Method of manufacturing an electroacoustic transducer

Abstract

This invention relates to a method of manufacturing an 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) to which the movable element (13) is coupled; in this method, a shield (24b) is used to protect the rigid structure (132) during a step (S7) of etching a substrate (21), the etching of the substrate enabling the definition of the first transmission arm and reducing the weight of the movable element (13). The electroacoustic transducer of this invention is capable of eliminating 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 rapidly expanding 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 relative to 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 into a first region and at least one second transmission arm extending into 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 limiting 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] - A second sacrificial layer is formed on the first structural layer, the second sacrificial layer including a first separation portion and a second separation portion;

[0016] - A second structural layer is formed on the first structural layer and the second sacrificial layer;

[0017] - Etch the second structural layer to expose a first portion of the second sacrificial layer and to define a rigid structure for the movable element, wherein a second portion of the second sacrificial layer is encapsulated by the rigid structure;

[0018] - Etch the first structural layer to the first sacrificial layer to define a membrane for the movable element;

[0019] - Etching a first portion of the second sacrificial layer to expose a first surface of the membrane, and etching a portion of the first sacrificial layer to form a cavity extending beneath the rigid structure;

[0020] - Etching the substrate to define the first transmission arm and at least partially release the movable element when opening into the cavity, the second portion of the first sacrificial layer and the second sacrificial layer serve as a stop layer for etching;

[0021] - Etch the first sacrificial layer to expose the second opposing side of the membrane.

[0022] During the substrate etching step, a second portion of the second sacrificial layer encapsulated in the structure used to rigidify the diaphragm serves as a protective layer or shield to prevent etching of the rigid structure. This prevents (supplementary) air leakage through movable elements or pistons.

[0023] Because the second part of the second sacrificial layer can also reduce the overlap distance between the substrate and the rigid structure, the extrusion diaphragm damping phenomenon that causes mechanical noise is reduced.

[0024] Preferably, a second portion of the second sacrificial layer extends around the diaphragm of the movable element, covering more than 80% of the periphery of the movable element, and advantageously extends around the entire diaphragm of the movable element.

[0025] In a preferred embodiment of the manufacturing method, the second sacrificial layer further includes a third portion separate from the first and second portions. The third portion of the second sacrificial layer is arranged such that it is encapsulated by the remaining portion of the second structural layer after the step of etching the second structural layer, and the third portion of the second sacrificial layer also serves as a stop layer during the step of etching the substrate.

[0026] The third part of the second sacrificial layer is advantageously located near the intersection between the position of the first transmission arm and the periphery of the rigid structure.

[0027] The manufacturing method may further include the following steps after the step of etching the first sacrificial layer and the second sacrificial layer, and before the step of etching the substrate:

[0028] - A covering is arranged on the second structural layer, thereby forming a component; and

[0029] - Flip the component.

[0030] In addition to the features already mentioned in the preceding paragraphs, the manufacturing method according to the invention may have one or more of the following supplementary features, either individually or in combination with all its technically possible features:

[0031] - Simultaneously etch the first and second structural layers to define the diaphragm and rigid structure of the movable element;

[0032] - Stacks are multilayer structures of the silicon-on-insulator (SOI) type;

[0033] - The substrate is made of silicon, the first sacrificial layer is made of silicon oxide, and the first structural layer is made of silicon oxide;

[0034] - The second sacrificial layer is made of silicon oxide;

[0035] -The thickness of the first structural layer is between 100 nm and 10 μm;

[0036] - The rigid structure of the movable element is at least partially placed on the diaphragm; and

[0037] - The rigid structure of the movable element contacts the diaphragm.

[0038] A second aspect of the present invention relates to an electroacoustic transducer comprising:

[0039] -frame;

[0040] - The movable element relative to the frame includes a diaphragm and a structure for rigidifying the diaphragm;

[0041] - First transmission arm, with a movable element coupled to the end of the first transmission arm;

[0042] The membrane 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.

[0043] Furthermore, the overlap between the substrate and the rigid structure is less than 10 μm, and the distance is measured in the cross-section of the rigid structure.

[0044] 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 hermetically isolated from each other, the transmission means including a second transmission arm extending into the second region in addition to a first transmission arm extending into the first region.

[0045] The invention and its applications will be better understood by reading the following description and examining the accompanying drawings. Attached Figure Description

[0046] 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:

[0047] Figure 1 An example of an electroacoustic transducer comprising pistons connected to two first transmission arms is shown schematically and in part.

[0048] Figures 2A to 2H The manufacturing process is shown. Figure 1 The steps of a method for developing an electroacoustic transducer;

[0049] 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.

[0050] Figure 4A , Figure 4B , Figure 4C and Figure 4D A cross-sectional view showing the steps of a method for manufacturing an electroacoustic transducer according to the present invention, instead of Figure 2B , 2D The steps of 2E and 2G;

[0051] Figure 5 It has been completed. Figure 4D Following the steps, a partial perspective view of the electroacoustic transducer; and

[0052] Figure 6A and Figure 6B express Figure 4B and 4D Steps, along Figure 5 The section P shown is different from the section shown. Figure 4B and 4D The cross section.

[0053] For clarity, identical or similar elements in all the accompanying drawings are labeled with the same reference numerals. Detailed Implementation

[0054] Figure 1 An example of an electroacoustic transducer 1 of the capacitance sensing microphone type is shown, which seeks to simplify manufacturing.

[0055] 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.

[0056] 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.

[0057] The diaphragm 131 of piston 13 partially defines a reference volume, which is dominated by a reference pressure. It separates this reference volume from the cavity that opens to the external environment (here, air). Therefore, one side of diaphragm 131 bears the reference pressure, while the opposite side of diaphragm 131 bears atmospheric pressure (in the case of a microphone, it is desirable to detect changes in atmospheric pressure).

[0058] 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.

[0059] 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 measure the pressure difference between its two sides. They preferably include a movable electrode 151 and at least one fixed electrode arranged relative to the movable electrode 151. The electrodes form the armature of a capacitor whose capacitance varies according to the displacement of the piston 13.

[0060] 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.

[0061] 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 into a first region 11, at least one second transmission arm 142 extending into a second region 12, and at least one transmission shaft 143 extending partially into the first region 11 and partially into 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.

[0062] Each first transmission arm 141 includes a first end coupled to the piston 13 and a second opposite end coupled to the associated transmission shaft 143. Each second transmission arm 142 includes a first end coupled to the movable electrode 151 of the capacitance detection device 15 and a second opposite end coupled to the associated transmission shaft 143.

[0063] For example, the transmission shaft 143 is a straight cylindrical shape. The transmission arms 141-142 preferably have a beam shape 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.

[0064] 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 the first region 11 and the second region 12 at the level of the pivot joint 16. The blades 162 are dimensioned to be torsionalally deformable and to allow the transmission device 14 to rotate. They are preferably arranged in a diaphragmatic manner relative to the transmission shaft 143. Preferably, the sealing isolation element 161 is deformable under the action of rotational displacement of the transmission device 14.

[0065] The framework may specifically include a support (formed from a first substrate), a structural layer (e.g., made of silicon) disposed on the support, and a cover (e.g., formed from a second substrate) transferred onto the structural layer.

[0066] 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.

[0067] Figures 2A to 2H The figures show steps S1 to S8 of the method for manufacturing the electrostatic transducer 1. 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.

[0068] Figure 2A , Figure 2A The first step S1 includes providing a stacked layer 20 as starting material for manufacturing the transducer. The stacked layer 20 sequentially includes a substrate 21, a first sacrificial layer 22, and a first structural layer 23, also referred to as a "thin layer". The first sacrificial layer 22 and the first structural layer 23 are disposed on the so-called main surface (also referred to as the front surface) of the substrate 21.

[0069] Substrate 21 is used in particular for fabricating 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.

[0070] The first structural layer 23 is used to fabricate the diaphragm 131 of the piston 13. It can also be used to fabricate the sealing diaphragm 161 of the pivot joint 16 and / or the movable electrode 151 of the capacitance sensing device 15. Its thickness is less than the thickness of the substrate 21, preferably between 100 nm and 10 μm, for example, equal to 1 μm. It is preferably made of the same material as the substrate, such as silicon.

[0071] 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 may be made 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.

[0072] Stack 20 can be a multilayer structure of silicon-on-insulator (SOI) type, commonly referred to as an SOI substrate.

[0073] Although not shown in the figure, the manufacturing method may then include the step of etching the first structural layer 23. This step of etching the first structural layer 23 may 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).

[0074] Figure 2B ,exist Figure 2B In step S2, 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.

[0075] 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, where the first structural layer 23 (not shown in the figure) has been pre-etched.

[0076] Figure 2C ,exist Figure 2CIn step S3, the second structural layer 25 is deposited on the first structural layer 23 (in the second region 20B of stack 20) ​​and the second sacrificial layer 24 (in the first region 20A of 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.

[0077] Figure 2D Then, in Figure 2D During step S4, 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., made of silicon oxide) serves as a stop layer for the etching of the second structural layer 25 (e.g., made of silicon), thus preserving the underlying first structural layer 23 (e.g., made of 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 into 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 uniquely relative to the first sacrificial layer 22), the first structural layer 23 and the second structural layer 25 are simultaneously etched downwards into the first sacrificial layer 22.

[0078] 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.

[0079] At the end of step S4, 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.

[0080] Figure 2D The etching technique used in step S4 is advantageously deep reactive ion etching (DRIE).

[0081] Figure 2E ,refer to Figure 2E The manufacturing method includes step S5, which involves 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 S5 can serve as the first step in releasing the piston 13.

[0082] 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 layers made of silicon oxide) of hydrofluoric acid (HF).

[0083] 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' within the first sacrificial layer 22. The etching can be precisely controlled so that the cavity 22' hardly extends.

[0084] 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).

[0085] Although not shown in the figures, the manufacturing method may then include the step of transferring a capping material onto the second structural layer 25, thereby forming a controlled atmosphere chamber, i.e., the second region 12. The capping material 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).

[0086] Figure 2F Then, in Figure 2F In step S6, 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.

[0087] Figure 2G , Figure 2G Step S7 includes etching (optionally thinning) the substrate 21 to the first sacrificial layer 22 to create a pathway to the piston 13, and to... 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.

[0088] 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 S5 (see...). Figure 2EThe etching in step S7 does not extend to the piston 13, which includes a first portion 23a (diaphragm 131) of the first structural layer 23 and a 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).

[0089] Finally, in step S8 (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 is then separated from the substrate 21. At the end of step S8, the piston 13 is freed. Therefore, step S8 can serve as a second step to release the piston 13.

[0090] 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 controlled time in a liquid or gas phase (in the case of layers made of silicon oxide) of hydrofluoric acid (HF).

[0091] Figure 3 In the second step S8 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 transferred onto the second structural layer 25 is shown.

[0092] The first region 31 located around the rigid structure 132 Figure 2H The middle section is shown as a cross-section.

[0093] The figure shows a vertical protrusion (i.e., perpendicular to the substrate) of the first transmission arm 141 traversing the periphery of the rigid structure 132 of the piston 13. However, a cavity 22' is found to be formed by etching the first sacrificial layer 22 in the vertical direction of this periphery.

[0094] Therefore, in the second region 32 of the stack around the intersection between the protrusion (or location) of the first transmission arm 141 and 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.

[0095] Furthermore, during the displacement of piston 13, air is compressed between rigid structure 132 and the remainder of substrate 21, and this extends almost the entire periphery of piston 13 (see [link]). Figure 2H &3). This air compression is due to the fact that the etched inner periphery of the piston 13 in the substrate 21 is inside. It is the source of the diaphragm damping phenomenon, which generates mechanical noise and leads to a degraded transducer performance. The force of this diaphragm damping phenomenon is inversely proportional to the cube of the overlap distance between the piston 13 and the frame (here, the remainder of the substrate 21).

[0096] Figure 4A , 4B Figures 4C and 4D illustrate different ways of steps S2, S4, S5, and S7 of the completed manufacturing method in cross-sectional views to limit air leakage between the first region and the reference volume while reducing damping phenomena.

[0097] Figure 4A , Figure 4A This refers to step S2, which describes the formation of the second sacrificial layer 24 on the first structural layer 23 of stack 20. Step S2 is performed such that the second sacrificial layer 24 includes a first portion 24a and a second portion 24b, which is different from the first portion 24a. Therefore, regarding... Figure 2B In step S2, the second sacrificial layer 24 comprises two distinct parts (at the level of the piston) instead of a single part.

[0098] The first portion 24a and the second portion 24b of the second sacrificial layer 24 are spaced apart from each other, such that the second structural layer 25, which is deposited later (and is intended to form a rigid structure 132), comes into contact with the first structural layer 23 (intended to form a membrane 131).

[0099] The first and second portions 24a-24b 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. This deposition can be conformal, such that the first and second portions 24a-24b have the same thickness. Alternatively, the deposition can be planarized if subsequently subjected to mechanical-chemical polishing.

[0100] Figure 4B , Figure 4B This refers to step S4, which involves etching the second structural layer 25 after the second structural layer 25 has been deposited on the first structural layer 23 and the second sacrificial layer 24, for example, by epitaxy ( Figure 2C Step S3). The second structural layer 25 is etched to expose the first portion 24a (piston relief) of the second sacrificial layer 24 and to define the rigid structure 132. Moreover, the rigid structure 132 is sized to completely cover the second portion 24b of the second sacrificial layer 24. Then, the second portion 24b of the second sacrificial layer 24 disposed on the first structural layer 23 is encapsulated by the rigid structure 132.

[0101] As previously referenced Figure 2D As described, the first structural layer 23 can be etched during the same step S4 to define the diaphragm 131 (this is typically the case when the first structural layer 23 and the second structural layer 25 are formed of the same material). The first structural layer 23 is thus divided into two parts: a first part 23a forming the diaphragm 131 of the piston and a second part 23b belonging to the transducer frame.

[0102] An alternative is to etch the second structural layer 25 and the first structural layer 23 separately using different etching chemicals when the second structural layer 25 and the first structural layer 23 are formed of different materials.

[0103] Figure 4C ,exist Figure 4C Step S5, for reference Figure 2E The second sacrificial layer 24 is etched in a manner described (etching is selective relative to the substrate 21, the first structural layer 23, and the second structural layer 25) until the first portion 24a is completely removed. Simultaneously, a portion of the first sacrificial layer 22 is etched, starting from the bottom of the trench corresponding to the periphery of the rigid structure 132, thereby forming a cavity 22'.

[0104] Since the second portion 24b of the second sacrificial layer 24 is surrounded by the material of the first structural layer 23 and the material of the second structural layer 25, it is unaffected by etching.

[0105] Cavity 22' extends below, but not beyond, the second portion 24b of the second sacrificial layer 24. The etching is actually time-controlled, such that the lateral ends of cavity 22 are aligned with the second portion 24b.

[0106] Figure 4D , Figure 4D Etching step S7 of substrate 21 may occur after cover transfer and / or component flipping. Figure 2F Step S6) makes it possible to approach the rear of piston 13 and to define the first transmission arm 141 (see step S6). Figure 3 ). and about Figure 2G The description method differs; substrate 21 is etched here to create openings into... Figure 4C The cavity 22' formed in step S5. As a result, piston 13 can now move freely.

[0107] Since the etching of substrate 21 is selective relative to the materials of the first sacrificial layer 22 and the second sacrificial layer 24, the etching does not propagate to the film 131 or the rigid structure 132. In fact, the second portion 24b of the first sacrificial layer 22 and the second sacrificial layer 24 serves as a stop layer for etching (the second portion 24b of the second sacrificial layer 24 is exposed by the etching of a portion of the first structural layer 23 and is not protected by the first sacrificial layer 22).

[0108] Therefore, the second portion 24b of the second sacrificial layer 24 not only limits leakage on either side of the piston and acts as a shield during the etching of the substrate 21, but also reduces the overlap distance d between the substrate 21 and the rigid structure 132. Then, relative to Figure 2G The configuration reduces diaphragm damping. Figure 4D The overlap distance d between the substrate 21 and the rigid structure 132 is measured parallel to the main surface of the substrate 21 in a cross-section; in other words, it is measured in the width direction of the rigid structure 132. Advantageously, it is less than 10 μm, preferably less than 6 μm. Figure 2G In such cases, the overlap distance is typically 15 μm.

[0109] The substrate 21 is advantageously etched in such a manner that it partially overlaps with the second portion 24b of the second sacrificial layer 24 after etching. Therefore, the edges of the rigid structure 132 are not cut off.

[0110] The manufacturing method is completed by step S8, which involves etching the first sacrificial layer 22, as per [reference to...]. Figure 2H As described, the second portion 24b of the second sacrificial layer 24 can be etched simultaneously (especially when it is formed of the same material).

[0111] Figure 5 This is a partial perspective view of the electroacoustic transducer after step S7, which involves etching the substrate 21. The second structural layer 25 has been made transparent.

[0112] The figure shows that a second portion 24b of the second sacrificial layer 24 lies beneath the rigid structure 132 and can extend around the diaphragm 131 over a large portion of the periphery of the piston 13, typically exceeding 80% of the periphery of the piston 13, and preferably exceeding 90%. Preferably, the second portion 24b covers the entire periphery of the diaphragm 131. In fact, the cavity 22' formed in the first sacrificial layer 22 extends along the periphery of the rigid structure 132. Therefore, the rigid structure 132 is preferably protected throughout the entire periphery of the piston 13 to minimize leakage.

[0113] When the second portion 24b of the second sacrificial layer 24 does not extend around the entire film (e.g., more than 80% of the periphery), the film 131 can be completely released only at the end of step S8, when the etching of the first sacrificial layer 22 is completed. In practice, a portion of the first sacrificial layer 22 can connect the film 131 to the substrate 21, such as... Figure 2G As shown (the etching of substrate 21 may not open into cavity 22' in the remaining 20% ​​of the periphery).

[0114] In the Figure 5 , 6A In the preferred embodiment of the manufacturing method indicated by 6B, the third portion 24c of the second sacrificial layer 24 is formed in step S2 (simultaneously formed with the first and second portions 24a-24b), and is encapsulated between the remaining portions of the first structural layer 23 and the second structural layer 25 in step S4 (see [link to previous section]). Figure 6A The third part 24c is different from the first and second parts 24a-24b, and is used to protect the remaining portion of the second structural layer 25 (belonging to the frame) during the etching of the substrate 2 (step S7); Figure 6B ).

[0115] refer to Figure 5 The substrate 21 is actually etched to define the first transmission arm 141. Then, two trenches 141' (here, straight) are formed on each side of the first transmission arm 141. These trenches 141' open into the cavity 22', and are known to extend along the first transmission arm 141 and intersect the periphery of the rigid structure 132.

[0116] Therefore, near the intersection between the first transmission arm 141 and the periphery of the rigid structure 132 (in other words, in the second region 32 of the stack, see...) Figure 3 The third portion 24c of the second sacrificial layer 24 is encapsulated by the remaining portion of the second structural layer 25 and serves exclusively as a shield against etching of the substrate 21 in this region. Therefore, it does not need to extend like the second portion 24b.

[0117] Figure 6A and 6BThe cross-sections of the electroacoustic transducer at the end of steps S4 and S7 are shown respectively, but along the line with... Figure 4B and 4D The cross sections are different and in Figure 5 The visible section P. Figure 6A and 6B The cross section P passes through one of the trenches 141' adjacent to the first transmission arm 141 (which is not present in any other part of the first transmission arm 141 or substrate 21). Figure 6B (The reasons in the middle).

[0118] like Figure 5 and 6B As shown, etching of substrate 21 results in supplemental etching of the second structural layer 25 between the second and third portions 24b-24c of the second sacrificial layer 24, which serves as a shield. The etched portion of the second structural layer 25 extends very little (a few square micrometers) because the etching occurs only perpendicular to the trench 141' that defines the first transmission arm 141. Therefore, supplemental air leakage is not significant, and the performance of the electroacoustic transducer remains unchanged.

[0119] The microphone has been tested using capacitance. Figure 1 Taking an example, a method for manufacturing an electroacoustic transducer according to the present invention is described, wherein one side of the transducer is subjected to atmospheric pressure and the other side to a reference pressure. However, regarding Figure 2A The manufacturing methods described in 2H and 4A-4D are applicable to other types of microphones and other types of electroacoustic transducers, especially loudspeakers (sound emitters) or ultrasonic emitters.

[0120] More typically, the microphone in the second region 12 (the controlled atmosphere chamber) 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).

[0121] 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 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 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); - A second sacrificial layer (24) is formed on the first structural layer (23), the second sacrificial layer (24) including a first separation portion (24a) and a second separation portion (24b), (S2); -A second structural layer (25) is formed on the first structural layer (23) and the second sacrificial layer (24), (S3); - Etch the second structural layer (25) to expose the first portion (24a) of the second sacrificial layer (24), and encapsulate the second portion (24b) of the second sacrificial layer (24) with the rigid structure (132) defining the movable element (13), (S4); - Etch the first structural layer (23) to the first sacrificial layer (22) to define the diaphragm (131) of the movable element (13), (S4); - Etch a first portion (24a) of the second sacrificial layer (24) to expose the first surface of the membrane (131), and etch a portion of the first sacrificial layer (22) to form a cavity (22') extending below the rigid structure (132), (S5); - Etching substrate (21) to define first transmission arm (141) and to at least partially release movable element (13) when opening into cavity, second portion (24b) of first sacrificial layer (22) and second sacrificial layer (24) serves as stop layer for etching (S7); - Etch the first sacrificial layer (22) to expose the second opposing surface of the film (131), (S8).

2. The method according to claim 1, wherein a second portion (24b) of the second sacrificial layer (24) extends more than 80% of the periphery of the movable element (13) around the diaphragm (131) of the movable element (13).

3. The method according to any one of claims 1 and 2, wherein the second sacrificial layer (24) further comprises a third portion (24c) separate from the first portion (24a) and the second portion (24b), the third portion of the second sacrificial layer being arranged such that after step (S4) of etching the second structural layer (25), it is encapsulated by the remaining portion of the second structural layer (25), and during step (S7) of etching the substrate (21), the third portion (24c) of the second sacrificial layer (24) also serves as a stop layer.

4. The method according to claim 3, wherein the third portion (24c) of the second sacrificial layer (24) is located near the intersection between the position of the first transmission arm (141) and the periphery of the rigid structure (132).

5. The method according to any one of claims 1 to 4, wherein the first structural layer (23) and the second structural layer (25) are etched simultaneously to define the diaphragm (131) and the rigid structure (132) of the movable element (13).

6. The method according to any one of claims 1 to 5, further comprising the following steps after step (S5) of etching the first sacrificial layer (22) and the second sacrificial layer (24), and before step (S7) of etching the substrate (21): - A covering (26) is arranged on the second structural layer (25), thereby forming a component; and - Flip the component, (S6).

7. The method according to any one of claims 1 to 6, wherein the stack (20) is a multilayer structure of the silicon-on-insulator (SOI) type.

8. The method according to any one of claims 1 to 7, 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.

9. The method according to any one of claims 1 to 8, wherein the second sacrificial layer (24) is made of silicon oxide.

10. The method according to any one of claims 1 to 9, wherein the first structural layer (23) has a thickness between 100 nm and 10 μm.

11. 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 membrane (131) is formed by a first portion (23a) of a first structural layer (23), the rigid structure is formed by 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); The overlap between the substrate (21) and the rigid structure (132) in the transducer is less than 10 μm by a distance (d), which is measured in the cross-section of the rigid structure (132).

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

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