JP2020022042A - MEMS microphone - Google Patents

Abstract

To provide a MEMS microphone whose characteristics are stabilized.SOLUTION: A temperature of an MEMS microphone 10 rises during its use, and an opposing surface 30a of a membrane 30 and an opposing surface 40a of a back plate 40 may be in a state where it is easily oxidized. However, in the MEMS microphone 10, since oxidation on the opposing surface 30a of the membrane 30 and the opposing surface 40a of the back plate 40 is suppressed by a passive film, changes in physical properties of the membrane 30 and the back plate 40 due to oxidation are suppressed. As a result, the characteristics are stabilized.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a MEMS microphone.

  In recent years, demand for ultra-small microphone modules including MEMS microphones has been increasing. For example, Patent Documents 1 to 3 below disclose a MEMS microphone having a configuration in which a membrane and a back plate are arranged to face each other via an air gap on a silicon substrate. In such a MEMS microphone, a capacitor structure is formed by the membrane and the back plate. When the membrane vibrates under the sound pressure, the capacitance of the capacitor structure changes. The change in capacitance is converted into an electric signal and amplified in the ASIC chip.

JP 2011-055087 A JP-A-2005-502693 JP 2007-295487 A

  In the above-described MEMS microphone, the surface of the membrane or the back plate may be oxidized with an increase in the temperature when the MEMS microphone is used (in particular, during continuous use). Such oxidation changes the physical properties of the membrane and the back plate, and may change the characteristics of the MEMS microphone. In particular, when the facing region of the membrane or the back plate is oxidized, the characteristics of the MEMS microphone change significantly.

  An object of the present invention is to provide a MEMS microphone whose characteristics are stabilized.

  A MEMS microphone according to one embodiment of the present invention includes a substrate having a through hole, a membrane that covers the through hole on one surface side of the substrate, and a through hole that covers the through hole on one surface side of the substrate. A plurality of layers including a back plate facing the back plate, a membrane, and a pair of terminal portions provided on the back plate, wherein the membrane includes a first passivation metal layer exposed on a facing surface facing the back plate. And the backplate has a multi-layer structure including a second passivating metal layer exposed on an opposing surface opposing the membrane, the passivation being on the opposing surface of the membrane and the opposing surface of the backplate. A film is formed.

  In the above MEMS microphone, a passivation film is formed on a facing surface of the membrane composed of the first passivation metal layer, and a back plate composed of the second passivation metal layer is opposed to the passivation film. A passive film is formed on the surface. Therefore, even when the temperature rises using the MEMS microphone, the situation where the facing surface of the membrane and the facing surface of the back plate are oxidized is suppressed. In the MEMS microphone, the oxidation is suppressed on the facing surface of the membrane and the facing surface of the back plate, thereby stabilizing characteristics.

  In a MEMS microphone according to another aspect, the first passivation metal layer and the second passivation metal layer are a metal selected from the group consisting of aluminum, chromium, titanium, and tantalum, or at least one selected from the group. It is composed of an alloy containing one type.

  According to the present invention, a MEMS microphone whose characteristics are stabilized is provided.

FIG. 1 is a schematic sectional view showing a microphone module according to one embodiment. FIG. 2 is a sectional view of the MEMS microphone shown in FIG. FIG. 3 is a plan view of the MEMS microphone shown in FIG. FIGS. 4A to 4C are views showing each step in manufacturing the MEMS microphone shown in FIG. FIGS. 5A to 5C are views showing each step in manufacturing the MEMS microphone shown in FIG. FIG. 6 is a diagram showing a passivation film formed on the surface of the membrane. FIG. 3 is a cross-sectional view illustrating a MEMS microphone of a mode different from that of FIG. 2. (A) to (c) of FIG. 8 are views showing each step in manufacturing the MEMS microphone shown in FIG. (A) to (c) of FIG. 9 are views showing each step in manufacturing the MEMS microphone shown in FIG.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. Note that the same or equivalent elements are denoted by the same reference numerals, and description thereof will be omitted if the description is duplicated.

  As shown in FIG. 1, the microphone module 1 according to the embodiment includes at least a module substrate 2, a control circuit chip 3 (ASIC), a cap 6, and a MEMS microphone 10.

  The module substrate 2 has a flat outer shape and is made of, for example, a ceramic material. The module substrate 2 may have a single-layer structure or a multi-layer structure including internal wiring. Terminal electrodes 4 and 5 are provided on one surface 2a and the other surface 2b of the module substrate 2, respectively. The terminal electrodes 4 and 5 are connected to each other via a through conductor (not shown) or an internal wiring.

  The MEMS microphone 10 is mounted on one surface 2a of the module substrate 2. The MEMS microphone 10 has a configuration in which a part thereof vibrates when receiving a sound pressure, and specifically has a structure shown in FIGS. 2 and 3. That is, the MEMS microphone 10 includes at least the substrate 20, the membrane 30, the back plate 40, and the pair of terminals 50A and 50B.

The substrate 20 has a rectangular flat outer shape, and is made of, for example, Si or quartz glass (SiO ₂ ). The thickness of the substrate 20 is, for example, 500 μm. As shown in FIG. 3, the substrate 20 can have a substantially square shape (for example, 1500 μm × 1500 μm) in plan view. The substrate 20 has a through hole 21 penetrating in the thickness direction of the substrate 20. The through hole 21 has, for example, a perfect circular shape in a plan view, and is provided in a central region of the substrate 20. The diameter of the through hole 21 is, for example, 1000 μm.

  The membrane 30 is also called a diaphragm, and is a film that vibrates due to sound pressure. The membrane 30 is located on the upper surface 20a side, which is one surface side of the substrate 20, and is directly overlaid on the upper surface 20a. The membrane 30 is provided so as to cover the entire through hole 21 of the substrate 20. The membrane 30 has a multi-layer structure, and has a two-layer structure in the present embodiment.

  The first layer 31 of the lower membrane 30 is made of an insulating material (SiN in the present embodiment). The thickness of the first layer 31 is, for example, 200 nm. The first layer 31 is provided over the entire upper surface 20 a of the substrate 20 including the through hole 21. The second layer 32 of the upper membrane 30 is composed of a passivating metal (Cr in this embodiment). The thickness of the second layer 32 is, for example, 100 nm. The second layer 32 is formed in a region corresponding to the through hole 21 of the substrate 20 and an edge region of the through hole 21 where one of the pair of terminal portions 50A and 50B (the terminal portion 50A in the present embodiment) is formed. , Are provided integrally.

  When the through hole 21 of the substrate 20 is completely closed by the membrane 30, a pressure difference may occur between the upper side and the lower side of the membrane 30. In this embodiment, a small through-hole 33 is provided in the membrane 30 to reduce such a pressure difference. A plurality of through holes 33 can be provided in the membrane 30.

  The back plate 40 is located on the upper surface 20 a side of the substrate 20 and is located above the membrane 30. The back plate 40 is provided so as to cover the entire through hole 21 of the substrate 20, similarly to the membrane 30. The back plate 40 faces the membrane 30 via the air gap G. More specifically, the facing surface 40a (the lower surface in FIG. 2) of the back plate 40 faces the facing surface 30a (the upper surface in FIG. 2) of the membrane 30 in a region where the through hole 21 of the substrate 20 is formed. The back plate 40 has a multi-layer structure like the membrane 30, and has a two-layer structure in the present embodiment.

  The first layer 41 of the lower back plate 40 is made of a passivating metal (Cr in this embodiment). The thickness of the first layer 41 is, for example, 300 nm. The second layer 42 of the back plate 40 located on the upper side is made of an insulator material (SiN in this embodiment). The thickness of the second layer 42 is, for example, 50 nm. The first layer 41 and the second layer 42 of the back plate 40 are a region corresponding to the through hole 21 of the substrate 20 and an edge region of the through hole 21 and the other of the pair of terminal portions 50A and 50B (this embodiment). Are integrally provided in the formation area of the terminal portion 50B). The second layer 42 of the back plate 40 is not provided in the region where the pair of terminal portions 50A and 50B are formed, and the second layer 32 of the membrane 30 and the back plate 40 are formed in the region where the pair of terminal portions 50A and 50B are formed. The first layer 41 is exposed. The back plate 40 has a plurality of holes 43. As shown in FIG. 3, it is preferable that each of the plurality of holes 43 has, for example, a perfect circular opening shape and is arranged regularly (in this embodiment, staggered).

  The pair of terminal portions 50A and 50B are made of a conductive material, and in this embodiment are made of Cu. Of the pair of terminal portions 50A and 50B, one terminal portion 50A is formed on the second layer 32 of the membrane 30 provided in the edge region of the through hole 21, and the other terminal portion 50B is formed on the through hole 21. It is formed on the first layer 41 of the back plate 40 provided in the edge region.

  As described above, in the MEMS microphone 10, the membrane 30 has the second layer 32 as a conductive layer, and the back plate 40 has the first layer 41 as a conductive layer. Therefore, in the MEMS microphone 10, a parallel plate type capacitor structure is formed by the membrane 30 and the back plate 40. When the membrane 30 vibrates due to sound pressure, the width of the air gap G between the membrane 30 and the back plate 40 changes, and the capacitance in the capacitor structure changes. The MEMS microphone 10 is a capacitance type microphone that outputs a change in the capacitance from a pair of terminals 50A and 50B.

  The control circuit chip 3 is mounted on one surface 2 a of the module substrate 2 so as to be close to the MEMS microphone 10. The above-described capacitance change is input to the control circuit chip 3 from the pair of terminal portions 50A and 50B of the MEMS microphone 10. In the present embodiment, the control circuit chip 3 and the MEMS microphone 10 are connected by wire bonding. The control circuit chip 3 has a function of converting a change in capacitance of the capacitor structure of the MEMS microphone 10 into an analog or digital electric signal and an amplifying function. The control circuit chip 3 is connected to a terminal electrode 4 provided on one surface 2 a of the module substrate 2, and a signal of the control circuit chip 3 is output to the outside via the terminal electrodes 4 and 5.

  The cap 6 has a hollow structure on the upper surface 20 a side of the substrate 20. Specifically, the cap 6 defines a cavity H between the cap 6 and the substrate 20, and the MEMS microphone 10 and the control circuit chip 3 are accommodated inside the cavity H. In the present embodiment, the cap 6 is a metal cap made of a metal material. The cap 6 is provided with a sound hole 6a connecting the outside and the cavity H.

  Next, a procedure for manufacturing the above-described MEMS microphone 10 will be described with reference to FIGS.

  When manufacturing the MEMS microphone 10, first, as shown in FIG. 4A, the first layer 31 of the membrane 30 and the first layer 31 on the upper surface 20 a of the flat substrate 20 in which the through-hole 21 is not formed. Two layers 32 are sequentially formed. The first layer 31 is formed by CVD of an insulator material (SiN in this embodiment). The second layer 32 is formed by sputtering a passivating metal (Cr in this embodiment). The first layer 31 and the second layer 32 can be patterned by a photoresist (not shown) and RIE.

  Next, as shown in FIG. 4B, a through hole 33 is provided in the membrane 30. The through hole 33 can be formed by, for example, RIE using a photoresist having an opening in the region of the through hole 33. The type of gas used for RIE is appropriately selected according to the material of the layer constituting the membrane 30. Thereafter, the entire surface is left in oxygen plasma for a predetermined time and subjected to oxygen plasma treatment, whereby the surface of the second layer 32 of the membrane 30 is passivated.

Further, as shown in FIG. 4C, a sacrifice layer 60 is formed in a region to be the air gap G described above. The sacrificial layer 60 is formed by, for example, CVD of SiO ₂ . The thickness of the sacrificial layer 60 is, for example, 2 μm. The sacrificial layer 60 can be patterned by a not-shown photoresist and RIE.

  Subsequently, as shown in FIG. 5A, a first layer 41 and a second layer 42 of the back plate 40 are sequentially formed. The first layer 41 is formed by sputtering a passivation metal (Cr in this embodiment). The second layer 42 is formed by CVD of an insulator material (in the present embodiment, SiN). The first layer 41 and the second layer 42 can be patterned by a not-shown photoresist and RIE.

  In addition, as shown in FIG. 5B, a pair of terminal portions 50A and 50B are formed. Specifically, the terminal unit 50A is formed on the second layer 32 of the membrane 30 and the terminal unit 50B is formed on the first layer 41 of the back plate 40. The terminal portions 50A and 50B are formed by sputtering a conductive material (Cu in the present embodiment). The terminal portions 50A and 50B can be patterned by a not-shown photoresist and RIE.

  Further, as shown in FIG. 5C, a through hole 21 is formed in the substrate 20 by etching. The through holes 21 are formed by wet etching using buffered hydrofluoric acid (BHF). The through holes 21 can also be formed by dry etching using hydrogen fluoride (HF) vapor. At the time of etching, the entire upper surface 20a of the substrate 20 and the lower surface 20b other than the region where the through holes 21 are formed are covered with a photoresist or the like. Further, an SiN layer having a thickness of about 50 nm may be formed on the upper surface 20a of the substrate 20 (below the membrane 30) as an etching stopper film. After the through-hole 21 is formed, a portion of the SiN layer exposed from the through-hole 21 can be removed by etching.

  Then, the sacrificial layer 60 is removed by etching. The sacrificial layer 60 is removed by wet etching using buffered hydrofluoric acid (BHF). The sacrificial layer 60 can be removed by dry etching using a vapor of hydrogen fluoride (HF). At the time of etching, the entire upper surface 20a and lower surface 20b of the substrate 20 other than the region where the sacrificial layer 60 is formed are covered with a photoresist or the like. Thereafter, the entire surface is left in oxygen plasma for a predetermined time and subjected to oxygen plasma treatment, whereby the surface of the first layer 41 of the back plate 40 is passivated.

  According to the procedure described above, the above-described MEMS microphone 10 is manufactured.

  In the MEMS microphone 10, the membrane 30 has a two-layer structure including the second layer (first passivation metal layer) 32 exposed on the facing surface 30a facing the back plate 40, as shown in FIG. As shown, a passivation film 32a is formed on the facing surface 30a side. Further, the back plate 40 has a two-layer structure including a first layer (second passivation metal layer) 41 exposed on the facing surface 40a facing the membrane 30, and the back plate 40 is provided on the facing surface 40a side. A passivation film similar to the passivation film 32a is formed.

  The temperature of the MEMS microphone 10 increases when the MEMS microphone 10 is used, and the MEMS microphone 10 may be in a situation where the facing surface 30a of the membrane 30 and the facing surface 40a of the back plate 40 are easily oxidized. However, in the MEMS microphone 10, since the oxidation on the opposing surface 30a of the membrane 30 and the opposing surface 40a of the back plate 40 is suppressed by the above-described passivation film, a change in the physical properties of the membrane 30 and the back plate 40 due to the oxidation is suppressed. As a result, the characteristics are stabilized.

  The passivation metal constituting the passivation metal layer (that is, the second layer 32 of the membrane 30 and the first layer of the back plate 40) is not only chromium but also aluminum, titanium, tantalum, or any of these. And alloys containing at least one of the following.

  Further, in the present embodiment, since the second layer 32 of the membrane 30 and the first layer 41 of the back plate 40 function as a conductive layer forming a capacitor structure, compared to a configuration in which a layer for suppressing oxidation is separately provided. Thus, the thickness of the membrane 30 and the back plate 40 is reduced.

  In the MEMS microphone 10, the membrane 30 and the back plate 40 can be configured such that the up and down positions are opposite to each other and the back plate 40 is directly overlaid on the upper surface 20 a of the substrate 20.

  In the MEMS microphone 10, the membrane 30 and the back plate 40 can be configured such that the up and down positions are opposite to each other and the back plate 40 is directly overlaid on the upper surface 20 a of the substrate 20.

  In the above-described embodiment, the MEMS microphone 10 including one back plate 40 has been described. However, as illustrated in FIG. 7, the MEMS microphone 10A may include two back plates 40A and 40B.

  In the MEMS microphone 10A, a first back plate 40A, a membrane 30, and a second back plate 40B are provided on the substrate 20. The first back plate 40A and the membrane 30 in the MEMS microphone 10A have the same configuration and positional relationship as the back plate 40 and the membrane 30 in the MEMS microphone 10 described above. The MEMS microphone 10A differs from the MEMS microphone 10 mainly in that a second back plate 40B is interposed between the substrate 20 and the membrane 30. The second back plate 40B has a layered structure in which the first back plate 40A is turned upside down. That is, in the second back plate 40B, the lower second layer 42 is made of an insulating material (SiN in the present embodiment), and the upper first layer 41 is made of a passivating metal (SiN). In this embodiment, it is composed of Cr). Then, a terminal portion 50C is formed on the first layer 41 of the second back plate 40B.

  In the MEMS microphone 10A, the membrane 30 faces the second back plate 40B via the air gap G1, and faces the first back plate 40A via the air gap G1.

  In the MEMS microphone 10A, two parallel plate capacitor structures are formed by the membrane 30 and the two back plates 40A and 40B. When the membrane 30 vibrates due to sound pressure, the width of the air gap G between the membrane 30 and the first back plate 40A changes, and the air gap G1 between the membrane 30 and the second back plate 40B. Changes in width. In the MEMS microphone 10A, a change in the capacitance of the capacitor structure due to a change in the width of the air gaps G1, G2 is output from the three terminals 50A, 50B, 50C. According to the MEMS microphone 10A, a higher SN ratio can be realized as compared with the MEMS microphone 10 described above.

  Also in the MEMS microphone 10A, similarly to the MEMS microphone 10, the second layer 32 exposed on the facing surface 30a of the membrane 30 and the first layer 41 exposed on the facing surface 40a of the back plate 40A are made of a passivating metal. , MEMS microphone 10 has the same effect as that described above.

  Next, a procedure for manufacturing the above-described MEMS microphone 10A will be described with reference to FIGS.

  When the MEMS microphone 10A is manufactured, first, as shown in FIG. 8A, the second back plate 40B has the second back plate 40B on the upper surface 20a of the flat substrate 20 in which the through-hole 21 is not formed. The layer 42 and the first layer 41 are sequentially formed. The first layer 41 is formed by sputtering a passivation metal (Cr in this embodiment). The second layer 42 is formed by CVD of an insulator material (in the present embodiment, SiN). The first layer 41 and the second layer 42 can be patterned by a not-shown photoresist and RIE. Thereafter, the entire surface is left in oxygen plasma for a predetermined time and subjected to oxygen plasma treatment, whereby the surface of the first layer 41 of the second back plate 40B is passivated. Note that an insulator film 34 is formed in the remaining region of the region where the second back plate 40B is formed for planarization of the surface. The insulator film 34 is formed by CVD of an insulator material (SiN in this embodiment). The insulator film 34 can also be patterned by a not-shown photoresist and RIE.

Next, as shown in FIG. 8B, each hole 43 of the second back plate 40B is filled with an insulator 61 (SiO _{2 in} this embodiment). The insulator 61 is obtained by depositing SiO ₂ by CVD and then polishing the surface by CMP.

Further, as shown in FIG. 8C, a sacrifice layer 62 is formed in a region to be the above-described air gap G1. The sacrificial layer 62 is formed, for example, by CVD of SiO ₂ . The thickness of the sacrificial layer 62 is, for example, 3 μm. The sacrificial layer 62 can be patterned by a not-shown photoresist and RIE. Note that the insulator film 35 is formed in the remaining region of the region where the sacrificial layer 62 is formed for planarization of the surface. The insulator film 35 is formed by CVD of an insulator material (in the present embodiment, SiN). The insulator film 35 can also be patterned by a not-shown photoresist and RIE. After the sacrifice layer 62 and the insulator film 35 are formed, the surfaces can be polished by CMP in order to planarize the surfaces of the sacrifice layer 62 and the insulator film 35.

  Then, on the sacrificial layer 62 and the insulator film 35, the membrane 30 and the first back plate 40A are formed in the same manner as the membrane 30 and the back plate 40 of the MEMS microphone 10. After the formation of the membrane 30 and the first back plate 40A, as shown in FIG. 9A, the second layer 32 and the back plate 40A of the membrane 30 in the region where the terminal portions 50A, 50B, 50C are formed. The first layer 41 of 40B is exposed.

  Then, as shown in FIG. 9B, the respective terminal portions 50A, 50B, 50C are formed. Specifically, the terminal portions 50A are formed on the second layer 32 of the membrane 30, and the terminal portions 50B and 50C are formed on the first layer 41 of the back plates 40A and 40B, respectively. The terminal portion 50C is formed by sputtering a conductive material (Cu in the present embodiment), like the terminal portions 50A and 50B. The terminal portions 50A, 50B, and 50C can be patterned by a photoresist (not shown) and RIE.

  Further, as shown in FIG. 9C, the through holes 21 are formed in the substrate 20 by etching, and the sacrificial layers 60 and 62 and the insulator 61 are removed by etching. The sacrificial layers 60 and 62 and the insulator 61 can be removed by wet etching using buffered hydrofluoric acid (BHF) or dry etching using hydrogen fluoride (HF) vapor. Thereafter, the whole is left in oxygen plasma for a predetermined time and subjected to oxygen plasma treatment, so that the surface of the second layer 32 of the membrane 30 and the surface of the first layer 41 of the first back plate 40A are separated. Passivated.

  According to the procedure described above, the above-described MEMS microphone 10A is manufactured.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made.

  For example, the membrane is not limited to a two-layer structure including a passivation metal layer and an insulator layer, and has a multilayer structure of three or more layers including a conductor layer and a non-conductor layer (semiconductor layer, insulator layer). Is also good. The back plate may have a multilayer structure of three or more layers including a conductive layer and a non-conductive layer. The order of lamination of the conductor layer and the non-conductor layer in the membrane and the back plate can be appropriately changed according to the characteristics required for the MEMS microphone as long as the passivation metal layer is exposed on the facing surface.

  The planar shape of the membrane, the back plate, and the through-hole of the MEMS microphone is not limited to a circle, and may be a polygonal shape or a rounded square shape.

  In order to prevent a phenomenon in which the membrane and the back plate do not come into contact with each other (so-called sticking), a projection extending toward the membrane may be provided on the facing surface side of the back plate.

DESCRIPTION OF SYMBOLS 1 ... Microphone module, 2 ... Module board, 3 ... Control circuit chip, 6 ... Cap, 10A ... MEMS microphone, 20 ... Substrate, 21 ... Through hole, 30 ... Membrane, 31 ... First layer, 32 ... Second Layers, 40, 40A, 40B: Back plate, 41: First layer, 42: Second layer, 50A, 50B, 50C: Terminal portion, 60, 62: Sacrificial layer, G, G1, G2: Air gap, H: cavity.

Claims (2)

A substrate having a through hole;
A membrane that covers the through hole on one side of the substrate,
A back plate that covers the through-hole on one surface side of the substrate, and faces the membrane via an air gap,
A pair of terminal portions provided on the membrane and the back plate,
The membrane has a multi-layer structure including a first passivation metal layer exposed on a facing surface facing the back plate;
The back plate has a multi-layer structure including a second passivation metal layer exposed on a facing surface facing the membrane,
A MEMS microphone, wherein a passivation film is formed on a facing surface of the membrane and a facing surface of the back plate. The first passivation metal layer and the second passivation metal layer are made of a metal selected from the group consisting of aluminum, chromium, titanium, and tantalum, or an alloy containing at least one selected from the group. The MEMS microphone of claim 1, wherein the MEMS microphone is configured.

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