JP2009291514

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DESCRIPTION JP2009291514
The present invention provides a method of manufacturing a capacitive transducer capable of
reducing bonding defects at a bonding interface in the manufacture of a capacitive transducer,
and a capacitive transducer. A method of manufacturing a capacitive transducer joins a substrate
(101) and a membrane member (108) provided with a thin film membrane portion, and forms a
sealed cavity (104) between the substrate and the membrane portion. . The substrate and the
membrane member are bonded to form the cavity 104 in a state where the gas release passage
105 penetrating from the bonding interface between the substrate and the membrane member to
the outside is provided. Since the substrate and the membrane member are joined in a state
where a passage leading from the joint portion to the outside is provided, the gas generated at
the time of manufacture is favorably released to the outside. [Selected figure] Figure 1
Method of manufacturing capacitive transducer, and capacitive transducer
[0001]
The present invention relates to a method of manufacturing a capacitive transducer such as an
ultrasonic transmitting / receiving element (ultrasonic transducer) used for an ultrasonic probe
of an ultrasonic diagnostic apparatus, and a capacitive transducer.
[0002]
An ultrasonic transducer is used for an ultrasonic probe of an ultrasonic diagnostic apparatus.
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An ultrasonic transducer is an element that converts an electrical signal into an ultrasonic wave
or converts an ultrasonic wave into an electrical signal. In the ultrasonic diagnostic apparatus,
the input electric signal is converted into an ultrasonic wave and transmitted into the living body,
and the ultrasonic wave reflected in the living body is received and converted into an electric
signal. One type of ultrasonic transducer is a capacitive ultrasonic transducer.
[0003]
There is a proposal regarding the technology of a capacitive ultrasonic transducer (see Patent
Document 1). FIG. 11 is a cross-sectional view of the basic structure. The silicon single crystal
layer 1101 has conductivity, and an insulating layer 1106 is formed on the surface. A recess
1104 is formed on the insulating layer 1106. The membrane 1102 is bonded to the surface on
which the recess 1104 is formed under a substantially vacuum atmosphere. The recess 1104 is a
substantially vacuum-sealed cavity to form a cavity. In the conventional example, since the recess
and the cavity indicate the same space, they may be indicated by the same reference numeral
1104.
[0004]
This conventional example is an example in which the silicon single crystal layer 1101 forms a
base of an ultrasonic transducer and also functions as an electrode. The membrane 1102 is
supported by a support 1103 formed on the insulating layer 1106. An electrode 1105 is formed
on the membrane 1102 in the central portion of the cavity 1104, and a parallel plate capacitor is
formed between the silicon single crystal layer 1101 and the electrode 1105.
[0005]
At the time of transmission of ultrasonic waves, a voltage waveform of an ultrasonic cycle is
applied between the silicon single crystal layer 1101 and the electrode 1105. At this time, the
capacitance change of the parallel plate capacitor occurs corresponding to the applied voltage
waveform, and the electrostatic attractive force acting between the silicon single crystal layer
1101 and the electrode 1105 changes. Since the cavity 1104 is substantially vacuum, the
electrode 1105 vibrates with the membrane 1102 and ultrasonic waves are transmitted. On the
other hand, at the time of receiving an ultrasonic wave, the electrode 1105 and the membrane
1102 receive an ultrasonic wave and vibrate. This vibration can be electrically detected as the
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aforementioned capacitance change of the parallel plate capacitor. In order to maintain insulation
between the silicon single crystal layer 1101 and the electrode 1105 even when the membrane
1102 and the electrode 1105 are flexed and come in contact with the bottom of the cavity 1104
due to ultrasonic vibration or external static pressure. 1106 is provided.
[0006]
FIGS. 12 (a) to 12 (d) illustrate the main steps of the method of manufacturing the ultrasonic
transducer shown in FIG. First, the substrate 1107 is formed in the pre-process of FIG. In the
substrate 1107, a silicon single crystal layer 1101, a support portion 1103, a concave portion
1104, and an insulating layer 1106 are formed. Also, an SOI (Silicon On Insulator) wafer 1108 is
prepared. The SOI wafer 1108 has a laminated structure in the order of a handle layer 1109
made of silicon single crystal, a buried oxide film layer 1110 made of silicon oxide, and a device
layer 1111 made of silicon single crystal. The device layer 1111 becomes a membrane 1102 in a
later step. Also, the handle layer 1109 and the buried oxide film layer 1110 function as a
membrane supporting layer until the device layer 1111, that is, the membrane 1102 is bonded to
the substrate 1107.
[0007]
As illustrated in FIG. 12B, direct bonding is performed between the surface of the substrate 1107
on which the support portion 1103 is formed and the device layer 1111 of the SOI wafer 1108.
This direct bonding is performed under a substantially vacuum atmosphere to seal the cavity
1104 in a substantially vacuum.
[0008]
Next, as illustrated in FIG. 12C, the handle layer 1109 and the buried oxide film layer 1110 are
removed by etching or polishing to form a membrane 1102. Finally, as illustrated in FIG. 12D, an
electrode 1105 is formed. Although only one element is illustrated in FIGS. 11 and 12, it is
general that a plurality of elements are arranged in a one-dimensional or two-dimensional array.
[0009]
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By the way, in the manufacturing method of the above-mentioned electric capacity type
ultrasonic transducer, there was a possibility that a poor bonding portion may be generated in
the bonding step between the silicon single crystal surface and the silicon oxide surface.
Elements with defective joints may not function well as ultrasound transducers. One cause of
poor bonding is the accumulation of water or oxygen generated at the bonding interface at the
bonding interface. Water and oxygen originate from hydroxyl groups (OH) involved in direct
bonding. As a method of solving this, there has been disclosed a proposal to reduce bonding
defects of direct bonding by annealing (see Non-Patent Document 1). There is also a proposal of
a technique for arranging an absorbent to absorb a gas generated at a bonding interface, and
arrangement of the absorbent (see Patent Document 2). U.S. Pat. No. 6,958,255 Patent Document
2: Japanese Patent Application Publication No. 2007-71700 Arturo A. Ayon et al.,
Characterization of silicon wafer bonding for Power MEMS applications, Sensors and Actuators A
103 (2003) 1-8.
[0010]
However, the method using annealing requires tens to hundreds of hours in the annealing step,
which may lower productivity. In addition, an ultrasonic transducer used for an ultrasonic probe
of an ultrasonic diagnostic apparatus needs to arrange a plurality of elements at high density in a
one-dimensional or two-dimensional array, but a method using a gas absorbent In this case, it is
possible to make it difficult to miniaturize an array.
[0011]
In addition, the gas absorbent may cause a change in the state of the bonding interface due to the
change accompanying absorption. Therefore, in a capacitive ultrasonic transducer requiring a
sufficient bonding strength with a narrow support, there is a possibility that a gas generated at
the time of manufacture may cause a bonding failure or the like.
[0012]
In view of the above problems, in the method of manufacturing a capacitive transducer according
to the present invention, a cavity is formed by bonding a substrate and a membrane member
provided with a thin membrane portion, and sealing between the substrate and the membrane
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portion. Form Then, the substrate and the membrane member are bonded to form the cavity in a
state where a gas release passage penetrating from the bonding interface between the substrate
and the membrane member to the outside is provided.
[0013]
Further, in view of the above problems, in the capacitive transducer according to the present
invention, a substrate and a membrane member provided with a membrane portion in the form
of a thin film are joined, and a cavity sealed between the substrate and the membrane portion is
It is a formed capacitive transducer. A gas discharge passage penetrating from the bonding
interface between the substrate and the membrane member to the outside is provided in at least
one of the substrate and the membrane member.
[0014]
According to the present invention, when the cavity is formed between the substrate and the
membrane portion, the gas release passage is provided, and the gas, moisture and the like
generated at the time of manufacture are released to the outside, so the capacitance Bonding
defects at the bonding interface in the manufacture of a mold transducer can be reduced.
[0015]
Hereinafter, embodiments of the present invention will be described.
In a basic embodiment of a method of manufacturing a capacitive transducer according to the
present invention, a substrate and a membrane member provided with a thin film membrane
portion are joined, and a cavity sealed between the substrate and the membrane portion is
formed. Form. At this time, the substrate and the membrane member are bonded to form a cavity
in a state where a gas release passage penetrating from the bonding interface between the
substrate and the membrane member to the outside is provided. Thus, at least at the time of
bonding, the substrate and the membrane member are bonded in a state in which a passage
communicating from the bonding portion to the outside is provided, so that gas, moisture and the
like generated at the time of manufacturing are favorably released to the outside.
[0016]
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The form of the substrate and the form of the membrane member may be any. By bonding the
two, a gap may be formed between the thin film membrane portion of the membrane member
and the surface of the substrate, and a cavity sealed there may be formed. For example, the
substrate is a substrate having a recess formed on the surface, and the membrane member is a
thin film membrane as a whole, and the substrate and the membrane member may be bonded to
form a cavity in the recess. is there. Further, a recess may be formed in the membrane member,
and by bonding the substrate and the membrane member, the recess may be sandwiched
between the surface of the substrate and the membrane portion to form a cavity. .
[0017]
The form of the gas release passage may be various. For example, the gas release passage can be
provided to extend along the periphery of the bonding interface between the substrate and the
membrane member and to be connected to the outside. In this case, the gas release passage may
be formed as a recess on the substrate side, may be formed as a recess on the membrane
member side, or may be formed as a recess on both sides and formed by combining the two. May
be
[0018]
Further, the gas release passage can be provided so as to extend through the membrane member
from the bonding interface between the substrate and the membrane member and be connected
to the outside. Alternatively, the gas release passage may be provided so as to extend through the
substrate from the bonding interface between the substrate and the membrane member and be
connected to the outside. Furthermore, in the step of bonding the substrate and the membrane
member, the membrane member is bonded in a state supported by the membrane support layer,
and the gas release passage extends from the bonding interface through the membrane member
and the membrane support layer to the outside The form provided so that it may be connected is
also possible. In this case, the membrane support layer is removed after the step of bonding the
substrate and the membrane member.
[0019]
The step of bonding the substrate and the membrane member is typically performed under a
pressure atmosphere lower than atmospheric pressure to form a sealed cavity under such
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pressure.
[0020]
Further, in the basic embodiment of the capacitive transducer according to the present invention,
a substrate and a membrane member provided with a thin film membrane portion are joined to
form a sealed cavity between the substrate and the membrane portion. It is done.
Further, a gas release passage penetrating from the bonding interface between the substrate and
the membrane member to the outside is provided in at least one of the substrate and the
membrane member. Also in the capacitive transducer embodiment, as described above, the form
of the substrate, the form of the membrane member, and the form of the gas discharge passage
can be various.
[0021]
Also, the capacitive transducer of the present invention comprises at least one cavity, but
typically comprises a plurality of cavities arranged in an array on a substrate. The size of the
cavity or the like also increases the electromechanical conversion coefficient of the element if the
gap between the substrate and the membrane portion is small, but may be designed variously
according to the application. Generally, it is designed in the range of several tens of nanometers
to several micrometers. Also in the application, the capacitive transducer of the present invention
can be used as various physical quantity sensors, etc. in addition to the capacitive ultrasonic
transducer of the embodiment described later.
[0022]
An embodiment of the present invention will be described below with reference to the drawings.
[0023]
(Example 1) Fig.1 (a) and (b) are sectional drawing and a top view explaining Example 1 which
concerns on the electrostatic capacitance type ultrasonic transducer of this invention.
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The same number is attached to the same part. The cross section of FIG. 1 (a) corresponds to the
A-A 'position of FIG. 1 (b). In the present embodiment, the substrate 101 is composed of a silicon
single crystal layer 102 and a silicon oxide film layer 103 formed on the upper surface thereof.
The silicon single crystal layer 102 is a base of the ultrasonic transducer, has conductivity, and
also functions as an electrode. In the silicon oxide film layer 103, a cavity (concave portion) 104,
a groove 105 which is a gas discharge passage, an electrode extraction portion 106, and an
insulating layer 107 are formed. Further, a membrane 108 is bonded to the silicon oxide film
layer 103. The membrane 108 is a membrane member which is a thin film membrane as a whole.
[0024]
The cavity 104 is sealed in a substantially vacuum by the membrane 108. The electrode lead-out
portion 106 is a portion where the membrane 108 and the silicon oxide film layer 103 are
removed, and an electrode 109 which is electrically connected to the silicon single crystal layer
102 is provided. As illustrated in FIG. 1 (b), the cavities 104 are square or rectangular, and are
arranged in a two-dimensional array at the center of the substrate 101. The square or
rectangular cavity shape can reduce the gap between the cavities 104 when arranged in a twodimensional array. Therefore, there is an advantage that the cavity area to the element area can
be increased. In the present embodiment, an example in which five cavities are arranged in the x
direction and three cavities are arranged in the y direction is illustrated. 2Grooves 105 are
provided around the cavities 104 arranged in a dimensional array. The groove 105 is formed in
the surface portion of the silicon oxide film layer 103, and its end reaches the end portion of the
substrate 101 and is opened to the outside.
[0025]
When bonding the silicon oxide film layer 103 and the membrane 108, the groove 105 extends
along the bonding interface to form a gas discharge hole penetrating to the outside. When the
silicon oxide film layer 103 and the membrane 108 are bonded, gas, moisture and the like
generated at the bonding interface are discharged to the outside by the gas release holes. Also,
the cavity 104 and the groove 105 do not communicate with each other. Thus, the cavity 104
can be substantially vacuum sealed by the membrane 108.
[0026]
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As described above, the electrode 109 is an electrode provided in the electrode lead-out portion
106 and electrically connected to the silicon single crystal layer 102. In addition, an electrode
110 is formed on the membrane 108 in the center of the cavity 104. 2The plurality of electrodes
110 arranged in a dimensional array are electrically connected to the electrodes 111 by the
wirings 112. The electrode 111 is an electrode for electrically extracting the electrode 110 to the
outside.
[0027]
An example of the manufacturing method of the capacitive ultrasonic transducer of the said
structure is demonstrated. 2 (a) to 2 (p) are diagrams for explaining a method of manufacturing
this capacitive ultrasonic transducer. The same number is attached to the same part. The
manufacturing method of this embodiment starts from a substrate 201 whose cross section is
illustrated in FIG. The substrate 201 is constituted of a silicon single crystal layer 202, a silicon
oxide film layer 203 formed on the upper surface and a lower surface thereof, and a silicon oxide
film layer 204.
[0028]
First, as shown in FIG. 2B, the silicon oxide film layer 203 is etched using the photoresist layer
205 as an etching resist to form a cavity (concave portion) 206 and a groove 207. The grooves
207 function as gas release holes in a later step. When hydrofluoric acid is used for etching, the
silicon single crystal layer 202 functions as an etch stop layer, and control of the etching amount
in the depth direction becomes easy. The planar shapes of the cavity 206 and the groove 207 as
viewed from the side of the silicon oxide film layer 203 are illustrated in FIG. 2C. The cross
section of FIG. 2 (b) corresponds to the B-B 'position of FIG. 2 (c). The cavities 206 are square or
rectangular, and are arranged in a two-dimensional array in the center of the substrate 201.
[0029]
As described above, the square or rectangular cavity shape can reduce the gap between the
cavities 206 when arranged in a two-dimensional array. Therefore, there is an advantage that the
cavity area to the element area can be increased. The groove 207 is provided to surround the
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periphery of the cavity 206 and reaches the end of the substrate 201.
[0030]
Next, as illustrated in FIG. 2D, after the photoresist layer 205 is removed, a silicon oxide film is
formed on the entire substrate 201. Thus, the insulating layer 208 is formed on the surface of
the silicon single crystal layer 202 in the cavity 206. The insulating layer 208 can be formed
with the silicon single crystal layer 202 even when the device layer (membrane member) 212
formed in a later step is bent by ultrasonic vibration or static pressure from the outside and
contacts the bottom of the cavity 206. Provided to maintain insulation between the
[0031]
Next, an SOI wafer 209 shown in FIG. 2 (e) is prepared. The SOI wafer 209 has a laminated
structure in the order of a handle layer 210 made of silicon single crystal, a buried oxide film
layer 211 made of silicon oxide, and a device layer 212 made of silicon single crystal.
[0032]
As illustrated in FIG. 2F, the surface of the device layer 212 of the SOI wafer 209 and the surface
of the substrate 201 on which the cavity 206 and the groove 207 are formed are bonded using
direct bonding. The bonding is performed in a substantially vacuum atmosphere, and the inside
of the cavity 206 is sealed in a substantially vacuum. The end faces of the bonded substrates are
illustrated in FIGS. 2 (g) and (h). FIGS. 2 (g) and 2 (h) are views of the substrate in the same
process as FIG. 2 (f) as viewed from the y direction and the x direction, respectively. As illustrated
in FIGS. 2 (g) and 2 (h), the groove 207 opens at the end face of the bonded substrate. Further,
although not shown, a groove 207 is also opened on the opposite surface of FIGS. 2 (g) and 2 (h).
The gas such as water and oxygen generated at the bonding interface at the time of direct
bonding is removed from the bonding interface to the outside through the groove 207 which is a
gas release passage.
[0033]
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Next, as shown in FIG. 2I, the handle layer 210 and the buried oxide film layer 211 of the SOI
wafer 209 are removed by etching or polishing. The remaining device layer 212 becomes a
membrane member. The handle layer 210 and the buried oxide layer 211 function as a
membrane support layer until the device layer 212, that is, the membrane member is bonded to
the substrate 201. When hydrofluoric acid is used to remove the buried oxide film layer 211, the
device layer 212 made of silicon single crystal can be selectively left.
[0034]
Next, as illustrated in FIG. 2 (j), the photoresist layer 213 is used as an etching resist, the device
layer 212 and the silicon oxide film layer 203 are removed to expose the surface of the silicon
single crystal layer 202, and the electrode extraction portion Form 214. After removing the
photoresist layer 213, an aluminum layer 215 is formed on the surfaces of the device layer 212
and the electrode lead-out portion 214, as shown in FIG. 2 (k).
[0035]
Next, as illustrated in FIG. 2L, the electrode 217, the electrode 218, and the electrode 219 are
formed using the photoresist layer 216 as an etching resist. In FIG. 2 (m), the top view seen from
the electrode 217 side of the process of FIG. 2 (l) is illustrated. The electrode in the step of FIG. 2
(m) is located under the photoresist layer 216. The electrode 217 is an electrode formed on the
exposed surface of the silicon single crystal layer 202 of the electrode lead-out portion 214 and
electrically connected to the silicon single crystal layer 202. An electrode 218 is formed on the
device layer 212 in the center of the cavity 206. 2The plurality of electrodes 218 arranged in a
dimensional array are electrically connected to the electrodes 219 by the wirings 220. The
electrode 219 is an electrode for electrically extracting the electrode 218 to the outside.
[0036]
After removing the photoresist layer 216, the periphery of the device layer 212 is etched using
the photoresist layer 221 as an etching resist as illustrated in FIGS. 2 (n) and 2 (o). This electrical
isolation is performed to prevent shorting between adjacent elements via the device layer 212
when a plurality of electrically independent elements are provided on the same substrate. Finally,
as illustrated in FIG. 2 (p), the photoresist layer 221 is removed.
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[0037]
FIGS. 3A and 3B show a modification of the present embodiment shown in FIG. FIGS. 3 (a) and 3
(b) are plan views corresponding to FIG. 2 (o). The same reference numerals as in FIG. 2 denote
the same parts. The cavity 301 and the electrode 302 in FIG. 3A are circular. Also, the electrode
302 is formed at the center of the cavity 301. When the cavity has a circular shape, the
deformation of the thin film membrane portion of the device layer 212 at the time of
transmission and reception of ultrasonic waves forms rotational symmetry about the center of
the cavity 301. Accordingly, the transmission and reception directivity of the ultrasonic waves for
each cavity 301 has a conical shape. In FIG. 3A, the plurality of electrodes 302 are electrically
connected to the electrodes 219 by the wiring 220.
[0038]
FIG. 3 (b) is an example in which the cavities 301 are arranged by being shifted by a half cycle as
shown in the figure, and there is an advantage that the cavity area with respect to the element
area can be increased. In FIG. 3B, the plurality of electrodes 302 are electrically connected to the
electrode 219 by the wiring 303.
[0039]
According to this embodiment, since the above-described gas release passage is provided, it is
possible to release gas, moisture and the like generated at the time of manufacturing the
capacitive ultrasonic transducer through the gas release passage. Therefore, it is possible to
reduce the bonding failure of the bonding portion caused by such gas and the like. In addition,
since the method of simply releasing gas, moisture and the like through the gas release passage
is adopted, the influence on the reduction in productivity and the miniaturization of the element
can be improved as compared with the conventional method.
[0040]
Second Embodiment FIGS. 4A to 4Q are diagrams for explaining a second embodiment according
to the method of manufacturing a capacitive ultrasonic transducer of the present invention. The
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same number is attached to the same part. The manufacturing method of this embodiment is
started from a substrate 401 whose cross section is illustrated in FIG. The substrate 401 is
constituted of a silicon single crystal layer 402, and a silicon oxide film layer 403 and a silicon
oxide film layer 404 formed on the upper surface and the lower surface thereof.
[0041]
First, as shown in FIG. 4B, the silicon oxide film layer 403 is etched using the photoresist layer
405 as an etching resist to form a cavity (recess). When hydrofluoric acid is used for etching, the
silicon single crystal layer 402 functions as an etch stop layer, and control of the etching amount
in the depth direction becomes easy. The planar shape of the cavity 406 viewed from the side of
the silicon oxide film layer 403 is illustrated in FIG. The cross section of FIG. 4 (b) corresponds to
the C-C 'position of FIG. 4 (c). Again, the cavities 406 are square or rectangular and are arranged
on the substrate 401 in a two-dimensional array. Also in the present embodiment, an example in
which five cavities are arranged in the x direction and three cavities are arranged in the y
direction is illustrated.
[0042]
Next, as illustrated in FIG. 4D, after removing the photoresist layer 405, a silicon oxide film is
formed again on the entire substrate 401, and an insulating layer 407 is formed on the surface of
the silicon single crystal layer 402 in the cavity 406. Do. The insulating layer 407 can provide
insulation between the single-crystal silicon layer 402 even when the device layer 411, which
will be formed in a later step, is bent by ultrasonic vibration or static pressure from the outside to
contact the bottom of the cavity 406. It is provided to keep.
[0043]
Next, an SOI wafer 408 shown in FIG. 4 (e) is prepared. The SOI wafer 408 has a laminated
structure in the order of a handle layer 409 made of silicon single crystal, a buried oxide film
layer 410 made of silicon oxide, and a device layer 411 made of silicon single crystal. Next, as
illustrated in FIG. 4F, the groove 413 is formed by etching the device layer 411 using the
photoresist layer 412 as an etching resist. The grooves 413 function as gas release holes in a
later step. The planar shape of the groove 413 is illustrated in FIG. FIG. 4G is a plan view of the
SOI wafer 408 viewed from the device layer 411 side in the same step as FIG. 4F, and the
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squares shown by dotted lines are the cavities of the substrate 401 to be bonded in a later step.
Position 406; As shown, a groove 413 is formed around the cavity 406. Also, the groove 413
reaches the end of the SOI wafer 408.
[0044]
Next, as illustrated in FIG. 4H, the surface of the substrate 401 on which the cavity 406 is formed
and the device layer 411 surface of the SOI wafer 408 are bonded using direct bonding. The
bonding is performed in a substantially vacuum atmosphere, and the inside of the cavity 406 is
sealed in a substantially vacuum. The end faces of the bonded substrates are illustrated in FIGS. 4
(i) and (j). FIGS. 4 (i) and 4 (j) are views of the substrate in the same step as FIG. 4 (h) as viewed in
the y direction and in the x direction. As shown in FIGS. 4 (i) and 4 (j), the groove 413 opens at
the end face of the bonded substrate. Although not shown, the groove 413 is also opened on the
opposite surface of FIGS. 4 (i) and 4 (j). Through the groove 413, water and gas such as oxygen
generated at the bonding interface at the time of direct bonding are removed from the bonding
interface to the outside.
[0045]
Next, as illustrated in FIG. 2 (k), the handle layer 409 and the buried oxide layer 410 of the SOI
wafer 408 are removed by etching or polishing. The remaining device layer 411 becomes a
membrane member. The handle layer 409 and the buried oxide layer 410 also function as a
membrane support layer until the device layer 411, that is, the membrane member is bonded to
the substrate 401. When hydrofluoric acid is used to remove the buried oxide film layer 410, the
device layer 411 made of silicon single crystal can be selectively left.
[0046]
Next, as illustrated in FIG. 4L, the photoresist layer 414 is used as an etching resist, the device
layer 411 and the silicon oxide film layer 403 are removed to expose the surface of the silicon
single crystal layer 402, and the electrode extraction portion Form 415. After removing the
photoresist layer 414, an aluminum layer 416 is formed on the surfaces of the device layer 411
and the electrode lead-out portion 415, as shown in FIG. 4 (m).
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[0047]
Next, as illustrated in FIG. 4N, an electrode 418, an electrode 419, and an electrode 420 are
formed using the photoresist layer 417 as an etching resist. The top view seen from the electrode
419 side of the process of FIG. 4 (n) to FIG. 4 (o) is illustrated in figure. The electrode in the step
of FIG. 4 (o) is in the lower layer of the photoresist layer 417. The electrode 418 is an electrode
formed on the exposed surface of the silicon single crystal layer 402 of the electrode lead-out
portion 415 and electrically connected to the silicon single crystal layer 402. An electrode 419 is
formed on the device layer 411 in the center of the cavity 406. 2The plurality of electrodes 419
arranged in a dimensional array are electrically connected to the electrode 420 by the wiring
421. The electrode 420 is an electrode for electrically extracting the electrode 419 to the
outside.
[0048]
Finally, the photoresist layer 417 is removed as illustrated in FIGS. 4 (p) and (q).
[0049]
5 (a) and 5 (b) illustrate an example of another form of capacitive ultrasonic transducer that can
be manufactured by the same process as that of FIG.
FIGS. 5 (a) and 5 (b) are plan views corresponding to FIG. 4 (q). The same reference numerals as
in FIG. 4 denote the same parts. The cavity 501 and the electrode 502 in FIG. 5A are circular.
Also, the electrode 502 is formed at the center of the cavity 501. When the cavity has a circular
shape, the deformation of the membrane portion of the device layer 411 at the time of
transmission and reception of ultrasonic waves forms rotational symmetry around the center of
the cavity 501. Therefore, it has a feature that the transmission and reception directivity of the
ultrasonic wave for each cavity has a conical shape. In FIG. 5A, the plurality of electrodes 502 are
electrically connected to the electrode 420 by the wiring 421.
[0050]
FIG. 5 (b) shows an example in which the cavities 501 are arranged by being shifted by a half
cycle, and there is an advantage that the cavity area with respect to the element area can be
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increased. In FIG. 5 (b), the plurality of electrodes 502 are electrically connected to the electrode
420 by the wiring 503. The form in which the groove 413 formed in the device layer 411 of the
present embodiment is provided as a gas release passage together with the groove 207 formed in
the silicon oxide film layer 203 of the first embodiment is also feasible. The other points of the
second embodiment are the same as the first embodiment.
[0051]
Example 3 FIGS. 6A to 6H are diagrams for explaining Example 3 according to the method of
manufacturing a capacitive ultrasonic transducer of the present invention. The same number is
attached to the same part.
[0052]
The substrate 401 illustrated in FIG. 6A is a substrate in the same process as FIG. 4D. The
substrate shown in FIG. 6 (b) is the same as the substrate shown in FIG. 4 (e): handle layer 409
made of silicon single crystal, buried oxide film layer 410 made of silicon oxide, and device layer
411 made of silicon single crystal. An SOI wafer 408 having a stacked structure in order. In the
present embodiment, as shown in FIG. 6C, a plurality of holes 601 penetrating in the vertical
direction are formed in the SOI wafer 408. The holes 601 function as gas release holes in a later
step. For example, DRIE (Deep Reactive Ion Etching) processing is suitable for processing the
holes 601. In DRIE, for example, etching by SF6 (sulfur hexafluoride) plasma and formation of a
sidewall protective film of holes by C4F8 (cyclopentafluoride octafluoride) are repeatedly
performed to dig holes.
[0053]
FIG. 6D is a plan view of the SOI wafer 408 as viewed from the handle layer 409 side. The cross
section in FIG. 6 (c) corresponds to the D-D 'position in FIG. 6 (d). The squares illustrated by
dotted lines are the positions of the cavities 406 of the substrate 401 to be bonded in a later
step. As shown, the holes 601 are discretely formed around the cavity 406.
[0054]
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Next, as illustrated in FIG. 6E, the surface of the substrate 401 on which the cavity 406 is formed
and the surface of the device layer 411 of the SOI wafer 408 are bonded using direct bonding.
The bonding is performed in a substantially vacuum atmosphere, and the inside of the cavity 406
is sealed in a substantially vacuum. The holes 601 are open to the outside of the substrate, and
through the holes 601, gases such as water and oxygen generated at the bonding interface
during direct bonding are removed from the bonding interface to the outside.
[0055]
Next, as illustrated in FIG. 6F, the handle layer 409 and the buried oxide layer 410 of the SOI
wafer 408 are removed by etching or polishing. The remaining device layer 411 becomes a
membrane member. The handle layer 409 and the buried oxide layer 410 also function as a
membrane support layer until the device layer 411, that is, the membrane member is bonded to
the substrate 401. When hydrofluoric acid is used to remove the buried oxide film layer 410, the
device layer 411 made of silicon single crystal can be selectively left.
[0056]
The following steps are the same as in the second embodiment, and therefore the description
thereof is omitted. 6 (f) is equivalent to FIG. 4 (k), and the steps of FIGS. 6 (f) to 6 (h) are
equivalent to the steps of FIGS. 4 (k) to 4 (q).
[0057]
FIG. 7 illustrates another embodiment of a capacitive ultrasonic transducer which can be
manufactured by the same process as that of FIG. The same reference numerals as in FIGS. 5 and
7 denote the same parts. FIG. 7 is a plan view corresponding to FIG. FIG. 7 shows an example in
which holes 601 are also formed between circular cavities 501 arranged in a two-dimensional
array. By forming more holes 601, the effect of removing the gas such as water and oxygen
generated at the bonding interface at the time of direct bonding from the bonding interface to
the outside is enhanced. A mode is also possible in which the hole 601 of this embodiment is
provided as a gas release passage together with at least one of the groove 207 of the first
embodiment and the groove 413 of the second embodiment. The other points of the third
embodiment are the same as those of the first embodiment.
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[0058]
Example 4 FIGS. 8A to 8H are diagrams for explaining Example 4 according to the method of
manufacturing a capacitive ultrasonic transducer of the present invention. The same number is
attached to the same part.
[0059]
A substrate 401 illustrated in FIG. 8A is a substrate in the same process as FIG. 4D. In the present
embodiment, as illustrated in FIG. 8B, the substrate 401 is etched using the photoresist layer 801
as an etching resist to form holes 802 penetrating in the vertical direction. The holes 802
function as gas release holes in a later step. The above-mentioned DRIE processing is suitable for
processing the holes 802. The planar shape of the cavity 406 and the hole 802 is illustrated in
FIG. The cross section of FIG. 8 (b) corresponds to the E-E 'position of FIG. 8 (c). The shape and
arrangement of the cavity 406 are the same as in the second embodiment. As shown, the holes
802 are discretely formed around the cavity 406. FIG. 8 (d) is an SOI wafer 408 equivalent to
FIG. 4 (e).
[0060]
Next, as illustrated in FIG. 8E, the surface of the substrate 401 on which the cavity 406 is formed
and the device layer 411 surface of the SOI wafer 408 are bonded using direct bonding. The
bonding is performed in a substantially vacuum atmosphere, and the inside of the cavity 406 is
sealed in a substantially vacuum. The holes 802 are opened to the outside of the substrate, and
water and gas such as oxygen generated at the bonding interface during direct bonding are
removed from the bonding interface to the outside.
[0061]
Next, as illustrated in FIG. 8F, the handle layer 409 and the buried oxide film layer 410 of the SOI
wafer 408 are removed by the same process as that of FIG. 4K of the second embodiment. The
remaining device layer 411 becomes a membrane member. The handle layer 409 and the buried
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oxide layer 410 also function as a membrane support layer until the device layer 411, that is, the
membrane member is bonded to the substrate 401.
[0062]
The following steps are equivalent to Example 2. That is, the steps of (f) to (h) of FIG. 8 are
equivalent to the steps of (k) to (q) of FIG.
[0063]
FIG. 9 illustrates another embodiment of a capacitive ultrasonic transducer which can be
manufactured by the same process as that of FIG. The same reference numerals as in FIGS. 5 and
9 denote the same parts. FIG. 9 is a plan view corresponding to FIG. FIG. 9 shows an example in
which the holes 802 are also formed between the substantially circular cavities 501 arranged in
a two-dimensional array. By forming more holes 802, the effect of removing water and gas such
as oxygen generated at the bonding interface at the time of direct bonding from the bonding
interface to the outside is enhanced. The embodiment in which the hole 802 of the present
embodiment is also provided as a gas release passage together with the groove 207 of the first
embodiment, the groove 413 of the second embodiment, and at least one of the holes 601 of the
third embodiment can be implemented. The fourth embodiment is the same as the previous
embodiment in the other points.
[0064]
Example 5 FIGS. 10 (a) to 10 (g) are diagrams for explaining Example 5 according to the method
of manufacturing a capacitive ultrasonic transducer of the present invention. The same number is
attached to the same part.
[0065]
The substrate 201 illustrated in FIG. 10 (a) is the same as FIG. 2 (d). In the present embodiment,
in the substrate 1001 illustrated in FIG. 10B, a silicon nitride compound layer 1003 is formed on
the surface of the silicon single crystal layer 1002 by CVD (chemical vapor phase reaction). As
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illustrated in FIG. 10C, the surface of the silicon nitride compound layer 1003 of the substrate
1001 and the surface of the substrate 201 on which the cavity 206 and the groove 207 are
formed are bonded by direct bonding. The bonding is performed in a substantially vacuum
atmosphere, and the inside of the cavity 206 is sealed in a substantially vacuum. The end faces of
the bonded substrates are illustrated in FIGS. 10 (d) and 10 (e). FIGS. 10 (d) and 10 (e) are views
of the substrate in the same process as FIG. 10 (c), as viewed from the y direction and the x
direction, respectively. As illustrated in FIGS. 10 (d) and 10 (e), the groove 207 opens at the end
face of the bonded substrate. Further, although not shown, a groove 207 is also opened on the
opposite surface of FIGS. 10 (d) and 10 (e). Through the groove 207, water and gas such as
oxygen generated at the bonding interface at the time of direct bonding are removed from the
bonding interface to the outside.
[0066]
Next, as illustrated in FIG. 10F, the silicon single crystal layer 1002 of the substrate 1001 is
removed by etching or polishing. When using a KOH (potassium hydroxide) aqueous solution for
removing the silicon single crystal layer 1002, the silicon nitride compound layer 1003 can be
selectively left. The remaining silicon nitride compound layer 1003 becomes a membrane
member. Further, the silicon single crystal layer 1002 functions as a membrane supporting layer
until the silicon nitride compound layer 1003, that is, the membrane member is bonded to the
substrate 201.
[0067]
The following steps are the same as FIG. 2 (j) to FIG. 2 (p), so the description will be omitted. The
step of FIG. 10 (f) is equivalent to the step of FIG. 2 (i), and the silicon nitride compound layer
1003 corresponds to the device layer 212 of FIG. 2 (i). It is also possible to combine the groove
207 of the present embodiment with at least one of the groove 413 of the second embodiment,
the hole 601 of the third embodiment, and the hole 802 of the fourth embodiment. The other
points of the fifth embodiment are the same as those of the first embodiment.
[0068]
It is a figure explaining Example 1 which concerns on the element of this invention. It is a figure
explaining an example of the manufacturing method of the element of FIG. It is an example of the
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other element shape which can be produced by the manufacturing method of FIG. It is a figure
explaining Example 2 which concerns on the manufacturing method and element of this
invention. It is an example of the other element shape which can be produced by the
manufacturing method of FIG. It is a figure explaining Example 3 which concerns on the
manufacturing method and element of this invention. It is an example of the other element shape
which can be produced by the manufacturing method of FIG. It is a figure explaining Example 4
which concerns on the manufacturing method and element of this invention. It is an example of
the other element shape which can be produced by the manufacturing method of FIG. It is a
figure explaining Example 5 which concerns on the manufacturing method and element of this
invention. It is a figure explaining a prior art. It is a figure explaining a prior art.
Explanation of sign
[0069]
101、201、401、1001 Substrate 102, 202, 402 Silicon single crystal layer (substrate) 103,
203, 204, 403, 404 Silicon oxide film layer (substrate) 104, 206, 301, 406, 501 Cavity (concave
portion) 105, 207, 413 Groove (gas Ejection passage 107, 208, 407 Insulating layer 108
Membrane (membrane member) 109, 217, 218, 219, 302, 418, 419, 420, 502 Electrode 209,
408 SOI wafer 210, 409 Handle layer 211, 410 Embedded oxide film Layer 212, 411 Device
layer (membrane member) 601, 802 Hole (gas release passage) 1002 Silicon single crystal layer
1003 Silicon nitride compound layer (membrane member)
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