JP6142023B2 - Elastic wave device, electronic component, and method of manufacturing elastic wave device - Google Patents

Description

The present invention relates to a surface acoustic wave (SAW) device or a piezoelectric thin film resonator (F).
The present invention relates to an elastic wave device such as a BAR (Film Bulk Acoustic Resonator), an electronic component using the elastic wave device, and a method of manufacturing the elastic wave device.

A so-called wafer level package (WLP: Wafer Level Package) type acoustic wave device for the purpose of downsizing is known. This WLP type acoustic wave device has a piezoelectric substrate, an excitation electrode provided on the piezoelectric substrate, and a cover for sealing the excitation electrode (see, for example, Patent Document 1).

  The cover has a recess, and the cover is arranged on the main surface of the piezoelectric substrate so that the excitation electrode is positioned in a vibration space that is a space surrounded by the inner wall of the recess and the main surface of the piezoelectric substrate.

JP 2008-227748 A

  Incidentally, in the acoustic wave device having the above-described structure, the cover may be peeled off from the piezoelectric substrate due to a difference in linear expansion coefficient between the cover and the piezoelectric substrate. When the cover is peeled off from the piezoelectric substrate in this way, the airtightness of the vibration space is not maintained, and external moisture and the like easily enter the vibration space. If external moisture enters the vibration space, it causes corrosion of the excitation electrode. When the excitation electrode corrodes, the electrical characteristics of the acoustic wave device deteriorate.

  When the electrical characteristics of the acoustic wave device are degraded, the electrical characteristics of the electronic component on which the acoustic wave device is mounted are also degraded.

  Therefore, it is desired to provide an elastic wave device that maintains the hermeticity of the vibration space over a long period of time.

  An elastic wave device as one embodiment of the present invention includes an element substrate, an excitation electrode disposed on a main surface of the element substrate, a recess, and is surrounded by an inner surface of the recess and the main surface of the element substrate. A cover in which the periphery of the concave portion is bonded to the main surface of the element substrate so that the excitation electrode is positioned in a vibration space that is a space, and the cover is a portion of the bonding portion with the element substrate. The outer surface is located on the inner side of the outer periphery of the element substrate, and the outer surface side of the joint portion with the element substrate has an extending portion extending toward the outer periphery of the element substrate along the main surface of the element substrate. It is provided.

  An electronic component as one aspect of the present invention includes a mounting substrate, and the acoustic wave device described above mounted via a conductor bump with the main surface of the element substrate facing the main surface of the mounting substrate. And an exterior resin that covers the acoustic wave device.

The acoustic wave device having the above-described configuration can maintain the airtightness of the vibration space in a normal state for a long time.

(A) is a top view of the SAW device concerning the 1st embodiment of the present invention, and (b) is a top view in the state where the lid part of the SAW device of Drawing 1 (a) was removed. It is sectional drawing in the II-II line | wire of Fig.1 (a). FIG. 3 is an enlarged view of a region indicated by III in FIG. 2. It is sectional drawing of the electronic component which concerns on embodiment of this invention. (A) to (c) are cross-sectional views illustrating a method for manufacturing the SAW device shown in FIG. (A) to (c) is a cross-sectional view for explaining a method of manufacturing the SAW device shown in FIG. 1, and shows a continuation of FIG. 5 (c). (A) And (b) is sectional drawing explaining the manufacturing method of the SAW apparatus shown in FIG. 1, and shows the continuation of FIG.6 (c). It is an expanded sectional view for demonstrating the shape of the expansion | extension part of the SAW apparatus shown in FIG. It is sectional drawing which shows the SAW apparatus which concerns on 2nd Embodiment.

  Hereinafter, a SAW device according to an embodiment of the present invention 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.

(Configuration of SAW device, etc.)
FIG. 1A is a plan view of the SAW device 1 according to the first embodiment of the present invention, and FIG. 1B is a plan view of the SAW device 1 with the lid 4 removed. FIG. 2 is a cross-sectional view taken along the line II-II in FIG.

  The SAW device 1 includes an element substrate 3, an excitation electrode 5 provided on the first main surface 3a of the element substrate 3, a pad 7 provided on the first main surface 3a and connected to the excitation electrode 5, The cover 9 covers the excitation electrode 5 and exposes the pad 7, and the back surface portion 11 is provided on the second main surface 3 b of the element substrate 3.

  Signals are input to the SAW device 1 via any of the plurality of pads 7. The input signal is filtered by the excitation electrode 5 or the like. Then, the SAW device 1 outputs the filtered signal via any of the plurality of pads 7. The specific configuration of each member is as follows.

  The element substrate 3 is constituted by a piezoelectric substrate. Specifically, the element substrate 3 is composed of a single crystal substrate having piezoelectricity such as a lithium tantalate single crystal or a lithium niobate single crystal. The element substrate 3 is formed in a rectangular parallelepiped shape, for example, and has a first main surface 3a and a second main surface 3b which are rectangular and parallel to each other and are flat. The size of the element substrate 3 may be set as appropriate. For example, the thickness (Z direction) is 0.2 mm to 0.5 mm, and the length of one side (X direction or Y direction) is 0.5 mm. ~ 3mm.

  The element substrate 3 is translucent. By using the translucent element substrate 3, the extended portion 10 can be easily formed on the cover 3 as described in the method for manufacturing an elastic wave device described later. The transmittance of the ultraviolet light of the element substrate 3 is, for example, 30% to 80%. This transmittance can be adjusted to an arbitrary range by adjusting the kind and amount of impurities doped into the element substrate 3, the oxygen content of the element substrate 3, and the like.

The excitation electrode 5 is formed on the first main surface 3a. The excitation electrode 5 is a so-called IDT (Interdigital Transducer) and has a pair of comb-like electrodes. Each comb-like electrode has a bus bar extending in the propagation direction of the surface acoustic wave on the element substrate 3 and a plurality of electrode fingers extending from the bus bar in a direction orthogonal to the propagation direction of the surface acoustic wave. The two comb-like electrodes are provided so that their electrode fingers mesh with each other.

  Since FIG. 1 and the like are schematic diagrams, a pair of comb-like electrodes having several electrode fingers is shown, but in practice, a plurality of pairs of combs having a larger number of electrode fingers are shown. Toothed electrodes may be provided. Further, a ladder-type SAW filter in which a plurality of excitation electrodes 5 are connected by a system such as series connection or parallel connection may be configured, or a plurality of excitation electrodes 5 are arranged in the propagation direction of a surface acoustic wave. A mode SAW resonator filter may be configured.

  The pad 7 is formed on the first main surface 3a. The planar shape of the pad 7 may be set as appropriate. For example, the planar shape is a circle. The number and arrangement position of the pads 7 are appropriately set according to the configuration of the filter constituted by the excitation electrodes 5. In the SAW device 1, a case where six pads 7 are arranged along the outer periphery of the first main surface 3a is illustrated.

  The excitation electrode 5 and the pad 7 are connected by a wiring 15. The wiring 15 is formed on the first main surface 3 a and connects the bus bar of the excitation electrode 5 and the pad 7. The wiring 15 may be three-dimensionally crossed with not only a portion formed on the first main surface 3a but also two wirings 15 through which different signals flow with an insulator interposed therebetween.

  The excitation electrode 5, the pad 7, and the wiring 15 are made of the same conductive material, for example. The conductive material is, for example, an Al alloy such as Al or an Al—Cu alloy. Moreover, the excitation electrode 5, the pad 7, and the wiring 15 are formed with the same thickness, for example, and these thicknesses are 100-500 nm, for example. When the wires 15 are three-dimensionally crossed, the wires 15 on the first main surface 3a side are formed of, for example, an Al—Cu alloy, and the wires 15 arranged thereon via an insulator are, for example, Cr / It is formed by wiring having a multilayer structure made of Ni / Au or Cr / Al. When the wiring on the upper side of the three-dimensional wiring is formed of Cr / Ni / Au, the adhesiveness between the uppermost Au and the resin is relatively weak, so the cover 9 made of resin is not laminated on the three-dimensional wiring. It is good to do so. Thereby, peeling of the cover 9 can be suppressed. On the other hand, when the wiring on the upper side of the three-dimensional wiring is formed of Cr / Al, the cover 9 may be laminated on the three-dimensional wiring.

  In addition to the layer of the same material and the same thickness as the excitation electrode 5, the pad 7 is provided with a connection reinforcing layer 6 for the purpose of improving the connectivity with the bump. The connection reinforcing layer 6 includes, for example, a nickel layer superimposed on the pad 7 and a gold layer superimposed on the nickel layer.

  The cover 9 has, for example, a protruding portion 9a that protrudes between adjacent pads 7, and the planar shape excluding the protruding portion 9a is generally rectangular. In other words, the cover 9 can be regarded as a shape that is cut out so that the pad 7 is exposed from a rectangle having a size that covers the pad 7.

  The cover 9 is provided on the first main surface 3 a, the frame portion 2 surrounding the excitation electrode 5 in a plan view of the first main surface 3 a, and the lid portion 4 that overlaps the frame portion 2 and closes the opening of the frame portion 2. And have. A vibration space 21 is formed to prevent the SAW vibration excited by the excitation electrode 5 from being surrounded by the first main surface 3 a, the frame portion 2, and the lid portion 4.

The planar shape of the vibration space 21 may be set as appropriate, but the SAW device 1 has a substantially rectangular shape. Note that the cover 9 may be regarded as having a shape in which a concave portion constituting the vibration space 21 is formed on the lower surface side.

  The frame portion 2 is configured by forming one or more openings serving as the vibration spaces 21 in a layer having a substantially constant thickness. The thickness of the frame part 2 (height of the vibration space 21) is, for example, several μm to 30 μm. The lid portion 4 is composed of a layer having a substantially constant thickness. The thickness of the lid part 4 is, for example, several μm to 30 μm.

  The flat shape of the cover 4 is, for example, substantially the same as the flat shape of the frame 2, and the cover 4 is formed to be slightly smaller than the frame 2. In other words, the frame portion 2 is sized so that a portion along the outer periphery of the frame portion 2 slightly protrudes from the lid portion 4 when viewed in plan.

  The frame part 2 and the cover part 4 may be formed of the same material, or may be formed of different materials. In the present application, for convenience of explanation, the boundary line between the frame 2 and the lid 4 is clearly shown. However, in an actual product, the frame 2 and the lid 4 are integrally formed of the same material. May be.

  The cover 9 (the frame portion 2 and the lid portion 4) is made of a photosensitive resin. The photosensitive resin is, for example, a urethane acrylate-based, polyester acrylate-based, or epoxy acrylate-based resin that is cured by radical polymerization of an acryl group or a methacryl group. In addition, a polyimide resin or the like can also be used.

  The back surface portion 11 includes, for example, a back electrode that covers substantially the entire second main surface 3b of the element substrate 3, and an insulating protective layer that covers the back electrode. Charges may be charged on the surface of the element substrate 3 due to temperature changes, etc., but the charged charges can be discharged by providing the back electrode, and the breakdown of the excitation electrode 5 due to static electricity is suppressed. can do. Further, the protective layer suppresses damage to the element substrate 3. In addition, below, illustration and description of the back surface part 11 may be omitted.

  FIG. 3 is an enlarged view of region III in FIG.

The protective layer 8 is disposed on the first main surface 3 a of the element substrate 3, and the cover 9 is disposed on the protective layer 8. The protective layer 8 covers the excitation electrode 5 and contributes to prevention of oxidation of the excitation electrode 5. The protective layer 8 is made of, for example, silicon oxide (such as SiO ₂ ), aluminum oxide, zinc oxide, titanium oxide, silicon nitride, or silicon. The thickness of the protective layer 8 is, for example, about 1/10 (10 to 30 nm) of the thickness of the excitation electrode 5 or 200 nm to 1500 nm, which is thicker than the excitation electrode 5.

  The pad 7 or the connection reinforcing layer 6 is exposed from the protective layer 8. The opening of the protective layer 8 for exposing the connection reinforcing layer 6 may have the same shape and area as the connection reinforcing layer 6 or may be larger than the connection reinforcing layer 6. Further, the opening of the protective layer 8 may be smaller than the connection reinforcing layer 6, and in this case, the portion around the opening of the protective layer 8 covers the outer peripheral portion of the connection reinforcing layer 6.

As shown in the figure, the SAW device 1 has a lid portion 4 having a hanging portion 4a. The hanging part 4 a is a part that covers at least a part of the inner surface 2 a of the frame part 2 in the lid part 4. In the SAW device 1, the hanging part 4 a covers almost the upper half of the inner surface 2 a of the frame part 2. By providing such a hanging part 4 a on the lid part 4, the contact area between the lid part 4 and the frame part 2 increases, so that peeling between the lid part 4 and the frame part 2 can be suppressed. In addition, when external moisture enters from the boundary portion between the lid portion 4 and the frame portion 2, the intrusion path becomes longer by the amount that the hanging portion 4 a is in contact with the inner wall of the frame portion 2. Moisture does not get into the water. Therefore, corrosion of the excitation electrode 5 and the like in the vibration space can be suppressed, and the electrical characteristics of the SAW device 1 can be stabilized over a long period of time.

  The hanging part 4a is formed in, for example, an annular shape when viewed in plan. That is, the inner surface 2a is covered so as to go around along the inner surface 2a of the frame portion 2. As a result, it is possible to further enhance the moisture intrusion suppression effect from the boundary between the lid 4 and the frame 2.

  The hanging part 4a can be formed, for example, by adjusting conditions such as temperature when the lid part 4 is attached to the frame part 2. For example, heating may be performed at a somewhat high temperature in order to attach the resin lid portion 4 and the resin frame portion 2 to each other, but the temperature at that time is slightly higher than usual, and the temperature holding time is longer than usual. By adjusting the temperature and holding time such as slightly longer, a part of the resin lid part 4 hangs down along the inner surface 2a of the frame part 2 and the part hardens so that the sag part 4a can be obtained. As the hanging part 4a is formed, a minute recess 4b may be formed in a region directly above the hanging part 4a in the upper surface of the lid part 4.

  The outer surface 2 b of the frame portion 2 is inclined so as to be directed outward as the first main surface 3 a side of the element substrate 3. The angle of the outer surface 2b of the frame part 2 with respect to the first main surface 3a is, for example, about 80 °.

  The outer surface 4c of the lid part 4 may be inclined so as to be directed outward as the first main surface 3a side of the element substrate 3 is the same as the outer surface 2b of the frame part 2, or may not be inclined. For example, the angle of the outer wall 4c of the lid 4 with respect to the main surface 3a may be the same as the angle of the outer surface 2b of the frame 2 with respect to the first main surface 3a, or may be larger or smaller. Further, the outer side surface 4 c of the lid part 4 is located slightly inside the outer surface 2 b of the frame part 2. In other words, the lid 4 is made slightly smaller than the frame 2 when viewed in plan. For example, the outer surface 4 c of the lid portion 4 is located on the inner side of several μm to several tens of μm from the outer surface 2 b of the frame portion 2.

  In addition, an extending portion 10 is provided at the lower end portion of the cover 9 (frame portion 2). The extending portion 10 extends along the first main surface 3 a of the element substrate 3 on the outer surface side and the inner surface side of the joint portion of the cover 9 with the element substrate 3. In other words, the extending portion 10 extends from the inner surface 2 a toward the vibration space 21 on the inner surface 2 a side of the frame portion 2, and the outer periphery of the piezoelectric substrate 3 from the outer surface 2 b on the outer surface 2 b side of the frame portion 2. It stretches toward. The extending portion 10 is provided over substantially the entire circumference of the lower end portion of the cover 9, but is not provided in the vicinity of the wiring 15.

  Since the extension portion 10 is formed, the infiltration path of moisture or the like into the vibration space 21 is increased by the extension portion 10, so that the airtightness of the vibration space 21 is maintained in a normal state for a long time. can do. Therefore, corrosion of the excitation electrode 5 and the like in the vibration space can be suppressed, and the electrical characteristics of the SAW device 1 can be stabilized over a long period of time.

  The extending portion 10 is made of the same material as the cover 9, for example, and is formed integrally with the cover 9. If the extending portion 10 is formed integrally with the cover 9 in this way, the contact area of the cover 9 on the first main surface 3a side can be considered to be increased by the extending portion 10, so that the element substrate of the cover 9 is formed. 3 can be improved, and peeling of the cover 9 from the element substrate 3 can be suppressed. The extending portion 10 may be formed of a material different from that of the cover 9.

From the viewpoint of lengthening the infiltration path for moisture or the like from the outside, it is also conceivable to increase the width of the frame 2 as it is. However, it is not possible to simply increase the thickness of the frame portion 2 such as the frame portion 2 because it needs to be separated from the excitation electrode 5 and the piezoelectric substrate 3 by a predetermined distance. This is because, on the excitation electrode 5 side, if a large thickness like the frame portion 2 touches the excitation electrode 5, the vibration of the excitation electrode 5 is greatly affected, resulting in deterioration of electrical characteristics. Since the portion of the substrate 3 is a wafer dicing line on the outer peripheral side of the substrate 3, if the thick frame portion 2 is present on the dicing line, chipping occurs in the element substrate 3 or the like when the wafer is cut. It is because it becomes easy to do. Furthermore, as will be described later, when the SAW device 1 is mounted on another mounting substrate and the entire SAW device 1 is covered with an exterior resin, the outer wall of the cover 9 is located near the outer periphery of the element substrate 2. In addition, the exterior resin is less likely to enter between the SAW device 1 and the main surface of the mounting substrate, and there is a problem that a gap is easily formed in that portion.

  On the other hand, since the extending portion 10 is formed so as to extend from the lower end portion of the cover 9, it is assumed that the extending portion 10 touches the excitation electrode 5 or extends to the vicinity of the outer periphery of the element substrate 3. The above problems are suppressed. In particular, if the elongated portion 10 is formed so that its thickness gradually decreases as it goes outward, even if its tip touches the excitation electrode 5, the electrical characteristics are not greatly affected. Even if it extends to the vicinity of the outer periphery, it is possible to more effectively suppress the chipping of the element substrate 3 and the like during wafer dicing. Furthermore, when the SAW device 1 is mounted on another mounting substrate and covered with an exterior resin, the formation of a gap between the SAW device 1 and the mounting substrate can be suppressed. For example, the thickness of the elongated portion 10 at the thickest portion, that is, the thickness of the connecting portion with the cover 9 is 1/30 to 1/10 of the thickness of the frame portion 2. Specifically, when the thickness of the frame portion 2 is 30 μm, the size of the thickest portion of the elongated portion 10 is 1.5 μm. The horizontal width of the extending portion 10 is, for example, about 40 μm.

  The cross-sectional shape of the elongated portion 10 is not limited to the triangular shape shown in FIG. 3, but the outer periphery has an arc shape as shown in FIG. 8 (FIG. 7A) or trapezoidal shape (FIG. 7B). )), A rectangular shape (FIG. 7C), and the like are also possible.

  FIG. 4 is a cross-sectional view showing a part of the electronic component 51 on which the SAW device 1 is mounted. Note that the cross-sectional view of the SAW device 1 in FIG. 4 corresponds to a cross section taken along line IV-IV in FIG.

  The electronic component 51 is mounted on the mounting surface 53 a via the mounting substrate 53, the pads 55 provided on the mounting surface 53 a of the mounting substrate 53, the conductor bumps 57 disposed on the pads 55, and the conductor bumps 57. A SAW device 1 and an exterior resin 59 for sealing the SAW device 1.

  In addition, the electronic component 51 includes, for example, an IC or the like mounted on the mounting substrate 53 and sealed together with the SAW device 1 by the exterior resin 59 to form a module.

  The mounting board 53 is configured by, for example, a printed wiring board. The printed wiring board may be a rigid board or a flexible board. The printed wiring board may be a single-layer board, a two-layer board, or a multilayer board having two or more layers. Moreover, the base material, insulating material, and conductive material of the printed wiring board may be selected from appropriate materials.

  The conductor bump 57 is in contact with both the pad 7 of the SAW device 1 and the pad 55 of the mounting substrate 53. The conductor bump 57 is formed of a metal that is melted by heating and bonded to the pad 7. The conductor bump 57 is made of, for example, solder. The solder may be a solder using lead such as Pb—Sn alloy solder, or lead-free solder such as Au—Sn alloy solder, Au—Ge alloy solder, Sn—Ag alloy solder, Sn—Cu alloy solder, etc. It may be.

The exterior resin 59 includes, for example, an epoxy resin, a curing material, and a filler as main components.
The exterior resin 59 not only covers the SAW device 1 from the side of the back surface 11 and from the side, but is also filled between the SAW device 1 and the mounting substrate 53. Specifically, the exterior resin 59 is also filled between the upper surface of the cover 9 and the mounting surface 53 a of the mounting substrate 53 and around the conductor bumps 57.

  The conductor bump 57 has a shape in which a sphere is roughly crushed by the pad 7 and the pad 55. That is, the conductor bump 57 has two planes in contact with the pad 7 and the pad 55 and an outer peripheral surface connecting the two planes. The two planes and the outer peripheral surface are circular in a plan view, and the outer peripheral surface is a center in a side view. It has a curved shape with the side protruding outward.

  The area of the plane contacting the pad 7 and the pad 55 of the conductor bump 57 is preferably equal to or less than the area of the pad 7 and the pad 55.

  The side wall 2b of the frame part 2 and the side wall 4b of the lid part 4 are not in contact with the conductor bumps 57 over the entirety. Therefore, a gap between the outer wall of the cover 9 (the frame portion 2 and the lid portion 4) and the conductor bump 57 is formed from the upper surface to the lower surface of the cover 9, and the outer resin 59 is filled in the gap.

  Thus, the side wall 2b of the frame portion 2 and the side wall 4b of the lid portion 4 are not in contact with the conductor bumps 57 throughout, and the exterior resin is filled between the side walls and the conductor bumps 57. Therefore, the conductor bump 57 is not easily affected by the shape of the outer wall of the cover 9. As a result, for example, the corners between the outer wall of the cover 9 and the upper surface of the cover are prevented from forming a shape that tends to cause stress concentration in the conductor bumps 57, and the occurrence of cracks in the conductor bumps 57 is suppressed. . These effects are particularly remarkable when the exterior resin 59 is filled between the conductor bump 57 and the outer wall of the cover 9 from the upper surface to the lower surface of the cover 9 as in the embodiment.

  Further, as described above, the outer surface 2b of the frame portion 2 constituting the cover 9 is inclined so as to expand toward the main surface 3a of the element substrate 3, and the exterior resin 59 is in contact with the inclined outer surface 2b. Yes.

  Therefore, for example, between the inclined outer surface 2 b and the conductor bump 57, the exterior resin 59 easily flows from the upper surface side to the lower surface side of the cover 9, and the formation of a cavity in the exterior resin 59 is suppressed. If there is a cavity in the exterior resin 59, when the heat is applied at the time of reflow, the cavity may expand and cause a mounting failure of the SAW device 1, but the formation of the cavity is suppressed. Generation | occurrence | production of mounting defect etc. is suppressed.

  Moreover, since the outer wall 4c of the cover part 4 is located inside the outer surface 2b of the frame part 2, the effect similar to the effect by the inclination of the outer surface 2b of the frame part 2 mentioned above is anticipated. That is, between the outer wall of the cover 9 and the conductor bump 57, the exterior resin 59 can easily flow from the upper surface side to the lower surface side of the cover 9.

(Method for manufacturing SAW device)
FIG. 5A to FIG. 7B are cross-sectional views (corresponding to the line III-III in FIG. 1) for explaining the method for manufacturing the SAW device 1. The manufacturing process proceeds in order from FIG. 5 (a) to FIG. 7 (b).

The steps of FIG. 5A to FIG. 7B corresponding to the method for manufacturing the SAW device 1 are realized in a so-called wafer process. That is, a thin film formation, a photolithography method, or the like is performed on the mother substrate that becomes the element substrate 3 by being divided, and then a plurality of SAW devices 1 are formed in parallel by dicing. . However, FIG. 5A to FIG.
In (b), only the part corresponding to the two SAW devices 1 is shown. In addition, although the shape of the conductive layer and the insulating layer changes with the progress of the process, a common code may be used before and after the change.

As shown in FIG. 5A, first, the excitation electrode 5 is formed in each region of the first region 41 and the second region 42 of the wafer 33 to be the element substrate 3. Specifically, first, a first thin film forming method such as a sputtering method, a vapor deposition method or a CVD (Chemical Vapor Deposition) method is used.
A metal layer is formed on main surface 3a. Next, the metal layer is patterned by a photolithography method using a reduction projection exposure machine (stepper) and an RIE (Reactive Ion Etching) apparatus. The excitation electrode 5 is formed by patterning the metal layer. Note that the wiring 15 and the pad 7 are simultaneously formed in each region by the same process as the excitation electrode 5.

  The wafer 33 used here is translucent. By using the semi-transparent wafer 33 in this way, irradiation light at the time of exposure is transmitted through the wafer 33 in the photolithography process when forming the cover 9 as will be described later. The first main surface 33a of the wafer 33 is mirror-finished, whereas the second main surface 33b, which is the main surface opposite to the first main surface 33a, is roughened. As the second main surface 33b is thus roughened, the irradiation light transmitted through the wafer 33 is irregularly reflected on the second main surface 33b.

  The transmittance of the wafer 33 is 30% to 80% when measured with ultraviolet light. This transmittance can be adjusted to an arbitrary range by adjusting the type and amount of impurities doped into the wafer 33, the oxygen content of the wafer 33, and the like. The impurity doped into the wafer 33 is, for example, Fe.

  Further, the roughening of the second main surface 33b of the wafer 33 is performed, for example, by polishing the second main surface 33b with a rough abrasive or by performing a honing process on the second main surface 33b. The arithmetic average roughness Ra of the roughened second main surface 33b is, for example, not less than 175 nm and not more than 500 nm. By setting the Ra of the second main surface 33b within this range, irregular reflection suitable for forming the elongated portion 10 can be achieved, and cracking of the wafer 33 can be suppressed.

  A metal layer 34 is formed on the roughened second main surface 33b. The metal layer 34 is made of a metal such as Al. By providing such a metal layer 34, the light transmitted through the wafer 33 is easily reflected on the second main surface 33b toward the first main surface 33a. The metal layer 34 becomes a back electrode by being cut for each region.

  When the excitation electrode 5 and the like are formed, the protective layer 8 is formed as shown in FIG. Specifically, first, a thin film to be the protective layer 8 is formed by an appropriate thin film forming method. The thin film forming method is, for example, a sputtering method or CVD. Next, a part of the thin film is removed by RIE or the like so that the pad 7 is exposed. Thereby, the protective layer 8 is formed.

  When the protective layer 8 is formed, a frame layer 35 is formed as shown in FIG. The frame layer 35 is made of a negative photosensitive resin. The frame layer 35 may be formed by a thin film forming method similar to that of the protective layer 8, or may be formed by a spin coating method or the like. Thereafter, the wafer 33 on which the frame layer 35 is formed is heat-treated. Thereby, the adhesion strength between the frame layer 35 and the wafer 33 can be increased.

  Next, the frame part layer 35 is patterned into a predetermined shape to form the frame part 2.

  Specifically, first, the frame layer 35 is irradiated with light L such as ultraviolet rays through the photomask 40 as shown in FIG. The photomask 40 is configured by forming a light shielding portion 39 on a transparent substrate 43. The light shielding portion 44 includes a frame portion layer 35 such as a portion that becomes the vibration space 21 and a boundary portion (a portion that becomes a dicing line) between the first region 41 and the second region 42 when the photomask 40 is set on the wafer 33. Is formed at a position corresponding to the portion to be removed. That is, in FIG. 1B, the light shielding portion 44 is formed at a position corresponding to the portion exposed from the frame portion 2 in the first main surface 3 a of the element substrate 3.

  In this exposure process, since the wafer 33 is translucent, part of the exposure light L passes through the wafer 33 in the thickness direction and reaches the second main surface 33b of the wafer 33. The light L that has reached the second main surface 33b is irregularly reflected by the roughened second main surface 33b, part of which reaches the first main surface 33a of the wafer 33, and the first of the frame layer 35 The surface on the main surface 33a side is exposed. The light amount of the light L reflected by the second main surface 33b and reaching the frame layer 35 is smaller than the light amount of the first light L. Therefore, the light L reflected by the second main surface 33b and reaching the first main surface 33a does not expose the frame layer 35 over the entire thickness direction, but only the lower surface side of the frame forming layer 5 is exposed. It becomes. Further, the light L that is reflected by the second main surface 33b and reaches the first main surface 33a gradually becomes weaker as it goes outward from the portion directly exposed from the photomask 40 side. Therefore, as a result of the unexposed portion of the frame layer 35 remaining in the subsequent development process, the elongated portion 10 shown in FIG. 3 can be formed at the lower end portion of the frame portion 2.

  The amount of light L reflected by the second main surface 33b and reaching the lower surface of the frame layer 35 is the transmittance of the wafer 33, the illuminance of the light L, the roughness of the second main surface 33b, the type of the metal layer 34, etc. Therefore, it is possible to change the shape and dimensions of the elongated portion 10 by adjusting them.

  After that, as shown in FIG. 6B, development processing is performed to leave the portion irradiated with the light L and remove the portion not irradiated with the light L from the frame layer 35. As a result, an opening 36 serving as the vibration space 21 is formed in the frame layer 35, and a groove 37 is formed at the boundary between the first region 41 and the second region 42. That is, the frame part 2 having the extending part 10 is formed.

  When the frame portion 2 is formed, a lid portion layer 38 to be the lid portion 4 is formed as shown in FIG. The lid layer 38 is made of the same material as the frame layer 35, for example. The lid portion layer 38 is placed on the frame portion 2 in a state where it is affixed to the base film 39. And the cover part layer 38 and the frame part 2 are adhere | attached by heating the cover part layer 38 in the state in which the base film 39 was stuck. Adhesion between the lid layer 38 and the frame 2 is performed, for example, by placing the wafer 33 on a stage 45 heated to about 40 ° C. to 50 ° C. and rotating a roller 46 that is also heated to about 40 ° C. to 50 ° C. The base film 39 is pressed against the lid layer 38 to which the base film 39 is attached. At this time, if the temperature of the stage 45 and the roller 46, the rotation speed of the roller, and the like are set to predetermined conditions, the softened lid portion layer 38 can be drooped along the inner surface 2a of the frame portion 2, and this dripping The part becomes the hanging part 4a. The shape of the hanging part 4a can be controlled by adjusting the temperature of the stage 45 and the roller 46, the holding time on the stage 45, the rotational speed of the roller 46, and the like. For example, when epoxy acrylate is used as the material of the frame portion 2 and the lid portion layer 38 and the thickness of both the frame portion 2 and the lid portion layer 38 is 30 μm, the stage 45 and the roller 46 are moved from the temperature during normal bonding. In addition, the drooping portion 4a covering the upper half of the inner surface 2a of the frame portion 2 can be formed by setting the temperature to about 42 ° C to 45 ° C, which is several degrees higher.

Thereafter, the base film 39 is peeled off, and as shown in FIG. 7A, the boundary portion between the first region 41 and the second region 42 of the lid layer 38 is removed by a photolithography method or the like to form the lid 4. . By forming the lid portion 4, a vibration space 21 including a space surrounded by the protective layer 8, the frame portion 2, and the lid portion 4 is formed.

  Thereafter, as shown in FIG. 7C, the SAW device 1 is formed by cutting the wafer 33 with a dicing blade 47 along the boundary line between the first region 41 and the second region 42.

<Second Embodiment>
FIG. 10 is a cross-sectional view showing the SAW device 201 according to the second embodiment. This cross section corresponds to a cross section taken along line IV-IV in FIG.

  The SAW device 201 has a terminal 25. The terminal 25 is located on the pad 7 in a state of being electrically connected to the pad 7. Further, the terminal 25 penetrates the cover 9 in the vertical direction, and the end portion not connected to the pad 7 is exposed from the upper surface of the cover 9. The terminal 7 is formed by plating using copper or the like, for example.

  Further, the SAW device 201 has a reinforcing layer 22 disposed on the upper surface of the cover 9. The reinforcing layer 22 is for reinforcing the strength of the cover 9 (particularly the lid portion 4). The reinforcing layer 22 is formed over a relatively wide range of the cover 9. For example, the reinforcing layer 22 is formed over substantially the entire upper surface of the cover 9. Therefore, the reinforcing layer 22 covers the entire vibration space 21 in a plan view, extends to the outside of the vibration space 21, and is supported by the frame portion 2 together with the lid portion 4.

  The reinforcing layer 22 is made of a material having a Young's modulus higher than that of the cover 9. For example, the cover 9 is made of a resin having a Young's modulus of 0.5 to 1 GPa, whereas the reinforcing layer 22 is made of a metal having a Young's modulus of 100 to 250 GPa. The thickness of the reinforcing layer 22 is, for example, 1 to 50 μm.

  In addition, when the terminal 25 penetrating the cover 9 is provided and the reinforcing layer 22 is also provided, the entire reinforcing layer 22 is preferably covered with the insulating film 24. Thereby, when the SAW device 201 is mounted on the mounting substrate, the reinforcing layer 22 and the terminal 25 can be prevented from being short-circuited.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects, and the above-described embodiments may be combined as appropriate.

  The elastic wave device is not limited to the SAW device. For example, the acoustic wave device may be a piezoelectric thin film resonator.

  In the acoustic wave device, the protective layer 8 and the back surface portion 11 are not essential requirements and may be omitted.

DESCRIPTION OF SYMBOLS 1 ... SAW apparatus 2 ... Frame part 3 ... Element board | substrate 4 ... Cover part 5 ... Excitation electrode 6 ... Connection reinforcement | strengthening layer 7 ... Pad 8 ... Protective layer 9 ..Cover 10 ... extension part 11 ... back part

Claims (7)

An element substrate;
An excitation electrode disposed on the main surface of the element substrate;
It has a recess, joining the inner surface and surrounding the recess as the excitation electrode is located in between the elements Ru space der surrounded by the main surface of the substrate sky of the recess within the main surface of the element substrate And a covered cover,
The cover is
The joint portion with the element substrate is located inside the outer periphery of the element substrate,
In cross-sectional view, the outer surface continues to the first surface and the first surface, and is located closer to the main surface of the element substrate than the first surface, and toward the outer peripheral side of the element substrate. An elastic wave device comprising: the first surface and a second surface having a different inclination angle so as to extend . 2. The elastic wave according to claim 1, wherein the cover includes a frame portion positioned on a main surface of the element substrate so as to surround the excitation electrode, and a lid portion that overlaps the frame portion and closes the frame portion. apparatus. The elastic wave device according to claim 2 , wherein an outer surface of the lid portion is located on an inner side than a side surface of the frame portion. The cover is
In a cross-sectional view, the inner surface continues to the third surface and the third surface, is located closer to the main surface of the element substrate than the third surface, and is directed toward the space of the element substrate. The third surface and the fourth surface with different inclination angles so as to extend,
The lid portion has a hanging portion in contact with the third surface .
The elastic wave device according to claim 2 or 3. The elastic wave device according to any one of claims 1 to 4 , wherein a second main surface of the element substrate facing the main surface is roughened . In the main surface of the element substrate, is formed on the outside of the outer surface of the cover, seen plurality contains electrically connected to pads on the excitation electrode,
The elastic wave device according to claim 1 , wherein the cover includes a projecting portion that projects between the adjacent pads in a plan view . A mounting board;
The acoustic wave device according to any one of claims 1 to 6, wherein the acoustic wave device is mounted via a conductor bump in a state where the main surface of the element substrate faces the main surface of the mounting substrate.
An electronic component comprising an exterior resin that covers the acoustic wave device.

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