JPH0778460B2 - Vibration type differential pressure sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a vibration type differential pressure sensor that detects a strain corresponding to a differential pressure of a semiconductor vibrating beam as a frequency signal, and particularly, has improved static pressure characteristics. The present invention relates to a vibration type differential pressure sensor.

<Prior Art> This is the basis of the improvement of the present invention of the type in which pressure or differential pressure is detected from the change in the resonance frequency of the vibrating beam which is formed on the silicon pressure-receiving diaphragm and whose both ends are fixed and which is excited by the excitation means. A known vibration type pressure sensor is disclosed in, for example, Japanese Patent Application No.
No. 59-42632 "Pressure Sensor". Although this proposal has been described as a pressure sensor, it can also be used as a differential pressure sensor, and will be described as a differential pressure sensor in the following description.

The outline of this vibration type differential pressure sensor will be described with reference to FIGS. 6 and 7.

FIG. 6 is a perspective view showing a structure of the conventional vibration type differential pressure sensor with a cover, and FIG. 7 is a sectional view with a cover taken along line XX in FIG.

In these figures, 1 is a cylindrical silicon substrate, and 2 is a pressure receiving member that receives a pressure S _P from the upper surface and a pressure (S _P + ΔP) from the lower surface by digging the center of the silicon substrate 1 to form a thin portion. It is a pressure receiving diaphragm which is formed by etching the silicon substrate 1, for example. Here, ΔP is the differential pressure to be measured.

Reference numeral 3 denotes a vibrating beam which is formed on the pressure receiving diaphragm 2 and whose both ends are fixed to the silicon substrate 1, and the vibrating beam 3 is provided substantially at the center of the pressure receiving diaphragm 2.

This vibrating beam 3 is specifically, for example, an n-type silicon substrate 1
First P ⁺ -type epitaxial layer is formed on top of it, the center part is cut to electrically separate left and right, and an n-type epitaxial layer is formed on this, and then a P ⁺ -type epitaxial layer is formed Then, this is protected by an oxide film S _i O ₂ . Then, the cavity 5 below the vibrating beam 3 is formed by under-etching this n-type epitaxial layer.

The vibrating beam 3 thus formed is, for example, l = 100 μm, h = 1, where l is length, h is thickness, and d is width.
The size is about μm and d = 5 μm.

The periphery of the vibrating beam 3 formed on the pressure receiving diaphragm 2 is covered with, for example, a silicon cover 6 bonded to the pressure receiving diaphragm 2 by anodic bonding or the like to keep the internal space 7 in a vacuum state.

The vibrating beam 3, the cover 6, the cavity 5, the internal space 7 and the like form a detection portion D of the vibration type differential pressure sensor.

In the above configuration, when the oscillation circuit is connected to the vibrating beam 3 which is the second P ⁺ -type epitaxial layer between the first left and right P ⁺ -type epitaxial layers to cause oscillation,
Causes self-excited oscillation at its natural frequency.

In this case, since the internal space 7 of the cover 6 is placed in a vacuum state and the vibrating beam 3 is held in a vacuum, Q that indicates the sharpness of resonance is obtained.
The value becomes large, and it becomes easy to detect the resonance frequency.

As shown in FIG. 7, the pressure difference Δ between the pressure S _P and the pressure (S _P + ΔP)
When P is applied to the pressure receiving diaphragm 2, the vibrating beam 3 receives a tensile stress.

Due to this tensile stress, the natural frequency of the vibrating beam 3 changes, and the differential pressure ΔP can be known.

However, in such a conventional vibration type differential pressure sensor,
A separately made silicon cover 6 is joined to the upper part of the vibrating beam 3 formed on the thin pressure receiving diaphragm 2 by anodic bonding or the like, and the internal space formed by the cover 6 and the pressure receiving diaphragm 2 is evacuated. Since it has to be pulled, there is a problem that the pressure characteristic or the temperature characteristic of the vibration type differential pressure sensor is deteriorated and the accuracy is lowered.

Therefore, in order to solve this problem, the present applicant
Japanese Patent Application No. 62-166175 "Title of Invention: Method for Manufacturing Vibration Transducer" is proposed on July 2, 2014. Less than,
The outline of this proposal will be described.

FIG. 8 is a process diagram showing a manufacturing process of a detection part which is a main part of the vibration type differential pressure sensor according to this proposal.

This shows the process of the detection unit D'shown in the axial cross section of the vibrating beam corresponding to the detection unit D in FIG.

FIG. 8 (a) shows a base n for making the detection unit D '.
3 shows a silicon substrate 8 in the shape of. Next, this silicon substrate 8
Is thermally oxidized to form an oxide film (S _i O ₂ ) 9 on its surface (FIG. 8B).

Further, in the step of FIG. 8C, the central portion of the oxide film 9 is photoetched in the direction perpendicular to the paper surface to form the groove 10.

In the process of FIG. 8D, hydrogen gas H _{2 is} heated at a temperature of 1050 ° C.
Etching is performed in an atmosphere in which hydrochloric acid HCl is mixed with the above to form a groove 11 through the groove 10 in the silicon substrate 8.

Next, as shown in FIG.
The first epi layer 12 is formed by selective epitaxial growth of boron (P-type) having a concentration of 10 ¹⁸ cm ^-3 in an atmosphere of hydrogen gas H ₂ at the temperature of.

After that, as shown in FIG. 8F, boron (P-type) having a concentration of 10 ²⁰ cm ⁻³ was formed on the first epilayer 12 at a temperature of 1050 ° C. in an atmosphere of hydrogen gas H _2. Selective epitaxial and vibrating beam
A second epi layer 14 to be 13 is formed.

If the initial tension is not applied to the vibrating beam 13 even if the differential pressure ΔP is zero, buckling occurs due to the application of the differential pressure ΔP, and the vibrating beam 13 cannot be measured. Also, the covalent bond radius of silicon is 1.
17 Å, and that of boron is 0.88 Å, so when boron is partially injected into silicon, that part undergoes tensile strain. Therefore, using this phenomenon, for example, boron of the second epilayer 14 An initial tension is applied here by adjusting the concentration, or the phosphorus (covalent bond radius is 1.10Å) concentration in the n-type silicon substrate 8 is adjusted so that the relative amount between the silicon substrate 8 and the second epi layer 14 is increased. Consider the strain so that the initial tension is applied.

Next, as shown in FIG.
Boron (P-type) having a concentration of 10 ¹⁸ cm ⁻³ is selectively epitaxially grown in a hydrogen gas H ₂ atmosphere at a temperature of 1050 ° C. to form a third epi layer 15.

Further, as shown in FIG. 8 (H), on the third epi layer 15
Phosphorus (n-type) having a concentration of 10 ¹⁷ cm ⁻³ is selectively epitaxially grown in a hydrogen gas H ₂ atmosphere at a temperature of 1050 ° C. to form a fourth epi layer 16.

FIG. 8 ( _i ) shows a state in which the oxide film 9 of SiO ₂ is removed by etching with hydrogen fluoride HF after the selective epitaxial step shown in FIG. 8 (h) (step is not shown). , First
An etching process for removing the epi layer 12 and the third epi layer 15 is shown.

In this etching process, although not shown, the whole is immersed in an alkali solution, and the n-type silicon substrate 8 is
The fourth repetition period at the peak of the DC pulse power supply 17 to the epi layer 16 becomes the positive potential with respect to the second epitaxial layer 14 of p-type is 5V is a positive pulse voltage of about 0.04H _Z is applied when ing. By applying this voltage, the n-type silicon substrate 8 and the fourth
Since the insoluble film is formed on the surface of the epi layer 16 and it is passivated, the etching rate thereof is significantly slower than that of the first epi layer 12 and the third epi layer 15.
The epi layer 12 and the third epi layer 15 are removed. Furthermore, the second epi layer 14 utilizes the phenomenon that when the concentration of doped boron is higher than 4 × 10 ¹⁹ , the etching rate is significantly delayed from the normal rate in the case of undoped silicon.
As shown in FIG. 8 (n), the epi layer 14 is left as a whole, and an opening 18 is formed in a part of the epi layer 14, and a gap is formed between the silicon substrate 8 and the second epi layer 14.

FIG. 8 (l) shows a process of thermal oxidation. In this process,
Oxide films (S _i O ₂ ) 8a, 14a, and 16a are formed on the entire inner and outer surfaces of the silicon substrate 8, the second epi layer 14, and the fourth epi layer 16, respectively.

FIG. 8 (e) shows the process of plasma etching. In this step, the silicon substrate 8 and the second
Of the oxide films 8a, 14a, and 16a formed on the entire inner and outer surfaces of the epi layer 14 and the fourth epi layer 16, respectively, the oxide film formed on the outer surface of the silicon substrate 8 and the fourth epi layer 16. Are removed by plasma etching to prepare for selective epitaxial growth in the next step.

In the process shown in Fig. 8 (wa), hydrogen is stored at a temperature of 1050 ° C.
In the H ₂ atmosphere, n-type selective epitaxial growth is performed on the silicon substrate 8 and the outer surface of the fourth epi layer 16. By this selective epitaxial growth, the opening 18 formed between the silicon substrate 8 and the fourth epi layer 16 is filled and the shell
20 is formed, and the detecting portion of the vibration type differential pressure sensor having the vibrating beam 13 formed of the rod-shaped fourth epi layer inside is formed.

In the process of FIG. 8 (W), since selective epitaxial growth was performed in an atmosphere of hydrogen H ₂ , a hollow chamber 21 formed between the silicon substrate 8 made of silicon single crystal and the shell 20 was formed. Is filled with hydrogen H ₂ .

Therefore, as shown in Fig. 8C, an oscillating differential pressure sensor with this detector is placed in an atmosphere of vacuum at 900 ° C to remove this hydrogen H ₂ through the crystal lattice of silicon. Carefully evacuate. The degree of vacuum thus obtained is 1
× 10 ^-3 Torr or less.

<Problems to be Solved by the Invention> As described above, in the vibrating differential pressure sensor according to the prior application, both the vibrating beam and the cover can be manufactured integrally with the silicon substrate. The drawbacks of the sensor can be eliminated, but they still have the drawbacks described below.

Using such a vibration type differential pressure sensor, for example, 500 Kgf / c
With a high static pressure S _P of up to m ² , for example (10 mmH ₂ O ~ ₁₀ Kgf / c
When measuring a small differential pressure ΔP such as m ² ), the static pressure S _P is applied to one surface of the pressure receiving diaphragm of the vibration type differential pressure sensor.
However, since static pressure (S _P + ΔP) is applied to the other surface, the static pressure S _P causes ε _{S to} move the substrate, pressure-receiving diaphragm, and vibrating beam.
= Shrink by S _P l / E _S. However, E _S is the volume compressibility and l is the length of the vibrating beam.

Therefore, a compressive strain of ε _S is applied to the vibrating beam, which causes a problem that the resonance frequency of the vibrating beam changes and a static pressure error occurs.

<Means for Solving Problems> In order to solve the above problems, the present invention provides a semiconductor substrate having a pressure receiving diaphragm which has a fixed portion in the periphery and is deformed by a differential pressure inside the fixed portion, and At least one or more vibrating beams that measure the strain generated near the surface of the pressure-receiving diaphragm due to the formed differential pressure; and a shell that is integrally formed on the substrate and that holds the periphery of the vibrating beams in a vacuum state.
A semiconductor base having a pressure guiding hole that is joined to the fixed part and introduces one pressure that forms a differential pressure, and a compensating chamber provided on the fixed part or the base opposite to this fixed part. is there.

<Operation> By forming a compensation chamber having a space in the fixed portion of the substrate or a base opposite to this fixed portion, the compensation chamber is formed by denting the compensation chamber by static pressure applied from the surroundings. The tensile stress is generated in the vibrating beam and the compressive strain due to static pressure is canceled.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an embodiment excluding the shell of the present invention, and FIG. 2 is a sectional view showing the configuration of the XX section with the shell.

In these figures, 22 is a cylindrical silicon substrate, and 23 is a pressure receiving portion for digging the center of the substrate 22 to form a thin portion to receive static pressure S _P , (S _P + ΔP). It is a diaphragm, made by etching silicon,
Around the periphery thereof, an annularly formed thick-walled fixing portion 24 is formed.

Reference numeral 25 is a vibrating beam that detects strain due to differential pressure, and 26 is a shell that holds the inside thereof in a vacuum, for example, and these are made by the manufacturing method described in FIG.

Compensation chamber with an annular recess on the annular bottom surface of the fixed part 24.
27 is formed by etching, for example.

The bottom surface of the fixed part 24 excluding the compensation chamber 27 has a pressure (S _P + Δ
P) disk-shaped silicon base with pressure guide holes 28
29 are joined by, for example, anodic bonding. In this bonding, if the bonding is performed in a vacuum state, the inside of the compensation chamber 27 becomes vacuum, and if the bonding is performed under atmospheric pressure, the inside of the compensation chamber 27 becomes atmospheric pressure.

Next, the operation of the embodiment shown in FIGS. 1 and 2 configured as described above will be described with reference to the operation explanatory view shown in FIG.

Since operation when the pressure difference ΔP is applied it is identical to the prior art, an operation when the applied static pressure S _P in the following description.

Even if the static pressure S _P is applied to the outer circumferences of the substrate 22 and the base 29 and the front and back of the pressure receiving diaphragm 23, the static pressure S _P is not applied because the compensation chamber 27 is sealed. For this reason, the fixed part at the top of the compensation chamber 27
The upper surface of 24 is dented by the static pressure S _{P and} is deformed by Δχ.
Due to this deformation Δχ, the pressure receiving diaphragm 23 is deformed into a convex shape, and a vibrating beam provided near the surface of the pressure receiving diaphragm 23.
A tensile strain ε _P occurs at 25.

On the other hand, the vibrating beam 25 has a compressive strain of ε _S = S _P l / E _S due to the static pressure S _P.

Therefore, by selecting the size of the compensation chamber 27 so that ε _P = ε _S , the static pressure error can be suppressed to be small.

FIG. 4 is a vertical sectional view showing the structure of the second embodiment of the present invention.

In this embodiment, the base is provided with recesses for the pressure receiving diaphragm and for the compensation chamber.

A vibrating beam 25 and a shell 26 are formed in the central portion of a disk-shaped substrate 30 in the same manner as in FIG. The central portion of the substrate 30 functions as a pressure receiving diaphragm 31, and the periphery thereof functions as a fixing portion 32.

The fixed portion 32 of the substrate 30 is bonded to a silicon base 33, and a concave portion is formed in an annular shape on a surface of the base 33 facing the fixed portion 32 to form a compensation chamber 34. In addition, a pressure guide hole 35 is penetrated through the center of the base 33, and a pressure receiving diaphragm is provided near the upper surface
A recess 36 is formed so as to face and be spaced apart from 31.

Even with the above configuration, the same operation as that of the embodiment shown in FIG. 1 is performed.

FIG. 5 shows a third embodiment in which a compensation chamber is formed in the substrate near the pressure receiving diaphragm.

The disk-shaped substrate 37 has a vibrating beam 25 and a shell 26 formed in the central portion thereof in the same manner as in FIG. 2, but in the vicinity of the pressure-receiving diaphragm 23 formed on the substrate 37, the substrate on the fixed portion 38 side. 37
A compensation chamber 39 is provided in the interior of the chamber by sealing by selective etching or epitaxial growth.

Even with this configuration, the same operation as that of the embodiment shown in FIG. 1 is performed.

When the static pressure compensation by these compensating chambers 27, 34, 39 is not sufficient because of the variation, the upper surface of the fixing portions 24, 32, 39 in FIG. 1 and FIG. For example, a strain gauge is formed inside by diffusion, or a vibrating beam similar to the vibrating beam 25 is separately provided and used as a static pressure sensor, and its output is used to generate the variation of static pressure compensation in the compensation chamber. More complete static pressure compensation can be achieved if the circuit is used for compensation. Further, this static pressure sensor may be provided on the bases 29, 33 side.

<Effects of the Invention> As described above in detail with reference to the embodiments, according to the present invention, a compensating chamber is provided in the vicinity of the vibrating beam so that a tensile strain is generated with respect to the static pressure and compression by the static pressure is performed. Since the distortion is compensated, the static pressure error can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of one embodiment of the present invention excluding the shell, FIG. 2 is a cross-sectional view showing the XX cross section of FIG. 1, and FIG. 3 is FIG. 1 and FIG. FIG. 4 is a sectional view showing the structure of the second embodiment of the present invention, and FIG. 5 is a sectional view showing the structure of the third embodiment of the present invention. FIG. 6 is a perspective view showing the configuration of a known conventional vibration type differential pressure sensor excluding the shell, FIG. 7 is a cross sectional view showing the XX cross section of FIG. 6, and FIG. It is process drawing explaining the process of manufacturing the conventional vibration type differential pressure sensor. 1 ... Silicon substrate, 2 ... Pressure receiving diaphragm, 3 ...
Vibrating beam, 5 ... cavity, 6 ... cover, 7 ... internal space, 8 ... silicon substrate, 12 ... first epi layer, 13 ... vibrating beam, 14 ... second epi layer, 15 ... … 3rd epi layer, 16 …… 4th epi layer, 18 …… opening, 20 …… shell, 21 …… hollow part, 22, 30 …… substrate, 23 …… pressure receiving diaphragm, 24, 38
…… Fixed part, 25 …… Vibration beam, 26 …… Shell, 27,34,39
…… Compensation room, 29, 33 …… Base,

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takashi Kobayashi 2-932 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. (72) Tetsuya Watanabe 2-39 Nakamachi, Musashino City, Tokyo Yoko Inside the Kawa Denki Co., Ltd. (72) Inventor Nao Nishikawa 2-9-32 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Co., Ltd. (72) Takashi Yoshida 2-9-32 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Within the corporation

Claims (1)

[Claims] 1. A semiconductor substrate having a pressure receiving diaphragm which has a fixed portion on the periphery and is deformed by a differential pressure inside thereof, and a strain which is formed on the substrate and which occurs near the surface of the pressure receiving diaphragm due to the differential pressure is measured at least. A semiconductor substrate having at least one vibrating beam, a shell integrally formed on the substrate and covering the periphery of the vibrating beam, and a pressure guiding hole that is joined to the fixing portion and introduces one of the pressures forming the differential pressure. An oscillating differential pressure sensor, comprising: a base; and a compensation chamber provided on the fixed portion or on the base opposite to the fixed portion.