JP2010078425A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensor of which the characteristic is stable to a stress in assembling. <P>SOLUTION: The acceleration sensor includes a movable electrode 13, first and second fixed electrodes 11 and 12, a substrate 20 and fixed electrode support parts 25. The first and second fixed electrodes 11 and 12 are so disposed as to be opposed to the movable electrode 13. The substrate 20 is for supporting the first and second fixed electrodes 11 and 12. The fixed electrode support parts 25 support the first and second fixed electrode 11 and 12 on the substrate 20 and the respective areas contacting with the first and second fixed electrodes 11 and 12 are smaller than the first and second fixed electrodes 11 and 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an acceleration sensor, and more particularly to a capacitance type acceleration sensor.

  As one of conventional Z-axis acceleration sensors that detect acceleration in a direction perpendicular to the substrate surface (Z-axis direction), there is a capacitance-type acceleration sensor that detects a change in capacitance due to acceleration. Such a Z-axis acceleration sensor is disclosed in, for example, Japanese Patent No. 3914694.

  The acceleration sensor described in this publication includes a substrate, first and second fixed electrodes, a movable electrode, a mass body, and a connecting portion. Each of the first and second fixed electrodes is formed on a substrate. The movable electrode is provided facing the first and second fixed electrodes. The mass body is movable in response to acceleration in a direction perpendicular to the substrate, and is connected to the movable electrode by a connecting portion.

In this acceleration sensor, when an acceleration in a direction perpendicular to the substrate is applied, an inertial force acts on the mass body, and the mass body is displaced in a direction opposite to the applied acceleration. Due to the displacement of the mass body, the movable electrode coupled to the mass body via the coupling portion is displaced like a seesaw. That is, one end of the movable electrode is displaced upward with respect to the substrate, and the other end is displaced downward. As a result, the capacitance C1 formed between the movable electrode and the first fixed electrode and the capacitance C2 formed between the movable electrode and the second fixed electrode are displaced. The applied acceleration is measured from the displacement of the capacitors C1 and C2.
Japanese Patent No. 3914694

  In the acceleration sensor as described above, when measuring acceleration from the capacitors C1 and C2, it is necessary to convert the capacitors C1 and C2 into electric signals. Therefore, the acceleration sensor chip is assembled into a mold resin package having the same shape as a general IC together with a specific application IC (hereinafter referred to as ASIC) chip that reads changes in the capacitors C1 and C2 and converts them into electrical signals. It is supplied to the market as an acceleration sensor that is easy to use at a low price.

  However, in the IC mold resin package, when the substrate of the acceleration sensor chip is fixed to the IC lead frame with a die bond resin (adhesive) or encapsulated with the mold resin after chip mounting, due to thermal stress due to a difference in thermal expansion coefficient, etc. There arises a problem that the substrate of the acceleration sensor chip is warped.

  Since each of the first and second fixed electrodes is formed on the substrate of the acceleration sensor chip, the first and second fixed electrodes also warp in conjunction with the warpage of the substrate. As a result, the interelectrode distance between the movable electrode and the first fixed electrode and the interelectrode distance between the movable electrode and the second fixed electrode change slightly. As a result, the capacitance C1 formed by the movable electrode and the first fixed electrode and the capacitance C2 formed by the movable electrode and the second fixed electrode vary due to factors other than acceleration. For this reason, the Z-axis acceleration sensor has a drawback that its characteristics are likely to change compared to the X-axis acceleration sensor.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an acceleration sensor having stable characteristics against stress during assembly.

  The acceleration sensor of the present invention has a movable electrode, a fixed electrode, a support member, and a fixed electrode support part. The fixed electrode is disposed so as to face the movable electrode. The support member is for supporting the fixed electrode. The fixed electrode support portion supports the fixed electrode on the support member, and the area in contact with the fixed electrode is smaller than the area of the fixed electrode.

  According to the acceleration sensor of the present invention, even if stress during assembly is applied to the acceleration sensor, the area of the fixed electrode supporting portion that is in contact with the fixed electrode is smaller than the area of the fixed electrode, so the stress is applied to the entire fixed electrode. Is not transmitted. Therefore, the problem that the fixed electrode warps due to external stress can be suppressed, and the change in the spatial distance between the movable electrode and the fixed electrode can be reduced. Therefore, the variation in characteristics is unlikely to occur because the variation in detection capacitance is small.

Hereinafter, the present embodiment will be described with reference to the drawings.
(Embodiment 1)
First, the configuration of the acceleration sensor according to the present embodiment will be described.

  FIG. 1 is a plan view showing the configuration of the acceleration sensor according to Embodiment 1 of the present invention. FIG. 2 is a schematic cross-sectional view of a portion taken along line II-II in FIG. FIG. 3 is a schematic cross-sectional view of a portion along line III-III in FIG. 1 to 3, the acceleration sensor according to the present embodiment mainly includes a first fixed electrode 11, a second fixed electrode 12, a movable electrode 13, an inertia mass body 14, and a link. The beam 15, the torsion beam 16, the anchor 17, the substrate 20, and the fixed electrode support portion 25 are provided.

  The substrate 20 is a support member for supporting the first and second fixed electrodes 11 and 12. On the surface of the substrate 20, a first silicon oxide film 21, a first sacrificial layer film 22, a second silicon oxide film 23, and a silicon nitride film 24 are sequentially stacked.

  The fixed electrode support portion 25 supports the first and second fixed electrodes 11 and 12 on the substrate 20 via the first silicon oxide film 21. In the first and second fixed electrodes 11 and 12, a plurality of etching holes 27 having a square shape with a side of several μm are typically formed. Electrical wirings 18 and 19 of the first and second fixed electrodes 11 and 12 are formed on the side surfaces of the first and second fixed electrodes 11 and 12. The silicon oxide film 21, the first sacrificial layer film 22, the second silicon oxide film 23 and the silicon nitride film 24 ensure electrical insulation between the first and second fixed electrodes 11 and 12 and the substrate 20. An insulating film is formed for this purpose. The fixed electrode support part 25 has one fixed electrode support column for each one fixed electrode of the first and second fixed electrodes 11 and 12 in the present embodiment. The fixed electrode support portion 25 is formed immediately below the center of gravity of the first and second fixed electrodes 11 and 12.

  The anchor 17 is supported on the substrate 20 via the electric wiring 101 of the movable electrode 13, the first sacrificial layer film 22, and the first silicon oxide film 21.

  The movable electrode 13 is arranged above the first fixed electrode 11 and the second fixed electrode 12 so as to face each of them with a spatial distance d1 and d2. The movable electrode 13 is supported by the anchor 17 via the torsion beam 16 so as to be rotatable about the torsion beam 16 as a central axis. The torsion beam 16 is disposed on a line passing through the center of the movable electrode 13 in a plan view (FIG. 1). The movable electrode 13 is electrically connected to the electrical wiring 101 via the anchor 17.

  The movable electrode 13 and the first fixed electrode 11 constitute a capacitor C1, and the movable electrode 13 and the second fixed electrode 12 constitute a capacitor C2.

  The inertial mass body 14 is supported by the movable electrode 13 via the link beam 15 so as to be vertically displaced with respect to the surface of the substrate 20. The link beam 15 is arranged at a position away from one line passing through the center of the torsion beam 16 in a plan view (FIG. 1).

  The fixed electrode support portion 25 is in contact with a part of each of the first and second fixed electrodes 11 and 12, and the area in contact with the first and second fixed electrodes 11 and 12 is the first and second fixed electrodes. 11 and 12 are smaller than the area in plan view. Thus, a gap 26 having a height corresponding to the approximate film thickness of the first sacrificial layer film 22 is formed below the first and second fixed electrodes 11 and 12 other than the fixed electrode support portion 25. The first sacrificial layer film 22 remains below the electrical wirings 18 and 19 of the first and second fixed electrodes 11 and 12.

  The first and second fixed electrodes 11 and 12 are formed of, for example, a polysilicon (polycrystalline silicon) film. Since the movable electrode 13, the inertial mass body 14, and the anchor 17 are coupled to each other via the link beam 15 and the torsion beam 16, they are simultaneously formed by, for example, a polysilicon film.

Next, a method for manufacturing the acceleration sensor according to the present embodiment will be described.
FIG. 4 is a schematic cross-sectional view taken along the line II-II in FIG. 1 showing the method for manufacturing the acceleration sensor according to the first embodiment. First, the first silicon oxide is typically formed on the substrate 20 with a thickness of about 2 μm as an electrically insulating film by, for example, thermal oxidation or CVD (Chemical Vapor Deposition) (chemical vapor deposition). A film 21 is formed. Subsequently, a PSG (Phospho-Silicate-Glass) film (silicon containing phosphorus element) is formed on the first silicon oxide film 21 by a CVD method or the like, preferably with a thickness of about 0.5 μm, which is easily wet-etched. A first sacrificial layer film 22 such as an oxide film is formed. Next, on the first sacrificial layer film 22, for example, an LP (Low Pressure) CVD method (low pressure chemical vapor deposition method) is typically used. A crystalline silicon) film is deposited.

  The polysilicon film is patterned by, for example, a dry etching method, whereby the first fixed electrode 11, the electric wiring 18 (FIG. 1), the second fixed electrode 12, and the electric wiring 19 (FIG. 1) The electric wiring 101 (FIG. 3) of the movable electrode 13 is collectively formed from the polysilicon film. Thereafter, a second silicon oxide film 23 is formed on the entire substrate 20. Next, the second silicon is exposed until the upper surfaces of the first fixed electrode 11, the second fixed electrode 12, and the electrical wirings 18, 19, 101 are exposed by, for example, CMP (Chemical Mechanical Polishing) technology (chemical mechanical polishing technology). The oxide film 23 is removed. Thereby, the heights of the upper surfaces of the second silicon oxide film 23, the first fixed electrode 11, the second fixed electrode 12, and the electric wirings 18, 19, 101 are made uniform. Thereafter, a silicon nitride film 24 is formed on the entire planarized surface. Thereafter, the silicon nitride film 24 on the portions to be the first fixed electrode 11, the second fixed electrode 12, and the anchor 17 is opened by photolithography and dry etching techniques.

  Subsequently, the exposed first fixed electrode 11 and second fixed electrode 12 are typically formed into a plurality of square shapes having a side of several μm as shown in FIG. 14 by photolithography and dry etching techniques. The etching hole 27 is formed.

  FIG. 14 is a bird's-eye view of the acceleration sensor of the present embodiment. The movable electrode 13, the inertial mass body 14, the link beam 15 and the torsion beam 16, and the first and second fixed electrodes 11 and 12 on the substrate 20 are shown. FIG. 5 is a diagram in which the electric wires 18 and 19 for the first and second fixed electrodes and the electric wire 101 for the movable electrode 13 are separated for convenience.

  As shown in FIGS. 2 and 14, the plurality of etching holes 27 allow the etching solution to flow down from the upper side of the first and second fixed electrodes 11, 12 during the etching of the first sacrificial layer film 22 in a later step. It is for passing to the side. In the plurality of etching holes 27, when the first sacrificial layer film 22 is etched in a later step, a part of the first sacrificial layer film 22 remains as the fixed electrode support portion 25, and all other portions are removed by etching. And arranged to disappear.

  Next, a second sacrificial layer film 28 such as a PSG film, typically about 2 μm thick, is formed on the entire surface of the substrate 20. Thereafter, the second sacrificial layer film 28 at the site where the anchor 17 is to be installed is removed by etching. As a result, a groove 28 a reaching a part of the surface of the electric wiring 101 of the movable electrode 13 is formed in the second sacrificial layer film 28. Subsequently, a polysilicon film typically having a thickness of about 4 μm is deposited on the entire surface of the second sacrificial layer film 28 by, eg, LPCVD. This polysilicon film is formed so as to fill the groove 28a. Next, the polysilicon film is patterned by, for example, a dry etching method. Thereby, the inertia mass body 14, the movable electrode 13, the anchor 17, the link beam 15 and the torsion beam 16 are simultaneously formed from the polysilicon film. A plurality of etching holes 102 having a square shape with a side of several μm are typically formed at the same time as shown in FIG. 1 and FIG.

  Thereafter, the first sacrificial layer film 22 and the second sacrificial layer film 28 temporarily fixing the movable electrode 13 are removed by etching with a highly corrosive etching solution. In this etching, the etching solution reaches the lower side of the movable electrode 13 through the etching hole 102, whereby the second sacrificial layer film 28 on the lower side of the movable electrode 13 is removed. Furthermore, the etching solution reaches the lower side of the first and second fixed electrodes 11 and 12 through the etching holes 27 of the first and second fixed electrodes 11 and 12, thereby the first and second fixed electrodes 11 and 12. The first sacrificial layer film 22 below 12 is removed leaving a portion that becomes the fixed electrode support portion 25 (FIG. 2).

  Further, in this etching, the second silicon oxide film 23 where the silicon nitride film 24 is not formed is removed. As a result, the second silicon oxide film 23 around the first and second fixed electrodes 11 and 12 is removed by etching.

  Referring to FIG. 2, fixed electrode support portion 25 and void 26 are formed by a release process in which first and second sacrificial layer films 22 and 28 are etched. Further, a gap is generated in the lower region of the movable electrode 13, the inertia mass body 14, the bending beam 103, and the torsion beam 104, and these are movable. For example, in the case where the second sacrificial layer films 22 and 28 are wet-etched using hydrofluoric acid that easily dissolves the PSG film in a short time, a silicon nitride film 24 that is difficult to be etched is formed on the portion that is not to be etched. Therefore, an acceleration sensor having a cross-sectional structure as shown in FIGS. 2 and 3 is manufactured by appropriately adjusting the etching time at the time of release.

  Thereafter, in order to connect the electrical wirings 18 and 19 of the first and second fixed electrodes and the electrical wiring 101 of the movable electrode 13 and the ASIC by wire bonding, a metal pad (not shown) is provided as an electrode pad at the end of these wirings. It is formed. Thereby, the manufacturing process of the acceleration sensor chip is completed.

  The acceleration sensor chip is sealed with a hermetically sealed protective cap having a recess made of, for example, low melting point powder glass. Next, the substrate of the acceleration sensor chip and the substrate of the ASIC chip are die-bonded to the IC lead frame with a die-bonding resin. Subsequently, wire bonding is performed using a gold wire, and the acceleration sensor chip and the ASIC chip are connected to each other. Finally, a mold resin is used to fill the mold resin, thereby manufacturing a Z-axis acceleration sensor in a resin mold package that can be handled in the same manner as a general IC.

Next, the operation of the acceleration sensor according to the present embodiment will be described.
Referring to FIG. 2, when acceleration in the Z-axis direction (normal direction of the surface of substrate 20) is applied to the acceleration sensor, an inertial force is generated in a direction opposite to the acceleration direction. When this inertial force acts on the inertial mass body 14, the inertial mass body 14 moves in the Z-axis direction. At this time, the torsion beam 16 is formed on a line passing through the center of the movable electrode 13, and the link mass 15 connects the inertial mass body 14 and the movable electrode 13 at a position away from the line passing through the center. Therefore, torque is generated in the movable electrode 13 around the torsion beam 16 by the inertial force transmitted from the inertial mass body 14 to the link beam 15. Thereby, the movable electrode 13 rotates around the torsion beam 16. When the movable electrode 13 rotates, one of the spatial distances d1 and d2 between the lower surface of the movable electrode 13 and the first fixed electrode 11 and the second fixed electrode 12 becomes closer and the other becomes longer. The detection capacity of the capacitor increases as the spatial distance decreases and decreases as the distance increases. Accordingly, since the detection capacities of the capacitors C1 and C2 change due to changes in the spatial distances d1 and d2, acceleration is detected from the change in the detection capacities.

Next, the effect of the acceleration sensor of this embodiment will be described.
In the conventional general Z-axis acceleration sensor, when the substrate 1200 and the ASIC chip 1401 of the acceleration sensor chip 1400 are fixed on the IC lead frame 1402 with a die bond resin (adhesive) 1403 as shown in FIGS. In addition, when encapsulating with the mold resin 1404 after chip mounting, the substrate 1200 of the acceleration sensor chip warps due to thermal stress due to a difference in thermal expansion coefficient or the like, and the first fixed electrode 1201 and the second fixed electrode 1201 formed on the substrate 1200 There is a problem that the fixed electrode 1202 also warps in conjunction.

  On the other hand, in the acceleration sensor of the present embodiment, the fixed electrode support portion 25 is in contact with a part of the first fixed electrode 11 and the second fixed electrode 12 rather than the entire surface, and the fixed electrode support portion 25 is the first fixed electrode support portion 25. The areas in contact with the fixed electrode 11 and the second fixed electrode 12 are smaller than the areas of the first and second fixed electrodes 11 and 12, respectively.

  Therefore, even if the substrate 20 is warped due to the stress of the die bond resin or the stress of the mold resin, the stress transmitted to the first fixed electrode 11 and the second fixed electrode 12 becomes very small. Therefore, warpage of the first and second fixed electrodes 11 and 12 is suppressed, and changes in the spatial distances d1 and d2 between the first fixed electrode 11 and the second fixed electrode 12 and the movable electrode 13 are also suppressed. Therefore, the capacitance values of the detection capacitor C1 formed between the first fixed electrode 11 and the movable electrode 13 and the detection capacitor C2 formed between the second fixed electrode 12 and the movable electrode 13 are assembled. It is possible to obtain an acceleration sensor having stable characteristics by suppressing the change due to the stress of time.

(Embodiment 2)
FIG. 5 is a schematic cross-sectional view of the acceleration sensor according to Embodiment 2 of the present invention. Compared with the configuration of the first embodiment, the acceleration sensor of the present embodiment includes a plurality of fixed electrode support portions 25 with respect to one fixed electrode of each of the first fixed electrode 11 and the second fixed electrode 12. This is mainly different in that it has a fixed electrode support column 29.

  As shown in FIGS. 5 and 15, two fixed electrode support columns 29 are formed immediately below the vicinity of the center of gravity of the first fixed electrode 11 and the second fixed electrode 12.

  In the method of manufacturing the acceleration sensor according to the present embodiment, the fixed electrode support column 29 is one fixed electrode each of the first fixed electrode 11 and the second fixed electrode 12 when the first sacrificial layer film 22 is etched. Two support pillars of a predetermined size remain immediately below the vicinity of the center of gravity, and all other portions are formed by etching away and disappearing.

  In addition, since the structure and manufacturing method other than this of this Embodiment are the same as that of Embodiment 1 mentioned above, the same code | symbol is attached | subjected about the same element and the description is abbreviate | omitted.

  In the first embodiment described above, the first fixed electrode 11 and the second fixed electrode 12 are fixed electrode support portions 25 having one fixed electrode support column installed immediately below the position of the center of gravity of each fixed electrode. Is supported by However, if the warping of the fixed electrode can be suppressed by the stress at the time of assembly of the acceleration sensor chip, the fixed electrode supporting column 25 is not limited to one, and there are a plurality of fixed electrode supporting columns as shown in FIG. May be.

  The acceleration sensor of the present embodiment is not affected by stress during assembly in a wide area of the first and second fixed electrodes 11 and 12 other than the area in contact with the plurality of fixed electrode support columns 29. As shown in FIGS. 5 and 15, for example, even if two fixed electrode support columns 29 are installed immediately below the positions of the center of gravity of the first fixed electrode 11 and the second fixed electrode 12, the first fixed electrode 11 and the first fixed electrode 11 It is possible to prevent the second fixed electrode 12 from warping.

  According to the present embodiment, it is possible to obtain an acceleration sensor with stable characteristics whose characteristics do not change due to stress during assembly. In addition, the acceleration sensor of the present embodiment has a plurality of fixed electrode support columns 29, so that when the acceleration is applied to the acceleration sensor chip from the outside, the first and second fixed electrodes 11 and 12 are not easily deformed. There are advantages. Therefore, the acceleration sensor according to the present embodiment has an effect of suppressing characteristic fluctuation due to acceleration applied from the outside in addition to the effect of suppressing characteristic fluctuation due to stress during assembly.

(Embodiment 3)
FIG. 6 is a schematic plan view showing the configuration of the acceleration sensor according to Embodiment 3 of the present invention. FIG. 16 is a bird's-eye view of the acceleration sensor of the present embodiment. FIG. 7 is a schematic sectional view taken along line VII-VII in FIG. FIG. 8 is a schematic sectional view taken along line VIII-VIII in FIG. The acceleration sensor of the present embodiment is mainly different from the configuration of the first embodiment in the configuration of the first and second fixed electrodes 11 and 12 and the fixed electrode support portion 25.

  In FIG. 6, the movable electrode 13, the inertial mass body 14, the link beam 15 and the torsion beam 16 in Embodiment 3 of the present invention are omitted. On the other hand, in FIG. 7 and FIG. 8, the movable electrode 13, the inertia mass body 14, the link beam 15, and the torsion beam 16 are not omitted. With reference to FIGS. 6 and 7, end portions 66 are arranged at the four corners of the first fixed electrode 11 and the second fixed electrode 12 in a plan view. End portions 66 of the first fixed electrode 11 and the second fixed electrode 12 in plan view are arranged so as to be in contact with the fixed electrode support portion 25. Approximate thickness of the first sacrificial layer film 22 between the central portion, which is a portion other than the end portion 66 in plan view, of the first fixed electrode 11 and the second fixed electrode 12 and the substrate 20 (support member). A gap 26 having a height corresponding to is disposed.

  In the acceleration sensor manufacturing method according to the present embodiment, as shown in FIG. 7, a polysilicon film is typically deposited on the first sacrificial layer film 22 to a thickness of about 0.5 μm, for example, by LPCVD. The The polysilicon film is patterned by, for example, a dry etching method, so that the first fixed electrode 11, the second fixed electrode 12, the electric wirings 18 and 19, and the electric wiring 101 of the movable electrode 13 are polycrystallized. It is formed from silicon at once. At the same time, end portions 66 are formed at the four corners of the first fixed electrode 11 and the second fixed electrode 12. Thereafter, a second silicon oxide film 23 is formed on the entire substrate 20. Next, the second silicon oxide film 23 is formed until the upper surfaces of the first fixed electrode 11, the second fixed electrode 12, the electric wirings 18 and 19, and the electric wiring 101 of the movable electrode 13 are exposed by, for example, CMP technology. Removed. As a result, the heights of the upper surfaces of the second silicon oxide film 23, the first fixed electrode 11, the second fixed electrode 12, the electric wires 18, 19 and the electric wire 101 of the movable electrode 13 are aligned. It is done. Thereafter, a silicon nitride film 24 is formed on the entire planarized surface. Thereafter, the silicon nitride film 24 on the portions to be the first fixed electrode 11, the second fixed electrode 12, and the anchor 17 is opened by photolithography and dry etching techniques.

  Subsequently, the exposed first fixed electrode 11 and second fixed electrode 12 are typically formed into a plurality of square shapes having a side of several μm as shown in FIG. 16 by photolithography and dry etching techniques. The etching hole 27 is formed.

  FIG. 16 is a bird's-eye view of the acceleration sensor according to the present embodiment. The movable electrode 13, the inertia mass body 14, the link beam 15, the torsion beam 16, and the first and second fixed electrodes 11 and 12 on the substrate 20 are illustrated. FIG. 5 is a diagram in which the electric wires 18 and 19 for the first and second fixed electrodes and the electric wire 101 for the movable electrode 13 are separated for convenience.

  As shown in FIGS. 6, 7, and 16, the plurality of etching holes 27 are used to etch the first and second fixed electrodes 11, 12 when etching the first sacrificial layer film 22 in a later step. It is for passing from the upper side to the lower side. When the first sacrificial layer film 22 is etched, a part of the first sacrificial layer film 22 remains as the fixed electrode support portion 25 and all other portions are removed by etching. Arranged to do.

  Next, a second sacrificial layer film 28 such as a PSG film, typically about 2 μm thick, is formed on the entire surface of the substrate 20. Thereafter, the second sacrificial layer film 28 at the site where the anchor 17 is to be installed is removed by etching. Thereby, a groove reaching the partial surface of the electric wiring 101 of the movable electrode 13 is formed in the second sacrificial layer film 28. Subsequently, a polysilicon film typically having a thickness of about 4 μm is deposited on the entire surface of the second sacrificial layer film 28 by, eg, LPCVD. This polysilicon film is formed so as to fill the trench. Next, the polysilicon film is patterned by, for example, a dry etching method. Thereby, the inertia mass body 14, the movable electrode 13, the anchor 17, the link beam 15 and the torsion beam 16 are simultaneously formed from the polysilicon film. A plurality of etching holes 102 having a square shape with a side of several μm are typically formed at the same time as shown in FIG. 1 and FIG.

  Thereafter, the first sacrificial layer film 22 and the second sacrificial layer film 28 temporarily fixing the movable electrode 13 are removed by etching with a highly corrosive etching solution. In this etching, the etching solution reaches the lower side of the movable electrode 13 through the etching hole 102, whereby the second sacrificial layer film 28 on the lower side of the movable electrode 13 is removed. Furthermore, the etching solution reaches the lower side of the first and second fixed electrodes 11 and 12 through the etching holes 27 of the first and second fixed electrodes 11 and 12, thereby the first and second fixed electrodes 11 and 12. The first sacrificial layer film 22 below 12 is removed. Thereby, the fixed electrode support part 25 and the space | gap 26 are formed.

  Further, in this etching, the second silicon oxide film 23 where the silicon nitride film 24 is not formed is removed. As a result, the second silicon oxide film 23 around the first and second fixed electrodes 11 and 12 is removed by etching.

  Further, a gap is generated in the lower region of the movable electrode 13, the inertia mass body 14, the bending beam 103, and the torsion beam 104, and these are movable. As a result, as shown in FIG. 7, there is a gap between the first and second fixed electrodes 11 and 12 having the end 66 and the central portion of the first and second fixed electrodes 11 and 12 and the substrate 20. An acceleration sensor with 26 is manufactured.

  Since the further configuration and the manufacturing method of the present embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference numerals, and the description thereof is omitted.

  The acceleration sensor according to the present embodiment is in contact with the fixed electrode support portion 25 at the end portion 66, but the end portion 66 is thin with a thickness of several μm, and the influence of the warp of the substrate 20 is limited to the vicinity of the end portion 66. Other than that, the first and second fixed electrodes 11 and 12 are not easily affected in a wide area.

  Therefore, even if the substrate 20 is warped by the stress of the die bond resin or the stress of the mold resin, the stress transmitted to the first fixed electrode 11 and the second fixed electrode 12 is very small. Therefore, warpage of the first and second fixed electrodes 11 and 12 is suppressed, and changes in the spatial distances d1 and d2 between the first fixed electrode 11 and the second fixed electrode 12 are also suppressed. Therefore, the capacitance values of the detection capacitor C1 formed between the first fixed electrode 61 and the movable electrode 13 and the detection capacitor C2 formed between the second fixed electrode 62 and the movable electrode 13 are assembled. It is possible to obtain an acceleration sensor having stable characteristics by suppressing the change due to the stress of time.

(Embodiment 4)
In the first to third embodiments, the first and second fixed electrodes 11 and 12 are installed below the movable electrode 13. However, the function of the acceleration sensor is exhibited even if the fixed electrode is installed above the movable electrode. In this case, a structure for supporting the fixed electrode is necessary, but an airtight sealing protective cap is optimal as a structure that satisfies this requirement. In the present embodiment, first and second fixed electrodes 902 and 903 are provided above the movable electrode 13.

The structure of the acceleration sensor according to the present embodiment will be described.
FIG. 9 is a schematic cross-sectional view showing the configuration of the acceleration sensor according to Embodiment 4 of the present invention. FIG. 10 is a schematic cross-sectional view showing the configuration of the hermetic sealing protective cap in the fourth embodiment. Referring to FIGS. 9 and 10, the acceleration sensor according to the present embodiment mainly includes movable electrode 13, inertial mass body 14, anchor 17, substrate 20, and hermetically sealed protective cap (support member). 90, a first fixed electrode 902, a second fixed electrode 903, a first fixed electrode anchor 908, a second fixed electrode anchor 909, and a fixed electrode support portion 912.

  A first silicon oxide film 21, a second silicon oxide film 23, and a silicon nitride film 24 are sequentially stacked on the surface of the substrate 20.

  The movable electrode 13 is supported by the anchor 17 via a torsion beam so as to be rotatable about a torsion beam 16 (not shown) as a central axis. The movable electrode 13 is electrically connected to the electric wiring 901 of the movable electrode 13 via the anchor 17. A torsion beam 16 (not shown) is disposed on a line passing through the center of the movable electrode 13. The first silicon oxide film 21, the second silicon oxide film 23, and the silicon nitride film 24 form an insulating film for ensuring electrical insulation from the movable electrode 13 and the like.

  The inertial mass body 14 is supported by the movable electrode 13 via a link beam 15 (not shown) so as to be vertically displaced with respect to the surface of the substrate 20. The link beam 15 (not shown) is arranged at a position away from one line passing through the center of the torsion beam 16.

  The anchor 17 is supported on the substrate 20 via the electric wiring 901 of the movable electrode and the first silicon oxide film 21.

  The hermetic sealing protective cap is a support member for supporting the first and second fixed electrodes 902 and 903. In the hermetic sealing protective cap 90, for example, a minute space (cavity 91) in which one side of the heat-resistant glass substrate is recessed is formed.

  The first fixed electrode 902 and the second fixed electrode 903 are arranged so as to face the upper surface of the movable electrode 13 with a spatial distance d1 and d2 therebetween. The first fixed electrode 902, the second fixed electrode 903, and the movable electrode 13 constitute a capacitor C1 and a capacitor C2, respectively. In the first and second fixed electrodes 902 and 903, a plurality of etching holes 27 having a square shape with a side of several μm are typically formed.

  The fixed electrode support portion 912 supports the first fixed electrode 902 and the second fixed electrode 903 on the hermetic sealing protective cap 90 via the anchor 908 of the first fixed electrode and the anchor 909 of the second fixed electrode. ing. In this embodiment, the fixed electrode support portion 912 has one fixed electrode support column for each of the first and second fixed electrodes 902 and 903. The fixed electrode support portion 912 is in contact with a part of the first and second fixed electrodes 902 and 903, and the area in contact with the first and second fixed electrodes 902 and 903 is the first and second fixed electrodes 11. , Smaller than 12 areas.

  The height from the surface of the first and second fixed electrodes 902 and 903 to the inner ceiling surface of the cavity 91 is hermetically sealed around the hermetic sealing protective cap 90 and the substrate 20 using, for example, a low melting powder glass 93 or the like. When fixed, the spatial distances d1 and d2 between the first and second fixed electrodes 902 and 903 and the movable electrode 13 are approximately 2 μm.

  The first through electrode 904 and the second through electrode 905 are arranged so as to penetrate outward from the cavity side of the hermetic sealing protective cap 90. The first through electrode 904 and the second through electrode 905 are provided to electrically draw the first fixed electrode 902 and the second fixed electrode 903 out of the hermetic sealing protective cap 90. The metal pad 906 of the first through electrode and the metal pad 907 of the second through electrode connect the first through electrode 904 and the second through electrode 905 and the ASIC by wire bonding with, for example, a gold wire. It is provided for.

Next, a method for manufacturing the acceleration sensor according to the present embodiment will be described.
First, as shown in FIG. 9, a first silicon oxide film 21 is formed on a substrate 20 as an insulating film, typically with a thickness of about 2 μm. Next, a highly conductive polysilicon film having a thickness of approximately 0.5 μm is typically deposited on the first silicon oxide film 21. By patterning the polysilicon film by, for example, a dry etching method, a portion to be the electric wiring 901 of the movable electrode 13 is formed. Subsequently, a second silicon oxide film 23 is formed on the entire surface of the substrate 20. Next, the heights of the upper surfaces of the second silicon oxide film 23 and the electric wiring 901 of the movable electrode 13 are made uniform by, for example, a CMP technique. Thereafter, a silicon nitride film 24 is formed on the entire planarized surface. Thereafter, the silicon nitride film 24 on the portion where the anchor 17 of the movable electrode 13 is installed is opened by photolithography and dry etching techniques.

  Next, a second sacrificial layer film typically having a thickness of about 2 μm, such as a PSG film (not shown), is formed on the entire surface of the substrate 20. Thereafter, the second sacrificial layer film at the site where the anchor 17 of the movable electrode 13 is installed is removed by etching. Thereby, a groove reaching a part of the surface of the electric wiring 901 of the movable electrode 13 is formed in the second sacrificial layer film. Subsequently, a polysilicon film typically having a thickness of about 4 μm is deposited on the entire surface of the second sacrificial layer film by, eg, LPCVD. This polysilicon film is formed so as to fill the trench. Next, the polysilicon film is patterned by, for example, a dry etching method. Thereby, the movable electrode 13, the inertia mass body 14, the anchor 17, the link beam and the torsion beam are simultaneously formed from the polysilicon film. During this etching, the part that becomes the movable electrode 13 typically has a side of several μm so that the second sacrificial layer film is etched away in a short time and the movable electrode 13 and the inertial mass body 14 can be moved. A plurality of etching holes having a square shape are simultaneously formed.

  Thereafter, the second sacrificial layer film on which the movable electrode 13, the inertia mass body 14, the anchor 17, the link beam and the torsion beam are temporarily fixed is removed by etching with a highly corrosive etching solution such as hydrofluoric acid. Thereby, an acceleration sensor chip is obtained. Thereafter, since the electrical wiring 901 of the movable electrode 13 and the ASIC are connected by wire bonding, a metal pad (not shown) is formed as an electrode pad at the end of the electrical wiring 901 of the movable electrode 13.

  However, this acceleration sensor chip does not yet function as an acceleration sensor because it is not integrated with the hermetic sealing protective cap in which the first fixed electrode 902 and the second fixed electrode 903 are formed. Next, a method for manufacturing an acceleration sensor in which the acceleration sensor chip and the hermetic sealing protective cap 90 are combined will be described.

  For example, a cavity 91 that can accommodate the acceleration sensor chip is formed on one side of, for example, a heat-resistant glass substrate that is the basis of the hermetic sealing protective cap 90 by etching with hydrofluoric acid or the like by photolithography. Next, from the opposite cavity surface 92 side opposite to the glass substrate surface on which the cavity 91 is formed, toward the portion where the first fixed electrode 902 and the second fixed electrode 903 are formed on the ceiling surface of the cavity 91. For example, the through hole is opened by a dry etching technique. A metal thin film such as chromium or gold is formed on a portion of the anti-cavity surface 92 where the first through electrode 904 and the second through electrode 905 are provided by a metal thin film forming apparatus such as a sputtering apparatus. The formed metal thin film is patterned into a predetermined shape by the photoengraving technique to form a metal pad 906 for the first through electrode and a metal pad 907 for the second through electrode. Next, using this metal pad as one electrode, the through hole is filled with a highly conductive metal such as gold, and a first through electrode 904 and a second through electrode 905 are formed. Next, polysilicon is deposited in the cavity 91 of the hermetic protective cap 90. Subsequently, an anchor 908 of the first fixed electrode 902 and an anchor 909 of the second fixed electrode 903 are formed by photolithography and dry etching. Next, as shown in FIG. 10, a first sacrificial layer film 910 such as PSG having a thickness of typically 0.5 μm is formed inside the cavity 91. Subsequently, an opening is formed at a position where the fixed electrode support portion 912 of the first sacrificial layer film 910 is formed by photolithography and etching techniques. The opening is formed in a region where the anchor 908 of the first fixed electrode 902 and the anchor 909 of the second fixed electrode 903 are formed, and the first fixed electrode 902 and the second fixed electrode 903 formed later. Are provided at positions corresponding to the vicinity of the respective gravity center positions. Next, a polysilicon film is deposited inside the cavity 91 by, for example, LPCVD. Subsequently, the first fixed electrode 902 and the second fixed electrode 903 are formed by photolithography. Further, on the first fixed electrode 902 and the second fixed electrode 903, a plurality of etching holes 27 typically having a square shape with a side of several μm are opened. Subsequently, the glass substrate is immersed in hydrofluoric acid, and the first sacrificial layer film 910 is removed by etching to obtain an airtight sealing protective cap as shown in FIG.

Next, the operation of the acceleration sensor according to the present embodiment will be described.
Referring to FIG. 9, when acceleration in the Z-axis direction (normal direction of the surface of substrate 20) is applied to the acceleration sensor, an inertial force is generated in a direction opposite to the acceleration direction. When this inertial force acts on the inertial mass body 14, the inertial mass body 14 moves in the Z-axis direction. At this time, the torsion beam is formed on a line passing through the center of the movable electrode 13, and the link mass connects the inertial mass body 14 and the movable electrode 13 at a position away from the line passing through the center. Torque is generated in the movable electrode 13 around the torsion beam by the inertia force transmitted from the inertia mass body 14 to the link beam. Thereby, the movable electrode 13 rotates around the torsion beam 16. When the movable electrode 13 rotates, one of the spatial distances d1 and d2 between the movable electrode 13 and the first fixed electrode 902 and the second fixed electrode 903 becomes closer and the other becomes longer. The detection capacity of the capacitor increases as the spatial distance decreases and decreases as the distance increases. Accordingly, since the detection capacities of the capacitors C1 and C2 change due to changes in the spatial distances d1 and d2, acceleration is detected from the change in the detection capacities.

  According to the acceleration sensor of the present embodiment, when die-bonding to the IC lead frame, the first fixed electrode 902 and the second fixed electrode 903 are formed on the hermetic sealing protective cap 90 side. No stress from the frame. When the mold resin is filled and molded, the first fixed electrode 902 and the second fixed electrode 903 are supported by the fixed electrode support portion 25 in a small area on the hermetic sealing protective cap 90 side. Therefore, the stress from the mold resin is not transmitted to the entire first and second fixed electrodes 902 and 903 through the hermetic sealing protective cap 90.

  Therefore, warpage of the first fixed electrode 902 and the second fixed electrode 903 is suppressed, and changes in the spatial distances d1 and d2 between the first and second fixed electrodes 902 and 903 and the movable electrode 13 are also suppressed. Therefore, the capacitance values of the detection capacitor C1 formed between the first fixed electrode 902 and the movable electrode 13 and the detection capacitor C2 formed between the second fixed electrode 903 and the movable electrode 13 are assembled. It is possible to obtain an acceleration sensor having stable characteristics by suppressing the change due to the stress of time.

(Embodiment 5)
FIG. 11 is a schematic cross-sectional view of the acceleration line sensor according to the fifth embodiment of the present invention. The acceleration sensor according to the present embodiment has a plurality of fixed electrode support portions with respect to one fixed electrode of each of the first and second fixed electrodes 902 and 903 as compared with the configuration of the fourth embodiment. The main difference is that the column 913 is provided.

  As shown in FIG. 11, two fixed electrode support columns 913 are respectively formed immediately below the vicinity of the center of gravity of the first fixed electrode 902 and the second fixed electrode 903.

  In the acceleration sensor manufacturing method of the present embodiment, the fixed electrode support column 913 is directly below the vicinity of the center of gravity of each of the first fixed electrode 902 and the second fixed electrode 903 when the first sacrificial layer film 910 is etched. The two support pillars are left in a predetermined size, and the other portions are formed by etching away and disappearing.

  Since the further configuration and manufacturing method of the present embodiment are the same as those of the above-described fourth embodiment, the same elements are denoted by the same reference numerals, and the description thereof is omitted.

  In the above-described fourth embodiment, the first fixed electrode 902 and the second fixed electrode 903 are fixed electrode support portions 912 having one fixed electrode support column installed immediately above the position of the center of gravity of each fixed electrode. It is done by. However, if the fixed electrode does not warp due to stress during assembly of the acceleration sensor chip, the fixed electrode support portion 912 does not have to be limited to a single fixed electrode support column. As shown in FIG. There may be.

  The acceleration sensor according to the present embodiment is not affected by stress during assembly in a wide area of the first and second fixed electrodes 902 and 903 other than the area in contact with the plurality of fixed electrode support columns 913. As shown in FIG. 5 and FIG. 15, for example, even if two fixed electrode support columns 913 are installed immediately above the positions of the center of gravity of the first fixed electrode 902 and the second fixed electrode 903, the first fixed electrode 902 and It is possible to prevent the second fixed electrode 903 from warping.

  According to the present embodiment, it is possible to obtain an acceleration sensor with stable characteristics whose characteristics do not change due to stress during assembly. In addition, since the acceleration sensor according to the present embodiment includes a plurality of fixed electrode support columns 913, the first and second fixed electrodes 902 and 903 are not easily deformed when acceleration is applied to the acceleration sensor chip from the outside. There is an advantage. Therefore, according to the acceleration sensor of the present embodiment, in addition to the effect of suppressing characteristic fluctuation due to stress during assembly, there is also an effect of suppressing characteristic fluctuation due to acceleration applied from the outside.

  In addition, although described about the Z-axis acceleration sensor, it is not limited to this, It can apply also to an X-axis acceleration sensor or a Y-axis acceleration sensor.

  Each embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be applied particularly advantageously to a capacitive acceleration sensor.

It is a schematic plan view which shows the structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing in alignment with the II-II line of FIG. It is a schematic sectional drawing in alignment with the III-III line of FIG. It is a schematic sectional drawing in alignment with the II-II line | wire of FIG. 1 which shows the manufacturing method of the acceleration sensor in this Embodiment 1. FIG. It is a schematic sectional drawing of the acceleration sensor in Embodiment 2 of this invention. It is a schematic plan view which shows the structure of the acceleration sensor in Embodiment 3 of this invention. It is a schematic sectional drawing which follows the VII-VII line of FIG. It is a schematic sectional drawing which follows the VIII-VIII line of FIG. It is a schematic sectional drawing which shows the structure of the acceleration sensor in Embodiment 4 of this invention. It is a schematic sectional drawing which shows the structure of the airtight sealing protection cap in this Embodiment 4. It is a schematic sectional drawing of the acceleration sensor in Embodiment 5 of this invention. It is a schematic block diagram of the conventional common Z-axis acceleration sensor. It is a schematic sectional drawing which follows the XIII-XIII line | wire of FIG. It is a schematic bird's-eye view which shows the structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic bird's-eye view which shows the structure of the acceleration sensor in Embodiment 2 of this invention. It is a schematic bird's-eye view which shows the structure of the acceleration sensor in Embodiment 3 of this invention.

Explanation of symbols

  11, 902 First fixed electrode, 12, 903 Second fixed electrode, 13 Movable electrode, 14 Inertial mass, 15 Link beam, 16 Twist beam, 17 Anchor, 18 Electrical wiring of first fixed electrode, 19 Second fixed electrode electrical wiring, 20 substrate, 21 first silicon oxide film, 22,910 first sacrificial layer film, 23 second silicon oxide film, 24 silicon nitride film, 25,912 fixed electrode support site , 26 void, 27 etching hole, 28 second sacrificial layer film, 29, 913 fixed electrode support pillar, 66 end, 90 hermetically sealed protective cap, 91 cavity, 92 anti-cavity surface, 93 low melting point powder glass, 101 , 901 Electric wiring of movable electrode, 102 etching hole, 904 first through electrode, 905 second through electrode, 906 gold of first through electrode Genus pad, 907 second through electrode metal pad, 908 first fixed electrode anchor, 909 second fixed electrode anchor.

Claims (5)

A movable electrode;
A fixed electrode disposed to face the movable electrode;
A support member for supporting the fixed electrode;
An acceleration sensor comprising: a fixed electrode supporting portion that supports the fixed electrode on the support member and has an area in contact with the fixed electrode that is smaller than an area of the fixed electrode.   The acceleration sensor according to claim 1, wherein the fixed electrode support portion has a plurality of fixed electrode support columns with respect to one fixed electrode.   2. The acceleration sensor according to claim 1, wherein an end portion of the fixed electrode in a plan view is in contact with the fixed electrode support portion, and a gap exists between a central portion of the fixed electrode in a plan view and the support member. .   The acceleration sensor according to claim 1, wherein the support member includes a substrate.   The acceleration sensor according to claim 1, wherein the support member includes an airtight sealing protective cap.

Images