JP2003156511A - Very small structure with movable structure part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a very small structure in which an increase in its thickness can be suppressed to a minimum, which does not have substantially any influence on its characteristic and which can be manufactured simply and at low costs. SOLUTION: The very small structure is provided with a substrate in which a movable structure part is housed so as to be movable in the three-dimensional direction. The movable structure part is set to a state that at least one face is exposed to the outside when it is housed in the substrate. The very small structure is provided with a wire which is stretched in the upper part of the exposed face of the movable structure part and which prevents the excessive movement of the movable structure part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microstructure having a movable structure, and more particularly to an acceleration sensor which obtains an output signal according to the movement of the movable structure.

[0002]

2. Description of the Related Art There are various types of sensors using a movable structure. For example, typical inertial sensors include an acceleration sensor and an angular acceleration sensor (vibration gyro).

An acceleration sensor for detecting the acceleration of a vehicle such as an automobile generally utilizes the piezoresistive effect of a semiconductor. In such a sensor, for example, a cavity is formed in a silicon substrate, and a box-shaped movable structure that can freely move in a three-dimensional direction is accommodated in the cavity. A piezo element is connected to the movable structure section, and a stress corresponding to the movement of the movable structure section is applied to the piezo element. Then, a change in stress applied to the piezo element is detected as a change in resistance, and the traveling result of the vehicle is controlled using the detection result.

By the way, it is important that the movable structure accommodated in the silicon substrate as described above can move freely, but if it moves excessively, it may lead to the destruction of the sensor. Therefore, in the past, for example, Japanese Patent Publication No.
As disclosed in JP-A-71148, a stopper made of glass is provided to prevent excessive movement of the movable structure in the vertical direction.

[0005]

However, when the glass stopper is provided as in the conventional case, there is a problem that the thickness of the sensor (chip) increases. Further, the glass bonding process is complicated, which leads to an increase in manufacturing cost. Furthermore, it cannot be denied that the stress due to the bonding of glass and silicon affects the sensor characteristics.

Therefore, an object of the present invention is to reduce the increase in thickness to a minimum, substantially without affecting the characteristics of the microstructure, and to manufacture the microstructure easily and at low cost. The purpose is to provide.

[0007]

In order to achieve the above-mentioned object, a microstructure according to the present invention comprises a base body in which a movable structure portion is housed so as to be movable in three dimensions. When stowed, at least one surface is exposed to the outside; stretched over the exposed surface of the moveable structure,
A stopper wire is provided to prevent excessive movement of the movable part.

According to the present invention having the above-mentioned structure, since the wire is used to prevent the excessive movement of the movable structure, the increase in the thickness is minimized as compared with the case where the stopper made of glass is used. It becomes possible to suppress it. Further, since there is almost no stress applied to the base body and the movable structure portion at the time of joining the wires, there is substantially no influence on the characteristics of the microstructure such as the sensor. Further, since the stopper wire can be formed in the wire bonding process, the manufacturing process does not become complicated, and the manufacturing process can be performed at a simpler and lower cost as compared with the conventional case of bonding a glass stopper. it can. Particularly, in the case of an acceleration sensor or the like, when wire bonding the electrode pad of the sensor chip and the lead pad of the package, the wire for the stopper can be formed in the same process as this, which is extremely rational.
It is efficient.

The stopper wire is fixed only to the base body, not to the movable structure. Also, the stopper wire is
It is bonded to the substrate by a wire bonding process. Furthermore, in order to increase the bonding strength between the stopper wire and the base body, the bonding bonding portion of the stopper wire may be sealed with resin.

At least one end of the stopper wire can be fixed to the lead pad of the package. Specifically, both ends of the stopper wire are fixed to the lead pads of the package. In this case, there is an advantage that the degree of freedom in arranging (tensioning) the stopper wire is increased. Also, when one end of the stopper wire is fixed to the lead pad of the package and the other end is fixed to the electrode pad of the base, the stopper wire can be used for electrical connection.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below by taking an acceleration sensor as an example. The present invention is applicable to all types of microstructures (MEMS) having a movable structure portion such as an actuator, in addition to other inertial sensors such as an angular acceleration sensor (vibration gyro).

1 and 2 are a perspective view and a plan view showing the structure of an acceleration sensor 10 according to a first embodiment of the present invention. Note that, in FIG. 2, for convenience of description, detailed configurations such as a piezoresistive element are omitted. FIG. 3 is a sectional view showing the internal structure of the acceleration sensor 10. The acceleration sensor 10 according to the present embodiment includes a silicon substrate 12 and a movable structure portion (movable mass) 14 that is housed near the center of the silicon substrate 12 so as to be movable in all directions of up, down, left and right. A box-shaped space is formed in the center of the silicon substrate 12, and the movable structure 14 is housed in the box-shaped space.
The movable structure portion 14 is formed in a so-called clover shape in which four squares are connected at the center in order to improve the inertial force. The upper surfaces of the silicon base 12 and the movable structure 14 are designed to be flush with each other.

The sensor 10 also includes four beams (support beams) 1 for connecting the movable structure portion 14 and the silicon substrate 12.
6 and eight piezoresistive elements 18 arranged across the connecting portion between the beam 16 and the silicon substrate 12. Each beam 16 is arranged at a corresponding position between leaves of the clover of the movable structure portion 14. Silicon substrate 1
An electrode pad 20 is formed on the upper surface of 2, and is electrically connected to the piezoresistive element 18 by a wiring (not shown).

The electrode pad 20 not connected to the piezoresistive element 18 is used as a bonding pad for the wire 22. That is, 4 that functions as a stopper
The wires 22 of the book are arranged so as to bridge the four corners of the movable structure portion 14, and the ends thereof are joined to the electrode pads 20 by a well-known wire bonding process.

As shown in FIG. 3, the silicon substrate 12 is
It is fixed on the die bond surface 24. As described above, the movable structure portion 14 can freely move vertically and horizontally in the space of the silicon substrate 12, but the downward movement is stopped by the die bond surface 24, and the horizontal movement is prevented from occurring. Stopped by twelve inner surfaces. The upward movement of the movable structure 14 is stopped by the wire 22. The height of the wire 22 can be adjusted by setting the bonding apparatus. Here, "over-movement" means a movement to the extent that a microstructure such as a sensor does not operate normally, for example, movement that causes the structure to be destroyed or movement that exceeds the sensor output maximum rating. To tell.

FIG. 4 is a sectional view showing a structure in the vicinity of the wire bonding position in the acceleration sensor 10 according to the embodiment. In the present invention, the bonding portion between the wire 22 and the electrode pad 20 of the silicon substrate 12 is made of resin 2
It may be sealed by 8. Such resin sealing increases the bonding strength of the wire 22.

In manufacturing the acceleration sensor 10 described above, first, an SOI substrate including an active layer (Si); a buried oxide film layer (SiO2); a Si substrate is formed. Next, the piezoresistive element 1 is formed so as to form a bridge circuit on the active layer of the SOI substrate by using semiconductor processing technology.
8, metal wiring and electrode pads 20 are formed in an array. Then, the portion excluding the electrode pad 20 is covered with a protective film such as SiN. Next, Si Deep RIE (Reactive Ion Etching)
The beam portion 16 is formed by. After that, the movable structure portion 14 is similarly formed by Si DeepRIE from the Si substrate side. Next, the movable structure portion 14 is released by etching the buried oxide film. After that, the individual sensor chips are cut by dicing. Next, this sensor chip is bonded to the package, and subsequently, the electrode pad 20 of the sensor chip 10 and the lead pad (not shown) of the package are wire bonded.
At this time, the wire 22 is formed on the sensor chip 10 in the same bonding process.

5 and 6 are plan views showing other examples of wire arrangement in the acceleration sensor according to the present invention. In the example shown in FIG. 5, the wire 122 is the silicon substrate 1.
Two pieces having the same length are arranged parallel to the side edge of 2. On the other hand, in the example shown in FIG. 6, three wires (2
22a, 222b) are arranged in parallel with the diagonal line of the silicon substrate 12. The longer wire 222a is arranged on the surface of the silicon substrate 12 along the diagonal line of the substrate 12. Also, the shorter wire 222b
Are arranged so as to span the corners as in the embodiment shown in FIG. In the example shown in FIG. 5, only the diagonal wire 222a may be provided and the other two wires 222b may be omitted. This is because the plane balance can be maintained even with only the wire 222a.

FIG. 7 is a sectional view showing the structure of an acceleration sensor 10 and a package 30 accommodating the same according to the second embodiment of the present invention. In the present embodiment, the first
Constituent elements that are the same as or correspond to those in the embodiment are designated by the same reference numerals, and duplicate description will be omitted. In this embodiment, the ends of the stopper wire 22 are connected to the package 30.
It is fixed to the lead pad 32. In this case, the degree of freedom in arranging (tensioning) the wire 22 is increased as compared with the case where the wire 22 is stretched over the sensor 10 as in the first embodiment.
The lead pad 32 to which the end of the stopper wire 22 is fixed can be provided exclusively. As a result, the stopper wire 22 can be electrically separated from the sensor 10, and the wire 22 can be freely arranged without considering the wiring design of the sensor 10.

8 to 12 are plan views showing arrangement examples of wires (stoppers) in the second embodiment. In the example shown in FIG. 8, two wires 22 are arranged in parallel with two opposite sides of the sensor 10. In the example shown in FIG.
Four wires 22 are stretched diagonally at the four corners of the sensor 10, but the wires 22 do not overlap each other. In the example shown in FIG. 10, four wires 22 are crossed on the sensor 10 so that a # is drawn. In the example shown in FIG. 11, two long wires 22 and two short wires 22 are arranged parallel to the diagonal direction of the sensor 10. In the example shown in FIG.
Four wires 22 are arranged on the sensor 10 so as to draw a rhombus, and each wire 22 crosses the four corners of the sensor 10.

FIG. 13 is a sectional view showing the structure of the acceleration sensor 10 and the package 30 accommodating the same according to the third embodiment of the present invention. In this embodiment, the same or corresponding components as those of the first and second embodiments are designated by the same reference numerals, and the duplicated description will be omitted. In this embodiment, one end of the stopper wire 22 is fixed to the lead pad 32 of the package 30, and the other end is fixed to the electrode pad 20 formed on the base 12 of the sensor 10. In this case, the stopper wire 22 can be used for the electrical connection between the sensor 10 and the package 30. The lead pad 32 and the electrode pad 20 to which the ends of the stopper wire 22 are fixed can be provided exclusively. As a result, the stopper wire 22 can be electrically separated from the sensor 10, and the wire 22 can be freely arranged without considering the wiring design of the sensor 10.

14 and 15 are plan views showing arrangement examples of wires (stoppers) in the third embodiment. Figure 1
In the example shown in FIG. 4, four wires 22 are crossed on the sensor 10 so as to draw a #. Further, in the example shown in FIG. 15, the four wires 22 extend in the diagonal direction of the sensor 10 without intersecting each other. Each wire 22 straddles the four corners of the sensor 10.

FIG. 16 is a sectional view showing the structure of the acceleration sensor 10 according to the fourth embodiment of the present invention. In this embodiment, the same or corresponding components as those in the above-described embodiments are designated by the same reference numerals, and the duplicated description will be omitted. A feature of the sensor 10 according to this embodiment is that the stopper wire 22 has the same potential as the SOI substrate 50. By setting the wire 22 and the substrate 50 to the same potential, the wire 22 acts as an antenna and the sensor 10
It is possible to prevent adverse effects on the environment.

In manufacturing the sensor 10 according to this embodiment, first, the active layer (Si); the buried oxide film layer (Si)
O2); An SOI substrate 50 made of a Si substrate is formed.
Next, the piezoresistive element 18 is formed on the active layer of the SOI substrate 50 by ion implantation or thermal diffusion so as to form a bridge circuit using a semiconductor processing technique. After that, the insulating layer 52 is formed by thermal oxidation. Next, the portion corresponding to the electrode pad connected to the stopper wire 22 is the active layer (Si).
A contact hole is formed so as to have the same potential as.
Then, the metal wiring and the electrode pad 20 are formed in an array, and the portion excluding the electrode pad 20 is covered with a protective film 54 such as SiN.

Next, Si Deep RIE (Reactive Ion Etc
The beam portion 16 is formed by hinging. After that, the movable structure portion 14 is similarly formed by Si Deep RIE from the Si substrate side. Next, the movable structure portion 14 is released by etching the buried oxide film. After that, the individual sensor chips 10 are cut by dicing. Next, the sensor chip 10 is bonded to the package 30, and then the electrode pad 20 of the sensor chip 10 and the lead pad 32 of the package 30 are wire bonded. At this time, the stopper wire 22 is formed on the sensor chip 10 in the same bonding process.

Although the embodiments (embodiments, embodiments) of the present invention have been described above, the present invention is not limited to these embodiments, and the technical idea shown in the scope of claims is not limited thereto. It can be changed in the category.

[0027]

As described above, in the present invention, since the wire is used to prevent the excessive movement of the movable structure, compared with the case where the glass stopper is used,
It is possible to minimize the increase in thickness. Also,
Since there is almost no stress applied to the base body and the movable structure portion at the time of joining the wires, there is substantially no influence on the characteristics of a microstructure such as a sensor. Further, since the stopper wire can be formed in the wire bonding process, the manufacturing process does not become complicated, and the manufacturing process can be performed at a simpler and lower cost as compared with the conventional case of bonding a glass stopper. it can. In particular, in the case of acceleration sensors etc., when wire bonding the electrode pad of the sensor chip and the lead pad of the package, the wire for the stopper can be formed in the same process as this, which is extremely rational and efficient. Is.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a plan view showing the structure of the acceleration sensor according to the first embodiment, and omits detailed configurations such as a piezoresistive element.

FIG. 3 is a sectional view taken along line I-I of FIG.

FIG. 4 is a cross-sectional view showing a configuration near a wire bonding position in the acceleration sensor according to the first embodiment.

FIG. 5 is a plan view showing another example of how to wire the acceleration sensor according to the present invention.

FIG. 6 is a plan view showing still another example of how to wire the acceleration sensor according to the present invention.

FIG. 7 is a sectional view showing a structure of an acceleration sensor and a package accommodating the same according to a second embodiment of the present invention.

FIG. 8 is a plan view showing an arrangement example of wires (stoppers) in the second embodiment.

FIG. 9 is a plan view showing an arrangement example of wires (stoppers) in the second embodiment.

FIG. 10 is a plan view showing an arrangement example of wires (stoppers) in the second embodiment.

FIG. 11 is a plan view showing an arrangement example of wires (stoppers) in the second embodiment.

FIG. 12 is a plan view showing an arrangement example of wires (stoppers) in the second embodiment.

FIG. 13 is a sectional view showing a structure of an acceleration sensor and a package accommodating the same according to a third embodiment of the present invention.

FIG. 14 is a plan view showing an arrangement example of wires (stoppers) in the third embodiment.

FIG. 15 is a plan view showing an arrangement example of wires (stoppers) in the third embodiment.

FIG. 16 is a cross-sectional view showing the structure of the acceleration sensor according to the fourth embodiment of the present invention.

[Explanation of symbols]

10 Accelerometer 12 Silicon substrate 14 Movable structure part (movable mass) 16 beams (support beams) 18 Piezoresistive element 20 electrode pads 22 wires 24 Die bond surface 28 resin

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoki Ikeuchi             4-53 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Sumitomo Metal Industries, Ltd. (72) Inventor Sosei Harada             4-53 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Sumitomo Metal Industries, Ltd. F term (reference) 2F105 AA02 BB01 BB15 CC04 CD01                       CD05                 4M112 AA02 BA01 CA21 CA24 CA26                       CA29 DA03 DA10 DA11 DA12                       DA16 DA18 EA02 EA06 EA07                       EA11 FA07 FA20

Claims (10)

[Claims] 1. A microstructure having a movable structure part, comprising a base body accommodating the movable structure part so as to be movable in a three-dimensional direction; the movable structure part has at least one surface when accommodated in the base body. Is exposed to the outside; a microstructure provided with a stopper wire stretched above the exposed surface of the movable structure to prevent excessive movement of the movable part. 2. The microstructure according to claim 1, wherein the stopper wire is fixed only to the base body and not fixed to the movable structure portion. 3. The microstructure according to claim 1, wherein the stopper wire is provided by a wire bonding process. 4. The microstructure according to claim 3, wherein a bonding joint between the stopper wire and the base is sealed with a resin. 5. The base body is provided with a dedicated pad to which the stopper wire is fixed.
The microstructure according to 2, 3, or 4. 6. The microstructure according to claim 1, 2, 3, 4, or 5, wherein the stopper wire and the base have the same potential. 7. The package containing the microstructure according to claim 1, further comprising a lead pad used for electrical connection, wherein at least one end of the stopper wire is fixed to the lead pad. The package structure to be. 8. The package structure according to claim 7, wherein both ends of the stopper wire are fixed to lead pads of the package. 9. The package structure according to claim 7, wherein one end of the stopper wire is fixed to a lead pad of the package and the other end is fixed to an electrode pad of the base. 10. The package structure according to claim 7, wherein a dedicated pad is provided as a pad to which the stopper wire is fixed.