JPH01127929A - Vibration type differential pressure sensor - Google Patents

Abstract

PURPOSE:To decrease a static pressure error by fixing the other end of a supporting beam whose one end is fixed to a substrate, to one end of a vibrating beam and negating a distortion applied to the vibrating beam by static pressure by a distortion in the reverse direction generated in the supporting beam. CONSTITUTION:In the center of a cylindrical silicon substrate 22, a pressure receiving diaphragm 23 is formed, and as for a vibrating beam 27 and supporting beams 28, 29 for constituting a vibrating beam part 25, each one end thereof is fixed to the diaphragm 23, and a shell 26 holds the inside in a vacuum. According to such constitution, when static pressure Sp is applied to the diaphragm 23, a compressive strain is generated in the supporting beams 28, 29 and they are deformed, and the vibrating beam 27 is displaced to the right but generates no distortion. Subsequently, when pressure Sp+DELTAp is led in from a lead hole 33 and differential pressure DELTAp is applied, a tensile strain is applied to the supporting beams 28, 29 and they are displaced, a compressive strain is applied to the vibrating beam 27, and by a variation of a resonance frequency corresponding to the differential pressure DELTAp, the differential pressure DELTAp can be detected.

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 vibrating beam as a frequency signal, and in particular has improved static pressure characteristics. Regarding a vibrating differential pressure sensor.

<Prior art> The base of the improvement of the present invention is a type in which pressure or differential pressure can be detected from changes in the resonance frequency of a vibrating beam formed on a silicon pressure-receiving diaphragm, fixed at both ends, and excited by an excitation means. Well-known 1! An auxiliary pressure sensor is disclosed, for example, in Japanese Patent Application No. 59-42632 entitled "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.

The essential points of this vibrating differential pressure sensor will be explained with reference to FIGS. 7 and 8.

FIG. 7 is a diagram 'Am showing the configuration of this conventional vibrating differential pressure sensor with the cover removed, and FIG. 8 is a sectional view taken along the line X--X in FIG. 7 with the cover attached.

In these figures, 1 is a cylindrical silicon substrate, and 2 is a pressure-receiving part that is formed by digging the center of the silicon substrate 1 to form a thin part and receiving pressure Sp from the top surface and pressure (Sp+ΔP) from the bottom surface. 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.

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

Specifically, this vibration beam 3 is, for example, an n-type silicon base plate 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 top of this, and then a P+ type epitaxial layer is roughly formed. This is then protected with an oxide film St02. The hollow portion 5 at the bottom of the illumination beam 3 is formed by under-etching this n-type epitaxial layer.

The vibrating beam 3 formed in this way is, for example, the shape of the beam 8!
, if the thickness is 11 and the width is d, then ll-1O0a, h-1
The size is on the order of μm, 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 to cause oscillation in response to vibration #R3, which is the second P-type epitaxial layer,
The vibrating beam 3 causes self-oscillation at its natural frequency.

In this case, the internal space 7 of the cover 6 is evacuated and shaken.
Since the JJ beam 3 is held in a vacuum, the Q value, which indicates the sharpness of resonance, becomes large (which makes it easy to detect the resonance frequency).

As shown in FIG. 8, when the pressure difference 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. Therefore, there is a problem in that the pressure characteristics or temperature characteristics of the vibrating differential pressure sensor deteriorate, causing a decrease in accuracy.

Therefore, in order to solve this problem, the applicant
On July 2, 1983, the company filed Japanese Patent Application No. 166175/1982 entitled "Method of Manufacturing Vibrating Transducer". The outline of this proposal will be explained below.

FIG. 9 is a process diagram showing the manufacturing process of the detection section, which is the main part of the imaging type 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 numbered in FIG.

Figure 9(a) shows n which is the base for making the detection part D'.
A shaped silicon substrate 8 is shown.

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

Further, in the step shown in FIG. 9(c), the central portion of this oxidized yA9 is photoetched in a direction perpendicular to the plane of the paper to form a full 10.

In the step shown in FIG. 9(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 105 ooC.

Next, as shown in FIG. 9(E), 105
10"cm" in an atmosphere of hydrogen gas H2 at a temperature of 0'C
A first shrimp 1112 is formed by selectively epitaxializing 3'a degree boron (P type).

This fusuma, as shown in FIG.
A second shrimp II! 114, which will become the vibrating beam 13, is formed by selectively epitaxializing boron (P type) with a leakage of 0 cm-'.

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. For example, by adjusting the temperature of boron in the second shrimp layer 14, an initial tension can be given to the boron in the n-type silicon substrate 8 (covalent bond radius is 1.10 > m). Adjust the degree of silicon substrate root 8
The initial tension is given in consideration of the relative strain between the shrimp layer and the second shrimp layer 14.

Next, as shown in FIG.
A third layer 15 is formed by selectively epitaxially using boron (n-type) having a degree of Q"cm-".

Furthermore, as shown in FIG. 9(d), 1 liter was applied on top of the third shrimp layer 15 at a temperature of 105,000 ℃ in an atmosphere of hydrogen gas H2.
A fourth shrimp [16] is formed by selectively epitaxializing 81 degree phosphorus (n-type) of 017 cm''.

FIG. 9(S) shows the oxide film 9 of 8.02 after the selective epitaxy cell process shown in FIG. 9(H).
This figure shows an etching process for removing the first shrimp layer 12 and the third shrimp layer 15 in a state where the first shrimp layer 12 and the third shrimp layer 15 are removed by etching (step not shown).

In this etching step, although not shown, the entire n-type silicon substrate 8 is immersed in an alkaline solution.
A DC pulse voltage [17] is applied with a positive pulse voltage with a peak value of 5 mm and a repetition period of about 0.048 Z so that the fourth shrimp layer 16 has a positive potential with respect to the p-type second shrimp layer 14. is being applied. As a result of this voltage application, an insoluble film is formed on the surfaces of the n-type silicon substrate 8 and the fourth shrimp layer 16 to passivate them, so that the etching rate is lower than that of the first shrimp layer 12 and the third shrimp layer 15. Since it becomes much slower, the first shrimp layer 12 and the 31st shrimp layer 15 are removed by taking advantage of this. Furthermore, the second shrimp layer 14 is doped with boron I! When the etching rate is larger than 4×10+9, the etching speed is much slower than the normal speed for undoped silicon.Using the present material, the second layer 14 is left and the entire etching process is performed as shown in FIG. opening 18 in part
, and a gap is formed between the silicon substrate 8 and the second shrimp layer 14.

FIG. 9(R) does not show the thermal oxidation process. In this process,
Silicon substrate 8, second shrimp &! 14, and the entire inner and outer surfaces of the fourth shrimp layer 16 are coated with liquefied IBS (St 0
2>8a, 14a1 and 16a are formed.

FIG. 9(e) shows the plasma etching process. 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 shrimp layer 14 and the fourth epitaxial layer 116, the oxide films formed on the outer surfaces of the silicon substrate 8 and the fourth shrimp FPIJ 16 are exposed to plasma. It is removed by etching to prepare for selective epitaxial growth in the next step.

In the process shown in FIG. 9 (wa), the entire silicon substrate 8 and the fourth shrimp 11 are placed in an atmosphere of hydrogen H2 at a temperature of 105,000 ℃.
Selective eviaxial growth of n-type is avoided on the outer surface portion of 116. Through this selective epitaxial growth, an opening 18 is formed between the silicon substrate 8 and the fourth shrimp layer 16.
is buried to form a shell 20, and a detecting section of a vibrating differential pressure sensor having a vibrating beam 13 formed of a rod-shaped fourth shrimp layer inside is formed.

In the process shown in FIG. 9(W), selective epitaxial growth was performed in an atmosphere of hydrogen tl 2, so that the hollow chamber 21 formed between the silicon substrate 8 made of single crystal silicon and the shell 20 was is filled with hydrogen 1-12.

Therefore, as shown in Figure 9 (force), a vibrating differential pressure sensor with this detection part was placed in a vacuum atmosphere at 9000G, and this hydrogen H was passed between the silicon crystal lattices.
2 is degassed to create a vacuum. The degree of vacuum thus obtained is 1×10″″3 Orr or less.

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

Using such a vibrating differential pressure sensor, for example, 500K
Qf/cm'k: For example, at a high D pressure of 5p(7)W (10mm H20~10K Qf/Om
When measuring a minute differential pressure ΔP like in 2), 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. , due to this static pressure SP, the substrate, pressure receiving diaphragm, vibration i
ll beam contracts by ε5-8p l/Es. However, E
s is the volumetric compressibility,! is the length of the beam.

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

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 vibrating beam that measures the strain generated near the surface of the pressure-receiving diaphragm due to differential pressure; and a support beam having one end fixed to the substrate and the other end coupled at a predetermined angle to at least one end of the vibrating beam. A shell that is integrally formed on the substrate and covers the vibrating beam and the support beam, and a semiconductor base that is connected to the fixed part and has a pressure conducting hole that introduces one pressure that forms a differential pressure. It is.

Function: One end of the support beam is fixed to the substrate, and the other end of the support beam is fixed to at least one end of the vibration beam, so that the strain applied to the vibration beam due to static pressure is canceled out by the strain in the opposite direction generated in the support beam due to static pressure. .

Embodiments of the present invention will be described below based on the drawings. Fig. 1 is a perspective view showing one embodiment of the present invention excluding the shell, Fig. 2 is a sectional view showing the configuration of the X-x cross section with the shell attached, and Fig. 30 is a view of the vibrating beam in Fig. 1. FIG. 3 is an enlarged view showing the vicinity.

In these figures, 22 is a cylindrical silicon substrate, and 23 is a pressure-receiving diaphragm that is formed by digging the center of this substrate 22 to form a thin part and serving as a pressure-receiving part that receives static pressure SP s (Sr+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 a vibrating beam portion 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 same manufacturing method as explained in FIG. M9.

1! Details of the moving beam section 25 are shown in FIG. In this figure, 27 is a bar-shaped vibration beam with a rectangular cross section, one end 27a of which is integrally fixed to the pressure receiving diaphragm 23 of the substrate 22, and the other end 27t) is a rod-shaped support beam 28 with a rectangular cross section.
．． 29 is integrally fixed to each one end 28a129a. The support beams 28 and 29 are inclined at an angle α with respect to the imaging @27, and the other ends 28b and 29b are integrally fixed to the pressure receiving diaphragm 23 of the substrate 22. Furthermore, the vibration beam 2
There are spaces 30 and 31 on the sides of the support beams 28 and 29, and spaces 32 on the sides of the support beams 28 and 29. ! There is also an empty rMJ on the bottom of JJ@27
33<Fig. 2) are formed respectively.

Therefore, the vibrating beam 27 and the supporting beams 28, 29 are floating in space except that one end of each of them is fixed to the pressure receiving diaphragm 23.

A disk-shaped silicon base 34 having a pressure guiding hole 33 for introducing pressure (<Sp+ΔP) in the center is bonded to the bottom surface of the fixed part 24 by, for example, anodic bonding.

Next, the operation of the embodiment shown in FIGS. 1 and 2 constructed as above will be explained using the "Ij operation explanatory diagrams shown in FIGS. FIG. 5 shows the deformation of the oscillating beam section 25 when the pressure Sp is applied, and the deformation of the oscillating beam section 25 when the differential pressure ΔP is applied.

First, the operation when static pressure SF is applied will be explained using FIG. 4.

When the static pressure Sp is applied to the pressure receiving diaphragm 23, the vibration beam 27 and the support beam 28, which initially have a shape like a solid line,
．． 29, but for the swing vJ beam 27, εs =
A compressive strain of Sp 1+ /Es is generated in the support beam 28.29, and a compressive strain of εs ``''Sp 12/Es is generated in the support beam 28.29, so that the support '! 28.29 is α for the vibration beam 27
Since they are connected at an angle, the beams are deformed as shown by the dotted line, and the right end of the vibrating beam 27 is displaced to the right by Δχi.

Therefore, if the selection is made so that the relationship is Δχ Hibiki - εS,
Even if the static pressure Sp is applied to the pressure receiving diaphragm 23, no strain is applied to the swing IJI beam 27 as a result.

Next, the operation when a differential pressure ΔP is applied as a compressive stress σd in the direction of the vibrating beam will be described using FIG. 5.

When the differential pressure ΔP is not applied, the vibration beam 27 and the support beam 2
8 and 29 have shapes as shown by solid lines.

Next, when a compressive stress σd is applied in the longitudinal direction of the vibrating beam 27 due to the differential pressure ΔP, a compressive strain εd is applied to one end 27a of the vibrating beam 27 depending on its quality. The tensile strain εa′−12ν depends on its length.
εd/i'+ (Sh: Poisson's ratio) is added.

Due to the distortion of εd and εd', each end 28a, 29a of the support beam 29 is displaced by Δχ2.

If each beam is designed so that this Δχ2 becomes Δχ2 kiO, a compressive strain εd is applied to the vibrating beam 27, resulting in a change in the resonance frequency corresponding to the differential pressure ΔP, and thereby the differential pressure ΔP can be detected.

FIG. 6 is a longitudinal cross-sectional view showing the structure of a second embodiment of the vibrating beam section according to the present invention.

In this embodiment, the other end 27b of the swing vJ beam 27 shown in FIG.
One end 33a of the support beam 33 is fixed to one end 288N 29a of the support #R28, 29, and the other end 33b is fixed to the pressure receiving diaphragm 23 in order to prevent vertical displacement with respect to the surface of the paper. It is. Even with this configuration, it operates in the same way as the embodiment shown in FIG.

In each of the embodiments, one end of the swing beam 27 is connected to the substrate, and a support beam is provided only at the other end.
The present invention is not limited to this, and a structure in which support beams are provided at both ends of the vibrating beam can also operate in the same manner.

In addition, due to variations, these support beams 28.29.3
If the static pressure compensation according to 3 is insufficient,
A strain gauge may be formed on the upper surface or inside the fixing part 24 in FIGS. 1 and 2 by diffusion, or a 4 [vibration #J beam may be provided separately in the same way as the vibrating beam 27 and this may be used as a static pressure sensor. If the output is used to compensate for variations in static pressure compensation in the vibrating beam using a direct electrical path, more complete static pressure compensation can be achieved. Further, this static pressure sensor may be provided on the base 34 side.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, a support beam is provided at at least one end of the vibrating beam to generate tensile strain against static pressure, thereby reducing the static pressure. Since the compressive strain caused by this is compensated for, the static pressure error can be reduced.

[Brief Description of the 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 taken along the line XX in Fig. 1, and Fig. 3 is An enlarged view of the vibrating beam section in Fig. 4.
The figure is an explanatory diagram of the operation of the embodiment shown in Figures 1 and 2 when static pressure is applied, and Figure 5 is the operation diagram of the embodiment shown in Figures 1 and 2.
An operation explanatory diagram illustrating the operation of the embodiment shown in the figure when differential pressure is applied, FIG. 6 is a sectional view showing the configuration of the second embodiment of the vibrating beam section of the present invention, and FIG. 7 is a shell FIG. 8 is a sectional view taken along the line X-X in FIG. 7, and FIG. 9 is a conventional vibrating differential pressure sensor of the prior application. It is a process diagram explaining the process of manufacturing senna. 1... Silicon substrate, 2... Pressure receiving diaphragm, 3
... Swing beam, 5... Hollow part, 6... Cover, 7.
...Internal space, 8...Silicon substrate, 12...First
Shrimp layer, 13... Vibration beam, 14... Second shrimp layer, 1
5...Third shrimp layer, 16...Fourth shrimp layer, 18...
・Frontage part, 20... Shell, 21... Hollow chamber, 22
...Substrate, 23...Pressure diaphragm, 24...
Fixed part, 25... Vibration beam part, 26... Shell, 27
... Vibration beam, 28.29.33... Support beam. Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Detection section D S+) Ap Fig. 9

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 support beam having one end fixed to the substrate and the other end coupled at a predetermined angle to at least one end of the vibration beam; and a shell integrally formed with the substrate and surrounding the vibration beam and the support beam. A vibrating differential pressure sensor, characterized in that it has a semiconductor base having a pressure guiding hole which is connected to the fixed part and introduces one pressure forming the differential pressure.