JPH04304679A - Pressure sensor - Google Patents

Abstract

PURPOSE:To provide a small-sized and easy-to-mount resonation-type pressure sensor which is capable of being formed by a single silicon chip. CONSTITUTION:A silicon nitride film 8 (insulation film) or a silicon nitride film 8 (insulation film)/polycrystal film/silicon nitride film 8, which constitute a three-layer film are used as a cap layer 13 where a cavity region is formed in a vacuum state between this cap layer 13 so as to grow a vibrator in this cavity region and form an integrated silicon pressure sensor.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pressure sensors, and more particularly to resonance type pressure sensors.

0002

[Prior Art] In recent years, ultra-small semiconductor strain detection devices have been developed to detect pressure, etc. by detecting resistance changes due to piezoresistance effects and minute capacitance changes due to displacement of semiconductor regions formed on semiconductor substrates. The device is attracting attention.

Since such pressure sensors are formed using integrated circuit technology, the length of the vibrating portion is, for example, 10 mm.
It is possible to form an extremely small element with a thickness of about 0 μm, a thickness of about 1 μm, and a total chip size of about 1 mm square. Furthermore, it has the excellent feature that it can be formed on the same substrate as other elements by using an integrated circuit.

For example, as an example of such a pressure sensor, as shown in FIGS. 16 and 17, a vibrator 1 is formed integrally with torsion springs 2, 3, and 4.
, 5, and a sensor chip whose back surface is attached to a thin diaphragm 96 is mounted on glass pedestals 93 and 94, and its upper surface is connected to a silicon ring 99 via a spacer 98. The cavity area formed between the fixed glass plate 7 and the diaphragm 96 is maintained in a vacuum by external pressure applied through the opening 100. There is a device in which the diaphragm 96 is deformed to bias the torsion spring inward into the cavity, and the resonant frequency corresponding to the external pressure is extracted. Here, 6 is a drive electrode, which is embedded in the glass plate 7.

[0005] External pressure can be measured by extracting this resonant frequency as an output.

[0006]

[Problems to be Solved by the Invention] However, such pressure sensors have a complicated structure and must be sealed to a glass substrate and a pedestal during mounting, resulting in excessive mounting costs, and it is difficult to control the gap. The problem was that it was extremely difficult.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a compact resonant pressure sensor that can be formed using a single silicon chip, is easy to mount, and is easy to mount.

[0008]

[Means for Solving the Problem] Therefore, in the present invention, a silicon nitride film or a three-layer film of silicon nitride film/polycrystalline silicon film/silicon nitride film, etc. is used as a cap layer, and an airtight state is maintained between the cap layer and the cap layer. The present invention is characterized in that a cavity region is formed, and a vibrator is extended within this cavity region to constitute an integrated silicon pressure sensor.

That is, in the first pressure sensor of the present invention,
A vibrator having a two-layer structure of a semiconductor layer and an insulating film extending into a recess formed in a semiconductor substrate, and a cap made of an insulating film formed on the surface of the substrate to airtightly seal the recess. layer, the deflection of the semiconductor layer is excited by a bimetallic effect caused by heat generation due to the conduction of electricity to the semiconductor layer, and an output change due to a piezoresistance effect is applied via the cap layer in response to a change in external pressure. The pressure change within the cavity caused by the change in pressure is detected.

A second pressure sensor of the present invention includes a vibrator made of a first semiconductor layer extending into a recess formed in a semiconductor substrate, and a vibrator formed on the surface of the substrate so as to airtightly seal the recess. and a cap layer having a sandwich structure in which the front and back surfaces of the second semiconductor layer are covered with an insulating film, and the second semiconductor layer is formed by electrostatic interaction between the first and second semiconductor layers. The deflection of the semiconductor layer is excited, and the change in pressure inside the cavity applied through the cap layer as the external pressure changes is detected.

[0011]

[Operation] According to the above structure, the cantilever and the space surrounding it are formed on the surface of the silicon substrate using thin film technology, and the pressure sensor is integrally formed, so there is no need for a mounting process and it is extremely It becomes possible to easily obtain a highly accurate and reliable sensor.

0012

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1 In this example, a resonator having a two-layer structure of a polycrystalline silicon layer and a silicon oxide layer extending into a recess formed in a semiconductor substrate, and a resonator designed to hermetically seal the recess are used. and a cap layer made of an insulating film formed on the surface of the substrate,
Exciting the deflection of the polycrystalline silicon layer due to a bimetallic effect accompanying heat generation due to energization of the polycrystalline silicon layer,
The device is characterized in that external pressure is detected as an output change due to a piezoresistance effect by detecting a pressure change in the cavity applied through the cap layer in response to a change in external pressure. be.

That is, as shown in FIG. 1 as a cross-sectional view and as shown in FIG. A resonator 9 consisting of four beams 14, 15, 17, and 18 having a two-layer structure with a silicon oxide film 11 is formed inside a hermetically sealed cavity region, and the lower part of the resonator 9 is etched in a well shape. The upper part of the groove 12 is a cap layer 13 made of a silicon nitride film formed with the silicon nitride film 8 interposed therebetween. A contact is then made through a heavily doped polycrystalline silicon layer region 90, the use of a heavily doped structure to minimize the resistance of this region. Further, the vibrator 21 of the resonator 9 is configured to increase the deflection of the beam.

This polycrystalline silicon layer 10 also functions as a heater and a sensor, and when the temperature rises due to the passage of current, the beam 9 bends due to the bimetal effect. Then, the deflection of this beam is detected by measuring the change in resistance value due to the piezoresistive effect of this polycrystalline silicon. Further, the sensor output is maximum in the resonant frequency region. In addition, the cap layer 13 is deflected by external pressure, thereby changing the pressure within the cavity region, and this pressure change causes the resonant frequency of the resonator to be modulated.

Next, the shape processing process of this pressure sensor will be explained with reference to FIG.

First, as shown in FIG. 3A, an n+ buried layer 32 is formed on an n-type silicon substrate 16 whose surface is (100) oriented, an epitaxial growth layer 33 is formed, and a silicon oxide film 11 and a boron-doped layer are formed. After sequentially forming the polycrystalline silicon film 10, the polycrystalline silicon film 10 is patterned into a beam shape using a normal photolithography method, and impurities are diffused using this as a mask to form the buried layer 32.
A deep, high concentration n+ silicon layer 67 is formed so as to reach . At this time, high concentration region 9 for contact
0 (see Figure 2).

As shown in FIG. 3(b), after lightly oxidizing the surface of this polycrystalline silicon film 10 to form a silicon oxide layer 20, a silicon nitride film 8 is formed on top of this layer. PSG by patterning and CVD method
After depositing the film 19 and planarizing the surface, a silicon nitride film 13 as a cap layer is further deposited.

The beams 9 are then formed by a triple etching technique performed through etching holes (not shown). First, in the first etching step, using buffered hydrofluoric acid, P
The SG film 19 is selectively etched away to form a free space in the upper half. And in the second etching process,
HF:HNO3 :CH3 COO as etching solution
Using a mixed solution of H=1:3:8, the n+ region under and around the beam 9, that is, the n+ buried layer 32 and the n+
Selectively remove the silicon layer 67 (FIG. 3(c))
.

After this, as shown in FIG. 3(d), KO
In the third etching process using H, the n-type silicon substrate 1 is etched using the (111) plane as an etching stopper.
Etch 6. Here, since a (100) oriented silicon substrate is used, this etching process is performed with a (100) orientation.
The etching rate in the 11) direction is extremely slow and etching stops at this plane, forming a cavity surrounded by the (111) plane. After that, a hole for contacting the high concentration region 90 is made.

After performing etching in this manner, the internal pressure within the cavity is determined and the etched hole is sealed, thereby forming the pressure sensor shown in FIGS. 1 and 2.

[0022] Here, if only the n layer is formed without forming the n+ layer and only etching with KOH is performed, a problem will occur in the etching below the vibrator 21. On the other hand, only the n+ layer is formed without forming the n layer, and HF:HNO3
If an attempt is made to perform etching using a mixed solution of :CH3COOH=1:3:8, the oxide layer 11 at the bottom of the beam will be etched.

[0023] In this way, a pressure sensor can be formed very easily.

According to this structure, since the pressure sensor is integrally formed on the surface of the silicon substrate using thin film technology, there is no need for a mounting process, and a highly accurate and reliable sensor can be obtained extremely easily. becomes possible.

[0025] In this example, the beam is composed of four;
The number is not limited to 1 or 2. however,
With two or four, the interconnection of the beams themselves can be omitted.

[0026] Furthermore, the materials constituting the resonator 9 are as follows:
It is not limited to the polycrystalline silicon film 10 and the silicon oxide film 11, but any combination of a semiconductor material that generates heat when energized, such as single crystal silicon, and an insulating film, and whose thermal expansion coefficients are not equal, may be used. good.

Example 2 Next, a second embodiment of the present invention will be described.

In this example, a vibrator made of a first polycrystalline silicon layer extending into a recess formed in a semiconductor substrate, a resonator formed on the surface of the substrate so as to hermetically seal the recess, and a cap layer having a sandwich structure in which the front and back surfaces of a second polycrystalline silicon film are covered with an insulating film, and the second polycrystalline silicon film is The present invention is characterized in that the displacement of the polycrystalline silicon layer is excited, and pressure is detected as an output change due to a capacitance change between the first and second polycrystalline silicon layers.

That is, in this resonance type pressure sensor, as shown in FIGS. 4 and 5, the cap layer is made of a silicon nitride film/
Polycrystalline silicon film/silicon nitride film (23, 24, 25
), and the resonator 69 is composed of a polycrystalline silicon film 26 having a single layer structure.

This resonator 69 (beam) is composed of the polycrystalline silicon film 24 of the cap layer and the polycrystalline silicon layer 2 of the beam.
6, and its output resonates between the polycrystalline silicon film 26 of the beam and the polycrystalline silicon layer 2 of the cap layer.
It is read as a capacitance change with respect to 4. The vibrator 60 also includes four beams 63, 64, 65, 66.
Supported by

The shape processing process for this pressure sensor will be explained with reference to FIG.

First, as shown in FIG. 6(a), after forming an n+ diffusion layer 61 on an n-type silicon substrate 16, surface oxidation is performed, and a silicon oxide film 29 and a boron-doped polycrystalline silicon film 26 are sequentially formed. do.

Next, as shown in FIG. 6(b), the beams 20 are formed by patterning using ordinary photolithography, and the surface is further lightly oxidized to form a silicon oxide layer 56.
After forming a silicon nitride layer 27 on top of this and patterning it, a PSG film 2 is formed by CVD.
8 is deposited and planarized to fill the recessed portion with a PSG film 28.

Then, as shown in FIG. 6C, a silicon nitride film 23, a polycrystalline silicon film 24, and a silicon nitride film 25 as a cap layer are sequentially deposited.

Then, as shown in FIG. 6(d), a beam 69 is formed by a double etching technique performed through an etching hole (not shown). First, in a first etching step, the PSG film 28 is selectively etched away using buffered hydrofluoric acid to form a free space in the upper half. In the second etching step, HF is used as the etching solution.
:HNO3 :CH3 COOH=1:3:8 mixed solution is used to selectively remove the n+ region under the beam 69, that is, the n+ diffusion layer 61. Then, light oxidation is performed to form a silicon oxide film 68 around the resonator, the internal pressure in the cavity is determined, and the etching hole is sealed.
Then, the pressure sensor shown in FIG. 5 is formed.

[0036] With this structure, as in the first embodiment,
Thin film technology can be used to form resonant pressure sensors that are easy to implement and highly reliable.

Although excitation of polycrystalline silicon by electrostatic interaction is used here, the material constituting the resonator is not limited to polycrystalline silicon, and other conductive materials may be used. You may also do so.

Example 3 Next, a third embodiment of the present invention will be described.

In this example, a first polycrystalline silicon layer extending into a recess formed in a semiconductor substrate and a second polycrystalline silicon layer serving as a lower member laminated thereon with an insulating film interposed therebetween. and a cap layer having a sandwich structure formed on the surface of the substrate so as to airtightly seal the recess, and covering the front and back surfaces of a third polycrystalline silicon film with an insulating film, The vibrator is excited by electrostatic interaction between the first polycrystalline silicon layer as its upper member and the third polycrystalline silicon layer as a cap layer, and the vibration of the vibrator is excited in the lower member. Pressure is detected as an output change due to the piezoresistance effect of a certain second polycrystalline silicon layer.

That is, in this example, as shown in FIGS. 7 and 8, the resonator 31 includes a polycrystalline silicon layer 35 as an upper member and a polycrystalline silicon layer 35 as a lower member laminated thereon with a silicon oxide film 36 interposed therebetween. The cap layer 70 is composed of a crystalline silicon layer 30 and a silicon nitride layer 71.
, a polycrystalline silicon layer 72, and a silicon nitride layer 73.

The resonator 31 is excited by the electrostatic interaction between the polycrystalline silicon layer 35, which is the upper member, and the cap layer 70, and the vibration of this resonator is caused by the vibration of the polycrystalline silicon piezoelectric material, which is the lower member. It is configured to be detected by the resistance element 30. Further, this vibrator 41 is supported by four beams 42, 43, 44, and 45.

The shape processing process of this pressure sensor will be explained with reference to FIG.

First, as shown in FIG. 9(a), after forming an n+ diffusion layer 38 on an n-type silicon substrate 16, surface oxidation is performed, and a silicon oxide film 34 and a boron-doped polycrystalline silicon film 30 are sequentially formed. Then, the surface of this polycrystalline silicon film 30 is further oxidized to form a silicon oxide layer 36, and a polycrystalline silicon layer 35 is further formed on top of this.

Next, as shown in FIG. 9(b), a polycrystalline silicon layer 35 is formed by a normal photolithography method.
, the silicon oxide layer 36, the polycrystalline silicon layer 30, and the silicon oxide layer 34 are patterned to form beams 31, and the surface is further lightly oxidized to form a silicon oxide layer 91, and a silicon nitride layer 37 is formed on top of this. After patterning this, a PSG film 39 is deposited by the CVD method and planarized to fill the recess with the PSG film 39.

Then, as shown in FIG. 9C, a silicon nitride film 71, a polycrystalline silicon film 72, and a silicon nitride film 73 as a cap layer 70 are sequentially deposited.

Then, as shown in FIG. 9(d), beams 31 are formed by a double etching technique performed through etching holes (not shown). First, in a first etching step, the PSG film 39 is selectively etched away using buffered hydrofluoric acid to form a free space in the upper half. In the second etching step, HF is used as the etching solution.
:HNO3 :CH3 COOH=1:3:8 mixed solution is used to selectively remove the n+ region under the beam 31, that is, the n+ diffusion layer 38. Light oxidation is then performed to form a silicon oxide film 92 inside the cavity, the internal pressure within the cavity is determined, and the etched hole is sealed, thereby forming the pressure sensor shown in FIGS. 7 and 8.

[0047] With this structure, as in the first embodiment,
Thin film technology can be used to form resonant pressure sensors that are easy to implement and highly reliable.

Although excitation of polycrystalline silicon by electrostatic interaction is used here, the material constituting the resonator is not limited to polycrystalline silicon, and other conductive materials may be used. You may also do so.

Example 4 Next, a fourth embodiment of the present invention will be described.

In this example, a vibrator made of a single crystal silicon layer extends into a recess formed in a semiconductor substrate, and an insulating film formed on the surface of the substrate to airtightly seal the recess. The vibrator is thermally excited to vibrate, and the vibration is used to detect external pressure as an output change due to the piezoresistive effect of the single crystal silicon layer.

In other words, in this example, FIGS. 10 and 11
As shown in , the resonator 46 is composed of a beam made of a p-type single crystal silicon layer (p-type silicon layer) 47 and a silicon oxide layer 48, and as in the first embodiment, the resonator 46 has a bimetallic effect due to thermal excitation. It is characterized by its use. Further, the cap layer 88 is composed of the silicon nitride layer 58.

The space between the resonator and the upper cap layer 88 is determined by the thickness of the silicon nitride film 57. This p-type silicon layer 47 also serves as both a thermal exciton and a sensor for the resonator. The deflection of the beam is measured by the change in resistance of the p-type silicon layer 47. This vibrator 51 is supported by four beams 52, 53, 54, and 55.

The shape processing process of this pressure sensor will be explained with reference to FIG. 12.

First, as shown in FIG. 12(a), an n+ buried layer 74 is formed on an n-type silicon substrate 16, and an n
After forming the type epitaxial growth layer 75, further SI
Ions are implanted into this n-type epitaxial growth layer 75 using MOX technology to form a silicon oxide buried layer 48. By doing so, the silicon oxide buried layer 48 can be formed while maintaining the crystallinity of silicon.

After this, p-type silicon layer 4 is formed by ion implantation.
form 7. This p-type silicon layer 47 is used to define the vibrator 51 and the four beams 52, 53, 54, and 55. The deep n+ type diffusion layer 76 is then used to define the etching region.

As shown in FIG. 12(b), the surface is lightly oxidized to form a silicon oxide film 56 and a silicon nitride film 57, and then the silicon nitride film 57 is patterned to form recesses. This silicon nitride layer 57
determines the spacing between the resonator and the cap layer 58.

Thereafter, a PSG film 59 is deposited and planarized by the CVD method to bury the PSG film 59 in the recess, and a silicon nitride film 58 as a cap layer 88 is formed.
Deposit.

Then, as shown in FIG. 12(c), a cavity is formed by a triple etching technique performed through etching holes (not shown). First, in a first etching step, the +PSG film 59 on the p-type diffusion layer 47 is selectively etched away using buffered hydrofluoric acid to form a free space in the upper half. In the second etching step, HF:HNO3:CH3 was used as the etching solution.
All n+ regions are selectively removed using a mixture of COOH=1:3:8. By leaving the n-type epitaxial layer 75 at this time, the silicon oxide layer 48 can be maintained during this etching.

[0059] In the third etching step, KOH
This n remaining under the beam by etching using
The mold epitaxial layer 75 is etched as shown in FIG. 12(d).
Form a cavity region as shown in .

[0060] Then, determine the internal pressure in the cavity,
The etched holes are sealed and the pressure sensor shown in FIGS. 10 and 11 is formed.

[0061] With this structure, as in Example 1,
Thin film technology can be used to form resonant pressure sensors that are easy to implement and highly reliable.

In the above embodiment, a single crystal silicon film and a silicon oxide film were used as the materials constituting the resonator. Any combination of material and insulating film may be used as long as they have unequal coefficients of thermal expansion.

Example 5 Next, a fifth embodiment of the present invention will be described.

In this example, a vibrator made of a single crystal silicon layer extends into a recess formed in a semiconductor substrate, and a polycrystalline silicon layer formed on the surface of the substrate so as to airtightly seal the recess. This resonator is excited by electrostatic interaction with the polycrystalline silicon layer, and the vibrations are caused by the vibration of the single crystal silicon layer. External pressure is detected as an output change due to piezoresistance effect.

In other words, in this example, FIGS. 13 and 14
As shown, the resonator 78 has a p-type region 83 in the upper half,
The lower half is composed of a single layer of single crystal silicon with an n-type region 79, and the excitation of the resonator 78 is caused by the p-type region 8 of the resonator 78.
3 and the cap layer 62. Furthermore, the deflection of the beam is detected by the piezoresistance effect within the p-type region 83 of the resonator 78. And this vibrator 6
0 is supported by four beams 63, 64, 65, and 66. Further, the cap layer 62 has a three-layer structure including a silicon nitride layer 80, a polycrystalline silicon layer 81, and a silicon nitride layer 82.

The shape processing process for this pressure sensor will be explained with reference to FIG. 15.

First, as shown in FIG. 15(a), (1
An n+ buried layer 84 is formed on the n-type silicon substrate 16 with a 00) orientation, and an n-type epitaxial growth layer 75 is formed. Here, this buried layer 84 defines the area under the resonator.

Thereafter, as shown in FIG. 15(b), a deep p+ type diffusion layer 85 is formed. This p+ type diffusion layer 85
is etched away later to define an etched area around the vibrator 60. Then, a shallow p-type diffusion layer 83 is formed, and this is used as the lower electrode of the piezoresistive element and the excitation capacitor. Here, the lower region 79 of the resonator is of n-type.

The surface of the substrate is then lightly oxidized to form a silicon oxide film 86 and a silicon nitride film 87, which are then patterned. This silicon nitride layer 87 determines the space between the resonator and the cap layer 88 .

Thereafter, the PSG film 89 is deposited and planarized by the CVD method, and the recesses formed by etching are filled with the PSG film 89, and the silicon nitride film 80 as the cap layer 62, the polycrystalline silicon layer 81, and the nitride A silicon layer 82 is sequentially deposited (FIG. 15(c)).

Then, as shown in FIG. 15(d), a cavity is formed by a double etching technique performed through an etching hole (not shown). First, in a first etching step, the PSG film 89 on the p-type diffusion layer 83 is selectively etched away using buffered hydrofluoric acid to form a free space in the upper half. In the second etching step, HF:HNO3:CH3COO is used as an etching solution.
Selectively remove all n+ regions around and below the beam using a mixture of H=1:3:8. As in Example 1, since a silicon substrate with (100) orientation is used here, the etching rate in the (111) direction is extremely slow in this etching process, and the etching stops at this plane, and the (111) It becomes an enclosed cavity. Oxidation is then performed to form a silicon oxide layer 92 within the cavity, determining the internal pressure within the cavity and sealing the etched hole to form the pressure sensor shown in FIGS. 13 and 14.

[0072] With this structure, as in Example 1,
Thin film technology can be used to form resonant pressure sensors that are easy to implement and highly reliable.

Although excitation of polycrystalline silicon by electrostatic interaction is used here, the material constituting the resonator is not limited to polycrystalline silicon, and other conductive materials may be used. You may also do so.

[0074]

[Effect] As explained above, according to the present invention, a cantilever beam and a space surrounding it are formed using micromachine technology, and the pressure sensor is integrally formed, so there is no need for a mounting process. This makes it possible to obtain a highly accurate and reliable sensor extremely easily.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a pressure sensor according to a first embodiment of the present invention.

[
FIG. 2 is a diagram showing a pressure sensor according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the manufacturing process of the pressure sensor according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a pressure sensor according to a second embodiment of the present invention.

[
FIG. 5 is a diagram showing a pressure sensor according to a second embodiment of the present invention.

FIG. 6 is a diagram showing the manufacturing process of a pressure sensor according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a pressure sensor according to a third embodiment of the present invention.

[
FIG. 8 is a diagram showing a pressure sensor according to a third embodiment of the present invention.

FIG. 9 is a diagram showing the manufacturing process of a pressure sensor according to a third embodiment of the present invention.

FIG. 10 is a diagram showing a pressure sensor according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing a pressure sensor according to a fourth embodiment of the present invention.

FIG. 12 is a diagram showing the manufacturing process of a pressure sensor according to a fourth embodiment of the present invention.

FIG. 13 is a diagram showing a pressure sensor according to a fifth embodiment of the present invention.

FIG. 14 is a diagram showing a pressure sensor according to a fifth embodiment of the present invention.

FIG. 15 is a diagram showing the manufacturing process of a pressure sensor according to a fifth embodiment of the present invention.

[Fig. 16] Diagram showing a conventional pressure sensor

[Fig. 17] Diagram showing a conventional pressure sensor

[Explanation of symbols]

1. Oscillator 2 Torsion spring 3 Torsion spring 4 Torsion spring 5 Torsion spring 6 Driving electrode 7 Glass plate 8 Silicon nitride film 9 Resonator 10 Polycrystalline silicon film 11 Silicon oxide film 12 Etching groove 13 Gap layer 14 Beam 15 Beam 17 Beam 18 Beam 21 Oscillator 90 Polycrystalline silicon layer

Claims (2)

[Claims] 1. A resonator having a two-layer structure of a semiconductor layer and an insulating film extending into a recess formed in a semiconductor substrate, and a resonator formed on the surface of the substrate so as to hermetically seal the recess. and a cap layer made of an insulating film, which excites the deflection of the semiconductor layer due to the bimetallic effect caused by heat generation due to energization of the semiconductor layer, and causes the cap layer to change as the external pressure changes as an output change due to the piezoresistive effect. A pressure sensor, characterized in that it detects a change in pressure within the cavity that is applied through a layer. 2. A vibrator made of a first semiconductor layer extending into a recess formed in a semiconductor substrate, and a second semiconductor layer formed on the surface of the substrate so as to hermetically seal the recess. a cap layer having a sandwich structure in which the front and back surfaces of the layer are covered with an insulating film;
excite a deflection of the second semiconductor layer by electrostatic interaction between the semiconductor layers of the second semiconductor layer, and detect a pressure change in the cavity applied through the cap layer with a change in external pressure; A pressure sensor characterized by: