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DESCRIPTION JP2007295405

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DESCRIPTION JP2007295405
An ultrasonic sensor capable of controlling a resonant frequency over a long period of time and a
method of manufacturing the same. A piezoelectric thin film 131 is disposed between two
detection electrodes 132 and 133 in a thickness direction of a substrate 110 in which a thin
portion 120 is partially formed, and the thin portion 120 is formed. And the adjustment
electrodes 141 and 142 for applying a predetermined voltage to the thin portion 120 of the thin
portion 120 forming the membrane structure and the piezoelectric vibrator 130 The membrane
structure is deformed in response to the predetermined voltage. [Selected figure] Figure 1
Ultrasonic sensor and method of manufacturing the same
[0001]
The present invention relates to an ultrasonic sensor and a method of manufacturing the same.
[0002]
Conventionally, ultrasonic sensors have been employed in obstacle detection systems for vehicles
and the like.
As such an ultrasonic sensor, a piezoelectric ultrasonic sensor manufactured using MEMS (Micro
Electro Mechanical System) technology is known (see Patent Document 1).
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1
[0003]
The ultrasonic sensor disclosed in Patent Document 1 has a thin portion (a semiconductor active
layer and an insulating film layer) formed on a semiconductor substrate having an SOI (Silicon
On Insulator) structure, and two ferroelectric electrodes (upper detection electrodes, The
piezoelectric vibrators interposed between the lower detection electrodes are formed so as to
cover the thin-walled portion in such a manner that the respective electrodes are disposed on the
upper and lower surfaces of the ferroelectric substance. Japanese Patent Application Publication
No. 2003-284182
[0004]
In a piezoelectric ultrasonic sensor manufactured using MEMS technology, the resonance
frequency of a membrane structure including a thin portion and a piezoelectric vibrator may
deviate from a desired resonance frequency due to manufacturing variations. Further, in the
sensor in which the membrane structures are arrayed, there is a problem that the resonance
frequency varies among the membrane structures (that is, the sensor sensitivity varies). A
method has been proposed in which the resonant frequency of the sensor is adjusted by applying
a predetermined voltage between the two electrodes during operation. In this case, the physical
property values (for example, film stress, Young's modulus) related to the rigidity change with
the change of the spontaneous polarization generated in the ferroelectric substance, and the
resonance frequency changes. However, when the voltage is continuously applied, the
polarization state gradually changes, which makes it difficult to control the resonance frequency
for a long time.
[0005]
Further, in Patent Document 1, a method of adjusting a resonant frequency of a sensor by
applying a predetermined voltage between two electrodes and changing (polling) the
spontaneous polarization of a ferroelectric in advance before operation of the sensor. Is also
proposed. However, in this method, for example, when left at room temperature, it is known that
the spontaneous polarization weakens, and it is difficult to control the resonance frequency over
a long period of time.
[0006]
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In these methods, it can not be adjusted unless it is a material having a spontaneous polarization
like a ferroelectric, and can not be applied to a piezoelectric such as aluminum nitride (AlN) or
zinc oxide (ZnO), for example.
[0007]
An object of the present invention is to provide an ultrasonic sensor capable of controlling a
resonant frequency over a long period of time and a method of manufacturing the same in view
of the above problems.
[0008]
In order to achieve the above object, in the ultrasonic sensor according to the first aspect of the
present invention, a piezoelectric thin film is disposed between two detection electrodes in a
substrate in which a thin portion is formed in part and the thickness direction of the substrate. A
piezoelectric vibrator formed on the thin-walled portion, and an adjusting electrode for applying
a predetermined voltage to the thin-walled portion of the thin-walled portion constituting the
membrane structure and the piezoelectric vibrator; The membrane structure is deformed in
accordance with the predetermined voltage.
[0009]
As described above, according to the present invention, it is possible to apply a predetermined
voltage to the thin-walled portion constituting the membrane structure, and when the
predetermined voltage is applied, an electrostatic force is generated and the membrane structure
is deformed (displaced).
That is, since the spring constant of the membrane structure substantially changes (so-called
negative electrostatic spring effect), the resonance frequency can be adjusted.
Further, since the predetermined voltage is not applied to the piezoelectric thin film forming the
piezoelectric vibrator (that is, the spontaneous polarization of the piezoelectric thin film is not
utilized), the resonance frequency can be controlled over a long period of time.
[0010]
As described above, since the spontaneous polarization of the piezoelectric thin film is not used
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to control the resonance frequency, for example, aluminum nitride (AlN) or zinc oxide (ZnO) may
be used as the piezoelectric thin film other than a ferroelectric such as PZT. Can be applied.
[0011]
For example, as described in claim 2, a first adjustment electrode and a second adjustment
electrode are included as adjustment electrodes, and a predetermined voltage is applied between
the first adjustment electrode and the second adjustment electrode. The configuration can be
adopted.
[0012]
Specifically, as described in claim 3, the substrate includes a semiconductor substrate of the first
conductivity type, and an insulating film laminated and arranged in multiple layers on the surface
of the semiconductor substrate on the piezoelectric vibrator side, and the first adjustment In the
surface layer on the side of the piezoelectric vibrator of the semiconductor substrate, the
electrode for the electrode is configured as a diffusion region of the second conductivity type
opposite to the first conductivity type, and the second adjustment electrode is insulated in the
thickness direction of the substrate The semiconductor substrate is removed while leaving the
first adjustment electrode in the formation region of the thin portion sandwiched between the
films, and the insulating film in contact with at least the surface of the semiconductor substrate is
removed among the insulating films, and the second adjustment is performed. It is preferable
that the membrane structure including the for-use electrode and the first adjustment electrode be
separated from each other.
[0013]
Thus, according to the present invention, since the membrane structure and the first adjustment
electrode are separated (that is, there is a gap between the membrane structure and the first
adjustment electrode), application of a predetermined voltage is performed. Thus, the membrane
structure can be deformed to adjust the resonance frequency.
The semiconductor substrate and the first adjustment electrode are isolated by PN junction.
[0014]
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As described in claim 4, when the semiconductor substrate is made of silicon, it is preferable to
adopt N conductivity type as the first conductivity type and P conductivity type as the second
conductivity type.
According to this structure, when the semiconductor substrate is etched with the strong alkaline
solution to form the thin portion, only the semiconductor substrate can be removed and the first
adjustment electrode of P conductivity type can be selectively left.
[0015]
According to the fifth aspect of the present invention, the semiconductor device is formed by
arranging the semiconductor layer on the supporting substrate with the embedded insulating
film interposed between the substrate and the semiconductor substrate. The first adjustment
electrode is configured by introducing an impurity into the semiconductor layer, and the second
adjustment electrode is disposed so as to be sandwiched by the insulation film in the thickness
direction of the substrate, and is thin. In the formation region of the portion, the semiconductor
substrate is removed leaving the first adjustment electrode, and the insulating film in contact
with at least the surface of the semiconductor substrate of the insulation film is removed, and the
membrane structure including the second adjustment electrode The first adjustment electrode
may be separated from the other.
[0016]
As described above, even when a semiconductor substrate (for example, an SOI structure
semiconductor substrate) having a buried insulating film is employed, the same structure as that
of the third aspect of the present invention can be realized.
[0017]
In the invention according to any one of claims 3 to 5, as described in claim 6, in the thickness
direction of the substrate, the thickness of the first adjustment electrode is thicker than the
thickness of the membrane structure. It is preferable to set it as the following.
Thereby, the deformation of the first adjustment electrode at the time of voltage application can
be suppressed, and the deformation amount of the membrane structure including the second
adjustment electrode can be increased.
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[0018]
Next, as a configuration different from the invention described in claim 2, as described in claim 7,
the lower portion on the substrate side which is one of the two detection electrodes includes the
first adjustment electrode as the adjustment electrode. A configuration in which a predetermined
voltage is applied between the detection electrode and the first adjustment electrode can also be
employed.
[0019]
As described above, the resonance frequency can be adjusted by the negative electrostatic spring
effect also by applying a predetermined voltage between the lower detection electrode and the
first adjustment electrode that constitute the detection electrode.
Further, since the predetermined voltage is not applied to the piezoelectric thin film forming the
piezoelectric vibrator (that is, the spontaneous polarization of the piezoelectric thin film is not
utilized), the resonance frequency can be controlled over a long period of time.
[0020]
Furthermore, since one of the adjustment electrodes and one of the detection electrodes are
shared, the configuration can be simplified as compared with the second aspect of the invention.
[0021]
The operational effects of the inventions of claims 8 and 9 are the same as the operational effects
of the inventions of claims 3 and 4, respectively, and thus the description thereof is omitted.
[0022]
The membrane structure is deformed by the reception of ultrasonic waves and the electrostatic
force due to the application of a predetermined voltage.
Therefore, it is preferable to prevent the lower detection electrode from being broken by stress
due to deformation.
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As described in claim 10, when adopting a configuration in which an impurity is introduced into
single crystal silicon without grain boundaries as the lower detection electrode, compared to a
configuration in which polycrystalline silicon in which grain boundaries exist is adopted, The
lower detection electrode can be made less likely to be destroyed.
That is, stability over time can be enhanced.
[0023]
The operational effects of the invention described in claim 11 are the same as the operational
effects of the invention described in claim 6, respectively, so the description thereof is omitted.
[0024]
In the invention according to any one of claims 1 to 11, the number of membrane structures is
not particularly limited.
For example, as described in claim 12, a plurality of membrane structures may be formed, and a
predetermined voltage may be applied to each of the thin portions forming the membrane
structure.
As described above, the invention described above can be applied to an ultrasonic sensor in
which a plurality of membrane structures are formed (in other words, ultrasonic elements are
arrayed).
In this case, it is possible to adjust the variation in resonant frequency of a plurality of membrane
structures (ultrasonic elements) formed in one ultrasonic sensor. For example, as described in
claim 13, by applying a predetermined voltage, the plurality of membrane structures can be
configured to be adjusted in resonance frequency to the same frequency.
[0025]
Next, according to the invention as recited in claim 14, a piezoelectric vibrator in which a
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piezoelectric thin film is disposed between two detection electrodes in the thickness direction of
the substrate is disposed on a thin portion formed on the substrate. In a method of
manufacturing an ultrasonic sensor, P is applied as a first adjustment electrode for applying a
predetermined voltage to a thin portion on a surface layer on the side of a piezoelectric vibrator
of a first silicon substrate of N conductivity type that constitutes the substrate. In the first
adjustment electrode forming step of forming a conductive type diffusion region, and after the
formation of the first adjustment electrode, the lower detection electrode and the piezoelectric
are formed on the portion of the substrate on which the thin portion is to be formed. A vibrator
forming step of forming a piezoelectric vibrator formed by laminating a body thin film and an
upper detection electrode in this order, and an etching process with a strong alkali liquid from
the back of the piezoelectric vibrator side surface of the first silicon substrate Leaving the first
adjustment electrode in the formation region of the In the etching step of removing the con
substrate, and in the formation region of the thin portion, the insulating film in contact with at
least the surface of the first silicon substrate in the insulating film is removed to separate the
membrane structure from the first adjustment electrode. A separation step is provided.
[0026]
As described above, according to the present invention, the first silicon substrate corresponding
to the formation region of the thin portion can be removed by the strong alkaline solution, and
the first adjustment electrode of P conductivity type can be selectively left.
Therefore, the first adjustment electrode and the thin portion can be efficiently formed. Note that,
as described in claim 15, the thin portion is formed between the first adjustment electrode and
the first adjustment electrode before the vibrator forming step. A second adjusting electrode
capable of applying a predetermined voltage is sandwiched between insulating films stacked in
multiple layers in the thickness direction of the substrate on the surface of the first silicon
substrate on which the first adjusting electrode is formed. It is good to have the 2nd adjustment
electrode formation process formed in a mode. Thus, an ultrasonic sensor configured to apply a
predetermined voltage between the first adjustment electrode and the second adjustment
electrode can be manufactured.
[0027]
Further, as described in claim 16, before the vibrator forming step, a second silicon on which a
silicon oxide film is formed as an insulating film on the surface of the first silicon substrate on
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which the first adjustment electrode is formed. A bonding step of bonding the substrate such that
the surface on the piezoelectric vibrator side and the silicon oxide film forming surface are in
contact with each other, and introducing the impurity into the second silicon substrate in the
vibrator forming step; Between the thin portions, lower detection electrodes to which a
predetermined voltage can be applied may be formed. Thus, an ultrasonic sensor configured to
apply a predetermined voltage between the first adjustment electrode and the lower detection
electrode can be manufactured.
[0028]
Hereinafter, embodiments of the present invention will be described based on the drawings. First
Embodiment FIG. 1 is a cross-sectional view showing a schematic configuration of an ultrasonic
sensor according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view
taken along the line A-A of FIG. FIG. 3 is a plan view of FIG. 1 as viewed from the piezoelectric
vibrator side.
[0029]
As shown in FIG. 1, the ultrasonic sensor 100 according to the present embodiment is a
piezoelectric ultrasonic sensor manufactured using MEMS technology, and is formed on a
substrate 110 and a thin portion 120 of the substrate 110. The piezoelectric vibrator 130 and
the adjustment electrode 140 for applying a predetermined voltage to the thin portion 120 are
included. The adjustment electrode 140 according to the present embodiment includes two
electrodes of a first adjustment electrode 141 and a second adjustment electrode 142.
[0030]
The substrate 110 includes a semiconductor substrate 111 of the first conductivity type. In the
present embodiment, an N-type silicon substrate with a plane orientation (100) is employed as
the semiconductor substrate 111, and a surface region on the piezoelectric vibrator side of the
semiconductor substrate 111 has a P conductivity type diffusion region as the first adjustment.
An electrode 141 is formed. Further, the through hole H is formed in the semiconductor
substrate 111 corresponding to the thin portion 120, and a part of the first adjustment electrode
141 is exposed in the through hole H. The first adjustment electrode 141 is disposed in part of
the formation region of the membrane structure in the planar direction of the substrate 110 so
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as not to completely close the through hole H. More specifically, as shown in FIG. 2, the first
adjustment electrode 141 is formed in a lattice shape in the formation region of the membrane
structure (the region surrounded by the broken line in FIG. 2).
[0031]
In the semiconductor substrate 111, as shown in FIG. 1, an N + diffusion region 111a is formed
in the surface layer on the piezoelectric vibrator side different from the formation portion of the
first adjustment electrode 141. Then, the potential of the pad 111b of the N + diffusion region
111a is set higher than that of the pad 141a of the first adjustment electrode 141 by, for
example, several volts or more, and the semiconductor substrate 111 and the first adjustment
electrode 141 are isolated by PN junction. It is done.
[0032]
In addition to the semiconductor substrate 111, the substrate 110 includes an insulating film
stacked and disposed on the semiconductor substrate 111 in multiple layers, and a second
adjustment electrode 142 interposed between the insulating films.
[0033]
The insulating film according to the present embodiment includes the first oxide film 112 made
of a silicon oxide film, the nitride film 113 made of a silicon nitride film, and the second oxide
film made of a silicon oxide film from the surface of the semiconductor substrate 111 on the
piezoelectric vibrator side. And 114 and a third oxide film 115 made of a silicon oxide film are
sequentially stacked.
Then, in a mode of being sandwiched between the second oxide film 114 and the third oxide film
115, the second adjustment electrode 142 made of a polycrystalline silicon film (polysilicon film)
into which an impurity (for example, boron or phosphorus) is introduced is disposed. ing. In the
present embodiment, boron is introduced into the polycrystalline silicon film to adjust to a
predetermined concentration.
[0034]
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The first oxide film 112 functions as an etching stopper when forming the through hole H in the
semiconductor substrate 111, and a portion corresponding to the thin portion 120 (membrane
structure) is removed and removed. Space S is configured. Further, of the above-described
insulating films 113 to 115 and the second adjustment electrode 142 stacked on the first oxide
film 112, a portion above the space S is a thin portion 120. That is, a space S is formed between
the lower surface (nitride film 113) of the thin portion 120 and the first adjustment electrode
141, and at least the piezoelectric vibrator 130 is separated so as not to vibrate.
[0035]
The nitride film 113 functions as an etching stopper when forming the space S in the first oxide
film 112, and in a state in which the piezoelectric vibrator 130 does not vibrate using the fact
that its film stress is tensile. It plays a function to prevent buckling of the membrane structure
(thin wall portion).
[0036]
The piezoelectric vibrator 130 has a piezoelectric thin film 131 disposed between two detection
electrodes 132 and 133.
In the present embodiment, as shown in FIG. 3, the lower detection electrode 132, the
piezoelectric, is formed on the third oxide film 115 so as to cover the formation region of the
membrane structure (the region surrounded by the broken line in FIG. 3). The body thin film 131
and the upper detection electrode 133 are stacked and arranged in this order.
[0037]
As a constituent material of the piezoelectric thin film 131, PZT which is a ferroelectric,
aluminum nitride (AlN), zinc oxide (ZnO) or the like can be adopted. Further, platinum (Pt), gold
(Au), aluminum (Al) or the like can be adopted as a constituent material of the detection
electrodes 132 and 133. In the present embodiment, PZT is employed as a constituent material
of the piezoelectric thin film 131, and Pt is employed as a constituent material of the detection
electrodes 132 and 133. Reference numerals 132a, 133a and 142a shown in FIG. 1 denote pads,
and reference numeral 118 denotes a silicon nitride film 118 serving as a mask when the
through holes H are formed.
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[0038]
As described above, in the ultrasonic sensor 100 according to the present embodiment, the thin
film portion 120 and the piezoelectric vibrator 130 constitute a membrane structure thinner
than the other portions, and the membrane structure applies an external force such as ultrasonic
waves. It is configured to be deformable along with it.
[0039]
As described above, in the piezoelectric ultrasonic sensor manufactured using the MEMS
technology, the resonance frequency of the membrane structure including the thin portion 120
and the piezoelectric vibrator 130 may be deviated from the desired resonance frequency due to
manufacturing variations. is there.
Further, in the ultrasonic sensor 100 in which the membrane structures are arrayed, there is a
problem that the resonance frequency varies among the membrane structures (that is, the sensor
sensitivity varies).
[0040]
On the other hand, in the ultrasonic sensor 100 according to the present embodiment, the
second adjustment electrode 142 constituting the thin portion 120 and the first adjustment
electrode 141 separated from the thin portion 120 via the space S. A predetermined voltage can
be applied in the meantime. That is, a predetermined voltage can be applied to the thin portion
120 of the membrane structure. Then, a predetermined voltage is applied between the first
adjustment electrode 141 and the second adjustment electrode 142, and the resilience of the
spring of the membrane structure when ultrasonic waves are received between the two
electrodes 141 and 142 is A reverse electrostatic force (electrostatic attraction) can be generated
to deform (displace) the membrane structure.
[0041]
Here, the electrostatic force acting in the vertical direction (the thickness direction of the
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substrate 110) is inversely proportional to the square of the distance between the two electrodes
141 and 142, and increases in proportion to the square of the applied voltage. Therefore, the
larger the applied voltage and the smaller the spacing, the smaller the net spring restoring force,
and the resonant frequency shifts to the lower frequency side. Thus, by means of the so-called
negative electrostatic spring effect, it is possible to substantially change the spring constant of
the membrane structure and to adjust the resonant frequency to the desired value. For example,
the voltage applied between the two electrodes 141 and 142 may be adjusted so that the output
of the ultrasonic sensor 100 is maximized in the state where the ultrasonic wave of a
predetermined frequency is received.
[0042]
In the present embodiment, in particular, the first adjustment electrode 141 is separated from
the thin portion 120 (membrane structure), and the thickness of the first adjustment electrode
141 is set to be larger than the thickness of the membrane structure. Therefore, when
electrostatic force (electrostatic attraction) is generated between the two electrodes 141 and
142, the first adjustment electrode 141 is not displaced, and the membrane structure including
the second adjustment electrode 142 is deformed (displacement) Do. As described above, when
the displacement of the first adjustment electrode 141 is suppressed and the membrane
structure including the second adjustment electrode 142 is deformed, the deformation amount of
the membrane structure can be increased. That is, the resonance frequency can be adjusted
efficiently.
[0043]
Further, according to the present embodiment, since the predetermined voltage is not applied to
the piezoelectric thin film 131 constituting the piezoelectric vibrator 130 (that is, the
spontaneous polarization of the piezoelectric thin film 131 is not used), the resonant frequency is
extended for a long time Can be controlled.
[0044]
The ultrasonic sensor 100 configured as described above can be formed, for example, by the
manufacturing method described below.
FIG. 4 is a cross-sectional view showing a part of a method of manufacturing the ultrasonic
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sensor 100 shown in FIG. 1, in which (a) is a first adjustment electrode forming step, (b) is a
second adjustment electrode forming step, (C) shows a vibrator formation process. FIG. 5 is a
cross-sectional view showing a part of a method of manufacturing the ultrasonic sensor 100,
following FIG. 4C, in which FIG. 5A shows an etching step and FIG. 5B shows a separation step.
[0045]
First, as shown in FIG. 4A, an N-type silicon substrate of plane orientation (100) is prepared as
the semiconductor substrate 111, and the adjustment electrode 140 is formed on the surface of
the semiconductor substrate 111 on the piezoelectric vibrator arrangement surface side. The first
adjustment electrode 141 which is one side is formed. Specifically, a mask (not shown) made of,
for example, a silicon oxide film with a thickness of 1 μm is formed on the surface of the
semiconductor substrate 111 on the side where the piezoelectric vibrator is disposed Boron ions
are implanted at a dose of 8.times.10 <16> / cm <2>) and heat-treated (e.g., 10 h at 1150 DEG
C.). Thus, the first adjustment electrode 141 having a thickness (depth) of about 3 μm is formed.
The above is the first adjustment electrode forming step.
[0046]
Further, impurities are ion-implanted (in this embodiment, phosphorus ions are implanted) into
the surface of the semiconductor substrate 111 on the side where the piezoelectric vibrator is
disposed which is different from the formation region of the first adjustment electrode 141
(phosphorus ion is implanted in this embodiment). Form an N + diffusion region 111a. A
diffusion method can also be applied to the formation of the first adjustment electrode 141 and
the N + diffusion region 111 a in addition to the ion implantation method.
[0047]
After the formation of the first adjustment electrode 141, as shown in FIG. 4B, a second
adjustment electrode, which is the other of the adjustment electrode 140, is formed on the
surface of the semiconductor substrate 111 on which the first adjustment electrode 141 is
formed. Form 142 Specifically, a first oxide film 112 made of a silicon oxide film is formed on the
surface of the semiconductor substrate 111. In the present embodiment, the first oxide film 112
having a thickness of about 4 μm is formed by plasma CVD. It may be formed by thermal
oxidation other than plasma CVD. After the first oxide film 112 is formed, a nitride film 113
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made of a silicon nitride film is formed on the first oxide film 112. In the present embodiment,
the nitride film 113 having a thickness of about 0.4 μm is formed by using the LP-CVD method.
At this time, a nitride film 116 made of a silicon nitride film is formed on the back surface of the
semiconductor substrate 111. After the nitride film 113 is formed, a second oxide film 114 made
of a silicon oxide film is formed on the nitride film 113. In the present embodiment, the second
oxide film 114 having a thickness of about 0.2 μm is formed by plasma CVD.
[0048]
After the second oxide film 114 is formed, for example, a polysilicon film is deposited on the
second oxide film 114 and impurity ions are implanted. In this embodiment, boron ions are
implanted at a dose of 2 × 10 <16> / cm <2> and then heat treatment (for example, 2 h at 1150
° C.). The impurity implanted into the polysilicon film is not limited to boron. For example,
phosphorus may be used. Further, the method of forming the polysilicon film into which the
impurity is introduced is not limited to the above example. An impurity-doped polysilicon film
may be formed. As described above, after the polysilicon film 142 into which the impurity is
introduced is formed, a third oxide film 115 made of a silicon oxide film is formed on the
polysilicon film 142. In the present embodiment, the third oxide film 115 having a thickness of
about 0.2 μm is formed by plasma CVD. At this time, a polysilicon film 117 is formed on the
back surface of the semiconductor substrate 111.
[0049]
Then, unnecessary portions are removed by, for example, dry etching in the order of the third
oxide film 115, the polysilicon film 142, the second oxide film 114, the nitride film 113, and the
first oxide film 112, as shown in FIG. Pattern each one. As a result, the polysilicon film 142 is
patterned, and the upper and lower surfaces of the polysilicon film 142 are sandwiched between
the third oxide film 115 and the second oxide film 114 to form a second adjustment electrode
142 covering the thin portion 120. The above is the second adjustment electrode forming step.
[0050]
After the second adjustment electrode 142 is formed, as shown in FIG. 4C, the piezoelectric
vibrator 130 is formed on the second adjustment electrode 142 so as to cover the region where
the thin portion 120 is formed. Specifically, a Pt film is deposited on the third oxide film 115 by
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vapor deposition, and unnecessary portions are removed by dry etching, for example. Thereby,
the lower detection electrode 132 patterned so as to cover the thin portion 120 is formed. In the
present embodiment, the lower detection electrode 132 having a thickness of about 0.25 μm is
formed. After the lower detection electrode 132 is formed, a PZT film as the piezoelectric thin
film 131 is formed on the lower detection electrode 132 so as to cover the thin portion 120 by a
sputtering method, a CVD method, a sol gel method, etc. For example, it is removed by dry
etching. In the present embodiment, the piezoelectric thin film 131 having a thickness of about
1.0 μm is formed by sputtering. After the piezoelectric thin film 131 is formed, a Pt film is
deposited on the piezoelectric thin film 131 by a vapor deposition method, and unnecessary
portions are removed by, for example, dry etching. Thereby, the upper detection electrode 133
patterned so as to cover the thin portion 120 is formed. In the present embodiment, the upper
detection electrode 133 having a thickness of about 0.25 μm is formed. The above is a
piezoelectric vibrator formation process.
[0051]
After the piezoelectric vibrator 130 is formed, as shown in FIG. 5A, the back surface of the
semiconductor substrate 111 is ground and polished to remove the nitride film 116 and the
polysilicon film 117. Thereafter, a silicon nitride film 118 is formed on the back surface of the
semiconductor substrate 111 by plasma CVD, and the unnecessary portion corresponding to the
formation portion of the thin portion 120 is removed by dry etching, for example. In the present
embodiment, a silicon nitride film 118 having a thickness of about 0.5 μm is formed and used as
a mask at the time of etching. After forming the mask, the back surface side of the semiconductor
substrate 111 is immersed in a strong alkaline solution such as TMAH or KOH, and the
semiconductor substrate 111 is anisotropically etched using the first oxide film 112 as an
etching stopper. Thereby, the through holes H are formed in the semiconductor substrate 111.
Although the semiconductor substrate 111 of N conductivity type is anisotropically etched by the
strong alkaline solution, the first adjustment electrode 141 of P conductivity type is not etched
and remains in the through hole H. The above is the etching step.
[0052]
The portion of the first adjustment electrode 141 present in the through hole H (that is, present
in the formation region of the membrane structure) has a lattice shape. Therefore, after forming
the through holes H, the portion of the first oxide film 112 corresponding to the thin-walled
portion 120 (membrane structure) is removed through the grid-like first adjustment electrode
141. Specifically, the back surface side of the semiconductor substrate 111 is immersed in, for
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example, a hydrofluoric acid solution to remove the first oxide film 112. Thus, the portion of the
first oxide film 112 corresponding to the thin portion 120 (membrane structure) is removed to
form the space S, and the thin portion 120 is formed on the substrate 110. That is, a membrane
structure including the thin portion 120 and the piezoelectric vibrator 130 is formed. In addition,
the thin portion 120 and the first adjustment electrode 141 are separated. The above is the
separation step.
[0053]
As described above, according to the method of manufacturing the ultrasonic sensor 100
according to the present embodiment, the ultrasonic sensor 100 configured to apply a
predetermined voltage between the first adjustment electrode 141 and the second adjustment
electrode 142 (FIG. Reference) can be formed.
[0054]
In addition, the semiconductor substrate 111 corresponding to the formation region of the thin
portion 120 can be removed by the strong alkaline solution, and the first adjustment electrode
141 of P conductivity type can be selectively left.
Therefore, the first adjustment electrode 141 and the thin portion 120 can be formed efficiently.
[0055]
The ultrasonic sensor 100 configured to apply a predetermined voltage between the first
adjustment electrode 141 and the second adjustment electrode 142 is not limited to the above
example. For example, as shown in FIG. 6, the stacking order of the second adjustment electrode
142 and the nitride film 113 may be reversed with respect to the configuration shown in FIG. 1.
In this case, since the distance between the first adjustment electrode 141 and the second
adjustment electrode 142 is reduced, the resonance frequency can be adjusted with a lower
voltage than the configuration shown in FIG. FIG. 6 is a cross-sectional view showing a
modification.
[0056]
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Second Embodiment Next, a second embodiment of the present invention will be described based
on FIG. FIG. 7 is a cross-sectional view showing a schematic configuration of an ultrasonic sensor
according to a second embodiment of the present invention.
[0057]
The ultrasonic sensor according to the second embodiment has many parts in common with the
ultrasonic sensor 100 according to the first embodiment. Therefore, detailed description of
common parts is omitted, and different parts will be mainly described.
[0058]
As shown in FIG. 7, the ultrasonic sensor 200 according to the present embodiment is also a
piezoelectric ultrasonic sensor manufactured using MEMS technology, and is formed on the
substrate 210 and the thin portion 220 of the substrate 210. The piezoelectric vibrator 230 and
the adjustment electrode 240 for applying a predetermined voltage to the thin portion 220 are
included, and the adjustment electrode 240 includes two electrodes of a first adjustment
electrode 241 and a second adjustment electrode 242. It consists of
[0059]
The substrate 210 includes a semiconductor substrate 211 in which a semiconductor layer is
disposed on a support substrate 211 b via a buried insulating film (silicon oxide film) 211 a.
An impurity (in this embodiment, boron) is introduced into this semiconductor layer, and is
patterned into a predetermined shape to constitute a first adjustment electrode 241 shown in
FIG.
Further, through holes H are formed in the support substrate 211 b corresponding to the thin
portions 220.
[0060]
The substrate 210 includes, in addition to the semiconductor substrate 211, an insulating film
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stacked and arranged in multiple layers on the semiconductor substrate 211, and a second
adjustment electrode 242 interposed between the insulating films. The configurations of the
insulating film and the second adjustment electrode 242 are basically the same as the insulating
film and the second adjustment electrode 142 of the ultrasonic sensor 100 shown in the first
embodiment. The difference is that a first oxide film 212 made of a silicon oxide film is formed
on the buried insulating film 211 a and the first adjustment electrode 241. Then, portions of the
buried insulating film 211 a and the first oxide film 212 corresponding to the thin-walled portion
120 (membrane structure) are respectively removed, and a space S is formed in the removed
portions. Therefore, also in this embodiment, the nitride film 213 stacked on the first oxide film
212, the second oxide film 214 made of a silicon oxide film, and the third oxide film 215 made of
a silicon oxide film and the second adjustment electrode Of the 242, a portion on the space S is a
thin portion 220. That is, a space S is formed between the lower surface (nitride film 213) of the
thin portion 220 and the first adjustment electrode 241, and at least the piezoelectric vibrator
230 is separated without separation. The other configuration is the same as that of the ultrasonic
sensor 100 shown in the first embodiment, and thus the description thereof is omitted.
[0061]
As described above, also in the ultrasonic sensor 200 according to the present embodiment,
between the second adjustment electrode 242 configuring the thin portion 220 and the first
adjustment electrode 241 separated from the thin portion 220 via the space S. Can be applied a
predetermined voltage. That is, a predetermined voltage can be applied to the thin portion 220 of
the membrane structure. Then, a predetermined voltage is applied between the first adjustment
electrode 241 and the second adjustment electrode 242, and the resilience of the spring of the
membrane structure when ultrasonic waves are received between the two electrodes 241 and
242 is A reverse electrostatic force (electrostatic attraction) can be generated to deform
(displace) the membrane structure. Therefore, the resonant frequency can be adjusted to a
desired value by substantially changing the spring constant of the membrane structure by the socalled negative electrostatic spring effect.
[0062]
Also in the present embodiment, the first adjustment electrode 241 is separated from the thin
portion 220 (membrane structure), and the thickness of the first adjustment electrode 241 is set
to be larger than the thickness of the membrane structure. . Therefore, since the displacement of
the first adjustment electrode 241 can be suppressed and the membrane structure including the
second adjustment electrode 242 can be deformed, the deformation amount of the membrane
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structure can be increased. That is, the resonance frequency can be adjusted efficiently.
[0063]
Further, since the predetermined voltage is not applied to the piezoelectric thin film 231
constituting the piezoelectric vibrator 230 (that is, the spontaneous polarization of the
piezoelectric thin film 231 is not utilized), the resonance frequency can be controlled over a long
period of time.
[0064]
The ultrasonic sensor 200 configured as described above can be formed, for example, by the
manufacturing method described below.
FIG. 8 is a cross-sectional view showing a part of a method of manufacturing the ultrasonic
sensor 200 shown in FIG. 7, in which (a) is a first adjustment electrode forming step, (b) is a
second adjustment electrode forming step (C) shows a vibrator formation process. FIG. 9 is a
cross-sectional view showing a part of a method of manufacturing the ultrasonic sensor 200
following FIG. 8C, in which FIG. 9A shows an etching process and FIG. 9B shows a separation
process.
[0065]
First, as shown in FIG. 8A, as a semiconductor substrate 211, a semiconductor substrate (SOI
substrate) 211 in which a semiconductor layer 211c is disposed on a supporting substrate 211b
via a buried insulating film 211a made of a silicon oxide film. Prepare. In the present
embodiment, the thickness of the semiconductor layer 211c is 3.5 μm, and the thickness of the
embedded insulating film 211a is about 0.5 μm. Then, impurities are ion-implanted into the
semiconductor layer 211c (in this embodiment, boron ions are implanted at a dose of 8 × 10
<16> / cm <2>) and heat treatment (eg, 10 h at 1150 ° C.) is performed. Pattern in shape.
Thereby, the first adjustment electrode 241 is formed. In the present embodiment, the structure
of the first adjustment electrode 241 is substantially the same as the structure of the first
adjustment electrode 141 shown in the first embodiment. That is, in the formation region of the
membrane structure, the first adjustment electrode 241 is formed in a lattice shape. The impurity
is not limited to boron, and other than that, for example, phosphorus can be adopted. The above
is the first adjustment electrode forming step.
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[0066]
After the formation of the first adjustment electrode 241, the second adjustment electrode 242,
which is the other of the adjustment electrodes 240, is formed. Specifically, as shown in FIG. 8B,
a first oxide film 212 made of a silicon oxide film is formed on the surfaces of the buried
insulating film 211a and the first adjustment electrode 241. In the present embodiment, a silicon
oxide film is formed by plasma CVD, and smoothing processing is performed by etch back to
form a first oxide film 212 having a thickness of about 5 μm. The smoothing process may be
omitted. After the formation of the first oxide film 212, the nitride film 213 consisting of a silicon
nitride film, the second oxide film 214, the second adjusting electrode 242, and the third oxide
film 215 are laminated by the same manufacturing method and configuration as in the first
embodiment. Do. The above is the second adjustment electrode forming step. Note that reference
numeral 216 shown in FIG. 8B is a nitride film formed on the back surface of the surface on
which the buried insulating film 211 a of the support substrate 211 b is disposed along with the
formation of the nitride film 213, and reference numeral 217 indicates the second adjustment. It
is a polysilicon film formed along with the formation of the electrode 242.
[0067]
After the formation of the second adjustment electrode 242, as shown in FIG. 8C, the
manufacturing method and the configuration are the same as in the first embodiment so as to
cover the formation region of the thin portion 220 on the second adjustment electrode 242. ,
And the piezoelectric vibrator 230 are formed. Therefore, the description is omitted.
[0068]
After the piezoelectric vibrator 230 is formed, as shown in FIG. 9A, the back surface of the
support substrate 211b is ground and polished to remove the nitride film 216 and the
polysilicon film 217. Thereafter, a silicon nitride film 218 is formed on the back surface of the
support substrate 211b by plasma CVD, and the unnecessary portion corresponding to the
formation portion of the thin portion 220 is removed by dry etching, for example. In the present
embodiment, a silicon nitride film 218 having a thickness of about 0.5 μm is formed and used as
a mask at the time of etching. After forming the mask, the back surface side of the support
substrate 211b is immersed in a strong alkaline solution such as TMAH or KOH, and the support
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substrate 211b is anisotropically etched using the embedded insulating film 211a as an etching
stopper. Thereby, the through holes H are formed in the support substrate 211b. The above is
the etching step.
[0069]
After the through holes H are formed, the portions of the embedded insulating film 211 a and the
first oxide film 212 corresponding to the thin portion 220 (membrane structure) are removed.
Specifically, the back surface side of the support substrate 211b is immersed in, for example, a
hydrofluoric acid solution to remove the embedded insulating film 211a and the first oxide film
212. As a result, the portions of the embedded insulating film 211 a and the first oxide film 212
corresponding to the thin portion 220 (membrane structure) are removed to form the space S,
and the thin portion 220 is formed on the substrate 210. That is, a membrane structure
including the thin portion 220 and the piezoelectric vibrator 230 is formed. In addition, the thin
portion 220 and the first adjustment electrode 241 are separated. The above is the separation
step.
[0070]
As described above, according to the method of manufacturing the ultrasonic sensor 200
according to the present embodiment, the ultrasonic sensor 200 configured to apply a
predetermined voltage between the first adjustment electrode 241 and the second adjustment
electrode 242 (see FIG. 7). Reference) can be formed.
[0071]
Further, in the present embodiment, the semiconductor substrate 211 having an SOI structure is
adopted as the semiconductor substrate 211, an impurity is introduced into the semiconductor
layer 211c, and patterning is performed to form the first adjustment electrode 241.
Therefore, as in the ultrasonic sensor 100 shown in the first embodiment, the N + diffusion
region and the pad for insulating and separating at the PN junction can be eliminated.
[0072]
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22
Third Embodiment Next, a third embodiment of the present invention will be described based on
FIG. FIG. 10 is a cross-sectional view showing a schematic configuration of an ultrasonic sensor
according to a third embodiment of the present invention.
[0073]
The ultrasonic sensor according to the second embodiment has many parts in common with the
ultrasonic sensors 100 and 200 according to the first and second embodiments, so the detailed
description of the common parts will be omitted hereinafter, and the different parts will be
emphasized Explain to.
[0074]
As shown in FIG. 10, the ultrasonic sensor 300 according to the present embodiment is also a
piezoelectric ultrasonic sensor manufactured using MEMS technology, and is formed on the
substrate 310 and the thin portion 320 of the substrate 310. A piezoelectric vibrator 330 and an
adjustment electrode 340 for applying a predetermined voltage to the thin portion 320 are
included.
The second adjustment electrode 342 of the two adjustment electrodes 340 is shared with the
lower detection electrode 332 of the piezoelectric vibrator 330.
[0075]
The substrate 310 includes a semiconductor substrate 311 of the first conductivity type, as in
the first embodiment. Also in the present embodiment, an N-type silicon substrate with a plane
orientation (100) is adopted as the semiconductor substrate 311, and a surface region on the
piezoelectric vibrator side of the semiconductor substrate 311 has a P conductivity type diffusion
region as the first adjustment. An electrode 341 is formed. Further, in the semiconductor
substrate 311, the through holes H are formed corresponding to the thin portions 320, and a
part of the first adjustment electrode 341 is exposed in the through holes H. The first adjustment
electrode 341 is formed in a lattice shape so as not to completely close the through holes H.
Reference numeral 311 a shown in FIG. 10 is an N + diffusion region for insulating and
separating the semiconductor substrate 311 and the first adjustment electrode 341 by PN
junction, and reference numeral 311 b is a pad.
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[0076]
In addition to the semiconductor substrate 311, the substrate 310 includes an insulating film
disposed on the semiconductor substrate 311 and a lower detection electrode 332 of the
piezoelectric vibrator 330 disposed on the insulating film.
[0077]
The insulating film according to the present embodiment is a first oxide film 313 made of a
silicon oxide film, disposed on the surface of the semiconductor substrate 311 on the
piezoelectric vibrator side.
Then, on the first oxide film 313, a lower detection electrode 332 made of single crystal silicon
into which an impurity (for example, boron or phosphorus) is introduced is disposed.
[0078]
The first oxide film 313 functions as an etching stopper when forming the through hole H in the
semiconductor substrate 311, and the portion corresponding to the thin portion 320 (membrane
structure) is removed and removed. Space S is configured. In the lower detection electrode 332
stacked on the first oxide film 313, a portion above the space S is a thin portion 320. That is, a
space S is formed between the lower surface (lower detection electrode 332) of the thin portion
320 and the first adjustment electrode 341, and at least the piezoelectric vibrator 330 does not
vibrate, and both are separated. As described above, in the present embodiment, the lower
detection electrode 332 is configured to perform the function as the second adjustment electrode
342 and the function as the thin portion 320. The other configuration is the same as that of the
ultrasonic sensor 100 shown in the first embodiment, and thus the description thereof is omitted.
[0079]
As described above, also in the ultrasonic sensor 300 according to the present embodiment, the
lower detection electrode 332 (second adjustment electrode 342) constituting the thin portion
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320 and the first portion separated from the thin portion 320 via the space S. A predetermined
voltage can be applied to the adjustment electrode 341. That is, a predetermined voltage can be
applied to the thin portion 320 of the membrane structure. Then, a predetermined voltage is
applied between the first adjustment electrode 341 and the lower detection electrode 332
(second adjustment electrode 342), and an ultrasonic wave is received between the two
electrodes 341, 332 (342). The membrane structure can be deformed (displaced) by causing an
electrostatic force (electrostatic attraction) opposite to the restoring force of the membrane
structure. Therefore, the resonant frequency can be adjusted to a desired value by substantially
changing the spring constant of the membrane structure by the so-called negative electrostatic
spring effect.
[0080]
Also in the present embodiment, the first adjustment electrode 341 is separated from the thin
portion 320 (membrane structure), and the thickness of the first adjustment electrode 341 is set
to be larger than the thickness of the membrane structure. . Therefore, the displacement of the
first adjustment electrode 341 can be suppressed, and the membrane structure including the
lower detection electrode 332 (the second adjustment electrode 342) can be deformed.
Therefore, the deformation amount of the membrane structure can be increased. Can. That is, the
resonance frequency can be adjusted efficiently.
[0081]
Further, since the predetermined voltage is not applied to the piezoelectric thin film 331
constituting the piezoelectric vibrator 330 (that is, the spontaneous polarization of the
piezoelectric thin film 331 is not utilized), the resonance frequency can be controlled over a long
period of time.
[0082]
Further, since the lower detection electrode 332 and the second adjustment electrode 342 are
shared, the structure can be simplified as compared with the configurations shown in the first
and second embodiments.
[0083]
In the present embodiment, an example is shown in which the lower detection electrode 332
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(second adjustment electrode 342) is formed by introducing an impurity into single crystal
silicon.
Other than that, as in the first embodiment, it is also possible to introduce an impurity into the
polysilicon film.
However, since grain boundaries are present in the polysilicon film, cracks are likely to occur
along grain boundaries starting from the grain boundaries as the membrane structure is
deformed. Therefore, as shown in this embodiment, it is preferable to form the lower detection
electrode 332 (second adjustment electrode 342) using single crystal silicon without grain
boundaries.
[0084]
The ultrasonic sensor 300 configured in this way can be formed, for example, by the
manufacturing method described below. 11 is a cross-sectional view showing a part of a method
of manufacturing the ultrasonic sensor 300 shown in FIG. 10, wherein (a) is a first adjustment
electrode forming step, (b) is a second silicon substrate preparation step, c) is a figure which
shows the formation part of the lower detection electrode (2nd electrode for adjustment) among
the bonding process and (d) is a vibrator | oscillator formation process. FIG. 12 is a crosssectional view showing a part of a method of manufacturing the ultrasonic sensor 300 following
FIG. 11 (d), wherein (a) is a vibrator forming step, (b) an etching step, and (c) The separation
process is shown.
[0085]
First, as shown in FIG. 11A, also in the present embodiment, an N-type silicon substrate with a
plane orientation (100) is prepared as the semiconductor substrate 311, and the surface layer of
the semiconductor substrate 311 on the piezoelectric vibrator arrangement surface side is
prepared. The first adjustment electrode 341 which is one of the adjustment electrodes 340 is
formed. Since this process is the same as the first adjustment electrode forming process shown in
the first embodiment, the description thereof is omitted. As in the first embodiment, in addition
to the first adjustment electrode 341, an N + diffusion region 311a for taking out a potential is
also formed in the semiconductor substrate 311.
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[0086]
Further, in the present embodiment, as shown in FIG. 11B, in parallel with the first adjustment
electrode forming step, the second silicon substrate 312 is prepared, and the surface of the
substrate 312 is made of a silicon oxide film. An oxide film 313 is formed. In the present
embodiment, an oxide film 313 having a thickness of about 2 μm is formed by thermal
oxidation. The preparation of the second silicon substrate 312 may be performed before and
after the formation of the first adjustment electrode 341. The above is the second silicon
substrate preparation step.
[0087]
Next, as shown in FIG. 11C, the second silicon substrate 312 is formed on the surface of the
semiconductor substrate 311 on which the first adjustment electrode 341 is formed, and the
oxide film 313 is formed on the first adjustment electrode formation surface. Arrange so as to be
in contact with each other and bond them together. Then, grinding and polishing are performed
from the back surface of the oxide film formation surface so that the thickness of the second
silicon substrate 312 becomes a predetermined thickness. In this embodiment, the thickness
(excluding the oxide film 313) of the second silicon substrate 312 is set to about 1 μm by this
grinding and polishing. The above is the bonding step.
[0088]
After completion of bonding, impurities are introduced into the second silicon substrate 312
adjusted to have a predetermined thickness, and heat treatment is performed, and the
unnecessary portion is dry etched, for example, and patterned into a predetermined shape. As a
result, as shown in FIG. 11D, the lower detection electrode 332 (second adjustment electrode
342) is formed. In the present embodiment, boron ions are implanted at a dose of 8 × 10 <16> /
cm <2> and then heat treatment (for example, 2 h at 1150 ° C.). The impurity implanted into the
second silicon substrate 312 is not limited to boron. For example, phosphorus may be used. The
above is the formation portion of the lower detection electrode 332 in the vibrator formation
step. The formation of the lower detection electrode corresponds to the second adjustment
electrode forming step described in the first and second embodiments. Further, in this step,
unnecessary portions of the oxide film 313 are dry etched, for example, to pattern the oxide film
313. In FIG. 11D, contact holes for the pads 341a and 311b are formed.
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[0089]
After the lower detection electrode 332 (second adjustment electrode 342) is formed, as shown
in FIG. 12A, the piezoelectric thin film 331 and the upper detection electrode 333 are
sequentially stacked and arranged on the lower detection electrode 332. , And the piezoelectric
vibrator 330 are formed. The configuration and manufacturing method of the piezoelectric thin
film 331 and the upper detection electrode 333 are the same as in the first embodiment, and
thus the description thereof is omitted. The above is a piezoelectric vibrator formation process.
[0090]
After the piezoelectric vibrator 330 is formed, the back surface of the semiconductor substrate
311 is ground and polished, and then a silicon nitride film 318 is formed on the back surface of
the semiconductor substrate 311 by plasma CVD method. Remove by dry etching. As a result, as
shown in FIG. 12B, the through holes H are formed in the semiconductor substrate 311. The
method of forming the through holes H is the same as that of the first embodiment, and thus the
description thereof is omitted. The above is the etching step.
[0091]
Also in the present embodiment, the portion of the first adjustment electrode 341 in the through
hole H (that is, in the formation region of the membrane structure) is in a lattice shape.
Therefore, after the through holes H are formed, the portion of the oxide film 313 corresponding
to the thin portion 320 (membrane structure) is removed through the grid-like first adjustment
electrode 341. Specifically, the back surface side of the semiconductor substrate 311 is
immersed in, for example, a hydrofluoric acid solution to remove the oxide film 313. Thus, as
shown in FIG. 12C, the portion of the oxide film 313 corresponding to the thin portion 320
(membrane structure) is removed to form the space S, and the thin portion 320 is formed on the
substrate 310. That is, a membrane structure including the thin portion 320 (lower detection
electrode 332) and the piezoelectric vibrator 330 is formed. In addition, the thin portion 320 and
the first adjustment electrode 341 are separated. The above is the separation step.
[0092]
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As described above, according to the method of manufacturing the ultrasonic sensor 300
according to the present embodiment, the first adjustment electrode 341 is included as the
adjustment electrode 340, and between the lower detection electrode 332 and the first
adjustment electrode 341, An ultrasonic sensor 300 (see FIG. 10) configured to apply a
predetermined voltage can be formed.
[0093]
Further, since the lower detection electrode 332 and the second adjustment electrode 342 are
shared, the manufacturing process can be simplified as compared with the configuration shown
in the first and second embodiments.
[0094]
The preferred embodiments of the present invention have been described above. However, the
present invention is not limited to the above-described embodiments, and various modifications
can be made without departing from the scope of the present invention.
The gist of the present invention is that a predetermined voltage is applied only to the thinwalled portion constituting the membrane structure, and the entire membrane structure can be
displaced (deformed) by the electrostatic force generated thereby to adjust the resonance
frequency. .
[0095]
In the present embodiment, the number of membrane structures formed on the substrates 110,
210, and 310 is not particularly limited.
The membrane structure is configured as one ultrasound element. For example, the present
invention described above may be applied to one membrane structure configured on one
substrate 110, 210, 310. In addition, with respect to an ultrasonic sensor in which a plurality of
membrane structures are arrayed on one substrate 110, 210, 310, the resonance frequency of
each membrane structure can be adjusted to reduce the variation of the resonance frequency. .
That is, by applying a predetermined voltage, the plurality of membrane structures can be
configured to be adjusted to have the same resonant frequency.
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[0096]
It is a sectional view showing a schematic structure of an ultrasonic sensor concerning a 1st
embodiment of the present invention. It is sectional drawing in alignment with the AA of FIG. It is
the top view which looked at FIG. 1 from the piezoelectric vibrator side. It is sectional drawing
which shows a part of 1 manufacturing method of the ultrasonic sensor shown in FIG. 1, (a) is a
1st electrode for adjustment electrode formation, (b) is a 2nd electrode for electrode formation,
and (c) is vibration. The child formation process is shown. It is sectional drawing which shows a
part of manufacturing method of an ultrasonic sensor following FIG.4 (c), (a) is an etching
process and (b) has shown the separation | isolation process. It is sectional drawing which shows
a modification. It is a sectional view showing a schematic structure of an ultrasonic sensor
concerning a 2nd embodiment of the present invention. It is sectional drawing which shows a
part of 1 manufacturing method of the ultrasonic sensor shown in FIG. 7, (a) is a 1st electrode
formation process for adjustment, (b) is a 2nd electrode formation process, (c) is vibration. The
child formation process is shown. It is sectional drawing which shows a part of manufacturing
method of an ultrasonic sensor following FIG.8 (c), (a) is an etching process and (b) has shown
the separation | isolation process. It is sectional drawing which shows schematic structure of the
ultrasonic sensor which concerns on 3rd Embodiment of this invention. It is sectional drawing
which shows a part of manufacturing method of the ultrasonic sensor shown in FIG. 10, (a) is a
1st electrode for adjustment electrode formation, (b) is a 2nd silicon substrate preparatory
process, (c) is bonding. A process and (d) are figures showing a formation part of a lower
detection electrode (second adjustment electrode) in a vibrator formation process. 11 (d) is a
cross-sectional view showing a part of a method of manufacturing an ultrasonic sensor, following
FIG. 11 (d), wherein (a) shows a vibrator forming step, (b) shows an etching step, and (c) shows a
separating step. There is.
Explanation of sign
[0097]
100 ... ultrasonic sensor 110 ... substrate 111 ... semiconductor substrate 120 ... thin portion 130
... piezoelectric vibrator 131 ... piezoelectric thin film 132 ... lower detection electrode 133 ...
Upper detection electrode 140 ... adjustment electrode 141 ... first adjustment electrode 142 ...
second adjustment electrode
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