JP2007090515A - Wafer polishing method and wafer - Google Patents

Abstract

A wafer substrate is interposed between a polishing cloth 2 and a plate 4 disposed on a polishing surface plate 1, and each of the polishing surface plate 1 and the plate 4 is rotated to thereby rotate the polishing substrate side of the wafer substrate. In this method, the surface of the wafer substrate is mirror-polished by the polishing cloth 2 and the wafer substrate is subjected to mirror polishing in a state in which the plate-side surface of the wafer substrate is directly held by the plate 4 by the liquid adsorption force through the liquid. Method.
According to the polishing method of a wafer substrate such as a piezoelectric oxide single crystal wafer of the present invention, the mechanical strength of the wafer substrate itself such as a thin piezoelectric oxide single crystal wafer such as a plate thickness of 100 μm or less is reduced. Thus, a wafer having excellent processing accuracy such as high flatness and high parallelism can be stably manufactured without causing problems such as a decrease in yield due to breakage during lapping or mirror polishing.
[Selection] Figure 1

Description

  The present invention relates to a wafer polishing method for mirror polishing a lithium tantalate single crystal wafer or the like used for a surface acoustic wave filter or the like, and a wafer obtained thereby.

  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. .

  The surface acoustic wave element is configured by using an oxide single crystal wafer exhibiting piezoelectricity 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 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.

  That is, these wafers are conventionally manufactured as follows. That is, for example, a single crystal ingot obtained by the Czochralski method or the like is cut using a slicer for an inner peripheral blade or a wire saw to obtain a plate-like wafer, and both sides of the obtained wafer are wrapped to a predetermined thickness. Then, only one surface is mirror-polished by a polishing apparatus, and the surface is washed after the polishing is finished.

  In recent years, along with the downsizing of devices such as PHS and mobile phones, the surface acoustic wave elements mounted on the devices have also been reduced in height, and piezoelectric oxide single crystal wafers used for surface acoustic wave filters and the like. The demand for thinner products is also increasing.

  For example, in the case of a lithium tantalate single crystal wafer used for a surface acoustic wave filter or the like, a plate thickness of 350 μm is currently common, but studies of thinner wafers with a plate thickness of 250 μm have begun.

  Furthermore, in the above-described element using surface acoustic waves, the required thickness of the piezoelectric oxide single crystal is theoretically calculated to be 10 times the wavelength, and a plate thickness of about 50 μm is sufficient in the present situation. it is conceivable that. Therefore, after obtaining a piezoelectric oxide single crystal wafer having a plate thickness of 350 μm at a device manufacturer, a metal electrode pattern is formed on the mirror surface side of the wafer by, for example, photoengraving, and finally the wafer is ground using a surface grinding method or the like. Consideration of processes such as scraping off unnecessary parts from the back side has also begun.

  From such a background, it can be expected that, as a wafer manufacturer, supplying a thinner piezoelectric oxide single crystal wafer can contribute to a reduction in man-hours at the device manufacturer. However, as the plate thickness of the piezoelectric oxide single crystal wafer becomes thinner in this way, the mechanical strength of the wafer itself is lowered, and there is a concern that the yield may be lowered due to damage in the wafer manufacturing process.

  In particular, in the processing process of the piezoelectric oxide single crystal wafer for the surface acoustic wave device described above, even if a relatively thick plate-shaped wafer can be prepared in advance by cutting, the target plate is used in the subsequent lapping and mirror polishing processes. There is a concern that the risk of wafer breakage due to a decrease in mechanical strength is greatly increased because the wafer must be processed to a thin thickness.

  On the other hand, when a piezoelectric oxide single crystal wafer is used as a surface acoustic wave filter, the transducer surface of the single crystal wafer needs to be mirror-polished because the surface acoustic wave is excited and received by the transducer. In order to eliminate unnecessary waves (disturbance waves) such as bulk waves excited and received simultaneously with excitation and reception of surface acoustic waves, the back surface of this single crystal wafer is roughened by polishing (lapping) or honing with a coarse abrasive. It is necessary to keep.

In addition, the following literature is mentioned as a prior art relevant to this invention.
Japanese Utility Model Publication No. 58-129658 Japanese Patent Laid-Open No. 2-98926 JP-A-62-297064 JP-A-63-93562

  When manufacturing thin wafers with a plate thickness of 100 μm or less in the processing process of piezoelectric oxide single crystal wafers used in conventional surface acoustic wave devices, etc., the wafers have good yield due to a decrease in the mechanical strength of the wafers themselves. It is difficult to manufacture.

  For this reason, in the processing process of thin piezoelectric oxide single crystal wafers with a plate thickness of 100 μm or less used for surface acoustic wave elements, etc., lapping and mirror surfaces accompanying the decrease in mechanical strength of the wafer itself Piezoelectricity such as the current plate thickness of 350μm, while maintaining the same front and back surface state as the piezoelectric oxide single crystal wafer such as the current plate thickness of 350μm, without causing problems such as a decrease in yield due to breakage during polishing. The problem is to stably manufacture a wafer having excellent processing accuracy such as high flatness and high parallelism equivalent to those of an oxide single crystal wafer.

  That is, the object of the present invention is to increase the prevention of breakage due to a decrease in mechanical strength at the time of lapping or mirror polishing of a wafer such as a thin piezoelectric oxide single crystal wafer having a thickness of 100 μm or less. Piezoelectric oxide single crystal wafers, etc. that enable the maintenance of the yield at the time of manufacturing 350 μm wafers and realize processing accuracy such as front and back surfaces and flatness and parallelism equivalent to the current plate thickness of 350 μm A wafer polishing method and a wafer obtained by the polishing method are provided.

  As a result of intensive studies to solve the above problems, the present inventors have performed a lapping process for wafers such as a thin piezoelectric oxide single crystal wafer having a thickness of 100 μm or less and a polishing process for mirror-finishing the wafer surface. The inventors have found that the following method is effective, in particular, that it is effective to increase the mechanical strength by bonding a piezoelectric oxide single crystal wafer to a support substrate (support substrate), and have led to the present invention.

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 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.
Claim 2:
When the diameter of the wafer substrate is Dmm, a template in which a die-cutting hole having a size of D to D + 5.0 mm is fixed to the plate, and the wafer substrate is fitted in the die-cutting hole of the template. 2. The polishing method according to claim 1, wherein the plate is directly held on the plate via a liquid.
Claim 3:
3. The polishing method according to claim 2, wherein the wafer substrate is bonded to a support substrate having a size of D to D + 2.5 mm, and one side surface of the wafer substrate is mirror-polished in this state.
Claim 4:
A polishing carrier in which a die-cut hole is formed is arranged between polishing cloths arranged on a pair of upper and lower polishing surface plates, and a wafer substrate is interposed in the die-cut hole of the polishing carrier, and the pair of polishings In the method in which the front and back surfaces of the wafer substrate are mirror-polished by the polishing cloth by rotating the platen respectively, when the diameter of the wafer substrate is D mm, the support substrate and the wafer substrate having a size of D to D + 2.5 mm And is set in a die-cutting hole having a size of D to D + 5.0 mm, and in this state, one side of the wafer substrate and the support substrate is mirror-finished.
Claim 5:
5. The polishing method according to claim 3, wherein the wafer substrate and the support substrate are made of the same material.
Claim 6:
6. The wafer polishing method according to claim 5, wherein the same polarization surfaces of the wafer substrate and the support substrate are bonded together.
Claim 7:
A wafer obtained by the polishing method according to claim 1.
Claim 8:
The wafer according to claim 7, wherein the wafer is a piezoelectric oxide single crystal.
Claim 9:
9. The wafer according to claim 8, wherein the piezoelectric oxide single crystal wafer is lithium tantalate.
Claim 10:
The single crystal wafer according to claim 9, wherein the lithium tantalate single crystal wafer has a thickness of 100 μm or less.

  According to the method for polishing a wafer substrate such as a piezoelectric oxide single crystal wafer according to the present invention, a lap associated with a decrease in mechanical strength of the wafer substrate itself such as a thin piezoelectric oxide single crystal wafer having a thickness of 100 μm or less. While maintaining the same front and back surface state as a wafer substrate such as a piezoelectric oxide single crystal wafer such as a current plate thickness of 350μm without causing problems such as a decrease in yield due to breakage during processing and mirror polishing It is possible to stably manufacture a wafer having excellent processing accuracy such as high flatness and high parallelism equivalent to a wafer substrate such as a piezoelectric oxide single crystal wafer having a thickness of 350 μm. And, by using a wafer substrate such as a piezoelectric oxide single crystal wafer for the device, it is possible to cut off unnecessary portions from the back surface of the wafer by using a surface grinding method or the like in the last step of the device manufacturing process. It can contribute to reduction.

  The method for polishing a wafer substrate according to the present invention comprises polishing a wafer substrate by interposing the wafer substrate between a polishing cloth and a plate disposed on a polishing surface plate and rotating the polishing surface plate and the plate, respectively. In the method in which the cloth side surface is mirror-polished with the polishing cloth, the plate side surface of the wafer substrate is directly mirror-polished with the liquid adsorbing force through the liquid. is there. Further, by interposing a wafer substrate between polishing cloths arranged on a pair of upper and lower polishing surface plates and rotating the pair of polishing surface plates, the front and back surfaces of the wafer substrate are mirror-polished by the polishing cloths. In this method, when the diameter of the wafer substrate is D mm, a polishing carrier in which a die-cutting hole having a size of D to D + 5.0 mm is formed is used.

  In the wafer polishing method of the present invention, the mirror polishing step is performed after the back surface of the wafer substrate is roughened, and the wafer substrate (product substrate) and the support substrate (support substrate) are bonded with wax, an adhesive, or the like. It is effective to hold the support substrate (support substrate) side directly on the plate via the liquid in this state.

  In this case, it is necessary to fix and hold the wafer at an arbitrary position on the plate, and the same diameter as the bonded substrate is not less than +5.0 mm (provided that the diameter of the wafer substrate is D mm, D + 5.0 mm or less), preferably A template in which a die-cutting hole having the same diameter and +2.5 mm or less is formed is fixed to the plate, and the bonded substrate is fitted in the die-cutting hole of the template and directly held on the plate via a liquid. It is preferable to do.

  In the wafer polishing method of the present invention, the mirror polishing step is performed after the back surface of the wafer is roughened, and the wafer substrate (product substrate) and the support substrate (support substrate) are bonded with wax or adhesive. In this state, the bonded substrate is interposed between the polishing cloths arranged on the pair of upper and lower polishing surface plates, and the pair of polishing surface plates are rotated, respectively. It is effective to mirror-polish the back surface with the polishing cloth.

  In this case, in the method for polishing a wafer substrate of the present invention, the bonded substrate is preferably planetarily moved between polishing cloths arranged on a pair of upper and lower polishing surface plates. It is preferable to use a polishing carrier in which a punched hole having a diameter of not less than the same diameter and not more than +2.5 mm is formed, where 0 mm or less (however, when the diameter of the wafer substrate is D mm, D + 5.0 mm or less).

  Here, as for the support substrate (support substrate), any material can be used as long as it has a diameter equal to or larger than that of the wafer substrate (product substrate). The same diameter as that of the substrate) and +2.5 mm or less, preferably the same diameter or more and +1.0 mm or less. In addition, the thickness of the support substrate (support substrate) is not specified, and in consideration of the mechanical strength of the wafer after bonding, it is preferably a thicker substrate, usually formed to a thickness of 0.1 to 30 mm. be able to.

  Regarding the support substrate (support substrate), when heat treatment is performed at the time of bonding, the wafer substrate (product substrate) is warped, so the thermal expansion coefficient and thermal expansion behavior equivalent to those of the wafer substrate (product substrate) are exhibited. The material which has is preferable, and it is preferable to bond together so that a thermal expansion behavior may express in the direction which mutually opposes. Specifically, by preparing a support substrate (support substrate) of the same material as the wafer substrate (product substrate) and bonding the same polarization surfaces of the wafer substrate (product substrate) and the support substrate (support substrate) together, Mutual warpage is corrected, which is preferable.

  Also, by preparing a support substrate (support substrate) made of the same material as the wafer substrate (product substrate) as described above, and bonding the same polarization surfaces of the wafer substrate (product substrate) and the support substrate (support substrate) together Since it is possible to form a bonded substrate in which mutual warpage is corrected, not only the wafer substrate (product substrate) obtained by polishing this substrate by the single-side polishing method but also the wafer substrate (product) polished by the double-side polishing method can be used. Substrate) and support substrate (support substrate) can be commercialized.

  In this way, the reduction in mechanical strength of thin wafers with a plate thickness of 100 μm or less can be compensated for by bonding, so the yield reduction due to breakage during mirror polishing can be avoided, and the wafer substrate (product substrate) and support substrate ( By appropriately selecting wax, adhesive or the like interposed between the supporting substrates), processing accuracy such as flatness and parallelism equivalent to the current 350 μm thick wafer can be realized.

  In addition, a relatively thick plate-like wafer is prepared in advance by cutting, and after producing a wafer lapped to a thickness equivalent to that at the time of manufacturing a current plate thickness of 350 μm, the above-mentioned bonding step and polishing step are performed to obtain the plate thickness Although it is possible to obtain a thin wafer of 100 μm or less, the surface side to be finally mirror-polished in the same manner as described above for the relatively thick plate-like wafer obtained by cutting is a support substrate (support substrate) and wax or adhesive. It is possible to form the back surface of the wafer in a rough surface state suitable for device characteristics by laminating and lapping via, for example. After this process, the wafer substrate (product substrate) and the support substrate (support substrate) are peeled off, and the back side of the roughened wafer is pasted again with the support substrate (support substrate) and wax or adhesive. By combining and mirror polishing, a final wafer front and back surface state is formed.

  As described above, the wafer substrate (product substrate) and the support substrate (support substrate) are bonded to each other, and lapping and mirror polishing are performed, resulting in a decrease in mechanical strength of the thin wafer itself having a thickness of 100 μm or less. Without causing problems such as a decrease in yield due to breakage during lapping and mirror polishing, while maintaining the same front and back surface state as a wafer with a current plate thickness of 350 μm, it is equivalent to a wafer with a current plate thickness of 350 μm. A wafer having excellent processing accuracy such as high flatness and high parallelism can be manufactured stably.

  Here, the method of the present invention will be described more specifically with reference to the drawings. First, FIG. 3 is a diagram showing a configuration example of a single-side polishing apparatus for explaining a conventional wafer manufacturing method. In the figure, reference numeral 1 denotes a polishing surface plate. A polishing cloth 2 is affixed to the 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 surface plate 1, and the illustration is omitted via the drive shaft 3, but the polishing surface plate 1 is rotated at an arbitrary rotational speed by a drive system (for example, a motor). Driven.

  A wafer 5 such as a piezoelectric oxide single crystal wafer held on a plate 4 made of a ceramic plate, for example, is set on the polishing surface plate 1 (actually on the polishing cloth 2) as described above. Various methods for setting the wafer 5 on the plate 4 have been proposed. For example, as proposed in Japanese Utility Model Laid-Open No. 58-129658, there is a method in which the plate 4 and the wafer 5 are bonded and set via wax. Further, as proposed in Japanese Patent Application Laid-Open No. 2-98926, there is a method in which the wafer 5 is vacuum suction set by providing innumerable suction holes in the portion of the plate 4 that holds the wafer. Further, as proposed in Japanese Patent Application Laid-Open Nos. 62-297064 and 63-93562, an adsorbent made of foamed polyurethane or the like called backing material (back pad) 15 is applied to the plate 4 as a double-sided tape. There is a method in which the wafer 5 is adsorbed and fixed by, for example, and the wafer 5 is adsorbed on the adsorbent and set. In FIG. 3, 6 is a template, and 8 is a rotating shaft.

  Of these, the method of directly adhering and holding the wafer to the plate via wax is excellent in processing accuracy such as flatness and parallelism, but requires an adhesion technique, and in the case of a thin wafer having a plate thickness of 100 μm or less, it has mechanical strength. From this point of view, there is a problem that cracks and the like are likely to occur when peeling from the plate.

  In addition, the method of directly holding the wafer by vacuum suction on the plate is excellent in processing accuracy such as flatness and parallelism. However, if a foreign substance is present between the wafer and the plate, the portion is extremely polished and distorted. There is a high risk of causing In particular, in the case of a thin wafer having a plate thickness of 100 μm or less, dents appear remarkably. 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.

  On the other hand, the method of adsorbing and holding a wafer using a backing material does not have the above-mentioned problems, and by changing the thickness of the template, it is possible to polish even a thin wafer having a thickness of 100 μm or less. Due to the variation in the thickness of the adsorbent, there are problems that the processing accuracy such as the flatness and parallelism of the wafer is likely to be lowered, and that the wafer is liable to be bent on the outer periphery of the wafer.

  In view of such a background, the present invention employs a method in which a wafer is directly held on a plate by the adsorption force of the liquid via the liquid. That is, FIG. 1 is a diagram showing a configuration example of a single-side polishing apparatus for explaining a method for manufacturing a thin wafer having a thickness of 100 μm or less according to the present invention. The polishing method and the polishing mechanism are the same as in FIG. The back side of a wafer (product substrate) 5a whose surface has been roughened in advance is bonded to a support substrate (support substrate) 5b of the same diameter via wax, adhesive or the like. The bonded substrate 5ab is polished on one side in the same manner as the wafer 5 shown in FIG. 3, so that only one side of the wafer (product substrate) 5a is mirror-polished. More specifically, prior to setting the wafer 5 on the plate 4, a template 6 having a punched hole made of, for example, an epoxy glass material is bonded and fixed to the plate 4 with double-sided tape or the like in advance. A concave portion (die-cut hole) 7 is provided. The wafer 5 can be held in the recess 7 by an adsorbing force of the liquid via a liquid such as water. However, in this holding method, there is a possibility that the wafer 5 is rubbed and scratched on the back surface of the wafer 4 by freely rotating in the recess 7 that is the wafer holding position of the plate 4 during the mirror polishing process. In such a case, as shown in FIG. 1, a substrate 5ab in which a wafer (product substrate) 5a and a support substrate (support substrate) 5b are bonded together with wax or adhesive is prepared, and a support substrate (support substrate) is prepared. The substrate (5b) side surface is held on the plate 4 by an adsorbing force of the liquid via a liquid such as water, so that the support substrate (support substrate) 5b is rubbed and scratched, but the wafer (product substrate) 5a The back surface of the substrate can be polished so as not to be rubbed and scratched. In addition, a thin piezoelectric oxide single crystal wafer (product substrate) 5a having a plate thickness of 100 μm or less can be advantageously manufactured.

  Each of these is a method in which only one surface of the wafer 5, that is, the sliding contact surface with the polishing pad 2 is mirror-polished. That is, the plate 4 holding the wafer 5 is rotationally driven by another drive system (not shown) via the rotary shaft 8. Further, although not shown in the figure, the abrasive is supplied from the abrasive supply device onto the polishing cloth 2. Then, the polishing platen 1 is rotated while supplying the abrasive, and the plate 4 is rotated in the opposite direction to the polishing platen 1 while the wafer 5 is pressed against the polishing cloth 2 by the plate 4. In this way, the mirror polishing of the surface of the wafer 5 (the sliding contact surface with the polishing pad 2) is performed.

  In the peeling step after the mirror polishing, the bonded substrate 5ab is peeled off to the wafer (product substrate) 5a and the support substrate (support substrate) 5b, and the support substrate (support substrate) 5b is not changed in thickness. Therefore, it can be reused as a support substrate (support substrate). Of course, if the support substrate (support substrate) 5b is made of the same material as the wafer (product substrate) 5a, it can be mirror-polished as the wafer (product substrate) 5a during the next mirror polishing process.

  Next, FIG. 2 shows a configuration example of a double-side polishing apparatus for explaining a method for manufacturing a wafer such as a thin piezoelectric oxide single crystal wafer having a thickness of 100 μm or less according to the present invention. In the figure, reference numerals 1 and 1 'denote polishing surface plates, and these polishing surface plates are arranged to face each other. Polishing cloths 2, 2 'are affixed to the opposing surfaces of these polishing surface plates 1, 1' to provide a polishing surface. Drive shafts 3 and 3 ′ are fixed to the polishing surface plates 1 and 1 ′, respectively, and the illustration is omitted through the drive shafts 3 and 3 ′. The polishing surface plates 1, 1 'are driven to rotate in the same direction or in the opposite direction at an arbitrary rotational speed.

  Between the pair of upper and lower polishing surface plates 1, 1 '(actually polishing cloths 2, 2'), there is an arrangement hole 10 for the bonded substrate 5ab (wafer (product substrate) 5a and support substrate (support substrate) 5b). A polishing carrier 9 having The polishing carrier 9 has a planetary gear meshed with the sun gear 12 of the central drive shaft 11 and the internal gear 14 of the outer peripheral member 13 on the outer periphery thereof, and the drive shaft 11 is rotated to drive the drive shaft. 11 is configured to make a planetary movement around. Further, although not shown, an abrasive is supplied between the upper and lower pair of polishing cloths 2 and 2 ′ from an abrasive supply device.

  Under such a configuration, a predetermined pressure is applied to the bonded substrate 5ab set in the arrangement hole 10 of the polishing carrier 9 with a pair of upper and lower polishing surface plates 1, 1 ′, and the polishing agent While rotating the lower polishing platen 1 and the upper polishing platen 1 ′, the polishing carrier 9 on which the bonded substrate 5ab is disposed is moved in a planetary motion. In this way, mirror polishing is performed on only one surface of the surface of the wafer (product substrate) 5a and the surface of the support substrate (support substrate) 5b (the sliding contact surface with the polishing cloths 2 and 2 ').

  In the peeling step after the mirror polishing process, the bonded substrate 5ab is peeled off to the wafer (product substrate) 5a and the support substrate (support substrate) 5b. Since the support substrate (support substrate) 5b is mirror-polished on one side, the plate thickness is thin. If the thickness cannot compensate for the mechanical strength of the wafer (product substrate) 5a, it cannot be reused. Otherwise, it can be reused as a support substrate (support substrate). Of course, if the support substrate (support substrate) 5b is made of the same material as the wafer (product substrate) 5a, and the wafer (product substrate) 5a and the support substrate (support substrate) 5b are bonded together with the same polarization plane. The support substrate (support substrate) 5b can also be processed as the same product substrate as the wafer (product substrate) 5a.

  Here, for example, as proposed in Japanese Patent Application Laid-Open No. 11-309665, two wafers 5 are stacked via a suction plate or the like, set in the arrangement hole 10 of the polishing carrier 9, and 2 It is also under consideration to mirror-polish the outer surface of each of the wafers 5 (the sliding contact surface with the polishing cloths 2 and 2 '). However, in the case of this method, since the wafers are not firmly bonded to each other, there is a concern about the occurrence of scratches on the back surface of the wafer due to the wafers rubbing with each other, and at the same time, the mechanical strength of the wafer is not compensated, The present invention is not suitable for manufacturing a thin wafer having a thickness of 100 μm or less.

  Next, a wafer manufacturing process according to the embodiment using the above-described single-side polishing apparatus and double-side polishing apparatus will be described. First, a wafer is grown by, for example, the Czochralski method to obtain its ingot, and then this is sliced to a predetermined thickness to obtain a plate-like wafer. This sliced wafer 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.

  Regarding the wafer (product substrate) 5a lapped (roughening the front and back surfaces) as described above, the back side is the same diameter or more and +2.5 mm or less (that is, when the diameter of the wafer is Dmm, D to D + 2. 5 mm), preferably a support substrate (support substrate) 5b having the same diameter or more and a size of +1.0 mm or less (D to D + 1.0 mm), and is bonded to each other through wax or an adhesive.

  The support substrate (support substrate) 5b has the same diameter as that of the wafer (product substrate) 5a and +2.5 mm or less (D to D + 2.5 mm), preferably the same diameter or more and +1.0 mm or less (D to D + 1.0 mm). Any material can be used as long as it has a diameter of 5 mm. However, considering the number of wafers filled in the polishing apparatus, it is preferable that the wafer (product substrate) 5a and the support substrate (support substrate) 5b have the same diameter. In addition, the thickness of the support substrate (support substrate) 5b is not specified, and the thicker support substrate (support substrate) 5b is preferable in consideration of the mechanical strength of the wafer after bonding.

  Regarding the support substrate (support substrate) 5b, when heat treatment is performed at the time of bonding, the wafer (product substrate) 5a is warped, so that the thermal expansion coefficient and thermal expansion behavior equivalent to those of the wafer (product substrate) 5a are generated. It is preferable to bond together so that the thermal expansion behavior is expressed in a direction opposite to each other. Specifically, a support substrate (support substrate) 5b made of the same material as the wafer (product substrate) 5a is prepared, and the same polarization surfaces of the wafer (product substrate) 5a and the support substrate (support substrate) 5b are bonded together. Therefore, the warpage of each other is corrected, which is preferable.

  The wafer (bonded substrate) 5ab bonded in this way is mirror-polished using the single-side polishing apparatus shown in FIG. In this mirror polishing step, first, the support substrate (support substrate) 5b surface of the bonded substrate 5ab is set on the plate 4.

  Next, the plate 4 holding the bonded substrate 5ab 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 8 is slowly lowered from directly above the plate 4 and brought into contact with the plate 4, and the plate 4 and the polishing surface plate 1 are driven to rotate while supplying the abrasive onto the polishing surface plate 1, whereby the wafer (product substrate) is driven. ) The surface of 5a (sliding contact surface with the polishing pad 2) is mirror-polished.

  At this time, even if the wafer (product substrate) 5a is a thin wafer having a plate thickness of 100 μm or less, it is bonded to the support substrate (support substrate) 5b through wax or adhesive, so that the plate thickness is reduced. The reduction in the mechanical strength of the wafer (product substrate) 5a accompanying this is compensated, and mirror polishing can be performed in the same manner as the current 350 μm thick wafer.

  Further, the wafer (bonded substrate) 5ab bonded in this way is subjected to mirror polishing using the double-side polishing apparatus shown in FIG. In this mirror polishing process, first, the bonded substrate 5ab is set in the arrangement hole 10 of the polishing carrier 9.

  Next, the polishing carrier 9 on which the bonded substrate 5ab is disposed is sandwiched between a pair of upper and lower polishing surface plates 1, 1 ', and the surface to be polished is set in contact with the polishing cloth 2, 2'. Then, a predetermined pressure is applied between the pair of upper and lower polishing surface plates 1, 1 ′, and an abrasive is supplied between the pair of upper and lower polishing cloths 2, 2 ′, while the lower polishing surface plate 1 and the upper polishing surface plate 1 ′. And rotating the polishing carrier 9 on which the bonded substrate 5ab is arranged in a planetary motion, the surface of the wafer (product substrate) 5a (the sliding contact surface with the polishing pad 2) and the support substrate (supporting substrate) 5b. The surface (sliding contact surface with the polishing pad 2 ') is mirror-polished.

  At this time, even if the wafer (product substrate) 5a is a thin wafer having a plate thickness of 100 μm or less, it is bonded to the support substrate (support substrate) 5b through wax or adhesive, so that the plate thickness is reduced. The reduction in the mechanical strength of the wafer (product substrate) 5a accompanying this is compensated, and mirror polishing can be performed in the same manner as the current 350 μm thick wafer.

  Further, the support substrate (support substrate) 5b is made of the same material as the wafer (product substrate) 5a, and the same polarization planes of the wafer (product substrate) 5a and the support substrate (support substrate) 5b are bonded to each other. The support substrate 5b can be processed as the same product substrate as the wafer (product substrate) 5a.

  The bonded substrate 5ab after the mirror polishing is peeled off into the wafer (product substrate) 5a and the support substrate (support substrate) 5b in the peeling step. The wafer (product substrate) 5a is not subjected to any processing on the back surface, and the front surface is mirror-polished like the current 350 μm wafer thickness, so the front and back surfaces are equivalent to the current 350 μm wafer thickness. At the same time, it has excellent processing accuracy such as high flatness and high parallelism equivalent to the current 350 μm thick wafer.

  As described above, according to the embodiment of the wafer manufacturing method described above, there is a problem in yield reduction due to breakage at the time of lapping or mirror polishing due to a decrease in mechanical strength of a thin wafer itself having a plate thickness of 100 μm or less. Thus, it is possible to stably manufacture a wafer having excellent processing accuracy such as high flatness and high parallelism while maintaining a front and back surface state equivalent to that of a wafer having a thickness of 350 μm. Therefore, it greatly contributes to the improvement of the yield and working efficiency of the surface acoustic wave device using a thin wafer having a thickness of 100 μm or less, which is increasingly required to be thin. In this case, according to the present invention, it is possible to polish to a thickness of about 50 μm.

  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.

[Example 1]
As a sample, a lithium tantalate (LiTaO ₃ ) single crystal wafer having a diameter of 4 inches (100 mm) was used. This single crystal manufactured by the Czochralski (CZ) method is sliced using a wire saw, and this slice wafer is used using an appropriate abrasive (free abrasive grains) so that the front and back surfaces are in a specified roughness state. Was polished to a desired thickness with double-sided lapping.
Thereafter, with respect to the two wafers lapped (roughening the front and back surfaces) as described above, using the wax (Nippon Seiko Co., Ltd. Sky Liquid TW-2511), the back surfaces (the same polarization surface) To each other). According to this bonding method, the two wafers of the same material are bonded so that the thermal expansion behavior appears in a direction opposite to each other even though heat treatment is performed at the time of bonding. Is corrected and can be easily put into the polishing process.

  Therefore, the bonded substrate 5ab was subjected to mirror polishing using a single-side polishing apparatus as shown in FIG. Specifically, a template 6 having a punched hole (hole diameter φ100.8 mm) made of an epoxy glass material is bonded and fixed to the ceramic plate 4 with double-sided tape in advance, and a concave portion (wafer holding position on the plate 4) ( 7) was provided. In this recess 7, the 5b side of the bonded substrate 5ab is held by the surface tension of water through water, and in this state, the plate 4 is placed on the polishing surface plate 1 and the surface to be polished is in contact with the polishing cloth 2. Set. Next, the rotary shaft 8 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.

After this mirror polishing, the bonded substrate 5ab is taken out from the recess 7 of the ceramic plate 4, and further subjected to heat treatment to obtain two wafers (a wafer (product substrate) 5a and a support substrate (support substrate) 5b). It peeled. With respect to these wafers, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution in order to remove the abrasive, particles, and wax that are colloidal silica adhering to the wafer surface.
After cleaning, when the thickness of each wafer (wafer (product substrate) 5a and support substrate (support substrate) 5b) was measured with a stylus type thickness meter, the thickness of the wafer (product substrate) 5a was 90 to 100 μm. On the other hand, the thickness of the support substrate (support substrate) 5b was the same as before the introduction of the single-side polishing apparatus. Furthermore, when the back surfaces of the respective wafers (wafer (product substrate) 5a and support substrate (support substrate) 5b) were observed under a fluorescent lamp, no generation of scratches was observed. In addition, since the wafer used as the support substrate (support substrate) 5b was not damaged on the back surface, the same mirror polishing process was performed as the wafer (product substrate) 5a in the next batch.

When such a process was performed on 100 wafers and the flatness of the wafer (product substrate) 5a was measured, the TTV (Total Thickness Variation) was 0.85 to 2.53 μm and the LTV _{max. At} 5 mm × 5 mm site _. It was 0.24-0.41 micrometer in (Local Thickness Variation Maximum). Further, no wafer cracking or the like occurred during the single-side polishing process, and a slight crack occurred when the two wafers after the mirror polishing process were peeled off, and the yield was 97%.

[Example 2]
As a sample, a lithium tantalate (LiTaO ₃ ) single crystal wafer having a diameter of 4 inches (100 mm) was used. This single crystal manufactured by the Czochralski (CZ) method is sliced using a wire saw, and this slice wafer is used using an appropriate abrasive (free abrasive grains) so that the front and back surfaces are in a specified roughness state. Was polished to a desired thickness with double-sided lapping.
Thereafter, for the two wafers lapped (roughening the front and back surfaces) as described above, using wax (Nippon Seiko Co., Ltd., Sky Liquid TW-2511), the surface sides (same polarization surfaces) ). According to this bonding method, the two wafers of the same material are bonded so that the thermal expansion behavior appears in a direction opposite to each other even though heat treatment is performed at the time of bonding. Is corrected and can be easily put into the double-sided lapping process.

Then, this bonded substrate was grind | polished to the desired thickness with the double-sided lapping apparatus using the suitable abrasive | polishing agent (free abrasive grain) similarly to the above.
The bonded substrate after the double-sided lapping was subjected to heat treatment to peel off the two wafers. With respect to these wafers, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution in order to remove abrasives (free abrasive grains), particles and wax adhering to the wafer surface.
After cleaning, the thickness of each wafer was measured with a stylus-type thickness measuring instrument, and finished to a thickness of 120 to 130 μm. It was confirmed that it was finished.

  In response to this result, a wafer (product substrate) 5a having a thickness of 120 to 130 μm lapped as described above and a support substrate (support substrate) 5b in which a sliced wafer is simply polished to a desired thickness by double-sided lapping are prepared, and wax is prepared. The back sides (the same polarization planes) were bonded together using (Nika Seiko Co., Ltd. Sky Liquid TW-2511). According to this bonding method, the two wafers of the same material are bonded so that the thermal expansion behavior appears in a direction opposite to each other even though heat treatment is performed at the time of bonding. Is corrected and can be easily put into the polishing process.

  Therefore, the bonded substrate 5ab was subjected to mirror polishing using a single-side polishing apparatus as shown in FIG. Specifically, a template 6 having a punched hole (hole diameter φ100.8 mm) made of an epoxy glass material is bonded and fixed to the ceramic plate 4 with double-sided tape in advance, and a concave portion (wafer holding position on the plate 4) ( 7) was provided. In this recess 7, the support substrate (support substrate) side is held by the surface tension of water through water, and in this state, the plate 4 is placed on the polishing surface plate 1 and the surface to be polished is in contact with the polishing cloth 2. Set. Next, the rotary shaft 8 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.

After this mirror polishing, the bonded substrate 5ab is taken out from the recess 7 of the ceramic plate 4, and further subjected to heat treatment to obtain two wafers (a wafer (product substrate) 5a and a support substrate (support substrate) 5b). It peeled. With respect to these wafers, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution in order to remove the abrasive, particles, and wax that are colloidal silica adhering to the wafer surface.
After cleaning, when the thickness of each wafer (wafer (product substrate) 5a and support substrate (support substrate) 5b) was measured with a stylus type thickness meter, the thickness of the wafer (product substrate) 5a was 90 to 100 μm. On the other hand, the thickness of the support substrate (support substrate) 5b was the same as before the introduction of the single-side polishing apparatus. Furthermore, when the back surfaces of the respective wafers (wafer (product substrate) 5a and support substrate (support substrate) 5b) were observed under a fluorescent lamp, no generation of scratches was observed. The wafer used as the support substrate (support substrate) 5b did not have any scratches on the back surface, but because of its large thickness, it was reused as the support substrate (support substrate) 5b in the next batch.

  Such a process was carried out on 100 wafers, and the flatness of the wafer (product substrate) 5a was measured. The TTV (Total Thickness Variation) was 0.76 to 2.85 μm, and LTVmax. At 5 mm × 5 mm site. (Local Thickness Variation Maximum) was 0.22-0.45 μm. Further, no wafer cracking or the like during the single-side polishing treatment was generated, and no cracks were generated when the two wafers after the mirror polishing were peeled off, and the yield was 100%.

[Example 3]
As a sample, a lithium tantalate (LiTaO ₃ ) single crystal wafer having a diameter of 4 inches (100 mm) was used. This single crystal manufactured by the Czochralski (CZ) method is sliced using a wire saw, and this slice wafer is used using an appropriate abrasive (free abrasive grains) so that the front and back surfaces are in a specified roughness state. Was polished to a desired thickness with double-sided lapping.
Thereafter, with respect to the two wafers lapped (roughening the front and back surfaces) as described above, using the wax (Nippon Seiko Co., Ltd. Sky Liquid TW-2511), the back surfaces (the same polarization surface) To each other). According to this bonding method, the two wafers of the same material are bonded so that the thermal expansion behavior appears in a direction opposite to each other even though heat treatment is performed at the time of bonding. Is corrected and can be easily put into the polishing process.

  Therefore, the bonded substrate 5ab was subjected to mirror polishing using a double-side polishing apparatus as shown in FIG. Specifically, the bonded substrate 5ab is set in the arrangement hole 10 (hole diameter φ100.8 mm) of the polishing carrier 9, and the polishing carrier 9 on which the bonded substrate 5ab is arranged is placed on a pair of upper and lower polishing surface plates 1. , 1 'and the surface to be polished was set so as to be in contact with the polishing cloth 2, 2'. Next, a predetermined pressure is applied between the pair of upper and lower polishing surface plates 1, 1 ′, and the lower polishing surface plate 1 and the upper polishing surface plate 1 ′ are supplied while supplying an abrasive between the pair of upper and lower polishing cloths 2, 2 ′. The mirror polishing process was performed while rotating the polishing carrier 9 on which the bonded substrate 5ab was disposed and planetary movement.

After this mirror polishing, the bonded substrate 5ab was taken out from the arrangement hole 10 of the polishing carrier 9, and subjected to heat treatment to separate the two wafers (wafer (product substrate) 5a and support substrate (support substrate) 5b). With respect to these wafers, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution in order to remove the abrasive, particles, and wax that are colloidal silica adhering to the wafer surface.
After cleaning, when the thickness of each wafer (wafer (product substrate) 5a and support substrate (support substrate) 5b) was measured with a stylus type thickness measuring device, wafer (product substrate) 5a, support substrate (support substrate) 5b was finished in a thickness of 90 to 100 μm. Furthermore, when the back surfaces of the respective wafers (wafer (product substrate) 5a and support substrate (support substrate) 5b) were observed under a fluorescent lamp, no generation of scratches was observed. Since the wafer used as the support substrate (support substrate) 5b was finished to the same quality level as the wafer (product substrate) 5a as described above, it was processed as the same product substrate.

When such a process was performed on 200 wafers and the flatness of the wafer (product substrate) 5a was measured, the TTV (Total Thickness Variation) was 0.72 to 2.02 μm and the LTV _{max. At} 5 mm × 5 mm site _. (Local Thickness Variation Maximum) was 0.18 to 0.37 μm. Further, no wafer cracking or the like occurred during the double-side polishing process, and a slight crack occurred when the two wafers after the mirror polishing process were peeled off, and the yield was 98%.

[Example 4]
As samples, were used lithium tantalate (LiTaO ₃₎ single crystal wafer of diameter of 4 inches (100 mm). This single crystal produced by the Czochralski (CZ) method is sliced using a wire saw, and this slice wafer is used using an appropriate abrasive (free abrasive grains) so that the front and back surfaces are in a specified roughness state. Was polished to the desired thickness with double-sided lapping.
Then, regarding the two wafers lapped (roughening the front and back surfaces) as described above, using wax (Nippon Seiko Co., Ltd., Sky Liquid TW-2511), the surface sides (same polarization surfaces) ). According to this bonding method, the two wafers of the same material are bonded so that the thermal expansion behavior appears in a direction opposite to each other even though the heat treatment is performed at the time of bonding. Is corrected and can be easily put into the double-sided lapping process.

Then, this bonded substrate was grind | polished to the desired thickness with the double-sided lapping apparatus using the suitable abrasive | polishing agent (free abrasive grain) similarly to the above.
The bonded substrate after the double-sided lapping was subjected to heat treatment to peel off the two wafers. With respect to these wafers, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution in order to remove abrasives (free abrasive grains), particles and wax adhering to the wafer surface.
After cleaning, the thickness of each wafer was measured with a stylus-type thickness meter, and it was finished to a thickness of 120 to 130 μm. The wafer (product substrate) 5a has an optimum thickness that can be loaded into a double-side polishing machine. It was confirmed that it was finished.

  Based on this result, a wafer (product substrate) 5a and a support substrate (support substrate) 5b having a thickness of 120 to 130 μm lapped as described above are prepared, and wax (Sky Liquid TW-2511 manufactured by Nikka Seiko Co., Ltd.) is prepared. ) Were used to bond the back surfaces (the same polarization surfaces) together. According to this bonding method, the two wafers of the same material are bonded so that the thermal expansion behavior appears in a direction opposite to each other even though heat treatment is performed at the time of bonding. Is corrected and can be easily put into the polishing process.

  Therefore, the bonded substrate 5ab was subjected to mirror polishing using a double-side polishing apparatus as shown in FIG. Specifically, the bonded substrate 5ab is set in the arrangement hole 10 (hole diameter φ100.8 mm) of the polishing carrier 9, and the polishing carrier 9 on which the bonded substrate 5ab is arranged is placed on a pair of upper and lower polishing surface plates 1. , 1 'and the surface to be polished was set so as to be in contact with the polishing cloth 2, 2'. Next, a predetermined pressure is applied between the pair of upper and lower polishing surface plates 1, 1 ′, and the lower polishing surface plate 1 and the upper polishing surface plate 1 ′ are supplied while supplying an abrasive between the pair of upper and lower polishing cloths 2, 2 ′. The mirror polishing process was performed while rotating the polishing carrier 9 on which the bonded substrate 5ab was disposed and planetary movement.

After this mirror polishing, the bonded substrate 5ab was taken out from the arrangement hole 10 of the polishing carrier 9, and subjected to heat treatment to separate the two wafers (wafer (product substrate) 5a and support substrate (support substrate) 5b). With respect to these wafers, ultrasonic cleaning at a specific frequency was performed with a predetermined chemical solution in order to remove the abrasive, particles, and wax that are colloidal silica adhering to the wafer surface.
After cleaning, when the thickness of each wafer (wafer (product substrate) 5a and support substrate (support substrate) 5b) was measured with a stylus type thickness measuring device, wafer (product substrate) 5a, support substrate (support substrate) 5b was finished in a thickness of 90 to 100 μm. Furthermore, when the back surfaces of the respective wafers (wafer (product substrate) 5a and support substrate (support substrate) 5b) were observed under a fluorescent lamp, no generation of scratches was observed. Since the wafer used as the support substrate (support substrate) 5b was finished to the same quality level as the wafer (product substrate) 5a as described above, it was processed as the same product substrate.

When such a process was performed on 200 wafers and the flatness of the wafer (product substrate) 5a was measured, the TTV (Total Thickness Variation) was 0.75 to 2.66 μm, and the LTV _{max. At} 5 mm × 5 mm site _. It was 0.20-0.39 micrometer in (Local Thickness Variation Maximum). Further, no wafer cracking or the like was generated during the double-side polishing treatment, and a slight crack occurred when the two wafers after the mirror polishing were peeled off, and the yield was 97%.

[Comparative Example 1]
As a sample, a lithium tantalate (LiTaO ₃ ) single crystal wafer having a diameter of 4 inches was used. This single crystal manufactured by the Czochralski (CZ) method is sliced using a wire saw, and this slice wafer is used using an appropriate abrasive (free abrasive grains) so that the front and back surfaces are in a specified roughness state. Was polished to a desired thickness with double-sided lapping.
With respect to the wafer lapped (roughening the front and back surfaces) as described above, mirror polishing was performed using a single-side polishing apparatus as shown in FIG. Specifically, a template 6 having a die-cutting hole made of an epoxy glass material is bonded and fixed to the ceramic plate 4 with a double-sided tape in advance, and a recess (die-cutting hole) 7 serving as a wafer holding position is provided on the plate 4. I left it. In this recess 7, the wafer lapped (roughening the front and back surfaces) is adsorbed and held via a foaming polyurethane backing material having a thickness of 0.4 mm. In this state, the plate 4 is placed on the polishing surface plate 1. The surface to be polished was set in contact with the polishing cloth 2. Next, the rotary shaft 8 is slowly lowered from directly above the plate 4 and brought into contact with the plate 4. While supplying an abrasive made of colloidal silica onto the polishing cloth 2, the pressure is gradually increased, and the specified rotational speed is maintained after being rotated slowly. While applying a predetermined pressure, mirror polishing was performed.

After this mirror polishing, the wafer is taken out from the concave portion 7 of the ceramic plate 4 and ultrasonic cleaning at a specific frequency is performed with a predetermined chemical solution to remove the abrasive and particles of colloidal silica adhering to the wafer surface. Carried out.
When the thickness of the wafer was measured with a stylus-type thickness measuring device after cleaning, it was finished to a thickness of 90 to 100 μm. Furthermore, when the back surface of the wafer was observed under a fluorescent lamp, no generation of scratches was observed.

When such a process was performed on 100 wafers and the flatness of the wafers was measured, TTV (Total Thickness Variation) was 3.24 to 4.07 μm, LTV _max. (Local Thickness Variation Maximum at 5 mm × 5 mm site) _. ) Was 1.86 to 2.53 μm. However, during the single-side polishing process, the wafer jumped out of the punched hole and a large amount of wafer cracking occurred. Furthermore, a large amount of cracking occurred when the wafer after mirror polishing was peeled off, and the yield was 23%.

[Comparative Example 2]
As a sample, a lithium tantalate (LiTaO ₃ ) single crystal wafer having a diameter of 4 inches was used. This single crystal manufactured by the Czochralski (CZ) method is sliced using a wire saw, and this slice wafer is used using an appropriate abrasive (free abrasive grains) so that the front and back surfaces are in a specified roughness state. Was polished to a desired thickness with double-sided lapping.
The wafer lapped (roughening the front and back surfaces) as described above was subjected to mirror polishing using a double-side polishing apparatus as shown in FIG. Specifically, two wafers are stacked via an adsorption plate, and this is set in the arrangement hole 10 (hole diameter φ100.8 mm) of the polishing carrier 9, and the polishing carrier 9 on which this stacked wafer is arranged is arranged. A pair of upper and lower polishing surface plates 1, 1 'was sandwiched, and the surface to be polished was set in contact with the polishing cloth 2, 2'. Next, a predetermined pressure is applied between the pair of upper and lower polishing surface plates 1, 1 ′, and the lower polishing surface plate 1 and the upper polishing surface plate 1 ′ are supplied while supplying an abrasive between the pair of upper and lower polishing cloths 2, 2 ′. Mirror polishing was performed while rotating each and rotating the polishing carrier 9 on which the laminated wafers were arranged in a planetary motion.
After this mirror polishing, the laminated wafer is taken out from the arrangement hole 10 of the polishing carrier 9, and in order to remove the abrasive and particles of colloidal silica adhering to the wafer surface, ultrasonic cleaning at a specific frequency is performed with a predetermined chemical solution. Carried out.
When the thickness of the wafer was measured with a stylus-type thickness measuring device after cleaning, it was finished to a thickness of 90 to 100 μm. Furthermore, when the back surface of the wafer was observed under a fluorescent lamp, rubbing and scratching occurred on a part of the back surface of the wafer.

When such a process was performed on 200 wafers and the flatness of the wafers was measured, the TTV (Total Thickness Variation) was 0.88 to 2.23 μm and the LTV _max. (Local Thickness Variation Maximum at 5 mm × 5 mm site) _. ) Was 0.20 to 0.41 μm. Further, during the double-side polishing process, the wafer jumped out of the arrangement hole 10 of the polishing carrier 8 to generate cracks, and cracks also occurred when the mirror-polished wafer was peeled off, and the yield was 35%.

  As described above, the production yield of the thin wafer such as the plate thickness of 100 μm or less is superior to that of the comparative example as described above. Therefore, while maintaining the front and back surfaces equivalent to the wafer with the current plate thickness of 350 μm, In addition, it is possible to stably supply a wafer having excellent processing accuracy such as high flatness and high parallelism equivalent to a wafer having a thickness of 350 μm.

  In the embodiments, a lithium tantalate wafer having a diameter of 4 inches has been described as an example. However, the present invention is not limited to lithium tantalate, lithium niobate, crystal, lithium tetraborate, or lanthanum used for surface acoustic wave filters. This is effective for a piezoelectric oxide single crystal wafer such as a site, and the thickness and diameter are not questioned.

  In addition, the present invention is preferably used for a piezoelectric oxide single crystal wafer, but can be applied to any material as long as the wafer substrate is mirror-finished only on one side, such as a silicon wafer, a compound semiconductor wafer, or a synthetic quartz wafer. It is.

It is a figure which shows the structure of the single-side polish apparatus used with embodiment of the manufacturing method of the wafer of this invention. It is a figure which shows the structure of the double-side polish apparatus used by embodiment of the manufacturing method of the wafer of this invention. It is a figure which shows the structure of the single-side polish apparatus used with the manufacturing method of the conventional wafer.

Explanation of symbols

1, 1 'polishing surface plate 2, 2' polishing cloth 3, 3 'drive shaft 4 plate 5 wafer 5a wafer (product substrate)
5b Support board (support board)
5ab bonded substrate 6 template 7 recess (made up of plate and template)
DESCRIPTION OF SYMBOLS 8 Rotating shaft 9 Polishing carrier 10 Wafer arrangement | positioning hole (of polishing carrier) 11 Drive shaft of center part 12 Sun gear 13 Outer peripheral member 14 Internal gear 15 Backing material

Claims (10)

  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.   When the diameter of the wafer substrate is Dmm, a template in which a die-cutting hole having a size of D to D + 5.0 mm is fixed to the plate, and the wafer substrate is fitted in the die-cutting hole of the template. 2. The polishing method according to claim 1, wherein the plate is directly held on the plate via a liquid.   3. The polishing method according to claim 2, wherein the wafer substrate is bonded to a support substrate having a size of D to D + 2.5 mm, and one side surface of the wafer substrate is mirror-polished in this state.   A polishing carrier in which a die-cut hole is formed is arranged between polishing cloths arranged on a pair of upper and lower polishing surface plates, and a wafer substrate is interposed in the die-cut hole of the polishing carrier, and the pair of polishings In the method in which the front and back surfaces of the wafer substrate are mirror-polished by the polishing cloth by rotating the platen respectively, when the diameter of the wafer substrate is D mm, the support substrate and the wafer substrate having a size of D to D + 2.5 mm And is set in a die-cutting hole having a size of D to D + 5.0 mm, and in this state, one side surfaces of the wafer substrate and the support substrate are mirror-finished.   The polishing method according to claim 3 or 4, wherein the wafer substrate and the support substrate are made of the same material.   6. The wafer polishing method according to claim 5, wherein the same polarization surfaces of the wafer substrate and the support substrate are bonded together.   A wafer obtained by the polishing method according to claim 1.   The wafer according to claim 7, wherein the wafer is a piezoelectric oxide single crystal.   9. The wafer according to claim 8, wherein the piezoelectric oxide single crystal wafer is lithium tantalate.   The single crystal wafer according to claim 9, wherein the lithium tantalate single crystal wafer has a thickness of 100 μm or less.

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