JP5309652B2 - Acceleration sensor - Google Patents

Description

  The present invention relates to an acceleration sensor of a type using a piezoresistive element as a detection element.

In recent years, a sensor using a piezoresistor as a detection element (so-called piezoresistive acceleration sensor) has been put into practical use as a sensor having a small and simple structure using a MEMS (Micro Electro Mechanical Systems) technology (Patent Document 1). . In the conventional acceleration sensor disclosed in Patent Document 1, the weight body portion is displaced according to the applied acceleration, and the flexible portion is bent according to the displacement. The piezoresistive element formed in the flexible part changes the resistance value according to the amount of bending (stress) of the flexible part. Then, a voltage is applied to the piezoresistive element, and the acceleration is detected by referring to the voltage value accompanying the resistance change.
JP 2003-92413 A

The stress generated in the flexible portion is concentrated at the connection portion of the frame portion and the weight portion, and rapidly decreases as the distance from the connection portion increases, and the stress is zero at the center of the flexible portion. The resistance change that occurs in the piezoresistive element is due to the average stress change of the entire length of the piezoresistive element, so to increase the sensitivity of the sensor, the length of the piezoresistive element is shortened, and the stress is concentrated at the connection location. It is efficient to arrange them selectively. Further, contact holes for connecting the piezoresistive element and the wiring are disposed only at both end portions of the piezoresistive element.
According to the above configuration, when the piezoresistive element is arranged in the stress concentration portion, the wiring in the contact portion may be peeled off due to the physical stress, and an electrical contact failure may occur. Further, since there is one contact between the piezoresistive element and the wiring, if a failure occurs at any one contact location, it leads to a failure of the entire sensor.

  Therefore, in view of the above, an object of the present invention is to provide a small-sized acceleration sensor that reduces electrical contact failure between a wiring and a piezoresistive element.

The acceleration sensor according to the present invention includes a frame part having an opening, a weight part disposed in the opening of the frame part, at least a pair of beam parts connecting the frame part and the weight part, and the beam part And a detection portion formed by diffusing impurities disposed in each of a region where one end of the beam portion is connected to the frame portion and a region where the other end of the beam portion is connected to the weight portion,
Away from the stress concentration portion of the stress acting on the beam portion is concentrated, is formed to extend in the frame portion or the weight portion from at least one end portion of the detecting portion, a plurality of impurity is formed by diffusion A plurality of terminal portions extending from at least one end portion of the detection portion and one end portion of the detection portion; an insulating layer covering at least the detection portion and the terminal portion; A plurality of contact holes formed on the insulating layer, and formed on the insulating layer, wherein the plurality of contact holes are disposed away from the stress concentration portion where the stress acting on the beam portion is concentrated. And a wiring electrically connected to the terminal portions extending from the one end portion of the detection portion and the one end portion of the detection portion through the contact hole.

  ADVANTAGE OF THE INVENTION According to this invention, the small acceleration sensor which reduced the electrical contact defect between wiring and a piezoresistive element can be provided.

Hereinafter, a semiconductor triaxial acceleration sensor according to the present invention will be described with reference to the drawings. FIG. 1 is an overall perspective view of an acceleration sensor according to the present invention.
As shown in FIG. 1, the acceleration sensor 1 is a substantially rectangular parallelepiped, and includes a sensor main body 2 made of a semiconductor substrate and a support substrate 3 made of glass. For the sake of explanation, in the figure, two axes (X axis and Y axis) perpendicular to the plane of the acceleration sensor are set, and a direction perpendicular to the two axes is defined as the Z axis. The sensor body 2 is composed of an SOI (Silicon On Insulator) substrate 110, and is formed by sequentially laminating a silicon film 120, a silicon oxide film 130, and a silicon substrate 140. A weight body (weight part 142) is arranged in a frame (frame part 121 and frame part 141) having an opening, and the weight body is supported by a flexible beam (beam part 123). Yes. The support substrate 3 has a function as a pedestal for supporting the sensor body 2 and a function as a stopper substrate for restricting excessive displacement of the weight body in the downward direction (Z-axis negative direction). Note that when the sensor body 2 is directly mounted on a package substrate (not shown), the support substrate 3 is not necessarily required.

FIG. 2 is an exploded perspective view of the acceleration sensor. The silicon film 120 includes a fixed frame part 121 (the upper part of the frame), a weight joint part 122 disposed in the frame part 121, and two pairs (four in total) that connect the frame part 121 and the weight joint part 122. The beam part 123 is provided. The frame portion 121, the weight joint portion 122, and the beam portion 123 are defined by the opening 124. The frame part 121 is joined to the frame part 141 (the lower part of the frame) via the silicon oxide film 130. Further, the weight joint portion 122 is joined to the weight portion 142 having a substantially crowbar shape in the vertical view through the silicon oxide film 130. The weight part 142 is disposed in the frame part 141 so as to be separated.
The support substrate 3 is made of, for example, a glass substrate and is bonded to the sensor body 2 by anodic bonding.

FIG. 3 is a plan view and a sectional view of the sensor body. FIG. 3A is a plan view of the sensor main body, and detection units Rx to Rz for detecting acceleration in three axis (XYZ) directions are arranged on the four beam portions 123. The detection unit is disposed in the vicinity of a region where the beam unit 123 is connected to the frame unit 121 and the weight joint unit 122. In the drawing, detectors Rx1 to Rx4 and Rz1 to Rz4 are arranged on a pair of beam portions arranged in a direction along the X axis in order to detect acceleration in the X direction and the Z direction. On the other hand, detection units Ry1 to Ry4 for detecting acceleration in the Y direction are arranged in a pair of beam portions arranged in the direction along the Y axis. In addition, you may arrange | position the detection parts Rz1-Rz4 to a pair of beam part arrange | positioned in the direction along the Y-axis.
FIG. 3B is a cross-sectional view of the sensor main body along X-X. The lower surface of the weight portion 142 is made higher than the lower end of the frame portion 141, and the Z-negative direction is caused by a gap between the sensor substrate 142 and the glass substrate 3. It is set so that a certain amount of displacement is possible. FIG. 3C is a cross-sectional view of the sensor main body along YY, and the beam portion 123 is a self-supporting thin film having flexibility.

FIG. 4 is a diagram for explaining the details of the detection unit, and shows a plan view and a cross-sectional view (cross section AA). The detection portion R is a piezoresistive element formed by diffusing impurities such as B (boron) and P (phosphorus) in the silicon film 120, and the boundary between the beam portion 123 and the frame portion 121, and the beam portion 123 and the weight junction. It is arranged near the boundary of the part 122. The detection unit R includes a plurality of terminal units C at both ends. The terminal portion C may be configured as a piezoresistive element integrated with the detection portion R, or may be formed as a layer in which impurities are separately diffused, as long as it is extended from the detection portion R and electrically connected. Good.
The detection part R is covered with an insulating layer 150, and the insulating layer 150 in the region where the terminal part C is formed and / or at both ends of the detection part R has a contact hole 151 opened. In order to reduce the connection resistance, the terminal portion C may be a high-concentration impurity diffusion layer (in this case, it may be a layer having a high impurity concentration by about two to three digits with respect to the detection portion R). In addition, a total of twelve detectors R including Rx1 to Rx4, Ry1 to Ry4, and Rz1 to Rz4 are connected for each detection direction together with the portion arranged in the beam part 123 not shown in FIG. Forming. Regarding the bridge circuit connection, Japanese Patent Application Laid-Open No. 2007-322297, which is a patent application of the present applicant, can be referred to. An electrode pad (not shown) for connecting to an external circuit is provided on the frame portion 121, and a wiring 152 is connected to the electrode pad to take out an electrical signal accompanying acceleration to the external circuit.

5 and 6 are diagrams showing the first and second embodiments of the present invention. Hereinafter, the first embodiment will be described in order.
(First embodiment)
The first embodiment will be described with reference to FIG. The detection part R is arrange | positioned in the area | region where the beam part 123 connects with the frame part 121 and the weight junction part 122, respectively. Terminal portions C are provided at both ends of the detection unit R. The detection part R and the terminal part C are substantially integrated piezoresistive elements. In addition, the terminal part C may exist only in one end of the detection part R.
As shown in FIG. 5A, the width L ₁ of the terminal portion C is designed to be larger than the width L ₂ of the detection portion R, and the contact hole 151 is formed by opening the insulating layer 150 in the region where the terminal portion C is formed. Forming. Note that the shape of the terminal portion C is not limited to the illustrated rectangular shape, and may be circular or other shapes. In this case, the width of the portion having the widest width is regarded as “the width L _{1 of the} terminal portion C”. . In view of design requirements, the width L ₂ of the detection unit R is preferably 1/10 or less of L ₀ which is the width of the beam unit 123. If the width L ₂ of the detection portion R is 1/10 or more of L ₀ , it is easy to detect the twist of the beam portion 123 and the other-axis sensitivity is increased.

5A and 5B illustrate the form of the contact hole 151 and the wiring 152. FIG.
(A) Form of the contact hole 151 The contact hole 151 is formed in both ends of the detection part R and in the formation region of the terminal part C. Thereby, the number of contacts between the detection unit R and the wiring 152 is increased, and the reliability is improved.
(B) Form of wiring 152 The wiring 152 is disposed in the contact hole 151, and an electric signal from the detection unit R is taken out. As described above, by increasing the number of contacts between the detection unit R and the wiring 152, even if a failure occurs in any one of the contact holes 151, electrical contact can be secured in the remaining contact holes 151. Therefore, it functions normally as a product. The terminal portions C are respectively connected in series, which is advantageous for detecting an electric signal from the detection portion R.

Next, a method for manufacturing the acceleration sensor according to the first embodiment will be described with reference to FIG. FIG. 7 is a drawing showing the manufacturing method of the first embodiment according to the present invention.
Acceleration sensor manufacturing method according to first embodiment (1) Preparation of SOI substrate (see FIG. 7A)
An SOI substrate 110 in which a silicon film 120, a silicon oxide film 130, and a silicon substrate 140 are stacked is prepared. As described above, the silicon film 120 is a layer constituting the frame part 121, the weight joint part 122, and the beam part 123. The silicon oxide film 130 is a layer that joins the silicon film 120 and the silicon substrate 140 and functions as an etching stopper layer. The silicon substrate 140 is a layer constituting the frame part 141 and the weight part 142. The SOI substrate 110 is produced by SIMOX or a bonding method. In the SOI substrate 110, the silicon film 120, the silicon oxide film 130, and the silicon substrate 140 have thicknesses of 10 μm, 2 μm, and 600 μm, respectively. Note that a plurality of small acceleration sensors 1 each having a square outer circumference of about 1 to 2 mm are arranged in a multifaceted manner on a wafer having a diameter of 150 mm to 200 mm. A single unit of 10 ⁴ sensors can be manufactured in one batch.

(2) Formation of detection part and terminal part (see FIG. 7B)
An impurity diffusion mask (not shown) is formed on the SOI film 110 on the silicon film 120 side. As this mask material, for example, a silicon nitride film (Si ₃ N ₄ ) or a silicon oxide film (SiO ₂ ) can be used. After the silicon nitride film is formed on the entire surface of the silicon film 120 by LP-CVD (Low Pressure Chemical Vapor Deposition) method, a resist pattern (not shown) is formed on the silicon nitride film, and the detection portion R and the silicon nitride film are formed on the silicon nitride film. An opening corresponding to the terminal portion C is formed by RIE (Reactive Ion Etching).

After removing the resist pattern, a diffusing agent containing B (boron) or the like is applied. Then, heat treatment (about 1000 ° C.) is performed to drive in the silicon film 120 to form the detection portion R and the terminal portion C. Unnecessary diffusing agent is removed using hydrofluoric acid or the like. In addition, you may form the detection part R and the terminal part C by ion implantation other than a thermal diffusion method. Thereafter, the silicon nitride film (Si ₃ N ₄ ) is removed by etching with hot phosphoric acid. The terminal portion C may be formed in a step different from that of the detection portion R. In that case, it is preferable to diffuse impurities at a higher concentration than the detection portion R so as to be a low resistance layer.

(3) Formation of insulating layer and contact hole (see FIG. 7C)
An insulating layer 150 is formed on the silicon film 120. For example, by thermally oxidizing the surface of the silicon film 120, a SiO ₂ layer can be formed as an insulating layer. A contact hole 151 is formed on the insulating layer 150 at a predetermined position by RIE using a resist as a mask. Impurities may be further injected into the opened contact hole 151 to form a high concentration impurity diffusion layer.

(4) Gap formation (see FIG. 7D)
The gap 160 is formed by etching the silicon substrate 140 using a mask having an opening along the inner frame of the frame portion 141. The gap 160 is an interval necessary for the weight portion 142 to be displaced downward (on the glass substrate 3 side), and is, for example, 5 to 10 μm.

(5) Processing of silicon substrate (see FIG. 7E)
Next, a mask for defining the frame part 141 and the weight part 142 is formed on the lower surface of the silicon substrate 140. Using this mask, the silicon substrate 140 is etched until the lower surface of the silicon oxide film 130 is exposed. It is preferable to use DRIE (Deep Reactive Ion Etching) for the etching.

In DRIE, an etching step of digging while eroding the material layer in the thickness direction and a deposition step of forming a polymer wall on the side wall of the carved hole are alternately repeated. Since the side wall of the hole that has been dug is protected by forming a polymer wall in sequence, it is possible to advance erosion almost only in the thickness direction. An ion / radical supply gas such as SF ₆ can be used as an etching gas, and C ₄ F ₈ or the like can be used as a deposition gas.

(6) Creation of wiring (see FIG. 7F)
A wiring 152 is formed. The wiring 152 is obtained by forming a metal material such as Al, Al—Si, or Al—Nd by sputtering or the like and patterning it. In order to form an ohmic contact between the wiring 152 and the terminal portion C, heat treatment (380 ° C. to 400 ° C.) is performed. Note that a film such as a silicon nitride film (Si ₃ N ₄ ) may be provided over the wiring 152 as a protective film.

(7) Processing of silicon film (see FIG. 7G)
The silicon film 120 is etched by RIE until the upper surface of the silicon oxide film 130 is exposed to form an opening 124, thereby defining the frame portion 121, the weight joint portion 122, and the beam portion 123.

(8) Removal of unnecessary silicon oxide film (see FIG. 7H)
The unnecessary silicon oxide film used as an etching stopper is removed by RIE or wet etching. As a result, the silicon oxide film 130 exists between the frame 121 and the frame 141, and the weight joint portion 122 and the weight portion 142.

(9) Bonding of glass substrates (see FIG. 7 (I))
The sensor body 2 and the glass substrate 3 are joined. The glass substrate 3 is so-called Pyrex (registered trademark) glass containing movable ions such as Na ions, and anodic bonding is used for bonding to the SOI substrate 110. In order to prevent the weight 142 from sticking to the upper surface of the glass substrate 3 due to electrostatic attraction during anodic bonding, a sticking prevention film (not shown) such as Cr is formed on the upper surface of the glass substrate 3 by sputtering. You may keep it. Thereby, the sensor main body 2 and the glass substrate 3 are joined, and the acceleration sensor 1 is comprised.

(10) Individualization The acceleration sensor 1 is diced with a dicing saw or the like, and is divided into individual acceleration sensors 1. In the present specification, the “acceleration sensor” arranged in a multi-face manner on the wafer and the “acceleration sensor” separated into pieces are referred to as the acceleration sensor 1 without any particular distinction. The above manufacturing process is an example, and the order can be changed as appropriate.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. Except for the fact that the position where the detector R is arranged is different, it is substantially the same as the first embodiment. A duplicate description is omitted.
The detection part R is arranged so as to straddle the boundary line of the region where the beam part 123 is connected to the frame part 121 and the weight joint part 122. A contact hole 151 is formed at a position away from the boundary line.

  FIG. 6 shows a schematic diagram of the stress distribution acting on the beam portion 123. With the peak on the boundary line, the stress acting on the detector R decreases rapidly as the distance from the boundary line increases. As described above, the resistance change that occurs in the detection unit R is due to the average stress change of the entire length of the piezoresistive element. Therefore, in order to increase the sensitivity of the sensor, the length of the detection unit R is shortened and It is efficient to selectively dispose in the stress concentration part. However, if the contact hole 151 is formed in the vicinity of the boundary line, excessive physical stress is applied to the connection portion between the wiring 152 and the terminal portion C. The contact hole 151 is preferably separated from the boundary line in order to prevent the wiring 152 from peeling off. Therefore, by placing the terminal part C at a position away from the boundary, physical stress applied to the terminal part C can be reduced. Therefore, a sensor having excellent long-term stability can be provided. Further, with the above-described configuration, the influence on the beam portion 123 can be reduced by arranging the terminal portion C, which is a heating element, on a solid frame portion or weight portion.

The first embodiment , except that the acceleration sensor manufacturing method detection unit R according to the second embodiment is arranged so as to straddle the boundary line and the contact hole 151 is formed at a position away from the boundary line. This is substantially the same as the method of manufacturing the acceleration sensor according to the embodiment, and the description is omitted.

The following 1) -3) are mentioned as advantages compared with the prior art in the first and second embodiments of the present application described above.
1) Increase in number of contact points Conventionally, electrical contact points provided only at both ends of the detection unit (piezoresistive element) are also provided at a plurality of terminal portions extending from both ends of the detection unit. Is increasing. Thereby, the defect of the whole sensor is not caused by the connection defect in a part of contact.

2) Application to small sensors To reduce the size of an acceleration sensor, the dimensions of the weight part and the frame part are reduced. Therefore, an attempt is made to reduce the beam width L ₀ in order to maintain the detection sensitivity. Therefore, the detection part and the contact hole must be reduced. However, since there is a limit to the size of the contact hole that can be stably processed, it can be seen that the conventional acceleration sensor has a high yield and is difficult to manufacture. For example, it is difficult to stably perform lithography having a dimensional accuracy of 2 μm or less, and when the contact hole has a size of 2 μm or less, there is a possibility that the hole is not opened due to processing defects.
Further, when the size of the contact hole is reduced, the connection resistance at the contact portion is increased, and desired characteristics cannot be obtained. Rather than providing a plurality of contact holes at both ends of the detection unit, it is difficult to be restricted by the size of the sensor by arranging a terminal portion extending from the detection unit, which is preferable from the viewpoints of both lithography and connection resistance. It is.

3) Improvement of long-term stability Since the terminal part is arranged out of the stress concentration part of the beam part, it is difficult for excessive physical stress to be applied to the position where the wiring contacts the terminal part, and the wiring is not peeled off at that point. Can be reduced. Therefore, when the acceleration sensor is used for a long period of time, it is possible to prevent defects in the contact portion.

  As described above, the embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and modified. The expanded and modified embodiments are also included in the technical scope of the present invention.

1 is an overall perspective view of an acceleration sensor according to the present invention. It is a disassembled perspective view of an acceleration sensor. It is the top view and sectional drawing of a sensor main body. It is drawing explaining the detail of a detection part. 1 is a diagram illustrating a first embodiment according to the present invention. It is drawing showing 2nd Embodiment which concerns on this invention. It is drawing showing the manufacturing method of 1st Embodiment which concerns on this invention.

Explanation of symbols

1: Acceleration sensor 2: Sensor body 3: Support substrate 110: SOI substrate 120: Silicon film 121: Frame portion 122: Weight joint portion 123: Beam portion 124: Opening 130: Silicon oxide film 140: Silicon substrate 141: Frame portion 142 : Weight 150: insulating layer 151: contact hole 152: wiring 160: gap R: detection part (piezoresistive element)
Rx1 to Rx4: detecting units Ry2 to Ry4 (for detecting acceleration in the X-axis direction): detecting units Rz1 to Rz4 (for detecting acceleration in the Y-axis direction): (for detecting acceleration in the Z-axis direction) ) Detection part C: Terminal part

Claims (4)

A frame portion having an opening;
A weight portion disposed in the opening of the frame portion;
At least a pair of beam portions connecting the frame portion and the weight portion;
Detected by diffusing impurities formed in each of the region where one end of the beam portion is connected to the frame portion and the region where the other end of the beam portion is connected to the weight portion. And
Away from the stress concentration portion of the stress acting on the beam portion is concentrated, is formed to extend in the frame portion or the weight portion from at least one end portion of the detecting portion, a plurality of impurity is formed by diffusion The terminal part of
An insulating layer covering at least the detection part and the terminal part;
The insulating layer is formed by opening a hole in at least one end of the detection portion and a plurality of terminal portions extending from one end of the detection portion , and acts on the beam portion. A plurality of contact holes arranged at positions away from the stress concentration part where stress is concentrated ;
A wiring formed on the insulating layer and electrically connected to the one end portion of the detection portion and the plurality of terminal portions extending from the one end portion of the detection portion via the plurality of contact holes;
An acceleration sensor comprising:   The acceleration sensor according to claim 1, wherein the contact holes are formed at both ends of the detection unit.   The acceleration sensor according to claim 1 or 2, wherein a width of the widest portion of the terminal portion is larger than a width of the detection portion.   The said detection part is arrange | positioned ranging over the boundary of the one end of the said beam part, and the said frame part, or the other end of the said beam part, and the said weight part, The one of Claim 1 thru | or 3 characterized by the above-mentioned. The acceleration sensor according to item 1.

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