JPH11218456A - Electrostatic capacitance type pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-sensitivity electrostatic capacitance type pressure sensor. SOLUTION: An Si diaphragm board 10 and first and second Si fixed boards 12, 13 bonded insulatively to both sides of the diaphragm board are provided, gaps G1, G2 are formed respectively at a diaphragm 10a of the diaphragm board and opposed faces of opposed first and second semiconductor fixed boards, and the diaphragm is deformable in the gaps. Both faces of the diaphragm become movable electrodes 21, 27, the opposed faces of first and second semiconductor fixed electrodes facing the movable electrodes are first and second fixed electrodes 17, 24, through-holes opened at the gaps are formed through the first and second semiconductor fixed boards to provide pressure introducing holes 19, 26. The bonding faces are of Si and hence the thermal expansion coefficients are equal to result in a thermally stable condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type pressure sensor.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional capacitance type pressure sensor. As shown in FIG.
And the glass substrate 2 are joined. A thin diaphragm 3 is formed at the center of the silicon substrate 1, and the glass substrate 2 side of the diaphragm 3 is used as a movable electrode 4, and aluminum or the like is deposited on the surface of the glass substrate 2 facing the movable electrode 4. Alternatively, the fixed electrode 5 is formed by sputtering. The movable electrode 4 and the fixed electrode 5 are separated by a predetermined distance, and a capacitance corresponding to the distance is generated between the electrodes 4 and 5. Further, an appropriate space 6 is formed between the electrodes 4 and 5, and the diaphragm 3 can be deformed in the space 6. And the glass substrate 2
Is provided with a pressure introducing hole 7 penetrating in the thickness direction, and a medium for pressure measurement can be supplied into the space 6 through the pressure introducing hole 7.

[0003] Thus, the pressure P through the pressure introducing hole 7
Is introduced into the space 6, the diaphragm 3 receives the pressure and bends and deforms almost entirely in a dome shape convex upward, so that the distance between the electrodes 4 and 5 changes. Therefore, the amount of deflection of the diaphragm 3 and, consequently, the pressure applied to the diaphragm 3 can be measured from the change in the capacitance generated between the electrodes 4 and 5.

As a mechanism for extracting a signal corresponding to the capacitance to the outside, as shown in FIG. 1B, an extraction wiring 8 continuous with the fixed electrode 5 is formed on the upper surface of the glass substrate 2 by a pattern. And a pad 9a is provided at the tip. Similarly, a pad 9b is provided on the surface of the glass substrate 2 exposed without the silicon substrate 1 present. At this time,
A part of the pad 9b is extended and positioned in the region where the silicon substrate 1 is present (joining region).

With this structure, in a state where the silicon substrate 1 and the glass substrate 2 are joined, the fixed electrode 5 is connected to the pad 9a via the lead-out wiring 8, and the movable electrode 4 is connected to the pad 9 via the silicon substrate 1. 9B, the pads 9a and 9b can be connected to an external device by attaching bonding wires to the pads 9a and 9b.

[0006] In the above-mentioned conventional sensor, a fixed / movable electrode for sensing pressure is provided as one set, so that in principle, only one pressure can be measured. Therefore, for example, when it is desired to measure the magnitude relationship between the pressures of two measurement media, two pressure sensors are prepared, and the pressure of the gas to be measured is measured by each pressure sensor. , Necessary information (pressure difference / large / small) can be obtained. As a sensor for realizing such processing, there is a sensor disclosed in Japanese Patent Application Laid-Open No. 8-35863.

Normally, a large number of sensor chips as shown in FIG. 1 are manufactured on a wafer at the same time, and then diced to separate and form individual sensor chips. However, in the invention disclosed in this publication, an integrated one-chip sensor is configured by cutting out two adjacent sensor chips S1 and S2 together at the time of dicing as described above ( (See FIG. 2).

[0008]

However, the integrated sensor disclosed in the above publication has a shape in which two pressure sensors are connected, so that the yield of one pressure sensor (sensor chip) is temporarily reduced. Assuming that it is 80% (the numerical value is an example and is different from the actual value), the yield of the whole sensor in which the two are integrated into one is required to be non-defective in each sensor part. (%)
× 80 (%) = 64 (%), resulting in a decrease in yield.

Further, in any of the conventional examples shown in FIGS. 1 and 2, since the silicon substrate 1 and the glass substrate 2 have different coefficients of thermal expansion, a tensile stress is generated on the joint surface. It will take. Since the magnitude of the stress varies depending on the temperature change, the displacement amount of the diaphragm when receiving the same pressure varies. That is, there is a problem that the temperature characteristics are deteriorated.

Further, in the structure shown in FIG. 1, since the pressure introduction hole is formed by providing the through hole in the glass substrate 2, it is not only complicated to form the through hole, but also by ultrasonic processing. Since it is formed by sandblasting, there is a drawback that the processing accuracy is low and the diameter of the introduction hole varies, and the minimum diameter that can be processed is limited to about 400 μm. That is, when the diameter of the pressure introducing hole is increased, the area of the fixed electrode is reduced, so that the sensitivity is reduced, and there is also a problem that the possibility of dust entering the inside of the sensor is increased.

In a conventional sensor, a fixed electrode, a lead wiring, and the like are formed by depositing a metal such as aluminum on a glass substrate. Therefore, not only does such a process become complicated, but also the portion where the lead wiring and the like are formed protrudes from the surface of the glass substrate 2 by the thickness thereof, and is not flush. As a result, when bonding the silicon substrate 1 and the glass substrate 2, the pads 9 electrically connected to the movable electrode 4 are provided on the bonding surface.
Since the protruding portion of b is interposed, it is not possible to make clean surface contact at that portion, and a gap is generated between the two substrates 1 and 2 at the contact portion of the pad, or stress is applied.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and an object of the present invention is to solve the above-mentioned problems and to perform high-sensitivity, high-temperature, and high-sensitivity measurement. Another object of the present invention is to provide a capacitance type pressure sensor that can exhibit desired effects for a long time without causing intrusion of dust and the like, and has a long life and high reliability.

[0013]

In order to achieve the above object, in a capacitance type pressure sensor according to the present invention, a semiconductor diaphragm substrate and a first diaphragm substrate joined to both surfaces of the diaphragm substrate in an insulated state. And a second semiconductor fixed substrate, wherein a gap is formed in each of the diaphragm provided on the diaphragm substrate and the opposing surfaces of the first and second semiconductor fixed substrates facing each other, and the diaphragm is formed within the gap. Can be deformed, and both surfaces of the diaphragm become movable electrodes, and opposing surfaces of the first and second semiconductor fixed electrodes facing the movable electrode are first and second fixed electrodes, and the first and second fixed electrodes are formed. A pressure introducing hole is provided in the semiconductor fixed substrate by forming a through hole opening in the gap (claim 1).

With this configuration, since the diaphragm substrate and the first and second semiconductor fixed substrates sandwiching the diaphragm substrate are both formed of semiconductors, the thermal expansion coefficients are equal or close to each other. The stress due to strain is reduced. Therefore, temperature characteristics are improved. Further, the pressure introduction hole is preferably provided that a hole is formed in a semiconductor such as silicon, so that processing can be performed easily and with high precision, and a minute hole can be formed. Further, since the substrate itself can be used for the wiring to be drawn to the outside, there is no problem that the drawn wiring is separately formed by evaporation or the like as in the conventional case, and the thickness is increased only at that portion so that the bonding surface is not uniform.

[0015] Preferably, a part of the side edge of the second semiconductor fixed substrate is removed to make a part of the side edge of the diaphragm substrate appear, and the exposed part is electrically connected to the movable electrode. A thinner side edge of the second semiconductor substrate close to the emerged portion of the diaphragm substrate, and a pad that is electrically connected to a second fixed electrode provided on the second semiconductor fixed substrate at the thinner portion. (Claim 2).

Further, a part of the side edge of the second semiconductor fixed substrate is removed to make a part of the side edge of the diaphragm substrate appear, and a pad that is electrically connected to the movable electrode is provided at the exposed part. A part of the side edge of the diaphragm substrate that has appeared is further removed to make a part of the side edge of the first semiconductor fixed substrate appear, and the exposed part is provided on the first semiconductor fixed substrate. A pad electrically connected to the first fixed electrode may be provided (claim 3).

With such a structure, since the height positions of two adjacent pads are close to each other, it is easy to bond a bonding wire to the pads, and the strength of the bonded portion is increased. In addition, since the pads are provided on each substrate, wiring can be easily routed.

[0018]

3 to 10 show a first embodiment of a capacitance type pressure sensor according to the present invention.
3 is a cross-sectional view, FIG. 4 is a plan view, FIGS. 5 to 7 are plan views showing a predetermined substrate taken out, FIG. 8 is an exploded perspective view, and FIG.
Is a perspective view, and FIG. 10 is a view for explaining an operation state. FIG.
As shown in FIG. 1, a first silicon fixed substrate 12 and a second silicon fixed substrate 13 are respectively bonded to upper and lower surfaces of a diaphragm substrate 10 therebetween. The diaphragm substrate 10 is also formed by reducing the thickness of the silicon wafer. In order to maintain an insulating state between the substrates 10, 12, and 13, a state in which insulating layers 15, 16 are interposed between the substrates. The joint is performed. That is, in the present embodiment, the basic structure is such that a three-layer structure of the silicon substrate is provided with an insulating layer interposed between the layers, and the specific configuration of each part is as follows.

First, the first silicon fixed substrate 12 has a rectangular shape having a predetermined thickness, and as shown in FIG. Provided. The upper surface of the first silicon fixed substrate 12 that is not covered with the insulating layer 15 becomes the first fixed electrode 17, and the surface of the first fixed electrode 17 is also provided with the protective film 18. This protective film 18 is also made of an insulating material (the protective film is not shown in FIG. 8). And this protective film 18
Is thinner than the thickness of the insulating layer 15. As a result, almost the entire surface (upper surface) on the bonding side of the first silicon fixed substrate 12 is covered with the insulating material. Further, a through-hole penetrating in the thickness direction is formed at the center of the first silicon fixed substrate 12, and serves as a first pressure introducing hole 19.

As will be described in a later-described manufacturing process, the protective film 18 and the insulating layer 15 are formed at positions and roles (the insulating layer 15 is used to prevent short-circuiting between substrates at the bonding portion, and the protective film 18 is used as the diaphragm 10a). Although different numbers are assigned to prevent the electrodes from contacting each other and short-circuiting when they are bent, they can be actually manufactured using the same material (for example, an oxide film is deposited and patterned). In addition, the protective film 18 and the insulating layer 15 may be provided separately at the boundary between them, but an oxide film forming the protective film 18 may be formed to extend to the insulating layer 15 and overlap. Then, in this case, the overlapped portion performs the function of the insulating layer 15.

Further, portions of the four corners of the insulating layer 15 are removed to expose the surface of the first silicon fixed substrate 12 (see FIGS. 5 and 8). The bonding pad 20 is provided on the exposed portion. As a result, the first fixed electrode 17 becomes conductive with the bonding pad 20 via the first silicon fixed substrate 12, and is therefore electrically connected to an external device via the bonding wire connected to the bonding pad 20. . In the illustrated example, a part of the insulating layer 15 is removed to expose the surface of the first silicon fixed substrate 12, and the surface of the first silicon fixed substrate 12 located around the bonding pad 20 is also exposed. However, the present invention is not limited to this. For example, instead of removing some of the four corners of the insulating layer, the insulating layer may be removed only at a portion connected to the bonding pad. In this case, the surface of the silicon substrate existing around the bonding pad is covered with the insulating layer, so that the insulating property is improved.

The diaphragm substrate 10 can be elastically deformed by making the silicon substrate thinner. The diaphragm substrate 10 is connected to the insulating layer 15 on the outer periphery of the lower surface, and is joined and integrated with the first silicon fixed substrate 12. And this insulating layer 15
The central portion that does not contact with is the diaphragm 10a.
In the joined state, as shown in FIG.
0a and the protective film 18, a first gap G1 is provided at a distance corresponding to the difference in thickness between the insulating layer 15 and the protective film 18, and the diaphragm 10a is located within the first gap G1.
Is deformable. Then, the medium whose pressure is to be measured is introduced into the first gap G1 through the first pressure introducing hole 19 described above, and the introduced pressure is applied to the lower surface of the diaphragm 10a. Further, the lower surface of the diaphragm 10a becomes the first movable electrode 21, and the first movable electrode 21
A capacitance corresponding to the distance is generated between the first fixed electrode 17 and the first fixed electrode 17.

On the upper surface of the diaphragm substrate 10,
An insulating layer 16 is formed. Similarly to the insulating layer 15, the insulating layer 16 is formed by forming an insulating film such as an oxide film on the entire surface of the substrate and then removing the center by etching, thereby patterning the outer periphery of the diaphragm substrate 10 into a substantially rectangular shape in a plane. Formed. Also, the diaphragm substrate 10
Although it is a thin rectangular flat plate, one of the four corners is cut out. The notch 10 b is formed on the insulating layer 15 formed on the surface of the first silicon fixed substrate 12.
, Ie, a portion corresponding to the region where the bonding pad 20 is formed. In other words, one third of the length of one side is cut off. Thereby, when the respective substrates are stacked, as shown in FIG. 4, the bonding pads 20 located on the lower side are exposed to the outside through the cutout portions 10b.

Further, the insulating layer 15 has a rectangular shape as described above, and is formed also on the upper surface of the outer bonding pad formation region. Thus, a hole 16a is provided at a predetermined position in the band-shaped pad formation region 10c that is continuous with the notch 10b on the upper surface of the diaphragm substrate 10, and the silicon surface is exposed through the hole 16a. Then, a bonding pad 23 is formed on the exposed surface. As a result, the first
The movable electrode 21 is electrically connected to the bonding pad 23 via the diaphragm substrate 10. Therefore, a signal corresponding to the capacitance generated between the first fixed electrode 17 and the first movable electrode 21 is output to both bonding pads 20 and 23.

The second silicon fixed substrate 13 includes an insulating layer 16
Is joined to the diaphragm substrate 10. The second silicon fixed substrate 13 also has basically the same shape as the first silicon fixed substrate 12, the surface facing the diaphragm 10a becomes the second fixed electrode 24, and the protective film 25 is formed on the entire lower surface on the bonding surface side. Form a film. Thus, in a state where the second silicon fixed substrate 13 and the diaphragm substrate 10 are joined, a second gap G2 opened by a distance corresponding to the thickness of the insulating layer 16 is secured between the diaphragm 10a and the protective film 25. Thus, the diaphragm 10a can be displaced within the second gap G2. And diaphragm 1
Even if 0a is bent and approaches the second silicon fixed substrate 13, there is no possibility that the diaphragm 10a and the second fixed electrode 24 come into contact with each other. Further, the upper surface side of the diaphragm 10a facing the second fixed electrode 24 is the second movable electrode 27.
Becomes Therefore, the second movable electrode 27 and the second fixed electrode 2
4, the capacitance corresponding to the distance is generated.

Further, a through-hole penetrating in the thickness direction is formed in the center of the second silicon fixed substrate 13, and serves as a second pressure introducing hole 26. Then, the pressure measurement target medium is introduced into the second gap G2 through the second pressure introduction hole 26, and the introduced pressure is applied to the upper surface of the diaphragm 10a.

Further, of the second silicon fixed substrate 13, the first silicon fixed substrate 12, the diaphragm substrate 10
In the side edge facing the bonding pads 20 and 23 formed in the above, the facing portion is cut away by 2/3 of the length of the side. Thereby, both bonding pads 20, 2
3 is exposed outside without being covered by the second silicon fixed substrate 13.

Further, in the upper surface of the second silicon fixed substrate 13, the bonding pad formation region 13a following the cut-out portion is thinned by removing the upper portion thereof, so that the diaphragm base 10 (protective layer 16 Steps with the surface are reduced. And the formation region 13
A bonding pad 29 is formed on the upper surface of a.
Thereby, the second fixed electrode 24 is electrically connected to the bonding pad 29 via the second silicon fixed substrate 13. Further, the second movable electrode 27 is electrically connected to the bonding pad 23 via the diaphragm substrate 10 in the same manner as the first movable electrode 21. Therefore, a signal corresponding to the capacitance generated between the second fixed electrode 24 and the second movable electrode 27 is output to both bonding pads 23 and 29.

By using the sensor having the above configuration, 2
When the difference between the pressures P1 and P2 of the two measurement target media is measured, the measurement can be accurately performed based on the following principle. That is, the two measurement target media are respectively referred to as first and second
The gas is supplied to the gaps G1 and G2 via the pressure introducing holes 19 and 26. Then, the pressures P1 and P2 of the respective measurement target media are applied to the upper and lower surfaces of the diaphragm 10a, respectively. Then, as shown in FIG. 10, the diaphragm 10a bends by an amount corresponding to the pressure difference (P1> P2 in the case shown).

As a result, the interval between the first gaps G1 is increased, and the capacitance generated between the first fixed electrode 17 and the first movable electrode 21 is reduced. On the contrary, the interval between the second gaps G2 is increased. The capacitance generated between the second fixed electrode 24 and the second movable electrode 27 increases. The larger the pressure difference, the larger the difference in capacitance. Thus, the pressure can be obtained by detecting the change in the two capacitances in a differential manner. Further, by performing such differential detection, disturbance noise can be canceled. Moreover, the pressures of the two comparison targets are set to one diaphragm 10a.
Can be obtained accurately from both sides.

Further, the sensor having this structure can measure a differential pressure with one sensor chip. Therefore, compared with a sensor that integrates and integrates two sensors described in the related art section and obtains a differential pressure, the yield is improved, and there is no possibility that most of the sensor chips are wasted due to a defective sensor. .

Further, in the present embodiment, since the diaphragm substrate 10 and the first and second silicon fixed substrates 12 and 13 are made of a material (silicon) having the same coefficient of thermal expansion, even when the temperature around the sensor changes, Since all the substrates have the same coefficient of thermal expansion, unnecessary stress is not applied to the substrate bonding surface. Therefore, even when a temperature change occurs, no stress is applied to the diaphragm 10a, and the diaphragm 10a is operated under the same conditions and conditions as before the temperature change.
Is displaced, and the output becomes stable. As a result, the temperature characteristics are significantly improved, and a highly reliable sensor is obtained. In addition,
A conventional type in which a glass substrate (fixed substrate) is bonded to a silicon substrate (diaphragm substrate) is applied to the present invention, two fixed substrates are formed of glass substrates, and fixed electrodes are provided on the formed two fixed substrates, respectively. When considering a sensor with a structure that detects differentially, the glass substrate is bonded to both sides of the diaphragm substrate. Tensile stress occurs on the surface. Therefore, a larger stress is applied compared to the conventional type in which a single glass substrate and a semiconductor substrate are joined, and when focusing on the temperature characteristics, the difference between the function and the effect of the present invention is remarkable. It will appear as a difference.

Further, in this embodiment, the electrodes and the bonding pads can be electrically connected via each substrate without arranging special wiring. This eliminates the need for a conventional process of forming a wiring pattern on the surface of a glass substrate by vapor deposition or the like, which not only simplifies the operation, but also allows the bonding surface to be flush, so that surface contact can be achieved. Therefore, it is possible to prevent the occurrence of a gap or the like and to ensure the airtightness at the joint surface.

Furthermore, in this embodiment, the bonding pads 23 are provided on the upper surface of the thin diaphragm substrate 10, a part of the second silicon fixed substrate 13 is formed thin, and the bonding pads 29 are formed thereon. The bond pad exists on a relatively close surface, and the step at the time of wire bonding is about sub-μm. Therefore, the condition of wire bonding to each pad is also the same, and high-strength wire bonding is possible in all pads, and the reliability of wire bonding is improved. Further, after exposing the silicon, it is not necessary to cover the exposed surface again with the oxide film, so that the bonding pad can be easily formed.

That is, if there is a large step on the surface on which the bonding pad is present, the distance from the wire down to the position where the wire is bonded (the position where the wire is actually connected to the pad) naturally differs. , The conditions for wire bonding differ. Therefore, there is a problem that the strength of the wire bond is different and the reliability of the wire is deteriorated. Further, in order to give the same strength to pads having different steps, it is necessary to set conditions for each pad height, and there remains a problem that unnecessary labor is required.
However, such a problem does not occur in the present embodiment as described above.

In the above-described embodiment, an example has been described in which there are two measured pressures and the difference or magnitude relation between the two is determined. However, it is needless to say that only one measurement target medium may be used.
In such a case, one will give the reference pressure (including the opening to the atmosphere).

Next, an example of a process for manufacturing the sensor having the above-described configuration will be described. First, as shown in FIG. 11A, the surface of the substrate used for the sensor is (1, 0,
0) plane P-type silicon single crystal substrate (first Si substrate) 1
'Prepared, the first 1Si substrate 12' 2 was applied to the entire upper surface in an insulating film (Si0 _2, etc.) 15 ', to remove the insulating film in a portion where the gap (oxide film). The thickness of the insulating film at this time is the lower gap amount.

Next, as shown in FIG. 3B, a thin oxide film is formed on the entire substrate. Of the oxide film, the portion of the oxide film from which the oxide film was removed in the previous step, that is, the oxide film deposited on the portion where the substrate surface is exposed becomes the protective film 18, and the surrounding oxide film and the insulating film formed in the previous step. Insulating layer 15
Is formed. Then, on the oxide film (insulating layer 15),
A silicon substrate 10 'serving as a diaphragm is placed and the first S
It is bonded to the i-substrate 12 '. In the figure, a thin film or the like is not formed on the diaphragm substrate, but by forming an insulating film, the effect of preventing a short circuit is improved ((C) in the figure).

Next, as shown in FIG. 12A, the silicon substrate 10 'joined in the previous step is thinned by wet etching or the like. By this processing, the thickness of the substrate is reduced to the thickness of the diaphragm 10a in the final sensor, and the diaphragm substrate 10 is manufactured. Next, an insulating film is formed on the upper surface of the thinned diaphragm substrate 10, and unnecessary portions are removed by etching and patterned. As a result, as shown in FIG.
The insulating layer 16 is formed on the outer periphery of the upper surface of the substrate. The P, of the (1,0,0) plane, on which a predetermined processing is applied to the joining surface,
A single crystal substrate (second Si substrate) 13 'of type silicon is prepared, and the second Si substrate 13' is joined (FIG. 3C).

Here, as shown in FIG. 14, the second Si substrate 13 'is doped with boron at a high concentration of about 7.times.10.sup.- ¹⁹ (cm.sup.- ³ ) as shown in FIG. Keep it. At this time, the region through which the pressure introducing hole penetrates and the region where the bonding pads of the first silicon substrate 12 and the diaphragm substrate 10 are formed are not doped with boron. Further, although not shown, an insulating film such as an oxide film is formed on the entire bonding surface of the second Si substrate 13 ', and a protective film 25 is formed.

The second processing which has been subjected to the predetermined processing as described above
With the Si substrate 13 'bonded, anisotropic etching by wet etching is performed, and the first and second Si substrates 1'
Holes (pressure introduction holes) for introducing pressure are formed in the gaps 2 'and 13'. At this time, a notch portion (one corner of one side of the silicon substrate is removed) necessary for exposing each bonding pad is also formed at the same time (FIG. 13A). Specifically, the first and second Si substrates 1
A resist is applied to a predetermined position on the non-bonding surface side of 2 ', 13' and a nitride film serving as a mask (not shown)
Pattern and cover the part to be left as a frame. When immersed in an etching solution in that state, the Si portion exposed without forming a mask is etched and removed,
After a lapse of a predetermined time, the P ⁺⁺ region is exposed. Then, the etching rate of the P ⁺⁺ region becomes slow, and the etching rate becomes an etch stop layer, and Si in which the P ⁺⁺ region is not formed is further removed. As a result, as shown in FIG.
And a notch portion is formed. At this time, the (1,1,1) plane appears on the oblique plane in the figure.

Finally, the three substrates 10, 12, 1
3 and a bonding pad made of aluminum or the like (in the illustrated example, the second silicon substrate 18).
(See FIG. 13 (B)) to complete the bonding pad 23 shown in FIG.

As described above, by using silicon for the fixed substrate, a hole can be formed very easily by dry etching, wet etching, or the like. Also, (1,0,
By using the silicon of the 0) plane, anisotropic etching in which the (1,1,1) plane appears on the side surface of the etched hole becomes possible. The shape of the hole becomes rectangular by anisotropic etching, and the cross-sectional area of the pressure introducing hole can be accurately and easily obtained. Since the cross-sectional area of the pressure introducing hole is accurately obtained, the calculation of the viscosity of the air and the conductance of the conduit becomes easy, and the simulation at the time of designing the sensor also becomes easy. Furthermore, a smooth design can be performed without spending time on designing a size of a sensor having characteristics required at the time of design change.

Further, when a hole is formed in the sensor by etching, unnecessary holes or the like are not produced, and a minute hole of about 10 μm or more is formed, so that a special operation is required. And can be processed at very low cost. Since the fine shavings do not adhere to the vicinity of the hole, there is no possibility that shavings enter the gap and the gap interval can be reduced. If the gap interval can be reduced, the capacitance accumulated in the gap also increases, and sufficient sensitivity can be obtained even if the electrode area is reduced. Since the electrode area can be reduced, the chip size can be reduced as a result, leading to cost reduction. As described above, various effects that cannot be obtained when the glass substrate is used are exhibited.

FIGS. 16 to 18 show a second embodiment of the present invention. This embodiment is basically the same as the above-described first embodiment, except that the structure for taking out the electrodes, more specifically, the structure of the portion for forming the bonding pad is changed. That is, each bonding pad is formed on the same surface of the chip.

In the illustrated example, the first silicon fixed substrate 13
An example in which a bonding pad is formed thereon is shown. In other words, the description will be given along the manufacturing process.
As shown in FIG. 17 which is a cross-sectional view taken along the line A-A ', a first hole 30 penetrating the second silicon fixed substrate 13 and the insulating layer 16 is formed by wet etching or the like at a position where a bonding pad is to be formed. A second hole 31 penetrating through the silicon fixed substrate 13, the insulating layer 16, the diaphragm substrate 10, and the insulating layer 15 is formed (FIG. 18A).

An insulating film 32 is formed on the inner peripheral surfaces (excluding the bottom surface) of the holes 30 and 31 and the surface of the second silicon fixed substrate 13.
Is formed. Specifically, an insulating film 32 is formed on the upper surface of the second silicon fixed substrate 13 (FIG. 2B). In this state, since the insulating film 32 also exists on the bottom surfaces of the holes 30 and 31, the bottom surface portion and a predetermined position of the upper surface of the second silicon fixed substrate 13 are etched, and the diaphragm substrate located on the bottom surface of each of the holes 30 and 31 is etched. 10 and the surface of the first silicon fixed substrate 12 are exposed, and a part of the surface of the second silicon fixed substrate 13 is exposed (FIG. 2C). A bonding pad 2 made of aluminum or the like is provided in the opening.
By forming 0, 23 and 29, a structure as shown in FIG. 17 is obtained.

With this configuration, the three bonding pads 20, 23, 29 can be formed on the same surface. Therefore, when the second silicon fixed substrate 13 side is used as a surface mounting surface on the mounting substrate side, when the sensor chip is die-bonded, signals can be directly taken out from the bonding pads by flip chip mounting. As a result, the number of wire bonding steps can be reduced. Further, even in the case of performing wire bonding, since each pad is on the same surface, wire bonding can be performed reliably and easily as in the above-described first embodiment.

FIG. 19 shows a specific application example of the pressure sensor according to the present invention. That is, there is a flow meter called a fluidic flow meter as one of flow meters for measuring the flow rate of a fluid such as city gas, and the pressure sensor of the present invention is incorporated in a part of this flow meter.

That is, the flow path forming wall 55 is provided in the pressure chamber 51.
a, 55b are provided to form a settling space 54, a conduit reducing portion 56, a jet nozzle 57, and a conduit enlarging portion 58. The fluid enters the settling space 54 from the inflow pipe 52, is rectified, flows at a high flow velocity in the conduit reduction section 56, and is discharged from the discharge nozzle 57 to the conduit expansion section 58. The ejected fluid becomes an oscillating fluid that flows alternately through the return flow paths 63a and 63b by the action of the partitions 60a, 60b, 61 and the exciter 62. The fluid that has come off from the return flow paths 63a and 63b is discharged from the discharge flow paths 64a and 64b to the downstream discharge pipe 53.
It flows to.

The change in the pressure of the fluid is taken out through the pressure guiding paths 65a and 65b provided in the partition wall 61, and the pressure sensor 4 of the present invention is used.
5 are guided to both sides of the diaphragm 10a. Then, an output corresponding to the difference between the two pressures is output from the pressure sensor 45, and is output to the sensor signal processing unit 45.
The signal is converted into an electric signal at a and supplied to the flow rate calculation circuit 70.

The flow rate calculation circuit 70 includes a waveform shaping circuit 72, a calculation circuit 73, and an output circuit 74. Spout nozzle 5
The pressure sensor 45 detects a pressure change caused by a change in the flow direction of the jet from the pressure sensor 7. Since the signal from the pressure sensor 45 at this time is a differential pressure signal associated with the pressure change as it is, the waveform shaping circuit 72 shapes this differential signal into a rectangular wave. Then, the arithmetic circuit 73 calculates the flow rate from the rectangular wave, and the output circuit 74 outputs the calculated flow rate value to the output terminal 56. Note that the specific arithmetic processing based on the above and the signal is the same as that of the related art, and a detailed description thereof will be omitted.

The pressure sensor 45 in this embodiment is made of silicon and oxide film (insulating film) having high corrosion resistance to city gas.
It is highly corrosion resistant to city gas, high reliability and long life.

Further, when used for flow rate measurement by differential pressure measurement such as fluidic, a flow meter with high accuracy (high frequency response, high resolution) and high reliability can be obtained. That is, for example, when detecting the flow rate by differential pressure measurement such as a fluidic type,
When there is no flow rate, the pressure applied to both surfaces of the diaphragm 10a may change simultaneously. At this time, if the pressure is applied to the diaphragm 10a and the pressure applied to the diaphragm 10a changes at the same time, the upper and lower pressures are canceled out because the pressure is applied to the single diaphragm 10a. Measurement is possible.

The above-mentioned flow rate calculation circuit sends the output of the sensor signal processing section 45a to the waveform shaping circuit 72 as it is. This is based on the pressure difference applied to the diaphragm 10a from the sensor signal processing section 45a. This is because positive and negative outputs are made. Therefore, for example, when the signal from the sensor signal processing unit 45a outputs a certain voltage when the pressure is balanced (differential pressure is 0), and changes based on the certain voltage according to the pressure difference, And
If you need to swing positive and negative when performing arithmetic processing,
The arithmetic circuit 73 takes an offset,
Alternatively, a comparison circuit is provided on the input side of the flow rate calculation circuit 70,
Various countermeasures can be taken such as inputting the output of the sensor signal processing unit 45a to the comparison circuit and using the constant voltage as the reference voltage of the comparison circuit.

In the above-described embodiments and application examples, an example in which the present invention is applied to a pressure sensor has been described. In this case, in order to make the diaphragm easily deformed by acceleration or the like, it is preferable to provide a weight protruding outward at the center of the diaphragm, for example.

[0057]

As described above, in the capacitance type pressure sensor according to the present invention, since both the diaphragm substrate and the two fixed substrates are composed of the semiconductor substrates, the tensile stress at the joint surface due to the temperature change is reduced. Occurrence is reduced. Therefore,
Good temperature characteristics. Further, the shape of the pressure introducing hole can be made small and the dimensional accuracy can be increased, and no shavings are generated at the time of machining, so that high-precision measurement and entry of dust can be suppressed, and stable operation can be performed for a long time. Further, according to the second and third aspects, wire bonding with high strength can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a conventional capacitance type pressure sensor.

FIG. 2 is a sectional view showing an example of a conventional capacitance type pressure sensor.

FIG. 3 is a sectional view showing a first embodiment of the sensor according to the present invention.

FIG. 4 is a plan view of the same.

FIG. 5 is a plan view showing a state where an insulating layer 15 is formed on a first silicon fixed substrate 12.

FIG. 6 shows a diaphragm substrate 10 and an insulating layer 16 thereon.
FIG. 3 is a plan view showing a state in which a film is formed.

FIG. 7 is a plan view showing a second silicon fixed substrate 13.

FIG. 8 is an exploded perspective view showing the first embodiment.

FIG. 9 is a perspective view of the same.

FIG. 10 is a diagram illustrating an operation state.

FIG. 11 is a diagram illustrating an example of a manufacturing process.

FIG. 12 is a diagram illustrating an example of a manufacturing process.

FIG. 13 is a diagram illustrating an example of a manufacturing process.

FIG. 14 is a diagram illustrating an example of a manufacturing process.

FIG. 15 is a diagram illustrating an example of a manufacturing process.

FIG. 16 is a plan view showing a second embodiment of the present invention.

FIG. 17 is a sectional view taken along line AA ′ of FIG.

FIG. 18 is a diagram illustrating an example of a manufacturing process.

FIG. 19 is a diagram illustrating an example of a use mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Diaphragm substrate 12 1st silicon fixed substrate 13 2nd silicon fixed substrate 15, 16 Insulating layer 17 1st fixed electrode 18, 24 Protective film 19 Pressure introduction hole 20, 23, 29 Bonding pad 21 1st movable electrode 24 2nd fixed Electrode 27 Second movable electrode

Claims (3)

[Claims] 1. A semiconductor substrate comprising: a semiconductor-made diaphragm substrate; and first and second semiconductor fixed substrates joined to both surfaces of the diaphragm substrate in an insulated state, wherein the diaphragm provided on the diaphragm substrate faces the first and second semiconductor fixed substrates. 1, on the surface facing the second semiconductor fixed substrate,
A gap is formed, and the diaphragm becomes deformable in the gap. Both surfaces of the diaphragm become movable electrodes, and the opposing surfaces of the first and second semiconductor fixed electrodes facing the movable electrode are the first and second surfaces. A capacitance type pressure sensor as a second fixed electrode, wherein a pressure introducing hole is provided in the first and second semiconductor fixed substrates by forming a through hole opening in the gap. 2. A part of a side edge of the second semiconductor fixed substrate is removed to make a part of the side edge of the diaphragm substrate appear, and a pad that is electrically connected to the movable electrode is provided at the part where the part is made to appear. A side edge of the second semiconductor substrate close to the emerged portion of the diaphragm substrate is thinned, and a pad that is electrically connected to a second fixed electrode provided on the second semiconductor fixed substrate is provided on the thinned portion. A capacitance type pressure sensor characterized by the above-mentioned. 3. A part of a side edge of the second semiconductor fixed substrate is removed to make a part of a side edge of the diaphragm substrate appear, and a pad that is electrically connected to the movable electrode is provided in the part where the part is made to appear. A part of the side edge of the diaphragm substrate that has appeared is further removed to expose a part of the side edge of the first semiconductor fixed substrate, and the first semiconductor fixed substrate is provided at the exposed portion. The capacitance type pressure sensor according to claim 1, further comprising a pad electrically connected to the first fixed electrode.