CN210609696U

CN210609696U - MEMS structure

Info

Publication number: CN210609696U
Application number: CN201921520786.4U
Authority: CN
Inventors: 刘端
Original assignee: Anhui Aofei Acoustics Technology Co ltd
Current assignee: Anhui Aofei Acoustics Technology Co ltd
Priority date: 2019-09-09
Filing date: 2019-09-09
Publication date: 2020-05-22
Anticipated expiration: 2029-09-09

Abstract

The application discloses a MEMS (micro electro mechanical system) structure, comprising: a substrate having a cavity; a piezoelectric composite vibration layer formed over the substrate and covering the cavity, the piezoelectric composite vibration layer having a dividing groove in a peripheral region; and the mass block is formed in the middle area of the upper surface of the piezoelectric composite vibration layer. The dividing grooves in the MEMS structure of the present application are formed in the peripheral region of the piezoelectric composite vibration layer, and the mass block is formed in the middle region of the upper surface of the piezoelectric composite vibration layer. Therefore, the middle area of the piezoelectric composite vibration layer is not isolated by the dividing groove, so that the stability of the MEMS structure and the consistency of products are improved.

Description

MEMS structure

Technical Field

The present application relates to the field of semiconductor technology, and more particularly, to a MEMS (micro electro mechanical Systems, abbreviated as micro electro mechanical Systems) structure.

Background

MEMS microphones (microphones) mainly include both capacitive type and piezoelectric type. The MEMS piezoelectric microphone is prepared by utilizing a micro-electro-mechanical system technology and a piezoelectric film technology, and has small size, small volume and good consistency due to the adoption of semiconductor planar technology, bulk silicon processing technology and other technologies. Meanwhile, compared with a capacitor microphone, the MEMS piezoelectric microphone also has the advantages of no bias voltage, large working temperature range, dust prevention, water prevention and the like, but the sensitivity is low, so that the development of the MEMS piezoelectric microphone is restricted. Also, the resonant frequency of piezoelectric MEMS microphones is difficult to adjust.

In order to solve the problem of how to adjust the resonant frequency of the piezoelectric MEMS microphone in the related art, no effective solution has been proposed.

SUMMERY OF THE UTILITY MODEL

Aiming at the problem of adjusting the resonant frequency of the MEMS structure in the related art, the application provides the MEMS structure, which can effectively adjust and control the resonant frequency 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; a piezoelectric composite vibration layer formed over the substrate and covering the cavity, the piezoelectric composite vibration layer having a dividing groove in a peripheral region; and the mass block is formed in the middle area of the upper surface of the piezoelectric composite vibration layer.

Wherein the dividing groove continuously extends from an upper surface of the piezoelectric composite vibration layer to a lower surface of the piezoelectric composite vibration layer in a first direction, and the dividing groove continuously extends from the peripheral region toward the intermediate region in a second direction, the first direction being perpendicular to the second direction.

Wherein the piezoelectric composite vibration layer includes: a first electrode layer formed over the substrate; a first piezoelectric layer formed over the first electrode layer; a second electrode layer formed over the first piezoelectric layer.

Wherein the piezoelectric composite vibration layer further includes: a vibration support layer formed between the substrate and the first electrode layer.

Wherein the piezoelectric composite vibration layer further includes: a second piezoelectric layer formed over the second electrode layer; a third electrode layer formed over the second piezoelectric layer.

Wherein the MEMS structure further comprises a sacrificial support layer formed below the piezoelectric composite vibration layer to support the piezoelectric composite vibration layer and then removed.

Wherein a part of the material of the substrate is formed directly below the piezoelectric composite vibration layer and between the cavities.

Wherein the area of the mass block is smaller than or equal to the area of the middle area, and the density of the mass block is greater than that of silicon nitride.

The material of the first electrode layer and the material of the second electrode layer in the peripheral area are provided with at least two mutually isolated partitions, the material of the first electrode layer and the material of the second electrode layer in the same partition form an electrode layer pair, and the electrode layer pairs between the partitions are sequentially connected in series.

The material of the first electrode layer, the material of the second electrode layer and the material of the third electrode layer in the peripheral area are provided with at least two mutually isolated partitions, the material of the first electrode layer and the material of the third electrode layer in the same partition are electrically connected and then form an electrode layer pair with the material of the second electrode layer, and the electrode layer pairs between the partitions are sequentially connected in series.

Wherein there is no electrode material in the middle region, and the dividing groove divides the first electrode layer, the second electrode layer or the third electrode layer in the peripheral region into at least two mutually isolated partitions.

Wherein the electrode material of the peripheral region and the electrode material of the middle region in the same level are separated, and the dividing groove divides the material of the first electrode layer, the material of the second electrode layer or the material of the third electrode layer in the peripheral region into at least two mutually isolated partitions.

The dividing grooves in the MEMS structure of the present application are formed in the peripheral region of the piezoelectric composite vibration layer, and the mass block is formed in the middle region of the upper surface of the piezoelectric composite vibration layer. Therefore, the middle area of the piezoelectric composite vibration layer is not isolated by the dividing groove, so that the stability of the MEMS structure and the consistency of products are improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used 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 it is obvious for those skilled in the art to obtain other drawings without creative efforts.

Various aspects of the present application may be better understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various elements may be arbitrarily increased or decreased for clarity of discussion.

FIG. 1 is a top view of a MEMS structure according to an embodiment of the present application;

FIGS. 2-4 are cross-sectional views along line B-B of the MEMS structure shown in FIG. 1 at intermediate stages of fabrication of the MEMS structure;

FIG. 5 is a cross-sectional view along line A-A of the MEMS structure shown in FIG. 1.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments that can be derived from the embodiments given herein by a person of ordinary skill in the art are intended to be within the scope of the present disclosure.

The following disclosure provides many different embodiments, or examples, for implementing different features of the application. Specific examples of components and arrangements are described below to simplify the present application. These are, of course, merely examples and are not intended to be limiting. For example, the dimensions of the elements are not limited to the disclosed ranges or values, but may depend on the process conditions and/or desired properties of the device. Further, in the following description, forming a first feature over or on a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. Various components may be arbitrarily drawn in different sizes for simplicity and clarity.

Furthermore, for ease of description, spatially relative terms such as "below", "lower", "above", "upper", and the like may be used herein to describe one element or component's relationship to another (or other) element or component as illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Additionally, the term "made of can mean" including "or" consisting of.

According to embodiments of the present application, a MEMS structure and a method of fabricating the same are provided, which may be applied to an acoustic-to-electrical transducer, such as a microphone.

In some embodiments, a method of fabricating a MEMS structure comprises the steps of:

referring to fig. 1 and 2 in combination, step S101 is to form a vibration supporting layer 24 on the front surface of the substrate 10. The substrate 10 comprises silicon or any suitable silicon-based compound or derivative (e.g., silicon wafer, SOI, polysilicon on SiO 2/Si). The vibration support layer 24 comprises a single or multi-layer composite membrane structure of silicon nitride (Si3N4), silicon oxide, single crystal silicon, polycrystalline silicon, or other suitable support material. In view of the problem of controlling the stress of the vibration support layer 24, the vibration support layer 24 may be provided as a multi-layer structure to reduce the stress. In some steps, this step S101 may be omitted or deleted. The method of forming the vibration support layer 24 includes a thermal oxidation method or a chemical vapor deposition method.

Step S102, a first electrode layer 21, a first piezoelectric layer 22, and a second electrode layer 23 are sequentially formed above the vibration support layer 24. In this embodiment, the first electrode layer 21, the first piezoelectric layer 22, and the second electrode layer 23 constitute a piezoelectric composite layer. The first piezoelectric layer 22 can convert the applied pressure into a voltage, and the first electrode layer 21 and the second electrode layer 23 can transmit the generated voltage to other integrated circuit devices. In some embodiments, the material of the first piezoelectric layer 22 includes one or more of zinc oxide, aluminum nitride, an organic piezoelectric film, lead zirconate titanate (PZT), a perovskite-type piezoelectric film, or other suitable materials. Methods of forming the first piezoelectric layer 22 include magnetron sputtering or other suitable methods. The material of the first electrode layer 21 and the second electrode layer 23 includes aluminum, gold, platinum, molybdenum, titanium, chromium, and a composite film composed of these or other suitable materials. Methods of forming the first electrode layer 21 and the second electrode layer 23 include physical vapor deposition or other suitable methods.

In step S103, a second piezoelectric layer (not shown) is formed on the second electrode layer 23, and a third electrode layer (not shown) is formed on the second piezoelectric layer. The material of the second piezoelectric layer includes one or more layers of zinc oxide, aluminum nitride, an organic piezoelectric film, lead zirconate titanate (PZT), a perovskite-type piezoelectric film, or other suitable materials. The material and method of formation of the second piezoelectric layer may be the same as or different from the material and method of formation of the first piezoelectric layer 22. The material of the third electrode layer includes aluminum, gold, platinum, molybdenum, titanium, chromium, and a composite film composed of these materials or other suitable materials. The material and the formation method of the third electrode layer may be the same as or different from those of the first electrode layer 21. In addition, in this embodiment, the piezoelectric composite layer of the MEMS structure has the first electrode layer 21, the first piezoelectric layer 22, the second electrode layer 23, the second piezoelectric layer, and the third electrode layer, so that a bimorph structure is formed, and the piezoelectric conversion efficiency of the MEMS structure is improved. In an embodiment where the vibration support layer 24 is not provided, a second piezoelectric layer and a third electrode layer may be formed in order above the second electrode layer 23. In some embodiments, this step S103 may be omitted or skipped. It is noted that in the embodiment shown in fig. 2, the piezoelectric composite vibration layer 20 includes a vibration support layer 24, a first electrode layer 21, a first piezoelectric layer 22, and a second electrode layer 23.

And 104, forming a mass block 30 in the middle area of the piezoelectric composite vibration layer 20, so as to be beneficial to reducing the resonance frequency of the piezoelectric composite vibration layer 20 and increasing the sensitivity of the MEMS structure. The mass 30 has a density greater than that of silicon nitride. The area of the mass 30 is less than or equal to the area of the middle region. In particular, the mass 30 has a density greater than 3.2kg/dm 3. The material of the mass 30 may include tungsten, gold, silver, and the like.

Referring to fig. 3, step 105, the back surface of the substrate 10 is etched to form a cavity 11, and the piezoelectric composite vibration layer 20 covers the cavity 11. The cavity 11 may be formed using DRIE (deep reactive ion etching) or wet etching. In some embodiments, a portion of the material 12 of the substrate 10 may remain directly below the proof mass 30 and between the cavities 11. The remaining portion of the material 12 of the substrate 10 may also be used to further tune the resonant frequency of the piezoelectric composite vibration layer 20. Thus, the cavity 11 includes a first region of a first depth D1 and a second region of a second depth D2, wherein the second region retains a portion of the material 12 of the substrate 10 and the second depth D2 is less than the first depth D1.

The remaining portion of material 12 of substrate 10 may be formed by, for example:

step S1051 may be employed to etch the substrate 10 of the first and second regions to the same depth, after which the substrate 10 of the second region is protected by masking with a masking layer and the etching of the substrate 10 of the first region is continued until reaching a layer above the substrate 10, thereby obtaining a portion 12 of the material of the remaining substrate 10.

Or step S1052 may be taken to mask the substrate 10 protecting the second area with a mask layer and etch the substrate 10 of the first and second areas to etch the substrate 10 to different depths until the substrate 10 of the first area is etched to reach a layer above the substrate 10. Here, use is made of the different etch rates between the mask layer and the substrate 10, so that a remaining part 12 of the material of the substrate 10 is obtained.

Referring to fig. 4, step S106, a sacrificial support layer 50 is conformally formed on the top surface and the sidewalls of the cavity 11, the sacrificial support layer 50 being under the piezoelectric composite vibration layer 20 to support the piezoelectric composite vibration layer 20. The material of the sacrificial support layer 50 includes a metal, such as aluminum or other suitable material. The sacrificial support layer 50 serves to support the piezoelectric composite vibration layer 20 in a subsequent process.

Referring to fig. 1 and 5 in combination, in step S107, the piezo-electric composite vibration layer 20 is etched to form dividing grooves 60 in the peripheral region of the piezo-electric composite vibration layer 20. The dividing grooves 60 continuously extend from the upper surface of the piezo-electric composite vibration layer 20 to the lower surface of the piezo-electric composite vibration layer 20 in the first direction, and the dividing grooves 60 continuously extend from the peripheral region toward the intermediate region in the second direction, the first direction being perpendicular to the second direction. In some embodiments, the dividing groove 60 may extend in the second direction from the peripheral region to the intermediate region up to adjacent the mass 30.

Step S108, removing the sacrificial support layer 50 after forming the dividing grooves 60, wherein the material of the sacrificial support layer 50 includes a metal.

Accordingly, the dividing groove 60 in the MEMS structure of the present application is formed at the peripheral region of the piezo-electric composite vibration layer 20, and the mass 30 is formed at the middle region of the upper surface of the piezo-electric composite vibration layer 20. Therefore, the middle region of the piezo-electric composite vibration layer 20 is not isolated by the dividing grooves 60, thereby improving the stability of the MEMS structure and the uniformity of the product. Moreover, compared with the cantilever beam structure, the structure in which the middle area is not isolated by the partition groove 60 reduces the process difficulty, and the reason is that the stress of each layer is strictly controlled by the complete cantilever beam structure, so that the process difficulty of realizing a smooth cantilever beam structure is large. But the requirement for controlling the stress of each layer is relatively reduced, and the process difficulty is reduced. Also, the structure in which the middle region is not isolated by the dividing grooves 60 increases the resonance frequency relative to the cantilever beam structure that is completely etched apart. The resonant frequency can be further reduced by the mass 30 to facilitate tuning to achieve the desired optimum resonant frequency.

In addition, in the embodiment where the piezoelectric composite layer of the MEMS structure has the first electrode layer 21, the first piezoelectric layer 22, and the second electrode layer 23, that is, the single chip, the material of the first electrode layer 21 and the material of the second electrode layer 23 in the peripheral region have at least two partitions isolated from each other, the material of the first electrode layer 21 and the material of the second electrode layer 23 in the same partition form an electrode layer pair, and the electrode layer pairs between different partitions are sequentially connected in series, so that the voltage generated by the MEMS structure is led out through a lead.

In the embodiment that the piezoelectric composite layer of the MEMS structure has a first electrode layer 21, a first piezoelectric layer 22, a second electrode layer 23, a second piezoelectric layer, and a third electrode layer, that is, a bimorph, the material of the first electrode layer 21, the material of the second electrode layer 23, and the material of the third electrode layer in the peripheral region have at least two mutually isolated partitions, the material of the first electrode layer 21 and the material of the third electrode layer in the same partition are electrically connected and then form an electrode layer pair with the material of the second electrode layer 23, and the electrode layer pairs between different partitions are sequentially connected in series to lead out the voltage generated by the MEMS structure through a lead.

In addition, as is apparent from fig. 1, since the middle region of the piezoelectric composite vibration layer 20 is not isolated by the dividing groove 60, there are two cases in the electrode layer arrangement in the present application, the first case is that the material of the electrode layer exists in the middle region. The second case is that there is no material of the electrode layers in the middle area, so that the electrode layers within a single level are separated into at least two current conductor parts by the dividing slots 60, and so that the mass 30 is formed above the piezoelectric layer. The electrode layer arrangement in both cases is specifically described below.

In the first case, when the material of the electrode layer is present in the middle region and the electrode material of the peripheral region is separated from the electrode material of the middle region in the same level, the electrode material of the peripheral region is divided into independent partitions by the dividing grooves 60, that is, the dividing grooves 60 divide the material of the first electrode layer 21, the material of the second electrode layer 23, or the material of the third electrode layer of the peripheral region into at least two mutually isolated partitions, and then the electrode layer pairs in different partitions are connected in series, so that the generated voltage of the peripheral region is led out through the lead, when the mass 30 is formed above the material of the electrode layer (i.e., the material of the uppermost electrode layer). Or when the material of the electrode layer exists in the middle area and the electrode material of the peripheral area and the electrode material of the middle area in the single level are not separated, the electrode layer in the single level forms a whole body of electric conductor, and the electrode layer pairs are not required to be connected in series and then led out through a lead.

In the second case, when there is no material of the first electrode layer 21 and no material of the second electrode layer 23 at the middle region of the piezoelectric composite vibration layer 20 (i.e. a single-chip structure), the mass block 30 is located above the first piezoelectric layer 22, and the first electrode layer 21 and the second electrode layer 23 have at least two mutually isolated partitions, the partitions of the first electrode layer 21 and the second electrode layer 23 in the same partition form electrode layer pairs, and the electrode layer pairs between different partitions are sequentially connected in series, so as to improve the sensitivity of the MEMS structure. Alternatively, the material of the first electrode layer 21, the material of the second electrode layer 23 and the material of the third electrode layer are absent at the middle region of the piezoelectric composite vibration layer 20 (i.e., the bimorph structure), with the mass 30 located above the second piezoelectric layer.

Correspondingly, the application also provides a MEMS structure obtained based on the manufacturing method, and the MEMS structure comprises a substrate 10, a cavity 11; a piezoelectric composite vibration layer 20 formed over the substrate 10 and covering the cavity 11, the piezoelectric composite vibration layer 20 having dividing grooves 60 in a peripheral region; and a mass 30 formed in a middle region of an upper surface of the piezoelectric composite vibration layer 20. Various details regarding the MEMS structure have been described in the process flow and are not described in detail herein.

The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A MEMS structure, comprising:

a substrate having a cavity;

a piezoelectric composite vibration layer formed over the substrate and covering the cavity, the piezoelectric composite vibration layer having a dividing groove in a peripheral region;

and the mass block is formed in the middle area of the upper surface of the piezoelectric composite vibration layer.

2. The MEMS structure of claim 1, wherein the dividing grooves extend continuously in a first direction from an upper surface of the piezo-electric composite vibration layer to a lower surface of the piezo-electric composite vibration layer, and the dividing grooves extend continuously in a second direction from the peripheral region toward the intermediate region, the first direction being perpendicular to the second direction.

3. The MEMS structure of claim 1, wherein the piezoelectric composite vibration layer comprises:

a first electrode layer formed over the substrate;

a first piezoelectric layer formed over the first electrode layer;

a second electrode layer formed over the first piezoelectric layer.

4. The MEMS structure of claim 3, wherein the piezoelectric composite vibration layer further comprises:

a vibration support layer formed between the substrate and the first electrode layer.

5. The MEMS structure of claim 3, wherein the piezoelectric composite vibration layer further comprises:

a second piezoelectric layer formed over the second electrode layer;

a third electrode layer formed over the second piezoelectric layer.

6. The MEMS structure of claim 1, further comprising a sacrificial support layer formed below the piezo-electric composite vibration layer to support the piezo-electric composite vibration layer and then removed.

7. The MEMS structure of claim 1, wherein a portion of the material of the substrate is formed directly beneath the piezoelectric composite vibration layer and between the cavities.

8. The MEMS structure of claim 1, wherein the mass has an area less than or equal to the area of the middle region, and a density greater than a density of silicon nitride.

9. The MEMS structure of claim 3, wherein the material of the first electrode layer and the material of the second electrode layer in the peripheral region have at least two isolated partitions, the material of the first electrode layer and the material of the second electrode layer in the same partition form an electrode layer pair, and the electrode layer pairs between different partitions are sequentially connected in series.

10. The MEMS structure of claim 5, wherein the material of the first electrode layer, the material of the second electrode layer and the material of the third electrode layer in the peripheral region have at least two partitions isolated from each other, the material of the first electrode layer and the material of the third electrode layer in the same partition are electrically connected and then form an electrode layer pair with the material of the second electrode layer, and the electrode layer pairs between different partitions are sequentially connected in series.

11. The MEMS structure of claim 10, wherein there is no electrode material at the middle region, and the dividing trench divides the first electrode layer, the second electrode layer, or the third electrode layer of the peripheral region into at least two mutually isolated partitions.

12. The MEMS structure of claim 10, wherein the electrode material of the peripheral region and the electrode material of the intermediate region within the same level are separated, and the dividing groove separates the material of the first electrode layer, the material of the second electrode layer, or the material of the third electrode layer of the peripheral region into at least two mutually isolated partitions.