JP2001004470A - Semiconductor pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a diaphragm from an excessive pressure and to prevent the transfer of residual distortion by increasing the maximum diameter of a rigid body larger than the minimum diameter of a diaphragm support. SOLUTION: A silicon substrate 52 for composing a semiconductor substrate along with a silicon substrate 51 is sealed to a post 55 with a pressure introduction port 34 via a spacer 54 for integration. Then, a diaphragm 31 (32) for detecting a differential pressure (static pressure) is formed at a gap 35 (36) that is connected to (not connected to) the pressure introduction port 34, and a tapered rigid body 33 toward the side of the diaphragm 31 is formed at the partial region of the diaphragm 31. In this case, the diameter of the maximum diameter part (lower end part) of the rigid part 33 is increased as compared with the diameter of the minimum diameter part (upper end part) of the tapered hollowed part, namely the minimum diameter part of a diaphragm support. As a result, when excessive pressure is applied from the lower surface side of the diaphragm, the side wall of the rigid body hits against the side wall of the diaphragm support as a stopper. Also, when the pressure is applied from the side of the upper surface, the lower surface of the rigid body 33 hits against the upper surface of a post 55 as a stopper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor pressure sensor,
In particular, the present invention relates to a semiconductor pressure sensor suitable for use in measuring pressure, flow rate, and the like in various plants.

[0002]

2. Description of the Related Art It is well known that a piezoresistor is disposed as a strain-sensitive gauge on a silicon diaphragm which is displaced by receiving a pressure of an object to be measured to constitute a pressure sensor. If excessive pressure is applied to this pressure sensor and it exceeds the mechanical strength of silicon, the diaphragm will be damaged and the pressure sensor will be broken, so it is necessary to provide some protection mechanism in case of excessive pressure . In a transmitter in which a pressure sensor is incorporated, a protection mechanism is often provided on the transmitter body so as not to apply excessive pressure 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 a main cause of transmitter output drift and hysteresis. Affects properties. Therefore, it is desirable to provide a protection mechanism against excessive pressure in the pressure sensor itself.

Japanese Patent Application Laid-Open No. Hei 10-132682 discloses a pressure sensor in which a rigid body is provided in a diaphragm in order to improve the linearity of output. In a pressure sensor, a plate member is attached to the tip of the rigid body to form a stopper against excessive pressure. Is described. Thus, by providing the pressure sensor itself with the excessive pressure protection mechanism, the size of the transmitter can be reduced, and the output characteristics of the transmitter can be stabilized.

[0004]

However, in such an example, since a plate made of a material different from silicon is adhered to the rigid portion formed in the diaphragm, residual strain occurs and the diaphragm is deformed. There is a problem that the output signal offset of the pressure sensor at the time of no load increases.

It is an object of the present invention to provide a semiconductor pressure sensor that protects a diaphragm against excessive pressure and prevents transmission of residual strain to the diaphragm.

[0006]

The semiconductor pressure sensor of the present invention is characterized in that it has a diaphragm and its support, a rigid body is formed in a partial region of the diaphragm, and a piezoresistor is arranged on the surface of the diaphragm. In a semiconductor pressure sensor, the maximum diameter of the rigid body is larger than the minimum diameter of the diaphragm support.

[0007]

FIG. 1 is a schematic top view of a semiconductor pressure sensor showing a first embodiment of the present invention, and FIG.
It is OB sectional drawing. The first silicon substrate 51 and the second silicon substrate 52 which are semiconductor substrates are n-type (10
0) Planar single crystal silicon, and these silicon substrates are arranged with a silicon oxide film layer 53 therebetween.
The second silicon substrate 52 is hollowed out from the rear surface side to the region of the silicon oxide film layer 53 except for the region of the rigid portion 33 at the center. The hollow is symmetric with respect to the central axis of the sensor chip and the first silicon substrate 5
Taper towards 1. In the silicon oxide film layer 53, voids 35 and 36 having a shape similar to the hollow pattern of the second silicon substrate 52 are formed.
The second silicon substrate 52 has a pressure introduction port 34 through a spacer 54 made of low melting point glass.
It is fixed to and integrated with a post 55 made of Ni. Thus, the differential pressure detection diaphragm 31 is provided on the gap 35 communicating with the pressure introduction port 34, and the static pressure detection diaphragm 32 is provided on the gap 36 not communicating with the pressure introduction port 34.
However, in the partial region of the differential pressure diaphragm 31, a rigid portion 33 having a circular, elliptical or polygonal cross section is formed. The rigid body portion 33 tapers toward the diaphragm 31 as in the case of the tapered hollow portion of the second silicon substrate 52. That is, there is a gap between the side wall of the rigid portion 33 and the side wall of the diaphragm support portion, and both side walls are substantially parallel to each other. In addition, the rigid body 3
The diameter of the maximum diameter portion (lower end portion) of 3 is larger than the diameter of the minimum diameter portion (upper end portion) of the tapered hollow portion, in other words, the diameter of the minimum diameter portion of the diaphragm support portion.

The differential pressure detecting p-type piezoresistors 21a to 21d for detecting the stress when the diaphragm is deformed by receiving the differential pressure on the differential pressure diaphragm 31, and receiving the static pressure on the static pressure diaphragm 32. Pressure detecting p-type piezoresistors 22a-22 for detecting stress when the diaphragm is deformed
d is formed. Further, on the same substrate as the first silicon substrate 51, a piezoresistor 23 for temperature detection is formed at a place that is not a diaphragm region. 25 is p
A high-concentration impurity layer wiring, 26 an aluminum wiring,
Reference numerals 1 to 12 are aluminum contact pads.

The p-type piezoresistors formed near the respective surfaces of the differential pressure detecting diaphragm 31 and the four static pressure detecting diaphragms 32 diffuse boron and are most sensitive to stress <110>. Made 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 of FIG. 1, all four piezoresistors on the differential pressure detecting diaphragm 31 are arranged in the vicinity of the diaphragm support, and two L gauges 21a and 21c whose longitudinal direction is parallel to the radial direction of the diaphragm. Two T gauges 21b and 21d that are parallel to the tangential direction of the diaphragm are arranged. The L gauge 22 is provided on the static pressure detecting diaphragm 32.
a, 22c and T gauges 22b, 22d.
The method of arranging the piezoresistors is, in addition to the example shown in FIG. 1, a method of arranging two L gauges and two T gauges all near the rigid part, two L gauges near the diaphragm support part and two L gauges near the rigid part.
There is a method of arranging two T gauges in the vicinity of the diaphragm support and two in the vicinity of the rigid body.

[0010] Piezoresistors 21a to 21d, 22a to 22
d constitutes two sets of Wheatstone bridges as shown in FIG. Here, the differential pressure detecting diaphragms 31 and 21
a part composed of bridges a to 21d is a differential pressure sensor,
The portion composed of the static pressure detecting diaphragm 32 and the bridge of 22a to 22d is called a static pressure sensor.

When pressure is applied to the diaphragms, the respective diaphragms bend, and the respective bridges formed by the piezoresistors formed on the diaphragm generate sensor outputs V1, V2 substantially proportional to the pressure difference between the upper surface and the lower surface. I do. 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 piezoresistor 23 for temperature detection, which is integrated on the same substrate as the diaphragm, is also formed by diffusing boron, but shows almost no resistance change with respect to stress change <100>. By arranging in the direction,
Make it sensitive only to temperature. A portion composed of the piezoresistor 23 is called a temperature sensor, and is connected to a piezoresistive bridge of a differential pressure sensor and a static pressure sensor as shown in FIG.

For the wiring between the piezoresistors and to the aluminum contact pads 1 to 12, a p-type high-concentration impurity diffusion layer wiring 25 in which boron is diffused at a higher concentration and an aluminum wiring 26 are used in combination. 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. On the diaphragm, a maximum tensile stress σ1 is generated near the diaphragm supporting portion, and a maximum compressive stress is generated near the rigid portion. As shown in FIG. 4A, assuming that 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, when the differential pressure ΔP is applied, σ1 is expressed by the following equation. Is done.

Σ1 = 3 (X2−Y2) ΔP / (16h2) (1) As shown in FIG. 1, when two L gauges and two T gauges are respectively arranged near the support portion of the diaphragm, the differential pressure The output V1 of the sensor is represented by the following equation.

V1 = (１ ／) · π44 (1-ν) σ1 · V (2) where ν is a Poisson's ratio, π44 is a shear piezoresistance coefficient, and V is an excitation voltage.

Next, the operation when an excessive pressure is applied to the diaphragm will be described. When an excessive pressure is applied from the upper surface side of the diaphragm, the diaphragm is deformed as shown in FIG. At this time, since the diameter of the pressure introducing port 34 formed in the post is smaller than the minimum diameter of the surface of the rigid portion facing the post, the surface 39 of the rigid portion facing the post faces the surface of the post facing the rigid portion. 40, and serves as a stopper against excessive pressure. When an excessive pressure is applied from the lower surface side of the diaphragm, the diaphragm is deformed as shown in FIG. In this case, since the maximum diameter of the rigid portion is larger than the minimum diameter of the diaphragm support portion, the rigid portion side wall 41 hits the diaphragm support portion side wall 42 and serves as a stopper against excessive pressure.

When detecting a small differential pressure, it is necessary to make the diaphragm thin to increase the sensitivity. At this time, as shown in FIGS. 7 and 8, the region 38 excluding the region 37 where the gauge on the thinned diaphragm is disposed is formed thin by dry etching or the like, so that the output linearity can be improved. FIG. 7 and FIG. 8 show processing examples of the arrangement of the piezoresistors shown in FIG.
When two gauges and two T gauges are all disposed near the rigid body portion, when two L gauges are disposed near the diaphragm support portion and two L gauges are disposed near the rigid body portion, two T gauges are disposed near the diaphragm support portion. The same processing can be performed when two pieces are arranged near the rigid portion.

FIGS. 9A to 9C and FIGS.
(F) is a sectional view showing a manufacturing step of the semiconductor pressure sensor of the first example. Hereinafter, the manufacturing process will be described.

(A) First, a SOI in which a first silicon substrate 51 and a second silicon substrate 52 made of n-type (100) plane single crystal silicon are arranged via a silicon oxide film layer 53 is provided.
By diffusing boron on the first silicon substrate 51 of an I (Silicon On Insulator) wafer,
A piezo resistance, a wiring of a p-type high concentration impurity layer, a wiring of aluminum, and a contact pad are formed.

(B) On the second silicon substrate side of the SOI wafer, a silicon nitride film 61 and a silicon oxide film 62 are formed by, for example, CVD, and an etching pattern is formed.

(C) A resist 63 is applied to the pattern which is not desired to be etched, and is protected by patterning.
The wafer is tilted and DR
IE (Deep-Reactive Ion Etchi
(ng) dry etching of silicon. DRI
E has a high etching selectivity of silicon to the silicon oxide film, and can stop the etching at the silicon oxide film surface.

(D) The resist is removed, a resist 63 is applied to a pattern that is not desired to be etched again, and is protected by patterning.
Is dry-etched by DRIE from the silicon substrate 52 side.

(E) The resist is removed, and the silicon oxide film layer is isotropically etched with HF. The silicon oxide film 62 serving as an etching mask also disappears in this process, but the silicon nitride film 61 subsequently serves as an etching mask.

(F) The silicon nitride film 61 is removed, and a post 55 made of Fe—Ni is fixed via a spacer 54 made of low-melting glass.

FIG. 11 is a schematic top view of a semiconductor sensor showing a second embodiment according to the present invention, and FIG. 12 is a sectional view taken along the line AOB of FIG. When an excessive pressure is applied from the lower surface side of the diaphragm, the diaphragm is deformed as shown in FIG.
In this case, the rigid portion side wall end 43 hits the diaphragm support portion side wall 42 and serves as a stopper against excessive pressure. As described above, the rigid part side wall 41 and the diaphragm support part side wall 42
The gap between the silicon oxide film layer and the silicon oxide film layer does not need to be formed by isotropic etching as shown in FIGS.

FIGS. 14A to 14D and FIG. 15E
FIGS. 13A to 13G are cross-sectional views illustrating manufacturing steps of the pressure sensor illustrated in FIGS. Hereinafter, the manufacturing process will be described.

(A) First, a first silicon substrate 51 and a second silicon substrate 52 made of n-type (100) plane single-crystal silicon are disposed with a silicon oxide film layer 53 interposed therebetween.
Boron is diffused on the first silicon substrate 51 of the OI wafer to form a piezoresistor, a p-type high-concentration impurity layer wiring, an aluminum wiring, and a contact pad.

(B) A silicon oxide film 62 is formed on the second silicon substrate side of the SOI wafer by, for example, CVD, and an etching pattern is formed.

(C) A resist 63 is applied to a pattern not to be etched, and is protected by patterning.
The wafer is tilted and DR
The silicon is dry-etched by IE.

(D) DR is changed again by changing the inclination of the wafer.
The silicon is dry-etched by IE.

(E) The resist is removed, a resist 63 is applied to a pattern that is not desired to be etched again, and is protected by patterning.
Is dry-etched by DRIE from the silicon substrate 52 side.

(F) DR is changed again by changing the inclination of the wafer.
The silicon is dry-etched by IE.

(G) The resist 63 and the silicon oxide film 62 are removed, and a post 55 made of Fe—Ni is fixed via a spacer 54 made of low-melting glass.

FIG. 16 shows an oblique DIR according to the present invention.
FIG. 17 is a schematic top view of a semiconductor pressure sensor showing a third embodiment not using E, and FIG. 17 is a sectional view taken along the line AOB of FIG.

In the case of such a structure, when an excessive pressure is applied from the lower surface of the diaphragm, the diaphragm facing surface 44 of the rigid portion comes into contact with the lower surface region 45 of the diaphragm supporting portion, thereby serving as a mechanical stopper.

FIGS. 18 (a) to 18 (d) and FIG. 19 (e)
FIGS. 18A to 18G are cross-sectional views illustrating a manufacturing process of the semiconductor pressure sensor illustrated in FIGS. Hereinafter, the manufacturing process will be described.

(A) First, an SO in which a first silicon substrate 51 and a second silicon substrate 52 made of n-type (100) plane single-crystal silicon are arranged via a silicon oxide film layer 53 is provided.
A partial region of the first silicon substrate 51 and the silicon oxide film layer 53 of the I wafer is processed by, for example, dry etching.

(B) Next, polysilicon is deposited and polished to flatten the surface.

(C) Boron is diffused on the first silicon substrate 51 to form a piezoresistor, a wiring of a p-type high concentration impurity layer, a wiring of aluminum, and a contact pad.

(D) On the second silicon substrate side, for example, C
A silicon nitride film 61 is formed by VD, and an etching pattern is formed.

(E) The first step is performed by alkali anisotropic etching.
Etch the 2 silicon substrate.

(F) Isotropically etching the silicon oxide film layer with HF.

(G) The silicon nitride film 61 is removed, and the post 5 made of Fe—Ni is fixed via the spacer 54 made of low melting point glass.

As described above, according to the embodiment of the present invention,
A stopper for both positive and negative overpressures can be formed. If the pressure sensor itself can be provided with a mechanical stopper for both positive and negative excessive pressures, the structure of the transmitter body on which it is mounted can be simplified, and a highly accurate pressure transmitter with stable output characteristics can be realized. Further, since no residual strain is transmitted to the diaphragm, the output signal offset of the pressure sensor during no load is suppressed.

[0046]

According to the present invention, there is provided a semiconductor pressure sensor capable of protecting the diaphragm against excessive pressure and preventing transmission of residual strain to the diaphragm.

[Brief description of the drawings]

FIG. 1 is a schematic top view of a semiconductor pressure sensor showing a first embodiment according to the present invention.

FIG. 2 is a schematic sectional view taken along the line AOB of FIG. 1;

FIG. 3 is a connection diagram of a piezo resistor.

FIG. 4 is a diagram showing deformation and stress distribution of a diaphragm when pressure is applied.

FIG. 5 is a diagram showing deformation of the diaphragm when an excessive pressure is applied from the upper surface side of the diaphragm.

FIG. 6 is a diagram showing deformation of the diaphragm when an excessive pressure is applied from the lower surface side of the diaphragm in the first embodiment.

FIG. 7 is a schematic top view of a semiconductor pressure sensor for measuring a small differential pressure, showing a modification of the embodiment of FIG. 1;

FIG. 8 is a schematic cross-sectional view along the line AOB of FIG. 7;

FIG. 9 is a diagram showing the first half of the manufacturing process of the first embodiment.

FIG. 10 is a diagram showing the latter half of the manufacturing process of the first embodiment.

FIG. 11 is a schematic top view of a semiconductor pressure sensor showing a second embodiment according to the present invention.

FIG. 12 is a schematic sectional view taken along the line AOB of FIG. 12;

FIG. 13 is a view showing deformation of the diaphragm when an excessive pressure is applied from the lower surface of the diaphragm in the second embodiment.

FIG. 14 is a diagram showing the first half of the manufacturing process of the second embodiment.

FIG. 15 is a diagram showing the latter half of the manufacturing process according to the second embodiment.

FIG. 16 is a schematic top view of a semiconductor pressure sensor showing a third embodiment according to the present invention.

FIG. 17 is a schematic sectional view taken along the line AOB of FIG. 16;

FIG. 18 is a diagram showing the first half of the manufacturing process of the third embodiment.

FIG. 19 is a diagram showing the latter half of the manufacturing process according to the third embodiment.

[Explanation of symbols]

21a to 21d: piezoresistors for detecting differential pressure, 22a to 22
d: piezoresistor for detecting static pressure, 23: piezoresistor for detecting temperature, 25: P-type high-concentration impurity layer wiring, 26: aluminum wiring, 31: diaphragm for detecting differential pressure, 32: diaphragm for detecting static pressure, 33: Rigid part, 34: pressure inlet,
35: a gap leading to the pressure inlet, 36: a gap leading to the pressure inlet, 37: a piezoresistor arrangement area on the diaphragm, 38: an area where the piezoresistor on the diaphragm is not arranged, 39: a post opposing the rigid body part Surface: 40: Rigid portion facing surface of post, 41: Rigid portion side wall, 42: Diaphragm support portion side wall, 43: Rigid portion side wall end, 44: Rigid portion diaphragm opposing surface, 45: Lower surface region of diaphragm support portion, 51: first silicon substrate, 52: second silicon substrate, 53: silicon oxide film layer, 54: spacer made of low melting point glass, 55: post, 61: silicon nitride film, 62: silicon oxide film, 63: Resist.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koji Shimizu 882, Omo, Ichihiro-shi, Hitachinaka-shi, Ibaraki F-term (Reference) 2F055 AA40 BB20 CC02 DD05 EE14 FF21 FF23 GG15 4M112 AA01 BA01 CA22 CA25 CA35 CA36 DA03 DA04 DA12 EA03 FA07 FA09

Claims (12)

[Claims] In a semiconductor pressure sensor having a diaphragm and a supporting portion thereof, wherein a rigid portion is formed in a partial area of the diaphragm, and a piezoresistor is disposed on a surface of the diaphragm, a diameter of the diaphragm supporting portion is smaller than a minimum diameter of the diaphragm supporting portion. A semiconductor pressure sensor, wherein a maximum diameter of the rigid portion is large. 2. The semiconductor pressure sensor according to claim 1, wherein said rigid portion is tapered toward said diaphragm. 3. The semiconductor pressure sensor according to claim 2, wherein a gap between a side wall of said rigid portion and a side wall of said diaphragm support portion gradually increases toward said diaphragm. Semiconductor pressure sensor. 4. The semiconductor pressure sensor according to claim 2, wherein a side wall of said support portion and a side wall of said rigid body portion are substantially parallel to each other. 5. A semiconductor pressure sensor according to claim 1, wherein said rigid portion has a polygonal, elliptical or circular cross section. 6. The semiconductor pressure sensor according to claim 1, wherein a region of said diaphragm other than said piezoresistive region is formed thinner than a thickness of said piezoresistive region. Semiconductor pressure sensor. 7. The semiconductor pressure sensor according to claim 1, wherein said diaphragm supporting portion includes a semiconductor substrate, and a diaphragm for a static pressure detecting element is provided on said semiconductor substrate. A semiconductor pressure sensor having a piezoresistor as a static pressure detection element formed on a detection element diaphragm. 8. A semiconductor pressure sensor according to claim 7, wherein a piezoresistor as a temperature detecting element is formed on said semiconductor substrate. 9. The semiconductor pressure sensor according to claim 1, further comprising a post having a pressure inlet integrated with said support, said rigid portion and said rigid portion of said post. A semiconductor pressure sensor having a predetermined gap between the diaphragm and a surface facing the pressure sensor in an initial state in which the diaphragm is not deformed. 10. The semiconductor pressure sensor according to claim 9, wherein the size of the pressure inlet of the post is smaller than the size of a surface of the rigid portion facing the post. . 11. The semiconductor pressure sensor according to claim 9, wherein said diaphragm supporting portion includes a semiconductor substrate, and a diaphragm for a static pressure detecting element is provided on said semiconductor substrate. A semiconductor pressure sensor wherein a piezoresistor as a static pressure detecting element is formed on a diaphragm. 12. A semiconductor pressure sensor according to claim 11, wherein a piezoresistor as a temperature detecting element is formed on said semiconductor substrate.