JP2018033097A - Method for manufacturing quartz vibration element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a quartz vibration element, by which a quartz vibration element having a quartz chip with a dopant added thereto can be suitably manufactured.SOLUTION: A method for manufacturing a vibration element 5 comprises: an etching step (ST3 to ST8); a conductive layer formation step (ST9); and a dividing step (ST10). In the etching step, a plurality of quartz chip parts 55 are formed by etching a quartz crystal wafer 51 at least partially including a dopant 39 including an element of Group IV of the periodic table, which is larger than silicon in atomic weight. In the conductive layer formation step, a plurality of excitation electrodes 17 are formed on the plurality of quartz chip parts 55. In the dividing step, the plurality of quartz chip parts 55 with the plurality of excitation electrodes 17 formed thereon are divided into individual chips.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for manufacturing a crystal resonator element. The crystal resonator element is used for a crystal resonator device such as a crystal resonator or a crystal oscillator.

  A crystal resonator element used in a crystal resonator or a crystal oscillator, for example, has a plate-shaped crystal piece and a pair of excitations that overlap a pair of main surfaces of the crystal piece (the widest surface; the front and back of the plate-like member). An electrode and a pair of extraction electrodes extracted from the pair of excitation electrodes. The quartz resonator element is mounted by bonding a pair of extraction electrodes to a pair of pads such as a package, and contributes to generation of an oscillation signal by applying an AC voltage to a crystal piece by a pair of excitation electrodes. Cause vibration.

  Patent Document 1 discloses a technique for providing a highly viscous region in a region other than a region where a pair of excitation electrodes is formed in a crystal piece. Further, the high-viscosity region is formed by infiltrating a crystal material with a metal material at a molecular level by ion implantation and thermal diffusion. Examples of the metal material include germanium (Ge), tin (Sn), lead (Pb), and the like. Moreover, in patent document 1, the technique which provided the highly viscous area | region in the whole crystal piece as a comparative example is also disclosed.

  Patent Document 2 discloses a technique of doping metal ions into a region where a pair of extraction electrodes is formed in a crystal piece. Examples of metal materials used for doping include Ge, Sn, and Pb.

JP 2008-154181 A JP-A-2015-70582

  In Patent Documents 1 and 2, it is mentioned that doping is performed with respect to a method for manufacturing a vibration element, but a specific aspect thereof is not mentioned. For example, there is no mention of the relationship between doping time and etching time. Therefore, it is desired to provide a method for manufacturing a crystal resonator element that can suitably manufacture a crystal resonator element having a crystal piece to which a dopant is added.

  According to an aspect of the present disclosure, there is provided a method for manufacturing a crystal resonator element, comprising: etching a crystal wafer including at least part of a dopant including a Group 4 element having a larger atomic weight than silicon; An etching step to form, a conductive layer forming step to form a plurality of excitation electrodes on the plurality of crystal pieces, and an individualization step to separate the plurality of crystal pieces on which the plurality of excitation electrodes are formed And having.

  For example, the manufacturing method further includes a doping step of adding the dopant to the crystal wafer before the etching step.

  For example, in the doping step, the crystal wafer and the metal are heated in a state where the metal containing the dopant is in contact with the crystal wafer.

  For example, in the doping step, a voltage is applied to the metal in a state where the metal containing the dopant is in contact with the crystal wafer.

  For example, in the doping step, the dopant is added to a region that is an edge of the plurality of crystal piece portions in the crystal wafer, and in the etching step, the portion of the crystal piece portion is added by a portion to which the dopant is added. Form the side.

  For example, the etching step etches the outer peripheral portion of each of the plurality of crystal piece portions, surrounds the mesa portion in each of the plurality of crystal piece portions, and the mesa portion in plan view, A thin mesa etching step for forming the outer peripheral portion, and in the doping step, the dopant is added to a region to be the mesa portion, and in the mesa etching step, the portion to which the dopant is added is added. A side surface of the mesa portion is formed.

  According to the above procedure, a quartz resonator element having a quartz piece to which a dopant is added can be suitably manufactured.

FIG. 3 is an exploded perspective view illustrating a schematic configuration of the crystal resonator according to the first embodiment of the present disclosure. Sectional drawing corresponding to the II-II line | wire of FIG. 1 which shows the crystal oscillator of FIG. FIG. 3A and FIG. 3B are a schematic plan view and a cross-sectional view for explaining the material of the crystal piece. The flowchart which shows an example of the outline | summary of the procedure of the manufacturing method of a crystal oscillation element. FIG. 5A and FIG. 5B are plan views showing a part of a crystal wafer from which a large number of crystal pieces are taken. The flowchart which shows an example of the procedure of doping in step ST2 of FIG. FIGS. 7A to 7D are schematic views showing examples of narrow doping in step ST22 of FIG. The figure for demonstrating an example of an effect | action of 1st Embodiment. FIG. 9A is a perspective view showing the crystal resonator element according to the second embodiment, and FIGS. 9B and 9C are diagrams for explaining the material of the crystal piece of the crystal resonator element of FIG. 9A. The typical top view and sectional drawing of these. FIG. 10A is a schematic plan view for explaining the material of the crystal piece according to the third embodiment, and FIGS. 10B and 10C form the crystal piece of FIG. Typical sectional drawing for demonstrating the external shape etching for this. FIG. 11A is a schematic plan view for explaining the material of the crystal piece according to the fourth embodiment, and FIGS. 11B and 11C form the crystal piece of FIG. Typical sectional drawing for demonstrating mesa etching for this. FIG. 12A to FIG. 12D are schematic cross-sectional views for explaining the material of the crystal piece according to the fifth to eighth embodiments. The flowchart for demonstrating the procedure of the manufacturing method of the vibration element which concerns on 9th Embodiment. 14A and 14B are schematic cross-sectional views for explaining the doping in step ST34 of FIG.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones. Even in a plurality of drawings showing the same member, dimensional ratios and the like may not coincide with each other in order to exaggerate the shape and the like. For convenience, the surface of the layered member (that is, a surface that is not a cross section) may be hatched.

  Any one of the crystal resonator or the crystal resonator element of the present disclosure may be set upward or downward. However, for the sake of convenience, the upper surface of FIG. 1 and FIG. 2 (the + Y′-axis direction) is the upper surface for the sake of convenience. Alternatively, terms such as the lower surface may be used. In addition, when simply referred to as planar view or planar perspective, unless otherwise specified, it means viewing in the vertical direction defined for convenience as described above.

  In the second and subsequent embodiments, configurations that are the same as or similar to the configurations of the embodiments that have already been described may be denoted by reference numerals assigned to the configurations of the embodiments that have already been described, and descriptions thereof may be omitted. Even in the case where a configuration corresponding to (similar to) the configuration of the embodiment already described is denoted by a reference numeral different from the configuration of the embodiment described above, the configuration of the embodiment described above is provided for matters that are not particularly noted. It is the same.

<First Embodiment>
(Whole structure of crystal unit)
FIG. 1 is an exploded perspective view illustrating a schematic configuration of a crystal resonator 1 (hereinafter, “crystal” may be omitted) according to an embodiment of the present disclosure. 2 is a cross-sectional view of the vibrator 1 (corresponding to II-II line in FIG. 1).

  The vibrator 1 is, for example, an electronic component that has a generally thin, rectangular parallelepiped shape as a whole. The dimensions may be set as appropriate. For example, in a comparatively small thing, the length of a long side (X-axis direction) or a short side (Z'-axis direction) is 1-2 mm, and thickness (Y'-axis direction) is 0.2-0.4 mm. It is.

  The vibrator 1 includes, for example, an element mounting member 3 in which a recess 3a is formed, a crystal vibrating element 5 (hereinafter, “crystal” may be omitted) accommodated in the recess 3a, and a lid that closes the recess 3a. Member 7.

  The vibration element 5 is a part that generates vibration used for generating an oscillation signal. The element mounting member 3 and the lid member 7 constitute a package 8 for packaging the vibration element 5. The concave portion 3a of the element mounting member 3 is sealed by the lid member 7, and the inside thereof is, for example, evacuated or filled with an appropriate gas (for example, nitrogen).

  The element mounting member 3 mounts, for example, a base body 9 as a main body of the element mounting member 3, a pair of element mounting pads 11 for mounting the vibration element 5, and the vibrator 1 on a circuit board (not shown). And a plurality of external terminals 13 (four in the illustrated example).

  The base 9 is made of an insulating material such as ceramic and constitutes the recess 3a. The element mounting pad 11 is composed of a conductive layer made of metal or the like, and is located on the bottom surface of the recess 3a. The external terminal 13 is composed of a conductive layer made of metal or the like, and is located on the lower surface of the base 9. The element mounting pad 11 and the external terminal 13 are connected to each other by a conductor (FIG. 2, not shown) disposed in the base body 9. The lid member 7 is made of metal, for example, and is joined to the upper surface of the element mounting member 3 by seam welding or the like.

  The vibration element 5 includes, for example, a crystal piece 15, a pair of excitation electrodes 17 for applying a voltage to the crystal piece 15, and a pair of drawers for mounting the vibration element 5 on a pair of element mounting pads 11. And an electrode 19. The vibration element 5 is configured in a generally plate shape as a whole.

  The vibration element 5 is accommodated in the recess 3a so as to face the bottom surface of the recess 3a. Then, the pair of extraction electrodes 19 are joined to the pair of element mounting pads 11 by the pair of bumps 21 (FIG. 2). Thereby, the vibration element 5 is supported by the element mounting member 3 like a cantilever. Further, the pair of excitation electrodes 17 is electrically connected to the pair of element mounting pads 11 via the pair of extraction electrodes 19, and as a result, is electrically connected to any two of the plurality of external terminals 13. The The bump 21 is made of, for example, a conductive adhesive. The conductive adhesive is configured, for example, by mixing a conductive filler into a thermosetting resin.

  The vibrator 1 configured as described above is disposed, for example, with the lower surface of the element mounting member 3 facing the mounting surface of a circuit board (not shown), and the external terminals 13 are joined to the pads of the circuit board with solder or the like. To be mounted on a circuit board. For example, an oscillation circuit 23 (FIG. 2) is configured on the circuit board. The oscillation circuit 23 applies an AC voltage to the pair of excitation electrodes 17 via the external terminal 13 and the element mounting pad 11 to generate an oscillation signal. At this time, the oscillation circuit 23 uses, for example, fundamental wave vibration among thickness shear vibrations of the crystal piece 15. Overtone vibration may be used.

(Basic structure of crystal resonator element)
The crystal piece 15 is a so-called AT cut plate. That is, as shown in FIG. 1, in a quartz crystal, an orthogonal coordinate system XYZ composed of an X axis (electric axis), a Y axis (mechanical axis), and a Z axis (optical axis) is 30 ° or more and 40 ° or less around the X axis. When the orthogonal coordinate system XY′Z ′ is defined by rotating (35 ° 15 ′ as an example), the crystal piece 15 has a plate shape cut out parallel to the XZ ′ plane.

  The shape of the outer edge of the crystal piece 15 in plan view is, for example, a substantially rectangular shape. The crystal piece 15 has a pair of main surfaces and a plurality of (four in a plan view rectangle) side surfaces connecting the outer edges of the pair of main surfaces. The main surface refers to the widest surface (front and back surfaces of the plate member) among a plurality of surfaces (six surfaces in the case of a plate member having a rectangular shape in plan view) of the plate member. In the AT cut plate, the main surface is a surface substantially along the XZ ′ plane, the long side of the main surface is a side generally along the X axis, and the short side of the main surface is a side generally along the Z ′ axis.

  In addition, the planar shape of the crystal piece 15 may not be a complete rectangle. For example, the corners of a rectangle may be chamfered with a flat surface or a curved surface, the long side and / or the short side may have an arc shape that bulges outward, or the lengths of two opposing sides may be different from each other. Good. The terms long side and short side are generally terms that refer to a rectangular side. In the present disclosure, in a plan view, the longitudinal direction and the short direction of the crystal piece 15 can be distinguished, and the outer edge has a total of four lines including two lines that are generally along the longitudinal direction and two lines that are generally along the short direction. The four lines in the plan view are called the long side and the short side even if they are not completely rectangular as described above.

  The crystal piece 15 (vibrating element 5) is a so-called mesa type, and surrounds the mesa portion 31 and the mesa portion 31 in a plan view, and the thickness between a pair of main surfaces (Y′-axis direction) is the mesa portion 31. And a thinner outer peripheral portion 33. Such a shape improves the energy confinement effect, for example.

  The shape of the mesa portion 31 is, for example, a plate shape having a pair of main surfaces parallel to the XZ ′ plane. The pair of main surfaces are parallel to each other from another viewpoint. The planar shape of the mesa unit 31 may be set as appropriate, for example, a rectangle (example shown in the drawing), a circle, an ellipse (not necessarily an exact ellipse defined in mathematics), or an oval (out of four sides). Each pair of short sides is generally semi-circular). The illustrated rectangular mesa portion 31 has, for example, four sides substantially parallel to the four sides of the outer edge of the crystal piece 15.

  The shape of the outer peripheral portion 33 is, for example, a plate shape having a pair of main surfaces substantially parallel to XZ ′ when the mesa portion 31 is ignored. The pair of main surfaces are parallel to each other from another viewpoint. The shape of the outer edge of the outer peripheral portion 33 is as described for the shape of the outer edge of the entire crystal piece 15 described above. The shape of the inner edge of the outer peripheral portion 33 is basically the same as the shape of the outer edge of the mesa portion 31.

  In plan view, for example, the mesa portion 31 is located at the center in the Z′-axis direction with respect to the outer edge of the crystal piece 15 (outer peripheral portion 33), and is on one side in the X-axis direction (opposite to the extraction electrode 19) Side). However, the mesa unit 31 may be positioned at the center of the crystal piece 15 in the X-axis direction.

  The outer peripheral portion 33 is located at the center of the mesa portion 31 in the Y′-axis direction. That is, the height of the mesa portion 31 from the outer peripheral portion 33 (the amount of digging in the outer peripheral portion 33 for making the crystal piece 15 into a mesa shape) is the same between the pair of main surfaces of the crystal piece 15.

  A pair of main surfaces of the mesa unit 31 is finally formed by polishing, for example. The pair of main surfaces of the outer peripheral portion 33, the outer peripheral surface of the mesa portion 31 (a plurality of side surfaces of the mesa portion 31), and the outer peripheral surface of the outer peripheral portion 33 (a plurality of side surfaces of the crystal piece 15) are formed by, for example, etching. In other words, it is constituted by a crystal plane that appears by etching.

  The thickness of the mesa unit 31 is set based on a desired natural frequency for the thickness shear vibration. For example, in the case of using the fundamental vibration, if the natural frequency is F, the basic formula for obtaining the thickness tm of the mesa portion 31 corresponding to the natural frequency F is tm = 1670 / F. In practice, the thickness of the mesa portion 31 is a value that is finely adjusted from the value of the basic formula in consideration of the weight of the excitation electrode 17 and the like.

  The thickness of the outer peripheral portion 33 is appropriately set from the viewpoint of the energy confinement effect. For example, the difference in height between the main surface of the mesa portion 31 and the main surface of the outer peripheral portion 33 on one side of the pair of main surfaces of the crystal piece 15 (the amount of digging in the outer peripheral portion 33) It is 5% or more and 15% or less of the thickness, for example, about 10%.

  Various dimensions of the crystal piece 15 may be appropriately set based on simulation calculations, experiments, and the like from various viewpoints such as reduction of equivalent series resistance. As an example, for example, the length of the crystal piece 15 (X-axis direction) is 600 μm or more and 1 mm or less, and the width of the crystal piece 15 (Z′-axis direction) is 500 μm or more and 700 μm or less (however, shorter than the length of the crystal piece 15). The mesa portion 31 has a thickness of 40 μm to 70 μm, the mesa portion 31 has a length (X-axis direction) of 450 μm to 750 μm (but shorter than the length of the crystal piece 15), and the mesa portion 31 has a width (Z′-axis direction). Is 400 μm or more and 650 μm or less (but shorter than the width of the crystal piece 15).

  The pair of excitation electrodes 17 and the pair of extraction electrodes 19 are configured by a conductive layer that overlaps the surface of the crystal piece 15. The conductive layer is, for example, a metal such as Au (gold), Ag (silver), or an Au—Ag alloy. The conductive layer may be composed of a plurality of layers having different materials. Although the thickness of the conductive layer may be set as appropriate, an example is 0.05 μm or more and 0.3 μm or less. In FIG. 2 and the like, the thickness of the conductive layer is shown to be thicker than the actual thickness.

  The pair of excitation electrodes 17 are located on a pair of main surfaces of the mesa unit 31 and face each other with the mesa unit 31 interposed therebetween. In other words, the pair of excitation electrodes 17 is located on the pair of main surfaces of the crystal piece 15 away from the outer edge of the crystal piece 15. The planar shape of the excitation electrode 17 is substantially similar to the planar shape of the mesa unit 31, for example, and is rectangular in the illustrated example. For example, the excitation electrode 17 is accommodated in the main surface of the mesa portion 31, and the center (graphic gravity center) coincides with the center of the mesa portion 31 (graphic gravity center). However, the excitation electrode 17 may protrude from the mesa portion 31 to the outer peripheral portion, or may be shifted from the center of the excitation electrode 17 and the center of the mesa portion 31.

  The pair of extraction electrodes 19 extends, for example, from the pair of excitation electrodes 17 to one side in the X-axis direction (in the present embodiment, the + X side), and a pair of main electrodes of the crystal piece 15 (outer peripheral portion 33). At least one main surface of the surfaces has a pair of pad portions 19a bonded to the pair of bumps 21. In the example shown in the figure, the vibration element 5 is formed to be 180 ° rotationally symmetric about the X axis so that any one of the pair of main surfaces may face the bottom surface of the recess 3a. 19 has a pair of pad portions 19a (a total of two pairs of pad portions 19a) on each of the pair of main surfaces. The excitation electrode 17 located on one principal surface of the pair of principal surfaces and the pad portion 19a located on the other principal surface are formed on the side surface (the side surface located on the short side and / or the long side) of the crystal piece 15. Are connected via side surfaces).

(Material of crystal piece)
FIG. 3A and FIG. 3B are schematic views for explaining the material of the crystal piece 15. Specifically, FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line IIIb-IIIb in FIG. However, in FIG. 3B, hatching indicating a cross section is omitted.

  In this figure, the mesa portion 31 is shown thicker than the actual thickness. The side surface of the mesa portion 31 and the side surface of the outer peripheral portion 33 are ideally orthogonal to the main surface of the mesa portion 31 (parallel to the Y ′ axis). Inclined with respect to the Y ′ axis. FIG. 3B also shows this inclination. However, the illustrated inclination angle does not necessarily match the actual one.

  The crystal piece 15 is composed of a crystal (doped crystal) containing a dopant (impurity). In FIG. 3A and FIG. 3B, a plurality of points schematically indicate a plurality of dopants 39. That is, a region hatched by a plurality of points indicates a region where the dopant 39 is included. As shown in this figure, the crystal piece 15 has a doped portion 35 including a dopant 39 and an undoped portion 37 not including the dopant 39.

  For example, the doping portion 35 is accommodated on the main surface (the top surface, a surface parallel to the XZ ′ plane) of the mesa portion 31 in plan view. The area may be equal to the main surface of the mesa unit 31 or may be narrower than the main surface of the mesa unit 31 (example shown in the figure). For example, in the illustrated example, the outer edge of the doping portion 35 is located slightly inside (for example, 5 μm or less) the outer edge over the entire outer edge of the main surface of the mesa portion 31. In addition, the doping portion 35 extends over the entire thickness of the crystal piece 15 (mesa portion 31) in the above range.

  The non-doping portion 37 is a portion other than the doping portion 35 in the crystal piece 15. That is, the non-doping portion 37 includes the outer peripheral portion 33 and the outer edge portion of the mesa portion 31. The outer edge portion of the mesa portion 31 includes at least a side surface of the mesa portion 31 that connects the outer peripheral portion 33 and the top surface of the mesa portion 31. In the illustrated example, the non-doping portion 37 also includes a range from the outer edge of the top surface of the mesa portion 31 to the inside of the mesa portion 31.

  Focusing on the relationship between the arrangement region of the dopant 39 and the conductive layer (excitation electrode 17 and the like), for example, in plan view, the planar shape of the doping portion 35 is, for example, one of the pair of excitation electrodes 17 (one pair of excitations). The electrodes 17 basically have the same shape as each other and may be any one). For example, the difference in area between the two is less than 10% of the area of the one excitation electrode 17.

  Moreover, the non-doping part 37 has overlapped with the whole one pair of extraction electrode 19 in planar perspective, for example. Specifically, for example, the non-doping portion 37 overlaps 90% or more or all of the pair of extraction electrodes 19 in a plan view. Ninety percent here is in perspective of the plane, and is 90% of the projected area of the pair of extraction electrodes 19 in the Y′-axis direction.

  In a plan view, the doping part 35 may be slightly wider than the excitation electrode 17 and the doping part 35 may slightly overlap the extraction electrode 19, or the doping part 35 may be slightly narrower than the excitation electrode 17 and the undoped part 37. May slightly overlap the excitation electrode 17.

  The dopant 39 is, for example, an element belonging to Group 4 of the periodic table as in the case of silicon, and an element having an atomic weight larger than that of silicon. Specifically, for example, the dopant 39 is germanium (Ge), tin (Sn), and / or lead (Pb).

As is well known, quartz (SiO ₂ ) is formed by three-dimensionally arranging tetrahedrons composed of one silicon atom and four oxygen atoms, and the oxygen at the apex of the tetrahedron is adjacent to 4. It is shared between the faces. Although not particularly illustrated, the dopant 39 is bonded to an oxygen atom, for example, approximately in place of a silicon atom. Such a structure can be observed by using, for example, a transmission electron microscope (TEM).

The concentration of the dopant 39 in the doping unit 35 may be set as appropriate. For example, in the doping part 35, the concentration of the dopant 39 is 1 × 10 ¹⁶ (number of atoms / cm ³ ) or more or 1 × 10 ¹⁸ (number of atoms / cm ³ ) or more. This concentration is higher than the concentration of impurities that are unintentionally mixed into the crystal. Further, from the viewpoint of increasing the effect described later, for example, the concentration of the dopant 39 is 1 × 10 ²⁰ (number of atoms / cm ³ ) or more. The number of atoms per unit volume may be measured by, for example, secondary ion mass spectrometry (SIMS).

  In the present embodiment, the doping portion 35 extends over the entire thickness of the crystal piece 15 (mesa portion 31), but is provided only on the surface of the crystal piece 15 as will be described later (FIG. 12A). May be. Even in this case, the concentration of the dopant 39 can be measured, for example, by performing SIMS using a device having a depth resolution of several nm.

When the doping portion 35 is extremely thin, the concentration of the dopant 39 may be measured by a total reflection X-ray fluorescence (TXRF) method. In general, for a quartz wafer (without doping) that has been sufficiently cleaned, the amount of surface impurities measured by the TXRF method is 1 × 10 ⁹ to 1 × 10 ¹² (number of atoms / cm ² ). Therefore, the concentration of the dopant 39 in the doping portion 35 is, for example, 1 × 10 ¹³ (number of atoms / cm ² ) or more.

Moreover, in the doping part 35, the mass of the dopant 39 may be, for example, 10% or more and 30% or less with respect to the mass of the crystal before doping. In this case, the concentration of the dopant 39 is sufficiently higher than the concentration of 1 × 10 ¹⁶ (number of atoms / cm ³ ).

  The undoped portion 37 ideally does not include the dopant 39. In practice, however, the dopant 39 may be added to the undoped portion 37 unintentionally in the process of doping the doped portion 35.

Therefore, for example, in the present disclosure, the non-doping portion 37 is a portion where the concentration of the dopant 39 is lower than the concentration of the dopant 39 in the doping portion 35 described above. For example, the portion where the concentration of the dopant 39 is less than 1 × 10 ¹⁶ (number of atoms / cm ³ ) is the undoped portion 37. In addition, in the case where the dopant concentration in the undoped portion 37 is lower than that in the doped portion 35, it includes a state in which the dopant 39 is not included in the undoped portion 37.

  Further, for example, when attention is paid to the manufacturing process of the crystal piece 15, a portion that is clearly not intended to be doped may be regarded as the non-doping portion 37 regardless of the dopant concentration of the portion. . However, normally, the concentration of the dopant 39 in a portion where doping is not intended is lower than the concentration of the dopant 39 in the doping portion 35 described above.

(Outline of manufacturing method of crystal resonator element)
FIG. 4 is a flowchart showing an example of the outline of the procedure of the method for manufacturing the vibration element 5. FIGS. 5A and 5B are plan views showing a part of a crystal wafer 51 (hereinafter, “crystal” may be omitted) from which a large number of crystal pieces 15 are taken. . In the following, even if the shape or material of the member changes with the progress of the manufacturing process, the same reference numerals may be used before and after the change.

  In step ST1, a wafer 51 made of quartz (not including the dopant 39) is prepared. In addition, the wafer here should just be a plate-shaped thing from which many crystal pieces 15 are taken, and does not need to be a disk shape. For example, the planar shape of the wafer 51 may be a rectangle.

  The preparation of the wafer 51 may be similar to a known method, for example. Specifically, for example, by performing lumbard processing and slicing on the artificial quartz, the wafer is cut out at the angle described with reference to FIG. Further, lapping, etching, and / or polishing are performed on the cut wafer to form a wafer 51 having a pair of main surfaces parallel to each other.

  Note that the wafer 51 formed in this way basically does not contain impurities. In reality, there are impurities that are unintentionally included. However, in a general production method, an element belonging to Group 4 of the periodic table having an atomic weight larger than that of silicon does not exist as an impurity.

  In step ST <b> 2, doping is performed on the portion of the wafer 51 that becomes the doping portion 35. Note that doping is not performed on the portion to be the non-doping portion 37. For example, doping is not performed on a portion of the wafer 51 that is removed by etching, which will be described later. However, doping may be performed.

  In step ST3, as shown in FIG. 5A, on the pair of main surfaces of the wafer 51, a first mask 53 (area shown by hatching) for etching the wafer 51 is formed. The first mask 53 is used for etching to form the outer shape of the crystal piece 15 (side surface of the outer peripheral portion 33), and a plurality of outer shape mask portions 53a each having a planar shape substantially similar to the planar shape of the crystal piece 15. And a frame portion 53b positioned between the plurality of outer shape mask portions 53a and a plurality of connection portions 53c connecting the plurality of outer shape mask portions 53a and the frame portion 53b. For example, the connection portion 53c is connected to the outer mask portion 53a at positions corresponding to both ends of the short side in the + X-axis direction (in another aspect, the extraction electrode 19 side).

  The first mask 53 is made of, for example, a combination of a metal film and a resist film overlapping thereover. The metal film is made of chromium, for example. The resist film may be either a positive type or a negative type photoresist. These formations may be similar to known methods. For example, first, a metal film is formed over the entire main surface of the wafer 51 by sputtering or the like. Next, a resist film is formed on the entire surface of the metal film by spin coating or the like. Next, the resist film is patterned into a shape shown in FIG. Next, the metal film is etched through the resist film, and the metal film is patterned into the shape shown in FIG. Thereby, the first mask 53 is formed. Thereafter, the resist film may be removed and the first mask 53 may be constituted only by the metal film.

  In step ST <b> 4, wet etching is performed on the wafer 51 through the first mask 53. For example, the wafer 51 is immersed in a liquid tank containing a chemical solution. This etching is performed immediately under the opening of the first mask 53 until a through hole is formed in the wafer 51. As a result, a plurality of crystal piece portions 55 (FIG. 5B) each having a plane shape substantially similar to the plane shape of the crystal piece 15 are formed immediately below the outer shape mask portion 53a. However, the plurality of crystal piece portions 55 are connected to each other via portions of the wafer 51 directly below the connection portion 53c and the frame portion 53b.

  In step ST5, the first mask 53 is removed from the wafer 51. For example, the wafer 51 is immersed in an appropriate chemical solution for removing the first mask 53.

  In step ST6, as shown in FIG. 5B, on the pair of main surfaces of the wafer 51, a second mask 57 (region shown by hatching) for etching the crystal piece 55 is formed. The second mask 57 is used for etching that makes the crystal piece 55 a mesa shape. The second mask 57 includes a plurality of mesa mask portions 57 a each having a plane shape substantially similar to the plane shape of the mesa portion 31, and the first mask 53. It has the frame part 57b and the connection part 57c which have the same shape as the frame part 53b and the connection part 53c. The configuration and formation method of the second mask 57 may be substantially the same as those of the first mask 53 except for a specific planar shape and the like.

  In step ST <b> 7, wet etching is performed on the wafer 51 through the second mask 57. For example, the wafer 51 is immersed in a liquid tank containing a chemical solution. Unlike the step ST4, this etching is not performed until a through hole is formed in the wafer 51, and the etching amount of the crystal piece 55 (the amount of digging of the outer peripheral portion 33) is just below the opening of the second mask 57. This is done until the desired value is reached. Then, the crystal piece portion 55 is dug in a region to be the outer peripheral portion 33, and the mesa portion 31 and the outer peripheral portion 33 are formed.

  In step ST8, the second mask 57 is removed from the wafer 51. For example, the wafer 51 is immersed in an appropriate chemical solution for removing the second mask 57.

  In step ST9, a pair of excitation electrodes 17 and a pair of extraction electrodes 19 are formed on each crystal piece 55. The method for forming these conductive layers may be the same as a known method, for example. Specifically, for example, these conductive layers are formed by forming a conductive material through a mask, or formed by etching through a mask after the conductive material is formed. .

  In step ST10, the plurality of crystal piece portions 55 are separated from the portion of the wafer 51 that is located immediately below the frame portion 57b of the second mask 57. For example, the crystal piece 55 is pressed or sucked to fold the portion of the wafer 51 that is located immediately below the connection portion 57 c of the second mask 57. Thereby, a plurality of oscillating elements 5 singulated are produced.

(doping)
FIG. 6 is a flowchart showing an example of the (in a broad sense) doping procedure in step ST2 of FIG. For example, the doping may be performed in the same manner as the doping of the semiconductor except for specific conditions. For example, it is as follows.

  In step ST <b> 21, a selection mask 61 (FIGS. 7A to 7D) is formed on a pair of main surfaces of the wafer 51. The selection mask 61 is formed so as to cover a region where doping is not performed (for example, a portion other than the portion serving as the doping portion 35).

The formation method of the selection mask 61 may be the same as a known method in the field of doping with respect to the semiconductor. For example, first, the organic cleaning of the wafer 51 is performed. Next, a mask material to be the selection mask 61 is formed on the entire main surface of the wafer 51 by CVD (chemical vapor deposition) or the like. The material of the selection mask 61 is, for example, silicon nitride (Si ₃ N ₄ ) or silicon dioxide (SiO ₂ ). CVD may use TEOS (tetraethoxysilane) in addition to general plasma CVD. Next, a resist film is formed on the mask material. Next, the resist film is patterned by photolithography into a shape having an opening only in a region to be doped (doping portion 35). Next, the mask material is etched through the resist film, and the mask material is patterned in the same shape as the resist film. Thereafter, the resist film is removed and the wafer 51 is cleaned.

  In step ST22, doping (in a narrow sense) is performed through the selection mask 61. Since the selection mask 61 has an opening only in the region where doping is performed, the doping is selectively performed on the wafer 51. As a result, the crystal piece 15 is provided with a doped portion 35 that is doped and an undoped portion 37 that is not doped.

  In step ST23, the selection mask 61 is removed. For example, first, the organic cleaning of the wafer 51 is performed. Next, the selection mask 61 is removed by dry etching or wet etching. Thereafter, the wafer 51 is cleaned by rinsing with pure water.

  FIG. 7A to FIG. 7D are schematic views showing examples of doping in a narrow sense in step ST22, respectively. In addition, although step ST22 is a process performed with respect to the wafer 51, in this schematic diagram, the wafer 51 shows only the part corresponding to one opening (one doping part 35).

  FIG. 7A is a schematic diagram showing an example in which doping is performed by ion implantation (ion implantation). In this example, for example, the dopant 39 ionized by the ion implantation apparatus 63 is accelerated and collides with the wafer 51. The ion implantation device 63 includes, for example, an ion source that generates ions, an accelerator that accelerates ions by applying a voltage, a mass analyzer that selects only an object to be implanted from ions, a lens that shapes an ion beam, and the like, although not particularly illustrated. Have.

  FIG. 7B is a schematic diagram showing an example of doping by thermal diffusion. In this example, for example, the wafer 51 and the metal 65 are heated by the furnace 67 in a state where the metal 65 containing the element that becomes the dopant 39 is in contact with the wafer 51. The metal 65 may be composed only of an element that becomes the dopant 39, or may be an alloy containing the element. Further, the metal 65 may be provided on the wafer 51 by a thin film forming method such as sputtering, or may be provided by disposing a metal plate on the wafer 51.

  FIG. 7C is a schematic diagram showing an example of doping by electron beam injection. In this example, for example, the electron 69 is accelerated by the electron gun 68 to collide with the metal 65 in a state where the metal 65 containing the element to be the dopant 39 is disposed on the wafer 51. Note that, as in the case of thermal diffusion, the metal 65 may be composed of only the element serving as the dopant 39, or may be an alloy containing the element, or provided by a thin film formation method. Alternatively, it may be provided by arranging a metal plate.

  FIG. 7D is a schematic diagram illustrating an example in which doping is performed by applying a voltage. In this example, for example, in a state where a pair of metals 65 including an element that becomes the dopant 39 is disposed on both main surfaces of the wafer 51, a voltage (for example, a DC voltage or an AC voltage) is applied to the pair of metals 65 by the power supply device 71. Is applied. Note that, as in the case of thermal diffusion, the metal 65 may be composed of only the element serving as the dopant 39, or may be an alloy containing the element, or provided by a thin film formation method. Alternatively, it may be provided by arranging a metal plate. The wafer 51 and the metal 65 may be appropriately heated. Heating promotes doping by voltage application.

  In addition to the above example, although not particularly illustrated, doping may be performed by, for example, cluster doping, plasma doping, or laser doping. Doping may be performed only from one main surface of the wafer 51, may be performed simultaneously on both main surfaces of the wafer 51, or sequentially performed on both main surfaces of the wafer 51. Also good. Also in the method of applying a voltage (FIG. 7D), for example, by providing two or more metals 65 on one main surface and applying a voltage to the two or more metals 65, one main surface It is possible to dope only at.

  As described above, in the present embodiment, the crystal resonator element 5 includes the crystal piece 15 and the pair of excitation electrodes 17. The crystal piece 15 has a pair of main surfaces. The excitation electrode 17 is located on the pair of main surfaces away from the outer edges of the pair of main surfaces of the crystal piece 15. The crystal piece 15 has a doping part 35 and a non-doping part 37. The doping part 35 includes a dopant 39 made of a Group 4 element having a larger atomic weight than silicon. The undoped portion 37 has a lower concentration of the dopant 39 than that of the doped portion 35 (including an embodiment that does not include the dopant 39 as described above). At least a part (all in the present embodiment) of the doping portion 35 is located between the pair of excitation electrodes 17.

  From another viewpoint, in the present embodiment, the crystal unit 1 includes the vibration element 5 as described above and the package 8 on which the vibration element 5 is mounted.

  Therefore, for example, the equivalent series resistance decreases. As a result, for example, a reduction in power consumption and a reduction in size of the vibration element 5 are facilitated. Examples of the reason why the equivalent series resistance is lowered by adding the dopant 39 made of an element of Group 4 of the periodic table having a larger atomic weight than silicon between the pair of excitation electrodes 17 include the following. When the dopant 39 having an atomic weight larger than that of silicon is bonded to oxygen instead of silicon, the interatomic distance is shortened, and the electron mobility and / or hole mobility is increased. As a result, the equivalent series resistance decreases. In addition, the electromechanical coupling coefficient increases in the doping section 35, and as a result, the equivalent series resistance decreases. That is, since at least a part of the doping part 35 is located between the pair of excitation electrodes, the crystal part contributing to excitation is doped, so that the equivalent series resistance is reduced.

  FIG. 8 is a diagram for explaining other actions or effects of the present embodiment. In the figure, the horizontal axis indicates the frequency f, and the vertical axis indicates the absolute value | Z | (hereinafter, simply referred to as “impedance”) of the impedance. A line L0 indicates the characteristics of the crystal resonator element of the comparative example. A line L1 indicates the characteristics of the crystal resonator element of the example. In the comparative example, the dopant 39 is not added to the crystal piece 15 with respect to the example. Other conditions are the same in the comparative example and the example. The dopant 39 is Ge. FIG. 8 is obtained by simulation calculation.

  As shown in this figure, in both the comparative example and the example, a resonance point (resonance frequencies fr0 and fr1) at which the impedance is minimized and an antiresonance point (antiresonance frequencies fa0 and fa1) at which the impedance is maximized appear. However, the resonance point (fr1) of the example has a higher frequency and a lower impedance than the resonance point (fr0) of the comparative example. Further, the anti-resonance point (fa1) of the example has a higher frequency and higher impedance than the anti-resonance point (fa0) of the comparative example. Further, the frequency difference Δf1 (= fa1−fr1) between the resonance frequency and the antiresonance frequency of the embodiment is larger than the frequency difference Δf0 (= fa0−fr0) of the comparative example.

  Since the resonance frequency and the antiresonance frequency are higher in the example than in the comparative example, it can be seen that the crystal piece 15 is easily vibrated by the addition of the dopant 39. In addition, since the minimum value of the impedance or the maximum value of the impedance is larger in the example than in the comparative example, it can be seen that the amplitude is increased by the addition of the dopant 39. Since the frequency difference between the resonance frequency and the antiresonance frequency is larger in the example than in the comparative example, it can be seen that the electromechanical coupling coefficient is increased by the addition of the dopant 39.

  In general, the vibration element 5 is reduced in size as the frequency increases. On the other hand, the example has a higher resonance frequency than the comparative example. Therefore, for example, by adding the dopant 39, the vibration element 5 having a high frequency can be realized without downsizing, and the degree of freedom in design is improved. In addition, since the impedance of the resonance point in the example is smaller than that in the comparative example, for example, it is easy to cause a resonance appropriately, and thus it is easy to obtain an oscillation signal. In addition, since the frequency difference between the resonance frequency and the antiresonance frequency is larger in the example than in the comparative example, it is easy to adjust the frequency of the oscillation signal by, for example, the load capacitance.

  In the present embodiment, the dopant 39 is, for example, germanium.

  The lattice constant (5.66 （) of germanium is larger than both the a-axis lattice constant (4.913Å) and the c-axis lattice constant (5.4040Å) of quartz. Therefore, the above-described effects of shortening the interatomic distance and increasing the mobility are favorably achieved. As a result, the equivalent series resistance can be suitably reduced.

  In the present embodiment, the non-doping portion 37 extends between a pair of main surfaces of the crystal piece 15 (for example, between the main surfaces of the outer peripheral portion 33) and more than half a circumference of the doping portion 35 in a plan view (this embodiment). In this case, a portion surrounding the doping portion 35 is included over the entire circumference.

  Therefore, the conductivity and the electromechanical coupling coefficient of the doping part 35 are relatively larger than those around the doping part 35. As a result, the energy confinement effect in the doping portion 35 is improved.

  In this embodiment, the crystal piece 15 has a mesa portion 31 and an outer peripheral portion 33. The mesa unit 31 includes at least a part (all in this embodiment) of the doping unit 35. The outer peripheral portion 33 surrounds the mesa portion 31 in plan view, is thinner than the mesa portion 31, and includes at least a part (most part in the present embodiment) of the non-doping portion 37.

  Therefore, for example, the energy confinement effect due to the mesa type and the energy confinement effect due to the doping portion 35 being provided between the pair of excitation electrodes 17 and the non-doping portion 37 being positioned therearound are achieved. Is done. As a result, for example, the equivalent series resistance decreases.

  The doping portion 35 is accommodated on the top surface (main surface) of the mesa portion 31 in plan view. The non-doping portion 37 includes a side surface of the mesa portion 31 that connects the outer peripheral portion 33 and the top surface of the mesa portion 31.

  Therefore, for example, the possibility of vibration leaking from the outer edge portion (including the side surface of the mesa portion 31) of the mesa portion 31 to the outer peripheral portion 33 is reduced, and as a result, the equivalent series resistance is lowered. Further, for example, the range in which the energy is confined is defined by the doping unit 35 in addition to or instead of the side surface of the mesa unit 31. As a result, for example, the influence of the machining error on the side surface of the mesa portion 31 on the vibration characteristics of the vibration element 5 is reduced. In addition, the crystal piece 15 changes the appearance of the crystal plane and / or the etching rate by adding the dopant 39. Therefore, for example, by forming the side surface of the mesa portion 31 formed by etching with the non-doping portion 37, it becomes easy to use the conventional know-how of etching.

  In the present embodiment, the vibration element 5 further includes a pair of extraction electrodes 19 extending from the pair of excitation electrodes 17. The non-doping portion 37 extends between a pair of main surfaces of the crystal piece 15 (for example, between a pair of main surfaces of the outer peripheral portion 33), and 90% or more of the pair of extraction electrodes 19 when seen in a plan view. The part which overlaps is included.

  Therefore, even when a voltage is applied to the pair of extraction electrodes 19, the risk of vibration leakage is reduced as compared with the case where the doping portion 35 is located under the extraction electrodes 19. As a result, the vibration characteristics of the crystal piece 15 are improved.

  Moreover, in this embodiment, the manufacturing method of the vibration element 5 has an etching process (ST3-ST8), a conductive layer formation process (ST9), and an individualization process (ST10). In the etching step, the crystal wafer 51 including at least a part of the dopant 39 made of an element of Group 4 of the periodic table having an atomic weight larger than that of silicon is etched to form a plurality of crystal piece portions 55. In the conductive layer forming step, a plurality of excitation electrodes 17 are formed on the plurality of crystal piece portions 55. In the singulation step, the plurality of crystal piece portions 55 on which the plurality of excitation electrodes 17 are formed are singulated.

  Therefore, for example, it is possible to realize the vibration element 5 that exhibits the various effects described above. Further, for example, since the dopant 39 is added to the wafer 51 prior to the etching, the etching is performed as compared with the aspect in which the doping is performed after the etching (the vibration element 5 of the present disclosure may be realized by this aspect). Doping is not performed from the side surface that appears, and doping can be performed only from the main surface. As a result, for example, the concentration and range of the dopant 39 can be easily controlled.

  The manufacturing method according to the present embodiment further includes a doping step of adding the dopant 39 to the wafer 51 before the etching step.

  Therefore, for example, the addition of the dopant 39 is easier compared to an embodiment in which the dopant 39 is added to the artificial quartz in the process of growing the crystal by hydrothermal synthesis (the manufacturing method according to the present disclosure may include this embodiment). It is. In addition, it is easy to dope the crystal piece 15 locally, and it is easy to realize the resonator element 5 having the various effects described above.

  In the doping step, for example, the wafer 51 and the metal 65 are heated in a state where the metal 65 containing the dopant 39 is in contact with the wafer 51.

  Therefore, for example, doping can be performed relatively inexpensively. For example, it is easy to obtain a structure in which the dopant 39 is substituted for silicon while maintaining the crystal structure. As a result, for example, the risk of unintended characteristics appearing can be reduced, and the effects and the like due to the shortened interatomic distance can be suitably obtained.

  In the doping step, for example, a voltage is applied to the metal 65 in a state where the metal 65 including the dopant 39 is in contact with the wafer 51.

  Therefore, for example, doping can be performed relatively inexpensively. In addition, as with thermal diffusion, it is easy to obtain a structure in which the dopant 39 is substituted for silicon while maintaining the crystal structure.

  Further, the etching steps (ST3 to ST8) (in a broad sense) are performed by etching the outer peripheral portion 33 in each of the plurality of crystal piece portions 55, and in each of the plurality of crystal piece portions 55, in the plan view. This includes a mesa etching step (ST7) that surrounds the mesa portion 31 and forms an outer peripheral portion 33 that is thinner than the mesa portion 31. In the doping step, a dopant 39 is doped into a region that becomes the mesa portion 31.

  Therefore, for example, the above-described doping unit 35 is located in the mesa unit 31, thereby realizing the resonator element 5 having various effects. Further, for example, since the doping is not performed in the outer peripheral portion 33 where etching is performed, waste of the dopant 39 is reduced.

Second Embodiment
FIG. 9A is a perspective view showing the configuration of the vibration element 205 according to the second embodiment.

  The vibration element 205 is basically different from the vibration element 5 of the first embodiment only in that it is not a mesa type. Specifically, it is as follows.

  Like the vibration element 5, the vibration element 205 includes a crystal piece 215, a pair of excitation electrodes 17 located on a pair of main surfaces of the crystal piece 215, and a pair of extractions drawn from the pair of excitation electrodes 17. And an electrode 19.

  The crystal piece 215 is different from the crystal piece 15 of the first embodiment only in shape (and dimensions). Specifically, the crystal piece 215 has a plate shape with a constant thickness over the whole. The planar shape of the crystal piece 215 is, for example, a rectangle like the shape of the outer edge of the crystal piece 15. The corners of the rectangle may be chamfered with a flat surface or a curved surface, the long side and / or the short side may be arcuate bulging outward, or the lengths of two opposing sides may be different from each other. This is the same as the crystal piece 15.

  The excitation electrode 17 and the extraction electrode 19 are the same as the excitation electrode 17 and the extraction electrode 19 of the first embodiment, as understood from the reference numerals. However, the shape (and dimensions) of the crystal piece 215 may differ slightly from the crystal piece 15 of the first embodiment, and there may be a slight difference in size and the like.

  FIG. 9B and FIG. 9C are schematic views for explaining the material of the crystal piece 215, and are the same views as FIG. 3A and FIG. 3B of the first embodiment. . Specifically, FIG. 9A is a plan view, and FIG. 9C is a cross-sectional view taken along the line IXc-IXc in FIG. 9B.

  Similarly to the crystal piece 15, the crystal piece 215 is configured by partially adding a dopant 39 to the crystal, and includes a doping portion 235 and an undoped portion 237.

  The doping part 235 and the non-doping part 237 are different from the doping part 35 and the non-doping part 37 of the first embodiment in that the shape of the crystal piece 215 is different from that of the crystal piece 15 of the first embodiment. The same as the doping part 35 and the non-doping part 37.

  The range of the doped portion 235 (undoped portion 237) in the crystal piece 215 is the same as that of the first embodiment except that the relationship with the mesa portion 31 is not defined. For example, the doping portion 235 is provided across the entire thickness of the crystal piece 215 between the pair of excitation electrodes 17, and the planar shape and width thereof are substantially the same as those of the one excitation electrode 17 (for example, both The difference in area is less than 10% of the area of one excitation electrode 17). The non-doping portion 237 is a region other than the doping portion 235 in the crystal piece 215 and overlaps substantially the entire pair (for example, 90% or more) of the pair of extraction electrodes 19 in a plan view.

  The method for manufacturing the vibration element 205 is the same as the method for manufacturing the vibration element 205 of the first embodiment, except that, for example, the steps (ST6 to ST8) for making the crystal piece 55 a mesa shape are unnecessary. It may be the same.

  As described above, also in the present embodiment, the crystal piece 215 includes the doping portion 235 and the non-doping portion 237, and the doping portion 235 is a dopant made of an element of Group 4 of the periodic table having a larger atomic weight than silicon. 39. At least a part of the doping portion 235 (all in the present embodiment) is located between the pair of excitation electrodes 17. Therefore, the same effect as the first embodiment is achieved. For example, the equivalent series resistance decreases.

<Third Embodiment>
(Configuration of vibration element)
FIG. 10A is a schematic plan view for explaining the material of the crystal piece 315 according to the third embodiment, and corresponds to FIG. 9B of the second embodiment. In the vibrating element 305 including the crystal piece 315, the pair of excitation electrodes 17 and the pair of extraction electrodes 19 (shown by dotted lines in FIG. 10A) are the same as those in the second embodiment.

  The crystal piece 315 is different from the crystal piece 215 of the second embodiment only in the range in plan view where the dopant 39 is added. Specifically, in the crystal piece 315, in addition to the doping unit 235 described in the second embodiment, doping units 336A and 336B (hereinafter, A and B may be omitted) located on the outer edge of the crystal piece 315. There is.)

  The doping part 336 is the same as the other doping parts 35 already described except for the arrangement range in plan view. When a plurality of doping portions are provided in one crystal piece as in this embodiment, the arrangement range of the doping portions and the concentration of the dopant 39 in the thickness direction are, for example, between the plurality of doping portions. Are the same. However, they may be different.

  For example, the doping portion 336 is located over the entire circumference except for the portion of the outer edge of the crystal piece 315 that overlaps with the pair of extraction electrodes 19 (indicated by dotted lines in FIG. 10A). From another viewpoint, the doping parts 336A and 336B as a whole or the doping part 336A extends over 2/3 or more of the outer edge of the crystal piece 315, for example.

  The doping portion 336 </ b> B is located in a portion between the pair of extraction electrodes 19 on the outer edge of the crystal piece 315. In the present embodiment, since the pair of extraction electrodes 19 is located on one short side of the four sides of the rectangular crystal piece 315, the doping portion 336B is located on the center side of the short side. .

  The doping part 336 </ b> A is located in a part of the outer edge of the crystal piece 315 that is outside the pair of extraction electrodes 19. In the present embodiment, since the pair of extraction electrodes 19 is located on one short side of the four sides of the rectangular crystal piece 315, the doping portion 336A includes the entire short side different from the short side. Of the two long sides, they are located on the other short side.

  The doping part 336 is separated from the doping part 235 over the entire circumference, and a non-doping part 337 is interposed between the doping part 235 and the doping part 336. From another viewpoint, the width of the doping part 336 is narrower than the distance between the excitation electrode 17 (doping part 235) and the outer edge of the crystal piece 315, for example, over the entire circumference of the doping part 336. The width of the doping part 336 is, for example, not less than 5 μm and not more than 20 μm. The width of the doping portion 336 may be constant over the entire circumference (example shown in the figure) or may vary depending on the position. The doping parts 336A and 336B may have the same width or may be different from each other.

  The non-doping portion 337 is a portion other than the doping portions 235 and 336 of the crystal piece 315, and surrounds the doping portion 235 over half a circumference (the whole circumference in the illustrated example) as in the second embodiment. At the same time, the whole of the pair of extraction electrodes 19 (for example, 90% or more) overlaps with each other in plan perspective.

(Manufacturing method of vibration element)
In the following description, for the sake of convenience, the reference numerals (51 or 61) used in the manufacturing method according to the first embodiment may be used regardless of the difference in shape or material.

  The manufacturing method of the vibration element 305 is basically the same as that of the second embodiment, and etching (ST6 to ST8) for forming a mesa shape is omitted from the manufacturing method of the first embodiment. However, in the doping in step ST2, the planar shape of the selection mask 61 (step ST21) is different from that in the second (first) embodiment. In other words, in the present embodiment, the selection mask 61 has openings in portions corresponding to the doping portions 235 and 336, whereby the doping portions 235 and 336 are formed.

  The planar shape of the opening corresponding to the doping portion 336 of the selection mask 61 may be the same as the planar shape of the doping portion 336. Further, the planar shape of the opening may be a shape in which the planar shape of the doping portion 336 is widened outward. In other words, the dopant 51 may be added to the wafer 51 even in the allowance (region removed by etching) located around the plurality of crystal piece portions 55. Even in this case, the doping unit 336 is realized.

  FIGS. 10B and 10C are schematic diagrams for explaining the external etching in step ST4, and a cross section of the wafer 51 on which the first mask 53 is formed is taken as Xc-Xc in FIG. This is shown in the area corresponding to the line.

  In the examples shown in these drawings, the state in which the dopant 39 is added also in the discard margin 51d (FIG. 10B) as described above is shown. In the example shown in the figure, the doping part (reference numeral omitted) in the discard margin 51d is formed to spread outward by a predetermined amount from the outer edge of the region to be the crystal piece 315, and the non-doping part (reference numeral omitted) is provided in the discard margin 51d. Is present. However, the doping part may be formed over the entire disposal allowance 51d.

  In such a case, the edge of the first mask 53 is located in the doping portion, and the side surface formed by etching is formed in the doping portion 336. Note that the edge of the first mask 53 ideally coincides with the boundary between the etched region and the non-etched region. However, this is not necessarily the case due to the influence of undercut (under etching). Unlike the illustration, the edge of the first mask 53 is located in the non-doping portion, and the boundary between the etched region and the non-etched region is finally inside the edge of the first mask 53 due to undercut or the like. It may be located in a doping part by this.

  As described above, also in the present embodiment, the crystal piece 315 includes the doping part 235 and the non-doping part 337, and the doping part 235 is a dopant made of a Group 4 element having a larger atomic weight than silicon. 39. At least a part of the doping portion 235 (all in the present embodiment) is located between the pair of excitation electrodes 17. Accordingly, the same effects as those of the first and second embodiments can be obtained. For example, the equivalent series resistance decreases.

  Further, in the present embodiment, the crystal piece 315 has a doped portion 336 </ b> B that is located between the pair of extraction electrodes 19 in a plan view and has a higher dopant 39 concentration than the undoped portion 337.

  Therefore, for example, vibration leakage can be reduced by the non-doping portion 337 under the pair of extraction electrodes 19 to which a voltage is applied, while spurious can be reduced by scattering of unnecessary vibration in the meantime. In addition, for example, a manufacturing method in which a doping portion is formed in the discard allowance 51d can be applied.

  In the present embodiment, the crystal piece 315 is located on the outer edge of the crystal piece 315 over 2/3 of the outer edge of the crystal piece 315, and the non-doping portion 337 is interposed between the doping portion 235 and the crystal piece 315. The doped portion 336A (or the entire 336) has a higher dopant concentration than the non-doped portion 337.

  Therefore, for example, spurious can be reduced by scattering of unnecessary vibration at the outer edge of the crystal piece 315 while reducing vibration leakage from the doping part 235 by the non-doping part 337. In addition, for example, a manufacturing method in which a doping portion is formed in the discard allowance 51d can be applied.

  Also in the present embodiment, the method for manufacturing the vibration element 5 includes an etching step (ST3 to ST5), a conductive layer forming step (ST9), and an individualization step (ST10). In the etching step, the crystal wafer 51 including at least a part of the dopant 39 made of an element of Group 4 of the periodic table having an atomic weight larger than that of silicon is etched to form a plurality of crystal piece portions 55. Therefore, the same effect as the manufacturing method of the first embodiment is achieved. For example, since the dopant 39 is added to the wafer 51 prior to the etching, the risk of doping from the side surface that appears by the etching is reduced.

  In the present embodiment, in the doping step (ST2), the dopant 39 is added to the region of the wafer 51 that becomes the edges of the plurality of crystal piece portions 55. In the etching step (ST4), the side surface of the crystal piece 55 is formed by the portion to which the dopant 39 is added.

  Therefore, for example, first, the vibration element 305 in which the doping portion 336 is provided on the edge portion of the crystal piece 315 described above is realized. Further, since the side surface is formed by the doping portion, it is possible to reduce the residue and shorten the etching time. Specifically, it is as follows.

  In crystal etching without dopant, due to the anisotropy of crystal etching, a crystal surface appears on the side surface formed by etching, or the etching time is lengthened to reduce residue on the side surface. There is a need to. On the other hand, in the etching of the doped portion, the appearance of the crystal plane and / or the etching rate changes. Specifically, for example, the inclusion of the dopant 39 reduces the anisotropy with respect to etching and / or increases the etching rate. As a result, the etching time for keeping the residue below a predetermined allowable amount is shortened.

  10 (a) to 10 (c), the description has been given of the aspect in which the doping portion 336 located at the outer edge of the crystal piece is provided in the crystal piece that is not a mesa type as in the second embodiment. The doping unit 336 may be applied to a mesa crystal piece as in the first embodiment.

<Fourth embodiment>
(Configuration of vibration element)
FIG. 11A is a schematic plan view for explaining the material of the crystal piece 415 according to the fourth embodiment, and corresponds to FIG. 3A of the first embodiment. In the vibration element 405 including the crystal piece 415, the pair of excitation electrodes 17 and the pair of extraction electrodes 19 (not shown here) are the same as those in the first embodiment.

  The crystal piece 415 is different from the crystal piece 15 of the first embodiment only in the range in plan view where the dopant 39 is added. Specifically, it is as follows.

  The crystal piece 415 has a doping portion 435 positioned between the pair of excitation electrodes 17. The doping part 435 is the same as the doping part 35 of the first embodiment except for the arrangement range in plan view, and at least a part of the doping part 435 is located in the mesa part 31. The shape and size of the mesa portion 31 and the outer peripheral portion 33 are basically the same as those of the first embodiment (except for the influence of the dopant 39 on the etching residue, for example).

  The area of the doping portion 435 in plan view is equal to or slightly larger than the mesa portion 31 (for example, 20 μm or less). The side surface of the mesa unit 31 is constituted by a doping unit 435.

  As illustrated in FIG. 1, when the pair of excitation electrodes 17 is smaller than the mesa portion 31 in plan view, the doping portion 435 overlaps with the entire pair of excitation electrodes 17. It overlaps with a part of the extraction electrode 19. In this case, the difference in area between the doping unit 435 and the one excitation electrode 17 may be less than 10% of the area of the one excitation electrode 17 as in the first embodiment, or larger than this. Also good. Note that the width of the pair of excitation electrodes 17 may be equal to or larger than the width of the mesa portion 31, and may be equal to or larger than the width of the doping portion 435. The non-doping portion 437 is a region other than the doping portion 435 in the crystal piece 415. For example, as in the other embodiments, the undoped portion 437 overlaps substantially the entire pair (for example, 90% or more) of the pair of extraction electrodes 19 in a plan view. Yes.

(Manufacturing method of vibration element)
In the following description, for the sake of convenience, the reference numerals (51 or 61) used in the manufacturing method according to the first embodiment may be used regardless of the difference in shape or material.

  The manufacturing method of the vibration element 405 is basically the same as that of the first embodiment. However, in the doping in step ST2, the planar shape of the selection mask 61 (step ST21) is different from that in the first embodiment. In other words, in the present embodiment, the opening of the selection mask 61 has a size equal to or larger than the region to be the mesa portion 31, and thus, the entire mesa portion 31 (from another viewpoint, the side surface of the mesa portion 31. ) Is formed.

  The planar shape of the opening for forming the doping portion 435 of the selection mask 61 may be the same as the planar shape of the mesa portion 31, or toward the region that becomes the outer peripheral portion 33 with respect to the planar shape of the mesa portion 31. An expanded shape may be used. From another viewpoint, the dopant 51 may be added to the wafer 51 even in a region dug down by mesa etching (ST6 to ST8). As illustrated in FIG. 3B, when the side surface of the mesa portion 31 is inclined so as to be positioned on the outer side in plan view as it approaches the main surface of the outer peripheral portion 33 in the thickness direction, The planar shape of the mesa portion 31 may be, for example, the planar shape at the position of the main surface of the outer peripheral portion 33.

  FIGS. 11B and 11C are schematic diagrams for explaining the mesa etching in steps ST6 to ST8, and show a cross section of the crystal piece 55 (wafer 51) on which the first mask 53 is formed. This is shown in a region corresponding to the XIc-XIc line of 11 (a).

  In the examples shown in these drawings, the dopant 39 is added to the region that becomes the outer peripheral portion 33 in plan view. As already described, the dopant 39 may only be added to a region equivalent to the region to be the mesa portion 31.

  Thus, when the dopant 39 is added, the edge part of the 2nd mask 57 is located in a doping part. The side surface of the mesa portion 31 formed by etching is formed in the doping portion 435. Note that the edge of the second mask 57 ideally coincides with the boundary between the etched region and the non-etched region. However, this is not necessarily the case due to the influence of undercut (under etching). The edge of the second mask 57 is located in the undoped part, and the boundary between the etched region and the non-etched region is finally located inside the edge of the second mask 57 by undercut or the like, Thereby, it may be located in the doping part.

  As described above, also in the present embodiment, the crystal piece 415 includes the doping part 435 and the non-doping part 437, and the doping part 435 is a dopant composed of an element of Group 4 of the periodic table having an atomic weight larger than that of silicon. 39. At least a part of the doping part 435 is located between the pair of excitation electrodes 17. Therefore, the same effects as those of the first to third embodiments are achieved. For example, the equivalent series resistance decreases. In the present embodiment, as in the first embodiment, since the mesa unit 31 includes the doping unit 435, the energy confinement effect is improved.

  Also in the present embodiment, the method for manufacturing the vibration element 5 includes an etching step (ST3 to ST8), a conductive layer forming step (ST9), and an individualization step (ST10). In the etching step, the crystal wafer 51 including at least a part of the dopant 39 made of an element of Group 4 of the periodic table having an atomic weight larger than that of silicon is etched to form a plurality of crystal piece portions 55. Therefore, the same effect as the manufacturing method of the first embodiment is achieved. For example, since the dopant 39 is added to the wafer 51 prior to the etching, the risk of doping from the side surface that appears by the etching is reduced.

  In the present embodiment, the etching process includes a mesa etching process (ST6 to ST8). In the mesa etching step, the outer peripheral portion 33 of each of the plurality of crystal piece portions 55 is etched to surround the mesa portion 31 in each of the plurality of crystal piece portions 55 and the mesa portion 31 in plan view. A thin outer peripheral portion 33 is formed. In the doping step, a dopant 39 is added to the region that becomes the mesa portion 31. In the mesa etching process, the side surface of the mesa portion 31 is formed by the portion to which the dopant 39 is added.

  Therefore, for example, first, the vibration element 405 in which the doping portion 435 is provided in the mesa portion 31 described above is realized. Further, since the side surface is formed by the doping part 435, the residue can be reduced and the etching time can be shortened similarly to the side surface of the crystal piece 315 in the manufacturing method of the third embodiment.

  In FIGS. 11A to 11C, a doping portion 336 located on the outer edge of the crystal piece 415 may be provided in this embodiment as in the third embodiment.

<Fifth Embodiment>
FIG. 12A is a schematic cross-sectional view for explaining the material of the crystal piece 515 of the vibration element 505 according to the fifth embodiment.

  The vibration element 505 (crystal piece 515) basically differs from the vibration element 205 (crystal piece 215) of the second embodiment only in the range of the doping portion in the thickness direction (Y′-axis direction). Specifically, the doping portions 535A and 535B (hereinafter, A and B may be omitted) positioned between the pair of excitation electrodes 17 in the crystal piece 515 are the main surface of the crystal piece 515 in the thickness direction. Located only on the side.

  The thickness of each doping part 535 may be set as appropriate. For example, the thickness of the doping portion 535 is 1 nm or more and (t−10 nm) / 2 or less, where t is the thickness of the crystal piece 515. If it is this range, it can confirm that the doping part 535 is provided only in the main surface side of the crystal piece 515 by SIMS and / or TXRF, for example. Moreover, the thickness of the doping part 535 is 0.1 micrometer or more, for example. Within this range, for example, the effect of reducing the equivalent series resistance by the doping portion 535 can be more reliably achieved.

  The non-doping portion 537 is a portion other than the doping portion 535 in the crystal piece 515, and is also located between the pair of excitation electrodes 17 in this embodiment.

  In the illustrated example, the doping portion 535 is provided on each of the pair of main surfaces of the crystal piece 515, but the doping portion 535 may be provided on only one of the pair of main surfaces. .

  The range of the doping unit 535 in plan view may be the same as in the first to fourth embodiments. Note that with respect to an aspect in which the doping portion 535 is provided on each of the pair of main surfaces of the crystal piece 515, for example, the area difference between the doping portion 535 and the one excitation electrode 17 in the plan view is one of the excitation electrodes 17. In the case of determining whether or not it is less than 10%, the determination may be made based on the area obtained by projecting the two doping parts 535 in the direction of plane perspective. The same applies to a seventh embodiment described later.

  The method for manufacturing the vibration element 505 may be basically the same as the method for manufacturing the vibration element 205 of the second embodiment. The thickness of the doping portion 535 can be set by appropriately adjusting specific conditions for doping. For example, in ion implantation, the acceleration voltage may be reduced, the ion current may be reduced, and / or the implantation time may be shortened as compared with the second embodiment. Further, for example, in thermal diffusion, it is only necessary to shorten the diffusion time and / or make the metal 65 thinner than in the second embodiment. Further, in most doping methods, the doping portion 535 of this embodiment can be realized if the doping time is relatively short.

  As described above, also in the present embodiment, the crystal piece 515 includes the doping part 535 and the non-doping part 537, and the doping part 535 is a dopant composed of a Group 4 element of the periodic table having an atomic weight larger than that of silicon. 39. At least a part of the doping portion 535 (all in the present embodiment) is located between the pair of excitation electrodes 17. Therefore, the same effect as the first embodiment is achieved. For example, the equivalent series resistance decreases.

  Further, in the present embodiment, the doping portion 535 is located only at a part of at least one side of the pair of main surfaces in the thickness of the crystal piece 515.

  Here, if the crystal piece 515 of this embodiment and the crystal piece 215 of the second embodiment have the same thickness, the doping portion 535 of this embodiment is thinner than the doping portion 235 of the second embodiment. Therefore, the effect produced in the doping portion itself is lower than that in the second embodiment. However, a portion of the non-doping portion 537 that overlaps with the doping portion 535 has a short interatomic distance due to the compressive action received from the doping portion 535, so that part of the reduction in the effect is compensated. On the other hand, the amount of the dopant 39 and the burden (such as power and time) of the doping process are reduced as compared with the second embodiment.

  In FIG. 12A, the doping portion between the pair of excitation electrodes 17 exemplifies a mode in which the range in the thickness direction is a part of the main surface side of the crystal piece 515, but doping at other positions is performed. In a portion (for example, a doping portion (FIG. 10A) located on the outer edge of the crystal piece), the range in the thickness direction may be a part on the main surface side of the crystal piece 515. The range in the thickness direction may be the same among the plurality of doping portions or may be different.

<Sixth Embodiment>
FIG. 12B is a schematic cross-sectional view for explaining the material of the crystal piece 615 of the vibration element 605 according to the sixth embodiment.

  The vibration element 605 (crystal piece 615) is different from the vibration element 205 (crystal piece 215) of the second embodiment only in that the concentration of the dopant 39 changes in the thickness direction. Specifically, for example, in the doping portion 635 of the crystal piece 615, the concentration of the dopant 39 is higher toward the pair of main surfaces.

  The change in the concentration of the dopant 39 in the doping unit 635 may be continuous (for example, the change rate is constant or the change of the change rate is smooth), or may be stepwise (stepwise). . Further, the highest concentration and the lowest concentration in the doping portion 635 may be set as appropriate.

In addition, as shown in FIG. 10B, the concentration of the dopant 39 on the central side in the thickness direction is lower than that on the main surface side, and the doped portion depends on whether the concentration of the dopant 39 is equal to or higher than a predetermined threshold. When determining whether or not the density on the central side in the thickness direction is higher than the threshold value, this is regarded as the present embodiment, and when it is low, it is regarded as the fifth embodiment (FIG. 12A). . The threshold value is, for example, 1 × 10 ¹⁶ (number of atoms / cm ³ ), 1 × 10 ¹⁸ (number of atoms / cm ³ ), or 1 × 10 ¹³ (number of atoms / cm ² ) described above.

Even if the concentration of the dopant 39 is intended to be substantially uniform in the thickness direction as in the second embodiment, the concentration may be high or low. In the doping unit 635 of this embodiment, the value obtained by dividing the high concentration by the low concentration is, for example, 1 × 10 (number of atoms / cm ³ ) or more, and about 1 × 10 ⁴ (number of atoms / cm ³ ). It is also possible.

  The undoped portion 637 is a portion other than the doped portion 635 in the crystal piece 615, and occupies the same range as the undoped portion 237 of the second embodiment in this embodiment.

  In the example shown in the figure, the doping portion 635 has a higher concentration of the dopant 39 on the pair of principal surfaces compared to the central side in the thickness direction, but on one side of the pair of principal surfaces. In comparison, the concentration of the dopant 39 may be higher on the other side of the pair of main surfaces.

  The manufacturing method of the vibration element 605 may be basically the same as the manufacturing method of the vibration element 205 of the second embodiment. As described in the first embodiment, the dopant 39 is added to the wafer 51 from its main surface.

  When doping is performed on the main surface of the wafer 51, the concentration of the dopant 39 in the wafer 51 gradually increases from the main surface side. Further, the maximum concentration of the dopant 39 is defined by, for example, various doping conditions (voltage or heat). Therefore, for example, by ending doping before the concentration of the dopant 39 reaches the maximum value (substantially uniform from another viewpoint) over the entire thickness direction of the wafer 51, the concentration in the thickness direction as in the present embodiment. A doping unit 635 in which is changed is realized.

  Further, if doping is performed from both main surfaces, a doped portion 635 having a higher concentration of the dopant 39 is realized on the pair of main surface sides as compared to the central side in the thickness direction as in the example shown in the figure. If only doping is performed, unlike the example shown in the figure, a doped portion having a higher concentration of the dopant 39 on the one main surface side than the other main surface is realized.

  As described above, also in the present embodiment, the crystal piece 615 includes the doping part 635 and the non-doping part 637, and the doping part 635 is a dopant made of an element of Group 4 of the periodic table having a larger atomic weight than silicon. 39. At least a part of the doping part 635 is located between the pair of excitation electrodes 17. Therefore, the same effect as the first embodiment is achieved. For example, the equivalent series resistance decreases.

  In the present embodiment, in the doping portion 635, the concentration of the dopant 39 is higher than the central side in the thickness direction of the crystal piece 615 on at least one side of the pair of main surfaces of the crystal piece 615.

  Here, if the concentration of the dopant 39 is the same in the main surface side portion of the doping portion 635 of the present embodiment and the doping portion 235 of the second embodiment, the doping portion 635 of the present embodiment Since the concentration of the dopant 39 is relatively low in the central portion in the thickness direction, the effect produced by the dopant 39 in the portion is relatively low. However, since the interatomic distance is shortened in the portion of the doping portion 635 on the central side in the thickness direction due to the compression action received from the main surface side portion of the doping portion 635, a part of the reduction in the effect is compensated. The On the other hand, the amount of the dopant 39 and the burden (such as power and time) of the doping process are reduced as compared with the second embodiment. Further, since the concentration of the dopant 39 is relatively low in the central portion in the thickness direction, the mechanical strength is increased by increasing the dopant concentration on the main surface side while maintaining the mechanical strength in the central portion. It is possible to manufacture the quartz crystal piece 615 that can increase the electromechanical bonding coefficient.

  When the dopant 39 is added to the crystal during crystal growth, the concentration of the dopant 39 is substantially uniform. Therefore, when the concentration of the dopant 39 is changed in the thickness direction as in the present embodiment, the wafer 51 is doped, that is, the manufacturing method described in the first embodiment is performed. Can be estimated from the product.

  In FIG. 12B, an example in which the concentration of the dopant 39 is changed in the thickness direction in the doping portion between the pair of excitation electrodes 17 is illustrated, but the doping portion in another position (for example, the outer edge of the crystal piece) The concentration of the dopant 39 may change in the thickness direction in the doping portion (FIG. 10A) located in the region. The change in the concentration may be the same or different between the plurality of doping portions.

<Seventh embodiment>
FIG. 12C is a schematic cross-sectional view for explaining the material of the crystal piece 715 of the vibration element 705 according to the seventh embodiment.

  The vibration element 705 (crystal piece 715) is obtained by applying the configuration in which the doping portion is provided only on the main surface side in the thickness direction of the fifth embodiment to the mesa-type crystal piece of the first or fourth embodiment. That is, this embodiment is different from the first or fourth embodiment only in the range of the doping portion in the thickness direction. From another viewpoint, this embodiment is different from the fifth embodiment only in that it is a mesa type. Accordingly, the doping portions 735A and 735B (hereinafter, A and B may be omitted) in which at least a part (all in the illustrated example) is located between the pair of excitation electrodes 17 (the mesa portion 31). In the direction, it is located only on the main surface side of the crystal piece 715.

  As in the fifth embodiment, the thickness of the doping portion 735 is, for example, 1 nm or more and (t−10 nm) / 2 or less, where t is the thickness of the mesa portion 31. In addition, the thickness of the doping portion 735 may be thinner or equivalent as compared to the digging amount Md from the main surface of the mesa portion 31 to the main surface of the outer peripheral portion 33 (example shown in the figure). It may be thick.

  The non-doping portion 737 is a portion other than the doping portion 735 in the crystal piece 715. Since the doping part 735 is located only on the main surface side of the crystal piece 715, the non-doping part 737 is located between the pair of excitation electrodes 17 as in the fifth embodiment.

  The method for manufacturing the vibration element 705 may be basically the same as the method for manufacturing the vibration element of the first or fourth embodiment. Similarly to the fifth embodiment, the doping portion 735 is provided only on the main surface side of the crystal piece 715 by appropriately setting specific doping conditions. For example, the doping time is shorter than that in the first or fourth embodiment.

  As in the first embodiment, when the doping portion 735 is within the region that is the main surface (top surface) of the mesa portion 31 in plan view, the side surface of the mesa portion 31 is the same as that of the first embodiment. Similarly to the above, it is formed by etching the undoped portion of the wafer 51. The non-doping portion 737 is located between the entire outer peripheral portion 33, the outer edge portion of the mesa portion 31 (including the side surface of the mesa portion 31), and the pair of doping portions 735.

  As in the fourth embodiment, the doping portion 735 is equal to or larger than the width of the mesa portion 31 (here, the width of the main surface of the outer peripheral portion 33) in plan view, and the doping portion 735 has a thickness of In the case where the digging amount Md is exceeded, the side surface of the mesa portion 31 is formed by etching the doping portion, as in the fourth embodiment. The doping portion 735 is located on the mesa portion 31 side of the outer peripheral portion 33 and on the main surface side of the outer peripheral portion 33. The depth of the doping portion 735 from the top surface of the mesa portion 31 is the same in the portion in the mesa portion 31 and the portion in the outer peripheral portion 33.

  As in the fourth embodiment, the doping portion 735 is equal to or larger than the width of the mesa portion 31 (here, the width of the main surface of the outer peripheral portion 33) in plan view, and the doping portion 735 has a thickness of When the digging amount is Md or less (example shown in the figure), the side surface of the mesa portion 31 is formed entirely or partially on the top surface side by etching of the doping portion. In addition, the doping portion 735 is not located on the outer peripheral portion 33 even though doping is performed in a wider range than the mesa portion 31.

  As described above, the range and thickness of the doping portion 735 have been described as being divided into three types, but in any case, the doping portion 735 is only partly from the top surface of the mesa portion 31 to a certain (same) depth. To position.

  In the case where the doping portion 735 is not less than the width of the mesa portion 31 (the width at the height of the main surface of the outer peripheral portion 33) in plan view and the thickness of the doping portion 735 is not more than the digging amount Md. The creation of the selection mask (ST21) and the removal of the selection mask (ST24) may be omitted. Even in this case, since the doped portion of the wafer 51 that overlaps the outer peripheral portion 33 is removed by mesa etching, the outer peripheral portion 33 is composed of only the non-doped portion 737 as shown in the example in the figure. A piece 715 is obtained.

  As described above, also in the present embodiment, the crystal piece 715 includes the doping part 735 and the non-doping part 737, and the doping part 735 is a dopant composed of a Group 4 element of the periodic table having an atomic weight larger than that of silicon. 39. At least a part of the doping part 735 is located between the pair of excitation electrodes 17. Therefore, the same effect as the first embodiment is achieved. For example, the equivalent series resistance decreases.

  Further, since the doping portion 735 is located only on the main surface side of the crystal piece 715, the same effect as in the fifth embodiment can be obtained. For example, even in the non-doping portion 737, the equivalent series resistance can be reduced by the compressive action received from the doping portion 735 for the portion overlapping the doping portion 735.

  Furthermore, in the present embodiment, the doping part 735 is located only in a part of the thickness of the crystal piece 715 from the top surface of the mesa part 31 to a certain depth.

  Therefore, an advantageous effect is obtained by combining the doping portion 735 located only on the main surface side and the mesa type. For example, even if the doping part 735 extends to the outer peripheral part 33, the ratio of the thickness of the doping part 735 to the thickness of the non-doping part 737 is larger in the mesa part 31 than in the outer peripheral part 33 (described above). (Including the case where the ratio is 0 at the outer peripheral portion 33). The same can be said for the concentration of the dopant 39 unintentionally spreading to the non-doping portion 737. Therefore, for example, the action of the dopant 39 can be relatively increased in the mesa portion 31 to increase the energy confinement effect and the like. In particular, when the thickness of the doping portion 735 is smaller than the digging amount Md, the possibility that the doping portion 735 is formed on the outer peripheral portion 33 can be more reliably reduced.

  In the illustrated example, the doping portion 735 is provided on each of a pair of main surfaces of the crystal piece 715. However, as described in the fifth embodiment, the doping portion 735 has a pair of main surfaces. It may be provided in only one of these.

<Eighth Embodiment>
FIG. 12D is a schematic cross-sectional view for explaining the material of the crystal piece 815 of the vibration element 805 according to the eighth embodiment.

  In the seventh embodiment described above, the feature that the doping portion is provided only on the main surface side of the crystal piece in the fifth embodiment is applied to the mesa type vibration element of the first or fourth embodiment. Similarly, in this embodiment, the feature that the concentration of the dopant 39 is high on the main surface side of the crystal piece in the sixth embodiment is applied to the mesa type vibration element of the first or fourth embodiment.

  That is, in the crystal piece 815, at least a part (all in the illustrated example) of the doping part 835 is located in the mesa part 31, and the concentration of the dopant 39 is lower toward the center in the thickness direction. The range of the doping part 835 (non-doping part 837) in plan view is as described in the first or fourth embodiment. The change in the thickness direction of the concentration of the dopant 39 is as described in the sixth embodiment.

  The manufacturing method of the vibration element 805 is basically the same as that of the first embodiment. However, in doping (ST2), as in the sixth embodiment, the dopant 39 on the main surface side is adjusted by adjusting specific doping conditions (for example, by making the doping time shorter than in the first embodiment). The concentration of is higher than the concentration of the dopant 39 on the center side in the thickness direction.

  As described above, also in this embodiment, the crystal piece 815 has the doping part 835 and the non-doping part 837, and the doping part 835 is a dopant made of an element of Group 4 of the periodic table having a larger atomic weight than silicon. 39. At least a part of the doping part 835 is located between the pair of excitation electrodes 17. Therefore, the same effect as the first embodiment is achieved. For example, the equivalent series resistance decreases.

  Further, in this embodiment, as can be inferred from the fifth to seventh embodiments, the dopant 39 is combined by combining the configuration in which the concentration of the dopant 39 is relatively high on the main surface side of the crystal piece 815 and the mesa type. The ratio of the thickness of the dopant 39 having a relatively high concentration with respect to the thickness of the relatively low concentration of the dopant 39 can be made larger in the mesa portion 31 than in the outer peripheral portion 33 to improve the energy confinement effect and the like.

<Ninth Embodiment>
The vibration element manufactured by the manufacturing method according to the present embodiment described below is the vibration element of any of the embodiments described above as long as the planar shape of the doping portion and the planar shape of the excitation electrode 17 are substantially the same. May be. Below, the code | symbol of 7th Embodiment may be used supposing the aspect in which a doping part is formed only in the mesa type and the main surface side of thickness direction.

  FIG. 13 is a flowchart for explaining the procedure of the method for manufacturing the resonator element according to the ninth embodiment.

  Step ST31 is the same process as step ST1, and a description thereof will be omitted.

  Step ST32 is the same process as steps ST3 to ST8 if the vibration element is a mesa type, and is the same process as steps ST3 to ST5 if the vibration element is a flat plate, and the description thereof is omitted.

  Step ST33 is basically the same as step ST9. However, the conductive layer (at least the excitation electrode 17) formed in step ST33 is formed of a metal containing an element that becomes the dopant 39. The metal may be composed of only the element that becomes the dopant 39, or may be an alloy containing the element that becomes the dopant 39. The alloy is, for example, a gold germanium (Au—Ge) alloy when the dopant 39 is germanium. In the gold germanium alloy, the ratio of germanium is, for example, 5% by mass or more and 15% by mass or less, and the ratio of gold is, for example, the content of germanium and the content of impurities inevitably mixed from 100% by mass. Subtracted value.

  In step ST34, doping is performed. As described above, in the first embodiment, doping is performed before the etching and formation of the conductive layer, whereas in this embodiment, doping is performed after the excitation electrode 17 is formed.

  Step ST35 is the same as step ST10, and a description thereof will be omitted.

  14A and 14B are schematic cross-sectional views for explaining the doping in step ST34.

  As understood from comparison between these figures and FIG. 7D, in step ST34, a voltage is applied to the pair of excitation electrodes 17 instead of the metal 65 in FIG. 7D. Thereby, the dopant 39 contained in the pair of excitation electrodes 17 is added to the crystal.

  In the example shown in FIG. 7, the metal 65 is replaced with the excitation electrode 17 in FIG. 7D, but the metal 65 is replaced with the excitation electrode 17 in other doping methods (for example, thermal diffusion). The manufacturing method of this embodiment may be realized.

  If only one of the pair of excitation electrodes 17 is the excitation electrode 17 containing the dopant 39, the doping portion 735 can be formed only on one main surface side. In addition, while the excitation electrode 17 is formed of a material containing the dopant 39, the extraction electrode 19 is formed of a material not containing the dopant 39. The range of the doping portion 735 can be arbitrarily set in a region overlapping with the.

  As described in the fifth to eighth embodiments, by adjusting specific doping conditions (for example, doping time and the like), the thickness of the crystal piece portion 55 is increased in the thickness direction while expanding the doping portion. It is also possible to reduce the concentration of the dopant 39 on the central side in the thickness direction, or to form a doping portion over the entire thickness direction. However, in consideration of realistic thicknesses of the crystal piece 715 and the excitation electrode 17, the manufacturing method of the present embodiment is an aspect in which the doping portion 735 is formed only on the main surface side as in the fifth or seventh embodiment. Easy to apply.

  As described above, the manufacturing method of the present embodiment includes the etching step (ST32), the conductive layer forming step (ST33), and the singulation step (ST35). In the etching step (ST32), the wafer 51 is etched to form a plurality of crystal piece portions 55. In the conductive layer forming step, the excitation electrode 17 is formed on a part of the main surface of each of the plurality of crystal piece portions 55. In the singulation step, the plurality of crystal piece portions 55 on which the plurality of excitation electrodes 17 are formed are singulated. The plurality of excitation electrodes 17 include a Group 4 element (dopant 39) having a larger atomic weight than silicon. The manufacturing method of this embodiment further includes a doping step of applying at least one of heat and voltage to the plurality of excitation electrodes 17 and adding the element (dopant 39) to the plurality of crystal pieces 55.

  Therefore, for example, first, the resonator element according to the first to eighth embodiments in which the doping portion is located between the pair of excitation electrodes 17 can be realized. Further, since the dopant 39 included in the excitation electrode 17 is added to the crystal piece, the arrangement and removal of the metal 65 described with reference to FIG. 7B or FIG. Further, the formation and removal of the selection mask 61 can be omitted.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The crystal vibration device having the crystal vibration element is not limited to a crystal resonator. For example, in addition to the crystal resonator element, an oscillator having an integrated circuit element (IC: Integrated Circuit) that generates an oscillation signal by applying a voltage to the crystal resonator element may be used. In addition, for example, the crystal vibrating device (quartz crystal resonator) may have other electronic elements such as a thermistor in addition to the crystal vibrating element. Further, the crystal vibrating device may be one with a thermostatic bath. In the crystal resonator device, the structure of the package for packaging the crystal resonator element may be an appropriate configuration. For example, the package may be of an H-shaped cross section having recesses on the upper and lower surfaces.

  The quartz resonator element is not limited to those utilizing thickness shear vibration, and the quartz piece is not limited to the AT cut plate. For example, the crystal piece may be a BT cut plate. Further, the planar shape of the crystal piece is not limited to a rectangular shape or a similar shape. For example, the planar shape of the crystal piece may be circular or elliptical.

  The quartz resonator element is not limited to one that is supported in a cantilever shape (one pair of pads is provided on one end side), and may be one in which both ends are supported, for example. In another aspect, the pair of extraction electrodes may be extracted from the pair of excitation electrodes to the opposite sides, or may be extracted in a direction intersecting with each other at a predetermined angle.

  In the doping part, the concentration of the dopant may change in the planar direction. For example, when doping is performed via the selection mask 61, the dopant 39 penetrates from the opening of the selection mask 61 into the area immediately below the selection mask 61 depending on the doping method or conditions. Therefore, the opening of the selection mask 61 is made smaller than the region where the doping portion is to be formed. Thereby, the doping part has a region where the dopant concentration is relatively low and a region where the dopant concentration is relatively high in plan view.

  The non-doping portion may not be provided in a region different from the doping portion in plan view. For example, the non-doping portion may be provided only in a part in the thickness direction of the crystal piece. Even in this case, an effect such as a reduction in equivalent series resistance can be obtained by the dopant being positioned between the pair of excitation electrodes.

  Further, for example, in the seventh embodiment (FIG. 12C), even if the doped portion 735 extends over the entire crystal piece 715 in plan view, the undoped portion 737 is located on the center side in the thickness direction. If so, as already described, the mesa portion 31 has a larger proportion of the doping portion 735 in the thickness than the outer peripheral portion 33, and effects such as energy confinement are exhibited.

  Further, when the undoped portion surrounds the doped portion (for example, 35) positioned between the pair of excitation electrodes in a plan view, the undoped portion does not need to surround the entire circumference of the doped portion. . For example, if the non-doping portion is located on at least a part of the outer periphery of the doping portion, the effect of reducing vibration leakage to the non-doping portion can be achieved. However, effects such as an energy confinement effect can be obtained more satisfactorily if the non-doped portion extending between the pair of main surfaces of the crystal piece surrounds the doped portion over the entire circumference of the doped portion. Note that whether or not it is a half circumference or more depends on, for example, whether or not the non-doping portion is located over an angular range of 180 ° or more around the figure centroid of the doping part or the figure centroid of the excitation electrode in plan view. You may judge.

  DESCRIPTION OF SYMBOLS 1 ... Quartz crystal resonator (crystal oscillating device), 5 ... Quartz oscillating element, 15 ... Crystal piece, 31 ... Mesa part, 33 ... Outer peripheral part, 17 ... Excitation electrode, 19 ... Extraction electrode, 35 ... Doping part, 37 ... Non Doping department.

Claims (6)

An etching step of etching a quartz wafer containing at least part of a dopant comprising an element of Group 4 of the periodic table having an atomic weight larger than that of silicon to form a plurality of quartz pieces;
A conductive layer forming step of forming a plurality of excitation electrodes on the plurality of crystal pieces;
A singulation step of dividing the plurality of crystal piece portions in which the plurality of excitation electrodes are formed,
A method for manufacturing a crystal resonator element having The method for manufacturing a crystal resonator element according to claim 1, further comprising a doping step of adding the dopant to the crystal wafer before the etching step. 3. The method for manufacturing a crystal resonator element according to claim 2, wherein in the doping step, the crystal wafer and the metal are heated in a state where the metal containing the dopant is in contact with the crystal wafer. The method for manufacturing a crystal resonator element according to claim 2, wherein in the doping step, a voltage is applied to the metal in a state where the metal containing the dopant is in contact with the crystal wafer. In the doping step, the dopant is added to a region to be an edge of the plurality of crystal pieces in the crystal wafer,
5. The method for manufacturing a crystal resonator element according to claim 2, wherein in the etching step, a side surface of the crystal piece portion is formed by a portion to which the dopant is added. The etching step etches an outer peripheral portion of each of the plurality of crystal piece portions, surrounds the mesa portion in each of the plurality of crystal piece portions, and is thinner than the mesa portion in a plan view. Including a mesa etching step for forming the outer peripheral portion,
In the doping step, the dopant is added to the region to be the mesa portion,
The method for manufacturing a crystal resonator element according to any one of claims 2 to 5, wherein in the mesa etching step, a side surface of the mesa portion is formed by a portion to which the dopant is added.

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