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JP2011239197

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DESCRIPTION JP2011239197
A protective film using a back plate protects an upper peripheral portion of a silicon substrate. A
conductive diaphragm (33) is disposed above a silicon substrate (32) having a back chamber
(35), and the diaphragm (33) is supported by an anchor (37). An insulating plate 39 is fixed on
the upper surface of the silicon substrate 32 so as to cover the diaphragm 33 with a gap. A
conductive fixed electrode film 40 is provided on the lower surface of the plate portion 39 to
constitute a back plate 34. The change in capacitance between the fixed electrode film 40 and
the diaphragm 33 is output as an electrical signal from the fixed electrode pad 45 and the
movable electrode pad 46 to the outside. A protective film 53 is provided on the outer periphery
of the plate portion 39 continuously with the plate portion 39, and the protective film 53 covers
the upper surface outer peripheral portion of the silicon substrate 32, and the outer periphery of
the protective film 53 Match. [Selected figure] Figure 3
Acoustic sensor and method of manufacturing the same
[0001]
The present invention relates to an acoustic sensor and a method of manufacturing the same, and
more particularly to a MEMS acoustic sensor manufactured using MEMS (Micro Electro
Mechanical Systems) technology and a method of manufacturing the same.
[0002]
Examples of MEMS-based acoustic sensors include those disclosed in Patent Document 1 and
those disclosed in Patent Document 2.
04-05-2019
1
[0003]
(Regarding Patent Document 1) FIGS. 1A and 1B are schematic cross-sectional views showing a
state in which the acoustic sensor disclosed in FIGS. 7 and 8 of Patent Document 1 is mounted in
a package.
In this acoustic sensor 11, a diaphragm 14 (oscillating thin film) is placed on a silicon substrate
12 in which a back chamber 13 is opened, and a back plate 15 is provided on the silicon
substrate 12 so as to cover the diaphragm 14.
Such an acoustic sensor 11 is usually mounted in a package 17 together with the IC circuit 16 as
shown in FIGS. 1A and 1B, and the electrode pad 18 of the acoustic sensor 11 and the IC circuit
The IC circuit 16 is connected to the electrode portion 21 of the package 17 by the bonding wire
20.
[0004]
However, in the acoustic sensor 11, the upper surface peripheral portion of the silicon substrate
12 is completely exposed. Therefore, as shown in FIG. 1A, when the bonding wire 19 connecting
the acoustic sensor 11 and the IC circuit 16 is bent downward due to any load, the bonding wire
19 contacts the silicon substrate 12 to make a sound. A short circuit may occur in the sensor 11.
Even when the bonding wire 19 is not bent, as shown in FIG. 1B, if the foreign matter 22 (for
example, fine dust or the like) is caught between the bonding wire 19 and the upper surface of
the silicon substrate 12, the foreign matter 22 is There is a possibility that a short circuit may
occur between the electrode pad 18 and the silicon substrate 12 through the
[0005]
In the IC circuit 16, since the whole is sealed by the resin 23, the bonding wire 19 is fixed by the
resin 23, and there is no fear that the bonding wire 19 is bent or foreign matter intrudes. In the
acoustic sensor 11, when resin sealing is performed, acoustic vibration is blocked, and therefore
it can not be sealed with resin.
[0006]
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2
In the acoustic sensor disclosed in FIGS. 4 and 5 of Patent Document 1, the surface of the silicon
substrate is covered with the insulating film (SiO 2 film), but since the insulating film is thin, it is
for preventing short circuit. Was unreliable.
In the cross-sectional view shown in FIG. 6 of Patent Document 1, the back plate extends to the
edge of the silicon substrate. However, as seen from the cross-sectional view of FIG. 4 of Patent
Document 1, this is a view in which the outer peripheral portion of the silicon substrate whose
upper surface is exposed is omitted, and the back plate actually extends to the edge of the silicon
substrate It is not
[0007]
(Regarding Patent Document 2) In FIG. 2 of Patent Document 2, a structure is provided up to the
outer peripheral edge of the upper surface of the silicon substrate to cover the upper surface of
the silicon substrate. However, in this acoustic sensor, the upper surface outer peripheral portion
of the silicon substrate is covered with a member (such as a surface layer protective film)
different from the back plate (plate provided with the upper layer conductive film). Therefore,
there is a problem that man-hours at the time of manufacture increase and productivity is bad.
[0008]
JP, 2008-3014, A JP, 2009-89097, A
[0009]
The present invention has been made in view of the above technical problems, and an object of
the present invention is to protect the upper peripheral portion of the silicon substrate with a
protective film using a back plate.
[0010]
The acoustic sensor according to the present invention is fixed to the upper surface of the
semiconductor substrate so as to cover the diaphragm with a gap between the semiconductor
substrate having the back chamber, the conductive diaphragm disposed above the semiconductor
substrate, and the conductive diaphragm. Of the insulating fixed film, the conductive fixed
electrode film provided on the fixed film at a position facing the diaphragm, and the change in
capacitance between the fixed electrode film and the diaphragm as an electrical signal An
04-05-2019
3
acoustic sensor comprising an electrode terminal for outputting to the semiconductor substrate,
wherein the upper surface outer peripheral portion of the semiconductor substrate is covered
with a protective film made of the same material as the fixed film, and the outer periphery of the
protective film is the semiconductor substrate It is characterized in that it coincides with the
upper surface periphery of.
[0011]
In the acoustic sensor according to the present invention, since the upper surface peripheral
portion to the outer periphery (edge) of the semiconductor substrate is covered with the
insulating protective film made of the same material as the fixed film, the thickness of the
protective film is large. As a result, it is possible to improve the insulation at the upper peripheral
portion of the semiconductor substrate.
Therefore, the bonding wire connected to the electrode terminal can be prevented from bending
and coming into contact with the upper surface of the semiconductor substrate, and foreign
matter can be prevented from being caught between the bonding wire and the upper surface of
the semiconductor substrate to cause a short circuit.
In addition, since the protective film is the same material as the fixed film, and the protective film
can be formed in the same process as the fixed film, provision of the protective film does not
increase the number of manufacturing steps of the acoustic sensor, and the productivity There is
no reduction in
[0012]
In an embodiment of the acoustic sensor according to the present invention, at least a part of the
protective film is fixed to the surface of the semiconductor substrate with an adhesive layer
which is different from the fixed film and thinner than the protective film. It is characterized by
According to this embodiment, by forming an adhesion layer of a thin film thinner than the
protective film between the protective film and the semiconductor substrate, it is possible to
reduce the film stress generated in the protective film, and the protective film by the film stress
Peeling can be reduced. In addition, since the protective film is a thin film, throughput is reduced
04-05-2019
4
even when a plurality of acoustic sensors are fabricated on a wafer in a manufacturing process
and then separated into individual acoustic sensors by laser dicing at the location where the
adhesion layer is formed. Hateful.
[0013]
In another embodiment of the acoustic sensor according to the present invention, the outer
peripheral portion of the protective film is fixed to the surface of the semiconductor substrate
with the adhesive layer interposed, and the inner peripheral portion of the protective film is the
fixed film The semiconductor device is characterized in that it is fixed to the surface of the
semiconductor substrate with a thick film layer made of different materials interposed. According
to this embodiment, peeling of the protective film can be alleviated, and throughput is less likely
to decrease even when the acoustic sensors formed on the wafer are individually separated by
laser dicing. Furthermore, since a thick film portion is formed on the inner peripheral portion and
the height of the surface of the protective film is high, the electrode terminal can be provided in
this portion. The thick film layer is preferably formed of the same material as the adhesion layer.
[0014]
Another embodiment of the acoustic sensor according to the present invention is characterized in
that the electrode terminal is provided on the protective film in the region where the thick film
layer is formed. According to this aspect, since the distance between the electrode terminal and
the upper surface of the semiconductor substrate can be increased, the parasitic capacitance
between the electrode terminal and the semiconductor substrate can be reduced, and the
sensitivity decrease of the acoustic sensor due to the parasitic capacitance is reduced. The sound
characteristics are improved.
[0015]
A further embodiment of the acoustic sensor according to the present invention is characterized
in that the adhesion layer and the thick film layer are formed of an insulating material. According
to this embodiment, the insulation between the protective film and the semiconductor substrate
can be improved.
04-05-2019
5
[0016]
In another embodiment of the acoustic sensor according to the present invention, the protective
film and the fixed film are continuous, and the boundary region between the protective film and
the fixed film is in close contact with the upper surface of the semiconductor substrate. It is
characterized by According to this embodiment, even if the protective film and the fixed film are
continuous, the adhesion layer or the thick film layer can be separated from the hollow portion,
and the manufacture of the acoustic sensor can be facilitated.
[0017]
In the method of manufacturing an acoustic sensor according to the present invention, a
semiconductor substrate having a back chamber, a conductive diaphragm disposed above the
semiconductor substrate, and the semiconductor substrate covering the diaphragm with a gap
therebetween. An insulating fixed film fixed on the upper surface, a conductive fixed electrode
film provided on the fixed film at a position facing the diaphragm, and a change in capacitance
between the fixed electrode film and the diaphragm A method of manufacturing an acoustic
sensor comprising an electrode terminal for outputting to the outside as a signal, comprising the
steps of: forming a diaphragm inside a sacrificial layer deposited on the upper surface of the
semiconductor substrate; and etching the sacrificial layer Forming the fixed film on the shaped
sacrificial layer, and forming the fixed film on the shaped sacrificial layer; Covering the upper
surface outer peripheral portion of the semiconductor substrate with a protective film made of
the same material as the fixed film so as to coincide with the upper surface outer periphery of
the body substrate, forming the back chamber in the semiconductor substrate, and the sacrificial
layer Are removed by etching to support the diaphragm in a space, and a gap is formed between
the diaphragm and the inner surface of the fixed film.
[0018]
In the method of manufacturing an acoustic sensor according to the present invention, since the
upper surface outer peripheral portion to the outer periphery (edge) of the semiconductor
substrate is covered with the insulating protective film made of the same material as the fixed
film, The thickness can be increased to improve the insulation at the upper peripheral portion of
the semiconductor substrate.
Therefore, the bonding wire connected to the electrode terminal can be prevented from bending
and coming into contact with the upper surface of the semiconductor substrate, and foreign
04-05-2019
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matter can be prevented from being caught between the bonding wire and the upper surface of
the semiconductor substrate to cause a short circuit. In addition, since the protective film is the
same material as the fixed film, and the protective film can be formed in the same process as the
fixed film, provision of the protective film does not increase the number of manufacturing steps
of the acoustic sensor, and the productivity There is no reduction in
[0019]
In one embodiment of the method of manufacturing an acoustic sensor according to the present
invention, after forming the space forming portion, at least a part of the upper surface outer
peripheral portion of the semiconductor substrate is made of a material different from the fixed
film and is more It is characterized in that a thin adhesion layer is formed. In particular, the
thickness of the adhesion layer is preferably smaller than the distance between the inner surface
of the back plate made of the fixed film and the fixed electrode film and the diaphragm.
According to this embodiment, by forming an adhesion layer of a thin film thinner than the
protective film between the protective film and the semiconductor substrate, the film stress
generated in the protective film can be reduced, and the protective film by the film stress can be
reduced. Can be reduced. In addition, since the adhesion layer is a thin film, throughput is
reduced even when a plurality of acoustic sensors are fabricated on a wafer in a manufacturing
process and then separated into individual acoustic sensors by laser dicing at the location where
the adhesion layer is formed. Hateful. In addition, since the adhesion film is provided separately
from the space forming portion after the formation of the space forming portion, the adhesion
film can be easily formed in a thin film shape.
[0020]
In another embodiment of the method of manufacturing an acoustic sensor according to the
present invention, when forming the space forming portion, a thick film layer is formed outside
the space forming portion separately from the space forming portion by the sacrificial layer.
Then, the adhesion layer is formed on the outside of the thick film layer. According to this
embodiment, since the thick film layer can be formed from the sacrificial layer simultaneously
with the space forming portion, the manufacturing process of the acoustic sensor can be
simplified. Preferably, the adhesion layer and the thick film layer are formed of the same
material.
[0021]
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7
A further embodiment of the method of manufacturing an acoustic sensor according to the
present invention is characterized in that the adhesion layer and the thick film layer are formed
of an insulating material. According to this embodiment, the insulation between the protective
film and the semiconductor substrate can be improved.
[0022]
In still another embodiment of the acoustic sensor according to the present invention, the
thickness of the thick film layer is larger than the distance between the fixed film and the inner
surface of the back plate consisting of the fixed electrode film and the diaphragm. It is
characterized. In particular, the thickness of the thick film layer is determined by the distance
between the fixed film and the inner surface of the back plate consisting of the fixed electrode
film and the diaphragm, and the distance between the upper surface of the semiconductor
substrate and the diaphragm It is desirable to be equal to the distance of the sum. According to
this embodiment, the thick film layer can be formed using the sacrificial layer for forming the
cavity portion in the fixed film, and the manufacture of the acoustic sensor can be facilitated.
[0023]
In still another embodiment of the method of manufacturing an acoustic sensor according to the
present invention, the protective film and the fixed film are continuously and simultaneously
formed, and the boundary region between the protective film and the fixed film is the upper
surface of the semiconductor substrate. It is characterized in that it adheres to According to this
embodiment, even if the protective film and the fixed film are continuous, the adhesion layer or
the thick film layer can be separated from the cavity portion, and when the sacrificial layer is
etched to form the cavity portion, the adhesion layer or the adhesion layer The thick film layer
can be prevented from being etched, and the manufacture of the acoustic sensor can be
facilitated.
[0024]
In addition, the means for solving the above-mentioned subject in the present invention has the
feature which combined suitably the component explained above, and the present invention
enables many variations by the combination of such a component. .
04-05-2019
8
[0025]
FIGS. 1A and 1B are cross-sectional views showing a state in which the acoustic sensor disclosed
in Patent Document 1 is mounted in a package.
FIG. 2 is an exploded perspective view of the acoustic sensor according to the first embodiment
of the present invention. FIG. 3 is a cross-sectional view of the acoustic sensor of the first
embodiment. 4 (A) to 4 (D) are schematic cross-sectional views for explaining the manufacturing
process of the acoustic sensor of the first embodiment. 5 (A) to 5 (C) are schematic crosssectional views for explaining the manufacturing process of the acoustic sensor of the first
embodiment, and show the process following FIG. 4 (D).
[0026]
Hereinafter, preferred embodiments of the present invention will be described with reference to
the accompanying drawings. However, the present invention is not limited to the following
embodiments, and various design changes can be made without departing from the scope of the
present invention.
[0027]
First, the structure of the acoustic sensor 31 according to the first embodiment of the present
invention will be described with reference to FIGS. 2 and 3. FIG. 2 is a perspective view showing
the acoustic sensor 31 partially disassembled. FIG. 3 is a cross-sectional view in the diagonal
direction showing the structure of the acoustic sensor 31. As shown in FIG.
[0028]
The acoustic sensor 31 is a minute capacitive element manufactured using MEMS technology,
and as shown in FIG. 3, a diaphragm 33 is provided on the upper surface of a silicon substrate 32
(semiconductor substrate) via an anchor 37. The back plate 34 is fixed thereon via a minute gap
(air gap).
04-05-2019
9
[0029]
The silicon substrate 32 is made of single crystal silicon.
As shown in FIG. 2, the silicon substrate 32 is formed in a rectangular plate shape, and has a
rectangular hole-shaped back chamber 35 penetrating from the front surface to the back surface.
The inner circumferential surface of the back chamber 35 may be vertical or may be tapered. The
lower surface opening of the back chamber 35 is closed by the package when the acoustic sensor
31 is mounted in the package (see FIG. 1).
[0030]
Further, four anchors 37 for supporting the beam portion 36a of the diaphragm 33 from the
lower surface are provided on the upper surface of the silicon substrate 32, and the base portion
41 (thick film layer) is further surrounded ) Is formed. In particular, the anchor 37 is located in a
recess formed to cut the inner peripheral edge of the base portion 41 in the diagonal direction of
the back chamber 35. Furthermore, the region outside the base portion 41 on the upper surface
of the silicon substrate 32 is covered with the adhesion layer 47 thinner than the base portion
41, and the outer periphery (edge) of the adhesion layer I do. The anchor 37 and the base
portion 41 are formed of SiO2. The adhesion layer 47 is formed of SiO 2 or polysilicon.
[0031]
The diaphragm 33 is formed of a thin polysilicon film having a small thickness, and has
conductivity. The diaphragm 33 is obtained by extending the beam portion 36a diagonally
outward from the four corners of the rectangular vibrating thin film 36b. Furthermore, a lead
wire 43 extends from one of the beam portions 36a.
[0032]
As shown in FIG. 3, the diaphragm 33 is disposed on the upper surface of the silicon substrate 32
such that the vibrating thin film 36 b covers the upper surface of the back chamber 35. Each
beam portion 36 a of the diaphragm 33 is located in the recess of the base portion 41, and the
04-05-2019
10
tip end lower surface of each beam portion 36 a is fixed to the anchor 37. Therefore, the
vibrating thin film 36b of the diaphragm 33 floats in the air above the back chamber 35, and can
vibrate in response to acoustic vibration (air vibration).
[0033]
The back plate 34 has a fixed electrode film 40 made of polysilicon provided on the lower
surface of a plate portion 39 (fixed film) made of a nitride film (SiN). The back plate 34 is shaped
like a canopy and has a hollow portion below it and covers the diaphragm 33. The height a of the
hollow portion under the back plate 34 (the height from the upper surface of the silicon
substrate 32 to the lower surface of the fixed electrode film 40) is equal to the thickness c of the
base portion 41 formed on the upper surface of the silicon substrate 32. ing. A minute air gap is
formed between the lower surface of the back plate 34 (that is, the lower surface of the fixed
electrode film 40) and the upper surface of the diaphragm 33. Further, the beam portion cover
area 49 formed at the corner of the back plate 34 covers the beam portion 36a with a minute
gap. The fixed electrode film 40 faces the vibrating thin film 36 b which is a movable electrode
film to constitute a capacitor.
[0034]
A large number of acoustic holes 38 are formed in the back plate 34 for passing acoustic
vibration so as to penetrate from the upper surface to the lower surface. Also, a small gap
(passage for acoustic vibration) is provided between the lower surface of the outer peripheral
portion of the vibrating thin film 36 b and the upper surface of the silicon substrate 32.
Therefore, the acoustic vibration entering the back plate 34 through the acoustic hole 38
vibrates the vibrating thin film 36 b and passes through the gap between the outer peripheral
portion of the vibrating thin film 36 b and the silicon substrate 32 to the back chamber 35. go.
[0035]
In addition, a large number of minute stoppers 42 protrude from the inner surface of the back
plate 34, and the diaphragm 33 is prevented from being adsorbed or stuck (sticked) to the lower
surface of the back plate 34 and prevented from returning.
[0036]
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11
A protective film 53 extends continuously from the outer peripheral edge of the canopy-like plate
portion 39 over the entire circumference.
Therefore, the protective film 53 is formed of a nitride film (SiN) like the plate portion 39, and
has a film thickness substantially the same as that of the plate portion 39. An inner peripheral
portion of the protective film 53 is a base covering portion 51 having a cross section reverse
groove shape, and an outer peripheral portion of the protective film 53 is a flat portion 52.
Further, the boundary region 50 between the outer periphery of the back plate 34 and the inner
periphery of the protective film 53 has a V-shaped cross section.
[0037]
The back plate 34 is fixed to the upper surface of the silicon substrate 32, and the protective film
53 covers the upper outer peripheral portion of the silicon substrate 32 with the base portion 41
and the adhesion layer 47 interposed. The base covering portion 51 of the protective film 53
covers the base portion 41, the flat portion 52 covers the upper surface of the adhesive layer 47,
and the outer periphery (edge) of the flat portion 52 is the outer periphery of the adhesive layer
47 and the silicon substrate 32. It corresponds with the upper surface circumference of. Further,
the lower surface of the boundary region 50 between the back plate 34 and the protective film
53 is in close contact with the exposed surface 48 of the inner periphery of the base portion 41,
and the hollow portion under the back plate 34 and the base portion 41 are It is separated by the
boundary area 50.
[0038]
The thickness b of the air gap between the upper surface of the diaphragm 33 and the lower
surface of the back plate 34 is about 2 μm. The thickness c of the base portion 41 is larger than
the thickness b of the space between the anchor 37 and the back plate 34 and is 2 μm or more.
On the other hand, the thickness d of the adhesion layer 47 is smaller than the thickness b of the
gap between the anchor 37 and the back plate 34 and is 2 μm or less. The width e of the
protective film 53 is preferably 400 μm or less, and the width f of the flat portion 52 is
preferably about 150 μm.
[0039]
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12
The base covering portion 51 has an opening, and the movable side electrode pad 46 (electrode
terminal) is formed on the top surface of the lead wire 43 through the opening, and the movable
side electrode pad 46 is formed on the lead wire 43 (therefore, the diaphragm 33). )). Further,
the fixed side electrode pad 45 (electrode terminal) provided on the upper surface of the plate
portion 39 is electrically connected to the lead wire 44 (therefore, to the fixed electrode film 40)
through a through hole or the like.
[0040]
Thus, in the acoustic sensor 31, when the acoustic vibration passes through the acoustic hole 38
and enters the space between the back plate 34 and the diaphragm 33, the diaphragm 33 which
is a thin film is excited by the acoustic vibration and the film Vibrate. When the diaphragm 33
vibrates and the gap distance between the diaphragm 33 and the fixed electrode film 40
changes, the capacitance between the diaphragm 33 and the fixed electrode film 40 changes. As
a result, in the acoustic sensor 31, the acoustic vibration (change in sound pressure) sensed by
the diaphragm 33 becomes a change in capacitance between the diaphragm 33 and the fixed
electrode film 40, and is output as an electrical signal. Ru.
[0041]
Further, according to the acoustic sensor 31, the upper surface outer peripheral portion of the
silicon substrate 32 (a region for cutting from a wafer, which may be referred to as a dicing
street portion). ) Is covered by the flat portion 52 of the protective film 53. Similar to the plate
portion 39, the protective film 53 is formed of a SiN film, and is formed to have a relatively large
thickness, so that the protective film 53 is excellent in insulation. Therefore, even if the bonding
wire connected to the fixed side electrode pad 45 or the movable side electrode pad 46 is bent
and lowered, the bonding wire only touches the protective film 53 and does not directly touch
the silicon substrate 32. Further, even if foreign matter is caught under the bonding wire, the
foreign matter is blocked by the protective film 53 and does not directly touch the silicon
substrate 32. Therefore, it is possible to effectively prevent a short circuit of the acoustic sensor
31.
[0042]
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13
The adhesion layer 47 is made of SiO 2 or polysilicon thinner than the thickness b of the air gap,
and the flat portion 52 is formed on the upper surface of the silicon substrate 32 with the
adhesion layer 47 interposed therebetween. The film stress can be reduced, and the peeling of
the protective film 53 due to the film stress can be reduced. Further, the adhesion of the flat
portion 52 can be improved by interposing the adhesion layer 47 made of SiO 2 or SiN.
[0043]
Furthermore, the base portion 41 is made of SiO 2 thicker than the thickness b of the air gap,
and the fixed side electrode pad 45 is provided on the protective film 53 (the base covering
portion 51) above the base portion 41. The distance between the pad 45 and the upper surface
of the silicon substrate 32 can be increased. As a result, since the parasitic capacitance between
the electrode pads 45 and 46 and the silicon substrate 32 can be reduced, the sensitivity
reduction of the acoustic sensor 31 due to the parasitic capacitance can be reduced, and the
acoustic characteristics of the acoustic sensor 31 can be improved. Further, since the base
covering portion 51 is formed on the base portion 41 made of SiO 2, the adhesion of the base
covering portion 51 can be improved.
[0044]
In the example of FIG. 2, the movable electrode pad 46 is manufactured at the end of the beam
36 a of the diaphragm 33, so increasing the thickness of the base 41 can reduce parasitic
capacitance. Can not. However, when the movable side electrode pad 46 has the same structure
as the fixed side electrode pad 45, that is, when the lead-out wiring is provided on the upper
surface of the plate portion 39 through a through hole or the like, the base portion 41 is formed.
The parasitic capacitance reduction effect can be obtained by thickening the
[0045]
Further, since the acoustic sensor 31 has the outermost surface covered with the highly
hygroscopic SiN layer (that is, the plate portion 39 and the protective film 53), the hygroscopicity
is also improved.
[0046]
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14
(Method of Manufacturing Acoustic Sensor) Next, a method of manufacturing the acoustic sensor
31 by the MEMS technology will be described.
FIG. 4A to FIG. 4D and FIG. 5A to FIG. 5C are schematic cross-sectional views showing the
manufacturing process of the acoustic sensor 31.
[0047]
First, as shown in FIG. 4A, a sacrificial layer 61 made of a silicon oxide film (SiO 2) is formed on
the surface of a single crystal silicon substrate 32 by thermal oxidation, CVD or the like. Then, a
polysilicon layer is formed on the sacrificial layer 61, and this polysilicon layer is patterned by
etching to form a flat diaphragm 33 in which beam portions 36a extend from the four corners of
the vibrating thin film 36b.
[0048]
A sacrificial layer 61 is further deposited on the diaphragm 33 and on the sacrificial layer 61 to
cover the diaphragm 33 with the sacrificial layer 61, and the diaphragm 33 is embedded in the
sacrificial layer 61 as shown in FIG. 4B.
[0049]
Next, as shown in FIG. 4C, the sacrificial layer 61 is etched to form a cavity forming portion 62
and a base portion 41 which are formed on the inner surface of the back plate 34 by the
sacrificial layer 61.
At this time, the cavity forming portion 62 and the base portion 41 are separated by the groove
63, and the upper surface of the silicon substrate 32 is exposed in the groove 63 (the bottom of
the groove 63 becomes the exposed surface 48). And expose the upper surface of the silicon
substrate 32 outside the base portion 41. Further, a hole 64 for forming the stopper 42 is dug in
the upper surface of the cavity forming portion 62.
[0050]
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15
Thereafter, a thin adhesion layer 47 is formed of SiO 2 or polysilicon on the upper surface of the
silicon substrate 32 outside the base portion 41 so as to be continuous with the outer peripheral
surface of the base portion 41.
[0051]
As shown in FIG. 5A, a polysilicon film is formed on the upper surface of the cavity forming
portion 62, and the polysilicon film is etched and patterned to produce the fixed electrode film
40.
At this time, the acoustic hole 38 is opened in the fixed electrode film 40, and a through hole is
opened in accordance with the hole 64. Further, a SiN layer having hydrofluoric acid resistance is
deposited on the fixed electrode film 40 to form a plate portion 39. At this time, the stopper 42
for sticking prevention is formed by the SiN layer deposited in the hole 64. Also in the plate
portion 39, the acoustic hole 38 is formed in alignment with the acoustic hole 38 of the fixed
electrode film 40, and the acoustic hole 38 is penetrated through the back plate 34. Furthermore,
electrode pads 45 and 46 are provided on the base covering portion 51.
[0052]
Thus, when the back plate 34 is completed, the central portion of the silicon substrate 32 is
etched from the lower surface side, and the back chamber 35 is penetrated through the silicon
substrate 32 as shown in FIG. Expose 62.
[0053]
Thereafter, hydrofluoric acid is introduced from the acoustic holes 38 of the back plate 34, the
back chamber 35 of the silicon substrate 32, etc. to selectively wet-etch the cavity forming
portion 62, as shown in FIG. 5C. Leaving only the lower sacrificial layer 61 as an anchor 37 and
removing the other cavity formations 62.
As a result, the diaphragm 33 is floated from the upper surface of the silicon substrate 32 by the
anchor 37, supported so as to be able to vibrate on the back chamber 35, and an air gap is
formed between the fixed electrode film 40 and the diaphragm 33. . However, since the base
portion 41 and the cavity forming portion 62 are partitioned by the boundary region 50, the
04-05-2019
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base portion 41 is not etched with hydrofluoric acid, and the base portion 41 and the adhesion
layer 47 remain as they are. Thus, the acoustic sensor 31 is manufactured.
[0054]
Making the thickness of the base portion 41 larger than the thickness b of the air gap between
the upper surface of the diaphragm 33 and the lower surface of the back plate 34 in the acoustic
sensor 31 has the following significance in terms of the method. . If the base portion 41 can be
manufactured from the same sacrificial layer 61 in the same process as the cavity forming
portion 62 as in the above manufacturing method, the productivity is the best. In order to enable
such a construction method, the thickness c of the base portion 41 must be thicker (cbb) than the
thickness b of the air gap.
[0055]
If the air gap between the diaphragm 33 and the back plate 34 is narrowed, the pull-in
phenomenon (a phenomenon in which the diaphragm 33 and the fixed electrode film 40 adhere
to each other by electrostatic attraction when voltage is applied) or the stick phenomenon (water
entering the air gap etc. In order to prevent the phenomenon in which the electrode film 40 is
stuck, it is preferable that the space be as wide as possible. Also, in order to reduce thermal noise
as a noise source, it is desirable that the air gap be as wide as possible. Therefore, the gap
between the diaphragm 33 and the back plate 34 can not be reduced to 2 μm or less, and
generally, the thickness b of the gap is 2 μm or more.
[0056]
On the other hand, in order to reduce the parasitic capacitance between the fixed side electrode
pad 45 and the silicon substrate 32, the base portion 41 is desirably as thick as possible.
Therefore, if the thickness c of the base portion 41 is made larger than the thickness b of the air
gap, the base portion 41 can secure a certain thickness or more (that is, a thickness of 2 μm or
more). Capacity can be reduced. In a better mode, the thickness c of the base portion 41 is the
same as the sum of the thickness b of the air gap and the thickness g of the anchor 37. This is
because it is most productive if the step of producing the base portion 41 is synchronized with
the step of producing the air gap and the anchor thickness. As a result, the thickness c of the
base portion 41 is the thickness c of the void and the anchor 37 It is equal to the sum of the
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thickness g of
[0057]
Further, making the thickness of the adhesive layer 47 smaller than the thickness b of the gap
between the upper surface of the diaphragm 33 and the lower surface of the back plate 34 has
the following significance in terms of the method. In the case of using laser dicing, it is desirable
that the adhesion layer 47 provided on the dicing street portion be thinner. However, when the
adhesion layer 47 is simultaneously manufactured using the sacrificial layer 61 for
manufacturing the cavity molding portion 62 and the base portion 41, the thickness of the
adhesion layer 47 is increased. Therefore, as shown in FIG. 4D, it is desirable that the adhesion
layer 47 be manufactured in a process separate from the base portion 41 and the cavity forming
portion 62. Since it is preferable that the thickness d of the adhesive layer 47 manufactured in
the step of FIG. 4D be as thin as possible, it is desirable to manufacture it with, for example, a SiO
2 film having a thickness of about 0.1 μm.
[0058]
Since the adhesion layer 47 is manufactured in the process after the cavity molding portion 62
and the base portion 41 are manufactured, depending on the method of manufacturing the
adhesion layer 47, the same film as the adhesion layer 47 is the cavity molding portion 62 and
the base portion 41 May also be applied to the surface of As a result, the thickness of the cavity
forming portion 62 and the base portion 41 is increased by the thickness of the adhesive layer
47. In such a case, the thickness of the sacrificial layer 61 manufactured in the step of FIG. 4B is
thinner than the thickness of the cavity molding portion 62 and the base portion 41 by the
thickness of the adhesion layer 47. You should do it.
[0059]
31 acoustic sensor 32 silicon substrate 33 diaphragm 34 back plate 35 back chamber 37 anchor
38 acoustic hole 39 plate portion 40 fixed electrode film 41 base portion 45 fixed side electrode
pad 46 movable side electrode pad 47 adhesion layer 49 beam portion cover area 50 boundary
area 51 base covering portion 52 flat portion 53 protective film 61 sacrificial layer 62 cavity
forming portion
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