JP2001121499A - Micromachine structure and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitive acceleration sensor made into a micromachine capable of detecting a lateral direction. SOLUTION: The capacitive acceleration sensor which straightens resistance for stiction of detection fingers forming capacitive elements and is made into a micromachine capable of detecting in a lateral direction includes fixed detection fingers (316, 318, 516, 518, 536, 538) formed like beams. Each finger (316, 318, 516, 518, 536, 538) is supported by a plurality of supporting elements or fixing bodies (320, 322, 330, 332, 334, 336, 522, 530). Finger elements (312, 512) added to inertial mass (304, 502) can be fastened with each other at the tips in the same way as the roots. As a result, also hardness of lateral directions and vertical directions of the fingers (316, 318, 516, 518, 536, 538) moving simultaneously is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a micromachine structure, and more particularly, to a micromachined acceleration detection device.

2. Description of the Related Art Micromachined sensors, such as, for example, micromachined pressure transducers, micromachined acceleration switches, and micromachined analog acceleration sensors, are compared to macro-type sensors of the same type. It is well known in the art that this is a cost-effective option. Because devices of this type use mechanical structures, the term "micromachined" is used in these respects, and uses photolithographic and etching techniques similar to those used in integrated circuit fabrication. Since it is manufactured, it is of a very small size. Often, a silicon substrate is used. Micro-machined sensors can use a variable capacitance effect that generates an electrical output signal in response to a physical input, such as acceleration. In a conventional laterally detectable capacitive acceleration sensor, a micromachined inertial mass is locked onto a substrate by a plurality of micromachined suspension arms that are subordinate in the detection direction. The proof mass typically has a plurality of cantilevered fingers, which extend out of the proof mass and perpendicular to the direction of detection. The plurality of fixed fingers are fixed at one end inwardly from the substrate in a finger-like structure, and extend between the fingers extending outward from the inertial mass. The inertial mass fingers cooperate with the stationary fingers to form a plurality of air gap capacitors, the distance of the gaps varying as the inertial mass moves in the direction of detection. The input acceleration moves the inertial mass, changes the gap distance, and changes the measured volume in proportion to the acceleration. The change in the measured capacitance is detected by a bridge circuit, an oscillator, or other electronic circuits, either of which is mounted on the sensor substrate or in a separate chip. A problem that continues to plague micromachined acceleration sensors and micromachined acceleration switches of general shape is that fixed and movable fingers tend to adhere to the substrate or to each other. , These are generally referred to as "stiction
n) "(technical term meaning" adhesion "), which is due to various causes such as capillary action, electrostatic force, van der Waals force, and the like. For example, if a finger of a movable structure moves in contact with one of the fixed fingers, the combination of electrostatic attraction and Van der Waals forces can cause the fingers to adhere or even fuse together. Adjacent fingers are observed to adhere to each other as well as to the underlying substrate. Fingers mounted on the moving mass are observed to adhere to adjacent fixed fingers or the underlying substrate. Although this stiction is also caused by electrostatic attraction or Van der Waals forces, the primary cause of stiction is the capillary force created during the process technology used to manufacture the device itself (process stiction). ). In a conventional micromachine fabrication process, the proof mass and movable and stationary fingers are formed by patterning a layer of semiconductor material over a sacrificial layer, typically comprising silicon dioxide. The sacrificial layer is then etched away by immersing the substrate in an etching solution. After the wet etching process is completed, the etchant is removed by immersing the wafer in pure water and the wafer is dried. Unfortunately, as the wafer dries, the evaporating pure water capillarity pulls delicate structures, such as cantilever fingers, down toward the substrate, where they can remain permanently. Capillary forces between adjacent fingers may also pull two adjacent fingers together, where they may remain permanently. Stiction is typically difficult to detect by conventional wafer inspection tests and can result in unpredictable changes in device parameter characteristics. This is a major concern for the reliability of micromachined transducers, especially when applied for security. Accordingly, there is a need for a laterally detectable micromachined acceleration sensor structure with improved resistance, generally for stiction, and more particularly for process stiction. The invention will be better understood with reference to the following detailed description and the accompanying drawings, in which corresponding elements are identified by corresponding reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The shapes shown are intended to illustrate the structure in a general manner and are not necessarily drawn to scale. In the description and claims, "left", "right",
The terms "before,""after," and the like, are used for descriptive purposes. However, it is understood that the embodiments of the invention described herein are capable of operation in other directions, and the terms shown and used are only used to describe relative positions. And are compatible under appropriate circumstances. FIG. 1 is a plan view of a prior art acceleration sensor 100, including a substrate 102,
An inertial mass 104 is locked thereon. Inertial mass 1
Numeral 04 is locked on the substrate 102 by a plurality of suspension arms 106, and each suspension arm is fixed to the substrate 102 by a fixing structure 108. The suspension arm 106 is indicated by an arrow in FIG.
The proof mass 104 moves proportionally to the substrate 102 in response to acceleration having components in the X-axis direction, as it is relatively dependent on the transverse direction (X-axis) indicated by AA. The suspension arm 106 is sufficiently fixed in the vertical (Y-axis) direction perpendicular to the horizontal direction. Inertial mass 104
Are typically constructed of conductive polysilicon and have a fixed structure 108 such that the proof mass 104 is maintained at a selected voltage.
Is electrically connected internally to the lead 110 through one of them. The inertial mass 104 includes a plurality of cantilevered fingers 11 extending outwardly from a central rail portion 114 of the inertial mass 104.
2 inclusive. The plurality of cantilevered fingers 116, 118 extend finger-like inwardly from their respective fixed structures 120, 122 toward the rail portion 114 of the proof mass 104. The cantilever fingers 116 are typically made of, for example, polysilicon, single crystal silicon, metal, or a conductive material equivalent thereto. The cantilevered fingers 116 are electrically interconnected to each lead 124 via their respective fixed structure 120. Similarly, cantilever finger 11
8 are typically made of a material similar to that used for the fingers 116 and are electrically interconnected to their respective leads 126 via their respective fixed structures 122. The cantilever fingers 112, 116, 118 cooperate to form a plurality of parallel plate capacitors. In addition, the conductive shield 128 intervenes between the substrate 102 and the proof mass 104 to control the stray capacitance,
It has another effect on its performance. 2, inwardly extending fingers 116, 118 as described herein.
Consists of a plurality of extending beam members, such as fingers 116, of which only one end is fixed from their fixed structure 120 towards the proof mass 104. As shown in FIG. 2, in a typical prior art device, a dielectric layer, such as a layer of silicon nitride 202, is deposited on the substrate 102 to electrically isolate the micro-mechanical structure from the substrate 102. As an example, the first polysilicon layer 204 includes the leads 124
And forming an optional shield 128 of the micromachined acceleration sensor. Then, a sacrificial layer such as the silicon oxide layer 206 is formed on the first polysilicon layer 2.
04. Oxide layer 206 is patterned to provide via 208 and form an interconnect between finger 116 and lead 124, as described below. Then, the second polysilicon layer 210 is formed on the sacrificial layer 20.
6 and patterned finger structures 116
To form Part 212 of second polysilicon layer 210
Fills vias 208 and fuses with leads 124,
Form an internal connection between finger 116 and lead 124. The current photolithography technology uses finger 11
6 with a footprint larger than the rest of 6
Up to now, the finger 11 has been used like a thin cantilever to maximize the capacitor component density.
Forming 6 was commonly done. However, as mentioned above, the cantilevered finger structure has poor resistance to stiction, and the prior art device therefore requires fingers 112, 116, 1 of the structure shown in FIG.
High range stiction between adjacent fingers, such as 18, resulted in poorer sensitivity and / or reliability of the completed device. FIG.
9 is an embodiment of a micromachined acceleration sensor 300 capable of detecting in the lateral direction, embodying the features of the present invention.
The acceleration sensor 300 comprises a substrate 302 having a vibration or inertial mass 304,
Are locked on the main surface of the substrate 302 by a plurality of suspension arms 306. The suspension arms 306 each comprise a thin cantilever element secured to the substrate 302 by a plurality of securing members or structures 308. Inertial mass 304 is electrically interconnected with lead 310 through one of fixed structures 308 such that inertial mass 304 is maintained at a predetermined voltage. The proof mass 304 includes a plurality of cantilevered finger elements 312 that extend outwardly from a central rail portion 314 of the proof mass 304. Finger element 3
12 is preferably a central rail section 3 as shown in FIG.
Stretch vertically from 14. However, the finger elements may interchangeably extend obliquely or in a curve from the central rail. A plurality of fixed finger members 316, 318
Extend between finger elements 312 that are arranged in a finger-like structure and extend out of the proof mass 304. The finger members 316 are connected to the leads 3 via their respective fixed structures 320.
24 and is internally connected. Similarly, the finger member 31
8 are connected to the leads 326 through their respective fixing structures 322.
Is electrically connected internally. As described above, when the finger element 312 has an oblique or curved shape, the finger members 316 and 318
2 can have a similar shape. If necessary, use a conductive shield structure 3 to reduce stray capacitance.
28 may be provided, which may affect the performance of the acceleration sensor 300 in another way. As shown in FIG. 4, an insulating dielectric layer 402, such as a layer of silicon nitride, is deposited on the substrate 302, isolating the overlying micromachine structure from the underlying substrate 302. First polysilicon layer 4
04 is deposited on dielectric layer 402 and patterned to form leads 324, conductive shields 328, and pads 410, the function of which will be described in more detail below. Sacrificial layer 406, such as a layer of silicon oxide
Is deposited on the first polysilicon layer 404. The sacrificial layer 406 is etched and the first via 414 and the second via 414 are removed.
A via 416 is formed. A second layer 420 of conductive polysilicon is deposited on the sacrificial layer 406 and then patterned to form finger members 316. The first portion 422 of the second polysilicon layer 420, as described above,
The vias 414 are filled to form the securing structure 320, provide mechanical support for the finger members 316, and
Lead 324 electrically connects with finger member 316. The second portion 424 of the second polysilicon layer 420
The via 416 is filled to form the tip fixation structure 330. To prevent the finger member 316 from shorting to the shield 328, the pad 410 is not in contact with the shield 328 and is electrically isolated as described above. The pad 410 is provided in a region directly below the tip fixing structure 330. Thus, the presence of the tip fixation structure 330, on the contrary, affects the width of the finger-like structures of the finger members 316, 318, since the sides of the tip fixation structure 330 are minimized within the limits of current photolithographic techniques. Do not give. Although not shown in FIG. 4, those skilled in the art will appreciate that the second polysilicon 420 may have a mass 304 as shown in FIG.
It will be understood that they can also be used to form Those skilled in the art will further appreciate that the fingers 312, shown in FIG.
It will be appreciated that 316 and 318 have the same thickness when manufactured by the preferred manufacturing method described above. Referring again to FIG. 3, in addition to the tip fixing structure 330,
A variety of other support members may be used to support the finger members 316, 318. For example, the anchoring structures may be located at regular intervals or at other locations along the longitudinal axis of the finger member 316, including at locations other than the bases of these tips. For example, the securing structure 332 is shown in the center at a distance d ₁ from the base of the finger member 316, and the securing structure 334 is shown at a distance d ₂ from the tip of the finger member 316. The distances d ₁ and d ₂ are
Preferably, it is less than or equal to 1/3 of the total length of the finger member 316, or 1/3 when the length is "1", in order to minimize the interval between adjacent fixing structures. Yes, at the same time to maximize the stiffness of the end of the short cantilever from the locking mechanism 334. Where only two securing structures are provided on a given finger member,
Another approach could be to place the anchoring structures 332, 334 at a quarter of the length from the end of the finger member 316, but this is due to the highest first bending mode natural frequency. )
This is to provide a finger structure having the following. All of the examples described above for the securing structure of FIG. 3 are locked in at least one portion for each of the finger members 316, 318 on the substrate 302, so that the securing structure is locked to the locked portion or each finger member. It does not exist directly under the part. The finger elements 312 are preferably finger-mounted or arranged between the locked portions of each set of finger members 316,318. As yet another option, instead of a separate securing structure, such as securing structures 330, 332, 334, a single continuous securing structure, such as securing structure 336, supports the finger members, in this case finger members 318. Can be provided for
The securing structure is along the entire length of the finger member or a substantial portion thereof. As used herein, a substantial portion of the length of the beam member means at least half the length of the beam, and extends from a stationary structure that is otherwise electrically interconnected. It is. The embodiment illustrated in connection with FIGS. 3 and 4 shows an outwardly extending finger element 3.
12, the subject matter of the present invention applies equally to a ladder-type structure as shown in FIG. 5, wherein the movable finger members are restrained at both ends, ie, at the root and tip. I have. As shown in FIG. 5, the inertial mass 502 includes a pair of side rails 504,
506 and extends in the lateral direction indicated by arrow BB. Each finger member 512 is connected to rails 504 and 5
06 and extends vertically to form a ladder structure. Finger members 512 are constrained at both ends rather than projecting to one side from the center rail,
The finger members 512 of the proof mass 502 are substantially more resistant to stiction generation than the finger elements of the embodiment of FIG. A mass 514 having a wide range of strengths may be formed at either end or both ends of the inertial mass 502 to further add thin film hardness to the ladder structure of the inertial mass 502. Optionally, a center rail (not shown in FIG. 5, but similar to center rail portion 314 of FIG. 3) may also be used to further increase the strength of the ladder structure of inertial mass 502. The inertial mass 502 is locked on the substrate 500 by the suspension arm 506, similarly to the function of the suspension arm 306 described above. The suspension arm 506 is attached to the substrate 500 by a conventional fixed structure 508 and electrically interconnects the proof mass 502 to external leads (not shown). Fixed finger members 516, 518
Are attached to the substrate 500 by conventional fixing structures 520, 522, respectively, and finger members 516,
518 are internally connected to their respective leads 524,526. The finger members 516, 518 are also preferably
Supported by an additional tip anchoring structure 530 or other support structure as described above. Additional finger structures
Each of the windows 540 defined by finger members 512 at both ends of the length of the inertial mass can be formed, with the additional finger structure being the same or different than finger members 516, 518. Here, it will be apparent to those skilled in the art that changes and modifications in the above-described embodiments may be made without departing from the spirit and scope of the invention. In addition, the illustrated embodiment is intended for a parallel plate capacitor that is perpendicular to the direction that the plate senses, but is a unidirectionally extending plate with at least the usual components, and as a result, Any plate array is considered to be within the scope of the present invention, as long as the capacitance changes as the inertial mass moves in the direction of detection. Similarly,
Polysilicon embodiments are disclosed, and conventional semiconductor fabrication techniques for fabricating similar structures with single crystal silicon or other electrically conductive materials are well known. Accordingly, it is intended that the invention be limited only by the scope of the appended claims and the rules and principles of applicable law.

[Brief description of the drawings]

FIG. 1 is a simplified plan view of a laterally detectable acceleration sensor according to the related art.

FIG. 2 is a cross-sectional view of the structure shown in FIG. 1, taken along line 2-2 in FIG. 1.

FIG. 3 is a plan view of a portion of an embodiment of a laterally detectable acceleration sensor incorporating features of the present invention.

FIG. 4 is a cross-sectional view of a portion of the structure shown in FIG. 3, taken along line 4-4 in FIG. 3;

FIG. 5 is a plan view of a portion of another embodiment of a laterally detectable acceleration sensor incorporating features of the present invention.

[Explanation of symbols]

 300: Micromachine structure 302, 500: Substrate 304, 502: Mass 306: Sensor 312, 512: Finger element 316, 516: Finger member 320: Fixed member (fixed body) 402: Dielectric layer 404: First polysilicon layer 410 : Pad 420: second polysilicon layer 428: shield 504, 506: rail

Continued on the front page (72) Inventor Jonathan H. Hammond United States Arizona 85251 S Cotsdale North 83rd Place 3020 (72) Inventor Gary Jay O'Brien Michigan 48105 Ann Arbor No. 204 Pointe Crossing 1895 (72) Inventor Jose El Torres 85233 Arizona, United States of America Gilbert West San Angelo Street 534

Claims (3)

[Claims] A substrate (302), a plurality of fixing members (320) coupled to the substrate, and the plurality of fixing members (320);
A finger member (316) coupled to 2), wherein a portion of said finger member (316) is locked onto said substrate (302) by said plurality of fixing members (320); A finger member (316), wherein the member (320) is not under the portion of the finger member and the finger member (316) is stably held against the substrate (302); A mass (304) coupled to the substrate (302) and locked onto the substrate (302), wherein the mass is adjacent to the finger member (316);
12), wherein the mass (304) is movable with respect to the substrate, and wherein the finger element (312) and the finger member (316) form a capacitor. A micromachine structure (300), characterized in that: 2. A silicon substrate (302) and an electrically insulating dielectric layer (40) on said silicon substrate.
2) a first polysilicon layer (404) on the electrically insulating dielectric layer (402), wherein the first polysilicon layer is an electrically conductive shield (428); And the electrically conductive shield (428).
A first polysilicon layer (404) configured to form the electrically conductive pad (410) electrically isolated from the first polysilicon layer (404), and configured to form a stationary body (320). The first
The second polysilicon layer (4) on the polysilicon layer (404)
20) wherein a stationary finger (316) is electrically coupled to the stationary body (320) and the electrically conductive pad (410) to provide a movable mass (30).
4) The fixed body (320), the fixed finger (31)
6), and the electrically conductive pad (41)
0) and a second polysilicon layer that is discontinuous, wherein the fixed body (320) is coupled to the silicon substrate (302) and fixed to the silicon substrate (302); The stationary fingers (316) are coupled to the silicon substrate (302) by at least two of the stationary bodies, and each of the stationary fingers (316) is locked on the silicon substrate (302) by at least two of the stationary bodies. The fixed fingers (31
6) the portion of the fixed finger (31) that is not on the fixed body and includes the portion of the fixed finger (316);
6) is fixed to the silicon substrate (302), and the movable mass (304) is fixed to the silicon substrate (302).
Coupled to and locked onto the silicon substrate (302), the movable mass (304) further includes movable fingers (312), each of the movable fingers (312) of the fixed finger (316). The movable mass (304) including the movable finger (312) is movable between the silicon substrate (302) and the movable finger (312) disposed between different sets to form two capacitors. And the fixed finger (316) has the same thickness. 3. A substrate (500), a finger member (516) coupled to the substrate (500) and fixed to the substrate (500), and a substrate (302) coupled to the substrate (302). Mass (502) locked on (302), wherein said mass (5)
02) has at least two rails (504, 506) and finger elements (512) extending therebetween, said mass (502) being movable with respect to said substrate (500) and said finger member (512). 516) and a mass (502), wherein the finger elements (512) are adjacent to each other to form a capacitor.