Method of forming bulk acoustic wave resonator device

Abstract

A method for forming a bulk acoustic wave resonator device, comprising: forming a first part, comprising: providing a first substrate; forming a piezoelectric layer over the first substrate; forming a first electrode layer over the piezoelectric layer; forming a cavity pre-treatment layer over the piezoelectric layer; forming the cavity pre-treatment layer comprises: forming a sacrificial layer over the piezoelectric layer, the sacrificial layer is made of a metal material; forming a second part, comprising: providing a second substrate; bonding the first part with the second part; removing the first substrate; forming a second electrode layer; removing the sacrificial layer to form a cavity. The bulk acoustic wave resonator device is formed by a bonding process, avoiding the need for planarization of the sacrificial layer, making the material selection of the sacrificial layer more flexible. By selecting a metal material for the sacrificial layer, the metal material can fully react with the release solution during the removal of the sacrificial layer. By controlling the reaction rate, the problem of collapse of the structure above the cavity can be avoided, and the problem of incomplete release of the sacrificial layer can also be avoided, thereby improving the performance of the bulk acoustic wave resonator device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a method for forming a bulk acoustic resonator. Background Technology

[0002] Radio frequency (RF) front-end chips in wireless communication devices include power amplifiers, antenna switches, RF filters, duplexers, multiplexers, and low-noise amplifiers. Among these, RF filters include surface acoustic wave (SAW) filters, bulk acoustic wave (BAW) filters, micro-electro-mechanical system (MEMS) filters, and integrated passive device (IPD) filters.

[0003] Compared to SAW resonators, BAW resonators offer better performance; however, due to their more complex manufacturing process, BAW resonators are more expensive to produce. Furthermore, as wireless communication technology evolves and more frequency bands are used, coupled with the application of technologies such as carrier aggregation, interference between wireless frequency bands is becoming increasingly severe. High-performance BAW technology can solve this problem. With the advent of the 5G era, wireless mobile networks are introducing even higher communication frequency bands, and currently only BAW technology can effectively address the filtering issues at these higher frequencies.

[0004] However, there are still many problems in the formation process of the existing bulk acoustic resonator. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a method for forming a bulk acoustic resonator to improve the performance of the bulk acoustic resonator.

[0006] To address the aforementioned problems, the present invention provides a method for forming a bulk acoustic resonator, comprising: forming a first portion, including: providing a first substrate; forming a piezoelectric layer located above the first substrate, the piezoelectric layer including a first side and a second side opposite to the first side, the first substrate being located on the second side; forming a first electrode layer located on the piezoelectric layer and in contact with the piezoelectric layer, the first electrode layer being located on the first side; forming a cavity pretreatment layer located on the piezoelectric layer and covering the first electrode layer, the cavity pretreatment layer being located on the first side; wherein forming the cavity pretreatment layer includes: forming a sacrificial layer located above the piezoelectric layer, the sacrificial layer covering at least one end of the first electrode layer, the sacrificial layer being made of a metallic material; forming a second portion, including: providing a second substrate; joining the first portion and the second portion, the second substrate being located on the first side; removing the first substrate; forming a second electrode layer located on the second side and in contact with the piezoelectric layer; removing the sacrificial layer to form a cavity, at least one end of the first electrode layer being located within the cavity.

[0007] Optionally, forming the cavity pretreatment layer further includes: before forming the sacrificial layer, forming a first protective layer on the surface of the first electrode layer and a portion of the piezoelectric layer; the sacrificial layer being located on the first protective layer and in contact with the first protective layer; and forming a second protective layer on the surface of the sacrificial layer, the second protective layer being in contact with the first protective layer and surrounding the sacrificial layer.

[0008] Optionally, the material of the first protective layer includes silicon nitride, aluminum nitride, or silicon oxide; the material of the second protective layer includes silicon nitride, aluminum nitride, or silicon oxide.

[0009] Optionally, when the metal material is aluminum, and the materials of the first protective layer and the second protective layer are silicon nitride or silicon oxide, respectively, the etching solution for removing the sacrificial layer includes: hydrogen chloride solution.

[0010] Optionally, when the metal material is titanium, and the materials of the first protective layer and the second protective layer are silicon nitride, the etching solution for removing the sacrificial layer includes: a titanium etching solution with added inhibitors; wherein the titanium etching solution includes: 10% to 40% potassium hydroxide solution and 30% hydrogen peroxide solution, the volume ratio of the potassium hydroxide solution to the hydrogen peroxide solution is 1:1 to 1:2; the inhibitors include: organophosphonic acid, polycarboxylic acid, sodium benzoate, benzotriazole, pyrazole copper, chromate, silicate or molybdate.

[0011] Optionally, when the metal material is titanium and the materials of the first protective layer and the second protective layer are aluminum nitride, the etching solution for removing the sacrificial layer includes: a hydrofluoric acid solution, wherein the volume ratio of hydrofluoric acid to water is 1:10 to 1:120.

[0012] Optionally, when the metal material is copper and the materials of the first protective layer and the second protective layer are aluminum nitride, the etching solution for removing the sacrificial layer includes: ferric chloride solution.

[0013] Optionally, forming the cavity pretreatment layer further includes: forming a first dielectric layer located on the piezoelectric layer and in contact with the piezoelectric layer, wherein the first dielectric layer is located on the first side and covers the first protective layer and the second protective layer.

[0014] Optionally, forming the cavity pretreatment layer further includes: before forming the sacrificial layer, forming a first protective layer on the surface of the first electrode layer and the piezoelectric layer, the first protective layer covering the first electrode layer and the piezoelectric layer; the sacrificial layer being located on the first protective layer and in contact with the first protective layer; and forming a second protective layer on the surface of the sacrificial layer and the first protective layer, the second protective layer covering the sacrificial layer and the first protective layer, the second protective layer being in contact with the first protective layer and surrounding the sacrificial layer.

[0015] Optionally, forming the cavity pretreatment layer further includes: forming a first dielectric layer located on the second protective layer and in contact with the second protective layer, wherein the first dielectric layer is located on the first side and covers the second protective layer.

[0016] Optionally, forming the second part further includes forming a second dielectric layer located on one side of the second substrate.

[0017] Optionally, joining the first part and the second part includes: joining the first dielectric layer and the second dielectric layer to form an intermediate layer located between the second substrate and the piezoelectric layer, the intermediate layer being located on the first side.

[0018] Optionally, the metallic material includes nickel, chromium, cobalt, zinc, titanium, aluminum, or copper.

[0019] Optionally, forming the first step further includes: before forming the piezoelectric layer, forming an electrode material layer located on the first substrate and in contact with the first substrate; the piezoelectric layer located on the electrode material layer and in contact with the electrode material layer, the electrode material layer being located on the second side.

[0020] Optionally, forming the second electrode layer includes: patterning the electrode material layer.

[0021] Optionally, forming the second electrode layer includes: after removing the first substrate, forming an electrode material layer located on the second side and in contact with the piezoelectric layer; and patterning the electrode material layer.

[0022] Optionally, the angle between the sidewall of the first electrode layer and the surface of the piezoelectric layer is less than 60°.

[0023] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0024] In the method for forming the bulk acoustic wave resonator of the present invention, the bulk acoustic wave resonator is formed by a bonding process, avoiding the flattening treatment of the sacrificial layer, thereby allowing for more flexible selection of the sacrificial layer material. The sacrificial layer can be made of a metallic material. During the removal of the sacrificial layer, the metallic material can react fully with the release solution. By controlling the reaction rate between the sacrificial layer and the release solution, the problem of structural collapse above the cavity due to excessively rapid reaction can be avoided, as can the problem of incomplete release of the sacrificial layer due to excessively slow reaction can also be avoided, thereby effectively improving the performance of the bulk acoustic wave resonator.

[0025] Furthermore, forming the cavity pretreatment layer further includes: before forming the sacrificial layer, forming a first protective layer on the surface of the first electrode layer and part of the piezoelectric layer; the sacrificial layer is located on the first protective layer and in contact with the first protective layer; a second protective layer is formed on the surface of the sacrificial layer, the second protective layer is in contact with the first protective layer, and surrounds the sacrificial layer. Alternatively, forming the cavity pretreatment layer further includes: before forming the sacrificial layer, forming a first protective layer on the surface of the first electrode layer and the piezoelectric layer, the first protective layer covering the first electrode layer and the piezoelectric layer; the sacrificial layer is located on the first protective layer and in contact with the first protective layer; a second protective layer is formed on the surface of the sacrificial layer and the first protective layer, the second protective layer covering the sacrificial layer and the first protective layer, the second protective layer is in contact with the first protective layer, and surrounds the sacrificial layer. By forming the first protective layer and the second protective layer, damage to the piezoelectric layer, the first electrode layer, and the second electrode layer during the removal of the sacrificial layer can be effectively reduced, thereby effectively improving the performance of the bulk acoustic wave resonator.

[0026] Furthermore, the angle between the sidewall of the first electrode layer and the surface of the piezoelectric layer is less than 60°, which makes it less likely for cracks to appear at the angle when the first protective layer and the sacrificial layer are deposited, thereby effectively preventing the release solution from contacting the first electrode layer and causing damage to the first electrode layer. Attached Figure Description

[0027] Figure 1 and Figure 2 This is a schematic diagram of the structural steps in the formation of a bulk acoustic resonant device.

[0028] Figures 3 to 15This is a schematic diagram of the structure of each step in the method for forming a bulk acoustic resonator in an embodiment of the present invention;

[0029] Figures 16 to 19 This is a schematic diagram of the steps in the method for forming a bulk acoustic resonator in another embodiment of the present invention. Detailed Implementation

[0030] As described in the background section, the formation process of existing bulk acoustic resonator devices still has many problems. These will be explained in detail below with reference to the accompanying drawings.

[0031] Figure 1 and Figure 2 This is a schematic diagram of the structural steps involved in the formation of a bulk acoustic resonant device.

[0032] Please refer to Figure 1 A substrate 100 is provided; a groove (not shown) is formed in the substrate 100; a sacrificial material layer (not shown) is formed in the groove and on the surface of the substrate 100; the sacrificial material layer is planarized until the surface of the substrate 100 is exposed, forming a sacrificial layer 101; a first electrode layer 102 is formed on the substrate 100, the first electrode layer 102 covering the sacrificial layer 101; a piezoelectric layer 103 is formed on the first electrode layer 102; and a second electrode layer 104 is formed on the piezoelectric layer 103.

[0033] Please refer to Figure 2 After the second electrode layer 104 is formed, the sacrificial layer 101 is removed, and a cavity 105 is formed between the substrate 100 and the first electrode layer 102.

[0034] In this embodiment, the formation of the sacrificial layer 101 requires material deposition followed by planarization. This planarization process employs Chemical Mechanical Polishing (CMP). Because CMP requires consideration of the material's polishing difficulty, the available materials for the sacrificial layer are limited, typically PSG. However, since the substrate 100 is made of silicon, the planarization interface in CMP, containing both silicon and PSG, is prone to dishing at the final polished interface. This dishing can negatively impact the growth quality of the piezoelectric layer 103 and reduce the resonator's quality factor (Q). In addition, since the sacrificial layer 101 of the PSG material is usually removed using a dilute hydrofluoric acid solution, if the concentration of the hydrofluoric acid solution is too high, it will cause significant damage to the piezoelectric layer 103, the first electrode layer 102 and the second electrode layer 104, and may even cause the structure above the cavity 105 to collapse; if the concentration of the hydrofluoric acid solution is too low, the sacrificial layer 101 may not be completely removed, thereby affecting the performance of the resonator.

[0035] Based on this, the present invention provides a method for forming a bulk acoustic wave resonator. The method involves forming the bulk acoustic wave resonator through a bonding process, avoiding the need for hardening the sacrificial layer, thus allowing for more flexible material selection for the sacrificial layer. The sacrificial layer can be made of a metallic material. During the removal of the sacrificial layer, the metallic material can react fully with the release solution. By controlling the reaction rate between the sacrificial layer and the release solution, the problem of structural collapse above the cavity due to excessively rapid reaction can be avoided, as can the problem of incomplete release of the sacrificial layer due to excessively slow reaction can also be avoided, thereby effectively improving the performance of the bulk acoustic wave resonator.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] Figures 3 to 15 This is a schematic diagram of the structure of each step in the method for forming a bulk acoustic resonator in an embodiment of the present invention.

[0038] The first part is formed; for details on the formation process of the first part, please refer to [link / reference]. Figures 3 to 10 .

[0039] Please refer to Figure 3 Provides the first substrate 200.

[0040] The material of the first substrate 200 includes, but is not limited to, at least one of the following: silicon, silicon carbide, and glass.

[0041] In this embodiment, the first substrate 200 is made of silicon.

[0042] Please refer to Figure 4 An electrode material layer 201 is formed on the first substrate 200 and in contact with the first substrate 200.

[0043] The electrode material layer 201 is made of at least one of the following materials: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0044] In this embodiment, the electrode material layer 201 is made of molybdenum.

[0045] Please refer to Figure 5 A piezoelectric layer 202 is formed above the first substrate 200. The piezoelectric layer 202 includes a first side 202a and a second side 202b opposite to the first side 202a. The first substrate 200 is located on the second side 202b.

[0046] In this embodiment, the piezoelectric layer 202 is located on the electrode material layer 201, and the electrode material layer 201 is located on the second side 202b and is in contact with the piezoelectric layer 202.

[0047] The piezoelectric layer 202 is made of at least one of the following materials: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0048] In this embodiment, the piezoelectric layer 202 is made of aluminum nitride.

[0049] Please refer to Figure 6 A first electrode layer 203 is formed on the piezoelectric layer 202 and in contact with the piezoelectric layer 202. The first electrode layer 203 is located on the first side 202a.

[0050] The material of the first electrode layer 203 includes, but is not limited to, at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0051] In this embodiment, the material of the first electrode layer 203 is molybdenum.

[0052] In this embodiment, the angle between the sidewall of the first electrode layer 203 and the surface of the piezoelectric layer 202 is less than 60°.

[0053] After the first electrode layer 203 is formed, a cavity pretreatment layer is formed on the piezoelectric layer 202, covering the first electrode layer 203. The cavity pretreatment layer is located on the first side 202a. Please refer to [link to documentation] for the specific formation process of the cavity pretreatment layer. Figures 7 to 10 .

[0054] Please refer to Figure 7A first protective layer 204 is formed on the surface of the first electrode layer 203 and the piezoelectric layer 202, and the first protective layer covers the first electrode layer 203 and the piezoelectric layer 202.

[0055] The material of the first protective layer includes silicon nitride, aluminum nitride, or silicon oxide.

[0056] In other embodiments, the first protective layer may be formed only on the surface of the first electrode layer and a portion of the piezoelectric layer.

[0057] Please refer to Figure 8 A sacrificial layer 205 is formed above the piezoelectric layer 202, and the sacrificial layer 205 covers at least one end of the first electrode layer 203. The material of the sacrificial layer 205 is a metallic material.

[0058] In this embodiment, the sacrificial layer 205 is located on the first protective layer 204 and is in contact with the first protective layer 204.

[0059] In this embodiment, the method for forming the sacrificial layer 205 includes: forming a photoresist layer (not shown) on the first protective layer 204, wherein the photoresist layer exposes a region for forming the sacrificial layer 205; forming a sacrificial material layer (not shown) on the first protective layer 204 and the photoresist layer; and removing the photoresist layer and the sacrificial material layer located on the photoresist layer using a stripping process to form the sacrificial layer 205.

[0060] In this embodiment, the metallic material includes: nickel, chromium, cobalt, zinc, titanium, aluminum, or copper.

[0061] Please refer to Figure 9 A second protective layer 206 is formed on the surface of the sacrificial layer 205 and the first protective layer 204. The second protective layer 206 covers the sacrificial layer 205 and the first protective layer 204, and the second protective layer 206 is in contact with the first protective layer 204. The first protective layer 204 and the second protective layer 206 surround the sacrificial layer 205.

[0062] The material of the second protective layer 206 includes silicon nitride, aluminum nitride, or silicon oxide.

[0063] In other embodiments, the second protective layer may be formed only on the surface of the sacrificial layer, the second protective layer covering the sacrificial layer, the second protective layer contacting the first protective layer, and the first and second protective layers surrounding the sacrificial layer.

[0064] Please refer to Figure 10A first dielectric layer 207 is formed, located on the second protective layer 206 and in contact with the second protective layer 206. The first dielectric layer 207 is located on the first side 202a and covers the second protective layer 206.

[0065] The material of the first dielectric layer 207 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon.

[0066] The polymers include, but are not limited to, at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), and polyimide.

[0067] The insulating dielectric includes, but is not limited to, at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, and titanium oxide.

[0068] In this embodiment, the material of the first dielectric layer 207 is silicon dioxide.

[0069] In other embodiments, when the first protective layer and the second protective layer do not completely cover the piezoelectric layer, the first dielectric layer may also be in contact with the piezoelectric layer, located on the first side, and covering the first protective layer, the second protective layer and the piezoelectric layer.

[0070] After the first part is formed, the second part is formed. Please refer to [link / reference needed] for the specific formation process of the second part. Figures 11 to 12 .

[0071] Please refer to Figure 11 Provides a second substrate 208.

[0072] The material of the second substrate 208 includes, but is not limited to, at least one of the following: silicon, silicon carbide, and glass.

[0073] In this embodiment, the material of the second substrate 208 is silicon.

[0074] Please refer to Figure 12 A second dielectric layer 209 is formed, located on one side of the second substrate 208.

[0075] The material of the second dielectric layer 209 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon.

[0076] The polymers include, but are not limited to, at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), and polyimide.

[0077] The insulating dielectric includes, but is not limited to, at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, and titanium oxide.

[0078] In this embodiment, the material of the second dielectric layer 209 is silicon dioxide.

[0079] Please refer to Figure 13 The first part and the second part are joined together, and the second base 208 is located on the first side 202a.

[0080] In this embodiment, joining the first part and the second part includes joining the first dielectric layer 207 and the second dielectric layer 209 to form an intermediate layer located between the second substrate 208 and the piezoelectric layer 202, wherein the intermediate layer is located on the first side 202a.

[0081] In this embodiment, bonding the first dielectric layer 207 and the second dielectric layer 209 includes: bonding or adhesiveting the first dielectric layer 207 and the second dielectric layer 209.

[0082] Please continue to refer to this. Figure 13 In this embodiment, after joining the first part and the second part, the method further includes removing the first substrate 200.

[0083] In this embodiment, the first substrate 200 is removed using a thinning process and an etching process.

[0084] Please refer to Figure 14 A second electrode layer 210 is formed, located on the second side 202b, and in contact with the piezoelectric layer 202.

[0085] In this embodiment, forming the second electrode layer 210 includes: performing patterning processing on the electrode material layer 201.

[0086] Please refer to Figure 15 After the second electrode layer 210 is formed, the sacrificial layer 205 is removed to form a cavity 211, with at least one end of the first electrode layer 203 located in the cavity 211.

[0087] In this embodiment, the bulk acoustic wave resonator is formed through a bonding process, avoiding the need for hardening treatment of the sacrificial layer 205, thus allowing for more flexible material selection for the sacrificial layer 205. The sacrificial layer 205 can be made of metal, which allows for sufficient reaction with the release solution during removal. By controlling the reaction rate between the sacrificial layer 205 and the release solution, the problem of structural collapse above the cavity 211 due to excessively rapid reaction can be avoided, as can the problem of incomplete release of the sacrificial layer 205 due to excessively slow reaction can also be avoided, thereby effectively improving the performance of the bulk acoustic wave resonator.

[0088] In this embodiment, since the angle between the sidewall of the first electrode layer 203 and the surface of the piezoelectric layer 202 is less than 60°, cracks are less likely to occur at the angle when the first protective layer 204 and the sacrificial layer 205 are deposited, thereby effectively preventing the release solution from contacting the first electrode layer 203 and causing damage to the first electrode layer 203.

[0089] In this embodiment, by forming the first protective layer 204 and the second protective layer 206, the damage to the piezoelectric layer 202, the first electrode layer 210 and the first electrode layer 203 during the removal of the sacrificial layer 205 can be effectively reduced, thereby effectively improving the performance of the bulk acoustic resonator.

[0090] In one specific embodiment, when the metal material is aluminum and the materials of the first protective layer 204 and the second protective layer 206 are silicon nitride or silicon oxide, respectively, the etching solution for removing the sacrificial layer 205 includes: hydrogen chloride solution.

[0091] In one specific embodiment, when the metal material is titanium and the materials of the first protective layer 204 and the second protective layer 206 are silicon nitride, the etching solution for removing the sacrificial layer 205 includes: a titanium etching solution with added inhibitors; wherein, the titanium etching solution includes: 10% to 40% potassium hydroxide solution and 30% hydrogen peroxide solution, the volume ratio of 10% to 40% potassium hydroxide solution to 30% hydrogen peroxide solution is 1:1 to 1:2; the inhibitors include: organophosphonic acid, polycarboxylic acid, sodium benzoate, benzotriazole, pyrazole copper, chromate, silicate or molybdate.

[0092] In one specific embodiment, when the metal material is titanium and the materials of the first protective layer 204 and the second protective layer 206 are aluminum nitride, the etching solution for removing the sacrificial layer 205 includes: a hydrofluoric acid solution, wherein the volume ratio of hydrofluoric acid to water is 1:10 to 1:120.

[0093] In one specific embodiment, when the metal material is copper and the materials of the first protective layer 204 and the second protective layer 206 are aluminum nitride, the etching solution for removing the sacrificial layer 205 includes: ferric chloride solution.

[0094] Figures 16 to 19 This is a schematic diagram of the steps in the method for forming a bulk acoustic resonator in another embodiment of the present invention.

[0095] This embodiment is based on the above embodiments. Figure 3The formation of the bulk acoustic resonator device will continue to be described above. The difference in this embodiment compared to the previous embodiment is that the formation of the first part does not include the formation of the electrode material layer; the electrode material layer is formed after the first substrate is removed. For the specific formation process, please refer to [link to documentation]. Figures 16 to 19 .

[0096] Please refer to Figure 16 A piezoelectric layer 202 is formed on the first substrate 200. The piezoelectric layer 202 includes a first side 202a and a second side 202b opposite to the first side 202a. The first substrate 200 is located on the second side 202b.

[0097] In this embodiment, the piezoelectric layer 202 is in contact with the first substrate 200.

[0098] In this embodiment, the material of the piezoelectric layer 202 is described in reference to [reference needed]. Figure 5 The relevant explanations will not be repeated here.

[0099] Please continue to refer to this. Figure 16 In this embodiment, after forming the piezoelectric layer 202, a first electrode layer 203 and a cavity pretreatment layer are formed. For details regarding the material of the first electrode layer 203, the specific formation process of the cavity pretreatment layer, and the material selection and function of each part of the cavity pretreatment layer, please refer to [reference needed]. Figures 6 to 10 The relevant explanations have already been provided and will not be repeated here.

[0100] Please refer to Figure 17 After the first part is formed, the second part is formed.

[0101] In this embodiment, please refer to the specific formation process of the second part, as well as the material selection and function of each part of the second part. Figures 11 to 12 The relevant explanations will not be repeated here.

[0102] Please continue to refer to this. Figure 17 In this embodiment, after forming the second part, the first part and the second part are joined, and the first substrate 200 is removed. For process selection for joining the first part and the second part, and for process selection for removing the first substrate 200, please refer to [reference needed]. Figure 13 The relevant explanations have already been provided and will not be repeated here.

[0103] Please refer to Figure 18 After removing the first substrate 200, an electrode material layer 201 is formed, located on the second side 202b, in contact with the piezoelectric layer 202.

[0104] In this embodiment, please refer to the material selection for the electrode material layer. Figure 4The relevant explanations will not be repeated here.

[0105] Please refer to Figure 19 The electrode material layer 201 is patterned to form a second electrode layer 210; after the second electrode layer 210 is formed, the sacrificial layer 205 is removed to form a cavity 211, and at least one end of the first electrode layer 203 is located in the cavity 211.

[0106] In this embodiment, please refer to the specific details regarding the process selection for removing the sacrificial layer 205 and the role of the bonding process in forming the bulk acoustic resonator. Figure 15 The relevant explanations will not be repeated here.

[0107] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for forming a bulk acoustic resonator, characterized in that, include: Forming a first part includes: providing a first substrate; forming a piezoelectric layer above the first substrate, the piezoelectric layer including a first side and a second side opposite to the first side, the first substrate being located on the second side; forming a first electrode layer on the piezoelectric layer and in contact with the piezoelectric layer, the first electrode layer being located on the first side; forming a cavity pretreatment layer on the piezoelectric layer and covering the first electrode layer, the cavity pretreatment layer being located on the first side; wherein forming the cavity pretreatment layer includes: forming a sacrificial layer above the piezoelectric layer, the sacrificial layer covering at least one end of the first electrode layer, the sacrificial layer being made of a metallic material; Forming the second part includes: providing a second base; The first part and the second part are joined together, with the second base located on the first side; Remove the first substrate; A second electrode layer is formed on the second side, in contact with the piezoelectric layer; The sacrificial layer is removed to form a cavity, with at least one end of the first electrode layer located within the cavity; The formation of the cavity pretreatment layer further includes: before forming the sacrificial layer, forming a first protective layer on the surface of the first electrode layer and at least a portion of the piezoelectric layer; the sacrificial layer being located on the first protective layer and in contact with the first protective layer; and forming a second protective layer on the surface of the sacrificial layer, the second protective layer being in contact with the first protective layer and surrounding the sacrificial layer.

2. The method for forming a bulk acoustic resonator as described in claim 1, characterized in that, The material of the first protective layer includes silicon nitride, aluminum nitride, or silicon oxide; the material of the second protective layer includes silicon nitride, aluminum nitride, or silicon oxide.

3. The method for forming a bulk acoustic resonator as described in claim 2, characterized in that, When the metal material is aluminum, and the materials of the first protective layer and the second protective layer are silicon nitride or silicon oxide, respectively, the etching solution for removing the sacrificial layer includes: hydrogen chloride solution.

4. The method for forming a bulk acoustic resonator as described in claim 2, characterized in that, When the metal material is titanium, and the materials of the first protective layer and the second protective layer are silicon nitride, the etching solution for removing the sacrificial layer includes: a titanium etching solution with added inhibitors; wherein the titanium etching solution includes: 10% to 40% potassium hydroxide solution and 30% hydrogen peroxide solution, and the volume ratio of the potassium hydroxide solution to the hydrogen peroxide solution is 1:1 to 1:2; the inhibitors include: organophosphonic acid, polycarboxylic acid, sodium benzoate, benzotriazole, pyrazole copper, chromate, silicate or molybdate.

5. The method for forming a bulk acoustic resonator as described in claim 2, characterized in that, When the metal material is titanium, and the materials of the first protective layer and the second protective layer are aluminum nitride, the etching solution for removing the sacrificial layer includes: a hydrofluoric acid solution, wherein the volume ratio of hydrofluoric acid to water is 1:10 to 1:

120.

6. The method for forming a bulk acoustic resonator as described in claim 2, characterized in that, When the metal material is copper, and the materials of the first protective layer and the second protective layer are aluminum nitride, the etching solution for removing the sacrificial layer includes: ferric chloride solution.

7. The method for forming a bulk acoustic resonator as described in claim 1, characterized in that, The first protective layer is located on the surface of a portion of the piezoelectric layer. The cavity pretreatment layer further includes: forming a first dielectric layer located on the piezoelectric layer and in contact with the piezoelectric layer. The first dielectric layer is located on the first side and covers the first protective layer and the second protective layer.

8. The method for forming a bulk acoustic resonator as described in claim 1, characterized in that, The first protective layer covers the first electrode layer and the piezoelectric layer; the second protective layer is also formed on the surface of the first protective layer, the second protective layer covers the sacrificial layer and the first protective layer, the second protective layer is in contact with the first protective layer, and surrounds the sacrificial layer.

9. The method for forming a bulk acoustic resonator as described in claim 8, characterized in that, The formation of the cavity pretreatment layer further includes: forming a first dielectric layer located on the second protective layer and in contact with the second protective layer, wherein the first dielectric layer is located on the first side and covers the second protective layer.

10. The method for forming a bulk acoustic resonator as described in claim 7 or 9, characterized in that, The second step also includes forming a second dielectric layer located on one side of the second substrate.

11. The method for forming a bulk acoustic resonator as described in claim 10, characterized in that, Joining the first part and the second part includes: joining the first dielectric layer and the second dielectric layer to form an intermediate layer located between the second substrate and the piezoelectric layer, the intermediate layer being located on the first side.

12. The method for forming a bulk acoustic resonator as described in claim 1, characterized in that, The metallic materials include: nickel, chromium, cobalt, zinc, titanium, aluminum, or copper.

13. The method for forming a bulk acoustic resonator as described in claim 1, characterized in that, The formation of the first part further includes: before forming the piezoelectric layer, forming an electrode material layer located on the first substrate and in contact with the first substrate; the piezoelectric layer located on the electrode material layer and in contact with the electrode material layer, the electrode material layer being located on the second side.

14. The method for forming a bulk acoustic resonator as described in claim 13, characterized in that, Forming the second electrode layer includes: patterning the electrode material layer.

15. The method for forming a bulk acoustic resonator as described in claim 1, characterized in that, Forming the second electrode layer includes: after removing the first substrate, forming an electrode material layer located on the second side and in contact with the piezoelectric layer; and performing patterning processing on the electrode material layer.

16. The method for forming a bulk acoustic resonator as described in claim 1, characterized in that, The angle between the sidewall of the first electrode layer and the surface of the piezoelectric layer is less than 60°.

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