Method of manufacturing an electroacoustic transducer

Abstract

This invention relates to a method of manufacturing an electroacoustic transducer (1), the electroacoustic transducer (1) comprising: - a frame; - a movable element (13) relative to the frame, the movable element (13) comprising a diaphragm (131) and a structure (132) for rigidifying the diaphragm; - a first transmission arm (141), the movable element (13) being coupled to an end of the first transmission arm (141); wherein the shaping of the diaphragm (131) and the shaping of the rigid structure (132) are related in the area around the intersection between the position of the first transmission arm and the periphery of the rigid structure. The electroacoustic transducer of this invention can eliminate air leakage between different volumes of the electroacoustic transducer.

Description

Technical Field

[0001] The technical field of this invention is the field of devices of the microelectromechanical systems (MEMS) or nanoelectromechanical systems (NEMS) type. More particularly, this invention relates to a method of manufacturing an electroacoustic transducer comprising means for transmitting motion and force between two regions that are hermetically isolated from each other. Such an electroacoustic transducer can be used as a microphone or a loudspeaker. Background Technology

[0002] Microelectromechanical or nanoelectromechanical microphones represent a growing market, particularly due to the development of mobile devices such as tablets, smartphones, and other connected objects, which are gradually replacing electret microphones.

[0003] Microphones measure rapid changes in atmospheric pressure, also known as sound pressure. Therefore, they include at least a portion that is in contact with the outside.

[0004] Most currently manufactured MEMS or NEMS microphones are capacitance-sensing microphones. Patent application FR3059659 describes an example of a capacitance-sensing microphone, which includes a movable element, a capacitance sensing device, and a device for transmitting motion between the movable element and the capacitance sensing device.

[0005] The movable element is capable of collecting pressure changes. It can be formed from a rigid piston comprising a diaphragm, also called a thin layer, and structures for rigidifying the diaphragm. The diaphragm forms a partition between a cavity leading to the external environment and the rear volume of the microphone, also called a reference volume, because a reference pressure dominates therein. Therefore, one side of the diaphragm bears the reference pressure, while the opposite side bears atmospheric pressure (despite the desire to detect changes therein). The movable element is connected to a motion transmission device in a first region of the microphone.

[0006] Capacitive sensing devices measure piston displacement and thus pressure changes. They are arranged in a sealed manner in a second region isolated from the first region. They include a movable electrode and at least one fixed electrode arranged facing the movable electrode. The electrodes form the armature of a capacitor whose capacitance changes according to piston displacement. The second region is a chamber under a controlled atmosphere (typically a vacuum) to reduce viscous friction and associated noise.

[0007] The transmission device includes at least one first transmission arm extending in a first region and at least one second transmission arm extending in a second region. A piston is coupled to a first end of the first transmission arm, while a movable electrode of a capacitance detection device is coupled to an end of the second transmission arm. The first and second transmission arms are connected to their second ends via a pivot joint. This pivot joint allows the transmission arms to rotate relative to the microphone frame while simultaneously ensuring a seal between the first and second regions.

[0008] The manufacture of this microphone specifically includes steps for trimming the piston and defining the transmission arms so that they are movable relative to the frame. These steps are difficult to perform without puncturing the piston and creating a significant air leak between the chamber subjected to atmospheric pressure and the rear volume of the microphone (subject to reference pressure). Summary of the Invention

[0009] More typically, it is necessary to manufacture an electroacoustic transducer while still eliminating air leakage between different volumes of the electroacoustic transducer, the transducer comprising:

[0010] -frame;

[0011] - The movable element relative to the frame includes a diaphragm and a structure for rigidifying the diaphragm;

[0012] - First transmission arm, with a movable element coupled to the end of the first transmission arm.

[0013] According to a first aspect of the invention, this need is tended to be met by providing a manufacturing method comprising the following steps:

[0014] - Provides a stack comprising a substrate, a first sacrificial layer, and a first structural layer in sequence;

[0015] - Etching the first structural layer to the first sacrificial layer to separate a first portion of the first structural layer from a second portion of the first structural layer, the first portion of the first structural layer being intended to form a membrane for a movable element;

[0016] - Forming a second sacrificial layer, including:

[0017] -The first part arranged on the first part of the first structural layer;

[0018] - A second portion spaced apart from the first portion and arranged on the first structural layer; and

[0019] - The third part is adjacent to the second part and is arranged on the first sacrificial layer between the first part and the second part of the first structural layer;

[0020] -A second structural layer is formed on the second sacrificial layer;

[0021] - Etch the second structural layer to define the rigid structure of the movable element and to expose a first portion of the second sacrificial layer; and

[0022] - Etch the second sacrificial layer to expose a first portion of the first structural layer.

[0023] Furthermore, the etching of the first structural layer and the second structural layer, which define the periphery of the rigid structure, are spaced apart from each other in the region around the location of the first transmission arm, such that the second portion of the second sacrificial layer serves as a stop layer for the etching of the second structural layer.

[0024] In the region where the first transport arm intersects with the periphery of the rigid structure, a second portion of the second sacrificial layer covers the first structural layer. The first structural layer is then unaffected by the etching of the second structural layer. Furthermore, by moving the etching of the first structural layer away from the etching of the second structural layer, the integrity of the first sacrificial layer can be preserved at the first transport arm after the step of etching the second sacrificial layer. The substrate can then be etched to define the first transport arm without the risk of etching propagation to both the first and second structural layers. This eliminates the risk of air leakage on each side of the first transport arm.

[0025] In a preferred embodiment of the manufacturing method, the first structural layer is etched outside the region, such that a third portion of the second sacrificial layer extends at least to the periphery of the rigid structure.

[0026] The etching of the first structural layer and the etching of the second structural layer can be spaced apart from each other by inserts in the first structural layer and / or by inserts in the second structural layer.

[0027] The second part of the second sacrificial layer can be arranged on the first part of the first structural layer or on the second part of the first structural layer.

[0028] The manufacturing method may also include the following steps after the step of etching the second sacrificial layer:

[0029] - Etch the substrate to the first sacrificial layer to define the first transport arm; and

[0030] - Etch the first sacrificial layer so that a first portion of the first structural layer is movable.

[0031] Preferably, the manufacturing method further includes the following steps after the step of etching the second sacrificial layer and before the step of etching the substrate:

[0032] - A covering is arranged on the second structural layer to form a component; and

[0033] - Flip the component.

[0034] In addition to the features just mentioned in the preceding paragraphs, the manufacturing method according to the invention may have one or more of the following additional features, either individually or in any technically permissible combination:

[0035] - The rigid structure of the movable element is located at least partially on the first portion of the first structural layer;

[0036] - The rigid structure of the movable element contacts the first part of the first structural layer;

[0037] - Stacks are multilayer structures of the silicon-on-insulator (SOI) type;

[0038] - The substrate is made of silicon, the first sacrificial layer is made of silicon oxide, and the first structural layer is made of silicon;

[0039] - The second sacrificial layer is made of silicon oxide; and

[0040] - The thickness of the first structural layer is between 100 nm and 10 μm.

[0041] A second aspect of the present invention relates to an electroacoustic transducer comprising:

[0042] -frame;

[0043] - The movable element relative to the frame includes a diaphragm and a structure for rigidifying the diaphragm;

[0044] - First transmission arm, with a movable element coupled to the end of the first transmission arm.

[0045] The diaphragm is formed by a first portion of a first structural layer, the rigid structure is formed by a first portion of a second structural layer disposed on the first structural layer, and the frame includes a substrate, a second portion of the first structural layer, and a second portion of the second structural layer.

[0046] One of the first and second portions of the first structural layer and / or one of the first and second portions of the second structural layer has an insert facing the other of the first and second portions, the insert being located in the area surrounding the intersection of the position of the first transmission arm and the periphery of the rigid structure.

[0047] In a preferred embodiment, the transducer includes means for transmitting motion and force between a first region and a second region having a controlled atmosphere, the first region and the second region being insulated from each other in a sealed manner, the transmission means including a first transmission arm extending in the first region and a second transmission arm extending in the second region.

[0048] Preferably, the frame includes a first portion of the substrate, and the first transmission arm is formed by a second portion of the substrate.

[0049] A better understanding of the invention and its various applications will be gained by reading the following description and examining the accompanying drawings. Attached Figure Description

[0050] Referring to the accompanying drawings, other features and advantages of the invention will become apparent from the following description, which is intended for illustrative purposes and not for limitation, wherein:

[0051] Figure 1 An example of an electroacoustic transducer comprising pistons connected to two first transmission arms is shown schematically and in part.

[0052] Figures 2A to 2H The manufacturing process is shown. Figure 1 The steps of a method for developing an electroacoustic transducer;

[0053] Figure 3 It is release Figure 2H The diagram shows a perspective view of an electroacoustic transducer after the diaphragm of the piston is applied.

[0054] Figures 4A to 4D The steps of a method for manufacturing an electroacoustic transducer according to the present invention are shown;

[0055] Figure 5 It has been completed. Figures 4A-4D A cross-sectional view of the electroacoustic transducer at the intersection of the piston periphery and the position of the first transmission arm, following steps 2F-2H.

[0056] Figure 6 This is a cross-sectional view of the electroacoustic transducer after steps 4A-4D have been completed in the manufacturing method of a preferred embodiment of the present invention to reduce damping phenomena.

[0057] Figures 7A to 7D The display can be used to complete Figure 4A , 4B Etching masks for steps 4C and 2G;

[0058] Figures 8A to 8C The display can be used to complete Figure 4A , 4B Other etching masks for the 4C step; and

[0059] Figure 9 An alternative embodiment of the manufacturing method according to the present invention is shown.

[0060] For clarity, identical or similar elements in all the accompanying drawings are labeled with the same reference numerals. Detailed Implementation

[0061] Figure 1 An example of an electroacoustic transducer 1 of the capacitance sensing microphone type is shown, which seeks to simplify manufacturing.

[0062] The electroacoustic transducer 1 includes a frame (not shown) that at least partially defines a first region 11 and a second region 12, an element 13 movable relative to the frame, and a device 14 for transmitting motion between the first region 11 and the second region 12. The first region and the second region 11-12 of the electroacoustic transducer 1 are subjected to different pressures. They are isolated from each other in a sealed manner.

[0063] The movable element 13, referred to below as the piston, contacts the first region 11. It includes a diaphragm 131 and a structure 132, also called a skeleton or armature, for rigidifying the diaphragm. The function of the diaphragm 131 of the piston 13 here is to collect the pressure difference between its two surfaces over its entire surface in order to infer changes in atmospheric pressure.

[0064] The diaphragm 131 of piston 13 partially defines a closed volume, known as the reference volume, in which the reference pressure is dominant. It separates this reference volume from the cavity that leads to the external environment (here, air). Thus, one side of the diaphragm 131 bears the reference pressure, while the opposite side of the diaphragm 131 bears atmospheric pressure (in the case of a microphone, seeking to detect changes in its atmospheric pressure).

[0065] The first region 11 may correspond to a cavity leading to the external environment and thus be subjected to atmospheric pressure. Alternatively, the first region 11 may be a reference volume subjected to a reference pressure.

[0066] Furthermore, in this particular example, the electroacoustic transducer 1 includes capacitance detection devices 15 arranged in the second region 12. These capacitance detection devices 15 can measure the displacement of the piston 13, and thus the pressure difference between its two sides. They preferably include a movable electrode 151 and at least one fixed electrode arranged facing the movable electrode 151. The electrodes form the armature of a capacitor whose capacitance changes according to the displacement of the piston 13.

[0067] The second region 12 is a chamber under a controlled atmosphere to reduce viscous friction and associated noise. The term "chamber under a controlled atmosphere" refers to a chamber under reduced pressure, typically less than 10 mbar, and preferably under vacuum.

[0068] The transmission device 14 is rotatably mounted relative to the frame via one or more pivot joints 16. The transmission device 14 includes at least one first transmission arm 141 extending in a first region 11, at least one second transmission arm 142 extending in a second region 12, and at least one transmission shaft 143 extending partially in the first region 11 and partially in the second region 12. Figure 1 In the example, the transmission device 14 includes two first transmission arms 141, two second transmission arms 142, and two transmission shafts 143, each transmission shaft 143 connecting the first transmission arm 141 to the second transmission arm 142.

[0069] Each first transmission arm 141 includes a first end coupled to the piston 13 and a second opposite end coupled to an associated transmission shaft 143. Each second transmission arm 142 includes a first end coupled to a movable electrode 151 of the capacitance detection device 15 and a second opposite end coupled to an associated transmission shaft 143.

[0070] For example, the transmission shaft 143 is in the form of a straight cylinder. The transmission arms 141-142 are preferably in the form of beams with a rectangular cross-section, where one dimension (length) is larger than the others (width and thickness). For example, the piston 13 has a rectangular shape. The first transmission arm 141 preferably extends perpendicular to the side of the piston 13, advantageously with a large side extension. They can be anchored to the inner periphery of the piston 13, such as... Figure 1 As shown, for example, through the first end of the cylinder.

[0071] Each pivot joint 16 preferably includes a sealing isolation element 161 through which the transmission shaft 143 passes, and two aligned blades 162 extending between the transmission shaft 143 and the frame. For example, the sealing isolation element 161 is in the form of a sealing diaphragm. It ensures a seal between a first region 11 and a second region 12 at the pivot joint 16. The blades 162 are dimensioned to be deformable upon torsion and to allow rotation of the transmission device 14. They are preferably arranged in a diaphragmatic manner relative to the transmission shaft 143. Preferably, the sealing isolation element 161 is deformable under the rotational displacement of the transmission device 14.

[0072] The framework may specifically include a support (formed from a first substrate), a structural layer disposed on the support (e.g., made of silicon), and a covering added to the structural layer (e.g., formed from a second substrate).

[0073] The structure 132 for rigidifying the diaphragm of piston 13 advantageously includes an edge extending at its periphery in a direction perpendicular to diaphragm 131. This edge increases the path of air around the piston and reduces leakage between the external environment and the enclosed volume used as a reference.

[0074] Figures 2A to 2H Steps S1, S3 to S9 of a method for manufacturing the electrostatic transducer 1 are shown. These figures illustrate how the piston 13 can be formed and separated from the frame. Therefore, only a portion of the electroacoustic transducer near the periphery of the piston 13 is shown. For simplicity, reference will be made only to a single first transmission arm 141, a single pivot joint 16, a single sealing diaphragm 161, etc., and it will be understood that all elements of the same type can be formed simultaneously.

[0075] Figure 2A , Figure 2A The first step S1 shown includes providing a stack layer 20 as starting material for manufacturing the transducer. The stack 20 sequentially includes a substrate 21, a first sacrificial layer 22, and a first structural layer 23, also referred to as a "thin layer".

[0076] Substrate 21 is specifically used to fabricate the first transmission arm 141 and a portion of the frame (support). Its initial thickness may include between 500 μm and 700 μm. Substrate 21c is made of a semiconductor material, such as silicon.

[0077] The first structural layer 23 is used to manufacture the diaphragm 131 of the piston 13. It can also be used to manufacture the sealing diaphragm 161 of the pivot joint 16 and / or the movable electrode 151 of the capacitance detection device 15.

[0078] Its thickness is less than that of the substrate 21, preferably between 100 nm and 10 μm, for example, equal to 1 μm. It is preferably formed of the same material as the substrate, such as silicon.

[0079] The first sacrificial layer 22 is intended to disappear partially during the fabrication of the transducer. This layer is particularly useful for defining the first transmission arm 141. It can also serve as a lower air gap in the capacitive sensing region of the transducer. It also enables mechanical connection between the substrate and the first structural layer. The first sacrificial layer 21 can be formed of a dielectric material, preferably silicon nitride or silicon oxide, such as silicon dioxide (SiO2). Its thickness includes, for example, between 100 nm and 10 μm.

[0080] Stack 20 can be a multilayer structure of silicon-on-insulator (SOI) type, commonly referred to as an SOI substrate.

[0081] Although not shown in the figure, the manufacturing method also includes step S2 of etching the first structural layer 23. This step of etching the first structural layer 23 can be used in particular to form a hole for releasing the movable electrode 151 (to allow the etching solution of the first sacrificial layer 22 to penetrate into the latter).

[0082] Figure 2B ,exist Figure 2B In step S3, a second sacrificial layer 24 is formed on the first structural layer 23 in the first region 20A of the stack 20. For this purpose, the second sacrificial layer 24 can be deposited first to completely cover the first structural layer 23, and then partially etched in the second region 20B of the stack 20, for example, through a resin mask formed by photolithography. The etching of the second sacrificial layer 24 is preferably selective relative to the first structural layer 23. The second sacrificial layer 24 is advantageously formed of the same dielectric material as the first sacrificial layer 22, such as silicon oxide. Its thickness can include between 100 nm and 10 μm.

[0083] The second sacrificial layer 24 can be used as the upper air gap for capacitance sensing. Etching of the second sacrificial layer 24 can lead to the etching of the first sacrificial layer 22, in which the first structural layer 23 (not shown) is pre-etched.

[0084] Figure 2C ,exist Figure 2C In step S4, the second structural layer 25 is deposited on the first structural layer 23 (in the second region 20B of the stack 20) ​​and the second sacrificial layer 24 (in the first region 20A of the stack 20), for example, by epitaxy. The second structural layer 25 is intended to form one or more (structural) elements of the transducer, particularly the rigid structure 132 of the piston 13. It is advantageously formed of the same material as the first structural layer 23, such as silicon. The thickness of the second structural layer 25 preferably includes between 5 μm and 50 μm, for example, equal to 20 μm.

[0085] Figure 2D Then, in Figure 2D During step S5, as shown, the second structural layer 25 is etched to define the outline of the rigid structure 132 (piston trimming) and to reduce the weight of the piston 13. In the first region 20A of the stack 20, the second sacrificial layer 24 (e.g., silicon oxide) serves as a stop layer for the etching of the second structural layer 25 (e.g., silicon), thus preserving the underlying first structural layer 23 (e.g., silicon). Therefore, the etching of the second structural layer 25 is selective relative to the second sacrificial layer 24. On the other hand, in the second region 20B of the stack 20, the etching of the second structural layer 25, which defines the periphery (or outer outline) of the rigid structure 132, opens onto the first structural layer 23. Because the etching of the second structural layer 25 is not selective relative to the first structural layer 23 (but only relative to the first sacrificial layer 22), the first structural layer 23 and the second structural layer 25 are simultaneously etched down to the first sacrificial layer 22.

[0086] Therefore, at the bottom of the trench corresponding to the periphery of the rigid structure 132, the first structural layer 23 has been etched and the first sacrificial layer 22 has been exposed.

[0087] At the end of step S5, the first structural layer 23 comprises a first portion 23a and a second portion 23b that are separated from each other. The first portion 23a of the first structural layer 23 (in...) Figure 2D The diaphragm 131 (on the left side) is designed to form the piston 13. It is covered by a separated portion of the second sacrificial layer 24 and the second structural layer 25, forming the rigid structure 132 of the piston 13.

[0088] Figure 2D The etching technique used in step S5 is advantageously deep reactive ion etching (DRIE).

[0089] Figure 2E ,refer to Figure 2E The manufacturing method then includes step S6 of etching the second sacrificial layer 24 to expose (partially) the first portion 23a of the first structural layer 23 (in other words, to expose the first surface of the diaphragm 131). This step S6 can serve as the first step in releasing the piston 13.

[0090] The etching of the second sacrificial layer 24 is preferably a selective isotropic etching relative to the substrate 21, the first structural layer 23, and the second structural layer 25. The second sacrificial layer 24 is preferably chemically etched, for example by immersing the stack in a controlled time in a liquid or gas phase (in the case of a silicon oxide layer) hydrofluoric acid (HF) bath.

[0091] On the other hand, the portion of the first sacrificial layer 22 aligned with the periphery of the rigid structure 132 is etched simultaneously with the second sacrificial layer 24, forming a cavity 22' in the first sacrificial layer 22. The etching can be precisely controlled so that the cavity 22' extends very little.

[0092] The etching of sacrificial layers 22 and 24 can also be used to release the movable electrode 151 of the capacitance detection device 15 (before it is enclosed in a chamber under a controlled atmosphere).

[0093] Although not shown in the figures, the manufacturing method may then include the step of transferring a cover onto the second structural layer 25, thereby forming a chamber, i.e., the second region 12, under a controlled atmosphere. The cover can be produced by machining a silicon substrate. It can be attached to the second structural layer 25, in particular, by direct bonding (e.g., Si-Si) or by eutectic sealing (e.g., Au-Si).

[0094] Figure 2F Then, in Figure 2F In step S7, the assembly formed by the stack layer 20 and the cover (not shown) is flipped over to facilitate subsequent etching of the substrate 21. After flipping, the substrate 21 is advantageously thinned, for example by DRIE etching, grinding and / or chemical mechanical polishing (CMP), preferably until a thickness between 30 μm and 300 μm is reached, which is the desired thickness of the first transport arm 141.

[0095] Figure 2G , Figure 2G Step S8 includes etching (optionally thinning) the substrate 21 to the first sacrificial layer 22 to create a pathway to the piston 13 and Figure 2F The first transport arm is defined in the area not shown. The etching of the substrate is preferably selective relative to the first sacrificial layer 22. The substrate 21 can be etched via DRIE.

[0096] like Figure 2G As shown, through partial (involuntary) etching of the first sacrificial layer 22, the substrate 21 is etched to create a passageway to the rear of the piston 13 that can be inscribed within the periphery of the piston 13, such that no opening is made in step S6 (see...). Figure 2EThe etching in step S8 does not extend into the cavity 22' formed by the first structural layer 23, which includes the first portion 23a (diaphragm 131) of the first structural layer 23 and the separated portion (rigid structure 132) of the second structural layer 25. On the inner periphery of the piston 13, the first sacrificial layer 22 (e.g., made of silicon oxide) serves as a stop layer for etching the substrate 21 (e.g., made of silicon), thereby preserving the first portion 23a of the underlying first structural layer 23 (e.g., made of silicon).

[0097] Finally, in step S9 (see...) Figure 2H The first sacrificial layer 22 is etched to expose a first portion 23a of the first structural layer 23 (in other words, to expose the second surface opposite the diaphragm 131), and this portion is separated from the substrate 21. At the end of step S9, the piston 13 is freed. Therefore, step S9 can serve as a second step to release the piston 13.

[0098] The etching of the first sacrificial layer 22 is preferably a selective isotropic etching relative to the substrate 21, the first structural layer 23, and the second structural layer 25. The first sacrificial layer 22 is preferably chemically etched, for example by immersing the component in a liquid or gas phase (in the case of a silicon oxide layer) hydrofluoric acid (HF) bath for a controlled period of time.

[0099] Figure 3 In the second step S9 of releasing the piston ( Figure 2H The following is a perspective view of the components, cut along the plane of symmetry of the transfer arm 141. A portion of the cover 26 is transferred onto the second structural layer 25 shown therein.

[0100] The first region 31 located around the rigid structure 132 Figure 2H The middle section is shown as a cross-section.

[0101] The figure shows the vertical projection (i.e., perpendicular to the substrate) of the first transport wall 141 across the periphery of the rigid structure 132 of the piston 13. However, perpendicular to this periphery is a cavity 22' formed by etching the first sacrificial layer 22.

[0102] Therefore, in the second region 32 of the stack around the intersection of the first transmission arm 141 (protrusion) or its location with the periphery of the rigid structure 132, the etching of the substrate 21 coincides with the etching of the first sacrificial layer 22. Thus, the first sacrificial layer 22 can no longer serve as a stop layer for the etching of the substrate 21. The etching is uninterrupted and extends to the first structural layer 23 and the second structural layer 25. This phenomenon is problematic because it creates significant air leakage between the first region 11 located on one side of the first structural layer 23 and the volume located on the opposite side of the first structural layer 23 (here, below the cover 26). When the transmission device has several first transmission arms 141, this leakage problem naturally occurs at each of the first transmission arms 141.

[0103] To overcome this problem, at least near each intersection between the protrusion of the first transmission arm 141 and the periphery of the rigid structure 132, steps S2, S3, S5, and S6 of the manufacturing method described above are performed in different ways.

[0104] Figures 4A to 4D A cross-sectional view is shown showing how steps S2, S3, S5, and S6 are implemented in each second region 32 (including the intersection between the protrusion of the first transmission arm 141 and the periphery of the rigid structure 132).

[0105] Figure 4A , Figure 4A Step S2, etching the first structural layer 23, is shown. A portion of the first structural layer 23 is etched to at least partially (i.e., in the second region 32) separate the first portion 23a and the second portion 23b of the first structural layer 23. It should be noted that the first portion 23a of the first structural layer 23 is intended to form the diaphragm 131 of the piston. Therefore, the diaphragm 131 is at least partially trimmed during this step S2.

[0106] Figure 4B Then, in Figure 4B In step S3, a second sacrificial layer 24 is formed on the stack 20. Step S3 can be performed such that the second sacrificial layer 24 includes a first portion 24a disposed on a first portion 23a of the first structural layer 23a and a second portion 24b spaced apart from the first portion 24a. The second portion 24b of the second sacrificial layer 24 is deposited on the first structural layer 23 (here on the second portion 23b) and extends to the location where the first structural layer 23 is etched.

[0107] The second sacrificial layer 24 also includes a third portion 24c (at the location where the first structural layer 23 is etched) disposed on the first sacrificial layer 22 between the first and second portions 23a-23b of the first structural layer 23. The third portion 24c is adjacent to the second portion 24b. It occupies all the space between the first and second portions 23a-23b of the first structural layer 23.

[0108] The first, second, and third portions 24a-24c of the second sacrificial layer 24 are preferably formed by etching a dielectric layer pre-deposited on the first structural layer 23, the etching being selective relative to the first structural layer 23. The deposition of the second sacrificial layer 24 can be conformal, such that the first, second, and third portions 24a-24c have the same thickness. Conversely, if a mechanical-chemical polishing is subsequently performed, the deposition can be planarized.

[0109] Figure 4C ,refer to Figure 4C Step S5, which involves etching the second structural layer 25 (to reduce piston weight and define the rigid structure 132), is performed such that the trenches corresponding to the periphery of the rigid structure 132 open onto the second portion 24b of the second sacrificial layer 24. Therefore, the second portion 24b of the second sacrificial layer 24 serves as a stop layer for etching. It prevents the first structural layer 23 from being etched and the first sacrificial layer 22 from being exposed (e.g., ...). Figure 2D ).

[0110] In step S6, which follows the etching of the second sacrificial layer 24 (see reference) Figure 4D Therefore, the first portion 24a can be completely removed without altering the first sacrificial layer 22. In fact, the second portion 23b of the first structural layer 23 remains intact and protects the underlying first sacrificial layer 22. Furthermore, the removal of the first portion 24a consumes the second portion 24b of the second sacrificial layer 24. In other words, the second portion 24b slows down the etching process, ensuring that the etched chemicals never reach the first sacrificial layer 22.

[0111] Then, the manufacturing method is about Figures 2F to 2H The description is expanded (steps S7-S9).

[0112] By separating the etching of the second structural layer 25 from the etching of the first structural layer 23 in the second region 32 of the stack, that is, by decoupling the trimming of the film 131 from the trimming of its rigid structure 132, the first sacrificial layer 22 can be fully preserved. Step S8 of etching the substrate 21 (to define the first transmission arm 141) is no longer a constraint, because the first sacrificial layer 22 fully performs its function as a stop layer.

[0113] The etching of the second structural layer 25 and the etching of the first structural layer 23 are preferably offset by a distance D (reference) between 0.5 μm and 15 μm. Figure 4C ).

[0114] The first portion 24a and the third portion 24c of the second sacrificial layer 24 are preferably spaced apart from each other, such that the second structural layer 25 (rigid structure 132) is in direct contact with the first portion 23a (diaphragm 31) of the first structural layer 23.

[0115] Figure 5 It has been completed. Figures 4A-4D During steps S2-S3 and S5-S6, a cross-sectional view of the structure obtained in the second region 32 after step S9 (the second step of releasing the piston 13) of etching the first sacrificial layer 21.

[0116] The piston 13 is free to move relative to a frame, which includes a substrate 21, the first sacrificial layer 22, the remainder of the second structural layer 25, and a second portion 23b of the first structural layer 23. A rigid structure 132 hangs over the second portion 23b of the first structural layer 23. The distance between the rigid structure 132 and the second portion 23b of the first structural layer 23 is equal to the thickness of the second portion 24b of the second sacrificial layer 24, typically between 100 nm and 10 μm.

[0117] During the displacement of piston 13, air is trapped between the rigid structure 132 and the remaining portion of the first structural layer 23. This air trapping is the origin of a damping phenomenon known as diaphragm damping, which generates mechanical noise and leads to a degraded transducer performance. The force of this damping phenomenon is inversely proportional to the cube of the distance between piston 13 and the frame (here, the second portion 23b of the first structural layer 23).

[0118] According to a preferred embodiment of the manufacturing method, the etching of the second structural layer 25 enables the definition of the periphery of the rigid structure 132 (step S5). Figure 4C Etching relative to the first structural layer 23 (step S2); Figure 4A The offset is only within the second region 32 of the stack. Outside of this second region 32 (i.e., for the remaining periphery of the rigid structure 132), for example in the first region 31 of the stack (see...) Figure 3 In step S2, the first structural layer 23 is etched such that the third portion 24c of the second sacrificial layer 24 (deposited in step S3) extends at least to the periphery of the rigid structure 132. Therefore, the first structural layer 23 is absent at the location where the substrate 21 and the rigid structure 132 are superimposed. Outside the second region 32, the etching of the second structural layer 25 (step S5) opens onto the third portion 24c of the second sacrificial layer 24, which occupies the space left by the etching of the first structural layer 23.

[0119] This preferred embodiment is shown in Figure 6 The figure shows the peripheral region of piston 13, excluding the second region 32 (e.g., Figure 3 A schematic cross-sectional view of the structure obtained in the first region 31) after the first step of releasing the piston (etching the second sacrificial layer 24).

[0120] The second portion 23b of the first structural layer 23 does not extend below the rigid structure 132. The rigid structure 132 is separated from the substrate 21 only by the first sacrificial layer 22 and the second sacrificial layer 24 (and specifically, the third portion 24c occupying the space left by the etching of the first structural layer 23). After the second step (step S9) of releasing the piston, the first sacrificial layer 22 and the second sacrificial layer 24 will disappear around the piston 13, forming a "gap" between the piston and the frame, which is larger than that in the second region 32 of the stack (refer to...). Figure 5 For example, when the two sacrificial layers 22 and 24 have the same thickness (especially when they are used to create the air gap for differential capacitance detection), the gap is twice as large.

[0121] Therefore, damping can be reduced while still addressing the air leakage problem specific to the second zone 32.

[0122] It can also be noted that, outside the second region 32, the second sacrificial layer 24 does not necessarily include the second portion 24b disposed on the second portion 23b of the first structural layer 23.

[0123] In an alternative embodiment of the manufacturing method, the etching of the second structural layer 25 enables etching of the first structural layer 25 over the entire periphery of the rigid structure 132 (step S2). Figure 4A ), offset the periphery of the rigid structure 132 (step S5); Figure 4C ).

[0124] In another alternative embodiment of the manufacturing method, in step S2, the first structural layer 23 remains intact outside the second region 32, but in step S5, it is etched simultaneously with the second structural layer 25. In this case, the second sacrificial layer 24 does not include the second portion 24b or the third portion 24c. In other words, the manufacturing method is based on... Figure 2A-2G The description is done outside of the second area 32 (because the leakage problem is specific to the second area 32).

[0125] Figure 7A , 7BFigures 7C and 7D illustrate examples of masks for etching the first structural layer 23 (step S2), the first sacrificial layer 24 (step S3), the second structural layer 25 (step S5), and the substrate 21 (step S8) respectively in a preferred embodiment of the manufacturing method (so that a hard mask can be produced on the stack of layers by photolithography or made of resin).

[0126] Figure 7A , Figure 7A The mask includes an opening (or recess) 71 for etching a portion of the first structural layer 23. Solid portions of the mask are present on each side of the opening 71, corresponding to the first and second portions 23a-23b of the first structural layer 23. The opening 71 is configured such that the second portion 23b of the first structural layer 23 forms an insert 70 (or protrusion) in a second region 32, the insert 70 being arranged facing the first portion 23a of the first structural layer 23. This insert 70, also called a tab, is a means used here to (locally) offset the etching of the first structural layer 23 and the etching of the second structural layer 25. The insert 70 forms a local offset 71 from the opening.

[0127] Figure 7B , Figure 7B The mask includes two openings 72 that allow etching of the second sacrificial layer 24. It shows (as a top view) the arrangement of the first portion 24a, the second portion 24b, and the third portion 24c of the second sacrificial layer 24 relative to the etched portion of the first structural layer 23 (now shown as dashed lines). It is observed that the second portion 24b actually covers the tab 70.

[0128] Figure 7C , Figure 7C The mask includes two openings 73a-73b, used to simultaneously reduce the weight of the piston and define the rigid structure 132 in the second structural layer 25. In the second region 32, the opening 73b corresponding to the periphery of the rigid structure 132 is offset (by a distance D) relative to the opening 71 of the etching mask of the first structural layer 23. On the other hand, outside the second region 32, the openings 73b and 71 are aligned with each other (they may also be juxtaposed).

[0129] Figure 7D , Figure 7D The mask includes two openings 74 (which are connected elsewhere) to define a first transmission arm 141 in the substrate. The first transmission arm 141 actually passes through the periphery of the rigid structure 132 (second region 32) at the tab 70.

[0130] exist Figures 8A-8CIn an alternative embodiment of the manufacturing method shown, the etching between the first structural layers 23 and the etching of the second structural layer 25 are separated from each other by the insert 80 of the rigid structure 132, rather than by the insert 70 of the second portion 23b of the first structural layer 23. The insert 80 of the rigid structure 132 faces the remaining portion of the second structural layer 25. The insert 80 here forms a local deviation of the opening 73b.

[0131] Figure 8A , 8B Figure 8C illustrates a mask according to this alternative embodiment that can be used to etch the first structural layer 23 (step S2), the first sacrificial layer 24 (step S3), and the second structural layer 25 (step S5), respectively. Since the etching of the substrate 21 (step S8) is unaffected, it can be reused. Figure 7D The mask.

[0132] Used to etch the first structural layer 23 and in Figure 8A The opening 71 of the mask shown is advantageously straight.

[0133] Figure 8B ,Depend on Figure 8B The solid portion of the mask showing the second portion 24b of the second sacrificial layer 24 can be compared to Figures 7A-7D Wider in the preferred embodiment (according to the desired distance D).

[0134] Figure 8C Finally, as Figure 8C As shown, the opening 73b of the etch mask of the second structural layer 25 is configured to form the insert 80 (or protrusion) of the rigid structure 132.

[0135] exist Figure 9 In the illustrated embodiment, (via the insertion of the first structural layer 23 or via the insertion of the second structural layer 25), the etching of the structural layer 25 can be offset relative to the etching of the first structural layer 23 on the side of the piston 13, rather than on the side of the frame. A second portion 24b of the second sacrificial layer 24, on which the etching of the second structural layer 25 stops, is then disposed on the first portion 23a of the first structural layer 23. The diaphragm 131 of the piston 13 then extends beyond the rigid structure 132 in the second region 32.

[0136] The method for manufacturing an electroacoustic transducer according to the present invention will be described using a capacitive detection microphone as an example. Figure 1 The microphone is subjected to atmospheric pressure on one side and a reference pressure on the other. However, regarding... Figure 2A-2H The manufacturing methods described in 4A-4D are applicable to other types of microphones and other types of electroacoustic transducers, especially loudspeakers (sound emitters) or ultrasonic emitters.

[0137] More typically, the microphone in the second region 12 (a chamber with a controlled atmosphere) includes means for measuring the motion of the transmission device and / or the forces applied to it. These measuring means include, for example, a vibrating beam (resonance detection microphone).

[0138] In the case of a loudspeaker or ultrasonic transmitter, an actuator (e.g., a capacitor) replaces the measuring device in the second region 12. The actuator causes the first end of the second transmission arm 142 to move. This movement is transmitted by the transmission device 14 to a piston 13 integral with the first end of the first transmission arm 141. Movement of the diaphragm 131 of the piston 13 enables the emission of sound (or ultrasound).

Claims

1. A method for manufacturing an electroacoustic transducer (1), the electroacoustic transducer (1) comprising: -frame; - The movable element (13) relative to the frame includes a diaphragm (131) and a structure (132) for rigidifying the diaphragm; - First transmission arm (141), movable element (13) coupled to the end of the first transmission arm (141); The method also includes the following steps: - Provide a stack (20) comprising a substrate (21), a first sacrificial layer (22) and a first structural layer (23) in sequence, (S1); - Etch the first structural layer (23) to the first sacrificial layer (22) to separate the first portion (23a) and the second portion (23b) of the first structural layer, the first portion (23a) of the first structural layer being intended to form a diaphragm (131) of the movable element (13), (S2); - Forming a second sacrificial layer (24), (S3), including: - The first part (24a) arranged on the first part (23a) of the first structural layer (23); - A second portion (24b) spaced apart from the first portion (24a) and arranged on the first structural layer (23); and, - The third part (24c) is adjacent to the second part (24b) and arranged on the first sacrificial layer (22) between the first part (23a) and the second part (23b) of the first structural layer (23); -A second structural layer (25), (S4) is formed on the second sacrificial layer (24); - Etch the second structural layer (25) to define the rigid structure (132) of the movable element (13) and to expose the first portion (24a) of the second sacrificial layer (24), (S5); and - Etch the second sacrificial layer (24) to expose the first portion (23a) of the first structural layer (23), (S6); In this method, the etching of the first structural layer (23) and the etching of the second structural layer (25) that define the periphery of the rigid structure (132) are spaced apart from each other in the region (32) around the piston of the first transmission arm (141), such that the second portion (24b) of the second sacrificial layer (24) serves as the stop layer for the etching of the second structural layer (25).

2. The method according to claim 1, wherein the first structural layer (23) is etched outside the region (32) such that the third portion (24c) of the second sacrificial layer (24) extends at least to the periphery of the rigid structure (132).

3. The method according to claim 1 or 2, wherein the etching of the first structural layer (23) and the etching of the second structural layer (25) are spaced apart from each other by the insert (70) of the first structural layer (23).

4. The method according to any one of claims 1 to 3, wherein the etching of the first structural layer (23) and the etching of the second structural layer (25) are spaced apart from each other by the insert (80) of the second structural layer (25).

5. The method of any one of claims 1 to 4, wherein, The second portion (24b) of the second sacrificial layer (24) is disposed on the second portion (23b) of the first structural layer (23).

6. The method of any one of claims 1 to 4, wherein, The second portion (24b) of the second sacrificial layer (24) is disposed on the first portion (23a) of the first structural layer (23).

7. The method according to any one of claims 1 to 6, further comprising the following steps after step (S6) of etching the second sacrificial layer (24): - Etch substrate (21) to first sacrificial layer (22) to define first transport arm (141), (S8); and - Etch the first sacrificial layer (22) so that the first portion (23a) of the first structural layer (23) is movable (S9).

8. The method of claim 7, further comprising the following steps after step (S6) of etching the second sacrificial layer (24) and before step (S8) of etching the substrate (21): - A covering (26) is arranged on the second structural layer (25) to form a component; and - Flip the component, (S7).

9. The method according to any one of claims 1 to 8, wherein the stack (20) is a multilayer structure of the silicon-on-insulator (SOI) type.

10. The method according to any one of claims 1 to 9, wherein the substrate (21) is made of silicon, the first sacrificial layer (22) is made of silicon oxide, and the first structural layer (23) is made of silicon.

11. The method according to any one of claims 1 to 10, wherein the second sacrificial layer (24) is made of silicon oxide.

12. The method according to any one of claims 1 to 11, wherein the thickness of the first structural layer (23) is between 100 nm and 10 μm.

13. An electroacoustic transducer (1), comprising: -frame; - The movable element (13) relative to the frame includes a diaphragm (131) and a structure (132) for rigidifying the diaphragm; - First transmission arm (141), movable element (13) coupled to the end of the first transmission arm (141); The diaphragm (131) is formed from a first portion (23a) of a first structural layer (23), the rigid structure (132) is formed from a first portion of a second structural layer (25) disposed on the first structural layer (23), and the frame includes a substrate (21), a second portion (23b) of the first structural layer (23), and a second portion of the second structural layer (25). An electroacoustic transducer wherein one of the first and second portions of the first structural layer (23) and / or one of the first and second portions of the second structural layer (25) has a plug (70, 80) facing the other of the first and second portions, the plug (70, 80) being located in the area (32) around the intersection of the position of the first transmission arm (141) and the periphery of the rigid structure (132).

14. The transducer according to claim 13, comprising a transmission device (14) for transmitting motion and force between a first region (11) and a second region (12) under a controlled atmosphere, the first region (11) and the second region (12) being hermetically isolated from each other, the transmission device (14) comprising, in addition to a first transmission arm (141) extending in the first region (11), a second transmission arm (142) extending in the second region (12).

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