JP2008053400A - Electret condenser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electret condenser that has reliability in humidity-proofing properties and the like improved. <P>SOLUTION: The electret condenser includes a polysilicon film 115 used as a fixed electrode, a polysilicon film 102 opposite to the polysilicon film 115 with an air gap 125 inbetween and serves as a vibrating electrode, and a silicon oxide film 105, provided on a surface on the side of air gap 125 in the polysilicon 102 and used as an electret film. The area of the polysilicon film 102, used as an vibrating electrode, is smaller than that of the polysilicon film 115 used as the fixed electrode. A capacity generating section of the polysilicon film 115, used as the fixed electrode, has two or more tone holes 124 that are to be connected with the air gap 125. In addition, the non-capacity generating section of the polysilicon film 115, used as the fixed electrode, has two or more through-holes 126 that are to be connected to the air gap 125. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electret capacitor having a vibrating electrode, and more particularly to an electret capacitor formed using a MEMS (Micro Electro Mechanical System) technology.

Conventionally, organic polymer polymers such as FEP (fluorinated ethylene propylene copolymer) resin materials have been used as electret elements, which are derivatives having permanent electric polarization, applied to elements such as condenser microphones. It was. However, since these materials lack heat resistance, it is difficult to apply them as reflow elements when mounting on a substrate. Therefore, in recent years, an electret-type silicon microphone using a silicon oxide film using a microfabrication technique has been proposed in order to achieve thinning, miniaturization and high performance of the electret (see Patent Document 1).
JP 2002-186075 A

  However, since the electret type silicon microphone has an air gap structure with a thickness of several μm, moisture taken into the air gap is not fully released, and reliability such as moisture resistance and condensation resistance There is a problem.

  In view of the above, an object of the present invention is to provide an electret capacitor having improved reliability such as moisture resistance and condensation resistance.

  In order to achieve the above object, the inventors of the present invention provide a through-hole connected to the air gap in the upper electrode separately from the sound hole provided in the upper electrode (upper electrode) of the air gap. The inventors have devised an invention in which the opening area of the upper electrode is increased so that moisture taken into the air gap can be easily released without stagnation. In addition, in order to prevent the capacitance value of the electret capacitor from decreasing due to the through hole, the through hole is formed in the non-capacitance generating portion of the upper electrode (the portion of the upper electrode not facing the lower electrode (vibrating electrode)). Is desirable.

  Specifically, an electret capacitor according to the present invention includes a first electrode, a second electrode that can vibrate opposite to the first electrode with an air gap interposed therebetween, and a surface on the air gap side of the second electrode. The area of the second electrode is smaller than the area of the first electrode, and a plurality of sound holes are formed in the capacitance generating portion of the first electrode facing the second electrode. At least one through hole is provided to connect to the air gap in the non-capacitance generating portion that is provided so as to be connected to the air gap and is not opposed to the second electrode in the first electrode. .

  According to the electret capacitor of the present invention, the first electrode, that is, the upper electrode is provided with a through hole connected to the air gap separately from the sound hole. improves. For this reason, since retention of moisture taken into the air gap can be avoided, reliability such as moisture resistance and condensation resistance can be improved. In addition, since the through hole is provided in the non-capacitance generating portion of the upper electrode, it is possible to prevent a decrease in the capacitance value of the electret capacitor due to the through hole.

  In order to obtain the above effect more reliably, in the electret capacitor of the present invention, the opening area of the through hole is larger than the opening area of each sound hole, specifically, the opening diameter of the through hole is It is preferable that the opening diameter of the sound hole is 1.5 times or more (that is, the opening area of the through hole is twice or more the opening area of each sound hole).

  In order to obtain the above effect more reliably, in the electret capacitor of the present invention, it is preferable that the opening area per unit area of the non-capacitance generation unit is larger than the opening area per unit area of the capacitance generation unit. . In this case, the opening area of the through hole may be the same as the opening area of each sound hole. Further, the opening area of the through hole may be increased as the formation position of the through hole is separated from the capacity generation unit. For example, the opening diameter of the through hole may be increased in proportion to the distance between the through hole and the center of the capacitance generation unit, that is, the center of the second electrode (vibration electrode). The opening shape of the through hole is not particularly limited. For example, the opening shape of the through hole may be a square (square or rectangular), and the opening shape of each sound hole may be a circle.

  In order to obtain the above effect more reliably, in the electret condenser of the present invention, it is preferable that a water repellent treatment is performed on the inside of the air gap.

  Furthermore, in order to obtain the above effect more reliably, in the electret capacitor of the present invention, it is preferable that the upper surface and the lower surface of the electret film are covered with an insulating film, specifically, a silicon nitride film.

  In the electret capacitor of the present invention, if the electret film is a silicon oxide film, the electret film can be made thinner, smaller, and higher in performance.

  As described above, according to the present invention, since the non-capacitance generating portion of the first electrode, that is, the upper electrode is provided with a through hole connected to the air gap separately from the sound hole, the capacitance value of the electret capacitor Electret capacitors that improve the air gap air permeability by increasing the opening area of the upper electrode without reducing the resistance, thereby improving reliability such as moisture resistance and condensation resistance compared to conventional products. Obtainable. That is, various application devices equipped with the electret capacitors of the present invention having high reliability can be widely supplied to society.

(First embodiment)
Hereinafter, an electret capacitor according to a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1A is a plan view of an electret capacitor according to the first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along the line II of FIG. In FIG. 1A, illustrations other than main members are omitted for easy understanding of the description.

  As shown in FIGS. 1A and 1B, a vibration film (lower layer) is formed on a semiconductor substrate 100 having a removal region (hereinafter referred to as a membrane region) 123 in the center via a first silicon oxide film 101. (A laminate of the first conductive polysilicon film 102 and the upper second silicon oxide film 105) is provided so as to cover the membrane region 123. The first conductive polysilicon film 102 becomes a lower electrode (vibration electrode), and the second silicon oxide film 105 becomes an electret film. The lower and upper surfaces of the second silicon oxide film 105 are covered with a first silicon nitride film 104 and a second silicon nitride film 107, respectively. A fixed film (second conductive polysilicon film 115) is provided on the vibration film with an air gap 125 interposed therebetween. The second conductive polysilicon film 115 serves as an upper electrode (fixed electrode), and its lower surface and upper surface are covered with a third silicon nitride film 114 and a fourth silicon nitride film 117, respectively. The fixed film is held on the semiconductor substrate 100 by the third silicon oxide film 109, and the air gap 125 is a removal region of the third silicon oxide film 109.

  Further, as shown in FIGS. 1A and 1B, the area of the first conductive polysilicon film 102 serving as the vibration electrode is larger than the area of the second conductive polysilicon film 115 serving as the fixed electrode. small. In addition, a plurality of sound holes 124 are connected to the air gap 125 in the capacitance generating portion of the second conductive polysilicon film 115 serving as the fixed electrode facing the first conductive polysilicon film 102 serving as the vibration electrode. Is provided. Furthermore, a plurality of through holes 126 are formed in the non-capacitance generating portion of the second conductive polysilicon film 115 serving as the fixed electrode that is not opposed to the first conductive polysilicon film 102 serving as the vibration electrode. It is provided to connect.

  In the present embodiment, the opening area of each through hole 126 is larger than the opening area of each sound hole 124. In addition, an electrode pad 127 is provided at an end portion of the second conductive polysilicon film 115 serving as a fixed electrode.

  According to the present embodiment, since the second conductive polysilicon film 115 serving as the fixed electrode is provided with the through hole 126 connected to the air gap 125 in addition to the sound hole 124, the opening area of the fixed electrode is increased. The air permeability of the air gap 125 is improved. For this reason, since retention of moisture taken into the air gap 125 can be avoided, reliability such as moisture resistance and condensation resistance can be improved. Moreover, since the through-hole 126 is provided in the non-capacitance generating portion of the fixed electrode, it is possible to prevent a decrease in the capacitance value of the electret capacitor due to the through-hole 126.

  Moreover, according to this embodiment, since the opening area of each through-hole 126 is larger than the opening area of each sound hole 124, the said effect can be acquired more reliably. Here, the opening diameter of each through hole 126 is at least 1.5 times the opening diameter of each sound hole 124 (that is, the opening area of each through hole 126 is at least twice the opening area of each sound hole 124). Are preferred).

  In addition, according to the present embodiment, the lower surface and the upper surface of the second silicon oxide film 105 serving as the electret film are covered with the first silicon nitride film 104 and the second silicon nitride film 107, respectively. It can be obtained more reliably. Further, since the silicon oxide film is used as the electret film, the electret film can be thinned, miniaturized, and enhanced in performance.

  In the present embodiment, it is preferable that the inside of the air gap 125 is subjected to a water repellent treatment using, for example, HMDS (hexamethyle disilazane). If it does in this way, the above-mentioned effect can be acquired more certainly.

(Second Embodiment)
Hereinafter, an electret capacitor according to a second embodiment of the present invention will be described with reference to the drawings.

  Fig.2 (a) is a top view of the electret capacitor | condenser which concerns on the 2nd Embodiment of this invention, FIG.2 (b) is sectional drawing of the II-II line | wire of Fig.2 (a). In FIG. 2A, illustrations other than main members are omitted for easy understanding of the description. 2 (a) and 2 (b), the same components as those in the first embodiment shown in FIGS. 1 (a) and 1 (b) are denoted by the same reference numerals, and redundant description is omitted. .

  This embodiment is different from the first embodiment in that it is provided in the non-capacitance generating portion of the second conductive polysilicon film 115 serving as a fixed electrode, as shown in FIGS. The number and size of the through holes 126 to be formed. Specifically, in the present embodiment, a large number of through holes 126 that are smaller than those in the first embodiment are provided in comparison with the first embodiment. As a result, the opening area per unit area in the non-capacitance generating portion of the second conductive polysilicon film 115 serving as the fixed electrode is larger than that in the capacitance generating portion.

  According to the present embodiment, similarly to the first embodiment, the second conductive polysilicon film 115 serving as the fixed electrode is provided with the through hole 126 connected to the air gap 125 in addition to the sound hole 124. Therefore, the opening area of the fixed electrode is increased, and the air permeability of the air gap 125 is improved. For this reason, since retention of moisture taken into the air gap 125 can be avoided, reliability such as moisture resistance and condensation resistance can be improved. Moreover, since the through-hole 126 is provided in the non-capacitance generating portion of the fixed electrode, it is possible to prevent a decrease in the capacitance value of the electret capacitor due to the through-hole 126.

  In addition, according to the present embodiment, since the opening area per unit area in the non-capacitance generation portion of the second conductive polysilicon film 115 serving as the fixed electrode is larger than that in the capacitance generation portion, the above effect can be more reliably achieved. Obtainable. Here, the opening area (opening diameter) of each through hole 126 and the opening area (opening diameter) of each sound hole 124 may be set to be the same.

  Further, according to the present embodiment, similarly to the first embodiment, the lower surface and the upper surface of the second silicon oxide film 105 serving as the electret film are formed by the first silicon nitride film 104 and the second silicon nitride film 107, respectively. Since it is covered, the said effect can be acquired more reliably. Further, since the silicon oxide film is used as the electret film, the electret film can be thinned, miniaturized, and enhanced in performance.

  In the present embodiment, as in the first embodiment, it is preferable that water repellent treatment is performed on the inside of the air gap 125 by, for example, HMDS. If it does in this way, the above-mentioned effect can be acquired more certainly.

(Third embodiment)
Hereinafter, an electret capacitor according to a third embodiment of the present invention will be described with reference to the drawings.

  FIG. 3A is a plan view of an electret capacitor according to the third embodiment of the present invention, and FIG. 3B is a cross-sectional view taken along line III-III in FIG. In FIG. 3A, illustrations other than main members are omitted for easy understanding. 3 (a) and 3 (b), the same components as those in the first embodiment shown in FIGS. 1 (a) and 1 (b) are denoted by the same reference numerals, and redundant description is omitted. .

  This embodiment is different from the first embodiment in that it is provided in the non-capacitance generating portion of the second conductive polysilicon film 115 serving as a fixed electrode, as shown in FIGS. The number and size of the through holes 126 to be formed. Specifically, in the present embodiment, the opening area of the through hole 126 increases as the formation position of the through hole 126 moves away from the capacitance generating portion of the second conductive polysilicon film 115 serving as the fixed electrode. As a result, the opening area per unit area in the non-capacitance generating portion of the second conductive polysilicon film 115 serving as the fixed electrode is larger than that in the capacitance generating portion.

  According to the present embodiment, similarly to the first embodiment, the second conductive polysilicon film 115 serving as the fixed electrode is provided with the through hole 126 connected to the air gap 125 in addition to the sound hole 124. Therefore, the opening area of the fixed electrode is increased, and the air permeability of the air gap 125 is improved. For this reason, since retention of moisture taken into the air gap 125 can be avoided, reliability such as moisture resistance and condensation resistance can be improved. Moreover, since the through-hole 126 is provided in the non-capacitance generating portion of the fixed electrode, it is possible to prevent a decrease in the capacitance value of the electret capacitor due to the through-hole 126.

  In addition, according to the present embodiment, since the opening area per unit area in the non-capacitance generation portion of the second conductive polysilicon film 115 serving as the fixed electrode is larger than that in the capacitance generation portion, the above effect can be more reliably achieved. Obtainable. Here, the opening diameter of the through-hole 126 is increased in proportion to the distance between the through-hole 126 and the center of the capacity generation portion (that is, the center of the first conductive polysilicon film 102 serving as the vibration electrode). Also good.

  Further, according to the present embodiment, similarly to the first embodiment, the lower surface and the upper surface of the second silicon oxide film 105 serving as the electret film are formed by the first silicon nitride film 104 and the second silicon nitride film 107, respectively. Since it is covered, the said effect can be acquired more reliably. Further, since the silicon oxide film is used as the electret film, the electret film can be thinned, miniaturized, and enhanced in performance.

  In the present embodiment, as in the first embodiment, it is preferable that water repellent treatment is performed on the inside of the air gap 125 by, for example, HMDS. If it does in this way, the above-mentioned effect can be acquired more certainly.

(Fourth embodiment)
Hereinafter, an electret capacitor according to a fourth embodiment of the present invention will be described with reference to the drawings.

  FIG. 4A is a plan view of an electret capacitor according to the fourth embodiment of the present invention, and FIG. 4B is a cross-sectional view taken along the line IV-IV in FIG. In FIG. 4A, illustrations other than main members are omitted for easy understanding. 4 (a) and 4 (b), the same components as those in the first embodiment shown in FIGS. 1 (a) and 1 (b) are denoted by the same reference numerals, and redundant description is omitted. .

  This embodiment is different from the first embodiment in that it is provided in the non-capacitance generating portion of the second conductive polysilicon film 115 serving as a fixed electrode, as shown in FIGS. The number, shape and size of the through holes 126 to be formed. Specifically, in the present embodiment, a large number of through holes 126 that are smaller than those in the first embodiment are provided in comparison with the first embodiment. As a result, the opening area per unit area in the non-capacitance generating portion of the second conductive polysilicon film 115 serving as the fixed electrode is larger than that in the capacitance generating portion.

  According to the present embodiment, similarly to the first embodiment, the second conductive polysilicon film 115 serving as the fixed electrode is provided with the through hole 126 connected to the air gap 125 in addition to the sound hole 124. Therefore, the opening area of the fixed electrode is increased, and the air permeability of the air gap 125 is improved. For this reason, since retention of moisture taken into the air gap 125 can be avoided, reliability such as moisture resistance and condensation resistance can be improved. Moreover, since the through-hole 126 is provided in the non-capacitance generating portion of the fixed electrode, it is possible to prevent a decrease in the capacitance value of the electret capacitor due to the through-hole 126.

  In addition, according to the present embodiment, since the opening area per unit area in the non-capacitance generation portion of the second conductive polysilicon film 115 serving as the fixed electrode is larger than that in the capacitance generation portion, the above effect can be more reliably achieved. Obtainable. Here, the opening shape of the through-hole 126 is not particularly limited. For example, the opening shape of each through-hole 126 is set to be square (square or rectangular), and the opening shape of each sound hole 124 is set to be circular. May be.

  Further, according to the present embodiment, similarly to the first embodiment, the lower surface and the upper surface of the second silicon oxide film 105 serving as the electret film are formed by the first silicon nitride film 104 and the second silicon nitride film 107, respectively. Since it is covered, the said effect can be acquired more reliably. Further, since the silicon oxide film is used as the electret film, the electret film can be thinned, miniaturized, and enhanced in performance.

  In the present embodiment, as in the first embodiment, it is preferable that water repellent treatment is performed on the inside of the air gap 125 by, for example, HMDS. If it does in this way, the above-mentioned effect can be acquired more certainly.

(Fifth embodiment)
Hereinafter, an electret capacitor manufacturing method according to a fifth embodiment of the present invention will be described with reference to the drawings. In addition, this embodiment can be used as any manufacturing method of the electret capacitor of the said 1st-4th embodiment by adjusting only the mask layout for through-hole formation.

  5 (a), (b), FIG. 6 (a), (b), FIG. 7 (a), (b), FIG. 8 (a), (b), FIG. 9 (a), (b) and 10 (a) and 10 (b) are cross-sectional views showing respective steps of the electret capacitor manufacturing method of the present embodiment. In each of the above drawings, the resist film is not shown, and the same components as those in the first embodiment shown in FIGS. Description to be omitted is omitted.

First, as shown in FIG. For example, a protective oxide film (first silicon oxide film) having a thickness of, for example, about 1000 nm is formed on a P-type semiconductor substrate 100 made of a silicon single crystal having a specific resistance of about 10 to 15 Ω · cm and having a (100) plane as a main surface. 101 is formed. Next, on the protective oxide film 101, for example, a P-type polycrystalline polysilicon film (first conductive polysilicon film) having a phosphorus concentration of about 2 × 10 ^{20 to} 3 × 10 ²⁰ atoms / cm ^{3 serving} as a vibration electrode. ) 102 is grown to a thickness of, for example, about 300 nm using low pressure CVD (chemical vapor deposition). Next, after using the resist pattern formed by the first photolithography mask 103 to process the polycrystalline polysilicon film 102 into a vibrating electrode shape by dry etching, the resist pattern is peeled off. Subsequently, for example, a silicon nitride film (first silicon nitride film) 104 is grown as an insulating film over the entire surface of the substrate to a thickness of about 100 nm.

  In the step shown in FIG. 5A, the protective oxide film 101, the polycrystalline polysilicon film 102, and the silicon nitride film 104 are also formed on the back side of the substrate.

  Next, as shown in FIG. 5B, a second silicon oxide film 105 made of, for example, TEOS (tetraethylorthosilicate) is grown on the entire surface of the substrate by using, for example, low pressure CVD, for example, with a thickness of about 1000 nm. Subsequently, the second silicon oxide film 105 is processed into an electret shape by dry etching, for example, using the resist pattern formed by the second photolithography mask 106, and then the resist pattern is peeled off.

  In the step shown in FIG. 5B, the second silicon oxide film 105 is also formed on the back side of the substrate.

  Subsequently, as shown in FIG. 6A, for example, a silicon nitride film (second silicon nitride film) 107 is grown as an insulating film on the entire surface of the substrate to a thickness of about 100 nm. Next, the silicon nitride film 107 is processed into a predetermined shape by dry etching using the resist pattern formed by the third photolithography mask 108, and then the resist pattern is peeled off.

  In the step shown in FIG. 6A, the silicon nitride film 107 is also formed on the back side of the substrate.

  Next, as shown in FIG. 6B, a BPSG (boron-doped phospho-silicate glass) film, which is an atmospheric pressure CVD oxide film, is formed on the entire surface of the substrate as the third silicon oxide film 109 serving as a sacrificial layer, for example. A thickness of about 3000 nm is grown. The third silicon oxide film 109 is not formed on the back side of the substrate. Next, using a resist pattern formed by the fourth photolithography mask 110, a recess 111 having a depth of, for example, about 1500 nm is formed at a predetermined position of the third silicon oxide film 109, and then the resist pattern is peeled off. .

  Next, as shown in FIG. 7A, the third silicon oxide film 109 and the like are etched by using a resist pattern formed by the fifth photolithography mask 112, and a plurality of vibration electrodes are formed. An electrode pad opening 113 reaching the crystalline polysilicon film 102 is formed.

Next, as shown in FIG. 7B, for example, a silicon nitride film (third silicon nitride film) 114 is formed on the entire surface of the substrate as an insulating film, for example, with a thickness of about 100 nm. Subsequently, on the silicon nitride film 114, for example, a P-type polycrystalline polysilicon film (first electrode) having a phosphorus concentration of 1 × 10 ²⁰ to 2 × 10 ²⁰ atoms / cm ³ to be an upper electrode (fixed electrode) at the time of capacitance formation. 2 conductive polysilicon film) 115 is grown to a thickness of, eg, about 1000 nm using low pressure CVD. Next, a silicon nitride film 114 and polycrystalline polysilicon are formed by using a resist pattern (electrode pad formation region, sound hole formation region and through hole formation region are opened) formed by the sixth photolithography mask 116. After the film 115 is processed into a predetermined shape by dry etching, the resist pattern is peeled off.

  In the step shown in FIG. 7B, the silicon nitride film 114 and the polycrystalline polysilicon film 115 are also formed on the back side of the substrate.

  Next, as shown in FIG. 8A, a silicon nitride film (fourth silicon nitride film) 117 is formed on the entire surface of the substrate, for example, to a thickness of about 150 nm. Next, the silicon nitride film 117 is predetermined by dry etching using a resist pattern (electrode pad formation region, sound hole formation region, and through hole formation region are opened) formed by the seventh photolithography mask 118. After processing into a shape, the resist pattern is peeled off.

  In the step shown in FIG. 8A, the silicon nitride film 117 is also formed on the back side of the substrate. Hereinafter, the laminated film formed on the back side of the substrate at this time is referred to as a laminated film 120.

  Next, as shown in FIG. 8B, a fourth silicon oxide film 119 made of FSG (fluorine-doped silicate glass) as a protective film is grown on the entire surface of the substrate to a thickness of about 500 nm, for example.

  Next, as illustrated in FIG. 9A, for example, using a back grind equipment, the laminated film 120 formed on the back surface of the semiconductor substrate 100 is peeled to expose the back surface of the substrate. Next, as shown in FIG. 9B, after a fifth silicon oxide film 121 is grown as a protective film on the back surface side of the substrate, for example, to a thickness of about 500 nm, a resist formed by an eighth photolithography mask 122 is formed. The silicon oxide film 121 is processed into a predetermined shape by dry etching using a pattern (a central region on the back surface of the substrate is opened), and then the resist pattern is peeled off.

  Next, as shown in FIG. 10A, anisotropic etching is performed on the semiconductor substrate 100 using a chemical solution such as TMAH (tetramethyl ammonium hydroxide) using the silicon oxide film 121 as a protective film. As a result, a removal region (membrane region) 123 is formed in the central portion of the semiconductor substrate 100.

  Next, as shown in FIG. 10B, by immersing the semiconductor substrate 100 in, for example, an HF stock solution, a silicon oxide film 119 that is a protective film on the front surface side of the substrate and a silicon oxide film 121 that is a protective film on the back surface side of the substrate. Is removed by wet etching, and a predetermined portion of the third silicon oxide film 109 serving as a sacrificial layer is removed. As a result, the first conductive polysilicon film 102 (more precisely, the silicon oxide film 105 (covered by the silicon nitride films 104 and 107) serving as the electret film formed thereon) serving as the vibration electrode, and An air gap 125 is formed between the second conductive polysilicon film 115 serving as a fixed electrode. In addition, a plurality of sound holes 124 are connected to the air gap 125 in the capacitance generating portion facing the first conductive polysilicon film 102 serving as the vibration electrode in the second conductive polysilicon film 115 serving as the fixed electrode. It is formed. Further, a plurality of through holes 126 are connected to the air gap 125 in the non-capacitance generating portion that is not opposed to the first conductive polysilicon film 102 serving as the vibration electrode in the second conductive polysilicon film 115 serving as the fixed electrode. To be formed.

  Thereafter, the silicon oxide film 105 covered with the silicon nitride films 104 and 107 is charged and charged, thereby completing the electret capacitor having the electret film.

  According to the present embodiment described above, any of the electret capacitors of the first to fourth embodiments can be surely adjusted only by adjusting the layout of the through-hole forming masks (the photolithography masks 116 and 118). Can be formed.

  In each of the above embodiments, the second conductive polysilicon film 115 serving as the fixed electrode and the silicon covering the second conductive polysilicon film 115 are increased by increasing the number of through holes 126 of the non-capacitance forming portion or increasing the opening area thereof. There is a possibility that the tensile strength of the fixed film made of the nitride films 114 and 117 is affected. In this case, for example, by increasing the film thickness of the silicon nitride film 114 formed in FIG. 7B and the film thickness of the silicon nitride film 117 formed in FIG. It is possible to maintain the strength necessary for the fixing film.

  In each of the above embodiments, a P-type polycrystalline polysilicon film is formed as an electrode forming material. Instead, after forming a non-doped polycrystalline polysilicon film, ions are formed on the polysilicon film. An injection may be performed. Further, an N-type polysilicon film may be formed instead of the P-type polycrystalline polysilicon.

  In each of the above-described embodiments, the process has been described in a limited manner. For example, as a process for forming a silicon oxide film, any of compatible thermal oxidation and CVD may be used, for example, an etching process. Any of dry etching and wet etching having compatibility may be used.

  As described above, the electret capacitor of the present invention has heat resistance, moisture resistance, condensation resistance, and the like, and is useful for realizing a high-performance and small-sized MEMS having excellent reliability.

FIG. 1A is a plan view of an electret capacitor according to the first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along the line II of FIG. Fig.2 (a) is a top view of the electret capacitor | condenser which concerns on the 2nd Embodiment of this invention, FIG.2 (b) is sectional drawing of the II-II line | wire of Fig.2 (a). FIG. 3A is a plan view of an electret capacitor according to the third embodiment of the present invention, and FIG. 3B is a cross-sectional view taken along line III-III in FIG. FIG. 4A is a plan view of an electret capacitor according to the fourth embodiment of the present invention, and FIG. 4B is a cross-sectional view taken along the line IV-IV in FIG. 5 (a) and 5 (b) are cross-sectional views showing respective steps of the electret capacitor manufacturing method according to the fifth embodiment of the present invention. 6 (a) and 6 (b) are cross-sectional views showing respective steps of the electret capacitor manufacturing method according to the fifth embodiment of the present invention. 7 (a) and 7 (b) are cross-sectional views showing respective steps of the electret capacitor manufacturing method according to the fifth embodiment of the present invention. 8 (a) and 8 (b) are cross-sectional views showing respective steps of the electret capacitor manufacturing method according to the fifth embodiment of the present invention. FIGS. 9A and 9B are cross-sectional views showing the respective steps of the electret capacitor manufacturing method according to the fifth embodiment of the present invention. 10 (a) and 10 (b) are cross-sectional views showing respective steps of the electret capacitor manufacturing method according to the fifth embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Semiconductor substrate 101 1st silicon oxide film 102 1st electroconductive polysilicon film 103 1st photolithographic mask 104 1st silicon nitride film 105 2nd silicon oxide film 106 2nd photolithographic mask 107 Second silicon nitride film 108 Third photolithography mask 109 Third silicon oxide film 110 Fourth photolithography mask 111 Third silicon oxide film recess 112 Fifth photolithography mask 113 Electrode pad opening Part 114 Third silicon nitride film 115 Second conductive polysilicon film 116 Sixth photolithography mask 117 Fourth silicon nitride film 118 Seventh photolithography mask 119 Fourth silicon oxide film 120 Semiconductor substrate Back side laminated film 1 1 fifth silicon oxide film 122 eighth photolithographic mask 123 membrane area 124 sound hole 125 air gap 126 through hole 127 electrode pads of the

Claims (11)

A first electrode;
A oscillating second electrode facing the first electrode across an air gap;
An electret film provided on the air gap side surface of the second electrode,
The area of the second electrode is smaller than the area of the first electrode,
A plurality of sound holes are provided in the capacitance generating portion of the first electrode facing the second electrode so as to be connected to the air gap,
The electret capacitor characterized in that at least one through hole is provided in the non-capacitance generating portion of the first electrode that is not opposed to the second electrode so as to be connected to the air gap. In the electret capacitor of Claim 1,
An electret capacitor, wherein an opening area of the through hole is larger than an opening area of each sound hole. The electret capacitor according to claim 2,
The electret capacitor according to claim 1, wherein an opening diameter of the through hole is 1.5 times or more of an opening diameter of each sound hole. In the electret capacitor of Claim 1,
The electret capacitor according to claim 1, wherein an opening area per unit area of the non-capacitance generation unit is larger than an opening area per unit area of the capacitance generation unit. The electret capacitor according to claim 4,
The electret capacitor according to claim 1, wherein an opening area of the through hole is the same as an opening area of each sound hole. The electret capacitor according to claim 4,
The electret capacitor according to claim 1, wherein an opening area of the through hole is increased as a position where the through hole is formed is away from the capacitance generation unit. The electret capacitor according to claim 4,
The opening shape of the through hole is a square,
The electret capacitor characterized in that the opening shape of each sound hole is circular. In the electret capacitor according to any one of claims 1 to 7,
An electret condenser in which a water repellent treatment is performed on the inside of the air gap. In the electret capacitor according to any one of claims 1 to 8,
An electret capacitor, wherein an upper surface and a lower surface of the electret film are covered with an insulating film. The electret capacitor according to claim 9,
The electret capacitor according to claim 1, wherein the insulating film is a silicon nitride film. In the electret capacitor according to any one of claims 1 to 10,
The electret capacitor is characterized in that the electret film is a silicon oxide film.

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