close

Вход

Забыли?

вход по аккаунту

?

JP2014236840

код для вставкиСкачать
Patent Translate
Powered by EPO and Google
Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JP2014236840
Abstract: To improve the reliability of sealing of a capacitive transducer. A capacitive transducer
has a cell including a first electrode and a vibrating membrane including a second electrode
disposed opposite to the first electrode via a cavity. Equipped with The height of the gap 9
around the sealing portion 11 sealing the etching opening 13 provided to form the cavity 8 by
the sacrificial layer etching is lower than the height of the cavity 8. In the manufacturing method,
in the step of forming a sacrificial layer for forming a gap connected to the cavity through the
cavity and the etching channel, the height of the portion of the sacrificial layer to be the gap is
the portion of the sacrificial layer to be the cavity. Lower than the height of the [Selected figure]
Figure 1
Capacitance transducer and method of manufacturing the same
[0001]
The present invention relates to a capacitive transducer used as an ultrasonic transducer or the
like, a method of manufacturing the same, and the like.
[0002]
In recent years, with the development of microfabrication technology, various micromechanical
devices machined with an accuracy on the order of micrometers have been realized.
Development of a capacitive transducer (CMUT: Capasitive-Micromachined-Ultrasonic-
04-05-2019
1
Transducer) has been promoted using such a technology. CMUT is an ultrasonic device that
vibrates a lightweight diaphragm and transmits / receives (at least one of transmission and
reception) an acoustic wave such as an ultrasonic wave (hereinafter, may be represented by an
ultrasonic wave). Among them, those having excellent broadband characteristics are easily
obtained. Therefore, when CMUT is used as a medical application, diagnosis can be performed
with higher accuracy than a conventionally used ultrasonic device made of a piezoelectric
element, and therefore, attention is being focused on as a substitute. In the present specification,
acoustic waves include those called sound waves, ultrasonic waves, and photoacoustic waves. For
example, the inside of the subject is irradiated with light (electromagnetic wave) such as visible
light or infrared light, and the photoacoustic wave generated inside the subject is included.
[0003]
The capacitive transducer includes, for example, a first electrode on a substrate such as Si, a
second electrode opposed to the first electrode via a gap (cavity), and a second electrode, and is
formed on the cavity. And a cell structure composed of a vibrating membrane made of a
membrane and a vibrating membrane support. And, the membrane has a structure for sealing the
cavity. As one of methods for manufacturing a capacitive transducer, there is a method in which
a material is laminated on a substrate such as Si. The cavity structure is formed by depositing a
sacrificial layer material in advance in a portion to be a gap and etching away the sacrificial layer
from the opening (etching opening) provided in a part of the vibrating film. Capacitance
transducers are sometimes used in liquids such as in water or in oil, and in transducers that
transmit and receive ultrasonic waves by vibration of the vibrating membrane, the vibrations of
the vibrating membrane when those liquids enter the cavity Deterioration occurs in the
characteristics. Therefore, it is necessary to seal and use the etching opening provided to form
the cavity.
[0004]
In the capacitance type transducer described in Non-Patent Document 1, the silicon nitride film
formed by LP-CVD is deposited in the flow path connected from the etching opening to the cavity
under the vibrating film. It is sealed. LP-CVD is an abbreviation of Low-Pressure-Chemical-VaporDeposition. In LP-CVD, due to the nature of the device, a film is deposited with a substantially
uniform thickness from the etching opening to the cavity through the channel, and the cavity is
sealed by depositing the film by the height of the channel. Be done. Therefore, the cavity can be
easily sealed by reducing the height of the flow path connected from the etching opening to the
cavity, and the sealing performance is improved. In the present specification, “height” means
04-05-2019
2
the width in the direction perpendicular to the substrate. If there is no misunderstanding about
this height, it may be called "thickness".
[0005]
Also in the capacitive transducer described in Patent Document 1, the cavity is formed by
removing the sacrificial layer from the etching opening as in Non-Patent Document 1.
Furthermore, sealing of the cavity is performed by depositing a film in the etching opening by
plasma-enhanced-chemical-vapor-deposition (PE-CVD). In PE-CVD, as in LP-CVD, a film does not
easily penetrate into the interior of the cavity or flow path, and the film is formed to be deposited
in the portion of the etching opening. Therefore, in order to seal the cavity, it is necessary to
deposit the sealing film high enough for the height of the cavity.
[0006]
U.S. Pat. No. 5,982,709
[0007]
Arif Sanli Ergunet al.
IEEE Transactions on
Ultrasonics,Vol52,No.12,DECEMBER
2005,2242−2257
[0008]
The seal for sealing the cavity of the capacitive transducer needs a membrane about three times
as thick as the height of the cavity. Thus, the higher the cavity, the greater the height or
thickness of the seal required, and the less reliable the seal.
[0009]
In view of the above problems, a capacitive transducer according to the present invention has a
04-05-2019
3
cell including a first electrode, and a vibrating film including a second electrode provided
opposite to the first electrode via a cavity. A capacitance type transducer, the height of the gap
around the sealing portion sealing the etching opening provided for forming the cavity by
sacrificial layer etching is It is characterized by being lower than height.
[0010]
Further, in view of the above problems, a method of manufacturing a capacitive transducer
according to the present invention includes a first electrode, and a vibrating film including a
second electrode provided opposite to the first electrode via a cavity. A method of manufacturing
a capacitive transducer comprising a cell having the following steps:
Forming a sacrificial layer for forming the cavity and a gap connected to the cavity via the
etching channel; forming a membrane on the structure on which the sacrificial layer is formed;
and the sacrificial layer to be the gap Forming an etching opening in the membrane on the
portion of the part; removing the sacrificial layer through the etching opening to form the cavity;
and sealing the etching opening. And forming a sealing portion in a region including the etching
opening. Then, in the step of forming the sacrificial layer, the height of the portion of the
sacrificial layer to be the gap is made lower than the height of the portion of the sacrificial layer
to be the cavity.
[0011]
In the present invention, the height of the gap below and around the etching opening is lower
than the height of the cavity below the vibrating membrane. According to this structure, the
height of the sealing portion required to seal the cavity is determined by the height of the gap in
the vicinity of the etching opening. Even in a structure having a cavity, the height of the sealing
portion required to seal the cavity is reduced. Therefore, since the cavity can be sealed with a
sealing portion thinner than the conventional one and sealing becomes easy, the reliability of the
sealing is improved.
[0012]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining an embodiment of a
04-05-2019
4
capacitive transducer of the present invention. FIG. 6 is a view for explaining another
embodiment of the capacitive transducer of the present invention. Sectional drawing explaining
the sealing part for sealing a cavity. FIG. 7 shows an embodiment of a method of manufacturing a
capacitive transducer of the present invention. FIG. 7 illustrates another embodiment of a method
of manufacturing a capacitive transducer according to the present invention. FIG. 7 shows an
embodiment of a method of manufacturing a capacitive transducer of the present invention. FIG.
7 illustrates another embodiment of a method of manufacturing a capacitive transducer
according to the present invention. Fig. 1 shows an embodiment of a device comprising a
capacitive transducer according to the invention.
[0013]
In the capacitance type transducer according to the present invention, in the state after the
sealing portion is formed, the height of the gap around the sealing portion sealing the etching
opening is the height of the cavity under the vibrating film. Less than height. Also, in the state
after the sacrificial layer is formed in the middle of the manufacturing method, the height of the
portion of the sacrificial layer to be a gap connected via the etching channel with the cavity is
Lower than Then, an etching opening is formed in the membrane on the portion of the sacrificial
layer to be the gap. Here, the sacrificial layer etching forms a gap under and around the etching
opening, an etching channel, and a cavity, and the gap communicates with the cavity through the
etching channel. That is, the sacrificial layer is three-dimensionally shaped including the gap, the
etching channel, and the portion to be the cavity, and the membrane is formed thereon. This
three-dimensional shape is, for example, a shape like an outer peripheral shape in which a large
circle and a small circle are connected by a passage as shown in FIG. For example, it has a step
shape as shown in FIG. Further, “a gap around the sealing portion” is a space adjacent to the
sealing portion, and is a space included in a gap below and around the etching opening formed
by the sacrificial layer etching. This gap leads on the one hand to the etching opening and on the
other hand to the cavity via the etching channel.
[0014]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings. Fig.1 (a) is an AB sectional view in FIG.1 (b) of one Embodiment of the electrostatic
capacitance type transducer of this invention, FIG.1 (b) is a top view of Fig.1 (a). 1 (a) and 1 (b)
show only one cell 10, but as shown in FIG. 1 (c) which is a top view, the number of cells 10 in
the transducer may be any number. Absent. Further, the arrangement of the cells 10 may be any
arrangement other than that shown in FIG. 1 (c). As shown in FIGS. 1A to 1C, the planar shape of
04-05-2019
5
the vibrating film 17 of the transducer of this embodiment is circular, but the planar shape may
be square, hexagonal or the like.
[0015]
The configuration of a capacitive transducer will be described. The transducer has a substrate 1
made of Si or the like, an insulating film 2 formed on the substrate 1, a first electrode (lower
electrode) 3 formed on the insulating film 2, and an insulating film 4 on the first electrode 3. . A
vibrating membrane 17 comprising a first membrane 5, a second membrane 6 and a second
electrode (lower electrode) 7 is provided on the insulating film 4 via a cavity 8, and the first
membrane is a vibrating membrane. It is supported by the membrane support 16. If the substrate
1 is an insulator such as a glass substrate, the insulating film 2 may be omitted.
[0016]
Further, in FIG. 1, the second electrode 7 opposed to the first electrode 3 is disposed on the
surface of the second membrane 6, but the second electrode 7 is a first electrode as shown in
FIG. 2. It may be disposed between the membrane 5 and the second membrane 6. That is, the
second electrode 7 may be disposed inside the vibrating film 17. With the configuration shown in
FIG. 2, the distance between the first electrode 3 and the second electrode 7 can be reduced,
thereby increasing the capacitance of the transducer to improve the performance. Can. The
transducer also has voltage application means for applying a voltage between the first electrode
3 and the second electrode 7.
[0017]
Ultrasonic waves can be transmitted and received by generating vibration of the vibrating film 17
in a state in which a voltage is applied between the first electrode 3 and the second electrode 7.
The driving principle is as follows. is there. Since the cell 10 has the first electrode 3 and the
second electrode 7 provided so as to sandwich the cavity 8, in order to receive the acoustic wave,
the direct current can be applied to the first electrode or the second electrode. Apply a voltage.
When an acoustic wave is received, the vibrating membrane 17 is deformed to change the gap of
the cavity 8, and thus the capacitance between the electrodes changes. An acoustic wave can be
detected by detecting this capacitance change from the first electrode or the second electrode. An
acoustic wave can also be transmitted by vibrating the vibrating film 17 by applying an
04-05-2019
6
alternating voltage to the first electrode or the second electrode. The capacitive transducer as
shown in FIG. 1 can convert an acoustic wave signal into an electrical signal or convert an
electrical signal into an acoustic wave through the lead wire from the upper electrode and the
lead wire from the lower electrode. . Through wiring or the like may be used instead of the lead
wiring.
[0018]
The cavities or gaps of the capacitive transducer are formed by sacrificial layer etching in which
sacrificial layers are placed in advance in these portions and removed from etching openings
opened in the membrane. Specifically, the portion where the cavity 8 under the vibrating film is
formed and the portion where the gap 9 is formed in the vicinity of the etching opening (this
portion is the sealing portion in the later step and the sealing portion A sacrificial layer 12 (see
FIG. 4A and the subsequent figures) is formed in the area including the peripheral gap. The
sacrificial layer 12 includes a portion where an etching channel 18 connecting the gap 9 in the
vicinity of the etching opening and the cavity 8 is formed. Then, after the first membrane 5 and
the vibrating membrane supporting portion 16 are formed on the sacrificial layer 12, the etching
opening 13 for removing the sacrificial layer is formed in the first membrane 5 above the gap 9.
By removing the sacrificial layer 12 from the etching opening 13 by sacrificial layer etching, a
gap including the gap 9, the cavity 8, and the flow path 18 is formed. After forming such a gap, a
sealing film that doubles as the second membrane 6 is deposited on the etching opening 13 to
form the sealing portion 11 that seals the etching opening 13. The material constituting the
capacitive transducer, in particular, the material forming the cavity 8 preferably has a small
surface roughness so that the vibrating membrane does not contact the lower surface of the
cavity 8 when the vibrating membrane vibrates.
[0019]
In order to stably and easily realize the formation of the sealing portion 11 for sealing the
etching opening 13, the width of the etching channel adjacent to the region where the etching
opening is formed (parallel to the in-plane direction of the substrate) It is preferable to make the
size of the direction wider than the width of the etching opening. In addition, it is preferable that
the width of the etching opening be small because the cells can be arranged more closely.
Specifically, the size of the orthographic projection of the etching channel adjacent to the region
where the etching opening is formed on the substrate is larger than the size of the orthographic
projection of the etching opening on the substrate. In addition, if the cross-sectional shape of the
structure in the vicinity of the etching opening (the cross-sectional shape in the plane
04-05-2019
7
perpendicular to the direction of the height) is rotationally symmetric (for example, circular),
sealing can be stably and easily realized. , The yield can be improved. That is, compared to the
case where the cross-sectional shape of the structure in the vicinity of the etching opening is not
rotationally symmetrical, the inflow conditions of gas or etching solution such as CVD become
uniform, and the sealing conditions become uniform regardless of the direction. It is difficult for
a failure to occur. Thus, it is preferable that the cross-sectional shape of the gap around the
sealing portion in a plane perpendicular to the direction of the height is rotationally symmetric. If
the width of the flow path is too wide, the strength of the vibrating membrane support decreases,
so it is preferable to make the width wider than the width of the etching opening. For example,
the width of the etching channel is set such that the width of the gap around the sealing portion
is wider than the width of the etching channel. The height of the flow path is preferably the same
as that of the cavity 8 to facilitate the passage of the etching solution, since the height does not
affect the ease of sealing.
[0020]
For the first electrode 3, materials such as titanium, aluminum, and molybdenum can be used. In
particular, titanium is preferable because the change in roughness due to the influence of heat
applied during the process is small, and furthermore, the etching selectivity with the material for
forming the sacrificial layer or the vibrating film is high. For the insulating film 4, a silicon oxide
film or the like can be used. In particular, the silicon oxide film formed by the PE-CVD apparatus
has a small surface roughness and can be formed at a low temperature of 400 ° C. or less, so
that the influence of heat on other constituent materials can be reduced. . The first membrane 5
and the second membrane 6 of the vibrating membrane 17 and the vibrating membrane support
16 are insulating films. In particular, since a silicon nitride film formed by a PE-CVD apparatus
can be formed at a low temperature of 400 ° C. or less, the influence of heat on other
constituent materials can be reduced. In addition, since the film can be formed with a low tensile
stress of 300 MPa or less, large deformation of the vibrating film due to residual stress of the
membrane can be prevented.
[0021]
Furthermore, in addition to the function as a vibrating membrane, the second membrane 6 needs
to be deposited in and on the etching opening 13 to seal the gap. As a material for sealing the
gap, in order to seal by being deposited in the etching opening 13, in addition to having high
coverage, the etching opening 13 enters the cavity 8 under the vibrating film through the flow
passage 18. It is desirable that the sealing film does not penetrate. When the sealing film
04-05-2019
8
intrudes into the cavity 8, the height of the cavity 8 which affects the transducer performance is
changed. For example, in the case of a silicon nitride film formed by LP-CVD, there is a high
possibility that the film may intrude into the interior of the cavity through the flow path 18, and
therefore the thickness of the cavity may be changed. As a material which satisfy | fills the
conditions of these sealing films, the silicon nitride film formed by PE-CVD is preferable.
[0022]
The material of the sacrificial layer 12 for forming a gap or a cavity can be relatively easily
removed in the sacrificial layer etching step, and a material having a sufficiently high etching
selectivity to other constituent materials can be selected. preferable. Furthermore, it is preferable
to select a material that has less influence on the roughness of the membrane and the like in the
heat step in forming the membrane. As a material that satisfies these requirements, for example,
metal materials such as chromium and molybdenum, amorphous silicon, and the like can be
selected. In particular, chromium is easily etchable with a mixed solution of ceric ammonium
nitrate and perchloric acid and has the following characteristics. That is, the etching selectivity
with the silicon which is the first electrode 3 material which is the constituent material in the
sacrificial layer etching step, the silicon oxide which is the material of the insulating film 4 and
the silicon nitride film which is the material of the membrane is sufficiently high. . Therefore, in
the sacrificial layer etching step, it is possible to form a gap or a cavity with less damage to
materials other than the sacrificial layer.
[0023]
In addition, the sacrificial layer is a portion of the cavity 8 which is a gap of a portion where the
vibrating film vibrates, and a gap 9 under and around the etching opening where the sacrificial
layer removing solution penetrates when etching the sacrificial layer. It is formed of a portion
and a portion of the flow passage 18 connecting them. The heights of the respective cavities 8
are set in accordance with the design specifications since they correspond to the vibrating
portion of the vibrating membrane. The portion of the gap 9 below and around the etching
opening and the portion of the flow path 18 need to have an etching solution for removing the
sacrificial layer penetrate into the gap in the sacrificial layer etching step. The lower limit of the
height is determined by the film thickness that can be This lower limit value is not determined as
a single value because it varies depending on the material of the sacrificial layer and the solvent
for removing the sacrificial layer, etc., but the sacrificial layer is chromium and is composed of
ammonium cerium nitrate and perchloric acid. In the case of etching the sacrificial layer with a
solution, the height of the sacrificial layer can be 100 nm or less (for example, about 80 nm).
04-05-2019
9
That is, in order to improve the sealability, it is necessary to make the height of the gap near the
etching opening (that is, the height of the sacrificial layer below and around the etching opening)
thinner, but there is a limit which can be made thinner. is there. The lower limit is determined by
the height to which an etchant having a certain viscosity can penetrate. Although the viscosity of
the etching solution is low, if it is made too thin (for example, 50 nm or less), the etching solution
may not enter the cavity. However, using a gas for the etching solution can make it thinner.
[0024]
Since the second electrode 7 is a material that constitutes a part of the vibrating film 17, the
second electrode 7 needs to be a material with a relatively small stress. For example, titanium or
aluminum can be used.
[0025]
A process for sealing by depositing a sealing film in and on the etching opening 13 after forming
a gap or a cavity by sacrificial layer etching will be described with reference to FIG. FIG. 3 shows
a process of depositing a sealing film of the second membrane 6 to seal the gap in and on the
etching opening 13 after removing the sacrificial layer 12 by sacrificial layer etching. When a
film is formed on the etching opening 13 by PE-CVD, the film is deposited on the surface under
the etching opening 13 and the side and top of the first membrane 5 in which the etching
opening 13 is opened. (FIG. 3 (a)-(c)). The etching opening is sealed by connecting the film
deposited on the lower surface of the etching opening 13 and the film deposited on the side
surface of the first membrane 5 to form a continuous film (FIG. 3 (d )). At this time, the film
required for sealing depends on the height of the gap in the portion where the etching opening is
formed, and the height about three times that height is necessary. In the capacitive transducer of
the present invention, the heights of the cavity 8 under the vibrating film and the gap 9 below
and around the etching opening are different, and the height of the gap 9 is greater than the
height of the cavity 8 small. Here, it is not the height of the cavity 8 that determines the sealing
thickness required to seal the gap of the capacitive transducer, but the gap near the etching
opening for removing the sacrificial layer It is nine high. Therefore, by making the height of the
gap 9 lower than the height of the cavity 8, the sealing thickness necessary to seal the gap is
reduced without changing the height of the cavity 8 which affects the performance. And the
reliability of the seal is improved.
[0026]
04-05-2019
10
The height of the cavity under the vibrating membrane of the capacitive transducer greatly
affects the performance because the vibrating membrane vibrates to transmit and receive
ultrasonic waves. For example, in the case of transmitting an ultrasonic wave by vibrating the
diaphragm, it is necessary to increase the vibration displacement of the diaphragm in order to
increase the sound pressure of the transmitted ultrasonic wave. Generally, since the vibrating
membrane is used under conditions not in contact with the lower surface of the cavity, it is
necessary to increase the height of the cavity in order to increase the vibration displacement of
the vibrating membrane. However, in order to seal the gap, it is necessary to deposit a sealing
film about three times as thick. Therefore, in design, if the cavity is made high, a thicker sealing
film must be formed to seal the gap, which makes it difficult to seal and the reliability of the seal
is lowered.
[0027]
The capacitance type transducer of the present invention can be applied to an object information
acquiring apparatus using an acoustic wave. Acoustic wave from the subject is received by the
transducer, and using the output electric signal, the subject information reflecting the optical
characteristic value of the subject such as the light absorption coefficient, the subject information
reflecting the difference in acoustic impedance, etc. It can be acquired. More specifically, in one
embodiment of the subject information acquisition apparatus, the subject is irradiated with light
(electromagnetic waves including visible light and infrared light). As a result, photoacoustic
waves generated at a plurality of positions (portions) in the subject are received, and a
characteristic distribution indicating the distribution of the characteristic information
respectively corresponding to the plurality of positions in the subject is obtained. The
characteristic information acquired by the photoacoustic wave indicates the characteristic
information related to light absorption, and the initial sound pressure of the photoacoustic wave
generated by the light irradiation, or the light energy absorption density derived from the initial
sound pressure, the absorption coefficient And the characteristic information reflecting the
concentration of the substance that constitutes the tissue. The concentration of the substance is,
for example, oxygen saturation, total hemoglobin concentration, oxyhemoglobin or
deoxyhemoglobin concentration, and the like. The subject information acquisition apparatus can
also be used for diagnosis of malignant tumors and vascular diseases of humans and animals and
follow-up of chemotherapy. Therefore, as a subject, diagnostic objects such as the breast, neck,
and abdomen of a living body, specifically, a human or an animal are assumed. The light absorber
inside the subject represents a tissue having a relatively high absorption coefficient inside the
subject. For example, when a part of the human body is a subject, there are oxyhemoglobin or
deoxyhemoglobin, a blood vessel containing a large amount of them, a tumor containing a large
04-05-2019
11
amount of new blood vessels, a plaque on a carotid artery wall, and the like. Furthermore,
molecular probes that bind specifically to malignant tumors and the like by using gold particles
and graphite, and capsules that transmit drugs also serve as light absorbers.
[0028]
In addition to the reception of the photoacoustic wave, the ultrasonic wave transmitted from the
probe including the transducer receives the reflected wave due to the ultrasonic echo reflected in
the subject, thereby acquiring the distribution regarding the acoustic characteristic in the subject
You can also The distribution relating to the acoustic characteristics includes a distribution
reflecting the difference in acoustic impedance of the tissue inside the subject. However, it is not
essential to obtain the transmission and reception of ultrasonic waves and the distribution of
acoustic characteristics.
[0029]
FIG. 6A shows an object information acquiring apparatus using a photoacoustic effect. The
pulsed light oscillated from the light source 2010 is irradiated to the subject 2014 via the optical
member 2012 such as a lens, a mirror, and an optical fiber. The light absorber 2016 inside the
object 2014 absorbs the energy of the pulsed light and generates a photoacoustic wave 2018
which is an acoustic wave. The capacitive transducer 2020 of the present invention in the probe
(probe) 2022 receives the photoacoustic wave 2018, converts it into an electric signal, and
outputs the signal to the signal processing unit 2024. The signal processing unit 2024 performs
signal processing such as A / D conversion and amplification on the input electric signal, and
outputs the signal processing to the data processing unit 2026. The data processing unit 2026
acquires object information (characteristic information reflecting the optical characteristic value
of the object such as a light absorption coefficient) as image data using the input signal. Here, the
signal processing unit 2024 and the data processing unit 2026 are collectively referred to as a
processing unit. The display unit 2028 displays an image based on the image data input from the
data processing unit 2026.
[0030]
FIG. 6B shows a subject information acquiring apparatus such as an ultrasonic echo diagnostic
apparatus using reflection of acoustic waves. The acoustic wave transmitted from the capacitive
04-05-2019
12
transducer 2120 of the present invention in the probe (probe) 2122 to the subject 2114 is
reflected by the reflector 2116. The transducer 2120 receives the reflected acoustic wave
(reflected wave) 2118, converts it into an electrical signal, and outputs the electrical signal to the
signal processing unit 2124. The signal processing unit 2124 performs signal processing such as
A / D conversion and amplification on the input electric signal, and outputs the signal processing
to the data processing unit 2126. The data processing unit 2126 acquires object information
(characteristic information reflecting a difference in acoustic impedance) as image data using the
input signal. Here, the signal processing unit 2124 and the data processing unit 2126 are also
referred to as a processing unit. The display unit 2128 displays an image based on the image
data input from the data processing unit 2126.
[0031]
The probe may be one that scans mechanically or one that is moved by a user such as a doctor or
an engineer relative to the subject (handheld type). Moreover, in the case of the apparatus using
a reflected wave like FIG.6 (b), you may provide the probe which transmits an acoustic wave
separately from the probe which receives. Further, the apparatus has both the functions of the
apparatus of FIGS. 6A and 6B, object information reflecting the optical characteristic value of the
object, and object information reflecting the difference in acoustic impedance. , And may be
acquired. In this case, the transducer 2020 in FIG. 6A may transmit not only the photoacoustic
wave but also the transmission of the acoustic wave and the reception of the reflected wave.
[0032]
Hereinafter, more specific examples will be described. Example 1 FIGS. 4A and 4B show Example
1 of a method of manufacturing a capacitive transducer according to the present invention. FIGS.
4-1 (a) to (e) and FIGS. 4-2 (f) to (j) show the process flow of this embodiment. In this
embodiment, a method of manufacturing a capacitive transducer having only one cell 10 is
described, but any number of cell structures may be used. Further, although a configuration in
which one etching opening is provided for one cell 10 is shown, the number of etching openings
may be any number for one cell 10. Furthermore, one etching opening may be provided for a
plurality of cells 10. Even in such a case, when the sealing portion is formed, the gap around the
sealing portion sealing one etching opening provided to form a plurality of cavities by sacrificial
layer etching The height is less than the height of the plurality of cavities. In addition, in the state
immediately after the formation of the sacrificial layer, the height of the portion of the sacrificial
layer which becomes a gap near the region where one etching opening is formed is the height of
the portion of the sacrificial layer which becomes a plurality of cavities. Lower than
04-05-2019
13
[0033]
The capacitive transducer according to the present embodiment includes a silicon substrate 1
with a thickness of 300 μm, an insulating film 2 made of a thermal oxide film formed on the
substrate 1, and a first electrode made of titanium formed on the insulating film 2. 3 has an
insulating film 4 formed of a silicon oxide film formed on the first electrode 3. The cell 10 further
includes a cavity formed between the first electrode 3 and the second electrode 7, a vibrating
membrane 17 formed on the cavity, and a support 16 for supporting the vibrating membrane 17.
The vibrating membrane 17 includes a first membrane 5 formed on the cavity, a second
membrane 6 for sealing the cavity, and a second electrode 7. It also comprises voltage
application means for applying a voltage between the first electrode 3 and the second electrode
7.
[0034]
The gap portion of the capacitive transducer in this embodiment is formed by performing a
sacrificial layer etching process shown in FIGS. 4-1 (d) to (e) and 4-2 (f) to (h). First, an insulating
film 2 made of a thermal oxide film, a first electrode 3 made of titanium, and an insulating film 4
made of a silicon oxide film are formed on a silicon substrate 1. Next, chromium which is a
sacrificial layer material having a thickness of 200 nm is formed on the insulating film 4. The
portion forming the etching opening for removing the sacrificial layer 12 is etched by
photolithography and dry etching using Cl 2 gas, and the portion is made 80 nm thick (FIG. 4D). .
Next, patterning is performed by photolithography and dry etching using a Cl 2 gas, except for
the sacrificial layer 15 in the portion to be the etching opening and the sacrificial layer 14 in the
portion to be the vibrating portion and the flow path (FIG. e)). By this process, it is possible to
form a structure in which the heights of the gaps are different between the etching opening and
the vibrating portion and the flow path.
[0035]
Next, on the structure where the sacrificial layer 12 is formed, a silicon nitride film to be the first
membrane 5 and the vibrating film supporting portion 16 is formed 400 nm by a PE-CVD
apparatus (FIG. 4-2 (f)). Next, patterning is performed on the first membrane by photolithography
and dry etching using CF 4 gas to form an etching opening 13 (FIG. 4-2 (g)). Next, a solution
04-05-2019
14
consisting of ceric ammonium nitrate and perchloric acid is introduced from the etching opening
13 and the sacrificial layer 12 is removed to form a gap including the cavity 8 in the vibrating
portion and the gap 9 near the etching opening. Form (Fig. 4-2 (h)). Then, a 300 nm thick silicon
nitride film to be the second membrane 6 is formed on the etching opening 13 by a PE-CVD
apparatus. By this process, the gap is sealed at the etching opening 13 (Fig. 4-2 (i)). Finally, the
second electrode 7 is formed on the second membrane 6 (Fig. 4-2 (j)).
[0036]
In the present embodiment, the height of the sacrificial layer 12 differs between the portion in
the vicinity of the etching opening 13 and the portion of the vibrating portion, 80 nm in the
former and 200 nm in the latter. The thickness of the membrane needed to seal the gap is about
three times the gap thickness. Therefore, in the conventional configuration, since the height of
the cavity under the vibrating film and the height of the gap near the etching opening 13 are the
same, in order to seal the cavity, the height of the gap 200 nm near the opening 13 A sealing
thickness of about 600 nm, which is three times that of In the present configuration, the sealing
thickness required for sealing is three times the height of the gap 80 nm in the vicinity of the
opening 13 and is about 240 nm. Therefore, the thickness of the sealing film necessary for
sealing the cavity can be reduced, and the sealing performance of the cavity is improved.
[0037]
Example 2 Example 2 of a method of manufacturing a capacitive transducer having the structure
of the present invention will be described with reference to FIGS. 5-1 and 5-2. In this
embodiment, the method of forming a sacrificial layer having portions with different heights is
different from that of the first embodiment. As in the first embodiment, after forming the
insulating film 2, the first electrode 3, and the insulating film 4 on the silicon substrate 1 (FIGS.
5-1 (a) to (c)), the thickness on the insulating film 4 is obtained. A chromium film is formed to be
a 150 nm thick sacrificial layer (FIG. 5-1 (d)). Next, patterning is performed by photolithography
and wet etching, leaving a sacrificial layer only in a portion to be a cavity under the vibrating film
(FIG. 5-1 (e)). Next, 50 nm of chromium which will be a sacrificial layer is formed again (FIG. 5-1
(f)). Next, patterning is performed by photolithography and wet etching, leaving the sacrificial
layer 14 in the portion to be the cavity and flow path under the vibrating film and the portion in
the vicinity of the etching opening (FIG. 5-1 (FIG. 5-1 g)).
[0038]
04-05-2019
15
Thereafter, as in the first embodiment, the membrane 5 and the etching opening 13 are formed,
the gap 9 and the cavity 8 are formed by etching the sacrificial layer, and then the etching
opening 13 is sealed to form a capacitive transducer. It produces (FIGS. 5-2 (h)-(l)).
[0039]
Since the height of the sacrificial layer 15 in the vicinity of the etching opening is related to the
sealing thickness, it is preferable that it can be precisely controlled.
In Example 1, the height of the sacrificial layer 15 in the vicinity of the etching opening is
determined by time control of dry etching. In this method, it is not easy to precisely control the
height because of time control. In the present embodiment, the step of forming the sacrificial
layer 12 is divided into two steps. This makes it possible to precisely control the height of the
sacrificial layer 15 in the vicinity of the etching opening. Therefore, the sealing thickness
required for sealing the etching opening 13 can be determined with good controllability from the
height of the sacrificial layer 15 in the vicinity of the etching opening, so that the sealing
reliability is further improved. .
[0040]
1: substrate, 3: first electrode, 5, 6: membrane, 7: second electrode, 8: cavity, 9: gap in the vicinity
of the etching opening (gap around the sealing portion), 10: cell , 12: sacrificial layer, 13: etching
opening, 14: portion of the sacrificial layer to be a cavity under the vibrating film, 15: portion of
the sacrificial layer near the etching opening (portion of the sacrificial layer to be a gap), 17 :
Vibrating film, 18: Etching channel
04-05-2019
16
Документ
Категория
Без категории
Просмотров
0
Размер файла
31 Кб
Теги
jp2014236840
1/--страниц
Пожаловаться на содержимое документа