Method of forming MEMS diaphragms including pleats

Abstract

The invention relates to a method of forming a MEMS diaphragm including pleats. A method of forming an acoustic transducer includes 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 a closed trench or a closed pillar on the first structural layer. A second structural layer is deposited on the first structural layer, and the second structural layer includes recesses or bumps corresponding to the closed trenches or pillars, respectively. At least the second structural layer is heated to a temperature above the glass transition temperature of the second structural layer, thereby 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 wrinkle corresponding to the recess or an upward facing wrinkle corresponding to the bump. The diaphragm layer is released, thereby forming a diaphragm suspended over the substrate.

Description

[0001] This application is a divisional application of the Chinese patent application (international application number PCT / US2019 / 054752) with application number 201980065031.6, application date October 4, 2019, and invention name “Method for forming a MEMS diaphragm including wrinkles”. Technical Field

[0002] The present disclosure generally relates to systems and methods for improving the compliance of an acoustic transducer including a diaphragm. Background Art

[0003] Microphone assemblies are commonly used in electronic devices to convert acoustic energy into electrical signals. Microphones typically include a diaphragm for converting acoustic signals into electrical signals. Pressure sensors may also include such a diaphragm. Advances in micro- and nano-fabrication technology have led to the development of increasingly smaller micro-electromechanical system (MEMS) microphone assemblies and pressure sensors. Some microphones include a diaphragm that is tensioned or constrained, which reduces the compliance of the diaphragm. Summary of the invention

[0004] Embodiments described herein generally relate to methods and processes for manufacturing a tensioned or constrained diaphragm for use in a MEMS acoustic transducer with enhanced compliance. Specifically, the described methods and processes enable the manufacture of a tensioned diaphragm having one or more upwardly and / or downwardly facing corrugations to increase the compliance of the diaphragm, the corrugations having smooth corners to reduce stress concentrations, thereby increasing diaphragm robustness and reducing failures.

[0005] In some embodiments, a method of forming an acoustic transducer includes providing a substrate and depositing a first structural layer on the substrate. Selectively etching the first structural layer to form at least one of a closed groove or a closed column on the structural layer. Depositing a second structural layer on the structural layer. The second structural layer includes a depression or a protrusion corresponding to the closed groove or the closed column. Heating at least the second structural layer to a temperature higher than a glass transition temperature of the second structural layer, thereby causing the second structural layer to reflow.

[0006] The diaphragm layer is deposited on the second structural layer so that the diaphragm layer includes at least one of downwardly facing wrinkles corresponding to the depressions formed in the second structural layer or upwardly facing wrinkles corresponding to the bumps formed in the second structural layer. The diaphragm layer is released, thereby forming a diaphragm suspended above the substrate.

[0007] In some embodiments, a method of forming an acoustic transducer includes providing a substrate and selectively etching the substrate to form at least one of a closed groove or a closed column on the substrate. A first structural layer is deposited on the substrate. The first structural layer includes at least one of a depression or a protrusion corresponding to the closed groove or the closed column. The first structural layer is heated to a temperature higher than the glass transition temperature of the first structural layer, thereby causing the first structural layer to reflow. A diaphragm layer is deposited on the first structural layer, so that the diaphragm layer includes at least one of a downward-facing wrinkle corresponding to the depression formed in the first structural layer or an upward-facing wrinkle corresponding to the protrusion formed in the first structural layer. The diaphragm layer is released, thereby forming a diaphragm suspended above the substrate.

[0008] In some embodiments, an acoustic transducer is formed by the following process: providing a substrate and selectively etching the substrate to form at least one of a closed groove or a closed column on the substrate. A first structural layer may be deposited on the substrate, wherein the first structural layer includes at least one of a depression or a protrusion corresponding to the closed groove or the closed column. The first structural layer may be heated to a temperature higher than the glass transition temperature of the first structural layer, thereby causing the first structural layer to reflow. A diaphragm layer is deposited on the first structural layer, so that the diaphragm layer includes at least one of a downward-facing wrinkle corresponding to the depression formed in the first structural layer or an upward-facing wrinkle corresponding to the protrusion formed in the first structural layer. The diaphragm may then be released, thereby forming a diaphragm suspended above the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above features and other features of the present disclosure will become fully apparent from the following description and the appended claims in conjunction with the accompanying drawings. It is necessary to understand that these drawings only depict several implementations according to the present disclosure and, therefore, are not to be considered as limiting the scope of the present disclosure, which will be described with additional features and details through the use of the accompanying drawings.

[0010] Figure 1A to Figure 1B is a schematic illustration of various operations included in a process of forming a diaphragm of an acoustic transducer including downward facing corrugations according to an embodiment, Figure 1C is used Figure 1A to Figure 1B A plan view of a diaphragm of an acoustic transducer formed by a process, wherein Figure 1B Operation 6 represents the Figure 1C The line XX intercepts Figure 1C Side sectional view of .

[0011] FIG. 2A to FIG. 2B is a schematic illustration of various operations included in a process of forming a diaphragm of an acoustic transducer including upward facing corrugations according to an embodiment, Figure 2C is used FIG. 2A to FIG. 2B A plan view of a diaphragm of an acoustic transducer formed by a process, wherein Figure 2BOperation 6 represents the Figure 2C The line YY intercepts Figure 2C Side sectional view of .

[0012] Figure 3 is a schematic flow chart of a method of manufacturing an acoustic transducer having a diaphragm having upward-facing or downward-facing corrugations defined therein according to an embodiment.

[0013] FIG. 4A to FIG. 4C is a schematic illustration of various operations involved in forming an acoustic transducer including upward-facing or downward-facing corrugations in accordance with an embodiment.

[0014] FIG. 5A to FIG. 5D is a schematic illustration of various operations involved in forming an acoustic transducer including upward-facing or downward-facing corrugations according to an embodiment; Figure 5E Is Figure 5D The operation 14a indicated by arrow A FIG. 5A to FIG. 5D A magnified view of a portion of an acoustic transducer.

[0015] Figure 6 According to the implementation method FIG. 5A to FIG. 5D A top view of a portion of a backplate layer of an acoustic transducer showing a plurality of holes formed therein.

[0016] Figure 7 Group A of is a table summarizing diaphragms including downward facing wrinkles formed in two wafer batches using various methods, the shapes of their edges (or corners), and the associated pressures that cause the diaphragms to fail; Figure 7 Groups B to E are scanning electron microscope (SEM) images of representative samples of two batches of wafers.

[0017] Figure 8 is Figure 7 A graph of the diaphragm strength of diaphragms formed from representative samples of two wafer batches of group A.

[0018] 9A to 9C is a schematic illustration of various operations involved in forming an acoustic transducer including upward-facing or downward-facing corrugations in accordance with an embodiment.

[0019] Fig.10 is a schematic flow chart of a method of manufacturing an acoustic transducer having a diaphragm having upward-facing or downward-facing corrugations defined therein according to another embodiment.

[0020] FIG. 11A to FIG. 11C is a schematic illustration of various operations involved in forming an acoustic transducer including upward-facing or downward-facing corrugations in accordance with an embodiment.

[0021] FIG. 12A to FIG. 12Dis a schematic illustration of various operations involved in forming an acoustic transducer including upward-facing or downward-facing corrugations in accordance with an embodiment.

[0022] FIG. 13A to FIG. 13E is a schematic illustration of various operations involved in forming an acoustic transducer including two corrugated diaphragms in accordance with an embodiment.

[0023] Throughout the following detailed description, reference is made to the accompanying drawings. In the drawings, similar symbols generally identify similar parts unless the context indicates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized and other changes may be made without departing from the spirit or scope of the subject matter presented herein. It will be readily appreciated that the various aspects of the present disclosure as generally described herein and illustrated in the drawings may be arranged, substituted, combined, and designed in a variety of different configurations, all of which are expressly contemplated and form a part of the present disclosure. DETAILED DESCRIPTION

[0024] Embodiments described herein generally relate to methods and processes for manufacturing a tensioned or constrained diaphragm of a MEMS acoustic transducer having enhanced compliance. Specifically, the described methods and processes enable the manufacture of a tensioned diaphragm having one or more upwardly and / or downwardly facing corrugations to increase the compliance of the diaphragm, the corrugations having smooth corners to reduce stress concentrations, thereby increasing diaphragm robustness and reducing failures.

[0025] Many acoustic transducers include one or more diaphragms suspended above, below, or with a backplate interposed therebetween. In some acoustic transducers, the diaphragm may be tensioned or constrained to provide high linearity. However, such a tensioned diaphragm may not have a sufficiently high compliance, which may cause low sensitivity or movement of the diaphragm when the acoustic transducer is exposed to sound pressure. Wrinkles or ridges (e.g., upward or downward facing wrinkles) may be formed in such a tensioned diaphragm to increase the compliance of the diaphragm. Some manufacturing processes may produce wrinkles with sharp corners (i.e., having a radius of curvature of less than 1 μm). For example, during impact and high pressure events, stress may be concentrated at such sharp corners, causing the diaphragm to fail and reduce robustness.

[0026] In contrast, the methods and processes described herein provide benefits including, for example: (1) enabling the manufacture of diaphragms including corrugations having smooth or rounded corners (i.e., having a radius of curvature greater than 1 μm and less than 50 μm at the corners) to reduce stress concentration and increase robustness; (2) using a simple PSG reflow process to smooth corners in depressions or bumps formed in a PSG layer, which is used as a template or mold to form a diaphragm having corrugations with smooth corners; (3) being easily integrated with current manufacturing methods, thereby reducing manufacturing complexity and cost; and (4) allowing the manufacture of upward-facing corrugations, downward-facing corrugations, or a combination thereof.

[0027] As described herein, the term "downward-facing corrugations" refers to corrugations or ridges extending from a diaphragm toward a substrate upon which the diaphragm is suspended, and "upward-facing corrugations" refers to corrugations or ridges extending from the diaphragm away from the substrate.

[0028] Figure 1A to Figure 1B A process flow 100 is illustrated for forming an acoustic transducer 10 having a diaphragm 110 including downward facing corrugations or ridges 112 according to an embodiment. The acoustic transducer 10 may include, for example, a MEMS acoustic transducer for use in a MEMS microphone assembly or a MEMS pressure sensor, and may be configured to generate an electrical signal in response to an acoustic signal or atmospheric pressure changes.

[0029] In operation 1, a substrate 102 is provided, which includes a first structure layer 104 disposed thereon. The substrate 102 may include, for example, silicon, glass, Pyrex, quartz, or any other substrate described herein. The first structure layer 104 may include a first PSG or BPSG layer having a first impurity content (e.g., a first phosphorus content in a range between 2% and 6%) and may be deposited on the substrate 102 using CVD, LPCVD, PECVD, ALD, any other suitable method, or a combination thereof.

[0030] In operation 2, one or more closed trenches 105 are formed in the first structural layer 104. The closed trenches 105 may be formed using wet etching (e.g., BHF etching) or dry etching (e.g., RIE or DRIE etching). Etching may cause the closed trenches 105 to have sharp corners and edges. In some embodiments, the one or more closed trenches 105 may have a circular cross-section, for example, defining a longitudinal axis A around the substrate 102. L Etched circular grooves.

[0031] In operation 3, a second structure layer 108 is deposited on the first structure layer 104 such that the second structure layer 108 includes one or more recesses 109 corresponding to the one or more closed trenches 105 defined in the first structure layer 104. The recesses 109 formed in the cavity may also have sharp corners and edges corresponding to the sharp edges or corners of the closed trenches 105 defined in the first structure layer 104. The second structure layer 108 may include a second PSG layer having a second impurity content (e.g., a second phosphorus content).

[0032] The second structure layer 108 may have a second phosphorus content greater than the first phosphorus content of the first PSG layer 104, for example, in a range between 4% and 10%. The higher phosphorus content in the second structure layer 108 causes the second structure layer 108 to have a lower glass transition temperature than the first structure layer 104. In operation 4, the second structure layer 108 is heated to a temperature higher than its glass transition temperature but lower than the glass temperature of the first structure layer 104, thereby causing only the second structure layer 108 to reflow, thereby smoothing or rounding the corners and edges of the recess 109.

[0033] In operation 5, the diaphragm layer 110 is deposited on the second structural layer 108 so that the diaphragm layer 110 includes one or more downward facing corrugations 112 extending therefrom toward the substrate 102. In addition, the downward facing corrugations 112 include smooth or rounded corners 113 corresponding to the smooth corners of the recesses 109.

[0034] In operation 6, at least a portion of the substrate 102, the first structural layer 104, and the second structural layer 108 are etched to leave the diaphragm 110 with the downward facing wrinkles 112 suspended above the substrate 102, thereby forming the acoustic transducer 10. In some embodiments, the downward facing wrinkles 112 may include, for example, circumferential wrinkles corresponding to the circular closed grooves 105 initially formed in the first structural layer 104. Figure 1C A plan view of a diaphragm 110 is shown showing downwardly facing corrugations 112. Although shown as including a pair of corrugations 112, any number of corrugations may be formed in the diaphragm 110. In various embodiments, the depth of the corrugations 112 may be in the range of 0.5 microns to 5 microns (e.g., 0.5, 1, 2, 3, 4, or 5 microns, including all ranges and values ​​therebetween).

[0035] FIG. 2A to FIG. 2B A process flow 200 is illustrated for forming an acoustic transducer 20 having a diaphragm 210 including upwardly facing corrugations 212 according to an embodiment. The acoustic transducer 20 may include, for example, a MEMS acoustic transducer for use in a MEMS microphone assembly or a MEMS pressure sensor, and may be configured to generate an electrical signal in response to an acoustic signal or atmospheric pressure changes.

[0036] In operation 1, a substrate 202 is provided, the substrate 202 including a first structural layer 204 disposed thereon. The substrate 202 may include, for example, glass, silicon, Pyrex, quartz, or any other substrate described with respect to methods 300, 700. The first structural layer 204 may have an impurity, for example, a first amount of phosphorus or a first phosphorus content in a range between 2% and 6%, and may be deposited on the substrate 202 using CVD, LPCVD, PECVD, ALD, any other suitable method, or a combination thereof.

[0037] In operation 2, one or more closed pillars 205 are formed in the first structure layer 204. The closed pillars 205 can be formed by removing a majority of the first structure layer 204 using wet etching (e.g., BHF etching) or dry etching (e.g., RIE or DRIE etching), thereby leaving the closed pillars 205 standing on the substrate 202. The closed pillars 205 can, for example, define a longitudinal axis A around the substrate 202. L A circular closed column is formed and extends toward the substrate 202. Etching causes the closed column 205 to have sharp corners and edges. In operation 3, a second structure layer 208 is deposited on the substrate and the closed column 205 formed by the first structure layer 204, so that the second structure layer 208 includes one or more bumps 209 corresponding to one or more columns. The bumps 209 formed on the closed column 205 will also have sharp corners and edges corresponding to the sharp edges or corners of the closed column 205 defined in the first structure layer 204.

[0038] The second structure layer 208 may have a second impurity content, for example, a second phosphorus content greater than the first phosphorus content of the first structure layer 204 in a range between 4% and 10%, thereby having a lower glass transition temperature than the first structure layer 204. In operation 4, the second structure layer 208 is heated to a temperature higher than its glass transition temperature but lower than the glass temperature of the first structure layer 204, thereby causing only the second structure layer 208 to reflow, thereby smoothing or rounding the corners and edges of the bump 209.

[0039] In operation 5, a diaphragm layer 210 is deposited on the second structural layer 208, so that the diaphragm layer 210 includes one or more upward-facing folds 212 extending from the diaphragm layer 210 away from the substrate 202. In addition, the upward-facing folds 212 include smooth or rounded corners 213 corresponding to the smooth corners of the bumps 209. In operation 6, the substrate 202 and the first structural layer 204 and at least a portion of the pillars 205 are etched to leave the diaphragm layer 210, thereby forming a diaphragm with upward-facing folds 212 suspended above the substrate 202, thereby forming an acoustic transducer 20. In some embodiments, the upward-facing folds 212 include closed circumferential folds and can have a height in the range of 0.5 microns to 5 microns (e.g., 0.5, 1, 2, 3, 4, or 5 microns, including all ranges and values ​​therebetween). For example, Figure 2C A plan view of the diaphragm 210 is shown exhibiting upwardly facing corrugations 212 formed as closed circular walls or circular columns extending away from the substrate 202 .

[0040] Figure 3 1 is a schematic flow chart of an example method 300 for manufacturing an acoustic transducer (e.g., acoustic transducer 10, 20, 40, 50, 80, 90) including a diaphragm including upward-facing or downward-facing corrugations with smooth or rounded corners. The acoustic transducer may include, for example, a MEMS acoustic transducer for use in a MEMS microphone assembly or a MEMS pressure sensor, and may be configured to generate an electrical signal in response to an acoustic signal or atmospheric pressure changes.

[0041] The method includes providing a substrate at step 302. The substrate may be formed of silicon, silicon oxide, glass, Pyrex, quartz, ceramic, or any other suitable material, and may include substrate 102, 202, 402, 502, or 802 as described in detail herein with respect to process 100, 200, 400, 500, or 800. In some embodiments, a backplate layer (e.g., backplate layer 403, 503) is deposited on substrate layer 304 at step 304. The backplate layer may be formed of a low stress material (e.g., low stress silicon nitride (LSN), a low stress oxide, or any other suitable material). The backplate layer may be deposited using physical vapor deposition (PVD), chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD), plasma enhanced CVD (PECVD), atomic layer deposition (ALD), any other suitable process, or a combination thereof. The backplate layer may be relatively inflexible relative to the diaphragm to be formed on the substrate.

[0042] In some embodiments, at step 306, a first conductive layer (e.g., first conductive layer 416, 516, 816, 916 described with respect to processes 400, 500, 800, 900) is deposited on the backplane layer. In some embodiments, the first conductive layer can be formed of polysilicon (poly). In other embodiments, the first conductive layer can be formed of metal (e.g., gold, platinum, etc.), doped silicon, or any other suitable conductive material. The first conductive layer can be deposited using PVD, thermal evaporation, electron beam evaporation, CVD, PECVD, LPCVD, ALD, or any other suitable process or combination thereof.

[0043] At step 308, holes may be formed through the backplate layer and the first conductive layer. For example, a wet etching process or a dry etching process (e.g., reactive ion etching (RIE), deep RIE (DRIE), focused ion beam etching (FIB), etc.) or any other suitable etching process may be used to form corresponding holes in the backplate and the first conductive layer. The holes may have any suitable shape, for example, square, rectangular, oblong, circular, elliptical, polygonal (e.g., hexagonal, octagonal, etc.), or any other suitable shape.

[0044] At step 310, the first conductive layer may be selectively etched (eg, using a wet etch process or a dry etch process) to form electrical contacts on the backplate. For example, a radial or circumferential etch of the first conductive layer may be selectively etched to form electrical contacts on the backplate.

[0045] At step 312, a first structural layer is deposited on the substrate. In various embodiments, the first structural layer may include a first PSG layer having a first phosphorus content. For example, the first PSG layer 406, 506, 806, 906 may be deposited on the substrate. In other embodiments, the structural layer may include a borophosphosilicate glass (BPSG) layer, an oxide, a nitride, or any other suitable material.

[0046] In step 314, the first structural layer is selectively etched to form one or more closed grooves or pillars in the structural layer. In some embodiments, a wet etching process (e.g., using buffered hydrofluoric acid (BHF)) is used to selectively etch the first structural layer (e.g., the first PSG layer) until the backplane layer, so that some portions of the structural layer in the etched area are completely removed (e.g., as described herein with respect to processes 100, 200, 400, 800). In such an embodiment, the backplane layer can be used as an etch barrier layer for the wet etching process. In other embodiments, a timed dry etching process (e.g., RIE or DRIE process) can be used to selectively etch the structural layer so that the dry etching does not reach the backplane layer (e.g., as described herein with respect to processes 500, 900). For example, the dry etching process can be performed for a predetermined time so that a portion of the first structural layer remains arranged on the substrate or (in some embodiments) remains arranged on the backplane layer. The closed grooves or closed pillars defined in the first structural layer will have sharp corners (e.g., having a radius of curvature of less than 1 μm). In some embodiments in which the first structural layer includes a first PSG layer, the first PSG layer can be heated above its glass transition temperature to cause the first PSG layer to reflow, thereby rounding the corners of the first PSG layer (e.g., causing the corners to have a radius of curvature greater than 1 μm and less than 50 μm).

[0047] At step 316, a second structure layer having an impurity content, for example, a second PSG layer having a phosphorus content (e.g., second PSG layer 108, 208, 408, 508, 808, 908) is deposited on the first structure layer. The second structure layer can be conformally deposited (i.e., uniformly disposed so as to adhere to the contours of the underlying first structure layer) such that the second structure layer includes one or more recesses or bumps corresponding to one or more cavities or pillars that have been formed in the first structure layer, respectively. In some embodiments, the impurity can include phosphorus such that the phosphorus content is greater than 2%.

[0048] In step 318, the second structural layer is heated to a temperature higher than the glass transition temperature of the second structural layer, thereby causing the second structural layer to reflow. Further expanding, the closed grooves or pillars formed in the structural layer in operation 314 will have sharp corners and edges (for example, having a radius of curvature less than 1 μm). Since the second structural layer is conformally deposited on the first structural layer, the second structural layer follows the contour of the first structural layer, so that the recesses and / or bumps included in the second structural layer also have sharp corners and edges. Heating the second structural layer to a temperature higher than the glass transition temperature causes the second structural layer to undergo a phase change, thereby enabling the second structural layer to reflow. Reflow smoothes or rounds the corners and edges of the recesses or bumps formed in the second structural layer, so that the corners and edges of the second structural layer may have a radius of curvature greater than 1 μm and less than 50 μm.

[0049] In some embodiments, the first structure layer is formed of PSG having a first phosphorus content, and the second structure layer is formed of PSG having a second phosphorus content different from the first phosphorus content. In other embodiments, the first phosphorus content may be equal to the second phosphorus content.

[0050] In some embodiments, the first phosphorus content included in the first structural layer may be between 2% and 6%, and the second phosphorus content included in the second structural layer may be between 4% and 10%. In such an embodiment, the second structural layer may have a higher phosphorus amount than the first structural layer. The higher phosphorus amount reduces the glass transition temperature of the second structural layer relative to the glass transition temperature of the first structural layer. Heating can be performed to a temperature higher than the glass transition temperature of the second structural layer but lower than the glass transition temperature of the first structural layer, thereby causing only the second structural layer to flow and round its corners without causing the first structural layer to reflow.

[0051] In other embodiments, the first phosphorus content included in the first structural layer is between 4% and 10%, and the second phosphorus content in the second structural layer is between 2% and 6%, so that the second structural layer has a lower phosphorus content and therefore has a higher glass transition temperature than the first structural layer. In such an embodiment, the first structural layer can be heated to its glass transition temperature before the second structural layer is deposited on the first structural layer. In some embodiments, the second structural layer can be heated to a temperature higher than the glass transition temperature of each of the first structural layer and the second structural layer so as to cause each of the first structural layer and the second structural layer to reflow. This can produce smoother corners and edges in the second structural layer.

[0052] In step 322, a diaphragm layer is deposited on the second structural layer so that the diaphragm layer includes downward-facing wrinkles corresponding to one or more recesses, upward-facing wrinkles corresponding to one or more bumps formed in the second structural layer, or a combination thereof. For example, a low-stress material, such as LSN or a low-stress ceramic, may be deposited on the second structural layer (e.g., via a physical or chemical vapor deposition process). In other embodiments, the diaphragm layer may include a dielectric or conductive material (e.g., silicon oxide, silicon nitride, silicon carbide, gold, aluminum, platinum, etc.). The second structural layer is used as a mold or template for the diaphragm layer so that each of the downward-facing wrinkles or upward-facing wrinkles defined in the diaphragm layer has a radius of curvature corresponding to a second radius of curvature (i.e., the radius of curvature after reflow). In this way, stress concentration at the edges or corners of the wrinkles is reduced, thereby increasing robustness and impact resistance.

[0053] In some embodiments, before depositing the diaphragm layer on the second structural layer, a second conductive layer is deposited on the second structural layer and patterned in step 320. The second conductive layer may be formed of polysilicon or any other conductive material. At least a portion of the diaphragm layer may contact the second conductive layer, so that the second conductive layer forms an electrical contact with the diaphragm layer.

[0054] At step 324, the diaphragm layer is released, thereby forming a diaphragm suspended on the substrate. For example, releasing the diaphragm may include etching through each of the substrate, the first structural layer, and the second structural layer. Further expanding, a backside etch may be performed to etch the substrate so as to define an opening through the substrate to release the diaphragm from the substrate side. In a particular embodiment, the substrate may include a thin oxide (e.g., SiO2) layer disposed on its first surface facing the diaphragm. For example, an oxide layer may be deposited or grown on the substrate before depositing the first structural layer or a backplane layer thereon. The oxide layer may be used as an etch stop for backside substrate etching.

[0055] The backside etching may continue, or another backside etching may be subsequently performed through the hole defined in the backplate layer to remove the first structural layer and the second structural layer and release the diaphragm. In other embodiments, the backplate layer may be disposed above the diaphragm such that the diaphragm is disposed between the substrate and the backplate. In such embodiments, subsequent etching may include a front side etching performed through the hole defined in the backplate.

[0056] In various embodiments, releasing the diaphragm also releases the back plate layer, thereby forming a back plate suspended above the substrate above or below the diaphragm. In some embodiments, the first structural layer and the second structural layer can be etched for a predetermined time so that a portion of the upward facing folds or downward facing folds of the first structural layer near the diaphragm layer and a portion of the upward facing folds or downward facing folds of the second structural layer near the diaphragm layer are not removed, thereby forming a peripheral (also referred to as a "peripheral") support structure (e.g., Figure 5E ). These portions of the first structural layer and / or the second structural layer can facilitate the rounding of the corners and edges of the upward or downward facing wrinkles in the diaphragm. In some embodiments, the inner radial edge of the portion of the second structural layer is positioned to be closer to the downward facing wrinkles or upward facing wrinkles defined in the diaphragm layer relative to the inner radial edge of the portion of the first structural layer. In other words, the inner sidewalls of these portions of the first structural layer and the second structural layer can taper from their first edge close to the substrate toward their second edge close to the diaphragm layer, so that the second edge is radially closer to the downward or upward facing wrinkles relative to the first edge.

[0057] In some embodiments, the compliance of a diaphragm formed using method 300 can be at least twice the compliance of a similar constrained diaphragm that does not include the wrinkles. In addition, the diaphragm can be able to withstand a pressure differential in the range of 50 to 70 psi. Although not shown, in some embodiments, method 300 can also include forming perforations or through-holes through the diaphragm and optionally through the back plate, for example to enable pressure equalization between the front and rear volumes of an acoustic transducer formed using method 300.

[0058] FIG. 4A to FIG. 4C Process flows 400a, 400b are illustrated for forming acoustic transducers 40a and 40b with downward-facing and upward-facing corrugations, respectively, according to embodiments. Processes 400a, 400b include providing substrates 402a, 402b (e.g., glass, Pyrex, quartz, silicon, silicon oxide, or any other suitable substrate) in operations 1a, 1b.

[0059] In operations 2a, 2b, a backplate layer 403a, 403b is deposited on the substrate 402a, 402b, and a first conductive layer 416a, 416b is deposited on the backplate layer 403a, 403b. In some embodiments, the backplate layer 403a, 403b may include, for example, an LSN layer, and the first conductive layer 416a, 416b may include a conductive material (e.g., polysilicon). In operations 3a, 3b, for example, a wet or dry etching process is used to define a plurality of holes 417a, 417b in the backplate layer 403a, 403b and the first conductive layer 416a, 416b. In operations 4a, 4b, the first conductive layer is selectively etched to form electrical contacts on the backplate layer 403a, 403b.

[0060] In operations 5a, 5b, a first structural layer 406a, 406b, for example, a first PSG or BPSG layer, is deposited on the backplate layer 403a, 403b. After being deposited on the backplate layer 403a, 403b, the first structural layer 406a, 406b may be planarized (for example, via CMP). The first structural layer 406a, 406b may have a certain impurity content, for example, a first phosphorus content in the range between 2% and 5%. In operation 6a, one or more closed grooves 407a are etched in the first structural layer 406a to serve as a template for forming downward-facing wrinkles in the diaphragm. In contrast, the first structural layer 406b is etched so as to form one or more closed columns 407b from the first structural layer 406b to serve as a template for forming upward-facing wrinkles in the diaphragm. In a specific embodiment, a wet etching process may be used to etch the first structure layer 406a, 406b down to the backplate layer 403a, 403b disposed thereunder, with the backplate layer 403a, 403b serving as an etch barrier for the wet etching.

[0061] In operations 7a, 7b, a second structure layer 408a, 408b, for example, a second PSG or BPSG layer having a second impurity content, for example, greater than the first impurity content, is deposited on the first structure layer 406a, 406b and the open area of ​​the back plate layer 403a, 403b. The second structure layer 408a, 408b is conformally deposited on the first structure layer 406a, 406b so as to include one or more recesses 409a corresponding to one or more closed trenches 407a formed in the first structure layer 406a or one or more bumps 409b corresponding to one or more closed pillars 407b formed from the first structure layer 406b. As previously described herein, the closed trenches 407a or closed pillars 407b may have sharp corners.

[0062] In operations 8a, 8b, the second structural layers 408a, 408b are heated to a temperature higher than the glass transition temperature of the second structural layers 408a, 408b. This causes the second structural layers 408a, 408b to reflow, thereby smoothing or rounding the sharp edges and corners of the recesses 409a and bumps 409b formed in the second structural layers 408a, 408b.

[0063] In operations 9a and 9b, a second conductive layer 418a and 418b (e.g., a polysilicon layer) is deposited on the second structure layer 408a and 408b and patterned. In operations 10a and 10b, each layer is etched along the edge of each of the second structure layer 408a and 408b and the first structure layer 406a and 406b until the back plate layer 403a and 403b, thereby providing a space for sealing the diaphragm layer 410a and 410b to the back plate layer 403a and 403b.

[0064] In operations 11a, 11b, a diaphragm layer 410a, 410b (e.g., an LSN layer) is deposited on the second structural layer 408a, 408b, so that the diaphragm layer 410a includes one or more downward-facing folds 412a corresponding to one or more recesses 409a formed in the second structural layer 408a or one or more upward-facing folds 412b corresponding to one or more protrusions 409b formed in the second structural layer 408b. In addition, the diaphragm layer 410a, 410b contacts the back plate layer 403a, 403b to seal the edges of the acoustic transducers 40a, 40b. In operations 12a, 12b, a portion of the substrate 402a, 402b and a majority of the first structural layer 406a, 406b and the second structural layer 408a, 408b are etched (for example, by defining holes 417a, 417b in the back plate layers 403a, 403b) so as to release the diaphragm layer 410a, 410b and the back plate layers 403a, 403b, thereby forming the diaphragm and back plate of the acoustic transducers 40a, 40b.

[0065] Although the operation of methods 400a, 400b results in backplates 416a, 416b being disposed below diaphragms 410a, 410b, in other embodiments, the backplate may be disposed above a diaphragm (e.g., diaphragms 410a, 410b) including pleats. In such an embodiment, a second structural layer is deposited on a diaphragm layer (e.g., diaphragm layers 410a, 410b). A backplate layer is deposited on the second structural layer; and a plurality of holes are formed (e.g., etched) in the backplate layer. These holes enable an etchant for releasing the diaphragm layer to pass through the backplate and etch the second structural layer, so that releasing the diaphragm also releases the backplate layer, thereby forming a backplate suspended above the diaphragm on a substrate (e.g., substrates 402a, 402b).

[0066] FIG. 5A to FIG. 5D Process flows 500a, 500b for forming acoustic transducers 50a and 50b with downward-facing and upward-facing corrugations, respectively, are illustrated in accordance with an embodiment. The processes 500a, 500b include providing substrates 502a, 502b (e.g., glass, Pyrex, quartz, silicon, silicon oxide, or any other suitable substrate) in operations 1a, 1b.

[0067] In operations 2a, 2b, a backplane layer 503a, 503b is deposited on the substrate 502a, 502b, and a first conductive layer 516a, 516b is deposited on the backplane layer 503a, 503b. In some embodiments, the backplane layer 503a, 503b may include, for example, an LSN layer, and the first conductive layer 516a, 516b may include a conductive material (e.g., polysilicon). In operations 3a, 3b, for example, a plurality of holes 517a, 517b are defined in the backplane layer 503a, 503b and the first conductive layer 516a, 516b using a wet or dry etching process. The holes 517a, 517b may have any suitable shape, such as a square, a rectangle, a circle, an ellipse, an oblong, a polygon, etc. In a specific embodiment, the holes 517a, 517b may have a hexagonal shape with rounded corners. For example, Figure 6 A top view of a portion of a backplane layer 503a, 503b is shown with hexagonal holes 517a, 517b defined therein. In a particular embodiment, the hexagonal holes 517a, 517b may have a width W between their parallel sides in a range between 10 microns and 20 microns (e.g., 10, 12, 14, 16, 18, and 20 microns, including all ranges and values ​​therebetween) and a pitch of 10 to 30 microns (e.g., 10, 15, 25, or 30 microns, including all ranges and values ​​therebetween).

[0068] In operations 4a, 4b, the first conductive layer 516a, 516b is selectively etched to form electrical contacts on the backplate layers 503a, 503b. In operations 5a, 5b, a first structural layer 506a, 506b is deposited on the substrate 502a, 502b. The first structural layer 506a, 506b may include a PSG or BPSG layer having a first impurity content (e.g., a first phosphorus content in a range between 4% and 10%). In some embodiments, the first structural layer 506a, 506b may be planarized (e.g., via CMP) after being deposited on the backplate layers 503a, 503b.

[0069] In operation 6a, closed grooves 507a are formed in the first structure layer 506a to serve as a template for forming downward-facing wrinkles in the diaphragm. In contrast, in operation 6b, the first structure layer 506b is etched to form closed posts 507b from the first structure layer 506b, which serve as a template for upward-facing wrinkles to be formed in the diaphragm. In a specific embodiment, the first structure layers 506a, 506b are etched using a timed dry etching process so that the dry etching does not reach the backplate layers 503a, 503b, and a portion of the first structure layers 506a, 506b remains on the entire backplate layers 503a, 503b.

[0070] In operations 7a and 7b, the first structure layers 506a and 506b are heated to a temperature higher than the glass transition temperature of the first structure layers 506a and 506b so as to cause the first structure layers 506a and 506b to reflow and smooth the edges or corners of the closed trenches 507a or closed pillars 507b respectively defined in the first structure layers 506a and 506b. In operations 8a and 8b, second structure layers 508a and 508b (e.g., second PSG or BPSG layers) are deposited on the first structure layers 506a and 506b so that the second structure layers 508a and 508b include recesses 509a and bumps 509b corresponding to the closed trenches 507a and closed pillars 507b respectively defined in the first structure layers 506a and 506b. The second structure layers 508a, 508b may have a second impurity content, for example, a second phosphorus content that is lower than the first impurity content (for example, the first phosphorus content) of the first structure layers 506a, 506b (for example, in a range between 2% and 6%), and therefore have a higher glass transition temperature than the first structure layers 506a, 506b.

[0071] In operations 9a, 9b, the second structure layers 508a, 508b are heated to a temperature higher than their glass transition temperature so as to cause the second structure layers 508a, 508b to reflow, thereby further rounding the corners of the recess 509a and the bump 509b. In operations 10a, 10b, second conductive layers 518a, 518b are deposited on the second structure layers 508a, 508b and patterned. In operations 11a, 11b, the layers are etched along the edges of each of the second structure layers 508a, 508b and the first structure layers 506a, 506b until the back plate layers 503a, 503b, thereby providing a space for sealing the diaphragm layers 510a, 510b to the back plate layers 503a, 503b.

[0072] In operations 12a, 12b, a diaphragm layer 510a, 510b (e.g., an LSN layer) is deposited on the second structural layer 508a, 508b, so that the diaphragm layer 510a includes one or more downward-facing folds 512a corresponding to one or more recesses 509a formed in the second structural layer 508a or one or more upward-facing folds 512b corresponding to one or more protrusions 509b formed in the second structural layer 508b. In addition, the diaphragm layer 510a, 510b contacts the radial edges of the back plate layers 503a, 503b to seal the edges of the acoustic transducers 50a, 50b. In operations 13a, 13b, a portion of the substrate 502a, 502b is etched, and in operations 14a, 14b, most of the first structural layer 506a, 506b and the second structural layer 508a, 508b are etched (for example, by defining holes 517a, 517b in the back plate layer 503a, 503b) to release the diaphragm layer 510a, 510b and the back plate layer 503a, 503b, thereby forming the diaphragm and back plate of the acoustic transducer 50a, 50b.

[0073] Figure 5E Shown in Figure 5D An enlarged view of a portion of the acoustic transducer 50a indicated by arrow A in operation 14a of FIG. Figure 5E As shown in FIG. 1 , the first structural layer 506a, 506b and the second structural layer 508a, 508b are etched for a predetermined time so that a portion 522a of the first structural layer 506a and a portion 522b of the second structural layer 508b are close to the periphery of the diaphragm layer 510a, 510b, and the corresponding downward-facing folds 512a or upward-facing folds 512b of the diaphragm layers 510a and 510b are not removed. By forming a peripheral support structure 522 for increasing the strength and firmness of the diaphragms 510a, 510b, the remaining portion 522a of the first structural layer 506a, 506b and / or the remaining portions 522a and 522b of the second structural layer 508a, 508b can facilitate the rounding of the corners and edges of the downward-facing folds 512a or upward-facing folds 512b formed in the diaphragm layers 510a, 510b. A portion 522b of the second structural layer 508a contacts the diaphragm layer 510a. In addition, an inner radial edge 524b of a portion 522b of the second structural layer 508a proximate to the diaphragm layer 510a is positioned radially closer to a downward-facing wrinkle 512a defined in the diaphragm layer 510a than an inner radial edge 524a of a portion 522a of the first structural layer 506a proximate to the substrate 502a. This may be caused, for example, by the first structural layer 506a and the second structural layer 508a having different impurity contents (e.g., different phosphorus contents) causing uneven etching, or by the first structural layer 506a being etched near an isotropic front surface.

[0074] Figure 7 Panel A of FIG. 1 summarizes the failure pressures of various representative sample wafers included in three wafer lots (Lots A, B, and C) that include diaphragms having edges with sharp and smooth degrees and wrinkles formed using wet or dry etching. The diaphragms included in each wafer lot were tested by applying pressure to one side of the diaphragm until the diaphragm failed.

[0075] A representative wafer 24 included in Lot A includes a diaphragm having downward facing corrugations formed by etching cavities in the PSG layer via dry etching. Figure 7 Group B is an SEM image of a representative sample wafer 24 included in Lot A. The wafer 24 was segmented using focused ion beam (FIB) etching, thereby enabling cross-sections of the diaphragms included in the wafer 24 to be imaged. The diaphragms included in the Lot A wafer 24 failed at a pressure of about 9 psi.

[0076] Representative wafer 5 included in lot B includes a diaphragm having downward facing corrugations formed by etching cavities in the PSG layer via a dry etching process. The corrugations have a depth of about 4.00 μm at the center of the diaphragm and about 4.45 μm at the edges, and include rounded corners. Figure 7 Group C is an SEM image of wafer 5 from lot B. The diaphragm included in wafer 5 failed at a pressure of about 18 psi.

[0077] A representative wafer 15 included in Lot B includes corrugations having a depth of about 4.45 μm at the center of the diaphragm and a depth of about 4.83 μm at the edge, and includes rounded corners. Figure 7 Group D is an SEM image of a representative sample wafer 15. The diaphragm included in the batch B wafer 15 failed at a pressure of about 34 psi.

[0078] A representative wafer 25 included in Lot C formed using dry etching includes corrugations having a depth of about 3.66 μm at the center of the diaphragm and a depth of about 3.32 μm at the edge, and includes rounded corners. Figure 7 The wrinkle depth is the shallowest among the wafers in group A. While etching the wrinkles, the unetched PSG is intentionally left at the bottom to obtain the smoothest corner after PSG reflow, as shown in FIG. Figure 5B The operations 6a, 6b and 7a, 7b are described. Figure 7 Group E is an SEM image of a representative sample wafer 25 of lot C. The diaphragm included in wafer 25 failed at a pressure of about 60 psi. Figure 8 is a scatter plot of diaphragm failures for various diaphragms formed using the methods described herein, showing that smoothing of the wrinkles increases the failure strength of the diaphragm.

[0079] 9A to 9C Process flows 600a, 600b for forming acoustic transducers 60a and 60b with downward-facing and upward-facing folds, respectively, are illustrated according to embodiments. Processes 600a, 600b include providing substrates 602a, 602b (e.g., glass, Pyrex, quartz, silicon, silicon oxide, or any other suitable substrate) in operations 1a, 1b. In operation 2a, one or more closed trenches 605a are etched in the substrate using wet or dry etching. In contrast, closed posts 605b are formed in substrate 602b in operation 2b (e.g., using a wet or dry etching process). As previously described herein, one or more closed trenches 605a or posts 605b may have sharp corners and edges.

[0080] In operations 3a, 3b, a first structure layer 608a, 608b, for example, a first PSG or BPSG layer having a first impurity content (e.g., a first phosphorus content) is deposited on the substrate 602a, 602b. The first structure layer 608a, 608b may be conformally deposited on the substrate 602a, 602b such that the first structure layer 608a, 608b includes a recess 609a and a bump 609b corresponding to the closed trench 605a or the pillar 605b, respectively. In addition, one or more recesses 609a and bumps 609b may have sharp corners and edges corresponding to the sharp corners and edges of the closed trench 605a and the pillar 605b.

[0081] In operations 4a, 4b, the first structure layer 608a, 608b is heated to a temperature above its glass transition temperature, thereby causing the first structure layer 608a, 608b to reflow and smooth its corners and edges, as previously described herein. In operations 5a, 5b, a diaphragm layer 610a, 610b is deposited on the first structure layer 608a, 608b, and a first conductive layer 618a, 618b (e.g., a polysilicon layer) is deposited on the diaphragm layer 610a, 610b. The diaphragm layers 610a, 610b are conformally deposited on the first structural layer, so that the diaphragm layer 610a includes a downward-facing wrinkle 612a corresponding to the recess 609a formed in the first structural layer 608a, and the diaphragm layer 610b includes an upward-facing wrinkle 612b corresponding to the protrusion 609b formed in the first structural layer 608b, and the downward-facing wrinkle 612a and the upward-facing wrinkle 612b include smooth or rounded corners and edges.

[0082] In operations 6a, 6b, the first conductive layers 618a, 618b are selectively etched to form electrical contacts on the diaphragm layers 610a, 610b. In operations 7a, 7b, a second structural layer 606a, 606b (e.g., an oxide layer, a second PSG or BPSG layer) is deposited on the diaphragm layers 610a, 610b and the first conductive layers 618a, 618b, and planarized (e.g., via chemical mechanical polishing (CMP)). The second structural layers 606a, 606b can be used as spacers to define a gap between the diaphragm layers 610a, 610b and the backplate layer.

[0083] In operations 8a, 8b, a second conductive layer 616a, 616b (e.g., a polysilicon layer) is deposited on the second structural layer 606a, 606b and patterned to define electrical contacts for the back plate layer. In operations 9a, 9b, the structural layer 606a, 606b is etched along its edges to the diaphragm layer 610a, 610b, thereby providing space for sealing the back plate layer to the diaphragm layer 610a, 610b.

[0084] In operations 10a, 10b, a backplate layer 603a, 603b (e.g., an LSN layer) is deposited on the second structural layer 606a, 606b and the second conductive layer 616a, 616b. The backplate layer 603a, 603b contacts the diaphragm layer 610a, 610b at the edge of the acoustic transducer 60a, 60b to seal the acoustic transducer 60a, 60b. In operations 11a, 11b, holes 617a, 617b are etched through the backplate layer 603a, 603b and the second conductive layer 616a, 616b. The holes 617a, 617b can have any suitable shape, for example, square, rectangular, circular, oblong, elliptical, hexagonal, polygonal, any other suitable shape, or a combination thereof.

[0085] In operations 12a, 12b, the substrate 602a, 602b is selectively etched down to the first PSG layer 606a, 606b to define a channel therein. In operations 13a, 13b, the first structural layer 608b is etched, thereby releasing the diaphragm layer 610a, 610b from the first side. The portion of the first structural layer 608a, 608b disposed on the remainder of the substrate 602a, 602b is left unetched and can serve as a support structure for the diaphragm layer 610a, 610b. In addition, the second structural layer 606a, 606b (e.g., the second PSG layer) is etched through the holes 617a, 617b to release the diaphragm layer 610a, 610b from the second side opposite to the first side, thereby forming an acoustic transducer 60a, 60b having a diaphragm 610a, 610b suspended above an opening in the substrate 602a, 602b. Etching the structural layers 606a, 606b also releases the back plate layers 603a, 603b. Portions of the structural layers 606a, 606b close to the wrinkles 612a, 612b at the edge of the diaphragm layer are left unetched and can facilitate smoothing of the wrinkles 612a, 612b formed in the diaphragm layers 606a, 606b and / or increase the strength of the diaphragm layers 610a, 610b.

[0086] Fig.10 7 is a schematic flow chart of another method 700 for forming an acoustic transducer (e.g., acoustic transducer 60) including a diaphragm having upward facing corrugations or downward facing corrugations with smooth corners and edges formed therein according to an embodiment. The acoustic transducer may include, for example, a MEMS acoustic transducer for use in a MEMS microphone assembly or a MEMS pressure sensor, and may be configured to generate an electrical signal in response to an acoustic signal or atmospheric pressure changes.

[0087] The method 700 includes providing a substrate at step 702. The substrate may be formed of silicon, silicon oxide, glass, Pyrex, quartz, ceramic, or any other suitable material, and may include the substrate 602 described in detail with respect to the process 600. At step 704, the substrate is selectively etched to form at least one of one or more closed trenches or closed pillars on the substrate. For example, the substrate may be etched using a wet etching or dry etching process to define closed trenches or pillars on the substrate. At step 706, a first structural layer (e.g., a first PSG layer 608) having a first impurity content is deposited on the substrate. In some embodiments, the first structural layer may include PSG or BPSG. In addition, the impurity may include phosphorus, such that the first phosphorus content of the first structural layer may be greater than 2% (e.g., in a range between 2% and 10%). The first structural layer is conformally deposited on the substrate such that the first structural layer includes one or more recesses or bumps defined thereon corresponding to one or more closed trenches or pillars formed in the substrate, respectively.

[0088] At step 708, the first structural layer is heated to a temperature above the glass transition temperature of the first structural layer, thereby causing the first structural layer to reflow. As previously described herein, the cavities or pillars formed in the substrate may have sharp corners and edges (e.g., having a radius of curvature less than 1 μm), such that the recesses or bumps formed in the first structural layer may have corresponding sharp corners and edges. Reflowing the first structural layer smoothes or rounds the corners and edges of the recesses or bumps formed in the first structural layer, such that the corners and edges of the first structural layer may have a radius of curvature greater than 1 μm and less than 50 μm.

[0089] In step 710, a diaphragm layer (e.g., diaphragm layer 610) is deposited on the first structural layer so that the diaphragm layer includes at least one of downward-facing wrinkles corresponding to depressions formed in the first structural layer or upward-facing wrinkles corresponding to bumps formed in the first structural layer. For example, a low-stress material, such as LSN or a low-stress ceramic, may be deposited on the first structural layer (e.g., via a physical or chemical vapor deposition process). In other embodiments, the diaphragm layer may include a dielectric or conductive material (e.g., silicon oxide, silicon nitride, silicon carbide, gold, aluminum, platinum, etc.). In addition, one or more downward-facing wrinkles or upward-facing wrinkles defined in the diaphragm layer have corners having a radius of curvature corresponding to the second radius of curvature (i.e., the radius of curvature after reflowing the first structural layer). In this way, stress concentration at the edges or corners of the wrinkles is reduced, thereby increasing robustness and impact resistance.

[0090] In some embodiments, method 700 further includes depositing a first conductive layer (e.g., first conductive layer 618) on the diaphragm layer at step 712. In some embodiments, the first conductive layer can be formed of polysilicon (poly). In other embodiments, the first conductive layer can be formed of metal, doped silicon, or any other suitable conductive material. At step 714, the first conductive layer is patterned to form electrical contacts on the diaphragm layer.

[0091] In some embodiments, method 700 also includes depositing a second structural layer on the diaphragm layer at step 716, the second structural layer may include, for example, a second PSG or BPSG layer (e.g., second PSG layer 606). The second structural layer may have a second impurity content that may be the same or different (e.g., higher or lower than) the first phosphorus content included in the first structural layer, for example, a second phosphorus content in a range between 2% and 10%. In other embodiments, the second structural layer may include an oxide, a nitride, or any other suitable layer used as a gap layer or separator between the diaphragm layer and the backplate layer. In some embodiments, the second structural layer may be planarized, for example, via a chemical mechanical planarization (CMP) process.

[0092] In some embodiments, at step 720, a backplate layer (e.g., backplate layer 603) may be deposited on the second structural layer. The backplate layer may be formed of a low stress material (e.g., low stress silicon nitride (LSN), a low stress oxide, or any other suitable material). The backplate layer may be deposited using PVD, LPCVD, PECVD, ALD, any other suitable process, or a combination thereof. The backplate layer may be relatively inflexible relative to the diaphragm to be formed from the diaphragm layer. As previously described with respect to method 300, at step 722, a plurality of holes may be formed in the backplate layer.

[0093] In some embodiments, method 700 may further include depositing a second conductive layer (e.g., second conductive layer 616) and patterning the second conductive layer before depositing the backplane layer on the structural layer in step 718. In some embodiments, the first conductive layer may be formed of polycrystalline silicon (poly). In other embodiments, the first conductive layer may be formed of metal, doped silicon, or any other suitable conductive material. The first conductive layer may be deposited using PVD, thermal evaporation, electron beam evaporation, CVD, LPCVD, PECVD, ALD, or any other suitable process or combination thereof. In other embodiments, the second conductive layer may be deposited on the backplane layer. The second conductive layer contacts the backplane layer and forms an electrical contact therewith. In addition, forming a plurality of holes also forms corresponding holes through the second conductive layer.

[0094] At step 724, the diaphragm layer is released, thereby forming a diaphragm suspended above the substrate. In some embodiments, releasing the diaphragm may include etching through each of the substrate and the first structural layer to release the diaphragm from a first side (e.g., the back side of the acoustic transducer). In addition, the second structural layer (e.g., the second PSG layer) may be etched through the holes to also release the diaphragm from a second side opposite the first side. Etching may also release the backplate layer to form a backplate suspended above the first diaphragm. In particular embodiments, etching is performed for a predetermined time so that a portion of the second structural layer that is proximate to the upward facing wrinkles or the downward facing wrinkles of the diaphragm layer is not removed. This portion of the second structural layer may facilitate rounding of corners and edges of the upward facing or downward facing wrinkles formed in the diaphragm.

[0095] In some embodiments, the compliance of a diaphragm formed using method 700 can be at least twice the compliance of a similar constrained diaphragm that does not include the wrinkles. In addition, the diaphragm can be able to withstand a pressure differential in the range of 50 to 70 psi. Although not shown, in some embodiments, method 700 can also include forming perforations or through-holes through the diaphragm and optionally through the back plate, for example to enable pressure equalization between the front and rear volumes of the acoustic transducer.

[0096] FIG. 11A to FIG. 11CProcess flows 800a, 800b for forming acoustic transducers 80a and 80b with downward-facing and upward-facing corrugations, respectively, are illustrated according to embodiments. Process 800 is substantially similar to process 500, but includes some differences highlighted herein. Processes 800a, 800b include providing substrates 802a, 802b (e.g., glass, Pyrex, quartz, silicon, silicon oxide, or any other suitable substrate) in operations 1a, 1b.

[0097] In operations 2a, 2b, a backplane layer 803a, 803b is deposited on the substrate 802a, 802b, and a first conductive layer 816a, 816b is deposited on the backplane layer 803a, 803b. In operations 3a, 3b, a plurality of holes 817a, 817b are defined in the backplane layer 803a, 803b and the first conductive layer 816a, 816b, for example, using a wet or dry etching process. In operations 4a, 4b, the first conductive layer is selectively etched to form electrical contacts on the backplane layer 803a, 803b.

[0098] In operations 5a, 5b, a first structural layer 806a, 806b (e.g., a first PSG or BPSG layer) is deposited on the backplate layer 803a, 803b. The first structural layer 806a, 806b may be planarized (e.g., via CMP) after being deposited on the backplate layer 803a, 803b. The first structural layer 806a, 806b may have a first impurity content, for example, a first phosphorus content in a range between 2% and 10%. In operation 6a, one or more closed trenches 807a are etched in the first structural layer 806a, and in operation 6b, the first structural layer 806b is etched to form closed pillars 807b from the first structural layer 806b, as previously described herein with respect to FIG. FIG. 4A to FIG. 4C In certain embodiments, a wet etching process may be used to etch the first structure layer 806a, 806b down to the back plate layer 803a, 803b disposed thereunder, and the back plate layer 803a, 803b serves as an etch barrier for the wet etching.

[0099] In operations 7a, 7b, a second structural layer 808a, 808b, such as a second PSG or BPSG layer, is deposited on the open areas of the first structural layer 806a, 806b and the back plate layer 803a, 803b. FIG. 4A to FIG. 4CUnlike the process 400 shown in FIG. 4 , the second structure layers 808a, 808b have the same impurity content as the first structure layers 806a, 806b, for example, the same phosphorus content (e.g., in a range between 2% and 10%). The second structure layers 808a, 808b are conformally deposited on the first structure layers 406a, 406b so as to include one or more recesses 809a corresponding to one or more closed trenches 807a formed in the first structure layer 806a or one or more bumps 809b corresponding to one or more closed pillars 807b formed from the first structure layer 806b. The cavities 809a or pillars 809b may have more rounded corners than the corners of the cavities 807a or pillars 807b of the underlying first structure layers 806a, 806b.

[0100] In operations 8a, 8b, the second structural layers 808a, 808b are heated to a temperature higher than the glass transition temperature of the second structural layers 808a, 808b, thereby also heating the first structural layer 806a, thereby causing the second structural layers 808a, 808b to reflow and in some embodiments also causing the first structural layer 806a to reflow. The reflow further smoothes or rounds the sharp edges and corners of the recesses 809a and bumps 809b formed in the second structural layers 808a, 808b.

[0101] In operations 9a and 9b, a second conductive layer 818a and 818b (e.g., a polysilicon layer) is deposited on the second structure layer 808a and 808b and the second conductive layer is patterned. In operations 10a and 10b, each layer is etched along each of the second structure layer 808a and 808b and the first structure layer 806a until the back plate layer 803a and 803b, thereby providing a space for sealing the diaphragm layer 810a and 810b to the back plate layer 803a and 803b.

[0102] In operations 11a, 11b, a diaphragm layer 810a, 810b (e.g., an LSN layer) is deposited on the second structural layer 808a, 808b, so that the diaphragm layer 810a includes one or more downward-facing folds 812a corresponding to one or more recesses 809a formed in the second structural layer 808a or one or more upward-facing folds 812b corresponding to one or more protrusions 809b formed in the second structural layer 808b. In addition, the diaphragm layer 810a, 810b contacts the back plate layer 803a, 803b to seal the edges of the acoustic transducers 80a, 80b. In operations 12a, 12b, a portion of the substrate 802a, 802b and a majority of the first structural layer 806a and the second structural layer 808a, 808b are etched (for example, by defining holes 817a, 817b in the back plate layers 803a, 803b) so as to release the diaphragm layer 810a, 810b and the back plate layers 803a, 803b, thereby forming the diaphragm and back plate of the acoustic transducers 80a, 80b.

[0103] As shown in operations 12a, 12b, a small portion of the structural layers 806a, 808a, 808b is flowed out near the periphery or edge of the diaphragm layer without being etched to provide a peripheral support structure. Using structural layers 806a, 808a, 808b having the same impurity content allows etching at the same rate for each of the structural layers 806a, 808a, 808b, and a tapered profile 808a, 808b can be formed for the remainder of the structural layers 806a, 808a. This is because the etching of the structural layers 806a, 808a, 808b starts from the holes 817a, 817b defined in the back plates 803a, 803b and occurs isotropically. Therefore, the portions of the structural layers 806a, 808a, 808b farthest from the holes 817a, 817b are etched last. The remaining portions of the structural layers 806a and 808a, 808b may be tilted inward from the backing layers 803a, 803b toward the diaphragm layers 810a, 810b and may be used to increase the strength of the diaphragm layers 810a, 810b and / or facilitate rounding of the diaphragms 812a, 812b.

[0104] FIG. 12A to FIG. 12D Process flows 900a, 900b for forming acoustic transducers 90a and 80b having downward-facing and upward-facing corrugations, respectively, are illustrated in accordance with an embodiment. Processes 900a, 900b are substantially similar to processes 500a, 500b, with some differences highlighted herein.

[0105] The process 900a, 900b includes providing a substrate 902a, 902b (e.g., glass, Pyrex, quartz, silicon, silicon oxide, or any other suitable substrate) in operations 1a, 1b. In operations 2a, 2b, a backplane layer 903a, 903b is deposited on the substrate 902a, 902b, and a first conductive layer 916a, 916b is deposited on the backplane layer 903a, 903b. In operations 3a, 3b, a plurality of holes 917a, 917b are defined in the backplane layer 903a, 903b and the first conductive layer 916a, 916b, for example, using a wet or dry etching process.

[0106] In operations 4a, 4b, the first conductive layer 916a, 916b is selectively etched to form electrical contacts on the backplate layer 903a, 903b. In operations 5a, 5b, a first structural layer 906a, 906b, for example, a first PSG or BPSG layer, is deposited on the substrate 902a, 902b. The first PSG layer 906a, 906b may have a first impurity content, for example, a first phosphorus content in a range between 2% and 10%. In some embodiments, the first structural layer 906a, 906b may be planarized (e.g., via CMP) after being deposited on the backplate layer 903a, 903b.

[0107] In operation 6a, one or more closed trenches 907a are formed in the first structure layer 906a, or the first structure layer 906b is etched to form one or more closed pillars 907b. In a specific embodiment, the first structure layers 906a, 906b are etched using a timed dry etching process so that the dry etching does not reach the back plate layers 903a, 903b, and a portion of the first structure layers 906a, 906b remains on the entire back plate layers 903a, 903b.

[0108] In operations 7a, 7b, the first structure layers 906a, 906b are heated to a temperature higher than their glass transition temperature so as to cause the first structure layers 906a, 906b to reflow and smooth the edges or corners of the closed trenches 907a or pillars 907b defined in the first structure layers 906a and 906b, respectively. In operations 8a, 8b, a second structure layer 908a, 908b (e.g., a second PSG or BPSG layer) is deposited on the first structure layers 906a, 906b so that the second structure layers 908a, 908b include recesses 909a or bumps 909b corresponding to the closed trenches 907a or pillars 907b defined in the first structure layers 906a, 906b, respectively. The edges or corners of the recesses 909a or bumps 909b may be smoother or more rounded than the corresponding closed trenches 907a and pillars 907b. Unlike processes 500a, 500b, the second structure layers 908a, 908b may have a second impurity content equal to the first impurity content, for example, a second phosphorus content (e.g., in a range between 2% and 10%). For example, the second structure layers 908a, 908b may include the same material as the first structure layers 906a, 906b.

[0109] In operations 9a, 9b, the second structural layers 908a, 908b are heated to a temperature above their glass transition temperature so as to cause the second structural layers 908a, 908b and, in some implementations, the first structural layer to reflow, thereby further rounding the corners of the recess 909a and the bump 909b. In operations 10a, 10b, a second conductive layer 918a, 918b is deposited on the second structural layers 908a, 908b and patterned. As shown in operations 10a, 10b, the layers are etched along each of the second structural layers 908a, 908b and the first structural layers 906a, 906b to the backplate layers 903a, 903b, thereby providing space for sealing the diaphragm layers 910a, 910b to the backplate layers 903a, 903b.

[0110] In operations 11a, 11b, a diaphragm layer 910a, 910b (e.g., an LSN layer) is deposited on the second structural layer 908a, 908b, so that the diaphragm layer 910a includes one or more downward-facing folds 912a corresponding to one or more recesses 909a formed in the second structural layer 908a or one or more upward-facing folds 912b corresponding to one or more bumps 909b formed in the second structural layer 908b. In addition, the diaphragm layer 910a, 910b contacts the radial edges of the back plate layers 903a, 903b to seal the edges of the acoustic transducers 90a, 90b. In operations 12a, 12b, a portion of the substrate 902a, 902b is etched, and in operations 13a, 13b, a majority of the first structural layer 906a, 906b and the second structural layer 908a, 908b are etched (e.g., through holes 917a, 917b defined in the back plate layer 903a, 903b) to release the diaphragm layer 910a, 910b and the back plate layer 903a, 903b, thereby forming the diaphragm and back plate of the acoustic transducer 90a, 90b. As shown in operations 13a, 13b, a small portion of the structural layers 906a, 906b and 908a, 908b is left unetched near the periphery or edge of the diaphragm layer to form a peripheral support structure. The remaining portions of the structural layers 906a, 906b and 908a, 908b may taper inward from the backing layers 903a, 903b toward the diaphragm layers 910a, 910b and may be used to increase the strength of the diaphragm layers 910a, 910b and / or facilitate rounding of the diaphragms 912a, 912b.

[0111] FIG. 13A to FIG. 13E A process flow 1000 for forming an acoustic transducer having downward facing corrugations and upward facing corrugations according to an embodiment is illustrated. In particular, the process flow 1000 can be used to form a dual diaphragm acoustic transducer 100 including downward and upward corrugations (as shown in 13E). The process 1000 includes providing a substrate 1002 (e.g., glass, Pyrex, quartz, silicon, silicon oxide, or any other suitable substrate) in operation 1. In operation 2, one or more closed trenches 1005 are etched in the substrate using wet or dry etching. As previously described herein, the one or more closed trenches 1005 will have sharp corners and edges.

[0112] In operation 3, a first structure layer 1008, for example, a first PSG or BPSG layer having a first impurity content (e.g., a first phosphorus content), is deposited on the substrate 1002. The first structure layer 1008 may be conformally deposited on the substrate 1002 such that the first structure layer 1008 includes recesses 1009 corresponding to the closed trenches 1005. In addition, one or more recesses 1009 may have sharp corners and edges corresponding to the sharp corners and edges of the closed trenches 1005.

[0113] In operation 4, the first structural layer 1008 is heated to a temperature above its glass transition temperature, thereby causing the first structural layer 1008 to reflow and smooth its corners and edges, as previously described herein. In operation 5, a first diaphragm layer 1010 is deposited on the first structural layer 1008, and a first conductive layer 1018 (e.g., a polysilicon layer) is deposited on the first diaphragm layer 1010. The first diaphragm layer 1010 is conformally deposited on the first structural layer so that the first diaphragm layer 1010 includes downwardly facing wrinkles 1012 corresponding to the recesses 1009 formed in the first structural layer 1008. The downwardly facing wrinkles 1012 may include smoothed or rounded corners and edges.

[0114] In operation 6, the first conductive layer 1018 is selectively etched to form electrical contacts on the first diaphragm layer 1010. In operation 7, a second structural layer 1006 (e.g., an oxide layer, a second PSG or BPSG layer) is deposited on the first diaphragm layer 1010 and the first conductive layer 1018, and planarized (e.g., via chemical mechanical polishing (CMP)). The second structural layer 1006 can be used as a spacer to define a gap between the diaphragm layer 1010 and the back plate layer.

[0115] In operation 8, the second structural layer 1006 is etched along the edge of the second structural layer 1006 to the first diaphragm layer 1010, thereby providing a space for sealing the back plate layer to the first diaphragm layer 1010. In operation 9, a back plate layer 1016 is deposited on the second structural layer 1006 and the back plate layer 1016 is patterned. The back plate layer 1016 may include one or more layers of polysilicon and silicon nitride. For example, the back plate layer 1016 may include a silicon nitride layer between two polysilicon layers. The back plate layer 1016 is patterned to form back plate holes that allow posts in the second diaphragm to pass through (discussed further below).

[0116] In operation 10, a third structural layer 1014 is deposited on the back plate layer 1016. In some embodiments, the composition of the third structural layer 1014 may be similar to the first structural layer 1008 and the second structural layer 1006 discussed above. In operation 11, the third structural layer 1014 is patterned to form a column 1024, which, as discussed further below, helps to form wrinkles in the second diaphragm. In operation 12, a fourth structural layer 1020 for supporting the second diaphragm is deposited, and the fourth structural layer 1020 may form part of the peripheral support structure. In some embodiments, the fourth structural layer 1020 may include one or more layers. For example, the fourth structural layer 1020 may include multiple PSG or BPSG layers with different concentration levels. As an example, the fourth structural layer 1020 may include two PSG or BPSG sublayers, the first sublayer having a concentration of 5%-9%, and the other sublayer having a concentration of 2.5%-6.5%. In some embodiments, these sublayers may be deposited on top of each other with increasing concentrations. In some embodiments, the middle sublayer may be sandwiched between two sublayers with a lower concentration than the middle layer. The fourth structural layer 1020 may be conformally deposited on the pillars 1024 formed using the third structural layer 1014, thereby obtaining fourth structural layer pillars 1022. At least a portion of the fourth structural layer 1020 is in contact with the backplane layer.

[0117] In operation 13, a second conductive layer 1026 is deposited on the fourth structure layer 1020 and patterned. The second conductive layer 1026 may have a material similar to the first conductive layer 1018 and may be patterned in some portions to form holes therethrough. At least some of the holes in the second conductive layer 1026 may be aligned with the holes in the back plate layer 1016. In operation 14, the fourth structure layer 1020, the second structure layer 1006 are patterned to expose the first conductive layer 1018 or the first diaphragm layer 1010. In particular, the fourth structure layer 1020 and the second structure layer 1006 may be etched primarily in the areas where the second conductive layer 1026 is not deposited on the fourth structure layer 1020 and the back plate layer 1016 is not deposited on the second structure layer 1006 and is located above the first conductive layer 1018. However, a portion of the fourth structure layer 1020 that forms the fourth structure layer column 1022 is retained. Etching of the fourth structural layer 1020 and the second structural layer 1006 may form one or more cavities 1028 defined at least in part by holes in the backplate layer 1016 and holes in the second conductive layer 1026. As discussed further below, the cavities 1028 may be used to form posts for the second diaphragm.

[0118] In operation 15, after the fourth structure layer 1020 and the second structure layer 1006 are patterned to form the cavity 1028, a spacer layer 1030 may be deposited and patterned. The spacer layer 1030 may be formed using silicon oxide and may be conformally deposited on the fourth structure layer 1020, the second conductive layer 1026, the exposed portion of the first conductive layer 1018 within the cavity 1028, and the fourth structure layer column 1022. The spacer layer 1030 may be patterned to form a hole 1032 that exposes a portion of the second conductive layer 1026 and the first conductive layer 1018 below. The spacer layer 1030 may allow a gap to be formed between a portion of the column of the second diaphragm and the first conductive layer 1018 of the first diaphragm layer 1008. The thickness of the spacer layer may be based on the desired size of the gap. In some embodiments, the spacer layer 1030 may not be deposited if a gap is not desired.

[0119] In operation 16, a second diaphragm layer 1034 is deposited on the spacer layer 1030, or if the spacer layer 1030 is not utilized, the second diaphragm layer 1034 is conformally deposited on the fourth structural layer 1020, the second conductive layer 1026, the exposed portion of the first conductive layer 1018 within the cavity 1028, and the fourth structural layer pillars 1022. The second diaphragm layer 1034 may be similar to the first diaphragm layer 1010. However, unlike the first diaphragm layer 1010 including the downward facing corrugations 1012, the second diaphragm 1034 may include upward facing corrugations 1038 formed on the fourth structural layer pillars 1022. The second diaphragm 1034 may also form at least one anchoring post 1040 and at least two posts 1042 spaced apart from the anchoring post 1040. The anchor post 1040 includes a vertex 1044 formed at the bottom of the cavity 1028 (operation 15) and contacts and couples to the first conductive layer 1018. A portion of the second diaphragm 1034 between the anchor post 1040 and the at least two posts 1042 contacts and couples to the second conductive layer 1026. The second diaphragm layer 1034 may be patterned to form a plurality of openings 1036 that may expose the underlying spacer layer 1030 or, in the case where the spacer layer 1030 is not used, may expose the underlying fourth structural layer 1020.

[0120] In operation 17, a portion of the apex 1044 (of the anchor post 1040) of the second diaphragm 1034, a portion of the first conductive layer 1018 below the apex 1044, and a portion of the first diaphragm layer 1008 below the apex 1044 are patterned to form a perforation or through-hole 1046. The through-hole 1046 enables pressure equalization between the front volume and the rear volume of the acoustic transducer.

[0121] In operation 18, a portion of the second structure layer 1006 (between the first diaphragm 1010 and the back plate 1016), a portion of the fourth structure layer 1020 (between the back plate 1016 and the second diaphragm 1034), and the third structure layer 1014 (e.g., the pillar 1024) are removed by an etchant. For example, an isotropic etchant (e.g., a wet etchant such as buffered hydrofluoric acid) may be allowed to flow through an opening 1036 formed in the second diaphragm 1034. Removing a portion of the fourth structure layer 1020 and the second structure layer 1006 results in an internal cavity 1048 defined by the second diaphragm 1034 and the first diaphragm 1010. However, the etching process may be controlled so that not all of the second structure layer 1006 and the fourth structure layer 1020 are removed. Alternatively, a peripheral support structure 1038 between the periphery of the first diaphragm layer 1010 and the periphery of the second diaphragm layer 1034 is retained. The peripheral support structure 1038 is disposed close to the pleats 1012 and 1038 and can increase the strength of the first diaphragm layer 1010 and the second diaphragm layer 1034 .

[0122] In some embodiments, the second structure layer 1006 and the fourth structure layer 1020 may have different concentrations of impurities such as phosphorus or boron. For example, in some embodiments, the second structure layer 1006 may have a phosphorus concentration between 2% and 6%, and the fourth structure layer 1020 may have a phosphorus concentration between 4% and 10%. Changing the concentration of phosphorus or other impurities may enable uneven etching of the second structure layer 1006 with respect to the fourth structure layer 1020, resulting in the formation of a tapered or conical peripheral support structure 1038 that can increase the strength of the first diaphragm 1010 and the second diaphragm 1034.

[0123] In operation 19 , a portion of the substrate 1002 and a majority of the first structural layer 1008 are etched, thereby releasing the first diaphragm layer 1010 and forming the acoustic transducer 100 .

[0124] In some embodiments, a method of forming an acoustic transducer includes 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 a closed groove or a closed column on the structural layer. A second structural layer is deposited on the structural layer. The second structural layer includes depressions or protrusions corresponding to the closed grooves or closed columns respectively formed in the first structural layer. At least the second structural layer is heated to a temperature higher than the glass transition temperature of the second structural layer, thereby causing the second structural layer to reflow. A diaphragm layer is deposited on the second structural layer, so that the diaphragm layer includes at least one of downward-facing wrinkles corresponding to the depressions formed in the second structural layer or upward-facing wrinkles corresponding to the protrusions formed in the second structural layer. The diaphragm layer is released, thereby forming a diaphragm suspended above the substrate.

[0125] In some embodiments, a method of forming an acoustic transducer includes providing a substrate and selectively etching the substrate to form at least one of a closed groove or a closed column on the substrate. A first structural layer is deposited on the substrate. The first structural layer includes at least one of a depression or a protrusion corresponding to the closed groove or the closed column formed in the substrate, respectively. The first structural layer is heated to a temperature higher than the glass transition temperature of the first structural layer, thereby causing the first structural layer to reflow. A diaphragm layer is deposited on the first structural layer, so that the diaphragm layer includes at least one of a downward-facing wrinkle corresponding to the depression formed in the first structural layer or an upward-facing wrinkle corresponding to the protrusion formed in the first structural layer. The diaphragm layer is released, thereby forming a diaphragm suspended above the substrate.

[0126] In some embodiments, an acoustic transducer is formed by 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 a closed groove or a closed column on the structural layer. A second structural layer is deposited on the structural layer. The second structural layer includes depressions or protrusions corresponding to the closed grooves or closed columns respectively formed in the first structural layer. At least the second structural layer is heated to a temperature higher than the glass transition temperature of the second structural layer, thereby causing the second structural layer to reflow. A diaphragm layer is deposited on the second structural layer, so that the diaphragm layer includes at least one of downward-facing wrinkles corresponding to the depressions formed in the second structural layer or upward-facing wrinkles corresponding to the protrusions formed in the second structural layer. The diaphragm layer is released, thereby forming a diaphragm suspended above the substrate.

[0127] In some embodiments, a method may include: providing a substrate; depositing a first structural layer on the substrate; selectively etching the first structural layer to form at least one of a closed groove or a closed column 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 recess or a protrusion, the at least one of the recess or the protrusion corresponding to at least one of the closed grooves or the closed columns formed in the first structural layer; heating at least the second structural layer to a temperature higher than the glass transition temperature of the second structural layer, thereby causing the second structural layer to reflow; depositing a diaphragm layer on the second structural layer, so that the diaphragm layer includes at least one of downward-facing wrinkles corresponding to the recesses formed in the second structural layer or upward-facing wrinkles corresponding to the protrusions formed in the second structural layer; and releasing the diaphragm layer, thereby forming a diaphragm suspended above the substrate.

[0128] In some embodiments, at least one of the first structure layer or the second structure has an impurity content. In some embodiments, at least one of the first structure layer and the second structure layer includes phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG), and wherein the impurity content in at least one of the first structure layer or the second structure layer includes phosphorus. In some embodiments, the first structure layer is a first PSG layer having a first phosphorus content, and the second structure layer is a second PSG layer having a second phosphorus content different from the first phosphorus content. In some embodiments, the first structure layer is a first PSG layer having a first phosphorus content, and the second structure layer is a second PSG layer having a second phosphorus content equal to the first phosphorus content. In some embodiments, the second phosphorus content is greater than 2%. In some embodiments, the first phosphorus content is between 4% and 10% and the second phosphorus content is between 2% and 6%, and the first phosphorus content is greater than the second phosphorus content. In some embodiments, the first phosphorus content is between 2% and 6% and the second phosphorus content is between 4% and 10%, and the second phosphorus content is greater than the first phosphorus content.

[0129] In some embodiments, the temperature during heating is higher than the glass transition temperature of the second PSG layer and lower than the glass transition temperature of the first PSG layer. In some embodiments, the temperature during heating is greater than the glass transition temperature of each of the first PSG layer and the second PSG layer. In some embodiments, the method further comprises heating the first PSG layer to a temperature higher than the glass transition temperature of the first PSG layer before depositing the second PSG layer, thereby causing the first PSG layer to reflow. In some embodiments, the depression or bump formed in the second structural layer before heating the second structural layer includes an edge having a first radius of curvature less than 1 mm, and wherein the depression or bump after heating the structural layer includes an edge having a second radius of curvature greater than 1 μm and less than 50 μm, so that each of the downward facing wrinkles or upward facing wrinkles defined in the diaphragm layer has a radius of curvature corresponding to the second radius of curvature. In some embodiments, releasing the diaphragm includes etching through each of the substrate, the first structural layer, and the second structural layer; and wherein the etching of the first structural layer and the second structural layer is performed so that a portion of the first structural layer close to the peripheral edge of the diaphragm layer and a portion of the second structural layer close to the peripheral edge of the diaphragm layer are not removed.

[0130] In some embodiments, 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 the diaphragm is disposed radially closer to a downward-facing wrinkle or an upward-facing wrinkle defined in the diaphragm layer than an inner radial edge of the portion of the first structural layer proximate the substrate. In some embodiments, the method further comprises: depositing a backplate layer on the substrate before depositing the first structural layer; depositing a first conductive layer on the backplate layer; forming a hole through the backplate layer and the first conductive layer; selectively etching the first conductive layer to form an electrical contact on the backplate layer; wherein the first structural layer is deposited on the first conductive layer, and wherein releasing the diaphragm layer also releases the backplate layer, thereby forming a backplate suspended above the substrate below the diaphragm.

[0131] In some embodiments, the first structural layer is selectively etched up to the backplate layer. In some embodiments, the first structural layer is selectively etched so that the etching process stops before reaching the backplate layer. In some embodiments, the method further includes: before depositing the diaphragm layer on the second structural layer, depositing a second conductive layer on the second structural layer and patterning the second conductive layer, wherein at least a portion of the diaphragm layer contacts the second conductive layer. In some embodiments, the method further includes planarizing the first structural layer after depositing the first structural layer on the backplate layer and before selectively etching the first structural layer. In some embodiments, the method further includes: before releasing the diaphragm layer, depositing a third structural layer on the diaphragm layer; depositing a backplate layer on the third structural layer; and forming a plurality of holes in the backplate layer, wherein releasing the diaphragm also releases the backplate layer, thereby forming a backplate suspended above the diaphragm on the substrate.

[0132] In some embodiments, an acoustic transducer may be formed by a process of providing a substrate. The process may also include depositing a first structural layer on the substrate. The process may also include selectively etching the first structural layer to form at least one of a closed groove or a closed column on the first structural layer. The process may also include depositing a second structural layer on the first structural layer, the second structural layer including at least one of a depression or a protrusion corresponding to at least one of the closed grooves or the closed columns formed in the first structural layer. The process may also include heating the second structural layer to a temperature higher than the glass transition temperature of the second structural layer, thereby causing the second structural layer to reflow. The process may also include depositing a diaphragm layer on the second structural layer, so that the diaphragm layer includes at least one of a downward-facing wrinkle corresponding to the depression formed in the second structural layer or an upward-facing wrinkle corresponding to the protrusion formed in the second structural layer. The process may also include releasing the diaphragm layer, thereby forming a diaphragm suspended above the substrate.

[0133] In some embodiments, at least one of the first structure layer or the second structure has an impurity content. In some embodiments, at least one of the first structure layer and the second structure layer includes phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG), and wherein the impurity includes phosphorus. In some embodiments, the first structure layer is a first PSG layer having a first phosphorus content, and the second structure layer is a second PSG layer having a second phosphorus content different from the first phosphorus content. In some embodiments, the temperature during heating is higher than the glass transition temperature of the second PSG layer and lower than the glass transition temperature of the first PSG layer. In some embodiments, the temperature during heating is greater than the glass transition temperature of each of the first PSG layer and the second PSG layer. In some embodiments, the first structure layer is a first PSG layer having a first phosphorus content, and the second structure layer is a second PSG layer having a second phosphorus content equal to the first phosphorus content. In some embodiments, the process further includes heating the first PSG layer to a glass transition temperature higher than the first PSG layer before depositing the second PSG layer, thereby causing the first PSG layer to reflow.

[0134] In some embodiments, the depression or bump formed in the second structural layer includes an edge having a first radius of curvature less than 1 mm, and wherein reflowing the second structural layer causes the corner to have a second radius of curvature greater than 1 μm and less than 50 μm, so that each of the downward-facing wrinkles or upward-facing wrinkles defined in the diaphragm layer has a radius of curvature corresponding to the second radius of curvature. In some embodiments, the process also includes depositing a backplate layer on the substrate before depositing the first structural layer. The process also includes depositing a first conductive layer on the backplate layer. The process also includes forming a hole through the backplate layer and the first conductive layer and selectively etching the first conductive layer to form electrical contacts on the backplate layer. In some embodiments, releasing the diaphragm also releases the backplate layer, thereby forming a backplate suspended above the substrate below the diaphragm.

[0135] In some embodiments, the process further includes: before depositing the diaphragm layer on the second structural layer, depositing a second conductive layer on the second structural layer and patterning the second conductive layer, wherein at least a portion of the diaphragm layer contacts the second conductive layer, and the second conductive layer forms an electrical contact with the diaphragm layer.

[0136] In some embodiments, a method may include: providing a substrate; selectively etching the substrate to form a closed groove on the substrate; depositing a first structural layer on the substrate, the first structural layer including a recess corresponding to the closed groove formed on the substrate; depositing a first diaphragm layer on the first structural layer, so that the first diaphragm layer includes downward-facing wrinkles corresponding to the recess; depositing a second structural layer on the first diaphragm layer; depositing a back plate layer on the second structural layer; depositing a third structural layer on the back plate, the third structural layer including closed columns; depositing a second diaphragm layer on the third structural layer, so that the second diaphragm layer includes upward-facing wrinkles corresponding to the closed columns in the third structural layer; and releasing the first diaphragm layer and the second diaphragm layer.

[0137] In some embodiments, the method also includes depositing a back plate layer on the second structural layer, the back plate layer including at least one hole; selectively etching the third structural layer and the second structural layer to form at least one cavity extending through the at least one hole; and depositing a second diaphragm layer on the third structural layer, so that the second diaphragm includes at least one column corresponding to the at least one cavity, and the at least one column is connected to the first diaphragm layer.

[0138] In some embodiments, the method further includes forming a through hole through the second diaphragm layer and the first diaphragm layer at a portion of at least one post. In some embodiments, the method further includes etching at least a portion of the first structural layer and the second structural layer to form at least one internal cavity at least partially defined by the first diaphragm layer and the second diaphragm layer. In some embodiments, the method further includes etching at least a portion of the first structural layer and the second structural layer to form a peripheral support structure between the first diaphragm layer and the second diaphragm layer, and wherein the peripheral support structure is positioned along a perimeter of the first diaphragm layer.

[0139] In some embodiments, at least one of the second structure layer and the third structure has an impurity content. In some embodiments, at least one of the second structure layer and the third structure layer includes phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG), and wherein the impurity content includes phosphorus. In some embodiments, the second structure layer is a first PSG layer having a first phosphorus content, and the third structure layer is a second PSG layer having a second phosphorus content different from the first phosphorus content. In some embodiments, the first phosphorus content is between 2% and 6% and the second phosphorus content is between 4% and 10%, and the second phosphorus content is greater than the first phosphorus content.

[0140] In some embodiments, an acoustic transducer can be formed by the following process: providing a substrate; selectively etching the substrate to form a closed groove on the substrate; depositing a first structural layer on the substrate, the first structural layer including a depression corresponding to the closed groove formed on the substrate; depositing a first diaphragm layer on the first structural layer, so that the first diaphragm layer includes downward-facing wrinkles corresponding to the depression; depositing a second structural layer on the first diaphragm layer; depositing a back plate layer on the second structural layer; depositing a third structural layer on the back plate, the third structural layer including closed columns; depositing a second diaphragm layer on the third structural layer, so that the second diaphragm layer includes upward-facing wrinkles corresponding to the closed columns in the third structural layer; and releasing the first diaphragm layer and the second diaphragm layer.

[0141] In some embodiments, the process also includes: depositing a back plate layer on the second structural layer, the back plate layer including at least one hole; selectively etching the third structural layer and the second structural layer to form at least one cavity extending through the at least one hole; and depositing a second diaphragm layer on the third structural layer, so that the second diaphragm includes at least one column corresponding to the at least one cavity, and the at least one column is connected to the first diaphragm layer.

[0142] In some embodiments, the process also includes forming a through hole through the second diaphragm layer and the first diaphragm layer at a portion of at least one column. In some embodiments, the process also includes etching at least a portion of the first structural layer and the second structural layer to form at least one internal cavity at least partially defined by the first diaphragm layer and the second diaphragm layer. In some embodiments, the process also includes etching at least a portion of the first structural layer and the second structural layer to form a peripheral support structure between the first diaphragm layer and the second diaphragm layer, and wherein the peripheral support structure is positioned along the periphery of the first diaphragm layer. In some embodiments, at least one of the second structural layer and the third structure has an impurity content. In some embodiments, at least one of the second structural layer and the third structural layer includes phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG), and wherein the impurity content includes phosphorus. In some embodiments, the second structural layer is a first PSG layer having a first phosphorus content, and the third structural layer is a second PSG layer having a second phosphorus content different from the first phosphorus content. In some embodiments, 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.

[0143] With respect to the use of substantially any plural and / or singular terms herein, one skilled in the art may convert the plural to the singular and / or the singular to the plural to be appropriate to the context and / or application. For clarity, various singular / plural permutations may be expressly set forth herein.

[0144] Those skilled in the art will understand that, generally, the terms used herein, especially in the following claims (e.g., the bodies of the following claims), are generally intended to be “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “comprising” should be interpreted as “including but not limited to,” etc.).

[0145] Those skilled in the art will further understand that if a specific number of introduced claim statements is intended, such intent will be explicitly stated in the claim, and in the absence of such a statement, no such intent exists. For example, to aid understanding, the following appended claims may contain the use of the introductory phrases "at least one" and "one or more" to introduce claim statements. However, the use of these phrases should not be construed as implying that the introduction of a claim statement by the indefinite article "a" or "an" will limit any particular claim containing such introduced claim statement to an invention containing only one such statement, even when the claim includes the introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should be construed to mean "at least one" and "one or more"). The same is true for the use of definite articles used to introduce claim statements. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should generally be interpreted to mean at least the recited number (e.g., the bare recitation "two recitations" without other modifications generally means at least two recitations or two or more recitations).

[0146] Furthermore, in those instances where idioms similar to “at least one of A, B, and C, etc.” are used, generally, such constructions are intended to have the meaning that one skilled in the art would understand the idiom to mean (e.g., “a system having at least one of A, B, and C” would include, but are not limited to, systems having A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In those instances where idioms similar to “at least one of A, B, or C, etc.” are used, generally, such constructions are intended to have the meaning that one skilled in the art would understand the idiom to mean (e.g., “a system having at least one of A, B, or C” would include, but are not limited to, systems having A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). One skilled in the art would further understand that, in practice, any conjunction words and / or phrases indicating two or more alternative terms, whether in the specification, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both of the terms. For example, the phrase "A or B" will be understood to include "A" or "B" or "A and B." Additionally, use of the terms "substantially," "about," "approximately," "substantially," and the like means plus or minus ten percent unless otherwise indicated.

[0147] The above description of the exemplary embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or limiting with respect to the precise forms disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. The scope of the invention is intended to be defined by the appended claims and their equivalents.

[0148] CROSS-REFERENCE TO RELATED APPLICATIONS

[0149] This application claims priority to U.S. Provisional Application No. 62 / 742,164, filed on October 5, 2018, entitled “METHODS OF FORMING MEMS DIAPHRAGMS INCLUDING CORRUGATIONS,” the entire contents of which are incorporated herein by reference.

Claims

1. A capacitive micro-electro-mechanical system chip, the micro-electro-mechanical system chip comprising: A substrate having a through hole; a diaphragm having an annular corrugation disposed between a substantially flat central portion and an outer portion, the substantially flat central portion having a conductive portion, the annular corrugation being defined by a softened edge or corner at an interface between the annular corrugation and the central and outer portions of the diaphragm; a back plate having a conductive portion; The back plate and the diaphragm are arranged in a spaced relationship to form a capacitor structure located above the through hole of the substrate and supported by the substrate, The annular corrugations extend in a direction toward the back plate and are spaced apart from the back plate, wherein the corrugations increase compliance of the diaphragm.

2. The micro-electromechanical system chip according to claim 1, wherein: The softened edge or corner is characterized by a radius of curvature greater than 1 μm and less than 50 μm, wherein the corrugated diaphragm has reduced stress at locations formed by the softened edge or corner.

3. The micro-electromechanical system chip according to claim 1, wherein: At least a portion of the annular corrugation is located radially outside the through hole.

4. The micro-electromechanical system chip according to claim 1, wherein: The annular folds are located radially outside the through hole.

5. The micro-electromechanical system chip according to claim 1, wherein: The conductive portion of the diaphragm and the conductive portion of the back plate are substantially aligned and positioned above the through hole.

6. The MEMS chip according to claim 1, further comprising a structural layer supporting the diaphragm at a peripheral corner of the diaphragm, wherein: The structural layer includes a material different from that of the diaphragm.

7. The micro-electromechanical system chip according to claim 6, wherein: The diaphragm includes silicon nitride, and the structural layer includes phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG).

8. The micro-electromechanical system chip according to claim 6, wherein: The structural layer includes multiple layers having different glass transition temperatures.

9. A capacitive micro-electro-mechanical system chip, the micro-electro-mechanical system chip comprising: a substrate having a through hole; a first electrode having a conductive center portion and peripheral corners; a structural element disposed in the peripheral corner of the first electrode, the structural element comprising a different material than the first electrode; a second electrode having a conductive central portion; The first electrode and the second electrode are arranged in a spaced-apart relationship to form a capacitor structure, the capacitor structure is located above the through hole of the substrate and supported by the substrate, The structural element increases the robustness of the MEMS chip.

10. The micro-electromechanical system chip according to claim 9, wherein: The perimeter corner is substantially annular.

11. The micro-electromechanical system chip according to claim 9, wherein: The first electrode includes silicon nitride, and the structural element includes phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG).

12. The micro-electromechanical system chip according to claim 9, wherein: The structural element comprises multiple layers having different glass transition temperatures.

13. The micro-electromechanical system chip according to claim 12, wherein: The first electrode includes silicon nitride, and the multilayer includes phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG) having different phosphorus contents.

14. The micro-electromechanical system chip according to claim 9, wherein: The first electrode or the second electrode comprises annular corrugations with softened edges or corners characterized by a radius of curvature greater than 1 μm and less than 50 μm.

15. The micro-electromechanical system chip according to claim 14, wherein: The annular folds are located radially outside the through hole.

16. A method for manufacturing a micro-electromechanical system chip, the method comprising: forming trenches or pillars by etching a first structural layer supported by a substrate; Depositing a second structural layer on the groove or the column, wherein the second structural layer includes a depression corresponding to the groove or a convex block corresponding to the column; Softening the edges or corners of the depression or the projection; Depositing a diaphragm layer on the second structural layer after softening, the diaphragm layer comprising downwardly facing wrinkles corresponding to the depressions or upwardly facing wrinkles corresponding to the bumps; as well as forming a diaphragm by releasing a portion of the diaphragm layer including the corrugations from the second structural layer, The diaphragm with wrinkles has greater compliance than the diaphragm without wrinkles.

17. The method according to claim 16, wherein: The edge or corner is softened by heating the second structure layer after etching, wherein the first structure layer comprises a higher glass transition temperature than the second structure layer.

18. The method according to claim 16, wherein: The edge or corner is softened by heating the second structure layer after etching, the first structure layer and the second structure layer comprising phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG) having different phosphorus contents, wherein the first structure layer comprises a higher glass transition temperature than the second structure layer.

19. The method according to claim 16, wherein: The edge or corner is softened by heating the second structural layer after etching to form an edge or corner with a curvature radius greater than 1 μm and less than 50 μm on the recess or the bump, wherein the wrinkles of the diaphragm have a curvature radius greater than 1 μm and less than 50 μm.

20. The method of claim 16, further comprising depositing a first conductive layer having patterned electrical contacts on the second structural layer before depositing the diaphragm layer, wherein: The first conductive layer is a portion of the diaphragm after the diaphragm layer is released.

21. The method according to claim 20, further comprising: depositing a backplane layer having a second conductive layer with patterned holes; as well as forming a backplane by releasing a portion of the backplane layer including the patterned holes, The diaphragm and the back plate form a capacitor structure located above the hole passing through the substrate and supported by the substrate.

22. The method of claim 21, further comprising depositing the first structural layer on the backplate layer before etching the first structural layer, the backplate layer being supported by the substrate.

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