L-shaped connecting beam acoustic emission device and preparation method thereof

Abstract

The present invention discloses an L-shaped connecting beam acoustic emission device and a preparation method thereof. The acoustic emission device comprises, from bottom to top, a substrate layer, an alternating dielectric layer and a metal layer, and a passivation layer. A rectangular cavity is etched on the nth dielectric layer, a rectangular diaphragm, an L-shaped connecting beam and an upper electrode are formed on the top of the cavity, and a lower electrode is formed at the bottom of the cavity. During preparation, the back end (BEOL) layer of the COMS process is used as the structural layer of the MEMS device, the COMS electronic layer is integrated below the MEMS device layer, the metal layers are interconnected by tungsten plugs, and finally a rectangular cavity, a rectangular diaphragm and an L-shaped connecting beam are formed by etching. The L-shaped connecting beam acoustic emission device of the present invention has the advantages of good reliability, small size, high sensitivity, low manufacturing cost, and easy mass production.

Description

Technical Field

[0001] The invention relates to the technical field of CMOS-MEMS integrated sensor manufacturing, in particular to an L-shaped connecting beam acoustic emission device and a preparation method thereof. Background Art

[0002] Acoustic emission is an instantaneous high-frequency stress wave (or sound wave) generated by the rapid release of energy due to the local redistribution of stress or strain in the process of crack expansion, plastic deformation or phase change inside an object. The frequency of the sound wave ranges from a few hertz to tens of megahertz. The emitted sound waves can be used for material research, quality control, determination of structural integrity and safety monitoring. In recent years, acoustic emission inspection technology has attracted the attention of some countries, and they have conducted a lot of research on this and achieved certain results. In the production and use of military products, the advantages of acoustic emission are also being used to ensure product quality. Acoustic emission devices manufactured with integrated CMOS-MEMS technology have the advantages of wide detection bandwidth, high sensitivity, miniaturization, integration, good consistency and batch production. Therefore, we urgently need to develop a CMOS-MEMS-based acoustic emission device with a new structure and preparation method to meet the needs of the current industry. Summary of the invention

[0003] The object of the present invention is to provide an L-shaped connecting beam acoustic emission device based on the above background technology, which can be applied to technical fields such as non-destructive testing.

[0004] The present invention is achieved through the following technical solutions:

[0005] An L-shaped connecting beam acoustic emission device comprises a base layer, on which a first dielectric layer, a first metal layer, a second dielectric layer, a second metal layer, ..., an (n-1)th dielectric layer, an (n-1)th metal layer, an nth dielectric layer, and an nth metal layer are sequentially arranged from bottom to top, where n is greater than or equal to 3; adjacent metal layers are interconnected by tungsten plugs, a passivation layer is arranged on the nth metal layer, and an upper electrode welding point and a lower electrode welding point are arranged on the passivation layer; a rectangular cavity is etched on the nth dielectric layer; The passivation layer and the nth metal layer at the top of the rectangular cavity form a rectangular diaphragm and four L-shaped connecting beams. The rectangular diaphragm is located at the center and its size is smaller than the lateral size of the rectangular cavity. The four L-shaped connecting beams are distributed at both ends of the upper membrane edge of the rectangular diaphragm and both ends of the lower membrane edge of the rectangular diaphragm. The nth metal layer in the rectangular diaphragm and the L-shaped connecting beam serves as an upper electrode, and the (n-1)th metal layer at the bottom of the rectangular cavity serves as a lower electrode, and the upper electrode and the lower electrode are interconnected through a tungsten plug. The first metal layer to the (n-2)th metal layer serve as an electronic layer.

[0006] As a preferred technical solution, the base layer is made of silicon wafer, the dielectric layer is made of silicon oxide, the metal layer is made of aluminum, and the passivation layer is made of silicon nitride.

[0007] As a preferred technical solution, a plurality of rectangular through holes arranged in an array and communicating with the rectangular cavity are evenly distributed on the rectangular diaphragm.

[0008] As a preferred technical solution, a CMOS signal processing circuit is provided on the electronic layer.

[0009] As a preferred technical solution, the silicon wafer is a lightly doped P-type (100) silicon wafer, with a typical doping concentration of N A ≈10 15 cm -3 .

[0010] Furthermore, the present invention also provides a method for preparing the L-shaped connecting beam acoustic emission device, comprising the following steps:

[0011] 1) A silicon wafer is selected as a starting base layer, and a CMOS process is used to complete the production of a CMOS active area, n dielectric layers, n metal layers and a passivation layer on the base layer, and each metal layer is interconnected through a tungsten plug; wherein the nth metal layer is used as a layer body for producing an upper electrode, the n-1th metal layer is used as a layer body for producing a lower electrode, the nth dielectric layer is used as a sacrificial layer for etching a rectangular cavity, the passivation layer and the nth metal layer are used as main layers for producing a rectangular diaphragm and an L-shaped connecting beam, and a plurality of rectangular through holes arranged in an array are formed on the passivation layer and the nth metal layer, the plurality of rectangular through holes are evenly distributed within the rectangular boundary range of the rectangular cavity, and the bottom ends of the rectangular through holes extend to the nth dielectric layer;

[0012] 2) Etching the passivation layer and the nth metal layer and patterning to form a rectangular diaphragm and an L-shaped connecting beam portion;

[0013] 3) Using dry etching, a rectangular cavity is formed in the nth dielectric layer, so that the rectangular diaphragm and the L-shaped connecting beam are partially suspended;

[0014] 4) Electrical welding to lead out electrode welding points, and finally obtaining the acoustic emission device based on CMOS-MEMS integration.

[0015] As a preferred technical solution, dry etching is performed using hydrofluoric acid gas.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1) The acoustic emission device of the present invention has the characteristics of good reliability, small size, wide frequency band, high sensitivity, low manufacturing cost, and easy batch production;

[0018] 2) The preparation method of the present invention can greatly improve the performance of acoustic emission, allowing for smaller packaging and achieving lower packaging and instrument costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a schematic top view of the overall structure of the acoustic emission device of the present invention (not packaged).

[0021] Figure 2 for Figure 1 AA section view in (unencapsulated).

[0022] Figure 3 Schematic diagram of the cross-sectional microstructure of the acoustic emission device of the present invention (unpackaged).

[0023] In the figure: 1-base layer, 2-tungsten plug, 3-passivation layer, 4-upper electrode solder joint, 5-lower electrode solder joint, 6-cavity, 7-rectangular through hole, 8-rectangular lower electrode, 9-rectangular diaphragm, 10-L-type cantilever beam, 11-first edge support, 12-second edge support;

[0024] L1-the first dielectric layer, L(n-1)-the (n-1)th dielectric layer, Ln-the nth dielectric layer, M1-the first metal layer, M(n-1)-the (n-1)th metal layer, Mn-the nth metal layer. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field without creative work, including the embodiments of the present invention, belong to the protection scope of the present invention.

[0026] In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate the orientation or position relationship as shown in the integrated drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance, quantity or position.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] like Figures 1 to 3 As shown, an L-shaped connecting beam acoustic emission device includes a substrate layer 1, the substrate layer 1 is made of a silicon wafer, and the silicon wafer is a lightly doped P-type (100) silicon wafer with a typical doping concentration of N A ≈10 15 cm -3 ; The base layer 1 is provided with a first dielectric layer L1, a first metal layer M1, a second dielectric layer, a second metal layer, ..., the (n-1)th dielectric layer L(n-1), the (n-1)th metal layer M(n-1), the nth dielectric layer Ln, the nth metal layer Mn in order from bottom to top, wherein n≥3, the dielectric layer is made of silicon oxide, and the metal layer is made of aluminum; the adjacent metal layers are interconnected by tungsten plugs 2, and a passivation layer is provided on the nth metal layer Mn. The passivation layer 3 is made of silicon nitride, and an upper electrode solder joint 4 and a lower electrode solder joint 5 are arranged on the passivation layer 3; a rectangular cavity 6 is etched on the nth dielectric layer Ln, and the rectangular cavity 6 is filled with air. The nth dielectric layer Ln around the rectangular cavity 6 forms a first edge support 11; the passivation layer 3 and the nth metal layer Mn on the top of the rectangular cavity 6 are partially etched to form a rectangular diaphragm 9 and four L-shaped connecting beams 10, and the rectangular diaphragm 9 is located at the center and its size is smaller than the lateral size of the rectangular cavity 6. The four L-shaped connecting beams 10 are distributed at both ends of the upper membrane edge and the lower membrane edge of the rectangular diaphragm 9. The passivation layer 3 and the n-th metal layer Mn except the rectangular diaphragm 9 and the four L-shaped connecting beams 10 form a second edge support 12 for supporting the four L-shaped connecting beams 10. The rectangular diaphragm 9 is evenly provided with a plurality of rectangular through holes 7 distributed in an array and communicating with the rectangular cavity 6. The rectangular through holes 7 are filled with air. The n-th metal layer Mn in the rectangular diaphragm 9 and the L-shaped connecting beam 10 serves as an upper electrode, and the (n-1)-th metal layer M(n-1) located at the bottom of the rectangular cavity 6 serves as a lower electrode. The lower electrode is a rectangular lower electrode 8. The size of the rectangular lower electrode 8 is the same as that of the rectangular diaphragm 9. The rectangular diaphragm 9 and the rectangular lower electrode 8 are aligned vertically. The upper electrode at the top of the rectangular cavity 6 and the rectangular lower electrode 8 at the bottom are interconnected through a tungsten plug 2. The first metal layer M1 to the (n-2)-th metal layer serve as an electronic layer, and a CMOS signal processing circuit is provided on the electronic layer.

[0029] The method for preparing the L-shaped connecting beam acoustic emission device uses the back-end (BEOL) layer of the COMS process as the structural layer of the MEMS device, the COMS electronic layer is integrated below the MEMS device layer, and the metal layers are interconnected through tungsten plugs 2, specifically comprising the following steps:

[0030] 1) A silicon wafer is selected as a starting base layer 1, and a CMOS process is used to complete the production of a CMOS active area, an n-layer dielectric layer, an n-layer metal layer and a passivation layer 3 on the base layer 1, and each metal layer is interconnected through a tungsten (W) plug; wherein the n-th metal layer Mn is used as an upper electrode, the n-1-th metal layer M(n-1) is used as a lower electrode, the n-th dielectric layer Ln is used as a sacrificial layer for etching a rectangular cavity 6, the passivation layer 3 and the n-th metal layer Mn are used as the main body of a rectangular diaphragm 9 and an L-shaped connecting beam 10, and a plurality of rectangular through holes 7 arranged in an array are formed on the passivation layer 3 and the n-th metal layer Mn, the plurality of rectangular through holes 7 are evenly distributed within the rectangular boundary range of the rectangular cavity 6, and the bottom end of the rectangular through hole 7 extends to the n-th dielectric layer Ln.

[0031] In this step, the base layer 1 is suitable for almost any flat substrate, such as silicon wafers, glass wafers, etc. In order to adapt to the CMOS process, a silicon wafer is selected as the base layer 1. The silicon wafer uses a lightly doped P-type (100) silicon wafer with a typical doping concentration of N A ≈10 15 cm -3 ;

[0032] The CMOS process includes a 0.18um process and an advanced process with a smaller characteristic line width. The four basic micro-manufacturing technologies of the CMOS process: deposition, photolithography, doping and etching are combined to complete the production of the CMOS active area, n dielectric layers, n metal layers and the passivation layer 3 layer by layer; when depositing the dielectric layer, plasma enhanced chemical vapor deposition (PECVD) can be used to deposit silicon oxide; a metal layer is formed on each dielectric layer by sputtering metal aluminum, a layer of photoresist is coated on the metal layer, and the mask pattern is transferred to the photoresist by photolithography technology. The photoresist pattern is used as a mask and then the pattern of each metal layer is defined by a wet etching process to realize the functions of different metal layers; the metal layer is often used for electrical interconnection, electrode material, resistor, etc. In the present invention, the metal layer is used to make upper and lower electrodes and electronic layers.

[0033] 2) etching the passivation layer 3 and the nth metal layer Mn, and patterning to form a rectangular diaphragm 9 and an L-shaped connecting beam 10;

[0034] 3) Dry etching is used to form a rectangular cavity 6 on the nth dielectric layer Ln, so that the rectangular diaphragm 9 and the four L-shaped connecting beams 10 are partially suspended; wherein the dry etching is performed using hydrofluoric acid gas, and the hydrofluoric acid gas is used to isotropically dry-etch the silicon oxide in the sacrificial layer. The hydrofluoric acid gas has a relatively high selectivity for the metal layer and will not corrode the metal layer during the dry etching process.

[0035] 4) The entire structure is air-encapsulated, and the rectangular cavity 6 on the structure forms an air-tight cavity; wherein, the air encapsulation forms an air-tight cavity by depositing parylene; in order to ensure the airtightness of the working environment of the device, the device needs to be air-tightly encapsulated, and the through hole can be sealed by chemical vapor deposition (CVD) oxide or nitride, and the device can be sealed by plating parylene.

[0036] The acoustic emission device prepared by the present invention has the characteristics of good reliability, small size, wide frequency band, high sensitivity, low manufacturing cost, and easy mass production. It has advantages in preparing small-size and large-scale array ultrasonic probes and can be applied to many fields such as medicine, military, industry, and agriculture.

[0037] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An L-shaped connecting beam acoustic emission device, characterized in that: The invention comprises a base layer, on which a first dielectric layer, a first metal layer, a second dielectric layer, a second metal layer, ..., an (n-1)th dielectric layer, an (n-1)th metal layer, an nth dielectric layer, and an nth metal layer are arranged in order from bottom to top, where n≥3; adjacent metal layers are interconnected by tungsten plugs, a passivation layer is arranged on the nth metal layer, and an upper electrode soldering point and a lower electrode soldering point are arranged on the passivation layer; a rectangular cavity is etched on the nth dielectric layer; a passivation layer on the top of the rectangular cavity The n-th metal layer is partially etched to form a rectangular diaphragm and four L-shaped connecting beams. The rectangular diaphragm is located at the center and its size is smaller than the lateral size of the rectangular cavity. The four L-shaped connecting beams are distributed at both ends of the upper membrane edge of the rectangular diaphragm and both ends of the lower membrane edge of the rectangular diaphragm. The n-th metal layer in the rectangular diaphragm and the L-shaped connecting beam serves as an upper electrode, the (n-1)-th metal layer at the bottom of the rectangular cavity serves as a lower electrode, and the upper electrode and the lower electrode are interconnected through a tungsten plug. The first metal layer to the (n-2)-th metal layer serve as an electronic layer.

2. The L-shaped connecting beam acoustic emission device according to claim 1, characterized in that: The base layer is made of silicon wafer, the dielectric layer is made of silicon oxide, the metal layer is made of aluminum, and the passivation layer is made of silicon nitride.

3. The L-shaped connecting beam acoustic emission device according to claim 2, characterized in that: A plurality of rectangular through holes arranged in an array and communicating with the rectangular cavity are evenly arranged on the rectangular diaphragm.

4. The L-shaped connecting beam acoustic emission device according to any one of claims 1 to 3, characterized in that: A CMOS signal processing circuit is provided on the electronic layer.

5. The L-shaped connecting beam acoustic emission device according to claim 2, characterized in that: The silicon wafer is a lightly doped P-type (100) silicon wafer.

6. The method for preparing the L-shaped connecting beam acoustic emission device according to claim 4, characterized in that: The steps include: 1) A silicon wafer is selected as a starting base layer, and a CMOS process is used to complete the production of a CMOS active area, n dielectric layers, n metal layers and a passivation layer on the base layer, and each metal layer is interconnected through a tungsten plug; wherein the nth metal layer is used as a layer body for producing an upper electrode, the n-1th metal layer is used as a layer body for producing a lower electrode, the nth dielectric layer is used as a sacrificial layer for etching a rectangular cavity, the passivation layer and the nth metal layer are used as main layers for producing a rectangular diaphragm and an L-shaped connecting beam, and a plurality of rectangular through holes arranged in an array are formed on the passivation layer and the nth metal layer, the plurality of rectangular through holes are evenly distributed within the rectangular boundary range of the rectangular cavity, and the bottom ends of the rectangular through holes extend to the nth dielectric layer; 2) Etching the passivation layer and the nth metal layer and patterning to form a rectangular diaphragm and an L-shaped connecting beam portion; 3) Using dry etching, a rectangular cavity is formed in the nth dielectric layer, so that the rectangular diaphragm and the L-shaped connecting beam are partially suspended; 4) Electric welding, lead out electrode welding points.

7. The method for preparing the L-shaped connecting beam acoustic emission device according to claim 6, characterized in that: The dry etching is performed using hydrofluoric acid gas.

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