JP2002236067A - Pressure sensor and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a touch-mode capacitance pressure sensor with a pressure resistance higher than conventional type sensors. SOLUTION: The pressure sensor is constituted by bonding a silicon structure (5), having a diaphragm (9) with conductivity formed by impurity doping and heterogeneous etching on a base (6) having an electrode (7) and an inductor film (8) covering it formed in a state that the diaphragm and the electrode face to each other and a gap (10) to the inductor film is provided. When the diaphragm receives pressure, the contact area with the inductor film varies, which is detected to measure the pressure. The production of the pressure sensor with an etch pit density of 5 per μm2 or less on the diaphragm surface includes a process for producing the silicon structure, by doping impurities on the silicon surface at a high concentration, when applying etching so that the etch pit density is to be 5 pieces per μm2 or less on the etching surface to form the diaphragm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a touch-mode capacitive pressure sensor, and more particularly to a structure of a pressure sensor having a high pressure resistance and a method of manufacturing the same.

[0002]

2. Description of the Related Art An electrostatic capacitance type pressure sensor is arranged such that a substrate having a diaphragm formed thereon and a substrate having an electrode formed thereon are deformed in response to pressure so that the diaphragm and the electrode are opposed to each other with a certain gap. The pressure is detected from a change in the capacitance between the diaphragm and the electrode. Since a silicon or glass wafer can be used as a substrate for forming a diaphragm or an electrode, a large number of sensors can be manufactured on the wafer at one time, which is suitable for mass production at low cost.

Among the capacitive pressure sensors, for example, a touch mode capacitive pressure sensor disclosed in US Pat. No. 5,528,452 discloses a metal thin film on a glass substrate as shown in FIG. An electrode 1 is formed, and a dielectric film 2 is formed thereon, and a diaphragm 3 having at least a surface having conductivity is arranged to face each other with a slight gap 4 therebetween. As shown in FIG. 3B, the diaphragm is bent and is in contact with the dielectric film 2 (referred to as a touch mode).

The diaphragm 3 is a P ⁺ layer in which n-type silicon is doped with boron at a high concentration. If the diaphragm 3 is regarded as one electrode, the electrode 1, the dielectric film 2 and the diaphragm 3 are used when pressure is detected. Is formed. By detecting a change in the contact area between the diaphragm 3 and the dielectric film 2 as a change in capacitance between both electrodes (between the diaphragm 3 and the electrode 1), it is possible to measure the pressure applied to the diaphragm 3. The touch mode capacitive pressure sensor has many excellent characteristics, such as high sensitivity and high pressure resistance, and a linear relationship between pressure and capacitance as compared with other capacitive pressure sensors.

FIG. 4 shows the relationship between the capacitance of the touch mode capacitive pressure sensor and the applied pressure. Due to the characteristics of the touch-mode capacitive pressure sensor, the sensitivity is almost zero in a low-pressure region (non-contact region) before the diaphragm contacts the dielectric film. When the diaphragm contacts the dielectric film,
The capacitance of the sensor increases almost linearly with pressure within a certain range (linear region), and when the pressure further increases, the sensitivity gradually decreases and the change in capacitance saturates (saturation region). .

For forming a diaphragm using a silicon single crystal, an inorganic solution such as KOH or NaOH or an organic solution such as ethylenediamine / pyrocatechol (EDP) or tetramethylammonium hydroxide (TMAH) is used. It is often performed by anisotropic etching utilizing a difference in etching rate depending on the crystal orientation of the crystal. Among the above etching solutions, KOH aqueous solution is
Because of its high etching rate and low cost compared to other etching solutions, it is often used for anisotropic etching of silicon single crystal. The etch stop effect in the P ⁺ layer, that is, the effect that the etching rate in the region where the boron concentration exceeds 10 ¹⁹ cm ⁻³ becomes several tenths to several hundredths in comparison with the silicon layer is used. Thus, a diaphragm having a thickness of several μm is usually formed.
By controlling the thickness of the diaphragm and the dimension of the electrode interval, the above-described linear region can be adapted to a desired operating range of the sensor. For example, a sensor for detecting tire pressure has a pressure range of about 10 kgf / cm ^2. What is necessary is just to obtain a stable operation within.

[0007]

As described above,
The conventional touch-mode capacitive pressure sensor has characteristics of high sensitivity and high withstand voltage, and a stable operation can be obtained within a desired pressure range by changing the diaphragm thickness and the electrode interval. However, depending on the use condition of the sensor, a pressure that greatly exceeds the actual operating pressure range, for example, a pressure resistance as high as 4 to 5 times the upper limit of the measurable pressure range may be required. When added, the sensor may be broken, such as a diaphragm crack. This cracking of the diaphragm mainly occurs on the long side or the short side of the diaphragm where the rectangular diaphragm bends and is most stressed when in contact with the dielectric film.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a touch-mode capacitive pressure sensor having a diaphragm with higher pressure resistance than conventional products. The present inventors have conducted intensive studies to achieve the above object, and as a result, it has been confirmed that a number of minute etch pits are present on the surface of a diaphragm manufactured by the conventional etch stop method. AFM; Atomic Force Microscopy) has revealed this. These pits were generated by etching to a region where the boron concentration exceeded 9 × 10 ¹⁹ cm ⁻³ in the boron doping layer, and it was confirmed that the density of the etch pits increased as the etching time increased. . Further, when the relationship between the etch pits and the pressure resistance was examined, it was found that the pressure resistance of the diaphragm was dramatically improved when the etch pit density was 5 / μm ² or less, particularly when the etch pit density was 1 / μm ² or less. The present invention has been completed.

In order to achieve the above object, the present invention provides a method of forming a silicon structure having a conductive diaphragm formed by impurity doping and anisotropic etching on a substrate on which electrodes and a dielectric film covering the electrodes are formed. The diaphragm and the electrode face each other and are joined in a state of leaving a gap with the dielectric film, and the pressure is measured by detecting a change in the contact area where the diaphragm comes into contact with the dielectric film under pressure. The present invention provides a pressure sensor wherein the density of etch pits on the surface of the diaphragm is set to 5 / μm ² or less. Further, the present invention provides a silicon structure having a conductive diaphragm formed by impurity doping and anisotropic etching, and forming the electrode and a dielectric film covering the same on a substrate on which the diaphragm and the electrode face each other. And a method for manufacturing a pressure sensor which is joined with a gap between the dielectric film and the dielectric film, and detects a change in a contact area where the diaphragm is in contact with the dielectric film under pressure to measure the pressure. Manufacturing a silicon structure by doping a silicon surface with a high concentration of impurities and then performing etching so that an etch pit density on an etching surface is 5 / μm ² or less to form a diaphragm. The present invention provides a method for manufacturing a pressure sensor, characterized by the following. In this method of manufacturing a pressure sensor, the etching may be performed using a KOH solution having a concentration of 1% by weight or more and less than 10% by weight so that the etch pit density on the etched surface is 1 / μm ² or less. desirable.

[0010]

FIG. 1 shows an embodiment of a pressure sensor according to the present invention. FIG. 1 (A) is a plan view of the pressure sensor.
(B) is a side sectional view. This pressure sensor is composed of a silicon substrate provided with a conductive diaphragm 9 which is deformable according to pressure on a substrate 6 provided with an electrode 7 made of a metal thin film and a dielectric film 8 formed so as to cover the electrode 7. Structure 5
Are joined in a state where the diaphragm 9 and the electrode 7 face each other and a gap 10 is provided between the diaphragm 9 and the dielectric film 8.

The diaphragm 9 of the silicon structure 5 is formed by etching a silicon wafer to make it concave. In order to form the diaphragm 9 on the silicon wafer, a layer to which a high concentration of impurity is added is formed on the silicon surface, and an etch stop technique by high concentration doping of an impurity such as boron can be used.

In the present invention, the density of etch pits on the surface of the diaphragm 9 is 5 / μm ² or less, preferably 3 / μm ² or less.
Pieces / μm ² or less, particularly preferably 2 pieces / μm ² or less, and most preferably 1 piece / μm ² or less. The etch pits are minute pits (holes) observed on the surface of the diaphragm 9 formed after the etching. If the etch pit density on the surface of the diaphragm 9 is more than 5 / μm ^{2, the} effect of improving the pressure resistance of the diaphragm according to the present invention cannot be sufficiently obtained. In a touch-mode capacitive pressure sensor having a diaphragm formed of silicon doped with an impurity such as boron, the density of etch pits on the surface of the diaphragm is 5 / μm ² or less, particularly for high pressure (for example, automobile tires). Pressure detection), the pressure resistance can be remarkably improved by setting it to 1 piece / μm ² or less.

[0013] Such etch pits are generated by etching a region of the boron doping layer such that the boron concentration exceeds 9 × 10 ¹⁹ cm ^-3 ,
It was confirmed that the density of the etch pits increased as the etching time increased. Therefore, the impurity (boron) concentration on the diaphragm surface is preferably 9 × 10 ¹⁹ cm ⁻³ or less, more preferably 1 × 10 ¹⁹ cm ⁻³ or more and less than 9 × 10 ¹⁹ cm ⁻³ . The density of the etch pits on the diaphragm surface is determined by the atomic force microscope (AFM).
copy). There are several methods for measuring the impurity (boron) concentration on the diaphragm surface, for example, by using the SR method (Spread Resistance: Spread Resistance Measurement Method). In this method, the resistance is measured in the depth direction from the surface of the boron diffusion layer, and the carrier concentration is determined from the resistance. The concentration is determined from the resistance value by calculation based on a theory, and the theory for this is established.

The thickness of the diaphragm 9 and the depth of the dent below the diaphragm (joint surface with the base 6) which define the height of the gap 10 between the diaphragm 9 and the dielectric film 8 are determined by the load pressure of the object to be measured. It can be set appropriately so that the linear region of the sensor matches the range.

The constituent material of the base 6 is not particularly limited as long as it can ensure an electrical insulation state with the electrode 7.
For example, a glass plate, a ceramic plate, a hard plastic plate, a silicon wafer having a surface oxide film formed thereon may be used, and a glass plate is particularly preferably used. The electrodes 7 formed on the base 6 are made of Al, Cr, Au, Ag,
Various metals generally used as electrode materials such as Cu and Ti are deposited on the surface of the substrate 6 by vapor deposition, sputtering, C
The film is formed using a thin film forming method such as a VD method or an electroless plating method. The shape of the electrode 7 may be a method of covering the non-electrode film-forming portion on the surface of the base 6 with a mask and forming a metal film only on the electrode forming portion, or a method of uniformly forming a metal film on one surface of the base 6 and then performing photolithography. A pattern can be formed by a method of etching into a desired shape using a technique, and is usually formed in the same shape as the diaphragm 9. The dielectric film 8 formed on the base 6 so as to cover the electrode 7 is made of a material known as an insulating material such as glass (quartz glass) or ceramic by using a thin film forming means such as a sputtering method or a CVD method. It is formed by forming a film. The thickness of the dielectric film 8 is appropriately set according to the required sensitivity of the pressure sensor, and is usually about 0.1 to several μm.

A terminal 11 connected to the electrode 7 and extending to the edge of the base 2 is provided on the base 6, and a terminal 11 provided on the dielectric film 8 and electrically connected to the structure 5. Are provided. These terminal portions 11 and 11 can be formed using the same metal material as the electrode 7 and the same kind of thin film forming means.

The gap 10 formed between the dielectric film 8 of the base 6 and the diaphragm 9 is formed by recessing the lower surface of the silicon structure 5 into a rectangular shape slightly larger than the electrode 7 and the diaphragm 9. . The height of the gap 10, that is, the dimension between the dielectric film 8 and the diaphragm 9 is appropriately selected according to the dimensions (length, width, and thickness) of the diaphragm 9. In this example, the inside of the gap 10 is evacuated.

Next, as an example of a method of manufacturing a pressure sensor according to the present invention, a method of manufacturing a pressure sensor having the above-described structure will be described. The substrate 6 is formed by connecting the electrode 7 and the terminal portion 11 connected thereto to a metal thin film by sputtering or the like.
A dielectric film 8 made of glass is formed by a sputtering method or the like, and covers the electrode 7 except for the terminal portion 11.
Further, the terminal portion 11 on the silicon structure 5 side is formed on the dielectric film 8.
Is formed in the same manner as the electrode 7.

The silicon structure 5 is doped with impurities such as boron at a high concentration from the bonding surface side of the silicon wafer with the substrate 6 by a thermal diffusion method, and then the surface (etched surface) has an etch pit density of 5%. Pieces / μm ² or less, preferably 3 pieces / μm ² or less, particularly preferably 2 pieces / μm ² or less, and most preferably 1 piece / μm ² or less. 9 are formed.

In this etching, KOH, NaOH, ethylenediamine pyrocatechol (EDP), tetramethylammonium hydroxide (T
MAH), and etching is performed so that the thickness of the diaphragm 9 becomes a predetermined thickness by using an etch stop effect that leaves a portion doped with a high concentration of impurities. This is done by controlling the time. At this time, the thickness of the diaphragm can be changed by controlling the distribution of impurities in the depth direction.

In order to form a diaphragm having an etch pit density of 1 / μm ² or less, a concentration of 1 wt% or more and 1
It is desirable to perform uniform etching using a KOH solution of less than 0 wt%. The impurity concentration of the diaphragm having such an etch pit density is 1 × 10 ¹⁹ c
It is preferably at least m ^{−3 and} less than 9 × 10 ¹⁹ cm ⁻³ .

The pressure sensor is manufactured by joining the substrate 6 and the silicon structure 5 thus manufactured to each other in a vacuum by an appropriate bonding method, for example, by heat fusion or an inorganic adhesive. You.

This pressure sensor is operated by connecting the terminal portion 11 to a measuring device for measuring capacitance, applying an AC voltage between the diaphragm 9 and the electrode 7, and detecting a change in the resonance frequency or impedance thereof. Is As shown in FIG. 4, when pressure is applied to the diaphragm 9 and comes into contact with the dielectric film 8, the capacitance of the sensor increases almost linearly with pressure within a certain range. Hereinafter, the effects of the present invention will be embodied by examples.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1A and 1B, a touch mode having a structure in which a silicon structure 5 provided with a diaphragm 9 is joined to a substrate 6 on which an electrode 7 and a dielectric film 8 are formed. A capacitive pressure sensor was manufactured. An electrode 7 made of a Cr thin film and a dielectric film 8 made of glass which cover the electrode 7 made of a Cr thin film on a substrate 6 made of a glass plate are each 0.1 μm thick and 0.1 μm thick.
It was formed with a thickness of 4 μm. The formation of the electrode 7 and the dielectric film 8 was performed by a series of steps of film deposition by sputtering and patterning by photolithography.

The diaphragm 9 facing the electrode 7 (lower electrode) is doped with boron at a high concentration so as to serve as an upper electrode, and has a shape of 0.4 mm × 1.
It was a 5 mm rectangle. As disclosed in U.S. Pat. No. 5,528,452, by making the shape of the diaphragm 9 a rectangle having a ratio of the long side to the short side of 3: 1 or more, the pressure and the capacitance change within a certain range can be reduced. It is possible to obtain linearity. The gap 10 between the dielectric film 8 and the diaphragm 9 was 3 μm. A terminal 11 made of Al for contact with the outside was formed on a part of the base 6 so that one was connected to the upper electrode and the other was connected to the lower electrode. A series of manufacturing processes are performed using silicon wafers and glass wafers,
Each sensor was obtained by cutting both wafers after bonding.

FIG. 2 shows a detailed structure of the diaphragm of the manufactured touch mode capacitive pressure sensor. When the diaphragm 12 is formed, the silicon substrate 13 is doped with boron by thermal diffusion from the bonding surface (the back surface of the diaphragm) with the glass substrate 14. In this embodiment, the temperature at the time of diffusion is 1125 ° C.
The diffusion time was set to 10 hours so that the boron concentration at a depth of μm was 1 × 10 ¹⁹ cm ⁻³ . The diffusion depth at this time was substantially uniform in the silicon wafer, and was 9.4 μm. The boron concentration shows a constant value of about 2 × 10 ²⁰ cm ⁻³ at a depth of 5.5 μm from the back surface of the diaphragm, and is 5.5.
It gradually started to decrease around about μm, and was 2 × 10 ¹⁴ cm ⁻³ at the diffusion depth of 9.4 μm. The formation of the diaphragm 12 was performed by anisotropic etching from a surface (diaphragm surface) opposite to the bonding surface. The etching solution is a 24 wt% KOH solution at 80 ° C., and the thickness of the diaphragm 12 is 6 μm using an etch stop effect.
The etching time was controlled so as to be about the same.

A pressure resistance test was conducted to investigate cracks in the diaphragm after applying a constant pressure to the touch mode capacitive pressure sensor having the structure described above for a long time. The test was performed on the wafer before being cut into elements, and the number of samples (the number of wafers) was set to 10 (A to J). Here, 500 sensor elements are formed on each wafer. When the application pressure was set to 40 kgf / cm ² and the application time was set to 1 hour, the presence / absence of diaphragm cracks after application of the pressure was examined. That is, the ratio varied greatly from the case where no diaphragm crack occurred to the case where 82% of the diaphragm cracked in the wafer. In addition, cracks in the diaphragm were generated on the long side and the short side of the diaphragm where the most stress was applied when the diaphragm was bent, and was in contact with the dielectric film.

From the wafers used in the above-mentioned withstand voltage test, 10 sensors each of a wafer with particularly high withstand voltage and a sensor with very low withstand voltage were extracted, and the surface morphology of the diaphragm was measured with an atomic force microscope (atomic force microscope). AFM; Atomic
Force Microscopy). As a result, it was recognized that pits having a diameter of about 0.2 μm were distributed at a high density of 6 to 8 per 1 μm ³ on the diaphragm surface of the sensor having extremely low withstand voltage. On the other hand, no pits having such a high density distribution were observed on the diaphragm surface of the sensor having extremely high pressure resistance, and the sensor was very smooth. It is considered that the pits distributed at a high density are caused by a different etching process for forming a diaphragm. Regardless of the presence or absence of a diaphragm crack, there was no significant difference in the thickness of the diaphragm in any of the sensors, and it was confirmed that this difference in pressure resistance was not a difference in the diaphragm thickness. Further, when the boron concentration on the diaphragm surface was investigated for each sensor, the surface boron concentration of the sensor having high pressure resistance was 9 × 10 ¹⁹ c.
In contrast, the surface boron concentration of the sensor having a low withstand voltage was 9 × 10 ¹⁹ cm ⁻³ or more, while it was less than m ⁻³ .

Since this difference in surface boron concentration is considered to be a difference in etching time when forming the diaphragm, a change in the diaphragm surface morphology with respect to the etching time was investigated. As a result, etch pits were generated on the diaphragm as the etching time increased.

The above results show that if etching is performed more than necessary at the time of diaphragm formation etching, etch pits are generated and the pressure resistance of the sensor is significantly reduced. Therefore, it is important for the diaphragm formation etching to perform uniform etching in the plane and to obtain a large etch stop effect. Therefore, a study focused on this point was conducted below.

The etch stop effect of the KOH solution on the P ⁺ layer depends on the concentration of the solution and is lower (<10 watts).
t%) and the etch stop effect will increase, for example
H. Seidel et al. (J. Electrochem.Soc.Vol.137, No.
11, 3629-3632, 1990). Therefore, the present inventors have attempted to improve the pressure resistance by increasing the KOH solution concentration to 8 wt% to enhance the effect of the etch stop and to prevent the occurrence of etch pits. The solution was kept at the same temperature of 80 ° C. as in the prior art, and the diaphragm etching was performed while stirring the solution so as to enable more uniform etching. The pressure resistance of the 500 sensors thus obtained was evaluated by the same method as in the above-described pressure test. As a result, 50 kgf / cm ²
No cracks in the diaphragm were observed in any of the sensors after the application. When the diaphragm of this sensor was observed with an atomic force microscope, it was confirmed that the number of pits as observed on a wafer having extremely low pressure resistance could be reduced to one or less per 1 μm ² . Further, in the case of a solution having a concentration of less than 1 wt%, uniform etching was difficult even if the solution was stirred and etched.

From the above results, it was found that the concentration was 1 wt% or more and 10 wt% or more.
By using a KOH solution of less than wt% and performing uniform etching, the etch pit density is suppressed to 1 / μm ² or less,
It has become possible to increase the pressure resistance of the diaphragm. Japanese Patent Laid-Open No. 11-3260 discloses a method for uniformly etching a diaphragm in a capacitance type pressure sensor.
As described in Japanese Patent Publication No. 95, two types of solutions having different concentrations can be used. The etch pit density may be lower than that of the conventional product (about 6 to 8 pits / μm ² ), and by setting it to 5 pits / μm ² or less, a higher pressure resistance than the conventional product can be obtained. As described above, especially for a high pressure type (for example, for detecting a tire pressure of an automobile), 1 piece / μm ²
With the following, the pressure resistance can be remarkably improved.

[0033]

As described above, the pressure sensor according to the present invention comprises a silicon structure having a conductive diaphragm formed by impurity doping and anisotropic etching, an electrode and a dielectric film covering the electrode. The diaphragm and the electrode are joined on the formed substrate in a state where the diaphragm and the electrode face each other and a gap is formed between the diaphragm and the dielectric film. The change in the contact area where the diaphragm contacts the dielectric film due to the pressure is detected and the pressure is detected. The pressure resistance of the diaphragm can be greatly improved by setting the etch pit density on the diaphragm surface to 5 / μm ² or less, particularly preferably 1 / μm ² or less. Therefore, according to the present invention, it is possible to provide a touch-mode capacitive pressure sensor that is more excellent in pressure resistance of the diaphragm than conventional products.
Further, in the pressure sensor according to the present invention, by setting the etch pit density on the diaphragm surface to 5 / μm ² or less, particularly preferably 1 / μm ² or less, the pressure resistance of the diaphragm is greatly improved, Since the diaphragm is not broken even when a pressure that greatly exceeds the operating pressure range is applied, the diaphragm can be particularly suitably used as a pressure sensor for detecting a vehicle tire pressure that requires safety.

[Brief description of the drawings]

FIG. 1 shows an example of a pressure sensor of the present invention.
(A) is a top view of a pressure sensor, (B) is a side sectional view.

FIG. 2 is an enlarged sectional view of a main part of the pressure sensor of the present invention.

FIG. 3 is a side view showing a conventional pressure sensor;
(A) shows a state where no pressure is applied, and (B) shows a state where the diaphragm contacts the dielectric film side due to the pressure.

FIG. 4 is a graph showing a relationship between pressure and capacitance in a conventional pressure sensor.

FIG. 5 is a frequency distribution graph showing the results of the example according to the present invention.

[Explanation of symbols]

5 ... structure, 6 ... substrate, 7 ... electrode, 8 ... dielectric film, 9 ... diaphragm, 10 ... gap, 12 ... diaphragm, 13 ... silicon substrate (structure), 14 ... …
Glass substrate (substrate).

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Jin Nishimura 1440, Mukurosaki, Sakura City, Chiba Prefecture Inside the Fujikura Sakura Office Co., Ltd. (72) Inventor Masahiro Sato 1440, Misaki, Sakura City, Chiba Prefecture Inside the Fujikura Sakura Office Co., Ltd. F term (reference) 2F055 AA40 BB20 CC02 DD05 EE18 EE25 FF38 GG01 GG11 4M112 AA01 BA07 CA03 CA04 CA05 DA06 DA08 DA09 EA10 EA11 EA13 EA14 EA20 FA07

Claims (3)

[Claims] 1. A silicon structure (5) having a conductive diaphragm (9) formed by impurity doping and anisotropic etching, an electrode (7) and a dielectric film (8) covering the same are formed. The diaphragm and the electrode are joined to each other on the substrate (6) in a state where the diaphragm and the electrode face each other and a gap (10) is formed between the diaphragm and the electrode. A pressure sensor for detecting a change and measuring the pressure, wherein the density of etch pits on the surface of the diaphragm is set to 5 / μm ² or less. 2. A silicon structure (5) having a conductive diaphragm (9) formed by impurity doping and anisotropic etching, an electrode (7) and a dielectric film (8) covering the electrode (7) are formed. The diaphragm and the electrode are joined to each other on the substrate (6) in a state where the diaphragm and the electrode face each other and a gap (10) is formed between the diaphragm and the electrode. A method for manufacturing a pressure sensor for detecting a change and measuring the pressure, wherein a silicon surface is doped with a high concentration of impurities and then etched so that an etch pit density on an etching surface is 5 / μm ² or less. And forming a diaphragm by applying a pressure to the silicon structure. 3. The method according to claim 1, wherein the etching is performed using a KOH solution having a concentration of 1% by weight or more and less than 10% by weight so that the etch pit density on the etched surface is 1 / μm ² or less. A method for manufacturing the pressure sensor according to claim 2.