JP3873630B2 - Manufacturing method of condenser microphone - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a small condenser microphone used for voice input to a hearing aid or the like, a manufacturing method thereof, and a voice input device such as a hearing aid.
[0002]
[Prior art]
A small microphone as an audio input element is currently mainly used for hearing aids. In the longevity society in the future, it is considered that the demand will increase more and more, but in order to meet the demand, miniaturized microphones are required to be further reduced in size and power consumption in the future. Silicon micromachining technology, on the other hand, is a technology that uses a semiconductor processing technology to fabricate a silicon substrate to produce a fine and high-precision three-dimensional structure / device. This technology is indispensable for manufacturing ultra-compact sensors and inkjet heads. It is. In recent years, many researchers have been conducting research and development of small microphones using micromachining technology from the viewpoint of miniaturizing microphones. As a conventional small condenser microphone, for example, “A HIGH SENSITIVITY POLYSILICON DIAPHRAGM CONDENSER MICROPHONE” Proc. As described in IEEE Micro Electro Mechanical Systems, 1998, pages 580-585, Hsu et al. From a back plate formed on a silicon substrate by a polysilicon thin film diaphragm and a boron highly doped and selective etching. The manufacturing technology of a small high-performance condenser microphone using a condenser as a detection unit is disclosed.
[0003]
[Problems to be solved by the invention]
However, the above-described small microphone has the following problems. In the microphone by Hsu et al., A polysilicon film formed by a low pressure CVD method is used as a diaphragm. In general, the internal stress of the polysilicon film can be adjusted, but the residual stress at the time of film formation is about 100 Pa, and even if doping and annealing treatments are performed as a treatment to alleviate this internal stress, the internal stress can be eliminated. It is difficult. In addition, when a polysilicon film is formed by a method such as low-pressure CVD using a dangerous gas such as monosilane (SiH ₄ ), incidental action items such as safety management of monosilane gas and detoxification of exhaust gas after CVD treatment occur. There is a problem that facility management becomes difficult.
[0004]
Therefore, the present invention solves the above-described problems, and its object is to provide a compact condenser microphone having an excellent diaphragm that eliminates internal stress without using a dangerous gas such as monosilane. Is to provide.
[0005]
Another object of the present invention is to provide an audio input device with excellent performance provided with this condenser microphone.
[0006]
[Means for Solving the Problems]
The capacitor microphone according to claim 1 is a capacitor microphone including a single crystal silicon substrate having a back plate and electrodes formed at a predetermined interval with respect to the back plate. Is doped with boron, a plurality of through holes are formed in the back plate, and boron is doped at a high concentration.
[0007]
For this reason, the condenser microphone according to the first aspect has a diaphragm formed by sputtering film formation and doped with boron, so that the internal stress can be eliminated and an excellent characteristic can be obtained.
[0008]
The diaphragm of the condenser microphone according to claim 2 is characterized in that the diaphragm is thinner than the back plate.
[0009]
For this reason, the condenser microphone according to the second aspect has an effect that, when receiving the sound pressure from the sound source, only the diaphragm vibrates according to the sound pressure, and a signal corresponding to the change in the capacitor capacity caused by the vibration can be output.
[0010]
The condenser microphone according to a third aspect is characterized in that the single crystal silicon substrate has a (100) plane orientation or a (110) plane orientation.
[0011]
For this reason, in the condenser microphone of claim 3, the bottom surface of the concave portion formed with high accuracy by alkali anisotropic etching becomes a back plate, and the back plate can have a high dimensional accuracy. Therefore, the condenser microphone as designed is reproduced. It has the effect of being well manufactured.
[0012]
The method of manufacturing the condenser microphone of the present invention includes:
A method of manufacturing a condenser microphone comprising a single crystal silicon substrate having a back plate and electrodes formed at a predetermined interval with respect to the back plate,
(A) forming a dope mask in which at least the portion corresponding to the back plate and through hole is an opening on the surface of the single crystal silicon substrate;
(B) doping boron with a high concentration to a predetermined depth in a portion where the surface of the single crystal silicon substrate is exposed;
(C) forming a sacrificial layer film that selectively etches the back plate and the diaphragm on the single crystal silicon substrate;
(D) forming a sputtered diaphragm on the sacrificial layer film and doping with boron;
(E) forming a recess having a predetermined depth by etching on the back surface of the single crystal silicon substrate;
(F) selectively etching the sacrificial layer film between the back plate and the diaphragm of the single crystal silicon substrate to form an arbitrarily separated space;
It is characterized by the following.
[0013]
For this reason, the method of claim 4 is to form highly uniform voids with an arbitrary sacrificial layer film thickness, and with high precision formed by high-concentration boron doping and high-precision etch stop by alkali etching. It is possible to form a condenser microphone having a simple back plate.
[0014]
According to a fifth aspect of the present invention, in the method for manufacturing a condenser microphone according to the fourth aspect, the boron doping method is a thermal diffusion method or an ion implantation method.
[0015]
For this reason, the method of claim 5 reliably causes an etch stop phenomenon in the portion that becomes the back plate when the unnecessary portion other than the back plate is etched away by alkali etching, and therefore the capacitor having a high-precision back plate. The microphone can be formed.
[0016]
A voice input device according to a sixth aspect includes the condenser microphone according to any one of the first to third aspects.
[0017]
For this reason, the voice input device according to the sixth aspect has an effect that the condenser microphone according to any one of the first to third aspects has the effect.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on examples.
[0019]
Example 1
FIG. 1 is a cross-sectional perspective view of the microphone 100 according to the first embodiment. The microphone 100 according to the first embodiment has a structure in which a multilayer film is formed on a single crystal silicon substrate, which is a structure necessary for constituting the microphone such as the diaphragm 102 and the back plate 103.
[0020]
A single-crystal silicon substrate 101 to be a microphone 100 is completed by, for example, a large number of silicon wafers formed on a 4-inch diameter silicon wafer being finally separated by means such as dicing. The size is 2 mm square on one side and the thickness is 500 μm. A large number of circular acoustic holes 106 having a diameter of 50 μm are formed on the back side of the single crystal silicon substrate corresponding to the bottoms of the recesses formed by the predetermined alkali anisotropic etching, and a square shape having a thickness of 13 μm and a side of 1 mm. A back plate 103, a lower electrode wiring 104 and a lower electrode pad 105 connected to the back plate 103 are formed. Further, a square diaphragm 102 having a thickness of 1.0 μm and a side of 1 mm, an upper electrode wiring 107 and an upper electrode pad 108 connected thereto are formed on the surface side of the single crystal silicon substrate.
[0021]
The diaphragm 102 and the back plate 103 are formed in parallel to each other with a gap 109 having a distance of 3 μm. A ground electrode 110 is formed on the surface side of the single crystal silicon substrate.
[0022]
FIG. 2 is a manufacturing process diagram of the microphone 100 according to the first embodiment.
[0023]
First, a 4-inch diameter single crystal silicon substrate 101 ((100) crystal plane orientation, thickness 500 μm) is thermally oxidized to form a 1 μm thick SiO ₂ film 201 serving as a mask for etching and doping on both sides thereof. Is patterned to form a circular acoustic hole 106 having a diameter of 50 μm (FIG. 2A).
[0024]
Next, doping is performed from the surface side of the single crystal silicon substrate. A solid boron diffusion source (not shown) is placed opposite to the single crystal silicon, and heat treatment is performed at 1175 ° C. for 15 hours. By this treatment, boron having a high concentration (concentration of 5 × 10 ¹⁹ atoms / cm ³ or more) is doped from the opening of the SiO ₂ film 201 to a region having a depth of 13 μm (FIG. 2B). Doping can be similarly processed by an ion implantation method or a method using a liquid diffusion source (using boron tribromide or the like). The SiO ₂ film 201 used as the doping mask is removed with a hydrofluoric acid solution after the doping is completed.
[0025]
Next, a SiO ₂ film 202 is formed by plasma CVD using TEOS (tetraethoxysilane) with a thickness of 3 μm as a sacrificial layer on the surface of the single crystal silicon substrate and a thickness of 1 μm as an etching mask on the back surface (FIG. 2 ( c)).
[0026]
Next, a Poly-Si film 102 having a thickness of 1 μm to be a diaphragm is formed by sputtering. Poly-Si is doped with boron to form an electrode. Doping can be performed in the same manner by an ion implantation method or a method using a liquid diffusion source (using boron tribromide or the like). As the last of the laminated film, the protective film 203 is formed again by TEOS-CVD to 1 μm (FIG. 2D).
[0027]
Next, the TEOS-SiO ₂ film 202 on the back surface side of the single crystal silicon substrate 101 is processed into a pattern corresponding to the recess 204, and alkaline etching, for example, an aqueous solution of TMAH (tetramethylammonium hydroxide) (25%, 80% The exposed silicon portion is etched at (° C.). Etching is performed in two stages. A high concentration aqueous solution is used in the first stage, and a low concentration aqueous solution is used in the second stage. Etching is stopped by the back plate 103 formed by doping at a high concentration. At this time, the portion selectively doped in the first step (b) remains as the back plate 103, and the portion not formed is etched to form the acoustic hole 106 (FIG. 2 (e)). .
[0028]
Next, in order to extract the electrode from the doping region on the surface of the single crystal silicon substrate, the TEOS-SiO ₂ protective film 203, the Poly-Si film diaphragm 102, and the TEOS-SiO ₂ sacrificial layer 202, which are stacked films, are etched in order, A take-out port is formed (FIG. 2 (f)).
[0029]
Next, in order to form a capacitor structure using the Poly-Si film diaphragm 102 and the back plate 103 as both electrodes on the surface side of the single crystal silicon substrate 101, the TEOS-SiO ₂ film 202 between them is removed, and the gap 109 is formed. Form. In this method, a hydrofluoric acid solution is prepared, the substrate is immersed, and the TEOS-SiO ₂ film 202 is etched through the acoustic holes selectively formed in the exposed back plate on the back side of the single crystal silicon 101 to form the void 109. . At this time, the TEOS-SiO ₂ protective film 203 is also etched at the same time so that only the diaphragm 102 and the back plate 103 are formed (FIG. 2G).
[0030]
Finally, the upper electrode pad 107 on the diaphragm side, the lower electrode pad 105 on the back plate side, and the ground electrode 110 are formed as pads that serve as extraction electrodes. The pad material is formed of a metal such as aluminum or gold (FIG. 2 (h)).
[0031]
Since the microphone of this embodiment is manufactured by micromachining, the dimensions of the diaphragm and the back plate (width, length, thickness, acoustic hole shape, dimensions, and arrangement) are also formed as designed. It is important for the condenser microphone that the gap distance and the dimensions of each part are constant, and as a result, a microphone with a stable output could be realized. Further, as described above, the thickness of the diaphragm 102 is very thin with respect to the thickness of the back plate 103, and since the acoustic holes having an appropriate shape and size are appropriately arranged on the back plate, the diaphragm is made from the sound source. When receiving sound pressure, only the diaphragm vibrates and deforms accordingly, and the change in capacitance between the diaphragm and the back plate is output as a signal. In the case of the present embodiment, the acoustic hole shape has been described as a cylindrical shape. However, if the acoustic characteristics of the acoustic hole are optimally designed, the microphone can be similarly formed even in a quadrangular prism shape. I can do it.
[0032]
(Example 2)
In this embodiment, an n-type single crystal silicon substrate having a (110) plane orientation is used as the single crystal silicon substrate 101 in place of the (100) plane single crystal silicon substrate. FIG. 3 shows the case of using the (100) -oriented single crystal silicon in the first embodiment of the present invention (FIG. 3A) and the case of using the (110) oriented single-crystal silicon substrate (FIG. 3). The shape of the concave part of (b)) is shown in comparison. In the second step, the recess 204 is formed by etching using an alkaline etchant. In any of the above cases, the (111) silicon crystal plane having a low etching rate serves as the side wall. In the case of a (100) silicon substrate, the surface of the recess 204 is composed of four (111) planes 302 that form 54.7 degrees with respect to the surface of the single crystal silicon substrate and a bottom surface 303 that is a (100) plane, 110) In the case of a silicon substrate, the surface of the recess 204 is four (111) planes 304 that form 90 degrees with respect to the silicon substrate surface, and two (111) planes 305 and (110) that also form 35 degrees. It consists of a bottom surface 306. In either case, the shape of the concave portion 204 with high accuracy based on the etching mask shape is realized by etching using an alkaline solution. In the second embodiment, a capacitor having the same performance as in the first embodiment is obtained by using the (110) silicon substrate as the single crystal silicon substrate 101 and performing the same steps as those described in the first embodiment. A microphone can be manufactured.
[0033]
FIG. 4 shows a perspective view of a hearing aid 300 as a voice input device including the condenser microphone 100 described above. The microphone 100 of the present invention is packaged in a portion indicated by a dotted line in the exterior member 301 of the hearing aid 300 so that the surface of the silicon substrate on which the diaphragm is formed faces the sound source direction. The diaphragm receives the sound pressure from the sound source and deforms according to the sound pressure, and takes out the change in electric capacity between the diaphragm and the back plate at that time as a signal corresponding to the sound pressure. The voice input device including the condenser microphone is not limited to this, and can be preferably used for a microphone portion of a mobile phone, for example.
[0034]
【The invention's effect】
As described above, according to the condenser microphone and the manufacturing method thereof according to the present invention, a small and high-performance condenser microphone having a high-accuracy diaphragm whose internal stress is appropriately adjusted can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional perspective view of a condenser microphone according to the present invention.
FIG. 2 is a cross-sectional view of a manufacturing process of a condenser microphone according to the present invention.
FIG. 3 is an explanatory diagram of the shape of a recess.
FIG. 4 is an explanatory diagram of a hearing aid according to the present invention.
[Explanation of symbols]
100 condenser microphone 101 single crystal silicon substrate 102 diaphragm 103 back plate 104 lower electrode wiring 105 lower electrode pad 106 acoustic hole 107 upper electrode wiring 108 upper electrode pad 109 gap 110 ground electrode 201 SiO ₂ film 202, 203 TEOS-SiO ₂ film 204 Recess 300 Hearing aid 301 Exterior member

Claims (1)

A method of manufacturing a condenser microphone comprising a single crystal silicon substrate having a back plate and electrodes formed at a predetermined interval with respect to the back plate,
(A) forming a dope mask in which at least the portion corresponding to the back plate and through hole is an opening on the surface of the single crystal silicon substrate;
(B) doping boron with a high concentration to a predetermined depth in a portion where the surface of the single crystal silicon substrate is exposed;
(C) forming a SiO ₂ film by plasma CVD on the single crystal silicon substrate as a sacrificial layer film that is selectively etched with respect to the back plate and the diaphragm;
(D) forming a Poly-Si film diaphragm by sputtering on the sacrificial layer film and doping with boron;
(E) forming a recess having a predetermined depth by etching on the back surface of the single crystal silicon substrate;
(F) selectively etching the sacrificial layer film between the back plate and the diaphragm of the single crystal silicon substrate to form an arbitrarily separated space;
A method of manufacturing a condenser microphone, comprising:

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