CN116260412A

CN116260412A - Method for manufacturing cavity type film bulk acoustic wave resonator

Info

Publication number: CN116260412A
Application number: CN202211597327.2A
Authority: CN
Inventors: 周国安; 卜德冲; 罗大杰; 贾会来
Original assignee: Silex Microsystems Technology Beijing Co ltd
Current assignee: Silex Microsystems Technology Beijing Co ltd
Priority date: 2022-12-12
Filing date: 2022-12-12
Publication date: 2023-06-13

Abstract

The invention discloses a manufacturing method of a cavity type film bulk acoustic resonator, which comprises the following steps: depositing a first sacrificial layer covering the groove on the surface of the substrate; removing the first sacrificial layer which is positioned outside the groove by orthographic projection on the substrate by adopting a mode of combining etching and end point detection; depositing a second sacrificial layer on the surface of the substrate, wherein the second sacrificial layer covers the rest of the first sacrificial layer; removing the second sacrificial layer and the first sacrificial layer above the surface of the substrate in a repeated polishing mode, so that the remaining first sacrificial layer in the groove and the surface of the substrate are positioned on the same plane; depositing a laminated structure covering the grooves on the surface of the substrate, wherein the laminated structure comprises a bottom electrode, a piezoelectric layer and a top electrode which are sequentially deposited; and removing the residual first sacrificial layer in the groove, and forming a cavity below the laminated structure. The manufacturing method can effectively avoid the problem of poor in-chip non-uniformity, and ensures the product quality of the prepared film bulk acoustic resonator.

Description

Method for manufacturing cavity type film bulk acoustic wave resonator

Technical Field

The invention relates to the technical field of microelectronic devices, in particular to a manufacturing method of a cavity type film bulk acoustic resonator.

Background

The film bulk acoustic resonator (Film Bulk Acoustic Resonator, FBAR) is a piezoelectric film resonator. The basic structure of the film bulk acoustic resonator is a laminated structure formed by an upper electrode, a piezoelectric layer and a lower electrode on a substrate; to suppress the dissipation of vibration energy, a cavity is provided below the laminate structure.

In the related art, in the fabrication of a thin film bulk acoustic resonator, a sacrificial layer is generally formed on a substrate, a stacked structure is fabricated on the sacrificial layer, and the sacrificial layer is etched after the stacked structure is fabricated to form a cavity between the stacked structure and the substrate. In the fabrication of the sacrificial layer, the sacrificial layer is typically etched to remove a portion of the sacrificial layer, and then the remaining portion of the sacrificial layer is subjected to chemical mechanical polishing (chemical mechanical polishing, CMP) to planarize the surface thereof.

However, the etching needs to be such that the sacrificial layer stays at a prescribed thickness, which is extremely difficult to control for the etching process, and the thickness of the sacrificial layer remaining from etching tends to be thick in order to prevent over etching. The residual thicker sacrificial layer is processed through the CMP process, so that the problem of poor on-chip non-uniformity (WWWNU) is easy to occur, the CMP process is difficult to stabilize, and the product quality of the prepared film bulk acoustic resonator is influenced.

Disclosure of Invention

The present invention has been made in view of the above-mentioned problems, and has as its object to provide a method of manufacturing a cavity type thin film bulk acoustic resonator which overcomes or at least partially solves the above-mentioned problems.

The invention provides a manufacturing method of a cavity type film bulk acoustic resonator, which comprises the following steps:

forming a groove on the surface of the substrate;

depositing a first sacrificial layer on the surface of the substrate, wherein the first sacrificial layer covers the groove;

removing the first sacrificial layer, which is positioned outside the groove, of the orthographic projection on the substrate by adopting a mode of combining etching and end point detection;

depositing a second sacrificial layer on the surface of the substrate, wherein the second sacrificial layer covers the rest of the first sacrificial layer;

removing the second sacrificial layer and the first sacrificial layer outside the groove in a repeated chemical mechanical polishing mode, so that the first sacrificial layer remained in the groove and the surface of the substrate are positioned on the same plane;

depositing a laminated structure covering the groove on the surface of the substrate, wherein the laminated structure comprises a bottom electrode, a piezoelectric layer and a top electrode which are sequentially deposited;

and removing the residual first sacrificial layer in the groove, and forming a cavity below the laminated structure.

Optionally, depositing a first sacrificial layer on the surface of the substrate includes:

and depositing a phosphosilicate glass or tetraethyl orthosilicate layer on the surface of the substrate to serve as the first sacrificial layer.

Optionally, the thickness of the first sacrificial layer is 1.2-2 times of the depth of the groove.

Optionally, the material of the second sacrificial layer is the same as the material of the first sacrificial layer.

Optionally, the thickness of the second sacrificial layer is greater than the depth of the groove.

Optionally, removing the second sacrificial layer and the first sacrificial layer outside the groove by using multiple chemical mechanical polishing, so that the first sacrificial layer remaining in the groove and the surface of the substrate are located on the same plane, including:

performing first polishing processing on the second sacrificial layer and the first sacrificial layer outside the groove by adopting a chemical mechanical polishing method until the thicknesses of the second sacrificial layer and the first sacrificial layer outside the groove away from the surface of the substrate are set thicknesses;

performing secondary polishing processing on the second sacrificial layer and the first sacrificial layer which are remained outside the groove by adopting a chemical mechanical polishing method until all the second sacrificial layer and the first sacrificial layer outside the groove are removed;

and carrying out third polishing processing on the surface of the substrate and the surface of the first sacrificial layer remained in the groove by adopting a chemical mechanical polishing method until the first sacrificial layer remained in the groove and the surface of the substrate are positioned on the same plane, and the roughness of the first sacrificial layer remained in the groove and the surface of the substrate meets the set requirement.

Optionally, the set thickness is 1-2 um.

Optionally, the method in combination with endpoint detection monitors whether the remaining thickness of the second sacrificial layer and the first sacrificial layer is completely removed while the second polishing process is performed.

Optionally, the forming a groove on the surface of the substrate includes:

and forming a groove with the depth of 3-30 um on the surface of the substrate by adopting a dry etching method or a wet etching method.

Optionally, before the forming of the groove on the surface of the substrate, the manufacturing method further includes:

and cleaning the substrate and drying the substrate for standby.

The technical scheme provided by the embodiment of the invention has at least the following technical effects or advantages:

according to the manufacturing method of the cavity type film bulk acoustic resonator, provided by the embodiment of the invention, the first sacrificial layer which is orthographic projected on the substrate and positioned outside the groove is removed by adopting a method combining etching and end point detection, so that only the first sacrificial layer in the groove and above the groove can be reserved, and the first sacrificial layer on the surface of the substrate can be completely removed. And then, depositing a second sacrificial layer on the surface of the substrate to cover the residual first sacrificial layer, wherein the second sacrificial layer and the residual first sacrificial layer can form a whole, so that the stability of the residual first sacrificial layer can be ensured. And then removing the second sacrificial layer and the first sacrificial layer which are positioned above the surface of the substrate by adopting a mode of chemical mechanical polishing for a plurality of times, so that the first sacrificial layer remained in the groove and the surface of the substrate are positioned on the same plane, and the planarization requirement of the subsequent growth laminated structure is met. The thickness and the duration of each polishing can be reduced by dividing the polishing process into a plurality of times of chemical mechanical polishing, and the imbalance of chemical reaction and dynamic balance removal caused by long-time polishing on a polishing table is avoided, so that the problem of poor on-chip non-uniformity is solved, and the product quality of the prepared film bulk acoustic resonator can be further ensured.

The foregoing description is only an overview of the present invention, and is intended to be implemented in accordance with the teachings of the present invention in order that the same may be more clearly understood and to make the same and other objects, features and advantages of the present invention more readily apparent.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to designate like parts throughout the figures.

In the drawings:

fig. 1 is a flowchart of a method for manufacturing a cavity type thin film bulk acoustic resonator according to the related art;

FIG. 2 is a flowchart of a method for manufacturing a cavity type thin film bulk acoustic resonator according to an embodiment of the present invention;

FIG. 3 is a flowchart of a method for manufacturing another cavity type thin film bulk acoustic resonator according to an embodiment of the present invention;

FIG. 4 is a schematic diagram showing the structure after performing step S302;

fig. 5 is a schematic diagram showing the structure after performing step S303;

FIG. 6 is a schematic diagram showing the structure after performing step S304;

fig. 7 is a schematic diagram showing the structure after performing step S305;

FIG. 8 is a schematic diagram showing the structure after performing step S306;

fig. 9 is a schematic diagram of the structure presented after performing step S307;

fig. 10 is a schematic diagram of the structure presented after step S308 is performed.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings.

Various structural schematic diagrams according to embodiments of the present disclosure are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated for clarity of presentation and may have been omitted. The shapes of the various regions, layers and relative sizes, positional relationships between them shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.

In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present therebetween. In addition, if one layer/element is located "on" another layer/element in one orientation, that layer/element may be located "under" the other layer/element when the orientation is turned. In the context of the present disclosure, similar or identical components may be indicated by identical or similar reference numerals.

In order to better understand the above technical solutions, the following detailed description will be made with reference to specific embodiments, and it should be understood that specific features in the embodiments and examples of the disclosure are detailed descriptions of the technical solutions of the present application, and not limit the technical solutions of the present application, and technical features in the embodiments and examples of the present application may be combined with each other without conflict.

For a better understanding of the present application, first, a brief description of related technologies related to embodiments of the present invention will be described:

fig. 1 is a flowchart of a method for manufacturing a cavity type thin film bulk acoustic resonator according to the related art, and as shown in fig. 1, the method includes:

step S101, forming a groove on the surface of the substrate.

Step S102, a sacrificial layer covering the groove is deposited on the surface of the substrate.

And step 103, removing part of the sacrificial layer outside the groove by adopting a dry etching method or a wet etching method, so that the surface of the remaining sacrificial layer is flattened.

And step S104, removing the residual sacrificial layer outside the groove by adopting a chemical mechanical polishing method, so that the residual sacrificial layer in the groove and the surface of the substrate are positioned on the same plane.

Step S105, depositing a laminated structure covering the grooves on the surface of the substrate, wherein the laminated structure comprises a bottom electrode, a piezoelectric layer and a top electrode which are sequentially deposited;

and S106, removing the residual first sacrificial layer in the groove, and forming a cavity below the laminated structure.

In the above method, the etching needs to make the sacrificial layer stay at a specified thickness, which is very difficult to control for the etching process, and the thickness of the remaining sacrificial layer is often thicker to prevent over etching. The residual thicker sacrificial layer is processed through the CMP process, so that the problem of poor on-chip non-uniformity (WWWNU) is easy to occur, the CMP process is difficult to stabilize, and the product quality of the prepared film bulk acoustic resonator is influenced.

Therefore, in order to solve the above technical problems, the embodiment of the invention provides a manufacturing method of a cavity type thin film bulk acoustic resonator.

Fig. 2 is a flowchart of a method for manufacturing a cavity type thin film bulk acoustic resonator according to an embodiment of the present invention, as shown in fig. 2, the method includes:

step S201, forming a groove on the surface of the substrate.

Step S202, depositing a first sacrificial layer on the surface of the substrate, wherein the first sacrificial layer covers the groove.

And step 203, removing the first sacrificial layer which is positioned outside the groove by orthographic projection on the substrate by adopting a mode of combining etching and end point detection.

Step S204, depositing a second sacrificial layer on the surface of the substrate, wherein the second sacrificial layer covers the rest of the first sacrificial layer.

And step S205, removing the second sacrificial layer and the first sacrificial layer outside the groove by adopting a mode of repeated chemical mechanical polishing, so that the remaining first sacrificial layer in the groove and the surface of the substrate are positioned on the same plane.

Step S206, depositing a laminated structure covering the grooves on the surface of the substrate, wherein the laminated structure comprises a bottom electrode, a piezoelectric layer and a top electrode which are sequentially deposited.

And S207, removing the residual first sacrificial layer in the groove, and forming a cavity below the laminated structure.

Fig. 3 is a flowchart of another method for manufacturing a cavity type thin film bulk acoustic resonator according to an embodiment of the present invention, and as a further explanation of the above embodiment, as shown in fig. 3, the manufacturing method includes:

step S301, cleaning the substrate and drying the substrate for standby.

Alternatively, the substrate is a substrate material such as silicon, sapphire, gallium arsenide, gallium nitride, silicon carbide, quartz, glass, or the like. In the embodiment of the invention, the substrate may be a silicon wafer.

For example, the wafer may be cleaned using a standard RCA cleaning process. The surface contamination of the silicon wafer refers to particles, metals, organics, moisture molecules and natural oxide films deposited on the surface of the silicon wafer. Because the organic matters can cover part of the surface of the silicon wafer, the contamination related to the oxide layer is difficult to remove. The cleaning thinking of the standard RCA cleaning process is that firstly, organic contamination on the surface of a silicon wafer is removed, and because the organic matters can cover part of the surface of the silicon wafer, the oxide film and the contamination related to the oxide film are difficult to remove; then dissolving the oxide film, which is a "contamination trap" and also introduces epitaxial defects; finally removing the contamination of particles, metals and the like, and passivating the surface of the silicon wafer. This is a conventional technique and will not be described in detail herein.

Step S302, forming a groove on the surface of the substrate.

By way of example, a recess having a depth of 2.3 to 30um (typically 2.6 to 3.7 um) may be formed in the surface of the substrate by dry or wet etching.

Fig. 4 is a schematic structural diagram showing a structure after step S302 is performed, and as shown in fig. 4, a groove 100a is formed on the surface of the substrate 100.

Step S303, depositing a first sacrificial layer on the surface of the substrate, wherein the first sacrificial layer covers the groove.

In this embodiment, a layer of phosphosilicate glass or tetraethyl orthosilicate may be deposited on the surface of the substrate as the first sacrificial layer by PECVD (Plasma Enhanced Chemical Vapor Deposition, plasma-enhanced chemical vapor deposition) method.

Optionally, the thickness of the first sacrificial layer is 1.2-2 times of the depth of the groove, so as to ensure that the first sacrificial layer can partially protrude from the groove.

Fig. 5 is a schematic diagram of the structure after performing step S303, as shown in fig. 5, in which a first sacrificial layer 110 is sequentially deposited on the substrate 100 with the grooves 100a formed thereon.

And step S304, removing the first sacrificial layer which is positioned outside the groove by orthographic projection on the substrate by adopting a mode of combining etching and end point detection.

In this embodiment, a dry etching or wet etching method may be used to remove the first sacrificial layer that is orthographic projected on the substrate and is located outside the groove, and in the etching process, endpoint detection is performed to detect whether the etching of the first sacrificial layer to be etched and removed is completed, so as to ensure that the first sacrificial layer on the surface of the substrate can be completely removed, and only the first sacrificial layer in the groove and above the groove is retained.

In the prior art, only part of the sacrificial layer needs to be etched, and the etching starting point and the etching end point are made of the same material, so that the end point detection method cannot be adopted for detection. In this embodiment, the first sacrificial layer on the surface of the substrate is completely removed, the substrate and the first sacrificial layer are made of different materials, and the immediate etching starting point is made of different materials, so that the method of detecting the end point can be used for detecting whether the etching is completed or not, and the etching precision is higher.

Fig. 6 is a schematic structural diagram of the structure after performing step S304, as shown in fig. 6, where the first sacrificial layer 110, which is located outside the recess 100a and is orthographically projected on the substrate 100, is removed. Only the first sacrificial layer 110 within the recess 100a and over the recess 100a remains.

Step S305, depositing a second sacrificial layer on the surface of the substrate, wherein the second sacrificial layer covers the remaining first sacrificial layer.

In this embodiment, the material of the second sacrificial layer is the same as the material of the first sacrificial layer so as to be better integrated with the first sacrificial layer. Specifically, a layer of phosphosilicate glass or tetraethyl orthosilicate layer is deposited on the surface of the substrate by a PECVD method and used as a second sacrificial layer.

Optionally, the thickness of the second sacrificial layer is greater than the depth of the recess.

Fig. 7 is a schematic diagram of the structure after performing step S305, as shown in fig. 7, at this time, a second sacrificial layer 120 is deposited on the surface of the substrate, where the second sacrificial layer 120 covers the remaining first sacrificial layer 110.

And step S306, removing the second sacrificial layer and the first sacrificial layer outside the groove in a mode of repeated chemical mechanical polishing, so that the remaining first sacrificial layer in the groove and the surface of the substrate are positioned on the same plane.

Optionally, step S306 may include:

and performing first polishing processing on the second sacrificial layer and the first sacrificial layer outside the groove by adopting a chemical mechanical polishing method until the thicknesses of the second sacrificial layer and the first sacrificial layer outside the groove away from the surface of the substrate are set.

and when the second polishing process is performed, monitoring whether the second sacrificial layer and the first sacrificial layer with the residual thickness are completely removed by combining an end point detection method so as to ensure the polishing precision.

And thirdly, polishing the surface of the substrate and the surface of the first sacrificial layer remained in the groove for the third time by adopting a chemical mechanical polishing method until the first sacrificial layer remained in the groove and the surface of the substrate are positioned on the same plane, and the roughness of the first sacrificial layer remained in the groove and the surface of the substrate reach the set requirement.

Among these, chemical mechanical polishing is the smoothing of silicon wafers or other substrate materials during processing by chemical etching and mechanical forces. The specific working principle is as follows:

the polishing structure is placed at the lowest part of the polishing head, the polishing pad is placed on the polishing disc, the rotating polishing head is pressed on the rotating polishing pad under a certain pressure during polishing, the polishing liquid composed of submicron or nanometer abrasive particles and chemical solution flows between the surface of the structure to be polished and the polishing pad, and then the polishing liquid is uniformly distributed on the polishing structure under the action of the transmission and centrifugal force of the polishing pad, so that a layer of polishing liquid film is formed between the structure to be polished and the polishing pad. Chemical components in the grinding liquid react with silicon wafer surface materials to convert insoluble substances into soluble substances or soften substances with high hardness, then the chemical reactants are removed from the surface of the silicon wafer through the micro-mechanical friction action of abrasive particles and dissolved into flowing liquid to be taken away, namely the planarization purpose is realized in the alternating process of chemical stripping and mechanical stripping.

Illustratively, in the first polishing process, the polishing head can be controlled to apply a pressure of 3-5.5PSI and a polishing pad rotation speed of 80-120RPM, and the polishing pad is processed by using a polishing liquid of a compound polishing pad and colloidal silica (colloidal silica) abrasive particles (the particle size of the abrasive particles can be 50-120 nm);

in the second polishing process, the pressure applied by the polishing head can be controlled to be 1.5-4PSI, the rotating speed of the polishing pad is 90-120RPM, and the composite polishing pad is matched with polishing liquid of colloidal silica (colloidal silica) abrasive particles (the particle size of the abrasive particles can be 50-120 nm) for processing;

in the third polishing process, the pressure applied by the polishing head can be controlled to be 1-3PSI, the rotating speed of the polishing pad is 100-130RPM, the polishing pad is matched with a fine polishing liquid (ultrapure water can also be used) for processing, and the polishing time is 10-40 seconds, so that the roughness after polishing is improved.

The process can not only effectively control the thickness of the sacrificial layer and reduce various defects inside and outside the interface, but also greatly improve the surface roughness and meet the requirements of the next process (such as wafer bonding and direct bonding with extremely high requirements on surface roughness).

Fig. 8 is a schematic structural diagram of the structure after performing step S306, as shown in fig. 8, at this time, all the second sacrificial layer 120 and the first sacrificial layer 110 outside the groove 100a are removed, and only the first sacrificial layer 110 inside the groove 100a is left.

Step S307, depositing a laminated structure covering the grooves on the surface of the substrate, wherein the laminated structure comprises a bottom electrode, a piezoelectric layer and a top electrode which are sequentially deposited.

In this embodiment, the bottom electrode and the top electrode may be a metal material such as aluminum, gold, aluminum-copper alloy, aluminum-silicon-copper alloy, tungsten, titanium-tungsten compound, molybdenum, platinum, or the like. The piezoelectric layer may be a piezoelectric material such as zinc oxide, PZT (Lead zirconate titanate ), aluminum nitride, or the like.

For example, a layer of metal may be grown on the surface of the substrate and then etched into the bottom electrode, for example, using sputtering, photolithography, and etching processes. The bottom electrode covers the position of the recess. A layer of piezoelectric material is then deposited over the bottom electrode and etched into the piezoelectric layer. Finally, a layer of metal is grown on the piezoelectric layer, and then the layer of metal is etched into a top electrode, for example, using deposition, photolithography, and etching processes.

Fig. 9 is a schematic diagram showing a structure after step S307 is performed, as shown in fig. 9, in which a stacked structure 130 covering the recess is deposited on the surface of the substrate, and the stacked structure 130 includes a bottom electrode 131, a piezoelectric layer 132, and a top electrode 133, which are sequentially deposited.

And step 308, removing the residual first sacrificial layer in the groove, and forming a cavity below the laminated structure.

In this embodiment, a release window may be obtained around the recess by dry etching, and then an aqueous solution of hydrofluoric acid (Hydrofluoric Acid, HF) is injected from the release window to remove the remaining first sacrificial layer located in the recess.

Fig. 10 is a schematic diagram of the structure presented after step S308 is performed, as shown in fig. 10, when a cavity S is formed under the stacked structure 130.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, the disclosed method should not be construed as reflecting the intention that: i.e., the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims.

Claims

1. A method of manufacturing a cavity type thin film bulk acoustic resonator, the method comprising:

forming a groove on the surface of the substrate;

2. The method of manufacturing of claim 1, wherein depositing a first sacrificial layer on the substrate surface comprises:

3. The method of manufacturing according to claim 2, wherein the thickness of the first sacrificial layer is 1.2 to 2 times the depth of the groove.

4. The method of manufacturing according to claim 2, wherein the material of the second sacrificial layer is the same as the material of the first sacrificial layer.

5. The method of manufacturing according to claim 4, wherein the thickness of the second sacrificial layer is greater than the depth of the groove.

6. The method of manufacturing according to claim 1, wherein the removing the second sacrificial layer and the first sacrificial layer outside the recess by a plurality of chemical mechanical polishing such that the first sacrificial layer remaining in the recess is in the same plane as the substrate surface, comprises:

7. The method of manufacturing according to claim 6, wherein the set thickness is 1 to 2um.

8. The method of manufacturing according to claim 6, wherein the second sacrificial layer and the first sacrificial layer of remaining thickness are monitored for complete removal in combination with an endpoint detection method at the time of the second polishing process.

9. The method of manufacturing according to any one of claims 1 to 8, wherein the forming a groove in the surface of the substrate comprises:

and forming a groove with the depth of 2.3-30 um on the surface of the substrate by adopting a dry etching method or a wet etching method.

10. The manufacturing method according to any one of claims 1 to 8, wherein before the forming of the grooves on the substrate surface, the manufacturing method further comprises:

and cleaning the substrate and drying the substrate for standby.