JP2002162303A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor capable of accurately measuring the pressure with stability so that the resistive value of gauge diffusion layer does not fluctuate nor vary over time. SOLUTION: The pressure sensor includes a diaphragm formed on a semiconductor substrate to be a first conductor type, a gauge diffusion layer to be a second conductor type being formed on the diaphragm and detecting strain generated by a pressure applied to the diaphragm, a lead diffusion layer to be the second conductor type formed on the semiconductor substrate so as to be in contact with the gauge diffusion layer, and a diode diffusion layer to be the first conductor type being formed on the semiconductor substrate so as to be in contact with the lead diffusion layer and forming a protective diode by the junction with the lead diffusion layer. Furthermore, the pressure sensor employs a buried layer to be the first conductor type with high concentration being formed on the lower section of the diaphragm and reducing the resistive value of the semiconductor substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor having a gauge diffusion layer for detecting a strain generated when a pressure is applied to a semiconductor diaphragm.

[0002]

2. Description of the Related Art FIG. 3A is a plan view showing the structure of a conventional pressure sensor, and FIG. 3B is a sectional view taken along line AA '. 3A and 3B, in the pressure sensor, a diaphragm 2 is formed on an N-type silicon substrate 1 as a first conductivity type, and a P-type gauge as a second conductivity type is formed on the diaphragm 2. The diffusion layers 3a, 3b, 3c,
3d and high-concentration P-type lead diffusion layers 4a, 4b, 4
c and 4d are formed by impurity diffusion.

In this case, the lead diffusion layer 4a is in contact with the gauge diffusion layers 3a and 3b,
b is in contact with the gauge diffusion layer 3b and the gauge diffusion layer 3c,
The lead diffusion layer 4c is in contact with the gauge diffusion layer 3c and the gauge diffusion layer 3d, and the lead diffusion layer 4d is
And the gauge diffusion layer 3a, and the gauge diffusion layers 3a, 3b, 3c, 3d are electrically connected to form a bridge circuit.

A high-concentration N-type polycrystal is formed on the gauge diffusion layers 3a, 3b, 3c and 3d via a silicon oxide film 5 and a silicon nitride film 6 as insulating films stacked on the silicon substrate 1. A silicon film 7 is formed.

A part of this polycrystalline silicon film 7 is formed by gauge diffusion layers 3a, 3a due to a shield effect of fixing a potential.
For the purpose of stabilizing the resistance values of b, 3c and 3d, they are in contact with and electrically connected to the silicon substrate 1.

Then, the lead diffusion layers 4a, 4b, 4c,
The electrodes 8a, 8b, 8c, and 8d are formed so as to be in contact with 4d, respectively. A high concentration N-type diffusion layer 9 is formed on the silicon substrate 1, and a substrate electrode 10 which is in contact with the diffusion layer 9 and is electrically connected to the silicon substrate 1 is formed.

When pressure is applied to the diaphragm 2, the resistance values of the gauge diffusion layers 3a, 3b, 3c, 3d change due to the piezoresistance effect, and for example, a voltage is applied between the electrodes 8d and 8b of the bridge circuit. Input to the electrode 8a
The pressure is detected based on the unbalanced voltage generated between the electrode and the electrode 8b.

The lead diffusion layer 4 on the silicon substrate 1
a, 4b, 4c, 4d and the electrodes 8a, 8b, 8
A high-concentration N-type diode diffusion layer 11 is provided in the vicinity of the position where it contacts with the first and second lead diffusion layers 4a, 4b, and 4d.
The protective diodes are formed so as to be in contact with c and 4d, respectively, and a protection diode is formed by a PN junction between the lead diffusion layers 4a, 4b, 4c and 4d and the diode diffusion layer 11.

When an excessive voltage such as static electricity or surge is applied between the electrodes 8a, 8b, 8c, 8d and the silicon substrate 1 (substrate electrode 10), the protection diode is first broken down and a current flows. Thus, the gauge diffusion layers 3a,
The bonding between the silicon substrates 1 or 3b, 3c and 3d or the bonding between the lead diffusion layers 4a, 4b, 4c and 4d and the silicon substrate 1 is prevented from being broken.

[0010]

However, the pressure sensor shown in FIG. 3 has the following problems. For example, the electrode 8d (minus) and the substrate electrode 10 (plus)
When an excessive voltage of about 200 V is instantaneously or pulsed applied as an electrostatic model between the above and the protection diode by the PN junction formed by the lead diffusion layer 4 d and the diode diffusion layer 11 breaks down at about 10 V, for example. Although a large amount of current flows through the PN junction of the protection diode 11, part of the current flows through the high-resistance N-type silicon substrate 1 as a whole.

Therefore, since the silicon substrate 1 has a high resistance as a whole, the value of the voltage drop due to the current increases, and the potential difference between the PN junction formed between the gauge diffusion layer 3a and the silicon substrate 1 is reduced by the protection diode 11 Breakdown voltage of 10
V, the potential difference between the polycrystalline silicon film 7 electrically connected to the silicon substrate 1 and the gauge diffusion layer 3a, that is, the silicon oxide film 5 and the silicon nitride film 6
Also becomes a value larger than 10V.

When a voltage exceeding a certain level is applied to the silicon oxide film 5 and the silicon nitride film 6, an avalanche phenomenon occurs in which electrons pass through the silicon oxide film 5, and as a result, the silicon oxide film Electric charges are accumulated at the interface between the film 5 and the silicon nitride film 6.

The accumulation of the electric charge causes the electric charge of the gauge diffusion layer 3a to move, thereby increasing the change in the width of the depletion layer. As a result, the resistance value of the gauge diffusion layer 3a changes. The fluctuation causes an offset in the unbalanced voltage of the bridge circuit, making it difficult to accurately detect the pressure.

Further, as the accumulated electric charge gradually leaks out with the passage of time and returns to the original state, the resistance value of the gauge diffusion layer 3a changes with time, and stable pressure detection becomes difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and reduces the amount of electric charge accumulated at the interface between a silicon oxide film and a silicon nitride film, thereby changing the resistance value of the gauge diffusion layer. It is an object of the present invention to provide a pressure sensor capable of stably and accurately measuring a pressure without causing the resistance value to change with time.

[0016]

According to a first aspect of the present invention, there is provided a diaphragm formed on a semiconductor substrate of a first conductivity type, and a strain formed on the diaphragm and generated by applying pressure to the diaphragm. The second conductivity type gauge diffusion layer for detecting the, the second conductivity type lead diffusion layer formed on the semiconductor substrate so as to contact the gauge diffusion layer, the said so as to contact the lead diffusion layer A first conductivity type diode diffusion layer formed on a semiconductor substrate and forming a protection diode by bonding with the lead diffusion layer;
And a high-concentration buried layer of the first conductivity type formed below the diaphragm and lowering the resistance of the semiconductor substrate.

According to a second aspect of the present invention, there is provided a diaphragm formed on a silicon substrate of the first conductivity type, and a second conductive film formed on the diaphragm and detecting a strain generated when a pressure is applied to the diaphragm. A pressure diffusion layer having a gauge diffusion layer of a mold type and a lead diffusion layer of a second conductivity type formed on the silicon substrate so as to be in contact with the gauge diffusion layer, wherein the lead diffusion is performed in the vicinity of the gauge diffusion layer. A first conductivity type diode diffusion layer formed on the semiconductor substrate so as to be in contact with a layer and forming a protection diode by bonding with the lead diffusion layer, and formed via an insulating film on the gauge diffusion layer; A polycrystalline silicon film electrically connected to the diode diffusion layer.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same parts as those in FIG. 3 are denoted by the same reference numerals, and the description thereof will be appropriately omitted. FIG. 1A is a plan view showing the configuration of the first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along the line AA ′.

1 (a) and 1 (b), a high concentration N-type buried layer 12 is formed below the diaphragm 2. As shown in FIG. The buried layer 12 is formed by, for example, diffusing As (arsenic) as an N-type impurity under the diaphragm 2 or epitaxially growing a silicon layer into which As is implanted at a high concentration.

In this case, since the buried layer 12 has a high impurity concentration, the resistance of the silicon substrate 1 is reduced, and the resistance of the entire pressure sensor is reduced, and the time constant of the current is reduced. Therefore, even when a voltage higher than a certain level is applied to the silicon oxide film 5 and the silicon nitride film 6 and an avalanche phenomenon occurs, the time during which the voltage is applied becomes shorter because the time constant is small, and the silicon oxide film 5 The amount of charge accumulated at the interface between the silicon nitride film 6 and the silicon nitride film 6 is reduced, and as a result, the fluctuation of the resistance value of the gauge diffusion layers 3a (3b, 3c, 3d) can be suppressed.

[0021] Therefore, since the offset of the unbalanced voltage of the bridge circuit becomes small, accurate pressure detection becomes possible, and since the amount of accumulated electric charge is small, the accumulated electric charge gradually leaks over time. The gauge diffusion layer 3a (3b, 3c, 3)
The change with time in the resistance value d) can be reduced, and stable pressure detection can be performed.

FIG. 2A is a plan view showing the structure of the second embodiment of the present invention, and FIG. 2B is a sectional view taken along the line AA '. 2A and 2B, the silicon substrate 1
A high-concentration N-type diode diffusion layer 13a is formed near the upper gauge diffusion layer 3a so that both ends thereof are in contact with the lead diffusion layers 4a and 4d, respectively. PN with diffusion layer 13a
The protection diodes are respectively formed by the junctions.

Similarly, a high-concentration N-type diode diffusion layer 13b is formed near the gauge diffusion layer 3b so that both ends thereof are in contact with the lead diffusion layers 4a and 4b, respectively. And 4b and the PN junction of the diode diffusion layer 13b form a protection diode.

Similarly, a high-concentration N-type diode diffusion layer 13c is formed near the gauge diffusion layer 3c so that both ends thereof are in contact with the lead diffusion layers 4b and 4c, respectively. And 4c and the PN junction of the diode diffusion layer 13c form a protection diode.

Similarly, a high-concentration N-type diode diffusion layer 13d is formed near the gauge diffusion layer 3d so that both ends thereof are in contact with the lead diffusion layers 4c and 4d, respectively. And 4d and the PN junction of the diode diffusion layer 13d form a protection diode.

Then, a high-concentration N-type polycrystal is formed on the gauge diffusion layers 3a, 3b, 3c and 3d through a silicon oxide film 5 and a silicon nitride film 6 as insulating films stacked on the silicon substrate 1. A silicon film 7 is formed, and this polycrystalline silicon film 7 is formed on diode diffusion layers 13a, 13b, 1
3c and 13d and are electrically connected.

In this case, the potential between the polycrystalline silicon film 7 and the gauge diffusion layers 3a, 3b, 3c, 3d, that is, the potential applied to the silicon oxide film 5 and the silicon nitride film 6 is the same as that of the lead diffusion layers 4a, 4b. , 4c, 4d and diode diffusion layer 1
It is fixed to the breakdown potential of the protection diode formed by the PN junction with 3a, 13b, 13c and 13d.

Therefore, the avalanche phenomenon does not occur, and the accumulation of electric charges at the interface between the silicon oxide film 5 and the silicon nitride film 6 can be prevented, so that the gauge diffusion layers 3a, 3b, 3c, The change in the resistance value of 3d does not change, and as a result, an offset can be prevented from occurring in the unbalanced voltage of the bridge circuit, and accurate pressure detection can be performed.

Further, since the accumulated electric charge gradually leaks with the passage of time and does not return to the original state, the resistance values of the gauge diffusion layers 3a, 3b, 3c and 3d do not change with time. Stable pressure detection becomes possible.

[0030]

As described above, according to the present invention,
Since a high-concentration buried layer that lowers the resistance of the semiconductor substrate is provided under the diaphragm, the amount of charge accumulated at the interface between the silicon oxide film and the silicon nitride film is reduced, and the resistance value of the gauge diffusion layer is reduced. It is possible to provide a pressure sensor capable of performing stable and accurate pressure measurement without fluctuating and its resistance value does not change with time.

Further, according to the present invention, the polysilicon layer is electrically connected to the diode diffusion layer so that the potential applied to the silicon oxide film and the silicon nitride film is fixed to the breakdown voltage of the protection diode. As a result, no charge is accumulated at the interface between the silicon oxide film and the silicon nitride film, and the resistance value of the gauge diffusion layer does not fluctuate, and the resistance value does not change with time. An enabled pressure sensor can be provided.

[0032]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a conventional pressure sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Diaphragm 3a, 3b, 3c, 3d Gauge diffusion layer 4a, 4b, 4c, 4d Lead diffusion layer 5 Silicon oxide film 6 Silicon nitride film 7 Polycrystalline silicon film 11 Diode diffusion layer 12 Buried layer 13a, 13b, 13c, 13d Diode diffusion layer

Claims (2)

[Claims] A diaphragm formed on a semiconductor substrate of a first conductivity type, a gauge diffusion layer of a second conductivity type formed on the diaphragm and detecting a strain generated by applying a pressure to the diaphragm; A second conductive type lead diffusion layer formed on the semiconductor substrate so as to be in contact with the gauge diffusion layer; and a junction with the lead diffusion layer formed on the semiconductor substrate so as to be in contact with the lead diffusion layer. A first conductivity type diode diffusion layer that forms a protection diode by: a high-concentration first conductivity type buried layer formed below the diaphragm and lowering the resistance of the semiconductor substrate. A pressure sensor characterized by being provided. 2. A diaphragm formed on a silicon substrate of a first conductivity type, a gauge diffusion layer of a second conductivity type formed on the diaphragm and detecting a strain generated when a pressure is applied to the diaphragm, A second conductive type lead diffusion layer formed on the silicon substrate so as to be in contact with the gauge diffusion layer; and wherein the pressure sensor is in contact with the lead diffusion layer in the vicinity of the gauge diffusion layer. A first-conductivity-type diode diffusion layer formed on a semiconductor substrate and forming a protection diode by bonding with the lead diffusion layer; formed on the gauge diffusion layer via an insulating film, and electrically connected to the diode diffusion layer. And a polycrystalline silicon film connected to the pressure sensor.