WO2021184591A1 - 一种mems麦克风的加工方法和mems麦克风 - Google Patents

一种mems麦克风的加工方法和mems麦克风 Download PDF

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Publication number
WO2021184591A1
WO2021184591A1 PCT/CN2020/099401 CN2020099401W WO2021184591A1 WO 2021184591 A1 WO2021184591 A1 WO 2021184591A1 CN 2020099401 W CN2020099401 W CN 2020099401W WO 2021184591 A1 WO2021184591 A1 WO 2021184591A1
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WIPO (PCT)
Prior art keywords
layer
polysilicon
sacrificial
phosphosilicate glass
silicon dioxide
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PCT/CN2020/099401
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English (en)
French (fr)
Inventor
王喆
邹泉波
邱冠勋
吴立德
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歌尔微电子有限公司
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Publication of WO2021184591A1 publication Critical patent/WO2021184591A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/005—Electrostatic transducers using semiconductor materials
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/04—Microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/003—Mems transducers or their use
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2231/00—Details of apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor covered by H04R31/00, not provided for in its subgroups
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2231/00—Details of apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor covered by H04R31/00, not provided for in its subgroups
    • H04R2231/003—Manufacturing aspects of the outer suspension of loudspeaker or microphone diaphragms or of their connecting aspects to said diaphragms

Definitions

  • the invention belongs to the technical field of micro-electromechanical processing, and specifically relates to a processing method of a MEMS microphone and a MEMS microphone.
  • a microphone In the structure of a microphone, it usually includes a substrate and a back plate and a diaphragm formed on the substrate. There is a gap between the back plate and the diaphragm, so that the back plate and the diaphragm together form a flat plate. Capacitor sensing structure.
  • a material layer of the required structure is formed on the substrate first, and then different areas of the material layer are etched away by an etching process, and the final structure is the microelectromechanical sensor .
  • the anisotropic etching characteristics in the etching process and the selective influence of the semiconductor material on the etching process it is difficult to control the etching degree of the region far from the starting position of the etching process.
  • the etching process used can show good anisotropic etching characteristics in one material, but cannot show such etching characteristics after etching to another material, resulting in further etching formation
  • the size of the cavity is difficult to meet the design requirements. In turn, the performance of the microelectromechanical sensor is affected.
  • An object of the present invention is to provide a new technical solution for processing MEMS microphones.
  • a processing method of a MEMS microphone including:
  • first cavity wet etch the first sacrificial layer and the second sacrificial layer around the suspended portion from the reference hole, and the polysilicon reference layer and the silicon nitride layer are wet-etched.
  • a second cavity is formed between the layers;
  • the suspended portion of the polysilicon diaphragm layer is suspended in the second cavity.
  • the second sacrificial layer includes a second phosphosilicate glass layer and a third phosphosilicate glass layer;
  • the second phosphosilicate glass layer is wet-etched to form a groove communicating with the polysilicon diaphragm layer.
  • the position of the groove corresponds to the position of the suspended part, and the groove is deposited Form polysilicon support pillars;
  • the silicon nitride layer is formed on the third phosphorous silicate glass layer.
  • the silicon nitride layer formed on the third phosphosilicate glass layer is embedded in the groove of the third phosphosilicate glass layer.
  • the thickness of the third phosphosilicate glass layer is 2 microns.
  • the first sacrificial layer includes a silicon dioxide sacrificial layer and a first phosphosilicate glass layer;
  • the thickness of the silicon dioxide sacrificial layer is 1 micron;
  • a first phosphosilicate glass layer is deposited on the sacrificial silicon dioxide layer, the first phosphosilicate glass layer forms grooves at the grooves corresponding to the sacrificial silicon dioxide layer, and the first phosphosilicate glass
  • the thickness of the glass layer is 5 microns, and the mass percentage of phosphorus is 5 wt%;
  • the polysilicon vibration film layer formed on the first phosphosilicate glass layer is embedded in the groove of the first phosphosilicate glass layer to form bumps of the diaphragm;
  • an escape gap is formed between the bumps of the diaphragm and the polysilicon reference layer.
  • the dry etching is reactive ion etching (RIE).
  • RIE reactive ion etching
  • LPCVD low pressure chemical vapor deposition
  • the polysilicon vibration film layer is formed by low pressure chemical vapor deposition (LPCVD).
  • LPCVD low pressure chemical vapor deposition
  • the thickness of the polysilicon reference layer is 0.5 micrometers
  • the thickness of the polysilicon vibration film layer is 1 micron.
  • a silicon dioxide protective layer is deposited on the substrate, and the polysilicon reference layer is directly deposited on the silicon dioxide protective layer;
  • RIE reactive ion etching
  • the thickness of the silicon dioxide protective layer is 0.5 micrometers.
  • a MEMS microphone is provided, and the MEMS microphone is manufactured by the above-mentioned processing method;
  • the polysilicon diaphragm layer has a connecting end and a suspension part, the connecting end is fixed between the polysilicon reference layer and the silicon nitride layer, and the suspension part is suspended between the silicon nitride layer and the polysilicon reference layer between.
  • Fig. 1 is a schematic side sectional view of a MEMS microphone provided by the present disclosure
  • FIG. 2 is a schematic side sectional view of a reference layer and a first sacrificial layer formed on a substrate in the processing method provided by the present disclosure
  • FIG. 3 is a schematic side sectional view of a polysilicon vibration film layer and a second sacrificial layer formed on the first sacrificial layer in the processing method provided by the present disclosure
  • FIG. 4 is a schematic side sectional view of a polysilicon support pillar and a second sacrificial layer formed on the polysilicon vibration film layer in the processing method provided by the present disclosure
  • FIG 5 is a schematic side sectional view of a silicon nitride layer formed on the second sacrificial layer in the processing method provided by the present disclosure.
  • a technical solution for processing a MEMS microphone is provided.
  • a polysilicon reference layer 2 is provided on the laminated semiconductor material, and the polysilicon reference layer 2 serves as a starting reference for etching the cavity inside the MEMS microphone.
  • the etching depth and the etching range of the cavity etching process can be effectively controlled, and the dimensional accuracy of the cavity in the MEMS microphone can be improved.
  • Fig. 1 shows the structure of a MEMS microphone made by this embodiment.
  • the MEMS processing method of the present technical solution first deposits and forms a polysilicon reference layer 2 on the substrate 1, as shown in FIG. 2.
  • the substrate 1 may be a silicon substrate 1, which is convenient for etching the substrate 1 by wet etching to form a cavity.
  • the polysilicon reference layer 2 serves as an etching reference point during the process of etching to form a cavity.
  • the wet etching process is usually implemented with an etching solution, and due to different types of etching solutions and different etching process conditions, wet etching can exhibit etching selectivity for different materials.
  • the polysilicon reference layer is a polysilicon material, which is not affected by the wet etching process, and will not be etched away during the wet etching process. Therefore, it can be used as an etching benchmark in the wet etching process to facilitate the control of the visible depth and width of the wet etching process.
  • a low pressure chemical vapor deposition (LPCVD) process can be used to form a polysilicon reference layer, so that the polysilicon reference layer 2 has a dense and complete structure and can fully play the role of an etching reference in the wet etching process.
  • the thickness of the polysilicon reference layer 2 is 0.5 micrometers.
  • the thickness of the polysilicon reference layer 2 is the above size, on the one hand, it has little effect on the overall thickness of the MEMS microphone device.
  • the structural stability and anti-corrosion isolation effect of the 0.5 micron thick polysilicon reference layer 2 can achieve its goal. Requirements for the reference position of the wet etching cavity.
  • the reference hole 21 is used as a starting hole for the wet etching liquid to spread into the MEMS device during subsequent processing. It can play the role of controlling the passage speed and the passage amount of the etching liquid and accurately restricting the passage position.
  • the polysilicon reference layer 2 is difficult to be etched by a wet etching process, so a dry etching process is used to etch the reference hole 21.
  • RIE reactive ion etching
  • the position of the reference hole 21 is located at the middle position in the width direction of the substrate 1 so that in the subsequent wet etching process, the etching solution is uniformly etched from the reference hole 21 to the surrounding area.
  • the polysilicon reference layer 2 needs to be completely etched away in the thickness direction to form a reference hole 21 penetrating the polysilicon reference layer 2. In this way, the subsequent wet etching solution can pass through.
  • a first sacrificial layer 31 may be deposited on the polysilicon reference layer 2. A large part of the first sacrificial layer 31 will be etched away in the final wet etching process, thereby forming a cavity. In addition, by doping specific elements in the sacrificial layer, the performance of structures such as the diaphragm can be improved, and the acoustic performance of the MEMS microphone can be improved.
  • the first sacrificial layer 31 may be formed by a combination of multiple laminated material layers, depending on different structure and performance requirements. In the embodiment shown in FIG. 2, the first sacrificial layer 31 includes a silicon dioxide sacrificial layer 32 and a first phosphosilicate glass layer 31. In other embodiments, the first sacrificial layer 31 may also include other material layers.
  • a polysilicon vibration film layer 4 is deposited on the first sacrificial layer 31, as shown in FIG. 4.
  • the polysilicon diaphragm layer 4 serves as the diaphragm in the MEMS microphone and will be retained in the subsequent wet etching process.
  • the surrounding sacrificial layer will be etched away, thereby forming a cavity around the polysilicon diaphragm layer 4 for the polysilicon diaphragm to vibrate.
  • Using polysilicon to make the diaphragm layer can prevent it from being etched away in the subsequent wet etching process.
  • the polysilicon diaphragm layer 4 has a connecting end 41 and a suspended portion 42.
  • the suspended portion 42 will form a suspended diaphragm during the period of the MEMS microphone after subsequent wet etching processing for responding to sound vibrations.
  • the connection terminal 41 forms a fixed connection with other structures to ensure the connection stability of the polysilicon diaphragm layer 4.
  • the polysilicon vibration film layer 4 is formed by a low pressure chemical vapor deposition (LPCVD) process.
  • the thickness of the polysilicon diaphragm layer 4 may be 1 micron.
  • the polysilicon diaphragm layer 4 with a thickness of 1 micron can satisfy the pressure of the diaphragm to withstand sound vibration, and at the same time exhibit good vibration performance, improve the acoustic performance of the MEMS microphone, and reduce the distortion of the sound signal.
  • a second sacrificial layer is deposited on the polysilicon diaphragm layer 4, and the second sacrificial layer is connected to the first sacrificial layer 31 at the periphery of the suspended portion 42.
  • the second sacrificial layer includes a three-layer structure, which is a second phosphosilicate glass layer 61 and a third phosphosilicate glass layer.
  • the third phosphosilicate glass layer includes a two-layer structure.
  • the second sacrificial layer may further include other materials and laminated structures.
  • the second sacrificial layer is connected to the first sacrificial layer 31 on the rightmost side of the polysilicon diaphragm layer 4, and this part of the second sacrificial layer directly covers the first sacrificial layer.
  • the polysilicon diaphragm layer 4 except for the connection end 41 on the leftmost side, most of the structures extending to the right are suspended portions 42.
  • a silicon nitride layer 7 is deposited and formed on the second sacrificial layer.
  • the silicon nitride layer 7 serves as the encapsulation shell structure of the MEMS microphone, which is retained in the subsequent wet etching process. Silicon nitride will not be affected by the wet etching process.
  • the silicon nitride layer 7 can be formed by pressure chemical vapor deposition (PECVD), which can increase the material density of the silicon nitride layer 7 as the packaging shell and ensure the structural reliability of the MEMS microphone.
  • FIG. 4 shows a structure in which a silicon nitride layer 7 is covered on the second sacrificial layer.
  • the silicon nitride layer 7 may be formed with materials such as a back electrode serving as an electrode, which may be formed by etching the silicon nitride layer 7 to form a groove, and then depositing a conductive material in the groove. .
  • the substrate 1 is etched from the side of the substrate 1, that is, the lower side as shown in FIG. 5, to form the first cavity 10 as shown in FIG. 1.
  • RIE reactive ion etching
  • the etching effect of the substrate 1 is better, the directionality is stronger, and the size of the obtained first cavity 10 can be Meet the size requirements of the first cavity 10.
  • FIG. 1 shows the first cavity 10 formed by etching.
  • first cavity 10 that is, the lower side of the polysilicon reference layer 2 as shown in FIG. 1.
  • wet etching to start from the reference hole 21, wet etch the first sacrificial layer 31 and the second sacrificial layer to etch away most of the first sacrificial layer 31 and the second sacrificial layer, That is, the first sacrificial layer 31 and the second sacrificial layer around the suspended portion 42 of the polysilicon diaphragm layer 4 are etched to form the second cavity 20.
  • the second cavity 20 is located between the polysilicon reference layer 2 and the silicon nitride layer 7.
  • the polysilicon layer has only a fixed portion connected to the first sacrificial layer 31 and the second sacrificial layer that have not been etched away, and is fixed at a position between the substrate 1 and the silicon nitride layer 7.
  • the etching liquid at 21 can pass through the reference hole 21, and spread like the first sacrificial layer 31 and the second sacrificial layer.
  • the starting position of the wet etching is precisely controlled.
  • the etching time it is possible to control the extent to which the first sacrificial layer and the second sacrificial layer are etched in the width and thickness directions. Furthermore, it is ensured that the shape and size of the formed second cavity meet the performance requirements.
  • the starting position for etching the second cavity is located inside the thickness direction of the substrate, it is difficult to etch the exact size and position of the starting point of the wet etching.
  • the first sacrifice will be caused.
  • the etching degree error of the layer and the second sacrificial layer is larger, and the shape and size of the second cavity are difficult to meet the requirements.
  • the second sacrificial layer may include a second phosphosilicate glass layer 61 and a third phosphosilicate glass layer, as shown in FIG. 4.
  • the third phosphosilicate glass layer may further include a first layer 62 and a second layer 63.
  • the requirements of different doping elements can be met, and on the other hand, other components can be easily formed in the MEMS microphone through the sacrificial layer.
  • first, pressurized chemical vapor deposition may be used to form a second phosphosilicate glass layer 61 on the polysilicon vibration film layer.
  • annealing treatment can also be used to release the stress of the second phosphosilicate glass layer 61 and improve the doping effect.
  • elements such as phosphorus can be doped into the polysilicon vibration film layer to improve the performance of the polysilicon vibration film layer.
  • the second phosphosilicate glass layer 61 may be wet-etched to form a groove connected to the polysilicon diaphragm layer 4, as shown in FIG. 3.
  • the position of the groove corresponds to the position of the suspended portion 42.
  • low-pressure chemical vapor deposition is performed on the groove to form a polysilicon layer with a thickness of 0.5 microns, and then a ⁇ -shaped polysilicon support column 5 can be formed through reactive ion etching.
  • the position of the polysilicon support column 5 is in the Hanging part 42 on.
  • the polysilicon support column can play a role in stabilizing the diaphragm when the MEMS microphone is working. For example, when the MEMS microphone starts to work, a bias voltage is applied to the electrodes provided in the silicon nitride layer and the polysilicon vibration film layer, so that the polysilicon vibration film is upwardly close to the silicon nitride layer. At this time, the polysilicon support column can be topped on the silicon nitride layer, so that a part of the suspended portion can form a top stop by the polysilicon support column and the silicon nitride layer, thereby stabilizing the suspended portion. However, there is no position of the support column on the suspended part, and the corresponding vibration can be generated according to the sound vibration to realize the function of the microphone.
  • the groove of the second phosphosilicate glass layer 61 is formed at a position corresponding to the edge of the suspended portion, so that the polysilicon support column can be formed on the edge of the suspended portion 42.
  • the central area of the suspended portion 42 is reserved as an area where vibration and sound can be collected, and the acoustic performance is better.
  • a third phosphosilicate glass layer is formed on the polysilicon support column and the second phosphosilicate glass layer 61.
  • the thickness of the third phosphosilicate glass layer may be 2 microns.
  • the third phosphosilicate glass layer covers the second phosphosilicate glass layer 61 and the polysilicon support column 5 below it.
  • the silicon nitride layer 7 is further formed on the third phosphorous silicate glass layer, as shown in FIG. 4.
  • the formation of the third phosphosilicate glass layer can perform elemental doping on the silicon nitride layer 7 on the one hand, and can separate the polysilicon support column 5 from the silicon nitride layer 7 on the other hand, so as to form the second cavity 20.
  • a groove may be formed on the third phosphosilicate glass layer by dry etching, and the position of the groove corresponds to the position of the polysilicon support column 5.
  • the silicon nitride layer 7 can form the first boss 76 embedded in the groove, as shown in FIG. 5.
  • the position of the first boss 76 corresponds to the polysilicon support column 5.
  • the third phosphosilicate glass layer includes a first layer 62 and a second layer 63.
  • the first layer 62 is deposited on the second phosphosilicate glass layer 61 by pressurized chemical vapor deposition. After that, the first layer 62 may be etched by dry etching first to form a groove connected to the polysilicon support column 5. The thickness of the first layer 62 may be 1.5 microns.
  • the second layer 63 is formed on the first layer 62 by pressurized chemical vapor deposition, and a part of it is embedded in the above-mentioned groove. The thickness of the second layer 63 may be 0.5 micrometers.
  • a silicon nitride layer 7 is deposited on the second layer 63. In this way, the first boss 76 on the silicon nitride layer 7 can form a certain gap with the polysilicon support pillar 5 and correspond to the position of the polysilicon support pillar 5.
  • the first sacrificial layer 31 may include a silicon dioxide sacrificial layer 32 and a first phosphosilicate glass layer 31.
  • the silica glass layer is formed in the reference hole 21 and on the reference layer by low pressure chemical vapor deposition.
  • the thickness of the silicon dioxide sacrificial layer 32 may be 1 micron. as shown in picture 2.
  • the silicon dioxide layer on the reference layer is wet-etched to form grooves on the silicon dioxide layer. Further, a first phosphosilicate glass layer 31 is deposited on the silicon dioxide sacrificial layer 32. The first phosphosilicate glass layer 31 can be embedded in the groove of the silicon dioxide sacrificial layer 32 to form a groove, as shown in FIG. 2.
  • the thickness of the first phosphosilicate glass layer 31 is 5 microns, and the mass percentage of the phosphorus element therein is 5 wt%.
  • the first phosphosilicate glass layer 31 can be used for doping the polysilicon vibration film layer 4 with phosphorus elements to improve the acoustic performance of the polysilicon vibration film layer 4.
  • a polysilicon diaphragm layer 4 is formed on the first phosphosilicate glass layer 31, and a part of the structure of the polysilicon diaphragm layer 4 will be embedded in the above-mentioned groove to form diaphragm bumps 43, as shown in FIG. 3.
  • an escape gap 44 is formed between the diaphragm bump 43 and the polysilicon reference layer 2, as shown in FIG. 1.
  • the function of the diaphragm bump 43 is to reduce the possibility of adhesion between the polysilicon diaphragm and the polysilicon reference layer 2. In particular, as shown in FIG.
  • the avoidance gap 44 can allow the first cavity 10 and the second cavity 20 on both sides of the polysilicon diaphragm to form air circulation, thereby reducing the actual operation of the MEMS microphone due to the first cavity 10 It is difficult to circulate the airflow between the second cavity and the second cavity, which causes the air pressure imbalance and affects the acoustic performance.
  • RIE reactive ion etching
  • low pressure chemical vapor deposition may be used to form the polysilicon reference layer 2 and/or the polysilicon vibration film layer 4.
  • This deposition method can form a polysilicon material with a moderate thickness and a moderate material density, and ensures that the polysilicon diaphragm layer 4 can achieve good acoustic performance.
  • the phosphosilicate glass layer and the silicon nitride layer can be formed by pressure chemical vapor deposition (PECVD).
  • PECVD pressure chemical vapor deposition
  • This deposition method can form a denser material layer, which is helpful to improve the structural strength of the material layer and improve the effect of the material layer on other elements being doped.
  • a silicon dioxide protective layer 11 may also be deposited on the sink bottom.
  • the polysilicon reference layer 2 is formed on the silicon dioxide protective layer 11.
  • the silicon dioxide protective layer 11 uses a different etching process from the other two, that is, different etching processes etch the material layer above. Erosion is selective.
  • the silicon dioxide protective layer 11 can be used to protect the substrate 1 and the polysilicon reference layer 2 so as not to provide protection through the selective etching process when one of them does not need to be etched.
  • the substrate 1 is etched by dry etching. Dry etching will not affect the silicon dioxide protective layer 11, but will affect the polysilicon reference layer 2. Through the role of the silicon dioxide protective layer 11, the dry etching will stop when the top surface of the substrate 1 is etched, and the silicon dioxide protective layer 11 and the polysilicon reference layer 2 will not be etched away. After that, the silicon dioxide protective layer 11 is etched by wet etching, and the polysilicon reference layer 2 will not be etched away by the wet etching. The wet etching can etch the silicon dioxide and the first sacrificial layer 31 and the second sacrificial layer on the reference hole 21. The polysilicon reference layer 2 and the reference hole 21 are used as the starting point of the wet etching to control the position and size of the wet etching.
  • the thickness of the silicon dioxide protective layer 11 may be 0.5 micrometers.
  • the thickness should be reduced as much as possible to prevent it from affecting the overall thickness of the MEMS microphone.
  • the second phosphosilicate glass layer 61 may be etched at a position corresponding to the connecting end 41 A groove is formed, and then a polysilicon electrical connection pillar 81 made of polysilicon material is deposited.
  • the polysilicon electrical connection pillar 81 is in contact and electrically connected with the polysilicon vibration film layer 4.
  • a bonding pad 8 may be formed on the polysilicon electrical connection pillar 81 to form an electrical connection between the MEMS microphone and an external device.
  • the silicon nitride layer 7 may include a first silicon nitride layer 71 and a second silicon nitride layer 72.
  • the thickness of the first silicon nitride layer 71 may be 1 micrometer
  • the thickness of the second silicon nitride layer 72 may be 1.5 micrometers.
  • the first silicon nitride layer 71 and the second silicon nitride layer 72 may be formed by pressurized chemical vapor deposition (PECVD), respectively.
  • PECVD pressurized chemical vapor deposition
  • a plate metal 75 with a thickness of 0.5 microns can be formed thereon.
  • the plate metal 75 is used as the back substrate in the MEMS microphone and can be used to attract polysilicon after being energized. Diaphragm layer 4.
  • a through hole 74 may be formed on the silicon nitride layer 7, as shown in FIGS. 1 and 5.
  • the through hole 74 can be formed by a dry etching process.
  • the perforation 74 can be used as a pressure relief and sound outlet hole of the second cavity 20 in the product.
  • it can be used as a liquid inlet hole when etching the second sacrificial layer.
  • the inner wall of the silicon nitride layer 7 may also be matched with a second boss 73 after forming a groove on the second sacrificial layer, as shown in FIG. 1.
  • the second boss 73 corresponds to the part of the polysilicon diaphragm layer 4 used for vibration and sound, and it is used to prevent the polysilicon diaphragm layer 4 from having too much amplitude during operation and directly colliding with the silicon nitride layer. damage.
  • the polysilicon vibration film layer 4 has a connecting end 41 and a suspension portion 42, and the connecting end 41 is fixed at a position between the polysilicon reference layer 2 and the silicon nitride layer 7.
  • the connecting terminal 41 is fixed between the first sacrificial layer 31 and the silicon nitride and the second sacrificial layer.
  • the suspended portion 42 is suspended between the silicon nitride layer 7 and the polysilicon reference layer 2.
  • the reference hole 21 of the polysilicon reference layer 2 serves as the sound inlet hole of the first cavity 10.

Abstract

本发明公开了一种MEMS麦克风的加工方法和MEMS麦克风。包括：在衬底之上沉积多晶硅基准层；从多晶硅基准层一侧，对多晶硅基准层进行干法刻蚀，在多晶硅基准层上形成基准孔；在多晶硅基准层上沉积第一牺牲层；在第一牺牲层上沉积多晶硅振膜层，多晶硅振膜层具有悬空部；在多晶硅振膜层上沉积第二牺牲层，第二牺牲层在悬空部的外围与第一牺牲层连接；在第二牺牲层上沉积氮化硅层；从衬底一侧，对衬底和二氧化硅保护层进行刻蚀形成第一空腔，第一空腔暴露基准孔；在第一空腔一侧，从基准孔对位于悬空部周围的第一牺牲层和第二牺牲层进行湿法刻蚀，在多晶硅基准层与氮化硅层之间形成第二空腔；多晶硅振膜层的悬空部悬于第二空腔中。

Description

一种MEMS麦克风的加工方法和MEMS麦克风 技术领域
本发明属于微机电加工技术领域，具体地，涉及一种MEMS麦克风的加工方法和MEMS麦克风。
背景技术
现有主流的传感器，例如麦克风、压力传感器、位移传感器等，均采用通过平板电容器的原理进行检测。例如在麦克风的结构中，通常包括衬底以及形成在衬底上的背极板、振膜，其中，背极板与振膜之间具有间隙，使得背极板、振膜共同构成了平板式的电容器感测结构。
在这种微机电传感器的加工过程中，通常先在衬底上形成所需结构的材料层，之后通过刻蚀工艺将材料层的不同区域刻蚀掉，最后留下的结构即为微机电传感器。但是，刻蚀工艺中各向异性的刻蚀特点以及半导体材料对刻蚀工艺的选择性影响，距离刻蚀工艺起始位置较远的区域的刻蚀程度难以把控。例如，所采用的刻蚀工艺在一种材料中能够表现出良好的各向异性刻蚀特点，而在刻蚀到另一种材料后则无法表现这种刻蚀特点，从而造成进一步刻蚀形成的空腔的尺寸难以达到设计要求。进而造成微机电传感器的性能受到影响。
发明内容
本发明的一个目的是提供一种加工MEMS麦克风的新技术方案。
根据本发明的第一方面，提供了一种MEMS麦克风的加工方法，包括：
在衬底之上沉积多晶硅基准层；
从多晶硅基准层一侧，对多晶硅基准层进行干法刻蚀，在多晶硅基准层上形成基准孔；
在多晶硅基准层上沉积第一牺牲层；
在第一牺牲层上沉积多晶硅振膜层，所述多晶硅振膜层具有悬空部；
在多晶硅振膜层上沉积第二牺牲层，所述第二牺牲层在所述悬空部的外围与所述第一牺牲层连接；
在所述第二牺牲层上沉积氮化硅层；
从衬底一侧，对衬底和二氧化硅保护层进行湿法刻蚀形成第一空腔，所述第一空腔暴露所述基准孔；
在所述第一空腔一侧，从所述基准孔对位于所述悬空部周围的所述第一牺牲层和第二牺牲层进行湿法刻蚀，在所述多晶硅基准层与氮化硅层之间形成第二空腔；
所述多晶硅振膜层的悬空部悬于所述第二空腔中。
可选地，所述第二牺牲层包括第二磷硅玻璃层和第三磷硅玻璃层；
在所述多晶硅振膜层上沉积形成所述第二磷硅玻璃层；
对所述第二磷硅玻璃层进行湿法刻蚀，形成与所述多晶硅振膜层连通的凹槽，所述凹槽的位置与所述悬空部的位置对应，在所述凹槽上沉积形成多晶硅支撑柱；
在所述第二磷硅玻璃层上沉积形成所述第三磷硅玻璃层；
所述氮化硅层形成在所述第三磷硅玻璃层上。
可选地，对所述第三磷硅玻璃层进行干法刻蚀，形成与所述多晶硅支撑柱位置对应的凹槽；
形成在所述第三磷硅玻璃层上的氮化硅层嵌入所述第三磷硅玻璃层的凹槽中。
可选地，所述第三磷硅玻璃层的厚度为2微米。
可选地，所述第一牺牲层包括二氧化硅牺牲层和第一磷硅玻璃层；
在所述多晶硅基准层的表面和基准孔中沉积形成二氧化硅牺牲层，所述二氧化硅牺牲层的厚度为1微米；
对多晶硅基准层上的二氧化硅牺牲层进行湿法刻蚀，在所述二氧化硅牺牲层上形成凹槽；
在所述二氧化硅牺牲层上沉积形成第一磷硅玻璃层，所述第一磷硅玻璃层在对应于所述二氧化硅牺牲层的凹槽处形成凹槽，所述第一磷硅玻璃 层的厚度为5微米，磷的质量百分比为5wt％；
形成在所述第一磷硅玻璃层上的多晶硅振膜层嵌入所述第一磷硅玻璃层的凹槽中，形成振膜凸点；
在刻蚀形成所述第二空腔后，所述振膜凸点与所述多晶硅基准层之间形成避让间隙。
可选地，所述干法刻蚀为反应离子刻蚀(RIE)。
可选地，采用低压化学气相沉积(LPCVD)形成所述多晶硅基准层；
和/或，采用低压化学气相沉积(LPCVD)形成所述多晶硅振膜层。
可选地，所述多晶硅基准层的厚度为0.5微米；
和/或，所述多晶硅振膜层的厚度为1微米。
可选地，沉积形成多晶硅基准层之前，在所述衬底上沉积形成二氧化硅保护层，在二氧化硅保护层上直接沉积形成所述多晶硅基准层；
在形成所述第一空腔的工艺中，采用反应离子刻蚀(RIE)对衬底进行刻蚀，采用湿法刻蚀对所述二氧化硅保护层进行刻蚀。
可选地，所述二氧化硅保护层的厚度为0.5微米。
根据本公开的另一个实施例，提供了一种MEMS麦克风，该MEMS麦克风采用上述加工方法制成；
所述多晶硅振膜层具有连接端和悬空部，所述连接端固定在所述多晶硅基准层与氮化硅层之间，所述悬空部悬于所述氮化硅层与所述多晶硅基准层之间。
通过以下参照附图对本发明的示例性实施例的详细描述，本发明的其它特征及其优点将会变得清楚。
附图说明
被结合在说明书中并构成说明书的一部分的附图示出了本发明的实施例，并且连同其说明一起用于解释本发明的原理。
图1是本公开的提供的MEMS麦克风的侧面剖视示意图；
图2是本公开提供的加工方法中衬底上形成基准层和第一牺牲层的侧面剖视示意图；
图3是本公开提供的加工方法中第一牺牲层上形成多晶硅振膜层和第二牺牲层的侧面剖视示意图；
图4是本公开提供的加工方法中多晶硅振膜层上形成多晶硅支撑柱和第二牺牲层的侧面剖视示意图；
图5是本公开提供的加工方法中第二牺牲层上形成氮化硅层的侧面剖视示意图。
具体实施方式
现在将参照附图来详细描述本发明的各种示例性实施例。应注意到：除非另外具体说明，否则在这些实施例中阐述的部件和步骤的相对布置、数字表达式和数值不限制本发明的范围。
以下对至少一个示例性实施例的描述实际上仅仅是说明性的，决不作为对本发明及其应用或使用的任何限制。
对于相关领域普通技术人员已知的技术、方法和设备可能不作详细讨论，但在适当情况下，所述技术、方法和设备应当被视为说明书的一部分。
在这里示出和讨论的所有例子中，任何具体值应被解释为仅仅是示例性的，而不是作为限制。因此，示例性实施例的其它例子可以具有不同的值。
应注意到：相似的标号和字母在下面的附图中表示类似项，因此，一旦某一项在一个附图中被定义，则在随后的附图中不需要对其进行进一步讨论。
根据本公开的一个实施例，提供了一种加工MEMS麦克风的技术方案。本技术方案通过在层叠的半导体材料上设置多晶硅基准层2，该多晶硅基准层2作为刻蚀MEMS麦克风内部空腔的起始基准。通过这种设计方式，能够有效对空腔刻蚀工艺的刻蚀深度、刻蚀范围进行控制，提高MEMS麦克风中空腔的尺寸精确度。图1示出了采用本实施方式制成的MEMS麦克风的结构。
本技术方案的MEMS加工方法首先在衬底1之上沉积形成多晶硅基准层2，如图2所示。所述衬底1可以为硅衬底1，便于采用湿法刻蚀对衬底 1进行刻蚀加工，形成腔体。所述多晶硅基准层2在刻蚀形成腔体的加工过程中作为刻蚀基准点。湿法刻蚀工艺通常采用腐蚀刻蚀液实施，而由于腐蚀刻蚀液的种类不同以及刻蚀工艺条件不同，湿法刻蚀能够表现出对不同材料的刻蚀选择性。
多晶硅基准层为多晶硅材料，不受到湿法刻蚀工艺的影响，在湿法刻蚀工艺中不会被刻蚀消除。因此在湿法刻蚀工艺中可以作为刻蚀基准，便于对湿法刻蚀工艺的可视深度、宽度等要求进行控制。
可选地，可以采用低压化学气相沉积(LPCVD)工艺形成多晶硅基准层，从而那个多晶硅基准层2具有致密、完整的结构，能够在湿法刻蚀工艺中充分发挥刻蚀基准的作用。可选地，所述多晶硅基准层2的厚度为0.5微米。多晶硅基准层2的厚度为上述尺寸时，一方面对MEMS麦克风器件的整体厚度尺寸影响较小，另一方面，0.5微米厚的多晶硅基准层2的结构稳定性和抗腐蚀隔离效果能够达到其作为湿法刻蚀腔体的基准位置的要求。
在形成多晶硅基准层2后，在多晶硅基准层2的一侧，也即如图2所示的上方，对所述多经过基准层实施干法刻蚀，在多晶硅基准层2上刻蚀形成基准孔21。所述基准孔21作为后续加工中，用于供湿法刻蚀液向MEMS器件内部蔓延刻蚀的起始孔。其能够起到控制刻蚀液通入速度、通入量以及准确限定通入位置的作用。如上所述，多晶硅基准层2难以通过湿法刻蚀工艺实现刻蚀，因此采用干法刻蚀工艺实现对基准孔21的刻蚀加工。
可选地，采用反应离子刻蚀(RIE)可以对多晶硅基准层2进行刻蚀，从而在中间区域形成基准孔21。所述基准孔21的位置位于所述衬底1宽度方向上的中间位置，以便于后续的湿法刻蚀工艺中，刻蚀液从基准孔21处均匀腐蚀到周围的区域。对于所述基准孔21的刻蚀，需将所述多晶硅基准层2在厚度方向上完全刻蚀掉，形成贯通多晶硅基准层2的基准孔21。这样才能让后续的湿法刻蚀液穿过。
在形成基准孔21后，可以在所述多晶硅基准层2层上沉积形成第一牺牲层31。所述第一牺牲层31在最后的湿法刻蚀工艺中会被刻蚀掉一大部分区域，从而形成空腔。此外，通过对牺牲层中掺杂特定元素，可以改 善振膜等结构的性能，提高MEMS麦克风的声学性能。所述第一牺牲层31可以由多个层叠材料层组合形成，视不同的结构、性能要求而定。在图2所述的实施方式中，所述第一牺牲层31包括了二氧化硅牺牲层32和第一磷硅玻璃层31。在其它实施方式中，所述第一牺牲层31还可以包括其它材料层。
进一步地，在所述第一牺牲层31上沉积多晶硅振膜层4，如图4所示。所述多晶硅振膜层4作为MEMS麦克风中的振膜，在后续的湿法刻蚀工艺中会保留下来。其周围的牺牲层会被刻蚀掉，从而在多晶硅振膜层4周围形成空腔，供多晶硅振膜振动。采用多晶硅制成振膜层，能够防止其在后续的湿法刻蚀工艺中被刻蚀掉。所述多晶硅振膜层4具有连接端41和悬空部42，该悬空部42经过后续的湿法刻蚀加工后会构成悬于MEMS麦克风期间内的悬空的振膜，用于对声音振动作出响应。连接端41则与其它结构形成固定连接，保证多晶硅振膜层4的连接稳定性。
可选地，采用低压化学气相沉积(LPCVD)工艺形成所述多晶硅振膜层4。多晶硅振膜层4的厚度可以为1微米。1微米厚的多晶硅振膜层4在能够满足振膜承受声音振动的压力的情况下，同时表现出良好的振动性能，提高MEMS麦克风的声学性能，降低声音信号的失真。
进一步地，在多晶硅振膜层4上沉积第二牺牲层，所述第二牺牲层在所述悬空部42的外围与所述第一牺牲层31连接在一起。在如图3、4所示的实施方式中，所述第二牺牲层包括了三层结构，分别为第二磷硅玻璃层61和第三磷硅玻璃层。其中第三磷硅玻璃层包括了两层结构。在其它实施方式中，所述第二牺牲层还可以包括其它材料和层叠结构。
与所述第一牺牲层31相似的，所述第二牺牲层在后续的湿法刻蚀工艺中也会被刻蚀掉一大部分结构，从而使多晶硅振膜层4的上方区域镂空，形成空腔。在如图3所示的实施方式中，所述第二牺牲层在多晶硅振膜层4的最右侧与所述第一牺牲层31连接，第二牺牲层的这一部分直接覆盖在第一牺牲层31上。对于所述多晶硅振膜层4而言，除了最左侧的连接端41处之外，向右侧延伸的大部分结构为悬空部42。
进一步地，在所述第二牺牲层上沉积形成氮化硅层7。所述氮化硅层 7作为MEMS麦克风的封装壳体结构，其在后续的湿法刻蚀工艺中被保留下来。氮化硅不会到湿法刻蚀工艺的影响。可选地，可以采用加压化学气相沉积(PECVD)形成所述氮化硅层7，这样可以增加氮化硅层7作为封装壳体的材料致密程度，保证MEMS麦克风的结构可靠性。图4示出了第二牺牲层上覆盖有氮化硅层7的结构。
可选地，所述氮化硅层7中可以形成有作为电极的背极等材料，其可以通过对氮化硅层7进行刻蚀形成凹槽，之后将导电材料沉积于凹槽中而形成。
此后，从所述衬底1一侧，也即如图5所示的下侧，对所述衬底1进行刻蚀，形成如图1所示的第一空腔10。对于衬底1的刻蚀，可以采用反应离子刻蚀(RIE)对沉积进行刻蚀，对衬底1的刻蚀效果更好，方向性更强，所得到的第一空腔10的尺寸能够符合对第一空腔10的尺寸要求。图1示出了刻蚀形成的第一空腔10。
进一步地，在所述第一空腔10的一侧，也即如图1所示的多晶硅基准层2的下侧。采用湿法刻蚀从所述基准孔21处开始，对第一牺牲层31和第二牺牲层进行湿法刻蚀，将第一牺牲层31和第二牺牲层的大部分区域刻蚀掉，也即对位于所述多晶硅振膜层4的悬空部42周围的第一牺牲层31和第二牺牲层进行刻蚀，从而形成第二空腔20。所述第二空腔20位于多晶硅基准层2和氮化硅层7之间。经过对第一牺牲层31和第二牺牲层的刻蚀，所述悬空部42悬于所述第二空腔20中。所述多晶硅层仅有固定部与未被刻蚀掉的第一牺牲层31和第二牺牲层连接，固定在衬底1与氮化硅层7之间的位置处。
在对第一牺牲层31和第二牺牲层进行刻蚀的湿法刻蚀工艺中，由于所述多晶硅基准层2不会受到施法刻蚀的影响，所以只有蔓延至多晶硅基准层2的基准孔21处的腐蚀液才能通过基准孔21，像第一牺牲层31和第二牺牲层蔓延。利用基准孔的设计，湿法刻蚀的起始位置得到了精确控制。进一步根据湿法刻蚀工艺的特点，通过对刻蚀时间的控制，就能够控制第一牺牲层和第二牺牲层在宽度和厚度方向上被刻蚀的程度。进而保证所形成的第二空腔的形状、尺寸满足性能要求。
通常的，由于对第二腔体进行刻蚀的起始位置位于衬底的厚度方向的内部，造成了难以对湿法刻蚀的起点准确尺寸、位置进行刻蚀。在对衬底进行刻蚀的过程中，由于衬底被刻蚀掉的厚度较深，往往会产生一些尺寸误差，如果以存在误差的位置作为湿法刻蚀的起点，则会造成第一牺牲层和第二牺牲层的刻蚀程度误差更大，第二空腔的形状尺寸难以达到要求。而采用本技术方案就可以对湿法刻蚀工艺的起点进行精确控制。在对多晶硅基准层进行干法刻蚀时，对厚度较薄的多晶硅基准层能够做到精确的刻蚀，形成所述基准孔，进而提供精确地湿法刻蚀起点位置。
可选地，所述第二牺牲层可以包括第二磷硅玻璃层61和第三磷硅玻璃层，如图4所示。其中所述第三磷硅玻璃层还可以包括第一层62和第二层63。在这种实施方式中，通过对第二牺牲层采用多层结构，一方面能够满足不同掺杂元素的需要，另一方面可以便于通过牺牲层在MEMS麦克风中形成其它部件。
对于所述第二牺牲层，首先可以采用加压化学气相沉积在所述多晶硅振膜层上形成第二磷硅玻璃层61。经过图案化处理后，还可以采用退火处理来释放第二磷硅玻璃层61的应力，提高掺杂作用。通过第二牺牲层可以向所述多晶硅振膜层中掺杂磷等元素，改善多晶硅振膜层的性能。
可选地，可以对第二磷硅玻璃层61进行湿法刻蚀，形成连通至多晶硅振膜层4的凹槽，如图3所示。凹槽的位置与所述悬空部42的位置对应。之后，在所述凹槽上经过低压化学气相沉积，形成厚度为0.5微米的多晶硅层，之后可以经过反应离子刻蚀处理形成呈π形状的多晶硅支撑柱5，多晶硅支撑柱5的位置在所述悬空部42上。
所述多晶硅支撑柱在MEMS麦克风工作时能够起到稳定振膜的作用。例如，在MEMS麦克风启动工作时，对氮化硅层中设置的电极以及多晶硅振膜层中通入偏置电压，使多晶硅振膜向上靠近氮化硅层。此时所述多晶硅支撑柱能够顶在氮化硅层上，使得所述悬空部有一部分能够经多晶硅支撑柱与氮化硅层形成止顶，稳定住悬空部。而悬空部上没有设置支撑柱的位置，就可以根据声音振动产生相应的相应振动，实现麦克风的功能。
优选地，第二磷硅玻璃层61的凹槽形成在与所述悬空部的边缘相对 应的位置，使得多晶硅支撑柱能够形成在悬空部42的边缘。这样，将悬空部42的中心区域留作可以振动收声的区域，声学性能更佳。
可选地，在形成所述多晶硅支撑柱后，再于多晶硅支撑柱以及第二磷硅玻璃层61上形成第三磷硅玻璃层。所述第三磷硅玻璃层的厚度可以为2微米。所述第三磷硅玻璃层将第二磷硅玻璃层61以及所述多晶硅支撑柱5覆盖在其下方。在第三磷硅玻璃层上再形成所述氮化硅层7，如图4所示。形成第三磷硅玻璃层一方面能够对氮化硅层7实施元素掺杂，另一方面能够将多晶硅支撑柱5与所述氮化硅层7隔开，以便形成第二空腔20。
可选地，所述第三磷硅玻璃层上可以通过干法刻蚀形成凹槽，该凹槽的位置与所述多晶硅支撑柱5的位置相对应。进一步地，使得氮化硅层7能够形成嵌入该凹槽的第一凸台76，如图5所示。在如图1所示的实施方式中，所述第一凸台76的位置与所述多晶硅支撑柱5相对应，在MEMS麦克风工作时，对极板和多晶硅振膜施加偏置电压时，多晶硅支撑柱5能够与第一凸台76形成止顶，实现稳定多晶硅振膜层4的作用。
可选地，所述第三磷硅玻璃层包括第一层62和第二层63。通过加压化学气相沉积将第一层62沉积在第二磷硅玻璃层61上。之后，可以先通过干法刻蚀对第一层62进行刻蚀，形成连通至多晶硅支撑柱5的凹槽。第一层62的厚度可以为1.5微米。之后，再将第二层63通过加压化学气相沉积形成在第一层62上，并有一部分嵌入上述凹槽中。第二层63的厚度可以为0.5微米。之后，再于第二层63上沉积氮化硅层7。这样，所述氮化硅层7上的第一凸台76就能够与多晶硅支撑柱5之间形成一定间隙，并且与多晶硅支撑柱5的位置对应。
可选地，所述第一牺牲层31可以包括二氧化硅牺牲层32和第一磷硅玻璃层31。所述二氧化硅玻璃层通过低压化学气相沉积形成在所述基准孔21中以及基准层上。所述二氧化硅牺牲层32的厚度可以为1微米。如图2所示。
对所述基准层上的二氧化硅层进行湿法刻蚀，从而在二氧化硅层上形成凹槽。进一步地，在二氧化硅牺牲层32上沉积形成第一磷硅玻璃层31。第一磷硅玻璃层31能够嵌入二氧化硅牺牲层32的凹槽处，并形成凹槽， 如图2所示。
可选地，所述第一磷硅玻璃层31的厚度为5微米，其中的磷元素的质量百分比为5wt％。所述第一磷硅玻璃层31可以用于对多晶硅振膜层4进行磷元素掺杂，改善多晶硅振膜层4的声学性能。
在所述第一磷硅玻璃层31上形成多晶硅振膜层4，多晶硅振膜层4的一部分结构会嵌入到上述凹槽中，形成振膜凸点43，如图3所示。在刻蚀形成所述第二空腔20后，所述振膜凸点43与所述多晶硅基准层2之间形成有避让间隙44，如图1所示。所述振膜凸点43的作用在于，能够降低多晶硅振膜与所述多晶硅基准层2发生粘连的可能性。特别地，如图1所示，所述避让间隙44能够使多晶硅振膜两侧的第一空腔10与第二空腔20形成空气流通，从而降低MEMS麦克风实际工作时由于第一空腔10与第二空腔之间的气流难以流通进而造成的气压不平衡、影响声学性能发挥的问题。
可选地，对于需要采用干法刻蚀形成特定形状的衬底1、多晶硅基准层2以及多晶硅振膜层4，可以采用反应离子刻蚀(RIE)实现干法刻蚀。这种刻蚀方式的刻蚀尺寸精确度高，能够提高结构的尺寸精度。
可选地，可以采用低压化学气相沉积(LPCVD)形成所述多晶硅基准层2和/或多晶硅振膜层4。这种沉积方式能够形成厚度适中且材料密实度适中的多晶硅材料，保证多晶硅振膜层4能够实现良好的声学性能。
可选地，对于磷硅玻璃层、氮化硅层可以采用加压化学气相沉积(PECVD)形成。这种沉积方式能够形成更致密的材料层，有助于提高材料层的结构强度、提高材料层对其它实现元素掺杂的效果。
可选地，如图2所示，在沉积形成多晶硅基准层2之前，还可以在沉底上沉积形成二氧化硅保护层11。所述多晶硅基准层2形成在二氧化硅保护层11上。在需要对二氧化硅保护层11、多晶硅基准层2以及衬底1进行刻蚀时，多晶硅基准层2与另外两者采用的刻蚀工艺不同，即不同的刻蚀工艺对上述材料层的刻蚀存在选择性。这样，可以利用二氧化硅保护层11对衬底1以及多晶硅基准层2进行保护，以免在不需要刻蚀其中一方时，通过刻蚀工艺的选择性提供保护。
例如，在形成第一空腔10的刻蚀工艺中，利用干法刻蚀对衬底1进行刻蚀。干法刻蚀不会影响二氧化硅保护层11，但是会影响多晶硅基准层2。通过二氧化硅保护层11的作用，干法刻蚀刻蚀至衬底1的顶面时就会停止，二氧化硅保护层11和多晶硅基准层2不会被刻蚀掉。之后，采用湿法刻蚀对二氧化硅保护层11进行刻蚀，而多晶硅基准层2不会被湿法刻蚀刻蚀掉。湿法刻蚀可以对二氧化硅以及基准孔21其上的第一牺牲层31和第二牺牲层进行刻蚀。多晶硅基准层2、基准孔21被作为湿法刻蚀的起始点，用于控制湿法刻蚀的位置和尺寸。
可选地，所述二氧化硅保护层11的厚度可以为0.5微米，在能够起到保护作用的前提下，尽量减小厚度，防止其对MEMS麦克风的整体厚度造成影响。
可选地，在形成所述第二磷硅玻璃层61后，如图3、4所示，可以在所述第二磷硅玻璃层61的与所述连接端41相对应的位置处刻蚀形成凹槽，进而沉积上有多晶硅材料形成的多晶硅电连接柱81。多晶硅电连接柱81与所述多晶硅振膜层4接触电连接。
可选地，在所述多晶硅电连接柱81上还可以形成有焊盘8，用于将MEMS麦克风与外部器件形成电连接。
可选地，所述氮化硅层7可以包括第一氮化硅层71和第二氮化硅层72，如图1、5所示，所述第一氮化硅层71的厚度可以为1微米，而第二氮化硅层72的厚度可以为1.5微米。第一氮化硅层71和第二氮化硅层72可以分别通过加压化学气相沉积(PECVD)形成。在形成了第一氮化硅层71后，可以在其上形成厚度为0.5微米的极板金属75，所述极板金属75被作为MEMS麦克风中的背基板使用，通电后可以用于吸引多晶硅振膜层4。
可选地，所述氮化硅层7上还可以形成有穿孔74，如图1、5所示。该穿孔74可以通过干法刻蚀工艺形成。所述穿孔74一方面在产品中可以作为第二空腔20的泄压、出声孔。另一方面，其可以作为刻蚀第二牺牲层时的进液孔。
可选地，所述氮化硅层7的内壁上还可以通过在所述第二牺牲层上形成凹槽后配合形成有第二凸台73，如图1所示。所述第二凸台73与所述 多晶硅振膜层4上用于振动收声的部分位置对应，其用于防止多晶硅振膜层4在工作中振幅过大，与氮化硅层直接撞击造成损坏。
本技术方案的另一方面还公开了一种采用上述加工方法制成的MEMS麦克风，如图1所示。所述多晶硅振膜层4具有连接端41和悬空部42，所述连接端41固定在所述多晶硅基准层2与氮化硅层7之间的位置。在如图1所示的实施方式中，所述连接端41固定在第一牺牲层31与氮化硅、第二牺牲层之间。所述悬空部42悬于所述氮化硅层7与所述多晶硅基准层2之间。多晶硅基准层2的基准孔21作为第一空腔10的进声孔。
上文实施例中重点描述的是各个实施例之间的不同，各个实施例之间不同的优化特征只要不矛盾，均可以组合形成更优的实施例，考虑到行文简洁，在此则不再赘述。
虽然已经通过例子对本发明的一些特定实施例进行了详细说明，但是本领域的技术人员应该理解，以上例子仅是为了进行说明，而不是为了限制本发明的范围。本领域的技术人员应该理解，可在不脱离本发明的范围和精神的情况下，对以上实施例进行修改。本发明的范围由所附权利要求来限定。

Claims (11)

  1. 一种MEMS麦克风的加工方法，其特征在于，包括：
    在衬底之上沉积多晶硅基准层；
    从多晶硅基准层一侧，对多晶硅基准层进行干法刻蚀，在多晶硅基准层上形成基准孔；
    在多晶硅基准层上沉积第一牺牲层；
    在第一牺牲层上沉积多晶硅振膜层，所述多晶硅振膜层具有悬空部；
    在多晶硅振膜层上沉积第二牺牲层，所述第二牺牲层在所述悬空部的外围与所述第一牺牲层连接；
    在所述第二牺牲层上沉积氮化硅层；
    从衬底一侧，对衬底和二氧化硅保护层进行刻蚀形成第一空腔，所述第一空腔暴露所述基准孔；
    在所述第一空腔一侧，从所述基准孔对位于所述悬空部周围的所述第一牺牲层和第二牺牲层进行湿法刻蚀，在所述多晶硅基准层与氮化硅层之间形成第二空腔；
    所述多晶硅振膜层的悬空部悬于所述第二空腔中。
  2. 根据权利要求1所述的加工方法，其特征在于，所述第二牺牲层包括第二磷硅玻璃层和第三磷硅玻璃层；
    在所述多晶硅振膜层上沉积形成所述第二磷硅玻璃层；
    对所述第二磷硅玻璃层进行湿法刻蚀，形成与所述多晶硅振膜层连通的凹槽，所述凹槽的位置与所述悬空部的位置对应，在所述凹槽上沉积形成多晶硅支撑柱；
    在所述第二磷硅玻璃层上沉积形成所述第三磷硅玻璃层；
    所述氮化硅层形成在所述第三磷硅玻璃层上。
  3. 根据权利要求2所述的加工方法，其特征在于，对所述第三磷硅玻璃层进行干法刻蚀，形成与所述多晶硅支撑柱位置对应的凹槽；
    形成在所述第三磷硅玻璃层上的氮化硅层嵌入所述第三磷硅玻璃层的凹槽中。
  4. 根据权利要求2所述的加工方法，其特征在于，所述第三磷硅玻璃层的厚度为2微米。
  5. 根据权利要求1所述的加工方法，其特征在于，所述第一牺牲层包括二氧化硅牺牲层和第一磷硅玻璃层；
    在所述多晶硅基准层的表面和基准孔中沉积形成二氧化硅牺牲层，所述二氧化硅牺牲层的厚度为1微米；
    对多晶硅基准层上的二氧化硅牺牲层进行湿法刻蚀，在所述二氧化硅牺牲层上形成凹槽；
    在所述二氧化硅牺牲层上沉积形成第一磷硅玻璃层，所述第一磷硅玻璃层在对应于所述二氧化硅牺牲层的凹槽处形成凹槽，所述第一磷硅玻璃层的厚度为5微米，磷的质量百分比为5wt％；
    形成在所述第一磷硅玻璃层上的多晶硅振膜层嵌入所述第一磷硅玻璃层的凹槽中，形成振膜凸点；
    在刻蚀形成所述第二空腔后，所述振膜凸点与所述多晶硅基准层之间形成避让间隙。
  6. 根据权利要求1所述的加工方法，其特征在于，所述干法刻蚀为反应离子刻蚀(RIE)。
  7. 根据权利要求1所述的加工方法，其特征在于，采用低压化学气相沉积(LPCVD)形成所述多晶硅基准层；
    和/或，采用低压化学气相沉积(LPCVD)形成所述多晶硅振膜层。
  8. 根据权利要求1所述的加工方法，其特征在于，所述多晶硅基准层的厚度为0.5微米；
    和/或，所述多晶硅振膜层的厚度为1微米。
  9. 根据权利要求1所述的加工方法，其特征在于，沉积形成多晶硅基准层之前，在所述衬底上沉积形成二氧化硅保护层，在二氧化硅保护层上直接沉积形成所述多晶硅基准层；
    在形成所述第一空腔的工艺中，采用反应离子刻蚀(RIE)对衬底进行刻蚀，采用湿法刻蚀对所述二氧化硅保护层进行刻蚀。
  10. 根据权利要求9所述的加工方法，其特征在于，所述二氧化硅保 护层的厚度为0.5微米。
  11. 一种MEMS麦克风，其特征在于，所述MEMS麦克风采用权利要求1-10任意之一所述的加工方法制成；
    所述多晶硅振膜层具有连接端和悬空部，所述连接端固定在所述多晶硅基准层与氮化硅层之间，所述悬空部悬于所述氮化硅层与所述多晶硅基准层之间。
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