JP2000275271A - Semiconductor acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor acceleration sensor with higher sensitivity by making deflection sections thin. SOLUTION: A semiconductor substrate is machined to form an overlap section 11, nearly flat plate-like deflection sections 12 protruded sidewards from the side faces of the overlap section 11 and interlocked with the overlap section 11, and support sections 13 supporting the tips of the deflection sections 12, and piezoelectric resistors 14 are formed on the deflection sections 12 to form this acceleration sensor. The deflection sections 12 are arranged so that the width direction of the deflection sections 12, coincides with the thickness direction of the overlap section 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor used for automobiles, aircrafts, home electric appliances and the like.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional semiconductor acceleration sensor of this type. This is a weight 1
A bending portion 2 protruding laterally from the side surface of the weight portion 1 and interlocking with the weight portion, and a support portion 3 for supporting the bending portion 2 are formed by processing a semiconductor substrate, and a piezo resistor 4 is formed on the bending portion. It is formed and formed. The flexure 2 of this is a flexure 2
Are aligned with the width direction of the weight portion 1, and the thickness direction of the flexible portion 2 is matched with the thickness direction of the weight portion 1. A semiconductor acceleration sensor having such a structure is described in, for example, Japanese Patent Application Laid-Open No. 6-109755, and can realize a small-sized and high-sensitivity sensor as compared with a conventional mechanical acceleration sensor. It can be manufactured at low cost.

As a method of manufacturing this semiconductor acceleration sensor, as disclosed in Japanese Patent Application Laid-Open No. 9-289327, a high-concentration impurity layer is embedded in a silicon substrate and then an epitaxial layer is formed. There is one using an embedded epi substrate. In this method, after the anisotropic etching, the high-concentration impurity layer is used as a sacrificial layer, and a hydrofluoric acid-based etchant (hydrofluoric acid: nitric acid: acetic acid = 1 :: 3:
The sacrifice layer is etched by an (8-system solution) to form a cut structure between the weight portion and the bent portion. Other manufacturing methods include electrolytic etching and SOI (Silic).
There is a method in which a sacrificial layer is etched using an on-insulator substrate, and the thickness of the bent portion is set to a predetermined value by this method.

[0004]

However, the semiconductor acceleration sensor in which the thickness direction of the bending portion 2 coincides with the thickness direction of the weight portion 1 has the following problems.

That is, in the case of manufacturing by sacrifice layer etching using a buried epi substrate, the thickness of the bent portion is determined by the concentration and expansion of the high-concentration impurity layer and the etching conditions for the epi thickness and sacrifice layer etching. In the case of manufacturing using an SOI substrate, the thickness of the bent portion 2 depends on the thickness of the active layer when the SOI substrate is formed. You have to get the substrate. Further, in the production by electrolytic etching, the thickness of the bent portion 2 depends on the epi thickness and the etching conditions of the sacrificial layer etching. In other words, the thickness of the flexure 2 is strictly controlled in any of the case of manufacturing by the sacrificial layer etching using the buried epi substrate, the case of manufacturing by using the SOI substrate, and the case of manufacturing by the electrolytic etching. There is a problem that it is difficult to obtain a desired value.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a semiconductor acceleration sensor with higher sensitivity by reducing the thickness of a bending portion.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a weight portion, a substantially flat plate-like flexible portion projecting laterally from a side surface of the weight portion and interlocking with the weight portion. A supporting portion for supporting a tip portion of the bending portion; and a semiconductor acceleration sensor formed by processing a semiconductor substrate and forming a piezoresistor in the bending portion, wherein a width direction of the bending portion is a thickness direction of the weight portion. It is characterized in that a bending portion is provided so as to match.

The semiconductor substrate is formed by processing a weight portion, a substantially plate-shaped bending portion projecting laterally from a side surface of the weight portion and interlocking with the weight portion, and a supporting portion for supporting a tip portion of the bending portion. In a semiconductor acceleration sensor having one side surface of the weight portion as a movable electrode and a fixed electrode opposed to the movable electrode, the width direction of the bent portion is made to coincide with the thickness direction of the weight portion. May be provided with a bending portion.

It is preferable to form cut grooves on both sides in the thickness direction of the base end portion of the bending portion in a direction opposite to the direction in which the bending portion protrudes, in that the bending portion can be lengthened.

A semiconductor acceleration sensor can be manufactured from a single silicon wafer by forming a stopper for restricting excessive movement of the weight with the same material as the weight.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a semiconductor acceleration sensor according to the present invention will be described with reference to FIGS. 1 and 2, and a second embodiment will be described with reference to FIG.

[First Embodiment] FIG. 1 shows a semiconductor acceleration sensor according to the present invention, wherein FIG.
(B) is a side sectional view cut along AA '. FIG. 2 is a perspective view of a main part of the semiconductor acceleration sensor of the present invention.

1 and 2, the semiconductor acceleration sensor includes a weight 11, a beam 12 corresponding to a flexure, a support 13, a piezoresistor 14, and a stopper 15. The weight 11, the beam 12, the support 13, and the stopper 15 are made of silicon.

The weight portion 11 is a portion for generating an inertial force for detecting acceleration, and is, for example, a substantially rectangular parallelepiped as shown in FIG. A beam 12 is provided to protrude from two opposing side surfaces of the weight portion 11 in a direction away from each other. This beam 12 is the weight 1
It is interlocked with 1 and is formed in a substantially flat plate shape.
The beam 12 is provided on the weight portion 11 such that the width direction W of the beam 12 matches the thickness direction D1 of the weight portion 11.

The support portion 13 is provided so as to surround the weight portion 11, and the tip of the beam 12 is connected to support the beam 12.

Notches 16 are formed on both sides in the thickness direction D2 of the base end portion 12a of the beam 12 toward the inside of the weight portion 12, which is opposite to the direction in which the beam 12 projects. The cut grooves 16 make the beam 12 substantially longer, so that a more highly sensitive semiconductor acceleration sensor can be obtained.

The piezoresistor 14 changes its resistance value in accordance with the strain, and is provided at the tip 12 b of the beam 12.

The stoppers 15 are provided so as to be opposed to the other pair of side surfaces of the weight portion 11, respectively, and restrict the excessive movement of the weight portion 11 to protect the beam 12 from excessive stress. is there.

In the semiconductor acceleration sensor having the above configuration, the beam 12 bends according to the acceleration, so that a bridge circuit (not shown) including the piezoresistor 14 outputs a voltage corresponding to the acceleration. Acceleration can be detected.

In the semiconductor acceleration sensor, since the beam 12 is provided on the weight portion 11 so that the width direction W of the beam 12 coincides with the thickness direction D1 of the weight portion 11, the beam is vertically dug by trench etching. Indentation formation is possible. Therefore, the thickness of the beam 12 can be accurately reduced. Silicon trench etching is RIE
(Reactive Ion Etching).

Further, since the stopper 15 can be formed by trench etching, there is no need to bond another member as in the conventional technique, and the manufacturing process is simplified. Further, in order for the weight 11 to be freely operable, a cavity 18 is required between the weight 11 and the base 17, but the cavity 18 can be provided by sacrificial layer etching. Cavity 1 by sacrificial layer etching
The provision of 8 makes it possible to manufacture a semiconductor acceleration sensor only from a silicon wafer without the need to attach a separate base 17.

[Second Embodiment] FIG. 3 shows a semiconductor acceleration sensor according to the present invention.
(B) is a side sectional view cut along BB '. In addition,
In FIG. 3, the same parts as those of the semiconductor acceleration sensor described in the first embodiment are denoted by the same reference numerals, and detailed description of the same parts will be omitted.

The semiconductor acceleration sensor of the present embodiment shown in FIG. 3 is different from the semiconductor acceleration sensor described in the first embodiment in the following features.

That is, one side surface of the weight portion 11 is
a, and a side surface of the stopper 15 facing the one side surface is used as a fixed electrode 15a to form a capacitance type semiconductor acceleration sensor. With this configuration, the fixed electrode 15
An insulating layer 19 is interposed between the stopper 15 provided with a and the base 18. The insulating layer 19 is a stopper 15
It is intended to insulate the weight and the weight 11 from each other.

In this embodiment, the movable electrode 11a of the weight 11 and the fixed electrode 15a of the stopper 15 are provided with a plurality of comb teeth 11b and 15b, respectively, so as to mesh with each other.

In the semiconductor acceleration sensor having the above configuration, the beam 12 bends in accordance with the acceleration, so that the distance between the movable electrode 11a and the fixed electrode 15a changes. Since the capacitance changes, acceleration can be detected from the capacitance.

In the semiconductor acceleration sensor, the beam 12 is provided on the weight portion 11 so that the width direction W of the beam 12 coincides with the thickness direction D1 of the weight portion 11, so that the beam is dug vertically by trench etching. Indentation formation is possible. Therefore, the thickness of the beam 12 can be accurately reduced.

In the first and second embodiments, a uniaxial semiconductor acceleration sensor is described. However, for example, as shown in FIGS. Multiple axes can be detected by disposing a plurality of chips 21 with different axes, or by mounting a plurality of chips 21 on which a single semiconductor acceleration sensor is arranged with different axes.

[0029]

Since the semiconductor acceleration sensor of the present invention is constructed as described above, according to the first aspect of the present invention, the weight portion and the weight portion projecting sideways from the side surface of the weight portion. A semiconductor acceleration sensor in which a substantially flat plate-shaped bending portion interlocked with a supporting portion for supporting a tip portion of the bending portion is formed by processing a semiconductor substrate, and a piezo resistor is formed in the bending portion. Since the bent portion is provided so that the width direction of the portion matches the thickness direction of the weight portion, it is possible to form a digging vertically by trench etching, so that the bent portion can be accurately thinned. It works.

According to the second aspect of the present invention, the weight portion, the substantially plate-shaped bent portion projecting laterally from the side surface of the weight portion and interlocking with the weight portion, and supporting the distal end portion of the bent portion. And a supporting portion to be formed by processing a semiconductor substrate, one side surface of the weight portion is a movable electrode, and in a semiconductor acceleration sensor provided with a fixed electrode opposed to the movable electrode, the width direction of the bending portion is Since the bent portion is provided so as to coincide with the thickness direction of the weight portion, it is possible to form a digging vertically by trench etching, and thus, the bent portion can be accurately reduced in thickness.

According to the third aspect of the present invention, since the cut grooves are formed on both sides in the thickness direction of the base end of the flexible portion in the direction opposite to the direction in which the flexible portion projects, the flexible portion is made longer. Therefore, the semiconductor acceleration sensor with higher sensitivity can be provided.

According to the fourth aspect of the present invention, since the stopper for restricting excessive movement of the weight is formed of the same material as the weight, the semiconductor acceleration sensor is manufactured from a single silicon wafer. It has the effect that it can be done.

[Brief description of the drawings]

FIGS. 1A and 1B show a configuration of a semiconductor acceleration sensor according to the present invention, in which FIG. 1A is a plan view, and FIG. 1B is a side sectional view cut along AA ′.

FIG. 2 is a perspective view of a main part of the semiconductor acceleration sensor of the present invention.

3A and 3B show another configuration of the semiconductor acceleration sensor of the present invention, wherein FIG. 3A is a plan view, and FIG. 3B is a side cross-sectional view cut along BB ′.

FIG. 4 is a plan view showing another configuration of the semiconductor acceleration sensor of the present invention.

FIG. 5 is a plan view showing another configuration of the semiconductor acceleration sensor of the present invention.

FIG. 6 is a plan view showing one configuration of a conventional semiconductor acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Weight part 12 Flexure part 13 Support part 14 Piezoresistance 11a Movable electrode 15a Fixed electrode 15 Stopper part 16 Cut groove

Claims (4)

[Claims] A semiconductor substrate comprising: a weight portion; a substantially flat bending portion protruding laterally from a side surface of the weight portion and interlocking with the weight portion; and a support portion supporting a distal end portion of the bending portion. A semiconductor acceleration sensor formed by processing and forming a piezoresistor in the bending portion, wherein a bending portion is provided so that a width direction of the bending portion coincides with a thickness direction of the weight portion. Sensor. 2. A semiconductor substrate comprising: a weight portion; a substantially plate-shaped bent portion projecting laterally from a side surface of the weight portion and interlocking with the weight portion; and a support portion for supporting a tip portion of the bent portion. In a semiconductor acceleration sensor having one side surface of the weight portion as a movable electrode and a fixed electrode opposed to the movable electrode, the width direction of the bent portion is made to coincide with the thickness direction of the weight portion. A semiconductor acceleration sensor, wherein a bending portion is provided on the semiconductor acceleration sensor. 3. The semiconductor acceleration sensor according to claim 1, wherein cut grooves are formed on both sides in a thickness direction of a base end portion of the flexible portion in a direction opposite to a direction in which the flexible portion protrudes. . 4. The semiconductor acceleration sensor according to claim 1, wherein a stopper for restricting excessive movement of the weight is formed of the same material as the weight.