Methods for manufacturing crystal wafers and crystal oscillators

Abstract

This invention provides a method for manufacturing a crystal wafer and a crystal oscillator, wherein the crystal wafer can reduce breakage during handling and transport, thereby improving productivity. The crystal wafer (10) includes a portion or all of a bicrystalline region (21) on its outer periphery (20). The bicrystalline region is a region extending at least 2 mm from the outer periphery to the center of the crystal wafer, and more than 80% of the region is bicrystalline. An etch-resistant mask (13) for forming the shape of multiple crystal oscillators is formed in a matrix on the crystal wafer including the bicrystalline region, and the crystal wafer is immersed in an etching solution mainly composed of hydrofluoric acid to form the shape.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a crystal wafer that is difficult to break during handling and transport, and a crystal oscillator. Prior Technology

[0002] In recent years, with the miniaturization of electronic devices and the increasing frequency of communication, there is a growing demand for small and thin crystal oscillators, making it difficult to manufacture them using mechanical processing methods. Therefore, the following method is used: multiple crystal oscillators are formed into a matrix on a crystal wafer using photolithography and wet etching techniques, and then each crystal oscillator is folded from the wafer for monolithization. Consequently, the photolithography or monolithization process involves repeated manipulation and transport of the crystal wafer.

[0003] In the wet etching step, a hydrofluoric acid-based etching solution is typically used. Moreover, Patent Document 1 discloses that the etching rate of BT cutting (non-vibration region), which forms a twin crystal, is about 2 / 7 compared to AT cutting (vibration region) (Patent Document 1, technical means to solve the problem, etc.). [Existing technical documents] [Patent Literature]

[0004] Patent Document 1: Japanese Patent Application Publication No. 2003-69374 Summary of the Invention

[0005] [Problem to be Solved by the Invention] However, when wet etching a crystal wafer, a metal film such as Au or a resist film is formed in areas where etching is not desired, specifically in the outer periphery of the crystal wafer, i.e., the outer frame, or in areas supporting the crystal oscillators within the crystal wafer, to protect the outer frame or the rods from erosion by the etching solution. However, when forming the metal film or resist film, a fixture must be used to hold, for example, a portion of the outer periphery of the crystal wafer, so the metal film or resist film cannot be attached to this portion, and therefore cannot be protected by the metal film or resist film. As a result, unintended etching occurs in a portion of the outer periphery of the crystal wafer. Consequently, the following problem, for example, arises, as illustrated with reference to FIG16. Figure 16(A) is a plan view of an existing crystal wafer 170. Furthermore, Figure 16(B) is a plan view of an example of a crack 190 occurring in an existing crystal wafer 170. In the existing crystal wafer 170, as shown in Figure 16(A), during the wet etching step, the outer periphery of the crystal wafer 170 is sometimes etched into an unintended state, resulting in bumps 180. These bumps 180 can cause cracks 190, as shown in Figure 16(B), due to the forces applied to the crystal wafer during handling and transport.

[0006] The present invention was made in view of the aforementioned problems, and therefore the object of this application is to provide a crystal wafer with a novel structure and a method for manufacturing a crystal oscillator, which can prevent unevenness from occurring on the outer periphery in a crystal wafer used to form multiple crystal oscillators in a matrix, thereby reducing cracking during operation and handling. [Technical means to solve the problem]

[0007] In order to achieve the aforementioned objective, according to the invention of the crystal wafer of this application, a crystal wafer is used to form a plurality of crystal oscillators in a matrix, wherein a portion or all of the outer periphery of the crystal wafer includes a bicrystalline region.

[0008] Furthermore, according to another invention of this application, a method for manufacturing a crystal oscillator is used to form the outline of multiple crystal oscillators in a matrix on a crystal wafer using lithography and an etching solution mainly composed of hydrofluoric acid. The method for manufacturing a crystal oscillator is characterized by including the following steps: forming a bicrystalline region in at least a portion or all of the outer periphery of the crystal wafer; and immersing the crystal wafer with the bicrystalline region formed in the etching solution to form the outline. Here, in the various inventions described, the so-called duocrystallization region refers to a region where other crystals have entered the first crystal, i.e., a region of infiltrated duocrystallization. That is, when the crystal wafer uses a right-handed crystal, the duocrystallization region is a region of left-handed crystal; conversely, when the crystal wafer uses a left-handed crystal, the duocrystallization region is a region of right-handed crystal. To further illustrate with a specific example, when the crystal wafer is an AT-cut crystal wafer, the duocrystallization region becomes a region approximately equivalent to a BT-cut region. [The effects of the invention]

[0009] According to the present invention, the crystal wafer includes a bicrystalline region on its outer periphery. This prevents (reduces) the outer periphery from being etched into an unintended state in a direction perpendicular to the main surface of the crystal wafer during wet etching, thus mitigating unevenness on the outer periphery. Consequently, it reduces breakage during crystal wafer handling and transport, improving productivity, for example, reducing defects such as breakage during crystal oscillator manufacturing. Furthermore, when a metal film or resist film is deposited in areas where etching is not desired, even if unprotected areas are created on the outer periphery due to the influence of the fixture, the bicrystalline region on the outer periphery can prevent or mitigate unintended etching. Therefore, productivity is improved, for example, reducing defects such as breakage during crystal oscillator manufacturing, and the influence of the fixture is not considered, thus increasing the freedom of fixture shape. Furthermore, according to the crystal oscillator manufacturing method of the present invention, a bicrystalline region is formed in a designated area of ​​the crystal wafer before the step of using an etching solution mainly composed of hydrofluoric acid, and then processing is performed using the etching solution. Therefore, it is possible to prevent the outer periphery from being etched into an unintended state during the wet etching step. Consequently, cracking caused during the handling and transport of the crystal wafer can be reduced, thus enabling the high-productivity manufacturing of crystal oscillators. Simple Explanation of the Diagram

[0010] Figure 1 is a plan view of the crystal wafer of the first embodiment. Figure 2 is a plan view of an example of a crystal wafer according to the first embodiment. Figure 3 is a plan view of an example of a crystal wafer according to the first embodiment. Figure 4 is a plan view of an example of a crystal wafer according to the first embodiment. Figure 5 is a plan view of an example of a crystal wafer according to the first embodiment. Figure 6 is a plan view of the crystal wafer of the second embodiment. Figure 7 is a plan view of the crystal wafer of the third embodiment. Figure 8 is an explanatory diagram illustrating an embodiment of the method for manufacturing the crystal oscillator of the present invention. Figure 9 is an explanatory diagram following the manufacturing example in Figure 8. Figure 10 is an explanatory diagram following the manufacturing example in Figure 9. Figure 11 is an explanatory diagram following the manufacturing example in Figure 10. Figure 12 is an explanatory diagram following the manufacturing example in Figure 11. Figure 13 is an explanatory diagram of the manufacturing method following Figure 12. Figure 14 is an explanatory diagram of the manufacturing method following Figure 13. Figure 15 is an explanatory diagram of the manufacturing method following Figure 14. In Figure 16, Figure 16(A) is a plan view of an existing crystal wafer. Figure 16(B) is a plan view of an example of a crack occurring in an existing wafer. Implementation

[0011] Hereinafter, embodiments of the manufacturing methods for the crystal wafer and crystal oscillator of the present invention will be described with reference to the accompanying drawings. Furthermore, the drawings used for description are only schematic representations to the extent that these inventions can be understood. Moreover, in the drawings used for description, the same structural components are indicated by the same numbers, and sometimes descriptions are omitted. Furthermore, the shapes, materials, etc., described below are only preferred examples within the scope of the present invention. Therefore, the present invention is not limited to the following embodiments.

[0012] 1. Structure of a crystal wafer Figure 1 is a plan view of the crystal wafer 10 according to the first embodiment. In Figure 1, P is a symbol representing a magnified portion of the crystal wafer 10. In this embodiment, the planar shape of the crystal wafer 10 is circular, and the cutting (cutting) from the raw crystal is AT cutting. However, the planar shape is not limited to circular; it can also be square. Furthermore, the cutting is not limited to AT cutting; other cutting methods can be used, such as Z cutting or stress-compensated (SC) cutting, or double-rotation cutting. The crystal wafer 10 of the first embodiment includes a frame forming predetermined region 20 that is not a predetermined region for forming crystal oscillators. The frame forming predetermined region 20 typically includes an outer frame 20a and a rod 20b connecting each crystal oscillator. In this embodiment, the outer frame 20a is referred to as the outer periphery. The example shown in Figure 1 is an example where the entire area of ​​the outer periphery 20a is a bicrystalline region 21. By bicrystallineizing the outer periphery 20a, even when wet etching is performed using hydrofluoric acid as the primary solvent, it is possible to prevent the outer periphery 20a of the crystal wafer 10 from being etched into an unintended state, thereby reducing the degree of unevenness in the outer periphery 20a of the crystal wafer 10. Therefore, it is possible to reduce cracking that occurs during the handling and transport of the crystal wafer 10.

[0013] When doubling the outer periphery 20a of the crystal wafer 10, ideally, as shown in FIG1, the entire outer periphery of the crystal wafer 10 should be doubled. However, as shown in FIGS. 2 and 3, a portion of the entire outer periphery 20a is not doubled, resulting in a non-doubled region 30, which is also a form of the present invention. In this case, the effect of reducing breakage during crystal wafer handling and transport can also be obtained. Moreover, the same effect can be obtained when a non-doubled region 30 is formed in a portion of the outer periphery 20a in the wafer thickness direction. Furthermore, as shown in FIG. 4, when a non-doubled region 30 is formed in the direction from the outermost periphery to the center of the crystal wafer 10 and the doubling region of the outer periphery is interrupted, the possibility of crystal wafer breakage may increase compared to the case where it is not interrupted. However, in this case, the effect of the doubling region existing in the area other than the non-doubled region can also reduce the concern about crystal wafer breakage.

[0014] Furthermore, as shown in FIG5(A), the case where bicrystalline regions 21 are respectively provided in a portion of the mutually separated areas 20aa of the outer periphery 20a of the crystal wafer 10 is also a form of the present invention. As a specific example of this form, for instance, in the case where a metal film is formed as a protective film on the crystal wafer, or in the case where a resist is applied, a portion of the crystal wafer is held by a fixture for forming the metal film or a fixture for applying the resist, and no metal film or resist is formed therein. In the example of FIG5(A), only the areas of the crystal wafer where the probability of unintentional etching due to the lack of a protective film is extremely high are bicrystalline regions. Therefore, compared to bicrystallineing the entire outer periphery 20a, the bicrystalline processing time can be shortened. Furthermore, the effects of the present invention can be obtained. Furthermore, the example in Figure 5(A) shows two partial regions 20aa near the orientation plane of the crystal wafer. However, the position or number of partial regions 20aa is not limited to the example in Figure 5(A) and can be changed to an appropriate position or number corresponding to the purpose. There may also be a case where the number of partial regions 20aa is only one.

[0015] Furthermore, when a portion of the outer periphery 20aa is a bicrystalline region 21, for example, as shown in FIG5(B), the edge of the crystal wafer sometimes becomes a non-bicrystalline region 30. Furthermore, after immersing such a crystal wafer in a hydrofluoric acid-based wet etching solution for a specified time, the edge, being a non-bicrystalline region 30, is etched more thoroughly than the bicrystalline region. FIG5(C) shows the observation results of this situation. That is, FIG5(C) is an observation of the cross-section of the etched crystal wafer along line AB of FIG5(B). In FIG5(C), the horizontal axis is the scanning distance along line AB (unit: mm), and the vertical axis is the height change in the region due to etching (unit: μm). In FIG5(C), it can be seen that the height of the bicrystalline region 20aa (21) does not change after etching, while the height of the non-bicrystalline region 30 at the edge of the crystal wafer decreases due to etching. However, even if the edge of the crystal wafer is etched, the presence of a bicrystalline region near the edge reduces the degree of etching-induced unevenness on the central side of the crystal wafer in the diameter direction.

[0016] That is, in the configuration shown in Figure 5, there is a metal film or a photoresist film in the areas where etching is not desired. On the other hand, there is a double crystallization region in areas where there is a high concern that the etching will result in an unintended state, such as in areas where a protective film such as a metal film or photoresist film cannot be formed due to the fixture used when forming the protective film. Therefore, by utilizing the effect of the double crystallization region, the phenomenon of unevenness from the edge of the crystal wafer can be reduced.

[0017] Furthermore, as shown in Figure 5(B), even when a non-bicrystalline region 30 is formed at the edge of the crystal wafer, if the non-bicrystalline region 30 is too large, the effectiveness of the present invention will be reduced. Therefore, when a non-bicrystalline region 30 is formed at the edge of the crystal wafer, the width (depth dimension) h1 from the edge of the non-bicrystalline region 30 of the crystal wafer towards the center should preferably be within 2 mm, more preferably within 1 mm, and even more preferably within 0.5 mm. Moreover, the width (depth dimension) h2 of the bicrystalline region 21 itself from the edge of the crystal wafer towards the center, or the dimensions W1 and W2 in the direction orthogonal to h2, can be determined by considering the size of the fixture when forming a protective film such as a metal film or a resist film. However, W1 and W2 can be the same or different. The dimensions h2, W1, and W2 are preferably, for example, at least 2 mm, but are not limited thereto. When the crystal wafer is, for example, a circular crystal wafer with a diameter of four inches, the h2 of the bicrystalline region from the outer periphery to the center is preferably, for example, 2 mm or more and 12.5 mm or less. More preferably, h2 is, for example, 3 mm or more and 12.5 mm or less. If expressed as a ratio to the diameter of the four-inch wafer, it is 2 / 101.6 ≈ 0.02 or more and 12.5 / 101.6 ≈ 0.213 or less, therefore the ratio is 2% or more and 12% or less. Moreover, W1 and W2 are preferably 3 mm or more and 16 mm or less, more preferably 4 mm or more and 16 mm or less. This is because, as described above, if the bicrystalline region is too narrow, the effect of preventing etching into an unintended state cannot be sufficiently obtained, and therefore the cracking caused during crystal wafer handling and transport cannot be mitigated. On the other hand, this is because if the bicrystalline region is too wide, the predetermined area for crystal oscillator formation becomes narrow, and the productivity of the crystal oscillator is impaired.

[0018] Furthermore, within the scope of the bisacrylated region, the bisacrylation rate is not limited to this, but is preferably above 80%. This is because, as shown in Figure 3, sometimes a portion of the outer periphery of the crystal wafer is not bisacrylated, resulting in a non-bisacrylated region 30. If the bisacrylated region is reduced, it is not possible to adequately prevent etching into an unintended state, and it is not possible to mitigate the cracking that occurs during the handling and transport of the crystal wafer.

[0019] Figure 6 is a plan view of the crystal wafer 40 according to the second embodiment. The crystal wafer 40 of the second embodiment includes a bicrystalline region 50 on its outer periphery, and a portion or all of the rods connecting each crystal oscillator 60 includes a bicrystalline region 70. By bicrystallineing a portion or all of the rods, it is possible to prevent the connecting portions of each crystal oscillator from being etched into an unintended state and maintain strength, thereby mitigating the phenomenon of cracking at the connecting portions of each crystal oscillator.

[0020] Figure 7 is a plan view of the crystal wafer 80 according to the third embodiment. The crystal wafer 80 of the third embodiment includes a bicrystalline region 90 on its outer periphery, and a bicrystalline region 110 is included only at the connection portions connecting each crystal oscillator 100 to the rod. By bicrystallineing only the connection portions, similar to the second embodiment, unintentional etching of the connection portions of each crystal oscillator can be prevented, and the phenomenon of cracking at the connection portions of each crystal oscillator can be reduced.

[0021] 2. Manufacturing method of crystal oscillator Next, embodiments of the crystal oscillator manufacturing method of the present invention will be described with reference to FIGS. 8 to 15. The manufacturing method of the present invention is a manufacturing method using lithography and wet etching techniques, and includes a special step called duocrystallization. Therefore, FIGS. 9 to 15 show a plan view of the crystal wafer and an enlarged plan view of a portion Q of the crystal wafer. Furthermore, in some of the diagrams in FIGS. 9 to 15, a cross-sectional view of a portion Q of the crystal wafer along the RR line is also shown.

[0022] In the manufacturing method described above, firstly, as shown in FIG8, a crystal wafer 11 is prepared, and the crystal wafer 11 is locally heated using, for example, a laser 130 from a heat source 120, to bicrystallize part or all of the outer periphery. Furthermore, the bicrystallization method is not limited to local heating using a laser; other methods such as a spot heater can also be used. Moreover, in an embodiment of the manufacturing method described above, an example of bicrystallizing the outer periphery 20a and bars 20b of the crystal wafer is shown for understanding the crystal wafer shown in FIG1. ​​Then, a metal film (not shown) for forming an etch-resistant mask is formed on the crystal wafer 11.

[0023] As shown in Figure 9, the metal film formed on the crystal wafer 11 is processed by the well-known lithography technique to form an etch-resistant mask 13 on both the front and back sides of the crystal wafer 11 to form the shape of the crystal sheet 12. In this embodiment, the etch-resistant mask 13 includes: a portion corresponding to the shape of the crystal wafer 12, a rod portion holding each crystal wafer, and a portion connecting the crystal wafer and the rod portion (connection portion 14 in FIG9). Moreover, the etch-resistant mask 13 is formed on the back surface of the crystal wafer 11 in an opposing manner.

[0024] Next, the crystal wafer 11, with the etch-resistant mask 13 already formed, is immersed in an etching solution mainly composed of hydrofluoric acid for a specified time. This process dissolves the portion of the crystal wafer 11 not covered by the etch-resistant mask 13, as shown in FIG10, thus obtaining the approximate shape of the crystal wafer. Because the outer periphery and rods of the crystal wafer 11 are double-crystallized, the etching step that forms the shape of the crystal wafer can prevent the outer periphery and rods from being etched into an unintended state.

[0025] Next, the etch-resistant mask 13 is removed from the crystal wafer 11. At this point, in the manufacturing method of the present invention, as shown in FIG11, only the portion of the etch-resistant mask 13 corresponding to the crystal wafer 12 is removed, leaving the portion corresponding to the rod or connector. This is to maintain the strength of the rod or connector. Of course, depending on the design, a portion or all of the etch-resistant mask corresponding to the rod and connector may also be removed.

[0026] Next, the crystal wafer 11 is immersed again in an etching solution mainly composed of hydrofluoric acid for a specified time. Here, the specified time refers to the time until the thickness of the predetermined region of the crystal wafer 12 reaches a thickness that meets the required oscillation frequency specification. Figure 12(B) shows the crystal wafer with the obtained thickness. Because the outer periphery and rods of the crystal wafer 11 are double-crystallized, it is possible to prevent the outer periphery and rods from being etched into an unintended state. In addition, in this embodiment, an etching step is provided to thin the thickness of the crystal wafer 12 forming the predetermined region, but if the crystal wafer itself is thick enough to obtain the specified oscillation frequency from the beginning, the above step is not required.

[0027] Next, as shown in FIG13, the etch-resistant mask 13 is removed from the crystal wafer 11 after etching, exposing the crystal surface. Then, a metal film (not shown) for forming the excitation electrode and lead-out electrode of the crystal oscillator is formed on the entire surface of the crystal wafer 11 by a well-known film deposition method.

[0028] Next, as shown in FIG14, the metal film is patterned into an electrode shape using well-known lithography and metal etching techniques, forming an excitation electrode 15a and a lead-out electrode 15b as electrodes 15 on the crystal wafer 11. Thus, a crystal oscillator 16 comprising a crystal wafer 12, an excitation electrode 15a, and a lead-out electrode 15b can be obtained.

[0029] In addition, generally speaking, the structure obtained by mounting the crystal oscillator 16 in a preferred container is often referred to as a crystal oscillator. Hereinafter, a typical example of the crystal oscillator will be described using FIG15. FIG15 shows the sequence of mounting the crystal oscillator 16 in the container 140 by means of a plan view and a cross-sectional view along line SS in the figure.

[0030] In the state shown in FIG14, the crystal oscillator 16 is attached to the crystal wafer 11 via the connecting portion 14. Therefore, firstly, an appropriate external force is applied to the connecting portion 14 to separate the crystal oscillator 16 from the crystal wafer 11, as shown in FIG15(A) for monolithization. On the other hand, as a container, for example, a well-known ceramic package 140 (hereinafter also referred to as package 140) is prepared. As shown in Figures 15(B) and 15(C), the package 140 in this case includes: a recess 140a for receiving a crystal oscillator 17, a bump 140b provided on the bottom surface of the recess 140a for fixing the crystal oscillator, and a mounting terminal 140c provided on the back side of the package 140. The bump 140b and the mounting terminal 140c are electrically connected by a via wiring (not shown).

[0031] As shown in Figure 15(D), a crystal oscillator 17 is installed in the recess 140a of the package 140. More specifically, as shown in Figure 15(E), a conductive adhesive 150 is applied to the bump 140b, and the crystal oscillator 17 is fixed to the bump 140b at the point where the lead-out electrode 15b is located by means of the conductive adhesive 150. Then, the oscillation frequency of the crystal chip 12 is adjusted to a specified value by a well-known method. Next, the recess 140a of the package 140 is made into a suitable vacuum or inert gas environment, and then the recess 140a is sealed by a cover 160 by a well-known method. Thus, a crystal oscillator with a structure in which the crystal oscillator 17 is housed in the package 140 is obtained.

[0032] Furthermore, in the embodiments of the manufacturing method described, an example of duocrystallizing the outer periphery 20a and the rod 20b of the crystal wafer was explained. However, as illustrated in FIG5, the invention of the manufacturing method of this application also includes the case where duocrystallization regions 21 are provided in separate portions 20aa of the outer periphery 20a of the crystal wafer 10. As a specific example of this case, for instance, when the crystal wafer is coated with a metal film as a protective film or with a resist, a portion of the crystal wafer is held by a fixture for metal film formation or a fixture for resist coating, and no metal film or resist is formed in that portion. When duocrystallization regions 21 are provided in separate portions 20aa of the outer periphery 20a of the crystal wafer 10 covered by the fixtures, the duocrystallization processing time can be shortened compared to duocrystallizing the entire outer periphery 20a, thus being preferable from the viewpoint of manufacturing throughput.

[0033] 10: Crystal wafer of the first embodiment 11: Crystal Wafer 12: Crystal sheet 13: Etch-resistant dome 14: Connecting parts 15: Electrode 15a: Excitation electrode 15b: Lead-out electrode 16: Crystal oscillator 20: The framework forms a predetermined area. 20a: Outer frame 20b: Rod 20aa: Part of the area 21: Twin crystallization region 30: Non-twinned region 40: Crystal wafer of the second embodiment 50: Bicrystallization region 60: Crystal oscillator 70: Twin crystallization region 80: Crystal wafer of the third embodiment 90: Bicrystallization region 100: Crystal oscillator 110: Twin crystallization region 120: Heat source 130: Laser 140: Ceramic package (package) (container) 140a: concave part 140b: Bump 140c: Mounting terminal 150: Conductive adhesive 160: Cover 170: Existing crystal wafers 180: Concave and convex 190: Rupture AB, RR, SS: lines h1: Width (Depth dimension) h2: Width (Depth dimension) (Dimension) P, Q: Part of a crystal wafer W1, W2: Dimensions

Claims

1. A crystal wafer for forming a plurality of crystal oscillators in a matrix, the crystal wafer being characterized in that: a portion or all of the outer periphery of the crystal wafer includes a bicrystalline region having a width of at least 2 mm from the outer periphery to the center of the crystal wafer.

2. The crystal wafer as claimed in claim 1, wherein a portion of the outer periphery of the crystal wafer is an unfilmed region, the unfilmed region being a region held by a fixture during the formation of an etch-resistant film, and thus unable to form the etch-resistant film, the etch-resistant film being an etch-resistant film formed when the crystal wafer is wet-etched.

3. The crystal wafer as described in claim 1 or 2, wherein, The bicrystalline region has a width of 2% to 12% of the diameter of the crystal wafer from the outer periphery to the center.

4. The crystal wafer as described in claim 1 or 2, wherein, The dicrystallization rate within the dicrystallization region is above 80%.

5. The crystal wafer as claimed in claim 1, including a rod for connecting the plurality of crystal oscillators, wherein a portion or all of the rod is a bicrystalline region.

6. The crystal wafer as claimed in claim 5, including a connection portion connecting the plurality of crystal oscillators and the rod, wherein the connection portion is a bicrystalline region.

7. A method for manufacturing a crystal oscillator, comprising using photolithography and an etching solution based on hydrofluoric acid to form the outline of a plurality of crystal oscillators in a matrix on a crystal wafer, the method being characterized by comprising the following steps: forming a bicrystalline region in at least a portion or all of the outer periphery of the crystal wafer; and immersing the crystal wafer with the bicrystalline region formed therein in the etching solution to form the outline.

8. The method for manufacturing a crystal oscillator as described in claim 7, wherein, The portion of the outer periphery is an unfilmed area. The unfilmed area is a portion of the crystal wafer that is held by the jig for film formation or the jig for resist coating when a protective film against the etching solution is formed on the surface or back of the crystal wafer in order to form the shape of the crystal oscillator, and no metal film or resist is formed therein.

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