JP2013051459

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DESCRIPTION JP2013051459
Abstract: To provide a technique for improving the performance variation of an
electromechanical transducer having through wiring. A through wire is obtained by obtaining a
structure in which an insulating portion 3 having a through hole is joined to a conductive
substrate 1 and filling the through hole with a conductive material to electrically connect with
the conductive substrate 1. Form The conductive substrate 1 is used as a first electrode, and a
second electrode is provided opposite to the first electrode 1 via a plurality of gaps 7 on the first
electrode 1 on the side opposite to the side where the insulating portion 3 is present. The
plurality of vibrating film portions 8, 9 and 10 including the electrode 9 are formed to form a
plurality of cells 11. Thus, an electromechanical transducer can be configured. [Selected figure]
Figure 1
Electromechanical converter and method of manufacturing the same
[0001]
The present invention relates to an electromechanical transducer used for an ultrasonic probe or
the like of an ultrasonic diagnostic apparatus and a method of manufacturing the same.
[0002]
An electromechanical transducer such as an ultrasonic transducer performs at least one of
conversion from electrical signals to ultrasonic waves and conversion from ultrasonic waves to
electrical signals, and is used for ultrasonic diagnosis and nondestructive testing in medical
applications. It is used as a probe or the like.
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In recent years, with the development of microfabrication technology, development of a
capacitive electromechanical transducer (CMUT: Capasitive Micromachined Ultrasonic
Transducer) manufactured using the technology has become active. The following are examples
of CMUT: It has a cell provided with a substrate having a lower electrode (the substrate may also
serve as the lower electrode), a vibrating film formed on the substrate at a predetermined
distance from the lower electrode, and an upper electrode. It is comprised by electrically
connecting an element board ¦ substrate to a drive circuit board. Furthermore, an element
substrate having a plurality of elements in which two or more cells are electrically connected is
electrically connected to a drive circuit substrate (see Patent Document 1). The CMUT transmits
or receives ultrasonic waves using a lightweight vibrating membrane, and one having excellent
broadband characteristics in liquid and air can be easily obtained. Therefore, the use of CMUTs is
attracting attention as a promising technology because diagnosis with higher accuracy than
conventional medical diagnosis is possible.
[0003]
The operating principle of the CMUT will be described. When transmitting ultrasonic waves, a DC
voltage and an AC voltage are superimposed and applied between the lower electrode and the
upper electrode. As a result, the vibrating membrane vibrates and an ultrasonic wave is
transmitted. When receiving an ultrasonic wave, the signal is changed from the capacitance
change between the lower electrode and the upper electrode due to the change of the distance
between the lower electrode and the upper electrode with the deformation of the vibrating film
which occurs when the vibrating film receives the ultrasonic wave To detect. As a method of
applying a voltage to the electrodes to drive the CMUT, there is a method of providing an
electrode on the substrate surface of the CMUT and drawing a wire leading to the upper and
lower electrodes, and a wiring from the upper and lower electrodes by the through wiring
provided on the substrate There is a method of leading to the back side and electrically
connecting. In the former case, since it is necessary to lead the wiring on the substrate surface, it
is difficult to arrange the element in the portion occupied by the wiring. Therefore, the fill factor
represented by the proportion of cells occupied by elements of the same area is reduced. In
addition, since it is necessary to arrange the element intervals apart by the area occupied by the
wiring, it is difficult to arrange the elements at high density. As a result, the performance of the
CMUT is degraded. On the other hand, in the method of using the through wiring, a method is
generally adopted in which the substrate is insulated for each element, the through wiring is
formed in each, and the electrical connection is performed. CMUTs produced in this manner are
described in Patent Documents 2 and 3. In the CMUT formed by using the through wiring, since
it is not necessary to lead the wiring on the surface, cells can be arranged in the portion occupied
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by the wiring, and the elements can be arranged with high density. Therefore, a CMUT having a
high fill factor and a high element arrangement density can be manufactured, leading to an
improvement in performance.
[0004]
JP-A-2006-319712 JP-A-2007-215177 JP-A-2010-35134
[0005]
In CMUT of patent document 2, the penetration wiring is formed in the board ¦ substrate of
CMUT.
As a method of forming a through wiring in a substrate, there are a method of forming a through
wiring in a substrate before producing an element of a CMUT, and a method of forming a
through wiring after forming an element. However, in the former method, generally by forming
the through wiring in the substrate, a level difference is generated between the substrate and the
through wiring on the substrate surface, and even if planarization is attempted by a CMP process
or the like, the substrate There is a limit to the surface flatness. Therefore, if the cells are
disposed on the substrate having the level difference, the lower electrode, the gap, the vibrating
film and the upper electrode may be affected by the level difference to have unevenness.
Therefore, the cell characteristics vary between the portion where the through wiring exists and
the portion where there is no through wiring, which leads to the performance deterioration of the
CMUT. In the latter case, it is difficult to arrange the cell immediately above the through wiring
because the through wiring is manufactured after the element substrate is manufactured.
Furthermore, since the cell is structurally formed of a weak thin film, the yield may be reduced in
the process of forming the through wiring.
[0006]
Further, in the method of Patent Document 3, after forming the elements of the CMUT, the
substrate on which the through wiring is formed is joined to the element substrate to form the
CMUT having the through wiring. Also in this method, since the through wiring substrate is
joined after the formation of the structure having a minute gap, there is a possibility that the
yield of the element may be lowered in the bonding step of the through wiring substrate or the
step after the connection.
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[0007]
In view of the above-mentioned subject, a manufacturing method of an electromechanical
transducer of the present invention is characterized by having the following processes. A step of
obtaining a structure in which an insulating portion (insulating substrate, photosensitive
insulating member, etc.) having through holes is joined to a conductive substrate. A step of filling
the through hole with a conductive material to form a through wiring electrically connected to
the conductive substrate; A second electrode facing the first electrode via a plurality of gaps on
the first electrode on the side opposite to the side where the insulating portion is provided, with
the conductive substrate being a first electrode; Forming a plurality of vibrating membrane
portions including the electrodes of (1) to form a plurality of cells.
[0008]
Further, in view of the above problems, the electro-mechanical transducer according to the
present invention is characterized by having the following configuration. A plurality of cells
formed by installing a plurality of vibrating film portions including a second electrode opposed to
the first electrode via a plurality of gaps respectively on the first electrode of the conductive
substrate Have. Then, an insulating portion (an insulating substrate, a photosensitive insulating
member, etc.) is joined to the first electrode on the side opposite to the side having the gap, and
the first portion is connected to the first portion. The through wiring electrically connected with
the electrode of (1) is formed.
[0009]
According to the present invention, after obtaining a structure in which the insulating portion
having the through holes is joined to the conductive substrate, the through holes are formed by
filling the through holes with the conductive material to form the conductive substrate and the
through holes. After securing the electrical connection of the wiring, an electro-mechanical
transducer is formed using the conductive substrate as an electrode. Therefore, since it can be
used as an electrode without losing the flatness of the conductive substrate, if a conductive
substrate with high accuracy of flatness is used, it will not be affected by the step between the
through wiring and the insulating portion. It is possible to arrange the cell immediately above the
through wiring. Therefore, the number of cells arranged in the element can be increased by
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arranging the cells right above the through wiring, so that the fill factor is improved, leading to
the improvement of the performance. In addition, variations among cells can be reduced.
Furthermore, since the formation of the cell having a structurally weak fine gap is performed
after the formation of the through wiring, the reduction in yield can be reduced.
[0010]
The figure which shows the cross section and upper surface of CMUT which is an
electromechanical transducer by this invention. Sectional drawing explaining the process flow of
1st Example of the manufacturing method of an electro-mechanical transducer. Sectional
drawing explaining the process flow of 1st Example of the manufacturing method of an electromechanical transducer. Sectional drawing explaining the process flow of 1st Example of the
manufacturing method of an electro-mechanical transducer. Sectional drawing explaining the
process flow of 2nd Example of the manufacturing method of an electro-mechanical transducer.
[0011]
The feature of the present invention is to manufacture a structure in which an insulating portion
having a through hole is joined to a conductive substrate, and then filling the through hole with a
conductive material to electrically connect the conductive substrate with the conductive
substrate. A plurality of cells are formed on the conductive substrate to form an
electromechanical transducer. Based on such a concept, the electromechanical transducer and
the method of manufacturing the same according to the present invention have the basic
configuration as described in the means for solving the above problems. As a method of
obtaining the structure, as described in Example 1 below, there is a method including a step of
bonding an insulating substrate which is the insulating portion in which a through hole is formed
on a conductive substrate. Also, as described in Example 2 below, a step of forming a
photosensitive insulating portion on a conductive substrate and bonding, and a step of forming a
through hole reaching the conductive substrate in the photosensitive insulating portion Methods
are also possible.
[0012]
Furthermore, in the case where the second electrode is common to a plurality of elements each
including at least one cell, a step of electrically separating the first electrode for each element
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may be included. In this case, a portion of the conductive substrate which is electrically separated
from the first electrode and which is electrically connected to any of the through wiring is
formed, and the common second electrode is electrically connected to the portion. You may
include the process of connecting. On the other hand, the first electrode may be common to a
plurality of elements. In this case, a plurality of portions of the conductive substrate which are
electrically separated from the first electrode and which are electrically connected to the
corresponding through wirings respectively are formed. The electrodes may be electrically
separated to electrically connect the respective second electrodes to the respective portions. In
addition, the vibrating membrane portion may have a vibrating membrane disposed via a gap and
a second electrode formed on the vibrating membrane, or the conductive vibration serving as the
second electrode. It may be made of a membrane.
[0013]
Hereinafter, an electromechanical transducer to which the present invention can be applied and a
method of manufacturing the same will be described with reference to the drawings, taking a
CMUT as an example. The same parts are given the same reference numerals in the following
embodiments to simplify the description.
[0014]
FIG. 1 is a schematic view showing the structure of a CMUT which is an example manufactured
by the manufacturing method of the present invention. Fig.1 (a) is sectional drawing of A-A 'of
FIG.1 (b), FIG.1 (b) is a top view of CMUT. The CMUT manufactured by the manufacturing
method of the present invention comprises a substrate 1, an insulating substrate or member 3
having a through wiring 4, and a CMUT device formed on the substrate 1. The CMUT device
includes a vibrating film 8 formed on a substrate 1 which also serves as a first electrode, with a
gap 7 (a substantially vacuum gap, a gap filled with gas, or the like), a second electrode 9, and a
seal. A cell 11 is provided that includes a barrier film 10. Here, the vibrating film 8, the second
electrode 9, and the sealing film 10 form a vibrating film portion. Moreover, it has many
elements which electrically connect the some cell 11, and they are arranged in two dimensions.
In each element, one or more (one in the illustrated example) through wirings 4 are connected to
the substrate 1 serving as a common first electrode. Here, the second electrode 9 is a common
electrode to all the elements. In this embodiment, the common second electrode 9 is a portion of
the substrate electrically separated from the substrate 1 of the first electrode and a through
wiring (a portion of the substrate 1 at the leftmost portion of FIG. 1A). And the through wiring 4)
are electrically connected and taken out to the outside. In this embodiment, as described above,
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the substrate 1 which is the first electrode is electrically separated individually corresponding to
each element, and the second electrode 9 is used as a common electrode for all the elements.
However, as described above, the substrate 1 of the first electrode may be used as a common
electrode, and the second electrode 9 may be separated individually corresponding to each
element.
[0015]
In the CMUT manufacturing method of this embodiment, an insulating substrate or member is
bonded to a conductive substrate 1 which also serves as the first electrode, and a through wiring
is formed in the insulating substrate to electrically connect to the substrate 1. After securing the
target connection, the electromechanical transducer is formed using the substrate 1 as a first
electrode. That is, by connecting in advance the insulating substrate having the through wiring to
the back surface of the substrate 1, the CMUT can be formed on the substrate 1 while
maintaining the flatness of the surface of the substrate 1. Therefore, if, for example, a low
resistivity Si substrate with guaranteed flatness is used as the substrate 1, the generation of a
step on the surface of the substrate that is likely to occur by forming the through wiring is
suppressed without being affected. , CMUT can be formed, and the uniformity of CMUT
performance can be improved. In addition, since the cell 11 of the CMUT can be formed
immediately above the through wiring, the fill factor can be improved and the performance of the
CMUT can be improved. Furthermore, since the formation of the through wiring is not performed
after the formation of the structurally weak CMUT having a minute gap, it is possible to reduce
the decrease in yield that accompanies it.
[0016]
The formation of the CMUT on a structure (through the substrate 1 and the insulating substrate
or member together) having through wiring is for forming the gap 7 on the substrate 1 which
also serves as the first electrode. The sacrificial layer 13 is formed and patterned, and for
example, the vibrating film 8 is formed thereon. Further, the second electrode 9 is formed and
patterned. Next, an etching hole for removing the sacrificial layer 13 is formed in the vibrating
film 8 and only the sacrificial layer 13 is selectively removed to form the gap 7. Then, the sealing
film 10 is formed, and the etching hole for removing the sacrificial layer is sealed to manufacture
an electromechanical transducer such as a CMUT.
[0017]
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As the substrate 1 used in the present embodiment, it is desirable to use a Si substrate which can
ensure the flatness of the surface (that is, has a small surface roughness) and which can be easily
microfabricated. Further, since the substrate 1 doubles as the first electrode, the resistivity of the
substrate 1 is desirably 0.02 Ωcm or less. This is because signal loss can be reduced as the
wiring resistance of the first electrode is smaller. Furthermore, it is desirable that the surface
roughness Rms of the substrate 1 be 0.5 nm or less. Since the CMUT is formed by stacking thin
films on the substrate 1, the smaller the surface roughness of the substrate 1, the smaller the
variation in CMUT can be formed.
[0018]
As the substrate 1, it is also possible to use an active layer of an SOI wafer manufactured by
including an SiO 2 film between Si and Si. Usually, after the element separation groove 6 is
formed, the second electrode 9 which is the upper electrode is well covered so as to get over the
step caused by the step between the substrate 1 formed by the groove 6 and the insulating
portion 3. It is necessary to form a film. However, if the substrate 1 is formed of the active layer
of SOI, the substrate 1 can be formed thin, so that the step formed by the element isolation
groove 6 becomes small, and the stability of the process is improved.
[0019]
The sacrificial layer 13 used in the manufacturing method of the present embodiment has
etching selectivity with the vibrating film 8, and in the process of forming the vibrating film 8,
the heat resistance that the surface roughness does not change significantly due to heat is
obtained. It is preferred to select certain materials. For example, Cr, Mo, etc. are desirable. In
addition, the second electrode (upper electrode) 9 used in the manufacturing method of the
present embodiment has heat resistance such that the surface roughness does not largely change
due to heat in the heat process at the time of forming the sealing film 10. In the step of etching
13, it is preferable to select one having selectivity to the sacrificial layer 13. For example,
materials such as Ti, W, TiW, Mo can be selected. In addition, as the vibrating film 8 used in the
manufacturing method of the present embodiment, it is desirable to use a SiN film which is
capable of stress control, is excellent in mechanical characteristics and insulating performance,
and is formed by PECVD.
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[0020]
Since the sealing film 10 is also used as a vibrating film portion, it is possible to control stress in
addition to forming a film with good coverage in the sealing portion, and to select a material
excellent in mechanical characteristics and insulation performance. preferable. For example, a
SiN film formed by PECVD can be selected. The insulating substrate or member for forming the
through wiring in this embodiment needs to be a material which can easily form the through hole
to be the through wiring and can be joined to the substrate 1. For example, Pyrex (registered
trademark) glass or quartz glass can be used. In quartz glass or Pyrex (registered trademark)
glass, fine through holes can be formed by sandblasting or the like, and, for example, bonding
with a Si substrate to be the substrate 1 can be easily performed. In particular, since Pyrex
(registered trademark) glass has a thermal expansion coefficient very close to that of Si, which is
the substrate 1, it has an advantage of high compatibility with the Si substrate in the heat
process.
[0021]
Furthermore, photosensitive resin or glass material can also be used as an insulating member for
forming the through wiring. With a photosensitive resin material that can be applied by spin
coating, for example, it is easy to form a coating film on a Si substrate, and through holes can
also be formed by photolithography. There are also materials excellent in heat resistance in the
process of forming an electromechanical transducer such as CMUT. For example, photosensitive
polyimide (manufactured by Toray Industries, Inc.) can be used. Furthermore, as the insulating
substrate or member, a photosensitive dry film (commercially available product such as
manufactured by Hitachi Ltd., manufactured by Asahi Kasei Corp., manufactured by Tokyo Ohka
Kogyo Co., Ltd.) can be used.
[0022]
Hereinafter, a more specific example of a method of manufacturing an electromechanical
transducer to which the present invention can be applied will be described in detail with
reference to the drawings. Example 1 Example 1 will be described. In this embodiment, a method
of manufacturing a CMUT manufactured on a substrate to which a through wiring formed of a
low resistance Si substrate and an insulating glass substrate is connected will be described. In
this embodiment, Pyrex (registered trademark) glass is used as the insulating substrate 3 with
through holes, but the basic manufacturing method is the same even when using other materials
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such as quartz glass.
[0023]
The process flow of the present embodiment will be described with reference to FIGS. In these
figures, a cross section of a device with two elements is shown for the sake of simplicity of the
figure, but other elements are produced as well. First, a Si substrate to be the substrate 1 is
prepared (FIG. 2A). Since the substrate 1 doubles as the first electrode which is to be the lower
electrode, it is desirable that the substrate 1 has low resistivity. In this embodiment, a Si substrate
having a resistivity of 0.02 Ωcm or less is used. Also, in order to form a CMUT on the surface of
the substrate 1, the surface roughness Rms is small, and the one having Rms of 0.5 nm or less is
used. Next, a thermal oxide film layer of about 1 μm is formed as the insulating film 15 on both
sides of the substrate 1. The thermal oxide film formed on the Si substrate is excellent in flatness,
and the insulating film 15 can be formed without substantially deteriorating the flatness of the Si
substrate. Since the vibrating film 8 to be described later is insulating, the insulating film 15 may
be able to be omitted if electrical separation between the upper and lower electrodes can be
sufficiently secured.
[0024]
Next, in order to obtain ohmic contact between the substrate 1 and the through wiring portion,
the oxide film on the back surface of the Si substrate is peeled off, and the ohmic metal 2 is
formed and patterned. Further, an annealing process is performed to form an ohmic contact layer
with the Si substrate 1. As a metal for forming an ohmic contact, a metal which easily forms an
alloy layer with Si, such as Al or Ti, is used (FIG. 2-1 (b)).
[0025]
Next, Pyrex (registered trademark) glass, which is an insulating substrate 3 with through holes in
which through holes are formed by sandblasting in portions where through wires are to be
formed, is prepared so that the ohmic metal 2 overlaps with the through holes. It joins to the
back (figure 2-1 (c)). Pyrex (registered trademark) glass and Si substrate can be bonded by
anodic bonding or direct bonding. Although the through holes are formed by the sand blast
method in the present embodiment, the present invention is not limited to this. Through holes
can also be formed by a drilling method, a laser processing method, an ultrasonic processing
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method, or a method combining photolithography technology and dry etching. In addition,
although Pyrex (registered trademark) glass and a Si substrate were bonded by anodization, the
present invention is not limited to this, and other bonding methods such as direct bonding can
also be used.
[0026]
Further, the through holes are filled with a conductive material to be the through wiring. As a
conductive material to be filled, Cu by plating is used (FIG. 2-1 (d)). After forming the through
wiring, the back surface is polished by CMP to make the surface heights of the through wiring 4
and the Pyrex (registered trademark) glass 3 uniform. Next, on the back surface of the joined
substrate, a protective material 12 is formed to protect the metal forming the through wiring in
various etching steps in the process. In this embodiment, Ti having a high etching selectivity and
a high resistance to heat is deposited by EB evaporation at 300 nm. In this process, the structure
of the substrate on which the through wiring 4 is formed is completed (FIG. 2 (e)).
[0027]
Next, the process of forming CMUT on the structure of the produced board ¦ substrate is
demonstrated (FIG. 2-2 (f)-(i) and FIGS. 2-3 (j)-(m)). In the method of manufacturing the CMUT of
this embodiment, a vibrating film is formed after patterning a material called a sacrificial layer in
advance, and a gap is formed by a method of selectively removing the sacrificial layer. Thus, the
conductive substrate is used as a first electrode, and a second electrode facing the first electrode
with a plurality of gaps is provided on the first electrode on the side opposite to the side having
the insulating portion. A plurality of vibrating membrane portions including electrodes can be
formed to form a plurality of cells. The CMUT manufactured in this process can be manufactured
at a relatively low temperature of 350 ° C. or less, so even if the CMUT is formed after the
through wiring 4 is formed, the influence of heat is small and the CMUT can be formed. It is.
[0028]
First, patterning of a resist is performed on the surface of the produced substrate having the
through wiring 4 by photolithography. Furthermore, dry etching is performed using SF6 as an
etching gas using the resist pattern as a mask, and the substrate 1 as the lower electrode is cut to
the bonding surface of the insulating substrate 3 and the substrate 1 to form the element
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separation groove 6. By this process, each part of the substrate 1 corresponding to each element
is electrically separated (FIG. 2F).
[0029]
Subsequently, a sacrificial layer 13 is formed on the substrate 1 and patterned (FIG. 2G). In the
step of forming the sacrificial layer 13, the sacrificial layer 13 made of Cr is produced by EB
evaporation. The conditions in this step are preferably as follows. After the vacuum degree is
reduced to 2.0 × 10 <-4> Pa, Cr is deposited to a thickness of about 200 nm by EB evaporation.
Subsequently, a resist mask is formed by a photolithography technique, and a pattern of the
sacrificial layer 13 is formed by etching Cr with a mixed acid etchant (chromium etching
solution, manufactured by Kanto Chemical Co., Ltd.).
[0030]
Next, the process of forming the vibrating film 8 on the sacrificial layer 13 will be described (FIG.
2H). In the film formation step of the SiN film to be the vibrating film 8, the vibrating film 8 is
formed by plasma CVD. The conditions in this step are preferably as follows. Deposition is
performed for about 200 seconds in a mixed gas of SiH 4, N 2, and NH 3 at a substrate heating
temperature of 350 ° C. and a chamber pressure of 1.6 Torr, to form a SiN film having a film
thickness of about 440 nm. Subsequently, in order to form a connection portion between the
second electrode 9 serving as the upper electrode and the through wiring 4, the vibrating film
and the insulating film 15 in the extraction portion of the upper electrode are etched by dry
etching using CF4 as an etching gas. (FIG. 2-2 (i)).
[0031]
Next, the process of forming the 2nd electrode 9 used as an upper electrode is demonstrated
(FIG. 2-3 (j)). The conditions of this process are preferably as follows. The film formation step of
the Ti film to be the upper electrode is performed by the EB evaporation method. A Ti film of 100
nm is formed at a degree of vacuum of 2.5 × 10 <-4> Pa. Further, a resist mask is formed by
photolithography. Also, a resist for Ti protection on the back surface is formed. Furthermore, the
pattern of the upper electrode 9 is formed by etching Ti with a Ti etching solution (WLC-T,
manufactured by Mitsubishi Gas Chemical Co., Ltd.).
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[0032]
Then, the process of removing the sacrificial layer 13 used as the clearance 7 is demonstrated
(FIG. 2-3 (k)). First, a resist mask formed by photolithography is provided, and etching holes for
etching the sacrificial layer 13 are formed in the vibrating film 8 using dry etching using CF 4 as
an etching gas. In FIG. 2-3 (k), the description of the etching holes is omitted for simplification of
the drawing. Furthermore, the sacrificial layer 13 is selectively removed through the etching
holes by immersing in a mixed acid etching solution, which is an etching solution for the
sacrificial layer, to form a gap 7. After the sacrificial layer 13 is completely removed, it is
thoroughly washed with water, replaced with water with isopropyl alcohol, and finally dried with
a fluorine-based low surface tension solvent (HFE 7100, manufactured by Sumitomo 3M). A gap
7 is formed.
[0033]
Next, the process of sealing the etching hole which formed the clearance 7 is demonstrated (FIG.
2-3 (l)). The sealing film 10 is formed by plasma CVD on the vibrating film 8 in which the etching
holes are formed. The conditions of this process are preferably as follows. The film is formed for
about 320 seconds in a mixed gas of SiH 4, N 2 and NH 3 at a substrate heating temperature of
350 ° C. and a chamber pressure of 1.6 Torr, to form a SiN film 10 having a film thickness of
about 700 nm. The gap 7 sealed by this process is a gap of about the same pressure as the
chamber pressure.
[0034]
Finally, the protective Ti film in the process on the back surface is removed, and the under bump
metal is formed on the through wiring 4 (FIG. 2-3 (m)). In the step of removing the Ti film, the Ti
is etched with a Ti etching solution (WLC-T, manufactured by Mitsubishi Gas Chemical Co., Ltd.)
which is an etching solution having etching selectivity to Cu which forms the Ti film and the
through wiring. By this, it is possible to remove only the Ti film (protective material 12) on the
back surface while maintaining the selectivity to Cu sufficiently. Further, an Au / Ni / Ti film to be
the under bump metal 5 is formed in a portion in contact with the through wiring 4 using a
stencil mask, whereby the CMUT is completed.
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[0035]
If manufactured by the above process, the electromechanical transducer is formed on the
structure of the substrate having a flat surface without being affected by the step between the
through wiring and the substrate which may occur by forming the through wiring. Because it can
be created and deployed, it is possible to produce one with reduced performance variation.
[0036]
Example 2 Example 2 will be described.
In the manufacturing method of this embodiment, a resin or glass material having a
photosensitive characteristic is applied on a low resistance Si substrate to form an insulating
member which is an insulating layer. And CMUT is produced on the structure of the board ¦
substrate to which penetration wiring was connected by patterning a penetration hole to it.
[0037]
In this embodiment, polyimide (commercially available from Toray Industries, Ltd., Asahi Kasei
Corporation, Hitachi Chemical Co., Ltd., etc.) is used as the photosensitive resin material.
Moreover, although polyimide was used as a photosensitive resin material here, KI-1000 series
(made by Hitachi Chemical Co., Ltd.), TMMR (made by Tokyo Ohka Co., Ltd.), SU-8 (made by
Kayaku Microchem) etc. are also used. be able to. Furthermore, photosensitive dry films
(commercial products such as Hitachi Ltd., Asahi Kasei Corporation, Tokyo Ohka Co., Ltd. and the
like) can also be used. However, in the film formation step of the SiN film of the vibrating film 8
formed by plasma CVD, it is necessary to adjust the film formation conditions with respect to the
heat resistance temperature of each resin material. In the present embodiment, the film
formation temperature of the vibrating film 8 is 350 ° C. However, if it is 300 ° C. or more, a
vibrating film having good mechanical performance and insulation performance can be formed.
[0038]
FIG. 3 shows a process flow of this embodiment. First, the process of connecting the through
wiring to the substrate will be described. FIG. 3A shows a substrate 1 used in the present
embodiment, which is a Si substrate having a low resistivity. Since the substrate 1 doubles as the
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first electrode, it is desirable that the substrate 1 has a small surface roughness and a low
efficiency as in the first embodiment. Specifically, it is desirable that Rms be 0.5 nm or less and
the resistivity be 0.02 Ωcm or less.
[0039]
Subsequently, an insulating layer 15 which is a thermal oxide film is formed to 1 μm on the
substrate 1, and an ohmic metal 2 for forming an ohmic contact is formed on the back surface of
the substrate by film formation and patterning. This process is the same as FIGS. 2-1 (a) and (b)
of Example 1. Next, a photosensitive polyimide solution to be an insulating member 14 having a
through wiring is uniformly applied on the back surface of the substrate 1 by a spin coating
method to a thickness of 50 μm, and dried by heating on a hot plate. Further, exposure is
performed through a photo mask by a photolithographic technique, and development is
performed with a developer of 2.38% TMAH (tetramethyl ammonium halide) to form through
holes in accordance with the ohmic metal 2. Subsequently, by heating and curing in a nitrogen
atmosphere at 300 ° C. to promote imidization, the process of providing the through holes for
the through wiring 4 in the insulating member is completed.
[0040]
If a metal is filled in the through holes provided as described above in the same step as FIG. 2D of
the first embodiment, the structure of the substrate to which the through wiring 4 is connected is
formed by this step. Be done. In the subsequent steps, the same steps as in FIG. 2E (FIG. 2E) to
FIG. 2D (m) of the first embodiment are developed on the structure of the substrate to form the
CMUT having the through wiring 4.
[0041]
Also by the above process, an electromechanical transducer is formed on the structure of the
substrate having a flat surface without being affected by the step between the through wiring
and the substrate which may occur by forming the through wiring. As it can be expanded, it is
possible to manufacture one with reduced performance variation.
[0042]
1 · · · Substrate (first electrode, lower electrode), 3, 14 · · · Insulating substrate or member
(insulating portion), 4 · · Through wiring, 6 · · · · Element separation groove, 7 · · · · (Space · · · · · · · ·
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· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Sacrificial layer
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