JPH05180866A - Dynamical quantity sensor - Google Patents

Abstract

PURPOSE:To provide a dynamical quantity sensor which can high-sensitively detect a dynamical quantity such as the quantity of displacement and acceleration or the like, and can be simply produced. CONSTITUTION:A source domain 12 and a drain domain 13 having a conductive type different from a semiconductor substrate 11 are formed on the surface of the semiconductor substrate 11. In addition, a displacement electrode 15 which is opposite to a domain including the source domain 12 and the drain domain 13 and can be displaced to the above domain is provided. A space between the displacement electrode 15 and the semiconductor substrate 11 is set up within extent where field effect is active. A dynamical quantity is detected on a phenomenon that, when reverse bias voltage is applied to the displacement electrode 15, the form of a channel 16 being an inversion layer alters according to the quantity of displacement of the displacement electrode 15, and resistance between the source domain 12 and the drain domain 13 therefore alters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical quantity sensor for detecting a mechanical quantity such as a displacement quantity and an acceleration, and more particularly to a mechanical quantity sensor which can be manufactured by using semiconductor manufacturing technology.

[0002]

2. Description of the Related Art Conventionally, a monolithically formed acceleration sensor is a vibrating electrode that vibrates in response to acceleration, and this vibrating electrode, as described in "10th SENSOR SYMPOSIUM", 1991, pp. 41-44. It has two detection electrodes arranged above and below, and the acceleration is detected by measuring the change in capacitance or capacitance difference between these electrodes.

However, in the above-mentioned conventional acceleration sensor, the capacitance between the electrodes cannot be increased so much due to the process limitation as compared with the wiring capacitance and the stray capacitance on the monolithic substrate. There is a problem that the change in capacitance due to a change in acceleration is small, and therefore this change is buried in noise, etc., and a minute change in acceleration cannot be detected. Further, in order to avoid such a problem, a bridge connection is devised to detect only the capacitance change differentially.
Although it is necessary to accurately form the detection electrodes above and below the diaphragm, it is extremely difficult to stack the three electrodes with high accuracy, and there are many process problems due to the complicated structure.

An object of the present invention is to provide a mechanical quantity sensor which can detect mechanical quantities such as displacement and acceleration with high sensitivity and can be easily manufactured.

[0004]

A mechanical quantity sensor of the present invention includes a semiconductor substrate of a first conductivity type and a second conductivity type provided in at least one surface of the semiconductor substrate and different from the first conductivity type. Conductive type source region, at least one second conductive type drain region provided in the surface of the semiconductor substrate away from the source region, and the source region and the drain on the surface of the semiconductor substrate. When the region integrally including the region is an element region, the displacement electrode is provided so as to be separated from the element region to such an extent that an electric field effect can be exerted and is displaceable with respect to the element region.

[0005]

[Operation] This mechanical quantity sensor is basically a MOS (Met
al-Oxide-Semiconductor) type field effect transistor (F
(ET) gate oxide film is removed so that the gate electrode can be displaced with respect to the channel region.
The gate electrode serves as a displacement electrode, and the element region corresponds to the channel region. Therefore, the space between the displacement electrode and the element region can be considered as a gate insulating layer formed by vacuum, and the operating principle of the mechanical quantity sensor of the present invention can be understood from the operating principle of the conventional MOS FET. it can.

Generally, in a MOSFET, when a reverse bias voltage is applied to the gate electrode, charges are induced on the surface of the semiconductor substrate in the portion facing the gate electrode, and a region (channel region) sandwiched between the source region and the drain region is formed. A channel is formed by the inversion layer according to the amount of induced charges. When a bias voltage is applied between the source region and the drain region in this state, carriers move in the channel region, and a current-voltage characteristic (I-V) represented by a certain resistance value.
Characteristic) is obtained. In this case, the larger the voltage applied to the gate electrode (gate voltage) and the smaller the voltage between the source and the drain, the larger the channel is formed, and the resistance between the source and the drain becomes smaller. Since the change in the channel resistance with respect to the gate voltage is extremely large, a minute change in the channel can be used as a detector.
The resistance between the source and the drain described above largely changes not only by the gate voltage but also by changing the thickness of the insulating layer directly under the gate (the insulating layer may be gas or solid). This is because the amount of charges induced in the inversion layer according to the gate voltage is inversely proportional to the thickness of the insulating layer if the gate voltage is constant.

In the mechanical quantity sensor of the present invention, the MOSF
When a reverse bias voltage is applied to the displacement electrode corresponding to the gate electrode of ET, a channel is formed in the portion sandwiched between the source region and the drain region, as in the case of the above MOSFET. By applying acceleration such as vibration, the displacement electrode is displaced in a direction away from or toward the surface of the semiconductor substrate, that is, the channel region. When the displacement electrode moves away from the surface of the semiconductor substrate, the amount of charge induced in the channel region sharply decreases,
The channel becomes thinner and the resistance between the source and drain increases. On the other hand, when the displacement electrode approaches the surface of the semiconductor substrate, the amount of charges induced in the channel region sharply increases, the channel becomes thicker, and the resistance between the source and the drain decreases. Therefore, it is possible to directly know the displacement amount of the displacement electrode by measuring the resistance between the source region and the drain region while a constant reverse bias voltage is applied to the displacement electrode. The applied acceleration can be calculated. The reverse bias voltage applied to the displacement electrode must be large enough to form the inversion layer, but the dielectric constant of vacuum is generally SiO.
_Since it is about 1/4 of the dielectric constant of the ₂ oxide film, the bias voltage needs to be about 4 times larger than that of the MOSFET having the same structure.

As the semiconductor used for the semiconductor substrate,
There is no particular limitation, and a compound semiconductor such as Si, Ge, or GaAs may be used. The conductivity type of the semiconductor substrate is p.
Although it may be of either the n-type or the n-type, it is preferable to use the p-type semiconductor for detecting the high-speed vibration because the effective mass of the carrier that can be formed in the n-type inversion channel is small. Also, p
A complementary type may be formed by combining a semiconductor of n-type and a semiconductor of n-type. At least one source region and at least one drain region are required, but the number is not limited to one, and a plurality of source regions and a plurality of drain regions may be provided for one displacement electrode. ..

By forming a plurality of such mechanical sensors in a single semiconductor substrate and devising their arrangement, a sensor capable of detecting acceleration vectors in various directions can be obtained.

In order to attach the displacement electrode to the semiconductor substrate, a spacer layer may be laminated on the surface of the semiconductor substrate other than the element region, and one end of the displacement electrode may be fixed to the upper surface of the spacer layer. According to this structure, the displacement electrode has a cantilever structure, and the displacement electrode is sensitive to displacement. As the spacer layer, an oxide film or the like formed by oxidizing the surface of the semiconductor substrate can be used. Alternatively, an elastic body may be laminated on the element region, and the displacement electrode may be bonded to the upper surface of the elastic body. in this case,
The elastic body is deformed by the acceleration and the mass of the displacement electrode, and a change in the distance between the displacement electrode and the element region due to this deformation is detected.

Between the surface of the semiconductor substrate and the displacement electrode,
Although a region for displacing the displacement electrode is necessary, an extremely thin oxide film may be provided on the surface of the semiconductor substrate in consideration of stabilization of the surface of the semiconductor substrate. In addition, dangling bonds on the surface of the semiconductor substrate may be stabilized by using a sulfide or a phosphorus compound.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 (A) is a schematic cross-sectional view showing the structure of the mechanical quantity sensor of the first embodiment of the present invention, FIG. 1 (B) is a cross-sectional view taken along line XX, and FIG. 1 (c) is a top view.

In this embodiment, the semiconductor substrate 11 made of p-type GaAs is used. As shown in the figure, the source region 12 and the drain region 13 are formed on the surface of the semiconductor substrate 11.
And a source region 12 and a drain region 13
The oxide film 1 is formed on the surface of the semiconductor substrate 11 at a position away from
4 are provided. One end of the displacement electrode 15 is fixed to the upper surface of the oxide film 14. The displacement electrode 15 has a rectangular plate shape, and the other end is a free end.
The protrusion is formed above the source region 12, the train region 13, and the region connecting the source region 12 and the drain region 13 of the semiconductor substrate 11. That is, the displacement electrode 15 has a cantilever structure in which one end is fixed to the oxide film 14. The material and size of the displacement electrode 15 are selected so that the free end side of the displacement electrode 15 bends toward or away from the semiconductor substrate 11 due to its own weight and acceleration. Then, at an acceleration that is normally applied, the free end of the displacement electrode 15 is moved to the semiconductor substrate 1.
It does not come into contact with the surface of 1. The thickness of the oxide film 14, that is, the distance between the displacement electrode 15 and the surface of the semiconductor substrate 11 depends on the field effect of the reverse bias voltage applied to the displacement electrode 15 so that the channel 16 which is an inversion layer is formed on the surface of the semiconductor substrate 11. It is set to be equal to or less than the interval at which it is formed. Source region 12 and drain region 1
3 and the displacement electrode 15 are connected to terminals S, D and G for applying a bias voltage, respectively.

Next, an example of a method of manufacturing the mechanical quantity sensor will be described. First, S is formed on the surface of the semiconductor substrate 11 made of p-type GaAs by a normal semiconductor process.
The source region 12 is activated by ion implantation of i ions for activation.
Then, the drain region 13 is formed, and the oxide film 14 is further formed to a thickness of 1000Å. Then, a photoresist layer (not shown) having the same thickness as the oxide film 14 is formed on the entire surface of the semiconductor substrate 11 (including the source region 12 and the drain region 13) except the oxide film 14. Form.
After that, a titanium film having a thickness of 3000 Å is formed on the entire upper surface of the photoresist layer and the oxide film 14 by vapor deposition, and the titanium film is patterned by a photolithography process to form a displacement electrode 15, and finally a wet etching process is performed. The photoresist layer may be removed by. In order to stabilize the surface of the semiconductor substrate 11, dangling bonds on the surface and sulfur atoms are bonded using sulfide.

Next, regarding the operation of this mechanical quantity sensor,
The description will be given mainly with reference to FIG.

When a constant reverse bias voltage is applied to the displacement electrode 15 corresponding to the gate electrode of the MOSFET, a channel 16 which is an inversion layer is formed on the surface of the semiconductor substrate 11 directly below the displacement electrode 15. Figure 1 (B)
Then, the channel 16 when acceleration is not applied is represented by the solid line a. Since the dielectric constant of the oxide film 14 is larger than that of vacuum or air, the thickness of the channel 16 is large at the portion where the oxide film 14 is provided.

It is assumed that acceleration due to vibration or the like is applied to the mechanical quantity sensor under the condition that a constant reverse bias voltage is applied to the displacement electrode 15. Then, the free end side of the displacement electrode 15 bends in accordance with the direction and magnitude of acceleration, and moves away from the direction of the semiconductor substrate 11 (dotted line in the figure) or approaches the surface of the semiconductor substrate 11 (dotted line in the figure). Displace. Since a reverse bias voltage is applied to the displacement electrode 15, with this displacement,
The shape of the channel 16 changes. That is, the displacement electrode 1
When 5 is displaced away from the semiconductor body 11, the shape of the channel 16 becomes thin as shown by the chain line b in the figure. On the other hand, the semiconductor substrate 11
When it is displaced in the direction of approaching, the shape of the channel 16 increases in thickness, as indicated by the dotted line c in the figure. The change in the cross-sectional shape of the channel 16 depends on the source region 12-
If an acceleration is applied that is directly connected to the change in the electric resistance value between the drain regions 13 and, in the end, the displacement electrode 15 is displaced away from the semiconductor substrate 11, the source region 12 is obtained.
The electric resistance between the drain regions 13 increases, and if an acceleration in the opposite direction is applied, this electric resistance decreases, and the amount of change in the electric resistance corresponds to the absolute value of the acceleration. Therefore, by monitoring the electrical resistance between the source region 12 and the drain region 13, the direction and magnitude of the acceleration applied to the mechanical quantity sensor can be detected.

In this case, since the mechanical quantity sensor is formed by an ordinary semiconductor manufacturing process, it is easy to manufacture, and the change of the channel 16 is sensitive to the displacement of the displacement electrode 15, so that it is highly sensitive. Acceleration can be detected. Further, since the displacement electrode 15 can be formed minutely, the displacement electrode 15 can immediately follow the change in acceleration, and a mechanical quantity sensor having a high response speed can be obtained.

Next, a second embodiment of this embodiment will be described. FIG. 2A is a schematic cross-sectional view showing the configuration of the mechanical quantity sensor of this embodiment, and FIG. 2B is a cross-sectional view taken along the line YY. This embodiment is an example in which p-type Si is used as the semiconductor substrate 11, and a thermal oxide film 17 is further provided on the surface of the semiconductor substrate 11.

An example of a method of manufacturing this mechanical quantity sensor will be described. First, the surface of the semiconductor substrate 21 made of p-type Si was thermally oxidized to form a thermal oxide film 17 having a thickness of 100Å.
Next, P (phosphorus) ions are implanted using ion implantation,
It was activated to form the source region 12 and the drain region 13. And the source region 12 and the drain region 1
1000 Å on the thermal oxide film 17 at a position away from 3
Oxide film 14 was formed. After that, the displacement electrode 15 was formed by the same method as in the above-described first embodiment. In this embodiment, a 1000 Å thick tungsten film is used as the displacement electrode 15.

In this mechanical quantity sensor, bias application,
The operation is the same as that of the first embodiment, but since the thermal oxide film 17 is formed on the surface of the semiconductor substrate 11, the electric capacitance of the portion immediately below the displacement electrode 15 is equivalent to that of capacitors connected in series, Therefore, the reverse bias voltage applied to the displacement electrode 15 needs to be higher than that in the first embodiment, but the stability is extremely good.

Next, a third embodiment of this embodiment will be described. FIG. 3 is a schematic cross-sectional view showing the structure of the mechanical quantity sensor of this embodiment. In this embodiment, p is used as the semiconductor substrate 11.
Type Si, a thermal oxide film 17 and an elastic body 18 are further laminated on the surface of the semiconductor substrate 11, and the displacement electrode 15 is made of the elastic body 18.
Is held by the semiconductor substrate 11. Therefore, the oxide film 14 for supporting the displacement electrode 15 in a cantilever structure is not provided.

An example of a method of manufacturing this mechanical quantity sensor will be described. First, the surface of the semiconductor substrate 11 made of p-type Si was thermally oxidized to form a thermal oxide film 17 having a thickness of 100Å.
Next, P (phosphorus) ions are implanted using ion implantation,
It was activated to form the source region 12 and the drain region 13. Then, an elastic body 18 having a thickness of 1000 Å was formed on the thermal oxide film 17 so as to extend over the positions corresponding to the source region 12 and the drain region 13. The elastic body 18 is made of, for example, silicon rubber having a thickness of about 2000 to 5000 Å and can be formed by a coating method using a spinner or the like. After that, the displacement electrode 15 was thermocompression bonded onto the elastic body 18. In this case, since the displacement electrode 15 is supported by the elastic body 18, in order to secure the displacement amount of the displacement electrode 15, it is necessary to make the mass of the displacement electrode 15 heavier than that in each of the above-described embodiments. Therefore, the displacement electrode has a thickness of 5
A silver plate of about 0 μm was used.

In this embodiment, the elastic body 18 is deformed by the own weight of the displacement electrode 15 when acceleration is applied, so that the distance between the displacement electrode 15 and the semiconductor substrate 11 changes, and the acceleration can be detected.

[0025]

As described above, according to the present invention, in the MOS type FET structure, the displacement electrode corresponding to the gate electrode can be displaced by the applied mechanical amount, so that the displacement of the minute displacement electrode can be reduced. Since it can be detected as a large change in, a mechanical quantity sensor that has high sensitivity, is easy to manufacture, and can easily process a detection signal can be obtained.

[Brief description of drawings]

1A is a schematic cross-sectional view showing the structure of a mechanical quantity sensor according to a first embodiment of the present invention, FIG. 1B is a cross-sectional view taken along line XX, and FIG. 1C is a top view of the mechanical quantity sensor. Is.

2A is a schematic cross-sectional view showing the configuration of a mechanical quantity sensor according to a second embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along the line YY.

FIG. 3 is a schematic cross-sectional view showing the configuration of the mechanical quantity sensor of the third embodiment of the present invention.

[Explanation of symbols]

 11 semiconductor substrate 12 source region 13 drain region 14 oxide film 15 displacement electrode 16 channel 17 thermal oxide film 18 elastic body

Claims (7)

[Claims] 1. A mechanical quantity sensor for detecting a mechanical quantity, comprising: a semiconductor body of a first conductivity type; and a second conductivity type provided in at least one of the semiconductor body and different from the first conductivity type. Source region of conductivity type, the second conductivity type drain region provided in the surface of the semiconductor substrate at a distance from the source region, and the source region and the drain of the surface of the semiconductor substrate. When a region integrally including a region is set as an element region, a mechanical quantity sensor having a displacement electrode which is provided so as to be separated from the element region to such an extent that an electric field effect can be exerted and is displaceable with respect to the element region. .. 2. The mechanical quantity sensor according to claim 1, wherein at least one solid layer is provided between the displacement electrode and the element region. 3. The mechanical quantity sensor according to claim 1, wherein the displacement electrode is attached to the semiconductor substrate via a spacer layer in a region other than the element region. 4. The mechanical quantity sensor according to claim 3, wherein the spacer layer is made of an oxide of the semiconductor material used for the semiconductor substrate. 5. The mechanical quantity sensor according to claim 1, wherein an elastic body is filled between the element region and the displacement electrode, and the displacement electrode is held on the semiconductor substrate by the elastic body. 6. The mechanical quantity sensor according to claim 1, wherein the displacement electrode is displaced by an acceleration applied to the mechanical quantity sensor. 7. A means for applying a bias voltage between the source region and the drain region, and a means for applying a bias voltage between any one of the source region and the drain region and the displacement electrode. The mechanical quantity sensor according to claim 1, further comprising: