JPH05273064A - Pressure sensor - Google Patents

Abstract

PURPOSE:To prevent a diaphragm from exceeding a yield limit when pressure within a reference chamber is increased by forming a silicon wafer in a triple structure where both surfaces of the silicon wafer are held by glass wafers and forming a mesa on either of a diaphragm or the glass wafer. CONSTITUTION:In a pressure sensor, a glass wafer (glass substrate) where an opposing electrode 7 is provided and a diffusion layer 6 and a junction prevention film 11 are provided on the surface and then a silicon wafer 10 with a diaphragm 2 where a mesa 3 is formed on the opposing rear surface and a glass wafer (stopper) 5 where an external air introducing hole 8 is provided are provided, thus forming a triple structure where the wafer 10 is sandwiched by a substrate 1 and the stopper 5. When the outer pressure is equal to or less than atmospheric pressure and then the diaphragm 2 is deflected and the reference chamber 3 is inflated, the mesa 3 collides with the stopper 5 in a specified inflation, thus preventing the diaphragm 2 from being damaged. When the sensor is pressurized to a preset pressure, the reference chamber 3 shrinks, the mesa 3 is separated from the stopper 5, and the diaphragm 2 is activated in response to pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor which receives a change in pressure of gas, liquid and solid as a change amount of a diaphragm and converts the change amount into an electric signal for output.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 3, a pressure sensor having a diaphragm structure has a two-layer structure in which a silicon wafer and a glass substrate are bonded together. This is the same for the piezoresistive type, the electrostatic capacitance type, and the contact switch type.

[0003]

However, in the conventional structure, the pressure in the reference chamber formed by the silicon diaphragm and the glass substrate becomes higher than the external pressure, and the diaphragm is damaged when the displacement of the silicon diaphragm exceeds the yield limit. However, as a result, there is a problem that the sensor does not function. In order to avoid this problem, in the conventional sensor, the diaphragm is made thicker to increase the pressure resistance. However, as shown in [Equation 1], when the thickness of the diaphragm is increased, the amount of displacement of the diaphragm under the same pressure becomes small, which causes a problem that sensitivity is lowered.

[Equation 1] W = K (a ⁴ / h ³ ) P where W is the displacement of the diaphragm K is the Poisson's ratio, a constant peculiar to the material including Young's modulus a is the length of one side of the diaphragm h It is the thickness of the diaphragm.

Further, if the diaphragm has the same thickness as that for low-pressure measurement, the sensitivity is the same, but when the external pressure becomes high, the diaphragm comes into contact with the glass and measurement becomes impossible. In order to solve these conventional problems, an object of the present invention is to obtain a sensor capable of measuring high pressure even when the diaphragm is thin.

[0006]

In order to solve the above problems, the present invention is directed to a diaphragm or a stopper provided so as to face the diaphragm so that the diaphragm does not exceed the yield limit when the pressure in the reference chamber increases. By providing a mesa in a part of either of the above, by preventing the diaphragm from exceeding the yield limit by hitting the mesa to the stopper, at the same time, by setting the pressure in the reference chamber to a pressure equivalent to the desired measurement pressure, Even in the high pressure region, the same sensitivity as in the low pressure region was obtained, and the diaphragm was not damaged.

[0007]

In the pressure sensor constructed as described above, since the pressure in the reference chamber is higher than the atmospheric pressure, when the diaphragm bends and the reference chamber swells under the atmospheric pressure, a predetermined swelling occurs. Diaphragm damage can be prevented by stopping the mesa part against the stopper. When this sensor is pressurized to a preset pressure, the reference chamber contracts, the mesa portion is separated from the stopper, and the diaphragm moves in response to the pressure. here,
Since the pressure and the deflection of the diaphragm are in direct proportion as shown in [Equation 1], the sensor having the same diaphragm shape (namely, side length) and the same diaphragm thickness has the same sensitivity. Therefore, it does not break even at low pressure,
Moreover, it is possible to obtain a pressure sensor that does not impair the sensitivity in the high pressure measurement region.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a first embodiment of a pressure sensor (electrostatic capacitance type) according to the present invention. A glass wafer (hereinafter referred to as a glass substrate) 1 provided with a counter electrode 7 and a diffusion layer on the surface are provided. The silicon wafer 10 is provided with a bonding prevention film and has a diaphragm 2 having a mesa 3 formed on the opposite back surface thereof, and a glass wafer (hereinafter, referred to as a stopper) 5 having an outside air introduction hole 8 formed therein. It is formed as a three-layer structure sandwiched between the glass substrate 1 and the stopper 5, FIG. 1 (a) shows the case where the external pressure is in the measurement region, and FIG. 1 (b) shows the case where the external pressure is atmospheric pressure. It is a thing.

FIG. 2 schematically shows the process of the pressure sensor (capacitance type) according to the present invention. First, the crystal orientation is (10
In step 0), the n-type silicon wafer 10 having a thickness of 300 μm is etched by 1 μm as a cavity portion using a photolithography method, and then SiO ₂ used as a mask material is peeled off to form SiNx. Etch to form a diaphragm. The diaphragm produced this time has a thickness of 30 μm.

Next, a boron diffusion layer 6 as an electrode is formed on the surface of the diaphragm on the reference chamber side, and SiO ₂ as a bonding prevention film 11 is formed on the surface of the diaphragm 2 and the surface of the mesa 3. On the other hand, a glass substrate 1 having a thickness of 300 μm, on which an Al pattern 7 is formed as a counter electrode, and a portion to which the mesa hits are etched by 2 μm to form a diaphragm displacement hole 9
Then, a stopper 5 having a thickness of 300 μm provided with an outside air introduction hole 8 is prepared by ultrasonic processing.

Next, the silicon wafer 10 and the stopper 5 are bonded by anodic bonding. However, the bonding atmosphere pressure in this case is atmospheric pressure. Further, the glass substrate 1 is bonded by anodic bonding to the facing surface side of the silicon wafer 10 to which the stopper 5 is anodically bonded. However, the bonding atmosphere in this case is the pressure of the measurement range (8 kg / cm ^{2 in} this example).
Is.

The sensor chip of the pressure sensor was completed through the above steps, and thereafter, the pressure sensor was connected to the capacitance meter by the usual method and the pressure reduction test was conducted. As a result, it was possible to obtain a capacitance change of about 35 pF with respect to a pressure change of 7.5 kg / cm ² to 8.5 kg / cm ² . On the other hand, the same pressurization / decompression test was applied to the pressure sensor having the same structure as that of the present embodiment (that is, the structure of this pressure sensor except for the stopper 5) manufactured by the conventional method shown in FIG. Where 7.
For a pressure change of 5 kg / cm ² to 8.5 kg / cm ² , only a capacity change of 4 pF was obtained.

Also, the anodic bonding performed while applying a pressure of 8 kg / cm ² in the process of manufacturing the conventional sensor structure broke while returning to the atmospheric pressure. Furthermore, when the same pressure sensor structure as that of the conventional pressure sensor having a diaphragm thickness of 40 μm was subjected to the same pressurization and depressurization test, the capacitance change in the same range was 12 pF.

Next, another embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a cross-sectional view of a pressure sensor (capacitance type) showing another embodiment of the present invention, in which a glass substrate 1 provided with a counter electrode 7 and a diffusion layer and an anti-bonding film are provided on the surface of the glass substrate 1. It is composed of a silicon wafer 10 having a diaphragm 2 having a mesa 3 formed on its back surface and a stopper 5 having an outside air introduction hole 8, and the silicon wafer 10 is formed as a three-layer structure sandwiched between the glass substrate 1 and the stopper 5. Has been done. 4A shows the case where the external pressure is in the measurement region, and FIG. 4B shows the case where the external pressure is the atmospheric pressure.

This embodiment differs from the first embodiment in that
The mesa 3 is formed on the stopper 5. Therefore, the manufacturing process, the overall configuration, etc. are almost the same as those of the first embodiment, but the stopper structure has the outside air introduction hole 8
After opening, the following processing is performed.

First, an n-type double-sided polished silicon wafer having a thickness of 265 μm is bonded to the bonding surface of the stopper 5 by an anodic bonding method, patterned using a diaphragm side length pattern, and anisotropically etched by KOH. Apply. Here, the etching is performed until the surface of the glass substrate appears to form the mesa 3.

The sensor chip of the pressure sensor was completed in the above steps, and thereafter, the pressure sensor was connected to the capacitance meter by the usual method and the pressure reduction test was conducted. As a result, it was possible to obtain a capacitance change of about 40 pF with respect to a pressure change of 7.5 kg / cm ² to 8.5 kg / cm ² . On the other hand, a pressure sensor manufactured by the conventional method shown in FIG. 5 and having the same structure as that of this embodiment (that is, a structure in which the stopper 5 is removed from the structure of this pressure sensor).
When the same pressurization / decompression test was applied at 7.5 kg / c
Only a capacitance change of 4 pF was obtained for a pressure change of m ² to 8.5 kg / cm ² .

In the conventional sensor structure, the anodic bonding was carried out while applying a pressure of 8 kg / cm ² , and it was destroyed during the return to atmospheric pressure. Furthermore, when the same pressure sensor structure as that of the conventional pressure sensor having a diaphragm thickness of 40 μm was subjected to the same pressurization and depressurization test, the capacitance change in the same range was 15 pF.

Finally, a conventional sensor structure is manufactured, and 1.
When a pressurization / decompression test was conducted in a range of 5 kg / cm ² to 2.5 kg / cm ² , the capacity change was 41 pF.

[0020]

As described above, according to the present invention, the pressure in the reference chamber is set to the measurement range, and the diaphragm does not exceed the breaking limit by the stopper. There is an effect that pressure can be sensed with the same sensitivity.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a first embodiment of a pressure sensor of the present invention.

FIG. 2 is an explanatory diagram of a pressure sensor manufacturing process according to the present invention.

FIG. 3 is an explanatory view showing another embodiment of the pressure sensor of the present invention.

FIG. 4 is an explanatory diagram showing a structure of a conventional pressure sensor.

[Explanation of symbols]

 1 Glass Substrate 2 Diaphragm 3 Mesa 4 Reference Chamber 5 Stopper 6 Diffusion Layer 7 Counter Electrode 8 Outside Air Introduction Hole 9 Diaphragm Displacement Hole 10 Silicon Wafer 11 Bonding Prevention Film

Claims (6)

[Claims] 1. A semiconductor pressure sensor in which a part of a silicon substrate has a diaphragm structure, a pressure change is detected as a deflection amount of the diaphragm, and the deflection amount is converted into an electric signal. A silicon wafer is sandwiched between glass wafers on both sides. A pressure sensor having a triple structure, wherein a mesa is formed on either the diaphragm or the glass wafer. 2. The pressure sensor according to claim 1, wherein the mesa is formed on a part of a diaphragm. 3. The pressure sensor according to claim 1, wherein the mesa is formed on a part of one glass wafer that does not form a reference chamber. 4. The pressure sensor according to claim 1, wherein the electric signal conversion mechanism is a piezoresistive type using a Wheatstone bridge. 5. The pressure sensor according to claim 1, wherein the electric signal conversion mechanism is a capacitance type using the counter electrode as a capacitor. 6. The pressure sensor according to claim 1, wherein the electric signal conversion mechanism is a contact switch.