JP4825952B2 - Piezoelectric wafer etching method and piezoelectric device - Google Patents

Description

  The present invention relates to a method for etching a piezoelectric wafer and a piezoelectric device.

  The outer shape of the piezoelectric vibrating piece preferably has a side surface perpendicular to the surface of the vibrating piece in order to ensure characteristics such as vibration and mechanical strength of the vibrating piece. This piezoelectric vibrating piece is manufactured by etching a piezoelectric wafer to form a plurality of piezoelectric substrates and forming an electrode pattern on the surface of the piezoelectric substrate. When the piezoelectric wafer is etched, a mask corresponding to the shape of the piezoelectric substrate (piezoelectric vibrating piece) is formed on the surface of the piezoelectric wafer, and the opening of the mask is etched.

  By the way, since many of piezoelectric materials including quartz have anisotropy in the crystal, it is known that the etching rate varies depending on the axial direction of the crystal due to the anisotropy of the crystal. When an AT-cut quartz crystal wafer is used as the piezoelectric wafer, the cross-sectional shape of the groove produced by etching becomes a trapezoid. That is, the groove has a side surface perpendicular to the surface of the quartz wafer and a side surface along the Z axis representing the crystal axis.

For this reason, Patent Document 1 discloses that an etched surface can be formed substantially perpendicular to the surface of the quartz wafer by forming a corrosion-resistant film on the surface of the AT-cut quartz wafer based on certain conditions. Is disclosed. Further, in Patent Document 2, an extension line connecting one upper surface end portion and the other lower surface end portion of the protective film formed on the upper and lower surfaces of the rotating Y plate is set in the Z-axis direction, and the distance between them is t / tan θ. It has been disclosed that the etching time is shortened and the characteristics of the crystal resonator are improved by shifting only by this amount.
Japanese Patent Laid-Open No. 4-11404 JP-A-1-179513

  However, when the experiment disclosed in the patent document 1 is tested, the portion where the piezoelectric wafer is covered with the mask is also removed by the lateral etching (overetching), and the etched portion is the opening of the mask. Sometimes it would be bigger. For this reason, when manufacturing a piezoelectric vibrating piece, it is necessary to form a mask on the piezoelectric wafer larger than the desired shape of the piezoelectric substrate in anticipation of the amount of overetching in advance. The number of obtained piezoelectric substrates (piezoelectric vibrating pieces) had to be reduced.

  In the invention disclosed in Patent Document 2, the side surface of the piezoelectric substrate obtained by etching is slanted. That is, a side surface perpendicular to the surface of the piezoelectric substrate cannot be obtained. For this reason, the piezoelectric vibrating piece obtained from the invention disclosed in Patent Document 2 cannot oscillate a stable frequency, so that stable characteristics cannot be obtained, and since the side surface is sharp, cracks and chipping are likely to occur. And so on.

  Conventionally, efforts have been made to form the side surface of the piezoelectric substrate perpendicular to the surface. Particularly in an AT-cut quartz crystal resonator element, an effort is made to make the shape of the crystal substrate (crystal resonator element) in the Z (Z ′) direction, that is, the side surface of the crystal substrate along the X axis perpendicular to the surface. This is because the side surface of the quartz substrate along the X axis has an effect on the vibration characteristics of the quartz crystal vibrating piece. However, in recent years, since the piezoelectric vibrating piece has been reduced in size, not only the shape of the piezoelectric substrate in the Z (Z ′) direction but also the piezoelectric substrate in the X direction can be secured in order to ensure the vibration characteristics of the piezoelectric vibrating piece. It is preferable that the shape, that is, the shape of the side surface of the piezoelectric substrate along the Z ′ axis is also perpendicular to the surface of the piezoelectric substrate.

An object of the present invention is to provide a method for etching a piezoelectric wafer in which an etching surface perpendicular to the surface of the piezoelectric wafer is formed in a short time.
Another object of the present invention is to provide a piezoelectric device using a piezoelectric substrate obtained by this etching method.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
According to a first aspect of the piezoelectric wafer etching method, a mask having openings is formed on one surface and the other surface of a piezoelectric wafer, and the piezoelectric wafer exposed from the openings is etched to form a through groove. In the piezoelectric wafer etching method, an end in the Z′-axis direction adjacent to the opening in the mask formed on the one surface is formed in the opening in the mask formed on the other surface. A shift of 50 ± 10% of the thickness of the piezoelectric wafer in the + Z ′ direction of the piezoelectric wafer with respect to the adjacent end in the Z′-axis direction, and the opening in the mask formed on the one surface The adjacent end in the X-axis direction is set in the + X direction of the piezoelectric wafer with respect to the end in the X-axis direction adjacent to the opening in the mask formed on the other surface. Etching method of a piezoelectric wafer, wherein the shifted 10 ± 5% of the thickness of the conductive wafer.
The piezoelectric wafer etching method according to the first embodiment is characterized in that the one surface is in a + Y ′ direction with respect to the other surface.
According to a third aspect of the piezoelectric wafer etching method, the opening of the mask has a width of 1.5 times or more the plate thickness of the piezoelectric wafer. The method for etching a piezoelectric wafer according to the embodiment.
4. The piezoelectric wafer etching method according to claim 1, wherein the piezoelectric wafer is a quartz crystal wafer. 5.
According to a fifth embodiment of the piezoelectric wafer etching method, the quartz wafer includes a crystal axis of quartz, an X axis as an electrical axis, a Y axis as a mechanical axis, and a Z axis as an optical axis. An axis obtained by inclining the Z axis in the −Y direction of the Y axis with the X axis of the orthogonal coordinate system as the center as a Z ′ axis, and an axis inclining the Y axis in the + Z direction of the Z axis as Y ′. 5. The piezoelectric wafer according to claim 4, wherein the piezoelectric wafer is an AT-cut quartz crystal wafer having a thickness parallel to the X ′ axis and the Z ′ axis and having a thickness parallel to the Y ′ axis. Etching method.
Application Example 1 This application example is a method for etching a piezoelectric wafer in which a mask having an opening is formed on one surface and the other surface of a piezoelectric wafer, and the opening is etched to form a through groove. An end in the Z′-axis direction adjacent to the opening in the mask formed on the one surface is an end in the Z′-axis direction adjacent to the opening in the mask formed on the other surface. On the other hand, the piezoelectric wafer etching method is characterized by being shifted by 50 ± 10% of the thickness of the piezoelectric wafer in the + Z ′ direction of the piezoelectric wafer.

  When the piezoelectric wafer exposed in the opening of the mask is etched, the side surface along the X-axis obtained by this etching can be made perpendicular to the surface of the piezoelectric wafer. When a piezoelectric substrate is formed using this method, a side surface (side surface along the X axis) perpendicular to the surface of the piezoelectric substrate can be obtained. Accordingly, cracks and burrs are less likely to occur on the side surfaces, and the mechanical strength can be improved.

  In addition, by shifting the mask on the piezoelectric wafer, the etching time until the side surface of the through groove is perpendicular to the surface of the piezoelectric wafer is shortened, so that the width of the through groove formed by etching is widened. Can be prevented. Therefore, when the piezoelectric substrate is obtained from the piezoelectric wafer, it is possible to prevent the outer shape of the piezoelectric substrate from being reduced, so that the number of piezoelectric substrates obtained from one piezoelectric wafer can be increased.

Application Example 2 In this application example, the end in the X-axis direction adjacent to the opening in the mask formed on the one surface is used as the opening in the mask formed on the other surface. The piezoelectric wafer etching method is characterized by being shifted by 10 ± 5% of the thickness of the piezoelectric wafer in the + X direction of the piezoelectric wafer with respect to the end portion in the X-axis direction adjacent to the piezoelectric wafer.

  When the piezoelectric wafer exposed in the opening of the mask is etched, the side surface along the Z ′ axis obtained by this etching can be made perpendicular to the surface of the piezoelectric wafer. When this method is used to form a piezoelectric substrate, a side surface (side surface along the Z ′ axis) perpendicular to the surface of the piezoelectric substrate can be obtained. Accordingly, cracks and burrs are less likely to occur on the side surfaces, and the mechanical strength can be improved.

  In addition, by shifting the mask on the piezoelectric wafer, the etching time until the side surface of the through groove is perpendicular to the surface of the piezoelectric wafer is shortened, so that the width of the through groove formed by etching is widened. Can be prevented. Therefore, when the piezoelectric substrate is obtained from the piezoelectric wafer, it is possible to prevent the outer shape of the piezoelectric substrate from being reduced, so that the number of piezoelectric substrates obtained from one piezoelectric wafer can be increased.

  Further, the mask provided on one surface of the piezoelectric wafer and the mask provided on the other surface are shifted by 50 ± 10% of the thickness of the piezoelectric wafer in the + Z ′ direction and 10 ± 5 of the thickness of the piezoelectric wafer in the + X direction. % Shift, a piezoelectric substrate having a vertical side surface along the X-axis and a vertical side surface along the Z′-axis can be obtained with the same etching time.

Application Example 3 In the piezoelectric wafer etching method according to this application example , the opening of the mask has a width of 1.5 times or more the plate thickness of the piezoelectric wafer. In this case, the width of the opening is at least 1.5 times the plate thickness of the piezoelectric wafer in both the Z′-axis direction and the X-axis direction. Thereby, the piezoelectric wafer exposed to the opening can be reliably etched.

Application Example 4 In the piezoelectric wafer etching method according to this application example , the piezoelectric wafer is an AT cut crystal. Thereby, an AT-cut quartz substrate having a side surface perpendicular to the surface can be obtained.

Application Example 5 This application example is a piezoelectric device characterized in that the piezoelectric wafer is chipped using the piezoelectric wafer etching method having the characteristics described above, and an electrode pattern is provided on the chipped piezoelectric substrate. It is . Thus, the piezoelectric device can constitute a piezoelectric vibrating piece. The piezoelectric substrate used for this piezoelectric vibrator can have a side surface perpendicular to the surface. Therefore, the piezoelectric device can oscillate at a stable frequency, and it is difficult for cracking and chipping to occur, so that the mechanical strength can be improved.

Application Example 6 A piezoelectric device according to this application example is characterized in that the piezoelectric substrate on which the electrode pattern is formed is mounted on a package. Accordingly, the piezoelectric device can constitute a piezoelectric vibrator. Therefore, a signal with a stable frequency can be output from the piezoelectric device.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a piezoelectric wafer etching method and a piezoelectric device according to the invention will be described below. In this embodiment, an embodiment using an AT-cut crystal as a piezoelectric wafer will be described.

  First, the first embodiment will be described. FIG. 1 is an explanatory view of an AT-cut quartz crystal wafer. The crystal axis of quartz is defined by the X axis, the Y axis, and the Z axis. The AT-cut quartz crystal wafer 10 is a rotating Y plate obtained by rotating the Y plate around the X axis by θ about the XY plane cut perpendicular to the Y axis, and θ is around 35 °. Say. The Z ′ axis and the Y ′ axis are axes that are newly set by rotating the Z axis and the Y axis by θ.

  A processing method in which a mask having an opening is formed on one surface and the other surface of such an AT-cut quartz crystal wafer and a through groove is formed by etching the opening will be described below. The end of the mask 18 formed in the direction along the Z ′ axis and adjacent to the opening 16 is formed as follows. FIG. 2 shows a quartz wafer provided with a mask, and is a cross-sectional view taken along the Z ′ axis. In FIG. 2, the left side of the drawing is the + Z ′ direction, the upper side is the + Y ′ direction, and the + X direction is from the back to the front of the drawing.

  A mask 18 is formed on one surface 12 and the other surface 14 of the quartz wafer 10, and the surface of the quartz wafer 10 where a through groove is to be formed is exposed. That is, on one surface 12 of the crystal wafer 10, a mask 18 is formed in a portion where etching is not desired, and a portion where a through groove is desired to be formed is an opening 16 of the mask 18. Further, on the other surface 14 of the crystal wafer 10, a mask 18 is formed in a portion where etching is not desired, and a portion where a through groove is desired to be formed is used as an opening 16 of the mask 18. One surface 12 of the quartz wafer 10 is located in the + Y ′ direction with respect to the other surface 14.

  An end A in the + Z ′ direction of the mask 18 formed on one surface 12 of the quartz wafer 10 and adjacent to the opening 16 is formed on the other surface 14 and + Z ′ of the mask 18 adjacent to the opening 16. The length L1 is shifted in the + Z ′ direction of the crystal wafer 10 from the end B in the direction. An end A ′ in the −Z ′ direction of the mask 18 formed on one surface 12 of the quartz wafer 10 and adjacent to the opening 16 is formed on the other surface 14 of the mask 18 adjacent to the opening 16. The length L1 is shifted in the + Z ′ direction of the crystal wafer 10 with respect to the end B ′ in the −Z ′ direction. This length L1 is 50 ± 10% of the plate thickness t of the quartz wafer 10. As an example, when the plate thickness t is 100 μm, the shift amount (length) L1 between the end A (A ′) and the end B (B ′) of the mask 18 is 40 to 60 μm.

  Further, the width in the direction along the Z ′ axis of the opening 16 of the mask 18 formed on the one surface 12 of the quartz wafer 10 and the Z ′ axis of the opening 16 of the mask 18 formed on the other surface 14. The width in the direction is the same length L3. This length L3 is 1.5 times or more the plate thickness t of the quartz wafer 10. As an example, when the plate thickness t is 100 μm, the length L3 of the opening 16 of the mask 18 is 150 μm or more.

  Further, the end portion of the mask 18 formed in the direction along the X axis is formed as follows. FIG. 3 shows a quartz wafer provided with a mask, and is a sectional view along the X-axis. In FIG. 3, the left side of the drawing is the + X direction, the upper side is the + Y ′ direction, and the + Z ′ direction is from the front toward the back of the drawing. Also in FIG. 3, one surface 12 of the quartz wafer 10 is located in the + Y ′ direction with respect to the other surface 14.

  An end C in the + X direction of the mask 18 formed on one surface 12 of the quartz wafer 10 and adjacent to the opening 16 is formed on the other surface 14 and the + X direction of the mask 18 adjacent to the opening 16 is formed. The length D2 is shifted in the + X direction of the crystal wafer 10 with respect to the end D. An end portion C ′ in the −X direction of the mask 18 formed on one surface 12 of the quartz wafer 10 and adjacent to the opening 16 is formed on the other surface 14 and − of the mask 18 adjacent to the opening 16. The length L2 is shifted in the + X direction of the crystal wafer 10 with respect to the end portion D ′ in the X direction. This length L2 is 10 ± 5% of the thickness t of the quartz wafer 10. As an example, when the plate thickness t is 100 μm, the shift amount (length) L2 between the end C (C ′) and the end D (D ′) of the mask 18 is 5 to 15 μm. Further, the width in the direction along the X axis of the opening 16 of the mask 18 formed on one surface 12 of the quartz wafer 10 and the direction along the X axis of the opening 16 of the mask 18 formed on the other surface 14. The width is the same length L3. This length L3 is 1.5 times or more the plate thickness t of the quartz wafer 10. As an example, when the plate thickness t is 100 μm, the length L3 of the opening 16 of the mask 18 is 150 μm or more.

  When a plurality of crystal substrates (piezoelectric substrates) are formed from one crystal wafer 10, a plurality of masks 18 having the above-described relationship may be formed on one surface 12 and the other surface 14 of the crystal wafer 10. . FIG. 4 is a plan view for explaining the positional relationship between the mask formed on one surface and the mask formed on the other surface. FIG. 4 is an example of obtaining a quartz substrate from one quartz wafer, and shows the positional relationship of the masks 18 (18a, 18b) for one quartz substrate. In FIG. 4, the left side of the drawing is the + X direction, the upper side is the + Z ′ direction, and the + Y ′ direction is from the back to the front of the drawing. In FIG. 4, the description of the crystal wafer is omitted. A mask 18a formed on one surface 12 is indicated by a solid line, and a mask 18b formed on the other surface 14 is indicated by a broken line.

  As shown in FIG. 4, the mask 18a formed on one surface 12 is shifted by a length L1 in the + X direction with respect to the mask 18b formed on the other surface 14, and has a length L2 in the + Z 'direction. It is shifted. As described above, the lengths L1 and L2 are 50 ± 10% of the plate thickness t of the crystal wafer 10 and 10 ± 5% of the plate thickness t, respectively.

  When the quartz crystal wafer 10 on which the mask 18 is thus formed is etched, the opening 16 of the mask 18 is etched to form a through groove. FIG. 5 shows a crystal substrate obtained by etching, and is a cross-sectional view along the Z′-axis. In FIG. 5, the right side of the drawing is the + Z ′ direction, and the + X direction is from the front to the back of the drawing. The side surface of the through groove obtained by etching is the side surface of the crystal substrate 20. Therefore, in the case shown in FIG. 5, the left and right side surfaces of the quartz substrate 20 are the side surfaces of the through grooves.

  As described above, when the mask 18 is formed with the length L1 set to 50 ± 10% of the thickness t of the quartz wafer 10, the side surface 22 of the quartz substrate 20 in the Z ′ direction (the quartz substrate 20 along the X axis). The side surface 22) is perpendicular to the surface 24 as shown in FIG. Here, the vertical surface includes a surface substantially perpendicular to the surface 24, and even if there is a slight residue or a slight penetration, it can be regarded as vertical. Although not shown, the side surface of the quartz substrate 20 in the X direction (side surface of the quartz substrate 20 along the Z ′ axis) when the mask 18 is formed with the length L2 of 10 ± 5% of the plate thickness t. Is perpendicular to the surface 24 in the same manner as the side surface 22 of the quartz substrate 20 in the Z ′ direction.

  On the other hand, when the length L1 is shorter than the length described above, for example, when the length L1 is zero, the side surface 22 of the quartz substrate 20 in the Z ′ direction has a large residue 26 as shown in FIG. Remains. Although not shown, the side surface of the quartz substrate 20 in the X direction when the length L2 is shorter than the length described above remains as in the side surface 22 of the quartz substrate 20 in the Z ′ direction. Further, in order to remove the residue 26, further etching may be performed, but the width of the quartz substrate 20 is reduced by the lateral etching.

  Further, when the length L1 is longer than the length described above, for example, the side surface 22 of the quartz substrate 20 in the Z ′ direction in the case where the length is the same as the plate thickness t of the quartz is large as shown in FIG. Intrusion 28 occurs. Although not shown in the drawing, the side surface of the quartz substrate 20 in the X direction when the length L2 is longer than the above-described length also causes large intrusion in the same manner as the side surface 22 of the quartz substrate 20 in the Z ′ direction.

  According to such an etching method of the quartz wafer 10, the thickness 18 of the quartz wafer 10 is changed in the Z′-axis direction from the mask 18 formed on the one surface 12 to the mask 18 formed on the other surface 14. By shifting by 50 ± 10%, the side surface 22 along the X-axis obtained by etching the opening 16 of the mask 18 can be made perpendicular to the surface. Further, the mask 18 formed on the one surface 12 is shifted by 10 ± 5% of the plate thickness t of the crystal wafer 10 in the X-axis direction with respect to the mask 18 formed on the other surface 14, thereby opening the opening of the mask 18. The side surface along the Z ′ axis obtained by etching 16 can be made perpendicular to the surface. If the lengths L1 and L2 are set as described above, the crystal substrate 20 having the side surface 22 along the X axis and the side surface along the Z ′ axis perpendicular to the surface can be obtained with the same etching time. Therefore, since the side surface of the quartz substrate 20 is formed perpendicular to the surface, cracks and chipping are less likely to occur, and the mechanical strength can be improved.

  As described above, if the mask 18 is provided on the crystal wafer 10 while being shifted, the vertical side crystal substrate 20 can be formed approximately three times faster than the case where the mask 18 is provided without being shifted. If the mask 18 is shifted on the quartz substrate 20, the etching time for forming the through groove is shortened compared to the case where the mask 18 is not shifted, so that the quartz substrate 20 having a large outer shape is obtained. Production speed can be improved. Therefore, the number of crystal substrates 20 obtained from one crystal wafer 10 can be increased.

  In addition, since the length L3 of the opening 16 is 1.5 times or more the thickness t of the quartz wafer 10, the surface of the quartz wafer 10 and the etching solution can be reliably contacted. Therefore, a through groove can be formed in the quartz wafer 10.

  Next, a second embodiment will be described. In the second embodiment, a plurality of crystal substrates are formed from one crystal wafer using the crystal wafer etching method described in the first embodiment, and a piezoelectric device is formed using the crystal substrates. Will be described. FIG. 6 is an explanatory diagram of a piezoelectric device. Here, FIG. 6A is a plan view of the crystal resonator element, and FIG. 6B is a cross-sectional view of the crystal resonator.

  The crystal vibrating piece 30 (piezoelectric vibrating piece, piezoelectric device) shown in FIG. 6A has a configuration in which an electrode pattern 32 is provided on the surface of the crystal substrate 20. The electrode pattern 32 includes an excitation electrode 34, a connection electrode 36, and a lead electrode 38. The excitation electrode 34 is provided at the center of the one surface 12 and the other surface 14 of the quartz substrate 20. The connection electrodes 36 are provided at both ends of one side of the crystal substrate 20. The connection electrode 36 is formed on each of the one surface 12 and the other surface 14 at each end, and is connected via a side surface. The excitation electrode 34 and the connection electrode 36 are connected one-to-one by the extraction electrode 38. In this manner, the AT-cut quartz crystal vibrating piece 30 that generates the thickness shear vibration shown in FIG. 6A is obtained.

  Since the side surface of the quartz crystal vibrating piece 30 is formed perpendicular to the surface, the vibration characteristics of the quartz crystal vibrating piece 30 can be improved and a stable frequency can be oscillated. Even when the crystal vibrating piece 30 is downsized, the crystal vibrating piece 30 can oscillate at a stable frequency. Further, since the side surface of the quartz crystal vibrating piece 30 is vertical, cracks and chips are less likely to occur, and the mechanical strength can be improved.

  Such a crystal vibrating piece 30 can be mounted on a package 42 to constitute a crystal resonator 40 (piezoelectric resonator, piezoelectric device) as shown in FIG. 6B. The package 42 has a package base 44 and a lid 46. External terminals 48 are provided on the back surface of the package base 44. The package base 44 has a recess 50 that opens upward. A mount electrode 52 is provided on the bottom surface of the recess 50, and the mount electrode 52 is electrically connected to the external terminal 48. The quartz crystal vibrating piece 30 is provided on the mount electrode 52 via a conductive bonding material 54. Specifically, after the conductive bonding material 54 is provided on the mount electrode 52, the crystal vibrating piece 30 is mounted on the package base so that the conductive bonding material 54 and the connection electrode 36 of the crystal vibrating piece 30 are bonded. 44. A lid 46 is bonded to the upper surface of the package base 44 on which the crystal vibrating piece 30 is mounted, and the recess 50 is hermetically sealed. This hermetic sealing may be performed so long as the recess 50 is sealed in a vacuum or sealed with an inert gas such as nitrogen. As a result, a signal with a stable frequency can be output from the crystal unit 40.

  It should be noted that a circuit for oscillating the crystal vibrating piece 30 may be mounted on the package 42 described above to form a crystal oscillator. In addition to a circuit that oscillates the crystal vibrating piece 30, a temperature compensation circuit that increases the stability of the frequency with respect to the temperature of the crystal vibrating piece 30 and a circuit that controls the output frequency of the crystal vibrating piece 30 according to the set voltage are mounted on the package 42. Thus, a temperature compensated crystal oscillator or a voltage controlled crystal oscillator can be used.

It is explanatory drawing of the quartz wafer by which AT cut was carried out. FIG. 3 is a cross-sectional view taken along the Z ′ axis, showing a quartz wafer provided with a mask. It is sectional drawing along the X-axis which shows the crystal wafer which provided the mask. It is a top view explaining the positional relationship of the mask formed in one surface, and the mask formed in the other surface. FIG. 4 is a cross-sectional view taken along the Z ′ axis, showing a quartz substrate obtained by etching. It is explanatory drawing of a piezoelectric device.

Explanation of symbols

10 ......... Quartz wafer, 12 ......... One surface, 14 ......... Other surface, 16 ......... Opening, 18 ......... Mask, 20 ......... Quartz substrate, 30 ......... Crystal vibrating piece , 32... Electrode pattern, 40... Quartz crystal, 42.

Claims (5)

In a method for etching a piezoelectric wafer , a mask having an opening is formed on one surface and the other surface of the piezoelectric wafer, and the piezoelectric wafer exposed from the opening is etched to form a through groove.
An end in the Z′-axis direction adjacent to the opening in the mask formed on the one surface is an end in the Z′-axis direction adjacent to the opening in the mask formed on the other surface. In contrast, the piezoelectric wafer is shifted by 50 ± 10% of the thickness of the piezoelectric wafer in the + Z ′ direction of the piezoelectric wafer,
The end in the X-axis direction adjacent to the opening in the mask formed on the one surface is the end in the X-axis direction adjacent to the opening in the mask formed on the other surface. In contrast, a method for etching a piezoelectric wafer, wherein the piezoelectric wafer is shifted by 10 ± 5% of the thickness of the piezoelectric wafer in the + X direction of the piezoelectric wafer.   The piezoelectric wafer etching method according to claim 1, wherein the one surface is in a + Y ′ direction with respect to the other surface.   3. The method for etching a piezoelectric wafer according to claim 1, wherein the opening of the mask has a width of 1.5 times or more the thickness of the piezoelectric wafer. 4. The method for etching a piezoelectric wafer according to claim 1, wherein the piezoelectric wafer is a quartz wafer. The quartz wafer is
  Centering on the X axis of an orthogonal coordinate system consisting of an X axis as an electric axis, a Y axis as a mechanical axis, and a Z axis as an optical axis, which are crystal axes of quartz, the Z axis is the Y axis. The axis tilted in the −Y direction is the Z ′ axis, the Y axis is tilted in the + Z direction of the Z axis, the Y ′ axis, and is configured by planes parallel to the X axis and the Z ′ axis. 5. The method for etching a piezoelectric wafer according to claim 4, wherein the wafer is an AT-cut quartz wafer having a thickness in a direction parallel to the Y ′ axis.

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