JPH11142269A - Semiconductor, pressure sensor and composite transmitter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly accurate pressure sensor with a protecting mechanism by utilizing a contact between a side face step area and a plate material as a mechanical stopper when an excessive pressure is applied. SOLUTION: When an excessive pressure is applied from a lower face of a diaphragm, the diaphragm is deformed. At this time, a diameter of a plate material 24 is set to be smaller than a maximum diameter of a surface area formed at a step part of a thick part supporting the diaphragm 21 and larger than a minimum diameter of the surface area formed at the step part of the thick part supporting the diaphragm 21. As a result, the plate material 24 hits a step area 20 of a side face, acting as a mechanical stopper. When an excessive pressure is applied from an upper face of the diaphragm, the plate material 24 comes in touch with a post material 28, whereby a mechanical stopper is formed. Since the mechanical stopper thus acts to the positive and the negative excessive pressures, this protecting mechanism realizes a highly accurate semiconductor pressure sensor with an excessive pressure-protecting mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor used for measuring pressure and the like in various plants and a composite transmitter using the same.

[0002]

2. Description of the Related Art It is widely known to construct a pressure sensor using a piezoresistor as a strain-sensitive gauge on a silicon diaphragm which is displaced under the pressure of an object to be measured. If excessive pressure is applied to the pressure sensor and exceeds the mechanical strength of silicon, the diaphragm will be broken and the pressure sensor will be broken. Therefore, it is necessary to provide some kind of protection mechanism in case of excessive pressure. In the transmitter,
In many cases, a protection mechanism is provided on the transmitter body in which the pressure sensor is incorporated so that excessive pressure is not applied to the pressure sensor.
However, providing a protection mechanism in the transmitter body not only increases the size of the transmitter itself, but also causes mechanical distortion caused by incorporating the protection mechanism to be the main cause of transmitter output drift and hysteresis. Adversely affect

Therefore, it is desirable to provide a protection mechanism against excessive pressure in the pressure sensor itself.

If a mechanical stopper is provided as an excessive pressure protection mechanism in the pressure sensor itself, the size of the transmitter can be reduced, and the output characteristics of the transmitter can be prevented from deteriorating.

[0005]

However, in the above prior art, a member acting as a mechanical stopper is often added to the inside of the diaphragm of the pressure sensor.
Therefore, if the attachment position between the sensor and the member is not accurately adhered as intended, a large variation occurs in the excessive pressure at which the member acts as a mechanical stopper.

It is an object of the present invention to provide an overpressure protection mechanism in which a mechanical stopper acts at a substantially constant prescribed overpressure. By using this protection mechanism, a stable semiconductor pressure sensor with an excessive pressure protection mechanism and a composite sensor can be realized.

[0007]

As a method for solving the above-mentioned problems, a step structure is provided on the side of the thick portion supporting the diaphragm on the side of the diaphragm, and a plate is attached to the tip of a rigid portion formed inside the diaphragm. To be attached. By utilizing the contact between the plate surface and the step surface area of the side surface of the diaphragm support as a mechanical stopper when a negative excessive pressure is applied, a protection mechanism against the negative excessive pressure is provided. Normally, when forming a diaphragm by hollowing out a single crystal silicon substrate from the back side, an alkali anisotropic etching technique is used, and the side of the thick portion supporting the diaphragm is wide on the back side opening side and narrow on the diaphragm forming side. Thus, it is formed in a tapered shape. By performing the alkali anisotropic etching in two steps, a step structure can be formed on the side surface. When an excessive pressure is applied from the back side of the single crystal silicon substrate, the plate material at the tip of the rigid portion formed inside the diaphragm hits the surface area of the step portion formed on the side of the thick portion supporting the diaphragm. By setting the diameter of, a mechanical stopper can be obtained.

[0008]

FIG. 1 is a top view showing a schematic structure of an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AOB of FIG. The substrate 51 is made of n-type (100) plane single crystal silicon, and the side surface step region 20 is formed in the differential pressure detecting diaphragm 21 by, for example, an alkali anisotropic etching technique.
It is formed by being used in stages. The shape of the side step region is octagon in FIGS. 1 and 2, but may be circular or another shape. At this time, the rigid portion 23 can be formed at the same time. Four static pressure detecting diaphragms 2 are provided outside the differential pressure detecting diaphragm 21.
2 are simultaneously formed by alkali anisotropic etching. A plate 24 made of, for example, Pyrex glass is formed at the tip of the rigid body 23.

The shape of the plate member 24 is circular in FIGS. 1 and 2, but may be any other shape.
25 is a base made of Pyrex glass, 27 is low-melting glass, 28 is a pressure inlet 29, for example, Fe-N
i is a post material. The diaphragms 21 and 22
Piezoresistors 31a to 31d and 32a to 32d for detecting stress when the diaphragm is deformed by receiving pressure
And a temperature sensor 33 are formed. 34 is a wiring of a p-type high concentration impurity layer, 35 is an aluminum wiring,
Reference numeral 12 denotes an aluminum contact pad.

FIGS. 3A to 3G are cross-sectional views showing the steps of manufacturing the semiconductor sensor of the above embodiment. Hereinafter, the manufacturing process will be described.

(A) First, boron is diffused on the upper surface of a diaphragm supporting substrate 51 made of n-type (100) plane single-crystal silicon to form a piezoresistor, p-type high-concentration impurity layer wiring, aluminum wiring, and contacts. Form pads.

(B) A SiO ₂ film 26 is deposited on the back side of the single crystal silicon substrate by, for example, CVD, and a pattern to be a mask at the time of alkali anisotropic etching is formed by photolithography and etching. At this time, photolithography and etching are performed twice to form the SiO ₂ film in two steps.

(C) Next, alkali anisotropic etching is performed using, for example, KOH.

(D) Thereafter, etching of SiO ₂ is performed. Of the two-stage SiO ₂ films formed earlier, the thinner one is eliminated and the thicker one is left.

(E) Next, alkali anisotropic etching with KOH is performed again to form the side surface step region 20, the diaphragms 21 and 22, and the rigid portion 23.

(F) Etch the SiO ₂ again to remove all the SiO ₂ film.

(G) Plate 2 made of Pyrex glass
4 by anodic bonding. Finally, a Pyrex glass table 25 is anodically bonded to the thick portion supported by the diaphragm, and a post material 28 made of Fe—Ni or the like is fixed via a low-melting glass 27. At this time, the diaphragm 21 to which the pressure inlet 29 is connected becomes a differential pressure detecting diaphragm, and the diaphragm 22 to which the pressure inlet 29 is not connected becomes a static pressure detecting diaphragm.

If the sum of the thickness of the rigid portion 23 and the thickness of the plate material 24 is substantially equal to or greater than the sum of the thickness of the thick film portion supporting the diaphragm and the thickness of the Pyrex glass table, FIG. By forming a hole 30 having a diameter E larger than the maximum diameter D of the plate member 24 on the surface of the post member 28 facing the plate member as shown in FIG. 5, the diaphragm displacement area when pressure is applied to the diaphragm. Can be secured.

If the sum of the thickness of the rigid portion 23 and the thickness of the plate member 24 is smaller than the sum of the thickness of the thick film portion supporting the diaphragm and the thickness of the Pyrex glass base, pressure is applied from the upper surface of the diaphragm. As long as the diaphragm displacement area when the voltage is applied can be sufficiently ensured, the surface of the post member facing the plate member can be made flat as shown in FIG. In each case, the hole diameter d of the pressure inlet is 24
Smaller than the maximum diameter D. 4 and 5, the plate member 24 and the post member 28 come into contact with each other when an excessive pressure is applied from the upper surface of the diaphragm, so that a mechanical stopper can be formed.

The p-type piezoresistors formed near the respective surfaces of the differential pressure detecting diaphragm 21 and the four static pressure detecting diaphragms 22 diffuse boron or the like and are most sensitive to stress <110. > Created in the direction.
The piezo resistance increases when a tensile stress acts in the longitudinal direction. Gauges arranged in this direction are called L gauges. When a tensile stress acts in the lateral direction, the resistance value decreases. Gauges arranged in this direction are called T gauges.

In the example shown in FIG. 1, the diaphragm 21 for detecting the differential pressure is used.
All four upper piezoresistors are arranged near the diaphragm support, and two L gauges 31a and 31c whose longitudinal direction is parallel to the radial direction of the diaphragm, and two L gauges whose longitudinal direction is parallel to the tangential direction of the diaphragm. T gauge 31b, 3
1d is arranged. L gauges 32a and 32c and T gauges 32b and 32d are arranged on the static pressure detecting diaphragm 22.

The method of arranging the piezoresistors is the same as that of FIG.
A method of arranging two gauges and two T gauges in the vicinity of the rigid body part, a method of arranging two L gauges in the vicinity of the diaphragm support part and two in the vicinity of the rigid body part, two T gauges in the vicinity of the diaphragm support part, There is a method of arranging two near the rigid body. The piezoresistors 31a to 31d and 32a to 32d constitute two sets of Wheatstone bridges as shown in FIG. Here, the differential pressure detecting diaphragms 21 and 31a-3
The portion composed of the 1d bridge is called a differential pressure sensor, and the portion composed of the static pressure detecting diaphragm 22 and the bridge of 32a to 32d is called a static pressure sensor.

When pressure is applied to the diaphragms, the respective diaphragms bend, and the bridges formed by the piezoresistors formed on the diaphragms output sensor outputs V ₁ and V _{2 which} are substantially proportional to the pressure difference between the upper and lower surfaces. Occurs.
Here, the differential pressure sensor measures the pressure difference (differential pressure) between the upper and lower surfaces of the diaphragm, while the static pressure sensor measures the pressure difference (static pressure) between the upper surface of the diaphragm and a sealed constant pressure portion. Will do.

On the other hand, the temperature sensor 33 integrated on the same substrate as the diaphragm is similarly formed by diffusing boron or the like, but is arranged in the <100> direction where there is almost no change in resistance to a change in stress. By doing so, sensitivity is given only to temperature. The temperature sensor 33 is connected to the piezoresistive bridge of the differential pressure sensor and the static pressure sensor as shown in FIG.

A p-type impurity diffusion layer 34 in which boron or the like is diffused at a higher concentration and an aluminum wiring 35 are used in combination between the arrangement of the piezoresistors and the wiring to the contact pads 1 to 12 of aluminum. In the present embodiment, aluminum wiring having a small resistance value is used in places where the influence of temperature hysteresis is relatively small, such as outside the diaphragm or in a place apart from the piezoresistor. A wiring method in which the wiring is a high-concentration impurity layer is also possible.

Next, the operation of the sensor when pressure is applied to the diaphragm will be described with reference to FIG. When a pressure difference occurs between the upper surface and the lower surface of the diaphragm, if the upper surface side has a higher pressure, the diaphragm is deformed as shown in FIG. When the diaphragm is deformed, the stress generated near the surface of the diaphragm where the piezoresistor is formed becomes as shown in FIG. 7B. On the diaphragm, a maximum tensile stress σ ₁ is generated near the diaphragm support portion, and a maximum compressive stress is generated near the rigid portion. As shown in FIG. 7A, when the outer diameter of the diaphragm is X, the outer diameter of the rigid portion is Y, and the thickness of the diaphragm is h, σ ₁ when the differential pressure ΔP is applied is expressed by the following equation. Is represented.

[0027]

Σ ₁ = 3 · (X ² −Y ² ) · ΔP / (16 · h ² ) As shown in FIG. 1, ^two L gauges and two T gauges are arranged in the vicinity of the support of the diaphragm. in this case, the output V ₁ of the differential pressure sensor is expressed by the following equation.

[0028]

[Number 2] _{V 1 = (1/2) · π} 44 · (1-ν) · σ 1 · V where, [nu is Poisson's ratio, the [pi ₄₄ piezoresistance coefficient of shear, V is the excitation voltage.

Next, the operation when an excessive pressure is applied from the lower surface of the diaphragm will be described. When an excessive pressure is applied from the lower surface side of the diaphragm, the diaphragm is deformed as shown in FIG. At this time, the diameter of the plate member 24 is smaller than the maximum diameter of the surface region formed in the step portion of the thick portion supporting the diaphragm 21 as shown in FIG. By making the diameter larger than the minimum diameter of the surface region formed in the portion, the plate material 24 hits the side surface step region 20 and the plate material 24 can function as a mechanical stopper.

Thereafter, the semiconductor pressure sensor is welded or bonded to an output take-out fitting (seal fitting) 75 as shown in FIG. 9, and the contact pads 1 to 12 of the sensor and the output take-out terminal 76 are connected by a lead wire 77. I do. This metal fitting has an airtight structure by a hermetic seal.

FIG. 10 shows an embodiment of a composite transmitter using the composite sensor of the present invention. The pressure sensor incorporated in the seal fitting is incorporated in the differential pressure transmitter pressure receiving section 81. The pressure applied to the high-pressure side seal diaphragm 82a and the low-pressure side seal diaphragm 82b is transmitted to the sensor chip 84 through a pressure transmission fluid 83 such as silicone oil. In a conventional differential pressure transmitter that does not have a mechanical stopper against excessive pressure on the sensor chip itself, it is necessary to take measures such as forming a center diaphragm that serves as a mechanical stopper in the transmitter body. Providing such a structure in the transmitter body not only complicates the manufacturing process, but also becomes a main cause of transmitter output drift and hysteresis.

In the pressure sensor of the present invention, since a mechanical stopper against both positive and negative overpressures can be formed in the pressure sensor itself, a special structure for protecting the sensor chip when an overpressure is applied is provided in the transmitter body. There is no need to provide them, the production becomes easy, and the output characteristics as a transmitter can be made more stable. The sensor output is transmitted to a signal processing unit through an FPC (flexible printed circuit) 85. In the case of the composite sensor of the present invention, three types of output signals of differential pressure, static pressure and temperature are selectively taken in via an MPX (multiplexer) 86.

Next, the output signal is amplified by a PGA (programmable gain amplifier) 87 and the A / D converter 88
To digital signal by MPU (microprocessor)
Send to 89. The MPU 89 corrects the sensor output based on the data of the ROM 90 in which the characteristics of the differential pressure, the static pressure, and the temperature sensor are stored, and calculates respective values of the differential pressure, the static pressure, and the temperature. The value thus obtained is again converted to an analog signal by the D / A converter 91, and a high-precision analog signal, digital signal or a signal in which analog and digital signals are superimposed is output via the V / I converter 92.

As described above, by using the structure of the present invention,
A mechanical stopper can be formed for both the specified positive and negative overpressures, and the pressure sensor itself can be provided with a mechanical stopper for both the positive and negative overpressures, simplifying the structure of the transmitter body. As a result, a highly accurate composite transmitter with stable output characteristics can be realized.

[0035]

The present invention provides a protection mechanism in which a mechanical stopper acts on prescribed positive and negative overpressures. By using this protection mechanism, a highly accurate semiconductor pressure sensor with an excessive pressure protection mechanism can be realized. In addition, since the pressure sensor itself can be provided with a mechanical stopper for both positive and negative excessive pressures, the structure of the transmitter body can be simplified, and a highly accurate composite transmitter with stable output characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view of a composite sensor showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view of the composite sensor of FIG.

FIG. 3 is a view showing a manufacturing process of the composite sensor of FIG. 2;

FIG. 4 is a view showing a shape of a post member provided with a hole having a diameter larger than that of a plate member.

FIG. 5 is a view showing a shape of a post material having no hole having a diameter larger than that of a plate material.

FIG. 6 is a connection diagram of a piezo resistor.

7A and 7B are a deformation diagram and a stress distribution diagram of a diaphragm when pressure is applied.

FIG. 8 is a modified view of the diaphragm when an excessive pressure is applied from the lower surface side of the diaphragm.

FIG. 9 is a diagram in which the pressure sensor of the present invention is incorporated in an output take-out fitting (seal fitting).

FIG. 10 is a configuration diagram of a composite transmitter using the pressure sensor of the present invention.

[Explanation of symbols]

1 to 12: aluminum contact pad for taking out the output of a composite sensor, 20: stepped side area, 21: diaphragm for detecting differential pressure, 22: diaphragm for detecting static pressure, 23: rigid body, 24: plate material, 25: Pyrex glass stand, 26 ...
Oxide film, 27 ... low melting point glass, 28 ... post material, 29 ...
Pressure inlets, 30: holes having a diameter larger than the maximum diameter of the plate material, 31a to 31d: piezoresistors on a diaphragm for detecting a differential pressure, 32a to 32d: piezoresistors on a diaphragm for detecting a static pressure, 33: for a temperature sensor Gauge, 34: p-type high concentration impurity layer wiring, 35: aluminum wiring, 51: n
Type single crystal silicon substrate, 75 ... hermetic seal, 7
6 ... Output extraction terminal, 77 ... Lead wire, 81 ...
Differential pressure transmitter pressure receiving section, 82a: high pressure side seal diaphragm, 82b: low pressure side seal diaphragm, 83: pressure transmitting fluid, 84: sensor chip, 85: flexible printed circuit, 86: multiplexer, 87: programmable gain amplifier, 88 A / D converter, 89 Microprocessor, 90 ROM, 91 D / A converter, 9
2. V / I converter.

Claims (12)

[Claims] 1. A single crystal silicon is cut out from the back side,
A diaphragm thin portion and a thick portion supporting the diaphragm are formed on the front surface side, a piezo resistor is arranged as a pressure receiving element on the diaphragm surface, and a rigid body having a thickness greater than the thin portion in a partial region of the diaphragm thin portion. In the semiconductor pressure sensor having a portion, a side surface on the diaphragm side of the thick portion supporting the diaphragm has a stepped structure, and a plate material is formed on a surface of the rigid portion opposite to the thin film portion side. Semiconductor pressure sensor. 2. The semiconductor pressure sensor according to claim 1, wherein the diaphragm is deformed between a surface region formed at a step portion of the thick portion supporting the diaphragm and a surface of the plate material opposed to the diaphragm. A semiconductor pressure sensor having a clearance in an initial state where no pressure is applied. 3. The semiconductor pressure sensor according to claim 1, wherein a shape of said diaphragm, a surface region formed in a step portion of a thick portion supporting said diaphragm, and a shape of said plate material are similar. A semiconductor pressure sensor, characterized in that: 4. A semiconductor pressure sensor according to claim 1, wherein a maximum diameter of said plate member is smaller than a maximum diameter of a surface region formed at a step portion of a thick portion supporting said diaphragm. Semiconductor pressure sensor. 5. A semiconductor pressure sensor according to claim 1, wherein a minimum diameter of said plate member is larger than a minimum diameter of a surface region formed at a step portion of a thick portion supporting said diaphragm. Semiconductor pressure sensor. 6. A semiconductor pressure sensor according to claim 1, wherein said thick portion supporting said diaphragm is fixed to a post member having a pressure inlet. A semiconductor pressure sensor which is formed to be larger than the maximum diameter of the plate on a surface facing the substrate and smaller than the maximum diameter of the plate on the opposite surface. 7. The semiconductor pressure sensor according to claim 1, wherein a thick portion supporting said diaphragm is fixed to a post member having a pressure inlet. The added plate thickness is smaller than the plate thickness of the thick portion supporting the diaphragm plus the plate thickness of the base supporting the thick portion, and the maximum diameter of the plate material is the pressure inlet of the post material. A semiconductor pressure sensor having a diameter larger than a hole diameter. 8. The semiconductor pressure sensor according to claim 1, wherein a temperature sensor is formed on the same substrate as the thin portion of the diaphragm. 9. A semiconductor pressure sensor according to claim 1, wherein a diaphragm is separately provided on the same substrate as the diaphragm thin portion, and a piezoresistor for detecting a static pressure is disposed thereon. A semiconductor pressure sensor forming a pressure sensor. 10. The output signal of the semiconductor pressure sensor according to claim 1, wherein the output of the static pressure detecting means is corrected by using a temperature detecting means, and the output of the differential pressure detecting means is corrected by the corrected static pressure output. A composite transmitter, wherein the correction is performed using temperature detecting means. 11. The signal processing means according to claim 10, wherein said signal processing means comprises a memory and a microprocessor, wherein said memory has a relation between a static pressure sensor output and a differential pressure sensor output with respect to a temperature change and a differential pressure sensor with respect to a static pressure change. A composite transmitter in which a relationship between outputs is recorded, and the detected sensor output is corrected based on data recorded in the memory using the microprocessor. 12. A first diaphragm, a first pressure receiving chamber filled with a first pressure transmitting fluid, a second diaphragm, and a second diaphragm.
A second pressure receiving chamber filled with a pressure transmitting fluid, wherein a first measured pressure is applied to the first diaphragm and a second measured pressure is applied to the second diaphragm, and a difference between the two pressures is detected by a semiconductor pressure sensor. 12. The composite transmitter according to claim 10, wherein the pressures in the first and second pressure receiving chambers are directly transmitted to the pressure receiving diaphragm of the semiconductor pressure sensor.