JP2001056343A - Micro machine and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deformation due to thermal expansion in a micro machine with a diaphragm structure, beam structure, or bridge structure. SOLUTION: Expansion suppressing members 15 made of a substance of a smaller coefficient of thermal expansion than that of a supporting body 14 are symmetrically arranged in a micro machine with a base 12, action body 13, and the supporting body 14 to support the action body 13 at the base 12. As a bending stress due to differences in lengths of expansion is symmetrically canceled out in this constitution, it is possible to make a strong expansion suppressing force work only in the direction of thermal expansion of the supporting body 14. Therefore, it is possible to effectively suppress deformations of the micro machine due to thermal expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micro-machine having a beam structure, a diaphragm structure or a bridge structure, and a method of manufacturing the same. In particular, the present invention relates to a technique for suppressing deformation of a micromachine due to thermal expansion.

[0002]

2. Description of the Related Art The structure of an acceleration sensor 70 shown in FIG. 7 will be described below as an example of a micromachine having a diaphragm structure. FIG. 7A is a top view of the acceleration sensor 70. The acceleration sensor 70 includes a base 72, an operating body 73 located at the center of the base 72, and a support 74 positioned between the operating body 73 and the base 72 and processed into a diaphragm shape (film shape). It is roughly composed of These structures are manufactured by applying a fine processing technique such as etching to a silicon wafer. A plurality of piezoresistors are formed on the surface of the support 74 by doping impurities of the opposite conductivity type. That is, on the axis in the predetermined direction (hereinafter referred to as “X axis”), 4
The piezo resistors Rx1 to Rx4 are formed in a line. This X
Four piezoresistors Ry1 to Ry4 are also formed in a line on an axis orthogonal to the axis (hereinafter referred to as “Y axis”). Furthermore, X
On an axis that is obliquely inclined from the axis (hereinafter referred to as the “Z axis”),
Four piezoresistors Rz1 to Rz4 are formed in a line. A plurality of terminals 76 for bonding connection are formed on the outer peripheral portion of the base 72. These piezoresistors and terminals 76
Between them, a wiring made of polycrystalline silicon or aluminum is formed as shown by a bold line pattern in FIG.

FIG. 7B is a cross-sectional view taken along the line AA 'in FIG. 7A to show the conventional structure of the support 74 in more detail. The material of the support 74 is silicon. A diffusion region corresponding to the piezoresistance (Rx3, Rz3 in this case) is formed on the main surface of the support 74. On the main surface of the support 74, an insulating layer 81 made of a silicon oxide film or a silicon nitride film is laminated to electrically insulate the support 74 from the wiring layer. Further, a protective layer 82 made of a silicon oxide film or a silicon nitride film is laminated on the insulating layer 81 to protect the wiring layer.

FIGS. 8A to 8C show an acceleration sensor 70.
FIG. 4 is a circuit diagram showing an example of the external connection of FIG. In this figure,
Each of the above-described piezoresistors is connected to a voltage source E outside the acceleration sensor 70, and forms three types of bridge circuits for each axis. The signal outputs Vx to V of these bridge circuits
z is output to the outside after being amplified through a highly sensitive differential amplifier circuit or the like.

<< Operation Principle of Acceleration Sensor 70 >> Next, the operation principle of the acceleration sensor 70 will be described. An appropriate weight (not shown) is adhered to the operating body 73 of the acceleration sensor 70, and the acceleration applied to the sensor itself is efficiently converted to a moment of inertia. Therefore, the acceleration sensor 7
When an acceleration acts on 0, the moment of inertia acts to displace the acting body 73 in a direction opposite to the acceleration. With the displacement of the acting body 73, the support 74 is curved. Hereinafter, the operating principle of the acceleration sensor 70 will be described in three cases for each direction of acceleration.

[Case in which acceleration acts in X-axis direction] FIG. 9 is a diagram showing a state in which acceleration (inertial force Fx) acts in the X-axis direction. In this case, as shown in FIG.
The piezoresistors Rx1 to Rx4 in the X-axis direction are compressed or expanded under the influence of the curvature of the support 74. As a result, the resistance values of the piezo resistors Rx1 to Rx4 increase and decrease. At this time, the equilibrium condition of the bridge circuit changes as (Rx1.Rx3)> (Rx2.Rx4), and a voltage change corresponding to the acceleration in the X-axis direction appears in the signal output Vx. On the other hand, as shown in FIG. 9B, the piezoresistors Ry1 to Ry4 in the Y-axis direction hardly change (they are slightly pulled by the displacement of the action body 73 in the X-axis direction, and the resistance value slightly increases). Only).
In this case, since the balance condition of the bridge circuit maintains (Ry1 · Ry3) = (Ry2 · Ry4), a voltage change hardly appears at the signal output Vy. As shown in FIG. 9C, the piezoresistors Rz1 to Rz4 in the Z-axis direction have substantially the same resistance value change as the piezoresistors Rx1 to Rx4 in the X-axis direction. However, since the resistance arrangement of the bridge circuit is different, the balance condition maintains (Rz1 · Rz4) = (Rz2 · Rz3), and the voltage change hardly appears at the signal output Vz.

[Case in which acceleration acts in the Y-axis direction] FIG. 10 is a diagram showing a state in which acceleration (inertial force Fy) acts in the Y-axis direction. In this case, the above-described equilibrium condition of the bridge circuit changes to (Rx1 · Rx3) = (Rx2 · Rx4) (Ry1 · Ry3)> (Ry2 · Ry4) (Rz1 · Rz4) = (Rz2 · Rz3). Therefore, a voltage change according to the acceleration in the Y-axis direction appears in the signal output Vy. On the other hand, voltage changes hardly appear in the other signal outputs Vx and Vz.

[Case where Acceleration Acts Vertically] FIG. 11 is a diagram showing a state where acceleration (inertial force Fz) acts in the vertical direction. In this case, the above-described equilibrium condition of the bridge circuit changes to (Rx1 · Rx3) = (Rx2 · Rx4) (Ry1 · Ry3) = (Ry2 · Ry4) (Rz1 · Rz4)> (Rz2 · Rz3). Therefore, a voltage change corresponding to the vertical acceleration appears in the signal output Vz. On the other hand, voltage changes hardly appear in the other signal outputs Vx and Vy.

As described above, three types of signal outputs V
acceleration sensor 7 based on the voltage change appearing in x to Vz.
The acceleration acting on zero can be detected separately for three components of the X axis, the Y axis, and the vertical axis.

[0010]

When energization of each piezo resistor of the acceleration sensor 70 is started, the signal output V
There is a problem in that z starts to fluctuate and it takes a long time to be stabilized. Further, there is a problem that the signal output Vz fluctuates sharply in response to a change in environmental temperature.

Conventionally, to solve these two problems, the acceleration sensor 7 has to be used regardless of the necessity of acceleration detection.
0 constantly, or the acceleration sensor 70
It was necessary to take sufficient heat insulation measures. Therefore, fundamental improvement measures for these two problems have been strongly demanded. Therefore, an object of the present invention is to provide a micromachine having a structure that can fundamentally improve these problems.

[0012]

An embodiment (FIG. 1, FIG. 1)
Means for solving the problem will be described while associating symbols (5, 6). Note that the association here is for reference and does not limit the present invention.

According to a first aspect of the present invention, there is provided a micromachine comprising: a base (12, 32, 42);
33, 43), and a support (14, 3) for supporting the working body in a diaphragm shape, a beam shape or a bridge shape with respect to the base.
4,44),
The thermal expansion of the support is suppressed by arranging the expansion suppressing members (15, 35, 45) made of a substance having a lower thermal expansion coefficient than the support in a symmetrical manner with respect to the support. .

The inventor of the present invention has proposed a signal output Vz in the prior art.
It has been clarified that the fluctuation of the thickness is caused by the minute thermal expansion of the support 74. That is, the support 74 undergoes thermal expansion due to the heat generated by the piezoresistor and the change in the environmental temperature. Due to this thermal expansion, the support 74 is slightly curved with the action body 73 interposed therebetween, and becomes in a state similar to that when acceleration is applied in the vertical direction (FIG. 11). Therefore, a fluctuation component due to the thermal expansion appears in the signal output Vz in addition to the vertical component of the acceleration. Such a fluctuation component of the signal output Vz is:
Until the whole sensor reaches thermal equilibrium, it keeps changing in a complicated manner and is not stable.

In order to prevent such a phenomenon, a method of increasing the resistance value of the piezoresistor to reduce the amount of heat generation can be considered. In this case, it is necessary to lower the impurity concentration of the piezoresistor or change the shape of the piezoresistor. However, as shown in FIG. 12, the value of the impurity concentration cannot be freely changed because it is limited from the viewpoint of suppressing the temperature coefficient of sensitivity of the piezo-resistance to be low. Further, when the piezoresistor is thinned to increase the resistance value, there is a problem that the disconnection is likely to occur and the yield is lowered.

Therefore, the present inventor has arranged an expansion suppressing member (a substance having a lower thermal expansion coefficient than the support) on the support. When materials having different expansion coefficients are simply combined as described above, a difference in expansion length occurs with an increase in temperature.
This difference in inflation length acts in the direction of further bending the support. However, in the present invention, the expansion suppressing member is arranged symmetrically with respect to the support. Therefore, the bending stress due to the difference in the expansion length is generated symmetrically and cancels out, and a strong force acts only in the direction of suppressing the thermal expansion of the support. Therefore, according to the present invention, it is possible to suppress the curvature of the support due to thermal expansion, and it is possible to fundamentally improve the problems as in the above-described conventional example.

Incidentally, also in the conventional example shown in FIG. 7B, an insulating layer 81 and a protective layer 82 are laminated on a support 74. However, the insulating layer 81 and the protective layer 82 are generally thin in thickness and do not have the function of suppressing the curvature of the support 74 due to thermal expansion. Even if the insulating layer 81 and the protective layer 82 are thickened, the layers 81 and 82 are arranged asymmetrically with respect to the support 74, and therefore, due to the difference in the expansion length, the layers 81 and 82 are formed on the support 74. Is subjected to bending stress. As a result, since the support 74 is further curved, the operation and effect as in the present invention are never obtained.

A second aspect of the present invention is directed to the micromachine according to the first aspect, further comprising a sensor for detecting a curvature of the support or a displacement of the operating body. Is characterized by detecting a force (including an acceleration) applied to the object.

[Claim 3] The micromachine according to claim 3 is the micromachine according to claim 1 or 2, wherein the expansion suppressing member (15) is a support (14).
Are arranged on both sides or on the center line of.

<Fourth aspect> The micromachine according to the fourth aspect is the micromachine according to the first or second aspect, wherein the expansion suppressing member (45) has a laminated structure or a support in which the support (44) is sandwiched. The body (44) has a laminated structure sandwiching the expansion suppressing member (45).

<Fifth aspect> The micromachine according to the fifth aspect is the micromachine according to any one of the first to fourth aspects, wherein the support (14, 34, 4)
4) is silicon, and the expansion suppressing member (15, 35,
45) is characterized by being silicon oxide or silicon nitride.

Silicon oxide or silicon nitride has a smaller coefficient of thermal expansion than silicon (for example, the coefficient of linear expansion of silicon oxide is about 1/5 of the coefficient of linear expansion of silicon). In addition, by forming silicon oxide or silicon nitride on the support, the support (here, silicon) is formed.
It is possible to increase the selectivity when etching is performed. Therefore, the thickness control of the support at the time of etching is further facilitated, and a support having a uniform thickness can be stably manufactured.

[Claim 6] A manufacturing method according to a sixth aspect of the present invention is the manufacturing method for manufacturing a micromachine according to the fifth aspect, wherein the expansion suppressing member made of silicon oxide is provided by LOCOS using oxygen ion implantation. It is formed by a method.

According to such a manufacturing method, thick silicon oxide can be efficiently manufactured in a short time. Further, the silicon oxide manufactured in this way is excellent in terms of thickness, uniformity of internal composition, crystalline state, state of a silicon boundary surface, and the like, and is suitable for use in suppressing expansion. Therefore, the manufacturing method of the present invention is a particularly excellent manufacturing method for manufacturing an expansion suppressing member (here, silicon oxide) in a micromachine.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

<< First Embodiment >> A first embodiment is an embodiment of the acceleration sensor 11 according to claims 1, 2, 3, 5, and 6. FIG. 1A is a perspective view illustrating a three-dimensional structure of the acceleration sensor 11. FIG. 1B is a top view of the acceleration sensor 11. FIG. 1 (c) shows the structure of the support 14 in more detail.
It is the figure showing the cross section of A 'part. In these figures, the acceleration sensor 11 is a base 1 made of a silicon substrate.
2, an operating body 13 located at the center of the base 12, and a support 14 for supporting the operating body 13 in a beam shape. The support 14 is made of silicon. In addition, on both sides of the beam portion of the support 14, expansion suppressing members 15 made of silicon oxide are provided. As shown in FIG. 1C, the expansion suppressing member 15 has the same thickness as the support 14 and is disposed so as to sandwich the support 14 from both sides. On the surface of the support 14, piezoresistors and wires for detecting the curvature of the support 14 are formed as shown by a bold line pattern in FIG. 1B.

[Explanation of Manufacturing Method] FIGS. 2 and 3 are views for explaining a manufacturing process of the BB 'section shown in FIG. 1B. Hereinafter, a manufacturing process of the acceleration sensor 11 will be described with reference to FIGS.

First, in the step of FIG. 2A, a silicon oxide film 302 is formed on the first surface of a silicon substrate 301 by thermal oxidation to a thickness of about 500 °. The silicon oxide film formed on the second surface is removed by etching. After that, by low pressure CVD or the like, 300
A silicon nitride film 303 of about 0 ° is formed. At this time, the silicon nitride film 304 is also formed on the second surface of the silicon substrate 301 at the same time. Next, the silicon nitride film 30
3, a resist 305 is applied.
Using the mask 5 as a mask, the silicon nitride film 303 is patterned by dry etching or the like. Using the resist 305 and the silicon nitride film 303 as a mask,
Oxygen ions 306 are implanted from the surface of the silicon substrate 301 to a depth of about 2 μm by an ion implantation method. The injection depth is determined according to the thickness of the support 14.

Next, in the step of FIG. 2B, after removing the resist 305, thermal oxidation in steam is performed to form a silicon oxide film. Through such processing and the like, the injection location of the oxygen ion 306 changes to the expansion suppressing member 15. The steps up to this point are the manufacturing steps of the expansion suppressing member 15 using both the LOCOS method (selective oxidation method using a silicon nitride film as an oxidation mask) and oxygen ion implantation. Next, a dry etching method or a wet etching method is performed, and etching is performed to a depth of a bonding interface between the silicon nitride film 303 and the silicon oxide film 302 shown in FIG. Complete.

Next, in the step of FIG. 2C, an impurity region 308 to be a piezoresistor is formed through the steps of resist pattern formation, ion implantation and annealing. Next, in the step of FIG. 2D, a contact hole 309 is provided in the silicon oxide film 307 through the process of forming and etching a resist pattern so as to be aligned with both ends of the impurity region 308 serving as a piezoresistance.

Subsequently, in the step of FIG. 2E, a polycrystalline silicon film formed by a CVD device or the like or an aluminum film formed by a sputtering device or the like is patterned by photolithography and etching to complete the wiring 310. . In this state, the protection film 3 made of a silicon nitride film or the like is formed.
11 (protective film 21) by a plasma CVD device or the like.
For example, it is formed with a thickness of about 3000 °. Further, a portion corresponding to the void portion 12a is removed through a process of photolithography and etching.

Next, in the step of FIG. 3F, the silicon nitride film 304 on the second surface of the silicon substrate 301 is patterned through a photolithography method and an etching process to form a mask pattern corresponding to the base 12. Is done. Through this mask pattern, a dry etching method or a wet etching method using a silicon etching solution such as a KOH solution is performed. By this etching, a portion corresponding to the support 14 is etched so as to have a thickness of about 2 μm, and a hole is formed in a portion corresponding to the gap 12a.

Further, in the step of FIG.
Glass is bonded to 3 and the base 12. As a bonding method in this case, for example, the silicon substrate 301 and the glass are heated to about 400 ° C.
A so-called anodic bonding method in which 1 is used as a positive electrode and a DC voltage of about 500 to 1000 V is applied. Note that a joining method using an adhesive such as a resin may be used. This glass is cut with a dicing saw or the like and separated into a pedestal 316 and a weight 315.

Subsequently, in the step shown in FIG. 3H, the silicon substrate 317 is mounted on the pedestal 31 by anodic bonding or resin bonding.
6 is adhered. The portion of the silicon substrate 317 that contacts the weight 315 is shaved in advance by etching or the like, and is processed so that the weight 315 can be freely displaced to some extent. After the above steps, the silicon wafer is cut by a dicing saw or the like, and the acceleration sensor 11 is completed.

[Description of Another Manufacturing Method] Next, another manufacturing method will be described. FIG. 4 is a cross-sectional view of FIG.
It is a figure explaining another manufacturing process of B 'section. Hereinafter, another method of manufacturing the acceleration sensor 11 will be described with reference to FIG.

First, in the step of FIG. 4A, a silicon oxide film 402 of about 500 ° is formed on the first surface of a silicon substrate 401 by thermal oxidation. At this time,
The silicon oxide film formed on the second surface of the silicon substrate 401 is removed by etching. After that, low pressure CV
The silicon nitride film 403 becomes 3000
It is formed on the silicon oxide film 402 with a thickness of approximately.
At this time, a silicon nitride film 404 is also formed on the second surface of the silicon substrate 401. This silicon nitride film 403
A resist 405 is patterned on the substrate. Using the resist 405 as a mask, etching such as dry etching is performed, and the silicon nitride film 403 and the silicon oxide film 402 are patterned. Using the silicon nitride film 403 and the silicon oxide film 402 thus patterned as a mask, the silicon substrate 401
Is further etched by a dry etching method or a wet etching method. Through such an etching process, a groove having a depth of about 2 μm is formed on a portion corresponding to the expansion suppressing member 15 on the silicon substrate 401.

Subsequently, in the step of FIG. 4B, after removing the unnecessary resist 405, a CVD device or the like is used.
PSG (Phosphor-Silicate GLASS) and BPSG (Boron
Deposit doped Phosphor-Silicate GLASS). As a result, the silicon oxide film 4
07. After that, SOG (Spin on Gl
After applying a silicon oxide film for planarization such as ass) and performing a heat treatment, a planarization process is performed. (Alternatively, a resist or the like having an etching rate equivalent to that of the deposited silicon oxide film may be applied, cured if necessary, and then subjected to planarization.) The silicon oxide film 407 planarized as described above A dry etching method is applied to the deposited layer of
The silicon nitride film 403 and the silicon oxide film 4 shown in FIG.
Etching to the depth of the bonding interface No. 02 completes the process up to the step of FIG. After that, the acceleration sensor 11 is completed through the same steps as those of FIGS. 2C to 3H described above.

[Effects of First Embodiment] As described above, in the first embodiment, the expansion suppressing members 15 are arranged on both sides of the support 14. Since the expansion suppressing member 15 is formed of silicon oxide, its linear expansion coefficient is as small as about 1/5 of the silicon ratio. By arranging the expansion suppressing member 15 symmetrically with respect to the support 14, there is almost no curvature due to a difference in expansion length, and the support 14
Strongly suppresses thermal expansion. With such an operation, the acceleration sensor 11 of the present embodiment can obtain the following advantages.

(1) Fluctuations in the signal output Vz due to thermal expansion are reliably reduced, and vertical acceleration can be detected with even higher accuracy. (2) Since the fluctuation of the signal output Vz due to the heat generated by the piezoresistor is reduced, it is possible to realize an energy-saving type acceleration sensor that is energized only during measurement. (3) Since a change in the signal output Vz due to a change in the ambient temperature is reduced, a configuration for insulating the acceleration sensor 11 can be omitted or simplified.

Further, in the first embodiment, the support 14
Before the etching process, the expansion suppressing member 15 is formed.
Therefore, it is possible to control the thickness of the support 14 uniformly and stably by utilizing the difference in the etching characteristics between the expansion suppressing member 15 and the support 14. in this way,
By making the thickness of the support 14 uniform, it is possible to remarkably reduce the variation in the detection of acceleration in three axial directions. Further, since the thickness of the support 14 is stabilized irrespective of the position on the silicon wafer, it is possible to surely reduce individual variations such as the detection sensitivity of the acceleration sensor 11. Further, in the manufacturing method according to the first embodiment, L
The OCOS method is used. As a result, it has enough thickness,
In addition, it is possible to form silicon oxide having a uniform composition. Such a silicon oxide is very excellent for use in suppressing expansion and has a remarkable effect in reducing fluctuations in the signal output Vz. Next, another embodiment will be described.

Second Embodiment A second embodiment is an acceleration sensor 31 having a diaphragm structure according to the first, second, fifth, and sixth aspects. FIG. 5 (a)
3 is a perspective view showing a three-dimensional structure of the acceleration sensor 31. FIG.
FIG. 5B is a top view of the acceleration sensor 31. FIG.
(C) shows the structure of the support 34 in more detail.
It is the figure showing the cross section of the AA 'part shown in Drawing 5 (a). In these drawings, the acceleration sensor 31 is schematically composed of a base 32 made of a silicon substrate, an operating body 33 located at the center of the base 32, and a support 34 made of silicon that supports the operating body 33. . This support 34 is
A configuration is provided in which the action body 33 is supported in a diaphragm shape. On the surface of the support 34, piezoresistors and wires for detecting the curvature of the support 34 are formed as shown by a bold line pattern in FIG. 5B. Further, the support 34 is provided with expansion suppressing members 35 made of silicon oxide on both sides of the piezoresistor, respectively. The acceleration sensor 31 can be obtained by omitting the step of forming the gap 12a in the manufacturing steps (FIGS. 2 and 3) of the first embodiment.
Manufacturing becomes possible.

[Effects of the Second Embodiment] With the above configuration, also in the second embodiment, since the expansion suppressing member 35 is arranged symmetrically with respect to the support 34, the support caused by the thermal expansion is provided. The curvature of the body 34 can be effectively suppressed. Next, another embodiment will be described.

<< Third Embodiment >> A third embodiment is an embodiment of the acceleration sensor 41 according to claims 1, 2, 4, and 5. FIG. 6A is a top view of the acceleration sensor 41. In these figures, the acceleration sensor 41
It is roughly composed of a base 42 made of a silicon substrate, an operating body 43 located at the center of the base 42, and a support 44 made of silicon that supports the operating body 43. This support 4
Reference numeral 4 denotes a configuration for supporting the action body 33 in a beam shape. On the surface of the support 44, piezoresistors and wires for detecting the curvature of the support 44 are formed as shown by a bold line pattern in FIG. 6A. FIG. 6B is a diagram showing an example of the AA ′ cross section in FIG. 6A. In this example, the expansion suppressing members 45 are provided so as to sandwich both surfaces of the support 44. FIG. 6C is a diagram showing another example of the AA ′ cross section in FIG. 6A. In this example, the support 44 is provided so as to sandwich both surfaces of the expansion suppressing member 45.

[Effect of Third Embodiment] With the above-described configuration, in the third embodiment, the expansion suppressing member 45 is
Since it is arranged symmetrically with respect to 4, it becomes possible to effectively suppress the curvature of the support 44 due to thermal expansion.

<< Supplementary Items of Embodiment >> In the above-described embodiment, the case where the present invention is applied to the acceleration sensor is described, but the application field of the present invention is not limited to this. In general, by applying the present invention to a micromachine having a diaphragm structure, a beam structure, or a bridge structure, a problem caused by thermal expansion of the micromachine can be effectively improved. Further, in the above-described embodiment, the curvature of the support is detected by using the piezoresistance, but the present invention is not limited to this. Generally, a sensor that detects the curvature of the support or the displacement of the working body can be used. For example, a capacitance sensor or the like can be used. In the above-described embodiment, silicon oxide is used as the material of the expansion suppressing member. This silicon oxide has a silicon ratio of 1/5
Since it exhibits a very low linear expansion coefficient, it is particularly excellent for use in suppressing expansion. However, the present invention is not limited to this. Generally, any substance having a lower thermal expansion coefficient than that of the support can be used as the expansion suppressing member. For example, silicon nitride may be used as the expansion suppressing member. In addition, an alloy, a silicide, or another substance having a small expansion coefficient, such as Invar or SuperInvar, may be used as the expansion suppressing member. Further, in the above-described embodiment, the expansion suppressing members are arranged on both sides or both sides of the support. With such a configuration, the thermal expansion of the support can be uniformly and strongly suppressed from both sides or both sides. However, the present invention is not limited to this. Generally, it is sufficient that the expansion suppressing member is arranged symmetrically with respect to the support, for example, a slight curvature is likely to occur as compared with the case where the expansion suppressing member is arranged on both sides or both sides, but on the center line of the support. An expansion suppressing member may be provided. It should be noted that the expression “symmetric” in the present application does not indicate a completely symmetrical shape in terms of dimensions, but means a sufficiently symmetrical shape to avoid bending due to a difference in expansion length.

[0046]

According to the micro machine of the present invention, the expansion suppressing member (a substance having a lower thermal expansion coefficient than the support) is symmetrically arranged with respect to the support, so that there is no curvature due to the difference in expansion length between the two. In addition, it is possible to effectively suppress the thermal expansion of the support.

Therefore, when the structure of the micromachine of the present invention is used for an application such as an acceleration sensor as in the second aspect of the present invention, there is a problem that the signal output Vz as described in the conventional example is not stable. Can be fundamentally improved.

In particular, in the micro machine according to the third aspect of the present invention, the expansion suppressing member is arranged on both sides or the center line of the support, so that the expansion due to the difference in expansion length can be avoided, and the thermal expansion of the support can be avoided. Can be reliably suppressed.

Further, in the micro machine according to the fourth aspect, since the expansion suppressing member and the support are laminated in a symmetric sandwich shape, the thermal expansion of the support can be ensured while avoiding bending due to a difference in expansion length. Can be suppressed.

Furthermore, in the micro machine according to the fifth aspect, since silicon oxide or silicon nitride having a smaller thermal expansion coefficient than silicon is used as the expansion suppressing member, the thermal expansion of the support can be surely suppressed. Further, it becomes easy to stably produce a support having a uniform thickness by utilizing a difference in etching characteristics between the expansion suppressing member and the support. As a result, it is possible to reduce individual differences (for example, variations in the detection sensitivity of acceleration) of the micromachine.

In the manufacturing method according to the sixth aspect, the LOCOS method using oxygen ion implantation is used.
It is possible to reliably and easily form silicon oxide having a sufficient thickness and a uniform composition. In addition, the silicon oxide formed in this way has characteristics suitable for use in suppressing expansion. Therefore, the production method of the present invention
This is a particularly excellent manufacturing method for manufacturing an expansion suppressing member (here, silicon oxide) in a micromachine.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of an acceleration sensor 11;

FIG. 2 is a diagram illustrating a manufacturing process of the acceleration sensor 11.

FIG. 3 is a diagram illustrating a manufacturing process of the acceleration sensor 11;

FIG. 4 is a diagram illustrating another manufacturing process of the acceleration sensor 11;

FIG. 5 is a diagram showing a structure of an acceleration sensor 31.

FIG. 6 is a diagram showing a structure of an acceleration sensor 41.

FIG. 7 is a diagram showing a structure of a conventional example.

FIG. 8 is a diagram showing a bridge circuit for detecting acceleration.

FIG. 9 is a diagram illustrating a curved state of the support 74 in a state where an acceleration (inertial force Fx) acts in the X-axis direction.

FIG. 10 is a diagram illustrating a curved state of the support 74 in a state where acceleration (inertial force Fy) acts in the Y-axis direction.

FIG. 11 is a diagram showing a curved state of the support 74 in a state where acceleration (inertial force Fz) acts in the vertical direction.

FIG. 12 shows “impurity concentration” in a P-type silicon diffusion layer.
FIG. 6 is a diagram showing a relationship between the “Sensitivity temperature coefficient” and “Sensitivity temperature coefficient”.

[Explanation of symbols]

 11, 31, 41, 70 Acceleration sensor 12, 32, 42, 72 Base 13, 33, 43, 73 Actuator 14, 34, 44, 74 Support 15, 35, 45 Expansion suppression member 81 Insulation layer 82 Protection layer 301 silicon substrate 302 silicon oxide film 303 silicon nitride film

Claims (6)

[Claims] 1. A micromachine comprising: a base, an operating body, and a support that supports the operating body in a diaphragm shape, a beam shape, or a bridge shape with respect to the base, wherein a thermal expansion is larger than that of the support. A micromachine characterized in that thermal expansion of the support is suppressed by arranging an expansion suppressing member made of a substance having a low coefficient symmetrically with respect to the support. 2. The micro machine according to claim 1, further comprising: a sensor that detects a curvature of the support or a displacement of the operating body, and a force (including an acceleration) applied to the operating body based on a detection output of the sensor. A micromachine characterized by detecting the following. 3. The micro machine according to claim 1, wherein the expansion suppressing member is disposed on both sides or a center line of the support. 4. The micromachine according to claim 1, wherein the expansion suppressing member has a laminated structure sandwiching the support, or the support has a laminated structure sandwiching the expansion suppressing member. And a micromachine. 5. The micro machine according to claim 1, wherein the support is made of silicon, and the expansion suppressing member is made of silicon oxide or silicon nitride. Micro machine. 6. The method for manufacturing a micromachine according to claim 5, further comprising a step of forming the expansion suppressing member made of silicon oxide by a LOCOS method using oxygen ion implantation. Micromachine manufacturing method.