JP6167520B2 - Device manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing an element using a quartz plate.

  A crystal resonator element using an AT-cut crystal resonator element as an example of the element has a vibration mode of thickness shear vibration and exhibits a cubic curve with excellent frequency temperature characteristics, so it is used in various fields such as electronic equipment. ing. Patent Document 1 discloses a so-called mesa structure resonator element (AT-cut crystal resonator element) having an energy confinement effect comparable to that of a bevel structure or a convex structure. In addition, it is disclosed that an etching process using a solution containing hydrogen fluoride (HF) is used for forming an outer shape of a vibration element having a mesa structure.

JP 2012-191300 A

  However, in the above-described method for forming the outer shape of the vibration element, when the crystal plate is etched by etching with a solution containing hydrogen fluoride (HF) to form a stepped mesa structure, the outer shape has already been formed, Then, the two exposed quartz plates are again exposed to a solution containing hydrogen fluoride (HF), and etching proceeds further. Similarly, in the case of a multi-stage mesa structure, when forming a second-stage mesa structure, the two exposed surfaces of the mesa structure that have already been processed are exposed again to hydrogen fluoride (HF). Etching progresses further due to exposure to the solution. As a result, the intersecting portion of the two surfaces exposed to intersect with each other exposed again to the solution containing hydrogen fluoride (HF) is eroded, and so-called shape variation in which the shape is not stable is generated. Due to this variation in shape, there is a risk that the energy confinement effect will vary, and the electrical characteristics of the vibration element, especially the CI (Crystal Impedance) value, which is a measure of the ease of oscillation, will deteriorate and vary. It was.

  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.

  [Application Example 1] A method of manufacturing an element according to this application example includes a step of preparing a crystal plate having a convex portion, and an etching solution containing HF and having a temperature in the range of 25 ° C. to 55 ° C. And a step of etching the surface of the convex portion.

  According to this application example, a solution containing HF (hydrogen fluoride) having a temperature of 25 ° C. or more and 50 ° C. or less is used for etching processing of a crystal plate including a convex portion constituted by two surfaces exposed to intersect each other. As a result, the erosion of the intersecting portions of the two surfaces of the quartz plate exposed by crossing is suppressed, and the shape of the intersecting portions of the two surfaces exposed by intersecting is stabilized. As a result, the variation in the energy confinement effect is reduced, and it becomes possible to prevent deterioration and variation in the electrical characteristics of the vibration element, particularly the CI value.

Application Example 2 In the device manufacturing method described in the application example, it is preferable that the etching solution includes NH ₄ FHF or a mixed solution of NH ₄ HF ₂ and HF.

  According to this application example, by using such an etching solution, it is possible to easily perform etching processing and reduce the shape variation.

  Application Example 3 In the device manufacturing method described in the application example, it is preferable that the temperature of the etching solution is in a range of 30 ° C. or more and 38 ° C. or less.

  According to this application example, the etching process can be performed particularly preferably from the etching rate and the progress of erosion.

Application Example 4 In the device manufacturing method according to the application example described above, the mixed solution of NH ₄ HF ₂ and HF has a weight ratio of NH ₄ HF ₂ to HF in the range of 1.5 to 2.5. It is preferable that

  According to this application example, by using such an etching solution, it is possible to easily perform etching processing and reduce the shape variation.

  Application Example 5 In the element manufacturing method according to the application example described above, it is preferable that the convex portion includes an outer end face of the crystal plate.

  According to this application example, since the shape of the outer end face of the element is stabilized, it is possible to improve the positioning accuracy of the element. Furthermore, the electrical characteristics of the element can be improved.

  Application Example 6 In the device manufacturing method described in the application example, it is preferable that the crystal plate is an AT cut plate.

  According to this application example, it is possible to provide an AT-cut vibration element having a mesa structure with stable electrical characteristics.

  Application Example 7 In the element manufacturing method according to the application example described above, it is preferable that the crystal plate has a mesa shape and the convex portion constitutes the mesa-shaped stepped portion.

  According to this application example, in the mesa-shaped step portion constituting the convex portion, the erosion of the intersecting portion of the two surfaces that are exposed and intersecting is suppressed, and the shape of the intersecting portion of the two surfaces that are exposed to intersect is the shape. Stabilize. As a result, the variation in the energy confinement effect is reduced, and it becomes possible to prevent deterioration and variation in the electrical characteristics of the vibration element, particularly the CI value.

  Application Example 8 In the device manufacturing method according to the application example described above, the mesa shape is preferably a forward mesa shape.

  According to this application example, in the forward mesa-shaped stepped portion constituting the convex portion, the erosion of the intersecting portion of the two surfaces exposed to intersect is suppressed, and the shape of the intersecting portion of the two surfaces exposed to intersect Is stable. As a result, the variation in the energy confinement effect is reduced, and it becomes possible to prevent deterioration and variation in the electrical characteristics of the vibration element, particularly the CI value.

  Application Example 9 In the element manufacturing method described in the application example, it is preferable that the mesa shape is at least a part of a multistage mesa shape.

  According to this application example, in the step portion that is a part of the multi-step mesa shape constituting the convex portion, the erosion of the intersecting portion of the two surfaces exposed to intersect is suppressed, and the two surfaces exposed to intersect The shape of the intersection is stable. As a result, the variation in the energy confinement effect is reduced, and it becomes possible to prevent deterioration and variation in the electrical characteristics of the vibration element, particularly the CI value.

The schematic structure of embodiment of the vibration element as an element which concerns on this invention is shown, (a) is a top view, (b) is PP sectional drawing shown to (a), (c) is Q- of (a). Q sectional drawing. The schematic diagram which shows the relationship between the new orthogonal coordinate axis | shaft X, Y ', Z' axis | shaft formed by rotating the crystal axes X, Y, and Z of quartz to theta around the X axis, and an AT cut quartz substrate. (A)-(f) is front sectional drawing which shows the outline of the manufacturing process of a vibration element. (G)-(k) is front sectional drawing which shows the outline of the manufacturing process of the vibration element following the manufacturing process shown in FIG. It is an enlarged view of the R part shown in Drawing 1 for explaining the etching state of an exposed surface, (a) and (b) show the etching state by the conventional method, and (c) and (d) are the embodiments. The front sectional view which shows the etching state by a method. It is an enlarged view for demonstrating the etching state of the exposed surface of the outer periphery of a vibration element which is a punching surface of a quartz plate, (a) shows the etching state by the conventional method, (b) is embodiment which concerns on this invention The front sectional view which shows the etching state by. It is a graph explaining the effect of this embodiment, (a) shows the external dimension distribution by a conventional method, (b) is a graph front sectional view showing the external dimension distribution by the embodiment concerning the present invention, (c) is The CI value distribution by a conventional method is shown, (d) is a graph which shows CI value distribution by embodiment which concerns on this invention. The graph which shows the relationship between the temperature of etching solution, and a defect rate. FIG. 3 is a front sectional view showing a vibrator as an electronic device using the vibration element according to the invention. The front sectional view showing the oscillator as an electronic device using the vibration element concerning the present invention. The perspective view which shows the structure of the mobile type personal computer as an example of an electronic device. The perspective view which shows the structure of the mobile telephone as an example of an electronic device. The perspective view which shows the structure of the digital still camera as an example of an electronic device. The perspective view which shows the structure of the motor vehicle as an example of a mobile body.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a vibration element as an example of the element and a manufacturing method thereof will be described, then a vibrator and an oscillator as an electronic device using the vibration element will be described, and then an electronic apparatus using the electronic device, and The moving body will be described.

<Vibration element>
First, a vibration element as an element according to the present invention will be described. FIG. 1: shows schematic structure in embodiment of the vibration element as an element which concerns on this invention, (a) is a top view, (b) is PP sectional drawing shown to (a), (c) is (a It is QQ sectional drawing of). FIG. 2 is a schematic diagram showing the relationship between the new orthogonal coordinate axes X, Y ′, Z ′ and the AT-cut quartz substrate obtained by rotating the crystal axes X, Y, Z of the crystal by θ around the X axis. . 3A to 3F are front sectional views illustrating an outline of the manufacturing process of the resonator element according to the embodiment. 4G to 4K are front sectional views showing an outline of the vibration element manufacturing process subsequent to the manufacturing process shown in FIG. 3.

(Configuration of vibration element)
As shown in FIG. 1, the piezoelectric resonator element 1 according to the present embodiment includes a piezoelectric multi-stage mesa structure excitation unit 14 located in the center and a thin peripheral part 12 continuously formed around the periphery of the excitation unit 14. A substrate 10; excitation electrodes 20a and 20b arranged opposite to each other on both main surfaces of the excitation unit 14; extraction electrodes 22a and 22b extending from the excitation electrodes 20a and 20b toward the end of the piezoelectric substrate 10; Pads 24a and 24b formed at two corners of the piezoelectric substrate 10 at the ends of the electrodes 22a and 22b, respectively.

  The piezoelectric substrate 10 has an excitation part 14 that is located at the center of the piezoelectric substrate 10 and serves as a main vibration area, and a peripheral part 12 that is thinner than the excitation part 14 and is formed so as to project in a bowl shape along the entire periphery of the excitation part 14. doing. The excitation unit 14 having a substantially rectangular planar shape has a configuration in which a substantially central portion of the piezoelectric substrate 10 is protruded in multiple stages (two stages) in both main surface directions. The peripheral portion 12 is formed so as to project from the intermediate portion in the thickness direction on the outer peripheral side surface of the excitation portion 14 in the outer diameter direction. As described above, the piezoelectric substrate 10 includes the excitation part 14 whose side surfaces are stepped and the peripheral part 12 connected to the periphery of the substantially central part of the thickness of the excitation part 14. In addition, although the peripheral part 12 which concerns on this example is protrudingly formed from the whole outer peripheral side surface of the excitation part 14 in the shape of a hook, it is extendedly formed from the intermediate part of the thickness direction at least one part of the outer peripheral side surface to the outer-diameter direction. It may be configured.

  As shown in FIG. 1A, the excitation unit 14 has a substantially rectangular shape with a long side in the X-axis direction and a short side in the Z′-axis direction, and a one-step mesa unit 15 is provided at the center. A two-stage mesa unit 16 is provided around the first-stage mesa unit 15. The two-stage mesa portion 16 has all side surfaces 17 stepped, and is surrounded by the peripheral portion 12 around the entire circumference, and has a thickness (thickness) larger than the thickness of the peripheral portion 12 in the Y′-axis direction. Have. The first-stage mesa portion 15 has all side surfaces 15a stepped, and the entire circumference thereof is surrounded by the second-step mesa portion 16, and has a thickness (thickness) larger than the thickness of the second-step mesa portion 16 in the Y′-axis direction. Meat). That is, as shown in FIGS. 1B and 1C, the excitation unit 14 protrudes in a two-stage structure in both directions in the Y′-axis direction with respect to the peripheral portion 12. In the illustrated example, the excitation unit 14 protrudes toward the + Y′-axis side and the −Y′-axis side with respect to the peripheral portion 12. Moreover, the excitation part 14 has a point (not shown) which becomes a symmetrical center, for example, and can be made into a shape which becomes point symmetrical (planar and three-dimensionally point symmetrical) with respect to this central point.

  As described above, the excitation unit 14 is configured by two types of steps having different thicknesses, the first-stage mesa unit 15 is provided at the center, and the second-stage mesa unit 16 is provided around the first-stage mesa unit 15. That is, it can be said that the piezoelectric vibration element 1 has a two-stage forward mesa structure. The excitation unit 14 vibrates with thickness-shear vibration as main vibration. Since the excitation unit 14 has a two-stage mesa structure, the piezoelectric vibration element 1 can have an energy confinement effect.

  Excitation electrodes 20a and 20b are arranged opposite to each other on both main surfaces of the one-step mesa portion 15 constituting the excitation portion. When an alternating voltage is applied to the front and back excitation electrodes 20a and 20b, the piezoelectric vibration element 1 is excited at a specific vibration frequency inversely proportional to the thickness. The excited vibration displacement spreads to the periphery, and pads 24a and 24b are provided on the front and back surfaces of the peripheral portion 12 in a region where the vibration displacement is sufficiently attenuated.

  A piezoelectric material such as quartz belongs to the trigonal system and has crystal axes X, Y, and Z orthogonal to each other as shown in FIG. The X axis, the Y axis, and the Z axis are referred to as an electric axis, a mechanical axis, and an optical axis, respectively. The AT-cut quartz crystal substrate 101 is a flat plate cut out from quartz along a plane obtained by rotating the XZ plane around the X axis by an angle θ. In the case of the AT-cut quartz substrate 101, θ is approximately 35 ° 15 ′. Note that the Y-axis and the Z-axis are also rotated by θ around the X-axis to be a Y′-axis and a Z′-axis, respectively. Accordingly, the AT-cut quartz crystal substrate 101 has crystal axes X, Y ′, and Z ′ that are orthogonal to each other. The AT-cut quartz substrate 101 has a Y′-axis thickness direction, an XZ ′ plane orthogonal to the Y′-axis (a plane including the X-axis and Z′-axis) is the main plane, and thickness-shear vibration is the main vibration. Excited. The AT-cut quartz substrate 101 can be processed to obtain the piezoelectric substrate 10.

  That is, as shown in FIG. 2, the piezoelectric substrate 10 is centered on the X axis of an orthogonal coordinate system composed of an X axis (electrical axis), a Y axis (mechanical axis), and a Z axis (optical axis), and the Z axis is the Y axis. The axis tilted in the −Y direction is the Z ′ axis, the Y axis is the Y ′ axis is the axis tilted in the + Z direction of the Z axis, and is composed of surfaces parallel to the X and Z ′ axes. It consists of an AT-cut quartz substrate 101 whose thickness is in a parallel direction.

  As shown in FIG. 1A, the piezoelectric substrate 10 has a direction parallel to the X axis (hereinafter referred to as “X axis”) with a direction parallel to the Y ′ axis (hereinafter referred to as “Y ′ axis direction”) as a thickness direction. It is possible to have a rectangular shape having a long side as a “direction” and a short side as a direction parallel to the Z ′ axis (hereinafter referred to as “Z ′ axis direction”). The piezoelectric substrate 10 has an excitation part 14 and a peripheral part 12 formed along the periphery of the excitation part 14. Here, the “rectangular shape” includes a literal rectangular shape and a substantially rectangular shape in which each corner is chamfered.

(Manufacturing method of vibration element)
Next, a method for manufacturing a vibration element will be described with reference to FIGS. 3 and 4 are front sectional views schematically showing the outline of the manufacturing process (manufacturing method) of the resonator element according to the invention. 4 and 5 correspond to FIG. 1B and show a cross section viewed from the Z′-axis direction.

  First, as shown in FIG. 3A, the corrosion-resistant film 30 is formed on the front and back main surfaces (surfaces parallel to the XZ ′ plane) of the AT-cut quartz crystal substrate 101. The corrosion resistant film 30 is formed by, for example, laminating chromium (Cr) and gold (Au) in this order by sputtering or vacuum deposition, and then patterning the chromium and gold into a desired shape. This patterning is performed by, for example, a photolithography technique and an etching technique described in the next paragraph. The corrosion-resistant film 30 has corrosion resistance to a solution containing hydrofluoric acid (HF) that becomes an etching solution when the AT-cut quartz crystal substrate 101 is processed.

  Next, as shown in FIG. 3B, after applying a photoresist film on the corrosion-resistant film 30, the photoresist film is exposed and developed, and the opening from which the photoresist film has been removed in a predetermined shape is formed. A resist film 40 having 41 and 42 is formed. In this way, the resist film 40 is formed so as to cover a part of the corrosion-resistant film 30.

Next, as shown in FIG. 3C, the corrosion resistant film 30 and the outer portions 31 and 32 of the AT-cut quartz crystal substrate 101 are etched using the resist film 40 as a mask. The etching of the corrosion-resistant film 30 is performed by etching (removing) the gold exposed in the openings 41 and 42 of the mask using, for example, a potassium iodide solution, and then removing the exposed chromium after removing the gold, for example, nitric acid 2 Etch (remove) with cerium ammonium solution. For the etching of the outer portions 31 and 32 of the AT-cut quartz substrate 101, the AT-cut quartz substrate 101 exposed by etching the corrosion resistant film 30, for example, ammonium fluoride (NH ₄ F) and hydrofluoric acid (hydrofluoric acid; hydrofluoric acid; A mixed aqueous solution (buffered hydrofluoric acid) of HF) and water (H ₂ O) is used as an etching solution.

In this example, the mixing ratio is ammonium fluoride (NH ₄ F): hydrofluoric acid (hydrofluoric acid; HF): water (H ₂ O) = 30.8 wt%: 14.2 wt%: 55.0 wt % Mixed aqueous solution (buffered hydrofluoric acid) was used. That is, the mixing ratio of ammonium fluoride (NH ₄ F) and hydrofluoric acid (hydrofluoric acid; HF) in this example is ammonium fluoride (NH ₄ F): hydrofluoric acid (hydrofluoric acid; HF). = 2.2 wt%: 1 wt%. As described above, in this example, a mixed solution having a mixing ratio of ammonium fluoride (NH ₄ F) and hydrofluoric acid (hydrofluoric acid; HF) of 2.2 wt%: 1 wt% was used. The mixing ratio of (NH ₄ F) and hydrofluoric acid (hydrofluoric acid; HF) is ammonium fluoride (NH ₄ F): hydrofluoric acid (hydrofluoric acid; HF) = 1.5 wt% or more and 2.5 wt% % Or less: 1 wt% is applicable. In addition, the temperature (liquid temperature) of the mixed aqueous solution (buffered hydrofluoric acid) in this step was set to 85 ° C. for etching.

  Subsequently, by ashing (resist stripping) the resist film 40, as shown in FIG. 3D, the outer shape (as viewed from the Y′-axis direction) of the piezoelectric substrate 10 provided with the corrosion-resistant film 30 on the front and back main surfaces. Time shape) is formed.

  Next, as shown in FIG. 3E, after applying a photoresist film on the corrosion-resistant film 30, the photoresist film is exposed and developed, and the opening from which the photoresist film is removed in a predetermined shape is formed. A resist film 50 having 51 is formed. In this manner, the resist film 50 is formed so as to cover a part of the corrosion-resistant film 30.

Next, using the resist film 50 shown in FIG. 3E as a mask, the corrosion resistant film 30 exposed in the opening 51 of the resist film 50 and the AT-cut quartz crystal substrate 101 are etched to form the peripheral portion 12. The etching of the corrosion resistant film 30 is performed by removing (removing) the gold exposed in the opening 51 of the resist film 50 as a mask using, for example, a potassium iodide solution, in the same manner as the outer shape formation of the AT cut quartz crystal substrate 101 described above. Then, the exposed chromium after the gold is removed is etched (removed) with a ceric ammonium nitrate solution, for example. The AT-cut quartz substrate 101 is etched by using, for example, hydrofluoric acid (hydrofluoric acid: HF), ammonium fluoride (NH ₄ F), and water (H A mixed aqueous solution with ₂ O) is used as an etching solution. The mixed aqueous solution (buffered hydrofluoric acid) used here is a mixed aqueous solution (buffered hydrofluoric acid) having the same composition as that used when forming the outer shape of the piezoelectric substrate 10 described above, and the same temperature (liquid temperature). Etching is performed at

  As shown in FIG. 3F, the AT cut quartz crystal substrate 101 is half-etched to a predetermined depth to form a thin peripheral portion 12. Thereafter, the resist film 50 is peeled off and the corrosion-resistant film 30 is ashed (corrosion-resistant film peeled off), so that the peripheral portion 12 is provided in the periphery as shown in FIG. The piezoelectric substrate 10 having a thick portion (convex portion) extending from the side surface 17 that is an intersecting surface is formed. Here, an outer frame 35 is also formed, and the piezoelectric substrate 10 and the outer frame 35 are partially connected, but the illustration is omitted.

  Next, a process for forming the two-step mesa portion 16 will be described. First, a corrosion-resistant film 60 as shown in FIG. 4 (h) is formed on the exposed surface of the AT-cut quartz crystal substrate 101 including the piezoelectric substrate 10 shown in FIG. 4 (g). The corrosion resistant film 60 is formed by, for example, laminating chromium (Cr) and gold (Au) in this order by sputtering or vacuum deposition, and then patterning the chromium and gold into a desired shape. This patterning is performed by, for example, a photolithography technique and an etching technique described in the next paragraph. The corrosion-resistant film 60 has corrosion resistance against a solution containing hydrofluoric acid that becomes an etching solution when the AT-cut quartz crystal substrate 101 is processed.

  Next, as shown in FIG. 4 (i), after applying a photoresist film on the corrosion-resistant film 60, the photoresist film is exposed and developed, and the opening from which the photoresist film is removed in a predetermined shape is formed. A resist film 70 having 71 is formed. In this way, the resist film 70 is formed so as to cover a part of the corrosion-resistant film 60.

Next, as shown in FIG. 4J, the corrosion resistant film 60 and the two-step mesa portion 16 of the piezoelectric substrate 10 are etched using the resist film 70 as a mask. The etching of the corrosion resistant film 60 is performed by etching (removing) gold exposed in the opening 71 of the mask using, for example, a potassium iodide solution, and then removing chromium exposed by removing the gold, for example, 2 ceric ammonium nitrate. Etch (remove) with solution. The etching of the piezoelectric substrate 10 is performed by using, for example, hydrofluoric acid (hydrofluoric acid: HF) and ammonium fluoride (NH ₄ F) for the AT-cut quartz crystal substrate 101 including the piezoelectric substrate 10 exposed by etching the corrosion-resistant film 60. A mixed aqueous solution (buffered hydrofluoric acid) of water (H ₂ O) is used as an etching solution.

In this example, similarly to the formation of the outer shape described above, the mixing ratio is ammonium fluoride (NH ₄ F): hydrofluoric acid (hydrofluoric acid; HF): water (H ₂ O) = 30.8 wt%. : 14.2 wt%: 55.0 wt% mixed aqueous solution (buffered hydrofluoric acid) was used. The mixing ratio of ammonium fluoride (NH ₄ F) and hydrofluoric acid (hydrofluoric acid; HF) in this example is ammonium fluoride (NH ₄ F): hydrofluoric acid (hydrofluoric acid; HF). : = 2.2 wt%: 1 wt% As described above, in this example, a mixed solution having a mixing ratio of ammonium fluoride (NH ₄ F) and hydrofluoric acid (hydrofluoric acid; HF) of 2.2 wt%: 1 wt% was used. (NH ₄ F) and hydrofluoric acid; mixing ratio of the (hydrofluoric acid HF) is hydrofluoric acid wherein the weight ratio of (hydrofluoric acid HF) ammonium fluoride for (NH ₄ F) of 1.5 or more 2 It can be applied within the range of .5 or less. In addition, the temperature (liquid temperature) of the mixed aqueous solution (buffered hydrofluoric acid) in this step was set to 35 ° C. for etching. The ammonium fluoride (NH ₄ F) may be NH ₄ HF ₂ .

  The AT-cut quartz substrate 101 is etched on the AT-cut quartz substrate 101 excluding the outer peripheral portion of the thick portion of the piezoelectric substrate 10 and half-etched to the middle portion of the side surface 17 that is a predetermined depth of the two-step mesa portion 16. By doing so, the two-stage mesa portion 16 is formed. Etching of the AT-cut quartz substrate 101 in this step is performed on the AT-cut quartz substrate 101 excluding the central portion of the piezoelectric substrate 10 on which the corrosion-resistant film 60 is formed. Etching is also performed on the surface 12 and the side surface 17 (the step portion (convex portion) of the two-step mesa portion 16). In other words, additional etching that further proceeds etching is performed.

  The influence of this additional etching and the effect of the etching method of this embodiment will be described with reference to FIGS. FIGS. 5A and 5B are enlarged views of the R portion shown in FIG. 1 for explaining the etching state of the exposed surface of the crystal plate. FIGS. 5A and 5B show the etching state by the conventional method, and FIGS. (D) is a front sectional view showing an etching state by the method of the present embodiment. FIG. 6 is an enlarged view for explaining an etching state of an exposed surface (crystal outer shape) on the outer periphery of the vibration element that is a punched surface of the crystal plate, and (a) shows an etching state by a conventional method, (B) is a front sectional view showing an etching state according to an embodiment of the present invention.

  First, the etching state of the crystal plate in the formation of the two-step mesa portion of the conventional etching method will be described with reference to FIGS. The formation of the two-step mesa portion 16 has already been subjected to outer shape processing, the peripheral portion 12 which is the two surfaces of the quartz plate exposed to intersect, the side surface 15a, and the crystal surface not covered with the corrosion-resistant film 60 (two-step mesa portion). And the portion 16 to be the portion 16) are etched by an etching solution containing hydrogen fluoride (HF).

As an etchant in a conventional quartz plate etching method, a mixed aqueous solution (buffered hydrofluoric acid) containing hydrofluoric acid (hydrofluoric acid: HF) described in the method for manufacturing a vibration element according to the present invention described above is used. Used. Specifically, the mixing ratio is ammonium fluoride (NH ₄ F): hydrofluoric acid (hydrofluoric acid; HF): water (H ₂ O) = 30.8 wt%: 14.2 wt%: 55.0 wt% A mixed aqueous solution (buffered hydrofluoric acid) is used. And it was performed by setting the temperature (liquid temperature) of etching liquid to 65 degreeC. This is because the etching rate is increased by increasing the temperature of the etching solution, and the number of etching steps is reduced.

  When the two-step mesa portion 16 is etched with a high-temperature etchant in this way, as shown by the arrows in FIG. 5A, the outer peripheral portion has already been processed, and the peripheral portion that is the two surfaces of the quartz plate exposed to cross each other. 12 and the side surface 17 are again exposed to an etching solution containing hydrogen fluoride (HF) and additionally etched. In particular, since the etching of the side surface 17 in the X-axis direction shown in the figure becomes large, the etching of the side surface 17 overlaps with the etching of the two-step mesa portion 16, and as shown in FIG. The portion 18 intersecting with 17 is greatly cut (eroded) and the variation in shape becomes large.

  As described above, when the shape of the outer peripheral side surface 17 of the two-step mesa portion 16 is greatly deformed or the shape is varied, the vibration energy confinement effect varies, and the electrical characteristics of the vibration element, in particular, easy oscillation. Deterioration and variation of CI (Crystal Impedance) value, which is a guideline for this, have occurred.

  In contrast to such a conventional etching method, according to the etching method of the present invention, the shape of the side surface 17 on the outer periphery of the two-step mesa portion 16 can be stabilized. This will be described with reference to FIGS. 5C and 5D. In the etching method according to the present invention, the etching solution is the same as the conventional one, but the temperature (liquid temperature) of the etching solution is different. Whereas the temperature of the conventional etching solution is 65 ° C., the temperature of the etching solution in the etching method according to the present invention is set to 35 ° C.

  Thus, the etching rate is lowered by setting the temperature of the etching solution to a low temperature of 35 ° C. and etching the two-stage mesa portion 16. In particular, as shown in FIG. 5C, the progress of etching in the X-axis direction becomes slow. Thereby, as shown in FIG.5 (d), the erosion of the part 19 where the two-step mesa part 16 and the side surface 17 cross | intersect can be made small. By reducing the erosion in this way, the variation in shape can be reduced.

  As described above, since the deformation of the shape of the outer side surface 17 of the two-step mesa portion 16 can be reduced and the variation in the shape can be reduced, the vibration energy confinement effect can be stably performed. It has become possible to provide a vibration element that can prevent deterioration of characteristics, particularly CI value, and can perform stable oscillation.

  Further, according to the etching method of the present invention, it is possible to reduce variations in the outer shape of the piezoelectric substrate 10 in forming the two-step mesa portion by etching. This will be described with reference to FIG. In addition, the description similar to the above is abbreviate | omitted and a different item is demonstrated. FIG. 6 is an enlarged view for explaining the etching state of the exposed surface (outer end face) of the outer periphery of the vibration element, which is the surface where the quartz plate is punched, and (a) shows the etching state by the conventional method. ) Is a front sectional view showing an etching state according to an embodiment of the present invention.

  In the etching method in which the temperature of the conventional etching solution shown in FIG. 6A is 85 ° C., the exposed surfaces 12a and 12b (outer end surfaces of the crystal plate) on the outer periphery of the vibration element, which is the punched surface of the crystal plate, and the exposure Two surfaces, the exposed surface of the peripheral portion 12 that intersects the surface 12b, are exposed to an etching solution for forming a two-stage mesa portion (not shown). The exposed surface 12a exposed to the etchant and the exposed surface 12b, which is the intersection of the exposed surface 12a and the exposed surface of the peripheral portion 12, are etched at a high etching rate as described above, and the shape of the inclined surface increases. The variation in the size also increases.

  On the other hand, in the etching method in which the temperature of the etching solution according to the embodiment of the present invention shown in FIG. The two surfaces of the quartz plate and the exposed surface of the peripheral portion 12 intersecting the exposed surface 12d are exposed to an etching solution for forming a two-stage mesa portion (not shown). Here, a convex portion is formed by the exposed surface 12c and the exposed surface 12d. The exposed surface 12c exposed to the etching solution and the exposed surface 12d, which is the intersection of the exposed surface 12c and the exposed surface of the peripheral portion 12, are etched in the same manner as described above, but the traveling speed is reduced, and as a result, an inclined surface is formed. The variation in shape can be reduced as the size is reduced.

  Next, returning to FIG. 4, a process following the process of etching the two-step mesa unit 16 will be described. As shown in FIG. 4K, the resist film 70 is ashed (resist stripped) from the AT-cut quartz crystal substrate 101 including the piezoelectric substrate 10 in which the two-step mesa portion 16 is etched. As a result, the piezoelectric substrate 10 in which the excitation electrodes 20a and 20b are provided on the front and back main surfaces of the one-step mesa portion 15 is formed. The excitation electrodes 20a and 20b are formed using the corrosion-resistant film 60 as it is.

  Through the above steps, two types of steps having different thicknesses, that is, a one-step mesa portion 15 is provided at the center portion, a two-step mesa portion 16 is provided around the one-step mesa portion 15, and a peripheral portion 12 is provided around the step portion. An AT-cut quartz crystal substrate 101 provided with the piezoelectric vibration element 1 is formed.

(Modification of manufacturing method)
Note that the AT-cut quartz substrate 101 provided with the piezoelectric vibration element 1 can be realized in the following modification example instead of the above-described vibration element manufacturing method. Note that the same configurations as those in the above-described embodiment are denoted by the same reference numerals as those in FIGS.

  After a positive photoresist film is applied on the corrosion-resistant film 30, the photoresist film is exposed and developed to form a resist film 40 having a predetermined shape (openings 41, 42, etc.). Then, the corrosion resistant film 30 in the openings 41 and 42 of the resist film 40 and the AT-cut quartz crystal substrate 101 are etched to form the outer shape of the piezoelectric vibration element 1.

  Next, a part of resist film 40 (a part corresponding to peripheral part 12) is exposed and developed again using a mask to form resist film 50 having a predetermined shape (opening 51). That is, exposure is performed with the mask disposed inside the outer edge of the resist film 40 as viewed from the Y′-axis direction. Then, the corrosion resistant film 30 in the opening 51 portion of the resist film 50 and the AT-cut quartz crystal substrate 101 are etched to form the peripheral portion 12 of the piezoelectric vibration element 1.

  Next, a part of the resist film 50 (a part corresponding to the two-step mesa part 16) is again exposed and developed using a mask to form a resist film 70 having a predetermined shape (opening 71). That is, exposure is performed with the mask disposed inside the outer edge of the resist film 50 as viewed from the Y′-axis direction. Then, the corrosion resistant film 30 in the opening 71 portion of the resist film 70 and the AT-cut quartz crystal substrate 101 are etched to form the two-step mesa portion 16 of the piezoelectric vibration element 1. Even if the manufacturing method as a modification as described above is used, the piezoelectric vibration element 1 having the two-step mesa portion 16 can be manufactured.

  According to the vibration element using the above-described method for manufacturing a vibration element, it is possible to reduce erosion of the portion 19 where the two-step mesa portion 16 and the side surface 17 intersect when the two-step mesa portion 16 is formed. Further, by reducing this erosion, variation in shape can be reduced. The effect in the manufacturing method of this embodiment is demonstrated along FIG. FIG. 7 shows the distribution of external dimensions and the distribution of vibration characteristics (CI value) of the piezoelectric vibration element 1. FIG. 7A shows the outer dimensions of the piezoelectric vibration element 1 (24 MHz) formed by the conventional method, and FIG. 7B shows the measured value distribution of the outer dimensions of the piezoelectric vibration element 1 (24 MHz) formed in the present embodiment. (C) is the CI value distribution of the piezoelectric vibration element 1 (24 MHz) formed by the conventional method, and (d) is the CI value distribution of the piezoelectric vibration element 1 (24 MHz) formed in the present embodiment. 7A and 7B are so-called dimensional variation distributions in which the vertical axis indicates the dimensional difference for each measurement product when the design value of the external dimension is zero, and the horizontal axis indicates the number of occurrences (frequency). (Deviation).

  As shown in FIGS. 7A and 7B, the variation in the outer dimensions of the piezoelectric vibration element 1 using the manufacturing method of the present embodiment is within ½ of the variation in the outer dimensions of the conventional method. I understand that. Further, as shown in FIGS. 7C and 7D, the piezoelectric vibration element 1 using the manufacturing method of the present embodiment also has a general standard value in the CI value distribution of the piezoelectric vibration element 1 (24 MHz). Is almost within 95Ω or less (non-defective product ratio is 95% or more). On the other hand, it can be seen that in the piezoelectric vibration element 1 using the manufacturing method of the conventional method, about 1/3 is more than the standard value, that is, defective.

  As described above, since the deformation of the shape of the outer side surface 17 of the two-step mesa portion 16 can be reduced and the variation in the shape can be reduced, the vibration energy confinement effect can be stably performed. It is possible to provide a vibration element that can prevent deterioration of characteristics, particularly, CI value and perform stable oscillation. In addition, since the non-defective product rate of the CI value can be increased, it leads to a reduction in defective costs, and as a result, a reduction in costs can be realized.

  In addition, although the temperature (liquid temperature) at the time of etching of etching liquid (buffered hydrofluoric acid) demonstrated by the example of 35 degreeC in the above-mentioned embodiment, it is not restricted to this temperature. FIG. 8 shows the correlation between the temperature of the buffered hydrofluoric acid and the defect rate of the piezoelectric vibration element 1. As shown in FIG. 8, by setting the temperature of buffered hydrofluoric acid to 25 ° C. or more and 55 ° C. or less (range 1 in the drawing), it is possible to achieve Pn = 10% or less, which is regarded as an acceptable defect rate. it can. In addition, if it is less than 25 degreeC, precipitation of a liquid mixture, management of liquid temperature, etc. become difficult, and it is not suitable for practical use. Thus, the temperature of the buffered hydrofluoric acid is preferably 25 ° C. or higher and 55 ° C. or lower.

  Further, the temperature (liquid temperature) at the time of etching with the etching solution (buffered hydrofluoric acid) is more preferably 30 ° C. or more and 38 ° C. or less (range 2 in the drawing). This is because the temperature of buffered hydrofluoric acid is easy to manage (improving processing accuracy), the etching speed is suitable (reducing processing man-hours), or the defect rate is small as shown in FIG. 8 (Pn = 5% or less) ), Thereby reducing the manufacturing cost.

  In the above description, the piezoelectric vibration element 1 using the AT-cut quartz substrate 101 as the vibration element has been described as an example, but the vibration element is not limited to this example. The present invention only needs to have a configuration using a quartz plate that is exposed and intersecting two surfaces exposed to an etching solution. For example, a quartz substrate cut out at another cut angle such as a tuning fork type quartz vibrating piece is used. It can also be provided for a vibrating piece. Further, the present invention is not limited to the vibrating piece, and can be applied to, for example, a pressure sensor element, a gyro sensor element, and the like.

  In the above description, the multi-stage (two-stage) forward mesa structure piezoelectric vibration element 1 using the AT-cut quartz crystal substrate 101 as the vibration element has been described as an example. The present invention can also be applied to a piezoelectric vibrating piece having a multi-stage forward mesa structure having more than one stage or a reverse mesa structure.

  In the above description, the example of forming the outer shape of the piezoelectric substrate 10 and the peripheral portion 12 has been described by performing the etching with the etching solution temperature set at 85 ° C. However, the present invention is not limited thereto, and the two-stage mesa portion 16 is formed. The same etching solution and temperature (liquid temperature) of the etching solution can be used.

<Electronic device>
Next, an electronic device including the vibration element described in the above embodiment will be described. First, the vibrator will be described with reference to FIG. 9, and then the oscillator will be described with reference to FIG.

(Vibrator)
A vibrator as an electronic device will be described with reference to FIG. FIG. 9 is a front sectional view showing a vibrator as an electronic device using the vibration element according to the present invention. As shown in FIG. 9, the vibrator 200 includes the piezoelectric vibration element 1 using the AT-cut quartz crystal substrate 101 described in the above embodiment, the package 204 containing the piezoelectric vibration element 1, and the package 204 hermetically sealed. And a lid 208 as a lid.

  The package 204 is formed by sequentially laminating and fixing a first substrate 201 on a flat plate and a frame-shaped second substrate 202 and a frame-shaped third substrate 203 on the first substrate 201. A recess is formed in which is accommodated. The first substrate 201, the second substrate 202, and the third substrate 203 are formed of, for example, ceramics.

  The second substrate 202 is formed in a frame shape having an opening having a size including the excitation portion of the piezoelectric vibration element 1. The third substrate 203 is formed in a frame shape having an opening wider than the opening of the second substrate 202, and is laminated and fixed on the second substrate 202. The piezoelectric substrate 1 is connected and fixed to the exposed surface of the second substrate 202 that is laminated on the second substrate 202 and appears inside the opening of the third substrate 203. An electrode (not shown) is provided on the exposed surface of the second substrate 202, and the piezoelectric vibration element 1 is connected and fixed to the electrode by the conductive adhesive 206. Note that electrodes (not shown) are electrically connected to a plurality of external connection terminals 209 provided on the outer bottom surface of the first substrate 201 by internal wiring of a package 204 (not shown).

  Further, a lid 208 as a lid is disposed above the opening of the third substrate 203, the opening of the package 204 is sealed, and the inside of the package 204 is hermetically sealed, whereby the vibrator 200 is obtained. The lid 208 can be formed using, for example, a metal such as 42 alloy (an alloy containing 42% nickel in iron) or Kovar (an alloy of iron, nickel, and cobalt), ceramics, glass, or the like. For example, when the lid 208 is formed of metal, it is joined to the package 204 by seam welding via a seal ring 207 formed by punching a Kovar alloy or the like into a rectangular ring shape. The recessed space 205 formed by the package 204 and the lid 208 is a space for the piezoelectric vibration element 1 to operate. Therefore, the recessed space 205 is sealed in a reduced pressure space (a space close to a vacuum) or an inert gas atmosphere such as nitrogen, helium, or argon. -It is preferable to seal.

  According to the vibrator 200 described above, since the piezoelectric vibration element 1 described above is provided, the vibration energy confinement effect can be stably performed, and the electrical characteristics, particularly, the CI value is deteriorated and stabilized. A vibrator capable of performing oscillation can be provided.

(Oscillator)
An oscillator as an electronic device will be described with reference to FIG. FIG. 10 is a front sectional view showing an oscillator as an electronic device using the resonator element according to the invention. As shown in FIG. 10, the oscillator 300 hermetically seals the piezoelectric vibration element 1 using the AT-cut quartz crystal substrate 101 described in the above embodiment, the package 304 containing the piezoelectric vibration element 1, and the package 304. And a lid 308 as a lid.

  The package 304 is formed by sequentially laminating and fixing a first substrate 301 on a flat plate, and a frame-shaped second substrate 302 and a third substrate 303 on the first substrate 301, and the semiconductor device 310 and the piezoelectric vibration element 1. A recess is formed in which is accommodated. The first substrate 301, the second substrate 302, and the third substrate 303 are formed of, for example, ceramics.

  The first substrate 301 is provided with a die pad (not shown) on which the semiconductor device 310 is mounted and fixed on an electronic component mounting surface on which the semiconductor device 310 on the concave side is mounted. The semiconductor device 310 is bonded and fixed on the die pad by, for example, a conductive adhesive (die attach material) (not shown). Furthermore, a plurality of IC connection terminals (not shown) to which bonding wires 311 that are electrically connected to electrode pads (not shown) of the semiconductor device 310 are connected are formed on the electronic component mounting surface of the first substrate 301. . The electrode pad of the semiconductor device 310 and the IC connection terminal are electrically connected using a wire bonding method. Any one of the IC connection terminals is electrically connected to a plurality of external connection terminals 309 provided on the external bottom surface of the first substrate 301 by an internal wiring (not shown) of the package 304.

  The semiconductor device 310 has a drive circuit or the like as excitation means for driving and vibrating the piezoelectric vibration element 1. Specifically, the drive circuit included in the semiconductor device 310 drives the piezoelectric vibration element 1 and amplifies the received drive signal and supplies the drive signal to the outside.

  The second substrate 302 is formed in a frame shape having an opening large enough to accommodate the semiconductor device 310 to be mounted. The third substrate 303 is formed in a frame shape having an opening wider than the opening of the second substrate 302, and is laminated and fixed on the second substrate 302. The third substrate 303 is laminated on the second substrate 302, and the piezoelectric vibration element 1 is connected and fixed to the exposed surface of the second substrate 302 that appears inside the opening of the third substrate 303. An electrode (not shown) is provided on the exposed surface of the second substrate 302, and the piezoelectric vibration element 1 is connected and fixed to the electrode with a conductive adhesive 306. An electrode (not shown) is electrically connected to an IC connection terminal (not shown) through an internal wiring of a package 204 (not shown).

  Further, a lid 308 as a lid is disposed above the opening of the third substrate 303, the opening of the package 304 is sealed, and the inside of the package 304 is hermetically sealed, whereby the oscillator 300 is obtained. The lid 308 can be formed using, for example, a metal such as 42 alloy (an alloy containing 42% nickel in iron) or Kovar (an alloy of iron, nickel, and cobalt), ceramics, or glass. For example, when the lid 308 is formed of metal, the lid 308 is joined to the package 304 by seam welding via a seal ring 307 formed by punching a Kovar alloy or the like into a rectangular ring shape. The recessed space 305 formed by the package 304 and the lid 308 is a space for operating the piezoelectric vibration element 1 and is therefore sealed in a reduced pressure space (a space close to a vacuum) or an inert gas atmosphere such as nitrogen, helium, or argon. -It is preferable to seal.

  According to the oscillator 300 described above, since the piezoelectric vibration element 1 described above is provided, the vibration energy confinement effect can be stably performed, and stable oscillation in which the electrical characteristics, particularly, the CI value is degraded. An oscillator capable of performing the above can be provided.

<Electronic equipment>
Next, regarding an electronic device to which the piezoelectric vibration element 1 as a vibration element according to an embodiment of the invention, the vibrator 200 using the piezoelectric vibration element 1, or the oscillator 300 using the piezoelectric vibration element 1 is applied, FIGS. This will be described in detail with reference to FIG. In the description, an example in which the vibrator 200 using the piezoelectric vibration element 1 is applied is shown.

  FIG. 11 is a perspective view schematically illustrating a configuration of a mobile (or notebook) personal computer as an electronic apparatus including the vibrator 200 according to the embodiment of the invention. In this figure, a personal computer 1100 includes a main body portion 1104 provided with a keyboard 1102 and a display unit 1106 provided with a display portion 100. The display unit 1106 is rotated with respect to the main body portion 1104 via a hinge structure portion. It is supported movably. Such a personal computer 1100 has a built-in vibrator 200 as a reference signal source.

  FIG. 12 is a perspective view schematically illustrating a configuration of a mobile phone (including PHS) as an electronic device including the vibrator 200 according to an embodiment of the present invention. In this figure, a cellular phone 1200 includes a plurality of operation buttons 1202, an earpiece 1204, and a mouthpiece 1206, and the display unit 100 is disposed between the operation buttons 1202 and the earpiece 1204. Such a cellular phone 1200 incorporates the vibrator 200 as a reference signal source or the like.

  FIG. 13 is a perspective view illustrating a schematic configuration of a digital still camera as an electronic apparatus including the vibrator 200 according to an embodiment of the present invention. In this figure, connection with an external device is also simply shown. Here, an ordinary camera sensitizes a silver halide photographic film with a light image of a subject, whereas a digital still camera 1300 photoelectrically converts a light image of a subject with an image sensor such as a CCD (Charge Coupled Device). An imaging signal (image signal) is generated. A display unit 100 is provided on the back of a case (body) 1302 in the digital still camera 1300, and is configured to display based on an imaging signal from the CCD. The display unit 100 displays an object as an electronic image. Functions as a viewfinder. A light receiving unit 1304 including an optical lens (imaging optical system), a CCD, and the like is provided on the front side (the back side in the drawing) of the case 1302.

  When the photographer confirms the subject image displayed on the display unit 100 and presses the shutter button 1306, the CCD image pickup signal at that time is transferred and stored in the memory 1308. In the digital still camera 1300, a video signal output terminal 1312 and an input / output terminal 1314 for data communication are provided on the side surface of the case 1302. As shown in the figure, a television monitor 1430 is connected to the video signal output terminal 1312 and a personal computer 1440 is connected to the input / output terminal 1314 for data communication as necessary. Further, the imaging signal stored in the memory 1308 is output to the television monitor 1430 or the personal computer 1440 by a predetermined operation. Such a digital still camera 1300 incorporates the vibrator 200 as a reference signal source or the like.

  The vibrator 200 according to the embodiment of the present invention includes, for example, an ink jet type ejection device in addition to the personal computer (mobile personal computer) in FIG. 11, the mobile phone in FIG. 12, and the digital still camera in FIG. (For example, inkjet printers), laptop personal computers, televisions, video cameras, video tape recorders, car navigation devices, pagers, electronic notebooks (including those with communication functions), electronic dictionaries, calculators, electronic game devices, word processors, workstations , Video phone, crime prevention TV monitor, electronic binoculars, POS terminal, medical equipment (eg, electronic thermometer, blood pressure monitor, blood glucose meter, electrocardiogram measuring device, ultrasonic diagnostic device, electronic endoscope), fish detector, various measuring devices , Instruments (e.g. vehicles, Sky machine, gauges of a ship), can be applied to electronic equipment such as a flight simulator.

<Moving object>
FIG. 14 is a perspective view schematically showing an automobile as an example of a moving body. The automobile 106 is equipped with a vibrator 200 using the piezoelectric vibration element 1 according to the present invention. For example, as shown in the figure, an automobile 106 as a moving body has an electronic control unit 108 that includes a vibrator 200 and controls a tire 109 and the like mounted on a vehicle body 107. In addition, vibrators using the piezoelectric vibration element 1 include keyless entry, immobilizer, car navigation system, car air conditioner, antilock brake system (ABS), air bag, tire pressure monitoring system (TPMS: Tire). It can be widely applied to electronic control units (ECUs) such as Pressure Monitoring System), engine control, battery monitors for hybrid and electric vehicles, and body posture control systems.

  DESCRIPTION OF SYMBOLS 1 ... Piezoelectric vibration element, 10 ... Piezoelectric substrate, 12 ... Peripheral part, 14 ... Excitation part, 15 ... One step mesa part, 15a ... Side surface of one step mesa part, 16 ... Two step mesa part, 17 ... Side surface of two step mesa part , 18, 19... Intersecting portions of two surfaces, 20a, 20b ... excitation electrodes, 22a, 22b ... extraction electrodes, 24a, 24b ... pads, 30, 60 ... corrosion resistant films, 31, 32 ... outer portions, 35 ... outer frame, DESCRIPTION OF SYMBOLS 40, 50, 70 ... Resist film, 41, 42, 51, 71 ... Opening of resist film, 101 ... AT cut quartz substrate, 106 ... Automobile as moving body, 200 ... Vibrator as electronic device, 300 ... Electron Oscillator as device, 1100... Personal computer as electronic device, 1200... Mobile phone as electronic device, 1300.

Claims (8)

Preparing a crystal plate having one main surface and the other main surface on the back side of the one main surface;
Etching the quartz plate using a first etching solution containing HF, and forming a convex portion on at least one side of the one main surface and the other main surface;
Comprises H F, and, using a second etching solution temperature is lower than the first etchant, and etching the surface of the convex portion,
A method for manufacturing an element comprising: 2. The device manufacturing method according to claim 1, wherein the temperature of the second etching solution is in a range of 25 ° C. or more and 55 ° C. or less. 2. The device manufacturing method according to claim 1, wherein the temperature of the second etching solution is in a range of 30 ° C. or more and 38 ° C. or less. 4. The device manufacturing method according to claim 1, wherein the second etching solution includes NH ₄ FHF or a mixed solution of NH ₄ HF ₂ and HF. 5. 5. The device manufacturing method according to claim 4, wherein the mixed solution of NH ₄ HF ₂ and HF has a weight ratio of NH ₄ HF ₂ to HF in the range of 1.5 to 2.5. . The convex portion, the manufacturing method of the device according to any one of claims 1 to 5, characterized in that it comprises an outer edge face of the quartz plate. The quartz plate, the manufacturing method of the device according to any one of claims 1 to 6, characterized in that a AT-cut plate. In the step of etching the surface of the convex portion, the manufacturing method of the device according to any one of claims 1 to 7, characterized in that to form a stepped portion on the projecting portion.

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