JPH01127931A - Vibration type differential pressure sensor - Google Patents

Abstract

PURPOSE:To decrease a static pressure error by providing a compensating chamber in the vicinity of a vibrating beam, generating a tensile strain against static pressure, and compensating compressive strain caused by the static pressure. CONSTITUTION:In the center of a cylindrical silicon substrate 22, a pressure receiving diaphragm 23, a vibrating beam 25 and a shell 26 are formed, and on the bottom face of a fixed part 24, a compensating chamber 27 is formed. According to such constitution, when static pressure Sp is applied, the upper face of the fixed part of the upper part of the compensating chamber 27 is dented by the static pressure Sp, a deformation DELTAx is generated, the diaphragm 23 is deformed in a convex shape by the deformation DELTAx, and a tensile strain epsilonp is generated in the vibrating beam 25 provided in the vicinity of the surface of the diaphragm 23. On the other hand, in the vibrating beam 25, a compressive strain epsilons is generated by the static pressure Sp, therefore, when a size of the compensating chamber 27 is selected so as to obtain epsilonp=epsilons, a static pressure error can be suppressed small. When differential pressure DELTAp of the static pressure Sp, Sp+DELTAp is applied to the diaphragm 23, the vibrating beam 25 receives a tensile stress and the natural frequency is varied, and the differen tial pressure DELTAp can be known.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a vibrating differential pressure sensor that detects strain corresponding to the differential pressure of a semiconductor beam as a frequency signal.
In particular, it relates to a vibrating differential pressure sensor with improved static pressure characteristics.

<Prior art> The present invention is based on a method of detecting pressure or differential pressure from changes in the resonant frequency of a vibrating beam formed on a silicon pressure receiving diaphragm, fixed at both ends, and excited by an excitation means. A known vibrating turgor pressure sensor is disclosed, for example, in Japanese Patent Application No. 59-42632 [Pressure Sensor].

In this proposal, it is explained as a pressure sensor, but it can also be used as a differential pressure sensor, so in the following explanation, it will be explained as a differential pressure sensor.

An outline of this vibrating differential pressure sensor will be explained using FIGS. 6 and 7.

FIG. 6 is a perspective view showing the configuration of this conventional vibrating differential pressure sensor with the cover removed, and FIG. 7 is a sectional view taken along the line XX in FIG. 6 with the cover attached.

In these figures, 1 is a cylindrical silicon substrate, and 2 is a pressure-receiving part that receives pressure Sp from the top surface and pressure <Sp+ΔP from the bottom surface by digging in the center of the silicon substrate 1 to form a thin part. This is a pressure receiving diaphragm, and is made by etching the silicon substrate 1, for example. Here, ΔP
is the differential pressure to be measured.

3 is a vibration beam formed on the pressure receiving diaphragm 2 and fixed to the silicon substrate 1 at both ends;
is provided approximately at the center of the pressure receiving diaphragm 2.

Specifically, this vibration beam 3 includes, for example, an n-type silicon substrate 1
A first P-type epitaxial layer is formed on top, a cut is made in the center to electrically separate the left and right sides, an n-type epitaxial layer is formed on this layer, and then a P-type epitaxial layer is formed. This is then protected with an oxide film 5t02.

The cavity 5 at the bottom of the vibrating beam 3 is formed by under-etching this n-type epitaxial layer.

The vibrating beam 3 formed in this way has a certain length, for example!
, if the thickness is 11 and the width is d, l=100um, h=1
．． The size is on the order of czm, 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, and this internal space 7 is maintained in a vacuum state.

The vibrating beam 3, cover 6, cavity 5, internal space 7, etc. form a detection section of the vibrating differential pressure sensor.

In the above configuration, when an oscillation circuit is connected between the first left and right P+ type epitaxial layers for the vibration beam 3, which is the second P-type epitaxial layer, to cause oscillation, the vibration #J beam 3 causes self-oscillation at its natural frequency.

In this case, the internal space 7 of the cover 6 is made into a vacuum state and the vibration @3 is kept in vacuum, so Q
The value becomes thicker, making it easier to detect the mutual frequency.

As shown in FIG. 7, when a differential pressure ΔP between the pressure Sp and the pressure (Sp+ΔP) is applied to the pressure receiving diaphragm 2, the vibrating beam 3 receives tensile stress.

This tensile stress changes the natural frequency of the vibrating beam 3, allowing the differential pressure ΔP to be determined.

However, with such conventional vibrating differential pressure sensors,
A separately made silicone cover 6 is bonded to the top 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. As a result, there is a problem in that the pressure characteristics or temperature characteristics of the @dynamic differential pressure sensor deteriorate, causing a decrease in accuracy.

Therefore, in order to solve this problem, the applicant
On July 2, 1982, he filed Japanese Patent Application No. 166175/1982 titled ``Method for manufacturing a two-vibration transducer''. Below is the I'! of this proposal! Let me explain the main points.

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

This shows the process of the detection part D' shown in the axial cross section of the vibrating beam corresponding to the detection part shown in FIG. 7().

FIG. 8(a) shows an n-type silicon substrate 8 which will be the base for making the detection section D'.

Next, this silicon substrate 8 is thermally oxidized to form an oxide film (SL02) 9 on its surface (FIG. 8(b)).

Further, in the step shown in FIG. 8(c), the central portion of this oxide film 9 is photo-etched in a direction perpendicular to the plane of the paper to form a groove 10.

In the step shown in FIG. 8(d), grooves 11 are formed in the silicon substrate 8 through the grooves 10 by etching in an atmosphere containing hydrogen gas H2 and hydrochloric acid HC1 at a temperature of 1050'C.

Next, as shown in FIG. 8(E), 105
10”cm− in an atmosphere of hydrogen gas H2 at a temperature of 0.000
The first shrimp layer 12 is formed by selectively epitaxially using boron (P type) having a concentration of .

After this, as shown in FIG.
A second shrimp layer 14 that becomes the vibrating beam 13 is formed by selectively epitaxially epitaxially using boron (P type) having a concentration of Q"am-".

Even if the differential pressure ΔP is zero, the vibrating beam 13 will buckle due to the application of the differential pressure ΔP and become unmeasurable unless an initial tension is applied to it. Also, the covalent bond radius of silicon is 1.17 and that of boron is 0.88, so when boron is partially implanted into silicon, that part undergoes tensile strain, so this phenomenon occurs. For example, by adjusting the concentration of boron in the second epitaxial layer 14 using The adjustment is made so that the initial tension is given in consideration of the relative strain between the silicon substrate 8 and the second shrimp 14.

Next, as shown in FIG.
A third shrimp layer 15 is formed by selectively epitaxially epitaxially using boron (p-type) having a concentration of Q''cm-'.

Furthermore, as shown in FIG.
A fourth shrimp layer 16 is formed by selectively epitaxializing 1017 cm''3 of C degree phosphorus (n type).

FIG. 8(S) shows the state in which the oxide film 9 of 5102 is removed by etching with hydrogen fluoride HF (step not shown) after the selective epitaxial process shown in FIG. 8(H). It shows an etching process for removing the shrimp layer 12 and the third shrimp layer 15.

In this etching step, although not shown, the entire n-type silicon substrate 8 is immersed in an alkaline solution.
A positive pulse voltage with a peak value of 5V and a repetition period of about 0.048Z is applied from the DC pulse power supply 17 so that the fourth shrimp layer 16 has a positive potential with respect to the p-type second shrimp layer 14. ing. By applying this voltage, an insoluble film is formed on the surfaces of the n-type silicon substrate 8 and the fourth layer 16, and the etching rate is increased relative to the first layer 12 and the third layer 15. Since it becomes much slower, the first shrimp layer 12 and the third shrimp layer 15 are removed by taking advantage of this. Further, the second shrimp layer 14 is formed by leaving the second shrimp layer 14 by taking advantage of the phenomenon that when the concentration of doped boron is greater than 4×101 g, the etching rate is significantly slower than the normal speed for undoped silicon. As a whole, it is formed to have an opening 18 in a part and a gap between the silicon substrate 8 and the second shrimp layer 14, as shown in FIG.

FIG. 8(R) shows the thermal oxidation process. In this process,
Silicon substrate 8, second shrimp layer 14, and fourth shrimp layer 1
Oxide film (SiC2) 8a on the entire inner and outer surfaces of 6, respectively.
14a, and 16a! Let it form.

FIG. 8(e) shows the plasma etching process. In this step, the silicon substrate 8 and the second
Shrimp! 114, and the oxide films 8a, 14a, and 1 formed on the entire inner and outer surfaces of the fourth shrimp layer 16, respectively.
In 6a, the oxide film formed on the outer surfaces of the silicon substrate 8 and the fourth layer 16 is removed by plasma etching to prepare for selective epitaxial growth in the next step.

In the process shown in FIG. 8(W), the entire silicon substrate 8 and the fourth shrimp layer 16 are heated in an atmosphere of hydrogen H2 at a temperature of 10,500C.
N-type selective epitaxial growth is performed on the outer surface of the substrate. By this selective epitaxial growth, the silicon substrate 8
and the fourth shrimp layer 16 is filled to form a shell 2o, and the detecting part of the vibrating differential pressure sensor has a vibrating beam 13 formed of a rod-shaped fourth shrimp layer inside. is formed.

In the process shown in FIG. 8(W), selective epitaxial growth was performed in a valley atmosphere of hydrogen H2, so that the hollow chamber 21 formed between the silicon substrate 8 made of a silicon single crystal and the shell 20 was formed. contains hydrogen H2.

Therefore, as shown in Figure 8 (force), a vibrating differential pressure sensor with this detection part is placed in a vacuum atmosphere at 9000C, and the hydrogen H2 is passed through the silicon crystal lattice.
Degas to create a vacuum. The thus obtained vacuum tube was 1X10-3T.

It will be less than rr.

<Problems to be Solved by the Invention> As described above, in the #i dynamic differential pressure sensor according to the prior application, both the vibrating beam and the cover can be manufactured integrally with the silicon substrate. Although the drawbacks of the vibrating differential pressure sensor can be eliminated, it still has the following drawbacks.

Using such a vibrating differential pressure sensor, for example, 500
For example, under a high static pressure Sp as high as K CJ f/cm'(10mm820~10KOf/cm')
When measuring a minute differential pressure ΔP, static pressure SP is applied to one side of the pressure receiving diaphragm of the vibrating differential pressure sensor, and static pressure (Sp + ΔP) is applied to the other side. The static pressure SP causes the board, pressure receiving diaphragm, and vibration! F.J.J.
The beam contracts by ε5=spj'/Es. However, Es is the volumetric compressibility, and l is the length of the vibrating beam.

Therefore, a compressive strain of εS is applied to the vibrating beam, which causes vibration! A problem arises in that the resonant frequency of the IJI beam changes, causing static pressure errors.

Means for Solving the Problems> In order to solve the above problems, the present invention provides a semiconductor substrate having a fixed portion around the periphery and a pressure-receiving diaphragm that is deformed by differential pressure inside the substrate; At least one or more vibrating beams that are formed to measure the strain generated near the surface of the pressure receiving diaphragm due to the differential pressure, a shell that is integrally formed with the substrate and that maintains the periphery of the vibrating beams in a vacuum state, and a shell that is joined to the fixed part. It has a semiconductor base having a pressure guide hole for introducing one pressure forming the differential pressure, and a compensation chamber provided in the fixed part or the base facing the fixed part.

Effect: By forming a compensation chamber with a space in the fixed part of the board or the base opposite to this fixed part, the static pressure applied from the surroundings will cause this compensation room to be depressed and formed in the board. A tensile stress is generated in the vibrating beam, and compressive strain due to static pressure is applied.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a perspective view showing one embodiment of the present invention without a shell, and FIG. 2 is a cross-sectional view showing the structure of the X-X cross section with the shell attached.

In these figures, 22 is a cylindrical silicon substrate, and 23 is a pressure receiving part and a pressure receiving diaphragm which is formed by digging the center of this substrate 22 to form a thin part to receive static pressure Sp N <Sp+ΔP). , made by etching silicone, for example, and surrounded by a thick-walled fixing part 24 in an annular shape.
It is said that

Reference numeral 25 is an e-beam for detecting strain due to differential pressure, and reference numeral 26 is a shell for maintaining the inside in a vacuum, and these are manufactured by the manufacturing method explained in FIG. 8.

A compensation chamber 27, which is an annular recess, is formed on the annular bottom surface of the fixing portion 24 by, for example, etching.

The bottom surface of the fixed part 24 except for the compensation chamber 27 has a pressure (Sp
A disk-shaped silicon base 29 having a pressure guiding hole 28 for introducing +ΔP) is bonded by, for example, anodic bonding. If this bonding is performed in a vacuum state, the compensation chamber 2
The inside of the compensation chamber 27 becomes a vacuum, and if they are bonded 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 constructed as above will be explained using the operation explanatory diagram shown in FIG. 3.

The operation when the differential pressure ΔP is applied is exactly the same as the conventional one, so in the following explanation, the operation when the static pressure SP is applied will be explained.

The outer periphery of the substrate 22 and the base 29 and the pressure receiving diaphragm 23
Even if static pressure SP is applied to the front and back sides of the compensating chamber 27, the static pressure Sp will not be applied because the compensation chamber 27 is sealed.

Therefore, the upper surface of the fixing portion 24 above the compensation chamber 27 is depressed by the static pressure Sp, and is deformed by ΔX.

Due to this deformation Δχ, the pressure receiving diaphragm 23 is deformed into a convex shape, and a tensile strain εP is generated in the vibrating beam 25 provided near the surface of the pressure receiving diaphragm 23.

On the other hand, due to the static pressure Sp in the vibrating beam 25, ε5=Spl/E
A compressive strain of s has occurred.

Therefore, by selecting the size of the compensation chamber 27 so that εP=εS, the static pressure error can be kept small.

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

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

A disk-shaped substrate 30 has a swinging beam 25 and a shell 26 formed at its center in the same manner as shown in FIG.

The center portion of the substrate 30 functions as a pressure receiving diaphragm 31, and the surrounding area functions as a fixing portion 32.

The fixing part 32 of the substrate 30 is joined to a silicon base 33, and on the surface of the base 33 facing the fixing part 32, four annular parts are formed to form a compensation chamber 34. Further, a pressure guiding hole 35 passes through the center of the base 33, and a recess 36 is formed in the vicinity of the upper surface of the base 33, facing and spaced apart from the pressure receiving diaphragm 31.

The above configuration also operates in the same way as the embodiment shown in FIG.

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 swing a@25 and a shell 2 in its center.
6 is formed in the same manner as in FIG.
The fixed part 3 is located near the pressure receiving diaphragm 23 formed at 7.
A compensation chamber 39 is provided inside the substrate 37 on the 8 side by sealing by selective etching, epitaxial growth, or the like.

This configuration also operates in the same way as the embodiment shown in FIG.

In addition, due to variations, these compensation chambers 27.34.3
If the static pressure compensation according to 9 is insufficient,
A strain gauge may be formed on the upper surface or inside of the fixed part 24, 32, 39 in FIGS. 1 and 2 by diffusion, or a separate vibrating beam similar to the vibrating beam 25 may be provided and used as a static pressure sensor. If the output is used to compensate for variations in static pressure compensation in the compensation chamber using an electric circuit, more complete static pressure compensation can be achieved. Moreover, this static pressure sensor may be provided on the base 29.33 side.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, a compensation chamber is provided near the vibrating beam to generate tensile strain against static pressure, thereby reducing compression due to static pressure. Since the distortion is compensated for, the static pressure error can be reduced.

[Brief explanation of the drawing]

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 taken along the line X-X in Fig. 1, and Fig. 3 is a diagram showing Figs. 1 and 2. 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 vibrating differential pressure sensor excluding the shell, FIG. 7 is a cross-sectional view taken along the line X-X in FIG. 6, and FIG. FIG. 2 is a process diagram illustrating a process of manufacturing a conventional vibrating differential pressure sensor (1). 1... Silicon substrate, 2... Pressure receiving diaphragm, 3
... Vibration beam, 5... Cavity, 6... Cover, 7.
...Internal space, 8...Silicon substrate, 12...First
Shrimp layer, 13... Shaking beam, 14... Second shrimp layer, 1
5...Third shrimp layer, 16...Fourth shrimp layer, 18...
- Opening, 20... Shell, 21... Hollow chamber, 22
．． 30... Substrate, 23... Pressure receiving diaphragm, 24
．． 38... Fixed part, 25... Vibration beam, 26... Shell, 27.34.39... Compensation chamber, 29.33...
・Base, 4I21 Fig. 5 Fig. 6 Fig. 7 Detection section o Sp Δp ゝ-I ゝ-' ~
I-ichino ・
N-・(NU) Etching binding (force) H2 gas degassing 8 Figure 7M-

Claims (1)

[Claims] A semiconductor substrate having a fixed part around it and a pressure receiving diaphragm deformed by differential pressure inside the semiconductor substrate, and at least one or more vibrations formed on this substrate to measure the strain generated near the surface of the pressure receiving diaphragm due to the differential pressure. a beam, a shell that is integrally formed on the substrate and covers the periphery of the vibrating beam, a semiconductor base that is joined to the fixed part and has a pressure guiding hole that introduces one pressure forming the differential pressure, and the fixed part. A vibrating differential pressure sensor characterized in that it has a compensation chamber provided in the base or the base facing the fixed part.