JPH09113534A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor which is composed of a silicon micromachine and can detect a multishaft directional acceleration component. SOLUTION: A structure layer is formed by polishing a directly joined silicon substrate surface, and a fixed body and a movable body are formed by using an oxide film of a joining part as a sacrificing layer, and a multishaft acceleration sensor 2 is constituted by detecting a capacity change between fixed bodies 18 and 28 being electrodes and movable bodies 19 and 29 and between a movable body (a mass part) 33 being an electrode and a silicon substrate 10. The structure layer formed by polishing can be made thick, and since it is not composed of polysilicon, but is composed of monocrystal silicon, the mechanical degradation of flexible bodies 15a, 15b, 25a, 25b and 351 to 354 can be reduced. A triaxial directional acceleration component of a space can be detected by an acceleration sensor 2 composed of a single substrate, and its detecting sensitivity can be set on various levels by adjusting a plane shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting acceleration, and more particularly to a multi-axis acceleration sensor which is composed of a silicon micromachine and which detects acceleration components of two or more axes with one acceleration sensor.

[0002]

2. Description of the Related Art In recent years, a sensor capable of detecting acceleration in two or three axes has been announced in place of a conventional acceleration sensor which can detect acceleration in only one axis. Among such acceleration sensors, a three-axis acceleration sensor that can detect acceleration components in three-axis directions is shown in FIG.
A cross section is shown in FIG.

Referring to FIG. 10 (a), reference numeral 102 denotes a triaxial acceleration sensor. The triaxial acceleration sensor 102 has a pedestal 104 having a cylindrical shape and a circular silicon substrate 105 adhered onto the pedestal 104. have. A columnar mass portion 107 made of Pyrex glass is bonded to the central bottom surface of the silicon substrate 105. Of the thickness of the silicon substrate 105, a region where the mass portion 107 and the pedestal 104 are bonded is thinned, and the thinned region constitutes a flexible portion 108.
When acceleration is applied to the axial acceleration sensor 102, the weight of the mass portion 107 causes the flexible portion 108 to move.
It is configured to be mechanically deformed by being stressed.

As shown in FIG. 10 (b), which is a plan view of the triaxial acceleration sensor 102, a positive portion on the Y-axis with the center of the silicon substrate 105 as the origin is formed on the surface of the flexible portion 108. In the negative part, the piezoresistive elements Ry ₁ , Ry ₂ ,
Two Ry ₃ and Ry ₄ are provided, and two negative and positive partial piezoresistive elements Rx ₁ , Rx ₂ , Rx ₃ and Rx ₄ on the X axis are provided, and further, The piezoresistive elements Rz ₁ , Rx _{1 and} Rx ₄ are arranged close to the piezoresistive elements Rx _{1 to} Rx ₄ on the X-axis.
z ₂ , Rz ₃ and Rz ₄ are arranged in parallel.

If three piezoresistive elements Rx _{1 to} Rx ₄ , each piezoresistive element Ry _{1 to} Ry _4, and each piezoresistive element Rz _{1 to} Rz ₄ form three resistance bridges,
The change state of the resistance value indicated by the resistance bridge differs depending on the direction and magnitude of the acceleration applied to the triaxial acceleration sensor 102. Therefore, if the resistance change of each resistance bridge is measured, the X, Y, and Z axes can be measured. It is possible to measure the acceleration components in the three axis directions.

However, when the piezo resistance change is used for detecting the acceleration, the detected value is easily influenced by the temperature, and reliable measurement cannot be performed. Further, depending on the application, it is necessary to test whether or not the acceleration sensor incorporated in the device is operating normally. For that purpose, it is desired to move the mass portion by a predetermined amount by a force such as an electrostatic force, detect the output of the acceleration sensor at that time, and judge whether or not it is operating normally. In this case, in the acceleration sensor 102, the mass portion 107 is large and heavy, and it is somewhat difficult to move it by electrostatic force or the like.

Furthermore, the silicon substrate 105 and the mass portion 107 are bonded together by the anodic bonding method, but the bonding process is complicated and requires a lot of man-hours, resulting in low yield and high cost.

Therefore, in recent years, an acceleration sensor having a silicon micromachine structure that can be manufactured by a process similar to the semiconductor device manufacturing process has been proposed, and if it can be manufactured by this process, it can be manufactured at low cost.

If the silicon micromachine structure is used, the acceleration can be detected by the change of the capacitance value instead of the change of the piezo resistance, so that there is no influence of the temperature change and the normal operation can be confirmed by the electrostatic force or the like. As such, it is expected to be applicable to applications requiring high reliability, such as being used for collision detection for air bag control of automobiles.

A conventional acceleration sensor having such a silicon micromachine structure will be described. Referring to FIG. 11A, which is a plan view, 112 is a conventional acceleration sensor having a silicon micromachine structure. The acceleration sensor 112 includes a silicon substrate, a fixing body fixed on the silicon substrate, and A movable body that is movable with respect to the silicon substrate and the fixed body; and a flexible body that elastically holds the movable body on the fixed body to mechanically and electrically connect the movable body and the fixed body. It is configured.

The acceleration sensor 112 comprises fixed arms 124a, 12 formed of the fixed body and formed in a linear shape.
4b, the fixed arm portion 124a, 124b,
A plurality of linearly formed fixed electrodes 134a and 134b formed of the movable body are connected at right angles to each other so that the fixed electrodes 134a and 134b do not move.

Between the fixed electrodes 134a and between the fixed electrodes 134b, movable electrodes 135a and 135b formed of the movable body and formed in a linear shape are inserted in parallel one by one. .

Since the fixed electrodes 134a, 134b and the movable electrodes 135a, 135b are arranged close to each other and face each other and have electrical conductivity, the fixed electrodes 134a, 134b are Parallel plate capacitors 123a and 123b are formed by the movable electrodes 135a and 135b, which are arranged opposite to the movable electrodes 135a and 135b. The movable electrodes 135a and 135b are movable arms 1 composed of the movable body.
Since the movable arm portion 126 is electrically and mechanically connected to the flexible portions 127 ₁ and 127 ₂ formed of the flexible body, the parallel arm capacitors 123a are connected to each other. , 123b are connected in parallel.

The flexible portions 127 ₁ and 127 ₂ are holding portions 12 formed by the fixed body and formed in a rectangular shape.
8 ₁ and 128 ₂ , and the flexible portions 127 ₁ and 127 ₂ elastically support the movable electrodes 135a and 135b with the holding portions 128 ₁ and 128 ₂ as fulcrums. Since the flexible portions 127 ₁ and 127 ₂ are formed so as to be easily deformed in the central axis direction of the movable electrodes 135a and 135b as shown in FIG. 11B, the movable electrodes 135a and 13
5b can be moved in and out between the fixed electrodes 134a and 134b.

Therefore, as shown in FIG. 11B, when acceleration is applied to the acceleration sensor 112 and the movable electrodes 135a and 135b are moved by Δx in the direction of the central axis thereof, the parallel plate type Condenser 123
Since the capacitance values of a and 123b change according to the magnitude of Δx, it is possible to obtain the acceleration component in the central axis direction by detecting the amount of change.

By the way, this acceleration sensor 112
Is manufactured by a manufacturing process as shown in FIGS. 12A to 12F. To explain the process, first, in the manufacturing process of the acceleration sensor 112, a silicon thermal oxide film is formed on the silicon substrate 153. It starts with film formation.

After the silicon thermal oxide film 154 is formed on the surface of the silicon substrate 153, the nitride film 155 is formed on the surface thereof.
Is formed ((a) in the figure), and after opening a window in a predetermined area,
A first polysilicon layer 156 is formed on the entire surface (FIG. 2B).

Next, after opening a window in a desired region of the first polysilicon layer, an insulating layer 157 made of a PSG film is formed on the entire surface (FIG. 7C), and a predetermined region of the insulating layer 157 is formed. After the window is opened in the second polysilicon layer 1 on its surface
58 is deposited on the entire surface ((d) of the figure), and the second polysilicon layer 158 is directly formed on the first polysilicon layer 156. Then, after a predetermined region of the second polysilicon layer 158 is opened ((e) in the figure), it is immersed in a selective dilute hydrofluoric acid solution, and the insulating layer 1 is exposed through the opening.
The etching of 57 is started, and the insulating layer 157 is removed by the dilute hydrofluoric acid solution (FIG. 6 (f)).

A portion of the second polysilicon layer 158 which is directly formed on the first polysilicon layer 156 is not etched, and the second polysilicon layer 158 is not etched.
Becomes a fixed body 165 fixed to the silicon substrate,
The portion where the insulating layer 157 is removed under the bottom is the movable body 166.
Becomes The insulating layer 15 is formed below the bottom surface of the movable body 166.
A gap 164 having a thickness of 7 is opened.

As described above, the second polysilicon layer 15 is formed.
If the movable body 166 and the fixed body 165 are configured by using 8 as a structure of a silicon micromachine, the same silicon micromachine manufacturing process as the semiconductor device manufacturing process can be applied, and the acceleration sensor can be mass-produced at low cost. .

By the way, in order to improve the detection accuracy of the acceleration sensor 112, it is necessary to increase the capacitance value of the capacitor used for detection. In the parallel plate capacitors 123a and 123b described above, the capacitance is the same as the fixed electrodes 134a and 134b and the movable electrode 13.
It is determined by the product of the length and the thickness of 5a and 135b.

However, the second polysilicon layer 15
Since No. 8 is formed by the LPCVD method (low pressure CVD method), there is a limit in increasing the film thickness. Therefore, in order to increase the capacitance value, it is necessary to increase the number of parallel plate type capacitors, resulting in a large element area.

If a mass portion similar to the mass portion 107 is formed on the second polysilicon layer 158 and an acceleration is detected by a capacitance change between the mass portion and the first polysilicon layer 156. The second polysilicon layer 15
Since 8 is thin, its weight is too small to detect a small acceleration, and for that purpose, the area of the mass portion must be made very large.

Further, there is a problem that polysilicon is warped because residual stress is generated after the film formation. Moreover, when the electrodes made of polysilicon warp in the direction of shortening the distance between the electrodes, if the electrodes stick to each other, a sticking phenomenon is caused and the reliability of the sensor is significantly reduced.

[0025]

SUMMARY OF THE INVENTION The present invention was created in order to solve the disadvantages of the prior art described above, and its object is to form an acceleration sensor having a silicon micromachine structure and capable of detecting acceleration components in multiaxial directions. And to provide a highly reliable acceleration sensor.

[0026]

In order to solve the above-mentioned problems, the invention according to claim 1 includes a silicon substrate, a sacrificial layer located on the silicon substrate, and a structural layer located on the sacrificial layer. An acceleration sensor having a structure in which a movable body is formed by patterning the structural layer and removing a sacrifice layer under the bottom surface of the sacrifice layer by etching, the movable body is elastically supported by the fixed body, and the sacrifice layer under the bottom surface is sacrificed. A fixed body is formed in a portion where the layer is left, and a capacitance change of a capacitor formed by arranging a side surface of the movable body and a side surface of the fixed body in parallel to each other, and the movable body and the silicon substrate. The change in the capacitance of the condenser is detected to detect the direction and magnitude of the acceleration,

According to a second aspect of the present invention, there is provided the acceleration sensor according to the first aspect, wherein the acceleration sensor has at least two capacitors in which a side surface of the movable body and a side surface of the fixed body are arranged to face each other. Characterized in that the normals of the electrode surfaces of the capacitors are arranged so as to intersect each other at a predetermined angle,

The invention according to claim 3 is the acceleration sensor according to claim 1 or 2, wherein the silicon substrate is an oxidation film formed on the surface of two silicon single crystal substrates. The sacrificial layer is composed of the oxide film, and the structural layer is formed by bonding the films to each other by a direct bonding method, and the structural layer is a silicon single crystal substrate surface of one of the substrates bonded by the direct bonding method. Characterized by being formed by polishing,

The invention according to claim 4 is the acceleration sensor according to claim 3, characterized in that the thickness of the structural layer remains at least 3 μm during the polishing.

According to the structure of the present invention, since the sacrificial layer and the structure layer are located in this order on the silicon substrate, the patterning of the structure layer and the etching of the sacrifice layer are performed. It is possible to form the movable body in a portion of the structural layer below the bottom surface where the sacrificial layer is removed, and to form the fixed body in a portion where the sacrifice layer below the bottom surface remains.

In this case, a parallel plate type capacitor can be constructed by arranging the side surface of the movable body and the side surface of the fixed body so as to be parallel to each other, and the parallel plate is composed of the movable body and the silicon substrate. A type of condenser can be constructed. When the movable body that constitutes the condenser is elastically supported by the support portion that is constituted by the fixed body, the capacitance of the condenser formed by the movable body and the fixed body when acceleration is applied to the acceleration sensor. The value changes according to the magnitude of the acceleration component in the direction perpendicular to the side surface of the movable body, and the capacitance value of the capacitor composed of the movable body and the silicon substrate is the direction perpendicular to the silicon substrate. It is possible to determine the direction and magnitude of acceleration by measuring the capacitance value of each capacitor, which changes depending on the magnitude of the acceleration component of.

In this case, if at least two of the capacitors composed of the movable body and the fixed body are arranged such that the normals of their electrode surfaces intersect at a predetermined angle, the two Since the acceleration component in the other direction can be detected by the condenser of 3, the triaxial acceleration sensor can be configured together with the acceleration component in the vertical direction detected by the silicon substrate and the movable body.

When manufacturing such an acceleration sensor, two silicon single crystal substrates are prepared, and the oxide films formed on the surfaces thereof are brought into close contact with each other, and one silicon substrate is formed by the direct bonding method. The sacrificial layer can be composed of an oxide film, and further, when the surface of one bonded silicon substrate is polished, the structural layer can be composed of the polished single crystal silicon substrate.

Since the structural layer formed by polishing is a single crystal, mechanical deterioration of the flexible portion is small, and a structural layer having a desired thickness can be easily obtained. In particular, it is difficult to form the structural layer by the LPCVD method. The thickness can be 3 μm or more.
Further, since the thickness of the structural layer is constant, the sensitivity can be individually set only by adjusting the planar shape.

[0035]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of an acceleration sensor 2 which is the best mode of the present invention. The acceleration sensor 2
Has three acceleration sensing elements 12, 22, 32 provided on one silicon substrate 10.

The three acceleration sensing elements 12, 22, 3
2 is formed at the same time by a silicon micromachine manufacturing process, which is a process similar to the manufacturing of a semiconductor element, and the acceleration sensing elements 12, 22, 32 are a fixed body fixed on the silicon substrate 10, and the silicon. A movable body that is movable with respect to the substrate 10 and the fixed body, and a flexible body that elastically holds the movable body on the fixed body to mechanically and electrically connect the movable body and the fixed body. It consists of and.

The steps of forming the fixed body, the movable body, and the flexible body are performed by the acceleration sensing elements 12, 22,
It will be described according to the manufacturing process of 32. 5 (a)-(c)
The process up to the formation of an aluminum thin film used as a mask for etching a silicon single crystal is shown in FIG.
Referring to FIGS. 5 (a) to 5 (c), first, two silicon single crystal substrates 50a and 50b each having a silicon thermal oxide film formed on its surface are formed.
Of the silicon single crystal substrates 50a and 50b are bonded to each other by a direct bonding method.
Make 2 (Fig. 5 (a)).

Next, the silicon single crystal substrate 50b on the surface of the silicon substrate 52 is polished to a thickness of about 10 μm, and the polished silicon single crystal substrate constitutes the structural layer 54.

On the other hand, the silicon single crystal substrate on the back surface is not polished, and the substrate 53 is constructed with the original thickness. The thickness of the silicon oxide film between the two silicon single crystal layers is approximately 1 μm, and the silicon oxide film forms the sacrificial layer 51 (FIG. 2B). Then, the structural layer 5
An aluminum thin film 55 was formed on the entire surface by vacuum deposition (FIG. 4 (c)).

Next, steps of forming the ohmic layer after forming the aluminum thin film 55 on the entire surface are shown in FIGS.
7G shows the steps from the formation of the ohmic layer to the removal of the sacrificial layer by etching, as shown in FIGS. 6 (d) to 6 (g) and 7 (h) to 7 (k) are shown on the left side of the process of forming a portion corresponding to the cross section of the acceleration sensing element 12 of FIG. The figure on the right side shows the cross section in the process of forming the portion corresponding to the line D-D of the acceleration sensing element 32 in FIG. 1.

Referring to FIGS. 6D to 6G, after the aluminum thin film 55 is formed on the entire surface, a predetermined region of the aluminum thin film 55 is removed by etching through a photolithography process to form a window opening 57. Form. A mask portion 58 is formed where it is left without being removed (FIG. 7D), and anisotropic dry etching is performed by RIE using an etching gas in which CHF gas and SF gas are mixed at a ratio of 7: 3. Then, the structural layer 54 and the sacrificial layer 51 are selectively removed from the window opening 57 to pattern the structural layer 54 (FIG. 8E). At this time, the mask portion 58
The structural layer 54 and the sacrificial layer 51 are left under the bottom surface of the.

The substrate layer 53 and the structural layer 5
4 is a p-type silicon single crystal and has ohmic contact with the metal electrode.
8 is removed to expose the structure layer 54 on the surface, and boron, which is a p-type dopant, is ion-implanted or thermally diffused.
((F) of the same figure). Then, it is diffused by heat treatment to form p ⁺ ohmic layers 63 and 64 on the surfaces of the substrate layer 53 and the structure layer 54, respectively (FIG. 5).
(g)).

Next, referring to FIGS. 7H to 7K, a resist 65 is applied to the surfaces of the ohmic layers 63 and 64 (see FIG. 7).
(h)) After opening a predetermined portion of the window, a chromium / platinum thin film 66 is formed by a vapor deposition method ((i) in the same figure). Then, the chromium-platinum thin film 66 formed on the resist 65 is removed together with the resist 65 by a lift-off method. The chromium / platinum thin film 66 formed in the window opening portion of the resist 65 remains, and metal electrodes 73 and 74 are formed on the surfaces of the ohmic layers 63 and 64, respectively (FIG. 7 (j)).

When the silicon substrate on which the metal electrodes 73 and 74 are formed is immersed in a hydrofluoric acid buffer solution (BHF), side etching of the side surface of the sacrificial layer 51 not covered with the structural layer 54 is started.

During the patterning of the structural layer 54, the structural layer 54 has a wide portion and a narrow portion. Therefore, with the progress of the side etching, the structural layer 54 has a certain etching time within a certain range. The sacrificial layer 51 can be completely removed under the bottom surface of the portion where 54 is formed narrow, and the sacrificial layer 5 is formed under the bottom surface of the portion where it is formed wide.
You can leave one. Therefore, the side body is appropriately etched for side etching to remove the sacrificial layer 51 to form the movable body 69, and the remaining portion to form the fixed body 68.

In the movable layer 69, a flexible body is formed when the movable layer 69 has a planar shape that facilitates mechanical deformation, and the movable body 69 has a movable electrode portion and an arm portion, which will be described later. Since the flexible body is connected to the fixed body 68 and held by the flexible body, the movable body 69 is movable, but the silicon substrate 53 is movable during etching.
Never separated from.

The single crystal silicon forming the structure layer 54 and the substrate 53 and the metal electrode 7 are formed.
Since the chromium-platinum thin films constituting 3, 74 are not etched with hydrofluoric acid, the metal electrodes 73, 74 are not peeled off.

By the way, by dry etching by the RIE method, the side surface of the structural layer 54 is formed to be perpendicular to the surface of the silicon substrate 53, and the side surface of the fixed body 68 and the side surface of the movable body 69. By arranging and in close proximity to each other, a parallel plate type capacitor can be constructed.

Each of the acceleration detecting elements 12 and 22 has six parallel plate type capacitors 11 and 21 having such a structure. The parallel plate type condenser 1
Reference numerals 1 and 21 are composed of the fixed body 68, and have fixed electrodes 18 and 28 formed in a linear shape, and movable electrodes 19 and 29 formed of the movable body 69 and formed in a linear shape. The parallel plate type capacitors 11 are configured such that the movable electrode 19 and the fixed electrode 18 are closely arranged in parallel, and the parallel plate type capacitors 21 are
The movable electrode 29 and the fixed electrode 28 are arranged close to each other in parallel.

Each fixed electrode 18 and each movable electrode 19
Are arranged in parallel so as to be staggered, and similarly, the fixed electrodes 28 and the movable electrodes 29 are similarly arranged.
Are also arranged in parallel so as to be staggered, and therefore two fixed electrodes 18 and 28 are arranged on both sides of one movable electrode 19 and 29, respectively, so that the sign of the acceleration component can be detected. The parallel plate type capacitors 11 and 21 are arranged close to only one fixed electrode, and are separated from the other fixed electrode so that the parallel plate type capacitors are not formed.

The movable electrodes 19 and 29 are composed of the movable body 69 and are formed in a linear shape.
6 and 26 are attached vertically to form a comb,
Further, since the fixed electrodes 18 and 28 are connected to the outer frames 13 and 23 formed of the fixed body 68, the parallel plate capacitors 11 and 12 are connected in parallel, and the parallel plate capacitors are connected to each other. Type capacitor 11 electrode surface (side surface of the fixed electrode 18 and side surface of the movable electrode 19)
Are arranged so as to face the same direction (here, the X-axis direction), and the normals of the electrode surfaces of the parallel plate type capacitors 21 are arranged so as to face the Y-axis direction perpendicular to the X-axis. ing. A metal electrode 74 connected to an external terminal for measuring the capacitance of the parallel plate capacitor is provided on the surfaces of the outer frames 13 and 23 and the surface of the supporting portion 14 ₃ .

The cross sections of the acceleration detecting element 12 and the acceleration detecting element 22 are similar to each other.
2A is a sectional view taken along line AA of FIG. 2 and FIG. 3 is a perspective view thereof. Next, the acceleration detecting element 32 will be described. The acceleration sensing element 32 has a large-area mass portion 33 formed by molding the structural layer 54 in a rectangular shape, and at the same time when forming the rectangular shape, a hole 37 is formed in the mass portion 33.
Are formed in an array arrangement so that the structural layer 54 forming the mass portion 33 does not have a wide portion. Therefore, when the sacrificial layer 51 is etched, the hydrofluoric acid buffer solution penetrates through the holes 37,
The sacrificial layer 51 under the bottom surface of the mass portion 33 is completely removed, and the structural layer 54 forming the mass portion 33 is removed.
Are configured to form the movable body 69 that is movable.

The movable body 6 is provided around the mass portion 33.
Flexible body 35 _{1 to} 3 formed of L-shape
5 ₄ is arranged, one end thereof respectively connected at right angles to the four corners of the mass portion 33, as a whole, the mass portion 33 in the center is configured to be swastika shape located.

[0054] wherein the other end of the flexible member 35 _{1-35 4,} the supporting portion 34 ₁ formed into a rectangular shape made of the fixing body 68
To 34 ₄ are connected, the flexible member 35 _{1-35 4} are as deflect in a direction perpendicular to the silicon substrate surface. 2 is a sectional view of the acceleration detecting element 32 taken along the line BB.
A perspective view is shown in FIG.

Since the sacrificial layer 51 located below the bottom surface of the mass portion 33 is formed without any step and is removed thereafter, the bottom surface of the mass portion 33 and the silicon substrate 10 are removed.
Of the sacrificial layer 51 that is removed by using the mass portion 33 and the silicon substrate 10 as electrodes.
A parallel plate type capacitor having the thickness of the electrode as the electrode interval is configured. In this parallel plate capacitor, when acceleration is applied to the acceleration sensor 2, the flexible member 35 _{1-35 4} is deflected, since the distance between electrodes the mass portion 33 is displaced changes, the capacitance value, The silicon substrate 10
With respect to the vertical direction, it changes according to the magnitude of the acceleration component. In this case, the influence of damping can be freely set by changing the size of the hole 37 provided in the mass portion 33.

That is, the holes 37 formed in the mass portion 33 are used not only for etching the sacrificial layer 51 but also for controlling air damping. By changing the number of the holes 37 or changing the area of each hole 37, it is possible to freely set the influence of the damping applied to the mass portion 33. This allows
It is possible to control the response time of the sensor itself, and if the influence of damping is reduced, it is possible to obtain a sensor with better response. Further, by increasing the effect of damping, it is possible to make the sensor strong against impact such as dropping.

In the acceleration sensing element 12, the flexible portion 1
When the movable electrode 19 is displaced in the X-axis direction, the capacitance value of the parallel plate type capacitor 11 changes, and in the acceleration sensing element 22, the flexible members 25a and 25b bend, When the movable electrode 29 is displaced in the Y-axis direction, the capacitance value of the parallel plate type capacitor 21 changes.

Therefore, each of the acceleration sensing elements 12, 2
If the capacitance change of 2 and 32 is detected, X axis, Y axis, Z axis
Acceleration components in the three (vertical) directions can be detected, and thereby the direction and magnitude of acceleration can be obtained.

However, the acceleration sensor of the present invention has X, Y,
The detection is not limited to the detection of three Z-axis directions. For example, like the acceleration sensor 82 shown in FIG. 8, when forming the movable electrode with the movable body 69, the movable electrode 69 is formed into a straight line having a relatively wide width to form a heavy movable electrode 87, and the width is wider than that of the movable electrode 87. A light movable electrode 88 is formed by forming a narrow linear shape, and two movable electrodes 87 having different weights are formed.
With 88, two types of parallel plate capacitors having different detection sensitivities can be configured.

In this case, the two types of acceleration detecting elements 83 and 84 having different detection sensitivities are arranged on the silicon substrate 86 so as to detect the acceleration in the same direction (here, the X-axis direction), and the acceleration in the vertical direction is set. If the acceleration detecting element 85 for detecting the component is also provided on the same substrate 86, the acceleration in the Z-axis direction is detected by the acceleration detecting element 85 and the minute acceleration in the X-axis direction is provided with the heavy movable electrode 87. A large G (impact) in the X-axis direction can be detected by the detection element 83, and can be detected by the acceleration detection element 84 having the light movable electrode 88.

Further, if a plurality of mass sections 33 having different areas are provided, it is possible to make the acceleration detection sensitivity in the Z-axis direction different. In any case, since the weight is such that it can be moved by static electricity, the movable electrode and the mass portion can be moved by electrostatic force, and it is possible to test whether the acceleration sensor can operate normally.

As described above, according to the present invention, since it is possible to form acceleration detecting elements having different sensitivities on one substrate, it is possible to board not only a frontal collision but also a side collision. In a so-called side airbag system that seeks to protect people, a field that requires a combination of direction and sensitivity of 50 G in the front-rear direction where the hood, which is a shock absorber, exists and 300 G in the lateral direction without a shock absorber. Also, it becomes possible to deal with it with one acceleration sensor. Furthermore, for example, airbag systems (front)
When an ABS system and a suspension control system are mounted, it is required to set detection levels of 50G and 2G in the front-rear direction and 2G in the up-down direction. According to the acceleration sensor of the present invention, It is possible to respond easily.

Although the flexible portions 15a and 15b and the flexible portions 25a and 25b are formed by linearly molding the movable body 54, the movable portions 54a and 25b can be moved like the acceleration detecting element 91 shown in FIG. The body 54 may be bent to form the flexible portions 95a and 95b. In that case, even if the width of the movable electrode 99 is not changed, acceleration detecting elements having various detection sensitivities in the horizontal direction can be formed. it can. These flexible portions 15a, 15b,
25a, 25b, 35a. When the acceleration becomes zero, the deformation of 35b, 95a, and 95b stops and returns to the original state. However, since they are made of single crystal silicon, they do not deteriorate even if repeatedly deformed, and have a long life and high reliability. Further, single crystal silicon has little residual stress and does not warp, so that it does not cause the sticking phenomenon and has high reliability.

The acceleration component in the horizontal direction with respect to the silicon substrate is not limited to the combination of detecting the X-axis direction and the Y-axis direction, but other than a right angle depending on the nature of the moving body in which the acceleration sensor is used. Acceleration components in various directions may be detected. Further, in the above-described embodiment, six parallel plate type capacitors are provided to provide the acceleration detection elements 13 and 2.
However, it is needless to say that the number is not limited to that.

[0065]

The acceleration component in the direction perpendicular to the substrate and the acceleration component in the direction horizontal to the substrate can be detected by one acceleration sensor. The detection sensitivity can be easily set to a plurality of levels. In particular, if the setting is made so as to detect the acceleration components in the directions of the X, Y, and Z axes, the triaxial acceleration sensor can be configured.

Since the flexible body is made of silicon single crystal, it does not undergo mechanical deterioration and does not undergo fatigue failure. Further, since no warpage occurs, the sticking phenomenon does not occur and the reliability is high.

Furthermore, since the movable body is thick, an acceleration sensor with high detection sensitivity can be constructed without increasing the area, and since the flexible part is easily deformed, normal operation of the acceleration sensor by electrostatic force or the like can be performed. You can check.

Further, since it can be mass-produced by the silicon micromachine manufacturing process similar to the semiconductor element manufacturing process, the manufacturing cost of the acceleration sensor can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view showing a best embodiment of the present invention.

2 (a) is a sectional view taken along line AA of FIG. 1 (b) is B- of FIG.
B line cross section

FIG. 3 is a perspective view of a condenser composed of a movable body and a fixed tight.

FIG. 4 is a perspective view of a capacitor composed of a movable body and a silicon substrate.

5 (a) to (c): Diagrams for explaining a manufacturing process up to forming an aluminum thin film of the acceleration detection sensor of the present invention.

6 (d) to (g): Diagrams for explaining a manufacturing process up to formation of an ohmic layer of the acceleration detection sensor of the present invention.

7 (h) to (k): Diagrams for explaining a manufacturing process until the sacrifice layer of the acceleration detection sensor of the present invention is removed by etching.

FIG. 8 is a diagram for explaining another embodiment of the present invention.

FIG. 9 is a plan view showing another example of a condenser composed of a movable body and a fixed body.

10A is a sectional view of a conventional triaxial acceleration sensor, and FIG. 10B is a plan view thereof.

FIG. 11A is a plan view of an example of a conventional acceleration sensor composed of a silicon micromachine, and FIG. 11B is a diagram for explaining its operating principle.

12A to 12F are views for explaining steps for manufacturing a conventional silicon micromachine.

[Explanation of symbols]

2, 82 ... Acceleration sensor 10, 53 ... Silicon substrate 50a, 50b ... Silicon single crystal substrate 51 ... Sacrificial layer 54 ... Structural layer 69, 16, 2
Movable member 15a constituting the 6 ...... movable member 19,29,33,88,87 ...... condenser, 15b, 25a, 25b, 35 1 ~35 4, 95a,
95b ... Flexible body 13, 18, 23, 28, 68, 14 _{1 to} 14 ₄ , 24 ₁
~ 24 ₄ , 34 ₁ ~ 34 ₄ ... Fixed body

Front Page Continuation (72) Inventor Tomoyuki Kubota No. 305, Tanaga, Oyama-cho, Sunto-gun, Shizuoka Prefecture Japan Texas Instruments Co., Ltd. Koyama Factory

Claims (4)

[Claims] 1. An acceleration sensor having a silicon substrate, a sacrificial layer located on the silicon substrate, and a structural layer located on the sacrificial layer, wherein the structural layer is patterned and a sacrificial layer under the bottom surface is formed. A movable body is formed in a portion where the layer is removed by etching, a fixed body is formed in a portion where the sacrificial layer under the bottom surface is left, the movable body is elastically supported by the fixed body, and the side surface of the movable body and the To detect the direction and magnitude of acceleration by detecting the capacitance change of a capacitor formed by the side surfaces of a fixed body arranged parallel to each other and the capacitance change of the capacitor composed of the movable body and the silicon substrate. Accelerometer characterized by having been 2. There is at least two capacitors in which a side surface of the movable body and a side surface of the fixed body are arranged so as to face each other, and normal lines of electrode surfaces of the two capacitors intersect each other at a predetermined angle. It has been arranged, The claim 1 characterized by the above
Acceleration sensor as described. 3. The silicon substrate comprises a substrate in which oxide films formed on the surfaces of two silicon single crystal substrates are in close contact with each other and bonded by a direct bonding method, and the sacrificial layer is composed of the oxide film. 3. The acceleration according to claim 1, wherein the structural layer is formed by polishing a surface of one of the silicon single crystal substrates of the substrates bonded by the direct bonding method. sensor. 4. The thickness of the structural layer is 3 μm during the polishing.
The acceleration sensor according to claim 3, wherein the acceleration sensor is configured to remain for m or more.