CN111866684A

CN111866684A - MEMS structure

Info

Publication number: CN111866684A
Application number: CN202010881828.8A
Authority: CN
Inventors: 刘端; 李冠华; 夏永禄
Original assignee: Anhui Aofei Acoustics Technology Co ltd
Current assignee: Anhui Aofei Acoustics Technology Co ltd
Priority date: 2020-08-28
Filing date: 2020-08-28
Publication date: 2020-10-30

Abstract

The application discloses MEMS structure includes: a substrate having a cavity; a vibration support layer formed over the substrate and covering the cavity; a first electrode layer formed over the vibration support layer; a piezoelectric layer formed over the first electrode layer; and a second electrode layer formed over the piezoelectric layer, one of the first and second electrode layers having a circumferential first dividing groove and a radial second dividing groove to divide the one of the first and second electrode layers into a middle region and a peripheral region that are separated, and the other of the first and second electrode layers having the middle region and the peripheral region connected. According to the MEMS structure, the second electrode layer or the first electrode layer with the first dividing groove is arranged in the MEMS structure, so that each film layer in the middle area and each film layer in the peripheral area can output voltage reversal signals, charge neutralization is effectively reduced, and the output sensitivity of the MEMS structure is improved.

Description

MEMS structure

Technical Field

The present application relates to the field of micro-electromechanical systems, and more particularly, to a MEMS structure.

Background

MEMS (Micro-Electro-Mechanical Systems ) microphones mainly include both capacitive type and piezoelectric type. The MEMS piezoelectric microphone is prepared by utilizing a micro-electromechanical 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 need of 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.

In order to solve the problem of how to improve the sensitivity of the MEMS structure in the related art, a common solution is to divide an electrode layer into a plurality of portions, but this method of dividing the electrode has a limited range for improving the sensitivity.

Disclosure of Invention

Aiming at the problem of how to improve the sensitivity of the MEMS structure in the related technology, the application provides the MEMS structure and the forming method thereof, which can effectively improve the sensitivity.

The technical scheme of the application is realized as follows:

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

a substrate having a cavity;

a vibration support layer formed over the substrate and covering the cavity;

a first electrode layer formed over the vibration support layer;

a piezoelectric layer formed over the first electrode layer;

and a second electrode layer formed over the piezoelectric layer, one of the first electrode layer and the second electrode layer having a circumferential first division groove and a radial second division groove to divide the one of the first electrode layer and the second electrode layer into a middle region and a peripheral region that are separated, and the other of the first electrode layer and the second electrode layer having a middle region and a peripheral region that are connected.

According to the MEMS structure, the second electrode layer or the first electrode layer with the first dividing groove is arranged in the MEMS structure, so that each film layer in the middle area and each film layer in the peripheral area can output voltage reversal signals, charge neutralization is effectively reduced, and the sensitivity of the MEMS structure is 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.

FIGS. 1-7 illustrate cross-sectional views of intermediate stages of a method of forming a MEMS structure, according to some embodiments;

FIG. 8 illustrates a perspective view of a MEMS structure according to some embodiments;

fig. 9 shows a sectional perspective view of fig. 8.

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 an embodiment of the present application, there is provided a MEMS structure and a method of forming the same, by which the MEMS structure will be described in detail below. The MEMS structure may be used for sensors or actuators, such as microphones, loudspeakers, hydrophones. In embodiments of the present application, the MEMS structure may comprise a piezoelectric MEMS microphone.

The forming method of the MEMS structure comprises the following steps:

referring to fig. 1, in step S101, a substrate 10 is provided, and a barrier layer 20, a vibration support layer 30 are formed over the substrate 10. The substrate 10 comprises silicon or any suitable silicon-based compound or derivative (e.g., silicon wafer, SOI, SiO)₂Polysilicon on Si). The substrate 10 may have various shapes, not limited to pentagons, hexagons, or other regular or irregular shapes. The material of barrier layer 20 includes silicon dioxide, phosphorous doped silicon oxide (PSG), zinc oxide, or other suitable sacrificial material. The barrier layer 20 may be formed by a CVD (Chemical Vapor Deposition), thermal oxidation process. In other embodiments, the step of forming the barrier layer 20 may be omitted. The material of the vibration support layer 30 includes silicon nitride (Si)₃N₄) Silicon oxide, monocrystalline silicon, polycrystalline silicon, or other suitable support material. In view of the problem of controlling the stress of the vibration support layer 30, the vibration support layer 30 may be provided in a multi-layered structure to reduce the stress. The method of forming the vibration support layer 30 includes a thermal oxidation method or a chemical vapor deposition method. It is noted that in some embodiments, the upper surface of the substrate 10 is flat, and thus the upper and lower surfaces of the barrier layer 20 and the vibration support layer 30 are both flatAnd (4) performing standing. In some embodiments, referring to fig. 6 and 7, a trench 11 may be formed over the substrate 10 by a photolithography process. The grooves 11 are used to form subsequent corrugated portions (not shown). A barrier layer 20 and a vibration support layer 30 are then conformally formed over the substrate 10 with the trenches 11.

Referring to fig. 2, in step S102, a first electrode material is formed over the vibration support layer 30 and patterned to form a first electrode layer 40. The first electrode material may be formed by electron beam evaporation, magnetron sputtering process. The first electrode material includes aluminum, gold, platinum, molybdenum, titanium, chromium, and composite films thereof or other suitable materials. For example, when the first electrode material is aluminum, the aluminum electrode layer may be formed by magnetron sputtering at a power of 300W and a pressure of 300MPa at normal temperature. In the process of patterning the first electrode material, the first electrode layer 40 may be divided into at least two partitions in a radial direction. In some embodiments, the zones are the same area. In some embodiments, the first electrode layer 40 has 12 equal partitions. It is noted that in embodiments where the substrate 10 has trenches 11, the first electrode layer 40 is conformally formed over the vibration support layer 30.

Referring to fig. 3, in step S103, a piezoelectric material is formed over the first electrode layer 40 and patterned to form the piezoelectric layer 50. The piezoelectric material 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 piezoelectric material may be formed by a CVD process or a magnetron sputtering process or other suitable process. When zinc oxide is used as the piezoelectric material, a radio frequency magnetron sputtering method can be adopted, the target material is ZnO, the radio frequency power is 80W, the pressure is 2Pa, and a zinc oxide film is formed on the substrate 10 at room temperature. When aluminum nitride is used as the piezoelectric material, a radio frequency magnetron sputtering method may be used, in which the target is aluminum, the radio frequency power is 200W, the pressure is 0.27Pa, the bias voltage is 0 to-320V, and the temperature is between room temperature and 80 ℃, so as to form an aluminum nitride film on the substrate 10.

Referring to fig. 4, in step S105, a second electrode material is formed over the piezoelectric layer 50 and patterned to form a second electrode layer 60 having first dividing grooves 61. The first dividing groove 61 is circumferentially disposed to divide the MEMS structure into a middle region 100 and a peripheral region 200. The material and formation process of the second electrode layer 60 may be the same as those of the first electrode layer 40. In addition, in the embodiment in which the substrate 10 has the grooves 11, the grooves 11 correspond to the positions of the first division grooves 61, and the vibration support layer 30, the first electrode layer 40, and the piezoelectric layer 50 directly below the first division grooves 61 have waved wrinkled portions (not shown in the drawings) between the central area 100 and the peripheral area 200. In some embodiments, an isolation layer (not shown) is disposed at a position between the first electrode layer 40 and the piezoelectric layer 50, or between the piezoelectric layer 50 and the second electrode layer 60, for preventing the first electrode layer 40 and the second electrode layer 60 from being short-circuited.

Specifically, referring to fig. 8 and 9, the first electrode layer 40 and the second electrode layer 60 each have a second division groove 65 in the radial direction, and the second division groove 65 divides each of the middle region 100 and the peripheral region 200 of the first electrode layer 40 and the second electrode layer 60 into corresponding at least two divided regions, in each of which the middle region 100 and the peripheral region 200 of the first electrode layer 40 are connected and the middle region 100 and the peripheral region 200 of the second electrode layer 60 are divided. The peripheral region 200 of the first aliquot of the second electrode layer 60 extends outward through the first conductive line 62 and the first conductive line 62 serves as one terminal of the MEMS structure. The middle region 100 of the first partition of the second electrode layer 60 is connected to the peripheral region 200 of the second partition of the second electrode layer 60 through the first conductive line 63 to realize series connection, the first partition is adjacent to the second partition, and adjacent two partitions are repeatedly connected in sequence through the plurality of first conductive lines 63. The middle region 100 of the last aliquot in the second electrode layer 60 extends outward through the third wire 64 and the third wire 64 serves as the other terminal of the MEMS structure. The third conductive line 64 extends outward in the second dividing groove 65.

In other embodiments, the arrangement of the first electrode layer 40 and the second electrode layer 60 may be interchanged, for example, the middle region 100 and the peripheral region 200 of the second electrode layer 60 are connected, and the middle region 100 and the peripheral region 200 of the first electrode layer 40 are separated. The first electrode layers 40 are connected in series by respective wires.

In step S106, through holes (not shown in the drawings) are formed in the first dividing grooves 61, the circumferentially arranged through holes extend through the piezoelectric layer 50, the first electrode layer 40 and the vibration supporting layer 30 to the cavities 12 to be formed later, and the projected areas of the first dividing grooves 61 are within the projected areas of the cavities 12. The via holes may be obtained by wet etching.

Referring to fig. 5, in step S107, the substrate 10 and the barrier layer 20 are bottom-etched up to the bottom surface of the vibration support layer 30 to form the cavity 12. Specifically, an insulating material and a photoresist are sequentially deposited and formed on the back surface of the substrate 10 through a standard photolithography process, the photoresist is patterned to form a mask layer, the exposed insulating material and the substrate 10 are dry-etched until the barrier layer 20 is exposed, and then the exposed barrier layer 20 is removed by wet etching. Finally, the insulating material on the back side of the substrate 10 is removed, thereby forming the cavity 12. To this end, the fabrication yields a MEMS structure. The piezoelectric layer 50 of the MEMS structure effects the conversion of acoustic energy into electrical energy under the piezoelectric effect. The first electrode layer 40 and the second electrode layer 60 transfer the generated electrical energy to other circuit elements.

In addition, in order to more clearly explain the structure of the MEMS, the following description will be made in detail. Referring to fig. 8 and 9, the MEMS structure includes:

a substrate 10 having a cavity 12;

a vibration support layer 30 formed over the substrate 10 and covering the cavity 12;

a first electrode layer 40 formed over the vibration support layer 30;

a piezoelectric layer 50 formed over the first electrode layer 40;

and a second electrode layer 60 formed over the piezoelectric layer 50 and having a first dividing groove 61 to divide the second electrode layer 60 into a middle area 100 and a peripheral area 200.

In summary, with the above technical solution of the present application, in the MEMS structure of the embodiment of the present application, the first dividing groove 61 divides the MEMS structure into the middle area 100 and the peripheral area 200, each film layer of the middle area 100 is equivalently suspended above the cavity 12, and the edge of each film layer of the peripheral area 200 is fixedly supported above the substrate 10, so that the suspended structure is beneficial to reducing the residual stress of the vibration support layer 30, the first electrode layer 40, the piezoelectric layer 50 and the second electrode layer 60. In the MEMS structure in which the first dividing groove 61 is not provided, since the electric charges generated from the entire membrane edge and the inner surface are opposite in sign, the electric charges generated from the piezoelectric layer 50 are mostly neutralized, resulting in a decrease in the output sensitivity of the MEMS structure. According to the MEMS structure, the second electrode layer 60 or the first electrode layer 40 with the first dividing groove 61 is arranged in the MEMS structure, so that each film layer of the middle area 100 and each film layer of the peripheral area 200 can output voltage opposite signs, charge neutralization is effectively reduced, and the output sensitivity of the MEMS structure is improved. Again, by opening the through-holes within the first dividing grooves 51, the residual stress of each film layer of the MEMS structure is further reduced.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A MEMS structure, comprising:

a substrate having a cavity;

a vibration support layer formed over the substrate and covering the cavity;

a first electrode layer formed over the vibration support layer;

a piezoelectric layer formed over the first electrode layer;

2. The MEMS structure of claim 1, wherein the first and second electrode layers each have the second dividing groove in a radial direction, and the second dividing groove divides each of the intermediate region and the peripheral region of the first and second electrode layers into corresponding at least two divided regions, in each divided region, the intermediate region and the peripheral region of one of the first and second electrode layers are connected, and the intermediate region and the peripheral region of the other of the first and second electrode layers are divided.

3. The MEMS structure of claim 2, wherein the peripheral region of the first partition of the other of the first electrode layer and the second electrode layer extends outward via a first wire and the first wire serves as one terminal of the MEMS structure;

the middle region of the first partition region of the other one of the first electrode layer and the second electrode layer is connected to the peripheral region of a second partition region of the other one of the first electrode layer and the second electrode layer through a second wire to realize series connection, the first partition region is adjacent to the second partition region, and two adjacent partition regions are repeatedly connected in sequence through a plurality of second wires;

the intermediate region of the last aliquot of the other of the first and second electrode layers extends outward via a third wire and the third wire serves as another terminal of the MEMS structure.

4. The MEMS structure of claim 3, wherein the third conductive line extends outward within the second split trench.

5. The MEMS structure of claim 1, wherein the vibration support layer directly below the first split trench has a flat upper surface, the MEMS structure further comprising a via extending through the first split trench to the cavity, a projected area of the first split trench being within a projected area of the cavity.

6. The MEMS structure of claim 5, wherein the vias are circumferentially arranged.

7. The MEMS structure of claim 1, wherein the vibration support layer directly below the first dividing groove has an undulating corrugated portion between the middle region and the peripheral region.

8. The MEMS structure of claim 1, further comprising a barrier layer formed between the substrate and the vibrating support layer.

9. The MEMS structure of claim 1, wherein the MEMS structure comprises a piezoelectric MEMS sensor.

10. The MEMS structure of claim 1, comprising an isolation layer formed at a location between the first electrode layer and the piezoelectric layer or at a location between the piezoelectric layer and the second electrode layer.