JPH11230982A - Mechanical quantity sensor - Google Patents

Abstract

(57) [Problem] To prevent a movable weight electrode supported by a beam from hanging down by its own weight, and to calculate a dynamic quantity based on a change in a distance between the movable weight electrode and a fixed electrode facing the movable movable electrode. Improve detection reliability when detecting. A weight movable electrode (17) supported by an anchor (15) on a support substrate (12) via a beam (16) is freely displaced in a two-dimensional plane direction parallel to the surface of the support substrate (12) in response to the application of acceleration. When an acceleration of a predetermined level or more is applied, the fixed electrode 14 on the support substrate comes into contact with the fixed electrode 14. Weight movable electrode 17
An annular magnetic body 19 is provided on the upper surface of the. A magnet for applying an attractive force to the magnetic body 19 in the direction of lifting the weight movable electrode is provided on the lower surface of the cap 24a of the case 24 for housing the acceleration sensor 1 including the support substrate 12, the fixed electrode, the movable electrode 17, and the like. 23 are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic quantity sensor for detecting a dynamic quantity such as acceleration based on a displacement of a weight movable electrode supported by an elastically deformable beam.

[0002]

2. Description of the Related Art For example, it is built in a gas flow meter and is used to close a valve of a gas pipe when vibration such as an earthquake is detected, or when it is built in a combustion stove and detects vibration such as an earthquake. 2. Description of the Related Art Acceleration sensors used for cutting off flames and fuel are generally configured to detect accelerations in multiple directions in a two-dimensional plane with almost the same sensitivity. In such an acceleration sensor, it is required to realize improvement in reliability and productivity as well as downsizing and low power consumption. A semiconductor acceleration sensor as disclosed in Japanese Patent Application Laid-Open No. 9-145740 is known.

More specifically, FIGS. 10 and 11 show a schematic longitudinal sectional structure and a planar structure of a semiconductor acceleration sensor described in the publication, respectively (however, hatching in FIG. 11 indicates a cross section). It is not a thing, but to make it easy to distinguish each structural element.) 10 and 11, an anchor portion 3 is fixed on a support substrate 1 made of single crystal silicon via a support anchor 2a. Each of the four beams 4 has one end integrally connected to the anchor 3 and is provided so as to be elastically deformable in a direction parallel to the surface of the support substrate 1. The planar shape is formed in a spiral shape. I have. An annular weight movable electrode 5 is integrally connected to each free end side of the beam portion 4 so as to be concentrically arranged with the anchor portion 3. The weight movable electrode 5 is configured such that its outer peripheral surface, that is, a cylindrical side surface in a direction perpendicular to the support substrate 1 functions as a conductive detection surface 5a.

[0004] On the support substrate 1, a fixed electrode 6 is arranged via a support anchor 2b. The fixed electrode 6 is provided so as to surround the weight movable electrode 5, and the inner peripheral surface of the cylindrical shape facing the weight movable electrode 5 functions as a conductive detection surface 6 a. . In this case, the anchor part 3, the beam part 4, the weight movable electrode 5, and the fixed electrode 6 are formed by trench-etching a silicon single crystal substrate having an SOI structure bonded to the support substrate 1 via a silicon oxide film, and etching the silicon substrate. The sacrifice layer is formed by etching a part of the oxide film. The bonding pads 7 and 8 for extracting signals are provided on the anchor portion 3 and the fixed electrode 6, respectively.

[0005]

In the above-described semiconductor acceleration sensor, the weight movable electrode 5 is installed so as to be displaced in the horizontal direction when acceleration is applied from the outside. Contact type sensor that detects acceleration by contact between the weight movable electrode 5 and the fixed electrode 6 corresponding to such displacement, or based on a change in capacitance between the weight movable electrode 5 and the fixed electrode 6 due to the displacement. The sensor functions as a capacitive sensor that detects acceleration.

However, in the semiconductor dynamic quantity sensor having such a configuration, as shown in FIG. 11, since the weight movable electrode 5 is supported by the elastically deformable beam portion 4, Then, the weight movable electrode 5 hangs down due to its own weight, and a phenomenon occurs in which the facing area between the weight movable electrode 5 and the fixed electrode 6 decreases. For this reason, when configured as a contact type sensor, there is a situation that the contact area between the two electrodes 5 and 6 is reduced, and the conduction resistance at the time of the contact is increased. In such a case, the absolute value of the capacitance formed between the electrodes 5 and 6 is reduced, and the S / N ratio is reduced.
In any case, the detection reliability is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to prevent the weight movable electrode from hanging down by its own weight. It is an object of the present invention to provide a physical quantity sensor capable of improving detection reliability when detecting a physical quantity based on a change in distance between them.

[0008]

Means for Solving the Problems In order to achieve the above object, means as described in claim 1 can be employed. According to this means, since the magnetic body provided integrally with the movable weight electrode is attracted upward by the magnet disposed above the movable weight electrode, the weight movable electrode hangs down by its own weight. Can be effectively prevented. For this reason, the situation where the opposing area between the weight movable electrode and the fixed electrode is reduced is prevented, and the detection reliability when detecting the physical quantity based on the change in the distance between the weight movable electrode and the fixed electrode is reduced. It is possible to prevent the deterioration beforehand.

When the means described in claim 2 is adopted, it is not necessary to separately provide a magnetic body, and the entire structure is simplified.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a semiconductor acceleration sensor will be described below with reference to FIGS. FIG. 1 shows an overall schematic vertical cross-sectional structure in a state of being housed in a case, and FIG. 2 shows an overall cross-sectional structure. In these FIGS. 1 and 2,
A semiconductor acceleration sensor 11 (hereinafter, referred to as a physical quantity sensor)
Basically, a beam structure 13 and a fixed electrode 14, which are also made of single-crystal silicon, are provided on a support substrate 12 made of single-crystal silicon, and support anchors 13 a and 14 a corresponding to the beams are formed. It has a structure supported through. The beam structure 13 includes a cylindrical anchor portion 1 supported by the support anchor 13a.
5 and, for example, 4
The structure includes a beam portion 16 and a weight movable electrode 17 supported by the beam portion 16.

In this case, the beam portion 16 has a spiral planar shape, and one end thereof is integrally connected to the peripheral wall of the anchor portion 15, thereby extending in a direction parallel to the surface of the support substrate 12. It is supported in the form. The above beam part 1
Reference numeral 6 is configured such that the ratio of the vertical dimension to the horizontal dimension of the vertical cross-sectional shape is set to be sufficiently large, so that it can be elastically deformed in a direction parallel to the surface of the support substrate 12.

The weight movable electrode 17 is formed in an annular shape (short cylindrical shape), and its inner peripheral surface is
Are connected integrally to the free end side of the. Thereby, the weight movable electrode 17 is placed on the support substrate 12.
The support substrate 12 is held so as to be freely displaceable in a two-dimensional plane direction parallel to the surface of the support substrate 12 in response to application of an acceleration, which is a mechanical quantity, in parallel with the surface of the support substrate 12 at a predetermined interval. The outer peripheral surface of the weight movable electrode 17 is an electrode surface 17a.

The fixed electrode 14 includes a weight movable electrode 17.
Is formed in a columnar shape so as to be arranged in the periphery of the support substrate 12, and the inner peripheral surface thereof is an electrode surface 14b. In this case, the electrode surface 14b is opposed to the electrode surface 17a of the weight movable electrode 17 with a predetermined gap. Specifically, the distance between the electrode surfaces 14b and 17a is substantially uniform in a state where the support substrate 12 is installed horizontally (a state where acceleration is not applied to the weight movable electrode 17). As a result, the gap between the two electrode surfaces 14b and 17a has an annular shape with the same width.

In the beam structure 13 including the weight movable electrode 17 and the fixed electrode 14, impurities such as phosphorus are introduced into at least the surface, or a conductive material is applied to the surface. By forming a film by means such as evaporation or plating, the resistivity is reduced.

On the beam structure 13 and the fixed electrode 14, a silicon nitride film 18 is formed as a protective film. An annular magnetic body 19 made of Ni or the like is provided integrally on the upper surface of the weight movable electrode 17 with the silicon nitride film 18 interposed therebetween. Further, on the upper surface of the anchor part 15, the silicon nitride film 18
Is provided on the upper surface of the fixed electrode 14, and a bonding pad 21 penetrating the silicon nitride film 18 and being ohmic-connected to the fixed electrode 14 is provided. In addition, beam structure 1
A silicon nitride film 22 is formed as a protective film on the uppermost layer of the fixed electrode 3 and the fixed electrode 14, and a portion of the silicon nitride film 22 corresponding to the bonding pads 20 and 21 is opened.

The magnet 2 is positioned above the weight movable electrode 17 at a position where an attractive force can be applied to the annular magnetic body 19.
3 are arranged. In this embodiment, the magnet 23
Is attached to the lower surface of a cap 24a of a case 24 for housing the acceleration sensor 11. in this case,
The size, the magnetic field strength, and the mounting position of the magnet 23 are set in consideration of the weight and size of the weight movable electrode 17 including the annular magnetic body 19 and the like. Specifically, the area where the electrode surface 17a of the weight movable electrode 17 and the electrode surface 14b of the fixed electrode 14 oppose each other is set so that the annular magnetic body 19 is attracted. The magnet 23
Are magnetized in a direction perpendicular to the surface of the support substrate 12 (vertical direction).

FIGS. 3 to 9 show the acceleration sensor 1.
1 is schematically illustrated, and will be described below with reference to FIGS. First, as shown in FIG.
An OI substrate 25 is prepared. The SOI substrate 25 has the beam structure 1 on a silicon oxide film 27 formed on the surface of a silicon wafer 26 which will eventually become the support substrate 12.
3 and a single crystal silicon wafer for forming the fixed electrode 14 are provided by a bonding method or the like, and a predetermined thickness is polished to form a single crystal silicon substrate 28. Incidentally, the silicon oxide film 27 finally becomes the support anchors 13a and 14a.

Next, as shown in FIG. 4, after the silicon nitride film 18 is formed on the single crystal silicon substrate 28 by LP-CVD or the like, the silicon nitride film 18 is patterned to form the bonding pad. Windows 20a and 21a for 20 and 21 are formed.

Thereafter, as shown in FIG.
Bonding pads 20, 21 and annular magnetic body 19
To form Specifically, an aluminum film is formed on the entire surface of the silicon nitride film 18 by a vapor deposition means, a sputtering means, a plating means, or the like to fill the windows 20a and 21 and then the aluminum film is patterned. To form bonding pads 20 and 21,
After that, a magnetic film such as Ni is formed in the same manner, and then the magnetic film is patterned to form the annular magnetic body 19.

Thereafter, as shown in FIG. 6, the silicon nitride film 18, the annular magnetic body 19 and the bonding pad 2 are formed.
After the silicon nitride film 22 is formed on the layers 0 and 21 by a CVD method or a plasma CVD method, a silicon oxide film 29 is formed on the silicon nitride film 22 by a similar method.

Next, as shown in FIG. 7, by sequentially performing an etching process on the silicon oxide film 29 and an etching process on the silicon nitride films 22 and 18, the silicon oxide film 29 and the silicon nitride film 22 are formed.
And 18, finally, the beam structure 13 and the fixed electrode 1
A window 30 having a shape corresponding to a region to be a groove between the four is formed, and the single crystal silicon substrate 28 of the SOI substrate 25 is exposed.

Further, as shown in FIG. 8, anisotropic etching (dry etching) is performed on the single crystal silicon substrate 28 using the uppermost silicon oxide film 29 as a mask, so that the window 30 is formed. A trench 31 having a corresponding shape is formed, and thus the silicon oxide film 2 of the SOI substrate 25 is formed.
7 is exposed.

Thereafter, as shown in FIG. 9, the silicon oxide film 27 is etched into a sacrifice layer using a hydrofluoric acid-based etchant to form a cavity in the lower surface of the single crystal silicon substrate 28. Form the support anchors 13a and 14a. That is, the beam structure 13 supported by the support anchors 13a is formed by such sacrifice layer etching. After this, silicon wafer 2
The basic structure of the acceleration sensor 1 shown in FIG. 1 and FIG. 2 is completed by performing a dicing step or the like for cutting 6 at a predetermined position.

At this time, the uppermost silicon oxide film 29 is also removed by etching. The sacrificial layer etching is performed by controlling the time. Further, at any stage of each of the above-described steps, the resistivity of the beam structure 13 and the fixed electrode is reduced by introducing an impurity such as phosphorus into the single crystal silicon substrate 28 by ion implantation, phosphorus deposition, or the like. Is done.

The acceleration sensor 1 according to the embodiment described above.
Is mounted so that the support substrate 12 is in a horizontal state. When an acceleration of a predetermined level or more is applied, the weight movable electrode 17 is moved in the horizontal direction, and the electrode surface 17a is fixed. It comes into contact with the electrode surface 14b of the electrode 14, and the applied acceleration can be detected according to such contact. In this case, in the acceleration sensor 1, the magnetic body 19 provided integrally with the weight movable electrode 17 is provided.
Is lifted in response to the magnet 23 being attracted upward by the magnet 23, whereby the weight movable electrode 17 is reliably prevented from hanging down by its own weight. You. In the suction state, the opposing area between the electrode surface 17a of the weight movable electrode 17 and the electrode surface 14b of the fixed electrode 14 is configured to be maximum.
4b, it is possible to prevent a situation where the conduction resistance at the time of contact between the electrodes 4b is increased as in the conventional configuration, and thereby the detection reliability when detecting acceleration based on the contact between the weight movable electrode 17 and the fixed electrode 14 is improved. Can be prevented beforehand.

It should be noted that the present invention is not limited to the above-described embodiment, but can be modified or expanded as follows. Although the configuration is such that the acceleration is detected by the contact between the weight movable electrode 17 and the fixed electrode 14, the configuration may be such that the acceleration is detected based on a change in capacitance between the electrodes 17 and 14. The weight movable electrode itself may be made of a magnetic material. According to such a configuration, it is not necessary to separately provide a magnetic material, and the entire structure is simplified. The invention can be applied not only to the semiconductor acceleration sensor but also to other physical quantity sensors.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a semiconductor acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the sensor.

FIG. 3 is a longitudinal sectional view schematically showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 4 is a longitudinal sectional view schematically showing the same manufacturing process.

FIG. 5 is a longitudinal sectional view schematically showing the same manufacturing process.

FIG. 6 is a longitudinal sectional view schematically showing the same manufacturing process.

FIG. 7 is a longitudinal sectional view schematically showing the same manufacturing process.

FIG. 8 is a longitudinal sectional view schematically showing the same manufacturing process.

FIG. 9 is a longitudinal sectional view 7 schematically showing the same manufacturing process.

FIG. 10 is a diagram corresponding to FIG. 1 for explaining a conventional configuration.

FIG. 11 is a plan view for explaining the conventional configuration.

[Explanation of symbols]

11 is a semiconductor acceleration sensor (dynamic quantity sensor), 12 is a support substrate, 13 is a beam structure, 13a is a support anchor, 14
Is a fixed electrode, 14a is a support anchor, 14b is an electrode surface,
Reference numeral 15 denotes an anchor portion, 16 denotes a beam portion, 17 denotes a movable weight electrode, 17a denotes an electrode surface, 19 denotes an annular magnetic body, 20 and 21 denote bonding pads, and 23 denotes a magnet.

Claims (4)

[Claims] A weight movable electrode which is supported by an elastically deformable beam portion with respect to an anchor portion on a support substrate and is provided so as to be displaceable in a horizontal direction in response to an action of a mechanical quantity; A fixed electrode disposed so as to face the weight movable electrode at a predetermined interval, and detecting a mechanical amount acting on the weight movable electrode based on a change in a distance between the weight movable electrode and the fixed electrode. A dynamic quantity sensor comprising: a magnetic body provided integrally with the weight movable electrode; and a magnet disposed above the weight movable electrode so as to apply an attractive force to the magnetic body. The physical quantity sensor characterized by that. 2. The physical quantity sensor according to claim 1, wherein the weight movable electrode itself is made of a magnetic material. 3. The physical quantity sensor according to claim 1, wherein a physical quantity detection operation is performed in accordance with a contact between the weight movable electrode and the fixed electrode. 4. The physical quantity sensor according to claim 1, wherein the physical quantity detection operation is performed based on a change in capacitance between the weight movable electrode and the fixed electrode. .