CN111246356B

CN111246356B - A MEMS structure and a method for forming the same

Info

Publication number: CN111246356B
Application number: CN202010249783.2A
Authority: CN
Inventors: 刘端
Original assignee: Anhui Aofei Acoustics Technology Co ltd
Current assignee: Anhui Aofei Acoustics Technology Co ltd
Priority date: 2020-04-01
Filing date: 2020-04-01
Publication date: 2024-11-26
Anticipated expiration: 2040-04-01
Also published as: CN111246356A

Abstract

The present application discloses a MEMS structure, comprising: a substrate having a cavity; a piezoelectric composite vibration layer formed directly above the cavity; and a connector formed above the substrate and connecting the substrate and the piezoelectric composite vibration layer, wherein the connector is at the periphery of the piezoelectric composite vibration layer and at least one of the upper surface and the lower surface of the connector is a flat surface. The MEMS structure provided by the present application connects the substrate and the piezoelectric composite vibration layer through the connector, thereby facilitating the piezoelectric composite vibration layer to release stress, increase the vibration amplitude, and thus improve the sensitivity of the MEMS structure.

Description

MEMS structure and forming method thereof

Technical Field

The application relates to the technical field of semiconductors, in particular to a MEMS (Microelectro MECHANICAL SYSTEMS short for microelectromechanical system) structure and a forming method thereof.

Background

MEMS microphones (microphones) mainly include both capacitive and piezoelectric. The MEMS piezoelectric microphone is a microphone prepared by using a micro-electromechanical system technology and a piezoelectric film technology, and has small size, small volume and good consistency due to the adoption of a semiconductor plane technology, bulk silicon processing and other technologies. Meanwhile, compared with a capacitor microphone, the MEMS piezoelectric microphone has the advantages of no need of bias voltage, large working temperature range, dust prevention, water prevention and the like, but has lower sensitivity, and restricts the development of the MEMS piezoelectric microphone.

Aiming at the problem of how to improve the sensitivity of the piezoelectric MEMS structure in the related art, no effective solution is proposed at present.

Disclosure of Invention

Aiming at the problems in the related art, the application provides an MEMS structure and a forming method thereof, which can effectively improve the sensitivity of the MEMS structure.

The technical scheme of the application is realized as follows:

according to one aspect of the present application, there is provided a MEMS structure comprising:

a substrate having a cavity;

The piezoelectric composite vibration layer is formed right above the cavity;

And a connection member formed over the substrate and connecting the substrate and the piezoelectric composite vibration layer, wherein the connection member is at a periphery of the piezoelectric composite vibration layer and at least one of an upper surface and a lower surface of the connection member is a flat surface.

The connecting piece is provided with a hollowed-out hole and/or a hollowed-out groove which longitudinally penetrate through the connecting piece.

Wherein the connection member includes one or more beams in a straight spoke shape or a curved spoke shape to connect the substrate and the piezoelectric composite vibration layer in a plan view.

Only one of the upper surface and the lower surface of the connecting piece is a flat surface, and the other surface of the upper surface and the lower surface of the connecting piece is uneven.

Wherein a recess is provided in the exposed substrate, the recess being adjacent to the connector.

Wherein the recess extends laterally below the connector.

Wherein, the piezoelectricity compound vibration layer includes:

A vibration supporting layer formed over the substrate and covering the cavity;

And a piezoelectric unit formed over the vibration supporting layer, and suspended over the cavity.

Wherein a first end of the connecting member is connected to the substrate, a second end of the connecting member is connected to the vibration supporting layer and has a common top surface with the vibration supporting layer, or a second end of the connecting member is connected above the exposed vibration supporting layer.

Wherein the MEMS structure further includes a dividing groove extending from an upper surface of the piezoelectric unit through the vibration supporting layer to the cavity.

The material of the connecting piece is the same as or different from that of the vibration supporting layer, and the material of the connecting piece comprises polyimide film, parylene and polyurethane.

According to another aspect of the present application, there is provided a method of forming a MEMS structure, comprising:

Sequentially forming a vibration supporting layer and a piezoelectric unit above a substrate, wherein the radius of the piezoelectric unit is smaller than that of the vibration supporting layer;

etching a bottom of the substrate to form a cavity penetrating the substrate;

A connecting member is formed to connect the substrate and the piezoelectric unit, and the connecting member is at a periphery of the piezoelectric unit, and at least one of an upper surface and a lower surface of the connecting member is in a flat plane.

Wherein the method of forming the connector comprises:

and connecting the substrate and the piezoelectric unit using the exposed vibration supporting layer as the connecting member.

Wherein the method of forming the connector comprises:

removing the vibration supporting layer at the periphery of the piezoelectric unit to expose the substrate;

A connection is formed to connect the substrate and the piezoelectric unit.

Wherein the method further comprises:

forming a layer of support material on the bottom surface of the substrate, the sidewalls and the top surface of the cavity prior to forming the connector;

Etching to form hollowed holes and/or hollowed grooves, or to form one or more beams, on the connection piece after forming the connection piece;

And removing the supporting material layer.

Wherein the method further comprises:

before removing the layer of support material, a recess is formed in the etched substrate extending longitudinally into the substrate.

Wherein the recess extends laterally within the substrate to below the connector.

In summary, the MEMS structure provided by the application is connected with the substrate and the piezoelectric composite vibration layer through the connecting piece, so that the stress release of the piezoelectric composite vibration layer is facilitated, the vibration amplitude is improved, and the sensitivity of the MEMS structure is improved. In addition, through improving the connecting piece, for example, a hollowed hole or a hollowed groove is formed in the connecting piece, or the connecting piece is arranged into one or more beam structures, the resonance frequency of the MEMS structure is reduced, and therefore the sensitivity of the MEMS structure is further improved. In addition, the preparation process is stable, the signal to noise ratio is effectively improved, and the performance stability is improved. The MEMS structure provided based on the preparation method has higher sensitivity.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 illustrates a schematic diagram of a MEMS structure provided in accordance with some embodiments;

fig. 2a, b, c, d show schematic diagrams of hollowed-out holes and hollowed-out grooves provided according to some embodiments;

FIG. 3 illustrates a schematic view of a beam provided in accordance with some embodiments;

FIG. 4 illustrates a schematic diagram of a MEMS structure provided in accordance with some embodiments;

FIGS. 5-8 illustrate intermediate stage schematic views of forming the MEMS structure of FIG. 1;

Fig. 9-11 illustrate intermediate stage schematic views of forming the MEMS structure of fig. 4.

Detailed Description

The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the application, fall within the scope of protection of the application.

Referring to fig. 1, in accordance with an embodiment of the present application, a MEMS structure is provided that may be used, but is not limited to, a microphone or microphone like sensor, or other actuator. In some embodiments, the MEMS structure includes a substrate 10, a piezoelectric composite vibration layer 20, and a connection 30. The MEMS structure will be described in detail below.

The material of the substrate 10 comprises silicon or any suitable silicon-based compound or derivative (e.g., silicon wafer, SOI, siO 2). The substrate 10 has a cavity 11 therein. The cavity 11 may be formed by DRIE (DEEP REACTIVE Ion Etching abbreviation), deep reactive Ion Etching, or wet Etching.

A piezoelectric composite vibration layer 20 is formed over the substrate 10. In some embodiments, the piezoelectric composite vibration layer 20 includes a vibration support layer 21 and a piezoelectric unit. A vibration supporting layer 21 is formed over the substrate 10 and covers the cavity 11. The vibration supporting layer 21 includes a single-layer or multi-layer composite film structure made of silicon nitride, silicon oxide, single crystal silicon, polysilicon. In view of the problem of controlling the stress of the vibration supporting layer 21, the vibration supporting layer 21 may be provided in a multi-layer structure to reduce the stress. The method of forming the vibration supporting layer 21 includes a thermal oxidation method or a chemical vapor deposition method. In some embodiments, the step of forming the vibration supporting layer 21 may be skipped or omitted. The piezoelectric unit is formed above the vibration supporting layer 21, and the piezoelectric unit is suspended above the cavity 11. The piezoelectric unit includes a first electrode layer 22, a first piezoelectric layer 23, and a second electrode layer 24. The first electrode layer 22 is formed above the vibration supporting layer 21. The first piezoelectric layer 23 is formed over the first electrode layer 22. The second electrode layer 24 is formed over the first piezoelectric layer 23. The first piezoelectric layer 23 includes one or more layers of zinc oxide, aluminum nitride, an organic piezoelectric film, lead zirconate titanate, or a perovskite-type piezoelectric film. The method of forming the first piezoelectric layer 23 includes magnetron sputtering, deposition, or other suitable methods. The materials of the first electrode layer 22 and the second electrode layer 24 include one of aluminum, gold, platinum, molybdenum, titanium, chromium, or a composite film composed of them, or other suitable materials. Methods of forming the first electrode layer 22 and the second electrode layer 24 include physical vapor deposition or other suitable methods. In this embodiment, the first electrode layer 22, the first piezoelectric layer 23, and the second electrode layer 24 constitute a piezoelectric composite layer. The first piezoelectric layer 23 may convert the applied pressure into a voltage, and the first electrode layer 22 and the second electrode layer 24 may transmit the generated voltage to other integrated circuit devices. The first electrode layer 22 and the second electrode layer 24 have at least two mutually isolated partitions, and the mutually corresponding partitions of the first electrode layer 22 and the second electrode layer 24 form electrode layer pairs, and a plurality of electrode layer pairs are sequentially connected in series.

In some embodiments, a second piezoelectric layer (not shown in fig. 1) and a third electrode layer (not shown in fig. 1) are sequentially formed over the second electrode layer 24, the material of the second piezoelectric layer including one or more of zinc oxide, aluminum nitride, an organic piezoelectric film, lead zirconate titanate, a perovskite-type piezoelectric film, or other suitable material. The material and forming method of the second piezoelectric layer may be the same as or different from those of the first piezoelectric layer 23. The material of the third electrode layer includes aluminum, gold, platinum, molybdenum, titanium, chromium, and a composite film or other suitable material composed of the same. The material and forming method of the third electrode layer may be the same as or different from those of the first electrode layer 22. Also, in this embodiment, the piezoelectric composite layer of the MEMS structure has the first electrode layer 22, the first piezoelectric layer 23, the second electrode layer 24, the second piezoelectric layer, and the third electrode layer, thereby constituting a bimorph structure and improving the piezoelectric conversion efficiency of the MEMS structure. In addition, in an embodiment in which the vibration supporting layer 21 is not provided, a second piezoelectric layer and a third electrode layer may be sequentially formed over the second electrode layer 24. In the embodiment provided with the vibration supporting layer 21, there is no second piezoelectric layer and no third electrode layer above the second electrode layer 24. It is noted that in the embodiment of the present application shown in fig. 1, the piezoelectric composite vibration layer 20 includes a vibration supporting layer 21, a first electrode layer 22, a first piezoelectric layer 23, and a second electrode layer 24.

The connection member 30 is formed over the substrate 10 and connects the substrate 10 and the piezoelectric composite vibration layer 20, wherein the connection member 30 is at the periphery of the piezoelectric composite vibration layer 20 and at least one of the upper surface and the lower surface of the connection member 30 is a flat surface. In some embodiments, the upper and lower surfaces of the connector 30 may each be flat. In some embodiments, when one surface of the connector 30 is planar, the other surface of the connector 30 is rugged. The uneven surface may be constituted by radial or circumferential protrusions or depressions, or may be constituted by irregular protrusions or depressions, which is advantageous in reducing residual stress and improving sensitivity.

As shown in fig. 2, in some embodiments, the connector 30 has a hollowed-out hole 32 and/or a hollowed-out groove 33 that longitudinally penetrate the connector 30, with one of the upper and lower surfaces of the connector 30 being planar. The hollow holes 32 or the hollow grooves 33 may be circumferentially arranged (as shown by a and b in fig. 2) on the connecting member 30, and the hollow holes 32 may be radially arranged (as shown by c in fig. 2) or irregularly arranged (as shown by d in fig. 2), so that the hollow holes 32 are staggered.

As shown in fig. 3, in some embodiments, the connector 30 includes one or more beams 34 from a top view, the beams 34 being in a straight spoke or a curved spoke to connect the substrate 10 and the piezoelectric composite vibration layer 20. The application can increase the sensitivity of the MEMS structure by providing the connecting piece 30 with the hollowed-out hole 32 or the hollowed-out groove 33 or the structure of one or more beams 34, and releasing the residual stress of the whole vibrating membrane. In particular, the MEMS structure in the embodiment shown in fig. 2 and 3 has a lower resonant frequency and a higher sensitivity than the connection 30 without the hollowed-out hole 32 or the hollowed-out groove 33.

As shown in fig. 1, in some embodiments, a first end of the connection member 30 is connected to the substrate 10, and a second end of the connection member 30 is connected to the vibration supporting layer 21 and has a common top surface with the vibration supporting layer 21. And in the embodiment shown in fig. 1 the material of the connection piece 30 is the same as the material of the vibration supporting layer 21. Or as shown in fig. 4, in some embodiments, the second end of the connecting member 30 is connected above the exposed vibration supporting layer 21, and when the material of the connecting member 30 and the material of the vibration supporting layer 21 are inconsistent, the bonding force of the connecting member 30 and the vibration supporting layer 21 is increased, so that the probability of fracture of the connecting member 30 and the vibration supporting layer 21 is reduced.

In some embodiments, the material of the connection member 30 is the same as or different from the material of the vibration supporting layer 21, and the material of the connection member 30 may include, but is not limited to, polyimide, parylene, polyurethane, or other organic film. When the connection member 30 is made of polyimide or the like which is softer than the vibration supporting layer 21, the piezoelectric composite vibration layer 20 is facilitated to release stress, and the vibration amplitude is improved, thereby improving the sensitivity of the MEMS structure. Notably, the Young's modulus of the material of the connector 30 is less than or equal to the Young's modulus of silicon nitride.

Furthermore, as shown in fig. 1, a groove 31 may be provided on the exposed substrate 10, the groove 31 being adjacent to the connection member 30. In other embodiments, the recess 31 extends laterally below the access member 30. By providing the recess 31, the vibration amplitude of the MEMS structure can be further increased to increase the sensitivity.

The MEMS structure may further include a dividing groove (not shown) extending from the upper surface of the piezoelectric unit through the vibration supporting layer 21 to the cavity 11, thereby dividing the piezoelectric unit of the MEMS structure into two or more pieces, improving sensitivity, and improving signal-to-noise ratio.

In some embodiments, the substrate 10 has a thickness of 50-500 μm, the first electrode layer 22 has a thickness ranging from 5-500nm, the first piezoelectric layer 23 has a thickness of 10-1000nm, the second electrode layer 24 has a thickness ranging from 5-500nm, and the first electrode layer 22, the first piezoelectric layer 23 and the second electrode layer 24 have a radius ranging from 50-5000nm, and the vibration supporting layer 21 has a radius ranging from 50-5000nm.

In summary, in the MEMS structure provided by the present application, the substrate 10 and the piezoelectric composite vibration layer 20 are connected through the connecting member 30, so that the piezoelectric composite vibration layer 20 is facilitated to release stress, and the vibration amplitude is improved, so that the sensitivity of the MEMS structure is improved. In addition, by improving the connecting piece 30 itself, for example, forming the hollow hole 32 or the hollow groove 33 on the connecting piece 30, or setting the connecting piece 30 to be one or more beams 34, the resonance frequency of the MEMS structure is reduced, so that the sensitivity of the MEMS structure is further improved.

In addition, the present application also provides a method of forming the MEMS structure, and it is noted that in the first embodiment, the material of the connection member 30 is the same as that of the vibration supporting layer 21. The method comprises the following specific steps:

As shown in fig. 5, in step S101, a substrate 10 is provided, and a vibration supporting layer 21, a first electrode layer 22, a first piezoelectric layer 23, and a second electrode layer 24 are sequentially formed on the substrate 10. Materials and forming methods of the substrate 10, the vibration supporting layer 21, the first electrode layer 22, the first piezoelectric layer 23, and the second electrode layer 24 have been described above, and are not described here again. Wherein the radius of the first electrode layer 22, the first piezoelectric layer 23 and the second electrode layer 24 is smaller than the radius of the vibration supporting layer 21. In some embodiments, a first electrode layer 22, a first piezoelectric layer 23, a second electrode layer 24, a second piezoelectric layer, and a third electrode layer may be sequentially formed over the substrate 10, resulting in a MEMS structure having a bimorph structure.

As shown in fig. 6, in step S102, the substrate 10 is bottom etched, thereby forming a cavity 11 penetrating the substrate 10.

As shown in fig. 7, in step S103, a support material layer 40 is formed on the bottom of the substrate 10. The support material layer 40 comprises aluminum or other metallic material. The support material layer 40 serves to support the piezoelectric composite vibration layer 20 in a subsequent step.

As shown in fig. 8, in step S104, the vibration supporting layer 21 is etched to form the hollowed-out hole 32 or the hollowed-out groove 33, or the beam 34.

As shown in fig. 8, in step S105, the grooves 31 extending into the substrate 10 are formed by etching the vibration supporting layer 21 and the substrate 10. In some embodiments, the recess 31 may also extend laterally under the connector 30 (not shown). In some embodiments, the order of step S104 and step S105 may be interchanged.

In step S106, the supporting material layer 40 is removed, thereby obtaining the MEMS structure shown in fig. 1.

In the second embodiment, the material of the connection member 30 may be different from that of the vibration supporting layer 21, which is the same as that of the first embodiment. Second embodiment after step S103 of the first embodiment, part of the vibration supporting layer 21 is removed to expose the substrate 10, and the area of the region of the vibration supporting layer 21 remains larger than that of the first electrode layer 22, thereby obtaining a structural diagram as shown in fig. 9. Then, the connection member 30 is formed over the substrate 10, the support material layer 40, and the vibration support layer 21, forming a structural diagram as shown in fig. 10. Then, the steps S104 and S106 in the first embodiment are continued, and the hollowed-out hole 32 is formed as shown in fig. 11, and then the supporting material layer 40 is removed, so as to obtain the MEMS structure shown in fig. 4.

In summary, by means of the technical scheme, the preparation process is stable, the signal to noise ratio is effectively improved, and the performance stability is improved. The MEMS structure provided based on the preparation method has higher sensitivity.

The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the application.

Claims

1. A MEMS structure, comprising:

a substrate having a cavity;

A piezoelectric composite vibration layer is formed directly above the cavity;

A connecting member, formed above the substrate and connecting the substrate and the piezoelectric composite vibration layer, wherein the connecting member is at the periphery of the piezoelectric composite vibration layer and at least one of the upper surface and the lower surface of the connecting member is a flat surface;

Wherein, the connecting member has a hollow hole and/or a hollow groove that penetrates the connecting member longitudinally; or, from a top view, the connecting member includes one or more beams, and the beams are in a straight spoke shape or a curved spoke shape to connect the substrate and the piezoelectric composite vibration layer;

Wherein, the piezoelectric composite vibration layer comprises: a vibration support layer formed above the substrate and covering the cavity; a piezoelectric unit formed above the vibration support layer, and the piezoelectric unit is suspended above the cavity;

Wherein, the first end of the connecting member is connected to the substrate, and the second end of the connecting member radially extends to connect to the vibration supporting layer.

2. The MEMS structure according to claim 1, characterized in that only one of the upper surface and the lower surface of the connecting member is a flat surface, and the other of the upper surface and the lower surface of the connecting member is uneven.

3 . The MEMS structure according to claim 1 , wherein a groove is provided on the exposed substrate, and the groove is adjacent to the connecting member.

The MEMS structure according to claim 3 , wherein the groove extends laterally to below the connecting member.

5 . The MEMS structure according to claim 1 , wherein the second end of the connector and the vibration support layer have a common top surface, or the second end of the connector is connected to the exposed top of the vibration support layer.

6 . The MEMS structure according to claim 1 , further comprising a dividing groove, wherein the dividing groove extends from an upper surface of the piezoelectric unit through the vibration supporting layer to the cavity.

7 . The MEMS structure according to claim 1 , wherein the material of the connecting member is the same as or different from the material of the vibration support layer, and the material of the connecting member comprises polyimide film, polyparaxylene, and polyurethane.

8. A method for forming a MEMS structure, comprising:

forming a vibration support layer and a piezoelectric unit in sequence above the substrate, wherein a radius of the piezoelectric unit is smaller than a radius of the vibration support layer;

etching a bottom of the substrate to form a cavity penetrating the substrate;

A connecting member is formed to connect the substrate and the piezoelectric unit, and the connecting member is at the periphery of the piezoelectric unit, at least one of the upper surface and the lower surface of the connecting member is a flat surface, a first end of the connecting member is connected to the substrate, and a second end of the connecting member radially extends to connect to the vibration support layer;

Wherein, it also includes: before forming the connecting member, forming a supporting material layer on the bottom surface of the substrate, the sidewall and the top surface of the cavity; after forming the connecting member, etching to form hollow holes and/or hollow grooves, or forming one or more beams on the connecting member; and removing the supporting material layer.

9. The forming method according to claim 8, characterized in that the method of forming the connecting member comprises:

The exposed vibration supporting layer is used as the connecting member to connect the substrate and the piezoelectric unit.

10. The forming method according to claim 8, characterized in that the method of forming the connecting member comprises:

removing the vibration support layer at the periphery of the piezoelectric unit to expose the substrate;

A connection member is formed to connect the substrate and the piezoelectric unit.

11. The forming method according to claim 8, characterized in that the method further comprises:

Prior to removing the support material layer, the substrate is etched to form a groove extending longitudinally into the substrate.

12 . The forming method according to claim 11 , wherein the groove extends laterally in the substrate to below the connecting member.