# US 10,870,577 B2 · Methods of forming MEMS diaphragms including corrugations > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,870,577 B2 - Document ID: US10870577B2 - Status: Granted - Kind: B2 - Application number: 16/593,498 - Filed: 2019-10-04 - Published: 2020-04-09 - Granted: 2020-12-22 - Earliest claimed: 2018-10-05 - Assignees: Knowles Electronics, LLC - Applicants: Knowles Electronics, LLC - Inventors: Sung Bok Lee; Vahid Naderyan; Bing Yu; Michael Kuntzman; Yunfei Ma; Michael Pedersen - Web page: https://patentgrep.com/patent/US10870577B2 ## CPC - B81C 1/00158: {Diaphragms, membranes (manufacture process for semi-permeable inorganic membranes B01D67/0039)} - B81B 3/0021: {Transducers for transforming electrical into mechanical energy or vice versa (dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00)} - B81B 3/007: {For controlling stiffness, e.g. ribs} - G01L 9/0042: {Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms (details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively)} - G01L 9/0048: {Details about the mounting of the diaphragm to its support or about the diaphragm edges, e.g. notches, round shapes for stress relief} - H04R 19/04: Microphones (H04R19/01 takes precedence) - H04R 31/003: {for diaphragms or their outer suspension} - B81B 2201/0257: Microphones or microspeakers - B81B 2201/0264: Pressure sensors - B81B 2203/0127: Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function - B81B 2203/019: characterized by their profile - B81C 2201/0132: Dry etching, i.e. plasma etching, barrel etching, reactive ion etching [RIE], sputter etching or ion milling - B81C 2201/0133: Wet etching - H04R 2201/003: Mems transducers or their use - B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01) - B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00) - G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G) - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract A method of forming an acoustic transducer comprises providing a substrate and depositing a first structural layer on the substrate. The first structural layer is selectively etched to form at least one of an enclosed trench or an enclosed pillar thereon. A second structural layer is deposited on the first structural layer and includes a depression or a bump corresponding to the enclosed trench or pillar, respectively. At least the second structural layer is heated to a temperature above a glass transition temperature of the second structural layer causing the second structural layer to reflow. A diaphragm layer is deposited on the second structural layer such that the diaphragm layer includes at least one of a downward facing corrugation corresponding to the depression or an upward facing corrugation corresponding to the bump. The diaphragm layer is released, thereby forming a diaphragm suspended over the substrate. ## Claims ### Claim 1 A method, comprising: providing a substrate; selectively etching the substrate to form at least one of an enclosed trench or an enclosed pillar on the substrate; depositing a first structural layer on the substrate, the first structural layer including at least one of a depression or a bump corresponding to the enclosed trench or the enclosed pillar; heating the first structural layer to a temperature above a glass transition temperature of the first structural layer causing the first structural layer to reflow; depositing a diaphragm layer on the first structural layer such that the diaphragm layer includes at least one of a downward facing corrugation corresponding to the depression or an upward facing corrugation corresponding to the bump formed in the first structural layer; and releasing the diaphragm layer, thereby forming a diaphragm suspended over the substrate. ### Claim 2 (depends on 1) The method of claim 1, wherein the first structural layer comprises a phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG) and includes a first impurity content. ### Claim 3 (depends on 2) The method of claim 2, wherein the first impurity content comprises phosphorus and wherein the first structural layer has a first phosphorus content in a range between 2% and 10%. ### Claim 4 (depends on 1) The method of claim 1, wherein the depression or the pillar formed in the first structural layer prior to heating the first structural layer has edges having a first radius of curvature of less than 1 μm, and wherein the depression or the pillar, after heating the first structural layer, has edges having a second radius of curvature of greater than 1 μm and less than 50 μm such that the downward facing corrugation or the upward facing corrugation defined in the diaphragm layer has a radius of curvature corresponding to the second radius of curvature. ### Claim 5 (depends on 1) The method of claim 1, further comprising: depositing a first conducting layer on the diaphragm layer; and patterning the first conducting layer so as to form an electrical contact on the diaphragm layer. ### Claim 6 (depends on 1) The method of claim 1, further comprising: depositing a second structural layer on the diaphragm layer; depositing a back plate layer on the second structural layer; and forming a plurality of apertures in the back plate layer. ### Claim 7 (depends on 6) The method of claim 6, wherein the second structural layer comprises a second PSG layer having a second phosphorus content in a range between 2% and 10%. ### Claim 8 (depends on 6) The method of claim 6, further comprising: before depositing the back plate layer, depositing and patterning a second conducting layer on the second structural layer, wherein at least a portion of the second conducting layer contacts the back plate layer, and wherein forming the plurality of apertures also forms corresponding apertures through the second conducting layer. ### Claim 9 (depends on 6) The method of claim 6, wherein releasing the diaphragm comprises: etching through each of the substrate and the first structural layer to release the diaphragm layer from a first side of the diaphragm layer; and etching the second structural layer through the apertures so as to also release the diaphragm layer from a second side of the diaphragm layer, opposite the first side, thereby forming the diaphragm, the etching also releasing the back plate layer so as to form a back plate suspended over the diaphragm. ### Claim 10 (depends on 9) The method of claim 9, wherein etching of the second structural layer is performed such that a portion of the second structural layer proximate to the upward facing corrugations or downward facing corrugations of the diaphragm layer is not removed. ### Claim 11 An acoustic transducer formed by the process of: providing a substrate; selectively etching the substrate to form at least one of an enclosed trench or an enclosed pillar on the substrate; depositing a first structural layer on the substrate, the first structural layer including at least one of a depression or a bump corresponding to the enclosed trench or the enclosed pillar; heating the first structural layer to a temperature above a glass transition temperature of the first structural layer causing the first structural layer to reflow; depositing a diaphragm layer on the first structural layer such that the diaphragm layer includes at least one of a downward facing corrugation corresponding to the depression or an upward facing corrugation corresponding to the bump formed in the first structural layer; and releasing the diaphragm layer, thereby forming a diaphragm suspended over the substrate. ### Claim 12 (depends on 11) The acoustic transducer of claim 11, wherein the first structural layer comprises a phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG) and includes a first impurity content. ### Claim 13 (depends on 11) The acoustic transducer of claim 11, wherein the first impurity content comprises phosphorus and wherein the first structural layer has a first phosphorus content in a range between 2% and 10%. ### Claim 14 (depends on 11) The acoustic transducer of claim 11, wherein the depression or the pillar formed in the first structural layer prior to heating the first structural layer has edges having a first radius of curvature of less than 1 μm, and wherein the depression or the pillar, after heating the first structural layer, has edges having a second radius of curvature of greater than 1 μm and less than 50 μm such that the downward facing corrugation or the upward facing corrugation defined in the diaphragm layer has a radius of curvature corresponding to the second radius of curvature. ### Claim 15 (depends on 11) The acoustic transducer of claim 11, further comprising: depositing a first conducting layer on the diaphragm layer; and patterning the first conducting layer so as to form an electrical contact on the diaphragm layer. ### Claim 16 (depends on 11) The acoustic transducer of claim 11, further comprising: depositing a second structural layer on the diaphragm layer; depositing a back plate layer on the second structural layer; and forming a plurality of apertures in the back plate layer. ### Claim 17 (depends on 16) The acoustic transducer of claim 16, wherein the second structural layer comprises a second PSG layer having a second phosphorus content in a range between 2% and 10%. ### Claim 18 (depends on 16) The acoustic transducer of claim 16, further comprising: before depositing the back plate layer, depositing and patterning a second conducting layer on the second structural layer, wherein at least a portion of the second conducting layer contacts the back plate layer, and wherein forming the plurality of apertures also forms corresponding apertures through the second conducting layer. ### Claim 19 (depends on 16) The acoustic transducer of claim 16, wherein releasing the diaphragm comprises: etching through each of the substrate and the first structural layer to release the diaphragm layer from a first side of the diaphragm layer; and etching the second structural layer through the apertures so as to also release the diaphragm layer from a second side of the diaphragm layer, opposite the first side, thereby forming the diaphragm, the etching also releasing the back plate layer so as to form a back plate suspended over the diaphragm. ### Claim 20 (depends on 19) The acoustic transducer of claim 19, wherein etching of the second structural layer is performed such that a portion of the second structural layer proximate to the upward facing corrugations or downward facing corrugations of the diaphragm layer is not removed. ### Claim 21 A method, comprising: providing a substrate; depositing a first structural layer on the substrate; selectively etching the first structural layer to form at least one of an enclosed trench or enclosed pillar on the first structural layer; depositing a second structural layer on the first structural layer, the second structural layer including at least one of a depression or a bump corresponding to the at least one of the enclosed trench or the enclosed pillar formed in the first structural layer; heating at least the second structural layer to a temperature above a glass transition temperature of the second structural layer causing the second structural layer to reflow; depositing a diaphragm layer on the second structural layer such that the diaphragm layer includes at least one of a downward facing corrugation corresponding to the depression or an upward facing corrugation corresponding to the bump formed in the second structural layer; and releasing the diaphragm layer, thereby forming a diaphragm suspended over the substrate. ### Claim 22 (depends on 21) The method of claim 21, wherein at least one of the first structural layer and the second structural layer comprises phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG), and wherein an impurity content in at least one of the first structural layer or the second structural layer comprises phosphorus. ### Claim 23 (depends on 22) The method of claim 22, wherein the first structural layer is a first PSG layer having a first phosphorus content, and the second structural layer is a second PSG layer having a second phosphorus content different from the first phosphorus content. ### Claim 24 (depends on 23) The method of claim 23, wherein the first phosphorus content is between 4% and 10% and the second phosphorus content is between 2% and 6%, the first phosphorus content being greater than the second phosphorus content. ### Claim 25 (depends on 23) The method of claim 23, wherein the first phosphorus content is between 2% and 6%, and the second phosphorus content is between 4% and 10%, the second phosphorus content being greater than the first phosphorus content. ### Claim 26 (depends on 25) The method of claim 25, wherein the temperature during heating is greater than a glass transition temperature of the second PSG layer but lower than a glass transition temperature of the first PSG layer. ### Claim 27 (depends on 22) The method of claim 22, wherein the first structural layer is a first PSG layer having a first phosphorus content, and the second structural layer is a second PSG layer having a second phosphorus content being equal to the first phosphorus content. ### Claim 28 (depends on 27) The method of claim 27, wherein the second phosphorus content is greater than 2%. ### Claim 29 (depends on 21) The method of claim 21, wherein releasing the diaphragm comprises etching through each of the substrate, the first structural layer and the second structural layer; and wherein etching of the first structural layer and the second structural layer is performed such that a portion of the first structural layer and a portion of the second structural layer proximate to a perimetral edge of the diaphragm layer is not removed. ### Claim 30 (depends on 29) The method of claim 29, wherein the portion of the second structural layer contacts the diaphragm layer, and wherein an inner radial edge of the portion of the second structural layer proximate to the diaphragm is positioned radially closer to the downward facing corrugation or upward facing corrugation defined in the diaphragm layer relative to an inner radial edge of the portion of the first structural layer proximate to the substrate.