JP2007132863A - Semiconductor acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize a sensor, improve its shock resistance, and reduce the manufacturing cost by facilitating its formation. <P>SOLUTION: An upper stopper 6 and a lower stopper 7 to be jointed to a support member 1 in the shape of a rectangular frame, cover a weight portion 4, having a stepped part 45 on its upper surface 44 and having a protruded part 5 on its undersurface 46, while forming air-gaps 47, 48. Rough surface portions 62, 72 are formed on faces facing the weight portion 4 of the upper stopper 6 and the lower stopper 7. The weight portion 4 is inclined, with respect to the support member 1 so that the air-gap 47 becomes wider, as it approaches the left end from the right end, by the deflection of a bending portion 2. When acceleration α is applied, a force F=Mα (M is the weight of the weight portion 4) is produced in the weight portion 4, according to the magnitude of the acceleration α. The bending portion 2 is bent due to the rocking of the weight portion 4 by the force F. As a result, the resistance value of each gauge resistance changes, and a sensor portion 3 detects the acceleration α by converting the change in the resistance value of each gauge resistance into a voltage signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor acceleration sensor used in, for example, an automobile, an aircraft, or a home appliance.

Conventionally, as disclosed in, for example, Patent Document 1, this type of semiconductor acceleration sensor includes a rectangular frame-shaped support portion and a weight portion (which is swingably supported by the support portion via a bending portion). (Weight part), a gauge resistor that detects the bending (deformation) of the bending part, and an upper cap (first stopper) and a lower cap (second stopper) that cover the bending part and the weight part are proposed. ing. A recess is formed in the upper cap and the lower cap to form an air gap (gap) between the bent portion and the weight portion. Further, the upper cap and the lower cap are provided with a plurality of stoppers (projections) on the bottom surface of the recess for reducing the impact when colliding with the weight portion.
JP 2000-338124 A (pages 5 to 8 and FIG. 2)

  However, in the conventional semiconductor acceleration sensor, if the gap between the first stopper or the second stopper and the weight portion is formed narrow in order to reduce the size, the first stopper or the second stopper There is a problem in that the first stopper or the second stopper and the weight portion are adsorbed when the support portion is joined. Further, when the first stopper or the second stopper is joined to the support portion, a positional deviation may occur, and the protrusions of the first stopper and the second stopper are accurately positioned at a desired position of the weight portion. There was also a problem that the impact resistance was reduced because it could not collide well. Further, since precise machining control is required when forming the recess of the first stopper, there is a problem that it is difficult to reduce the manufacturing cost.

  The present invention has been made in view of the above points, and the object of the present invention is to realize downsizing, improve impact resistance, and facilitate formation. An object of the present invention is to provide a semiconductor acceleration sensor capable of reducing the manufacturing cost.

  The invention according to claim 1 is based on a support portion formed in a frame shape by a semiconductor substrate, a flexure portion that protrudes from an inner surface of the support portion and bends when acceleration is applied, and a flexure of the flexure portion. A sensor part that converts the acceleration into an electrical signal, and a weight part that is spaced apart from the support part, has one end joined to the flexure part, and is swingably supported, and has a step part on the other end side of one surface And a protrusion provided on the other surface of the weight portion, and the support portion so as to cover the bent portion and the weight portion from the one surface side of the weight portion, and at least faces the weight portion A plate-like first stopper whose surface to be roughened is joined to the support portion so as to cover the flexible portion and the weight portion from the other surface side of the weight portion, and at least the weight portion A second stopper having a roughened recess formed on the opposing surface, the weight portion , And characterized by being inclined with respect to the support part so as to widen the gap between the end of the first stopper and the first surface toward the second end.

  The invention according to claim 2 is the invention according to claim 1, wherein a length a from the one end to the other end of the weight part and a distance b from the other end of the weight part to the projection part The ratio is 0.2 ≦ b / a ≦ 0.5.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, at least a spacer is provided between the first stopper and the support portion, and the flexible portion is the first stopper. A nitride film whose film thickness is controlled to be inclined with respect to the support portion is provided on the opposing surface.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the protrusion has a trapezoidal cross-sectional shape and is formed integrally with the weight portion.

  According to the present invention, the semiconductor acceleration sensor can be miniaturized, impact resistance can be improved, and manufacturing cost can be reduced by easily forming the semiconductor acceleration sensor.

  This embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view of the semiconductor acceleration sensor of the present embodiment. FIG. 2 is a schematic plan view of the semiconductor acceleration sensor of the present embodiment when the upper stopper is removed. FIG. 3 is a diagram showing the stress at the bending portion of the semiconductor acceleration sensor of the present embodiment. FIG. 1 shows an AA cross section of FIG. Also, the dimensions in FIG. 1 and FIG. 2 do not necessarily match, and a specific component may be emphasized only in one drawing.

  First, the basic configuration of this embodiment will be described. The semiconductor acceleration sensor of the present embodiment is installed in, for example, an automobile, an aircraft, or a home appliance, and detects applied acceleration. As shown in FIG. 1, a support portion 1, a flexure portion 2, and a sensor A portion 3, a weight portion 4, a protruding portion 5, an upper stopper 6, and a lower stopper 7 are provided.

  The support portion 1 is formed in a rectangular frame shape when viewed from the Y-axis direction in FIG. 1 by a semiconductor substrate such as an n-type SOI (Silicon On Insulator) substrate. The height of the support portion 1 (the length in the Y-axis direction in FIG. 1) is 400 μm. Further, the support portion 1 includes chamfered portions 11 and 11 on the inner side surfaces 10 and 10. The height of each chamfered portion 11 (the length in the X-axis direction in FIG. 1) is 10 μm. By providing the chamfered portions 11 and 11 as described above, it is possible to reduce stress concentration.

  The flexure 2 is thinner than the weight 4 in the Y-axis direction in FIG. 1 and protrudes from the inner side surface 10 of the support 1. In addition, the bending portion 2 is formed, for example, by a CVD (Chemical Vapor Deposition) method with a nitride film 82 having a film thickness of 150 nm to 200 nm on the upper surface 20 facing the upper stopper 6 together with the upper surface 12 of the support portion 1 and the upper surface 44 of the weight portion 4. I have. A more preferable film thickness of the nitride film 82 is 150 nm to 180 nm. Thereby, the bending part 2 inclines downward from the right end joined to the support part 1 toward the left end joined to the weight part 4, and separates the weight part 4 from the upper stopper 6. Note that the tilt angle is controlled by the thickness of the nitride film 82.

  As shown in FIG. 2, the sensor unit 3 includes four gauge resistors 30 (see FIG. 2), a plurality of diffusion resistance wirings 31, and a plurality of metal films 32. Yes. The four gauge resistors 30 are bridge-connected and are formed in the flexure 2 so as to detect the flexure (deformation) of the flexure 2 as a change in resistance value due to the piezoresistive effect. . Further, the four gauge resistors 30... Convert acceleration into an electrical signal based on the detected bending of the bending portion 2. Each diffusion resistance wiring 31 is a p + type diffusion resistance wiring, and is formed from the gauge resistance 30 to a predetermined portion of the support portion 1. Each metal film 32 is formed on the support portion 1 and connected to the diffusion resistance wiring 31. Each metal film 32 is bonded to the other end of a bonding wire (not shown) whose one end is externally connected.

  As shown in FIG. 1, the weight portion 4 is separated from the support portion 1, and the right end is joined to the bending portion 2 so as to be swingably supported. Slits 41 and 42 are formed between the outer side surfaces 40 and 40 of the weight portion 4 and the inner side surfaces 10 and 10 of the support portion 1. In the present embodiment, the width of the slits 41 and 42 (the distance between the inner surface 10 of the support portion 1 and the outer surface 40 of the weight portion 4) is set to 40 to 70 μm, but the above numerical range is an example. Therefore, it is not limited, and is appropriately set according to the application. The weight portion 4 includes chamfered portions 43 and 43 on the outer side surfaces 40 and 40. The height of each chamfered portion 43 (the length in the X-axis direction in FIG. 1) is 10 μm. By providing the chamfered portions 43 and 43 as described above, it is possible to reduce stress concentration. Further, the weight portion 4 is provided with a step portion 45 at the left end of the upper surface 44. Such a weight portion 4 is inclined with respect to the support portion 1 such that a gap 47 between the upper surface 44 and the upper stopper 6 becomes wider from the right end toward the left end due to the bending of the bending portion 2.

  The protrusion 5 is rectangular when viewed from the Y-axis direction in FIG. 1 by etching the SOI substrate, for example, and has a cross-sectional shape (shape viewed from the Z-axis direction in FIG. 1) as a trapezoidal shape. 4 is formed integrally with the support portion 1, the bending portion 2, and the weight portion 4. Further, the protrusion 5 is formed in a taper shape on all four sides. Here, the ratio b between the length a from the apex of the chamfered portion 43 at the right end of the weight portion 4 to the apex of the chamfered portion 43 at the left end and the distance b from the left end of the weight portion 4 to the left end of the lower surface 50 of the projection portion 5 / A will be described with reference to FIG. From FIG. 3, in the range from 0 to 0.5, as b / a increases, the stress generated in the flexure 2 decreases. On the contrary, when b / a becomes small, the stress of the bending part 2 becomes large. From the above, when the range of b / a is 0.2 ≦ b / a ≦ 0.5, the stress of the bending portion 2 becomes a small value, and good characteristics can be obtained. Instead of the length a, the length a ′ from the right end to the left end of the outer side surface 40 of the weight part 4 is used, and instead of the distance b, the left side of the outer side surface 40 of the weight part 4 extends from the left side of the projection part 5. It is good also as distance b 'to any position. In the X-axis direction in FIG. 1, the width of the chamfered portion 43 and the width of the inclined portion of the protruding portion 5 are about an error in view of the lengths a and a ′ and the distances b and b ′. Even as a ′, the stress of the bending portion 2 can obtain substantially the same characteristics as FIG. 3 with respect to b ′ / a ′.

  The upper stopper 6 is formed of heat-resistant glass having a thermal expansion coefficient substantially equal to that of the support portion 1 and is provided on the upper surface 12 of the support portion 1 so as to cover the bent portion 2 and the weight portion 4 from the upper surface 44 side of the weight portion 4. The support portion 1 is bonded by anodic bonding through the bonded aluminum thin film 60. The upper stopper 6 has a thickness in the Y-axis direction of FIG. Further, the upper stopper 6 is subjected to a wet etching process using an HF solution, a sand blast process, a dry etching process using RIE (Reactive Ion Etching), or the like, so that a rough surface portion 62 is formed on at least a portion of the lower surface 61 facing the weight portion 4. It has. The rough surface portion 62 is for preventing the surface portion 44 from adsorbing to the upper surface 44 of the weight portion 4, and is roughened in a range where the surface roughness is 4 μm or less. A more preferable range of the surface roughness of the rough surface portion 62 is about 2 μm.

  The bonding aluminum thin film 60 functions as a spacer, and the gap 47 can be widened by the thickness of the bonding aluminum thin film 60. Further, the length of the upper stopper 6 can be increased so that the upper stopper 6 completely covers the bent portion 2 up to the right end without contacting the bent portion 2. Thereby, the bending part 2 can be more reliably protected by the upper stopper 6. The film thickness of the bonding aluminum thin film 60 is not limited, and can be set as appropriate according to the application.

  The lower stopper 7 is formed of heat-resistant glass having a thermal expansion coefficient substantially equal to that of the support portion 1 and is joined to the support portion 1 by anodic bonding so as to cover the bent portion 2 and the weight portion 4 from the lower surface 46 side of the weight portion 4. is doing. The lower stopper 7 has a thickness of 500 μm in the Y-axis direction of FIG. A recess 70 is formed on the upper surface 71 of the lower stopper 7 facing the weight 4 by, for example, etching or sandblasting. The depth of the recess 70 is 10 μm. A gap 48 is formed between the recess 70 and the weight portion 4. Further, the lower stopper 7 is formed at least on the bottom surface of the recess 70 in the upper surface 71 by performing a wet etching process using an HF solution, a sand blast process, a dry etching process using RIE (Reactive Ion Etching), or the like. 4 is provided with a rough surface portion 72 at a portion facing 4. The rough surface portion 72 is for preventing the surface portion from adsorbing to the lower surface 46 of the weight portion 4 and the protruding portion 5, and the surface roughness is roughened in a range of 4 μm or less. A more preferable range of the surface roughness of the rough surface portion 72 is about 2 μm.

  Next, the manufacturing method of the semiconductor acceleration sensor of this embodiment is demonstrated using FIG. First, the manufacturing method of the support part 1, the bending part 2, and the weight part 4 is demonstrated. First, oxide films 81 are formed on the upper and lower surfaces of the n-type SOI substrate 80 by thermal oxidation. The SOI substrate 80 includes a Si support substrate 800, an intermediate oxide film 801, and a Si active layer 802. After the oxide film 81 is formed, a photolithographic process is performed to open a window at a desired location, and p-type impurity implantation and diffusion processes are repeated to form the gauge resistor 30 and the diffusion resistance wiring 31. Subsequently, a nitride film 82 is formed with a film thickness of less than 200 nm on the oxide films 81 on the upper and lower surfaces of the SOI substrate 80 by a CVD method. After the nitride film 82 is formed, a photolithography process is performed to open a window at a desired location on the SOI substrate 80. Thereafter, the metal film 32 and the bonding aluminum thin film 60 are formed by a sputtering method.

  Thereafter, a photolithography process is performed on the lower surface of the SOI substrate 80, and the oxide film and the nitride film formed on the lower surface are removed by etching to open a window. Subsequently, a thin portion including the bent portion 2 is formed around the weight portion 4 by performing anisotropic etching to a predetermined depth. After forming the thin portion, anisotropic etching is further performed around the weight portion 4 to form the slits 41 and 42. At this time, a plurality of chamfered portions 11, 11, 43, 43 are also formed. Thereafter, by performing a photolithography process and anisotropic etching on the upper surface of the SOI substrate 80, the thin portion other than the bent portion 2 is removed, and the support portion 1 and the weight portion 4 are formed. At this time, the bending part 2 warps and falls downward.

  Then, the manufacturing method of the upper stopper 6 and the lower stopper 7 is demonstrated. First, anisotropic etching is performed to form the recess 70 in the lower stopper 7. After the recess 70 is formed, the upper stopper 6 and the lower stopper 7 are wet-etched with an HF solution to form rough surface portions 62 and 72 at portions facing the weight portion 4. After the rough surface portions 62 and 72 are formed, the upper stopper 6 is bonded to the bonding aluminum thin film 60 by anodic bonding, and the lower stopper 7 is directly bonded to the lower surface 13 of the support portion 1 by anodic bonding. At this time, since the rough surface portions 62 and 72 are formed on the upper stopper 6 and the lower stopper 7, the upper stopper 6 or the lower stopper 7 and the weight portion 4 are not adsorbed.

  Next, the operation of the semiconductor acceleration sensor of this embodiment will be described with reference to FIG. First, when the acceleration α is applied in the Y-axis direction in FIG. 1, a force F = Mα (M is the weight of the weight portion 4) is generated in the weight portion 4 in accordance with the magnitude of the acceleration α. Subsequently, the bending portion 2 is bent as the weight portion 4 is swung by the force F. As a result, a stress is generated in the bent portion 2 and the resistance value of each gauge resistor 30 changes. Finally, the sensor unit 3 detects the acceleration α by taking out the change in resistance value of each gauge resistor 30 as a voltage signal.

  Even when the weight portion 4 collides with the upper stopper 6 during the operation of the semiconductor acceleration sensor of the present embodiment as described above, the impact can be reduced by the step portion 45. Even if the weight portion 4 collides with the lower stopper 7, the impact can be reduced by the projection portion 5.

  As described above, according to the present embodiment, the upper stopper 6 or the lower stopper 7 is roughened, the protrusion 5 and the step 45 are provided on the weight 4, and the weight 4 is inclined with respect to the support 1. Thus, when the upper stopper 6 or the lower stopper 7 and the support portion 1 are joined, the upper stopper 6 or the lower stopper 7 and the weight portion 4 can be prevented from being attracted, and the weight portion 4 collides with the upper stopper 6. Sometimes the step 45 can be used as a stopper to reduce the stress of the flexure 2 and to shape the upper stopper 6 in order to form a gap 47 between the upper stopper 6 and the weight 4. There is no need to do. Accordingly, it is not necessary to provide a large gap between the upper stopper 6 or the lower stopper 7 and the weight portion 4 in advance, and the upper stopper 6 or the lower stopper 7 and the Since the gaps 47 and 48 between the weight part 4 can be formed, the semiconductor acceleration sensor can be downsized, the impact resistance can be improved, and the formation can be easily performed. Manufacturing costs can be reduced.

  Further, by setting the ratio of the length a from one end of the weight part 4 to the other end to the distance b from the other end of the weight part 4 to the projection part 5 to be 0.2 ≦ b / a ≦ 0.5, The stress of the bending part 2 can be reduced more and impact resistance can be improved more.

  Further, since the bent portion 2 is warped by the nitride film 82 of the bent portion 2, the weight portion is formed so that the gap 47 between the upper stopper 6 and the weight portion 4 becomes wider from one end of the weight portion 4 to the other end. 4 can be easily inclined with respect to the support portion 1.

  By forming the weight part 4 and the protrusion part 5 integrally, the coefficient of thermal expansion of the weight part 4 and the protrusion part 5 can be made equal, so that favorable temperature characteristics can be obtained.

It is a schematic sectional drawing of the semiconductor acceleration sensor of this embodiment by this invention. It is a schematic plan view of a semiconductor acceleration sensor same as the above. It is a figure which shows the stress of the bending part of a semiconductor acceleration sensor same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support part 2 Bending part 3 Sensor part 4 Weight part 44 Upper surface 45 Step part 46 Lower surface 47, 48 Cavity 5 Projection part 6 Upper stopper 62 Rough surface part 7 Lower stopper 72 Rough surface part

Claims (4)

A support portion formed in a frame shape by a semiconductor substrate;
Projecting from the inner surface of the support, and flexed when applied with acceleration;
A sensor unit that converts the acceleration into an electrical signal based on the deflection of the deflection unit;
A weight portion that is spaced apart from the support portion, has one end joined to the flexure portion and is swingably supported, and has a step portion on the other end side of one surface;
A protrusion provided on the other surface of the weight portion;
A plate-like first stopper that is joined to the support portion so as to cover the bent portion and the weight portion from the one surface side of the weight portion, and at least a surface facing the weight portion is roughened; ,
The second portion is joined to the support portion so as to cover the bent portion and the weight portion from the other surface side of the weight portion, and a roughened concave portion is formed at least on a surface facing the weight portion. With a stopper and
The semiconductor is characterized in that the weight portion is inclined with respect to the support portion so as to widen a gap between the one surface and the first stopper as it goes from the one end to the other end. Acceleration sensor.   The ratio of the length a from the one end to the other end of the weight portion and the distance b from the other end of the weight portion to the projection portion is 0.2 ≦ b / a ≦ 0.5. The semiconductor acceleration sensor according to claim 1. At least a spacer is provided between the first stopper and the support part,
3. The semiconductor acceleration sensor according to claim 1, wherein the bending portion includes a nitride film whose thickness is controlled so as to be inclined with respect to the support portion on a surface facing the first stopper. 4. .   The semiconductor acceleration sensor according to claim 1, wherein the protrusion has a trapezoidal cross-sectional shape and is formed integrally with the weight portion.

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