JP5033690B2 - Method for manufacturing bulk acoustic wave device - Google Patents

Description

  The present invention relates to a method for manufacturing a bulk acoustic wave device in which a resonator having electrode films facing each other across a piezoelectric thin film is separated from a support substrate by a cavity.

  As shown in Patent Document 1, a bulk acoustic wave device including a resonator with electrode films facing each other with a piezoelectric thin film sandwiched thereon is sputter-deposited with a lower electrode film, a piezoelectric thin film, and an upper electrode film on a support substrate. In general, it is manufactured by sequentially forming by additional processing such as vapor deposition.

  However, in the method for manufacturing the bulk acoustic wave device disclosed in Patent Document 1, the piezoelectric material constituting the piezoelectric thin film and the crystal orientation of the piezoelectric thin film are limited to those that can be formed on the underlying lower electrode film. In other words, the bulk acoustic wave device manufacturing method disclosed in Patent Document 1 manufactures a bulk acoustic wave device having a desired characteristic with a low degree of freedom in selection of the crystal orientation of the piezoelectric material and piezoelectric thin film constituting the piezoelectric thin film. It may be difficult to do.

  In order to solve this problem, Patent Document 2 discloses a method in which a first plate-like structure including a piezoelectric substrate is bonded to a second plate-like structure including a support substrate, and then the piezoelectric substrate is polished. It has been proposed to form a piezoelectric thin film that constitutes a bulk acoustic wave device. According to the method for manufacturing a bulk acoustic wave device shown in Patent Document 2, a bulk acoustic wave device having a desired characteristic with a high degree of freedom in selecting a crystal orientation in a piezoelectric material or a piezoelectric thin film constituting the piezoelectric thin film. Is easy.

JP 2000-69594 A JP 2007-228319 A

  However, it is extremely difficult to uniformly process the piezoelectric substrate by polishing. For this reason, the bulk acoustic wave device manufacturing method proposed in Patent Document 2 has a problem that it is difficult to ensure the uniformity of the thickness of the formed piezoelectric thin film.

  In addition, in the method for manufacturing a bulk acoustic wave device proposed in Patent Document 2, the piezoelectric thin film above the cavity is curved during polishing, and the film thickness uniformity of the piezoelectric thin film is further impaired. There is. The bending of the piezoelectric thin film during polishing causes a large stress on the piezoelectric thin film because the electrode film thickness cannot be ignored compared to the piezoelectric thin film thickness, and the piezoelectric thin film thickness changes due to polishing. As a result, the ratio between the film thickness of the piezoelectric thin film and the film thickness of the electrode film changes to cause the stress to change.

  The present invention has been made to solve this problem, and an object thereof is to provide a method for manufacturing a bulk acoustic wave device capable of improving the uniformity of the film thickness of a piezoelectric thin film.

  In order to solve the above-mentioned problems, the invention of claim 1 is a method for manufacturing a bulk acoustic wave device in which a resonator having electrode films facing each other with a piezoelectric thin film interposed therebetween is separated from a support substrate by a cavity. Exposed on the second main surface of the piezoelectric substrate having the first main surface having a relatively high etching rate and the second main surface having a relatively low etching rate, and not exposed on the first main surface. Reversing the polarization direction of the portion; and (b) after the step (a), a first plate-like structure including the piezoelectric substrate and a second plate-like structure including the support substrate. A step of joining the second main surface to the side of the plate-like structure of 2 and (c) a state of joining the first plate-like structure and the second plate-like structure In the step (a), the piezoelectric substrate is etched from the first main surface side while maintaining And a step of removing the non-polar direction is inverted portion.

  According to a second aspect of the present invention, in the method for manufacturing a bulk acoustic wave device according to the first aspect of the present invention, (d) the portion of the polarization direction reversed in the step (a) remaining after the step (c). A step of planarizing the surface by ion milling.

  According to a third aspect of the present invention, in the method for manufacturing a bulk acoustic wave device according to the first or second aspect, (e) the cavity is planned to finally become the cavity before the piezoelectric substrate is etched. And (f) a step of removing the sacrificial body after etching the piezoelectric substrate.

  According to a fourth aspect of the present invention, in the method for manufacturing a bulk acoustic wave device according to any one of the first to third aspects, the piezoelectric substrate is a Z-plate of lithium tantalate.

  According to the first aspect of the present invention, since the film thickness of the piezoelectric thin film can be controlled by controlling the depth of the portion where the polarization direction is reversed, the film thickness of the piezoelectric thin film can be easily controlled. The uniformity of the film thickness of the piezoelectric thin film can be improved.

  According to the invention of claim 2, the uniformity of the film thickness of the piezoelectric thin film can be further improved.

  According to the invention of claim 3, since the sacrificial body suppresses the upward and downward bending of the piezoelectric thin film, it can be suppressed that the film thickness of the piezoelectric thin film is not uniform.

  According to the invention of claim 4, the reversal of the polarization direction is facilitated.

<1 Introduction>
1 to 3 are schematic views for explaining the principle of processing of a piezoelectric substrate described below. 1 to 3 are cross-sectional views of the piezoelectric substrate being processed.

As shown in FIG. 1, in the piezoelectric substrate 802 having the first main surface 804 and the second main surface 806 that are parallel to each other, the polarity of the first main surface 804 and the polarity of the second main surface 806 are different. The etching rate of the first main surface 804 and the etching rate of the second main surface 806 are different. For example, when the piezoelectric substrate 802 is a lithium niobate (LiNbO ₃ ) Z plate and the polarization direction is from the first main surface 804 to the second main surface 806, the first Z becomes the −Z plane. The etching rate of the main surface 804 is relatively fast, and the etching rate of the second main surface 806 that is the + Z surface is relatively slow.

  Therefore, in the processing of the piezoelectric substrate described below, as shown in FIG. 2, the first portion 808 of the piezoelectric substrate 802 that is exposed on the second main surface 806 and is not exposed on the first main surface 804. The piezoelectric substrate 802 is etched from the first main surface 804 side. Then, an interface 812 between the first portion 808 and the second portion 810 other than the first portion 808 becomes an etch stop surface, and the second portion 810 is removed and the first portion 808 is removed as shown in FIG. Remains. That is, if the polarization direction of the portion of the piezoelectric substrate 802 that is desired to remain as a piezoelectric thin film is reversed, the piezoelectric substrate 802 can be processed by etching to produce a piezoelectric thin film. The polarization direction inversion method includes an electric field application method in which an electric field is applied to the piezoelectric substrate, an ion exchange method in which the piezoelectric substrate is subjected to heat treatment after ion exchange is performed on the piezoelectric substrate, and an electron beam is applied to the piezoelectric substrate. An electron beam method or the like is known.

  Note that names representing the polarities of the main surfaces such as the “−Z plane” and the “+ Z plane” differ depending on the type of piezoelectric material constituting the piezoelectric substrate 802.

  FIG. 4 is a flowchart for explaining the processing procedure of the piezoelectric substrate when the above-described principle of processing the piezoelectric substrate is used.

  When the above-described principle of processing a piezoelectric substrate is used, the produced piezoelectric thin film cannot withstand its own weight. Therefore, the first plate-like structure including the piezoelectric substrate and the second plate including the support substrate are used. The substrate is bonded in advance (step S801), and the piezoelectric substrate is etched (step S802) while maintaining the bonded state of the first plate structure and the second plate structure. A piezoelectric thin film is produced.

  Here, the “first plate-like structure” may be composed of only a piezoelectric substrate, or may be composed of components other than the piezoelectric substrate. The “second plate-like structure” may be composed of only the support substrate or may be composed of components other than the support substrate.

<2 First Embodiment>
<2-1 Configuration of Bulk Acoustic Wave Device 1>
FIG. 5 is a schematic diagram showing the configuration of the bulk acoustic wave device 1 according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view of the bulk acoustic wave device 1. The bulk acoustic wave device 1 shown in FIG. 5 includes a resonator 138 in which the lower excitation electrode 114 and the upper excitation electrode 130 face each other with the piezoelectric thin film 124 therebetween, and a lower excitation electrode 120 and an upper excitation electrode with the piezoelectric thin film 126 interposed therebetween. Reference numeral 132 denotes a ladder type filter in which the resonator 140 facing the ladder 140 is connected in a ladder type. It should be noted that the configuration of the bulk acoustic wave device 1 and the method for manufacturing the bulk acoustic wave device 1 described below can be applied to other types of bulk acoustic wave devices, for example, filters other than ladder filters, oscillators, traps, duplexers, and triplexers. Or the like. The term “bulk elastic wave device” as used herein refers to an electrical device derived from a resonance phenomenon caused by a bulk elastic wave excited by a resonator including one or a plurality of resonators whose electrode films face each other across a piezoelectric thin film. It means all devices that use typical responses.

  As shown in FIG. 5, the bulk acoustic wave device 1 has a structure in which the lower electrode films 112 and 118, the piezoelectric thin films 124 and 126, the upper electrode film 128, and the passivation film 136 are supported by the support substrate 102. In the bulk acoustic wave device 1, the resonator 138 in which the lower excitation electrode 114 that is a part of the lower electrode film 112 and the upper excitation electrode 130 that is a part of the upper electrode film 128 are opposed to each other with the piezoelectric thin film 124 interposed therebetween is cavityd. The resonator 140 is separated from the support substrate 102 by the 106, and the lower excitation electrode 120 which is a part of the lower electrode film 118 and the upper excitation electrode 132 which is a part of the upper electrode film 128 are opposed to each other with the piezoelectric thin film 126 interposed therebetween. Is separated from the support substrate 102 by a cavity 110.

{Piezoelectric thin films 124, 126}
The piezoelectric material that constitutes the piezoelectric thin films 124 and 126 is not particularly limited, but quartz (SiO ₂ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), lithium tetraborate (Li ₂ B ₄ O) ₇ ) ・ Single crystal materials that do not contain grain boundaries such as zinc oxide (ZnO), potassium niobate (KNbO ₃ ), langasite (La ₃ Ga ₃ SiO ₁₄ ), gallium nitride (GaN), and aluminum nitride (AlN) It is desirable to choose. This is because if the single crystal material is selected, the electromechanical coupling coefficient and the mechanical quality coefficient of the piezoelectric thin films 124 and 126 can be improved.

  The crystal orientation in the piezoelectric thin films 124 and 126 is not particularly limited, but is determined in consideration of the electromechanical coupling coefficient, the temperature characteristics of the resonance frequency and antiresonance frequency of the resonators 138 and 140, and the like. This is because if such a crystal orientation is selected, a temperature change in the filtering characteristics of the bulk acoustic wave device 1 can be suppressed, and an interval between the resonance frequency and the anti-resonance frequency can be appropriately selected.

  The piezoelectric thin film 124 is generally formed in a two-dimensional region in which the cavity 106 is formed (hereinafter referred to as “first cavity region”), and its lower surface is in contact with the upper surface of the lower excitation electrode 114, and the upper surface is the upper part. It is in contact with the lower surface of the excitation electrode 130. The piezoelectric thin film 126 is generally formed in a two-dimensional region (hereinafter referred to as “second cavity region”) in which the cavity 110 is formed, and the lower surface thereof is in contact with the upper surface of the lower excitation electrode 120, and the upper surface is the upper part. It is in contact with the lower surface of the excitation electrode 132. The “two-dimensional region” means a region that occupies a two-dimensional area parallel to the piezoelectric thin films 124 and 126.

{Lower electrode films 112, 118 and upper electrode film 128}
The conductive material constituting the lower electrode films 112, 118 and the upper electrode film 128 is not particularly limited, but from the viewpoint of reducing mechanical loss, tungsten (W), ruthenium (Ru), iridium (Ir), molybdenum (Mo From the viewpoint of reducing electrical loss, it is desirable to select a metal having a low electrical resistance such as gold (Au). For this reason, all or part of the lower excitation electrodes 114 and 120 and the upper excitation electrodes 130 and 132 are configured only by the former, and the lower wiring electrode serving as a feeding path to the lower excitation electrodes 114 and 120 and the upper excitation electrodes 130 and 132 It is desirable that all or a part of 116, 122 and the upper wiring electrode 134 be configured by overlapping the former and the latter. As a result, both mechanical loss and electrical loss can be reduced, so that the “Q” of the resonators 138 and 140 can be improved, the in-band loss of the bulk acoustic wave device 1 is reduced, and the out-of-band attenuation is reduced. Increase the skirt characteristics. Note that the lower electrode films 112 and 118 and the upper electrode film 128 may be made of different types of conductive materials.

  The lower excitation electrode 114 is generally formed in the first cavity region, the lower surface thereof is separated from the support substrate 102 by the cavity 106, and the upper surface thereof is in contact with the lower surface of the piezoelectric thin film 124. The lower wiring electrode 116 is generally formed in a two-dimensional region (hereinafter referred to as “first wiring region”) adjacent to the first cavity region, and the lower surface thereof is in contact with the upper surface of the support substrate 102. At least a portion is exposed. The lower excitation electrode 120 is generally formed in the second cavity region, the lower surface thereof is separated from the support substrate 102 by the cavity 110, and the upper surface thereof is in contact with the lower surface of the piezoelectric thin film 126. The lower wiring electrode 122 is generally formed in a two-dimensional region (hereinafter referred to as “second wiring region”) adjacent to the second cavity region, and the lower surface thereof is in contact with the upper surface of the support substrate 102. At least a portion is exposed. The upper excitation electrode 130 is generally formed in the first cavity region, and the lower surface thereof is in contact with the upper surface of the piezoelectric thin film 124. The upper excitation electrode 132 is generally formed in the second cavity region, and the lower surface thereof is in contact with the upper surface of the piezoelectric thin film 126. The upper wiring electrode 134 is generally formed in a two-dimensional region (hereinafter referred to as “third wiring region”) between the first cavity region and the second cavity region, and the lower surface thereof is the upper surface of the passivation film 136. Is in contact with In FIG. 5, the upper surface of the upper wiring electrode 134 is exposed, but a passivation film may be further formed on the upper surface of the upper wiring electrode 134. Of course, the first wiring region, the second wiring region, and the third wiring region are different two-dimensional regions.

{Passivation film 136}
The insulating material constituting the passivation film 136 is not particularly limited, but it is desirable to select silicon nitride (Si ₃ N ₄ ), silicon oxide (SiO ₂ ), or the like.

  The passivation film 136 is generally formed in a two-dimensional region other than the first cavity region, the second cavity region, and the two-dimensional region where the lower electrode films 112 and 118 are exposed (hereinafter referred to as “exposed region”). Has been. The passivation film 136 plays a role of protecting the bulk acoustic wave device 1 from moisture and the like in the atmosphere.

{Supporting substrate 102}
The insulating material constituting the support substrate 102 is not particularly limited, but is a single element of an IV element such as silicon (Si), germanium (Ge), sapphire (Al ₂ O ₃ ), magnesium oxide (MgO), zinc oxide (ZnO). Simple oxides such as zirconium boride (ZrB ₂ ), lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), lithium aluminate (LiAlO ₂ ), lithium gallate (LiGaO ₂ ), Complex oxides such as spinel (MgAl ₂ O ₄ ), lanthanum strontium tantalate aluminate ((LaSr) (AlTa) O ₃ ), neodymium gallate (NdGaO ₃ ), IV-IV group such as silicon germanium (SiGe) It is desirable to select compounds such as III-IV group compounds such as gallium arsenide (GaAs), aluminum nitride (AlN), gallium nitride (GaN), and aluminum gallium nitride (AlGaN). However, in the bulk acoustic wave device 1, since the support substrate 102 and the lower electrode films 112 and 118 are in direct contact with each other, when silicon is selected as the material constituting the support substrate 102, high resistance silicon having high insulation is adopted. Alternatively, it is desirable to form an oxide film as an insulating film on the surface.

  On the upper surface of the support substrate 102, non-through holes 104 and 108 whose interiors are used as cavities 106 and 110 are exposed. Instead of the non-through holes 104 and 108, the inside of the through hole penetrating the upper surface and the lower surface of the support substrate 102 may be used as a cavity. In order to form a through hole, a drilling technique capable of deep drilling such as deep reactive ion etching (Deep RIE) is required, but the through hole can be drilled from the lower surface of the support substrate 102. is there.

{Via hole 142, 144}
In the bulk acoustic wave device 1, via holes 142 and 144 extending from the outside to the cavities 106 and 110 are formed. The via holes 142 and 144 may be drilled from the upper surface side or may be drilled from the lower surface side. Of course, when the via holes 142 and 144 are drilled from the upper surface side, the via holes 142 and 144 are provided in the vicinity of the end portions of the first cavity region and the second cavity region that have a small influence on the excited elastic wave. It is desirable to drill. On the other hand, when a via hole is drilled from the lower surface side, a deep hole is required, but a via hole can also be drilled in the center of the first cavity region and the second cavity region.

{Excitation of bulk elastic waves}
In the bulk acoustic wave device 1, when an excitation signal is applied between the lower wiring electrode 116 and the upper wiring electrode 134, an electric field corresponding to the excitation signal is applied to the piezoelectric thin film 124 of the resonator 138 and the resonator 138. A bulk acoustic wave is excited in the piezoelectric thin film 124. Similarly, when an excitation signal is applied between the lower wiring electrode 122 and the upper wiring electrode 134, an electric field corresponding to the excitation signal is applied to the piezoelectric thin film 126 of the resonator 140, and the piezoelectric thin film of the resonator 140. A bulk acoustic wave is excited at 126. The vibration mode used in the resonators 138 and 140 is not particularly limited, and may be either a thickness longitudinal vibration mode or a thickness shear vibration mode.

<2-2 Manufacturing Method of Bulk Acoustic Wave Device 1>
6-18 is a figure explaining the manufacturing method of the bulk acoustic wave apparatus 1 which concerns on 1st Embodiment of this invention. 6-18 is sectional drawing of the bulk acoustic wave apparatus 1 in the middle of manufacture. In the method for manufacturing the bulk acoustic wave device 1 described below, films other than the piezoelectric thin films 124 and 126 can be formed by a known film forming technique such as sputtering deposition or resistance heating deposition.

{Preparation of piezoelectric substrate 158 on which polarization inversion portion 160 is formed}
In manufacturing the bulk acoustic wave device 1, the piezoelectric substrate 158 on which the polarization inversion unit 160 is formed is manufactured. In producing the piezoelectric substrate 158 on which the domain-inverted portion 160 is formed, first, as shown in FIG. 6, a piezoelectric body having an upper surface 152 having a relatively high etching rate and a lower surface 154 having a relatively slow etching rate. A protective film 156 is formed on the lower surface 154 of the substrate 150.

  The two-dimensional region where the protective film 156 is formed is a two-dimensional region where the polarization inversion unit 160 described below is not formed. The protective film 156 may be any film as long as it inhibits proton exchange described below. For example, a tantalum film can be suitably selected as the protective film 156.

  Of course, the piezoelectric material constituting the piezoelectric substrate 150 and the crystal orientation of the piezoelectric substrate 150 are selected according to the piezoelectric material constituting the piezoelectric thin films 124 and 126 and the crystal orientation of the piezoelectric thin films 124 and 126. However, taking into account the use of the above-described principle of processing of a piezoelectric substrate, a piezoelectric substrate in which the polarization direction can be easily reversed, that is, a piezoelectric in which the Curie temperature is relatively low and the thickness direction is the polarization direction. It is desirable to select a body substrate or a piezoelectric substrate whose polarization direction is close to the thickness direction. For example, a Z-plate of lithium tantalate can be suitably selected as the piezoelectric substrate 150.

  Subsequently, as shown in FIG. 7, the polarization direction of the portion exposed to the two-dimensional region where the protective film 156 occupying a part of the lower surface 154 of the piezoelectric substrate 150 is not formed and not exposed to the upper surface 152 is reversed. A piezoelectric substrate 158 is obtained in which a polarization reversal unit 160 whose direction is reversed and a non-polarization reversal unit 162 whose polarization direction is not reversed are formed.

  In the first embodiment, the polarization direction is reversed by a proton exchange method (more generally, an “ion exchange method”). The reversal of the polarization direction by the proton exchange method is performed when, for example, a lithium tantalate Z-plate is selected as the piezoelectric substrate 150, for example, by applying pyrophosphoric acid at about 260 ° C. to a portion that becomes the polarization reversal unit 160. Then, proton exchange is performed on the portion to be, and then heat treatment is performed at about 620 ° C. which is the Curie temperature of lithium tantalate. When the polarization direction is reversed in this way, the depth of the polarization reversal unit 160 can be controlled by the time for proton exchange and the temperature of the heat treatment after proton exchange. Of course, the processing conditions described above vary depending on the type of the piezoelectric substrate 150.

  Subsequently, as shown in FIG. 8, the protective film 156 is removed by etching or the like. Thereby, the piezoelectric substrate 158 on which the polarization inversion portion 160 is formed is completed.

{Production of plate-like structure 170 including support substrate 102}
A plate-like structure 170 including the support substrate 102 is produced separately from the production of the piezoelectric substrate 158 on which the domain inversion unit 160 is formed. In producing the plate-like structure 170 including the support substrate 102, first, as shown in FIG. 9, the upper surface of the material substrate having a flat upper surface and a lower surface is etched to form the non-through holes 104 and 108. The substrate 102 is manufactured. The inside of the non-through holes 104 and 108 is a planned area which is a three-dimensional area that is finally planned to become the cavities 106 and 110.

  Subsequently, as shown in FIG. 10, a sacrificial material film 164 made of a material constituting the sacrificial body 166 is formed on the entire upper surface of the support substrate 102 where the non-through holes 104 and 108 are exposed.

  The material constituting the sacrificial body 166 is not particularly limited, but a material to be removed when a liquid or gas removing agent is applied is selected. For example, a diazonaphthoquinone / novolak resist that can be removed by applying an etching solution such as hydrofluoric acid or an etching gas containing fluorine plasma or the like, or an inorganic material such as silicon, or a developing solution such as tetramethylammonium hydroxide. Select organic materials such as Of course, when removing the sacrifice body 166, elements other than the sacrifice body 166, that is, the support substrate 102, the lower electrode films 112 and 118, the piezoelectric thin films 124 and 126, the upper electrode film 128, the passivation film 136, and the like are removed. The combination of the removing agent, the material constituting the sacrificial body 166, and the material constituting the elements other than the sacrificial body 166 is limited because it must not be damaged. That is, the lower electrode films 112 and 118, the piezoelectric thin films 124 and 126, and the upper electrode films, in which the solubility of the sacrificial body 166 directly affects the elements other than the sacrificial body 166, in particular, the excitation of bulk acoustic waves. Combine the remover and material to be more soluble than 128 remover. Further, when the solubility of the material with respect to the remover is anisotropic, the solubility of the sacrificial body 166 with respect to the remover is higher than the solubility with respect to the remover of elements other than the sacrificial body 166 in terms of orientation and polarity. Choose to be. For example, when hydrofluoric acid is selected as the remover and silicon oxide that dissolves in hydrofluoric acid is selected as the material constituting the sacrificial body 166, the material is substantially dissolved in hydrofluoric acid as the material constituting the lower electrode films 112 and 118 and the upper electrode film 128. As the material constituting the piezoelectric thin films 124 and 126, lithium tantalate that hardly dissolves in hydrofluoric acid, silicon nitride that hardly dissolves in hydrofluoric acid, or the like is selected as the material constituting the passivation film 126. In the case of selecting lithium tantalate having an anisotropic etching rate as a material constituting the piezoelectric thin films 124 and 126, for example, a thinned 36 ° or 47 ° rotated Y plate having a slow etching rate on the main surface is used. use. It is desirable that there is a difference of 10 times or more in etching rate between “dissolving” material and “almost insoluble” material.

  Subsequently, as shown in FIG. 11, the sacrificial material film 164 is polished until the sacrificial material film 164 formed outside the non-through holes 104 and 108 is removed and the upper surface of the support substrate 102 is exposed. Thereby, the support substrate 102 in which the planned region is filled with the sacrifice body 166 is manufactured.

  When the sacrificial material film 164 is formed, it is desirable that the inside of the non-through hole 104 is filled with the sacrificial material film 164 without any gap. Thereby, after polishing the sacrificial material film 164, the upper surface of the sacrificial body 166 and the upper surface of the support substrate 102 are substantially flush with each other, so that the non-through hole 104 in which the interior is filled with the sacrificial body 166 is exposed. The upper surface of the support substrate 102 can be flattened. This contributes to eliminating the gap between the conductive material film 168 and the sacrificial body 166 to be formed later, and flattening the bonding surface of the plate-like structure 170.

  When the inside of the through hole is used as a cavity, the sacrificial body can be injected from the lower surface side of the support substrate 102 or even after the piezoelectric substrate 158 and the plate-like structure 170 are joined. A sacrificial body can be implanted.

  Next, as shown in FIG. 12, a conductive material film 168 made of a material constituting the lower electrode films 112 and 118 is formed on the entire upper surface of the support substrate 102. Thereby, the plate-like structure 170 including the support substrate 102, the sacrificial body 166, and the conductive material film 168 is completed.

  Here, if a piezoelectric substrate is selected as the material substrate, the material substrate can be processed by a processing method similar to the above-described piezoelectric substrate processing method. 19-20 is a figure explaining the production method of the support substrate 102 at the time of employ | adopting the processing method of such a raw material board | substrate. In the manufacturing method of the support substrate 102, first, as shown in FIG. 19, the protective film 178 is formed on the upper surface 174 of the material substrate 172 having the upper surface 174 having a relatively slow etching rate and the lower surface 176 having a relatively fast etching rate. Form. Subsequently, as shown in FIG. 20, the polarization direction of the portion exposed in the two-dimensional region where the protective film 178 occupying a part of the upper surface 174 of the material substrate 172 is reversed is reversed, and the polarization direction is reversed. Thus, the substrate 180 having the polarization inversion portion 182 and the non-polarization inversion portion 184 in which the polarization direction is not inverted is obtained. Subsequently, the protective film 178 and the polarization inversion portion 182 are removed by etching, whereby the support substrate 102 in which the non-through holes 104 and 108 as shown in FIG. 9 are formed is completed. According to such a method for manufacturing the support substrate 102, the equipment used for manufacturing the support substrate 102 and the equipment used for manufacturing the piezoelectric substrate 158 can be shared.

{Junction of piezoelectric substrate 158 and plate-like structure 170}
After producing the piezoelectric substrate 158 and the plate-like structure 170, as shown in FIG. 13, the lower surface of the piezoelectric substrate 158 and the upper surface of the plate-like structure 170 are joined to produce a joined body 172. Since the joining surfaces of the piezoelectric substrate 158 and the plate-like structure 170 are both flat, joining is easy. The bonding between the piezoelectric substrate 158 and the plate-like structure 170 is not particularly limited, but can be performed by surface activation bonding, adhesive bonding, thermocompression bonding, anodic bonding, eutectic bonding, or the like.

{Etching of piezoelectric substrate 158}
After joining the piezoelectric substrate 158 and the plate-like structure 150, as shown in FIG. 14, the piezoelectric substrate 158 is attached to the upper surface 159 while maintaining the joined state of the piezoelectric substrate 158 and the plate-like structure 170. Etching is performed from the side to remove the non-polarization inversion portion 162. When a Z-plate of lithium tantalate is selected as the piezoelectric substrate 150, a mixed liquid of hydrofluoric acid and nitric acid can be used as the etching liquid. As a result, among the piezoelectric substrate 158 having a plate thickness (for example, 50 μm or more) that can withstand its own weight alone, a polarization that is a thin film having a thickness (for example, 10 μm or less) that cannot withstand its own weight. Only the inversion unit 160 remains.

  Subsequently, as shown in FIG. 15, the upper surface of the polarization inversion unit 160 is flattened by ion milling to form the piezoelectric thin films 124 and 126. This ion milling step can be omitted.

  According to such a method of forming the piezoelectric thin films 124 and 126, the film thickness of the piezoelectric thin films 124 and 126 can be controlled by controlling the depth of the polarization inversion portion 160. The film thickness of 126 can be easily controlled, and the film thickness uniformity of the piezoelectric thin films 124 and 126 can be improved. In addition, if the planarization is performed by ion milling, the film thickness uniformity of the piezoelectric thin films 124 and 126 can be further improved.

  Further, if the piezoelectric substrate 158 is etched after the planned space is filled with the sacrificial body 166, the sacrificial body 166 suppresses the upward and downward bending of the piezoelectric material film 154, so that the film thickness of the piezoelectric thin films 124 and 126 is increased. Can be prevented from becoming non-uniform. However, this does not prevent the step of filling the planned space with the sacrifice body 166 from being omitted.

{Formation of lower electrode film 112, upper electrode film 128, and passivation film 136}
After removing the piezoelectric substrate 158, unnecessary portions of the conductive material film 168 are removed by etching to pattern the conductive material film 168 to form lower electrode films 112 and 118, as shown in FIG.

  Subsequently, as shown in FIG. 17, a passivation film 136 is formed. The passivation film 136 protects a region where the passivation film 136 is not formed with a resist film, forms an insulating material film on the entire upper surface of the support substrate 102 over the resist film, and overlays the resist film on the resist film. It is formed by removing the formed insulating material film.

  Subsequently, as shown in FIG. 18, an upper electrode film 128 is formed. The upper electrode film 128 is formed by forming a conductive material film that covers the entire upper surface of the support substrate 102, removing unnecessary portions of the conductive material film by etching, and patterning the conductive material film.

{Removal of sacrificial body 166}
Finally, the sacrificial body 166 inside the non-through holes 104 and 108 is removed. The sacrificial body 166 pierces the via holes 144 and 142, introduces the remover of the sacrificial body 166 into the non-through holes 104 and 108 from the via holes 144 and 142, and causes the remover to act on the sacrificial body 166. Remove. Thereby, the bulk acoustic wave device 1 shown in FIG. 5 is completed.

<3 Second Embodiment>
In the second embodiment, the piezoelectric thin films 224 and 226 are provided on the upper surface that can be used instead of the plate-like structure 170 (FIG. 15) in which the piezoelectric thin films 124 and 126 are formed on the upper surface according to the first embodiment. It relates to the formed plate-like structure 270. FIG. 21 to FIG. 26 are schematic views for explaining a method for producing the plate-like structure 270 in which the piezoelectric thin films 224 and 226 are formed on the upper surface according to the second embodiment. FIGS. 21 to 26 are cross-sectional views of the bulk acoustic wave device in the course of manufacturing.

{Preparation of piezoelectric substrate 258 on which polarization inversion portion 260 is formed}
In manufacturing the plate-like structure 270 having the piezoelectric thin films 224 and 226 formed on the upper surface, the piezoelectric substrate 258 on which the polarization inversion portion 260 is formed is manufactured. In the piezoelectric substrate 258 on which the domain inversion unit 260 is formed, first, as shown in FIG. 21, a piezoelectric substrate 250 having an upper surface 252 having a relatively fast etching rate and a lower surface 254 having a relatively slow etching rate. The polarization direction of the portion exposed on the entire lower surface 254 and not exposed on the upper surface 252 is reversed. As shown in FIG. 22, the polarization inversion unit 260 in which the polarization direction is inverted and the non-polarization inversion unit 262 in which the polarization direction is not inverted are provided. The formed piezoelectric substrate 258 is obtained.

  The piezoelectric material constituting the piezoelectric substrate 250 and the crystal orientation of the piezoelectric substrate 250 can be selected in the same manner as in the first embodiment. Further, the reversal of the polarization direction can be performed in the same manner as in the first embodiment except that the protective film is not formed.

{Junction of piezoelectric substrate 258 and plate-like structure 270}
After producing the plate-like structure 270 including the piezoelectric substrate 258 and the support substrate 202, the sacrificial body 266, and the conductive material film 268, the lower surface of the piezoelectric substrate 258 and the upper surface of the plate-like structure 270 are shown in FIG. And a joined body 272 is manufactured. The piezoelectric substrate 258 and the plate-like structure 270 can be joined in the same manner as in the first embodiment.

{Etching of piezoelectric substrate 258}
After joining the piezoelectric substrate 258 and the plate-like structure 270, as shown in FIG. 24, the piezoelectric substrate 258 is attached to the upper surface 252 while maintaining the joined state of the piezoelectric substrate 258 and the plate-like structure 270. Etching is performed from the side to remove the non-polarized inversion portion 262. Etching of the piezoelectric substrate 258 can be performed in the same manner as in the first embodiment. Accordingly, among the piezoelectric substrate 258 having a plate thickness (for example, 50 μm or more) that can withstand its own weight alone, polarization that is a thin film having a film thickness (for example, 10 μm or less) that cannot withstand its own weight. Only the inversion part 260 remains.

  Subsequently, as illustrated in FIG. 25, the upper surface of the polarization inversion unit 260 is planarized by ion milling to form a piezoelectric material film 261.

{Formation of piezoelectric thin films 224 and 226}
After the piezoelectric substrate 258 is etched, unnecessary portions of the piezoelectric material film 261 are removed by dry etching to pattern the piezoelectric material film 261 to form piezoelectric thin films 224 and 226, as shown in FIG. The plate-like structure 270 in which the piezoelectric thin films 224 and 226 are formed on the upper surface thus obtained is the plate-like structure 170 in which the piezoelectric thin films 124 and 126 are formed on the upper surface according to the first embodiment. Similarly, it can be used for manufacturing bulk acoustic wave devices.

  A manufacturing method of the plate-like structure 170 in which the piezoelectric thin films 124 and 126 are formed on the upper surface according to the first embodiment and the plate-like structure 270 in which the piezoelectric thin films 224 and 226 are formed on the upper surface according to the second embodiment. In the first embodiment, the patterning of the planar shape of the piezoelectric thin films 124 and 126 is performed when the polarization inversion unit 160 is formed, whereas in the second embodiment, the difference from the manufacturing method is the piezoelectric body. The planar patterning of the thin films 224 and 226 is performed after the piezoelectric material film 261 is formed. That is, the patterning of the planar shape of the piezoelectric thin film can be performed either before or after the thin film is formed. In addition, the bulk acoustic wave device can be configured using the piezoelectric thin film formed over the entire surface without patterning the planar shape of the piezoelectric thin film.

<4 Third Embodiment>
The third embodiment relates to a joined body 372 that can be employed instead of the joined body 172 (FIG. 13) according to the first embodiment. FIG. 27 to FIG. 28 are schematic views for explaining a manufacturing method of the joined body 372 according to the third embodiment. 27 to 28 are cross-sectional views of the piezoelectric thin film resonator that is being manufactured.

  In manufacturing the bonded body 372, first, as shown in FIG. 27, a piezoelectric material substrate in which a polarization inversion portion 360 and a non-polarization inversion portion 362 are formed on a conductive material film 368 made of a material constituting the lower electrode film. 358 is formed on the entire lower surface of 358.

  Subsequently, as shown in FIG. 28, the lower surface of the plate-like structure 369 including the piezoelectric substrate 358 and the conductive material film 368 and the upper surface of the plate-like structure 370 including the support substrate 302 and the sacrificial body 360 are joined. A joined body 372 is manufactured.

  The joined body 372 according to the third embodiment can be used for manufacturing a bulk acoustic wave device, similarly to the joined body 172 according to the first embodiment.

  The third embodiment means that a component of the bulk acoustic wave device or a precursor thereof (here, the conductive material film 368) may be added to either side of the piezoelectric thin film and the support substrate. .

<5 Fourth Embodiment>
The fourth embodiment relates to a piezoelectric substrate 458 having a polarization inversion portion 460 that can be employed instead of the piezoelectric substrate 158 having the polarization inversion portion 160 according to the first embodiment. FIG. 29 to FIG. 30 are schematic diagrams for explaining a method of manufacturing the piezoelectric substrate 458 on which the polarization inverting unit 460 according to the fourth embodiment is formed. 29-30 is sectional drawing of the bulk acoustic wave apparatus in the middle of manufacture.

  In producing the piezoelectric substrate 458 on which the domain-inverted portion 460 is formed, first, as shown in FIG. 29, a piezoelectric body having an upper surface 452 having a relatively fast etching rate and a lower surface 454 having a relatively slow etching rate. An electrode film 486 is formed over substantially the entire upper surface 452 of the substrate 450, and an electrode film 488 is formed over part of the lower surface 454.

  The two-dimensional region in which the electrode film 488 is formed is a two-dimensional region in which the polarization inversion unit 460 described below is formed.

  The piezoelectric material constituting the piezoelectric substrate 450 and the crystal orientation of the piezoelectric substrate 450 can be selected in the same manner as in the first embodiment.

  Subsequently, as shown in FIG. 30, the polarization direction of the portion exposed to the two-dimensional region where the electrode film 488 occupying a part of the lower surface 454 of the piezoelectric substrate 450 is formed but not exposed to the upper surface 452 is reversed. A piezoelectric substrate 458 is obtained in which a polarization reversal unit 460 whose direction is reversed and a non-polarization reversal unit 462 whose polarization direction is not reversed are formed.

  In the third embodiment, the polarization direction is reversed by an electric field application method. Therefore, when forming the polarization inversion portion 460, a voltage is applied between the electrode film 486 and the electrode film 488, and an electric field is applied to the piezoelectric substrate 462. Thereby, the piezoelectric substrate 458 on which the polarization inversion portion 460 is formed is completed.

  The piezoelectric substrate 458 on which the domain inversion unit 460 according to the fourth embodiment is formed is used for manufacturing a bulk acoustic wave device, similarly to the piezoelectric substrate 158 on which the domain inversion unit 160 according to the first embodiment is formed. be able to.

  Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention. In particular, it is naturally planned to use a combination of what has been described in the first to fourth embodiments.

It is sectional drawing explaining the principle of a process of a piezoelectric material board | substrate. It is sectional drawing explaining the principle of a process of a piezoelectric material board | substrate. It is sectional drawing explaining the principle of a process of a piezoelectric material board | substrate. It is a flowchart explaining the procedure of a process of a piezoelectric material board. It is sectional drawing of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is sectional drawing explaining the manufacturing method of the bulk acoustic wave apparatus which concerns on 1st Embodiment. It is a figure explaining the preparation methods of a support substrate. It is a figure explaining the preparation methods of a support substrate. It is a figure explaining the processing method of the piezoelectric substrate which concerns on 2nd Embodiment. It is a figure explaining the processing method of the piezoelectric substrate which concerns on 2nd Embodiment. It is a figure explaining the processing method of the piezoelectric substrate which concerns on 2nd Embodiment. It is a figure explaining the processing method of the piezoelectric substrate which concerns on 2nd Embodiment. It is a figure explaining the processing method of the piezoelectric substrate which concerns on 2nd Embodiment. It is a figure explaining the processing method of the piezoelectric substrate which concerns on 2nd Embodiment. It is sectional drawing explaining the manufacturing method of the conjugate | zygote which concerns on 3rd Embodiment. It is sectional drawing explaining the manufacturing method of the conjugate | zygote which concerns on 3rd Embodiment. It is sectional drawing explaining the manufacturing method of the piezoelectric substrate in which the polarization inversion part based on 4th Embodiment was formed. It is sectional drawing explaining the manufacturing method of the piezoelectric substrate in which the polarization inversion part based on 4th Embodiment was formed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bulk acoustic wave apparatus 102 Support substrate 106,110 Cavity 112,118 Lower electrode film 124,126 Piezoelectric thin film 128 Upper electrode film 150,158,172,180,250,258,450,462 Piezoelectric substrate 166 Sacrificial body 170 , 270, 370, 390 Plate-like structure 808, 160, 260, 460 Polarization inversion part

Claims (4)

A method of manufacturing a bulk acoustic wave device in which a resonator having electrode films facing each other across a piezoelectric thin film is separated from a support substrate by a cavity,
(a) The first main surface exposed to the second main surface of the piezoelectric substrate having a first main surface with a relatively high etching rate and a second main surface with a relatively low etching rate. Reversing the polarization direction of the portion not exposed to
(b) After the step (a), the first plate-like structure including the piezoelectric substrate and the second plate-like structure including the support substrate are placed on the second plate-like structure side. Bonding with the second main surface facing;
(c) etching the piezoelectric substrate from the first main surface side while maintaining the state where the first plate-like structure and the second plate-like structure are joined to each other. removing a part other than the part in which the polarization direction is reversed in a);
A method for manufacturing a bulk acoustic wave device. In the manufacturing method of the bulk acoustic wave device according to claim 1,
(d) a step of planarizing the surface of the portion whose polarization direction is reversed in the step (a) remaining after the step (c) by ion milling,
A method for manufacturing a bulk acoustic wave device. In the manufacturing method of the bulk acoustic wave device according to claim 1 or 2,
(e) filling a planned region, which is a three-dimensional region finally planned to become the cavity, with a sacrificial body before etching the piezoelectric substrate;
(f) removing the sacrificial body after etching the piezoelectric substrate;
A method for manufacturing a bulk acoustic wave device. In the manufacturing method of the bulk acoustic wave device according to any one of claims 1 to 3,
The piezoelectric substrate is a Z-plate of lithium tantalate;
Manufacturing method of bulk acoustic wave device.

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