JP4998401B2 - Acceleration sensor and manufacturing method thereof - Google Patents

Description

  The present invention relates to an acceleration sensor and a method for manufacturing the same, and more particularly, to an acceleration sensor and a method for manufacturing the same that can prevent destruction even when excessive acceleration is applied.

  In recent years, development of small sensors using MEMS (Micro Electromechanical Systems) technology has been progressing, and sensors for detecting acceleration are used for various applications such as mobile phones and game machines, and applications have been studied. ing. Such an acceleration sensor is manufactured using, for example, an SOI (Silicon On Insulator) wafer having a three-layer structure of silicon layer / silicon oxide layer / silicon layer. As shown in FIGS. 10 and 11, this type of sensor includes an opening 54 formed so as to penetrate an SOI wafer 52 having a three-layer structure of silicon layer 52a / silicon oxide layer 52b / silicon layer 52c. And a weight 55 that is supported by the frame 53 via a plurality of beams 56 and that can be displaced when an external force is applied. The weight 55 includes a base portion 55A supported by a plurality of beams 56, and four projecting portions 55B protruding from the base portion 55A in the direction between the cross-shaped beams 56. The beam 56 is provided with a piezoresistive element 57. When an external force (acceleration) is applied to the weight 55 to cause displacement, the piezoresistive element 57 detects a change in resistance due to the deflection of the beam 56 and measures acceleration. To do.

In such an acceleration sensor, when excessive acceleration is applied, the weight 55 may be greatly displaced and the beam 56 may be damaged. For this reason, stopper portions 59 (shown by hatching in FIG. 10) as shown in FIGS. 10 and 12 are provided in the four openings 54 and project when excessive acceleration is applied to the weight 55. The portion 55B comes into contact with the stopper portion 59 so that excessive displacement is prevented and damage to the beam 56 is prevented. Such a stopper portion 59 is made of a silicon layer 52a, and it is necessary to remove the silicon oxide layer 52b by etching to separate it from the protruding portion 55B of the weight 55 made of the silicon layer 52c. In order to facilitate removal of the silicon oxide layer 52b by etching, a stopper portion (Patent Document 1) having a plurality of small openings for inflow of a chemical solution for etching is obliquely installed from the frame 53 to the opening portion 54. A rod-like stopper portion (Patent Document 2) has been proposed.
JP 2004-198243 A JP 2004-317478 A

However, the conventional stopper portion, which has sought to facilitate etching removal of the silicon oxide layer 52b, is provided with a plurality of small openings or a rod shape in order to enhance the contact between the etching solution and the silicon oxide layer 52b. There is a problem in that the strength is insufficient and the original function of preventing excessive displacement of the weight 55 is impaired.
The present invention has been made in view of the above circumstances, and includes an acceleration sensor that has a stopper portion having sufficient strength and prevents destruction even when excessive acceleration is applied. It aims at providing the manufacturing method for manufacturing a sensor simply.

  In order to achieve such an object, the acceleration sensor of the present invention comprises an SOI (Silicon On Insulator) substrate having a three-layer structure of silicon layer (active layer silicon) / silicon oxide layer / silicon layer (substrate silicon). The frame portion is made of the silicon layer (active layer silicon), protrudes inward from each side of the frame portion, a weight joint supported by the beam, and the silicon layer (substrate silicon). 4 bases joined to the weight joints via the silicon oxide layer, and four projecting parts projecting from the base parts to the four window parts surrounded by the four beams and the frame part And a weight composed of a protrusion projecting from each projecting portion and having a step on the silicon layer (active layer silicon) side of the projecting portion and an engaging convex portion having a step, and the silicon layer (active layer silicon). , Corner of the frame At least four plate-like stopper portions erected on two sides of the engaging projection, and the engaging convex portion protrudes downward from the stopper portion between the top portion of the engaging convex portion and the stopper portion. The configuration is such that a predetermined gap is provided.

As another aspect of the present invention, the stopper portion has a triangular shape with a corner portion of the frame portion as one point.
As another aspect of the present invention, the gap between the top of the engaging projection and the stopper is in the range of 5 to 30 μm.

  The acceleration sensor manufacturing method of the present invention also includes a silicon layer (active layer silicon) of an SOI (Silicon On Insulator) substrate having a three-layer structure of silicon layer (active layer silicon) / silicon oxide layer / silicon layer (substrate silicon). ), A frame, four beams projecting inward from each side of the frame, a weight joint supported by the beam, and two sides sandwiching a corner of the frame A step of forming four stopper portions; a frame portion on the silicon layer (substrate silicon); and a weight positioned in a non-contact manner inside the frame portion, wherein the silicon oxide layer is formed on the weight joint portion. A base part joined and held via the four beams, four projecting parts projecting from the base part to the four window parts surrounded by the four beams and the frame part, and projecting from the projecting part and the stopper part And an engaging convex part that reaches the tip part in a non-contact manner. The step of forming a weight and the step of removing the exposed silicon oxide layer, and the step of forming the frame portion and the weight on the silicon layer (substrate silicon) includes the step of forming the silicon oxide The silicon layer (substrate silicon) is exposed until a layer is exposed and side etching occurs on the engaging protrusions that are in contact with the silicon oxide, so that the top of the engaging protrusions is separated from the silicon oxide. An opening was formed from the side by dry etching by RIE (Reactive Ion Etching) method through a mask pattern.

In such an acceleration sensor of the present invention, when excessive acceleration is applied to the weight, the engaging convex portion comes into contact with the stopper portion to prevent excessive displacement, and the stopper portion prevents the corner portion of the frame portion. Since it is a plate-like shape installed on the two sides, the strength is sufficiently high, so that even if excessive acceleration is applied, damage such as damage to the beam is surely prevented, and the acceleration sensor is highly reliable.
Further, the acceleration sensor manufacturing method of the present invention is such that, in the step of forming the frame portion and the weight on the silicon layer (substrate silicon), the tip portion protrudes from the four protrusion portions and below the silicon oxide layer of the stopper portion. Is formed by the RIE method, and the formed stopper portion is a plate-like structure that is installed on two sides sandwiching the corner of the frame portion. Therefore, it is possible to manufacture a highly reliable acceleration sensor in which destruction such as damage to a beam is prevented even when a high acceleration is applied.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Acceleration sensor]
FIG. 1 is a plan view showing an embodiment of the acceleration sensor of the present invention, FIG. 2 is a cross-sectional view taken along line II of the acceleration sensor shown in FIG. 1, and FIG. 3 is a diagram of the acceleration sensor shown in FIG. It is sectional drawing in the II-II line. 1 to 3, the acceleration sensor 1 includes a sensor main body 2 and a support substrate 3 bonded to the sensor main body 2. The sensor body 2 includes an SOI (Silicon On Insulator) substrate 11 having a three-layer structure in which a silicon oxide layer 13 is sandwiched between a silicon layer 12 (active layer silicon) and a silicon layer 14 (substrate silicon). Note that the acceleration sensor of the present invention may be composed of the sensor body 2 and may not include the support substrate 3. In this case, the acceleration sensor may be directly mounted on the package substrate.

As shown in FIGS. 1 to 3, the silicon layer 12 (active layer silicon) constituting the sensor body 2 includes a weight joint portion 21, four beams 22 for supporting the weight joint portion 21, A frame portion 23 and four window portions 24 surrounded by the beams 22 and the frame portion 23 are provided. In addition, piezoresistive elements 31 are disposed on the four beams 22. That is, four piezoresistive elements 31x that detect external force in the X-axis direction, four piezoresistive elements 31y that detect external force in the Y-axis direction, and four piezoresistive elements that detect external force in the Z-axis direction 31z is arranged.
In addition, the silicon layer 12 (active layer silicon) constituting the sensor main body 2 is provided with plate-like stopper portions 29 (in FIG. 1) that are installed at two corners of the frame portion 23 on two sides sandwiching the corner portions. (Shown with diagonal lines). In the illustrated example, the stopper portion 29 has a triangular shape with a corner portion of the frame portion 23 as one point, and has a plate shape without a small opening or the like.
Further, the silicon layer 14 (substrate silicon) constituting the sensor body 2 includes a weight 25 and a frame portion 26 positioned around the weight 25 via an opening 27. The weight 25 is thinner than the frame portion 26, and includes a base portion 25A and four protruding portions 25B protruding from the base portion 25A in the direction between the cross-shaped beams 22 (window portions 24). . The base portion 25A of the weight 25 is joined to the weight joint portion 21 of the silicon layer 12 (active layer silicon) via the silicon oxide layer 13.

  4 is a plan view of the weight 25 constituting the acceleration sensor 1 shown in FIG. 1, and FIG. 5 is a partial perspective view of the protruding portion 25 </ b> B constituting the weight 25. As shown in FIGS. 1 and 3 to 5, each protruding portion 25 </ b> B has a wall surface 25 b that is opposite to the corner portion of the frame portion 23 and that has a shape along the shape formed by the tip portion 29 a of the stopper portion 29. Have. And the convex part 28 for engagement protruding in the corner | angular part direction of the frame part 23 from this wall surface 25b is provided. The engaging convex portion 28 has a tip portion 28a protruding below the stopper portion 29, and a top portion 28b having a step with the flat surface 25b 'on the silicon layer 12 (active layer silicon) side of the protruding portion 25B. . Therefore, a predetermined gap is provided between the top portion 28 b of the engaging convex portion 28 and the stopper portion 29.

  The length L at which the tip 28a of the engaging convex portion 28 enters below the stopper portion 29 and the width W (see FIG. 1) of the engaging convex portion 28 are such that when excessive acceleration is applied to the weight 25, the convex portion for engaging The area where the portion 28 comes into contact with the stopper portion 29 is defined and can be appropriately set in consideration of the strength of the engaging convex portion 28. For example, the length L is about 20 to 60 μm, and the width W is It can be about 20-60 micrometers. Further, the gap G (see FIG. 3) between the top portion 28b of the engaging convex portion 28 and the stopper portion 29 defines an allowable displacement amount when an external force (acceleration) is applied to the weight 25. It can be appropriately set in consideration of the strength of the beam 22 and can be set to about 5 to 30 μm, for example. If the gap G is less than 5 μm, a sufficient measurement range cannot be secured, and if it exceeds 30 μm, the displacement above the weight 25 (in the direction of the stopper portion 29) becomes too large, causing damage to the beam 22 There is a fear.

In the acceleration sensor 1 as described above, when an external force acts on the weight 25 supported by the four beams 22 in the X-axis, Y-axis, or Z-axis (see FIG. 1) direction, the weight 25 is displaced. . Due to this displacement, the beam 22 is bent, and an external force acting on the weight 25 is detected by the piezo element 31. When excessive acceleration is applied to the weight 25, the engaging convex portion 28 comes into contact with the stopper portion 29 to prevent excessive displacement. The stopper portion 29 has a plate shape that is constructed on two sides sandwiching the corner portion of the frame portion 23, and therefore has a sufficiently high strength. Therefore, the acceleration sensor 1 of the present invention is highly reliable because destruction such as damage to the beam is reliably prevented even when excessive acceleration is applied.
The engaging convex portion 28 described above has a rectangular cross-sectional shape, but the present invention is not limited to this, and for example, various forms as illustrated in FIG. 6 can be employed. That is, the shape of the engaging convex portion 28 may be trapezoidal (FIG. 6A) or semicircular (FIG. 6B) in cross section. Further, the wall surface 25b of the projecting portion 25B may include a plurality (two in the illustrated example) of engaging convex portions 28 (FIG. 6C).

Further, the stopper portion 29 described above has a triangular shape with the corner portion of the frame portion 23 as one point. However, the present invention is not limited to this, and for example, various shapes such as those illustrated in FIG. can do. That is, even if the tip portion 29a of the stopper portion 29 forms an arc (FIG. 7A) and the tip portion 29a of the stopper portion 29 protrudes in a mountain shape (FIG. 7B). Good. Moreover, the part which the stopper part 29 connects with the frame part 23 may be made into round shape (FIG.7 (C)), and the further prevention effect of the damage of the stopper part 29 by stress concentration may be aimed at.
The above-described embodiment of the acceleration sensor is an exemplification, and the present invention is not limited to this.

[Method of manufacturing acceleration sensor]
FIG. 8 is a process diagram illustrating an example of a method for manufacturing an acceleration sensor according to the present invention, and illustrates an example of manufacturing the acceleration sensor 1 described above. FIG. 8 shows a portion corresponding to the cross-sectional shape shown in FIG.
In the present invention, an SOI (Silicon On Insulator) wafer 11 ′ having a three-layer structure of a silicon layer 12 (active layer silicon), a silicon oxide layer 13, and a silicon layer 14 (substrate silicon) can be processed in a multifaceted manner. . In FIG. 8, first, the groove 16 for forming the weight joint portion 21, the beam 22, the frame portion 23, and the stopper portion 29 is formed in the silicon layer 12 (active layer silicon) for each imposition. A recess 17 for setting the thickness of 25 is formed in the silicon layer 14 (substrate silicon) (FIG. 8A). The grooves 16 and the recesses 17 can be formed by, for example, a RIE (Reactive Ion Etching) method, which is a silicon deep etching method, through a mask pattern. As this RIE method, an ICP (Inductive Coupled Plasma) method, a CCP (Capacitively Coupled Plasma) method, an ECP (Electron Coupled Plasma) method, a SWP (Surface Wave Plasma) method, an HWP (Helicon Wave Plasma) method, or the like may be used. it can. Moreover, the groove part 16 and the recessed part 17 can also be formed by the sandblasting method, the wet etching method, and the femtosecond laser method.

  Next, for each imposition, an opening 27 is drilled from the silicon layer 14 (substrate silicon) side (recess 17 side) of the SOI wafer 11 ′ until the silicon oxide layer 13 is exposed through the mask pattern 31. The weight 25 (base 25A, protrusion 25B, engaging protrusion 28) and the frame 26 are formed (FIG. 8B). Formation of the frame portion 26 and the weight 25 by forming the opening 27 can be performed via the mask pattern 31 by the RIE method. In this step, the engaging protrusion 28 is formed so that the tip 28 a of the engaging protrusion 28 reaches the lower portion of the stopper portion 29 below the silicon oxide layer 13 in a non-contact manner. Such processing can be performed as follows. First, dry etching is performed by the RIE method from the silicon layer (substrate silicon) 14 side until the silicon oxide layer 13 is exposed through the mask pattern 31. Thereafter, when dry etching is further continued by the RIE method, side etching occurs in the engaging convex portions 28 that come into contact with the silicon oxide 13 as shown in FIG. The reason why such side etching occurs is that the positively charged silicon oxide 13 and the positive ions of the etching gas repel, and that dry etching from the silicon layer (substrate silicon) 14 side reaches the silicon oxide 13. It is conceivable that positive ions of the etching gas become excessive due to the difference in etching rate. Then, a desired gap G is formed between the top portion 28b of the engaging convex portion 28 and the silicon oxide layer 13, that is, between the top portion 28b of the engaging convex portion 28 and the silicon oxide layer 13 of the stopper portion 29. By the way (FIG. 9B), the dry etching by the RIE method is finished.

Next, the silicon oxide layer 13 exposed in the groove 16 and the opening 27 is removed (FIG. 8C). As a result, the sensor body 2 is obtained, and then the support sensor 3 (not shown) is joined to the frame portion 26 of the silicon layer (substrate silicon) 14 so as not to contact the weight 25, whereby the acceleration sensor 1 is can get. The removal of the silicon oxide layer 13 can be performed, for example, by dry etching using a reactive gas.
In addition, there is no restriction | limiting in particular in the formation method of the mask pattern 31, For example, the method of forming by photolithography using a photosensitive resist, the method of arrange | positioning a resin layer and a metal layer, and patterning directly by this on a laser drawing etc. Can be used.
In the manufacturing method of the present invention, in the step of forming the frame portion 26 and the weight 25 on the silicon layer 14 (substrate silicon), the silicon oxide layer 13 of the stopper portion 29 protrudes from the four protruding portions 25B. Since the engaging convex portion 28 that reaches the tip portion 28a in a non-contact manner is formed by the RIE method, the structure of the stopper portion 29 is changed to a conventional stopper portion structure (a plurality of stopper portions structure) that seeks the ease of etching removal of the silicon oxide layer. There is no need for a structure having a small opening or a bar-like structure), and a plate-like structure can be obtained, and the strength is remarkably improved. Thereby, it is possible to manufacture a highly reliable acceleration sensor in which destruction such as damage to the beam is prevented even when excessive acceleration is applied.

The above-described embodiment of the acceleration sensor manufacturing method is an exemplification, and the present invention is not limited to this.
In the above-described embodiment, the piezoresistive acceleration sensor has been described as an example. However, the present invention is also applicable to a capacitive acceleration sensor.

  The present invention can be applied in various fields where a small and highly reliable acceleration sensor is required.

It is a top view which shows one Embodiment of the acceleration sensor of this invention. It is sectional drawing in the II line of the acceleration sensor shown by FIG. It is sectional drawing in the II-II line of the acceleration sensor shown by FIG. It is a top view of the weight which comprises the acceleration sensor shown by FIG. It is a fragmentary perspective view of the protrusion part which comprises the weight shown by FIG. It is a figure for demonstrating the other aspect of the convex part for engagement. It is a figure for demonstrating the other aspect of a stopper part. It is process drawing for demonstrating the manufacturing method of the acceleration sensor of this invention. It is a figure for demonstrating the side etching of the convex part for engagement. It is a top view which shows an example of the conventional acceleration sensor. It is sectional drawing in the III-III line of the acceleration sensor shown by FIG. It is sectional drawing in the IV-IV line of the acceleration sensor shown by FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Acceleration sensor 2 ... Sensor main body 3 ... Supporting substrate 11 ... SOI substrate 11 '... SOI wafer 12 ... Silicon layer (active layer silicon)
13 ... Silicon oxide layer 14 ... Silicon layer (substrate silicon)
DESCRIPTION OF SYMBOLS 21 ... Weight joint part 22 ... Beam 23 ... Frame part 24 ... Window part 25 ... Weight 25A ... Weight base 25B ... Weight protrusion part 26 ... Frame part 27 ... Opening part 28 ... Engaging convex part 28a ... Engaging convex part 28b ... the top of the engaging convex part 29 ... the stopper part 31 ... the mask pattern

Claims (4)

A frame part composed of an SOI (Silicon On Insulator) substrate having a three-layer structure of silicon layer (active layer silicon) / silicon oxide layer / silicon layer (substrate silicon);
Consisting of the silicon layer (active layer silicon), four beams projecting inward from each side of the frame, and a weight joint supported by the beams;
It consists of the silicon layer (substrate silicon), and protrudes from the base to the base part joined to the weight joint part via the silicon oxide layer and the four window parts surrounded by the four beams and the frame part. A weight composed of four projecting portions, a projecting portion projecting from each projecting portion, and a projecting portion having a step and a flat surface on the silicon layer (active layer silicon) side of the projecting portion;
It is composed of the silicon layer (active layer silicon), and includes at least four plate-like stopper portions laid on two sides sandwiching the corner portion of the frame portion,
The acceleration sensor according to claim 1, wherein a tip end side of the engaging convex portion protrudes below the stopper portion, and a predetermined gap is provided between a top portion of the engaging convex portion and the stopper portion.   The acceleration sensor according to claim 1, wherein the stopper portion has a triangular shape with a corner portion of the frame portion as one point.   The acceleration sensor according to claim 1 or 2, wherein a gap between the top of the engaging convex portion and the stopper portion is in a range of 5 to 30 µm. In the method of manufacturing the acceleration sensor,
In a silicon layer (active layer silicon) of an SOI (Silicon On Insulator) substrate having a three-layer structure of silicon layer (active layer silicon) / silicon oxide layer / silicon layer (substrate silicon), a frame portion and each of the frame portions Forming four beams projecting inward from the side, a weight joint supported by the beam, and four stoppers erected on the two sides sandwiching the corner of the frame portion;
A frame portion on the silicon layer (substrate silicon), a weight positioned in a non-contact manner inside the frame portion, and a base portion bonded and held to the weight joint portion via the silicon oxide layer; Four projecting parts projecting from the base part to four window parts surrounded by a beam and a frame part, and for engaging the projecting part projecting from the projecting part and reaching the lower part of the stopper part in a non-contact manner A step of forming a weight comprising a convex portion;
And a step of removing the exposed silicon oxide layer,
In the step of forming the frame portion and the weight on the silicon layer (substrate silicon), the silicon oxide layer is exposed, and further, side etching occurs on the engaging convex portion that contacts the silicon oxide, thereby causing the engagement. Opening an opening by dry etching by a RIE (Reactive Ion Etching) method through a mask pattern from the silicon layer (substrate silicon) side until the top of the joint protrusion is separated from the silicon oxide. A method for manufacturing a sensor.

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