CN110677795A

CN110677795A - MEMS structure

Info

Publication number: CN110677795A
Application number: CN201911099148.4A
Authority: CN
Inventors: 刘端
Original assignee: Anhui Afei Acoustic Technology Co Ltd
Current assignee: Anhui Afei Acoustic Technology Co Ltd
Priority date: 2019-11-12
Filing date: 2019-11-12
Publication date: 2020-01-10

Abstract

The application discloses MEMS structure includes: a substrate having a cavity and a post located within the cavity; and the piezoelectric composite vibration layer is formed right above the cavity, the first end of the strut is connected with the substrate, and the second end of the strut supports the piezoelectric composite vibration layer. The MEMS structure adopts the support to support the piezoelectric composite vibration layer, thereby being beneficial to improving the sensitivity of the MEMS structure.

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.

Aiming at the problem of how to improve the sensitivity of a piezoelectric MEMS structure in the related art, an effective solution is not provided at present.

Disclosure of Invention

The MEMS structure is provided for solving the problem that the sensitivity of the MEMS structure in the related art is low, and the sensitivity of the MEMS structure can be improved.

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 and a post located within the cavity;

and the piezoelectric composite vibration layer is formed right above the cavity, the first end of the strut is connected with the substrate, and the second end of the strut supports the piezoelectric composite vibration layer.

Wherein the second ends of the struts are connected to the middle portion and/or the edge portion of the piezoelectric composite vibration layer.

Wherein the depth of the cavity is less than the thickness of the substrate, and the substrate at the bottom of the cavity is provided with a through hole.

Wherein the first end of the post is connected to the middle portion of the substrate at the bottom of the cavity.

Wherein the MEMS structure further comprises a barrier layer formed over the substrate at the bottom of the cavity.

Wherein the support column extends to the outside of the substrate in the thickness direction of the substrate, and the piezoelectric composite vibration layer is separated from the substrate by a gap in the thickness direction of the substrate.

Wherein the MEMS structure further comprises a first sacrificial layer formed within the cavity and underlying the piezoelectric composite vibration layer, the first sacrificial layer being subsequently removed.

Wherein the MEMS structure further comprises a second sacrificial layer formed over and on the sidewalls of the piezoelectric composite vibration layer and contacting the first sacrificial layer, the second sacrificial layer being subsequently removed.

The MEMS structure further comprises a limiting piece, the limiting piece is suspended above the piezoelectric composite vibration layer to limit the vibration of the piezoelectric composite vibration layer, and the area of the limiting piece is partially overlapped with the area of the piezoelectric composite vibration layer in the thickness direction of the substrate.

Wherein the piezoelectric composite vibration layer covers the cavity, and the area of the piezoelectric composite vibration layer is larger than that of the cavity.

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 comprises an isolation layer formed on the top surface and the side wall of the first piezoelectric layer, and the isolation layer is located below the second electrode layer.

The MEMS structure adopts the support to support the piezoelectric composite vibration layer, thereby being beneficial to improving the sensitivity of the MEMS structure. The limit piece prevents the piezoelectric composite vibration layer from being damaged due to overlarge amplitude, so that the reliability and the stability of the MEMS structure are improved. On the other hand, the MEMS structure increases the acoustic resistance through the limiting piece, and low-frequency sound leakage is prevented. In addition, the MEMS structure provided by the application connects the support pillar to the substrate with the second through hole, so that the vibration stability of the piezoelectric composite vibration layer is increased.

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 schematic diagram of a MEMS structure from a first perspective in accordance with an embodiment of the present application;

FIG. 2 is a schematic diagram of a MEMS structure from a second perspective in accordance with an embodiment of the present application;

fig. 3-10 are cross-sectional views of intermediate stages of a method of forming a MEMS structure according to an embodiment of the application.

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, spatially relative terms such as "below … … (beneath)", "below … … (below)", "lower (lower)", "above … … (above)", "upper (upper)" and the like may be used herein to describe the relationship of one element or component to another (or other) element or component as illustrated in the figures for ease of description. 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. In addition, the term "made from … …" can mean "including" or "consisting of … …".

Referring collectively to fig. 1 and 2, in accordance with embodiments of the present application, a MEMS structure is provided that may be used, but is not limited to, for a sensor such as a microphone or microphone, or other actuator. The MEMS structure includes a substrate 10, a support post 40, and a piezoelectric composite vibration layer 30. The MEMS structure will be described in detail below.

The substrate 10 has a cavity 11, and the pillars 40 are located within the cavity 11. In some embodiments, the depth of the cavity 11 is less than the thickness of the substrate 10, the substrate 10 at the bottom of the cavity 11 having a through second via 12. In some embodiments, the MEMS structure further comprises a barrier layer 20 (to be shown in fig. 5), the barrier layer 20 being formed over the substrate 10 at the bottom of the cavity 11. In some embodiments, the support posts 40 extend out of the substrate 10 in the thickness direction of the substrate 10.

The piezoelectric composite vibration layer 30 is formed right above the cavity 11, and a first end of the support pillar 40 is connected to the substrate 10 and a second end of the support pillar 40 supports the piezoelectric composite vibration layer 30. In some embodiments, the piezoelectric composite vibration layer 30 covers the cavity 11, and the area of the piezoelectric composite vibration layer 30 is larger than that of the cavity 11. In some embodiments, the area of the piezoelectric composite vibration layer 30 may also be smaller than or equal to the area of the cavity 11. In some embodiments, since the support posts 40 extend outside the substrate 10 in the thickness direction of the substrate 10, the piezoelectric composite vibration layer 30 is separated from the substrate 10 by a gap in the thickness direction of the substrate 10. In some embodiments, the first end of the post 40 is connected to a middle portion of the substrate 10 at the bottom of the cavity 11. In some embodiments, the second ends of the struts 40 are connected to the middle portion and/or the edge portion of the piezoelectric composite vibration layer 30. When the second end of the support post 40 is connected to the edge portion of the piezoelectric composite vibration layer 30, it is advantageous to electrically connect the first electrode layer 31 and the second electrode layer 33 of the piezoelectric composite vibration layer 30 to an external circuit. Also, in the embodiment shown in the drawings, the support posts 40 are all in a columnar shape, but in other embodiments, the support posts 40 may be in a plate shape and the second ends of the support posts 40 support the piezoelectric composite vibration layer 30 in the radial direction of the piezoelectric composite vibration layer 30, and furthermore, the support posts 40 may also extend beyond the piezoelectric composite vibration layer 30 in the radial direction of the piezoelectric composite vibration layer 30, thereby facilitating the wiring connection of the first electrode layer 31 and the second electrode layer 33.

In some embodiments, the MEMS structure further includes a stopper 60 (to be shown in fig. 10), the stopper 60 being suspended above the piezoelectric composite vibration layer 30 to restrict vibration of the piezoelectric composite vibration layer 30, a region of the stopper 60 partially overlapping with a region of the piezoelectric composite vibration layer 30 in a thickness direction of the substrate 10. In some embodiments, the stoppers 60 may surround the outer periphery of the composite piezoelectric vibrating layer 30, or may be distributed only at several positions of the composite piezoelectric vibrating layer 30.

In the MEMS structure, the radius of the piezoelectric composite vibration layer 30 is a constant value, and the larger the contact area between the support post 40 and the piezoelectric composite vibration layer 30 is, the higher the eigenfrequency of the MEMS structure is. Further, when the contact area of the pillar 40 is constant (i.e., the radius of the pillar 40 is constant), and the inner diameter of the ring electrode (i.e., at least one of the first electrode layer 31 and the second electrode layer 33 is in a ring shape) is also constant and larger than the radius of the pillar 40, the smaller the outer diameter of the ring electrode is, the greater the sensitivity of the MEMS structure is.

The MEMS structure supports the piezoelectric composite vibration layer 30 by the support posts 40, thereby contributing to improvement of the sensitivity of the MEMS structure. The limit member 60 prevents the piezoelectric composite vibration layer 20 from being damaged due to excessive vibration amplitude, thereby increasing the reliability and stability of the MEMS structure. On the other hand, the MEMS structure increases the acoustic resistance through the stopper 60, preventing low frequency sound leakage. In addition, the MEMS structure provided by the present application connects the support post 40 to the substrate 10 having the second through hole 12, thereby increasing the vibration stability of the piezoelectric composite vibration layer 30.

According to an embodiment of the present application, a MEMS structure and a method of forming the same are provided, and a method of forming the MEMS structure will be described in detail below.

In step S101, a first sacrificial layer 51 and a pillar 40 protruding from the substrate 10 are formed on the front surface of the substrate 10, and the top surface of the first sacrificial layer 51 is flush with the top surface of the pillar 40. Two methods are shown below to form the first sacrificial layer 51 and the pillars 40.

The first method of forming the first sacrificial layer 51 and the support post 40 is as follows: referring to fig. 3 and 4, a patterned hard mask layer 41 is formed on the front surface of the substrate 10, and the substrate 10 is etched to form a cavity 11, wherein a portion of the material of the substrate 10 and a portion of the material of the hard mask layer 41 within the cavity 11 form the pillars 40. The substrate 10 comprises silicon or any suitable silicon-based compound or derivative (e.g., silicon wafer, SOI). The cavity 11 may be formed by a dry etching or wet etching process. It is noted that the depth of the cavity 11 is less than the thickness of the substrate 10, so that the bottom of the cavity 11 still retains a portion of the substrate 10 material.

The second method of forming the first sacrificial layer 51 and the support post 40 is as follows: a patterned first mask layer (not shown) is formed on the front surface of the substrate 10, the substrate 10 is etched for the first time by using the patterned first mask layer to form a protrusion in the middle of the substrate 10, and then the patterned first mask layer is removed. A patterned second mask layer (not shown) is then formed over the edge portions and the protrusions of the substrate 10, the substrate 10 is subjected to a second etching using the patterned second mask layer, thereby forming the pillars 40 and the cavities 11, and then the patterned second mask layer is removed.

Referring to fig. 5, a barrier layer 20 is then conformally formed over the substrate 10 having the cavity 11, and this barrier layer 20 will serve to protect the first sacrificial layer 51 formed in the subsequent step. The material of the barrier layer 20 includes, but is not limited to, SiO formed by a thermal oxidation process₂. The specific method for forming the barrier layer 20 comprises the following steps: the barrier layer 20 is formed by conformally forming a barrier material on the bottom surface of the cavity 11, the top surface and sidewalls of the substrate 10, and the top surface of the pillar 40, and then removing the barrier material on the top surface and sidewalls of the substrate 10 and the top surface of the pillar 40.

Next, referring to fig. 6, the cavity 11 is filled with the first sacrificial layer 51. The first sacrificial layer 51 may be filled beyond the top surface of the support post 40, and then the top surface of the first sacrificial layer 51 may be made flush with the top surface of the support post 40 by a CMP (Chemical Mechanical Polishing) method. The material of the first sacrificial layer 51 includes zinc Oxide or LTO (short for Low Temperature Oxide) or other corrosion prone material.

In step S102, referring to fig. 6, the piezoelectric composite vibration layer 30 is formed over the support post 40 and the first sacrificial layer 51. Wherein the piezoelectric composite vibration layer 30 covers the cavity 11, and the area of the piezoelectric composite vibration layer 30 is larger than that of the cavity 11, or the area of the piezoelectric composite vibration layer 30 is smaller than or equal to that of the cavity 11.

The method of forming the piezoelectric composite vibration layer 30 includes:

a vibration support layer (not shown) is formed over the pillars 40 and the first sacrificial layer 51. The vibration support layer comprises silicon nitride (Si)₃N₄) Silicon oxide, monocrystalline silicon, polycrystalline silicon, or other suitable support material. In some embodiments, the step of forming the vibrating support layer may be skipped or omitted.

A first electrode material is formed over the vibration support layer, the first electrode material is patterned to form a first electrode layer 31, and a portion of the first sacrificial layer 51 is exposed, the first electrode layer 31 comprising aluminum, gold, platinum, molybdenum, titanium, chromium, and composite films thereof or other suitable materials.

A first piezoelectric material is formed over the first electrode layer 31 and patterned to form a first piezoelectric layer 32, the first piezoelectric layer 32 comprising zinc oxide, aluminum nitride, an organic piezoelectric film, lead zirconate titanate (PZT), a perovskite-type piezoelectric film, or other suitable material.

An isolation layer (not shown) is conformally formed over the first piezoelectric layer 32, covering the top surface and sidewalls of the first piezoelectric layer 32. The material of the isolation layer includes a low-temperature oxide such as low-temperature silicon oxide to prevent the first electrode layer 31 and the second electrode layer 33 above and below the first piezoelectric layer 32 from being short-circuited, and also to protect the first piezoelectric layer 32 from etching in a step of removing the second sacrificial layer 52 in a subsequent step. The step of forming the isolation layer may be skipped or omitted.

A second electrode material is formed over the isolation layer and patterned to form a second electrode layer 33, the second electrode layer 33 comprising aluminum, gold, platinum, molybdenum, titanium, chromium, and composite films thereof or other suitable materials. The first piezoelectric layer 32 may convert the applied pressure into a voltage, and the first electrode layer 31 and the second electrode layer 33 may transmit the generated voltage to other integrated circuit devices. In some embodiments, the first electrode layer 31 and the second electrode layer 33 have at least two partitions isolated from each other, the partitions of the first electrode layer 31 and the second electrode layer 33 corresponding to each other constitute an electrode layer pair, and the electrode layer pairs are sequentially connected in series. Therefore, the piezoelectric thin film transducers of a plurality of independent cantilever-like structures are electrically connected in series, so that the sensitivity of the MEMS structure is further improved.

A second piezoelectric material is formed over the second electrode layer 33 and patterned to form a second piezoelectric layer (not shown). A third electrode material is formed over the second piezoelectric material and patterned to form a third electrode layer (not shown). In the embodiment where the piezoelectric composite vibration layer 30 has the second piezoelectric layer and the third electrode layer, the step of forming the vibration support layer may be omitted. Alternatively, in an embodiment in which the piezoelectric composite vibration layer 30 has a vibration support layer, the first electrode layer 31, the first piezoelectric layer 32, and the second electrode layer 33, the step of forming the second piezoelectric layer and the third electrode layer may be omitted.

Step S103, referring to fig. 7, forms a second sacrificial layer 52 over the piezoelectric composite vibration layer 30 and the first sacrificial layer 51, and then removes a part of the material of the first sacrificial layer 51 and a part of the material of the second sacrificial layer 52 outside the sidewall of the second sacrificial layer 52 to expose the substrate 10. Referring to fig. 8, a stopper material is formed over the substrate 10 and the second sacrificial layer 52.

Step S104, etching the limiting material to form a first through hole 61 extending to the second sacrificial layer 52, wherein the area of the first through hole 61 is smaller than the area of the second sacrificial layer 52, the limiting material with the first through hole 61 forms a limiting member 60, and the area of the limiting member 60 overlaps with the area of the piezoelectric composite vibration layer 30 in the thickness direction of the substrate 10. The limiting member 60 is used to limit the vibration amplitude of the piezoelectric composite vibration layer 30, and avoid excessive deformation of the piezoelectric composite vibration layer 30. In some embodiments, the position-limiting elements 60 may completely and continuously surround the top of the composite piezoelectric vibration layer 30 when viewed from the top, or the position-limiting elements 60 may be provided only at a plurality of discrete positions of the composite piezoelectric vibration layer 30. The material of the position-limiting member 60 is different from the material of the first sacrificial layer 51 and the second sacrificial layer 52, and the material of the position-limiting member 60 includes, but is not limited to, metal, oxide, nitride, silicon, polyimide, paraxylene, and SU-8 photoresist.

In step S105, referring to fig. 9, the bottom surface of the substrate 10 is etched until the second via 12 contacting the first sacrificial layer 51 is formed, the second via 12 being located at the bottom of the first sacrificial layer 51. In some embodiments, prior to performing step S101, the substrate 10 may be subjected to boron ion (or other suitable ion) implantation, and the boron ions may diffuse to a depth of the substrate 10 that is less than or equal to the thickness of the substrate 10. Thereby allowing the material of the substrate 10 with the implanted boron ions to have a reduced etching rate compared to the material of the substrate 10 without the implanted boron ions, and therefore, the bottom surface of the substrate 10 without the implanted boron ions can be removed using wet etching to form the second via hole 12. In embodiments with a barrier layer 20, the barrier layer 20 may also be removed until reaching the first sacrificial layer 51. In some embodiments, the bottom surface of the substrate 10 may be dry etched to form the second via 12. When the dry etching process is employed, the second through-hole 12 is rectangular in longitudinal section.

Step S106, referring to fig. 10, removes the first sacrificial layer 51 and the second sacrificial layer 52 in the same etching process or different etching processes to form the cavity 11 and the gap between the piezoelectric vibrating layer and the stopper 60. The material of the second sacrificial layer 52 may be the same as the material of the first sacrificial layer 51, thereby facilitating the removal of the first sacrificial layer 51 and the second sacrificial layer 52 in the same etching process. Or the material of the second sacrificial layer 52 may be different from that of the first sacrificial layer 51.

After removing the first and second sacrificial layers 51 and 52, the first end of the support post 40 is connected to the middle portion of the substrate 10 at the bottom of the cavity 11, and the second end of the support post 40 is connected to the middle portion and/or the edge portion of the piezoelectric composite vibration layer 30.

The MEMS structure formed based on the above method uses the support post 40 to support the piezoelectric composite vibration layer 30, thereby facilitating to improve the sensitivity of the MEMS structure. The limit member 60 prevents the piezoelectric composite vibration layer 20 from being damaged due to excessive vibration amplitude, thereby increasing the reliability and stability of the MEMS structure. On the other hand, the MEMS structure increases the acoustic resistance through the stopper 60, preventing low frequency sound leakage. In addition, the MEMS structure provided by the present application connects the support post 40 to the substrate 10 having the second through hole 12, thereby increasing the vibration stability of the piezoelectric composite vibration layer 30. In addition, the method for forming the MEMS structure has simpler process steps.

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 and a post located within the cavity;

2. The MEMS structure of claim 1, wherein the second ends of the posts are connected to a middle portion and/or an edge portion of the piezoelectric composite vibrating layer.

3. The MEMS structure, as set forth in claim 1, wherein the depth of the cavity is less than the thickness of the substrate, the substrate at the bottom of the cavity having a through via.

4. The MEMS structure of claim 3, wherein the first end of the post is connected to a middle portion of the substrate at the bottom of the cavity.

5. The MEMS structure of claim 3, further comprising a barrier layer formed over the substrate at the bottom of the cavity.

6. The MEMS structure of claim 1, wherein the posts extend out of the substrate in a thickness direction of the substrate, and the piezoelectric composite vibration layer is separated from the substrate by a gap in the thickness direction of the substrate.

7. The MEMS structure of claim 1, further comprising a first sacrificial layer formed within the cavity and underlying the piezoelectric composite vibration layer, the first sacrificial layer being subsequently removed.

8. The MEMS structure of claim 7, further comprising a second sacrificial layer formed over and on sidewalls of the piezoelectric composite vibration layer and contacting the first sacrificial layer, the second sacrificial layer being subsequently removed.

9. The MEMS structure of claim 1, further comprising a stop suspended above the piezoelectric composite vibration layer to limit vibration of the piezoelectric composite vibration layer, a region of the stop partially overlapping with a region of the piezoelectric composite vibration layer in a thickness direction of the substrate.

10. The MEMS structure of claim 1, wherein the piezoelectric composite vibration layer covers the cavity, and an area of the piezoelectric composite vibration layer is larger than an area of the cavity.

11. 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.

12. The MEMS structure of claim 11, wherein the piezoelectric composite vibration layer further comprises an isolation layer formed on a top surface and a sidewall of the first piezoelectric layer, and the isolation layer is located below the second electrode layer.