Preparation method of MEMS microphone chip and suspended membrane unit based on piezoelectric film

Abstract

The present invention relates to a MEMS microphone chip based on a piezoelectric film, including a MEMS chip substrate, a cavity that runs through from top to bottom, a suspended film body formed by a plurality of suspended film units connected in series installed on the cavity, the suspended film body sealingly covers the cavity, the suspended film unit uses a piezoelectric layer as a substrate, and a metal molybdenum layer, a silicon oxide layer and a silicon nitride layer are sequentially stacked on the upper and lower surfaces of the piezoelectric layer. The suspended film body is a pentagonal structure, and the suspended film body is composed of five suspended film units combined and spliced, and each suspended film unit is triangular. The present invention uses a piezoelectric film instead of a capacitor, and uses the piezoelectric effect to achieve zero-power monitoring, and sets a plurality of suspended films, which are connected in series to effectively improve the sensitivity to sound.

Description

Technical Field

[0001] The present invention belongs to the technical field of chip design, and in particular, relates to a method for preparing a MEMS microphone chip and a suspended membrane unit based on a piezoelectric film. Background Art

[0002] A MEMS microphone is a capacitor integrated on a micro-silicon wafer. It can be manufactured using a surface mount process, can withstand very high reflow temperatures, is easily integrated with CMOS processes and other audio circuits, and has improved noise cancellation performance and good RF and EMI suppression capabilities. The full potential of MEMS microphones has yet to be tapped, but products using this technology have already demonstrated many advantages in a variety of applications, especially in mid- to high-end mobile phone applications.

[0003] MEMS manufacturing process (Microfabrication Process) is a general term for microstructure processing technology from nanometer scale to millimeter scale. In a broad sense, MEMS manufacturing process has a wide range of methods, involving almost all modern processing technologies. Originated from semiconductor and microelectronics technology, it uses photolithography, epitaxy, thin film deposition, oxidation, diffusion, injection, sputtering, evaporation, etching, dicing and packaging as basic process steps to manufacture complex three-dimensional micro-processing technology.

[0004] 1. Lithography Editing

[0005] Photolithography is the process of transferring the pattern made on the photolithography mask to the surface of the substrate. Regardless of the type of micro device being processed, the microfabrication process can be decomposed into one or more cycles of the three process steps of thin film deposition, photolithography and etching. Photolithography is at the forefront of the MEMS manufacturing process, and its performance such as pattern resolution, overlay accuracy, photoresist sidewall morphology, photoresist defects and photoresist etching resistance directly affects the success or failure of subsequent processes.

[0006] 2. Stripping

[0007] The lift-off process is to first coat the substrate with glue and perform photolithography, and then prepare a metal film. Where there is photoresist, the metal film is formed on the photoresist, and where there is no photoresist, the metal film is directly formed on the substrate. When a solvent is used to remove the photoresist on the substrate, the unnecessary metal falls off in the solvent as the photoresist dissolves, while the metal part directly formed on the substrate is retained to form a pattern. Lift-off is commonly used for the patterning of platinum, gold, silicide and refractory metals.

[0008] 3. Wet etching

[0009] Wet etching is widely used to prepare microstructures such as probes, cantilever beams, V-grooves and thin films due to its simple equipment, mass production and good selectivity.

[0010] 4. Dry etching

[0011] Dry etching is a technique that uses plasma to perform etching.

[0012] 5. Oxidation

[0013] Silicon oxide films are widely used as selective diffusion masks in device production. At the same time, the silicon dioxide film grown on the silicon surface not only has good adhesion to silicon, but also has stable chemical properties and electrical insulation. The resistivity of SiO2 prepared by high-temperature oxidation can be as high as 10Ω·cm or more, and its intrinsic breakdown electric field strength is about 10~10V / cm. The density of SiO2 prepared by different methods is between 2.0 and 2.3g / cm, and the refractive index is between 1.43 and 1.47. The oxide layer has multiple applications in MEMS manufacturing:

[0014] 1) Device protection and isolation

[0015] 2) Surface passivation,

[0016] 3) Gate oxide dielectric,

[0017] 4) Doping barrier,

[0018] 5) Dielectric layer between metal layers.

[0019] 6. Doping

[0020] Intrinsic semiconductors have very few carriers and low conductivity. Therefore, if a small amount of impurities are added to them, the conductivity of the impurity semiconductor will be greatly enhanced. The main doping methods are diffusion and implantation.

[0021] 7. Chemical Vapor Deposition

[0022] Chemical Vapor Deposition (CVD) is a technology that uses various energy sources such as heating, plasma excitation or light radiation to form solid thin films through chemical reactions in gaseous or vaporous chemical substances in the gas phase or gas-solid interface in a reactor. There are three commonly used chemical vapor deposition technologies:

[0023] 1) Atmospheric pressure chemical vapor deposition;

[0024] 2) Low pressure chemical vapor deposition;

[0025] 3) Plasma enhanced chemical vapor deposition.

[0026] 8. Vacuum coating

[0027] Vacuum coating is to place solid materials in a vacuum chamber, and under vacuum conditions, use a certain energy form to force the atoms or molecules of the solid materials to detach from the surface and spread freely on the wall of the container. When the substrate is placed in a vacuum container, the spread atoms or molecules will be adsorbed on the substrate and gradually form a thin film.

[0028] Most microphones in use are ECM (electret capacitor) microphones, a technology that has been around for decades. The working principle of ECM is to use a polymer diaphragm that has a permanent charge. Compared with the polymer diaphragm of ECM, the performance of MEMS microphones is very stable at different temperatures, and its sensitivity is not affected by temperature, vibration, humidity and time. Due to its strong heat resistance, MEMS microphones can withstand high-temperature reflow soldering at 260°C without any change in performance. Since the sensitivity changes little before and after assembly, it can also save audio debugging costs during the manufacturing process. MEMS microphones require external bias provided by ASIC, while ECM does not have such bias. Effective biasing will enable MEMS microphones to maintain stable acoustic and electrical parameters over the entire operating temperature range, and also support microphone designs with different sensitivities. Traditional ECMs are usually larger than MEMS microphones and cannot be operated by SMT (surface mount technology). In the manufacturing process of MEMS microphones, SMT reflow soldering simplifies the manufacturing process and can omit a manufacturing step that is usually performed manually. In an ECM microphone, electronic components for signal processing must be added; in a MEMS microphone, only additional dedicated functions need to be added on top. The advantage of this additional function compared to an ECM is that the microphone has a high power supply rejection ratio, which can effectively suppress fluctuations in the power supply voltage. Another advantage is the broadband RF suppression function integrated on the chip, which is not only particularly important for RF applications such as mobile phones, but also for all devices that operate similarly to mobile phones, such as hearing aids. The small diaphragm of a MEMS microphone has another advantage. The small membrane with a diameter of less than 1mm is also light in weight, which means that compared to an ECM, a MEMS microphone will have lower vibration coupling to the PCB noise caused by a speaker mounted on the same PCB.

[0029] Currently, most MEMS microphone chips use the capacitive principle and are processed into suspended membranes using the MEMS process. The suspended membrane structure is a capacitor composed of upper and lower electrodes. It is not sensitive enough to sound and needs to be improved. Summary of the invention

[0030] The present invention provides a MEMS microphone chip based on a piezoelectric film, which uses a piezoelectric film to replace a capacitor, realizes zero-power monitoring by means of the piezoelectric effect, and arranges multiple groups of suspended membranes, which are connected in series, effectively improving the sensitivity to sound.

[0031] To achieve the above object, the present invention adopts the following technical solutions:

[0032] The present invention provides a MEMS microphone chip based on a piezoelectric film, comprising a MEMS chip substrate, wherein a cavity penetrating from top to bottom is opened on the MEMS chip substrate, a suspended film body formed by a plurality of suspended film units connected in series is installed on the cavity, the suspended film body is sealed and covers the cavity, the suspended film unit takes a piezoelectric layer as a substrate, and a metal molybdenum layer, a silicon oxide layer and a silicon nitride layer are sequentially stacked on the upper and lower surfaces of the piezoelectric layer respectively.

[0033] Furthermore, the suspended membrane body is a pentagonal structure, and the suspended membrane body is composed of five suspended membrane units combined and spliced, and each suspended membrane unit is triangular.

[0034] A method for preparing a suspended film unit, comprising the following steps:

[0035] Step 1: RCA clean the silicon wafer and laser mark it;

[0036] Step 2: The marked silicon wafer is placed in the growth chamber of the PECVD equipment to grow SiO2 / Si3N4;

[0037] Step 3: After the SiO2 / Si3N4 is grown, the silicon wafer is coated with photoresist, and the photoresist is cured by a coating and developing machine, and the wafer is placed in a photolithography machine for photolithography according to mask 1, followed by a developing operation, and cured by a hot plate;

[0038] Step 4: magnetron sputtering to grow the lower electrode plate, that is, sputtering a layer of metal molybdenum;

[0039] Step 5: Remove the glue, apply glue again, and use mask plate 2 to photolithography the electrode connection area;

[0040] Step 6: Remove the glue, apply glue again, and use a mask to three-photolithography the piezoelectric layer growth area, and use MOCVD equipment to grow the piezoelectric layer;

[0041] Step 7: Remove the glue, apply glue again, and photoetch the upper electrode area on the mask plate 4, and grow the upper electrode by magnetron sputtering, that is, sputtering a layer of metal molybdenum;

[0042] Step 8: Remove the glue, apply glue again, and use mask plate 5 to photolithography the electrode connection area;

[0043] Step nine, remove the glue, apply glue again, and use the mask plate six to photolithography the protective layer area, and use PECVD equipment to grow a silicon oxide layer;

[0044] Step 10, remove the glue, apply glue again, and use mask plate 7 to photolithography the back overhanging film area;

[0045] Step 11: grow a layer of metal aluminum on the front and back surfaces using PVD equipment, and then etch the suspended film area on the back surface using a deep silicon etching process to prepare a suspended film unit.

[0046] Furthermore, the thickness of the silicon wafer in step 1 is 400um.

[0047] Furthermore, in step 2, the growth thickness of SiO2 / Si3N4 is 1.5 um and the growth time is 30 minutes.

[0048] Furthermore, in step 4, the thickness of the sputtered metal molybdenum is 0.5 um, and the sputtering time is 1 hour; in step 7, the thickness of the sputtered metal molybdenum is 0.5 um, and the sputtering time is 1 hour.

[0049] Furthermore, in step six, the piezoelectric layer is grown using MOCVD equipment with a growth thickness of 400 nm and a growth time of 40 minutes.

[0050] Furthermore, in step nine, a silicon oxide layer is grown using PECVD equipment with a thickness of 200 nm and a growth time of 10 minutes.

[0051] Furthermore, in step eleven, the PVD equipment grows metal aluminum with a thickness of 200 nm; the deep silicon etching process etches the suspended film area for 1.5 hours.

[0052] The beneficial effects of the present invention are:

[0053] 1. Using piezoelectric film instead of capacitors can achieve zero-power monitoring, that is, the chip itself does not consume power when not awakened by external sound waves; it has great potential to further reduce the signal-to-noise ratio;

[0054] 2. Compared with condenser microphones, the present invention avoids the chip failure problem caused by the adhesion of the upper and lower plates;

[0055] 3. The present invention adopts pentagonal suspension membranes to manufacture 5 groups of triangular piezoelectric suspension membranes respectively, and connects them in series through metal interconnection or ohmic contact, so as to further improve the sensitivity and reliability of the chip to sound waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a structural schematic diagram of the present invention;

[0057] Figure 2 for Figure 1 A top view of

[0058] Figure 3 for Figure 1 Left view of;

[0059] Figure 4 Schematic diagram of the structure of the suspended membrane unit.

[0060] Wherein: the reference numerals are: suspension membrane unit 1, MEMS chip substrate 2, cavity 3, silicon nitride layer 4, silicon oxide layer 5, metal molybdenum layer 6, piezoelectric layer 7. DETAILED DESCRIPTION

[0061] The present invention will be further described below in conjunction with the accompanying drawings.

[0062] In the description of the present invention, it is necessary to understand that the terms "center", "up", "down", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0063] 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. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0064] A MEMS microphone chip based on a piezoelectric film comprises a MEMS chip substrate 2, on which a cavity 3 is provided which passes through from top to bottom, on which a suspended film body formed by a plurality of suspended film units 1 connected in series is installed, and which is sealed and covers the cavity 3, wherein the suspended film unit 1 takes a piezoelectric layer 7 as a substrate, and a metal molybdenum layer 6, a silicon oxide layer 5 and a silicon nitride layer 4 are stacked in sequence on the upper and lower surfaces of the piezoelectric layer 7 respectively.

[0065] The suspended membrane body is a pentagonal structure, and is formed by combining and splicing five suspended membrane units 1, and each suspended membrane unit 1 is triangular.

[0066] A method for preparing a suspended film unit, comprising the following steps:

[0067] (1) RCA cleaning and laser marking are performed on silicon wafers with a thickness of 400um.

[0068] (2) The marked silicon wafer is placed in the growth chamber of the PECVD equipment to grow SiO2 / Si3N4 with a growth thickness of 1.5 μm and a growth time of about 30 minutes;

[0069] (3) applying photoresist, solidifying the photoresist with a photoresist developer, placing the photoresist in a photolithography machine for photolithography according to mask 1, and then performing a development operation and solidifying the photoresist with a hot plate;

[0070] (4) magnetron sputtering growth of the lower electrode, that is, sputtering a layer of metal Mo with a thickness of 0.5 μm and a sputtering time of about 1 hour;

[0071] (5) Remove the glue, apply glue again, and use mask 2 to photolithography the electrode connection area;

[0072] (6) removing the glue, applying glue again, and photolithography the piezoelectric layer growth area with mask 3, and growing the piezoelectric layer with MOCVD equipment, with a growth thickness of 400 nm and a growth time of 40 minutes;

[0073] (7) Remove the glue, apply glue again, and photoetch the upper electrode area on the mask 4, and grow the upper electrode by magnetron sputtering, that is, sputter a layer of metal Mo with a thickness of 0.5 μm and a sputtering time of 1 hour;

[0074] (8) Removing the glue, applying glue again, and photolithography the electrode connection area using mask 5;

[0075] (9) Remove the glue, apply glue again, and use mask 6 to photolithography the protective layer area, and use PECVD equipment to grow a silicon oxide layer with a thickness of 200 nm for 10 minutes;

[0076] (10) removing the glue, applying glue again, and photolithography the overhanging film area on the back side with mask 7;

[0077] (11) A layer of metal Al with a thickness of 200 nm is grown on the front and back surfaces using PVD equipment; the suspended film area is etched on the back surface using a deep silicon etching process for 1.5 hours.

[0078] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a suspended film unit, characterized in that: A suspended membrane unit (1) in a MEMS microphone chip based on a piezoelectric film is prepared. The MEMS microphone chip based on a piezoelectric film comprises a MEMS chip substrate (2). A cavity (3) extending vertically through the MEMS chip substrate (2) is provided. A suspended membrane body formed by a plurality of groups of suspended membrane units (1) connected in series is installed on the cavity (3). The suspended membrane body is sealed and covers the cavity (3). The suspended membrane unit (1) has a piezoelectric layer (7) as a substrate. A metal molybdenum layer (6), a silicon oxide layer (5) and a silicon nitride layer (4) are sequentially stacked on the upper and lower surfaces of the piezoelectric layer (7). The suspended membrane body is a pentagonal structure. The suspended membrane body is formed by combining and splicing five suspended membrane units (1). Each suspended membrane unit (1) is triangular in shape. The steps of preparing the suspended membrane unit (1) are as follows: Step 1: RCA clean the silicon wafer and laser mark it; Step 2: The marked silicon wafer is placed in the growth chamber of the PECVD equipment to grow SiO2 / Si3N4; Step 3: After the SiO2 / Si3N4 is grown, the silicon wafer is coated with photoresist, and the photoresist is cured by a coating and developing machine, and the wafer is placed in a photolithography machine for photolithography according to mask 1, followed by a developing operation, and cured by a hot plate; Step 4: magnetron sputtering to grow the lower electrode plate, that is, sputtering a layer of metal molybdenum; Step 5: Remove the glue, apply glue again, and use mask plate 2 to photolithography the electrode connection area; Step 6: Remove the glue, apply glue again, and use a mask to three-photolithography the piezoelectric layer growth area, and use MOCVD equipment to grow the piezoelectric layer; Step 7: Remove the glue, apply glue again, and photoetch the upper electrode area on the mask plate 4, and grow the upper electrode by magnetron sputtering, that is, sputtering a layer of metal molybdenum; Step 8: Remove the glue, apply glue again, and use mask plate 5 to photolithography the electrode connection area; Step nine, remove the glue, apply glue again, and use the mask plate six to photolithography the protective layer area, and use PECVD equipment to grow a silicon oxide layer; Step 10, remove the glue, apply glue again, and use mask plate 7 to photolithography the back overhanging film area; Step 11: grow a layer of metal aluminum on the front and back surfaces using PVD equipment, and then etch the suspended film area on the back surface using a deep silicon etching process to prepare a suspended film unit (1).

2. The method for preparing a suspended film unit according to claim 1, characterized in that: The thickness of the silicon wafer in step 1 is 400um.

3. The method for preparing a suspended film unit according to claim 2, characterized in that: Step 2 The growth thickness of SiO2 / Si3N4 is 1.5um and the growth time is 30 minutes.

4. The method for preparing a suspended film unit according to claim 1, characterized in that: In step 4, the thickness of the sputtered metal molybdenum is 0.5 um, and the sputtering time is 1 hour; in step 7, the thickness of the sputtered metal molybdenum is 0.5 um, and the sputtering time is 1 hour.

5. The method for preparing a suspended film unit according to claim 1, characterized in that: In step six, a piezoelectric layer is grown using MOCVD equipment with a growth thickness of 400 nm and a growth time of 40 minutes.

6. The method for preparing a suspended film unit according to claim 1, characterized in that: In step nine, a silicon oxide layer is grown using PECVD equipment with a thickness of 200 nm and a growth time of 10 minutes.

7. The method for preparing a suspended film unit according to claim 1, characterized in that: In step eleven, the PVD equipment grows metal aluminum with a thickness of 200 nm; the deep silicon etching process etches the suspended film area for 1.5 hours.

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