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JPH09257618

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH09257618
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
capacitive pressure sensor in which a diaphragm is formed on the surface of a substrate using
silicon micromachining technology combining semiconductor processing technology and special
etching technology, and a method of manufacturing the same. It is.
[0002]
2. Description of the Related Art Conventionally, various pressure sensors are known, among
which there is a capacitive pressure sensor in which a diaphragm is formed on the surface of a
semiconductor substrate. FIG. 9 shows the cross-sectional structure of such a conventional
capacitive pressure sensor.
[0003]
This capacitance type pressure sensor pastes a silicon structure 10 provided with a diaphragm
11 functioning as a movable electrode and a glass substrate 20 provided with a fixed electrode
21 formed so as to face the diaphragm 11 by anodic bonding. It has a combined structure. When
the pressure P is applied from the direction indicated by the arrow in the figure, the diaphragm
11 is deformed accordingly, the gap between the diaphragm 11 and the fixed electrode 21 is
changed, and the diaphragm 11 is formed by the fixed electrode 21. The capacitance of the
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capacitor changes. Therefore, the pressure P is detected by detecting this capacitance.
[0004]
Here, a (100) plane single crystal silicon substrate is used as the silicon structure 10, and the
diaphragm 11 is formed by anisotropically etching a part of the silicon structure 10. Generally, a
potassium hydroxide aqueous solution, a tetramethyl ammonium hydroxide aqueous solution or
the like is used as the etching solution. Further, the diaphragm 11 is treated so as to contain a
high concentration of p-type or n-type impurities in order to function as one movable electrode
of the capacitor, so as to obtain high conductivity characteristics.
[0005]
In addition, Pyrex glass is generally used for the glass substrate 20, and etching processing of a
desired depth is performed on the bonding surface side with the silicon structure 10 so as to
cover the diaphragm 11. Generally, a hydrofluoric acid based solution is used for this etching
solution. In addition, a metal film is deposited on the etched surface 22 so as to face the
diaphragm 11, and this is photo-etched to form one fixed electrode 21 of the capacitor. As the
metal film of the fixed electrode 21, for example, a laminated film in which aluminum is formed
on titanium and a film is used is used.
[0006]
Then, the bonding surfaces of the silicon structure 10 and the glass substrate 20 formed as
described above are superposed and aligned, and heated to, for example, 300 ° C., with the
silicon structure 10 as an anode and the glass substrate 20 as a cathode. By applying a DC
voltage of 600 V, the silicon structure 10 and the glass substrate 20 are airtightly bonded
(anodically bonded) without using an adhesive or the like.
[0007]
When this pressure sensor is used as an absolute pressure measurement type, bonding is
performed while maintaining the surrounding atmosphere in a vacuum state at the time of
anodic bonding of the silicon substrate 10 and the glass substrate 20.
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As a result, the space obtained by etching the surface side of the silicon substrate 10 becomes a
pressure reference chamber of vacuum, and the diaphragm is bent in proportion to the applied
absolute pressure, and the capacitance value is changed due to this bending. Therefore, the
change in capacitance can be taken out as a pressure detection signal for vacuum, and the
absolute pressure applied to the diaphragm 11 can be measured.
[0008]
In such a capacitive sensor, the sensitivity can be increased by narrowing the gap between a pair
of electrodes (counter electrodes) forming a capacitor. In addition, in principle, the sensitivity is
not dependent on temperature, etc.
[0009]
However, in such a conventional capacitance type pressure sensor, the thermal expansion
coefficient of the glass substrate 20 made of pyrex glass is slightly smaller than that of the silicon
structure 10 made of single crystal silicon. Therefore, when the ambient temperature changes,
the thermal stress changes due to the difference in the thermal expansion coefficient, and there
is a problem that the temperature characteristics of the zero point and sensitivity of the sensor
are deteriorated. In addition, the glass substrate 20 is deformed by heating at the time of anodic
bonding, and the fixed electrode 21 formed on the glass substrate 20 may be in contact with the
diaphragm 11 depending on the gap of the counter electrode. In such a case, it does not function
as a sensor There was a problem that.
[0010]
The present invention has been made in view of such conventional problems, and the purpose
thereof is a capacitive pressure sensor having a zero point, a small temperature dependency of
sensitivity, and requiring no anodic bonding for assembling the sensor, and a method of
manufacturing the same. To provide.
[0011]
According to the present invention, a pressure reference chamber is provided on a fixed
electrode formed on the main surface of a substrate, and an insulation coated on the main
surface of the substrate so as to cover the pressure reference chamber. Capacitive pressure
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sensor in which a movable electrode made of a conductive film is formed in a pressure receiving
area of a conductive diaphragm film, the insulating diaphragm film is made of an insulating
material containing at least silicon, aluminum, and nitrogen I assume.
[0012]
The insulating diaphragm film contains 10 to 40 atm% of silicon, 10 to 40 atm% of aluminum,
and 30 to 50 atm% of nitrogen, and the content of oxygen is 25 atm% or less.
[0013]
Thus, in the present invention, the insulating diaphragm film is made of an insulating material
containing silicon, aluminum, and nitrogen.
The thermal expansion coefficient of the insulating diaphragm film can be adjusted by adjusting
the composition of the insulating diaphragm film (for example, adjusting the composition ratio as
described above).
Therefore, by setting the composition of the insulating diaphragm in accordance with the thermal
expansion coefficient of the substrate, the thermal expansion coefficients of the two can be made
equal.
Therefore, it is possible to solve the problem that the thermal stress changes due to the
difference in the thermal expansion coefficient, and the temperature characteristics of the sensor
zero point and sensitivity deteriorate.
[0014]
Further, according to the present invention, there is provided a substrate having a fixed electrode
formed on the main surface, and a first surface formed on the main surface of the substrate and
separated from the main surface by a predetermined distance in a pressure receiving area. A
movable electrode formed of an insulating diaphragm film, a conductive film formed in a
pressure receiving area of the first insulating diaphragm film, and a second covering formed on
the main surface of the substrate to cover the movable electrode An insulating diaphragm film, at
least one opening formed to penetrate the second insulating diaphragm film and the first
insulating diaphragm film to reach the pressure reference chamber; and the at least one opening
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Sealing the opening to seal the pressure reference chamber.
[0015]
Furthermore, the present invention provides a step of forming a fixed electrode on the main
surface of the substrate, a step of forming a sacrificial film covering the pressure receiving area
of the main surface of the substrate, and covering the main surface of the substrate so as to cover
the sacrificial film. Forming a first insulating diaphragm film, forming a movable electrode made
of a conductive film in the first pressure receiving area, and forming a second insulating
diaphragm film to cover the movable electrode Forming at least one etching solution inlet to
penetrate the second insulating diaphragm film and the first insulating diaphragm film to reach
the sacrificial film; Forming a pressure reference chamber by etching away the sacrificial film
through a liquid inlet; and sealing the etching inlet so as to maintain the pressure reference
chamber at a desired pressure. And wherein the Mukoto.
[0016]
According to the capacitive pressure sensor thus obtained, when pressure is applied to the
sensor, the pressure causes the insulating diaphragm film to be deformed, and the distance
between the movable electrode and the fixed electrode changes.
Then, in accordance with this change in distance, the capacitance of the capacitor including the
movable electrode and the fixed electrode changes.
Therefore, the pressure can be detected by detecting this change in capacitance. The pressure in
the pressure reference chamber is the pressure of the atmosphere at the time of sealing of the
etching inlet. Therefore, if the etching inlet is sealed in a vacuum atmosphere, the reference
pressure is in a vacuum state, and an absolute pressure can be detected by this sensor.
[0017]
Here, according to the capacitive pressure sensor of the present invention, the first insulating
diaphragm film is formed on the sacrificial film, and then the sacrificial film is removed by
etching. Therefore, no anodic bonding or the like is necessary to form the pressure reference
chamber. Therefore, as in the prior art, the glass substrate does not deform due to anodic
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bonding.
[0018]
As described above, in the present invention, by using a thin film material substantially equal to
the thermal expansion coefficient of the substrate for the diaphragm, the zero point and
sensitivity can be improved as compared with those made of materials having different thermal
expansion coefficients like conventional products. Temperature dependency is reduced.
[0019]
Further, bonding for forming a pressure reference chamber is unnecessary, there is no problem
such as deformation of the glass substrate at the time of anodic bonding as in the conventional
product, and sensor characteristics are stabilized.
[0020]
The reference electrode is formed in a pressure receiving area of the first insulating diaphragm
film so as to surround the movable electrode, and is formed in a part between the first insulating
diaphragm film and the substrate, and the reference is formed. And a diaphragm fixing portion
for restricting the movement of the electrode.
[0021]
Thus, by providing the reference electrode, in addition to the capacitance formed by the movable
electrode, the capacitance formed by the reference electrode can be configured.
Thus, the pressure can be detected according to the difference between the two volumes.
The two electrodes are in almost the same place, and by taking the difference between these
capacitances, it is possible to almost completely eliminate the influence of temperature and the
like.
[0022]
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Also, this capacitance difference can be easily detected by a switched capacitor circuit or the like.
Furthermore, since the switched capacitor circuit can be easily formed by the ordinary
semiconductor processing process, it is also easy to form on the same substrate. Therefore, the
circuit portion can also be integrated on the same substrate.
[0023]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the
present invention (hereinafter referred to as "embodiments") will be described below based on
the drawings.
[0024]
(Basic Configuration) FIG. 1 is a plan view showing a structure of a basic configuration example
of a capacitive pressure sensor according to the present invention, and FIG. 2 is a cross-sectional
view taken along the line A-B-C of FIG. A cross-sectional illustration along the line is shown.
3 and 4 show enlarged views of the movable electrode connection hole and the fixed electrode
connection hole.
[0025]
The substrate 30 of the capacitive pressure sensor according to the present invention is made of,
for example, single crystal silicon, and the fixed electrode 40, fixed electrode lead processed on
this surface to contain p-type or n-type impurities at a high concentration 41 and a fixed
electrode connection terminal 42 are formed. In addition, a substrate protective film 50 having
etching resistance characteristics is formed over the entire surface of the substrate 30 as
necessary.
[0026]
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A sacrificial film 60 having isotropic etching characteristics is formed on the surface of the
substrate protective film 50 so as to cover the pressure receiving area. The sacrificial film 60 is
removed in the manufacturing process and is not present in the product. In addition, a first
insulating diaphragm film 70 is formed on the main surface of the substrate 30 so as to cover the
sacrificial film 60 over the entire area.
[0027]
Furthermore, the movable electrode 81 disposed in the pressure receiving area of the first
insulating diaphragm film 70, and the movable electrode lead 82 and the movable electrode
connection terminal 83 disposed outside the pressure receiving area are formed from the
semiconductor film 80. . For example, when a polycrystalline silicon film is used as the
semiconductor film 80, the semiconductor film 80 made of a polycrystalline silicon film is
processed to contain a p-type or n-type impurity at a high concentration to obtain high
conductivity characteristics. Do.
[0028]
Here, the feature of the present invention is that the insulating diaphragm film 70 is made of a
material containing at least silicon, aluminum, and nitrogen, and has a thermal expansion
coefficient (3.68 × 10 −6 / ° C.) of the substrate 30. It is to be equal. For example, when single
crystal silicon of (100) orientation is used for the substrate 30, the composition of the insulating
diaphragm film 70 is 33 atm% silicon, 17 atm% aluminum, and 50 atm% nitrogen. As a result, the
thermal expansion coefficient of the insulating diaphragm film 70 becomes substantially equal to
that of the substrate 100 made of (100) oriented single crystal silicon, and no thermal stress is
generated due to a change in ambient temperature of the sensor as in the prior art. Therefore, it
is possible to provide a capacitive pressure sensor having a zero temperature and a small
temperature dependency of sensitivity. The insulating diaphragm film 70 has a thermal
expansion of 3.5 × 10 −6 / ° C. to 4.1 × 10 −6 / ° C. by controlling the composition in the
film (changing the component ratio). One with a coefficient is obtained.
[0029]
Further, the semiconductor film 80 is preferably protected by an insulating film. Therefore, the
second insulating diaphragm film 90 is formed to cover the semiconductor film 80. A movable
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electrode connection hole 110 which penetrates the second insulating diaphragm film 90 and
reaches the movable electrode connection terminal 83 is formed, and the movable electrode 81
is connected to the movable electrode output terminal 120 through the movable electrode
connection hole 110. It is done. An enlarged view of this portion is shown in FIG.
[0030]
Furthermore, as shown in FIG. 1, the first insulating diaphragm film 70 and the second insulating
diaphragm film 90 are penetrated at a position opposite to the movable electrode connection
port 110 to reach the fixed electrode connection terminal 42. The fixed electrode connection
hole 130 is formed. The fixed electrode 40 is connected to the fixed electrode output terminal
140 via the fixed electrode connection hole 130. The fixed electrode 40 extends between the
fixed electrode connection terminals 42 via the fixed electrode lead 41. An enlarged view of this
portion is shown in FIG.
[0031]
Then, at least one etching solution which penetrates the first insulating diaphragm film 70 and
the second insulating diaphragm film 90 and reaches the sacrificial film 60 at a predetermined
position of the pressure receiving area of the capacitive pressure sensor. The inlet 100 is formed
open, and the sacrificial film 60 that was originally formed is completely etched away through
the etching solution inlet 100.
[0032]
That is, by removing all of the sacrificial film 60, the pressure reference chamber 200
surrounded by the substrate 30 and the first insulating diaphragm film 70 is formed, and at the
same time, the pressure reference chamber 200 separated from the substrate 30 is formed. A
movable diaphragm 400 composed of the first insulating diaphragm film 70, the semiconductor
film 80, and the second insulating diaphragm film 90 located on the upper surface side is
formed.
[0033]
When this capacitance type pressure sensor is used as an absolute pressure measurement type,
all of the etching solution inlet 100 is sealed with a sealing cap 300 in a vacuum atmosphere.
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As a result, the pressure reference chamber 200 is in a vacuum state, and the movable
diaphragm 400 bends in proportion to the applied absolute pressure, and the deflection changes
the capacitance value between the fixed electrode 40 and the movable electrode 81.
Therefore, the absolute pressure applied to the movable diaphragm 400 can be measured by
extracting the change in capacitance as a pressure detection signal.
[0034]
(Manufacturing Method) Next, an example of a method for manufacturing a capacitive pressure
sensor according to the present invention will be specifically described.
[0035]
First, the fixed electrode 40, the fixed electrode lead 41 and the fixed electrode connection
terminal 42, which contain p-type or n-type impurities at high concentration, are formed on the
surface of the substrate 30 made of single crystal silicon by ion implantation or thermal
diffusion.
Next, a substrate protective film 50 having etching resistance is coated on the entire surface of
the substrate 30, and a sacrificial film 60 having isotropic etching is coated on the surface of the
substrate protective film 50. Next, the peripheral portion of the pressure receiving area of the
sacrificial film 60 is etched away.
[0036]
Next, a first insulating diaphragm film 70 is formed to cover the sacrificial film 60 over the entire
main surface of the substrate 30. For example, when single crystal silicon of (100) orientation is
used for the substrate 30, the composition of the insulating diaphragm film 70 is 33 atm%
silicon, 17 atm% aluminum, and 50 atm% nitrogen. As a result, the thermal expansion coefficient
of the insulating diaphragm film 70 becomes substantially equal to that of the substrate 30 made
of (100) oriented single crystal silicon.
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[0037]
Next, a semiconductor film 80 is formed on the surface of the first insulating diaphragm film 70.
For example, when a polycrystalline silicon film is used as the semiconductor film 80, a p-type or
n-type impurity is contained at a high concentration by ion implantation or thermal diffusion, and
processing is performed to obtain high conductivity characteristics.
[0038]
Next, the movable electrode 81 formed in the pressure receiving area, the movable electrode lead
82 formed outside the pressure receiving area, and the semiconductor film 80 around the
movable electrode connection terminal 83 are etched away. Next, a second insulating diaphragm
film 90 is formed to cover the semiconductor film 80 over the entire main surface of the
substrate 30.
[0039]
Next, at least one etching solution injection port 100 is passed through the first insulating
diaphragm film 70 and the second insulating diaphragm film 90 to reach the sacrificial film 60 at
a predetermined position in the pressure receiving area. Form.
[0040]
Then, the etching solution is injected through the etching solution injection port 100 to etch and
remove all the sacrificial film 60, and the sacrificial film 60 is formed between the substrate 30
and the first insulating diaphragm film 70. A pressure reference chamber 200 of a size according
to the geometry is formed.
For example, when polycrystalline silicon is used for the sacrificial film 60, an etching solution
used for etching and removing the sacrificial film 60 uses ethylenediamine pyrocatechol (EPW)
solution. The first and second insulating diaphragm films 70 and 90 located on the upper surface
side of the pressure reference chamber 200 are not etched away because they have etching
resistance to the EPW solution. As a result, the laminated film of the first insulating diaphragm
film 70, the semiconductor film 80 and the second insulating diaphragm film 90 located on the
upper surface side of the pressure reference chamber 200 functions as the movable diaphragm
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400.
[0041]
Next, the movable electrode connection hole 110 which penetrates the second insulating
diaphragm film 90 to reach the movable electrode connection terminal 82, the second insulating
diaphragm film 90, the first insulating diaphragm film 70, and the substrate protective film A
fixed electrode connection hole 130 which passes through 50 and reaches the fixed electrode
connection terminal 42 is formed.
[0042]
Next, aluminum is coated over the entire surface of the substrate 30, and the aluminum in the
peripheral portions of the first wiring 150 and the second wiring 160 is etched away.
Thereby, the movable electrode 81 is connected to the movable electrode output terminal 120
through the movable electrode connection hole 110 and the first wiring 150, and the fixed
electrode 40 is fixed to the fixed electrode through the fixed electrode connection hole 130 and
the second wiring 160. It is connected to the output terminal 140.
[0043]
Next, in the case of using this capacitance type pressure sensor as an absolute pressure
measurement type, a seal made of an insulating material having such a thickness that the etching
solution inlet 100 can be hermetically sealed all over the surface of the substrate 30 in a vacuum
atmosphere. Coating material is applied. Finally, the unnecessary portion is removed by
photoetching to form the sealing cap 300, and at the same time, the movable electrode output
terminal 120 and the fixed electrode output terminal 140 are opened to obtain an absolute
pressure measurement type capacitive pressure sensor. Be
[0044]
First Embodiment Next, a capacitance type pressure sensor according to a first embodiment will
be described based on FIGS. 1 to 4 used in the description of the above-described basic
configuration example.
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[0045]
In the capacitive pressure sensor of the present embodiment, an n-type (100) -oriented single
crystal silicon substrate is used as the substrate 30.
[0046]
First, boron as an impurity is added to the main surface of the single crystal silicon substrate 30
by using an ion implantation method so as to be contained at a high concentration, diffused, and
fixed electrode 40 with a depth of 3 μm processed into a p-type semiconductor, fixed electrode
lead 41 and the fixed electrode connection terminal 42 are formed.
Next, a thermal oxide film is formed over the entire surface of the single crystal silicon substrate
30 to a thickness of 100 nm as a substrate protective film 50 having etching resistance.
[0047]
Then, a sacrificial film 60 is formed on the surface of the substrate protective film 50 so as to
cover the pressure receiving area.
The sacrificial film 60 is removed in a later step. In this embodiment, the sacrificial film 60 is
made of polycrystalline silicon having a thickness of 200 nm formed by low pressure CVD. Next,
on the main surface of the single crystal silicon substrate 30, a thin film material made of silicon,
aluminum, and nitrogen is formed to a film thickness of 650 nm as a first insulating diaphragm
film 70 so as to cover the sacrificial film 60 over the entire area. Form a coating.
[0048]
Polycrystalline silicon is deposited to a film thickness of 200 nm as a semiconductor film 80 on
the surface of the first insulating diaphragm film 70. Further, the movable electrode 81, the
movable electrode lead 82, and the movable electrode connection terminal 83 are formed on the
semiconductor film 80 by photoetching. In this embodiment, the polycrystalline silicon film used
as the semiconductor film 80 is treated as a p-type semiconductor in which boron is added and
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diffused so as to be contained at a high concentration using an ion implantation method.
[0049]
Furthermore, as the second insulating diaphragm film 90, a thin film material composed of
silicon, aluminum, and nitrogen is coated to a film thickness of 650 nm so as to cover the
semiconductor film 80 over the entire main surface of the single crystal silicon substrate 30. . In
the present embodiment, a thin film material having a composition of 33 atm% of silicon, 17
atm% of aluminum, and 50 atm% of nitrogen is used for the first insulating diaphragm film 70
and the second insulating diaphragm film 90.
[0050]
Then, the etching solution inlet 100 with a diameter of 5 μm which penetrates the first
insulating diaphragm film 70 and the second insulating diaphragm film 90 and reaches the
sacrificial film 60 is photoetched at a predetermined position of the pressure receiving area. Do.
By injecting the etching solution through the formed etching solution injection port 100, all of
the sacrificial film 60 initially formed is removed by etching, and a cavity serving as the pressure
reference chamber 200 is formed.
[0051]
In the present embodiment, an ethylenediamine pyrocatechol (EPW) solution is used as the
etching solution. At this time, the substrate protective film 50 located on the lower surface side
of the pressure reference chamber 200 and the first and second insulating diaphragm films 70
and 90 located on the upper surface side have etching resistance to the EPW solution. It is not
etched away. Therefore, the laminated film of the first insulating diaphragm film 70, the
semiconductor film 80 and the second insulating diaphragm film 90 located on the upper surface
side of the pressure reference chamber 200 functions as the movable diaphragm 400.
[0052]
Next, the movable electrode connection hole 110 which penetrates the second insulating
diaphragm film 90 to reach the movable electrode connection terminal 83, the second insulating
diaphragm film 90, the first insulating diaphragm film 70, and the substrate protective film The
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fixed electrode connection hole 130 which passes through 50 and reaches the fixed electrode
connection terminal 42 is formed by photoetching.
[0053]
Furthermore, on a predetermined portion of the second insulating diaphragm film 90 of the
single crystal silicon substrate 30, a first wiring 150 and a second wiring 160 are formed.
These wirings are formed by coating aluminum with a thickness of 1 μm over the entire surface
of the single crystal silicon substrate 30 by vacuum evaporation or sputtering, and removing
unnecessary portions of aluminum by photoetching. At this time, the movable electrode 81 is
connected to the movable electrode output terminal 120 through the movable electrode
connection hole 110 and the first wiring 150, and the fixed electrode 40 is fixed to the fixed
electrode through the fixed electrode connection hole 130 and the second wiring 160. It is
connected to the output terminal 140 (see FIGS. 3 and 4).
[0054]
Furthermore, a sealing member including a sealing cap is formed in a predetermined portion of
the single crystal silicon substrate 30 with the etching solution inlet 100. In the case of forming
the sealing member, first, the sealing material made of a silicon nitride film can be hermetically
sealed over the entire surface of the single crystal silicon substrate 30 by plasma CVD in a
substantially vacuum state. Deposit to a degree thickness. Then, unnecessary portions are
removed by photoetching to form the sealing cap 300, and at the same time, the movable
electrode output terminal 120 and the fixed electrode output terminal 140 are partially opened.
By doing this, the pressure reference chamber 200 is hermetically sealed with the inside thereof
kept in a vacuum state, and the absolute pressure applied to the movable diaphragm 400 can be
measured.
[0055]
In the present embodiment, the diameter and the film thickness of the movable diaphragm 400
are as small as 100 μm and 1.5 μm, respectively, and are precisely formed. This sensor has an
electrostatic capacity change of 1 × 10 -14 F (farad) or more, and a non-linearity of ± 2% F., for
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an absolute pressure of 100 kPa. S. It was experimentally confirmed that the temperature
coefficient of the zero point and sensitivity in the temperature range of -30 to 100 ° C was
excellent, that is, ± 0.02% / ° C or less.
[0056]
As described above, according to the capacitance type pressure sensor of the present
embodiment, it is understood that a capacitance type pressure sensor which is compact and has a
zero point and a small temperature dependency of sensitivity can be realized. . In this
embodiment, an n-type (100) -oriented single crystal silicon substrate is used as the substrate 30,
and 33 atm% of silicon, 17 atm% of aluminum, and 50 atm of nitrogen are used as the first and
second insulating diaphragm films 70 and 90. The combination using the thin film material of%
composition was used. However, thin film materials composed of silicon, aluminum, nitrogen and
oxygen can control the thermal expansion coefficient by changing their composition in the film.
[0057]
Table 1 shows the measurement results of the thermal expansion coefficients of thin film
materials having different compositions of silicon, aluminum, nitrogen and oxygen.
[0058]
Here, sample no. The composition of the thin film material of 1 to 8 was quantified by X-ray
photoelectron spectroscopy.
In addition, the thermal expansion coefficient of sample No. 1 on a single crystal silicon
substrate. The thin film materials of 1 to 8 were formed, and were obtained based on the amount
of warpage of the single crystal silicon substrate due to temperature change.
[0059]
As shown in Table 1, the thermal expansion coefficient of the thin film material composed of
silicon, aluminum, nitrogen and oxygen is in the range of 3.5 × 10 −6 / ° C. to 4.1 × 10 −6 /
° C. It turns out that it can control. From this, if it is a substrate having a thermal expansion
04-05-2019
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coefficient in the range of 3.5 × 10 −6 / ° C. to 4.1 × 10 −6 / ° C., the first and second
insulating diaphragm films 70, It can be understood that by changing the composition of 90, it is
possible to realize a capacitive pressure sensor having a zero temperature and a small
temperature dependency of sensitivity.
[0060]
Second Embodiment Next, a second preferred embodiment of the present invention will be
described. The members corresponding to those of the first embodiment are denoted by the same
reference numerals, and the description thereof is omitted.
[0061]
FIG. 5 is a plan view showing a second preferred embodiment of a capacitive pressure sensor
according to the present invention, and FIG. 6 is a cross-sectional view taken along the line D-E of
FIG.
[0062]
First, the fixed electrode 40, the fixed electrode lead 41 and the fixed electrode connection
terminal 42 are formed on the main surface of the single crystal silicon substrate 30.
Further, a substrate protective film 50 made of a thermal oxide film with a thickness of 100 nm
is formed over the entire surface of the single crystal silicon substrate 30. Then, a sacrificial film
60 made of polycrystalline silicon having a thickness of 200 nm is formed to cover the pressure
receiving region on the substrate protective film 50, and then a region corresponding to the
diaphragm fixing portion 170 of the sacrificial film 60 is doped as an impurity. Boron is added
and diffused by thermal diffusion or ion implantation to form a p-type semiconductor region
having an impurity concentration of 1 × 10 20 / cm 3 or more. As a result, the region
corresponding to the diaphragm fixing portion 170 has etching resistance, and the sacrificial film
60 in the region where the impurity is not added or diffused has isotropic etching. The sacrificial
film 60 is removed later.
[0063]
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Next, as in the first embodiment, the first insulating diaphragm film 70 and the semiconductor
film 80 are formed. In this embodiment, the movable electrode 81, the movable electrode lead
82, the movable electrode connection terminal 83, the reference electrode 180, the reference
electrode lead 181, and the reference electrode connection terminal 182 are formed by
photoetching the semiconductor film 80. The movable electrode 81 is formed inside the
diaphragm fixing part 170 in the pressure receiving area, and the reference electrode 180 is
formed outside the diaphragm fixing part 170 in the pressure receiving area. The movable
electrode 81 and the reference electrode 180 are formed to have the same area.
[0064]
Next, a second insulating diaphragm film 90 is formed so as to cover the entire surface of the
main surface of the single crystal silicon substrate 30 so as to cover the semiconductor film 80,
and the etching solution inlet 100 is opened. By injecting ethylenediaminepyrocatechol (EPW)
etching solution through the etching solution injection port 100, the sacrificial film 60 in the
region which is not treated to have etching resistance is etched away, and the diaphragm fixing
portion 170 and the pressure reference are obtained. A cavity to be the chamber 200 is formed.
As a result, the outer area of the diaphragm fixing portion 170 in the pressure receiving area
becomes high in rigidity and becomes an area which is less likely to be bent with respect to the
pressure to be measured. The reference electrode 180 is formed in this area.
[0065]
Next, the movable electrode connection hole 110 which penetrates the second insulating
diaphragm film 90 to reach the movable electrode connection terminal 83, the reference
electrode connection hole 185 which reaches the reference electrode connection terminal 182,
and the second insulating diaphragm film 90, the fixed electrode connection hole 130 which
penetrates the first insulating diaphragm film 70 and the substrate protective film 50 and
reaches the fixed electrode connection terminal 42 is formed by photoetching. Next, aluminum
having a thickness of 1 μm is coated on the entire surface of the single crystal silicon substrate
30, and the first wiring 150, the second wiring 160, and the third wiring 190 are formed by
photoetching. Thereafter, as in the first embodiment, the sealing cap 300 is formed, and the
movable electrode output terminal 120, the fixed electrode output terminal 140, and a part of
the reference electrode output terminal 183 are opened.
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[0066]
Here, in the present embodiment, a movable diaphragm 400 having a diameter of 100 μm and a
film thickness of 1.5 μm is formed in the pressure receiving area having a diameter of 150 μm
by supporting the diaphragm fixing portion 170. The movable electrode 81 and the fixed
electrode 40 form a pressure detection capacitor Cx, and the reference electrode 180 and the
fixed electrode 40 form a reference capacitor Cr. Therefore, since the pressure detection
capacitor Cx and the reference capacitor Cr are made of the same material and formed close to
each other, the temperature characteristics are almost equal.
[0067]
One of the methods for detecting a change in capacitance is a charge / discharge type switched
capacitor circuit that converts capacitance into voltage. FIG. 7 shows a switched capacitor type
capacitance detection circuit.
[0068]
In this circuit, four switches SW1 to SW4 are provided, and the four switches SW1 to SW4 are
switched by a clock signal of a predetermined frequency or more. SW1 and SW2 alternately
connect one end of the pressure detection capacitor Cx and one end of the reference capacitor Cr
to the ground or the power supply Vp. That is, one of the capacitors Cx or Cr is connected to the
ground, and the other is connected to the power supply Vp.
[0069]
The other ends of the pressure detection capacitor Cx and the reference capacitor Cr are
connected to the negative input end of the operational amplifier. The positive input end is
connected to the ground. A feedback capacitor Cf and a switch SW3 are connected in parallel
between the output terminal and the negative input terminal of the operational amplifier. The
output of the operational amplifier is connected to the output end via the switch SW4. A
smoothing capacitor C0 whose other end is connected to the ground is connected to the output
terminal. In the illustrated example, when the switch SW1 is connected to the power supply Vp,
the SW2 is connected to the ground, the SW3 is on, the SW4 is off, and the switch SW2 is
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connected to the power supply Vp, the SW1 is grounded. , SW3 is off and SW4 is on.
[0070]
In the switched capacitor circuit, Cx, Cr, and Cf are substantially resistors by switching, and the
amplification factor of the operational amplifier is the capacitance on the input side (the
difference between the two capacitances Cx and Cr is alternately connected) And the capacity of
the feedback side. Therefore, assuming that the output voltage of this switched capacitor circuit
is E0, this E0 is expressed by E0 = Vp (Cx-Cr) / Cf, and the output voltage E0 is proportional to
the capacitance difference between the two capacitors Cx and Cr . Therefore, by detecting the
output voltage E0, the capacitance difference between the two capacitors Cx and Cr can be
detected, and the applied pressure can be detected.
[0071]
Therefore, as a result of evaluating the sensor characteristics by connecting the sensor of this
embodiment to this switched capacitor type capacitance detection circuit, the output
characteristic is 20 mV or more and the non-linearity is -2 with respect to the absolute pressure
of 100 kPa. % F. S. The temperature characteristics were as follows: in the temperature range of 30 to 100 ° C, it was experimentally confirmed that the temperature coefficient of the zero
point and the sensitivity was ± 0.01% / ° C or less, in the temperature range of -30 to 100 ° C.
[0072]
As described above, in the present embodiment, the reference electrode 180 is formed in the
pressure receiving area so as to surround the movable electrode 81, and the diaphragm fixing
portion 170 is provided at the boundary between the two. Thereby, the pressure detection
capacitor Cx is formed by the movable electrode 81, and the reference capacitor Cr is formed by
the reference electrode 180. Then, a pressure change can be detected by detecting the
capacitance difference between the two capacitors Cx and Cr. In particular, since two adjacent
capacitors have almost the same temperature, the influence of the temperature on the pressure
detection value can be almost completely eliminated. Further, by providing the diaphragm fixing
portion 170, deformation of the reference electrode 180 due to the pressure can be prevented,
and the capacitance difference between the two capacitors can be maintained sufficiently.
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[0073]
Third Embodiment FIG. 8 is a plan view of a capacitive pressure sensor according to a third
embodiment of the present invention.
[0074]
A characteristic matter of this embodiment is that the capacitive pressure sensor and the
integrated capacitance detection circuit are integrated.
[0075]
In the embodiment, the capacitive pressure sensor 500 described in the second embodiment is
formed at a predetermined position of the single crystal silicon substrate 30.
Furthermore, a circuit portion 600 is formed on the single crystal silicon substrate 30 using
semiconductor manufacturing technology.
The circuit unit 600 is configured of a switched capacitor type capacitance detection circuit that
converts the above-mentioned capacitance change into a voltage.
[0076]
The fixed electrode 40, the movable electrode 81 and the reference electrode 180 of the
capacitive pressure sensor 500 are connected to the circuit unit 600 via the fixed electrode
output terminal 140, the movable electrode output terminal 120 and the reference electrode
output terminal 183, respectively. .
[0077]
As described above, by integrating the circuit portion on the same substrate, it is possible to
manufacture a capacitive pressure sensor capable of obtaining an electrical output by one
semiconductor processing process, and integrated with an integrated circuit, so-called An
integrated sensor can be obtained.
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[0078]
As is apparent from the above description, the capacitive pressure sensor of the present
invention uses a thin film material approximately equal to the thermal expansion coefficient of
the substrate for the diaphragm, so the temperature dependence of the zero point and sensitivity
is Is small.
In addition, the movable diaphragm can be formed with high accuracy using the thin film
forming technology of the semiconductor process and the etching technology of the sacrificial
film, and the formation of the narrow gap of the counter electrode constituting the capacitor
becomes easy. Miniaturization is possible.
And since it can manufacture by processing of one side of a substrate altogether, it is very
suitable for manufacture of what is called an integrated sensor which integrated with an
integrated circuit.
[0079]
Brief description of the drawings
[0080]
FIG. 1 is a plan view showing a first embodiment of a capacitive pressure sensor according to the
present invention.
[0081]
2 is a cross-sectional view of the capacitive pressure sensor shown in FIG.
[0082]
3 is a cross-sectional view of a movable electrode portion of the capacitive pressure sensor
shown in FIG.
[0083]
5 is a cross-sectional view of a fixed electrode portion of the capacitive pressure sensor shown in
FIG.
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[0084]
FIG. 5 is a plan view showing a second embodiment of a capacitive pressure sensor according to
the present invention.
[0085]
6 is a cross-sectional view of the capacitive pressure sensor shown in FIG.
[0086]
FIG. 7 is a circuit diagram showing a configuration of a capacitance detection circuit.
[0087]
FIG. 8 is a plan view showing a third embodiment of a capacitive pressure sensor according to
the present invention.
[0088]
FIG. 9 is a cross-sectional view of a conventional capacitive pressure sensor.
[0089]
Explanation of sign
[0090]
30 substrates, 40 fixed electrodes, 60 sacrificial films, 70 insulating diaphragm films, 81
movable electrodes, 200 pressure reference chambers, 300 sealing caps, 400 movable
diaphragms.
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