JP2011206891A - Method for polishing wafer substrate, and polishing plate - Google Patents

Abstract

A method of mirror polishing a piezoelectric oxide single crystal wafer substrate used for a surface acoustic wave filter or the like is provided.
A method for polishing a wafer substrate by sandwiching a wafer substrate between a polishing cloth and a plate placed on a polishing surface plate and rotating the polishing surface plate and the plate, wherein the plate 1 includes: It has a cylindrical convex part 1a on one side, and a template 2 having an opening that fits into this convex part 1a is attached to the plate, and the upper surface of the convex part 1a of the plate and the inner wall surface of the opening of the template And a wafer housing part 3 having a concave shape is formed, and the wafer substrate 4 housed in the wafer housing part 3 is held on the upper surface of the convex part 1a of the wafer housing part by a liquid adsorbing force through the liquid. It is characterized by polishing the wafer substrate.
[Selection] Figure 1

Description

  The present invention relates to a method of mirror polishing a piezoelectric oxide single crystal wafer substrate or the like used for a surface acoustic wave filter or the like and a polishing plate, and in particular, a wafer substrate polishing method excellent in processing accuracy such as flatness and the like. The present invention relates to improvement of a polishing plate.

  In recent years, the demand for surface acoustic wave devices has increased due to the development of mobile communication fields such as mobile phones, and as the substrate of this surface acoustic wave device, lithium tantalate, lithium niobate, lithium tetraborate, crystal, langasite Such a piezoelectric oxide single crystal wafer substrate is used. In addition, along with the thinning of mobile phones and the like, the surface acoustic wave element, which is one of the main devices, has been reduced in profile, and the thickness of the piezoelectric oxide single crystal wafer substrate used for this surface acoustic wave element has been reduced. On the other hand, the demand for thinning is increasing year by year.

  By the way, a wafer substrate used as a surface acoustic wave element is generally provided with a comb-shaped electrode on its main surface side, and a desired surface acoustic wave is generated between the electrodes by applying a voltage signal. Must be mirror-polished. In addition, if the surface opposite to the surface on which the electrode is formed is also mirror-polished, obstacle waves such as bulk waves that pass through the inside of the substrate generated along with the surface acoustic wave are reflected from the opposite surface that is mirrored. As a result, a spurious abnormality or the like in the frequency characteristic is caused. For this reason, one of the wafer substrates used for the surface acoustic wave element needs to be a mirror surface and the other is a rough surface. Usually, only one surface of a wafer substrate having both surfaces roughened is mirror-polished. Alternatively, the surface of the wafer substrate on which both surfaces are mirrored is not roughened by polishing or honing with a rough abrasive.

  Further, as a shape characteristic required for a piezoelectric oxide single crystal wafer substrate used for a surface acoustic wave element or the like, there is flatness of the wafer surface. That is, in the process of manufacturing a surface acoustic wave device, when a metal electrode is patterned on the wafer substrate surface by an exposure technique using a photochemical reaction, if there are irregular irregularities on the wafer substrate surface, it causes defocusing, etc. This causes a problem that the metal electrode is not formed. For this reason, there is a demand for a wafer having a surface shape of the wafer substrate that has small unevenness such as irregularities, that is, good flatness. In particular, in recent years, with the aim of obtaining as many elements as possible from one wafer, the demand for high flatness is increasing year by year in the processing accuracy in the vicinity of the outermost periphery as well as the central part of the wafer substrate. In addition, slight surface sagging of the outer peripheral portion of the wafer substrate is often a problem from the viewpoint of yield. In general, when the edge exclusion region is 1 mm, the TTV (Total Thickness Variation) is 3 μm or less, and when the maximum LTV (Local Thickness Variation) is 0.5 μm or less, the PLTV (Percent Local Thickness Variation) 100% is required.

  In order to mirror-polish only one side of the wafer substrate described above, it is necessary to fix and hold the non-polished surface, and various methods have been devised as means for holding the wafer substrate.

  For example, a method of bonding a wafer substrate to a ceramic plate or the like via heated wax (see Patent Document 1), a method of vacuum-adsorbing a wafer substrate by providing innumerable suction holes in a wafer holding portion of the ceramic plate (Patent Document 2) (See reference), a method of water adsorbing a wafer substrate with an adsorbent made of foamed polyurethane or the like called a backing material (see Patent Document 3 and Patent Document 4), a template having a punched hole and a ceramic plate to form a recess. Further, a method of adsorbing a wafer substrate accommodated in a recess through a liquid such as water (see Patent Document 5), or forming a recess with a template provided with a die-cut hole and a ceramic plate, and supporting substrate in this recess A method of accommodating a wafer substrate to which a wafer is attached and adsorbing the wafer substrate through a liquid such as water (see Patent Document 6) ), And the like are known.

  By the way, the method described in Patent Document 1 for adhering a wafer substrate with wax has an advantage that it is excellent in processing accuracy such as flatness and can fix and hold a wafer substrate of an arbitrary thickness, but requires a high technique for adhesion. At the same time, there is a problem that a process of washing the wax is necessary and the operation becomes complicated. In addition, if the wax adhering to the roughened wafer substrate surface cannot be completely removed, there has been a problem such as electrode peeling in the process of device fabrication. In addition, since the wafer substrate is heated and bonded, the pyroelectric property of the piezoelectric oxide single crystal wafer causes a problem that the wafer substrate is easily cracked in the heating process.

  In addition, the method described in Patent Document 2 in which a wafer substrate is vacuum-adsorbed to a ceramic plate can hold a wafer substrate having an arbitrary thickness, but requires a hole for vacuum adsorption in the ceramic plate, and there is a hole. There is a problem in flatness, such as a difference in the load that the wafer substrate receives during polishing between the portion that does not and the portion that does not, and unevenness on the mirror-polished surface due to this. In addition, if foreign matter is present between the wafer substrate and the ceramic plate, there is a risk that the polished surface of the portion where the foreign matter is present will be extremely polished, resulting in dents called dimples. Therefore, there were problems such as requiring highly clean environmental facilities.

  Furthermore, although the method described in Patent Document 3 and Patent Document 4 for adsorbing and holding a wafer substrate using a backing material can fix and hold a wafer substrate of an arbitrary thickness, there are few problems such as residual foreign matter, Since the variation in the thickness of the adsorbent made of foamed polyurethane or the like is transferred to the wafer surface, there has been a problem that the flatness of the wafer substrate surface tends to decrease.

  On the other hand, the method described in Patent Document 5 in which a recess is formed with a template provided with a die-cut hole and the wafer substrate accommodated in the recess is directly adsorbed to the ceramic plate through water or the like is disclosed in Patent Documents 1 to 4. However, the template for forming the recess is a template body (base material part) made of a cured resin and the like, and both surfaces for fixing the template body (base material part) to the ceramic plate. As a result of the load being applied to the adhesive part together with the template main body (base material part), the adhesive part peels off from the ceramic plate. Damage to the outer peripheral portion of the wafer substrate is likely to occur, and the finished thickness of the wafer substrate is determined by the template body (base material portion) and the adhesive portion. There is a problem such that thinning of the wafer substrate from the inability to polish thinner than the total thickness of the double-sided tape) may become difficult.

  Also, a patent in which a recess is formed by a template having a punched hole and a ceramic plate, a wafer substrate having a support substrate attached to the recess is accommodated, and the wafer substrate is sucked and fixed via a liquid such as water. In the method described in Document 6, the wafer side surface is held only by the template main body (base material part), so that it is difficult for the adhesive part to break, and the support substrate thickness can be changed arbitrarily. However, there is a problem that the variation in the thickness of the support substrate located on the back side of the wafer is transferred to the wafer surface, and the flatness of the wafer surface is likely to be lowered. In addition, there is a problem that the possibility of foreign matter increases due to the increase in the number of bonding portions between the wafer substrate and the support substrate and between the support substrate and the plate, and unevenness is likely to occur on the wafer surface.

Japanese Utility Model Publication No. 58-129658 Japanese Patent Laid-Open No. 2-98926 JP-A-62-297064 JP-A-63-93562 JP 2005-34926 A JP 2007-90515 A

  The present invention has been made paying attention to such problems, and the problem is that polishing is performed in single-sided mirror polishing of a piezoelectric oxide single crystal wafer substrate used for a surface acoustic wave device or the like. It does not cause problems in handling such as post-processing after polishing and polishing, does not require enormous investment, especially has high processing accuracy with high flatness without surface sagging, etc. An object of the present invention is to provide a polishing method capable of manufacturing a single-sided mirror wafer substrate having a finished thickness of 2 mm with good reproducibility, and to provide a polishing plate applied to this polishing method.

  Therefore, as a result of intensive studies by the inventor in order to solve the above problems, the following is not obtained by the conventional holding method by devising the wafer holding method when performing single-side polishing of the wafer substrate as follows. Has come to find technical advantages such as

  That is, a method in which a wafer substrate is sandwiched between a polishing cloth and a plate installed on a polishing surface plate, and the surface on the polishing cloth side of the wafer substrate is polished with the polishing cloth by rotating the polishing surface plate and the plate, respectively. A template main body (base material portion) having a plurality of openings that are fitted or loosely fitted to the convex portions, and that is a plate having a plurality of substantially cylindrical convex portions on one side as the plate. Is attached to the plate by an adhesive portion, and a concave wafer housing portion is formed by the upper surface of each convex portion of the plate and the inner wall surface of each opening of the template main body (base material portion). During polishing, the wafer substrate is polished while holding the wafer substrate held on the upper surface of the convex portion of the wafer holding portion through the liquid by the adsorption force of the liquid. It is possible to reduce the deterioration such as the adhesive part being peeled off from the plate because it is difficult to apply a load to the adhesive part from the wafer substrate, and it has a high flatness and in particular there is no surface sagging on the outer peripheral part of the wafer. The wafer substrate can be polished, and the height of the recess that forms the wafer receiving part is arbitrarily changed by changing the thickness of the template body (base material part), so that the finished thickness after polishing is relatively thin. The inventors have found a technical advantage that a mirror surface wafer substrate can be obtained with good reproducibility.

  Here, the height H0 of the substantially cylindrical convex portion in the plate is larger than the thickness of the adhesive portion of the template, and the thickness of the template body (base material portion) is the thickness of the wafer substrate after polishing (that is, Any thickness can be used as long as it is smaller than the finished thickness H2) of the wafer, but the thickness of the adhesive portion for bonding the template main body (base material portion) and the plate having the convex portion is 0 to ensure sufficient adhesive strength. .05mm or more is desirable. Therefore, the height H0 of the substantially cylindrical convex portion of the plate is desirably 0.05 mm or more.

  Further, when the diameter of the upper surface of the convex portion is D1 and the diameter of the wafer substrate is D2, it is necessary to satisfy the relationship of D2 ≦ D1. If the diameter D1 of the upper surface of the convex portion is smaller than the diameter D2 of the wafer substrate (that is, D2> D1), the polishing rate during polishing of the surface of the wafer substrate that is not in contact with the upper surface of the convex portion is reduced. Unevenness is formed on the surface, resulting in deterioration of flatness. On the other hand, if the diameter D1 of the upper surface of the convex portion is too larger than the diameter D2 of the wafer substrate, a concave shaped wafer constituted by the upper surface of the convex portion of the plate and the inner wall surface of the opening of the template body (base material portion). Since there is a risk of the wafer coming off during polishing because the gap between the accommodated wafer substrate and the wafer accommodating portion becomes large in the accommodating portion, the diameter of the upper surface of the convex portion is set to D1, and the diameter of the wafer substrate is increased. In the case of D2, it is necessary to satisfy the relationship of D2 ≦ D1 ≦ D2 + 5 mm.

  Further, when the height of the concave portion forming the wafer accommodating portion is H1, and the finished thickness of the wafer is H2, it is necessary to satisfy the relationship of H1 ≦ H2. If the height H1 of the concave portion forming the wafer accommodating portion is larger than the finished thickness H2 of the wafer, the load received from the polishing surface such as a polishing cloth reaches the template surface, so that the polishing rate is extremely reduced. Alternatively, since there is a risk of surface sag in the outer peripheral portion of the wafer due to a difference in polishing rate between the wafer central portion and the outer peripheral portion, the height H1 of the concave portion forming the wafer accommodating portion is particularly The height is preferably 30 μm or less than the finished thickness H2. However, no limitation is imposed on the condition that the relationship of H1 ≦ H2 is satisfied.

  Next, the height H1 of the concave portion forming the wafer accommodating portion is arbitrarily changed in the thickness of the template [that is, the thickness of the template main body (base material portion) and the thickness of the adhesive portion such as the double-sided tape is arbitrarily changed]. However, when the finished thickness H2 of the wafer is 0.05 mm or less, it becomes difficult to handle the wafer itself, for example, when the wafer after polishing is peeled off. Accordingly, the height of the concave portion forming the wafer accommodating portion is preferably 0.05 mm or more.

  In addition, regarding the concave-shaped wafer housing portion constituted by the upper surface of the convex portion of the plate and the inner wall surface of the opening of the template main body (base material portion), the inner wall surface of the concave portion forming the wafer housing portion has a relatively high strength. Since it is preferable to be constituted by the template body (base material part), the height (thickness) of the adhesive part having low strength needs to be set lower than the convex part height H0 of the plate. is there. The template main body (base material) is selected from resin materials such as epoxy glass and aramid in consideration of damage to the wafer substrate, but is not limited to these materials. The material of the adhesive part of the template is preferably natural rubber or acrylic in consideration of the adhesive strength with the plate having the convex part and the chemical resistance to the slurry, including the material of the adhesive tape substrate. The material is not limited.

  Next, the surface roughness of the top surface of the convex part in the plate that contacts the wafer substrate suppresses the occurrence of scratches on the back surface of the wafer due to friction between the wafer back surface and the top surface of the convex part due to rotation of the wafer during polishing, etc. From this viewpoint, when the surface roughness of the upper surface of the convex portion is Ra1 and the wafer surface roughness in contact with the upper surface of the convex portion is Ra2, it is preferable that the relationship of Ra1 / Ra2 ≦ 2 is satisfied. Ra2 is preferably of the same degree of roughness.

  According to the method for polishing a wafer substrate according to the present invention to which a plate having a novel structure having a plurality of substantially cylindrical convex portions is applied, no conventional capital investment or the like is required, and the conventional wafer bonding method is applied as it is. No wax residue or cracking during heating occurs when bonding with heated wax, flatness due to the presence of suction holes due to vacuum suction does not occur, flatness due to thickness variation in the backing material Degradation does not occur. Furthermore, it is not affected by the adhesive part of the template when the wafer substrate is attracted and held on a flat plate using water or other liquid, and as a result, the flatness of the support substrate is taken into consideration, such as bonding of the wafer and the support substrate. Without this, it is possible to realize polishing of a single-sided mirror wafer substrate having high flatness processing accuracy and having an arbitrary finished thickness.

The method for polishing a wafer substrate according to the present invention includes sandwiching the wafer substrate between a polishing cloth and a plate installed on a polishing surface plate, and rotating the polishing surface plate and the plate, respectively, thereby rotating the polishing cloth on the wafer substrate. In the method of polishing the side surface with a polishing cloth,
The plate has a plurality of substantially cylindrical convex portions on one side thereof, and a template having a plurality of openings fitted or loosely fitted on the convex portions is attached to the plate and attached to the plate. The upper surface of each convex portion and the inner wall surface of each opening portion of the template constitute a concave-shaped wafer accommodating portion, and the wafer substrate accommodated in the wafer accommodating portion is placed on the upper surface of the convex portion of the wafer accommodating portion via a liquid. Held by the adsorption force of the liquid,
When the height of the concave portion forming the concave-shaped wafer accommodating portion is H1, the finished thickness of the wafer is H2, the diameter of the upper surface of the convex portion is D1, and the diameter of the wafer substrate is D2,
The wafer substrate is polished under conditions that satisfy the relationship of H1 ≦ H2 and D2 ≦ D1 ≦ D2 + 5 mm.

  Then, according to the method for polishing a wafer substrate according to the present invention, in single-sided mirror polishing of a piezoelectric oxide single crystal wafer substrate used for a surface acoustic wave element or the like, handling of post-polishing and other post-polishing processes Manufacturing of single-sided mirror wafers with high finishing accuracy with high flatness and no surface sagging, and with any finished thickness without reproducibility. It becomes possible to do.

  Therefore, in the manufacturing process of the surface acoustic wave device, when the metal electrode is patterned on the wafer surface by the exposure technique, the problem of defocus due to the unevenness of the wafer surface is solved, so that the yield can be improved. In addition, the present invention has an effect of providing an arbitrary thin single-sided mirror substrate corresponding to the demand for thinning the wafer accompanying the recent reduction in device height.

FIG. 1A is a schematic cross-sectional explanatory view showing a wafer substrate holding method according to the present invention, and FIG. 1B is a partially enlarged view of a portion indicated by a mark A in FIG. It is a schematic sectional explanatory drawing which shows the grinding | polishing method of the wafer substrate which concerns on this invention.

  Embodiments of the present invention will be specifically described below, but the present invention is not limited to these embodiments.

  First, the manufacturing process of a piezoelectric oxide single crystal wafer will be described. For example, the outer periphery of an ingot grown by the Czochralski method is formed into a cylindrical shape by cylindrical grinding or the like, and this is sliced to a predetermined thickness to obtain a circular plate-shaped wafer substrate. Next, the sliced wafer substrate is polished to a predetermined thickness by double-sided lapping or the like to obtain a wafer substrate having both surfaces roughened. The slicing step and the lapping step may be performed by using the same processing method as in the prior art, and the main point of the present invention is applied to single-sided mirror polishing described below for a wafer having both surfaces roughened. It is to provide a wafer holding method and a single-side mirror polishing processing method.

  1A is a schematic cross-sectional explanatory view for explaining a method of holding a wafer substrate according to the present invention, and FIG. 1B is a partially enlarged view of a portion indicated by a mark A in FIG. is there.

  First, a wafer substrate holding method according to the present invention includes a plate 1 having a plurality of substantially cylindrical convex portions 1a on one side and a plurality of openings that are fitted or loosely fitted to the convex portions 1a. Template 2 is used. In addition, the template 2 is provided in a portion excluding the template main body (base material portion) 2a having a plurality of openings and the opening on one side of the template main body (base material portion) 2a, and the template main body (base material portion) 2a. And an adhesive portion 2b for fixing the plate to the plate 1.

  And the template main body (base material part) 2a which has the some opening part fitted or loosely fitted to the said convex-shaped part 1a is affixed on the plate 1 by the said adhesion part 2b, and each said convex-shaped part of the plate 1 is attached. A recess-shaped wafer accommodating portion 3 is constituted by the upper surface 1a and the inner wall surface of each opening of the template main body (base material portion) 2a. At this time, the plate 1 to be applied may be selected such that the surface of the substantially cylindrical convex portion 1a has a predetermined flatness and roughness. The height of the convex portion 1a of the plate 1 and the thickness of the template main body (base material portion) 2a and the adhesive portion 2b are selected to satisfy a predetermined relationship.

  Next, the wafer substrate 4 is attached to the concave portion that forms the wafer accommodating portion 3 by attaching the back side of the wafer substrate 4 whose both surfaces are rough-polished via a liquid such as water, so that the wafer substrate 4 becomes a convex portion of the wafer accommodating portion 3. It is held on the upper surface of 1a by the adsorption force of the liquid through the liquid. At this time, the height of the surface of the wafer substrate 4 is slightly higher than the surface height of the template main body (base material portion) 2a and protrudes outward.

  Next, FIG. 2 is a schematic cross-sectional explanatory view showing a wafer substrate polishing method according to the present invention. In FIG. 2, a polishing cloth 6 is affixed to the upper surface of the polishing surface plate 5, and a polishing surface (not shown) is supplied onto the polishing cloth 6 to provide a polishing surface. Further, the polishing surface plate 5 is rotationally driven at an arbitrary rotational speed by motor control or the like via a drive shaft 7 connected to the surface plate 5.

  Further, the plate 1 holding the wafer substrate 4 accommodated in the wafer accommodating portion is set so that the surface of the wafer substrate 4 faces the polishing cloth 6, and the pressing mechanism portion toward the back side of the plate 1. By contacting 8, an arbitrary load can be applied to the wafer substrate 4 through the plate 1. The pressing mechanism 8 is connected to a drive shaft 9 and is driven to rotate at an arbitrary rotational speed by motor control or the like, whereby the plate 1 rotates together with the pressing mechanism 8.

  Then, the polishing surface plate 5 is rotated while supplying the polishing liquid onto the polishing cloth 6, and the pressing mechanism 8 is rotated together with the plate 1 in the opposite direction to the polishing surface plate 5, thereby pressing the polishing cloth 6. The surface of the wafer substrate 4 that has been subjected to mirror polishing is performed, and the polishing process ends when a predetermined thickness is reached.

  In addition, about the template 2 used by the said grinding | polishing method, even if it grind | polishes repeatedly, the technical effect which hardly produces malfunctions, such as the adhesion part 2b peeling from the plate 1, or being damaged, is confirmed, As for the obtained wafer substrate 4 as well, the high flatness region in the wafer surface is expanded, for example, the surface sagging of the wafer outer peripheral portion is remarkably improved, and this can contribute to the improvement of the yield of the surface acoustic wave device and the like. It is confirmed that it is a thing.

  Next, examples of the present invention will be specifically described with reference to comparative examples.

  A wafer substrate having a diameter D2 = 100 mm was used as a sample.

  First, the ingot side surface of a lithium tantalate single crystal grown by the Czochralski method is cylindrically ground to form a cylindrical shape. In addition, OF (orientation flat) grinding is performed, followed by slicing using a wire saw. Thus, a disk-shaped wafer was obtained.

  Next, it polished until the wafer thickness became 0.25 mm by the double-sided lapping process using the loose abrasive grains having an appropriate particle size such that the wafer front and back surface roughness Ra2 was 0.30 μm.

  Next, a ceramic plate 1 and a template 2 for holding the wafer substrate 4 shown in FIGS. 1A and 1B were prepared in order to perform a single-side mirror polishing process on the obtained wafer substrate. That is, the height H0 (plate surface height) of the cylindrical convex portion 1a is 0.50 mm, the diameter D1 of the upper surface of the convex portion 1a is 101.0 mm, and the wafer substrate 4 is in contact with the diameter D2 = 100 mm. A ceramic plate 1 having a surface roughness Ra1 of 0.30 μm on the upper surface of the convex part 1a is prepared, and has a plurality of openings fitted or loosely fitted to the convex part 1a, and is formed of epoxy glass. A template body (base material portion) 2a having a thickness of 0.55 mm and a natural rubber having a thickness of 0.10 mm, and an adhesive provided on a portion excluding the opening on one side of the template body (base material portion) 2a. A template 2 composed of a portion 2b is prepared, and a template main body (base material portion) 2a is attached to the ceramic plate 1 via an adhesive portion 2b, and the upper surface of each convex portion 1a and each opening To form the wafer accommodating section 3 of the concave shape formed by the inner wall surface. Then, the wafer substrate 4 was accommodated in the wafer accommodating portion 3, and the back surface side of the wafer substrate 4 was adsorbed and held on the upper surface of the convex portion 1a via pure water.

  At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.15 mm, The surface of the wafer substrate 4 protruded 0.10 mm outward from the surface of the template main body (base material portion) 2a.

  The ceramic plate 1 thus configured was set on the polishing cloth 6 shown in FIG. 2 so that the surface of the wafer substrate 4 was in contact with the polishing cloth 6. Next, the pressing mechanism portion 8 is slowly lowered from directly above the ceramic plate 1 and brought into contact with the plate 1, and the polishing surface plate 5 and the pressing mechanism portion 8 are slowly rotated and raised while supplying the colloidal silica polishing liquid to the polishing cloth 6. At the same time, the pressing mechanism 8 is gradually pressurized and reached a predetermined rotational speed and pressure, and then this state is maintained for a certain period of time to perform a single-side mirror polishing process, and the finished thickness H2 of the wafer is reduced. It was 0.20 mm. After this mirror polishing process, the wafer substrate 4 taken out was ultrasonically cleaned with a predetermined chemical solution to remove the polishing liquid adhering to the wafer by the polishing process.

  And the said process was implemented with respect to 200 wafer substrates, and the flatness of the obtained wafer was measured. The measurement conditions were an edge exclusion area of 1.0 mm and a site size of 5.0 × 5.0 mm.

  As a result, the site occupancy rate (PLTV) of 1.65 μm and LTV ≦ 0.5 μm or less as an average value of TTV was as good as 100%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are shown in Table 1 below.

  The height H0 (plate surface height) of the cylindrical convex portion 1a in the ceramic plate 1 is 0.05 mm, the thickness of the template body (base material portion) 2a formed of epoxy glass is 0.15 mm, and One-side mirror polishing of 100 lithium tantalate single crystal wafer substrates was performed in the same manner as in Example 1 except that the thickness of the adhesive portion 2b made of natural rubber was 0.05 mm. At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.15 mm, The surface of the wafer substrate 4 protruded 0.10 mm outward from the surface of the template main body (base material portion) 2a.

  As in Example 1, wafer cleaning after mirror polishing was performed and the flatness of the wafer was measured. The average value of TTV was 1.87 μm, and PLTV was 100%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

  The height H0 (plate surface height) of the cylindrical convex portion 1a in the ceramic plate 1 is 1.00 mm, the thickness of the template body (base material portion) 2a formed of epoxy glass is 1.05 mm, and 100 single-sided lithium tantalate single crystal wafer substrates were mirror-polished in the same manner as in Example 1 except that the thickness of the adhesive portion 2b made of natural rubber was changed to 0.10 mm. At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.15 mm, The surface of the wafer substrate 4 protruded 0.10 mm outward from the surface of the template main body (base material portion) 2a.

  Then, as in Example 1, wafer cleaning after mirror polishing was performed and the flatness of the wafer was measured. The average value of TTV was 1.94 μm, and PLTV was 100%, which was good. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

  One-side mirror polishing of 100 lithium tantalate single crystal wafer substrates was performed in the same manner as in Example 1 except that the thickness of the template main body (base material portion) 2a formed of epoxy glass was 0.60 mm. At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.20 mm, The surface of the wafer substrate 4 protruded outward by 0.05 mm from the surface of the template main body (base material portion) 2a.

  As in Example 1, wafer cleaning after mirror polishing was performed and the flatness of the wafer was measured. The average value of TTV was 2.04 μm, and PLTV was 100%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

  A lithium tantalate single crystal wafer substrate in the same manner as in Example 1 except that the diameter D2 of the wafer substrate was 100.0 mm and the diameter D1 of the upper surface of the cylindrical convex portion 1a in the ceramic plate 1 was 105.0 mm. 100 sheets were mirror-polished on one side.

  Then, as in Example 1, wafer cleaning after mirror polishing was performed and the flatness of the wafer was measured. The average value of TTV was 2.13 μm, and PLTV was 100%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

  100 lithium tantalate single crystal wafer substrates in the same manner as in Example 1 except that the ceramic plate 1 having a surface roughness Ra1 of 0.60 μm on the upper surface of the convex portion 1a in contact with the wafer substrate 4 was applied. One-side mirror polishing was performed.

  Then, as in Example 1, wafer cleaning after mirror polishing was performed, and the flatness of the wafer was measured. As a result, the average value of TTV was 1.72 μm, and PLTV was 100%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

  100 lithium tantalate single crystal wafer substrates in the same manner as in Example 1 except that the ceramic plate 1 having a surface roughness Ra1 of 0.70 μm on the upper surface of the convex portion 1a in contact with the wafer substrate 4 was applied. One-side mirror polishing was performed.

  Then, as in Example 1, the wafer was cleaned after mirror polishing and the flatness of the wafer was measured. The average value of TTV was 1.73 μm, and PLTV was 100%, which was good.

  Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no stain-like dirt or cracks were generated, but extremely small scratches were observed on the back surfaces of the two wafer substrates. However, this scratch was not so bad as to be a defective product.

  These results are also shown in Table 1 below.

  A lithium tantalate single crystal wafer substrate was prepared in the same manner as in Example 1 except that the thickness of the wafer 4 obtained by double-sided lapping was 0.20 mm and the finished thickness H2 of the wafer obtained by single-sided mirror polishing was 0.15 mm. One hundred mirrors were polished on one side. At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.15 mm, The surface of the wafer substrate 4 protruded outward by 0.05 mm from the surface of the template main body (base material portion) 2a.

  As in Example 1, wafer cleaning after mirror polishing was performed, and the flatness of the wafer was measured. The average value of TTV was 1.81 μm, and PLTV was 100%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

  The thickness of the wafer 4 obtained by double-sided lapping is 0.15 mm, the thickness of the template body (base material part) 2a formed of epoxy glass is 0.50 mm, and the finished thickness H2 of the wafer obtained by single-side mirror polishing 100 pieces of lithium tantalate single crystal wafer substrates were subjected to single-side mirror polishing in the same manner as in Example 1 except that the thickness was changed to 0.10 mm. At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.10 mm. The surface of the wafer substrate 4 protruded outward by 0.05 mm from the surface of the template main body (base material portion) 2a.

  As in Example 1, wafer cleaning after mirror polishing was performed, and the flatness of the wafer was measured. The average value of TTV was 1.88 μm, and PLTV was 100%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

  The thickness of the wafer 4 obtained by double-sided lapping is 0.10 mm, the thickness of the template body (base material part) 2a formed of epoxy glass is 0.45 mm, and the finished thickness H2 of the wafer obtained by single-side mirror polishing The single-sided mirror polishing of 20 lithium tantalate single crystal wafer substrates was performed in the same manner as in Example 1 except that the thickness was 0.05 mm. At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.05 mm, The surface of the wafer substrate 4 protruded outward by 0.05 mm from the surface of the template main body (base material portion) 2a.

  As in Example 1, wafer cleaning after mirror polishing was performed and the flatness of the wafer was measured. The average value of TTV was 2.05 μm, and PLTV was 100%, which was favorable. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

[Comparative Example 1]
One-side mirror polishing of 100 lithium tantalate single crystal wafer substrates was performed in the same manner as in Example 1 except that the thickness of the template main body (base material portion) 2a formed of epoxy glass was 0.65 mm. At this time, the height of the concave portion forming the wafer accommodating portion 3 [that is, the height at which the surface of the template body (base material portion) 2a protrudes from the convex portion 1a of the plate 1] H1 is 0.25 mm, The surface of the wafer substrate 4 was the same height as the surface of the template main body (base material portion) 2a, and the polishing rate during polishing was reduced to about ½ of that in Example 1.

  As in Example 1, the wafer was cleaned after mirror polishing and the flatness of the wafer was measured. The average value of TTV was 4.75 μm, and PLTV was 91.8%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

[Comparative Example 2]
A lithium tantalate single crystal wafer substrate in the same manner as in Example 1 except that the diameter D2 of the wafer substrate was 100.0 mm and the diameter D1 of the upper surface of the cylindrical convex portion 1a of the ceramic plate 1 was 97.0 mm. 100 sheets were mirror-polished on one side.

  Then, as in Example 1, wafer cleaning after mirror polishing was performed and the flatness of the wafer was measured. As a result, the average value of TTV was 3.83 μm, and PLTV was 94.3%. Further, when the outer peripheral portion of the surface of the wafer substrate was visually observed under a fluorescent lamp, unevenness was found on the outer peripheral portion of the wafer surface. Similarly, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

[Comparative Example 3]
A lithium tantalate single crystal wafer substrate in the same manner as in Example 1 except that the diameter D2 of the wafer substrate was 100.0 mm and the diameter D1 of the upper surface of the cylindrical convex portion 1a in the ceramic plate 1 was 108.0 mm. When 100-sided polishing was attempted, a phenomenon that the wafer substrate was detached during polishing occurred, and 20 of them were broken due to cracking.

  As in Example 1, the remaining wafer substrate after mirror polishing was cleaned and the flatness of the wafer was measured. As a result, the average value of TTV was 2.43 μm and PLTV was 99.2%. It was. Further, when the surface of the wafer substrate was visually observed under a fluorescent lamp, innumerable scratches believed to have occurred due to broken wafer fragments during polishing were observed on the wafer surface. Similarly, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches or dirt were observed.

  These results are also shown in Table 1 below.

[Comparative Example 4]
Comparative Example 4 is an example in which a wafer is bonded to a ceramic plate via a heated wax and single-sided mirror-polished based on the technique described in Patent Document 1.

  A double-sided lapped lithium tantalate single crystal wafer substrate obtained in the same manner as in Example 1 was bonded to a flat ceramic plate with heated wax (Sky Liquid manufactured by Nikka Seiko Co., Ltd.). Then, single-side mirror polishing was performed using a single-side polishing apparatus. Similar to Example 1, the finished thickness H2 of the wafer was 0.20 mm. At this time, the polishing rate during the polishing process was almost the same as in Example 1.

  When the above process was performed on 100 wafer substrates, cracks occurred in 6% of the wafers at the stage of wafer attachment by heating with wax.

  For the remaining wafers for which the mirror polishing was completed, wafer cleaning after mirror polishing was performed and the flatness of the wafer was measured in the same manner as in Example 1. The average value of TTV was 1.87 μm, and PLTV was 100. % And good. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no flaws were observed, but spot-like stains occurred in 12% of the whole.

  These results are also shown in Table 1 below.

[Comparative Example 5]
Comparative Example 5 is an example in which an infinite number of suction holes are provided in the wafer holding portion of the ceramic plate based on the technique described in Patent Document 2 to suck the wafer substrate and perform single-side mirror polishing.

  The single-sided lithium tantalate single crystal wafer substrate with both front and back rough surfaces obtained in the same manner as in Example 1 was adsorbed by a flat ceramic plate having 24 vacuum suction holes with a diameter of 1 mm. Then, single-side mirror polishing was performed using a single-side polishing apparatus. Similar to Example 1, the finished thickness H2 of the wafer was 0.20 mm. At this time, the polishing rate during the polishing process was almost the same as in Example 1.

  The above-described process was performed on 100 wafer substrates, and wafer cleaning after mirror polishing was performed in the same manner as in Example 1 to measure the flatness of the wafer. The average value of TTV was 2.87 μm, PLTV was getting worse at 98.1%. When the surface of the wafer substrate was visually observed under a fluorescent lamp, dents called dimples were found on the wafer surface corresponding to the vacuum suction holes. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

[Comparative Example 6]
Comparative Example 6 is an example in which a wafer substrate is adsorbed with water by a foamed polyurethane adsorbent called a backing material and mirror-polished on one side based on the technique described in Patent Document 3 and Patent Document 4.

  A lithium tantalate single crystal wafer substrate with front and back rough surfaces obtained by double-sided lapping obtained in the same manner as in Example 1 was bonded to a flat ceramic plate with a backing material made of foamed polyurethane having a thickness of 0.40 mm. Then, single-sided mirror polishing was performed using a single-side polishing apparatus. Similar to Example 1, the finished thickness H2 of the wafer was 0.20 mm. At this time, the polishing rate during the polishing process was almost the same as in Example 1.

  The above-described process was performed on 100 wafer substrates, and the wafer was cleaned after mirror polishing in the same manner as in Example 1. The wafer flatness was measured, and the average value of TTV was 4.28 μm. PLTV was getting worse with 93.8%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

[Comparative Example 7]
In Comparative Example 7, a recess is formed by a template provided with a punching hole and a ceramic plate based on the technique described in Patent Document 5, and the wafer substrate accommodated in the recess is adsorbed via water. This is an example of single-side mirror polishing.

  That is, a template (with a base material portion thickness of 0.10 mm and an adhesive portion thickness of 0.05 mm) provided with a die-cut hole is attached to a flat ceramic plate to form a recess-shaped wafer housing portion. After the double-sided lapped lithium tantalate single crystal wafer substrate obtained in the same manner as in No. 1 is accommodated in the wafer accommodating portion, and the wafer substrate is attached to the wafer accommodating portion via pure water. Then, single-side mirror polishing was performed using a single-side polishing apparatus. Similar to Example 1, the finished thickness H2 of the wafer was 0.20 mm. At this time, the polishing rate during the polishing process was almost the same as in Example 1.

  The above-described process was performed on 100 wafer substrates, the wafer was cleaned after mirror polishing in the same manner as in Example 1, and the flatness of the wafer was measured. The average value of TTV was 2.52 μm, PLTV was 98.8%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no scratches, dirt, or cracks were observed.

  These results are also shown in Table 1 below.

[Comparative Example 8]
Comparative Example 8 is based on the technique described in Patent Document 6 and forms a recess with a template provided with a die-cut hole and a ceramic plate, and accommodates a wafer substrate with a support substrate attached to the recess, In this example, the wafer substrate is adsorbed through water and subjected to single-side mirror polishing.

  That is, a template (with a base material portion thickness of 0.25 mm and an adhesive portion thickness of 0.10 mm) provided with a punched hole is attached to a flat ceramic plate to form a recess-shaped wafer housing portion. A support substrate (material: lithium tantalate, thickness: 0.20 mm, front / back roughness: 0.30 μm, flatness: TTV ≦ 1.0 μm) is stored in the storage portion and water is the same as the wafer to be mirror-polished. Further, the single-side polishing apparatus was attached to the support substrate through wax using a double-sided lapped lithium tantalate single crystal wafer substrate obtained in the same manner as in Example 1 and adhered to the support substrate. A single-sided mirror polishing process was performed. Similar to Example 1, the finished thickness H2 of the wafer was 0.20 mm. At this time, the polishing rate during the polishing process was almost the same as in Example 1.

  The above-described process was performed on 100 wafer substrates, the wafer was cleaned after mirror polishing in the same manner as in Example 1, and the flatness of the wafer was measured. The average value of TTV was 3.41 μm, PLTV was 97.0%. Further, when the back surface of the wafer substrate was visually observed under a fluorescent lamp, no flaws or cracks were observed, but spot-like stains occurred in 8% of the whole.

（注）表１中「○」は「有」、「△」は「僅かに有」、「×」は「無」を示す。

(Note) In Table 1, “◯” indicates “Yes”, “Δ” indicates “Slightly”, and “X” indicates “No”.

[Evaluation]
(1) As shown in Table 1, compared with Comparative Examples 1 to 8, since the flatness of the wafer substrate is better in Examples 1 to 10, in the manufacturing process of the surface acoustic wave element, Since the metal electrode pattern can be formed over the entire surface of the wafer substrate, the device yield can be improved.
(2) Further, in Examples 1 to 10, since no scratches or dirt are generated on the back surface of the wafer substrate, it is possible to avoid process cracks or electrode peeling due to scratches.
(3) Furthermore, it becomes possible to manufacture an arbitrary thin single-sided mirror substrate corresponding to the demand for thinning the wafer accompanying the recent reduction in device height.

  According to the polishing method of the present invention, there is no problem in handling during and after polishing, there is no surface sagging, high flatness with excellent processing accuracy, and an arbitrary finished thickness. Since a mirror-surface wafer substrate can be manufactured, it has industrial applicability applied as a single-sided mirror-surface substrate corresponding to the demand for thin wafers accompanying the recent reduction in device height.

DESCRIPTION OF SYMBOLS 1 Plate 1a Convex part 2 Template 2a Template base material part 2b Template adhesion part 3 Wafer accommodating part 4 Wafer board | substrate 5 Polishing surface plate 6 Polishing cloth 7 Driving shaft of polishing surface plate 8 Pressing mechanism part 9 Driving shaft of pressing mechanism part H0 Height of cylindrical convex part in plate H1 Height of concave part forming wafer accommodating part H2 Finished thickness of wafer

Claims (13)

In a method of polishing the surface of the wafer substrate on the polishing cloth side with the polishing cloth by sandwiching the wafer substrate between the polishing cloth and plate installed on the polishing surface plate and rotating the polishing surface plate and the plate, respectively. ,
The plate has a plurality of substantially cylindrical convex portions on one side thereof, and a template having a plurality of openings fitted or loosely fitted on the convex portions is attached to the plate and attached to the plate. The upper surface of each convex portion and the inner wall surface of each opening portion of the template constitute a concave-shaped wafer accommodating portion, and the wafer substrate accommodated in the wafer accommodating portion is placed on the upper surface of the convex portion of the wafer accommodating portion via a liquid. Held by the adsorption force of the liquid,
When the height of the concave portion forming the concave-shaped wafer accommodating portion is H1, the finished thickness of the wafer is H2, the diameter of the upper surface of the convex portion is D1, and the diameter of the wafer substrate is D2,
A method for polishing a wafer substrate, comprising polishing the wafer substrate under conditions satisfying a relationship of H1 ≦ H2 and D2 ≦ D1 ≦ D2 + 5 mm.   The method for polishing a wafer substrate according to claim 1, wherein the height H0 of the substantially cylindrical convex portion of the plate is 0.05 mm or more and 1.00 mm or less.   2. The method of polishing a wafer substrate according to claim 1, wherein the height H1 of the concave portion forming the wafer accommodating portion is adjusted by arbitrarily setting the thickness of the template having the opening.   2. The method for polishing a wafer substrate according to claim 1, wherein a height H1 of the concave portion forming the wafer accommodating portion is 0.05 mm or more.   2. The method for polishing a wafer substrate according to claim 1, wherein a finishing thickness H2 of the wafer is 0.05 mm or more.   The template pasted on the plate is provided in a portion excluding a template main body (base material portion) having a plurality of openings and an opening on one side of the template main body (base material portion). The method for polishing a wafer substrate according to claim 1, comprising: an adhesive portion that fixes the substrate to the plate.   The wafer accommodating part is composed of the upper surface of each convex part of the plate and the inner wall surface of each opening of the template main body (base material part), and the adhesive part of the template is not exposed in the concave part forming the wafer accommodating part. The method for polishing a wafer substrate according to claim 1, wherein:   The method for polishing a wafer substrate according to claim 1, wherein the wafer substrate is a piezoelectric oxide single crystal substrate.   9. The method for polishing a wafer substrate according to claim 8, wherein the piezoelectric oxide single crystal substrate is lithium tantalate or lithium niobate.   A plurality of substantially cylindrical convex portions that are fitted or loosely fitted into the openings of the template having a plurality of openings are provided on one side, and the template is attached to the upper surface of each convex portion and the template. A polishing plate comprising a recess-shaped wafer container with each opening inner wall surface.   11. The polishing plate according to claim 10, wherein a relationship of D2 ≦ D1 ≦ D2 + 5 mm is satisfied between the diameter D1 of the upper surface of the convex portion and the diameter D2 of the wafer substrate.   The polishing plate according to claim 10 or 11, wherein a height H0 of the convex portion is 0.05 mm or more and 1.00 mm or less.   The surface roughness of the upper surface of the convex part is Ra1 and the roughness of the wafer surface in contact with the upper surface of the convex part is Ra2, and the relationship of Ra1 / Ra2 ≦ 2 is satisfied. The polishing plate according to any one of the above.

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