JP4771329B2 - Capacitive sensor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a capacitive sensor.

  Capacitive sensors are widely used for pressure sensors, acceleration sensors, and the like. This capacitive sensor uses the fact that the capacitance between the electrodes changes depending on the distance between the electrodes, as one of the two electrodes is fixed, and the other changes the position by receiving pressure. Is.

A problem with this method is that the dielectric constant that determines the amount of charge stored in the capacitor is low. This is because a gas having a low dielectric constant such as vacuum or air must be used in order to make the distance between the electrodes variable. Therefore, in order to improve sensitivity, the electrode area must be increased. This leads to an increase in the element area, which causes a decrease in manufacturing yield and hinders miniaturization. In order to solve this problem, it is conceivable that the element has a signal amplification function. As one of the methods, there is a capacitance pressure sensor using a field effect transistor (FET) (Non-patent Document 1).
S. Buschnakowski, A. Bertz, W. Brauer, S. Heinz, R. Schuberth, G. Ebest and T. Gessner: "DEVELOPMENT AND CHARACTERISATION OF A HIGH ASPECT RATIO VERTICAL FET SENSOR FOR MOTION DETECTION" TRANSDUCERS '03, Boston, June 8-12, 2003, p. 1391-1394.

However, although the capacitive sensor disclosed in Non-Patent Document 1 can detect pressure applied in one direction and acceleration received in one direction with high sensitivity, it has a vertical structure. Therefore, there is a problem that the structure is complicated and the manufacturing process is complicated.
Further, the capacitive sensor disclosed in Non-Patent Document 1 can detect pressure applied in one direction and acceleration received in one direction with high sensitivity. There was a problem that acceleration could not be detected.

Therefore, a first object of the present invention is to provide a capacitive sensor that has a simple structure and is easy to manufacture.
A second object of the present invention is to provide a capacitive sensor that can detect pressure and acceleration in two or more directions with high sensitivity.

In order to achieve the first object described above, a first capacitive sensor according to the present invention has two main surfaces facing each other, and a source region of a first conductivity type on one surface thereof. A substrate having first conductivity type drain regions provided at predetermined intervals and having a second conductivity type region located between the source region and the drain region as a channel region, and a gate electrode plate facing the channel region The gate electrode plate is made of a second conductivity type silicon single crystal and is movably provided in one direction parallel to the surface of the channel region, and the channel region and the gate electrode plate are opposed to each other. A force applied to the gate electrode plate is detected based on a change in area.

In order to achieve the first object, the second capacitive sensor according to the present invention has two main surfaces facing each other, and a first conductivity type source region is formed on one surface thereof. A drain region of the first conductivity type is provided at a predetermined interval, a substrate having a second conductivity type region located between the source region and the drain region as a channel region, and a predetermined interval from the channel region. The gate electrode plate is made of a second conductivity type silicon single crystal, and a force applied to the gate electrode plate based on a change in the distance between the channel region and the gate electrode plate. It is characterized by detecting.

  Furthermore, a capacitive sensor according to the present invention for achieving the second object includes two first capacitive sensors capable of detecting forces applied in different directions. Or a first capacitive sensor and a second capacitive sensor.

According to the first and second capacitive sensors according to the present invention configured as described above, it is possible to provide a capacitive sensor that is simple in structure and easy to manufacture.
Further, two first capacitive sensors capable of detecting forces applied in different directions are provided, or the first capacitive sensor and the second capacitive sensor are provided. By providing this, it is possible to provide a capacitive sensor capable of detecting pressure and acceleration in two or more directions.

The capacitance type sensor according to the embodiment of the present invention will be described below.
In the capacitive sensor according to this embodiment, for example, a detection unit 100z that detects pressure or acceleration in the z direction, which is a direction perpendicular to the substrate, on a p-type silicon substrate, and in one direction parallel to the substrate. A detection unit 100x that detects pressure or acceleration in a certain x direction and a detection unit 100y that detects pressure or acceleration in the y direction that is parallel to the substrate and orthogonal to the x direction are provided.

  In the capacitive sensor according to the present embodiment, the detection units 100x to 100z each have an n-type drain region, an n-type source region, a drain region, and an n-type formed on one surface of the p-type silicon substrate 10. A movable gate electrode plate movably provided in a direction to be detected on the channel region between the source regions of the mold, and movable based on the change in the gate capacitance accompanying the displacement of the movable gate electrode plate The pressure or acceleration applied to the gate electrode plate is detected.

Hereinafter, the capacitive sensor according to the embodiment of the present invention will be described in more detail.
In the capacitive sensor according to the embodiment, the detection unit 100x includes an n-type drain region 4x and an n-type source region 5x provided on one surface of the p-type silicon substrate 10 with a predetermined interval therebetween. A movable gate electrode plate 1x is provided so as to be movable in the x direction above a channel region 6x that is a region between the drain region 4x and the source region 5x.

  The movable gate electrode plate 1x is a columnar beam that is long in one direction so that the position is displaced in the x direction by a distance corresponding to the force received when the gate electrode plate 1 receives a force in the x direction. Are held by two support beams 2x. The two support beams 2x are provided so that the major axes thereof coincide with each other in the y direction orthogonal to the x direction. One side of the two support beams 2x is connected to one side of the movable gate electrode plate 1x and the other is connected to the other side. A side opposite to the one side of the movable gate electrode plate 1x is connected to the central portion.

  A columnar fixing portion 3x for lifting and fixing the support beam 2x is provided at each end of the support beam 2x. In this way, the two support beams 2x and the movable gate electrode plate 1x are held hollow, and when the gate electrode plate 1x receives a force in the x direction, the support beam 2x is elastically deformed according to the received force. The position of the movable gate electrode plate 1x is displaced in the x direction by a distance corresponding to the received force.

  Here, in the detection unit 100x, the connection to the gate power supply circuit for applying a predetermined gate voltage to the gate electrode plate 1x does not hinder the displacement of the movable gate electrode plate 1x, for example, both ends of the support beam 2x. Done in

The detection unit 100y has the same configuration as that of the detection unit 100x except that each configuration unit is arranged so that the arrangement in the detection unit 100x is rotated 90 degrees.
In the detection unit 100y, the same elements as those in the detection unit 100x are denoted by the same reference numerals, and y is denoted as a subscript.

  In the detection unit 100y configured as described above, the two support beams 2y and the movable gate electrode plate 1y are held in a hollow state, and when the gate electrode plate 1y receives a force in the x direction, it corresponds to the received force. As a result, the support beam 2y is elastically deformed, and the position of the movable gate electrode plate 1y is displaced in the y direction by a distance corresponding to the received force.

  In the capacitive sensor of the embodiment, the detection unit 100z includes an n-type drain region 4z and an n-type source region 5z provided on one surface of the p-type silicon substrate 10 at a predetermined interval. A movable gate electrode plate 1z provided so as to face the channel region 6z, which is a region between the drain region 4z and the source region 5z, with a predetermined interval, and to change the interval according to the force applied in the z direction. It is comprised including.

  The movable gate electrode plate 1z has a diaphragm structure with one end fixedly connected to the fixed portion 3z and fixed at both ends, and the gate electrode plate 1z received when receiving a force in the z direction. The other end is displaced in the z direction by a distance corresponding to the force.

  Here, in the detection unit 100z, the connection with the gate power supply circuit for applying a predetermined gate voltage to the gate electrode plate 1z is, for example, on the fixed unit 3z so as not to inhibit the displacement of the movable gate electrode plate 1z. Done.

  In the detection unit 100z configured as described above, when the gate electrode plate 1z having a diaphragm structure fixed at both ends receives a force in the z direction, the gate electrode plate 1z is elastically deformed according to the received force and is movable. As a result, the distance between the channel region 6z and the movable gate electrode plate 1z is changed according to the force applied in the z direction.

Hereinafter, the operation of the capacitive sensor according to the present embodiment will be described.
Here, first, the principle of operation of the field effect transistor will be briefly described by taking an n-channel MOSFET as an example. In this MOSFET, a gate electrode is arranged on a silicon layer with an oxide film interposed therebetween, thereby controlling the current flowing between the source and drain regions formed in the silicon. In this structure, the laminated structure of the gate electrode, the oxide film, and the silicon layer behaves like a capacitor. First, when no voltage is applied to the gate electrode, the semiconductor layer immediately below the gate is p-type, so that it becomes an n + type source, p-type silicon, and n + drain, and no current flows between the source and drain. Next, when a positive charge is applied to the gate electrode, a positive charge (hole) is accumulated in the gate electrode due to the capacitor structure of the gate portion. Accordingly, electrons that are negative charges are induced near the oxide film interface in the silicon region. When the density of the induced electrons exceeds the density of holes, which are majority carriers of p-type silicon, the properties of the semiconductor layer are reversed and become n-type. This is called an inversion layer. By forming the inversion layer, the source and drain of n + type are conducted, and current flows.

The characteristics of the drain current at this time are shown in FIG. As can be seen from FIG. 2, in the MOSFET, the drain current shows a characteristic that it is saturated after abrupt increase as the drain voltage increases at a certain gate voltage. The amount of current is proportional to the square of the gate voltage. A bias region in which the drain current is saturated is referred to as a saturation region, and the drain current _ID in this region is expressed by Expression (1).

Here, μ is the mobility, L is the gate length, W is the gate width, V _G is the gate voltage, and V _t is the threshold voltage. C _ox is the capacitance per unit area of the oxide film, and C _ox = ε _r · ε ₀ A / t _ox (ε _r : relative dielectric constant, ε ₀ : dielectric constant of vacuum, A: area, t _ox : Oxide film thickness).

  The above is a general principle of operation of a MOSFET. In the present invention, the pressure or acceleration is detected as follows using a movable gate electrode plate whose relative position with respect to the channel region changes according to the applied force. ing.

First, in the detectors 100x and 100y that detect the force applied in the direction parallel to the substrate, the drain width ID changes because the gate width W changes as shown in FIG. 3 due to the displacement of the movable gate electrode plates 1x and 1y. To do. At this time, it is considered that the mobility μ, the gate length L, the unit capacitance C _ox and the threshold voltage V _t in the equation (1) do not change, so that the drain under the constant gate voltage Vg The change in the current ID may be considered to be due to the change in the gate width W. Further, the elastic displacement amount with respect to the force applied by the support beams 2x and 2y can be easily obtained from the Young's modulus of the support beams 22x and 2y and the structural parameters such as the length and cross-sectional shape of the support beams 2x and 2y. Therefore, it is possible to detect the pressure or acceleration applied in the x direction and the y direction by the detectors 100x and 100y, respectively.

Further, in the detector 100z that detects the force applied in the direction perpendicular to the substrate (z direction), the distance between the channel region 6z and the movable gate electrode plate 1z changes due to the displacement of the movable gate electrode plate 1z. ) Changes in unit capacitance C _ox , and the drain current ID changes. At this time, it is considered that the mobility μ, the gate length L, the gate width W and the threshold voltage Vt in the equation (1) do not change, so that the drain current under a constant gate voltage V _G The change in ID may be considered to be due to the change in the distance between the channel region 6z and the movable gate electrode plate 1z. Further, the elastic displacement amount with respect to the force applied by the gate electrode plate 1z can be easily obtained from the Young's modulus of the gate electrode plate 1z and the structural parameters such as the length and cross-sectional shape of the gate electrode plate 1z. Therefore, the pressure or acceleration applied in the z direction can be detected by the detector 100z.

In the capacitance type sensor of the present embodiment, since there is a space between the movable gate electrode plate and the channel region instead of the oxide film, ε _r is 1 in the equation for _obtaining the unit capacitance C _ox . t _ox needs to be the distance between the movable gate electrode plate and the channel region surface.

  The capacitive sensor according to the embodiment of the present invention configured as described above includes a detection unit 100z that detects pressure or acceleration in the z direction, which is a direction perpendicular to the substrate, and a direction parallel to the substrate. Since the detection unit 100x that detects pressure or acceleration in a certain x direction and the detection unit 100y that detects pressure or acceleration in the y direction that is parallel to the substrate and orthogonal to the x direction are provided, the applied pressure or acceleration The x component, y component, and z component can be detected, and the magnitude and direction of the applied pressure or acceleration can be specified.

  Further, since the capacitance type sensor of the present embodiment detects the force applied to the movable gate electrode plate based on the change of the drain current ID proportional to the square of the gate voltage, it is detected by the applied gate voltage. The detected pressure change can be amplified and extracted, and detection with high sensitivity is possible. Further, the detection sensitivity can be adjusted by the gate voltage, an appropriate sensitivity can be set according to the magnitude of the pressure or acceleration, and the pressure or acceleration can be detected with high accuracy. That is, a wide range of pressures or accelerations can be detected while maintaining high sensitivity by setting the gate voltage to an appropriate value according to the range of pressures or accelerations to be measured.

Furthermore, while the capacitance in the conventional capacitance pressure sensor is proportional to the area between the counter electrodes constituting the capacitor, in the capacitance type sensor of the present embodiment, as can be seen from the equation (1), The detected drain current ID is inversely proportional to the gate length and proportional to the gate width. Therefore, by shortening the gate length, it is possible to improve the sensitivity while reducing the area of the portion that is displaced by receiving pressure or acceleration.
Therefore, it is possible to further reduce the size in combination with being able to amplify and output with the gate voltage.

  In the capacitive sensor according to the present embodiment configured as described above, the detector 100x and the detector 100y may change in the z direction in response to the force applied in the z direction. In this case, based on the force applied in the z direction detected by the detector 100z, the influence of the force applied in the z direction in the detector 100x and the detector 100y is subtracted and applied in the x direction or the y direction. Only the force can be calculated.

Hereinafter, a method for manufacturing the capacitance pressure sensor of the present embodiment will be described.
4A to 4L used in the following description show cross sections taken along line AA ′ in FIG. 1 in the order of steps.

First, for example, an SOI substrate having a thickness of 600 μm is prepared. In this SOI substrate, an SiO ₂ layer 12 having a thickness of 2 μm, which is an insulating layer, is formed on a p-type silicon substrate having a thickness of about 510 μm, and a p-type silicon layer 11a having a thickness of 90 μm is formed on the SiO ₂ layer 12. (FIG. 4A).
The SiO ₂ layer 12 that is an insulating layer can use a buried oxide film.

  Next, an aluminum film 13 is formed on the surface of the p-type silicon layer 11a, and the aluminum film 13 is patterned using a resist film 14 patterned into a predetermined pattern (FIG. 4B). Here, the aluminum film 13 has a planar shape in which the movable gate electrode plate 1z and the fixed portion 3z are combined in the detection unit 100z, and the movable gate electrode plates 1x and 1y and the support beams 2x and 2y in the detection units 100x and 100y. Patterned so as to have a combined planar shape.

  Then, using the patterned aluminum film, the p-type silicon layer 11a is etched by, for example, a Bosch process (FIG. 4C). As a result, the portion where the movable gate electrode plate 1z and the fixed portion 3z are integrated, the portion where the movable gate electrode plate 1x and the support beam 2x are integrated, and the movable gate electrode plate 1y and the support beam 2y are integrated. The p-type silicon layer 11a is removed leaving the formed portion (FIG. 4D).

In this etching for gate processing, it is preferable to add oxygen gas to the etching gas in order to obtain an etching shape with excellent perpendicularity. When oxygen gas is not included in the etching gas, the shape after etching becomes an inversely tapered shape with a wide top and a narrow bottom, and a large number of needle-like Si pillars that may be caused by the micromask tend to occur It is in. However, when an etching gas to which oxygen gas is added is used, a good etching shape with a very small difference between the upper and lower widths can be obtained. This is considered to be due to the fact that the Si surface on the side wall by oxidation was protected by the addition of oxygen, and the etching surface was cleaned by oxygen radicals.
Specifically, for example, etching mixed at a ratio of SF ₆ : 100 (sccm), C ₄ F ₈ : 0.5 (sccm), Ar: 0.5 (sccm), and O ₂ : 10 (sccm). When a gas is used, a gate electrode plate with a very small difference between the upper and lower widths can be formed.

  Next, a source region 5 (x, y, z) and a drain region 4 (x, y, z) are formed on both sides of the movable gate electrode plate 1 (x, y, z) by an ion implantation method. At the same time, ion implantation is performed to impart conductivity to the gate electrode plates 1x, 1y, 1z (including the support beams 2x, 2y and the fixing portion 3z).

Specifically, in order to expose the surface of the region to be ion-implanted using the resist 15, the SiO ₂ layer 12 is patterned (FIG. 4E) and, for example, an n-type dopant such as phosphorus is ion-implanted. As a result, an n-type source region 5 (x, y, z) and an n-type drain region 4 (x, y, z) are formed (FIG. 4F). In FIG. 4F, what is indicated by reference numeral 16 is a protective film for ion implantation for protecting the surface at the time of ion implantation, and is formed by thinly oxidizing the surface of the substrate 10. .
After forming the gate portion, since there is a step of about 100 μm, it is difficult to apply the resist by spin coating. However, for example, the resist can be formed by spray coating.

Next, predetermined wiring is performed.
First, in order to form ohmic electrodes 41, 51, and 31 that are in ohmic contact with the source region 5 (x, y, z), the drain region 4 (x, y, z), and the gate electrode 1, a part of the protective film 16 is formed. And the surface of the source region 5 (x, y, z), the drain region 4 (x, y, z) and the gate electrode 1 is exposed in the removed portion (FIG. 4G), and the exposed portion is exposed. Ohmic electrodes 41, 51, and 31 are formed, and then the protective film 16 and the like are removed (FIG. 4H).

Then, aluminum wirings 42 and 52 connected to the ohmic electrodes 41 and 51, respectively, are formed (FIG. 4J).
As described above, a MOSFET is manufactured in which the p-type Si layer on the upper part of the SOI substrate serves as a gate and the buried oxide film serves as a gate oxide film.

In the present invention, furthermore, under the SiO ₂ layer 12, the movable gate electrode plate 1y support plate SiO ₂ layer 12 under the 2y and movable gate electrode plates 1z, under the movable gate electrode plate 1x support plate 2x The capacitive sensor of the embodiment shown in FIG. 1 is completed by removing the SiO ₂ layer 12 in the buffered hydrofluoric acid. When removing the SiO ₂ layer 12, the fixed portion 3x for fixing the ends of the two ends and the support plate 2y of the support plate 2x, and SiO ₂ layer 12 serving as a 3y, SiO ₂ layer for fixing the fixing portion 3z to the substrate By preventing them from being removed, the respective fixing portions can be formed simultaneously.

According to the manufacturing method as described above, the capacitive sensor according to the embodiment having the movable gate structure can be easily obtained by finally removing the predetermined SiO ₂ layer 12 using the MOSFET manufacturing process. Can be produced.

  Here, for example, the gate lengths and gate widths of the detectors 100x, 100y, and 100z can be set to ranges of 10 to 100 μm and 50 to 500 μm, respectively, but the present invention is not limited to this.

It is a perspective view which shows the structure of the electrostatic type sensor of embodiment which concerns on this invention. It is a graph which shows the drain current with respect to the drain voltage of a MOS field effect transistor. It is a top view which shows typically the change of the gate width W in the electrostatic capacitance type sensor of embodiment. It is sectional drawing of the SOI substrate used for manufacture of the electrostatic capacitance type sensor of embodiment. It is sectional drawing after forming the mask for forming a gate electrode plate in the manufacture process of the capacitive sensor of embodiment. It is sectional drawing in the middle of etching in order to form a gate electrode plate in the manufacture process of the capacitive sensor of embodiment. It is sectional drawing when the etching is completed in order to form the gate electrode plate in the manufacturing process of the capacitive sensor of the embodiment. FIG. 6 is a cross-sectional view after forming a mask for ion implantation to form a drain region and a source region in the manufacturing process of the capacitive sensor according to the embodiment. FIG. 10 is a cross-sectional view after forming a drain region and a source region by ion implantation in the manufacturing process of the capacitive sensor according to the embodiment. It is sectional drawing after forming the mask for forming a drain electrode and a source electrode in the manufacture process of the capacitive sensor of embodiment. It is sectional drawing after forming a drain electrode and a source electrode in the manufacture process of the capacitive sensor of embodiment. It is sectional drawing after forming the aluminum wiring connected to the drain electrode and the source electrode in the manufacture process of the capacitive sensor of embodiment. FIG. 5 is a cross-sectional view after forming a SiO 2 film under a gate electrode plate in the manufacturing process of the capacitive sensor according to the embodiment.

Explanation of symbols

1x, 1y, 1z: movable gate electrode plate,
2x, 2y: support beam,
3x, 3y, 3z: fixed part,
4x, 4y, 4z: drain region,
5x, 5y, 5z: source region,
6x, 6y, 6z: channel region.

Claims (7)

There are two opposing main surfaces, and a first conductivity type source region and a first conductivity type drain region are provided at a predetermined interval on one surface, and located between the source region and the drain region. A substrate having a second conductivity type region as a channel region;
A gate electrode plate facing the channel region,
The gate electrode plate is made of a second conductivity type silicon single crystal and is movably provided in one direction parallel to the surface of the channel region, so that the facing area of the channel region and the gate electrode plate changes. A capacitive sensor that detects a force applied to the gate electrode plate based on the capacitance sensor.   The gate electrode plate is supported by two support beams having a long axis perpendicular to the one direction and provided in parallel to the one surface with a predetermined distance from the one surface. The capacitive sensor according to claim 1, wherein each of the two support beams is solid on the one surface. In the one surface, apart from the source region and the drain region, a second source region of the first conductivity type and a second drain region of the first conductivity type are provided at a predetermined interval, and the second source region A second channel region of a second conductivity type is formed between the second drain regions, and a second gate electrode plate facing the second channel region is further provided;
The second gate electrode plate is made of a second conductivity type silicon single crystal , and is provided so as to be movable in a direction parallel to the one surface and perpendicular to the one direction. The capacitive sensor according to claim 1, wherein a force applied to the second gate electrode plate is detected based on a displacement of an area facing the two gate electrode plate.   The second gate electrode plate is supported by two second support beams which have a long axis in the one direction and are provided in parallel to the one surface with a predetermined distance from the one surface, The capacitive sensor according to claim 3, wherein both ends of each of the two second support beams are solid on the one surface. On the one surface, a third source region of the first conductivity type and a third drain region of the first conductivity type are further provided at a predetermined interval, and a second gap is provided between the third source region and the third drain region. A third channel region of conductivity type is provided, and further includes a third gate electrode plate facing the third channel region;
The third gate electrode plate is made of a second conductivity type silicon single crystal and is added to the third gate electrode plate based on a change in the distance between the third channel region and the third gate electrode plate. The capacitive sensor according to any one of claims 1 to 4, wherein the electrostatic force sensor detects an applied force. There are two opposing main surfaces, and a first conductivity type source region and a first conductivity type drain region are provided at a predetermined interval on one surface, and located between the source region and the drain region. A substrate having a second conductivity type region as a channel region;
A gate electrode plate facing the channel region at a predetermined interval;
The gate electrode plate is made of a second conductivity type silicon single crystal and detects a force applied to the gate electrode plate based on a change in a distance between the channel region and the gate electrode plate. Type sensor. A method of manufacturing a capacitive sensor comprising a substrate having a channel region between a first conductivity type source region and a first conductivity type drain region, and a gate electrode plate facing the channel region,
In an SOI substrate having a second conductivity type single crystal silicon layer over an insulating layer on a second conductivity type silicon substrate, the second conductivity type single crystal silicon layer is etched to form the gate electrode plate and the gate electrode plate Removing the second conductivity type single crystal silicon layer leaving a portion to be a fixed portion;
Removing the insulating layer on both sides of the portion to be the gate electrode plate and implanting impurities into the removed portion to form the source region and the drain region;
Removing an insulating film under a portion to be the gate electrode plate;
A method of manufacturing a capacitive sensor, comprising:

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