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DESCRIPTION JP2007228345

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DESCRIPTION JP2007228345
To provide a condenser microphone with high sensitivity. A plate having a fixed electrode, a
support formed on the outside of the plate and supporting the plate, and a movable electrode, the
gap being formed between the plate and the plate And a diaphragm which is supported in a
supportive beam shape on the support portion and which is deformed into a bowl shape by a
sound wave and vibrates. [Selected figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone.
[0002]
Condenser microphones and acceleration sensors that can be manufactured by applying the
manufacturing process of semiconductor devices are known.
The condenser microphone has an electrode on each of the diaphragm and the plate that vibrates
by the sound wave, and the diaphragm and the plate are supported in a separated state by the
support. The condenser microphone is a condenser formed between electrodes (hereinafter
referred to as a microphone condenser). The change in capacitance due to the vibration of the
diaphragm in) is converted to an electrical signal and output. Patent Document 1 discloses a
condenser microphone in which an end portion of a diaphragm is fixed to a support portion all
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around. In the condenser microphone described in Patent Document 1, the near end portion
(near end portion means the portion near the end) of the entire circumference of the diaphragm.
Since the displacement of the diaphragm is hardly displaced, the sound amplitude of the evened
diaphragm across the diaphragm is small and sufficient sensitivity can not be obtained.
[0003]
JP 2002-95093 A
[0004]
The present invention has been made to solve the above-mentioned problems, and it is an object
of the present invention to provide a condenser microphone with high sensitivity.
[0005]
(1) A condenser microphone for achieving the above object comprises a plate having a fixed
electrode, a support formed on the outside of the plate and supporting the plate, and a movable
electrode And a diaphragm which is supported in the form of a double beam on the support
portion while forming an air gap therebetween, and which is deformed in a bowl shape by a
sound wave to vibrate.
Since the diaphragm is supported by the support portion in a double-supported beam shape, it is
deformed into a bowl shape by a sound wave and vibrates.
According to the diaphragm-like vibration of the diaphragm, the free end of the diaphragm is
displaced by the sound wave, so that the leveling of the diaphragm across the entire diaphragm
is made as compared with the substantially conical vibration of the diaphragm fixed at the entire
circumference. The amplitude of the sound wave is large. Here, the amplitude of the diaphragm
averaged over the entire diaphragm is the amplitude of a virtual capacitor in which the entire
diaphragm vibrates in parallel to the plate, and is a capacitive component that fluctuates due to
the sound of the microphone capacitor (hereinafter referred to as variable capacitance). It
represents. Since the variable capacitance of the microphone capacitor can be increased by
vibrating the diaphragm like a hook like this, the sensitivity of the condenser microphone can be
enhanced.
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[0006]
(2) A condenser microphone for achieving the above object comprises a plate having a fixed
electrode, a support formed on the outside of the plate and supporting the plate, and a movable
electrode And a diaphragm which is supported by the support portion to form an air gap
therebetween and vibrates by sound waves, the diaphragm being substantially rectangular, and a
pair of opposing end portions are fixed to the support portion, and are opposed The other set of
ends is freed from the support. The diaphragm is substantially square, and one set of opposing
ends is fixed to the support, and the other set of ends is freed from the support. The amplitude of
the sound wave leveled over the entire diaphragm of such a diaphragm is that the conventional
end is fixed to the whole circumference of the diaphragm by the sound wave displacement of the
other end separated from the support portion of the diaphragm. It is large compared with.
Therefore, by thus releasing the other end portion of the diaphragm from the support portion,
the amplitude of the sound wave leveled over the entire diaphragm of the diaphragm can be
increased, so that the sensitivity of the condenser microphone can be enhanced.
[0007]
(3) In the condenser microphone for achieving the above object, the diaphragm extends in a
wave-like manner from the central portion in the installation direction to the end portion of the
pair, and a spring portion which absorbs the residual stress of the central portion by
deformation. May be included. The spring portion is referred to as a central portion in the
direction in which the diaphragm is installed (hereinafter referred to as the central portion). ) To
a set of end portions fixed to the support portion, and absorbs residual stress in the central
portion of the diaphragm by deformation. In this way, by relaxing the residual stress in the
central portion of the diaphragm, the central portion of the diaphragm can be vibrated by the
sound wave with a large amplitude, so that the sensitivity of the condenser microphone can be
enhanced.
[0008]
(4) In the condenser microphone for achieving the above object, the diaphragm may be
substantially rectangular long in the installation direction. By mounting the diaphragm in the low
rigidity longitudinal direction, it is possible to increase the sound wave amplitude of the
diaphragm, so that the sensitivity of the condenser microphone can be enhanced.
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[0009]
(5) In the condenser microphone for achieving the above object, the plate three-dimensionally
intersects with the diaphragm inside the pair of ends of the diaphragm, and the end of the plate
on the diaphragm is the support portion It may be released from The plate intersects with the
diaphragm inside the set of ends of the diaphragm, the end of the plate on the diaphragm being
freed from the support. That is, the plate does not at least oppose the set of ends of the
diaphragm. As a result, even if the plate and the diaphragm are conductive, no capacitance is
generated between the pair of ends fixed to the support of the diaphragm and the plate. In this
way, a capacitance component that does not change due to the sound wave of the microphone
capacitor (hereinafter referred to as invariable capacitance). Can be reduced, so that the
sensitivity of the condenser microphone can be increased.
[0010]
(6) In the condenser microphone for achieving the above object, the diaphragm may be so
narrow that the width between the ends of the other set is separated from the end of the one set.
As described above, since the other end of the diaphragm is separated from the support portion,
it is called a portion near the end of the other diaphragm of the diaphragm (hereinafter referred
to as the other end of the other set). ) Is relieved. As a result, the near end of the other set of
diaphragms may hang relative to the inner portion. At this time, since the residual stress of the
other end of the other set is effectively relieved as it is separated from the one end fixed to the
support, the width of the hanging portion of the other end of the other end is one. The farther
from the end of the set, the wider it becomes. Therefore, in this condenser microphone, the width
between the ends of the other set of diaphragms is narrowed as the distance from the end of one
set is increased, thereby preventing the other set of the near end from hanging down.
[0011]
In the present specification, "formed on ..." means "formed directly on ..." and "... on an
intermediate" unless there is a technical hindrance. It is meant to include both of “form
through”.
[0012]
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Hereinafter, embodiments of the present invention will be described based on a plurality of
examples.
The components with the same reference numerals in the embodiments correspond to the
components of the other embodiments with the reference numbers. First Embodiment FIGS. 1
and 2 are schematic views showing the configuration of a condenser microphone according to a
first embodiment of the present invention. 1A is a cross-sectional view taken along line A1-A1 of
FIG. 2, and FIG. 1B is a cross-sectional view taken along line B1-B1 of FIG. FIG. 2B is a crosssectional view taken along the line B2-B2 of FIG.
[0013]
The condenser microphone 1 according to the first embodiment of the present invention is a socalled silicon microphone manufactured using a semiconductor manufacturing process. The
condenser microphone 1 includes a sound sensing unit depicted as a cross-sectional view in FIGS.
1A and 1B and a detection unit depicted as a circuit diagram in FIG. 1A. Hereinafter, the
configuration of the sound sensing unit, the configuration of the detection unit, and the method
of manufacturing the condenser microphone 1 will be described in this order.
[0014]
(Structure of Sound Sensing Unit) As shown in FIG. 1, the sound sensing unit of the condenser
microphone 1 has a diaphragm 10, a back plate 30, a support portion 40, and the like. The
diaphragm 10 is configured of a portion of the conductive film 122 which is not fixed to the
insulating film 110. The conductive film 122 is, for example, polycrystalline silicon (hereinafter
referred to as polysilicon). Etc.). The conductive film 122 also functions as a movable electrode.
The diaphragm 10 is substantially rectangular, and is supported by the support portion 40 in a
double support manner.
[0015]
Specifically, both end portions 10a in the longitudinal direction of the diaphragm 10 are fixed to
the support portion 40 (see FIG. 1B), and both end portions 10b in the lateral direction of the
diaphragm 10 are free from the support portion 40 (see FIG. 1 (A)). More specifically, both end
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portions 10a of the diaphragm 10 are fixed to both opposing wall surfaces 42a of the opening
42 formed in the support portion 40, and both end portions 10b of the diaphragm 10 and both
wall surfaces 42a of the opening 42 It is free from adjacent wall surfaces 42b. As described
above, by straddling the diaphragm 10 in the longitudinal direction of the support portion 40,
the diaphragm 10 can be vibrated by a sound wave with a large amplitude.
[0016]
Both ends 10a in the longitudinal direction of the diaphragm 10 correspond to "one set of ends"
described in the claims, and both ends 10b in the width direction of the diaphragm 10
correspond to "others of the other set". The longitudinal direction of the diaphragm 10
corresponds to the "construction direction" described in the claims. The shape of the diaphragm
10 may be a square, or may be a shape other than a square as long as there is no technical
obstacle. Specifically, for example, as shown in FIG. 3, both ends 10a of the diaphragm 10 may be
curved, and as shown in FIG. 4, both ends 10b of the diaphragm 10 may be curved. In addition,
the diaphragm 10 may be bridged to the support portion 40 in the short direction. In that case,
the short direction of the diaphragm 10 corresponds to the “construction direction” described
in the claims.
[0017]
The diaphragm 10 has a spring portion 12. The spring portion 12 is referred to as a central
portion in the longitudinal direction of the diaphragm 10 (hereinafter referred to as the central
portion. ) Extends from the end 10a to the end 10a. The spring portion 12 absorbs residual
stress in the central portion of the diaphragm 10 by deformation. Specifically, the spring portion
12 extends in response to the tensile stress in the central portion of the diaphragm 10 and
contracts in response to the compressive stress in the central portion of the diaphragm 10. The
spring portion 12 may have any shape as long as residual stress in the central portion of the
diaphragm 10 can be absorbed by deformation. For example, the spring portion 12 may be
undulated in the plate surface direction of the diaphragm 10.
[0018]
The back plate 30 as a plate is configured of a portion of the conductive film 140 which is not
fixed to the insulating film 130. The conductive film 140 is, for example, a semiconductor film
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such as polysilicon. The conductive film 140 also functions as a fixed electrode. The back plate
30 has a substantially rectangular shape, and is supported by the support portion 40 in a doublesupported beam shape, and intersects with the diaphragm 10 inside the both end portions 10 a
in the longitudinal direction of the diaphragm 10.
[0019]
Specifically, both end portions 30a of the back plate 30 in the longitudinal direction are fixed to
both wall surfaces 42b of the opening 42 (see FIG. 1A), and both end portions 30b of the back
plate 30 in the width direction are the opening 42. It is free from both wall surfaces 42a of (see
FIG. 1 (B)). That is, the back plate 30 is not at least opposed to the both ends 10 a which is the
fixed end of the diaphragm 10. As a result, the invariant capacity of the microphone capacitor
formed by the diaphragm 10 and the back plate 30 can be reduced, and the sensitivity of the
capacitor microphone 1 can be enhanced. Details will be described later.
[0020]
The back plate 30 has a plurality of through holes 32. Sound waves from the sound source pass
through the through holes 32 and are propagated to the diaphragm 10. The back plate 30 is not
limited to a rectangular shape, and may have any shape as long as there is no technical obstacle.
Also, the back plate 30 may be supported by the support portion 40 in any manner. For example,
the back plate 30 may extend over the support 40 in the lateral direction or may be fixed to the
support 40 all around.
[0021]
The supporting portion 40 includes a portion fixed to the insulating film 130 of the conductive
film 140, a portion fixed to the insulating film 110 of the conductive film 122, the insulating film
130, the conductive film 124, the insulating film 110, and the substrate 100. It consists of The
insulating film 110 and the insulating film 130 are oxide films such as SiO 2, the conductive film
124 is a semiconductor film such as polysilicon, and the substrate 100 is a single crystal silicon
substrate, for example. In the support portion 40, an opening 42 penetrating the substrate 100
and the insulating film 110 is formed. The opening 42 and the diaphragm 10 form a back cavity
of the condenser microphone 1.
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[0022]
The electrode 60 shown in FIG. 2 is an electrode for connecting the diaphragm 10 and the
detection unit. The electrode 60 is connected to the conductive film 122 through a conducting
wire 125 extending from the electrode 60 to the conductive film 122. The electrode 61 is an
electrode for connecting the back plate 30 and the detection unit. The electrode 61 is connected
to the conductive film 140 via a conducting wire 141 extending from the electrode 61 to the
conductive film 140.
[0023]
The electrode 62 is connected to the conductive film 124 through a conducting wire 126
extending from the electrode 62 to the conductive film 124 as shown in FIG. 10 (A4). The
conductive film 124 is electrically insulated from other conductive films, and is formed between
the back plate 30 and the substrate 100. The conductive film 124 can be used as a guard
electrode by applying the same voltage as the output voltage of the detection unit to the
electrode 62. Details will be described later.
[0024]
The condenser microphone 1 may be configured such that the diaphragm 10 is located closer to
the sound source than the back plate 30 and sound waves are directly propagated to the
diaphragm 10. In this case, the through hole 32 of the back plate 30 functions as a passage that
brings the air gap 50 formed between the diaphragm 10 and the back plate 30 into
communication with the back cavity.
[0025]
(Structure of Detection Unit) As shown in FIG. 1A, the diaphragm 10 is connected to the bias
power supply circuit 1000, and the back plate 30 is connected to the ground via the resistor
1002. The back plate 30 is also connected to the preamp 1010. The detection unit of the
condenser microphone 1 outputs a signal correlating to the voltage between the back plate 30
and the ground from the preamplifier 1010.
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[0026]
Specifically, for example, the lead wire 1004 connected to the output end of the bias power
supply circuit 1000 is connected to the electrode 60 and the substrate 100, and the lead wire
1006 connected to one end of the resistor 1002 is connected to the electrode 61 A lead wire
1008 connected to the other end of the resistor 1002 is connected to the ground of the
mounting substrate of the condenser microphone 1. As the resistor 1002, one having a large
resistance value is used. Specifically, the resistor 1002 desirably has an electrical resistance of
GΩ order. The lead wire 1006 connecting the back plate 30 and the resistor 1002 is also
connected to the input end of the preamplifier 1010. It is desirable to use a preamplifier with a
high input impedance as the preamplifier 1010.
[0027]
The conductive film 124 can be used as a guard electrode by applying the same voltage as the
output voltage of the detection unit to the electrode 62 as described above. The guard electrode
is an electrode for reducing parasitic capacitance generated between the conductive film 140
forming the back plate 30 and the substrate 100. Specifically, for example, in the case of using
the conductive film 124 as a guard electrode, a voltage follower circuit may be formed by the
preamplifier 1010 illustrated in FIG. 1A and an output end of the preamplifier 1010 may be
connected to the electrode 62. By setting the conductive film 140 and the conductive film 124
forming the back plate 30 to the same potential, parasitic capacitance generated between the
conductive film 140 and the conductive film 124 can be removed, and the conductive film 140
and the substrate 100 can be removed. The parasitic capacitance generated during the period
can be reduced.
[0028]
(Operation of Condenser Microphone) When the sound wave passes through the through hole 32
of the back plate 30 and propagates to the diaphragm 10, the diaphragm 10 vibrates by the
sound wave. When the diaphragm 10 vibrates, the vibration changes the distance between the
back plate 30 and the diaphragm 10, and the capacitance of the microphone capacitor formed by
the diaphragm 10 and the back plate 30 changes.
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[0029]
As described above, since the back plate 30 is connected to the resistor 1002 having a large
resistance value, even if the capacitance of the microphone capacitor changes due to the
vibration of the diaphragm 10, the charge accumulated in the microphone capacitor causes the
resistor 1002 to It hardly flows. That is, the charge stored in the microphone capacitor can be
regarded as not changing. Therefore, the change in capacitance of the microphone capacitor can
be taken out as a change in voltage between the back plate 30 and the ground.
[0030]
Thus, the condenser microphone 1 outputs an extremely slight change in the capacitance of the
microphone condenser as an electrical signal. That is, the capacitor microphone 1 converts a
change in sound pressure applied to the diaphragm 10 into a change in capacitance of the
microphone capacitor, and converts a change in capacitance of the microphone capacitor into a
change in voltage to change the sound pressure. Output a correlated electrical signal.
[0031]
FIG. 5 is a schematic view for explaining the vibration of the diaphragm 10 due to the sound
wave. As described above, since the diaphragm 10 is supported by the support portion 40 in a
double-supported beam shape, the diaphragm 10 is deformed into a bowl shape by a sound wave
and vibrates. Here, the wedge-like deformation of the diaphragm 10 is a deformation in which
each portion of the diaphragm 10 is displaced with a large amplitude as it is separated from the
both ends 10 a, and the amplitude becomes maximum at the center in the longitudinal direction
of the diaphragm 10. That is, in the wedge-shaped vibration of the diaphragm 10, the both end
portions 10b are also displaced at substantially the same amplitude as the center in the short
side direction where the distances from the both end portions 10a of the diaphragm 10 are
equal.
[0032]
Therefore, the vibration due to the wedge-like deformation of the diaphragm 10 is large
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compared to the vibration due to the substantially conical deformation of the conventional
circumferentially fixed diaphragm (see Patent Document 1). As described above, in the condenser
microphone 1, the sensitivity is enhanced by vibrating the diaphragm 10 in a bowl shape.
However, as the distance to the opening 42 increases, the displacement of both ends 10 b of the
diaphragm 10 may be smaller than the center in the short direction. However, the displacement
of the both ends 10b of the diaphragm 10 due to the sound wave is larger than that of the end of
the diaphragm fixed at the entire circumference. Therefore, even if the displacement of both ends
10b of the diaphragm 10 becomes smaller than the center in the lateral direction, the sensitivity
of the condenser microphone 1 is higher than that of the conventional condenser microphone.
[0033]
Furthermore, in the condenser microphone 1, as described above, the back plate 30 is not at
least opposed to the both ends 10 a which is the fixed end of the diaphragm 10. As a result, since
the invariant capacity of the microphone capacitor can be reduced, the sensitivity of the
condenser microphone 1 can be enhanced.
[0034]
However, when the width in the width direction of the back plate 30 is narrowed in order to
make the back plate 30 intersect the diaphragm 10 three-dimensionally at the inside of both end
portions 10 a in the longitudinal direction of the diaphragm 10, the area where the diaphragm
10 and the back plate 30 oppose each other Reduces the capacitance of the microphone
capacitor. As a result, the noise of the condenser microphone 1 increases and the SN ratio
(signal-to-noise ratio) of the condenser microphone 1 decreases. Therefore, it is desirable to
design the width in the short direction of the back plate 30 in consideration of the SN ratio of the
condenser microphone 1.
[0035]
Hereinafter, an example of a design method based on the SN ratio of the condenser microphone
1 having a width in the short direction of the back plate 30 will be described with reference to
FIGS. FIG. 6 is a schematic view for explaining the relationship between the width in the
longitudinal direction of the diaphragm 10, the width in the lateral direction of the back plate 30,
and the SN ratio of the condenser microphone 1. As shown in FIG. In a three-dimensional space
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in which the longitudinal direction of the diaphragm 10 is the X axis, the thickness direction of
the diaphragm 10 is the Y axis, and the short direction of the diaphragm 10 is the Z axis, It can
be approximated (see curved surface 90 shown in FIG. 6). The center in the lateral direction of
the diaphragm 10 is located on the X axis, and the longitudinal center of the diaphragm 10 and
the center in the lateral direction of the back plate 30 are located on the Z axis. Further, the
width of the back plate 30 in the lateral direction is 2a, the width in the longitudinal direction of
the diaphragm 10 is 2b, and the width in the lateral direction of the diaphragm 10 is 2c.
[0036]
[0037]
Since both ends 10a of the diaphragm 10 are not displaced, the relationships of the following
equations (2) and (3) hold.
As a result, the wedge-like deformation of the diaphragm 10 can be expressed by the following
equation (4), and the sensitivity s of the condenser microphone 1 can be expressed by the
following equation (5). The sensitivity s of the condenser microphone 1 is normalized by dividing
by d.
[0038]
[0039]
[0040]
[0041]
[0042]
FIG. 7 is a schematic view showing the relationship between the width in the lateral direction of
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the back plate 30 and the sensitivity of the condenser microphone 1.
The graph 91 shows the sensitivity s when the width 2b in the longitudinal direction of the
diaphragm 10 is 1.0 mm and the width 2a in the lateral direction of the back plate 30 is changed
from 0 mm to 1.0 mm.
According to the graph 91, it can be understood that the sensitivity s increases as the width 2a in
the width direction of the back plate 30 is narrowed.
However, if the width 2a in the width direction of the back plate 30 is narrowed, the capacitance
of the microphone capacitor decreases, so the noise n (see the following equation (6)) inversely
proportional to the square root of the capacitance of the microphone capacitor increases. Do.
[0043]
[0044]
Therefore, it is desirable to design the width in the short side direction of the back plate 30 in
consideration of the SN ratio of the condenser microphone 1 (see the following equation (7)) as
described above.
[0045]
[0046]
FIG. 8 is a schematic view showing the relationship between the width in the lateral direction of
the back plate 30 and the SN ratio of the condenser microphone 1.
The graph 92 shows the SN ratio when the width 2b in the longitudinal direction of the
diaphragm 10 is 1.0 mm and the width 2a in the lateral direction of the back plate 30 is changed
from 0 mm to 1.0 mm.
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According to the graph 92, it can be seen that the SN ratio of the condenser microphone 1 has a
maximum value with respect to the width 2a in the width direction of the back plate 30.
The width 2a in the width direction of the back plate 30 in which the SN ratio of the condenser
microphone 1 indicates the maximum value can be calculated by obtaining a where the first
derivative of the equation (7) is zero.
[0047]
As a result, it can be seen that when the width 2a in the short direction of the back plate 30 is
about 0.6 times the width 2b in the longitudinal direction of the diaphragm 10, the SN ratio of
the condenser microphone 1 becomes maximum.
Therefore, when the width in the longitudinal direction of the diaphragm 10 is 1.0 mm, the back
plate 30 is opposed to the portion about 0.3 mm on both sides from the center in the
longitudinal direction of the diaphragm 10 and 0.2 mm from the both ends 10 a of the
diaphragm 10 It is desirable not to face the part of the degree. According to an example of the
design method described above, the width in the short side direction of the back plate 30 can be
designed based on the SN ratio of the condenser microphone 1.
[0048]
(Manufacturing Method) FIGS. 9 to 11 are schematic views showing a method of manufacturing
the condenser microphone 1. (B) is a cross-sectional view taken along line B9-B9 shown in FIG. 9
(B1) of (A), (C) is a cross-sectional view taken along line C9-C9 shown in FIG. 9 (A1) of (A). First,
as shown in FIG. 9C, the insulating film 110 is formed over the substrate 100. The substrate 100
is a semiconductor substrate such as a single crystal silicon substrate, for example. Specifically,
the insulating film 110 is formed on the substrate 100 by depositing an insulating material on
the surface of the substrate 100 by, for example, CVD (Chemical Vapor Deposition). Note that
this process can be omitted by using an SOI substrate.
[0049]
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Next, as shown in FIGS. 9A2 and 9C2, a linear recess 111 is formed in the insulating film 110.
Specifically, for example, the recess 111 is performed as follows. First, a resist film which
exposes a portion of the insulating film 110 where the concave portion 111 is to be formed is
formed on the insulating film 110 using lithography. More specifically, a resist is applied to the
insulating film 110 to form a resist film. Then, a mask of a predetermined shape is disposed, and
the resist film is exposed and developed to remove unnecessary resist film. Thus, a resist film is
formed on the insulating film 110 to expose a portion of the insulating film 110 where the
concave portion 111 is to be formed. For removing the resist film, a resist stripping solution such
as NMP (N-methyl-2-pyrrolidone) is used. Next, the recess 111 is formed in the insulating film
110 by etching the insulating film 110 exposed from the resist film by RIE (Reactive Ion Etching)
or the like. Then, the resist film is removed.
[0050]
Next, as shown in FIG. 9C, the conductive film 120 is formed over the insulating film 110 by CVD
or the like. The conductive film 120 is, for example, a polysilicon film. Next, as illustrated in FIG.
10A4, the conductive film 120 is patterned to form the conductive film 122, the conductive film
124, the conducting wire 125, the conducting wire 126, the electrode 60, and the electrode 62.
Specifically, for example, patterning of the conductive film 120 is performed as follows. First, a
resist film which exposes unnecessary portions of the conductive film 120 is formed on the
conductive film 120 using lithography. Next, the conductive film 120 exposed from the resist
film is etched by RIE or the like to form the conductive film 122, the conductive film 124, the
conducting wire 125, the conducting wire 126, the electrode 60, and the electrode 62. Then, the
resist film is removed.
[0051]
The conductive film 122 is substantially rectangular, and a portion of the conductive film 122 on
the recess 111 is undulated. The undulating portion of the conductive film 122 is the spring
portion 12 of the diaphragm 10. The conductive film 124 is formed in accordance with the shape
and arrangement of the conductive film 140 in order to face the conductive film 140 formed in a
process described later. Although it has been described that the spring portion 12 of the
diaphragm 10 is formed by forming the conductive film 122 on the insulating film 110 in which
the concave portion 111 is formed, the spring portion 12 may be formed by any method. The
spring portion 12 may be formed, for example, by forming the conductive film 122 on the
insulating film 110 in which the linear convex portion is formed, or may be formed by laminating
thin films.
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[0052]
Next, as shown in FIG. 10C 5, an insulating film 130 thicker than the conductive film 120 is
formed over the insulating film 110 by CVD or the like. In steps to be described later, the
conductive film 122, the conductive film 124, and the conductive film 140 (hereinafter, referred
to as a conductive film). Insulating film 110 and insulating film 130 (hereinafter referred to as
insulating film). In order to selectively remove the insulating film, the insulating film is formed of
a material having a high selectivity to the conductive film. For example, in the case where the
conductive film is formed of polysilicon, the insulating film may be formed of SiO 2. Further, in
the step of selectively removing the insulating film relative to the conductive film, the insulating
film 110 and the insulating film 130 are made of the same material in order to remove a part of
the insulating film and leave the insulating film constituting the capacitor microphone 1. It is
desirable to form. By forming the insulating film 110 and the insulating film 130 with the same
material, the etching rates of the both can be equal. As a result, the etching amount of the
insulating film can be easily controlled.
[0053]
Next, the conductive film 140, the conducting wire 141, and the electrode 62 which constitute
the back plate 30 are formed over the insulating film 130 (see FIG. 10 (A5)). The conductive film
140, the conducting wire 141, and the electrode 62 are, for example, polysilicon films.
Specifically, for example, the conductive film 140, the conducting wire 141, and the electrode 62
are formed as follows. First, a conductive film is formed on the insulating film 130 by CVD or the
like. Next, the conductive film is patterned to form the conductive film 140, the conducting wire
141, and the electrode 62. The conductive film 140 is substantially rectangular, and intersects
with the conductive film 122 through the insulating film 130.
[0054]
Next, as shown in FIG. 11 (C6), the opening portion 101 forming the opening portion 42 of the
support portion 40 is formed in the substrate 100. Specifically, the opening 101 is formed, for
example, as described below. First, a resist film is formed using lithography to expose a portion
of the substrate 100 where the opening 101 is to be formed. Next, the opening portion 101 is
formed in the substrate 100 by removing the portion exposed from the resist film of the
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substrate 100 by Deep RIE or the like until the insulating film 110 is reached. Then, the resist
film is removed.
[0055]
Next, as shown in FIG. 11 (C7), each part of the condenser microphone 1 is formed by removing
a part of the insulating film. Specifically, for example, part of the insulating film is removed as
follows. First, a resist film 150 covering a portion to be left as the support portion 40 is formed
on the insulating film 130. Next, the insulating film is removed by wet etching. For example,
when the insulating film 110 and the insulating film 130 are formed of SiO 2, hydrofluoric acid
or the like may be used as the etching solution.
[0056]
The etching solution infiltrates from the through holes 32, the opening 101 of the substrate 100,
and the like to dissolve the insulating film. For example, when the etching solution dissolves the
insulating film 130 between the conductive film 122 and the conductive film 140, a void 50
between the diaphragm 10 and the back plate 30 is formed, and the resist film 150 of the
insulating film and the substrate 100 are formed. The support part 40 is formed by the covered
part remaining. By forming each part of the capacitor microphone 1 by removing a part of the
insulating film as described above, a sound sensing unit of the capacitor microphone 1 can be
obtained.
[0057]
Second Embodiment FIG. 12 is a schematic view showing a condenser microphone according to a
second embodiment of the present invention. (B) is a cross-sectional view taken along line B12B12 of (A). The components of the condenser microphone 2 according to the second embodiment
are substantially the same as the corresponding components of the condenser microphone 1
according to the first embodiment, except for the shape of the diaphragm 210. Both ends 210 b
of the diaphragm 210 free from the support 40 are curved inward. Specifically, the width
between the end portions 210 b of the diaphragm 210 is narrower as it is separated from the
end portions 210 a fixed to the support portion 40. The diaphragm 210 has a spring portion 212
substantially the same as the spring portion 12 of the diaphragm 10 according to the first
embodiment.
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[0058]
Here, in the diaphragm 10 according to the first embodiment, the residual stress at the near end
close to the both ends 10b released from the support portion 40 is relaxed, so that the near end
closer to the both ends 10b is It may also hang down against the inner part (see Figure 13). On
the other hand, in the diaphragm 210 according to the second embodiment, the both end
portions 210b are bent inward to prevent the near end portions of the both end portions 210b
from hanging down.
[0059]
The schematic diagram which shows the condenser microphone by 1st Example. The schematic
diagram which shows the condenser microphone by 1st Example. The schematic diagram which
shows the modification of the capacitor | condenser microphone by 1st Example. The schematic
diagram which shows the modification of the capacitor | condenser microphone by 1st Example.
The schematic diagram for demonstrating the vibration by the sound wave of a diaphragm. The
schematic diagram for demonstrating the design method of the width | variety of the transversal
direction of a back plate. The schematic diagram for demonstrating the design method of the
width | variety of the transversal direction of a back plate. The schematic diagram for
demonstrating the design method of the width of the width direction of a back plate. FIG. 7 is a
schematic view showing the method of manufacturing the condenser microphone according to
the first embodiment. FIG. 7 is a schematic view showing the method of manufacturing the
condenser microphone according to the first embodiment. FIG. 7 is a schematic view showing the
method of manufacturing the condenser microphone according to the first embodiment. The
schematic diagram which shows the capacitor | condenser microphone by 2nd Example. The
schematic diagram for demonstrating the capacitor | condenser microphone by 2nd Example.
Explanation of sign
[0060]
1, 2: Condenser microphone, 10, 210: Diaphragm, 12, 212: Spring portion, 30: Back plate (plate),
32: Through hole, 40: Support portion, 50: Air gap
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