JP2006226924A - Dynamic quantity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently form a gap between electrodes constituting an electrostatic capacity element, in a capacitance detecting type dynamic quantity sensor. <P>SOLUTION: A layered substrate having three-layer structure with an insulating layer 2 formed between a support layer 1 and an active layer 3 is processed to form this dynamic quantity sensor. A frame 11, a beam 12 and a weight body 13 are formed by etching the support layer 1. An electrode support part 21 and a gap 22 are formed by wet-etching the insulating layer 2. A fixed electrode 31 is formed by etching the active layer 3. The beam 12 is a flexible member fixed onto the frame 11, and supports movably the weight body 13. The weight body 13 is able to be vibrated and moved twistedly by force applied from an outside. Holes are formed further in the fixed electrode 31 to enhance a turn-around characteristic of an etching solution when forming the gap 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mechanical quantity sensor such as an acceleration sensor or an angular velocity sensor that detects a mechanical quantity acting on an object, and more particularly to a capacitance detection type mechanical quantity sensor that detects a working mechanical quantity from a change in capacitance. .

In a wide range of fields such as a camera shake correction device for a video camera, an in-vehicle airbag device, and a robot posture control device, a mechanical amount sensor for detecting a mechanical amount acting on an object is used.
One of the mechanical quantity sensors is an angular velocity sensor called a gyro that detects the rotational motion of an object, that is, the angular velocity.
The gyroscope is a sensor that detects a rotational motion of an object, that is, an angular velocity, and can detect an acting angular velocity regardless of an attachment site or a rotation center position.
The gyro is classified into several types according to the difference in operation principle, and a thing using a vibrating body is called a vibration type angular velocity sensor.

A vibration type angular velocity sensor (hereinafter referred to as an angular velocity sensor) detects an angular velocity acting by vibrating a weight supported by a flexible member at a constant period and detecting a generated Coriolis force.
Specifically, when an angular velocity Ω acts around the x-axis or y-axis in a state where a mass m is vibrated at a velocity v in the z-axis direction, “F = 2 mvΩ” Coriolis is formed at the center of the mass. A force F is generated.
And since a twist arises by the effect | action of the generated Coriolis force, a weight body inclines with respect to the surface orthogonal to a vibration direction.
The angular velocity sensor detects the direction and amount of inclination of the weight body, and calculates the angular velocity acting on the weight body based on these detected values.

In such an angular velocity sensor, one of methods for detecting the direction and amount of inclination of the weight body is to measure the amount of change in capacitance. Such an angular velocity sensor is called a capacitive angular velocity sensor.
In the capacitive angular velocity sensor, an electrode is provided at a position facing the side surface of the weight body via a gap. Then, the inclination of the weight body is detected by measuring the amount of change in the capacitance of the capacitance element formed by this electrode and the weight body.

In such a capacitance detection type mechanical quantity sensor, the detection accuracy can be improved as the electrostatic capacity of the electrostatic capacitance element in the initial state where the mechanical quantity does not act increases. This is because the amount of change in the capacitance when the posture of the weight changes is large.
The capacitance C of the capacitance element is expressed by the following equation.
(Formula 1) C = εS / d
Where ε is the dielectric constant of the dielectric between the electrodes, S is the area of the electrodes, and d is the distance (gap) between the electrodes.
Thus, the capacitance C of the capacitance element is proportional to the area S of the electrodes and inversely proportional to the distance d between the electrodes. That is, the capacitance can be increased by reducing the distance d between the electrodes, that is, the gap.

Conventionally, such a capacitive element is configured by forming a pair of electrodes on different substrates and bonding these substrates.
Since the electrode formed in this manner is affected by protrusions such as hillocks formed on the surface of the metal electrode and warpage of the substrate, the flatness cannot be appropriately maintained.
Therefore, it is difficult to provide a minute gap between the electrodes with high accuracy.
In particular, when anodically bonding a glass substrate and a silicon substrate, if the gap between the electrodes is small, the opposing electrodes at the time of bonding tend to stick. Therefore, processing for preventing the sticking of the electrodes has to be performed.
In view of this, techniques for providing a minute gap with high accuracy have been proposed, including the following patent documents.
JP-A-5-335596

Patent Document 1 proposes a technique of forming a stopper gap by etching an insulating film layer in a single crystal semiconductor three-layer structure sandwiching the insulating film layer.
Thus, when the gap of the stopper is formed, the gap can be accurately controlled by changing the thickness of the insulating film layer.

When etching an insulating film layer of an intermediate layer in a wafer having a three-layer structure as shown in Patent Document 1, a wet etching technique is used.
This wet etching has a characteristic that etching proceeds isotropically in order from a region in contact with an etching solution (chemical solution).
For this reason, when the region to be etched exists in a narrow portion sandwiched between non-etched regions, this etching process requires a long time.
SUMMARY OF THE INVENTION An object of the present invention is to provide a mechanical quantity sensor capable of more efficiently forming a gap between electrodes constituting a capacitive element in a capacitive detection type mechanical quantity sensor.

  In the first aspect of the present invention, a movable portion having a flexible beam portion, a weight portion supported by the beam portion, a fixed electrode disposed opposite to the movable portion, the beam portion, and the beam An insulating layer disposed between the fixed electrodes and having an air gap formed between the movable part and the fixed electrode by erosion of an erosion liquid, and formed in at least one of the fixed electrode and the beam part, the air gap in the insulating layer A hole for allowing the erosion liquid to enter during formation, a detection means for detecting a change in capacitance generated between the movable part and the fixed electrode, and a mechanical quantity based on the capacitance detected by the detection means The above-mentioned object is achieved by providing a mechanical quantity acquisition means for acquiring.

  According to a second aspect of the present invention, in the first aspect of the invention, the mechanical quantity sensor includes a laminated substrate in which a first layer, a second layer, and a third layer are laminated in order, and the fixed electrode is The first layer is formed by processing, the insulating layer is formed by the second layer, and the beam portion is formed by processing the third layer.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, a plurality of the holes are provided at equal intervals.

  According to a fourth aspect of the present invention, in the first, second, or third aspect of the invention, there is provided vibration means that vibrates the weight portion at a predetermined period, and the mechanical quantity acquisition means is the detection means. The angular velocity is acquired based on the capacitance detected in step (1).

  According to a fifth aspect of the present invention, in the second, third, or fourth aspect of the present invention, the laminated substrate includes the first layer and the third layer formed of silicon, and the second layer. It is an SOI (silicon on insulator) substrate in which a layer is formed of an oxide film.

  According to a sixth aspect of the present invention, in the second, third, fourth, or fifth aspect of the present invention, the third layer is formed by processing, and one end of the beam portion is fixed. A frame; and a support portion formed in a region of the second layer that does not contact the beam portion and to which the fixed electrode and the frame are fixed.

  According to the present invention, it is possible to more efficiently form the erosion of the insulating layer by providing the hole into which the erosion liquid is allowed to enter.

(1) Outline of Embodiment As shown in FIG. 1, a laminated substrate having a three-layer structure in which an insulating layer 2 is formed between a support layer 1 and an active layer 3 is processed to obtain dynamics such as acceleration and angular velocity. A mechanical quantity sensor for detecting the quantity is formed. The support layer 1 and the active layer 3 are made of a conductor such as silicon crystal and form a conductive layer.
The mechanical quantity sensor includes a frame 11, a beam 12, a weight body 13, an electrode support portion 21, a gap 22, and a fixed electrode 31.
The frame 11, the beam 12, and the weight body 13 are formed by performing an etching process on the support layer 1.
The electrode support portion 21 and the gap 22 are formed by subjecting the insulating layer 2 to a wet etching process.

The fixed electrode 31 is formed by performing an etching process on the active layer 3.
The beam 12 is a flexible member having one end fixed to the frame 11 and supports the weight body 13 in a movable state. By the action of the beam 12, the weight body 13 can be vibrated or twisted by a force applied from the outside.
The fixed electrode 31 is formed with etching promoting holes (holes) for improving the flow of the etching solution (chemical solution) when forming the gap 22 in the insulating layer 2.
By providing a hole for promoting etching that penetrates the fixed electrode 31 in the thickness direction, the wraparound characteristic of the etching solution can be improved.
In the mechanical quantity sensor configured as described above, the acting mechanical quantity is detected based on the posture change of the weight body 13.
The posture change of the weight body 13 is detected based on the change in the gap 22 derived from the change in the capacitance of the capacitance element formed by the movable electrode and the fixed electrode 31.

(2) Details of Embodiments Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
In the present embodiment, an acceleration sensor and an angular velocity sensor will be described as examples of the mechanical quantity sensor.
The mechanical quantity sensor according to the present embodiment is a semiconductor sensor element formed by processing a semiconductor substrate. The processing of the semiconductor substrate can be performed using MEMS (micro electro mechanical system) technology.
The same direction as the stacking direction of the layers in the substrate constituting the acceleration sensor is defined as the vertical direction, that is, the z-axis (direction). The axes orthogonal to the z-axis and orthogonal to each other are defined as an x-axis (direction) and a y-axis (direction). That is, the x axis, the y axis, and the z axis are three axes that are orthogonal to each other.

(First embodiment)
FIG. 1 is a cross-sectional view showing a schematic configuration of the acceleration sensor according to the first embodiment.
2A is a plan view of the acceleration sensor shown in FIG. 1 as viewed from above, and FIG. 2B is a diagram showing a cross section along the plane B shown in FIG. ) Is a diagram showing a cross section in the C plane shown in FIG. 1.
1 is a view showing a cross section of the acceleration sensor at the position of the line segment AA ′ shown in FIG.
The acceleration sensor according to the first embodiment is formed from an SOI (silicon-on-insulator) substrate having a three-layer structure of a support layer 1, a buried oxide layer 2, and an active layer 3.
The support layer 1 is made of a silicon (Si) layer having a thickness of several hundred μm. The buried oxide layer 2 is composed of a silicon oxide (SiO 2) film layer that is an insulator having a thickness of several nm to several μm. The active layer 3 is composed of a silicon (Si) layer having a thickness of several μm to several hundred μm.
The support layer 1 is formed with a frame 11, a beam 12, and a weight body 13 by performing an etching process. The weight body 13 has conductivity and functions as a movable electrode.

As shown in FIG. 2C, the frame 11 is a fixed portion provided at the peripheral edge so as to surround the weight body 13, and constitutes a frame of the acceleration sensor. The frame 11 is a hollow prism-shaped member and has a height equivalent to the thickness of the support layer 1.
The beam 12 is four strip-shaped thin members extending in a cross direction in the radial direction (in the direction of the frame 11) from the center of the weight body 13, and has flexibility. The beam 12 is fixed to the frame 11 and the weight body 13.
Here, the bending characteristics of the beam 12 will be described.
The bending characteristics of the beam 12 change based on a spring constant k determined based on factors such as the shape and material of the beam 12. Further, the spring constant k acts as an important parameter for determining the resonance frequency of the weight body 13.
This spring constant k is related to the length L of the beam 12, that is, the distance between the weight 13 and the frame 11. The spring constant k is proportional to the value of (1 / L to the third power).
Therefore, in order to construct the beam 12 having an appropriate spring constant k, it is necessary to accurately form the beam 12 having a length L.

However, when the electrode support portion 21 is formed over the region overlapping the beam 12, the substantial length of the beam 12, that is, the region functioning as a flexible member is shortened.
Due to the influence of the range (region) in which the electrode support portion 21 is formed, an error of the spring constant k of the beam 12 occurs, and there is a possibility that a problem such that a desired vibration characteristic cannot be obtained appropriately in the weight body 13 may occur. There is.
Therefore, in the acceleration sensor according to the present embodiment, the range of the formation region of the electrode support portion 21 is specified.
Specifically, the electrode support portion 21 is formed in a region on the outer side (outer surface side of the frame 11) than the formation portion of the beam 12 (the position of the base of the beam 12) in the frame 11.

That is, the electrode support portion 21 is formed so as not to come out to the beam 12 side, that is, so as not to overlap the formation region of the beam 12.
In other words, as shown in FIG. 1, the distance d between the inner surface of the electrode support portion 21 and the inner surface of the frame 11 satisfies the relationship d ≧ 0.
However, the distance d indicates a difference obtained by subtracting the distance (interval) from the outer surface of the frame 11 to the inner surface of the electrode support portion 21 from the distance (interval) from the outer surface to the inner surface of the frame 11.
In this way, the electrode support 21 is formed so as to be eroded to the outside of the extension region in the z-axis direction of the frame 11 (opposite to the formation position of the beam 12), so that the beam not affected by the electrode support 21 12 can be formed appropriately.

The weight body 13 is a hexahedral mass body fixed to the frame 11 by four beams 12. The weight 13 can be vibrated or twisted by the force applied from the outside by the action of the beam 12.
A movable gap 14 for making the weight body 13 movable is formed on the periphery of the weight body 13.
In addition, a movable gap 15 which is a space for moving the weight 13 is also formed on the bottom surface of the weight 13, that is, the lower region of the lower surface.
The movable gap 15 is formed by making the thickness of the weight body 13 smaller than the thickness of the frame 11.

An electrode support portion 21 is formed on the buried oxide layer 2 by performing an etching process. As shown in FIG. 2B, the electrode support portion 21 is a rectangular member provided in the extended region of the beam 12, that is, in the central portion of each side (wall) constituting the frame 11. The electrode support portion 21 has a thickness equal to that of the buried oxide layer 2.
In the buried oxide layer 2, a gap (gap) 22 is formed by a region etched when the electrode support portion 21 is formed.

A fixed electrode 31 is formed on the active layer 3 by performing an etching process. In the acceleration sensor according to the first embodiment, four fixed electrodes 31 are provided as shown in FIG.
The fixed electrode 31 includes an electrode portion 31a having a right isosceles triangle shape and a rectangular support portion 31b. A support portion 31b is formed to extend outward from the central portion of the hypotenuse opposite to the right angle in the electrode portion 31a.
And it arrange | positions every 90 degrees surrounding the center so that the vertex of two sides which make a right angle in the electrode part 31a may face the center direction of the weight body 13.
Opposing electrodes on the same plane, that is, electrodes located on the opposite side across the center are paired, and each axial component of the posture state of the weight body 13 is detected.

The fixed electrode 31 for detecting the x-axis direction component of the posture state of the weight 13 is arranged at a position where a bisector (center line) that bisects a right angle of a right isosceles triangle overlaps the x axis. Yes.
Similarly, the fixed electrode 31 for detecting the y-axis direction component of the posture state of the weight body 13 is also at a position where the bisector (center line) that bisects the right angle of the right-angled isosceles triangle overlaps the y-axis. Has been placed.
Although not shown, the fixed electrode 31 is connected to a signal processing circuit (signal processing device) provided outside by a lead wiring (lead wiring). Various signals are applied to the electrodes via these lead wires.
The capacitance between the electrodes can be electrically detected using a capacitance / voltage conversion (C / V conversion) circuit.

As a C / V conversion circuit, for example, there is a method in which a carrier signal (reference signal) having a sufficiently high frequency is applied to a capacitance element, and the amount of change in the amplitude of the output signal is detected as capacitance.
The amplitude of the output of the carrier signal applied to the capacitance element is proportional to the capacitance. Therefore, the capacitance can be detected by comparing the amplitudes of the input carrier signal and the output carrier signal.
In the acceleration sensor according to the first embodiment, an AC signal having a frequency band of several hundred kHz to several MHz is applied to the fixed electrode 31 as a carrier signal.

The acceleration sensor according to the first embodiment is provided with a fixed electrode pad 41 and a common electrode pad 42.
The fixed electrode pad 41 is a terminal pad for extracting the potential of the fixed electrode 31, and the lead-out wiring is connected to the signal processing circuit through the fixed electrode pad 41.
Similarly, the common electrode pad 42 is a common electrode, that is, a pad for extracting the potential of the support layer 1, and the lead-out wiring is connected to the signal processing circuit through the common electrode pad 42.

In the acceleration sensor configured as described above, the posture change of the weight body 13 that is changed by the action of acceleration is detected based on the change of the gap 22 formed between the movable electrode and the fixed electrode 31 in the weight body 13. To do.
Specifically, the change in the gap 22 is detected based on the change in the capacitance of the capacitance element formed by the movable electrode and the fixed electrode 31 in the weight body 13. The capacitance is changed using a C / V conversion circuit. Then, the detected change amount of the capacitance is converted into an acceleration corresponding thereto.

Next, a method for manufacturing the acceleration sensor described above will be described.
The acceleration sensor according to the first embodiment is formed by processing an SOI substrate having a three-layer structure of a support layer 1, a buried oxide layer 2, and an active layer 3.
First, the active layer 3 is etched to form the fixed electrode 31. Specifically, an etching mask is formed on the surface of the active layer 3, and etching is performed along this mask.
Subsequently, the fixed electrode pad 41 and the common electrode pad 42 are formed. That is, the electrodes for securing the potential of the fixed electrode 31 and the weight body 13 are joined.
As the electrode material, a single metal such as aluminum or a bimetal is used.

Next, the support layer 1 is etched to form the frame 11, the beam 12, and the weight body 13.
Specifically, an etching mask is formed on the surface of the support layer 1, and etching is performed along the mask.
The support layer 1 is etched using a D-RIE (Deep-Reactive Ion Etching) technique that performs deep trench etching using plasma.
D-RIE is classified into anisotropic etching in which etching proceeds in a specific direction, which is a kind of dry etching.
In the etching process in the support layer 1 and the active layer 3, silicon oxide, silicon nitride, or resist is used as a mask material for etching. Further, dry etching such as reactive ion etching or inductively coupled plasma etching is used as the type of etching.

Finally, the buried oxide layer 2 is etched to form a gap 22.
Because of the structure of the acceleration sensor, it is difficult to perform a dry etching process, so the etching process for the buried oxide layer 2 is performed using a wet etching technique. Hydrofluoric acid (HF) or ammonium fluoride (NH 4 F) is used as a chemical solution for etching the buried oxide layer 2.
In the acceleration sensor according to the first embodiment, a hydrofluoric acid (HF) aqueous solution is used as ammonium fluoride (NH 4 F) in order to cause a reaction slowly in the etching process (photolithography process) of the buried oxide layer 2. Etching solution (chemical solution) mixed with a buffer solution such as

Thus, in the acceleration sensor according to the first embodiment, the gap 22, that is, the gap (gap 22) between the movable electrode and the fixed electrode 31 in the weight body 13 is formed by eroding the buried oxide layer 2. .
Therefore, the electrode interval of the capacitive element for detecting the posture change of the weight 13, that is, the length (interval) of the gap 22 between the movable electrode and the fixed electrode 31 is controlled (adjusted) in the buried oxide layer 2 by the thickness. )can do.
Thereby, the length (interval) of the minute gap 22 can be easily formed with high accuracy.

As described above, in the acceleration sensor according to the first embodiment, the gap 22 between the movable electrode and the fixed electrode 31 in the weight body 13 is formed by wet etching.
Therefore, when the etching site (that is, the gap 22) is narrow and has a deep shape (for example, when the fixed electrode 31 is wide and the buried oxide layer 2 is thin), the etching solution (chemical solution) approaches the center of the fixed electrode 31. ) May deteriorate.
Then, the progress of the etching is delayed with the passage of time, and it may take time to form the intended gap 22 or may cause an etching failure.
If etching failure occurs, for example, if silicon oxide that has not been removed remains on the fixed electrode 31 or the weight body 13, the gap 22 may not be formed flat.

Therefore, in the acceleration sensor according to the first embodiment, in order to suppress variations in the etching process, etching promoting holes (holes) are formed in the fixed electrode 31 to improve the circulation of the etching solution (chemical solution). To do. By forming the hole for promoting etching (hole), the gap 22 can be formed flatly and efficiently with high accuracy.
Specifically, as shown in FIG. 3A, slits 32 extending along the x-axis direction or the y-axis direction are formed adjacent to the fixed electrode 31 at equal intervals.
When such a slit 32 is provided, it is possible to arbitrarily control the progress of etching while maintaining the strength in the direction perpendicular to the slit 32 in the fixed electrode 31.

As shown in FIG. 3B, instead of the slits 32, the square holes 33 may be formed in the fixed electrode 31 at equal intervals along the x-axis direction and the y-axis direction.
Further, instead of a square shape such as the square hole 33, polygonal holes such as a circle and a hexagon may be arranged at equal intervals. Such an arrangement structure is a honeycomb structure.
When such a hole having a honeycomb structure is provided, it is possible to arbitrarily control the progress of etching while suppressing the directionality while maintaining the overall strength of the fixed electrode 31.
In addition, since it is necessary to leave the buried oxide layer 2 on the frame 11 formed on the support layer 1 in order to form the electrode support portion 21, the region overlapping the frame 11 in the fixed electrode 31 is used for promoting etching. No holes are provided.
By providing the hole for promoting etching, the fixed electrode 31 can be reduced in weight. Accordingly, the resonance frequency band of the fixed electrode 31 can be shifted in a higher direction, and as a result, the vibration resistance of the fixed electrode 31 can be improved.

2A, the fixed electrode 31 includes an electrode portion 31a and a support portion 31b, and is fixed to the frame 11 via the electrode support portion 21 at the end portion of the support portion 31b.
And the support part 31b is comprised so that it may become as small as possible in order to suppress the influence which it has on the variation | change_quantity of the electrostatic capacitance detected in the electrode part 31a. That is, the support part 31b is configured to be extremely small compared to the electrode part 31a. The length of the active layer 3 forming the fixed electrode 31 in the thickness direction is also small.
Therefore, it is difficult to configure the fixed electrode 31 having high strength. Therefore, in the acceleration sensor according to the present embodiment, reinforcing means for improving the strength of the fixed electrode 31 may be added.
As a reinforcing means for the fixed electrode 31, for example, there is a reinforcing member 100 shown in FIG. 8, and the reinforcing member 100 is joined (adhered) to each fixed electrode 31. FIG. 8 shows an example in which the reinforcing member 100 is provided on one fixed electrode 31.

The reinforcing member 100 is formed of an insulator so as not to function as an electrode.
The reinforcing member 100 has a shape in which a right-angled triangle having the same shape as that of the electrode portion 31a in the fixed electrode 31 is combined with a square having a hypotenuse opposite to the right angle in the right-angled triangle. In addition, the square area | region in the reinforcement member 100 has an area to the extent that all the support parts 31b in the fixed electrode 31 are included.
The reinforcing member 100 is bonded and bonded to the outer surface of the fixed electrode 31. Here, since the length of the gap 22 between the fixed electrode 31 and the movable electrode may be affected, the reinforcing member is not directly fixed to the frame 11.
When the reinforcing member 100 is provided, the fixed electrode pad 41 is provided on the reinforcing member 100. In this case, since the reinforcing member 100 functions as an insulating material, a contact for connecting the fixed electrode 31 and the fixed electrode pad 41 to the reinforcing member 100 is provided.
Thus, by providing the reinforcing member 100, that is, the reinforcing means for the fixed electrode 31, the strength of the fixed electrode 31 can be improved.

In the first embodiment described above, the acceleration sensor that detects the acceleration acting in the biaxial direction has been described as an example. However, the mechanical quantity sensor formed using the SOI substrate is not limited to this. Absent.
For example, it may be a single axis detection acceleration sensor that detects acceleration acting in a single axis direction constituted by a single beam structure.
The single beam structure refers to a structure in which the weight body is supported on a fixed part such as a frame via a beam from one direction.

Next, a modified example of the acceleration sensor described above will be described.
4A to 4C are diagrams illustrating a schematic configuration of a modification of the acceleration sensor according to the first embodiment. However, portions that overlap with the acceleration sensor shown in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof is omitted.
4A is a plan view of the acceleration sensor as viewed from above, FIG. 4B is a diagram showing a cross section in the buried oxide layer 2 (B plane), and FIG. 4C is a support. It is the figure which showed the cross section in the layer 1 (C plane).
4 (a) to 4 (c) is a modification of the acceleration sensor in which the shape of the weight body 13 and the fixed electrode 31 in the above-described acceleration sensor is changed, and the direction of the detection axis (x axis and y axis) is rotated by 45 °. It has a structure.
Note that the cross section taken along the line AA ′ is substantially the same as that of the acceleration sensor shown in FIG. However, the depiction of the gap between the opposed fixed electrode 31 ′ and the gap between the weight body 13 ′ and the frame 11 is slightly different.

The support layer 1 is formed with a frame 11, a beam 12, and a weight 13 'by performing an etching process.
In the modification of the acceleration sensor according to the first embodiment, as shown in FIG. 4C, the weight body 13 ′ has a prismatic weight portion 131 located at the center, and four corners of the weight portion 131. Each of them is composed of prismatic weight portions 132 arranged in a balanced manner. The weight part 131 and the weight part 132 are integrally formed as a continuous solid.
A movable gap 14 ′ for moving the weight body 13 ′ is formed in the peripheral portion of the weight body 13 ′, specifically, the peripheral portion of the weight portion 132. The movable gap 14 ′ is formed between the frame 11 and the weight body 13 ′.

A fixed electrode 31 ′ is formed on the active layer 3 by performing an etching process. In the modification of the acceleration sensor according to the first embodiment, as shown in FIG. 4A, four fixed electrodes 31 ′ are provided.
The fixed electrode 31 ′ is composed of a rectangular electrode portion 31a ′ and a rectangular support portion 31b ′. The fixed electrode 31 ′ is formed in an L shape (shape) by the electrode portion 31 a ′ and the support portion 31 b ′.
The end portion of the support portion 31 b ′ is fixed to the electrode support portion 21 on the frame 11. The electrode portion 31a ′ is formed so as to face the upper end surface of the weight portion 132, respectively.
Opposing electrodes on the same plane, that is, electrodes positioned on the opposite side across the center are paired to detect each axial component of the posture state of the weight 13 ′.

Note that a modification of the thus configured acceleration sensor is also formed by the same manufacturing method as the above-described acceleration sensor.
Therefore, the gap 22 between the weight body 13 ′ and the fixed electrode 31 ′ in the acceleration sensor according to the modification is formed by etching the buried oxide layer 2.
Therefore, also in the acceleration sensor configured as described above, the above-described etching promoting hole (hole) is formed in the fixed electrode 31 ′ as shown in FIGS. Thereby, the wraparound characteristic of the etching solution (chemical solution) is improved, and variations in the etching process can be suppressed.

Next, an angular velocity sensor to which a technique for forming the gap 22 between the weight body 13 and the fixed electrode 31 by etching the buried oxide layer 2 in the acceleration sensor described above will be described.
FIG. 5A is a plan view of the angular velocity sensor as viewed from above, FIG. 5B is a diagram showing a cross section of the buried oxide layer 2 (B plane), and FIG. It is the figure which showed the cross section in the layer 1 (C plane).
FIGS. 5A to 5C are diagrams showing a schematic configuration of the angular velocity sensor according to the first embodiment. However, portions that overlap with the acceleration sensor shown in FIGS. 1 and 2 (a) to 2 (c) and the variation of the acceleration sensor shown in FIGS. 4 (a) to 4 (c) are denoted by the same reference numerals and details. Detailed explanation is omitted.
The angular velocity sensor according to the first embodiment is also formed from an SOI substrate having a three-layer structure of the support layer 1, the buried oxide layer 2, and the active layer 3, similarly to the acceleration sensor described above.
Note that the cross section taken along the line AA ′ is substantially the same in the portion excluding the acceleration sensor and the active layer 3 shown in FIG. However, a drive electrode 312 is provided at a corresponding position instead of the fixed electrode 31 facing the electrode. Moreover, the depiction of the gap between the weight 13 'and the frame 11 is slightly different.

The buried oxide layer 2 in the angular velocity sensor according to the first embodiment is formed with an electrode support portion 21 ′ by performing an etching process. As shown in FIG. 5B, the electrode support portion 21 ′ is slightly displaced in the x-axis or y-axis direction from the extension region of the beam 12, that is, the center portion of each side (wall) constituting the frame 11. It is a provided square member. The electrode support portion 21 ′ has a thickness equal to that of the buried oxide layer 2.
A gap (gap) 22 is formed in the buried oxide layer 2 by a region etched when the electrode support portion 21 ′ is formed.

The active layer 3 in the angular velocity sensor according to the first embodiment is formed with a fixed electrode 311 and a drive electrode 312 by performing an etching process.
In the angular velocity sensor according to the first embodiment, four fixed electrodes 311 are provided as shown in FIG.
The fixed electrode 311 includes a substantially rectangular electrode portion 311a, a rectangular support portion 311b, and a rectangular support portion 311c.
The electrode portions 311a are formed so as to face the upper end surface of the weight portion 132, respectively. A support portion 311b and a support portion 311c are formed so as to extend from the electrode portion 311a toward the adjacent electrode support portion 21 ′. End portions of the support portion 311b and the support portion 311c are fixed to the electrode support portion 21 ′ on the frame 11.
A fixed electrode pad 41 is provided on the bonding region between the support portion 311b and the electrode support portion 21 ′.

The drive electrode 312 is an electrode extending in the cross direction with the weight portion 131 as the center, and is fixed to the electrode support portion 21 ′ at each end in the cross direction. In addition, a drive electrode pad 43 is provided at one place in a fixed portion between the drive electrode 312 and the electrode support portion 21 ′.
The drive electrode pad 43 is a terminal pad for extracting the potential of the drive electrode 312, and the lead-out wiring is connected to the control circuit via the drive electrode pad 43.

Next, the angular velocity detection operation in the angular velocity sensor having such a configuration will be described.
The angular velocity sensor applies an AC voltage between the drive electrode 312 and the weight body 13 ′. Specifically, an AC voltage is applied between the drive electrode pad 43 and the common electrode pad 42.
Then, an electrostatic force is applied between the drive electrode 312 and the weight body 13 ′, and the weight body 13 ′ is vibrated up and down.
The vertical direction is the same direction as the stacking direction of the SOI substrate, that is, the z-axis direction.

The frequency of the alternating voltage applied to vibrate the weight body 13 ', that is, the vibration frequency of the weight body 13' is set to a resonance frequency f (for example, about 3 kHz) at which the weight body 13 'resonates. Thus, a large displacement amount of the weight body 13 ′ can be obtained by vibrating the weight body 13 ′ at the resonance frequency f.
When an angular velocity Ω is applied around the mass 13 ′ oscillating at the velocity v, a Coriolis force of “F = 2 mvΩ” is applied to the center of the mass 13 ′ in the direction of movement of the mass 13 ′. It occurs in a direction perpendicular to the direction.

When this Coriolis force F is generated, the weight 13 'is twisted and the posture of the weight 13' changes. In other words, the weight body 13 ′ is inclined with respect to a plane orthogonal to the vibration direction of the weight body 13 ′. The direction and magnitude of the acting angular velocity are detected by detecting the change in the posture (tilt, twist amount) of the weight 13 ′.
The change in the posture of the weight body 13 ′ is performed by detecting a change in capacitance in a capacitance element formed by the fixed electrode 311 and the weight portion 132 facing the fixed electrode 311.
That is, a change in the posture of the weight body 13 ′ is detected by detecting a change in the distance between the fixed electrode 311 and the movable electrode (the weight portion 132).

Note that the capacitance of the capacitance element can be electrically detected using a capacitance / voltage conversion (C / V conversion) circuit.
The Coriolis force F generated based on the detected change in the posture of the weight body 13 ′ (inclination direction, inclination degree, etc.) is detected. Then, the angular velocity Ω is calculated (derived) based on the detected Coriolis force F. That is, the amount of change in the posture of the weight 13 ′ is converted into an angular velocity.
The amount of change in the posture of the weight 13 'is converted into an angular velocity by starting an angular velocity calculation program stored in advance in the control device and performing a predetermined calculation process.

The angular velocity sensor configured as described above is also formed by the same manufacturing method as the acceleration sensor described above.
Therefore, the gap 22 between the weight body 13 ′ and the fixed electrode 311 in the angular velocity sensor according to the modification is formed by etching the buried oxide layer 2.
Therefore, also in the angular velocity sensor configured in this way, the above-described etching promotion hole is formed in the fixed electrode 311 as shown in FIGS. Thereby, the wraparound characteristic of the etching solution (chemical solution) is improved, and variations in the etching process can be suppressed.

(Second Embodiment)
Next, a second embodiment of the mechanical quantity sensor different from the first embodiment described above will be described.
6A is a cross-sectional view showing a schematic configuration of the acceleration sensor according to the second embodiment, and FIG. 6B is a plan view of the acceleration sensor shown in FIG. It is.
FIG. 7A is a diagram showing a cross section in the B plane shown in FIG. 6A, and FIG. 7B is a diagram showing a cross section in the C plane shown in FIG. FIG.7 (c) is the figure which showed the cross section in D plane shown to Fig.6 (a).
Note that the cross-sectional view of FIG. 6A is a cross-sectional view of the acceleration sensor at the position of the line segment AA ′ shown in FIG.

The acceleration sensor according to the second embodiment is formed of an SOI (silicon-on-insulator) substrate having a three-layer structure of a support layer 5, a buried oxide layer 6, and an active layer 7.
The support layer 5 is made of a silicon (Si) layer having a thickness of several hundred μm. The buried oxide layer 6 is composed of a silicon oxide (SiO 2) film layer which is an insulator having a thickness of several nm to several μm. The active layer 7 is composed of a silicon (Si) layer having a thickness of several μm to several hundred μm.
The support layer 5 is formed with a frame 51, a weight body 52, and a fixed electrode 53 by performing an etching process.

As shown in FIG. 7 (c), the frame 51 is a fixed portion arranged at the peripheral edge so as to surround the weight body 52, and constitutes a frame of the acceleration sensor. The frame 51 has a height equivalent to the thickness of the support layer 5.
The weight body 52 is a hexahedron mass body, and can be vibrated or twisted by a force applied from the outside by the action of a beam 72 described later.
In the peripheral part of the weight body 52, movable gaps 54 and 55 for making the weight body 52 movable are formed.
In addition, a movable gap 56 that is a space for moving the weight body 52 is also formed in the bottom surface of the weight body 52, that is, the lower region of the lower surface.
The movable gap 56 is formed by making the thickness of the weight body 52 smaller than the thickness of the frame 51.

A movable gap 55 for making the weight body 52 movable is formed between the inner surface of the frame 51 (the surface facing the weight body 52) and the side surface of the weight body 52.
The fixed electrode 53 is a plate-like electrode portion protruding in the direction of the weight body 52 from the inner side surface (surface facing the weight body 52) of the frame 51, and is formed integrally with the frame 51. The fixed electrode 53 is formed along an xy plane orthogonal to the z axis.
The fixed electrode 53 is formed on each of the four frames 51 that are independently formed (not integrally formed). Therefore, each fixed electrode 53 is electrically insulated.
A movable gap 54 for moving the weight body 52 is formed between the distal end portion (end surface) of the fixed electrode 53 and the weight body 52.

The buried oxide layer 6 is formed with an electrode support 61 by performing an etching process. As shown in FIG. 7B, the electrode support 61 is a rectangular member provided in an extension region of a beam 72 described later in the extension region of the frame 51 in the z-axis direction. The electrode support 61 has a thickness equal to that of the buried oxide layer 2.
The buried oxide layer 6 is formed with a weight support portion 62 by performing an etching process.
The weight support part 62 is a part for fixing (supporting) the weight 52 to a beam structure 71 described later, and is formed in the extension region of the weight 52 in the z-axis direction, that is, in the center of the beam structure 71. Has been.
In the buried oxide layer 6, there is a gap 63 between the electrode support 61 and the weight support 62 in the region etched when forming the electrode support 61 and the weight support 62. Is formed.

A beam structure 71 is formed on the active layer 7 by performing an etching process. As shown in FIG. 6B, the beam structure 71 is a member that extends in a cross direction in the radial direction from the formation region of the weight body 52.
The beam structure 71 is fixed to the frame 51 via electrode support portions 61 at the end portions extending in the cross direction.
Further, a region of the beam structure 71 that is not in contact with the electrode support portion 61 and the weight support portion 62, that is, a region that is in contact with the gap 63 and faces the fixed electrode 53 is interposed via the weight support portion 62. A beam 72 for supporting the weight body 52 fixed to the frame 51 with respect to the frame 51 is formed.
The beam 72 has flexibility and conductivity and functions as a movable electrode.
Note that the weight body 52 and the beam structure 71 are electrically insulated by fixing the weight body 52 to the beam structure 71 via the weight support section 62.

Similar to the beam 12 in the first embodiment, the bending characteristics of the beam 72 change based on a spring constant k determined based on factors such as the shape and material of the beam 72. Further, the spring constant k acts as an important parameter for determining the resonance frequency of the weight body 52.
This spring constant k is related to the thickness t of the beam 72. Specifically, the spring constant k is proportional to the cube of the thickness t of the beam 72.
Therefore, in order to construct the beam 72 having an appropriate spring constant k, the beam 72 having a thickness t must be formed with high accuracy.
In the acceleration sensor according to the second embodiment, the beam 72 (beam structure 71) is formed by etching the active layer 7.
Since the active layer 7 is a silicon (Si) layer of an SOI substrate, the active layer thickness can be accurately formed in the state of the substrate. Further, since it is a silicon (Si) layer, it is not affected by the etching of the buried oxide film layer. That is, since the thickness does not change due to erosion when the buried oxide film layer is etched, the beam 72 (beam structure 71) can be formed with high accuracy.

Although not shown, a signal processing circuit (signal processing device) is provided outside the acceleration sensor according to the present embodiment.
The acceleration sensor according to the second embodiment is provided with a common electrode pad 81 and a fixed electrode pad 82.
The common electrode pad 81 is an electrode pad provided at one of the end portions of the beam structure 71 extending in the cross direction. The common electrode pad 81 is a terminal pad for drawing out the potential of the movable electrode (common electrode) formed in the beam structure 71, and the lead-out wiring is connected to the signal processing circuit through the common electrode pad 81.
The fixed electrode pad is an electrode pad provided on the upper end surface of each frame 51. The fixed electrode pad 82 is a terminal pad for extracting the potential of the fixed electrode 53, and the lead-out wiring is connected to the signal processing circuit through the fixed electrode pad 82.

In the acceleration sensor configured as described above, the posture change of the weight body 52 that changes due to the action of acceleration is measured based on the change of the gap 63 formed between the fixed electrode 53 and the beam 72 that functions as the movable electrode. To detect.
Specifically, the change in the gap 63 is detected based on the change in the capacitance of the capacitance element formed by the fixed electrode 53 and the beam 72. The capacitance is changed using a C / V conversion circuit. Then, the detected change amount of the capacitance is converted into an acceleration corresponding thereto.
Note that the C / V conversion processing is performed using the angular velocity sensor and the method similar to the angular velocity sensor shown in the first embodiment.

The acceleration sensor configured as described above can be configured to function as an angular velocity sensor by providing a driving unit that vibrates the weight body 52 in the z-axis direction.
The weight 52 is vibrated in the z-axis direction by the driving means, and the change in the gap 63 is detected based on the detected change in the gap 63 based on the inclination of the weight 52 with respect to the plane orthogonal to the vibration direction. The angular velocity acting on the weight body 52 is detected.
Specifically, the Coriolis force acting on the weight body 52 is detected based on a change in capacitance in the capacitive element formed by the fixed electrode 53 and the movable electrode (beam 72). Then, the angular velocity is calculated (derived) based on the detected Coriolis force. That is, the amount of change in the posture of the weight body 52 is converted into an angular velocity.

Next, a method for manufacturing the acceleration sensor described above will be described.
The acceleration sensor according to the second embodiment is formed by processing an SOI substrate having a three-layer structure of a support layer 5, a buried oxide layer 6, and an active layer 7.
First, the active layer 7 is etched to form a beam structure 71. Specifically, an etching mask is formed on the surface of the active layer 7, and etching is performed along the mask.

Next, the support layer 5 is etched to form the frame 51, the weight body 52, and the fixed electrode 53.
Specifically, an etching mask is formed on the surface of the support layer 5, and etching is performed along the mask.
The support layer 5 is etched using a D-RIE technique for performing deep trench etching using plasma.
In the etching process in the support layer 5 and the active layer 7, silicon oxide, silicon nitride, or resist is used as a mask material for etching. Further, dry etching such as reactive ion etching or inductively coupled plasma etching is used as the type of etching.

Subsequently, the buried oxide layer 6 is etched to form an electrode support 61, a weight support 62, and a gap 63.
Due to the structure of the acceleration sensor, it is difficult to perform a dry etching process. Therefore, the etching process for the buried oxide layer 6 is performed using a wet etching technique.
This wet etching is also performed using the same method as the acceleration sensor according to the first embodiment.
Finally, the common electrode pad 81 and the fixed electrode pad 82 are formed. That is, the electrodes for securing the potentials of the fixed electrode 53 and the beam 72 (movable electrode) are joined.
As the electrode material, a single metal such as aluminum or a bimetal is used.

Also in the acceleration sensor according to the second embodiment, the buried oxide layer 6 is removed from the gap (gap 63) between the fixed electrode 53 and the movable electrode (beam 72) in the same manner as the acceleration sensor according to the first embodiment. It is formed by.
Therefore, the electrode interval of the capacitive element for detecting the posture change of the weight body 52, that is, the length (interval) of the gap 63 between the movable electrode (beam 72) and the fixed electrode 53 is the thickness of the buried oxide layer 6. Can be controlled (adjusted).
Thereby, it is possible to easily form the length (interval) of the minute gap 63 with high accuracy.

In the acceleration sensor according to the second embodiment, the gap 63 is formed by removing the buried oxide layer 6 by wet etching, as in the acceleration sensor according to the first embodiment.
Therefore, also in the thus configured acceleration sensor, the above-described etching promoting hole is formed in the fixed electrode 53 or the movable electrode (beam 72) as shown in FIGS. . Thereby, the wraparound characteristic of the etching solution (chemical solution) is improved, and variations in the etching process can be suppressed.
Specifically, a hole (hole) for promoting etching is provided in a region a indicated by a broken line in FIG. 7B, that is, in a region facing the beam 72 in the fixed electrode 53.
Alternatively, a hole (hole) for promoting etching is provided in a region facing the fixed electrode 53 in the beam structure 71.
Thereby, the wraparound characteristic of the etching solution (chemical solution) is improved, and variations in the etching process can be suppressed.

Etching promoting holes (holes) may be formed in both the fixed electrode 53 and the movable electrode (beam 72). Thus, by providing holes for promoting etching (holes) on both sides of the fixed electrode 53 and the movable electrode (beam 72), that is, the gap 63, the time required for etching the buried oxide layer 6 can be reduced. Shortening can be achieved.
Note that the holes for promoting etching provided in the fixed electrode 53 and the movable electrode (beam 72) are slits, square holes, circular holes, hexagonal holes arranged at equal intervals, as in the first embodiment. It is constituted by a honeycomb structure of holes (polygonal holes).

When the slit is provided, the progress of etching can be arbitrarily controlled while maintaining the strength in the direction perpendicular to the slit in the fixed electrode 53 or the movable electrode (beam 72).
When the holes having the honeycomb structure are provided, it is possible to arbitrarily control the progress of etching while suppressing the directionality while maintaining the overall strength of the fixed electrode 53 or the movable electrode (beam 72).
By providing the hole for promoting etching, the fixed electrode 53 or the movable electrode (beam 72) can be reduced in weight. As a result, the resonance frequency band of the fixed electrode 53 or the movable electrode (beam 72) can be shifted to a higher direction, and as a result, the vibration resistance of the fixed electrode 53 or the movable electrode (beam 72) can be improved.

In the acceleration sensor according to the second embodiment, an acceleration sensor that detects acceleration acting in two axial directions is configured by providing two pairs of opposing fixed electrodes 53.
This biaxial acceleration sensor configuration may be applied to form a uniaxial angular velocity sensor.
Specifically, one of the two pairs of opposing fixed electrodes 53 is used as a drive electrode for vibrating the weight body 52 in the z-axis direction, and the other is used to detect a posture change (tilt) of the weight body 52. Detection electrode.

According to the first and second embodiments, the electrodes of the capacitance elements in the capacitance detection type mechanical quantity sensor can be formed on the same SOI substrate. Further, the gap (interval) between the electrodes can be adjusted by the thickness of the intermediate layer (buried oxide layer) of the SOI substrate.
Thereby, it is possible to easily form a gap between minute electrodes with high accuracy. Therefore, the capacitance can be increased, and a highly sensitive mechanical quantity sensor can be easily manufactured.
Unlike the prior art, it is not necessary to provide a separate substrate (bonding substrate) such as a glass substrate for disposing (fixing) the fixed electrode 31, so that the mechanical quantity sensor can be downsized.

The acceleration sensor and the angular velocity sensor according to the first and second embodiments described above are formed by processing an SOI substrate. However, the multilayer substrate forming these sensors is not limited to the SOI substrate. . That is, the insulating layer is formed of silicon oxide (SiO 2) as a buried oxide layer, but is not limited to this.
For example, the insulating layer may be formed of a layer of another insulating material. Further, another laminated substrate may be used instead of the SOI substrate.

It is sectional drawing which showed schematic structure of the acceleration sensor which concerns on 1st Embodiment. (A) is a top view seen from the upper direction of the acceleration sensor shown in FIG. 1, (b) is the figure which showed the cross section in the B plane shown in FIG. 1, (c) is C plane shown in FIG. It is the figure which showed the cross section in. It is the figure which showed the example of arrangement | positioning of the hole for an etching promotion. (A) is the top view seen from the upper direction of the acceleration sensor, (b) is the figure which showed the cross section in a buried oxide layer, (c) is the figure which showed the cross section in a support layer. (A) is the top view seen from the upper direction of the angular velocity sensor which concerns on 1st Embodiment, (b) is the figure which showed the cross section in a buried oxide layer, (c) is the cross section in a support layer. FIG. (A) is sectional drawing which showed schematic structure of the acceleration sensor which concerns on 2nd Embodiment, (b) is the top view seen from the upper direction of the acceleration sensor shown to (a). (A) is the figure which showed the cross section in the B plane shown to Fig.6 (a), (b) is the figure which showed the cross section in the C plane shown to Fig.6 (a), (c) is FIG. It is the figure which showed the cross section in D plane shown to (a). It is the figure which showed the example of arrangement | positioning of a reinforcement member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support layer 2 Embedded oxide layer 3 Active layer 5 Support layer 6 Embedded oxide layer 7 Active layer 11 Frame 12 Beam 13 Weight body 14 Movable gap 15 Movable gap 21 Electrode support part 22 Gap 31 Fixed electrode 31a Electrode part 31b Support part 32 slit 33 square hole 41 fixed electrode pad 42 common electrode pad 43 drive electrode pad 51 frame 52 weight body 53 fixed electrode 54 movable gap 55 movable gap 56 movable gap 61 electrode support section 62 weight support section 63 gap 71 beam structure 72 Beam 81 Common electrode pad 82 Fixed electrode pad 100 Reinforcing member 131 Weight portion 132 Weight portion 311 Fixed electrode 311a Electrode portion 311b Support portion 312 Drive electrode

Claims (6)

A movable portion having a flexible beam portion and a weight portion supported by the beam portion;
A fixed electrode disposed opposite to the movable part;
An insulating layer disposed between the beam portion and the fixed electrode, and having a gap formed between the movable portion and the fixed electrode by erosion of an erosion liquid;
A hole that is formed in at least one of the fixed electrode and the beam portion, and allows an erosion liquid to enter when forming a gap in the insulating layer;
Detection means for detecting a change in capacitance generated between the movable part and the fixed electrode;
A mechanical quantity acquisition means for acquiring a mechanical quantity based on the capacitance detected by the detection means;
A mechanical quantity sensor comprising: The mechanical quantity sensor includes a laminated substrate in which a first layer, a second layer, and a third layer are laminated in order,
The fixed electrode is formed by processing the first layer,
The insulating layer comprises the second layer;
The mechanical quantity sensor according to claim 1, wherein the beam portion is formed by processing the third layer.   The mechanical quantity sensor according to claim 1, wherein a plurality of the holes are provided at equal intervals. Vibrating means for vibrating the weight portion at a predetermined cycle,
The mechanical quantity sensor according to claim 1, wherein the mechanical quantity acquisition unit acquires an angular velocity based on the capacitance detected by the detection unit.   The multilayer substrate is an SOI (Silicon On Insulator) substrate in which the first layer and the third layer are formed of silicon and the second layer is formed of an oxide film. The mechanical quantity sensor according to claim 2, claim 3, or claim 4. A frame formed by processing the third layer and having one end of the beam portion fixed thereto;
A support portion that is formed in a region of the second layer that does not contact the beam portion, and to which the fixed electrode and the frame are fixed;
The mechanical quantity sensor according to claim 2, wherein the mechanical quantity sensor is provided.

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