A method for fabricating a cavity-type bulk acoustic resonator

Abstract

This application discloses a method for fabricating a cavity-type bulk acoustic wave resonator, which includes a first substrate, resonator units, and a second substrate. The method comprises the following steps: forming resonator units on the upper surface of the first substrate; excavating a trench on the lower surface of the first substrate, extending the trench through to the upper surface of the first substrate; and bonding a second substrate to the lower surface of the first substrate, thus forming a cavity from the trench. This application forms the resonator units on the upper surface of the first substrate before creating the trench, and the cavity is formed at the trench through the bonding of the first and second substrates. This eliminates the need for a sacrificial layer, allowing for more precise cavity dimensions. It avoids the problem of reduced film quality of functional layers such as piezoelectric layers and structural damage to the device due to sacrificial layer release, which could lead to decreased mechanical stability and electrical performance of the device.

Description

Technical Field

[0001] This application relates to the field of semiconductor manufacturing, and in particular to a method for fabricating a cavity-type bulk acoustic resonator. Background Technology

[0002] The rapid development of wireless mobile communication has led to higher performance requirements for radio frequency (RF) devices. Filters, as a crucial component of the RF front-end, offer advantages such as large bandwidth, low insertion loss, and small size. Among these, thin-film bulk acoustic wave (FBAR) filters have become the mainstream choice due to the high sound velocity and good temperature stability of their piezoelectric thin film materials. FBARs are an important structure of thin-film bulk acoustic wave resonators, boasting advantages such as high resonant frequency, high Q value, and small size for easy integration. They primarily work by creating a suspended thin film and cavity, suspending the piezoelectric thin film above the cavity, confining the resonant signal and energy within the cavity to achieve sound wave transmission and selection. FBARs are mainly constructed in two forms: back-etched and cavity-type. Back-etched FBARs require etching from the back of the substrate to form an air interface; however, because a large portion of the silicon on the substrate is etched away, the mechanical stability of the device is relatively poor. In contrast, cavity-type FBARs offer greater advantages.

[0003] For cavity-type FBARs, there are currently two main fabrication methods: convex arched cavities and recessed cavities. The convex arched cavity method involves first depositing a sacrificial layer and then using wet etching to etch the sacrificial layer into an arched structure. However, the arched cavity requires extremely high stress control technology for the piezoelectric thin film material. If the material's rigidity is insufficient, the electrodes and piezoelectric thin film around the cavity are prone to collapse and deformation, causing stress concentration and potentially leading to transducer breakage. Furthermore, the complete release of the sacrificial layer takes a long time, and the etchant used in the release process can cause some damage to the transducer. The recessed cavity method involves etching a recess into the substrate, filling it with a sacrificial layer, then sequentially fabricating the bottom electrode, piezoelectric layer, top electrode, and passivation layer, and finally releasing the sacrificial layer to obtain the recessed structure. This method also has drawbacks: chemical mechanical polishing is required to ensure that the height of the sacrificial layer inside the shallow trench is consistent with that outside, thus presenting a problem of difficulty in controlling the precision due to the polishing process.

[0004] Therefore, regardless of whether the fabrication method is a convex arched cavity or a grooved cavity, the sacrificial layer needs to be released later. When releasing the sacrificial layer by injecting etchant, it is necessary to pass through a through hole that penetrates the bottom electrode, piezoelectric layer, top electrode and passivation layer. This will damage the structure of the device, and the etchant will corrode other functional layers during the release process, which will cause problems such as low film quality, corrosion residue in the cavity and damage to the device structure. Summary of the Invention

[0005] The purpose of this application is to at least solve one of the technical problems existing in the prior art, and to provide a method for fabricating a cavity-type bulk acoustic resonator, which can improve the dimensional accuracy of the cavity and improve the device structure and performance of the bulk acoustic resonator.

[0006] According to an embodiment of this application, a method for fabricating a cavity-type bulk acoustic resonator is provided, comprising:

[0007] A cavity-type bulk acoustic resonator, the cavity-type bulk acoustic resonator comprising:

[0008] A first substrate has a slot formed therein, with the two ends of the slot extending to the upper and lower surfaces of the first substrate, respectively.

[0009] A resonator unit, comprising a bottom electrode, a piezoelectric layer, and a top electrode, wherein the bottom electrode is located on the upper surface of the first substrate, the piezoelectric layer is located on the upper surface of the bottom electrode, and the top electrode is located on the upper surface of the piezoelectric layer;

[0010] A second substrate, located on the lower surface of the first substrate;

[0011] The fabrication method of the cavity-type bulk acoustic resonator includes the following steps:

[0012] The resonator unit is formed on the upper surface of the first substrate, and the bottom electrode is formed on the upper surface of the first substrate, the piezoelectric layer is formed on the upper surface of the bottom electrode, and the top electrode is formed on the upper surface of the piezoelectric layer.

[0013] The slot is excavated on the lower surface of the first substrate, and the slot extends through to the upper surface of the first substrate;

[0014] The second substrate is bonded to the lower surface of the first substrate, and the slots form a cavity.

[0015] According to an embodiment of this application, the method for forming the bottom electrode further includes the following steps:

[0016] A first conductive material layer is formed on the upper surface of the first substrate;

[0017] A patterned first shielding layer is formed on the upper surface of the first conductive material layer;

[0018] The bottom electrode is obtained by etching the first conductive material layer based on the first shielding layer.

[0019] According to an embodiment of this application, the method for forming the first conductive material layer further includes chemical vapor deposition, physical vapor deposition, and magnetron sputtering.

[0020] According to an embodiment of this application, the method for forming the piezoelectric layer further includes the following steps:

[0021] A piezoelectric material layer is formed on the upper surface of the bottom electrode;

[0022] A patterned second shielding layer is formed on the upper surface of the piezoelectric material layer;

[0023] The piezoelectric layer is obtained by etching the piezoelectric material layer based on the second shielding layer.

[0024] According to an embodiment of this application, the method for etching the piezoelectric material layer is further described as dry etching or wet etching.

[0025] According to an embodiment of this application, the method for forming the top electrode further includes the following steps:

[0026] A second conductive material layer is formed on the upper surface of the piezoelectric layer;

[0027] A patterned third shielding layer is formed on the upper surface of the second conductive material layer;

[0028] The top electrode is obtained by etching the second conductive material layer based on the third shielding layer.

[0029] According to an embodiment of this application, the method for forming the second conductive material layer further includes chemical vapor deposition, physical vapor deposition, and magnetron sputtering.

[0030] According to an embodiment of this application, before bonding the second substrate to the first substrate, the second substrate is cleaned and wet activated, and after bonding, it is annealed.

[0031] According to an embodiment of this application, the bonding between the first substrate and the second substrate is further performed by direct bonding, anodic bonding, or eutectic bonding.

[0032] According to an embodiment of this application, the bonding between the first substrate and the second substrate may or may not involve the introduction of a bonding compound, wherein the bonding compound is one or more of silicon oxide, silicon nitride, aluminum oxide, and aluminum nitride.

[0033] The beneficial effects of the embodiments of this application include at least the following: after forming the resonator unit on the upper surface of the first substrate, the application opens the slot, and forms a cavity in the slot through the bonding of the first substrate and the second substrate. It is not necessary to grow the sacrificial layer first, and the opening size of the cavity can be more precise. This avoids the problem of reduced film quality of functional layers such as piezoelectric layer and damage to the device structure caused by the release of the sacrificial layer, which in turn leads to a decrease in the mechanical stability and electrical performance of the device. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly explained below. Obviously, the described drawings are only a part of the embodiments of this application, and not all of them. Those skilled in the art can obtain other design schemes and drawings based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the fabrication process of the cavity-type bulk acoustic resonator according to an embodiment of this application.

[0036] Reference numerals: 100-first substrate, 110-empty trench, 200-resonator unit, 210-bottom electrode, 220-piezoelectric layer, 230-top electrode, 300-second substrate. Detailed Implementation

[0037] This section will describe in detail the specific embodiments of this application. Preferred embodiments of this application are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of this application, but they should not be construed as limiting the scope of protection of this application.

[0038] In the description of this application, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0039] In the description of this application, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0040] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0041] For cavity-type FBARs, there are currently two main fabrication methods: convex arched cavities and recessed cavities. The convex arched cavity method involves first depositing a sacrificial layer and then using wet etching to etch the sacrificial layer into an arched structure. However, the arched cavity requires extremely high stress control technology for the piezoelectric thin film material. If the material's rigidity is insufficient, the electrodes and piezoelectric thin film around the cavity are prone to collapse and deformation, causing stress concentration and potentially leading to transducer breakage. Furthermore, the complete release of the sacrificial layer takes a long time, and the etchant used in the release process can cause some damage to the transducer. The recessed cavity method involves etching a recess into the substrate, filling it with a sacrificial layer, then sequentially fabricating the bottom electrode, piezoelectric layer, top electrode, and passivation layer, and finally releasing the sacrificial layer to obtain the recessed structure. This method also has drawbacks: chemical mechanical polishing is required to ensure that the height of the sacrificial layer inside the shallow trench is consistent with that outside, thus presenting a problem of difficulty in controlling the precision due to the polishing process.

[0042] Therefore, regardless of whether the fabrication method is a convex arched cavity or a grooved cavity, the sacrificial layer needs to be released later. When releasing the sacrificial layer by injecting etchant, it is necessary to pass through a through hole that penetrates the bottom electrode, piezoelectric layer, top electrode and passivation layer. This will damage the structure of the device, and the etchant will corrode other functional layers during the release process, which will cause problems such as low film quality, corrosion residue in the cavity and damage to the device structure.

[0043] In response, this application proposes a method for fabricating a cavity-type bulk acoustic wave resonator. After forming a resonator unit 200 on the upper surface of a first substrate 100, a cavity 110 is then formed. The cavity is formed at the cavity 110 by bonding the first substrate 100 and the second substrate 300. This eliminates the need to grow a sacrificial layer first, and the cavity size can be more precise, avoiding the situation where the device is affected by incomplete release of the sacrificial layer.

[0044] Reference Figure 1The method for fabricating a cavity-type bulk acoustic wave resonator in the embodiments of this application includes a cavity-type bulk acoustic wave resonator, which includes a first substrate 100, a resonator unit 200, and a second substrate 300.

[0045] The first substrate 100 has a slot 110, with its two ends extending to the upper and lower surfaces of the first substrate 100, respectively. The resonator unit 200 is the core working element of this cavity-type bulk acoustic wave resonator, including a bottom electrode 210, a piezoelectric layer 220, and a top electrode 230. The bottom electrode 210 is located on the upper surface of the first substrate 100, the piezoelectric layer 220 is located on the upper surface of the bottom electrode 210, and the top electrode 230 is located on the upper surface of the piezoelectric layer 220. The second substrate 300 is located on the lower surface of the first substrate 100. When both the resonator unit 200 and the second substrate 300 are bonded to the first substrate 100, the upper and lower ends of the slot 110 are covered by the resonator unit 200 and the second substrate 300, respectively, thus forming a cavity in the slot 110.

[0046] The first substrate 100 and the second substrate 300 are made of materials including Si, SiC, Ge and sapphire; the bottom electrode 210 is made of at least one of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf; the top electrode 230 is made of at least one of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf; the piezoelectric layer 220 is made of one of quartz, lithium niobate, lithium tantalate, aluminum nitride, zinc oxide, barium titanate, potassium dihydrogen phosphate and lead magnesium niobate; the growth methods of the bottom electrode 210 and the top electrode 230 include, but are not limited to, any one or two of PVD, MOCVD, PLD, ALD and MBE.

[0047] The fabrication method of this cavity-type bulk acoustic resonator includes the following steps:

[0048] S100. A resonator unit 200 is formed on the upper surface of the first substrate 100, and a bottom electrode 210 is formed on the upper surface of the first substrate 100, a piezoelectric layer 220 is formed on the upper surface of the bottom electrode 210, and a top electrode 230 is formed on the upper surface of the piezoelectric layer 220.

[0049] S200. A groove 110 is excavated on the lower surface of the first substrate 100, and the groove 110 extends through to the upper surface of the first substrate 100.

[0050] S300. The second substrate 300 is bonded to the lower surface of the first substrate 100, and the slot 110 forms a cavity.

[0051] Furthermore, the method for forming the bottom electrode 210 includes the following steps:

[0052] S110. A first conductive material layer is formed on the upper surface of the first substrate 100. The method for forming the first conductive material layer includes chemical vapor deposition, physical vapor deposition and magnetron sputtering.

[0053] S120. A patterned first shielding layer is formed on the upper surface of the first conductive material layer; the first shielding layer has development characteristics, for example, it can be a photoresist layer or a dry film. The method of patterning the first shielding layer is a commonly used development method, which will not be described in detail here.

[0054] S130. The first conductive material layer is etched based on the first shielding layer to obtain the bottom electrode 210.

[0055] Furthermore, the method for forming the piezoelectric layer 220 includes the following steps:

[0056] S140. A piezoelectric material layer is formed on the upper surface of the bottom electrode 210;

[0057] S150. A patterned second shielding layer is formed on the upper surface of the piezoelectric material layer; the second shielding layer has development characteristics, for example, it can be a photoresist layer or a dry film. The method of patterning the second shielding layer is a common development method, which will not be described in detail here.

[0058] S160. The piezoelectric material layer is etched based on the second shielding layer to obtain the piezoelectric layer 220, wherein the method of etching the piezoelectric material layer is dry etching or wet etching.

[0059] Furthermore, the method for forming the top electrode 230 includes the following steps:

[0060] S170. A second conductive material layer is formed on the upper surface of the piezoelectric layer 220. The method for forming the second conductive material layer includes chemical vapor deposition, physical vapor deposition and magnetron sputtering.

[0061] S180. A patterned third shielding layer is formed on the upper surface of the second conductive material layer;

[0062] S190. The second conductive material layer is etched based on the third shielding layer to obtain the top electrode 230.

[0063] Furthermore, before bonding the second substrate 300 to the first substrate 100, the second substrate 300 is cleaned and wet activated, and then annealed after bonding.

[0064] The bonding between the first substrate 100 and the second substrate 300 is achieved through direct bonding, anodic bonding, or eutectic bonding. The bonding may or may not involve the introduction of a bonding compound. If no bonding compound is introduced, the bonding conditions are high-temperature hot pressing or low-temperature bonding, and the substrates involved in the bonding can be silicon materials, SOI insulating silicon wafers, etc. If a bonding compound is introduced, the bonding compound is specifically one or more of silicon oxide, silicon nitride, aluminum oxide, and aluminum nitride.

[0065] The above is a detailed description of the preferred embodiments of this application. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of this application. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for fabricating a cavity-type bulk acoustic resonator, characterized in that, include: A cavity-type bulk acoustic resonator, the cavity-type bulk acoustic resonator comprising: A first substrate (100) has a slot (110) formed therein, and the two ends of the slot (110) extend to the upper surface and the lower surface of the first substrate (100), respectively. A resonator unit (200) includes a bottom electrode (210), a piezoelectric layer (220), and a top electrode (230). The bottom electrode (210) is located on the upper surface of the first substrate (100), the piezoelectric layer (220) is located on the upper surface of the bottom electrode (210), and the top electrode (230) is located on the upper surface of the piezoelectric layer (220). A second substrate (300) is located on the lower surface of the first substrate (100); The fabrication method of the cavity-type bulk acoustic resonator includes the following steps: The resonator unit (220) is formed on the upper surface of the first substrate (100), the bottom electrode (210) is formed on the upper surface of the first substrate (100), the piezoelectric layer (220) is formed on the upper surface of the bottom electrode (210), and the top electrode (230) is formed on the upper surface of the piezoelectric layer (200). The slot (110) is excavated on the lower surface of the first substrate (100) and the slot (110) extends to the upper surface of the first substrate (100); The second substrate (300) is bonded to the lower surface of the first substrate (100), and the slot (110) forms a cavity.

2. The method for fabricating a cavity-type bulk acoustic resonator according to claim 1, characterized in that: The method for forming the bottom electrode (210) includes the following steps: A first conductive material layer is formed on the upper surface of the first substrate (100); A patterned first shielding layer is formed on the upper surface of the first conductive material layer; The bottom electrode (210) is obtained by etching the first conductive material layer based on the first shielding layer.

3. The method for fabricating a cavity-type bulk acoustic resonator according to claim 2, characterized in that: The methods for forming the first conductive material layer include chemical vapor deposition, physical vapor deposition, and magnetron sputtering.

4. The method for fabricating a cavity-type bulk acoustic resonator according to claim 1, characterized in that: The method for forming the piezoelectric layer (220) includes the following steps: A piezoelectric material layer is formed on the upper surface of the bottom electrode (210); A patterned second shielding layer is formed on the upper surface of the piezoelectric material layer; The piezoelectric material layer is etched based on the second shielding layer to obtain the piezoelectric layer (220).

5. The method for fabricating a cavity-type bulk acoustic resonator according to claim 4, characterized in that: The method for etching the piezoelectric material layer is either dry etching or wet etching.

6. The method for fabricating a cavity-type bulk acoustic resonator according to claim 1, characterized in that: The method for forming the top electrode (230) includes the following steps: A second conductive material layer is formed on the upper surface of the piezoelectric layer (220); A patterned third shielding layer is formed on the upper surface of the second conductive material layer; The second conductive material layer is etched based on the third shielding layer to obtain the top electrode (230).

7. The method for fabricating a cavity-type bulk acoustic resonator according to claim 6, characterized in that: Methods for forming the second conductive material layer include chemical vapor deposition, physical vapor deposition, and magnetron sputtering.

8. The method for fabricating a cavity-type bulk acoustic resonator according to claim 1, characterized in that: Before bonding the second substrate (300) to the first substrate (100), the second substrate (300) is cleaned and wet activated, and then annealed after bonding.

9. The method for fabricating a cavity-type bulk acoustic resonator according to claim 1, characterized in that: The bonding between the first substrate (100) and the second substrate (300) is performed by direct bonding, anodic bonding or eutectic bonding.

10. The method for fabricating a cavity-type bulk acoustic resonator according to claim 1, characterized in that: The bonding between the first substrate (100) and the second substrate (300) may or may not involve the introduction of a bonding compound, wherein the bonding compound is one or more of silicon oxide, silicon nitride, aluminum oxide, and aluminum nitride.

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