JP3355812B2 - Semiconductor yaw rate sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor yaw rate sensor using a semiconductor substrate, and more particularly, to a semiconductor yaw rate sensor that can be used for vehicle body control, navigation, and the like.

[0002]

2. Description of the Related Art As a yaw rate sensor for detecting, for example, a yaw rate acting on the body of an automobile, a vibration gyroscope as disclosed in Japanese Patent Application Laid-Open No. 2-113817 is known.

In this vibrating gyroscope, a piezoelectric element is adhered to a specified surface of a metal square bar to form a vibrating body.
This is configured to be supported by a thin rod. The angular velocity sensor disclosed in Japanese Patent Application Laid-Open No. 4-142420 is configured by bonding a piezoelectric element to a metal sound or a wire.

That is, in any of these devices for detecting an acceleration such as a yaw rate, a piezoelectric element vibrates the main body, and a distortion caused by the Coriolis force generated by the yaw rate to be measured is detected by the piezoelectric element. To detect by the change of the applied voltage.

[0005] The performance of the sensor mechanism configured as described above, such as the detection sensitivity, depends on the method of supporting the vibrating body and the processing accuracy. Therefore, in order to create a high-performance sensor mechanism, the processing is required. In addition to the difficulty in assembling, there is a problem that it is inevitably expensive, and it is not easy to reduce the size of the sensor mechanism due to restrictions on processing and assembling.

In order to solve such a problem, the present applicant has previously filed an application for a transistor-type yaw rate sensor to which semiconductor technology is applied by utilizing a transistor-type displacement detection mechanism (Japanese Patent Application No. Hei 5 (1994) -58139). 311762
issue).

[0007] This transistor type yaw rate sensor,
A movable electrode having a beam structure disposed at a predetermined interval above the semiconductor substrate, a movable electrode having a beam structure formed on the semiconductor substrate with respect to the movable electrode, and a movable electrode having a beam structure formed on the semiconductor substrate with respect to the movable electrode. When the movable electrode having the beam structure is vibrated by using an electrostatic force, the movable electrode is vertically displaced by the action of the yaw rate, and a current change between the source and drain electrodes due to this displacement is provided. Is used to detect the yaw rate.

[0008]

However, in such a transistor-type yaw rate sensor, since the transistor-type displacement detection mechanism has temperature dependence, the reference position drifts due to temperature and the angular velocity .omega. There is a problem that the detection accuracy is reduced due to the apparent change in the displacement due to the temperature change. Then, this invention was made in view of the said problem, and it aims at providing the semiconductor yaw rate sensor which reduced the temperature dependence and improved the detection accuracy.

[0009]

According to the present invention, in order to attain the above object, according to the first aspect of the present invention, a semiconductor substrate is located above a surface of the semiconductor substrate at a predetermined interval. A movable electrode and a position above the semiconductor substrate.
At a predetermined distance from the surface of the semiconductor substrate and
The movable electrode is disposed with a gap between the movable electrode and the movable electrode.
The fixed electrodes for excitation that vibrate the poles using static electricity
A vibration means for vibrating in the horizontal direction the movable electrode with respect to the semiconductor substrate Te, the movable surface of said semiconductor substrate
Formed by an impurity diffusion region at a position facing the electrode
Having a lower electrode with a vertical displacement of the movable electrode.
Detected by the capacitance between the movable electrode and the lower electrode
By doing so, a vertical displacement detecting means for detecting a vertical displacement of the movable electrode with respect to the semiconductor substrate, and a vertical displacement detecting means when the movable electrode is displaced in the horizontal direction by the vibration means. and coercive Chi an interval between the semiconductor substrate and the movable electrode according to the displacement of the movable electrode fixed with the movable conductive in the initial position of the movable electrode
On the basis of the capacitance between a pole and the lower electrode,
Vertical displacement control means for controlling vertical displacement of the movable electrode so that the capacitance becomes the reference capacitance , wherein the vertical displacement control means is formed on the movable electrode.
Movable electrode for displacement control, and movable electrode for displacement control
Above the semiconductor substrate so as to face the
The same height as the movable electrode and the semiconductor substrate
Between the fixed electrode for displacement control provided as described above.
In accordance with the displacement of the movable electrode detected by the position detecting means.
Between the movable electrode for displacement control and the fixed electrode for displacement control.
Control voltage, and the displacement control movable electrode and the displacement control
The movable electrode and the half-electrode are caused by electrostatic force between the fixed electrodes.
Voltage control means for keeping the distance between the conductive substrates constant.
And a semiconductor yaw rate sensor characterized by the following.

[0010]

[0011]

[0012]

[0013]

[0014]

According to the first aspect of the invention, when the movable electrode is vibrated in the horizontal direction, when the yaw rate is applied to the movable electrode, the movable electrode is displaced in the vertical direction with respect to the semiconductor substrate by Coriolis force. .

Since the present invention uses a capacitance as a means for detecting the displacement, high-precision detection in which the influence of temperature dependence is reduced in principle can be performed. Further, in the present invention, this displacement is detected, the displacement of the movable electrode in the vertical direction is controlled in a direction in which the displacement is eliminated, the distance between the movable electrode and the semiconductor substrate is kept constant, and the vertical direction of the movable electrode is controlled. The yaw rate is detected by the control amount for controlling the displacement of the yaw.

As described above, the yaw rate is detected by the control amount as a feedback configuration for keeping the distance between the movable electrode and the semiconductor substrate constant with respect to the vertical displacement of the movable electrode. By using a control amount based on feedback instead of displacement itself, it is possible to perform high-accuracy yaw rate detection with less influence of temperature dependence.

[0017]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a planar configuration of the yaw rate sensor. That is, in FIG. 1, the semiconductor substrate 11 is configured by a P-type silicon substrate.

On this semiconductor substrate 11, an anchor 1
21 to 124 are formed at four places, and the anchor portion 121 is formed.
Beams 134 to 134 each having one end supported by
Supports the weight 14.

Therefore, the weight 14 is formed by the beam structure shown in FIG.
Are supported so as to be displaceable in a vertical direction and a horizontal direction (the direction of arrow V in FIG. 1) on the paper surface in FIG. The weight 14 is set to increase the displacement amount due to the yaw rate.

Furthermore, the movable movable electrodes 161 to 164 in which a pair of small pieces are set in parallel with the teeth of a comb are formed so as to project from the weight 14 on both sides of the weight 14 in the displacement direction. I have.

The movable movable electrodes 161 to 164 act to give vibration to the weight 14. These anchor portions 12
1 to 124, the beams 131 to 134, the weight 14, and the excitation movable electrodes 161 to 164 are integrally formed of a heat-resistant metal such as polysilicon or tungsten, for example. Polysilicon is used as the material.

The weight 14 and the movable movable electrodes 161 to 164 formed integrally therewith are arranged on the main surface of the semiconductor substrate 11 at a predetermined interval, and the beams 131 to 134 are provided.
And is held by the anchor portions 121 to 124 via.

The movable electrode constituted by the weight 14, the movable electrodes for excitation 161 to 164 and the beams 131 to 134 formed integrally therewith, and the main surface of the semiconductor substrate 11 corresponding to each of the movable electrodes And a lower fixed electrode 151 formed of a diffusion layer formed by introducing an N-type impurity by means such as ion implantation.

The lower fixed electrode 151 is connected to an external circuit via an aluminum wiring. In addition, fixed excitation electrodes 191 to 194 are arranged corresponding to the movable movable electrodes 161 to 164, respectively.

The fixed excitation electrodes 191 to 194 are respectively connected to the movable excitation electrode 161 on the main surface of the semiconductor substrate 11.
It is fixedly set at the same height position as ~ 164,
Each has a comb-shaped strip, and the strips are arranged so that they are in the center of each other, and a predetermined interval is formed between the teeth of each comb.

Each of these excitation fixed electrodes 191 to 194 is connected to an excitation power supply (not shown) through an aluminum wiring and supplied with a voltage signal of a predetermined frequency. The weight 14 and the movable gate electrode 151 are excited by the
154 are vibrated.

The weight 14, on which the excitation electrodes 161 to 164 are integrally provided, is connected to an external circuit via aluminum wiring. The fixed electrode for excitation is 90
Fixed electrodes 171 and 172 for vertical displacement control are formed on both sides of the weight 14 in directions shifted by degrees.

The vertical displacement control fixed electrodes 171, 17
The capacitance is composed of the weight 2 and the weight 14. Each of these displacement control fixed electrodes 171 and 172 is connected to an external circuit via aluminum wiring.

FIG. 2A shows a cross section taken along the line aa in FIG.
That is, in FIG. 2A, a weight 14 which is supported by an insulating film 22 formed on a P-type silicon semiconductor substrate 11 and made of, for example, polysilicon is set. It is held between the beams 133 and 134 between them.

Here, the insulating film 22 is for setting the air gap 24 and is made of SiO ₂ or Si ₃ N ₄ or the like. In addition, weight 1 as a movable part
4, a lower fixed electrode 151 is formed on the semiconductor substrate 11 below the beams 133 and 134 by ion implantation or the like, and the weight 14 and the lower electrode 151 which are substantially movable electrodes are formed.
Constitute a yaw rate detection capacitance.

The insulating film 22 is composed of the weight 14 and the beams 131 to 13
The air gap 24 is formed by a sacrifice layer which sets the distance between the semiconductor substrate 11 and the semiconductor substrate 11 except for portions corresponding to the anchor portions 121 to 124.

In this etching, an etching solution is used in which the polysilicon constituting the weight 14, the beams 131 to 134 and the semiconductor substrate 11 are not etched, but only the insulating film 22 which is a sacrificial layer is etched.

FIG. 2B shows a bb section of FIG. That is, in FIG. 2B, the weight 14 and the semiconductor substrate 1
1, an air gap 24 is set, and the weight 14 serving as a movable electrode can be displaced in a direction perpendicular to the semiconductor substrate 11 and in a direction perpendicular to the paper surface.

The weight 14 serving as a movable electrode and the lower fixed electrode 151 constitute an electrostatic capacity. Further, an interval is set between the excitation fixed electrodes 193, 194 and the excitation movable electrodes 163, 164 (not shown), and the excitation fixed electrodes 193, 194 and the excitation movable electrodes 163, 164 are attached to the semiconductor substrate 11. It is set so that it is the same height with respect to it.

FIG. 2C shows a cross section taken along the line cc of FIG. That is, in FIG. 2C, the weight 14 and the semiconductor substrate 1
1, an air gap 24 is set.

The vertical displacement control fixed electrodes 171, 1
An interval is set between 72 and the weight 14, and the vertical displacement control fixed electrodes 171 and 172 and the weight 14 are set to be at the same height with respect to the semiconductor substrate 11.

Next, a method of manufacturing the yaw rate sensor thus configured will be described with reference to FIGS.
This will be described with reference to (a) to (d). In these figures, the left half has a sensor portion and the right half has a sensor processing circuit M.
An OSFET is assumed and its manufacturing process is also shown.

First, as shown in FIG. 3A, a lower electrode 15 is formed on a semiconductor substrate 11 made of P-type silicon by ion implantation or the like. Next, as shown in FIG. 3B, an insulating film 22 serving as a sacrificial layer is formed on the surface of the semiconductor substrate 11 corresponding to the sensor forming portion.

This insulating film 22 may be formed first on the entire main surface of the semiconductor substrate 11, and then formed so as to remove the insulating film on the transistor forming portion. And FIG.
As shown in (c), a gate insulating film 25 is formed on the main surface of the semiconductor substrate 11 corresponding to the transistor forming portion by gate oxidation.

Next, as shown in FIG.
2 and 25, a film made of polysilicon is formed, and through a photolithography process, the weight 14 and the gate 26 of the transistor are formed.
To process.

At the same time, anchor portions 121 to 124, beams 131 to 134, etc., which are not shown in FIG. Then, as shown in FIG. 3E, in order to form the source electrode 30 and the drain electrode 31 of the transistor,
Impurities are introduced into the gate electrode 26 by ion implantation in a self-aligned manner to form an N-type diffusion layer.

Next, as shown in FIG. 4A, an interlayer insulating film 32 is formed on the entire surface to electrically insulate the aluminum wiring from the movable electrode 14, the gate electrode 26 of the transistor, and the like.

Then, as shown in FIG. 4B, contact holes 311 to 313 corresponding to the lower electrode 15 and the source electrode 30 and the drain electrode 31 of the transistor are formed in the interlayer insulating film.

Thereafter, as shown in FIG. 4C, aluminum as an electrode material is formed corresponding to each of the contact holes 311 to 313, and the aluminum wiring 32 is formed.
1 to 323 are formed.

Then, as shown in FIG. 4D, the insulating film 22 below the weight (movable electrode) 14 is etched as a sacrificial layer, and an air gap 24 is formed below the weight (movable electrode) 14. The yaw rate sensor is completed.

In this yaw rate sensor, beam 131
As a material forming the elements 134 to 134, a thin film formed on the silicon substrate 11, for example, a material such as polysilicon doped with impurities at a high concentration or a heat-resistant metal is used.

Therefore, it is possible to sufficiently reduce the variation in the thickness of the beams 131 to 134. Typically,
When a one-point load is applied to a cantilever beam or a double-supported beam, the displacement is inversely proportional to the cube of the beam thickness and the first power of the width. Very high precision is required for the processing of

Further, a beam-shaped polysilicon layer is formed on the semiconductor substrate 11 after forming a sacrificial layer in advance, and the sacrificial layer is removed by etching to form a beam having a predetermined interval on the surface of the semiconductor substrate 11. 131 to 134 are formed.

Here, the sacrifice layer is a thin film formed in advance for the purpose of final removal. In this embodiment, the distance between the movable electrode 14 and the lower fixed electrode 15 is controlled by the thickness of the sacrifice layer. In this case, the controllability of the thickness of the sacrifice layer is good. The controllability of the capacitance between the movable electrode 14 and the lower fixed electrode 15 is also improved.

Further, in the manufacturing method for producing the yaw rate sensor, all the processes can be performed by the IC producing process itself or the diversion thereof, and the sensor structure can be formed in the IC producing process. Can be easily integrated.

In the yaw rate sensor described in this embodiment, the yaw rate detecting section is constituted by a double-supported beam structure. However, this can be realized by a cantilever beam structure, and the number of beams is also four. Need not be.

Although the excitation electrode and the vertical displacement control electrode are provided on both sides of the weight, they may be provided on one side. In addition, the excitation electrode and the vertical displacement control electrode are provided to be shifted by 90 degrees, but they may be provided on the same side.

Further, the number of excitation electrodes is shown as two on the movable side and three on the fixed side as shown in the figure, but may be constituted by a combination of other numbers. The vertical displacement control electrodes 171 and 172 are shown on a straight line parallel to the movable electrode 14 as shown in FIG.
This may be formed in a comb-like shape like an excitation electrode.

Further, although the description has been made using a P-type semiconductor substrate as the substrate, the substrate may be formed of an N-type semiconductor substrate. In this case, the diffusion electrode is formed of a P-type. Further, the weight 14 does not need to be a quadrangle, and may be formed, for example, in a triangular shape.

Next, the operation of the yaw rate sensor configured as described above will be described. In this yaw rate sensor, a fixed lower electrode 15 is provided on a semiconductor substrate 11 vertically opposed to a weight (movable electrode) 14,
4 changes the capacitance between the movable electrode 14 and the fixed lower electrode 15.

Therefore, the movable electrode 14 and the fixed lower electrode 15
The yaw rate can be detected by detecting the displacement of the movable electrode 14 from the change in capacitance between the two. When an excitation voltage of a certain frequency is applied between the excitation fixed electrodes 191 to 194 and the excitation movable electrodes 161 to 164, horizontal vibrations are generated in the excitation movable electrodes 161 to 164 by electrostatic force. The weight (movable electrode) 14 also vibrates.

The Coriolis force generated by the yaw rate is proportional to the speed of this vibration. In order to increase the vibration speed, it is preferable to select the frequency near the resonance point where the amplitude increases.

In this way, the movable electrodes for excitation 161 to 1
64, by applying an excitation periodic voltage between the excitation fixed electrodes 191 to 194, the weight (movable electrode) 14 vibrates as shown in FIG.

When a yaw rate ω having an axis horizontal to the semiconductor substrate 11 and perpendicular to the vibration is generated, a Coriolis force proportional to the vibration speed and the mass of the vibrating body is generated in a direction perpendicular to the semiconductor substrate 11. , Weight (movable electrode) 1
4 is displaced about the Z0 in the direction perpendicular to the semiconductor substrate 11.

FIG. 5B shows the displacement when the yaw rate ω is applied. Since the vertical displacement Z of the movable electrode is proportional to the vibration speed, the phase shifts by π / 2 from the horizontal displacement.

When the weight (movable electrode) 14 is displaced in the direction perpendicular to the semiconductor substrate 11, the movable electrode 14
And the fixed lower electrode 15 changes in capacitance. In the present embodiment, feedback control is performed so that the movable electrode is not displaced.

That is, the movable electrode 14 and the fixed lower electrode 1
A voltage is applied between the vertical displacement control electrode 171 and the movable electrode 14 so as to keep the capacitance between the electrodes 5 constant, and the voltage is controlled to a certain value Z0, and the yaw rate is detected by the control voltage. ing.

This is achieved by applying a voltage as shown in FIG. 5 (c) between the vertical displacement control electrode 171 and the movable electrode 14, and
As shown in (d), the vertical displacement of the movable electrode is suppressed, and the yaw rate can be detected by the voltage shown in FIG. 5C applied to the vertical displacement control electrode 171.

[0064]

Therefore, as described in detail above, according to the present invention, the capacitance is used as a means for detecting the displacement of the movable electrode, and the temperature dependence is reduced in principle to improve the detection accuracy. Semiconductor yaw rate sensor can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a yaw rate sensor according to one embodiment of the present invention.

2 (a) to 2 (c) are respectively aa, FIG.
It is a figure which shows bb and cc cross section.

3 (a) to 3 (e) are cross-sectional views for sequentially explaining manufacturing steps of the yaw rate sensor.

4 (a) to 4 (d) are cross-sectional views for sequentially explaining manufacturing steps of the yaw rate sensor.

5A is a diagram showing the displacement of the movable electrode in the horizontal direction, FIG. 5B is a diagram showing the displacement of the movable electrode when a yaw rate is applied, and FIG. 5C is a vertical displacement control. FIG. 5D is a diagram showing a change in voltage between the working electrode and the movable electrode, and FIG. 5D is a diagram showing displacement of the movable electrode by closed loop control.

[Explanation of symbols]

11: semiconductor substrate, 121 to 124: anchor part, 13
1 to 134: beam, 14: weight (movable electrode), 151: lower fixed electrode, 161 to 164: movable electrode for excitation, 17
1,172: fixed electrode for vertical displacement control, 191-194
... fixed electrode for excitation, 22 ... insulating film.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-61959 (JP, A) JP-A-4-27864 (JP, A) JP-A-6-196721 (JP, A) JP-A-6-196721 196722 (JP, A) JP-A-6-204502 (JP, A) JP-A-4-25764 (JP, A) JP-A-61-114123 (JP, A) JP-A-7-231102 (JP, A) European Patent Application Publication 194953 (EP, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 19/56 G01P 9/04

Claims (1)

(57) [Claims] A semiconductor substrate; a movable electrode located above the surface of the semiconductor substrate at a predetermined distance from the surface of the semiconductor substrate; and a surface of the semiconductor substrate located above the semiconductor substrate.
At a predetermined distance from and with a gap between the movable electrode
The movable electrode is vibrated by using static electricity.
Vibrating means for vibrating the movable electrode in a horizontal direction with respect to the semiconductor substrate by an excitation fixed electrode to be excited; and a vibrating means on a surface of the semiconductor substrate facing the movable electrode.
Having a lower electrode formed by an impurity diffusion region;
The displacement of the movable electrode in the vertical direction is controlled by the movable electrode and the lower part.
Vertical displacement detecting means for detecting a displacement of the movable electrode in a vertical direction with respect to the semiconductor substrate by detecting the capacitance with an electrode, and the movable electrode is displaced in a horizontal direction by the vibration means. sometimes, the coercive Chi an interval between the semiconductor substrate and the movable electrode at a constant depending on the displacement of the movable electrode detected by the vertical displacement detecting means, before the initial position of the movable electrode
Based on the capacitance between the movable electrode and the lower electrode,
And vertical displacement control means for controlling vertical displacement of the movable electrode so that the capacitance becomes the reference capacitance.The vertical displacement control means is formed on the movable electrode. Strange
Position control movable electrode and the displacement control movable electrode.
So that the displacement control is movable above the semiconductor substrate.
The electrode and the semiconductor substrate are set at the same height.
Between the displacement control fixed electrode and the displacement detection fixed electrode.
The displacement control is performed according to the displacement of the movable electrode detected in the step.
A control voltage is applied between the control movable electrode and the displacement control fixed electrode.
Apply the displacement control movable electrode and the displacement control fixation
The movable electrode and the semiconductor substrate by electrostatic force between the electrodes;
And a voltage control means for making the intervals of the semiconductor yaw rates constant .