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DESCRIPTION JP2008112755

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DESCRIPTION JP2008112755
A dielectric film of a capacitor microphone formed by micromachining a silicon substrate can be
electretized without difficulty, and variation in microphone sensitivity caused due to
manufacturing variation or component characteristic variation Provide a new electretization
technology for condenser microphones that can also be addressed. A fixed electrode having a
plurality of sound holes by processing a silicon wafer, a conductive vibrating film disposed at a
predetermined distance from the fixed electrode, and a dielectric provided on the vibrating film
Forming a capacitor microphone having a film, dicing the silicon wafer along a dicing line to form
a capacitor microphone, and performing corona discharge prior to dicing to generate ions
generated by the fixed electrode And an electretization step of electretizing the dielectric film via
the plurality of sound holes provided in [Selected figure] Figure 1
Electretizing method and electretizing apparatus
[0001]
The present invention relates to a method of electretizing a dielectric film in a condenser
microphone formed using a silicon microfabrication technique, and an electretizing apparatus.
[0002]
The electret condenser microphone (ECM) detects the capacitance change of the condenser due
to the acoustic wave as an electric signal, and uses an electret film with semipermanent
polarization, thereby eliminating the need for direct current bias of the condenser, which is small
in size. It is an electrical conversion device.
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[0003]
An electret film (a dielectric film at least a part of which is polarized) in the ECM is made of, for
example, an organic dielectric film such as FEP (fluoroethylene · propylene), and a charge is
injected and fixed to the dielectric film. Formed by
The electric field formed by the charges injected into the dielectric film generates a potential
difference between both electrodes of the capacitor.
Note that injecting and fixing a charge to a dielectric film is called electretization.
[0004]
The dielectric film is formed of a thin film such as FEP, and a metal such as gold or nickel
constituting the electrode is attached to the outer surface by vapor deposition or the like.
[0005]
As a method of injecting a charge into a dielectric film for forming an electret, there are methods
shown in FIGS. 9 and 10 (see, for example, Non-Patent Document 1 and Patent Document 1).
[0006]
FIG. 9 is a cross-sectional view of an essential part of an apparatus for producing a corona
discharge using a needle electrode to electretize a dielectric film.
[0007]
In the apparatus shown in FIG. 9, the FEP thin film 4 is placed on the ground electrode 5, and a
direct current corona discharge is generated by the needle electrode 6 to inject and fix ions into
the FEP thin film 4 to perform electretization.
Reference numeral 7 denotes a high voltage source.
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[0008]
FIG. 10 is a cross-sectional view of an essential part of an apparatus for generating a corona
discharge using a wire electrode to electretize a dielectric film.
In FIG. 10, parts common to the apparatus of FIG. 9 are given the same reference numerals.
[0009]
In the apparatus shown in FIG. 10, the FEP thin film 4 is placed on the ground electrode (metal
tray) 5, a direct current corona discharge is generated by the wire electrode 21, and ions are
injected into the FEP thin film 4 and fixed. .
The device shown in FIG. 10 has an advantage that ions can be irradiated over a wide range
because the wire electrode 21 has a two-dimensional spread.
[0010]
Therefore, usually, in the production of ECM, in consideration of mass productivity, a plurality of
FEP thin films (dielectric films) are arranged in a metallic tray, and corona discharge is performed
by the apparatus of FIG. It is However, in this method, since the radiation of ions may not be
made uniform, the electret amount may vary depending on the position on the tray. This causes
variations in the sensitivity of the microphone. In addition to this, variations in sensitivity may
occur due to variations in parasitic capacitance, FET capacitance, and the like.
[0011]
In the above example, the dielectric film itself which is the target of electretization is taken out
and the electretization processing is performed. This technology can be said to be a technology
based on ECM constructed by assembling mechanical parts.
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[0012]
On the other hand, in recent years, a technology has been proposed in which a microminiaturized
condenser microphone is formed by micromachining a silicon substrate instead of assembling
mechanical parts (for example, patent documents 2, patent documents 3, patent documents 4)
reference).
[0013]
Silicon condenser microphones manufactured using the so-called MEMS (micro-electromechanical system) device manufacturing technology are called “silicon microphones (or silicon
microphones)”, and mobile phones are becoming smaller and thinner. It attracts attention as a
manufacturing technology of ECM for carrying in a terminal etc. (for example, refer to patent
documents 2).
[0014]
Here, since the condenser microphone is manufactured by processing a silicon substrate using
semiconductor process technology, electretization processing unrelated to semiconductor
processing can not enter into the manufacturing process (that is, , It is not possible to take out
only the dielectric film and individually electretize it).
[0015]
Therefore, the condenser microphone described in Patent Document 3 is a condenser
microphone not having an electret film.
[0016]
However, electretization in a condenser microphone is not necessarily impossible, and in the
condenser microphone described in Patent Document 4, electretization of a dielectric film is
possible.
[0017]
That is, the capacitor microphone described in Patent Document 4 includes a first silicon
substrate (microphone film) including a dielectric film formed on a semiconductor substrate, and
a second silicon substrate bonded to the first silicon substrate. The dielectric film is electretized
at the end of the manufacturing process of the first substrate, and then the second silicon
substrate is bonded.
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Microphone course for broadcast engineers (Jinichiro Nakamura, Broadcasting Technology &
Rokukan Publishing, November, 1975 issue) JP-A-56-58220 JP-A-11-88992 JP-A-2005-20411
(FIG. 1) ) Japanese Patent Application Publication No. 2000-508860 (FIGS. 1A and 1B)
[0018]
As described above, a capacitor microphone obtained by micromachining a silicon substrate
using a semiconductor manufacturing process inherently has a problem that it is difficult to
manufacture an ECM because it can not take out only a dielectric film to be electretized. .
[0019]
According to the method described in Patent Document 4, a capacitor microphone is divided into
two substrates and each is manufactured separately, and finally each substrate is bonded
together, although electretization of the dielectric film is possible, The manufacturing process of
the microphone is complicated.
[0020]
In addition, when microfabrication of a silicon substrate, variations in device dimensions are
likely to occur, or variations in the performance of electronic components such as FETs (field
effect transistors) mounted on a mounting substrate may not be ignored in some cases.
Therefore, the sensitivity of the condenser microphone varies.
In Patent Document 4, no measures are taken with regard to measures against such variations in
sensitivity of the condenser microphone.
[0021]
The present invention has been made in view of the above situation, and it is possible to
electretize a dielectric film of a capacitor microphone formed by micromachining a silicon
substrate without difficulty, and manufacturing variations and parts It is an object of the present
invention to provide a novel electretization technique for condenser microphones, which can also
cope with the fluctuation of microphone sensitivity caused due to the characteristic variation of.
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[0022]
The present invention is an electretization method for forming a electret film by electretizing a
dielectric film in a condenser microphone formed by micromachining a silicon wafer, wherein a
plurality of sounds are processed by processing the silicon wafer. Forming a capacitor
microphone having a fixed electrode having a hole, a conductive vibrating film disposed at a
predetermined distance from the fixed electrode, and a dielectric film provided on the vibrating
film, and the silicon wafer Dicing along the dicing line to form a condenser microphone, corona
discharge is performed prior to dicing, and ions generated by the corona discharge are provided
in the plurality of sound holes provided in the fixed electrode. Supply to the dielectric film via the
Including an electret step of performing reduction.
[0023]
As described above, the condenser microphone manufactured using the MEMS technology can
not take out the electret films individually to be electretized.
In addition, when the condenser microphone is divided into two parts and manufactured, the
manufacturing process becomes complicated.
Therefore, in the present invention, a silicon substrate is processed to form a condenser
microphone, and this is used to electretize a dielectric film at wafer level prior to dicing.
The electretization is carried out by corona discharge from the needle electrode to the dielectric
film of the condenser microphone.
At this time, corona discharge from one needle electrode is individually performed on the
dielectric of one microphone at wafer level.
Alternatively, electretization is performed collectively at the wafer level.
[0024]
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According to this method, since the annealing process after electretization processing can be
realized at the wafer level, the number of times of handling can be reduced.
Therefore, the yield can be improved.
Furthermore, since the electretization process is performed prior to the dicing process, the
process at the chip level after dicing can be reduced, and handling can be facilitated.
[0025]
Furthermore, in the case of batch electretization or in the case of electretization for each
individual condenser microphone, this can be realized by one alignment (alignment) at the wafer
level, and the probe position accuracy is improved with good workability. It becomes possible.
Therefore, it is possible to reduce the contact failure between the electrode pad and the probe
which cause corona discharge by energizing in the electretization process, and to improve the
reliability of the contact.
[0026]
According to the corona discharge of the needle electrode, more ions can be concentrated and
irradiated to the dielectric film of the microphone than in the case of the corona discharge by the
wire electrode. Therefore, due to the structure of the microphone, for example, even when ion
irradiation to the dielectric film is performed through the opening of the fixed electrode, it is
possible to supply an appropriate amount of ions, and an electret of the appropriate dielectric
film Is possible. In addition, since electretization at the wafer level is possible, handling is easy.
Since corona discharge is performed between one needle electrode and the conductive film in
contact with the dielectric film to perform electretization of the dielectric film of the microphone,
it is easy to perform the condition setting. Therefore, the accuracy of the electretization It is
advantageous in terms of improvement.
[0027]
Further, in the electretization method of the present invention, in the electretization step, the
diaphragm is energized through the electrode pad for energization, and the needle-like electrode
is disposed above the diaphragm and the fixed electrode. And a step of collectively performing
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electretization processing on the dielectric film on the vibrating film.
[0028]
In the electretization method of the present invention, the electretization step includes the step of
setting the dielectric film in the condenser microphone to a ground potential.
During electretization, ions from corona discharge reach the dielectric film via a plurality of
sound holes (openings for guiding sound waves to the vibrating film) provided in the fixed
electrode. Since ion irradiation is performed under a predetermined condition from one needle
electrode after fixing at a predetermined potential, for example, a ground potential, a large
amount of ions can be intensively supplied to the dielectric film. Therefore, even if it becomes a
situation unsuitable for applying ions to the dielectric film due to the internal structure of the
microphone, the dielectric film can be electretized.
[0029]
The electretization method of the present invention includes a plurality of electretization steps.
[0030]
That is, the electretization processing is performed in several times, and according to this
configuration, electretization can be performed without difficulty, and it is also advantageous in
that the accuracy of the electretization processing is enhanced.
[0031]
Further, in the electretization method of the present invention, an initial electretization step of
carrying out an initial electretization treatment of the dielectric film by corona discharge under
predetermined conditions, and then resetting the conditions again and re-charging the corona
discharge. And E. additional electretization steps to carry out additional electretization processing
according to
[0032]
This is, for example, to achieve minimum electretization by initial electretization, and then change
conditions to perform additional electretization to achieve desired electretization, according to
this configuration, Electretization can be performed without unreasonableness, and it is also
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advantageous in terms of enhancing the accuracy of the electretization processing.
[0033]
In the electretization method of the present invention, after the initial electretization step, the
sensitivity of the condenser microphone is measured, the conditions of the additional
electretization process are determined based on the measurement results, and the addition is
performed under the determined conditions. Including the implementation of the electretization
process of
[0034]
In order to eliminate variations in sensitivity due to manufacturing variations (film thickness
variations and the like) of the condenser microphone, this method electretizes the dielectric film
one by one to obtain an electret condenser microphone, and then determines the sensitivity of
the electret condenser microphone. The conditions for electretization by corona discharge are
determined again based on the measurement results based on the measurement results.
According to this configuration, the electret amount in one electretization processing is for each
individual element (or wafer) By adjusting each time, the microphone can be adjusted to a
specified sensitivity.
In particular, variations in sensitivity of the microphone due to variations in manufacturing (such
as variations in film thickness) can be absorbed by adjusting the electret amount of the additional
electretization process, and furthermore, the capacitance of the FET (field effect transistor) and
parasitics Variations in sensitivity due to capacity etc. can also be absorbed by adjusting the
electret amount of the additional electret processing.
Therefore, it is possible to take measures against variations in microphone sensitivity caused by
variations in manufacturing and characteristics of parts.
[0035]
The electretizing method of the present invention includes the one in which the charge amount
of the dielectric film is adjusted by the applied voltage of corona discharge.
[0036]
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This is to adjust the electretization amount by the applied voltage at the time of corona
discharge, and with this configuration, it is possible to control the electretization amount with
high accuracy by adjusting the applied voltage.
[0037]
In the electretization method of the present invention, the method includes adjusting the charge
amount of the dielectric film by the distance between the needle-like electrode which performs
corona discharge and the dielectric film.
[0038]
This is to adjust the electretization amount by adjusting the distance between the needle
electrode and the dielectric film, and this configuration makes it possible to control the
electretization amount with high accuracy.
[0039]
The electretizing method of the present invention includes the one in which the amount of
charge of the dielectric film is adjusted by the time of corona discharge.
[0040]
This is to adjust the electretization amount by adjusting the duration of the corona discharge, and
this configuration makes it possible to easily control the electretization amount with high
accuracy.
[0041]
In the electret forming method of the present invention, the charge amount of the dielectric film
is adjusted by the ratio of the negative ion and the positive ion generated by corona discharge.
[0042]
Here, the applied power is adjusted by adjusting the magnitude or the duty ratio of the positive
voltage and the negative voltage applied to the ion generator for ion generation.
This makes it possible to adjust the proportion of positive ions and negative ions generated by
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corona discharge.
Thus, the amount of electretization can be controlled with high accuracy by adjusting the
proportion of positive ions and negative ions.
[0043]
Further, the electretization method of the present invention includes one in which the charge
amount of the dielectric film is adjusted by setting the diaphragm to the ground potential and
adjusting the potential of the fixed electrode.
As a result, by performing measurement and feedback in advance and finely adjusting the
potential, highly accurate adjustment becomes possible.
[0044]
In the electretization method of the present invention, in the step of forming the condenser
microphone, at least one conductive electrode pad and the electrode pads are commonly
connected in common in each condenser microphone formation region of the silicon wafer. And a
step of forming a connection line, wherein the electretization step is to conduct electricity to the
vibrating membrane through the energizing electrode pad, and to form the vibrating membrane
and a needle-like electrode disposed above the fixed electrode. And a step of collectively
performing electretization processing on the dielectric film on the vibrating film.
With this configuration, energization can be performed collectively for each wafer, and
electretization can be performed collectively.
[0045]
In the electretization method of the present invention, the common connection line is formed on
the dicing line, and includes one configured to be cut out in the dicing step.
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With this configuration, after the wiring pattern is left in the unnecessary region and used in the
electretization step, the wiring is naturally cut off in the dicing step, which leads to a decrease in
the number of elements (yield) extracted from one wafer. It is possible to easily realize
electretization without
[0046]
In addition, the condenser microphone of the present invention has the dielectric film which has
been electretized by the electretization method of the present invention as a component of the
condenser.
[0047]
It is a condenser microphone formed by microfabrication of a silicon substrate having a dielectric
film manufactured using the electretization method of the present invention as a component of a
capacitor.
An electret silicon capacitor microphone (ESCM) is obtained which is ultra-compact and has a
practical sensitivity.
[0048]
An electretization apparatus according to the present invention is an electretization apparatus for
carrying out the electretization method according to the present invention, and one needle for
individually performing at least one corona discharge on one condenser microphone. Electrode, a
high voltage power supply for applying a high voltage to the needle electrode, a conducting pin
for setting a film to be electretized in the condenser microphone to a desired potential, and a
mounting on which the condenser microphone is mounted And a stage for mounting the
substrate.
[0049]
This is a configuration for irradiating one capacitor microphone with ions by corona discharge
(including a grounding pin for grounding a film to be electretized) and a stage for setting a wafer
(mounting table) The electretization device enables the electretization processing to be
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performed for the condenser microphone in the mounted state.
In addition, electretization processing or sensitivity measurement can be realized using a
conventional semiconductor inspection apparatus.
Preferably, the desired potential is a ground potential.
[0050]
The electretization apparatus of the present invention further includes one having a sensitivity
measurement unit that measures the sensitivity of the condenser microphone.
[0051]
This is to add the sensitivity measurement unit of the electretized silicon condenser microphone
to the electretization device, and measure the sensitivity of the microphone after electretization
processing with this configuration, and based on the measurement result, It becomes possible to
set conditions for electretization processing.
[0052]
Further, in the electretization device of the present invention, the applied voltage of corona
discharge, the distance between an electrode for corona discharge and the dielectric portion, the
time for corona discharge, and the ratio of negative ions to positive ions generated in corona
discharge, At least one of which is adjustable.
[0053]
It is possible to adjust at least one of the applied voltage of corona discharge, the distance to the
dielectric film, the discharge time, and the polarity of discharge ions in order to adjust the
electret amount of one electretization treatment. Means is provided, and this configuration
enables fine adjustment of the electret amount.
In particular, by adjusting the electret amount for the second time, it is possible to obtain a
specified microphone sensitivity, and thereby to adjust to the specified sensitivity even for a
microphone having manufacturing variations or characteristic variations of electronic
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components. It becomes possible.
[0054]
According to the present invention, with regard to a condenser microphone obtained by
micromachining a silicon substrate, it becomes possible to electretize a dielectric film to a
specified value at wafer level.
[0055]
That is, conventionally, it has been considered difficult to adopt the electret system because the
condenser microphone (silicon microphone) can not take out only the dielectric film and
electretize it, but according to the present invention, a practical method is realized. This makes it
possible to manufacture an electret condenser microphone.
[0056]
According to this method, since the annealing process after electretization processing can be
realized at the wafer level, the number of times of handling can be reduced.
Therefore, the yield can be improved.
Furthermore, since the electretization process is performed prior to the dicing process, the
process at the chip level after dicing can be reduced, and handling can be facilitated.
[0057]
Furthermore, it is possible to improve the probe position accuracy by one alignment (alignment).
Therefore, it is possible to reduce the contact failure between the electrode pad and the probe
which cause corona discharge by energizing in the electretization process, and to improve the
reliability of the contact.
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[0058]
In addition, variations in the sensitivity of the microphone due to variations in film thickness and
the like (device fabrication variations) can be compensated by adjusting the electretization
amount.
[0059]
Furthermore, variations in microphone sensitivity caused by variations in electret amount,
parasitic capacitance, FET capacitance, etc. can be compensated by the present invention.
[0060]
According to the present invention, the silicon condenser microphone can be electretized at the
wafer level, and the electretization amount can be adjusted individually or for each wafer to
adjust the sensitivity of the microphone. Specification) Defective products with outside sensitivity
are reduced, and the yield of microphone production is dramatically improved.
Therefore, mass production of an electret condenser microphone is possible.
[0061]
Embodiments of the present invention will be described with reference to the drawings.
Embodiment 1
[0062]
FIG. 1 is an explanatory view showing wafer-level electretization steps of a condenser
microphone manufactured by micromachining a silicon wafer, and FIG. 1 (a) is a view showing a
silicon wafer, and FIG. 1 (b) is a diagram It is AA sectional drawing of Fig.1 (a), and one capacitor
microphone is shown.
[0063]
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The present embodiment is characterized in that as shown in FIG. 1, the capacitor microphone 43
is formed by processing the silicon wafer 1, and electretization is performed at the wafer level
prior to dicing.
That is, in the present embodiment, first, silicon wafer 1 is processed using MEMS technology,
fixed electrode 31 having a plurality of sound holes 35, and conductive arranged at a
predetermined distance from fixed electrode 31. A capacitor microphone having a vibrating film
33 made of an inorganic film and a dielectric film 32 provided on the vibrating film 33 is formed.
Then, prior to dicing the silicon wafer along the dicing line DL, corona discharge is performed,
and ions generated by the corona discharge are transmitted through the plurality of sound holes
35 provided in the fixed electrode 31 and the dielectric The film 32 is supplied, and the dielectric
film 32 is electretized.
Here, in order to set the dielectric film 32 to a desired potential, voltage supply is performed
through a conduction pin provided on the vibrating film 33.
[0064]
The capacitor microphone 43 is formed on a silicon substrate 34 obtained by dicing the silicon
wafer 1 and includes a vibrating film 33 functioning as one pole of a capacitor, and a dielectric
film 32 as a film to be electretized. , And a fixed electrode 31 functioning as the other electrode
of the capacitor.
The fixed electrode 31 is provided with a plurality of sound holes (openings for guiding sound
waves to the vibrating film 33) 35.
Reference numeral 36 denotes an air gap.
[0065]
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Then, the condenser microphone 43 that has been electretized is mounted on the mounting
substrate 42.
The vibrating film 33 as one of the capacitors and the fixed electrode 31 as the other of the
capacitor are electrically connected to the wiring patterns 60a and 60b on the mounting
substrate via the bonding wires 44a and 44b, respectively. Each of the wiring patterns 60a and
60b is electrically connected to the ground pattern 46 and the microphone signal output pattern
47 provided on the back surface of the mounting substrate 42 through the wirings L1 and L2
inside the mounting substrate, respectively. .
[0066]
The vibrating film 33, the fixed electrode 31, and the dielectric film 32 constituting the
microphone are manufactured by using silicon fine processing technology and CMOS
(complementary field effect transistor) manufacturing process technology.
[0067]
That is, a silicon substrate 34 is prepared, and a high concentration impurity region doped with
boron or phosphorus to be a high concentration to be the vibrating film 33 and a silicon oxide
film (dielectric film as the dielectric film 32) are also provided. A tetrafluoroethylene resin or the
like can also be used, and a silicon layer is formed thereon using a selective epitaxial technique
or the like.
Impurities such as phosphorus and boron are implanted and diffused at a high concentration in a
region 36 to be a sacrificial layer (portion to be removed by etching) of the silicon layer, and a
silicon layer 31 to be a fixed electrode is formed on the silicon layer. And patterning to form an
opening (sound hole) 35. Then, the etching solution is made to penetrate through the opening
35, and the portion of the sacrificial layer 36 is removed by utilizing the difference in etching
rate between the silicon layer in which the impurity is introduced at a high concentration and the
non-doped layer. As a result, the portion of the sacrificial layer becomes the air gap 36, and at
the same time, the spacer portion 37 is formed. Further, the back surface of the silicon substrate
34 is etched with an alkaline etching solution such as KOH to form a deep groove 38. Thus, a
condenser microphone 43 as shown in FIG. 1 (b) is obtained.
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[0068]
As described above, the condenser microphone can not take out only the dielectric film to
electretize it like the conventional ECM. Therefore, in the present invention, prior to dicing a
silicon wafer in which a microphone is formed, corona discharge is used to electretize the
dielectric film 32 in a wafer state.
[0069]
However, in the condenser microphone 43 of FIG. 1, the inorganic dielectric 32 is located
between the fixed electrode 31 and the vibrating film (electrode) 33 on the silicon substrate 34,
and ions generated by corona discharge are generated in the fixed electrode 31. The dielectric
film 32 is reached via the provided opening (sound hole) 35. Further, the dielectric film 32 is
connected to a desired potential via a conducting pin (not shown) connected to the vibrating film
electrode 33. Thus, by adjusting the potential of the dielectric film 32, it is possible to control the
amount of charge injected in the electretization process. Originally, the capacitor microphone
using this MEMS technology has a structure in which ions by corona discharge do not easily
reach the dielectric film 32, and it is necessary to devise the electretization of the dielectric film
32, but this method The desired electret film can be easily obtained by using
[0070]
Further, when manufacturing the capacitor microphone 43, a silicon oxide film is laminated to
form a sacrificial film electrode 33, a dielectric film 32, a fixed electrode 31, and a sacrificial
layer for becoming an air gap 36, and the end of the diffusion process. After that, this portion
becomes an air gap 36 by etching the sacrificial layer. In this manufacturing process, the
variation in the film thickness of the silicon layer at the time of mass production (this film
thickness determines the value of the air gap 36) occurs about 10%. Therefore, the distance
between the vibrating membrane electrode 33 and the fixed electrode 31 also varies by about
10%. In ECM, the sensitivity of the microphone is inversely proportional to the distance between
the electrodes. Therefore, if the inter-electrode distance varies, the sensitivity of the microphone
will vary.
[0071]
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In the present invention, taking this point into consideration, the dielectric film 32 is electretized
without difficulty, and furthermore, variations in the sensitivity of the microphone due to
variations in device manufacture or variations in the characteristics of electronic components are
It can absorb by adjusting. In particular, variations in sensitivity of the microphone due to
variations in manufacturing (such as variations in film thickness) can be absorbed by adjusting
the electret amount of the additional electretization process, and are further caused by FET
capacitance, parasitic capacitance, etc. Variations in sensitivity can also be absorbed by adjusting
the electret amount of the additional electretization process. Therefore, it is possible to take
measures against variations in microphone sensitivity caused by variations in manufacturing and
characteristics of parts.
[0072]
As a method of adjustment, there is a method of adjusting the amount of electrification of the
dielectric film by the applied voltage at the time of corona discharge.
[0073]
In addition, the electretization amount is adjusted by adjusting the distance between the needle
electrode and the dielectric film.
[0074]
Alternatively, the electretization amount may be adjusted by adjusting the duration of the corona
discharge.
[0075]
Further, the electretization amount may be adjusted by the ratio of the negative ion and the
positive ion generated by the corona discharge.
[0076]
FIG. 2 is a cross-sectional view showing a mounting structure (a structure after case sealing) of
an electret microphone using a silicon substrate.
In FIG. 2, parts common to FIG. 1 are assigned the same reference numerals.
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Further, in FIG. 2, the condenser microphone 43 is drawn in a simplified manner (the actual
structure is as shown in FIG. 1 (b)).
[0077]
As shown in FIG. 2, a capacitor microphone 43 and other elements (FET, resistance element, etc.)
45 are mounted on a plastic or ceramic mounting substrate 42.
[0078]
A ground pattern 46 and a microphone signal output pattern 47 are disposed on the back
surface of the mounting substrate 42.
As shown in FIG. 1, the fixed electrode 31 and the diaphragm electrode 33 of the condenser
microphone (semiconductor device) 43 are connected to the wiring patterns 60a and 60b on the
mounting substrate 42 through the wires 44a and 44b.
In FIG. 2, only the wire 44a and the wiring pattern 60a are shown.
[0079]
In the present embodiment, after the electretization process is completed, dicing is performed,
the chip is divided into individual chips, and the shield case 41 is mounted on the mounting
substrate 42 after being mounted on the mounting substrate 42.
The shield case 41 is provided with a wide opening 49 for guiding a sound wave.
[0080]
Hereinafter, the electretization method of the present invention (as well as the electretization
device of the present invention) will be specifically described with reference to FIGS. 3 to 6.
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[0081]
FIG. 3 is a view showing the main configuration of the electretization apparatus of the present
invention.
[0082]
The electretization apparatus shown in FIG. 3 performs so-called sheet-fed processing in which
electretization is performed by irradiating ions by corona discharge of one needle electrode to a
large number of condenser microphones formed on a silicon wafer 1 It is an apparatus.
Here, instead of batch processing multiple devices provided on a silicon wafer at a time, each
device is processed individually, but multiple devices are processed at one time May be
[0083]
As shown in FIG. 3, at the time of electretization, a desired voltage is applied to the fixed
electrode 31 from the adjustment voltage supply 55 via the power supply terminal 54, and
corona discharge using the needle electrode 51 is used. Do.
The needle electrode 51 is positioned above the condenser microphone (semiconductor device)
43. The needle electrode 51 is connected to a high voltage source 53 for generating a corona
discharge.
[0084]
In this state, the dielectric film 32 (see FIG. 1) inside the condenser microphone 43 is irradiated
with ions of corona discharge by the needle electrode 51. Thereby, the dielectric film 32 (see FIG.
1) of the condenser microphone 43 can be electretized without difficulty.
[0085]
That is, according to the corona discharge of the needle-like electrode 51, more ions can be
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concentrated and irradiated to the dielectric film 32 of the condenser microphone 43 than in the
case of the corona discharge by the wire electrode shown in FIG.
[0086]
Therefore, as shown in FIG. 1, due to the structure of the microphone, even when the dielectric
film 32 is irradiated with ions through the opening 35 of the fixed electrode 31, an appropriate
amount of ions can be supplied. Therefore, electretization of the dielectric film 32 is possible.
Further, since the electretization of the dielectric film 32 of one condenser microphone 43 is
performed by one needle electrode 51, it is easy to set conditions, and therefore, it is
advantageous in improving the accuracy of electretization.
[0087]
In addition, since the dielectric film 32 is fixed to the ground potential and ion irradiation is
performed under a predetermined condition from one needle electrode 51, a large amount of
ions can be focused on the dielectric film 32. . Therefore, even if the dielectric film 32 is not
suitable for ion bombardment due to the internal structure of the microphone, the dielectric film
32 can be electretized without difficulty.
[0088]
After the electretization process, a condenser microphone is mounted on the mounting substrate
42. A grounding pin (charging device pin) 52 is connected to the ground pattern 46 on the back
surface of the mounting substrate 42. As described above, the diaphragm electrode 33 (see FIG.
1) of the condenser microphone is the ground pattern 46 provided on the back surface of the
mounting substrate 42 via the wire 44a, the wiring pattern 60a on the substrate 42, and the
internal wiring L1. Electrically connected to At the time of electretization, one of the ground pin
(charging device pin) 52 and the voltage supply terminal 54 is connected to a region
corresponding to the fixed electrode on the silicon wafer through the pad. 55 is a voltage supply
for adjustment. This voltage is determined according to the variation of the film thickness of the
dielectric film 32 or the like. It is also possible to stably electretize the vibrating membrane
electrode 33 in a state in which it is connected to the ground pin 52 in accordance with the
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connection to the ground pin 52.
[0089]
Next, specific examples of the electretization method of the present invention will be described.
[0090]
FIG. 5 is a process flow diagram showing the main steps of the electretization method of the
present invention.
[0091]
As illustrated, the electretization method of FIG. 6 electretizes the dielectric film by a plurality of
corona discharges.
[0092]
That is, first, a condenser microphone is processed on the silicon wafer 1 using a semiconductor
process to form a condenser microphone (step S100).
That is, the condenser microphone 43 is formed.
That is, as shown in FIG. 4, a silicon wafer 1 in which a large number of condenser microphones
43 are formed is obtained.
[0093]
Next, the dielectric film 32 in the condenser microphone 43 on the silicon wafer 1 is electretized
by a fixed amount by corona discharge of the needle electrode 51 using the electretization
apparatus of FIG. 3 (step S101).
As a result, as shown in FIG. 5, the silicon wafer 1 on which the electret condenser microphone is
mounted can be obtained.
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[0094]
Next, the sensitivity of the condenser microphone 43 is measured (step S102).
[0095]
Returning to FIG. 5, next, based on the measurement result of the sensitivity of the condenser
microphone 43, the electretization amount required in the next electretization processing
(additional electretization processing) is determined (step S103).
[0096]
That is, usually, the desired microphone sensitivity can not be obtained by one electretization.
Therefore, the electretization amount required to obtain the desired sensitivity is determined
according to the current measurement sensitivity and the characteristic information indicating
the relationship between the electretization amount and the microphone sensitivity which are
obtained in advance.
[0097]
Once the electretization amount in the second electretization process is determined, next, the
condition setting in the electretization device (charging device) of FIG. 3 is performed in order to
perform electretization of the determined amount. (Step 104: Details of this process will be
described later).
[0098]
Then, additional electretization processing is performed (step S105) to form a desired condenser
microphone.
Next, the chip is divided into individual chips (dicing step S106). As shown in FIG. 2, the shield
case 41 is mounted (step S107), whereby the condenser microphone shown in FIG. 2 is
completed (step S108).
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[0099]
Next, step S104 (setting of conditions in the electretization apparatus) in FIG. 5 will be described.
[0100]
Four elements can be considered as elements of condition setting in the electretization apparatus
(FIG. 3).
Voltage, polarity of ions, distance, time.
By combining one or a plurality of them, accurate electretization of the target electret amount
can be performed on the dielectric film 32.
[0101]
As described above, the electretization amount can be adjusted by adjusting the corona discharge
voltage. Adjustment of the corona discharge voltage is realized by changing the voltage value of
the power supply voltage of the high voltage source 53 in the electretization apparatus of FIG.
[0102]
As the discharge voltage is increased, more ions are generated, which results in a higher amount
of charge (amount of electretization). At this time, if the voltage is lower than a predetermined
level, corona discharge does not occur. Further, when the voltage reaches a certain value or
more, the electret material is damaged by the discharge. Therefore, it is necessary to set an
appropriate discharge voltage between the upper limit value and the lower limit value.
[0103]
Further, as described above, the electretization amount can also be adjusted by adjusting the
ratio of positive ions to negative ions of discharge ions by changing the polarity of the power
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supply voltage of the high voltage source 53 with time.
[0104]
Further, as described above, the electretization amount can also be adjusted by changing the
distance a (see FIG. 3) between the dielectric film 32 and the needle-like electrode 51.
As the distance a is shorter, the amount of charge increases.
[0105]
Further, as described above, the electretization amount can also be adjusted by changing the
corona discharge time. As the discharge time is longer, the amount of charge increases.
[0106]
In this way, performing electretization processing in several times (for example, achieving
minimum electretization by initial electretization, and then changing the conditions to perform
additional electretization to achieve desired electretization By achieving this, the electretization
can be performed without difficulty, and the accuracy of the electretization processing can also
be enhanced.
[0107]
Also, after the first electretization, the microphone sensitivity can be adjusted to the specified
(standard) sensitivity by measuring the sensitivity of the microphone and determining the next
electretization amount from the measurement result.
[0108]
In particular, variations in sensitivity of the microphone due to variations in manufacturing (such
as variations in film thickness) can be absorbed by adjusting the electret amount of the additional
electretization process, and are further caused by FET capacitance, parasitic capacitance, etc.
Variations in sensitivity can also be absorbed by adjusting the electret amount of the additional
electretization process.
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[0109]
Therefore, according to the present invention, it is possible to take measures against variations in
microphone sensitivity caused by variations in manufacturing and characteristics of parts.
[0110]
The condenser microphone of the present invention manufactured through the steps including
the electret processing as described above is a microminiature condenser microphone formed by
micro-machining a silicon substrate and having a dielectric film as a component of the
condenser. .
Thus, the present invention provides an electret silicon capacitor microphone (ESCM) with very
excellent characteristics, which is very compact and has a sensitivity to practical use.
[0111]
As described above, according to the present invention, with regard to a condenser microphone
obtained by micromachining a silicon substrate, it becomes possible to electretize the dielectric
film to a prescribed amount while maintaining the wafer state prior to dicing.
[0112]
That is, conventionally, it has been considered difficult to adopt the electret system because the
condenser microphone can not take out only the dielectric film and electretize it, but according to
the present invention, the electret system is selected using a realistic method. It is possible to
manufacture a conventional condenser microphone.
[0113]
In addition, variations in the sensitivity of the microphone due to variations in film thickness and
the like (device fabrication variations) can be compensated by adjusting the electretization
amount.
[0114]
Furthermore, variations in microphone sensitivity caused by variations in electret amount,
parasitic capacitance, FET capacitance, etc. can be compensated by the present invention.
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[0115]
According to the present invention, electretization is performed in a completed state (mounted on
a mounting substrate) of a silicon capacitor microphone, and the electretization amount is
adjusted individually to adjust the sensitivity of the microphone. As a result, the number of
defective products outside the standard (specification) is reduced, and the yield of microphone
manufacture is dramatically improved.
[0116]
Therefore, mass production of an electret condenser microphone is possible.
[0117]
The following device is used to measure the sensitivity of the condenser microphone.
FIG. 6 is a diagram showing a configuration for measuring the sensitivity of a condenser
microphone, which is added to the electretization apparatus of FIG.
In this figure, although what measures the sensitivity of a condenser microphone chip is
explained, the same may be said of using a silicon wafer.
In FIG. 6, parts common to those in the above-mentioned drawings are denoted by the same
reference numerals.
In FIG. 6, reference numeral 71 denotes a speaker, reference numeral 72 denotes a speaker
amplifier, and reference numeral 73 denotes a sensitivity measuring device.
Reference numeral 76 denotes a shield case for measuring sensitivity.
The shield case 76 is used only at the time of sensitivity measurement (that is, it replaces the
shield case 41 of FIG. 2).
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The shield case 76 is provided with an opening 77 for allowing sound waves to pass
therethrough.
In the apparatus of FIG. 6, when measuring the sensitivity at the wafer level, a sound of constant
pressure is emitted from the speaker 71 to the condenser microphone 43 on the silicon wafer
SW.
At this time, the measurement pins 74 and 75 are connected to the ground pattern and the
microphone signal output pattern connected to the common connection line 81 on the silicon
wafer SW shown in FIG. 4 through the pad 80. The measuring pin is connected to a device 73 for
measuring the output signal of the microphone. The sound emitted from the speaker 71 reaches
the vibrating film 33 of each condenser microphone 43 on the silicon wafer SW, whereby the
vibrating film 33 vibrates. In response to this, the capacitance of the capacitor changes, and the
change in the capacitance is taken out as an electrical signal, and the electrical signal is sent to
the sensitivity measuring device 73 through the measuring pins 74 and 75. As a result, the
sensitivity of the condenser microphone 43 subjected to the constant amount of electretization
processing is collectively measured. However, since this information is output in a state where
the outputs from all the condenser microphones are synthesized, this information can not be
used for adjustment as sensitivity information. In addition, when measuring about each one of
the capacitor microphones 43, the silicon wafer having the capacitor microphones 43 built
therein is mounted on the mounting substrate at wafer level and divided into individual capacitor
microphones 43 after the measurement. Just do it.
[0118]
Second Embodiment In the above embodiment, although the electretization is performed
individually on the wafer, when the condenser microphone is formed on the silicon wafer 1, as
shown in FIG. A common connection line 81 is formed in a region corresponding to the dicing
line DL so as to be connected to the film electrode pad 80a and the fixed electrode pad 80b), and
a desired voltage is applied to the common connection line. And electret processing. Finally,
dicing is performed along the dicing lines DL to divide into individual chips. At this time, the
common connection line 81 is cut off. Although not described, this method also forms a
condenser microphone as shown in FIGS. 1 and 2. Since batch processing enables electretization,
TAT (Turn Around time) can be further shortened. When power is supplied to the diaphragm
electrode pad 80a and the fixed electrode pad 80b, as shown in FIG. 8A, regarding the
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arrangement of the common connection line 81, the respective wirings are sandwiched between
the insulating layers. It can be formed in a multilayer structure. Moreover, by showing in FIG.8
(b), arrange | positioning by single layer structure is also possible.
[0119]
The present invention achieves an effect of realizing electretization of a dielectric film with high
accuracy without difficulty in a capacitor microphone (silicon microphone) using a
semiconductor chip formed by finely processing a silicon substrate, and mobile communication It
is useful as an ultra-compact condenser microphone mounted on a machine, an electretization
method thereof, and an electretization device used for the manufacture thereof.
[0120]
Cross-sectional view of a structure of a capacitor microphone manufactured by micro-machining
a silicon substrate, and a cross-sectional view of a device for describing the mounting aspect
thereof Figure showing the configuration of the main part of the electretization apparatus of the
invention Figure showing the silicon wafer on which the condenser microphone of the present
invention is formed Step flow diagram showing the main steps of the electretization method of
the present invention The figure which shows the structure for measuring The figure which
shows the silicon wafer which formed the capacitor | condenser microphone of Embodiment 2 of
this invention The figure which shows the example of the wiring layout in the electretization
method of Embodiment 2 of this invention An apparatus for generating a corona discharge to
electretize a dielectric film Fragmentary cross-sectional view of an apparatus for electretizing a
dielectric film by causing corona discharge using a part cross-sectional view the wire electrode
Explanation of sign
[0121]
DESCRIPTION OF SYMBOLS 1 silicon wafer 31 fixed electrode 32 dielectric film (dielectric film)
33 vibrating film electrode (vibration film) 34 silicon substrate (silicon diaphragm) 35 sound hole
(opening) provided in fixed electrode 36 formed by etching of sacrificial layer 41 Air gap 41
Shield case 42 Mounting board made of plastic or ceramic 43 Semiconductor chip (capacitor
microphone chip) using silicon substrate 44 (44a, 44b) Bonding wire 45 (45a, 45b) Electronic
parts (FET, resistor, amplifier etc.) 46 Grounding pattern 47 Microphone signal output pattern 49
Sound hole of microphone package (opening) 51 Needle electrode 52 Grounding pin (charging
device pin) 53 High voltage power supply 54 Power supply terminal 55 Adjustment voltage
supply power 71 Speaker 72 Speaker amplifier 73 Sensitivity measuring device 74 Pin for
sensitivity measuring device (for ground pattern) 75 Pin for sensitivity measuring device (for
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microphone signal pattern) 76 Shield case for sensitivity measuring device (for grounding
pattern) L1, L2 Wiring in mounting board 80 Pad 81 Common connection line DL dicing line
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