JP4539413B2 - Structure of capacitive sensor - Google Patents

Description

  The present invention relates to a physical quantity sensor such as an acceleration sensor or a gyro sensor, and more particularly to a structure of a capacitive sensor that detects a physical quantity from a capacitance between a fixed electrode and a movable electrode.

  Conventionally, as a capacitance type sensor, a capacitance change caused by displacement of an electrode interval between a fixed electrode formed on a glass substrate and a movable electrode formed on a semiconductor substrate facing the fixed electrode by external pressure. Capacitance sensors that detect physical quantities such as acceleration by using are widely used.

  In such a sensor, airtightness can be maintained over a long period of time, and even when used in a corrosive gas atmosphere, it is necessary to protect the movable electrode and fixed electrode that form the capacitance inside the sensor, Since a physical quantity is detected by a change in capacitance, a sensor structure that generates as little parasitic capacitance as possible is desired.

  As a configuration of such a conventional capacitance type sensor, as shown in Patent Document 1, a method is known in which a glass hole is covered with a silicon substrate and then bonded in a vacuum. In this conventional capacitive sensor joining method, a lid plate is separately formed on a silicon substrate by etching, and after sealing the glass hole of the glass substrate with the lid plate formed on the silicon substrate, the silicon substrate is further etched. Unnecessary portions other than the cover plate of the substrate need to be removed, and the process is complicated and takes time and cost.

Moreover, as shown in Patent Document 2, a fixed substrate that is provided with an independent region electrically separated from the support portion in the support portion that supports the weight portion formed on the semiconductor substrate, and is bonded to both surfaces of the support portion. A connection hole is provided opposite to the independent region, and each connection hole is sealed by being joined to the independent region. The airtightness of the sealed space such as the weight portion is maintained, and the lead wire of the movable electrode or the fixed electrode is used as a sensor. There is known a capacitive acceleration sensor that is taken out from the outside. However, in this sensor configuration, it is not possible to completely separate the independent regions by a single etching. Therefore, first, the semiconductor substrate is completely separated by etching once so that the weights and independent regions are not separated. The surface where the weighted portion, the independent region, etc. not formed are formed, and then the fixed substrate is bonded to one surface of the semiconductor substrate to temporarily fix the weighted portion, the independent region, etc., and the fixed substrate is joined again. It was necessary to etch the semiconductor substrate for the second time from the opposite surface to electrically separate the weight portion and the independent region from the support portion. Therefore, the etching process is required twice, which complicates the processing process and requires time and accuracy.
Japanese Patent No. 2772111 JP-A-7-245417

  The present invention has been made to solve the above problems, and the present invention provides a sensor with a sealed structure that can be easily formed by a single etching without forming a lid by the above-described two etchings. An object of the present invention is to provide a capacitive sensor structure that can form a chip pattern, has a simple manufacturing process, and has high reliability.

In order to achieve the above object, the invention of claim 1 comprises a glass substrate on which a fixed electrode is formed and a semiconductor substrate on which a movable electrode is formed, and wiring from each electrode through a through hole provided in the glass substrate. In the structure of the capacitance type sensor that pulls out, an SOI (Silicon on Insulator) wafer substrate having an upper Si substrate and a lower Si substrate bonded to each other through an insulating layer is used as the semiconductor substrate. Forming an island-shaped separation portion electrically separated from the Si substrate on the upper Si substrate, and anodic bonding the semiconductor substrate and the glass substrate to seal a through hole in the glass substrate; there row electrical connection between the wiring of the fixed electrode and Jo separation unit, a portion of the lower Si substrate on the back of the island-like isolation portion obtained by removing to the insulating layer That.

According to a second aspect of the present invention, in the structure of the capacitive sensor according to the first aspect, the lower Si substrate on the back surface of the island-shaped separation portion is removed in an area larger than the size of the island-shaped separation portion, The island-shaped separation part is separated from the lower Si substrate.

According to a third aspect of the present invention, in the structure of the capacitive sensor according to the first or second aspect , wire bonding is directly performed from the outside of the glass substrate to the island-shaped separation portion at the lower portion of the through hole. The electrical wiring including is formed.

According to a fourth aspect of the present invention, in the structure of the capacitive sensor according to any one of the first to third aspects, a protective glass substrate is bonded to the back surface of the SOI substrate.

According to the first aspect of the present invention, the electrical connection between the island-shaped separation portion and the wiring of the fixed electrode can be performed simultaneously with the sealing of the through hole of the glass substrate. Therefore, it is possible to easily take out the electrically independent wiring from the fixed electrode to the outside while keeping the airtight state inside the sensor, and it is possible to obtain a highly reliable and compact capacitive sensor.

Moreover , since a part of the lower Si substrate on the back surface of the island-shaped isolation portion is removed up to the insulating layer, the parasitic capacitance between the island-shaped isolation portion and the lower Si substrate generated through the insulating layer is reduced, Parasitic capacitance between the island-shaped isolation portion and the other upper Si substrate is also reduced. Thereby, it is possible to reduce the parasitic capacitance generated between the island-shaped separation portion to which the wiring from the fixed electrode is connected and the upper Si substrate on which the movable electrode is formed, that is, the parasitic capacitance between the fixed electrode and the movable electrode, The linearity of the sensitivity and sensitivity characteristic of the sensor can be improved.

According to the second aspect of the present invention, since there is no lower Si substrate on the back side of the island-shaped isolation portion, the parasitic capacitance between the island-shaped isolation portion and the other upper Si substrate can be almost ignored. The effect can be almost completely eliminated.

According to the invention of claim 3 , since signals can be taken out by bonding directly to the electrodes of the upper Si substrate, the number of connections for taking out the wiring is reduced, and the reliability of drawing out the electrodes can be improved. it can.

According to the invention of claim 4 , the support of the sensor is strengthened by bonding the protective glass substrate to the back surface, and the lower Si substrate on the back side of the island-shaped separation part and the portion where the insulating layer does not exist, Since the protective glass substrate is almost completely sealed, the influence of the external environment can be eliminated, and the reliability of the sensor as a device can be further improved.

  Hereinafter, the structure of the capacitive sensor according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2 show the structure of a capacitive sensor 10a (hereinafter abbreviated as a sensor) according to the present embodiment.

1 and 2, the sensor 10a includes a sensor chip 1b (refer to FIG. 3B) of an SOI (Silicon on Insulator) wafer (hereinafter abbreviated as SOI substrate) on which the movable electrode 6a is formed, and a fixed electrode 9. It is comprised by the glass substrate 8 in which these were formed. The sensor chip 1b is composed of an upper Si substrate 2 serving as an active layer bonded via an insulating layer 3 made of an insulating SiO ₂ and a lower Si substrate 4 serving as a support substrate. The upper Si substrate 2 of the sensor chip 1b is formed. The glass substrate 8 is provided with a fixed electrode 9 on the surface facing the movable electrode 6a and through holes 11a and 11b for taking out electric signals from the fixed electrode 9 and the movable electrode 6a to the outside. The lead wire 12 is led from 9 to the vicinity of the through hole 11a having the metal film 11c serving as the wiring to the outside. The glass substrate 8 and the sensor chip 1b are bonded with high accuracy by anodic bonding. By this joining, the island-shaped separating portion 15 formed by electrically separating the lead wire 12 and the upper Si substrate 2 is electrically connected via the metal contact portion 13 disposed in the concave recess 14. The island-shaped separation portion 15 is joined to the metal film 11c formed on the inner wall of the through hole 11a so as to seal the through hole 11a. Further, the metal film 11c is connected to an external connection terminal 17a made of a metal pattern formed on the upper surface of the glass substrate 8, and a signal from the fixed electrode 9 is taken out to the outside. Similarly, the signal from the movable electrode 6a is also taken out from the external connection terminal 17b made of another metal pattern formed on the upper surface of the glass substrate 8 through the metal film on the inner wall of another through-hole 11b. A physical quantity such as acceleration is detected by the capacitance change between the extracted movable electrode 6a and the fixed electrode 9.

  FIG. 3 shows a configuration of a semiconductor substrate on which the sensor chip 1b of the sensor 10a shown in FIG. 2 is formed and each sensor chip on which a movable portion is formed on the semiconductor substrate. FIG. 3A shows a configuration of an SOI substrate 1a which is a semiconductor substrate used in the present embodiment, and FIG. 3B shows a sensor chip 1b serving as a sensor detection unit. The sensor chip 1b is an SOI substrate 1a. A movable electrode 6a having a diaphragm is provided as a movable portion formed on the substrate. (C) shows a sensor chip 1c different from the above, and this sensor chip 1c includes a movable electrode 6b having a weight body portion 6c as a movable portion.

  The movable electrode 6a has a cavity 7a in the lower Si substrate 4 on the back surface thereof to form a diaphragm. The movable electrode 6b is formed integrally with a weight body portion 6c supported by a beam and displaced by acceleration, and the weight body portion 6c is separated from the lower Si substrate 4 by a cavity 7b. Since both of the movable electrodes 6a or 6b use SOI substrates, they are electrically separated from the lower Si substrate 4 by the insulating layer 3 and are formed as electrodes on one side of the capacitive sensor. Since the movable electrodes 6a and 6b basically have the same function as the movable electrode, only the movable electrode 6a will be described here, and the description of the movable electrode 6b will be omitted.

  4A and 4B show a state in which the metal contact portion 13 and the concave depression 14 are formed on the sensor chip 1b shown in FIG. 3B. A capacitance gap 5 (hereinafter abbreviated as a capacitance gap) is formed above the movable electrode 6a of the sensor chip 1b. A concave recess 14 is formed from one end of the cavity of the capacity gap 5 to the vicinity of the portion facing the through hole 11a of the glass substrate 8 shown in FIG. The depression 14 is arranged such that the lead wire 12 of the fixed electrode 9 shown in FIG. 2 passes over the depression 14 when the glass substrate 8 is bonded to the upper Si substrate 2. Thereby, a short circuit between the lead wire 12 and the upper Si substrate 2 can be prevented. Further, a metal contact portion 13 for joining to the lead wire 12 is formed at the end portion of the recess 14, and the metal contact portion 13 is made of a metal material such as aluminum and is electrically connected to the upper Si substrate 2. Has been.

  FIGS. 5A and 5B show a state in which island-shaped separation portions 15 for separating the metal contact portions 13 are further formed on the sensor chip 1b of FIG. The upper Si substrate 2 is etched to the insulating layer 3 by deep etching of the Si substrate around the upper Si substrate 2 including the metal contact portion 13 and facing the through hole 11a, and is separated into islands in the upper Si substrate 2 An island-shaped separation portion 15 is formed. This island-shaped separation portion 15 is electrically separated from the surrounding upper Si substrate 2 by a separation groove 16 by etching.

  FIGS. 6A and 6B show the configuration of the glass substrate 8 of the sensor 10a shown in FIGS. 1 and 2 described above. The glass substrate 8 includes a movable electrode 6a of the sensor 10a and a fixed electrode 9 serving as one electrode for forming a capacitance. The fixed electrode 9 is arranged on the upper Si substrate 2 with the capacitance gap 5 shown in FIG. It arrange | positions so that it may oppose. Further, the glass substrate 8 is provided with two or more through holes 11a, 11b and the like for drawing out the wiring from the movable electrode 6a, the fixed electrode 9 and the like. The fixed electrode 9 is formed to a predetermined size by etching or the like after depositing a metal thin film to a thickness of 0.1 to 1 μm by vapor deposition or sputtering, and from this fixed electrode 9 to the vicinity of the through hole 11a. An extended lead wire 12 is formed. In addition, a metal film 11c is formed on the inner wall of the through hole 11a or 11b. This metal film 11c serves as a lead-out wiring for the fixed electrode 9 and the movable electrode 6a, and an external connection formed on the surface of the glass substrate 8. Connected to the terminal 17a or 17b, the sensor signal is extracted outside.

  According to the sensor 10 a according to the first embodiment having the configuration shown in FIGS. 1 to 6, the glass substrate 8 and the upper Si substrate 2 are bonded to the upper Si substrate 2 to be anodically bonded. Are closely joined and sealed around them. At this time, the lead-out line 12 of the glass substrate 8 and the metal contact portion 13 of the upper Si substrate 2 are joined, and the island-shaped separation portion 15 of the upper Si substrate 2 is connected to the through-hole 11a in which the metal film of the glass substrate 8 is formed. Are physically and electrically joined to the through-hole 11a in such a manner as to completely block. Since the lead wire 12 of the fixed electrode 9 is electrically connected to the metal contact portion 13 of the upper Si substrate 2, the fixed electrode 9 and the island-shaped separation portion 15 are electrically connected, and the glass substrate is passed through the through hole 11a. The signal from the fixed electrode 9 can be taken out from the external connection terminal 17 a on the surface of 8.

  Accordingly, the lead wires from the movable electrode 6a and the fixed electrode 9 can be electrically separated while the through holes 11a and 11b of the glass substrate 8 are sealed, and the wires can be taken out to the outside with the shortest length. As a result, it is possible to obtain a capacitive sensor with good airtightness, high reliability, small size and compactness.

  Next, the structure of the capacitive sensor according to the second embodiment of the present invention will be described with reference to FIGS. The capacitive sensor 10b of the present embodiment is different from the above-described embodiment in that a part of the lower Si substrate 4 on the back surface of the island-shaped separation portion 15 is removed up to the insulating layer 3. In FIG. 7, the sensor 10 b is formed with a cavity 19 in which a part thereof is removed to the insulating layer on the lower Si substrate 4 on the back surface of the island-shaped separation portion 15.

Parasitic capacitance in the sensor 10b will be described with reference to FIG. As shown in the figure, in the sensor 10b, when there is no cavity 19, a parasitic capacitance C1 is generated between the movable electrode 6a and the lower Si substrate 4 via the insulating layer 3, and similarly. A parasitic capacitance C2 is also generated between the island-shaped isolation part 15 connected to the fixed electrode 9 and the lower Si substrate 4 via the insulating layer 3. These total parasitic capacitance Cs of the parasitic capacitance C1 and C2 (Cs = C1 * C2 / C1 + C2) is electrically inserted in parallel to the measured capacitance _{C 0} between the fixed electrode 9 and the movable electrode 6a as the sensor detects the amount of Is done. Therefore, the parasitic capacitance Cs is a minute capacitance, but is unnecessary for the measurement capacitance C ₀ , and deteriorates the accuracy of the sensor and the linearity of the sensitivity characteristic. It is desirable to make it as small as possible.

  In the capacitive sensor 10b of the present embodiment, by providing the cavity 19, the lower Si substrate 4 on the back surface of the island-shaped separation portion 15 is eliminated, and the island-shaped separation portion 15 and the lower Si substrate 4 are separated from each other. Since one of the electrodes forming the capacitance capacitor is eliminated, the parasitic capacitance C2 can be greatly reduced. Thereby, the influence of the parasitic capacitance Cs on the sensor 10b can be reduced, and the linearity of the sensor accuracy and the sensitivity characteristic can be improved.

  Next, a capacitive sensor according to a third embodiment of the present invention will be described with reference to FIG. The capacitive sensor 10c of the present embodiment is different from the above-described embodiment in that the lower Si substrate 4 on the back surface of the island-shaped separation portion 15 is formed in an island shape that is electrically separated in the same manner as described above. .

  In the present sensor 10 c, the back-side island-shaped separation portion 21 electrically separated by the separation groove 21 a is provided on the lower Si substrate 4 corresponding to the island-shaped separation portion 15 of the upper Si substrate 2. It is formed independently from the island. Due to the back surface island-shaped separation portion 21, the parasitic capacitance C2 between the island-shaped separation portion 15 and the lower Si substrate 4 is changed to the parasitic capacitance between the island-shaped separation portion 15 and the back surface island-shaped separation portion 21, and the back surface island-shaped separation portion. 21 and the parasitic capacitance between the lower Si substrate 4. However, since the back surface island-shaped isolation portion 21 is electrically isolated from the other lower Si substrate 4, the parasitic capacitance C2 between the island-shaped isolation portion 15 and the lower Si substrate 4 can be greatly reduced. . Thereby, the parasitic capacitance between the island-shaped isolation | separation part 15 connected with the fixed electrode 9 and the movable electrode 6a can be reduced by simple processing only to dig a groove | channel, and the precision of a sensor can be improved more.

  Next, the structure of the capacitive sensor according to the fourth embodiment of the present invention will be described with reference to FIG. The capacitive sensor 10d according to the present embodiment removes a portion having an area larger than the size of the island-shaped separation portion 15 from the lower Si substrate 4 facing the back surface of the island-shaped separation portion 15 to obtain an island-shaped separation portion. This is different from the above embodiment in that 15 is separated from the lower Si substrate 4.

  In this sensor 10 d, a cavity 22 is formed in the lower Si substrate 4 on the back side of the island-shaped separation portion 15 of the upper Si substrate 2 by removing a portion having an area larger than the size of the island-shaped separation portion 15. The island-like separation portion 15 is almost completely separated from the lower Si substrate 4 by the hollow portion 22. By this separation, there is no conductor corresponding to the island-shaped separation portion 15 and the electrode plate forming the capacitor, and therefore, the parasitic capacitance between the island-shaped separation portion and the other upper Si substrate can be almost ignored. Can be almost completely eliminated. Thereby, according to the sensor 10d of this embodiment, generation | occurrence | production of the parasitic capacitance between the island-shaped isolation | separation part 15 and the lower Si substrate 4 can be made very small, and the accuracy of a sensor can further be improved.

  Next, the structure of a capacitive sensor according to the fifth embodiment of the present invention will be described with reference to FIG. The capacitive sensor 10e of the present embodiment is implemented in that the electrical wiring including the wire bonding 23 is formed directly from the outside of the glass substrate 8 to the island-shaped separation portion 15 below the through hole 11a. Different from form.

  The sensor 10e includes a bonding pad 23a on the upper surface of the island-shaped separation portion 15 of the upper Si substrate 2 below the through hole 11a, and the wire bonding 23 is directly bonded to the bonding pad 23a from the outside of the glass substrate 8. The wires from the fixed electrode 9 and the movable electrode 6a are taken out. As described above, since the signal can be directly taken out from the inside of the sensor by bonding, the connection process from the electrode can be reduced, and the reliability of the lead-out wiring from the electrode can be improved.

  Next, the structure of the capacitive sensor according to the fifth embodiment of the present invention will be described with reference to FIG. The capacitive sensor 20 of this embodiment is different from the above-described embodiment in that a protective glass substrate 24 is bonded to the back surface of the lower Si substrate 4.

  In the sensor 20, a protective glass substrate 24 covering the back surface thereof is bonded to the lower Si substrate 4, and a through hole 25 having a function and a role as a pressure introducing portion is provided in the central portion. The support of the sensor is strengthened by the protective glass substrate 24, and in the portion where the lower Si substrate 4 and the insulating layer 3 on the back side of the island-shaped separation portion 15 are not present, the protective glass substrate 24 almost completely completes. Thus, the influence of the external environment such as intrusion of moisture can be eliminated, and the reliability of the device as a sensor can be improved.

  As described above, according to the structure of the sensors 10a to 10d according to the present embodiment, by using the SOI substrate as the semiconductor substrate, it is possible to easily form the electrically isolated island-shaped isolation portion 15. it can. Then, the semiconductor substrate and the glass substrate 8 are anodically bonded to each other with high accuracy, and the island-shaped separation portion 15 provided on the upper Si substrate 2 of the SOI substrate serves as an extraction wiring from the fixed electrode 9 to the outside. The through hole 11a can be sealed. At the same time, each electrode and the through hole 11a are electrically connected, whereby a signal can be easily taken out from the through hole 11a. As described above, it is possible to obtain a compact and highly reliable capacitive sensor structure with good airtightness.

  Further, removing a part of the lower Si substrate on the back surface of the island-shaped separation portion up to the insulating layer, or forming a back-surface island-shaped separation portion on the lower Si substrate on the back surface of the island-shaped separation portion, or By separating the island-shaped isolation part from the lower Si substrate, the parasitic capacitance generated between the island-shaped isolation part and the other lower Si substrate can be reduced, and the linearity of the sensitivity and sensitivity characteristics of the sensor can be reduced. Can be improved.

  Furthermore, by extracting the signal directly by bonding to the electrode inside the sensor, the reliability of the extraction of the electrode can be improved, and a protective glass substrate is bonded to the back surface of the SOI substrate by anodic bonding or the like. The sensor is almost completely hermetically sealed, and the reliability of the device as the sensor can be improved.

1 is a plan view of a capacitive sensor according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line A1-A2 of FIG. (A) is a cross-sectional view of an SOI substrate used in the structure of the sensor, (b) is a cross-sectional view of a sensor chip formed on the substrate, and (c) is a cross-sectional view of another sensor chip formed on the substrate. . (A) is a top view of the state in which the metal contact part and the hollow were formed in the sensor chip shown in the said FIG.3 (b), (b) is B1-B2 sectional view taken on the line of (a). (A) is a top view of the state in which the island-shaped isolation | separation part was formed in the said sensor chip, (b) is the C1-C2 sectional view taken on the line of (a). (A) is a top view of the glass substrate of the structure of the said sensor, (b) is D1-D2 sectional view taken on the line of (a). Sectional drawing of the capacitive sensor which concerns on the 2nd Embodiment of this invention. The figure explaining the parasitic capacitance of the structure of the said sensor. Sectional drawing of the capacitive sensor which concerns on the 3rd Embodiment of this invention. Sectional drawing of the capacitive sensor which concerns on the 4th Embodiment of this invention. Sectional drawing of the capacitive sensor which concerns on the 5th Embodiment of this invention. Sectional drawing of the capacitive sensor which concerns on the 6th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Semiconductor substrate, SOI wafer substrate 1b, 1c Sensor chip 2 Upper Si substrate 3 Insulating layer 4 Lower Si substrate 6a, 6b Movable electrode 8 Glass substrate 9 Fixed electrode 10a, 10b, 20 Capacitive sensor 11a, 11b Through hole 15 island-like separation part 21 backside island-like separation part 23 wire bonding 24 glass substrate for protection

Claims (4)

In the structure of a capacitive sensor comprising a glass substrate on which a fixed electrode is formed and a semiconductor substrate on which a movable electrode is formed, and drawing out wiring from each electrode through a through hole provided in the glass substrate,
An SOI (Silicon on Insulator) wafer substrate having an upper Si substrate and a lower Si substrate bonded via an insulating layer is used as the semiconductor substrate, and the upper Si substrate is electrically separated from the Si substrate. Formed island-shaped separation part,
Sealing the through hole of the glass substrate by anodically bonding the semiconductor substrate and the glass substrate, and electrically connecting the island-shaped separation portion and the wiring of the fixed electrode;
A structure of a capacitive sensor, wherein a part of a lower Si substrate on a back surface of the island-shaped separation portion is removed up to an insulating layer.   The lower Si substrate on the back surface of the island-shaped separation portion is removed in an area larger than the size of the island-shaped separation portion, and the island-shaped separation portion is separated from the lower Si substrate. The structure of the described capacitive sensor. The relative island separation unit at the bottom of the through hole, the electrostatic capacitance according to claim 1 or claim 2, characterized in that the formation of the electrical wiring, including a direct wire bonding from the outside of the glass substrate Type sensor structure. The structure of the capacitive sensor according to any one of claims 1 to 3 , wherein a protective glass substrate is bonded to the back surface of the SOI substrate.

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