JP2007279056A - Semiconductor mechanical mass sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide semiconductor mechanical mass sensor, in which circumferential parasitic capacitance, existing in circumference of sensor element, prevents deterioration in sensor sensitivity. <P>SOLUTION: This sensor comprises support substrate and element forming film 200 formed on the supporting substrate. The element forming film 200 is demarcated into sensor element section which has a movable section 2A for detecting capacity variation involving in displacement of the movable section 2A and a periphery section 201 circumferentially-located around the sensor element section, via a groove formed on the element forming film 200; and the periphery section 201 includes a means 202 for stabilizing the electric potential of the periphery section 201. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes a semiconductor dynamic quantity sensor that has a movable part and a fixed part of a beam structure, and detects a mechanical quantity such as acceleration, yaw rate, vibration, etc., for example, by detecting a change in capacitance between the movable part and the fixed part. About.

Conventionally, a servo-controlled differential capacitance type acceleration sensor using a bonded substrate has been proposed as a semiconductor mechanical quantity sensor having a movable part having a beam structure (see, for example, Patent Document 1). This is configured by forming a beam structure and a fixed part that form a movable part on a substrate (supporting substrate), and by detecting a change in capacitance between the beam structure and the fixed part, a mechanical quantity can be obtained. To detect. The beam structure has a first anchor portion and a mass portion that is supported by the first anchor portion via the beam portion and is displaced by acceleration. A movable electrode is provided on the mass portion. ing. Further, the fixed portion has a fixed electrode having a shape fixed on the substrate by the second anchor portion and facing the movable electrode. Furthermore, the above-described substrate has a structure in which a thin film for bonding, an insulating film, and a conductive thin film are formed on a semiconductor substrate, and the first and second anchor portions are formed of a conductive thin film. Yes.
JP 9-2111022 A

  When the present inventors further studied the acceleration sensor, it was found that the parasitic capacitance generated between the conductive thin film and the insulating film or the thin film for bonding greatly affects the sensitivity of the sensor. That is, when detecting the capacitance between the beam structure and the fixed portion, the output of the sensor is expressed by (change in capacitance) / (total capacitance + parasitic capacitance). When the thin film for bonding is in an electrically floating state, the parasitic capacitance increases, so that the sensitivity of the sensor decreases.

  A semiconductor dynamic quantity sensor having a movable part and a fixed part of a beam structure is generally applied to an element forming film (element forming substrate) formed on a supporting substrate by using a semiconductor manufacturing technique such as etching. It is manufactured by forming a groove that delimits the movable part and the fixed part. On the outer periphery of the sensor element part composed of the movable part (beam structure) and the fixed part, an element other than the sensor element part is provided. There is a forming film portion, that is, an outer peripheral portion.

  And although this outer peripheral part is also supported on the support board | substrate, since it is in the electrically floating state, the output of a sensor may be fluctuated like the case of the thin film for bonding.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent the sensor sensitivity from being lowered by the parasitic capacitance due to the outer peripheral portion existing in the outer peripheral portion of the sensor element portion.

  In order to achieve the above object, according to the first aspect of the present invention, the element forming film (200, 302) formed on the supporting substrate (1, 301) is formed into grooves formed in the element forming film. A sensor element unit that has a movable part (2A) and detects a change in capacitance due to the displacement of the movable part, and an outer peripheral part (201, 313) arranged on the outer periphery of the sensor element part, The outer peripheral portion is provided with means (202, 350 to 352) for fixing the electric potential of the outer peripheral portion, and it is possible to prevent the sensor sensitivity from being lowered by the parasitic capacitance due to the outer peripheral portion.

  According to a second aspect of the present invention, in the sensor according to the first aspect, when the sensor element unit includes a plurality of capacitance detection units (304 to 307), the potential of the outer peripheral portion is fixed. Means (350, 351) is provided corresponding to each of the plurality of capacitance detection units. Accordingly, an arbitrary potential can be applied to each capacitance detection unit, and the charge accumulated in the parasitic capacitance can be controlled in accordance with each capacitance detection unit, that is, the offset generated in each capacitance detection unit can be controlled more efficiently.

  According to a third aspect of the present invention, in the sensor according to the second aspect of the present invention, there are two capacitance detection units (304 to 307), and each capacitance detection unit is accompanied by a capacitance change having a magnitude of substantially the same level. When it is assumed, the distance between the first capacitance detection unit (304, 306) and the means (350) for fixing the potential of the outer peripheral portion corresponding thereto, and the second capacitance detection unit (305, 307) And a distance (351) for fixing the electric potential of the outer peripheral portion corresponding thereto is made substantially the same.

  As a result, the voltage applied to the means for fixing the potentials of the respective outer peripheral portions corresponding to the first capacitance detection unit and the second capacitance detection unit can be made the same, and the control is facilitated. According to a fourth aspect of the present invention, each outer peripheral portion with respect to an axis of symmetry perpendicular to a line connecting the first capacitance detection unit (304, 306) and the second capacitance detection unit (305, 307). It is characterized in that the means (350, 351) for fixing the potential is symmetrically arranged, and the distance relationship in the sensor according to claim 3 can be efficiently realized.

  According to a fifth aspect of the present invention, in the sensor according to the second to fourth aspects of the present invention, the sensor element portion is a pad for extracting a change in capacitance provided for each capacitance detection portion (304 to 307). 310, 311) and conductor portions (310a, 311a) that electrically connect the respective capacitance detection portions and the respective pads, the resistance values of the respective conductor portions. Are substantially the same, and grooves (S2) located around the respective conductor portions are formed with substantially the same volume.

  For example, by adjusting the width and depth of the groove so that the volume of the groove located around each conductor portion is substantially the same, the parasitic capacitance between each conductor portion and the outer peripheral portion is substantially the same, and each Since the resistance values of the conductor portions are substantially the same, it is possible to make a structure that hardly generates an offset, and it is possible to make the voltage applied to the means for fixing the potential of each outer peripheral portion the same, thereby making it easy to control the sensor.

  According to a sixth aspect of the present invention, in the sensor according to the first aspect, the sensor element unit includes two capacitance detection units (304 to 307), and each of the capacitance detection units has a size of substantially the same level. A line (352) for fixing the potential at the outer peripheral portion when the capacitance change is involved is a line connecting the first capacitance detection unit (304, 306) and the second capacitance detection unit (305, 307). It is characterized by being arranged on an axis of symmetry orthogonal to.

  According to this, by the means for fixing the potential of one outer peripheral portion, the distance between this and each capacitance detection unit can be made the same, so by applying a voltage to the means for fixing the potential of one outer peripheral portion, The charge accumulated in the parasitic capacitance can be controlled in accordance with the capacitance detection unit. In addition, in the case where each capacitance detection unit is provided with a means for fixing the potential of the outer peripheral portion, wiring corresponding to that is necessary, and a minute potential difference generated between the means for fixing the potential of each outer peripheral portion. However, in the present invention, such a situation does not occur, and simple and stable control is possible.

  The invention according to claim 7 adds a configuration in which the potential to be fixed in the means for fixing the potential of the outer peripheral portion (350 to 352) is set to the same potential as the movable electrode in the sensor according to claims 1 to 6. It is a thing. The invention according to claim 8 is the sensor according to claims 1 to 7, wherein the outer peripheral portion (201, 313) is more external than the means (202, 350-352) for fixing the electric potential of the outer peripheral portion. An insulating groove (360) is formed on the edge side, and the outer edge side and the inner edge side of the insulating groove are insulated.

  According to this, the fixed potential at the outer peripheral portion fixed by the means for fixing the potential at the outer peripheral portion is not applied to the outer edge side of the outer peripheral portion with respect to the insulating groove. Therefore, even when a conductive substance or the like adheres to the outer edge side of the outer peripheral portion, that is, the outer peripheral portion of the sensor, the fixed potential is not transmitted to the outer edge side of the insulating groove and generates a leakage current to the supporting substrate side. There is an effect of not.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below.
(First embodiment)
FIG. 1 is a plan view of an acceleration sensor according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line AA in FIG.

  1 and 2, on the upper surface of the substrate 1, a beam structure 2A forming a movable portion formed by separating single crystal silicon (single crystal semiconductor material, element forming film as referred to in the present invention) 200 by a groove and The fixing part 2B is arranged. The beam structure 2 </ b> A is constructed by four anchor portions 3 a, 3 b, 3 c, and 3 d that protrude from the substrate 1 side, and is disposed at positions spaced apart from each other on the upper surface of the substrate 1. The anchor portions 3a to 3d are made of a polysilicon thin film. A beam portion 4 is constructed between the anchor portion 3a and the anchor portion 3b, and a beam portion 5 is constructed between the anchor portion 3c and the anchor portion 3d.

  A rectangular mass portion (mass portion) 6 is installed between the beam portion 4 and the beam portion 5. The mass portion 6 is provided with a through hole 6a penetrating vertically. By providing this through hole 6a, it is possible to facilitate the entry of the etchant during the sacrifice layer etching described later. Furthermore, four movable electrodes 7a, 7b, 7c, and 7d protrude from one side surface (the left side surface in FIG. 1) of the mass portion 6. The movable electrodes 7a to 7d have a rod shape and extend in parallel at equal intervals. Further, four movable electrodes 8a, 8b, 8c, 8d protrude from the other side surface (the right side surface in FIG. 1) of the mass portion 6. The movable electrodes 8a to 8d have a rod shape and extend in parallel at equal intervals. Here, the beam portions 4 and 5, the mass portion 6, and the movable electrodes 7 a to 7 d and 8 a to 8 d are movable by removing a part or all of a sacrificial layer oxide film described later.

  Further, on the side where the movable electrodes 7a to 7d are formed, the first fixed electrodes 9a, 9b, 9c, 9d and the second fixed electrodes 11a, 11b, 11c, 11d are fixed to the upper surface of the substrate 1. Yes. The first fixed electrodes 9a to 9d are supported by anchor portions 10a, 10b, 10c, and 10d protruding from the substrate 1 side, and one side surface of each movable electrode (bar-shaped portion) 7a to 7d of the beam structure 2A. It is arranged to face. The second fixed electrodes 11a to 11d are supported by anchor portions 12a, 12b, 12c, and 12d protruding from the substrate 1, and the other of the movable electrodes (rod-like portions) 7a to 7d of the beam structure 2A. It is arrange | positioned facing the side surface.

  Similarly, on the side where the movable electrodes 8a to 8d are formed, the first fixed electrodes 13a, 13b, 13c, 13d and the second fixed electrodes 15a, 15b, 15c, 15d are fixed to the upper surface of the substrate 1. ing. The first fixed electrodes 13a to 13d are supported by the anchor portions 14a, 14b, 14c, and 14d, and are arranged to face one side surface of each movable electrode (rod-shaped portion) 8a to 8d of the beam structure 2A. Yes. The second fixed electrodes 15a to 15d are supported by anchor portions 16a, 16b, 16c, and 16d protruding from the substrate 1, and the other of the movable electrodes (rod-like portions) 8a to 8d of the beam structure 2A. It is arrange | positioned facing the side surface.

  Electrode extraction portions 27a, 27b, 27c, and 27d are formed on the upper surface of the substrate 1, and the electrode extraction portions 27a to 27d are supported by anchor portions 28a, 28b, 28c, and 28d that protrude from the substrate 1. As shown in FIG. 2, the substrate 1 has a thin film for bonding (polysilicon thin film) 32, an insulating film (silicon oxide film) 33, an insulating film 34, and a conductive thin film on a silicon substrate 30 through an oxide film 31. (For example, a polysilicon thin film doped with an impurity such as phosphorus) 35 and an insulating film 36 are stacked, and the conductive thin film 35 is embedded in the insulating films 34 and 36. Here, the insulating films 34 and 36 are formed of a thin film that is less likely to be eroded by an etching solution when performing sacrificial layer etching described later. For example, when HF (fluoric acid) is used as the etchant, a silicon nitride film having a smaller erosion amount than the silicon oxide film is used as the insulating films 34 and 36.

  As shown in FIG. 2, the anchor portions 3a and 3b are composed of a conductive thin film 35. Other anchor portions 3c, 3d, 10a to 10d, 12a to 12d, 14a to 14d, which are not shown in FIG. Similarly, 16 a to 16 d and 28 a to 28 d are also formed of the conductive thin film 35. In addition, the conductive thin film 35 is formed between the first fixed electrodes 9a to 9d and the electrode extraction part 27a, between the first fixed electrodes 13a to 13d and the electrode extraction part 27b, and between the second fixed electrodes 11a to 11d and the electrode. In addition to forming wirings that electrically connect between the extraction portions 27c and between the second fixed electrodes 15a to 15d and the electrode extraction portions 27d, a lower electrode (static force canceling fixed electrode) 26 is formed. ing. The lower electrode 26 is formed in a region facing the beam structure 2 </ b> A on the upper surface portion of the substrate 1.

  As shown in FIGS. 1 and 2, an electrode pad (bonding pad) 43 made of an aluminum thin film is provided above the electrode extraction portion 3a. In addition, electrode pads (bonding pads) 44a, 44b, 44c, and 44d made of an aluminum thin film are provided on the upper surfaces of the electrode extraction portions 27a to 27d, respectively. In the configuration described above, the first capacitor is provided between the movable electrodes 7a to 7d and the first fixed electrodes 9a to 9d of the beam structure 2A, and the movable electrodes 7a to 7d and the second fixed electrode of the beam structure 2A. A second capacitor is formed between 11a to 11d. Similarly, a first capacitor is provided between the movable electrodes 8a to 8d and the first fixed electrodes 13a to 13d of the beam structure 2A, and the movable electrodes 8a to 8d and the second fixed electrodes 15a to 15a of the beam structure 2A. A second capacitor is formed between 15d.

  Based on the capacities of the first and second capacitors, an acceleration acting on the beam structure 2A is detected by a control circuit (not shown). Specifically, two differential capacitances are formed by the movable electrode and the fixed electrode, and acceleration is detected by the circuit of FIG. In this embodiment, as shown in FIGS. 1 and 2, a potential extraction portion 50 is formed in order to fix the potential of the thin film 32 for bonding, and the potential extraction portion 50 is an anchor protruding from the substrate 1. Supported by the portion 51. The anchor portion 51 is also composed of the conductive thin film 35. In addition, an opening 52 is formed in the silicon oxide film 33 and the insulating film 34 at a portion where the potential extraction portion 50 is formed, and the bonding thin film 32 is connected to the potential extraction portion via the anchor portion 51 in that portion. 50 is electrically connected. Further, an electrode pad (bonding pad) 53 made of an aluminum thin film is provided above the potential extraction unit 50. As a result, the potential of the bonding thin film 32 can be fixed, so that parasitic capacitance can be reduced and sensor sensitivity can be prevented from decreasing.

  Next, a manufacturing method of the above-described semiconductor acceleration sensor will be described with reference to a process diagram using a BB cross section in FIG. First, as shown in FIG. 3A, a single crystal silicon substrate 60 as a first semiconductor substrate is prepared. Then, a trench 61 is formed in the silicon substrate 60 by trench etching. The groove 61 is for defining the beam structure 2A and the fixed portion 2B.

  Next, as shown in FIG. 3B, a silicon oxide film 62 as a sacrificial layer thin film is formed by CVD or the like, and the surface of the silicon oxide film 62 is planarized. Next, as shown in FIG. 3C, the silicon oxide film 62 is partially etched through photolithography to form a recess 63. Thereafter, a silicon nitride film 64 is formed to increase the unevenness of the surface and to serve as an etching stopper at the time of sacrifice layer etching.

  Then, as shown in FIG. 3D, openings 65a, 65b, 65c, 65d, and 65e are formed in the anchor portion formation region by dry etching or the like through photolithography on the stacked body of the silicon oxide film 62 and the silicon nitride film 64. Form. The openings 65a to 65e are for connecting the beam structure and the lower electrode, and for connecting the fixed electrode and the electrode extraction portion and the wiring pattern.

  Subsequently, as shown in FIG. 3E, a polysilicon thin film is formed on the silicon nitride film 64 including the openings 65a to 65e, and then impurities are introduced by phosphorus diffusion or the like, and photolithography is performed. Then, anchor portions, wirings, and lower electrode patterns 66a, 66b, 66c, 66d, 66e, 66f, and 66g are formed. Thus, impurity doped polysilicon thin film 66 (66a-66g) is formed as a conductive thin film in a predetermined region on silicon nitride film 64 including openings 65a-65e. The thickness of the polysilicon thin film is about 1-2 μm.

  In this step (the step of forming the impurity-doped polysilicon 66 in a predetermined region on the silicon nitride film 64 including the opening), the polysilicon thin film 66 is thin (1 to 2 μm) to the extent that the lower pattern resolution of the stepper is satisfied. The shapes of the openings 65a to 65e of the silicon nitride film 64 under the polysilicon thin film 66 can be seen through, and photomask alignment can be performed accurately.

  Then, as shown in FIG. 4A, a silicon nitride film 67 is formed on the polysilicon thin film 66 and the silicon nitride film 64, and a silicon oxide film 68 is further formed thereon. Thereafter, as shown in FIG. 4B, an opening 69 is formed in the silicon oxide film 68 and the silicon nitride film 67 by dry etching or the like through photolithography.

  Then, as shown in FIG. 4C, a polysilicon thin film 70 as a thin film for bonding is formed on the silicon oxide film 68 including the opening 69. Since the polysilicon thin film 70 is connected to the polysilicon thin film 66a through the opening 69, the potential of the polysilicon thin film 70 can be taken out electrically. Next, as shown in FIG. 4D, the surface of the polysilicon thin film 70 is flattened by mechanical polishing or the like for bonding, and a silicon oxide film is formed on the polysilicon thin film 70 for easy bonding. 71 is deposited.

  Next, as shown in FIG. 4E, a single crystal silicon substrate (supporting substrate) 72 as a second semiconductor substrate is prepared, and the surface of the polysilicon thin film 70 and the silicon substrate 72 are bonded together. Then, the silicon substrates 60 and 72 are turned upside down as shown in FIG. 5A, and as shown in FIG. 5B, the silicon substrate 60 side is thinned by mechanical polishing or the like. At this time, polishing is performed until a layer of the silicon oxide film 62 in the groove 61 appears. If polishing is performed until the layer of the silicon oxide film 62 appears in this way, the hardness in polishing changes, so that the end point of polishing can be easily detected.

  Thereafter, as shown in FIG. 5C, an aluminum electrode 82 is formed through film formation and photolithography. Finally, as shown in FIG. 5 (d), the silicon oxide film 62 is removed by etching with an HF-based etchant to make the beam structure having movable electrodes movable. That is, the silicon oxide film 62 in a predetermined region is removed by sacrificial layer etching using an etching solution, and the silicon substrate 60 is made a movable structure. At this time, a sublimation agent such as paradichlorobenzene is used to prevent the movable part from adhering to the substrate during the drying process after etching.

  In this way, it is possible to form a semiconductor acceleration sensor using an embedded SOI substrate and having a wiring pattern and a lower electrode formed by insulator separation. In the above-described embodiment, the silicon oxide film 62 is used as the sacrificial layer thin film and the silicon thin film 66 is used as the conductive thin film. Therefore, in the sacrificial layer etching step, silicon is used when an HF-based etchant is used. The oxide film 62 is melted by HF, but the polysilicon thin film 66 is not melted. Therefore, it is not necessary to accurately control the concentration and temperature of the HF-based etching solution or to accurately complete the etching by time management. Becomes easier.

  In the first embodiment, the following modifications are possible. In the manufacturing method described above, the silicon nitride film 67 (the silicon nitride film 34 in FIG. 2) is formed under the anchor portion, so that the upper silicon nitride film 64 (the silicon nitride film 36 in FIG. 2) is etched during the sacrificial layer etching. ) Can be prevented from peeling off even if overetching. However, if the silicon oxide film 68 is eliminated, the silicon oxide film 64 can be omitted. In this case, since only the silicon nitride film 67 is formed on the polysilicon thin film 66, the level difference of the polysilicon thin film 70 for bonding in the opening 69 is reduced, and planarization polishing can be facilitated. The structure in this case is shown in FIG. 6 in comparison with FIG.

  In the present embodiment, the electrode pads 43, 44a to 44d, 53 are provided on the upper surfaces of the electrode extraction portions 3a, 27a to 27d and the potential extraction portion 50. However, as shown in FIG. The electrode pads 104 to 108 may be provided on one side. In this case, the electrode pad 104 is electrically connected to the beam structure 2 </ b> A by the wiring 101 using the conductive thin film 35. The electrode pad 105 is electrically connected to the fixed electrodes 9 a to 9 d and 13 a to 13 d by the wiring 102 using the conductive thin film 35, and the electrode pad 106 is fixed to the fixed electrode by the wiring 103 using the conductive thin film 35. 11a to 11d and 15a to 15d are electrically connected.

  The electrode pad 107 is electrically connected to the bonding thin film 32 via the conductive thin film 35 forming the anchor portion below the electrode pad 107, and the electrode pad 108 is used to fix the potential of the silicon substrate on the surface side. Is provided. In the case of such a configuration, as shown in the figure, there are portions where the wirings 101 and 102 intersect. At this time, as shown in FIGS. 8A and 8B, the intersecting portion is surrounded by the insulating film 108, and the wiring 101 is formed by bypassing the silicon substrate, that is, a construction structure through the silicon substrate. It is possible. In addition, in FIG. 8, (b) is CC sectional drawing of (a). In order to obtain such a structure, a groove is formed so as to surround a portion where the wiring intersects in the step of FIG. 3A, and the groove is filled with a silicon oxide film in the step of FIG. An opening may be formed where the wiring is bypassed in the step 3 (d). However, when such a method is used, an extra groove is formed in the silicon substrate, so that disconnection due to the ingress of an etchant or the like, and the side wall processing accuracy of the structure change.

  Therefore, as shown in FIGS. 9A and 9B, if the silicon oxide film 33 and the silicon nitride film 34 are provided with openings and the wiring 101 is formed so as to be bypassed by the thin film 32 for bonding, As described above, since it is not necessary to form an extra groove in the silicon substrate, a change in the side wall processing accuracy of the structure can be suppressed. In addition, in FIG. 9, (b) is DD sectional drawing of (a).

(Second Embodiment)
An acceleration sensor according to the second embodiment is shown in FIG. The planar configuration of this sensor is the same as that shown in FIG. 1, and FIG. 10 shows this sensor in the same cross section as FIG. This sensor is a modification of the first embodiment, and is different from the first embodiment in that the oxide film 31 is not provided. This point will be described below. When the oxide film 31 is not provided with respect to FIG. 2, the bonding thin film 32 is bonded and electrically connected to the silicon substrate 30, but the package is formed when the silicon substrate 30 is mounted after being formed into a chip. The silicon substrate 30 is considered to have a very high contact resistance due to the influence of a natural oxide film or the like on the back surface of the silicon substrate 30 (the lower side in FIG. 10).

  Thus, as in the present embodiment, even when the oxide film 31 is not present, the parasitic capacitance can be reduced by taking out the potential of the bonding thin film 32 (and the potential of the connected silicon substrate 30), resulting in a decrease in sensor sensitivity. Can be prevented.

(Third embodiment)
Including the first and second embodiments described above, the parasitic capacitance parasitic on the sensor structure was examined. The third embodiment is based on this study. In the present embodiment, each part of the sensor structure that forms the movable electrode and the parasitic capacitance is verified, and the point of eliminating the influence of the parasitic capacitance will be described in more detail.

  FIG. 11 is an explanatory diagram for explaining an equivalent circuit of parasitic capacitance in the sensors of both the above embodiments. In FIG. 11, the supporting Si substrate is the silicon substrate 30, and the element forming film is the groove S1 on the outer periphery of the beam structure 2A and the fixed electrodes 9a to 9d, 11a to 11d, 13a to 13d, and 15a to 15d (that is, the sensor element portion). The lower electrode shows the lower electrode 26 and the stopper is not shown, and the movable electrodes 7a to 7d and 8a to 8d are shown in FIG. It is intended to prevent excessive movement.

  Here, as shown in FIG. 2, the outer peripheral portion 201 is made of single crystal silicon 200 fixed to the second conductive thin film 35, and is a part of the fixed portion 2 </ b> B in the single crystal silicon 200. Further, in FIG. 11, the fixed electrode 1 indicates first fixed electrodes 9a to 9d and 13a to 13d, the fixed electrode 2 indicates second fixed electrodes 11a to 11d and 15a to 15d, and the movable electrode is the movable electrode 7a. ˜7d, 8a-8d, C1 ′ and C2 ′ respectively indicate the capacitance of the first capacitor and the capacitance of the second capacitor, and C1 to C15 are parasitic capacitances generated between the respective parts. These parasitic capacitances include not only the electrode part but also those attached to the wiring.

  And in the sensor of both the said embodiment, the capacitance change between a movable electrode and a fixed electrode is obtained as an output from a movable electrode, The detection principle is demonstrated using FIG. In FIG. 12, the fixed electrode 1, the fixed electrode 2, the movable electrode, C1 ', and C2' are defined in the same manner as in FIG. The detection circuit shown in FIG. 12 is a circuit called a switched capacitor circuit. First, the capacitor Cf is short-circuited by the switch SW. At this time, voltages applied to the fixed electrodes 1 and 2 are V and 0 volts, respectively, and V / 2 is applied to the movable electrode by an OP amplifier (shown as OPA in FIG. 12). Next, when the voltage applied to the fixed electrodes 1 and 2 is reversed after the switch SW is turned off, the balance of charges between the fixed electrodes 1 and 2 and the movable electrode changes, and the amount of change is charged in the capacitor Cf. . The value of the capacitor Cf at this time is converted into a voltage as a capacitance change and output.

  Accordingly, as shown in FIG. 11, among the parasitic capacitances C1 to C10 and C12 generated for the movable electrode, the parasitic capacitance whose potential is not fixed affects the output. Specifically, since the amount of charge charged to the parasitic capacitance changes due to potential fluctuation, the amount of charge charged to the capacitor Cf fluctuates due to the influence, and the output fluctuates. At this time, the lower electrode of the part forming the parasitic capacitance with the movable electrode is intended to prevent the movable electrode from sticking to the substrate 1, and the stopper also restricts the movable range of the movable electrode. Therefore, the purpose is to prevent the movable electrode from sticking even when contact is made, and the stopper and the lower electrode are given the same potential as the movable electrode. Accordingly, the amount of charge of the parasitic capacitors C4 and C12 does not change, so the output is not affected.

  In addition, the parasitic capacitances C5, C6, and C8 formed between the wirings of the fixed electrode and the movable electrode have no influence on the output because a predetermined potential is applied to the fixed electrode. Therefore, the remaining parasitic capacitances, that is, parasitic capacitances C1, C7, C10 and C2, C3, C9 formed by the bonded Poly-Si (the bonding thin film 32) and the element forming film (the outer peripheral portion 201) with the movable electrode. Affects the output.

  In the said 1st and 2nd embodiment, in order to eliminate the influence of parasitic capacitance C1, C7, C10 among these parasitic capacitances, the electric potential of bonding Poly-Si is fixed. The third embodiment is characterized in that the influence of parasitic capacitance is eliminated by fixing the potential of the element formation film (outer peripheral portion 201). Parasitic capacitance formed by the element forming film, that is, the outer peripheral portion 201 and the movable electrode is mainly formed in a region adjacent to the beam portions 4 and 5 shown in FIG. The gap S1 is on the order of 10 μm or less. Since the gap S1 is narrow, the influence of parasitic capacitance is increased.

  Therefore, as shown in FIGS. 1 and 2, a pad 202 is provided on the outer peripheral portion 201 as a means for fixing the potential of the outer peripheral portion 201. By applying a voltage to the pad 202 from a control circuit (not shown) and fixing the potential of the outer peripheral portion 201 (element formation film potential), there is no change in the charge amount of the parasitic capacitance formed by the outer peripheral portion 201 and the movable electrode. The fluctuation of the output voltage due to the parasitic capacitance can be suppressed. The pad 202 can be made of an aluminum thin film or the like.

  Of course, as a more preferable mode, the potential of the outer peripheral portion 201 described in the present embodiment and the potential of the bonding thin film 32 described in the first and second embodiments are taken. By implementing this simultaneously, the influence of parasitic capacitance can be sufficiently eliminated. Further, as a more preferable form, the potential fixed to the outer peripheral portion 201 or the thin film for bonding 32 is the potential applied to the movable electrodes 7a to 7d, 8a to 8d, that is, the non-inverting input terminal of the OP amplifier shown in FIG. It is desirable to apply V / 2 applied to the. This is because if the outer peripheral portion 201 and the bonding thin film 32 have the same potential as the movable electrode, the charge is not charged up to the parasitic capacitance, and can be sufficiently eliminated due to the influence of charge fluctuations on the output. Note that the non-inverting input terminal applied voltage of the OP amplifier may be between 0 and V.

(Fourth embodiment)
In the third embodiment, the provision of means for fixing the potential of the outer peripheral portion (hereinafter referred to as outer peripheral portion potential fixing means) has been described. However, in the present embodiment, the outer peripheral portion potential fixing means is provided as described above. The present invention is applied to an acceleration sensor having a configuration different from the form, that is, a capacitive acceleration sensor using an SOI wafer.

  Here, this kind of possible acceleration sensor J1 is shown in FIG. In FIG. 13, (a) is a plan view, (b) is a cross-sectional view taken along the line AA in (a), and (c) is a cross-sectional view taken along the line BB in (a). This sensor J1 is obtained by processing an SOI wafer 300 in which a first silicon substrate 301 as a supporting substrate and a second silicon substrate 302 as an element forming film are bonded together via an insulating film 303 made of SiO2. It is.

  Similarly to the above-described embodiment, in the second silicon substrate (element formation film) 302, the movable electrodes 304 and 305, the fixed electrodes 306 and 307, the anchor portions 308 and 309, and the pad 310 that applies a potential to the fixed electrodes. 311, a pad 312 for taking out the output from the movable electrode, and structures necessary for the sensor structure such as each wiring (conductor portion) 310 a, 311 a, that is, a sensor element portion is formed, and a groove S 2 is formed on the outer periphery of the sensor element portion. An outer peripheral portion 313 exists through the.

  Specifically, two anchor portions 308 and 309 are supported on the first silicon substrate 301 via the insulating film 303. Bending beams 314 and 315 are suspended from the anchor portions 308 and 309, respectively. Further, a rectangular mass portion 316 connected to each of the beams 314 and 315 exists between the beams 314 and 315.

  Rod-shaped movable electrodes 304 and 305 extend on both sides from the mass portion 316, and fixed electrodes 306 and 307 are arranged to face the movable electrodes 304 and 305, respectively. Here, in FIG. 13, the first capacitance detection unit is configured by the movable electrode 304 and the fixed electrode 306 facing each other on the left side of the mass unit 316, and the movable electrode 305 and the fixed electrode 307 facing each other on the right side of the mass unit 316. Thus, the second capacitance detection unit is configured. That is, in the present embodiment, the sensor element unit has two capacitance detection units.

  Also in the present embodiment, similarly to the above-described embodiment, the movable electrodes 304 and 305, the beams 314 and 315, and the mass portion 316 constitute a beam structure 2A as a movable portion. The movable electrodes 304 and 305 are electrically connected to the movable electrode pad 312 via the anchor portion 309, the fixed electrode 306 is electrically connected to the fixed electrode pad 310 via the wiring 310a, and the fixed electrode 307 is connected to the wiring. It is electrically connected to the fixed electrode pad 311 via 311a.

  Further, the first silicon substrate 301 and the insulating film 303 have a cavity portion 300a from which the inner peripheral portion is removed. As shown in FIG. 13, the cavity 300a is formed below the movable electrodes 304 and 305 and the mass portion 316, and below the region where the fixed electrodes 306 and 307 overlap the movable electrode. Note that a frame indicated by a broken line in FIG. 13A indicates an opening of the first silicon substrate 301.

  When acceleration is applied to the sensor J1 in the horizontal plane direction of the substrate 301, the mass unit 316 is displaced in the same horizontal direction. The amount of displacement is determined by the mass of the mass portion 316, the restoring force of the beams 314 and 315, and the electrostatic attractive force between the electrodes. Since the amount of displacement is a change in capacitance, the acceleration can be detected by changing the amount of charge between the electrodes in the capacitance detection unit, as in the above embodiment.

  In addition, as a manufacturing method of such a sensor structure, etching is performed from the surface of the second silicon substrate 302 in the SOI wafer 300 by dry etching or the like to create a movable electrode, a fixed electrode, a pad, and the like. The silicon substrate 301 side is anisotropically etched with an alkaline solution such as KOH, and the insulating film 303 to which the movable electrode and the fixed electrode are fixed is removed by etching, so that the beam structure 2A including the movable electrode is made movable. Can be formed.

  As described above, in the acceleration sensor J1, since the cavity 300a exists, the first silicon substrate 301 as a support substrate does not exist below the movable electrode and the fixed electrode. Therefore, since the bonding thin film does not exist below the movable electrode and the fixed electrode, there is no parasitic capacitance as formed by the bonding thin film 32 and the movable electrode described in the above embodiment.

  However, even in the case of the capacitive acceleration sensor J1 using this SOI substrate, the potential is not fixed (floating) in the portions other than the electrodes, and the capacitance detection unit between the movable electrode and the fixed electrode remains in the state. In addition to the capacitance, there is a parasitic capacitance due to the outer peripheral portion 313. Therefore, unless the charge accumulated in the parasitic capacitance is controlled, the capacitance of the capacitance of the capacitance detection unit fluctuates due to the coupling of the capacitance, so that the acceleration cannot be detected accurately or the output voltage fluctuates. .

  This defect will be specifically described with reference to FIG. FIG. 14 is an explanatory diagram showing an equivalent circuit in the acceleration sensor J1 shown in FIG. In FIG. 14, the fixed electrode 1 indicates the fixed electrode 306 side, the fixed electrode 2 indicates the fixed electrode 307 side, the movable electrode indicates the movable electrodes 304 and 305, and the capacitance between the fixed electrode and the movable electrode (capacitance of the capacitance detection unit) is C1. ', C2', and R1 to R5 indicate resistance values of the respective parts. The capacitances C1 'and C2' are changed by acceleration.

  In the case of the structure using the SOI wafer, there is a parasitic capacitance due to the outer peripheral portion 313 as indicated by symbols CK1, CK2, and CK3. Therefore, it is necessary to prevent the charges of the parasitic capacitors CK1 to CK3 from fluctuating. However, in the conventional structure, since one potential of the parasitic capacitance (that is, the potential of the outer peripheral portion 313) is floating, it has been found that the charges accumulated in the parasitic capacitances CK1 to CK3 change due to disturbance and affect the output.

  Therefore, in the capacitive acceleration sensor J1 using the SOI wafer, attention is paid only to the parasitic capacitance formed between the outer peripheral portion 313 and the movable and fixed electrodes 304 to 307, as in the above-described embodiment. What is necessary is just to fix the electric potential of the outer peripheral part 313. In the fourth embodiment, various examples using the peripheral portion potential fixing means are shown.

  In addition, each example shown below deform | transforms said acceleration sensor J1, A different part is described, The same code | symbol is attached | subjected to the same part in a figure, and description is abbreviate | omitted. Moreover, in each figure shown below, like FIG. 13, (a) is a top view, (b) is an AA sectional view in (a), (c) is a BB section in (a). The figure is shown.

  FIGS. 15A, 15B, and 15C show the configuration of an acceleration sensor as a first example of the present embodiment, and FIG. 16 shows an equivalent circuit in the acceleration sensor. In this acceleration sensor, pads 350 and 351 as means for fixing the potential of the outer peripheral portion 313 are formed on the outer peripheral portion 313 of the second silicon substrate 302 as an element forming film. The pads 350 and 351 can be made of, for example, an aluminum thin film as in the above embodiment.

  The pads 350 and 351 fix the potential of the outer peripheral portion 313 (element formation film potential) in the same manner as in the above embodiment, so that the parasitic capacitances CK1 to CK3 are fixed at a certain potential and affected by disturbance noise. It can be difficult. Here, the pads 350 and 351 are provided corresponding to each of the two capacitance detection units. Of the two capacitance detection units, the fixed electrode 306 side is defined as a first capacitance detection unit, and the fixed electrode 307 side is defined as a second capacitance detection unit. The pad 350 is for parasitic capacitances CK1 and CK3 between the outer periphery 313 and the first capacitance detection unit, and the pad 351 is for parasitic capacitances CK2 and CK3 between the outer periphery 313 and the second capacitance detection unit. Each reduces the parasitic capacitance.

  As described above, since the pad as the peripheral portion potential fixing means is provided corresponding to each capacitance detection unit, an arbitrary potential can be applied to each capacitance detection unit, and the parasitic capacitance is adapted to each capacitance detection unit. The electric charge which accumulates in can be controlled. That is, the offset generated in each capacitance detection unit can be controlled more efficiently. Further, in this example, the two capacitance detection units are accompanied by capacitance changes of approximately the same level. Specifically, this means that the beam structure (for example, the shape of the beam, the number of electrodes, etc.) is set so that the capacitance changes of the capacitances C1 ′ and C2 ′ of the capacitance detection units shown in FIG. ) Is possible.

  The distance between the first capacitance detection unit (304, 306) and the corresponding pad 350 and the distance between the second capacitance detection unit (305, 307) and the corresponding pad 351 are substantially the same. The voltages applied to the pads 350 and 351 corresponding to the first capacitance detection unit and the second capacitance detection unit can be made the same. That is, the voltage applied to the parasitic capacitance (CK1) with the fixed electrode 1 and the voltage applied to the parasitic capacitance (CK2) with the fixed electrode 2 can be made equal.

  Specifically, as shown in FIG. 15, each pad 350, 351 has an axis of symmetry perpendicular to the line connecting the first capacitance detection unit and the second capacitance detection unit (in the example shown, the center line of the sensor chip). (Corresponding to B-B). If it is not symmetrical, R4 and R5 are different in FIG. Therefore, the voltages applied to the parasitic capacitors CK1 and CK2 are different, which affects the offset voltage.

  Further, in the sensor element unit of this example, fixed electrode pads 310 and 311 are provided as pads for extracting a capacitance change for each capacitance detection unit, and each capacitance detection unit and each pad 310 and 311 are provided. Wirings 310a and 311a are provided as conductors that electrically connect the two. Here, the resistance values of the respective wirings 310a and 311a are made substantially the same, and the grooves S2 positioned around the respective wirings 310a and 311a are made to have substantially the same volume by adjusting, for example, the width and depth of the grooves. It is formed with.

  In this way, by making the volumes of the grooves S2 positioned around the respective wirings 310a and 311a substantially the same, the parasitic capacitances CK1 and CK2 shown in FIG. 16 are made substantially the same, and the resistance values R1 and R2 are made almost the same. In addition, the structure in which the offset is hardly generated can be obtained, and the voltage applied to each of the pads 350 and 351 can be the same, so that the sensor can be easily controlled.

  Next, the 2nd example of this embodiment is shown to Fig.17 (a), (b), (c). In the acceleration sensor of this example, there is one pad 352 as an outer peripheral portion potential fixing means, and this pad 352 is arranged on the above-mentioned axis of symmetry (corresponding to the center line BB of the sensor chip in the illustrated example). It is a feature. Since the pad 352 is arranged on the axis of symmetry, the following advantages are obtained as compared with the first example shown in FIG.

  In the first example, the number of wire bond wires to the circuit chip (control circuit) is five corresponding to the pads 310 to 312, 350 and 351, whereas in the second example, the pads 310 to 312 and Corresponding to 352, the number is four, and the manufacturing work time is shortened. Further, in this example, since there is one pad 352 as the outer peripheral portion potential fixing means, the potential of the outer peripheral portion 313 is likely to be stabilized. In the case of the first example, since there are two pads 350 and 351 as the peripheral portion potential fixing means, if a small potential difference occurs between these two portions, a current is generated between them, and the potential of the peripheral portion 313 fluctuates. To do.

  Next, as a modification of the second example, a third example of this embodiment is shown in FIGS. 18 (a), 18 (b), and 18 (c). In this acceleration sensor, an insulating groove 360 is formed on the outer peripheral side of the outer peripheral portion 313 on the outer edge side of the pad 352 as the outer peripheral portion potential fixing means, and the outer edge side and the inner edge side of the insulating groove 360 are insulated. It is said. Accordingly, the potential of the outer peripheral portion 313 fixed by the pad 352 is not applied to the outer peripheral side of the outer peripheral portion 313 with respect to the insulating groove 360. Therefore, even if Si debris or a conductive substance adheres to the outer edge side of the outer peripheral portion 313, that is, the outer peripheral side surface of the sensor, the potential of the fixed outer peripheral portion 313 is transmitted to the outer edge side from the insulating groove 360. As a result, no leakage current is generated on the support substrate 301 side.

  The acceleration sensor is formed in a plurality of units in the wafer and then cut into chips by dicing cut. The effect of the insulating groove 360 on the outer periphery of the sensor chip is to make the wafer into a chip. It can be used as a blade alignment mark when cutting. Further, the progress of chipping during dicing cut can be stopped.

  In addition, the same effect is acquired not only by this insulation groove | channel 360 but by multiple grooves. The present invention can also be applied to the acceleration sensors described in the first and second examples and the first to third embodiments. Further, in the second example, if the width of the first silicon substrate 301 shown in FIGS. 17B and 17C, that is, the frame widths F1, F2, F3, and F4 in the sensor chip are the same, it occurs in the sensor chip. The distortion due to the temperature change becomes uniform, and the temperature characteristic is stabilized. The same applies to the first and third examples.

  Further, as in the fourth example of the present embodiment shown in FIG. 19, even if the first silicon substrate 301 as the supporting substrate is present under the movable portion (beam structure), the present embodiment is implemented. Each example of the form is applicable, and the same effect can be obtained. FIG. 19 shows a cross section corresponding to (b) of FIGS. Also in this embodiment, as described in the third embodiment, the voltage applied to the pads 350 to 352 as the peripheral portion potential fixing means is the same as that of the movable electrode, and the potential of the peripheral portion 313 is set to the movable electrode. It is preferable to set the same potential as that.

  The present invention is not limited to the semiconductor acceleration sensor described above, but can be applied to other semiconductor dynamic quantity sensors such as a semiconductor yaw rate sensor.

It is a figure showing the plane composition of the semiconductor acceleration sensor concerning a 1st embodiment of the present invention. It is AA sectional drawing in FIG. It is process drawing which shows the manufacturing method of the semiconductor acceleration sensor shown in FIG. It is process drawing which shows the process following FIG. It is process drawing which shows the process following FIG. It is a figure which shows the cross-sectional structure of the semiconductor acceleration sensor concerning the modification of the said 1st Embodiment. It is a figure which shows the planar structure of the semiconductor acceleration sensor concerning the other modification of the said 1st Embodiment. FIG. 8 is a diagram illustrating a first configuration example of a location where a wiring 101 and a wiring 102 intersect in another modification example illustrated in FIG. 7. FIG. 8 is a diagram illustrating a second configuration example of a portion where a wiring 101 and a wiring 102 intersect with each other in another modification example illustrated in FIG. 7. It is a figure which shows the cross-sectional structure of the semiconductor acceleration sensor which concerns on 2nd Embodiment of this invention. It is explanatory drawing of the equivalent circuit of the parasitic capacitance in the semiconductor acceleration sensor which concerns on the said 1st and 2nd embodiment. It is explanatory drawing of the detection principle in the semiconductor acceleration sensor which concerns on the said 1st and 2nd embodiment. It is a figure which shows the capacity | capacitance type acceleration sensor using an SOI wafer. It is explanatory drawing which shows the equivalent circuit in the acceleration sensor shown in FIG. It is a figure which shows the 1st example of the semiconductor acceleration sensor which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows the equivalent circuit in the acceleration sensor shown in FIG. It is a figure which shows the 2nd example of the semiconductor acceleration sensor which concerns on the said 3rd Embodiment. It is a figure which shows the 3rd example of the semiconductor acceleration sensor which concerns on the said 3rd Embodiment. It is a figure which shows the 4th example of the semiconductor acceleration sensor which concerns on the said 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2A ... Beam structure, 2B ... Fixed part, 3a-3d ... 1st anchor part, 4, 5 ... Beam part, 6, 316 ... Mass part, 7a-7d, 8a-8d, 304,305 ... movable electrodes, 9a to 9d, 11a to 11d, 13a to 13d, 15a to 15d, 306, 307 ... fixed electrodes, 10a to 10d, 12a to 12d, 14a to 14d, 16a to 16d ... second anchor part, 50 , 51, 202, 350 to 352... Pad, 60... First semiconductor substrate, 61... Groove, 62... Silicon oxide film as a sacrificial layer thin film, 64 and 67. ... Polysilicon thin film as conductive thin film, 70 ... Polysilicon thin film as thin film for bonding, 72 ... Second semiconductor substrate, 200 ... Single crystal silicon, 201, 313 ... Outer peripheral portion, 302 ... Second Silicon substrate, 310, 311 ... fixed electrode pads, 310a, 311a ... wire, 360 ... insulating grooves, S2 ... groove.

Claims (8)

A support substrate (1, 301) and an element formation film (200, 302) formed on the support substrate;
The element forming film has a movable part (2A) through a groove formed in the element forming film and detects a change in capacitance due to displacement of the movable part, and an outer periphery of the sensor element part And the outer peripheral part (201, 313) arranged in
A semiconductor dynamic quantity sensor characterized in that the outer peripheral portion is provided with means (202, 350 to 352) for fixing the electric potential of the outer peripheral portion. The sensor element unit includes a plurality of capacitance detection units (304 to 307), and means (350, 351) for fixing the potential of the outer periphery corresponds to each of the plurality of capacitance detection units. The semiconductor dynamic quantity sensor according to claim 1, wherein the semiconductor dynamic quantity sensor is provided. The capacity detectors (304 to 307) are two, and each of the capacity detectors is accompanied by a capacity change of approximately the same level,
The distance between the first capacitance detection unit (304, 306) and the corresponding means (350) for fixing the potential of the outer peripheral portion, and the second capacitance detection unit (305, 307) and the corresponding one. 3. The semiconductor dynamic quantity sensor according to claim 2, wherein the distance from the outer peripheral portion fixing means (351) is substantially the same. Means for fixing the potential of each outer peripheral portion with respect to an axis of symmetry perpendicular to a line connecting the first capacitance detection unit (304, 306) and the second capacitance detection unit (305, 307) ( The semiconductor dynamic quantity sensor according to claim 3, wherein 350, 351) are arranged symmetrically. The sensor element unit electrically connects a pad (310, 311) provided for each capacitance detection unit (304 to 307) for extracting a capacitance change, each capacitance detection unit, and each pad. And conductive parts (310a, 311a) to be connected to each other,
5. The resistance value of each said conductor part is substantially the same, and the said groove | channel (S2) located in the circumference | surroundings of each said conductor part is formed by the substantially same volume, The thru | or 4 characterized by the above-mentioned. The semiconductor dynamic quantity sensor according to any one of the above. The sensor element unit includes two capacitance detection units (304 to 307), and each of the capacitance detection units is accompanied by a capacitance change having a magnitude of substantially the same level.
The means (352) for fixing the potential of the outer peripheral portion is on an axis of symmetry perpendicular to a line connecting the first capacitance detection unit (304, 306) and the second capacitance detection unit (305, 307). The semiconductor dynamic quantity sensor according to claim 1, wherein the semiconductor dynamic quantity sensor is arranged. The capacitance detection units (304 to 307) are fixedly supported by the movable substrate (304, 305) provided in the movable unit (2A) and the movable substrate (301), which are arranged to face the movable electrode. Electrodes (306, 307),
From the movable electrode, the capacitance change between the movable electrode and the fixed electrode is output,
The semiconductor dynamic quantity sensor according to any one of claims 1 to 6, wherein a potential fixed in the means (350 to 352) for fixing the potential of the outer peripheral portion is set to the same potential as that of the movable electrode. In the outer peripheral portion (201, 313), an insulating groove (360) is formed on the outer edge side of the means (202, 350 to 352) for fixing the electric potential of the outer peripheral portion, and an outer edge side and an inner edge side of the insulating groove. The semiconductor dynamic quantity sensor according to claim 1, wherein the semiconductor dynamic quantity sensor is insulated from the semiconductor dynamic quantity sensor.

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