Classifications

• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
  • B81B7/02—Microstructural systems; Auxiliary parts of microstructural devices or systems containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
  • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
  • B81C1/00222—Integrating an electronic processing unit with a micromechanical structure
  • B81C1/00246—Monolithic integration, i.e. micromechanical structure and electronic processing unit are integrated on the same substrate
• • 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
  • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2201/00—Specific applications of microelectromechanical systems
  • B81B2201/02—Sensors
  • B81B2201/0257—Microphones or microspeakers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2201/00—Specific applications of microelectromechanical systems
  • B81B2201/02—Sensors
  • B81B2201/0264—Pressure sensors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C2201/00—Manufacture or treatment of microstructural devices or systems
  • B81C2201/01—Manufacture or treatment of microstructural devices or systems in or on a substrate
  • B81C2201/0101—Shaping material; Structuring the bulk substrate or layers on the substrate; Film patterning
  • B81C2201/0128—Processes for removing material
  • B81C2201/013—Etching
  • B81C2201/0135—Controlling etch progression
  • B81C2201/014—Controlling etch progression by depositing an etch stop layer, e.g. silicon nitride, silicon oxide, metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C2203/00—Forming microstructural systems
  • B81C2203/07—Integrating an electronic processing unit with a micromechanical structure
  • B81C2203/0707—Monolithic integration, i.e. the electronic processing unit is formed on or in the same substrate as the micromechanical structure
  • B81C2203/0714—Forming the micromechanical structure with a CMOS process

Definitions

• This disclosure relates generally to microphones, and, in particular, to microelectromechanical systems (MEMS) microphones.
• MEMS microelectromechanical systems
• MEMS micro-electrical-mechanical-systems
• CMOS complementary-metal-oxide-semiconductor
• FIG. 1 depicts a cross-sectional view of an embodiment of a MEMS
• FIG. 2 depicts the substrate of FIG. 1 after thermal oxidation.
• FIG. 3 depicts the substrate of FIG. 2 after the membrane layer for the MEMS microphone has been deposited and a thermal oxidation layer has been formed on the membrane layer.
• FIG. 4 depicts the substrate of FIG. 3 after a first sacrificial silicon layer has been deposited and portions of the plug structures formed therein.
• FIG. 5 depicts the substrate of FIG. 4 after the second sacrificial layer has been deposited and the remaining portions of the plug structures formed therein and after the backplate layer has been deposited onto the second sacrificial layer.
• FIG. 6 depicts the substrate of FIG. 5 after the backplate layer has been patterned and the bond pad regions have been formed.
• FIG. 7 is a schematic view of an embodiment of a MEMS microphone integrated into the same CMOS substrate with a MEMS pressures sensor.
• FIG. 8 depicts the substrate of FIG. 7 after the substrate has been processed to form the backside trench and air gap for the MEMS microphone and to form the capacitive gap for the MEMS pressures sensor.
• FIG. 1 depicts a perspective view of an embodiment of a MEMS acoustic transducer 10 in accordance with the present disclosure.
• the MEMS acoustic transducer can be a microphone, a receiver, a speaker, or combination thereof.
• a MEMS microphone 10 is illustrated herein.
• the MEMS microphone includes a substrate 12, a flexible membrane 14, and a stationary backplate 16.
• the substrate 12 comprises a complementary metal oxide semiconductor (CMOS) substrate, such as a silicon wafer or silicon on insulator (SOI) substrate, for integration into CMOS
• CMOS complementary metal oxide semiconductor
• the silicon substrate 12 is subjected to thermal oxidation which forms thermal oxidation layers 18 and 20 on the front and back sides of the substrate, respectively.
• thermal oxidation the oxide layers may be deposited using, for example, a plasma enhanced chemical vapor deposition (PECVD). Other techniques are also possible.
• PECVD plasma enhanced chemical vapor deposition
• the membrane 14 comprises a layer of flexible material, such as polysilicon, deposited onto the front side thermal oxidation layer 18 on the front side of the substrate 12.
• the substrate 12 includes a backside trench 22 that exposes the bottom surface of the membrane 14.
• the membrane 14 is configured to serve as a lower electrode for the MEMS microphone 10.
• the lower electrode may be integrated into the membrane 14 in any suitable manner, such as by implant doping of the membrane layer or by the deposition of a conductive film.
• the full membrane layer 14 can be conductive due to inclusion of dopants.
• the definition of the electrode is realized by patterning processes of the fully conductive film.
• the backplate 16 is suspended above the membrane 14 and is configured to serve as a fixed upper electrode for the capacitive MEMS microphone 10.
• the backplate 16 is supported by a silicon spacer 24 that is formed on a thermal oxide layer 23 on the membrane 14.
• the silicon material of the spacer 24 is removed between the backplate 16 and the membrane 14 to form an acoustic chamber 26 that forms an air gap for the microphone.
• the backplate 16 includes a plurality of perforations or openings 28 that are configured to permit air to flow into the acoustic chamber 26 to impinge on the membrane 14.
• the backplate is formed by a low stress silicon rich nitride (SiN) which is an etch-resistant, insulative material with good mechanical properties.
• a local metallization (not visible) is deposited onto the backplate 16 to form the upper electrode for the capacitive microphone.
• the metallization for the electrode may comprise any suitable metal material, such as platinum (Pt), aluminum (Al), titanium (Ti), and the like.
• the metallization is deposited using an atomic layer deposition (ALD) process as a very thin film, e.g., 10nm or less, so that it has little or no impact on the mechanical properties of the backplate 16.
• ALD atomic layer deposition
• Another possibility is the use of a doped silicon film on top of a thin oxide.
• the silicon film serves as conductive electrode
• the oxide film serves as a protection layer in the si-sacrificial layer etch step and is etched away in the later oxide etch process.
• the lower electrode of the membrane 14 and the fixed upper electrode of the backplate 16 together form a parallel plate capacitor.
• sound waves entering the acoustic chamber through the porous backplate 16 cause the flexible membrane 14 to vibrate.
• the distance between the membrane 14 and backplate 16 changes which causes a corresponding change in the capacitance between the lower and upper electrodes.
• the electrodes of the membrane 14 and the backplate 16 are electrically connected to bond pads 32 provided in bond pad regions 30 of the substrate.
• the bond pads are configured to connect the electrodes to readout and control circuitry (not shown).
• the readout and control circuitry is configured to monitor the capacitance between the membrane and the backplate and to output signals that are representative of the sound waves impinging on the membrane.
• SiN low stress silicon rich nitride
• SiN materials can provide a rigid, mechanically stable structure at small layer thicknesses, e.g., 1 -3 ⁇ , and that can be patterned to achieve a relatively high porosity without impacting the structural integrity of the backplate. This allows the dimensions of the air gap to be increased so that air flow behavior can be optimized without significantly impacting performance. This also enables the membrane 14 to be provided with low porosity which can enhance coupling to the device.
• SiN materials are more resistant to certain etchants, such as vapor-HF (hydrofluoric acid), that are typically used to etch silicon and silicon oxide materials during CMOS processing
• etchants such as vapor-HF (hydrofluoric acid)
• the removal of the silicon sacrificial layers to release the backplate and form the air gap between the backplate and membrane can be performed as part of a normal CMOS flow.
• SiN, or similar type of material such as tetraethyl orthosilicate (TEOS) is used to form plug structures 34 that extend between the backplate 16 and the substrate membrane 14.
• the plug structures are configured to serve as etch stops for the acoustic chamber as well as to increase mechanical stability and provide electrical insulation between the backplate 16 and the membrane 14.
• a SiN/TEOS plug structure 36 may also be incorporated into the device to provide electrical insulation and increased electrical resistance from the bondpads to the substrate in the bond pad regions 32 of the device.
• the SiN/TEOS plug structure 36 is provided between the bond bad region 32 and the membrane layer 14 and forms a support framework that allows the conductive layers between the bond pads 32 and the membrane layer 14 to be removed or partially removed thereby increasing the electrical resistance.
• FIGS. 2-6 schematically depict an embodiment of a fabrication process for a MEMS microphone such as depicted in FIG. 1 .
• the fabrication process of the MEMS microphone starts with a silicon substrate 12 which is subjected to thermal oxidation to form thermal oxidation layers 18, 20 on opposing sides of the substrate 12.
• the thermal oxide layers 18, 20 may then be patterned to define features, such as contact regions or etch stops, such as etch stop 38 in FIG. 3.
• a membrane/electrode layer 14 is deposited on the upper thermal oxidation layer 18 at a suitable thickness depending on the desired performance characteristics and patterned to define the desired size and shape of the lower electrode.
• the membrane layer 14 comprises polysilicon deposited using low-pressure chemical vapor deposition (LPCVD) process.
• LPCVD low-pressure chemical vapor deposition
• the membrane layer 14 can be patterned with the desired perforation degree in order to allow a static pressure exchange from both sides of the membrane.
• the membrane (area and shape) itself is to be patterned.
• a thermal oxidation process is then performed to form the thin thermal oxide layer 23 on the upper surface of the membrane 14.
• the thermal oxide layer 23 protects the membrane 14 from the Si sacrificial etch that is used to form the air gap.
• the thermal oxide layer 23 is then patterned to define any desired features, such as contact region 40 (FIG. 4) and through holes for the plug structures 34, 36.
• the silicon sacrificial/spacer layer structure 24 is then formed on the thermal oxide layer 23.
• the sacrificial silicon layer structure 24 may be formed in any suitable manner.
• the silicon sacrificial layer structure comprises one or more layers of epitaxially grown silicon. The thickness and/or the number of silicon layers depends on the desired thickness of the air gap as well as the configuration of any structures, such as plugs and interconnects, incorporated into the device.
• the MEMS microphone 10 includes a stacked SiN/TEOS plug structure that is used to form etch stops and electrical insulation at the perimeter of the acoustic chamber 26.
• a first sacrificial silicon layer 42 is deposited, e.g, epitaxially, on the thermal oxide layer 23 as depicted in FIG. 4.
• Plug trenches 44 for the plug structures 34, 36 are then formed in the first sacrificial silicon layer 42, e.g., by etching, at appropriate locations.
• the plug trenches 44 formed in the first sacrificial silicon layer 42 are then filled with an etch- resistant, insulative material, such as SiN or TEOS.
• a second sacrificial silicon layer 50 is then deposited, e.g. by epitaxial deposition, onto the first sacrificial silicon layer 42.
• the total width of the silicon layer deposition corresponds to the desired air gap thickness.
• a planarizing process, such as chemical-mechanical polishing (CMP) may then be performed to ensure a constant and uniform upper surface of the sacrificial silicon is provided at the desired distance from the membrane 14.
• CMP chemical-mechanical polishing
• Plug trenches 52 are then formed in the second sacrificial layer 50 that are aligned with the first plug trenches formed in the first silicon sacrificial layer and that extend down to the horizontal parts of the plug structures.
• the plug trenches formed in the first sacrificial silicon layer are then filled with an etch-resistant, insulative material, such as SiN or TEOS.
• Additional features are then etched into the upper surface of the second sacrificial layer 50 to define the functional shape of the backplate 16.
• U- shaped trenches 54 are etched into the second sacrificial layer 50 which will define U- shaped folds or corrugations in the backplate 16 for reducing stress, adding mechanical stability, forming over-travel stops, and the like.
• a metallization layer 56 is deposited and patterned to form an electrode structure in the bottom of the trenches 54. Any suitable type of metal or doped silicon above a protective oxide layer may be used for the metallization.
• the metallization may be deposited using an atomic layer deposition (ALD) process as a very thin film, e.g., 10nm or less, so that it has little or no impact on the mechanical properties of the backplate 16.
• ALD atomic layer deposition
• a SiN layer for the backplate 16 is then deposited on top of the second sacrificial layer 50 which conforms to the U-shaped trenches 54 and extends over the plug structures 34, 36.
• the SiN layer for the backplate 16 is deposited to a thickness of approximately 1 -3 ⁇ .
• the SiN layer is patterned, e.g., by etching, to form the openings or perforations 28 and to define the final shape of the backplate 16.
• Another metallization layer 58 is then deposited onto the backplate 16 that extends into the bonding region 30 for connecting the backplate 16 to a bonding pad 32. Additional layers and structures may also be provided on the device, such as passivation or insulation layers, packaging structures, mounting structures, and the like.
• the fabrication of the MEMS microphone 10 is then completed by forming the backside trench 22, e.g., by etching, using the thermal oxide 18 as an etch stop to protect the membrane and by removing the sacrificial silicon 24 beneath the backplate 16, e.g. by etching, using the thermal oxide layer 23 and the plug structures 34, 36 as etch stops.
• the thermal oxide layers 18, 23 that remain on the upper and lower surfaces of the membrane 14 are then removed, e.g., using a vHF (vapor hydrofluoric acid) release etch or another suitable procedure.
• the acoustic chamber 26 is formed which provides the air gap between the backplate 16 and the membrane of the MEMS microphone.
• the silicon spacer layer and plug structures have been described as having multiple layers and a stacked configuration, the process may be simplified by using a single sacrificial silicon layer and single level SiN/TEOS plug trench (not shown).
• the plug structure 36 that defines a support framework may be omitted or may be provided at other locations or multiple locations where increased electrical resistance and insulation is desired.
• air gaps may be left in the framework of the plug structure 36.
• the air gaps may be refilled with SiN/TEOS or another compatible insulating material for improving mechanical stability.
• FIGS. 7 and 8 An embodiment of a MEMS microphone 70 incorporated into a MEMS pressures sensor 72 or onto the same chip as a MEMS pressure sensor 7 is depicted in FIGS. 7 and 8. In the embodiment of FIGS. 7 and 8, the device is provided with a similar layer
• the MEMS microphone 10 such as a substrate 12, a membrane layer 14, oxide layers 18, 23, a first sacrificial silicon layer 42 and a second sacrificial silicon layer 52 for defining plug structures 34 and features in the backplate layer 16.
• the pressure sensor 72 is arranged on the same substrate 12 with the microphone 70 and is configured to utilize the both sacrificial layers 42, 50 to form the flexible membrane or diaphragm for the pressure sensor.
• the second oxide layer 23 is used as a sacrificial layer for releasing the membrane or diaphragm (e.g., layers 42, 50) that will form the movable electrode for the pressure sensor.
• Etch stops 88 are formed in the sacrificial oxide 23 for defining the boundary for the gap between the flexible membrane and the polysilicon layer 14 which is configured to serve as the fixed electrode for the pressure sensor 72.
• the MEMS microphone region of the substrate is processed to form the backside trench 22 and the air gap 26.
• the MEMS pressure sensor region of the substrate is processed by removing the sacrificial oxide layer to form a capacitive gap 94 for the pressure sensor 70. All of the process steps to form the device of FIG. 8 can be performed during normal CMOS flow.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Manufacturing & Machinery (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Computer Hardware Design (AREA)
• Pressure Sensors (AREA)

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• 2014
  • 2014-03-12 WO PCT/US2014/024147 patent/WO2014159552A1/en active Application Filing
  • 2014-03-12 CN CN201480027801.5A patent/CN105531220A/zh active Pending
  • 2014-03-12 EP EP14775941.9A patent/EP2969911A4/de not_active Withdrawn

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