JPH05281067A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To provide a semiconductor pressure sensor which can be used for accurate measurement even in the temperature range of -80-300 deg.C. CONSTITUTION:A semiconductor pressure sensor is composed of two diaphragms 22 formed on a SOI substrate 20 at a fixed distance, a strain detecting element 23 formed on the diaphragm 22, cavities 26 formed above the diaphragms, and a partitioning wall member 31 to partition a middle part between the diaphragms 22. The cavities are vacuumized, and the diaphragm on one side is arranged on the side of a process, and the diaphragm on the other side is arranged in the atmosphere.

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, and more particularly to a pressure sensor usable in a wide range of -80 to 300 ° C.

[0002]

2. Description of the Related Art FIG. 4 is a sectional view showing a conventional example of a semiconductor pressure sensor. In the figure, reference numeral 1 is a body, and 2 is a supporting member made of Pyrex glass fixed in a recess of the body 1, and a through hole 8 is formed in this supporting member.
A sensor chip 3 is joined to the support member 2 by anodic bonding, and a measuring diaphragm 4 is formed by forming a hole 9 in the sensor chip 3. Reference numeral 5 is a strain detecting element formed on the diaphragm. 6 is a seal diaphragm arranged on the sensor chip,
The edges are airtightly fixed to the body. Reference numeral 7 is a sealing liquid sealed between the seal diaphragm and the sensor chip, and 10 is a lead wire for taking out an electric signal from the strain detecting element to the outside. When the measurement pressure is applied to the seal diaphragm in the above configuration, the measurement diaphragm is deformed according to the pressure and an electric signal corresponding to the pressure is generated in the strain detection element.

[0003]

By the way, when the strain detecting element is formed on a substrate insulated by a pn junction, the effectiveness of the insulation by the pn junction decreases as the temperature of the sensor rises. That is, when the temperature is 125 ° C. to 175 ° C. or higher, the insulating property of the joint surface deteriorates. Further, since the sealing oil is used, the operating temperature is limited to about -40 ° C, and the operating temperature range is limited to about -40 to 125 ° C. The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a semiconductor pressure sensor that can be used even at about -80 to 300 ° C.

[0004]

In order to solve the above problems, the present invention provides two diaphragms formed on an SOI substrate at a predetermined distance, a strain detecting element formed on the diaphragm, and A cavity formed in the upper part of the two diaphragms and a partition wall partitioning the middle of the two diaphragms. The cavity is evacuated and one of the diaphragms is placed on the process side and the other diaphragm is placed in the atmosphere. It is characterized by.

[0005]

Since the strain detecting element is formed on the SOI substrate, the electrical insulation can be maintained even at about 300 ° C. Moreover, since no enclosed oil is used, it is not affected by the thermal expansion of the sealing liquid. The vacuum chamber prevents the sensing elements from touching the process fluid directly, and the partition that separates the middle of each diaphragm cancels the output error of each sensing element due to fixed strain or thermal strain.

[0006]

The present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a semiconductor pressure sensor of the present invention, and FIG. 2 is a sectional view showing a sensor portion. In FIG. 2, reference numeral 20 denotes an SOI (Silicon On Insurator) substrate, in which a single crystal silicon film 20c is formed on a silicon plate 20a via an oxide film 20b. Reference numeral 21 denotes two concave portions formed on the back surface of the substrate by a predetermined distance by anisotropic etching, and the diaphragm 22 is formed on the front surface of the substrate by the concave portions.

Reference numeral 23 is a strain detecting element formed by implanting impurities of a predetermined concentration on the diaphragm of the silicon film 20c. Reference numeral 24 is a partition wall layer made of polysilicon laminated except the diaphragm portion, and 25 is a plate body made of Pyrex glass bonded on the partition wall layer, and a cavity 26 is formed between the plate body 25 and the diaphragm 22. The cavity 26 serves as a vacuum chamber. The diaphragm 22 and the strain detecting element 23 are arranged symmetrically with respect to the partition layer 24, and the output from each strain detecting element 23 is outside the partition layer (shown by A) by a well-known wiring method in which impurities are highly concentrated. Part).

Next, a method of manufacturing the semiconductor pressure sensor of the present invention will be described with reference to the schematic steps of FIG. Step 1 (see FIG. A)) A strain detecting element 23 is formed at a desired position at a predetermined distance on the Si layer 20C on the surface of the SOI substrate, and at the same time, impurities are doped in a high concentration to obtain a wiring for extracting an output (Omitted in the figure) (shown as a rectangle in the figure, but the shape is not limited to this. Further, the wiring and the strain detection element may be formed in any order.

Next, the back surface of the substrate is anisotropically etched to form holes 21 and form diaphragms 22. This etching is performed so that the strain detecting element 23 is located on the diaphragm and symmetrical with respect to the central axis B. Step 2 (see FIG. B ... A is a plan view and B is a cross-sectional view) Next, except for the upper part of the diaphragm 21, polysilicon is laminated by a CVD apparatus or the like to form a partition layer 24. The partition layer 24 is also formed at a position symmetrical with respect to the central axis B.

Step 3 (see FIG. 3c) Next, the substrate 20a is placed in a vacuum, and a plate body 25 made of Pyrex glass is brought into close contact with the partition wall layer 24 and joined by anodic bonding. As a result, the upper portion of the diaphragm 22 of the partition wall 24 is closed by the plate body 25, and the cavity 26 becomes a vacuum chamber.

FIG. 1 shows a state in which the sensor portion 30 of FIG. 2 is fixed to the mounting member 27, and the partition member 31 is a diaphragm 22 of the sensor portion 30 and the strain detecting element 2.
It is fixed in an airtight manner by supporting a position symmetrical with respect to 3. Three
Reference numeral 3 is a lead wire for taking out an electric signal from the strain detecting element to the outside, and 28 is a mounting screw for fixing the mounting member 27 to the measurement target.

In the above configuration, the diaphragm 22a is fixed to the process side and the diaphragm 22b is arranged to the atmospheric pressure side by fixing it to the measuring object side (not shown) by the mounting screw 28. According to the above configuration, the gauge pressure is obtained by calculating the difference between the output of the detection element placed on the process side and the output of the detection element placed in the atmosphere, and when measuring the absolute pressure, it is placed on the process side. It can be determined by the output of the detection element.

Further, in the present invention, since the sealing liquid is not used and the strain detecting element is formed on the SOI substrate, -80 to
It can be used at about 300 ° C. Further, since the two diaphragms are formed symmetrically with respect to the partition layer 24 and the partition member 31, fixed strain and thermal strain act on both detection elements in the same manner. As a result, the error due to the distortion can be canceled and the accuracy can be improved.

[0014]

According to the pressure sensor of the present invention, since the enclosed liquid is not used and the insulation by the pn junction is also not used,
It can be used over a wide range of about 80 to 300 ° C., and since the two diaphragms are formed symmetrically with respect to the partition layer and the partition member, a highly accurate semiconductor sensor can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a semiconductor pressure sensor of the present invention.

FIG. 2 is a sectional view of a sensor portion.

FIG. 3 is a schematic process drawing showing a manufacturing process of the semiconductor pressure sensor of the present invention.

FIG. 4 is a cross-sectional view showing a conventional example.

[Explanation of symbols]

 20 SOI Substrate 21 Recess 22 Diaphragm 23 Strain Detection Element 24 Partition Layer 25 Plate 26 Cavity 27 Mounting Member 28 Mounting Screw 30 Sensor Part 31 Partition Member 33 Lead Wire

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Suzuki 2-9-32 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A two-diaphragm formed at a predetermined distance on an SOI substrate, a strain sensing element formed on the diaphragm, a cavity formed above the two diaphragms, and the two diaphragms. A semiconductor pressure sensor comprising a partition member partitioning the middle of the diaphragm, wherein the cavity is evacuated and one of the diaphragms is arranged on the process side and the other diaphragm is arranged in the atmosphere.