JP2016072860A - Manufacturing method of piezoelectric element, and piezoelectric device employing the piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a piezoelectric element which is adaptive to downsizing and reduction in height, suppresses distortion in a contour of the piezoelectric element and also improves production efficiency, and a piezoelectric device employing the piezoelectric element.SOLUTION: A manufacturing method of a crystal element includes: a crystal element group formation step of forming a pattern comprised of a metal film M in which a number of crystal element regions 24 in a rectangular shape in a planar view are aligned in a matrix shape on front and rear principal surfaces of a crystal wafer 200; a groove formation step of forming a groove G1 relatively to a boundary line BL1; an etching step of performing etching after the groove formation step to make a central part on a principal surface of each of the crystal element regions thin to predetermined thickness, simultaneously penetrating the groove G1 and making a region of a boundary line BL2 thin, thereby forming a bridge part; and a division step of folding away the bridge part, thereby the wafer into individual crystal elements.SELECTED DRAWING: Figure 13

Description

  The present invention relates to a method for manufacturing a piezoelectric element and a piezoelectric device using the piezoelectric element obtained by the manufacturing method.

  Piezoelectric devices such as crystal resonators and crystal filters are widely used in various fields such as mobile communication base stations. For example, a general surface-mount type crystal resonator includes a crystal element in which an excitation electrode or the like is added to the front and back main surfaces of an AT-cut crystal diaphragm, a container having a recess for housing the crystal element, The main component is a lid that hermetically seals the recess by joining with the container. The crystal element has a substantially rectangular shape in plan view, and both end portions on one short side thereof are cantilevered to an electrode pad provided in a recess of the container via a conductive adhesive or the like.

  Incidentally, in recent years, there has been a demand for higher oscillation frequencies of crystal resonators. For example, when the frequency band becomes 100 MHz or higher, the quartz-crystal diaphragm becomes extremely thin because the oscillation frequency of the AT-cut quartz-crystal diaphragm is inversely proportional to its thickness. For this reason, a structure is known in which the vibration part is thinned to increase the frequency and the mechanical strength is compensated by providing a thick part thicker than the thin part around the thin part (so-called, Reverse mesa structure).

  A large number of such quartz crystal diaphragms can be formed simultaneously from a single quartz wafer by using a photolithographic technique and wet etching (wet etching). Then, after forming excitation electrodes and the like on the quartz wafer, a large number of quartz elements can be obtained efficiently by dividing the wafer.

  Along with the downsizing of electronic devices on which crystal units are mounted, the size of crystal units is also being reduced. For example, the package has a rectangular shape in plan view, and the external dimension has shifted from 2.5 mm long by 2.0 mm wide to 1.6 mm long by 1.2 mm wide. When the external dimensions of the package are 2.5mm in length x 2.0mm in width, there is no problem in terms of the characteristics of the crystal unit even if the crystal plate has a structure in which the thick part surrounds the entire periphery of the thin part. I was able to respond. However, since the crystal diaphragm accommodated in the package becomes very small when the external dimension of the package is reduced to 1.6 mm in length × 1.2 mm or less in width, the region of the vibration part is narrow in the above structure. It becomes difficult to obtain good characteristics. In view of this, a configuration has been considered in which the area of the vibration part is increased by preventing the thick part from being formed on a part of the thick part that circulates outside the thin part. A quartz diaphragm having such a configuration is disclosed in Patent Document 1, for example.

Patent No. 4600692

  However, when a quartz diaphragm in which a part of the thick part is not formed as shown in Patent Document 1 is formed only by wet etching, the end face of the region where the thick part is not formed is distorted as the etching time increases. It may become. If the end face of the region where the thick part is not formed has a distorted shape, there is an increased risk of chipping from the end face and cracking when receiving an external impact such as dropping. In addition, even if the thick portion is formed over the entire circumference of the thin portion, when the outer shape of the crystal diaphragm is formed only by wet etching, the manufacturing process becomes complicated, and the crystal diaphragm There is a problem in that the side surface of the material is formed as an inclined surface instead of a vertical surface due to the anisotropy of quartz.

  In addition to wet etching, there is a dicing method for dividing the crystal wafer into each crystal element. However, in the case of dicing, there is a problem that the rate of occurrence of chipping of the crystal diaphragm is higher than that of wet etching.

  Further, in a method of obtaining a large number of crystal elements from one crystal wafer using dicing, it is difficult to form a side electrode for routing the electrode on one main surface side of the crystal diaphragm to the other main surface side. For this reason, when the crystal element divided into pieces is conductively bonded in the container using a conductive adhesive, an adhesive is applied so as to extend from the electrode pad of the container to the electrode on the upper surface side of the crystal diaphragm (overcoating). There is a need to. Applying the adhesive to the upper surface side of the quartz crystal diaphragm in this way hinders a reduction in the height of the quartz crystal unit.

  As a method for electrically connecting the electrode pad and the electrode on the upper surface side of the crystal element without forming the side electrode, there is the following method. For example, a “through hole” in which a through hole is formed in a quartz diaphragm and a conductor is attached to the inner wall surface of the through hole, or a “via” (Via Hole) in which a conductor is filled in the through hole is formed. There is a way. However, in these methods, it is necessary to drill through holes, form conductors, and the like, which complicates the manufacturing process. Furthermore, the smaller the quartz diaphragm, the higher the proportion of the area of the through-hole with respect to the area of the vibration region, and as a result it becomes impossible to secure a sufficient vibration region, making it difficult to obtain good crystal resonator characteristics. Come.

  The present invention has been made in view of the above points, and is a method for manufacturing a piezoelectric element that can be reduced in size and reduced in height, suppresses distortion of the outer shape of the piezoelectric element, and is excellent in production efficiency. An object of the present invention is to provide a piezoelectric device using the element.

  In order to achieve the above object, the invention according to claim 1 is a method of manufacturing a piezoelectric element that obtains a large number of piezoelectric elements from a single wafer, wherein the piezoelectric element has a rectangular shape in plan view on at least one main surface of the wafer. At least one boundary line among a piezoelectric element pattern forming step for forming a pattern made of a metal film in which a large number of element regions are arranged in a matrix and a vertical and horizontal boundary line extending along the long side and the short side of the piezoelectric element region A groove forming step for forming the groove by mechanical means, and etching is performed after the groove forming step, and the central portion or the outer peripheral portion of the main surface of each piezoelectric element region is thinned to a predetermined thickness and at the same time the groove is formed. Etching to form a bridge portion connected to the outer surface of the piezoelectric element by thinning a region of the boundary line where the groove is not formed among the vertical and horizontal boundary lines. A step, which is a method for manufacturing a piezoelectric element characterized by having a dividing step of dividing the piezoelectric element of individuals by taking folding the bridge portion.

  According to the above invention, even if the piezoelectric diaphragm has a structure in which a part of the thick part is not formed, it is possible to prevent the end face of the region where the thick part is not formed from being distorted. it can. This is because by forming grooves by the groove forming process and reducing the thickness of the wafer in advance, the thickness that is reduced by etching is reduced, and the time required for etching can be reduced. Further, by reducing the time required for etching, the influence of the anisotropy of the piezoelectric material can be suppressed, and the side surface of the piezoelectric diaphragm can be brought close to a vertical state in a sectional view.

  Moreover, according to the said invention, the manufacturing efficiency of the piezoelectric element by which the center part or outer peripheral part of the main surface was thinned can be improved significantly. This is because, in the etching step, the central portion or the outer peripheral portion of the main surface of the piezoelectric element region can be thinned to a predetermined thickness by etching, and at the same time, the groove can be penetrated.

  In the conventional method, since the amount (thickness) of thinning the central portion or outer peripheral portion of the main surface of the piezoelectric element region is different from the amount (thickness) penetrating the outer peripheral portion of the piezoelectric element region, etching is performed collectively. I could not. For this reason, it is necessary to apply the resist at least twice, which increases the number of manufacturing steps and is complicated.

  On the other hand, in the present invention, thinning of the central portion or outer peripheral portion of the main surface of the piezoelectric element region and penetration of the outer peripheral portion of the piezoelectric element region can be performed with only one resist application.

  In order to achieve the above object, the invention according to claim 2 is characterized in that the remaining thickness of the wafer in the region where the groove of the boundary line is formed is smaller than the thickness in which the piezoelectric element region is thinned in the etching step. This is a method for manufacturing a piezoelectric element.

  According to the above invention, the shaping of the outer shape of the piezoelectric element region and the thinning of the piezoelectric element region can be completed by only one etching. This is the outer peripheral portion of the piezoelectric element region when the thinning of the piezoelectric element region is completed because the remaining thickness of the wafer at the boundary line portion where the groove is formed is smaller than the thickness of the piezoelectric element region to be thinned. This is because the groove portion is surely penetrated. Thereby, the number of times of applying the resist can be reduced as in the conventional case, and the manufacturing efficiency of the piezoelectric element in which the central portion or the outer peripheral portion of the main surface is thinned can be greatly improved.

  In order to achieve the above object, the invention according to claim 3 is a method of manufacturing a piezoelectric element characterized in that the groove is discontinuous.

  According to the above invention, since the grooves are discontinuous, the frame portion can be left in the vicinity of the outer peripheral edge of the wafer in the state after the completion of the etching process, and between the large number of piezoelectric element regions inside the outer peripheral edge of the wafer Can be secured. Thereby, since the area | region which hold | maintains many piezoelectric element area | regions continued in matrix form increases, the fall of the rigidity of a wafer can be suppressed. As a result, the wafer can be easily handled in the manufacturing process of the piezoelectric element.

  In order to achieve the above object, according to a fourth aspect of the present invention, the groove forming means lowers the rotated dicing blade from above the wafer to cut a part of the wafer, and from that state, the horizontal direction Either or both of dicing for raising the blade upward without moving it to the upper side, or dicing the dicing blade horizontally after moving the dicing blade down from the upper side of the wafer and cutting by a predetermined distance It is the manufacturing method of the piezoelectric element characterized by these.

  According to the above invention, discontinuous grooves can be efficiently formed. This is because the rotating dicing blade is lowered vertically from above the wafer to cut a part of the wafer, and the dicing blade is lifted upward without moving horizontally from that state (in the present invention). "Chopper cut dicing") or dicing blades that have been rotated in a vertical direction after the rotated dicing blade is lowered vertically from above the wafer to cut a distance longer than the chopper cut dicing (this invention) Is called “chopper traverse cut dicing”). In other words, the chopper cut dicing and the chopper traverse cut dicing are not a process of continuously cutting the wafer from one outer peripheral end to the other outer peripheral end in a straight line, but an area spaced inward from the outer peripheral end of the wafer. The inside is cut linearly and discontinuously. By such a cutting method, a minute crystal element can be integrally handled in a wafer state without being separated in the manufacturing process.

  By using both or one of the above-mentioned chopper cut dicing and chopper traverse cut dicing, the frame portion can be left near the outer periphery of the wafer. This is because a frame portion can be left in the vicinity of the outer peripheral edge of the wafer by setting a region spaced inward from the end portion of one wafer on which a large number of minute piezoelectric element regions are formed as a start point and an end point. Further, by using chopper cut dicing or chopper traverse cut dicing, it is possible to leave an abandoned area between a large number of piezoelectric element areas on the inner side from the outer peripheral edge of the wafer. Thereby, since the area | region which hold | maintains many piezoelectric element area | regions continued in matrix form increases, the rigidity of a wafer can be improved. As a result, the wafer can be easily handled in the manufacturing process of the piezoelectric element.

  By using a dicing blade, damage to the main surface of the wafer can be reduced as compared to forming a groove by dry processing such as laser beam or dry etching. In addition, since the processing with a dicing blade can be thermally suppressed to a lower temperature rise during processing than the processing with a laser beam or dry etching, the influence of heat on the wafer can be reduced.

  In the case of wet processing such as wet etching, the influence of the heat can be reduced, but the processing speed is slower than processing with a dicing blade. In the case of wet etching, especially in a wafer made of quartz, a difference in dissolution rate occurs depending on the crystal axis of the quartz. Therefore, when the etching amount (etching time) increases, a distorted cross-sectional shape tends to be formed. On the other hand, these disadvantages can be compensated for by processing with a dicing blade.

  In order to achieve the above object, the invention according to claim 5 is a container in which the piezoelectric element obtained by the method for manufacturing a piezoelectric element according to any one of claims 1 to 4 is accommodated in a container. The piezoelectric element is hermetically sealed by bonding a lid to the piezoelectric device.

  According to the above invention, since the piezoelectric device uses a piezoelectric element in which the end face of the thin portion does not have a distorted shape, it is possible to suppress the occurrence of chipping from the end face when subjected to an external impact such as dropping. it can. In addition, a piezoelectric device having good characteristics can be obtained because a vibration region of a piezoelectric element having an inverted mesa structure in which a part of the thick wall portion is not formed can be secured in a particularly small and high frequency band piezoelectric device. it can.

  As described above, according to the present invention, a method of manufacturing a piezoelectric element that can be reduced in size and height, suppress distortion of the outer shape of the piezoelectric element, and is excellent in production efficiency, and a piezoelectric element using the piezoelectric element. A device can be provided.

Schematic top view of a crystal resonator according to the present invention The upper surface schematic diagram showing the manufacturing method of the crystal element concerning the present invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. The upper surface schematic diagram showing the manufacturing method of the crystal element concerning the present invention. Part B enlarged view of FIG. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. The perspective view showing the manufacturing method of the crystal element based on this invention The elements on larger scale showing the manufacturing method of the crystal element based on this invention Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. The elements on larger scale showing the manufacturing method of the crystal element based on this invention Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. Schematic top view of the crystal element according to the present invention before the dividing step Schematic top view after the crystal element splitting process according to the present invention. The figure showing the relationship between the depth ratio of the groove | channel in the groove | channel formation process which concerns on this invention, and a crystal element end surface The upper surface schematic diagram of the crystal element before the division | segmentation process which concerns on the other Example of this invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention. Cross-sectional schematic diagram showing a method for manufacturing a crystal element according to the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, taking a crystal resonator as an example of a piezoelectric device. In this embodiment, the crystal unit 1 is a surface-mount type crystal unit having a substantially rectangular parallelepiped package structure.

  FIG. 1 is a schematic top view of a crystal resonator according to an embodiment of the present invention. Note that FIG. 1 shows a state in which a lid described later is removed. The crystal resonator 1 is mainly composed of a container 3 having a recess 6, a crystal element 2, and a flat lid (not shown) that seals the recess 6. The crystal element 2 is hermetically sealed in a space formed by joining the lid and the container 3 together. In this embodiment, the container 3 and the lid are joined by a fusion method in which an alloy such as a gold-tin alloy (AuSn) is melted in a heated atmosphere. In addition, the joining of the container 3 and the lid can be applied not only by the fusion method but also by other joining methods. For example, a method in which a glass resin is melted in a heated atmosphere to join the lid and the container, or a seam welding method can be applied.

  In FIG. 1, a container 3 is a box-shaped body made of an insulating material mainly composed of ceramic such as alumina, and is formed by laminating ceramic green sheets and integrally firing them. The container 3 has a concave portion 6 having a rectangular shape in a plan view inside the frame-shaped bank portion 30, and a pair of crystal element mounting pads (electrodes) 4, 4 are provided on one end side of the inner bottom surface 300 of the concave portion 6. They are formed in parallel. The pair of quartz element mounting pads 4 and 4 are formed by, for example, laminating a metal layer on the upper surface of the tungsten metallized layer by a technique such as plating in the order of nickel and gold. The pair of quartz element mounting pads 4, 4 are connected to a plurality of external connection terminals (not shown) provided on the outer bottom surface of the container 3 via internal wiring (not shown) formed inside the container 3. It is electrically connected to some parts.

  In FIG. 1, a bonding material (not shown) is formed on the upper surface of the bank portion 30 in an annular shape in plan view. In this embodiment, the bonding material is composed of three layers, and has a structure of a tungsten metallized layer, a nickel plating layer, and a gold plating layer in order from the bottom. This bonding material corresponds to the outer peripheral portion of the flat lid. Note that molybdenum may be used instead of tungsten.

  The above-described lid is a flat plate made of metal having a rectangular shape in plan view with Kovar as a base. Nickel plating layers are formed on the front and back surfaces of the lid. In addition, a gold-tin alloy (AuSn) as a sealing material is formed in a circumferential shape on the nickel plating layer at the peripheral edge portion of the lid on the joint surface side. The lid and the container are fused by being heated while being positioned so that the sealing material of the lid and the bonding material on the upper surface of the bank of the container are in contact with each other.

  The crystal element 2 is a piezoelectric element in which various electrodes are added to the front and back main surfaces of an AT-cut crystal diaphragm having a rectangular shape in plan view. The quartz diaphragm is formed with a thin portion 20 which is a vibrating portion and whose central portion is processed to be thinner than the surroundings, and a thick portion 21 which is thicker than the thin portion outside the thin portion 20 ( So-called reverse mesa shape). Between the thick part 21 and the thin part 20, an inclined surface 22 that gradually becomes thinner toward the thin part 20 is formed. In the present embodiment, the X axis is set in the long side direction of the crystal diaphragm, and the Z axis is set in the short side direction of the crystal diaphragm.

  In the present embodiment, the thick portion 21 is formed so as to surround the thin portion 20, but the region including the central portion of one long side of the crystal diaphragm is in a discontinuous state. That is, the thick-walled portion 21 is formed in a letter “C” shape in a plan view. By forming the thick portion in such a shape, it is possible to secure a larger area of the thin portion compared to a configuration in which the thick portion surrounds the entire circumference of the thin portion. As a result, a wider vibration region can be secured, so that the equivalent resistance value of the crystal resonator can be reduced.

  The external shape of the quartz diaphragm is formed by using wet etching (wet etching) and photolithography technology. The inclined surface 22 is a crystal surface that appears when the AT-cut quartz crystal plate is wet etched.

  As shown in FIG. 1, a pair of excitation electrodes 7 a and 7 b having a rectangular shape in plan view are formed opposite to each other across the thin portion 20 at the approximate center of the front and back main surfaces of the thin portion 20 of the crystal diaphragm. From the region including the corner of the excitation electrode 7a provided on one main surface of the thin portion 20, the extraction electrode 8a is drawn obliquely toward one corner on the short side 2a of the quartz diaphragm. Yes. The terminal end of the extraction electrode 8a is an adhesive electrode 9a.

  Similarly, from the region including the corner of the excitation electrode 7b provided on the other main surface of the thin-walled portion 20, the extraction electrode 8b is obliquely directed toward the other corner of the short side 2a of the crystal diaphragm. Has been pulled out. The termination of the extraction electrode 8b is an adhesive electrode 9b.

  The extraction electrodes 8a and 8b and the bonding electrodes 9a and 9b are in pairs, and have a positional relationship that does not overlap in plan view. The adhesive electrode 9a is formed so as to extend over the entire thickness direction of the crystal diaphragm in a region near the short side 2a of the side surface L1 on the long side of the crystal diaphragm. Similarly, the adhesive electrode 9b is formed so as to cover the entire thickness direction of the crystal diaphragm in a region near the short side 2a of the side surface L2 on the long side of the crystal diaphragm. The adhesive electrode 9a is formed so as to extend to the vicinity of the ridge on the upper side of the side surface W1 on the short side of the crystal diaphragm. That is, the adhesive electrode 9a is formed so as to extend to the upper surface of the quartz diaphragm, the long side surface L1, and the vicinity of the ridge on the upper side of the short side surface W1. This is because the electrode material is also sputtered inside the slit portion described later. Similarly, the adhesive electrode 9b is formed so as to extend to the lower surface of the quartz diaphragm, the long side surface L2, and the vicinity of the lower edge of the short side surface W1.

  In the present embodiment, the pair of extraction electrodes 8a and 8b are not formed with the same width, but are formed so as to gradually increase from the corner of the excitation electrode 7a or 7b toward the adhesive electrode 9a or 9b. With such a shape, occurrence of spurious (unnecessary vibration) can be suppressed. Note that it is desirable that unnecessary vibrations are not generated as much as possible due to the characteristics of the crystal unit.

  In the present embodiment, the excitation electrodes 7a and 7b, the extraction electrodes 8a and 8b, and the adhesion electrodes 9a and 9b have a configuration in which chromium (Cr) is used as a base and gold (Au) is stacked on the upper layer. The film is formed by sputtering. Note that the excitation electrode, the extraction electrode, and the adhesive electrode are patterned using a photolithography technique and an etching technique. By using a photolithographic technique, these electrodes can be formed with high accuracy even if the external size of the quartz crystal diaphragm is small.

  Adhesive electrodes 9 a and 9 b provided on one end side in the long side direction of the crystal element 2 are conductively bonded onto the crystal element mounting pads 4 and 4 via conductive adhesives 5 and 5. Specifically, the conductive adhesive 5 is applied in advance to the quartz element mounting pad 4 (undercoating), and the short side 2a of the crystal diaphragm is positioned on the conductive adhesive. The element 2 is positioned and mounted. In the present embodiment, the adhesive is not overcoated (overcoated) on the undercoat adhesive so as to reach the adhesive electrode on the upper surface side of the crystal diaphragm. This is because the adhesive electrode is formed so as to extend over each of the long side surface and the short side surface of the quartz diaphragm, and the undercoat adhesive is applied to the electrodes on these side portions, so This is because conduction can be secured. As a result, it is not necessary to apply the conductive adhesive to the upper surface side of the quartz diaphragm, and the quartz resonator can be reduced in height.

  In this embodiment, a silicone-based conductive resin adhesive is used as the conductive adhesive 5. It is also possible to use a conductive adhesive other than silicone. Further, the bonding means between the crystal element and the crystal element mounting pad is not limited to the conductive adhesive, but may be other bonding means. For example, using a conductive bump, the crystal element and the crystal element mounting pad may be conductively bonded by a thermocompression FCB method (Flip Chip Bonding) to which ultrasonic waves are applied.

Next, main steps of the manufacturing method of the crystal element according to the present invention will be described with reference to FIGS.
-Piezoelectric element pattern formation process-
The piezoelectric element pattern forming process will be described with reference to FIGS. First, as shown in FIG. 2, a metal film M is formed by sputtering on the entire surface of one main surface 201 and the other main surface 202 of a quartz crystal wafer 200 (hereinafter abbreviated as a wafer) made of AT cut (metal film formation). Process). The wafer 200 has a rectangular shape in plan view, and is 56 mm long and 54 mm wide. The wafer thickness is 0.08 mm. In the present embodiment, the X axis is set in the longitudinal direction of the wafer, and the Z axis is set in the short direction of the wafer. The shape of the wafer is not limited to a plate shape but may be a disk shape.

  FIG. 3 shows a part of a sectional view taken along line AA in FIG. The metal film M has a structure in which gold is laminated on a chromium base. Here, since the thickness of the chromium layer is extremely thin compared to the thickness of the gold layer, the description of the chromium layer is omitted in all the cross-sectional views used in the description of the embodiment of the present invention.

  Next, as shown in FIG. 4, a resist R is formed on the metal film M formed on the entire front and back main surfaces of the wafer 200. In the present embodiment, a positive resist is used as the resist R.

  Then, as shown in FIG. 5, ultraviolet rays UV are irradiated through a photomask PM having an opening pattern E formed in a predetermined shape, and the opening pattern of the photomask is transferred to a resist (exposure process). FIG. 5 shows a state in which exposure on one side (one main surface 201) of the wafer 200 is performed. Next, by developing, the resist in the exposed region is removed as shown in FIG. 6, and the metal film M under the region is exposed (developing step). In the schematic cross-sectional views in FIG. 5 and subsequent figures, this is indicated as “one section” in the drawing in order to clearly indicate the region of one unit of the crystal element.

  Next, the metal film M in a region not covered with the resist R is removed by immersing the wafer in an etching solution (metal etching solution) that is corrosive to gold (metal etching step). As shown in FIG. 7, the metal etching process removes the gold in the region not covered with the resist and exposes the quartz substrate. In this embodiment, a nitric acid-based etching solution is used, but other types of etching solutions may be used.

  Next, the remaining resist R is peeled off to form a pattern in which a large number of metal films M formed in an alphabet “C” shape in a plan view are arranged in a matrix. In the present embodiment, when the four corners on the outer periphery of the “C” -shaped metal film M are connected by a straight line, it is rectangular in a plan view, and the rectangular region is a crystal element region. In the present embodiment, the outer dimensions of the unit piezoelectric element region in plan view have a long side of 0.86 mm and a short side of 0.64 mm.

  A piezoelectric element region (hereinafter referred to as a crystal element region 24) having a rectangular shape in a plan view formed in the piezoelectric element pattern forming step is provided with a region serving as a boundary line between adjacent crystal element regions (see FIG. 9). The boundary line is formed in the wafer so as to extend vertically and horizontally along the long side and the short side of the crystal element region 24 (see the dotted line frame in FIG. 9). Specifically, as shown in FIG. 9, the boundary line extending along the long side of the crystal element region 24 is BL1, and the boundary line extending along the short side of the crystal element region 24 is BL2. . The boundary line BL1 has a line width (0.06 mm) indicated by BL1W, and the boundary line BL2 has a line width (0.04 mm) indicated by BL2W. In the present embodiment, the line width of the boundary line BL2 extending along the short side is smaller than the line width of the boundary line BL1 extending along the long side. The vertical and horizontal boundary lines may have the same line width, or the boundary line BL2 may have a larger line width than the boundary line BL1.

-Groove formation process-
Next, the groove forming step will be described with reference to FIGS. In addition, the cross-sectional schematic diagram after FIG. 10 represents the cross-sectional view in CC line of FIG. Of the vertical and horizontal boundary lines BL1 and BL2, a groove having a predetermined depth is formed by mechanical means on the boundary line BL1 extending along the long side of the crystal element region as shown in FIGS. (Groove forming step). In this embodiment, the grooves are formed only on one side (one main surface 201) of the wafer 200, but may be formed on both sides (201, 202) of the wafer 200.

  In this embodiment, a dicing blade is used as the groove forming means. The dicing blade D has a disk shape in which abrasive grains are fixed on the surface of the blade with a resin. In this embodiment, the dicing blade D has a blade thickness of 0.05 mm and a diameter of 51.5 mm. In this embodiment, a dicing blade having a diameter of 50 mm to 60 mm can be used. It has become. The rotated dicing blade D (hereinafter abbreviated as “blade”) is intermittently run vertically only along the boundary line BL1 of the vertical and horizontal boundary lines BL1 and BL2.

  Specifically, as shown in FIG. 11, a groove is formed from the boundary line BL1 that is the end in the short direction of the wafer among the plurality of boundary lines BL1 formed on one main surface 201 of the wafer 200.

  The blade D is lowered onto the wafer aiming at the approximate center of the line width of the boundary line BL1. At this time, the first descending position of the blade D is not the outer peripheral edge of the wafer 200 but the end of the crystal element region closest to the outer peripheral edge. Here, the blade D is controlled so as to enter the wafer by a predetermined depth. Then, while maintaining a predetermined depth (about 0.03 mm in this embodiment), scribing is performed for a preset distance along the extending direction of the boundary line BL1 (so-called chopper traverse cut).

  Thereafter, the blade D rises and is moved in the air by a predetermined distance along the extending direction of the boundary line BL1. Thereafter, a series of these operations are repeated, and if the vicinity of the end on the same boundary line is reached, the similar groove formation is performed on the next adjacent boundary line BL1. Thereafter, the discontinuous grooves are sequentially formed so as to be parallel to each other in the direction of the arrow F shown in FIG. In FIG. 11, for convenience of explanation, the crystal element region is displayed larger than the actual size. The above-described groove formation by the blade may be performed by fixing the blade and relatively moving the wafer. Further, depending on the size of the dicing blade, the size of the crystal element region, etc., either one or both of the chopper traverse cut and the chopper cut may be used in combination.

  FIG. 12 shows a partially enlarged view of the wafer in which the grooves are formed by the groove forming process. The groove G1 is formed in a discontinuous state with respect to a boundary line BL1 extending along the long side of the crystal element region. In FIG. 12, the groove G1 includes a region where no groove is formed in the vicinity of the center in the vertical direction in the drawing among the plurality of boundary lines BL1. In the present embodiment, from the relationship between the diameter of the blade D and the external dimensions of the wafer 200 and the depth of the groove, the distance scribed along the boundary line BL1 is about 10 crystal element regions. Thus, by intermittently forming a region where no groove is formed on the boundary line BL1, it is possible to secure a region (abandoned region) where the wafer does not penetrate in a state after an etching process described later. Thereby, a decrease in the rigidity of the wafer can be suppressed, and the wafer can be easily handled in the process of manufacturing the crystal element. As described above, since the groove G1 is discontinuous, a frame portion can be left near the outer periphery of the wafer in the state after the completion of the etching process, and a large number of crystal element regions on the inner side from the outer periphery of the wafer can be left. A crosspiece (abandonment area) can be secured between them.

  FIG. 13 is a schematic cross-sectional view of the wafer 200 after the groove forming step. The depth d1 of the groove G1 formed in the groove forming step is about 0.03 mm. In this embodiment, the thickness of the wafer 200 is 0.08 mm, and the ratio of the depth of the groove d1 to the total thickness of the wafer is 37.5%. Since the inner wall surface of the groove G1 is a crushing surface by a dicing blade, minute irregularities are formed on the surface. Since the blade D has a disk shape, the curvature of the blade is transferred to the wafer near the start point and the end point of the scribe. As a result, there are regions where the depth of the groove gradually decreases in the vicinity of the outer peripheral edge of the wafer or in the region where the groove of the boundary line BL1 is not formed. On the other hand, the groove in the region corresponding to the long side of the crystal element region in the boundary line BL1 has a substantially constant depth.

-Etching process-
Next, the etching process will be described with reference to FIGS. The etching step is a step of chemically etching (wet etching) by immersing a wafer in which a groove is formed along the long side of the crystal element region in an etching solution that is corrosive to the crystal. In this embodiment, an ammonium fluoride solution is used as the etching solution.

  When the wafer 200 is immersed in the etching solution, the region not covered with the metal film M is dissolved as shown in FIG. 14 (reference symbol TH in the figure). Since the metal film M functions as a mask having resistance to the etching solution, the crystal under the region covered with the metal film M remains without being dissolved by the etching solution.

  In the etching process, the central portion of the crystal main surface of the crystal element region and the crystal region extending from the central portion to one long edge are thinned to a predetermined thickness. At this time, since quartz is an anisotropic material, the rate of dissolution during etching differs depending on the axial direction, and an inclined surface 22 appears as shown in FIGS.

  In the etching process, the crystal portion (d2) remaining under the groove G1 at this time is also melted and penetrates to the other main surface 202. Thereby, the penetration part TH is formed. The penetrating portion TH penetrates at least the full length of the long side of the crystal element region 24, and a part of the inner wall surface of the penetrating portion TH is a region corresponding to the side surface of the long side of the crystal element region. . As shown in FIG. 15, the inner wall surface of the penetrating part TH is in a state of being nearly perpendicular to the one main surface 201 and the other main surface 202 of the wafer 200. In addition, the inner wall surface of the groove formed in the groove forming step is in a state in which minute unevenness formed by dicing is smoothed by wet etching. Thereby, generation | occurrence | production of the chipping etc. in the edge part of the long side of a crystal element can be suppressed. As a result, the impact resistance performance of the crystal resonator can be improved.

  As described above, the inner wall surface of the through-hole TH is in a state of being almost perpendicular to the main surface of the wafer 200. Therefore, the side surface of the long side of the crystal element obtained by the division process described later is machined. A “quasi-smooth region” in which minute irregularities in the generated groove are smoothed by etching and a “smooth region” drilled only by dissolution by etching are continuous side surfaces. That is, in this embodiment, since the groove is formed only on the one principal surface 201 side, the side surface of the long side of the separated crystal element is a quasi-smooth region near the ridge portion near the one principal surface 201 of the crystal. A smooth region is formed on the other main surface 202 side continuously to the semi-smooth region.

  For example, when the lead electrode for electrical connection between the front and back surfaces of the excitation electrode of the quartz crystal element is formed on the side surface of the long side due to such a surface state side surface, the region including a ridge portion that is easily disconnected is a quasi-smooth surface Therefore, the adhesion strength of the electrode film can be increased by the anchor effect. Further, since the region other than the ridge portion is a smooth surface, it is possible to suppress occurrence of chipping in the crystal element when receiving an external impact.

  In the present embodiment, the remaining thickness (d2) of the wafer in the region where the groove of the boundary line BL1 is formed is smaller than the total thickness (d3 × 2) in which the crystal element region is thinned in the etching process.

  Thereby, the shaping of the outer shape of the crystal element region and the thinning of the crystal element region can be completed by only one etching. This is because the remaining thickness d2 of the wafer in the boundary line portion BL1 in which the groove G1 is formed is smaller than the thickness d3 of the crystal element region to be thinned. It is because the groove part which is an outer peripheral part is penetrated reliably. As a result, the number of times of resist application can be reduced as in the prior art, and the manufacturing efficiency of the crystal element in which the central portion or the outer peripheral portion of the main surface is thinned can be greatly improved.

  Further, in the etching process, the region of the boundary line BL2 where no groove is formed in the vertical and horizontal boundary lines BL1 and BL2, as shown in FIG. 16, that is, the region outside the two short sides facing each other of the crystal element region is thinned. Will be. These thinned areas are minute gaps visually, and are shown as slits SL1 and SL2 in FIG. The thickness of the crystal in the slits SL1 and SL2 is substantially the same as that of the thin portion 20.

  Sites connected to adjacent crystal elements in the areas of the slits SL1 and SL2 are bridge portions BG1 and BG2, respectively. In FIG. 16, a plurality of crystal element regions 24 are connected in the longitudinal direction by bridge portions BG1 and BG2 in the longitudinal direction of the wafer. In addition, the plurality of crystal element regions 24 are connected in the lateral direction in the short direction of the wafer by a region where the through portion TH is not formed (abandoned portion U) via the bridge portions BG1 and BG2. Since the rigidity of the wafer can be supplemented by the presence of the surplus portion U, the wafer can be hardly bent in the etching process.

  As described above, after the outer shape of the crystal element is formed by the etching process, the metal film M is peeled off with a metal etching solution. This results in a wafer with only the quartz substrate exposed.

―Electrode formation process―
The electrode forming step is a step of forming electrodes having a predetermined shape in each crystal element region in the wafer (not shown). The electrodes include the aforementioned excitation electrodes (23a, 23b), extraction electrodes (8a, 8b), and adhesive electrodes (9a, 9b). In this embodiment, these electrodes are formed by sputtering. At this time, the electrode material also penetrates into the slit portions (SL1, SL2) and is sputtered. The adhesive electrodes (9a, 9b) are formed so as to cover the entire region near the one short side of the two long sides facing each other of the quartz crystal diaphragm. That is, the adhesive electrode at one short side end portion on one main surface side is formed to extend to the long side surface near the end portion. Similarly, the adhesive electrode at one short side end portion on the other main surface side is formed to extend to the long side surface near the end portion.

―Division process―
In the dividing step, mechanical stress is applied to one of the bridge portions BG1 and BG2 in the wafer to separate the portion. Then, the crystal element regions connected by the remaining bridge portions are divided into individual crystal elements by bringing the suction nozzle into contact with suction (division process). Breaking marks 25 are formed on the side surfaces of the two opposing short sides of the divided crystal element. Since this breakage mark is a broken surface, the bonding strength between the crystal element and the conductive adhesive can be improved by the anchor effect.
The above is the description of the main steps of the method for manufacturing a crystal resonator according to the present invention.

  In this embodiment, the depth of the groove (G1) formed in the groove forming step is 0.03 mm, which is 37.5% of the thickness of the wafer 200 of 0.08 mm. The depth of this groove will be described with reference to FIG.

  FIG. 18 shows the relationship between the depth of the groove formed in the groove forming step and the width of the unevenness of the end face of the side where the thick portion is not formed in the C-shaped crystal element in plan view where a part of the thick portion is not formed. It is a graph showing. Here, the unevenness on the end face of the side where the thick part is not formed means the maximum value of the distance between the protruding part on the outer side in the short side direction and the entering part on the inner side in the short side direction in the plan view of the end face of the long side pointing.

  In FIG. 18, samples having groove depths of 0.03 mm, 0.05 mm, and 0.07 mm formed along the long side of the crystal element are prepared, and various electrodes are formed by wet etching. A piece is used. The oscillation frequency of the crystal element is 550 MHz, and the initial thickness of the wafer is 0.08 mm. The horizontal axis in FIG. 18 represents the ratio of the groove depth to the initial wafer thickness. That is, the depth ratio is 37.5% (0.03 mm), 62.5% (0.05 mm), and 87.5% (0.07 mm).

  According to FIG. 18, it can be seen that the uneven width of the end face of the long side increases with the increase in the groove depth ratio. That is, the concave-convex width of the long side end face can be reduced as the depth ratio is reduced. However, if the depth ratio is smaller than 37.5%, the thickness to be dissolved by wet etching increases, so the side surface of the long side starts to taper and finally the side surface of the long side that is nearly perpendicular to the main surface Getting difficult. Further, an etching process that requires more time than dicing requires more time, which causes a deterioration in productivity.

  Conversely, when the depth ratio becomes larger than 87.5%, the time required for the etching process can be reduced, but the processing depth by dicing increases, so that the uneven width of the long side end face increases. . Further, since the groove becomes deep, the mechanical strength of the wafer is lowered and cracks are likely to occur.

  From the above, considering that there is no practical problem if the long side end face uneven width is smaller than 0.01 mm, the depth of the groove is set so that the depth ratio is in the range of 37.5% to 62.5%. It is preferable to set the length. The depth of the groove is set in accordance with the thickness of the quartz element made of AT cut (in other words, the oscillation frequency).

  According to the present invention, it is possible to prevent the end face of the region where the thick part is not formed from having a distorted shape even in the case of the crystal diaphragm having a structure in which a part of the thick part is not formed. it can. This is because by forming grooves by the groove forming process and reducing the thickness of the wafer in advance, the thickness that is reduced by etching is reduced, and the time required for etching can be reduced. Further, by reducing the time required for etching, it is possible to suppress the influence of crystal anisotropy and bring the side surface of the crystal element closer to a vertical state in cross-sectional view.

  In addition, according to the present invention, it is possible to greatly improve the manufacturing efficiency of a quartz crystal element in which the central portion or outer peripheral portion of the main surface is thinned. This is because, in the etching process, the central portion or the outer peripheral portion of the main surface of the crystal element region can be thinned to a predetermined thickness by etching, and at the same time, the groove can be penetrated.

  When a wafer made of AT-cut quartz is wet-etched, the dissolution rate varies depending on the direction of the crystal axis, so that the cross-sectional shape becomes distorted as the etching time increases. This is due to the fact that the inclined surface in the Z-axis direction of the crystal diaphragm becomes more obvious. That is, in the case of an AT-cut quartz crystal plate in which the X axis is set on the long side and the Z axis is set on the short side, the inclined surface in the short side direction is inclined with respect to the main surface rather than the inclined surface in the long side direction. Therefore, the side surface of the long side does not become a vertical surface but becomes an inclined surface.

  On the other hand, according to the method for manufacturing a crystal element according to the present invention, the side surface of the long side of the crystal element is viewed in cross section, even if the crystal plate has the X axis on the long side and the Z axis on the short side. You can get close to vertical. In addition, in the crystal diaphragm having a rectangular shape in plan view, the Z axis may be set on the long side and the X axis may be set on the short side. In this case, the formation of the inclined surface in the Z-axis direction is suppressed by setting the boundary line to be grooved to be a boundary line (corresponding to BL2 in this embodiment) extending along the short side of the crystal element region. be able to.

  As a modification of the embodiment of the present invention, grooves may be formed on the three outer sides of the crystal element region having a rectangular shape in plan view. That is, in addition to the boundary line BL1 extending along two long sides of the crystal element region 24, a groove may be formed on the boundary line BL2 extending along one short side of the crystal element region 24.

  By penetrating these grooves in the etching process, as shown in FIG. 19, a through portion TH2 penetrating so as to cover three sides of the four sides of the outer periphery of the quartz crystal element region in a plan view is formed. As a result, the crystal element region is connected to another adjacent crystal element only via the bridge portion BG3. In this way, since the bridge portion is only one place of BG3, the crystal element can be divided more easily in the dividing step.

  The present invention can also be applied to a “mesa shape” in which the outer peripheral portion of the quartz diaphragm is formed thinner than the central portion. A part of the manufacturing process in the case of a mesa-shaped quartz diaphragm is shown in FIGS. 20 to 22, the same components as those in the embodiment of the present invention described above are denoted by the same reference numerals and description thereof is omitted.

  FIG. 20 is a schematic cross-sectional view of the wafer 400 in a state where development is completed and the resist is peeled off in the piezoelectric element pattern forming step. In FIG. 20, a metal film M2 is formed on the inner side by the distance TA in the main surface direction of the thinned region from the end of the boundary line BL1 extending along the long side of the crystal element region. Note that the width of the boundary line BL1 is the same as that of the above-described embodiment of the present invention.

  Next, the dicing blade is lowered with respect to the wafer aiming at the approximate center of the line width of the boundary line BL1. In the groove forming step, a chopper traverse cut is used as in the above-described embodiment of the present invention. The state after the groove forming step is shown in FIG. In FIG. 21, the depth of the groove G2 is represented by d4, and the remaining thickness of the wafer in the region where the groove G2 is formed is represented by d5.

  Next, in the etching process, the outer peripheral portion of the main surface of the crystal element region is thinned and simultaneously the groove G2 is penetrated. Thereby, a “mesa-type” crystal diaphragm having a cross-sectional shape as shown in FIG. 22 can be obtained. The remaining thickness d5 of the wafer is smaller than the total thickness (d6 × 2) at which the crystal element region is thinned in the etching process.

  In the embodiment of the present invention, the grooves are formed only on one main surface of the crystal wafer, but the grooves may be formed on both main surfaces of the one main surface and the other main surface of the crystal wafer. In this case, the groove formation depth is preferably set so that the total depth of the grooves on the front and back main surfaces of the quartz wafer falls within the range of 37.5% to 62.5% with respect to the thickness of the quartz wafer. .

  In the embodiment of the present invention, a surface-mounted crystal resonator is taken as an example, but the present invention can be applied to other piezoelectric devices such as a crystal filter and a crystal oscillator in addition to the crystal resonator.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  It can be applied to mass production of piezoelectric vibration elements and piezoelectric devices.

DESCRIPTION OF SYMBOLS 1 Crystal resonator 2 Crystal element 24 Crystal element area | region 3 Container BL1, BL2 Boundary line G1, G2 Groove BG1, BG2, BG3 Bridge part TH, TH2 Through part

Claims (5)

A method of manufacturing a piezoelectric element that obtains a large number of piezoelectric elements from a single wafer,
A piezoelectric element pattern forming step of forming a pattern of a metal film in which a plurality of rectangular piezoelectric element regions in a plan view are arranged in a matrix on at least one main surface of the wafer;
A groove forming step of forming a groove by mechanical means for at least one of the vertical and horizontal boundary lines extending along the long side and the short side of the piezoelectric element region;
Etching is performed after the groove forming step, and the central portion or outer peripheral portion of the main surface of each piezoelectric element region is thinned to a predetermined thickness. At the same time, the groove is penetrated, and the groove is formed among the vertical and horizontal boundary lines. An etching process for forming a bridge portion connected to the outer surface of the piezoelectric element by thinning the area of the boundary line that is not,
A dividing step of dividing the bridge portion into individual piezoelectric elements by breaking the bridge portion;
A method for manufacturing a piezoelectric element, comprising:   2. The method of manufacturing a piezoelectric element according to claim 1, wherein a remaining thickness of the wafer in a region where the groove of the boundary line is formed is smaller than a thickness in which the piezoelectric element region is thinned in the etching step.   The method for manufacturing a piezoelectric element according to claim 1, wherein the groove is discontinuous.   The groove forming means lowers the rotated dicing blade from above the wafer to cut a part of the wafer, and then lifts the blade upward without moving horizontally from that state, or rotated dicing. 4. The dicing method according to claim 1, wherein the dicing blade is moved at a predetermined distance by moving the dicing blade in a horizontal direction after the blade is lowered from above the wafer. 5. The manufacturing method of the piezoelectric element as described in 2.   The piezoelectric element obtained by the method for manufacturing a piezoelectric element according to any one of claims 1 to 4 is housed in a container and the piezoelectric element is hermetically sealed by joining a lid to the container. A piezoelectric device characterized by the above.

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