JP2009147798A - Capacitor microphone and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitor microphone having improved sensitivity and frequency characteristics, and to provide a manufacturing method thereof. <P>SOLUTION: A capacitor microphone comprises: an insulating film including a plurality of holes through which sonic waves pass; a fixed electrode which is held by the insulating film and includes a plurality of holes through which sonic waves pass; a fixed part provided in the center on a rear side of the fixed electrode; and a diaphragm electrode which is disposed in parallel with the fixed electrode, of which only the center is fixed in the fixed electrode by the fixed part, which vibrates in response to sonic waves passing through the fixed electrode, and in which the amplitude of vibration increases toward the outer periphery from the center. The sonic wave is converted into a capacitance change between the fixed electrode and the diaphragm electrode and detected as an electric signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a highly sensitive condenser microphone manufactured using MEMS (Micro Electro Mechanical Systems) and a manufacturing method thereof.

  In recent years, condenser microphones manufactured using MEMS technology have been replaced by electret condenser microphones that have been used so far, thereby expanding the market. In particular, the use of condenser microphones is expanding in fields that require miniaturization and thinning. In this condenser microphone, a diaphragm electrode and a fixed electrode that are movable with respect to sound pressure are provided in parallel, and the diaphragm electrode is vibrated by the sound pressure to change the capacitance between the diaphragm electrode and the fixed electrode. Sound is converted into an electrical signal by converting it into a change. The sensitivity of this condenser microphone is proportional to the ratio (ΔCp / Cp) of the capacitance change (ΔCp) to the capacitance value (Cp) between the parallel plate electrodes at a certain sound pressure.

  FIG. 15 is a cross-sectional view of a conventional general condenser microphone, and FIG. 16 is a plan view thereof. 15 is a cross-sectional view showing a DD cross section of FIG. 16. A conventional general condenser microphone includes a substrate 41, a diaphragm electrode 42 provided on the substrate 41, and a fixed electrode 44 disposed in parallel with the diaphragm electrode 42 via a spacer 43. An insulating film 45 is provided on the fixed electrode 44. In a conventional general condenser microphone structure, the diaphragm electrode 42 is formed in a circular shape or a square shape, and is fixed around the diaphragm electrode 42 by, for example, a substrate 41 and / or a spacer 43. The diaphragm electrode 42 is connected to a diaphragm electrode lead electrode 46, and a diaphragm electrode portion 47 is formed. On the other hand, the fixed electrode 44 is connected to a fixed electrode lead electrode 48 to form a fixed electrode portion 49.

  In the conventional general condenser microphone, by making the diaphragm electrode 42 thin, the diaphragm electrode 42 is formed so as to be easily movable with respect to the sound pressure, and the capacitance change of the diaphragm electrode 42 is increased so that the sensitivity of the condenser microphone is increased. We are trying to improve. However, in the conventional general condenser microphone, since the periphery of the diaphragm electrode 42 is fixed, the capacitance change with respect to the sound pressure change is small in the peripheral portion of the diaphragm electrode 42 and the sensitivity of the condenser microphone is improved. It was difficult.

  Further, in the conventional general condenser microphone, when the tensile stress of the diaphragm film is large, the sensitivity of the condenser microphone is lowered. Therefore, when the tensile stress of the diaphragm film is reduced, the performance variation of the diaphragm electrode is increased, and the sensitivity variation is increased accordingly. On the other hand, when the stress of the diaphragm film is on the compression side, the diaphragm electrode is bent and does not operate as a condenser microphone. For this reason, there is a limit to reducing the tensile stress of the diaphragm film. On the other hand, the sensitivity can also be improved by making the diaphragm film thinner. However, when the diaphragm film is made thinner, the mechanical strength of the diaphragm electrode is also lowered, and there is a limit to making the diaphragm film thinner.

  Various attempts have been made to solve these problems. These attempts are briefly described below.

  In the condenser microphones of Patent Document 1 and Patent Document 2, a diaphragm electrode is held in an operating relationship via a clamp with respect to a fixed electrode having a large number of holes. Since the displacement at the periphery of the diaphragm electrode is restricted by the clamp and / or the spring, the sensitivity of the condenser microphone is improved.

  In the condenser microphone of Patent Document 3, the diaphragm electrode is suspended by a cross-shaped beam with respect to the fixed electrode. Since the cross-shaped beam portion does not operate with respect to sound pressure, there is a limitation in improving the sensitivity of the condenser microphone.

  In the condenser microphone of Patent Document 4, by increasing the resistivity around the diaphragm electrode, the surrounding capacitance is lowered, and the substantial capacitance change rate (ΔCp / Cp) is increased. However, the improvement in sensitivity is limited due to the stress of the diaphragm electrode.

  In the condenser microphone of Patent Document 5, the capacitance change rate (ΔCp / Cp) is increased by adopting a configuration in which a movable electrode is suspended by a diaphragm. However, there is a problem that the structure is complicated and manufacturing is difficult. In addition, since the periphery of the diaphragm is fixed, there is a limitation in improving the sensitivity.

In the condenser microphone of Non-Patent Document 1, it is proposed that gear-shaped fixed electrodes and gear-shaped diaphragm electrodes are alternately arranged. Since there is no fixed electrode portion at a position corresponding to the fixed and non-displaced portion of the diaphragm electrode, the capacity (Cp) inevitably decreases, and the capacity change rate (ΔCp / Cp) increases. However, although the sensitivity is improved as compared with the case where the entire periphery of the diaphragm electrode is fixed, the improvement of the sensitivity is limited because the periphery of the diaphragm electrode is still partially fixed.
Japanese Patent No. 3451593 JP-T-2004-506394 JP 2005-110204 A JP 2007-067659 A JP 2007-067483 A Seiji Hiraide, “The latest technology of Si microphones by acoustic manufacturers”, MENS International 2007, C7-1, June 7, 2007

  In the condenser microphone manufactured using the MEMS technology, in order to improve the sensitivity, various methods for fixing the diaphragm have been made, and various studies have been made on the tensile stress of the diaphragm and the thickness of the diaphragm. However, there is a trade-off problem for each, and solving this problem is an issue.

  The capacitance (Cp) of the capacitor microphone includes not only the capacitance between the parallel electrodes but also the pad electrode, the wiring, and the floating capacitance of the substrate. By reducing such stray capacitance, the capacitance change rate (ΔCp / Cp) can be increased and the sensitivity can be improved even with the same capacitance change (ΔCp). For this reason, in order to improve sensitivity, it has become a subject to reduce stray capacitance. In order to reduce the stray capacitance, it is necessary not only to devise the layout of the conventional condenser microphone but also to fundamentally study the basic structure of the condenser microphone.

  Furthermore, regarding the frequency characteristics of the condenser microphone, how to control the ventilation between the sound pressure sensing side and the back cavity via the diaphragm is a problem. If a vent is not provided, problems of atmospheric pressure change and noise generation at extremely low frequencies occur. However, if the vent is too large, there is a problem that the sensitivity at low sound is lowered.

  An object of the present invention is to solve these problems, and to provide a capacitor microphone having high sensitivity and excellent frequency characteristics and a method for manufacturing the same using MEMS technology.

  In order to achieve the above object, a condenser microphone according to the present invention includes an insulating film having a plurality of holes through which sound waves pass, a fixed electrode held by the insulating film and having a plurality of holes through which sound waves pass, and the fixed A fixed portion provided at the center of the back surface of the electrode, and arranged in parallel with the fixed electrode, only the central portion is fixed to the fixed electrode by the fixed portion, and receives and vibrates a sound wave that has passed through the fixed electrode; A diaphragm electrode that increases as the amplitude of vibration approaches the outer periphery from the center, and converts a sound wave into a capacitance change between the fixed electrode and the diaphragm electrode and detects it as an electrical signal. .

  The condenser microphone according to the present invention includes an insulating film having a plurality of holes through which sound waves pass, a fixed electrode having a plurality of holes held by the insulating film and through which sound waves pass, and a central portion of the back surface of the fixed electrode A fixed portion provided in the fixed electrode, and arranged in parallel with the fixed electrode, and only the central portion is fixed to the fixed electrode by the fixed portion, receives the sound wave that has passed through the fixed electrode, vibrates, and the amplitude of vibration starts from the center. A diaphragm electrode that increases as it approaches the outer periphery, and an outer electrode that is formed on the same plane as the diaphragm electrode and forms a vent between the diaphragm electrode, and transmits sound waves to the fixed electrode and the diaphragm electrode It is characterized in that it is detected as an electric signal after being converted into a capacitance change between and.

  The condenser microphone according to the present invention is the condenser microphone according to claim 1, wherein the condenser microphone is formed on the same plane as the fixed electrode, is electrically insulated from the fixed electrode, and the outer periphery of the fixed electrode from the fixed portion. It has a shape extending in a direction, and comprises an electrical connection part for a diaphragm electrode that is electrically connected to the diaphragm electrode through the fixed part.

  The method of manufacturing a condenser microphone according to the present invention includes a step of forming a first insulating film and a first conductive film on a surface of a substrate, and processing the first conductive film into a predetermined shape to form a diaphragm electrode shape. Forming a sacrificial layer on the first conductive film, forming a groove penetrating the sacrificial layer concentrically with the diaphragm electrode in the sacrificial layer, and the sacrificial layer Forming a second conductive film on the layer and in the groove; forming a shape of a fixed electrode and a shape of an electrical connection portion for the diaphragm electrode on the second conductive film; Forming a second insulating film on the second conductive film; and a plurality of holes reaching the sacrificial layer through the second insulating film and the second conductive film in the shape of the fixed electrode And forming the substrate by etching from the back surface of the substrate. Forming an opening having a larger area than the diaphragm electrode and reaching the first insulating film; and etching the plurality of holes and the opening of the substrate to form the first insulating film and the sacrificial layer. Forming a fixing portion for partially removing the diaphragm electrode to fix the fixed electrode, a spacer for supporting the fixed electrode on the substrate, and a vent. And

  The method of manufacturing a condenser microphone according to the present invention includes a step of forming a first insulating film and a first conductive film on a surface of a substrate, and penetrating the first conductive film into the first conductive film. A first groove is formed, a diaphragm electrode shape is formed inside the first groove, and an outer electrode shape provided on the same plane as the diaphragm electrode is formed outside the first groove. Forming a sacrificial layer on the first conductive film, filling the first groove penetrating the first conductive film with the sacrificial layer, and forming the diaphragm electrode in the sacrificial layer And forming a second groove penetrating the sacrificial layer, forming a second conductive film on the sacrificial layer and in the second groove, and the second conductive layer. The shape of the fixed electrode and the shape of the electrical connection part for the diaphragm electrode are formed on the conductive film. A step of forming a second insulating film on the second conductive film, the second insulating film and the second conductive film in the shape of the fixed electrode, and reaching the sacrificial layer. A step of forming a plurality of holes, a step of forming an opening reaching the first insulating film in the substrate, the area being larger than the diaphragm electrode, by etching from the back surface of the substrate, and the plurality of holes Etching from the opening of the substrate partially removes the first insulating film and the sacrificial layer, and fixes the diaphragm electrode to the fixed electrode; and the fixed electrode on the substrate. And a step of forming a ventilation hole.

  According to the present invention, since the diaphragm electrode is fixed only at the center and not fixed at the outer periphery of the diaphragm electrode, the amplitude of the vibration of the diaphragm electrode due to the sound wave increases from the center toward the outer periphery. For this reason, a large capacitance change is generated in the peripheral portion due to the sound pressure. Since the diaphragm electrode has a larger area in the periphery, the capacitance change rate (ΔCp / Cp) can be increased, and the sensitivity of the condenser microphone can be improved.

  According to the present invention, the diaphragm electrode is electrically connected to the extraction electrode for the diaphragm electrode through the fixing portion that fixes the diaphragm electrode at the center portion of the diaphragm electrode and the electrical connection portion that is in the same plane as the fixed electrode. Therefore, the structure around the outer periphery of the diaphragm electrode can be simplified. As a result, the stray capacitance can be reduced, and the capacitance (Cp) can be reduced even with the same diaphragm electrode area, and the capacitance change rate (ΔCp / Cp) can be increased to improve the sensitivity of the condenser microphone. Is possible.

  According to the present invention, it is possible to improve the processing accuracy of the vent hole provided between the substrate and the diaphragm electrode by using the film forming and lithography processes, so that the sound pressure sensing side via the diaphragm electrode can be improved. And control of ventilation between the back cavity and the back cavity. Thereby, it is possible to improve the acoustic characteristics of the condenser microphone by improving the frequency characteristics of the condenser microphone, reducing noise, and improving the sensitivity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, about the same component, the same referential mark is attached | subjected and description is abbreviate | omitted.

  A condenser microphone according to a first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing a condenser microphone according to the first embodiment of the present invention, FIG. 2 is a plan view showing the condenser microphone according to the first embodiment of the present invention, and FIG. Sectional drawing which shows the cross section of both the fixed electrode of the capacitor | condenser microphone which concerns on 1 embodiment, and the electrical connection part for diaphragm electrodes, FIG. 4 shows the cross section of the capacitor | condenser microphone which concerns on the 1st Embodiment of this invention from diagonally upward FIG. 5 is a perspective sectional view, FIG. 5 and FIG. 6 are diagrams showing a manufacturing process of the condenser microphone according to the first embodiment of the present invention. FIG. 7 is a manufacturing process of the condenser microphone according to the first embodiment of the present invention. It is a perspective view shown from diagonally upward.

  Here, FIG. 1 is a cross-sectional view showing the condenser microphone according to the first embodiment of the present invention viewed from the AA cross section of FIG. 2, and FIG. 3 is the present invention viewed from the BB cross section of FIG. It is sectional drawing which shows the condenser microphone which concerns on 1st Embodiment. FIG. 4 is a diagram showing the shape of the condenser microphone according to the first embodiment when the AA cross section of FIG. 2 is viewed obliquely from above.

  As shown in FIG. 1, the condenser microphone according to the first embodiment of the present invention includes a substrate 1 having an opening penetrating in the center, and a spacer 2 formed on the substrate 1 and having an opening penetrating in the center. The fixed electrode 4 formed on the spacer 2 and formed of the conductive film 3, the insulating film 5 formed on the fixed electrode 4 and holding the fixed electrode 4, and the insulating film 5 of the fixed electrode 4 are in contact with each other. The fixed part 6 installed in the center part of the surface on the opposite side to the surface has a diaphragm electrode 7 that is arranged in parallel with the fixed electrode 4 and that is fixed to the fixed electrode 4 only at the center part by the fixed part 6. The fixed electrode 4 and the insulating film 5 provided thereon are provided with a plurality of holes 8 penetrating the fixed electrode 4 and the insulating film 5. A gap 9 is formed between the fixed electrode 4 and the diaphragm electrode 7.

  The sound wave enters from the surface side of the insulating film 5 and passes through a plurality of holes 8 that penetrate the insulating film 5 and the fixed electrode 4. The diaphragm electrode 7 vibrates in response to the sound wave that has passed through the hole 8. The diaphragm electrode 7 is fixed to the fixed electrode 4 only at the center by the fixing portion 6 and is movable without being fixed at the outer periphery, so that the amplitude of vibration due to the sound wave increases as it approaches the outer periphery from the center. The condenser microphone according to the present embodiment operates by converting a capacitance change between the fixed electrode 4 and the diaphragm electrode 7 generated when the diaphragm electrode 7 receives a sound wave and vibrates into an electric signal. By providing the vent hole 10, the pressure difference between the space 9 and the cavity 11 can be eliminated.

  As shown in FIGS. 2 and 3, the conductive film 3 is separated into a fixed electrode 4 and a diaphragm electrode electrical connection portion 12 that is electrically insulated from the fixed electrode 4. The fixed electrode 4 has a surface area necessary for forming a pair of capacitors with the diaphragm electrode 7 and operating as a condenser microphone. The diaphragm electrode electrical connecting portion 12 has a shape extending from the center of the condenser microphone to the outer periphery, and has a smaller area than the fixed electrode 4. The fixing part 6 is made of an insulating material, and the conductive film 13 is formed on the side surface of the fixing part 6.

  The diaphragm electrode 7 is connected to the diaphragm electrode lead electrode 14 via the conductive film 13 formed on the side surface of the fixed portion 6 and the diaphragm electrode electrical connection portion 12, and the diaphragm electrode portion 15 is formed. On the other hand, the fixed electrode 4 is connected to a fixed electrode lead electrode 16 to form a fixed electrode portion 17. By electrically connecting the diaphragm electrode 7 through the conductive film 13 on the side surface of the fixed portion 6 and the diaphragm electrode electrical connecting portion 12, the structure in the vicinity of the outer periphery of the diaphragm electrode 7 is simplified, and the stray capacitance is reduced. It becomes possible to reduce.

  The case where the diaphragm electrode 7 is electrically connected to the diaphragm electrode lead electrode 14 via the diaphragm electrode electrical connection portion 12 in the same plane as the fixed electrode 4 has been described. The diaphragm electrode 7 is connected to the diaphragm electrode 7. You may make it electrically connect with the extraction electrode 14 for diaphragm electrodes through the electrical connection part in the same plane.

  In one example of the condenser microphone according to the first embodiment of the present invention, a silicon substrate 21 is used as the substrate 1, and the spacer 2 includes a sacrificial layer 24 made of a CVD oxide film on a thermal oxide film 22. The conductive film 3 and the insulating film 5 on the spacer 2 are respectively formed of a conductive polysilicon film and a silicon nitride film, and the fixing portion 6 is formed of a CVD oxide film. The conductive film 13 on the side surface may be formed of conductive polysilicon, and the diaphragm electrode 7 may be formed of conductive polysilicon.

  Next, with reference to FIG. 5, FIG. 6 and FIG. 7, a method for manufacturing a condenser microphone according to the first embodiment of the present invention will be described as an example of the condenser microphone according to this embodiment.

  The silicon substrate 21 is thermally oxidized on the silicon substrate 21 to form a thermal oxide film 22. On the thermal oxide film 22, a first conductive polysilicon film 23 to which impurities are added is formed. The first conductive polysilicon film 23 may be formed by depositing a polysilicon film while adding impurities, or using a known method such as ion implantation after forming a non-doped polysilicon film. The film may be formed accordingly. Thereafter, heat treatment is performed to adjust the stress (FIG. 5a).

  Next, the first conductive polysilicon film 23 is processed into the shape of the diaphragm electrode 7 using normal photolithography. Here, the case where the shape of the diaphragm electrode 7 is processed into a circle has been described. However, the shape of the diaphragm electrode is not limited to a circle, and may be any polygon, ellipse, or the like suitable for the operation of the diaphragm electrode according to the usage. (FIGS. 5b and 7a).

Next, the sacrificial layer 24 is formed. The sacrificial layer 24 is formed, for example, by depositing a silicon oxide (SiO ₂ ) film by a thermal CVD (Chemical Vapor Deposition) method (FIG. 5c).

  Next, in order to form a fixed portion for fixing the diaphragm electrode 7 to the fixed electrode at the center of the diaphragm electrode 7, a groove 24a penetrating the sacrifice layer 24 is formed, and the sacrifice layer 24 is located inside the groove 24a. The sacrificial layer 24b and the sacrificial layer 24c outside the groove 24a are separated. The groove 24a is formed in, for example, an annular shape, but is polygonal as long as it is a closed loop shape that separates the sacrificial layer 24 into a sacrificial layer 24b inside the groove 24a and a sacrificial layer 24c outside the groove 24a. May be formed in an arbitrary shape (FIGS. 5d and 7b). Here, the sacrificial layer 24b inside the groove 24a is not necessarily required, but it is preferable to leave the sacrificial layer 24b inside the groove 24a in order to increase the adhesive strength with the diaphragm electrode 7.

  Next, a second conductive polysilicon film 25 to which an impurity serving as a fixed electrode is added is formed. The second conductive polysilicon film 25 may be formed by depositing a polysilicon film while adding impurities, or using a known method such as ion implantation after forming a non-doped polysilicon film. An impurity may be added to form a film. Here, the second conductive polysilicon film 25 fills the groove 24a provided in the sacrificial layer 24, is electrically connected to the diaphragm electrode 7 at the bottom of the groove 24a, and the side wall of the sacrificial layer 24b inside the groove 24a. It is formed to cover. As shown in FIG. 1, the sacrificial layer 24b inside the groove 24a is processed into the fixing portion 6 in a later step, and the second conductive polysilicon film formed on the side wall of the sacrificial layer 24b inside the groove 24a. 25 (FIG. 1:13) electrically connects the diaphragm electrode 7 and the diaphragm electrode electrical connection (FIG. 1:12) (FIG. 5e, FIG. 1).

  Next, the second conductive polysilicon film 25 to be a fixed electrode is processed by etching. As shown in FIG. 7C, the second conductive polysilicon film 25 is separated and insulated into the fixed electrode 4 and the diaphragm electrode electrical connecting portion 12. The diaphragm electrode electrical connecting portion 12 is formed so as to include a center portion 12a having a diameter and area from the center larger than the groove 24a provided thereunder, and a connecting portion 12b connected to the center portion 12a and extending outward from the center. Is done. The diaphragm electrode electrical connecting portion 12 is connected to the diaphragm electrode lead electrode 14, and the fixed electrode 4 is connected to the fixed electrode lead electrode 16 (FIGS. 6a and 7c).

  Next, a silicon nitride film 26 is formed using a plasma CVD method. The silicon nitride film 26 carries the fixed electrode 4 and the diaphragm electrode electrical connecting portion 12. Next, as shown in FIG. 2, the silicon nitride film 26 is processed so that the second conductive polysilicon film is exposed on the surface to form the diaphragm electrode portion 15 and the fixed electrode portion 17 (FIG. 6b, Figure 2).

  Thereafter, a metal film is deposited and patterned to leave the metal film only on the diaphragm electrode portion 15 and the fixed electrode portion 17 to form a metal electrode (not shown). For example, an aluminum film can be used as the metal film.

  A plurality of holes 8 that penetrates both the silicon nitride film 26 and the second conductive polysilicon film 25 and reaches the sacrificial layer 24 are formed using normal photolithography. Thereby, the shape of the fixed electrode 4 with a hole through which the sound wave passes through the hole 8 to the diaphragm electrode 7 is formed (FIG. 6c). 2 and 4, a plurality of holes are also formed in the diaphragm electrode lead-out electrode 12, but these holes allow an etching solution to pass through when the sacrificial layer 24 described later is removed. It is formed.

  Next, the silicon substrate 21 is processed from the back surface of the silicon substrate 21 using an alkali solution, and an opening larger in diameter than the diaphragm electrode 7 reaching the thermal oxide film 22 is formed. Thereby, the cavity 11 is formed in the back surface of the silicon substrate 21 (FIG. 6c).

  The sacrificial layer 24 is partially removed through the holes 8 formed in the silicon nitride film 26 and the second conductive polysilicon film 25 by wet etching using a buffered hydrofluoric acid solution. At this time, the thermal oxide film 22 is also removed from the opening on the back surface of the silicon substrate 21, and the sacrificial layer 24 is also removed from this opening. The sacrificial layer 24b is not etched because it is protected by the polysilicon film 25 formed on the side wall of the sacrificial layer 24b. Thereby, the diaphragm electrode 7 is fixed to the central portion 12a of the diaphragm electrode electrical connecting portion 12 only by the central portion thereof by the fixing portion 6, and is processed into a shape in which the peripheral portion is not fixed. The gap 9 is formed between the fixed electrode 4 and the diaphragm electrode 7 by removing most of the sacrificial layer 24c outside the groove 24a by wet etching, but the outer peripheral portion remains without being removed, A spacer 2 is formed. In addition, the vent 10 is formed between the silicon substrate 21 and the diaphragm electrode 7 by this wet etching. By using the steps of film formation and photolithography, the vent can be formed with high accuracy, so that the acoustic performance of the condenser microphone can be improved (FIGS. 6d and 4).

  The operation of the condenser microphone according to the first embodiment of the present invention will be described in comparison with the operation of a conventional condenser microphone having a diaphragm electrode with a fixed peripheral portion shown in FIG.

  In order to compare the structure and operation of the condenser microphone according to the first embodiment and the conventional condenser microphone of FIG. 15, the displacement amount of the diaphragm electrode when a constant sound pressure is applied using the three-dimensional axial object method Was calculated. FIG. 8 shows an example of this calculation result. The displacement in the axial direction (Z direction) is shown as 1000 times so that the change in the vertical axis can be identified.

  As shown in FIG. 8A, in the condenser microphone according to the first embodiment, the central portion of the diaphragm electrode is fixed and the peripheral portion is not fixed, so that the peripheral portion is greatly displaced. On the other hand, as shown in FIG. 8B, in the conventional condenser microphone, the peripheral part of the diaphragm electrode is fixed and the central part is not fixed. Therefore, the central part is displaced, and the diaphragm electrode film has a sound pressure. Although it extends and changes in the axial direction (Z direction), the displacement of the central portion of the membrane of the diaphragm electrode is constrained by the fixed peripheral portion. Therefore, it can be seen that the amount of displacement of the central portion is considerably smaller than the amount of displacement of the peripheral portion that is freely displaced without being fixed according to the present invention.

  FIG. 9 shows a comparison of the maximum displacement amount with respect to the radius of the center fixed diaphragm electrode of the present invention and the conventional peripheral fixed diaphragm electrode at the same sound pressure. As shown in FIG. 9, the maximum displacement amount of the diaphragm electrode increases nonlinearly as the diameter of the diaphragm electrode increases. In any diameter, the maximum displacement amount of the center fixed type of the present invention is 5 to 7 times larger in the calculation range than the maximum displacement amount of the conventional peripheral fixed type, and this ratio ( (Magnification value) increases. As described above, the center fixed type of the present invention has an effect that the maximum displacement can be increased as the diameter of the diaphragm electrode is smaller than the conventional peripheral fixed type, which is very advantageous for downsizing the microphone. It is.

  Next, the sensitivity to the same sound pressure was compared between the actually created microphone of the present invention and the conventional microphone. FIG. 10 is an example of comparison of sensitivity. When the diaphragm electrode of the same diameter is used, the sensitivity of the center fixed type of the present invention is about 16 times larger than the sensitivity of the conventional peripheral fixed type. The effect of increasing sensitivity compared to the amount of displacement is greater because the area of the peripheral part is larger than the center part, and the present invention having a large amount of displacement in the peripheral part has a larger capacity change amount, This is probably because the microphone of the present invention has a very small stray capacitance. Thus, the sensitivity of the microphone can be increased by using the present invention. Further, if the sensitivity of the microphone is the same, the microphone can be miniaturized.

  A modification of the method for manufacturing the condenser microphone according to the first embodiment will be described. In the method of manufacturing the condenser microphone according to the first embodiment, the processing accuracy may be further improved by adding one more film to be stacked. For example, a silicon nitride film is formed on the thermal oxide film 22 by a CVD method. The silicon nitride film is removed larger than the diameter of the diaphragm electrode. A first conductive polysilicon film 23 is formed thereon and processed into a diaphragm electrode shape. After that, when the sacrificial layer 24c outside the groove 24a is removed according to the above-described process, a vent between the sound pressure sensing side of the diaphragm electrode and the cavity is formed between the diaphragm electrode and the silicon nitride film, Since the silicon nitride film and the diaphragm electrode are formed with the alignment accuracy from the front surface side of the substrate without being affected by the alignment between the silicon substrate and the back surface and the processing of thick silicon, the dimensional accuracy of the vent is further improved. Thereby, the variation in the dimension of the vent of the microphone can be reduced, the accuracy of the ventilation control between the sound pressure sensing side of the diaphragm electrode and the back surface cavity can be improved, and the acoustic performance of the condenser microphone can be improved.

  A condenser microphone according to a second embodiment of the present invention will be described. FIG. 11 is a cross-sectional view showing a condenser microphone according to a second embodiment of the present invention, FIG. 12 is a plan view showing a condenser microphone according to the second embodiment of the present invention, and FIGS. It is a figure which shows the manufacturing process of the condenser microphone which concerns on the 2nd Embodiment of invention. Here, FIG. 11 is a cross-sectional view showing a condenser microphone according to the second embodiment of the present invention as seen from the CC cross section of FIG.

  A condenser microphone according to a second embodiment of the present invention will be described with reference to FIGS. Note that the same components as those of the condenser microphone according to the first embodiment are denoted by the same reference numerals and description thereof is omitted. The condenser microphone according to the second embodiment of the present invention has an outer electrode 30 formed on the same plane as the diaphragm electrode 7 on the outside of the diaphragm electrode 7. A vent 31 is formed between the diaphragm electrode 7 and the outer electrode 30. In the condenser microphone according to the second embodiment of the present invention, the conductive film 32 may be provided on the side wall of the spacer 2. The respective effects of having the outer electrode 30 and the conductive film 32 on the side wall of the spacer 2 will be described in the following description of the method of manufacturing a condenser microphone according to the present embodiment.

  With reference to FIGS. 13 and 14, an example of a method for manufacturing a condenser microphone according to a second embodiment of the present invention will be described. Of the manufacturing steps of the condenser microphone according to the second embodiment, the same manufacturing steps as those of the first embodiment are not described.

  Similar to the first embodiment, the silicon substrate 21 is thermally oxidized on the silicon substrate 21 to form a thermal oxide film 22, and impurities are added on the thermal oxide film 22. A polysilicon film 23 is formed. Thereafter, heat treatment is performed to adjust the stress (FIG. 13a).

  Next, a groove 33a penetrating the first conductive polysilicon film 23 is formed in the first conductive polysilicon film 23 by using normal photolithography, and the first conductive polysilicon film inside the groove 33a is formed. 33b is processed into the shape of the diaphragm electrode 7. In the present embodiment, the groove 33a becomes the vent 31 (FIG. 11) between the sound pressure sensing side of the diaphragm electrode 7 and the cavity after the condenser microphone of the present embodiment is completed. The first conductive polysilicon film 33c outside the trench 33a later becomes the outer electrode 30 (FIG. 11). Here, the case of processing the shape of the diaphragm electrode into a circle has been described. However, the shape of the diaphragm electrode is not limited to a circle, and any closed loop such as a polygon or an ellipse suitable for the operation of the diaphragm electrode according to the usage. It may be formed into a shape. Depending on the shape of the diaphragm electrode, the groove 33a may be formed in an arbitrary shape (FIG. 13b).

  Next, as in the first embodiment, a sacrificial layer 24 is formed. The sacrificial layer 24 is formed, for example, by forming a silicon oxide film by a thermal CVD method. In the present embodiment, the groove 33a formed in the previous step is filled with a sacrificial layer (FIG. 13c).

  Next, a groove 34a penetrating the sacrificial layer 24 for forming the fixing portion 6 (FIG. 11) for fixing the diaphragm electrode 7 to the fixed electrode and a side wall spacer 32 (FIG. 11) are formed at the center of the diaphragm electrode 7. A groove 34b for forming, a sacrificial layer 24 with a sacrificial layer 34c inside the groove 34a, a sacrificial layer 34d between the groove 34a and the groove 34b, and a sacrificial layer 34e outside the groove 34b, The three are separated. Each of the grooves 34a and 34b is formed in an annular shape, for example, but may be formed in an arbitrary shape including a polygon as long as it is a closed loop shape separating the sacrificial layer 24 (FIG. 13d).

  Next, a second conductive polysilicon film 25 to be a fixed electrode to which impurities are added is formed. The second conductive polysilicon film 25 may be formed by depositing a polysilicon film while adding impurities, or using a known method such as ion implantation after forming a non-doped polysilicon film. An impurity may be added to form a film. Here, the inner groove 34a and the outer groove 34b provided in the sacrificial layer 24 are filled with the second conductive polysilicon film 25, and the second conductive polysilicon film 25 is a diaphragm electrode on the bottom surface of the groove 34a. 7 is formed so as to cover the side surface of the sacrificial layer 34c on the inside. The second conductive polysilicon film 25 is formed so as to be electrically connected to the outer electrode 30 at the bottom surface of the groove 34b and to cover the side wall of the sacrificial layer 34e on the outer side. As shown in FIG. 11, the second conductive polysilicon film formed on the side wall of the sacrificial layer 34 c inside the groove 34 a is a conductive material that electrically connects the diaphragm electrode 7 and the diaphragm electrode electrical connection portion 12. Film formation 13 is obtained. The second conductive polysilicon film formed on the side wall of the sacrificial layer 34 e electrically connects the fixed electrode 4 and the outer electrode 30. In addition, the second conductive polysilicon film formed on the side wall of the sacrificial layer 34e outside the trench 34b allows the sacrificial layer 34b outside the trench 34b to be removed when the sacrificial layer 34d located between the trench 34a and the trench 34b is removed. Side etching of the layer 34e is prevented, and the shape of the spacer 2 (FIG. 14d) is controlled. When the fixed electrode 4 and the outer electrode 30 are not electrically connected, the formation of the groove 34b may be omitted (FIGS. 13e and 11).

  Next, the same manufacturing process as that of the first embodiment shown in FIGS. 6A to 6C is performed (FIGS. 14a to 14c).

  Finally, the manufacturing process similar to the manufacturing process of the first embodiment shown in FIG. 6D is performed to form the condenser microphone according to the second embodiment. The final process of the second embodiment will be briefly described below.

  By performing wet etching with a buffered hydrofluoric acid solution from the openings of the plurality of holes 8 and the silicon substrate 21, the first conductive polysilicon film 23, the second conductive polysilicon film 25, and the conductive film 13 are used as protective films. The sacrificial layer 24 between them is partially removed to form a fixed portion 6 and a gap 9 for fixing the diaphragm electrode 7 to the fixed electrode 4. At the same time, a spacer 2 that supports the fixed electrode 4 on the substrate 1 is formed. In the case where the conductive film 32 is formed on the side wall of the sacrificial layer 34e outside the groove 34b, the spacer 2 is formed using the conductive film 32 as a protective film, so that the shape of the spacer 2 can be controlled. it can. In this step, the sacrificial layer 24 filling the groove 33a of the conductive film 23 is removed, and the vent 31 is formed (FIG. 14d).

  Next, specific effects of the condenser microphone and the manufacturing method thereof according to the second embodiment will be described.

  A vent 31 between the sound pressure sensing side of the diaphragm electrode 7 and the cavity 11 is formed by processing the first conductive polysilicon film 23 using lithography with the same mask from the surface side of the substrate. The This makes it possible to finely and accurately process the vent until the lithography limit is reached, and improve the dimensional system of the vent 31. As a result, variation in the dimensions of the vent 31 can be reduced, and the accuracy of vent control between the sound pressure sensing side of the diaphragm electrode 7 and the cavity 11 can be improved.

  In the present embodiment, the groove between the electrodes is formed in a circular shape, for example, but it is possible to optimize the characteristics by forming it into a polygonal shape or an arbitrary shape including a gear shape. It is. The width of the groove between the electrodes may be constant, but the width of the groove may be changed depending on the location in order to optimize the ventilation control.

  Further, in the second embodiment, it is possible to improve the processing accuracy of the vent 31 without increasing the number of film formations as in the modification of the first embodiment without complicating the manufacturing process. It becomes.

  In the second embodiment, the case where the outer electrode 30 and the fixed electrode 4 are electrically connected has been described. By electrically connecting the outer electrode 30 and the fixed electrode 4, the electric potential between the outer electrode 30 and the fixed electrode 4 is fixed, and an unstable factor of the electric potential is removed, and the periphery of the diaphragm electrode 7 (cap 9). Can be stabilized. Therefore, the outer electrode 30 may be electrically connected to the diaphragm electrode 7 instead of the fixed electrode 4, thereby eliminating the potential instability factor and reducing the potential around the diaphragm electrode 7 (cap 9). It becomes possible to stabilize.

  When the outer electrode 30 and the fixed electrode 4 are electrically connected, an electrostatic attractive force is generated between the outer electrode 30 and the diaphragm electrode 7 having a polarity opposite to that of the outer electrode 30 when the condenser microphone is actually used. Acts, and braking is applied to the operation of the diaphragm electrode 7. Applying braking to the operation of the diaphragm electrode 7 by electrostatic attraction has an adverse effect on improving the sensitivity of the condenser microphone. However, the braking applied to the operation of the diaphragm electrode 7 by electrostatic attraction causes an effect of protecting the diaphragm electrode 7 from physical vibration and acceleration generated in the diaphragm electrode during operation. By optimally designing the trade-off between the relationship between the electrostatic attractive force and the degree of freedom of operation of the diaphragm electrode 7, it is possible to realize a condenser microphone having sufficiently high sensitivity and mechanically strong.

It is sectional drawing which shows the condenser microphone which concerns on the 1st Embodiment of this invention. 1 is a plan view showing a condenser microphone according to a first embodiment of the present invention. It is sectional drawing which shows the stationary electrode of the capacitor | condenser microphone which concerns on the 1st Embodiment of this invention, and the electrical connection part for diaphragm electrodes. It is a perspective sectional view showing the section of the condenser microphone concerning a 1st embodiment of the present invention from the slanting upper part. It is a figure which shows the manufacturing process of the capacitor | condenser microphone which concerns on the 1st Embodiment of this invention. It is a figure which shows the manufacturing process of the capacitor | condenser microphone which concerns on the 1st Embodiment of this invention. It is a perspective view which shows the manufacturing process of the condenser microphone which concerns on the 1st Embodiment of this invention from diagonally upward. It is a figure which compares and shows the displacement amount of a diaphragm electrode when a fixed sound pressure is applied. It is a figure which compares and shows the maximum displacement amount with respect to the radius of the diaphragm electrode of this invention and the conventional diaphragm electrode in the same sound pressure. It is a figure which compares and shows the sensitivity with respect to the same sound pressure of the microphone of this invention and the conventional microphone. It is sectional drawing which shows the condenser microphone which concerns on the 2nd Embodiment of this invention. It is a top view which shows the condenser microphone which concerns on the 2nd Embodiment of this invention. It is a figure which shows the manufacturing process of the condenser microphone which concerns on the 2nd Embodiment of this invention. It is a figure which shows the manufacturing process of the condenser microphone which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the conventional common condenser microphone. It is a top view which shows the conventional common condenser microphone.

Explanation of symbols

1: Substrate, 2: Spacer, 3: Conductive film, 4: Fixed electrode, 5: Insulating film, 6: Fixed part, 7: Diaphragm electrode, 8: Hole, 9: Gap, 10: Vent, 11: Cavity Tee, 12: Electric connection part for diaphragm electrode, 13: Conductive film, 14: Extraction electrode for diaphragm electrode, 15: Diaphragm electrode part, 16: Extraction electrode for fixed electrode, 17: Fixed electrode part, 21: Silicon substrate, 22: thermal oxide film, 23: first conductive polysilicon film, 24: sacrificial layer, 24a: groove, 24b: sacrificial layer inside groove 24a, 24c: sacrificial layer outside groove 24a, 25: first 2 conductive polysilicon film, 26: silicon nitride film, 30: outer electrode, 31: vent hole, 32: conductive film, 33a: groove, 33b: first conductive polysilicon film inside groove 33a, 33c : Groove 33a First conductive polysilicon film on the outside, 34a, 34b: groove, 34c: sacrificial layer inside the groove 34a, 34d: sacrificial layer between the groove 34a and the groove 34b, 34e: outside the groove 34b Sacrificial layer, 41: substrate, 42: diaphragm electrode, 43: spacer, 44: fixed electrode, 45: insulating film, 46: extraction electrode for diaphragm electrode, 47: diaphragm electrode portion, 48: extraction electrode for fixed electrode, 49: Fixed electrode section

Claims (5)

An insulating film having a plurality of holes through which sound waves pass;
A fixed electrode held by the insulating film and having a plurality of holes through which sound waves pass;
A fixed portion provided at the center of the back surface of the fixed electrode;
Arranged in parallel with the fixed electrode, only the central part is fixed to the fixed electrode by the fixed part, vibrates in response to a sound wave that has passed through the fixed electrode, and the amplitude of the vibration increases from the center toward the outer periphery. A diaphragm electrode;
The condenser microphone is characterized in that a sound wave is converted into a change in capacitance between the fixed electrode and the diaphragm electrode and detected as an electric signal. An insulating film having a plurality of holes through which sound waves pass;
A fixed electrode held by the insulating film and having a plurality of holes through which sound waves pass;
A fixed portion provided at the center of the back surface of the fixed electrode;
Arranged in parallel with the fixed electrode, only the central part is fixed to the fixed electrode by the fixed part, vibrates in response to a sound wave that has passed through the fixed electrode, and the amplitude of the vibration increases from the center toward the outer periphery. A diaphragm electrode;
An outer electrode that is formed in the same plane as the diaphragm electrode, and that forms a vent between the diaphragm electrode;
The condenser microphone is characterized in that a sound wave is converted into a change in capacitance between the fixed electrode and the diaphragm electrode and detected as an electric signal.   It is formed on the same plane as the fixed electrode, is electrically insulated from the fixed electrode, has a shape extending from the fixed portion in the outer peripheral direction of the fixed electrode, and is electrically connected to the diaphragm electrode through the fixed portion. The condenser microphone according to claim 1, further comprising a diaphragm electrode electrical connection portion connected to the diaphragm. Forming a first insulating film and a first conductive film on the surface of the substrate;
Processing the first conductive film into a predetermined shape to form the shape of the diaphragm electrode;
Forming a sacrificial layer on the first conductive film;
Forming a groove penetrating the sacrificial layer concentrically with the diaphragm electrode in the sacrificial layer;
Forming a second conductive film on the sacrificial layer and in the groove;
Forming a shape of a fixed electrode and a shape of an electrical connection portion for a diaphragm electrode on the second conductive film;
Forming a second insulating film on the second conductive film;
Forming a plurality of holes reaching the sacrificial layer through the second insulating film and the second conductive film in the shape of the fixed electrode;
Etching from the back surface of the substrate to form an opening in the substrate that has a larger area than the diaphragm electrode and reaches the first insulating film;
Etching from the plurality of holes and the opening of the substrate to partially remove the first insulating film and the sacrificial layer, and to fix the diaphragm electrode to the fixed electrode; and the fixed electrode Forming a spacer and a vent for supporting the substrate on the substrate;
A method of manufacturing a condenser microphone. Forming a surface of the substrate, a first insulating film and a first conductive film;
A first groove penetrating the first conductive film is formed in the first conductive film, a shape of a diaphragm electrode is formed inside the first groove, and the first groove is formed outside the first groove. Forming the shape of the outer electrode provided in the same plane as the diaphragm electrode;
Depositing a sacrificial layer on the first conductive film, and filling the first groove penetrating the first conductive film with the sacrificial layer;
Forming a second groove penetrating the sacrificial layer concentrically with the diaphragm electrode in the sacrificial layer;
Forming a second conductive film on the sacrificial layer and in the second groove;
Forming a shape of a fixed electrode and a shape of an electrical connection portion for a diaphragm electrode on the second conductive film;
Forming a second insulating film on the second conductive film;
Forming a plurality of holes reaching the sacrificial layer through the second insulating film and the second conductive film in the shape of the fixed electrode;
Etching from the back surface of the substrate to form an opening in the substrate that has a larger area than the diaphragm electrode and reaches the first insulating film;
Etching from the plurality of holes and the opening of the substrate to partially remove the first insulating film and the sacrificial layer, and to fix the diaphragm electrode to the fixed electrode; and the fixed electrode Forming a spacer and a vent for supporting the substrate on the substrate;
A method for manufacturing a condenser microphone.

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