 9.8 km with a backing material (backing material: foamed polyurethane, thickness 0.4 mm) as shown in FIG. Mirror polishing was performed in the same manner as in Example 1 except that a plate having a plate shape with a projection height of 3 μm at the center was used. In order to remove the abrasive and particles of colloidal silica adhering to the wafer substrate surface after the mirror polishing, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution.
[0044]
When such a process was performed on 100 wafer substrates and the flatness was measured, LTV at 2.18 to 4.68 μm, 5 mm × 5 mmsite by TTV. _max It was 0.78 to 2.08 μm.
When the back surface of the wafer substrate was observed under a fluorescent lamp, no scratches were observed.
[0045]
[0046]
As described above, the processing accuracy of the wafer substrate flatness is superior to that of the comparative example, and the metal electrodes can be formed according to the designed pattern over the entire surface of the wafer substrate, so that the device yield can be improved. Can do. Further, since there is no rubbing scratch on the back surface of the wafer substrate, it is possible to avoid worrying about cracks due to scratches.
[0047]
In the embodiment, a lithium tantalate wafer having a diameter of 4 inches has been described as an example. However, the present invention relates to lithium tantalate, lithium niobate, crystal, lithium tetraborate, or langasite used for a surface acoustic wave filter or the like. The piezoelectric oxide single crystal wafer such as the above is effective, and the thickness and diameter are not limited to the above examples.
[0048]
In addition to the piezoelectric oxide single crystal wafer, the wafer can be applied to any material as long as it is a wafer-like substrate having only one side mirrored, such as a silicon wafer, a compound semiconductor wafer, or a synthetic quartz wafer.
[0049]
【The invention's effect】
According to the method for polishing a wafer substrate of the present invention, it is possible to improve processing accuracy such as flatness while improving workability during mirror polishing and subsequent processes. And by using such a single-sided mirror polished wafer, it becomes possible to improve the yield in the subsequent device fabrication process.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the configuration of a single-side polishing apparatus used in an embodiment of a wafer substrate polishing method of the present invention.
FIG. 2 is a plan view showing an example of a template shape used in the embodiment of the wafer substrate polishing method of the present invention.
FIG. 3 is a plan view showing another example of the template shape used in the embodiment of the wafer substrate polishing method of the present invention.
FIG. 4 is a schematic cross-sectional view showing a configuration of a single-side polishing apparatus used in a conventional wafer substrate polishing method.
FIG. 5 is a plan view showing an example of a template shape used in a conventional wafer substrate polishing method.
FIG. 6 is a plan view showing an example of a template shape used in a comparative form.
[Explanation of symbols]
1 Polishing surface plate
2 Abrasive cloth
3 Drive shaft
4 plates
5 wafers
6,9 template
7 Rotating shaft
8 Backing material

Claims (7)

By interposing a wafer substrate between a polishing cloth and a plate disposed on the polishing surface plate and rotating the polishing surface plate and the plate, respectively, the surface on the polishing cloth side of the wafer substrate is mirrored by the polishing cloth. A method for polishing a wafer substrate, comprising performing mirror polishing in a state where the surface of the wafer substrate on the plate side is directly held on the plate by a liquid adsorption force through the liquid. A template in which an orientation flat is formed on the wafer substrate and a die-cutting hole having the same shape as the wafer substrate having the orientation flat is fixed to the plate, and the wafer substrate is fitted into the die-cutting hole of the template. The polishing method according to claim 1, wherein the plates are directly held via a liquid in a combined state. The polishing method according to claim 1, wherein the wafer substrate holding surface of the plate is formed so as to gradually protrude toward the wafer substrate side from the peripheral portion toward the central portion. The polishing method according to claim 3, wherein the wafer substrate holding surface of the plate is formed on a convex surface having a curvature radius R of 5.0 km or more. The polishing method according to claim 1, wherein the wafer substrate is a piezoelectric oxide single crystal substrate. The polishing method according to claim 5, wherein the piezoelectric oxide single crystal substrate is a lithium tantalate single crystal substrate. A wafer obtained by mirror polishing one side by the polishing method according to claim 1.

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