Bulk acoustic resonator, and preparation method therefor

Abstract

The present invention relates to the technical field of radio frequency communications. Provided are a bulk acoustic resonator, and a preparation method therefor. The preparation method comprises the following steps: step S1, performing mask-aligned ultraviolet exposure on a photosensitive glass substrate; step S2, annealing the photosensitive glass substrate to form a crystallized sacrificial layer; step S3, growing and forming a seed layer on the photosensitive glass substrate; step S4, growing a bottom electrode on the seed layer; step S5, growing and forming a piezoelectric material layer on the upper surface of the bottom electrode and the upper surface of the seed layer; step S6, growing a top electrode on the upper surface of the piezoelectric material layer; step S7, etching the piezoelectric material layer to expose the bottom electrode; step S8, performing etching to form a through hole; and step S9, releasing an etching gas or solution via the through hole to etch the sacrificial layer, so as to form a cavity. The present invention can reduce process steps, lower the process difficulty and costs, decrease the insertion loss of a resonator, and improve the structural stability.

Description

Bulk acoustic resonator and method for manufacturing the same TECHNICAL FIELD

[0001] The present application relates to the field of radio frequency communication, and in particular to a method for manufacturing a bulk acoustic resonator and the bulk acoustic resonator. BACKGROUND

[0002] With the rapid development of 5G technology, filters as core components of radio frequency front-end continue to move towards high frequency, low loss and miniaturization. In the existing technology, the cavity type film bulk acoustic resonator (FBAR) based on piezoelectric material has been widely used in the field of radio frequency communication due to its high quality factor (Q), high operating frequency, small size and low power consumption. The typical structure of the cavity type film bulk acoustic resonator from bottom to top is substrate material, cavity, lower electrode, piezoelectric material and upper electrode. The cavity is a necessary structure for this type of resonator, which reflects the acoustic waves generated by the vibration of the piezoelectric material to ensure the ultra-high performance of the resonator.

[0003] The typical scheme for forming the cavity of the existing cavity type film bulk acoustic resonator is to form the cavity on the surface of the substrate material by photolithography and etching in advance, then fill the cavity with a sacrificial layer, and use the chemical mechanical polishing (CMP) process to make the sacrificial layer flush with the surface of the substrate, then generate electrodes and piezoelectric layers on the upper surface, and finally release the sacrificial layer to form the cavity.

[0004] However, the above-mentioned traditional process needs to form the cavity in advance, then fill the cavity, and finally release the sacrificial layer to form the cavity. This multiple release and filling increases the process steps and difficulty, increases the process cost, and reduces the device yield. In order to improve the quality of the subsequent functional layer film, the CMP process is used to polish the surface of the sacrificial layer to the nanometer level, which is complex and difficult, and seriously affects the device yield. SUMMARY

[0005] The embodiments of the present application provide a method for manufacturing a bulk acoustic resonator to solve the problems of multiple process steps, high difficulty, high cost and poor structure quality of the existing resonator cavity.

[0006] In a first aspect, the embodiments of the present application provide a method for manufacturing a bulk acoustic resonator, the bulk acoustic resonator comprising a photosensitive glass substrate, a cavity, a seed layer, a lower electrode, a piezoelectric material layer and an upper electrode, the upper surface of the photosensitive glass substrate being sequentially stacked with the seed layer, the lower electrode, the piezoelectric material layer and the upper electrode, and the cavity being formed in the photosensitive glass substrate; the manufacturing method comprises the following steps:

[0007] Step S1, providing a photosensitive glass substrate, and the photosensitive glass substrate is exposed to ultraviolet light under a mask;

[0008] Step S2, annealing the exposed photosensitive glass substrate to form a crystallized sacrificial layer;

[0009] Step S3, growing a seed layer on the upper surface of the photosensitive glass substrate;

[0010] Step S4, growing a metal on the upper surface of the seed layer and patterning to form a lower electrode, and etching the lower electrode to expose the seed layer; wherein one end of the lower electrode corresponds to one end of the photosensitive glass substrate, and the other end of the lower electrode corresponds to the sacrificial layer;

[0011] Step S5, growing a piezoelectric material layer on the upper surface of the lower electrode and the upper surface of the seed layer, and etching the piezoelectric material layer to expose the lower electrode;

[0012] Step S6, growing a metal on the upper surface of the piezoelectric material layer and patterning to form an upper electrode, and etching part of the upper electrode to expose the piezoelectric layer; wherein the orthographic projection of the etched upper electrode is located entirely in the other end of the sacrificial layer and the photosensitive glass substrate;

[0013] Step S7, etching the piezoelectric material layer to expose the lower electrode;

[0014] Step S8, etching the upper electrode, the piezoelectric layer, the lower electrode and the seed layer in turn to release at least one via hole to the upper surface of the sacrificial layer;

[0015] Step S9, releasing etching gas or solution through the via hole to etch the sacrificial layer to form a cavity.

[0016] Preferably, in step S2, the etching selectivity ratio of the sacrificial layer to the unexposed photosensitive glass substrate is 30:1-50:1.

[0017] Preferably, the seed layer, the lower electrode, the piezoelectric layer and the upper electrode are all grown by magnetron sputtering or chemical vapor deposition.

[0018] Preferably, in step S4, the lower electrode is etched by photolithography stripping or photolithography etching to expose the seed layer.

[0019] Preferably, in step S5, the piezoelectric material layer is etched by gas or solution to expose the lower electrode.

[0020] Preferably, the seed layer and the piezoelectric layer are one or more combinations of lithium tantalate, lithium niobate, aluminum nitride and zinc oxide.

[0021] Preferably, the thickness of the seed layer is 0.01-0.2um, the thickness of the piezoelectric layer is 0.1-5um, and the thickness of the lower electrode and the thickness of the upper electrode are both 0.1-1um.

[0022] Preferably, the lower electrode and the upper electrode are both an alloy formed by one or more of molybdenum, aluminum, tungsten, platinum and titanium.

[0023] Preferably, the depth of the cavity is 0.1-10um, and the width of the cavity is 50-400um.

[0024] Preferably, the depth of the cavity can be controlled by exposure time and dose, and the shape of the cavity is arbitrary.

[0025] In a second aspect, an embodiment of the present application provides a bulk acoustic wave resonator, which is made by the method for making a bulk acoustic wave resonator described above; the structure of the bulk acoustic wave resonator comprises, from bottom to top, a photosensitive glass substrate, a cavity, a seed layer, a lower electrode, a piezoelectric material layer and an upper electrode.

[0026] The photosensitive glass substrate has a front surface and a back surface; the seed layer, the lower electrode, the upper electrode and the piezoelectric material layer are located above the front surface of the photosensitive glass substrate; the lower electrode, the piezoelectric material layer and the upper electrode are located directly above the cavity; and the cavity is recessed in the front surface of the photosensitive glass substrate.

[0027] In an embodiment of the present application, by the steps S1-S9 described above, by using the crystallized photosensitive glass as a sacrificial layer, without adding an additional sacrificial layer and without CMP process, not only the process steps are reduced, the process difficulty is lowered and the cost is reduced, but also the thin film quality is improved, the resonator insertion loss is reduced and the structural stability is improved; meanwhile, the photosensitive glass substrate of the present application is an electrical insulating material with low parasitic capacitance and resistance, without separately depositing an electrical insulating layer, which reduces the process steps, lowers the process difficulty and reduces the cost, reduces the resonator insertion loss and improves the structural stability. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort based on these drawings.

[0029] Fig. 1 is a flow chart of the method for making a bulk acoustic wave resonator provided by an embodiment of the present application;

[0030] Fig. 2a is a flowchart of step S1 according to an embodiment of the present application;

[0031] Fig. 2b is a flowchart of step S2 according to an embodiment of the present application;

[0032] Fig. 2c is a flowchart of step S3 according to an embodiment of the present application;

[0033] Fig. 2d is a flowchart of step S4 according to an embodiment of the present application;

[0034] Fig. 2e is a flowchart of step S5 according to an embodiment of the present application;

[0035] Fig. 2f is a flowchart of step S6 according to an embodiment of the present application;

[0036] Fig. 2g is a flowchart of step S7 according to an embodiment of the present application;

[0037] Fig. 2h is a flowchart of step S8 according to an embodiment of the present application;

[0038] Fig. 2i is a flowchart of step S9 according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, any person skilled in the art can obtain other embodiments without creative effort, which are within the scope of protection of the present application.

[0040] Embodiment one

[0041] In combination with Figs. 1-2i, the present application provides a preparation method of a bulk acoustic wave resonator, which comprises a photosensitive glass substrate 1, a cavity 2, a seed layer 4, a lower electrode 5, a piezoelectric material layer 6 and an upper electrode 7. The upper surface of the photosensitive glass substrate 1 is sequentially stacked with the seed layer 4, the lower electrode 5, the piezoelectric material layer 6 and the upper electrode 7. The cavity 2 is formed in the photosensitive glass substrate 1. The preparation method comprises the following steps:

[0042] Step S1, providing a photosensitive glass substrate 1, and the photosensitive glass substrate 1 is exposed to ultraviolet light under a mask.

[0043] The photosensitive glass is an electrically insulating glass. After ultraviolet exposure and annealing, the exposed area is crystallized, while the unexposed area is not crystallized. The cavity 2 is formed by high etching selectivity, which has been maturely applied in the technical field of MEMS and other technologies.

[0044] The mask pattern is transferred to the photosensitive glass substrate 1, and the pattern can be any shape according to requirements, not only a rectangle or a circle.

[0045] Step S2, annealing the exposed photosensitive glass substrate 1 to form a crystallized sacrificial layer 3.

[0046] The photosensitive glass substrate 1 is an electrically insulating material with low dielectric constant and low dielectric loss, low parasitic capacitance and resistance, and can effectively reduce device loss; after ultraviolet exposure and annealing, a crystallized photosensitive glass is formed, which is the sacrificial layer 3 described above.

[0047] The photosensitive glass substrate 1 is exposed to ultraviolet light, and the exposed photosensitive glass substrate 1 is annealed at high temperature to realize direct transfer of the pattern, without photolithography process, and reduce the process steps.

[0048] Step S3, growing a seed layer 4 on the upper surface of the photosensitive glass substrate 1.

[0049] The seed layer 4 is directly grown on the surface of the photosensitive glass substrate 1 with a thickness of several nanometers, and the thin film growth quality is high, which can effectively improve the device performance and yield.

[0050] Preferably, step S3 is performed first, and step S2 is performed, without affecting the simplicity of the process and the performance of the device.

[0051] Step S4, growing a metal and patterning a lower electrode 5 on the upper surface of the seed layer 4, and etching the lower electrode 5 to expose the seed layer 4; one end of the lower electrode 5 corresponds to one end of the photosensitive glass substrate 1, and the other end of the lower electrode 5 corresponds to the sacrificial layer 3.

[0052] Step S5, growing a piezoelectric material layer 6 on the upper surface of the lower electrode 5 and the upper surface of the seed layer 4, and etching the piezoelectric material layer 6 to expose the lower electrode 5.

[0053] Step S6, growing a metal and patterning an upper electrode 7 on the upper surface of the piezoelectric material layer 6, and etching part of the upper electrode 7 to expose the piezoelectric layer; the orthographic projection of the etched upper electrode 7 is located at the other end of the sacrificial layer 3 and the photosensitive glass substrate 1.

[0054] Step S7, etching the piezoelectric material layer 6 to expose the lower electrode 5.

[0055] Step S8, etching the upper electrode 7, the piezoelectric layer, the lower electrode 5 and the seed layer 4 in sequence to release at least one through hole 8 to the upper surface of the sacrificial layer 3.

[0056] The inner wall of the through hole 8 can be plated with copper, so that the upper electrode 7, the piezoelectric layer, the lower electrode 5 and the seed layer 4 are electrically connected.

[0057] Optionally, the through hole 8 is two oppositely arranged through holes, and the end of the through hole 8 reaches the sacrificial layer 3.

[0058] In step S9, the etching gas or solution is released through the through hole 8 to etch the sacrificial layer 3 to form the cavity 2. Optionally, the crystallized glass can be selectively etched away through this step to obtain a desired cavity structure.

[0059] The crystallized photosensitive glass serving as the sacrificial layer 3 is formed from the material of the photosensitive glass substrate 1, there is no need to pre-etch the cavity 2, there is no need to coat and fill the cavity 2, the process steps are simple, and the yield of finished products is high.

[0060] Specifically, through the above steps S1-S9, the crystallized photosensitive glass is used as the sacrificial layer 3, without adding a sacrificial layer 3, and without the CMP process, which not only reduces the process steps, reduces the process difficulty and reduces the cost, but also improves the thin film quality, reduces the insertion loss of the resonator, and improves the structural stability. At the same time, the photosensitive glass substrate 1 of the present application is an electrical insulating material with low parasitic capacitance and resistance, without the need to deposit a separate electrical insulating layer, which reduces the process steps, reduces the process difficulty and reduces the cost, reduces the insertion loss of the resonator, and improves the structural stability.

[0061] In the present embodiment, in step S2, the etching selectivity ratio of the sacrificial layer 3 to the unexposed photosensitive glass substrate 1 is 30:1-50:1.

[0062] The exposed area of the electrical insulating glass is crystallized after ultraviolet exposure and annealing, while the unexposed area is not crystallized, the etching liquid such as HF acid has a selectivity ratio of 30-50:1 for the exposed area and the unexposed area, and the cavity 2 is formed through the high etching selectivity ratio, which has mature applications in the technical field of MEMS.

[0063] In the present embodiment, the seed layer 4, the lower electrode 5, the piezoelectric layer and the upper electrode 7 are all grown by magnetron sputtering or chemical vapor deposition. The thin film growth quality is high, which effectively improves the device performance and yield.

[0064] In the present embodiment, in step S4, the lower electrode 5 is etched by photolithography stripping or photolithography etching to expose the seed layer 4.

[0065] In the present embodiment, in step S5, the piezoelectric material layer 6 is exposed to the lower electrode 5 by gas or solution etching.

[0066] In the embodiment, the seed layer 4 and the piezoelectric layer are one or more combinations of lithium tantalate, lithium niobate, aluminum nitride and zinc oxide.

[0067] In the embodiment, the thickness of the seed layer 4 is 0.01-0.2um, the thickness of the piezoelectric layer is 0.1-5um, and the thickness of the lower electrode 5 and the thickness of the upper electrode 7 are both 0.1-1um.

[0068] In the embodiment, the lower electrode 5 and the upper electrode 7 are both alloys formed by one or more combinations of molybdenum, aluminum, tungsten, platinum and titanium, so that the lower electrode 5 and the upper electrode 7 have good conductivity.

[0069] In the embodiment, the depth of the cavity 2 is 0.1-10um, and the width of the cavity 2 is 50-400um.

[0070] Specifically, the depth of the crystallized glass is controlled by the exposure dose and time in step S1, and the depth and width are moderate, and the structural performance is stable.

[0071] In the embodiment, the depth of the cavity 2 is controlled by the exposure time and dose, and the shape of the cavity 2 is any shape. The structure of the cavity 2 is, for example, rectangular, circular, etc.

[0072] Embodiment two

[0073] The embodiment of the present application provides a bulk acoustic wave resonator, which is made by the preparation method of the bulk acoustic wave resonator. The structure of the bulk acoustic wave resonator includes, from bottom to top, a photosensitive glass substrate 1, a cavity 2, a seed layer 4, a lower electrode 5, a piezoelectric material layer 6 and an upper electrode 7. The photosensitive glass substrate 1 has a front surface and a back surface. The seed layer 4, the lower electrode 5, the upper electrode 7 and the piezoelectric material layer 6 are located above the front surface of the photosensitive glass substrate 1. The lower electrode 5, the piezoelectric material layer 6 and the upper electrode 7 are located directly above the cavity 2. The cavity 2 is recessed on the front surface of the photosensitive glass substrate 1. In this way, the insertion loss of the resonator can be reduced, and the structural stability can be improved.

[0074] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or drawings of this application are used to distinguish different objects, not to describe a particular order. References to "embodiment" herein mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0075] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method of fabricating a bulk acoustic resonator, comprising: The bulk acoustic wave resonator comprises a photosensitive glass substrate, a cavity, a seed layer, a lower electrode, a piezoelectric material layer and an upper electrode, the upper surface of the photosensitive glass substrate is sequentially stacked with the seed layer, the lower electrode, the piezoelectric material layer and the upper electrode, and the cavity is formed in the photosensitive glass substrate; the preparation method comprises the following steps: Step S1, providing a photosensitive glass substrate, and the photosensitive glass substrate is exposed to ultraviolet light under a mask; Step S2, annealing the exposed photosensitive glass substrate to form a crystallized sacrificial layer; Step S3, growing a seed layer on the upper surface of the photosensitive glass substrate; Step S4, growing a metal on the upper surface of the seed layer and patterning to form a lower electrode, and etching the lower electrode to expose the seed layer; wherein one end of the lower electrode corresponds to one end of the photosensitive glass substrate, and the other end of the lower electrode corresponds to the sacrificial layer; Step S5, growing a piezoelectric material layer on the upper surface of the lower electrode and the upper surface of the seed layer and etching the piezoelectric material layer to expose the lower electrode; Step S6, growing a metal on the upper surface of the piezoelectric material layer and patterning to form an upper electrode, and etching part of the upper electrode to expose the piezoelectric layer; wherein the orthographic projection of the etched upper electrode is located in the other end of the sacrificial layer and the photosensitive glass substrate; Step S7, etching the piezoelectric material layer to expose the lower electrode; Step S8, sequentially etching the upper electrode, the piezoelectric layer, the lower electrode and the seed layer to release at least one through hole to the upper surface of the sacrificial layer; Step S9, releasing etching gas or solution through the through hole to etch the sacrificial layer to form a cavity.

2. The bulk acoustic resonator fabrication method of claim 1, wherein, In step S2, the etching selectivity ratio of the sacrificial layer to the unexposed photosensitive glass substrate is 30:1-50:

1.

3. The method of claim 1, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. The seed layer, the lower electrode, the piezoelectric layer and the upper electrode are all grown by magnetron sputtering or chemical vapor deposition.

4. The method of claim 1, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. In step S4, the lower electrode is etched by photolithography stripping or photolithography etching to expose the seed layer.

5. The method of claim 1, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. In step S5, the piezoelectric material layer is exposed by gas or solution etching to expose the lower electrode.

6. The method of claim 1, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. The seed layer and the piezoelectric layer are one or more combinations of lithium tantalate, lithium niobate, aluminum nitride and zinc oxide.

7. The method of claim 1, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. The thickness of the seed layer is 0.01-0.2um, the thickness of the piezoelectric layer is 0.1-5um, and the thickness of the lower electrode and the upper electrode is 0.1-1um.

8. The method of claim 1, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. The lower electrode and the upper electrode are all alloys formed by one or more combinations of molybdenum, aluminum, tungsten, platinum and titanium.

9. The method of claim 1, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. The depth of the cavity is 0.1-10um, and the width of the cavity is 50-400um.

10. The method of claim 9, wherein the thickness of the piezoelectric layer is 0.5-2.0 μm. The depth of the cavity can be controlled by exposure time and dose, and the shape of the cavity is any shape.

11. A bulk acoustic resonator, comprising: The bulk acoustic wave resonator is made by the preparation method of the bulk acoustic wave resonator of any one of claims 1-10, and the structure comprises a photosensitive glass substrate, a cavity, a seed layer, a lower electrode, a piezoelectric material layer and an upper electrode from bottom to top. The photosensitive glass substrate has a front surface and a back surface; the seed layer, the lower electrode, the upper electrode and the piezoelectric material layer are located above the front surface of the photosensitive glass substrate; the lower electrode, the piezoelectric material layer and the upper electrode are directly above the cavity; and the cavity is recessed in the front surface of the photosensitive glass substrate.

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