JP2006123020A - Method of polishing piezoelectric wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method considerably reducing the manufacturing cost of a thickness shear vibrator with little dispersion in thickness even if using a large bore piezoelectric wafer in machining the piezoelectric wafer using a planetary gear type polishing machine. <P>SOLUTION: In the case of polishing in two or more stages in polishing the piezoelectric wafer, polishing is temporarily stopped halfway in final stage polishing, and after reversing the piezoelectric wafer, polishing is restarted to polish it up to the final thickness. Thickness dispersion in the whole plane of the piezoelectric wafer is thereby minimized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for polishing a piezoelectric wafer made of a thin plate.

  A communication module such as a digital information camera (DSC), a portable information (terminal) device such as a small-sized liquid crystal television or a notebook PC, or Bluetooth (Bluetooth) that wirelessly connects between portable information (terminal) devices is represented by crystal. Many piezoelectric vibrators are used. One method for reducing the manufacturing cost of such a widely used piezoelectric vibrator is to enlarge the diameter of the wafer of piezoelectric material and greatly increase the number of vibrating pieces formed in the wafer. For example, in the case of a tuning fork type crystal resonator, 800 or more vibrating pieces are formed in a wafer having a diameter of 3 inches Φ. However, even with the same quartz material, the thickness of a Berri vibrator (AT vibrator and BT vibrator) having a vibration mode different from that of a tuning fork vibrator depends on the thickness of the vibrating piece. When the thickness variation is large in the wafer surface, the frequency variation between the vibrating pieces also increases. The final frequency adjustment of the vibrator is achieved by adjusting the frequency by scraping one side of the metal electrode film formed on both sides of the vibrating piece with ion irradiation in the assembly process, so that the frequency can be adjusted to a predetermined range. However, if the thickness variation is large, a lot of time is spent on this frequency adjustment process. As a result, it is difficult to reduce the manufacturing cost even if the diameter of the wafer is increased. The in-plane variation of the wafer needs to be 0.1 μm or less in a frequency range of about 10 MHz to 50 MHz often used for portable terminals. Therefore, for the manufacture of the thickness shear vibrator, for a long time, a 9 mm square or 11 mm square small wafer (base plate) was used to avoid an increase in thickness variation. In the following description, the term “vibration piece” refers to the individual chip shape at the stage of being formed on the piezoelectric wafer or the stage at which it is cut out, and the vibrator means a complete body in which the vibration piece is enclosed in a predetermined airtight container. Shall be pointed to.

  However, as long as a small wafer of 9 mm square or 11 mm square is used, it is difficult to significantly reduce the manufacturing cost of the resonator element, and it is indispensable to use a wafer as large as possible. For this purpose, a technique is required in which, after the wafer is cut from the raw crystal ore, the thickness of the wafer is not varied as much as possible within the wide wafer surface in the polishing process.

  As a document for the purpose of improving polishing accuracy such as flatness of a workpiece (wafer) to be polished, there is Patent Document 1. In this Patent Document 1, a thick glass or metal workpiece (an example of a workpiece having a thickness of 30 mm is described) is divided into a main processing for high-speed polishing and a finishing processing for the purpose of improving accuracy. In finishing processing, it is said that polishing accuracy such as flatness can be improved by changing the processing conditions. However, in the processing of extremely thin wafers such as vibrators, greatly changing the rotational speed and load conditions can easily induce yield reduction due to wafer cracks, chipping of wafer end faces and carrier damage. In addition, the polishing accuracy required for the vibrator wafer is also difficult to implement because the flatness (thickness variation) is extremely high at 0.1 μm or less. Therefore, consideration from another viewpoint is necessary.

  In a normal wafer polishing process, the processing trajectory length between the wafer and the surface plate of the polishing apparatus (the path along which the wafer passes on the surface plate) varies depending on the location on the wafer, which reduces the amount of polishing processing. Depending on the location on the wafer, there is a final thickness variation. There is a method to change the revolving ratio (the ratio between the number of revolutions of the carrier per unit time and the number of revolutions per unit time) of the carrier holding the wafer as a method of adjusting the processing trajectory length, but there is a limit to the minimum thickness variation that can be realized is there. This will be briefly described below.

  Preliminary experiments were conducted using an AT-cut quartz wafer as a piezoelectric material, and the thickness variation was investigated. The wafer size used in the experiment is 34 mm × 30 mm. The area of this square wafer is about 8.4 times the area of the 11 mm square wafer currently used for production, and is selected with the intention of forming a much larger number of vibrating pieces. The thickness of the wafer before polishing was about 80 μm, and this was polished to about 60 μm. As the abrasive, FO # 4000 containing zirconium oxide as a main component was used. After the wafer is cut from the raw stone, the wafer is polished up to 80 μm using FO # 2000 as a pre-process.

The polishing apparatus is a general-purpose double-sided lapping apparatus, and has a planetary gear mechanism comprising a sun gear (sun gear) 6, an internal gear (internal gear) 7, and a carrier (planetary gear) 2 as shown in FIG. The surface plate is a three-way system in which the lower surface plate 8 rotates and the upper surface plate 9 is fixed. Although the respective rotation directions are indicated by arrows 12 to 15, the rotation direction 15 of the carrier may differ depending on the rotation ratio. Further, as shown in FIG. 8B, a wafer thickness measuring sensor 10 to be described later is embedded in one place of the upper surface plate. The carrier has a diameter of 6 inches and is designed so that five wafers can enter the carrier as shown in FIG. 55 wafers were polished by one batch of polishing. As for the thickness of the wafer after polishing, arbitrary 5 wafers were measured per batch. As shown in FIG. 6, the measurement points were 25 points (5 × 5 points) at equal intervals in the range 3 mm or more from the wafer outer periphery. Black circles represent measurement points, and numbers from P1 to P25 are assigned. After measuring the oscillation frequency at each point, it was converted into thickness by a known relational expression (not specified) between the oscillation frequency of the AT vibrator and the wafer thickness. The maximum value and the minimum value of the thickness of the entire 25 points of the wafer were defined as the thickness variation of the wafer (herein referred to as Δt). As a result of an experiment in which the rotation / revolution ratio was changed by 7 points in the range of 0.608 to 1.308, the variation in thickness was small even when the rotation / revolution ratio was changed to a large value, and was in the range of 0.18 to 0.25 μm. . This cannot achieve the target of 0.1 μm. As described above, in the polishing method by adjusting the carrier revolution ratio, the difference in the finished thickness due to the wafer polishing trajectory length between the carrier outer peripheral side and the center side occurs, and as a result, the in-plane thickness variation Δt of the processed wafer. There is a limit to reducing this.
JP 2001-260013 A

  The present invention solves the above-mentioned problems, and in the polishing of a piezoelectric wafer using a planetary gear type polishing machine, the thickness variation is small even when a large diameter piezoelectric wafer is used, and the manufacturing cost of the thickness shear vibrator is greatly increased. It is an object of the present invention to provide a polishing method that can be reduced.

  According to the first aspect of the present invention, in the polishing of the piezoelectric wafer using the planetary gear system, when two or more stages of polishing are performed, the polishing is temporarily stopped in the middle of the final stage of polishing. After reversing, the polishing was started again to polish to the final thickness.

  According to a second aspect of the present invention, in the method for polishing a piezoelectric wafer according to the first aspect, the wafer to be a workpiece is a square shape, and the long side and short side dimensions of the wafer both exceed 11 mm, and the long side Was about 34 mm or less and the short side was about 30 mm or less.

  According to a third aspect of the present invention, in the piezoelectric wafer polishing method according to the first or second aspect, the material of the piezoelectric wafer serving as a workpiece is quartz.

  According to a fourth aspect of the present invention, in the piezoelectric wafer polishing method according to the third aspect, the quartz wafer serving as a workpiece is an AT cut or BT cut wafer.

  According to a fifth aspect of the present invention, in the method for polishing a piezoelectric wafer according to the fourth aspect, the timing at which the polishing is temporarily stopped in the middle of the final stage polishing process and the crystal wafer is reversed is determined. The thickness was determined to be equal to or less than the final target thickness plus approximately 1.2 μm.

  According to a sixth aspect of the present invention, in the piezoelectric wafer polishing method according to the fourth aspect, the timing when the polishing is temporarily stopped in the middle of the final stage polishing process and the crystal wafer is inverted is determined by the thickness of the wafer. It was set as the time when it reached below the thickness which added about 0.5 micrometer to the thickness of the last target value.

  According to a seventh aspect of the present invention, in the method for polishing a piezoelectric wafer according to any one of the fourth to sixth aspects, the control signal for temporarily stopping the polishing during the polishing process is applied to the thickness of the wafer using the gap method. It was decided to use field measurement (in-situ measurement).

  According to an eighth aspect of the present invention, in the method for polishing a piezoelectric wafer according to any one of the fifth to seventh aspects, the thickness of the polishing finish of the wafer is about 30 μm or more and 160 μm or less.

  In the polishing process of a piezoelectric wafer using a planetary gear system, when two or more stages of polishing are performed, the polishing process is temporarily stopped and the piezoelectric wafer is reversed in the middle of the final stage polishing process. By starting polishing again and polishing to the final thickness, it is possible to minimize the thickness variation in the entire surface of the piezoelectric wafer. As a result of paying attention to the difference in wafer finished thickness between the carrier outer peripheral side and the center side in the planetary gear type polishing machine, the piezoelectric wafer is reversed between the carrier outer peripheral side and the center side, and a certain amount of polishing processing is performed again. Thus, it is possible to minimize the difference in the finished thickness due to the position of the wafer in the carrier at the time of finishing. Hereinafter, this method is called an inversion method.

  In addition to the reversal method, the piezoelectric wafer serving as a workpiece to be polished is square, and the wafer has a long side and a short side both of which exceed 11 mm, the long side is approximately 34 mm or less, and the short side is approximately By setting the thickness to 30 mm or less, it is possible to reduce the thickness variation in the wafer surface even though the wafer has an area of 8 times or more that of a conventionally used wafer. Accordingly, the number of vibrating pieces to be picked up can be increased, a large number of vibrating pieces having a uniform thickness can be manufactured by polishing, and the manufacturing cost of the vibrating pieces can be greatly reduced.

  In addition to the inversion method, the piezoelectric wafer material is made of quartz, so that it has much superior oscillation frequency temperature stability compared to other piezoelectric materials such as LiTaO3 and LiNbO3, and the timing of various control signals. As a reference source, a reference signal, or a time source, it can be applied to the manufacture of vibrating pieces for a very wide range of applications from portable information (terminal) devices to home appliances, office equipment, and medical equipment.

  Further, by making the quartz wafer into an AT-cut or BT-cut wafer, the effect of shortening the manufacturing tact time becomes larger, and as a result, the manufacturing cost can be further reduced. The vibration mode of AT cut and BT cut is thickness shear vibration, and the oscillation frequency depends on the thickness of the resonator element (having an inversely proportional relationship). If the variation in thickness within the wafer surface is large, the variation in oscillation frequency between the resonator elements also increases, and therefore, the adjustment time takes a lot of time in the frequency adjustment process. Therefore, reduction in thickness variation in an AT-cut or BT-cut wafer has a great effect on shortening the manufacturing tact time, and as a result, achieves a reduction in manufacturing cost.

  In the piezoelectric wafer polishing method, the timing when the polishing is temporarily stopped in the middle of the polishing process at the final stage and the quartz wafer as the workpiece is reversed, the thickness of the quartz wafer is approximately the thickness of the final target value. By reaching the point of time when the thickness reaches 1.2 μm or less, it is possible to reduce the variation in the wafer in-plane thickness at least as compared with the case where the workpiece is not reversed. There is an effective range for the timing at which the polishing process is temporarily stopped.

  Further, the timing of reversing the quartz wafer is set to the time when the thickness of the quartz wafer reaches below the final target thickness plus approximately 0.5 μm, thereby reducing in-plane thickness variation. About 0.1 μm or less. Even in a 34 mm × 30 mm square wafer having an area more than eight times that of a currently used 11 mm square small wafer, by increasing the in-plane thickness variation Δt to 0.10 μm, the frequency adjustment time in the subsequent process is about 11 mm. It can be made substantially the same as the adjustment time required when the resonator element is manufactured from a small corner wafer. Therefore, the wafer can be enlarged to reduce the manufacturing cost of the vibrator.

  Furthermore, in the method for polishing a piezoelectric wafer, a control signal for temporarily stopping polishing during polishing processing is obtained by using in-situ measurement of wafer thickness using an air gap method. Therefore, it is possible to constantly monitor the thickness of the wafer during the polishing process. If a network analyzer is used for the main body of monitoring, it is excellent in signal processing of measured values, and a change in resonance curve and thickness information can be displayed on the monitor screen, which is excellent in operator visibility.

  Furthermore, in the method for polishing piezoelectric wafers, the thickness of the polished wafer is set to approximately 30 μm or more and 160 μm or less, so that AT vibrators and BT vibrators in a practical frequency range can be manufactured, and mass production of these vibrators is performed. The yield of time can be improved. The upper and lower limit values of the wafer thickness are determined in consideration of a practical polishing yield in mass production and a required polishing finish thickness when the wafer is polished using the planetary gear system. The lower limit of about 30 μm is a value that takes into account yield reduction due to wafer cracking, chipping or carrier breakage during polishing. On the other hand, the upper limit of 160 μm is a value that takes into account the thickness corresponding to the frequency band required for AT cut or BT cut and the margin for rough polishing performed after cutting the quartz crystal. Since the practical frequency range of the AT vibrator and the BT vibrator is in the range of 30 μm to 160 μm in terms of the thickness of the wafer, the present invention can be applied to polishing of a vibrating piece in a wide frequency band. .

  The present invention will be described in detail based on examples. The wafer used in the examples is an AT-cut quartz crystal wafer. The dimensions are the same as in the preliminary experiment described above, a square wafer with a long side of 34 mm × short side of 30 mm, and the wafer thickness is about 80 μm. This was polished on both sides to about 60 μm. As the abrasive, FO # 4000 containing zirconium oxide as a main component was used. After the wafer is cut from the raw stone, it is polished using FO # 2000 as a first-stage process up to 80 μm. The polishing apparatus is the same as that used in the preliminary experiment. The thickness of the polished wafer was also converted to the thickness at each point by measuring the oscillation frequency at 25 points on one wafer, just as in the preliminary experiment. The following description will be given for an AT cut wafer, but the same holds true for a BT cut wafer that vibrates in the same thickness sliding mode.

  The polishing process flow of the present invention is shown in FIG. The polishing process is started (step 30). The operator first sets a wafer on the carrier (step 31). Next, processing conditions such as the load and the number of rotations of the surface plate are set (step 31). Subsequently, the polishing target value is set to a value (target value + α) slightly thicker than the final target value (step 33). Here, how α is determined will be described later. After the input is thus completed, the polishing process is started (step 34). When polishing is started, the wafer is polished while the processing conditions are automatically changed according to the program. The thickness of the wafer being polished can be measured momentarily with a thickness measuring device (known by the name of an auto lap controller or the like) using a gap method (step 35). In the present embodiment, the sensor unit 6 has a diameter of 6 mm and is embedded in the upper surface plate, and the measurement apparatus main body 11 is configured to constantly monitor the thickness of the wafer being polished using a network analyzer. (In-situ measurement). When the thickness of the wafer reaches (target value + α), a stop control signal is output from the network analyzer 11 to the polishing apparatus, and the polishing apparatus automatically pauses processing (step 36).

  Next, the operator removes the wafer from the carrier, reverses the orientation of the wafer, and resets it. That is, the front and back of the taken-out wafer are turned upside down, and then set on the carrier while being rotated 180 degrees in the in-plane direction (step 37). In this state, the portion that was on the outer peripheral side of the carrier before the temporary stop comes to the inner peripheral side of the carrier. Conversely, the portion that has been on the inner peripheral side of the carrier is placed on the outer peripheral side of the carrier. This is shown in FIG. After the wafer is set, the target value is set to the original final target value (step 38). When the polishing process is resumed (step 39), the thickness measuring device functions again, and when the wafer thickness reaches the target value, the process automatically ends (step 41). The operator removes the wafer from the carrier (step 42), and the polishing process is completed (step 43).

  Next, how to determine the value of α will be described. α is a value indicating how much thicker the target value is to be stopped and reversed. Perform an experiment in advance to determine the optimum value. An example of this will be described based on experimental results. As the value of α, four values of 0.5 μm, 0.8 μm, 1.0 μm, and 2.0 μm were selected, and the optimum value was selected among them.

  FIG. 3 shows a result of measuring five wafers for one α with respect to a thickness variation Δt of the wafer with respect to each α value. Here, α = 0 indicates the case of the conventional polishing method in which the wafer is not reversed halfway. In the case of α = 2.0 μm, the thickness variation Δt increased in contrast to the case where it was not reversed. However, when α = 1.0 μm, the thickness variation decreased, and when α = 0.8 μm, Δt further decreased. became. When α = 0.5 μm, the thickness variation Δt of four of the five wafers is less than 0.1 μm, the thickness variation Δt of the remaining one is 0.11 μm, and an average value of 0.10 μm is obtained. It was. From this, it can be said that when α = 0.5 μm, the wafer thickness variation Δt satisfies approximately 0.1 μm.

  FIG. 4 is a graph showing the average thickness variation Δt of five wafers at each α shown in FIG. According to this, the thickness variation is less than the thickness variation in the case of α = 1.26 μm and no reversal, and it works more effectively below this value. As described above, the target thickness variation is approximately equal to α = 0.5 μm. It has reached 0.1 μm. A value of α = 1.26 μm is practically easy to handle by setting it to 1.2 μm by rounding down to the safe side.

  On the wafer, the wafer is based on thickness data at P3, P8, P13, P18, and P23 which are five measurement points on the center line 3 (line connecting the outer periphery side, the center, and the inner periphery side) shown in FIG. The shape of will be described. FIG. 5 is an experiment in the case of α = 2.0 μm, 1.0 μm, and 0.5 μm. One wafer is arbitrarily selected for each α, and the maximum thickness at the five measurement points for each wafer is selected. The values are normalized and shown as 1. Looking at the shape of the wafer after polishing in detail, the wafer inverted at α = 2.0 μm is rapidly thinned by polishing the portion (measurement point P3) located on the outer peripheral side after the inversion, and conversely becomes thin. ing. This portion placed on the outer peripheral side after the reversal is a portion that is on the inner peripheral side of the carrier before the reversal and is relatively thick in the wafer. That is, during the polishing of 2.0 μm after the reversal, not only the original inner and outer peripheral differences are removed, but also the outer peripheral portion is further polished. When the polishing amount after inversion is reduced to 1.0 μm, the polishing amount on the outer peripheral side (measurement point P3) gradually decreases, and the inner periphery (measurement point P23) and the outer periphery (measurement point P3) are polished in a well-balanced manner. The state approaches. The wafer inverted at the timing of α = 0.5 μm approached the flattest state. At this time, the difference in thickness between the points P3, P8, P13, P18, and P23, which are the five points on the center line 3 of the wafer, is 0.1% or less, that is, about 0.06 μm or less. Therefore, under the present processing conditions, it is optimal to reverse at a stage 0.5 μm thicker than the final target value of the wafer.

  As described above, the in-plane thickness variation is improved from the value Δt = 0.18 to 0.25 μm by the conventional method to Δt = 0.10 μm by performing reversal in the wafer carrier during the polishing process. I was able to. As a result, the tact time in the frequency adjustment step in the post-process conventionally requires about 8 seconds in the case of the mainstream frequency adjustment method in which the electrode metal thin film formed on the resonator element is adjusted by irradiation with argon ions. However, this could be reduced to less than half. This frequency adjustment time is substantially the same as the adjustment time required when the resonator element is manufactured from a small wafer having a size of about 11 mm square.

  In this embodiment, the case where the final thickness of polishing is about 60 μm is described. A vibrating piece for a 24 MHz or 27 MHz AT vibrator used in a digital video camera or a digital still camera has a finish polishing thickness of about 60 μm to 65 μm, and this embodiment can be applied immediately. Of course, the present invention is also applicable when the thickness of the wafer is greater than 65 μm. Specifically, when the oscillation frequency is in the 10 MHz range, that is, a thickness of about 160 μm is possible. A wafer for an AT vibrator is usually cut into a thickness of about 200 μm to 220 μm from a quartz lumbard rough using a band saw or a wire saw. After cutting, preferably about 40 μm is processed by rough polishing, so the upper limit is about 160 μm as the thickness of the finish polishing.

On the other hand, the present invention is more effective when the thickness of the wafer is thinner than 60 μm. For example, in the case of the 48 MHz AT vibrator used in the above-described liquid crystal television, the thickness of the finish polishing is about 34 μm. At this time, the thickness variation of 0.1 μm corresponds to the frequency variation of about 2930 ppm. In the case of 27 MHz, the thickness variation of 0.1 μm corresponds to about 1620 ppm in terms of frequency. Therefore, in the case of the 48 MHz AT vibrator, the sensitivity of the thickness variation is about twice as large as that of 27 MHz. Therefore, when the thickness of the piezoelectric material becomes thinner, that is, as the vibration piece becomes more compatible with high frequency, it is more important to manage the thickness variation in the wafer surface, and the thickness variation reducing method of the present invention is more effective. Become.
When the wafer thickness is in the 20 μm range, carrier breakage and wafer cracking frequently occur during the polishing process, and polishing a large wafer as described in the present invention with a planetary gear type polishing machine. Becomes practically difficult. Therefore, the practical lower limit of the wafer thickness is about 30 μm.

  Since the range of the thickness of the wafer to which the present invention is applied has such a wide range, the number of times of polishing required for the polishing of the wafer in the previous stage varies depending on the final target wafer thickness. This is because a carrier having an appropriate thickness must be prepared so that the wafer does not jump out of the holding hole of the carrier holding the wafer. In the case of the AT wafer shown in the present embodiment, the first polishing is carried out after cutting from a rough lumbard crystal with a cutting angle of 35 degrees 10 minutes ± 1 minute with a wire saw to a thickness of about 220 μm. Polishing was carried out to a thickness of 220 μm to 130 μm, and then, as a second polishing, the carrier was exchanged to polish to a thickness of 130 μm to 80 μm. In the first polishing, a carrier having a thickness of 120 μm was used, and in the second polishing, a carrier having a thickness of 70 μm was used. The thickness of the carrier is preferably selected to be smaller than the target thickness for polishing and thicker than about half the thickness of the wafer to be held. For example, in the first case, 120 μm is selected which is thinner than the target value of 130 μm and thicker than 110 μm which is half the thickness of the wafer. By using the carrier having such a thickness, the polishing process can be stably performed. When the final finish thickness is approximately 30 μm, the previous stage polishing process requires one more time, and the previous stage polishing process is three times and the final stage polishing process is one time. In total, four polishing processes are required. On the contrary, when the final finished thickness is about 160 μm, the polishing process in the previous stage can be performed once, and the polishing process is performed twice in total, including the final polishing process once.

It is a flowchart of the grinding | polishing process of the piezoelectric material wafer which concerns on this invention. It is a figure explaining the inversion of the wafer in the grinding | polishing process of the piezoelectric material wafer which concerns on this invention, (a) is a figure which shows the wafer upside down, (b) is a figure which shows the front-back inversion of a wafer. It is a figure which shows thickness variation (DELTA) t of the five piezoelectric material wafers in each (alpha) by the grinding | polishing process of this invention. It is a figure which shows the average value of thickness variation (DELTA) t of five wafers in each (alpha) by the grinding | polishing process of this invention. It is a figure which shows the normalized thickness of 5 points | pieces on a wafer centerline in (alpha) = 2.0micrometer, 1.0 micrometer, and 0.5 micrometer. It is a figure which shows the thickness measurement point of a wafer. It is a figure which shows the positional relationship of a carrier and a wafer. It is a schematic diagram which shows the relationship between the surface plate of a grinder and a carrier, (a) is a top view seen from the upper direction of a grinder, (b) is AA 'sectional drawing in (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wafer 2 Carrier 3 Wafer center line 4 Carrier outer peripheral side 5 Carrier center side 6 Sun gear (sun gear)
7 Internal gear (internal gear)
8 Lower surface plate 9 Upper surface plate 10 Wafer frequency measuring device sensor unit 11 Wafer frequency measuring device body 12 Sun gear rotation direction (direction of arrow)
13 Direction of rotation of internal gear (direction of arrow)
14 Lower platen rotation direction (direction of arrow)
15 Carrier rotation direction (direction of arrow)

Claims (8)

  In the polishing process of a piezoelectric wafer using a planetary gear type polishing machine, when two or more polishing processes are performed, the polishing process is temporarily stopped during the final polishing process, and the piezoelectric wafer is reversed. A method for polishing a piezoelectric wafer, wherein polishing is started again and polishing is performed to a final thickness.   2. The polishing method according to claim 1, wherein the shape of the piezoelectric wafer serving as a workpiece is a square shape, both the long side and the short side of the piezoelectric wafer exceed 11 mm, the long side is approximately 34 mm or less, and the short side is A method for polishing a piezoelectric wafer, characterized by being approximately 30 mm or less.   3. The method for polishing a piezoelectric wafer according to claim 1, wherein a material of the piezoelectric wafer to be a workpiece is quartz.   4. The polishing method according to claim 3, wherein the quartz wafer serving as a workpiece is an AT-cut or BT-cut wafer.   5. The polishing method according to claim 4, wherein when the polishing is temporarily stopped during the final polishing process and the quartz wafer is inverted, the thickness of the quartz wafer is approximately equal to the final target thickness. A method for polishing a piezoelectric wafer, characterized by being at a time when the thickness reaches 2 μm or less.   5. The polishing method according to claim 4, wherein when the polishing is temporarily stopped during the polishing process in the final stage and the quartz wafer is turned over, the thickness of the quartz wafer is about 0. 0 to the final target thickness. A method for polishing a piezoelectric wafer, characterized in that it is a point of time when the thickness reaches 5 μm or less.   7. The polishing method according to claim 4, wherein a control signal for temporarily stopping polishing during polishing processing is performed using in-situ measurement of wafer thickness (in-situ measurement) using a gap method. A method for polishing a piezoelectric wafer, characterized by:   8. The polishing method according to claim 4, wherein the quartz wafer has a polished finish thickness of about 30 μm to about 160 μm. 9.

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