JPH09126922A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor with improved pressure sensitivity. SOLUTION: Boron is diffused onto 300μm thick (110) silicon substrate 1 by thermal diffusion to form a piezo resistance element 3. Then, an electrode wire 4 made from diffusion resistance is formed in the similar manner as the piezo resistance element 3 is formed. Then, an aluminum layer is formed on the (110) silicon substrate 1 by the electron beam deposition method and the aluminum layer is patterned in a specific shape by the photolithography process to form an electrode pad 5. Finally, anisotropic etching is performed from the reverse side of the (110) silicon substrate 1 to form a diaphragm 1a, where the piezo resistance element 3 is arranged in nearly the same direction as the (111) shaft of the (110) silicon substrate 1 to improve pressure sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor that detects pressure using a piezoresistive element.

[0002]

2. Description of the Related Art FIG. 5 is a top view showing an example of a conventional pressure sensor, and FIG. 6 is a schematic sectional view showing an example of a conventional pressure sensor. This pressure sensor is (1
10) By etching the silicon substrate 1 from the back surface side, a recess having a thickness of 10 to 50 μm is formed in the center thereof to form the diaphragm 1a and the support portion 1b.
The support portion 1b is fixed to the pedestal 2 having the atmospheric pressure through hole 2a in the center on the back surface side. Further, on the upper surfaces of the diaphragm 1a and the support portion 1b, a piezoresistive element 3 for detecting the distortion of the diaphragm 1a due to pressure, an electrode wiring 4 and an electrode pad made of a diffusion resistance electrically connected to each piezoresistive element 3. 5 is formed using a semiconductor fine processing technique. In this way, if the pressure sensor as described above is manufactured using the semiconductor microfabrication technology,
It is easy to miniaturize, and as a result, mass production is possible and cost can be reduced.

In the pressure sensor having the above structure, the diaphragm 1a bends when pressure is applied. Therefore, the piezo-resistive element 3 formed on the upper surface of the diaphragm 1a converts the deflection corresponding to the pressure into a change in resistance value and the pressure is changed. Is being detected. Therefore, the thinner the thickness of the diaphragm 1a, the greater the amount of deflection of the diaphragm 1a for the same pressure, and the pressure detection sensitivity is inversely proportional to the square of the thickness of the diaphragm 1a. It is desirable to reduce the thickness.

[0004]

By the way, the conventional pressure sensor has the problems listed below.

1) In a conventional pressure sensor using a (110) silicon substrate, the direction of the piezoresistive element 3 is changed to (11
0) It was directed in the axial direction. However, as apparent from FIGS. 2 and 3, the longitudinal piezoresistive coefficient and the lateral piezoresistive coefficient in the (110) axis direction are smaller than the longitudinal piezoresistive coefficient and the lateral piezoresistive coefficient in the (111) axis direction. I understand. As a result, the direction of the piezoresistive element 3 is changed to (11
1) The sensitivity is lower than that in the case of being oriented in the axial direction.

2) (100) silicon substrate and (11)
0) When the silicon substrate is anisotropically etched to form a diaphragm structure, the angle θ formed by the (111) plane and the pedestal 2 is tan θ = √2 ... (100) Silicon substrate tan θ = 1 / √2 ... (110) Since the case of a silicon substrate is satisfied, if the chip size is the same, (11
The area of the diaphragm is smaller in the 0) silicon substrate than in the (100) silicon substrate. In particular, when the thickness of the substrate is h, the sensitivity decreases when the size of one side of the chip approaches 2√2h and the area of the diaphragm approaches 0.

The present invention has been made in view of the above points, and an object thereof is to provide a pressure sensor with improved pressure sensitivity.

[0008]

According to the first aspect of the present invention,
In a pressure sensor in which a diaphragm is formed on a single crystal silicon substrate and a piezoresistive element is formed on the surface of the diaphragm, the direction of the piezoresistive element is substantially the same as the (111) axis direction of the single crystal silicon substrate. It is characterized in that it is arranged as follows.

According to a second aspect of the present invention, in the pressure sensor according to the first aspect, the single crystal silicon substrate is (10
0) A frame-shaped support portion made of a silicon substrate, and a (110) silicon substrate serving as a diaphragm formed on the upper surface of the support portion.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a top view showing a pressure sensor according to an embodiment of the present invention, and FIG. 2 is a graph showing a result of simulating the crystal axis dependence of the longitudinal piezoresistance coefficient of single crystal silicon, and FIG. FIG. 4 is a graph showing the result of simulating the crystal axis dependence of the lateral piezoresistive coefficient of single crystal silicon. The schematic sectional view of the pressure sensor according to the present embodiment has the same configuration as that shown in FIG.

The pressure sensor according to this embodiment has a thickness of 30.
On the 0 μm (110) silicon substrate 1, boron is diffused by thermal diffusion to form the piezoresistive element 3. However, the surface concentration of boron is 1.0 × 10 ¹⁸ / cm ³ . Subsequently, the electrode wiring 4 made of diffusion resistance is formed by the same method as that for forming the piezoresistive element 3. However, the surface concentration of boron is 1.0 × 10 ²⁰ / cm ³ . And (1
10) An aluminum layer is formed on the silicon substrate 1 by the electron beam evaporation method. At this time, the substrate temperature during the deposition of the aluminum layer is 100 to 200 ° C. Then, the aluminum layer is patterned into a predetermined shape by a photolithography process to form the electrode pad 5.

In this way, the piezoresistive element 3, the electrode wiring 4 and the electrode pad 5 are formed on the (110) silicon substrate 1.
Then, anisotropic etching is performed with potassium hydroxide from the back surface side of the (110) silicon substrate 1 to form the diaphragm 1a.

Here, from the simulation results of the crystal axis dependence of the piezoresistive coefficient of single crystal silicon shown in FIGS. 2 and 3, as compared with the pressure sensor in which the direction of the piezoresistive element 3 is oriented in the (110) axis direction. , The sensitivity of the pressure sensor in the (111) axis direction is very good, so in the present embodiment, the direction of the piezoresistive element 3 is formed in the (111) axis direction.

Therefore, as compared with the conventional pressure sensor in which the direction of the piezoresistive element 3 is oriented in the (110) axis direction, the pressure sensor according to the present embodiment changes the direction of the piezoresistive element 3 in the direction of (1).
11) Since it is formed in the axial direction, pressure sensitivity can be improved.

As shown in FIG. 4, the thickness is 300 μm.
(100) silicon substrate 6 of 300 μm thick (1
10) After bonding with the silicon substrate 1, the (110) silicon substrate 1 is polished so as to leave 20 μm, and further (10)
(0) If the silicon substrate 6 is anisotropically etched with potassium hydroxide to form the diaphragm 1a, (1)
10) Compared with the case where the pressure sensor is configured using only the silicon substrate 1, the area of the diaphragm can be increased even with the same chip size, so that the pressure sensitivity is improved.
Alternatively, the size of the chip can be reduced.

[0016]

According to the invention of claim 1, in a pressure sensor in which a diaphragm is formed on a single crystal silicon substrate and a piezoresistive element is formed on the surface of the diaphragm, the direction of the piezoresistive element is set to the direction of the single crystal silicon substrate. Since it was arranged so as to be substantially in the same direction as the (111) axis direction, it was possible to provide a pressure sensor with improved pressure sensitivity.

According to a second aspect of the present invention, in the pressure sensor according to the first aspect, the single crystal silicon substrate is (100).
Since it is composed of a frame-shaped support portion made of a silicon substrate and a (110) silicon substrate which is a diaphragm formed on the upper surface of the support portion, it is possible to configure a pressure sensor using only the (110) silicon substrate. In comparison, even with the same chip size, the area of the diaphragm can be made large, and the pressure sensitivity can be improved or the chip can be downsized.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the results of simulating the crystal axis dependence of the longitudinal piezoresistive coefficient of single crystal silicon.

FIG. 3 is a graph showing the results of simulating the crystal axis dependence of the lateral piezoresistance coefficient of single crystal silicon.

FIG. 4 is a schematic sectional view showing a pressure sensor according to the present embodiment.

FIG. 5 is a top view showing an example of a pressure sensor according to a conventional example.

FIG. 6 is a schematic cross-sectional view showing an example of a pressure sensor according to a conventional example.

[Explanation of symbols]

 1 (110) Silicon Substrate 1a Diaphragm 1b Support 2 Base 2a Atmospheric Pressure Through Hole 3 Piezoresistive Element 4 Electrode Wiring 5 Electrode Pad 6 (100) Silicon Substrate

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[Procedure amendment]

[Submission date] December 28, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

2) (100) silicon substrate and (11)
0) When the silicon substrate is anisotropically etched to form a diaphragm structure, the angle θ formed by the (111) plane and the pedestal 2 is tan θ = √2 ... (100) Silicon substrate tan θ = 1 / √2 ... (110) Since the case of a silicon substrate is satisfied, if the chip size is the same, (11
The area of the diaphragm is smaller in the 0) silicon substrate than in the (100) silicon substrate. Especially for the thickness h
When a (110) substrate is used, the support on one side of the chip opening is
Iz approaches 2√2h and at the same time the diaphragm thickness becomes 0
When approaching, there was a problem that the area of the diaphragm approached 0 and the sensitivity decreased.

Claims (2)

[Claims] 1. In a pressure sensor having a diaphragm formed on a single crystal silicon substrate and a piezoresistive element formed on the surface of the diaphragm, the direction of the piezoresistive element is the (111) axis direction of the single crystal silicon substrate. A pressure sensor characterized by being arranged so as to be substantially in the same direction as. 2. The single crystal silicon substrate is (100)
2. The pressure sensor according to claim 1, comprising a frame-shaped support portion made of a silicon substrate, and a (110) silicon substrate serving as a diaphragm formed on an upper surface of the support portion.