WO2012121030A1 - Absolute pressure sensor - Google Patents

Absolute pressure sensor Download PDF

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Publication number
WO2012121030A1
WO2012121030A1 PCT/JP2012/054584 JP2012054584W WO2012121030A1 WO 2012121030 A1 WO2012121030 A1 WO 2012121030A1 JP 2012054584 W JP2012054584 W JP 2012054584W WO 2012121030 A1 WO2012121030 A1 WO 2012121030A1
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WIPO (PCT)
Prior art keywords
substrate
pressure sensor
cavity
absolute pressure
thickness
Prior art date
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PCT/JP2012/054584
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French (fr)
Japanese (ja)
Inventor
田中　純一
真良 塩▲崎▼
佐々木　昌
憲一 伴
正男 清水
佳孝 安達
聡庸 金井
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オムロン株式会社
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Publication of WO2012121030A1 publication Critical patent/WO2012121030A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/84—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by variation of applied mechanical force, e.g. of pressure

Definitions

  • the present invention relates to a diaphragm type absolute pressure sensor, and in particular, to a reduction in the overall thickness of the absolute pressure sensor and long-term quality stability.
  • a pressure sensor is a device that measures the pressure of a gas or liquid with a pressure-sensitive element via a diaphragm, converts the pressure into an electrical signal, and outputs the electrical signal.
  • a semiconductor strain gauge is formed on the surface of the diaphragm, and a change in electric resistance due to a piezoresistance effect generated by deformation of the diaphragm by an external force (pressure) is converted into an electric signal.
  • the above pressure sensor measures absolute pressure based on the absolute vacuum, and any comparison pressure such as atmospheric pressure It is roughly classified into two types: a differential pressure (relative pressure) pressure sensor that measures a pressure expressed with respect to (reference pressure).
  • a semiconductor pressure sensor disclosed in Patent Document 1 As a conventional technique related to the above absolute pressure sensor, for example, a semiconductor pressure sensor disclosed in Patent Document 1 is known. As shown in FIG. 8A, a semiconductor pressure sensor 100 disclosed as a prior art in Patent Document 1 is formed at a peripheral edge of a diaphragm 101 to form a plurality of pressure sensitive resistance elements 102 and 102, and the pressure A base substrate 120 is bonded to a semiconductor substrate 110A having a cavity 103A formed on the side surface opposite to the surface on which the sensitive resistance elements 102 and 102 are formed, so that the cavity 103A is closed in a vacuum.
  • the cavity 103A has a vertical side wall.
  • the bonding area between the semiconductor substrate 110A and the base substrate 120 is reduced. Decreases, and the substrate bonding strength becomes weak.
  • the vacuum sealing of the cavity 103A becomes unstable, which is not preferable.
  • the bonding area between the semiconductor substrate 110A and the base substrate 120 is sufficiently secured and the chip size is reduced, the diaphragm size is reduced and the sensitivity is lowered.
  • the cavity 103 ⁇ / b> B is formed in an inversely tapered cross section that expands from the base substrate 120 side toward the semiconductor substrate 110 ⁇ / b> B.
  • the opening width at the joint surface with the base substrate 120 is improved to be set smaller than the element spacing between the pressure-sensitive resistance elements 102 and 102 adjacent to each other.
  • the bonding area between the semiconductor substrate 110B and the base substrate 120 can be ensured without reducing the diaphragm size, and the semiconductor pressure sensor 100 advantageous for downsizing can be obtained while maintaining the sensor sensitivity. .
  • the pressure sensor 200 disclosed in Patent Document 2 has a cavity that extends substantially parallel to the semiconductor substrate surface 201 in the central region ⁇ inside the semiconductor substrate 210.
  • the first gap 211 is provided.
  • a thinned diaphragm portion 212 and pressure sensitive elements 213 and 213 are provided.
  • the pressure-sensitive element 213 is electrically connected to the bumps 220 and 220 provided in the outer edge region ⁇ of the semiconductor substrate surface 201.
  • the pressure sensor 200 disclosed in Patent Document 2 is further provided with second gaps 214 closed to the semiconductor substrate surface 201 in at least a part of the outer edge region ⁇ inside the semiconductor substrate 210. ing.
  • pressure fluctuations other than the pressure to be measured include, for example, (1) characteristic fluctuations that occur in the pressure sensor due to residual stress immediately after mounting, and (2) thermal stress that occurs between the mounting board due to temperature changes. Examples of characteristic fluctuations that occur and (3) characteristic fluctuations that occur in the pressure sensor due to mechanical external factors such as substrate deformation and vibration are shown.
  • Japanese Patent Publication Japanese Patent Laid-Open No. 2009-276155 (published on November 26, 2009)” Japanese Patent Publication “JP 2009-264905 A (published on November 12, 2009)”
  • the conventional absolute pressure sensor has the following problems.
  • Patent Document 1 As shown in FIG. 10, as a basic configuration of an absolute pressure sensor, a sensor substrate having a diaphragm and a piezoresistor on the upper side of a cavity, and a cap substrate that is a base substrate It is made of what is joined.
  • the total thickness T, the diaphragm thickness T1, the absolute pressure sensor length D, and the cavity length D1 are limited by the size and sensitivity of the mounting device and the adhesive strength between the sensor substrate and the cap substrate.
  • the thickness T3 of the cap substrate located below the cavity is made as thick as possible so that external stress is not applied to the piezoresistor.
  • the absolute pressure sensor is mainly manufactured by a wafer process, and at this time, the sensor substrate side is subjected to patterning and the like, so that there are many wafer warps and irregularities. Therefore, when thinning a wafer using a grinder or the like, there is a problem that flatness of tape attachment is necessary and there is a limitation on the load. As a result, there is a problem that the entire thickness of the absolute pressure sensor cannot be reduced.
  • the present invention has been made in view of the above-described conventional problems, and an object thereof is to provide an absolute pressure sensor capable of reducing the entire thickness of the absolute pressure sensor.
  • the absolute pressure sensor of the present invention has a plurality of pressure sensitive resistance elements formed on the periphery of the diaphragm, and a cavity is formed on the surface opposite to the surface on which the pressure sensitive resistance elements are formed.
  • the thickness of the cavity is equal to or greater than the thickness of the cap substrate.
  • the cap substrate located below the cavity is made as thick as possible so that external stress is not applied to the pressure sensitive resistance element.
  • the thickness of the cavity is thinner than the thickness of the cap substrate.
  • a limit is often imposed on the total thickness of the absolute pressure sensor, and in order to maintain sensitivity corresponding to the limit, it is necessary to make the diaphragm thin.
  • there is a limit to making the diaphragm thinner and there is a problem that it cannot be made thinner than a certain level.
  • a tape is applied to the cap substrate to reinforce it, and then the upper side of the cavity on the sensor substrate is made thinner. It is difficult to increase, and it is necessary to consider the variation in the thickness of the diaphragm.
  • the thickness of the cavity is equal to or greater than the thickness of the cap substrate.
  • the cap substrate without the wiring pattern and the pressure sensitive resistance element, so that it is possible to grind easily without considering the uniformity of the tape and the variation in the diaphragm thickness.
  • the entire thickness of the absolute pressure sensor can be made smaller than before.
  • the thickness of the cavity is equal to or greater than the thickness of the cap substrate.
  • FIG. 1 shows an embodiment of an absolute pressure sensor according to the present invention, and is a cross-sectional view showing a configuration of an absolute pressure sensor.
  • the manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a piezoresistance creation process.
  • the manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows the grinding process of a 2nd silicon substrate.
  • the manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a cavity formation process.
  • the manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a cap board
  • the manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a cap board
  • (A) is sectional drawing which shows the structure of the prior art absolute pressure sensor described in the conventional patent document 1
  • (b) is sectional drawing which shows the structure of the absolute pressure sensor described in the conventional patent document 1 It is.
  • (A) is sectional drawing which shows the structure of the other conventional absolute pressure sensor, (b) is the top view. It is sectional drawing which shows the basic composition of the conventional absolute pressure sensor.
  • FIGS. 1 to 7 An embodiment of the present invention will be described with reference to FIGS. 1 to 7 as follows.
  • the absolute pressure sensor 1 of the present embodiment forms a plurality of piezoresistors 12 and 12 as pressure-sensitive resistance elements on the periphery of a diaphragm 11, and a surface on which the piezoresistors 12 and 12 are formed.
  • the sensor substrate 10 in which the cavity 13 is formed on the opposite surface is joined to the cap substrate 20 that closes the cavity 13.
  • the sensor substrate 10 is composed of an SOI (silicon-on-insulator) substrate formed by bonding a first silicon substrate 10a and a second silicon substrate 10b with a silicon oxide film (SiO 2 ) 14 interposed therebetween. Yes. That is, the first silicon substrate 10a and the second silicon substrate 10b are both made of silicon (Si).
  • SOI silicon-on-insulator
  • the first silicon substrate 10a has a circuit forming surface on which piezoresistors 12 and 12 which are a plurality of pressure sensitive resistance elements are formed.
  • the circuit formation surface is covered with a silicon oxide film (not shown) except for the upper positions of the plurality of piezoresistors 12 and 12.
  • a cavity 13 is formed in the sensor substrate 10 by removing the second silicon substrate 10b and a part of the silicon oxide film (SiO 2 ) 14 from the second silicon substrate 10b side, and the upper surface of the cavity 13 is configured.
  • a diaphragm 11 is formed by the first silicon substrate 10a.
  • the diaphragm 11 has a planar shape, for example, a circular shape, and a plurality of piezoresistors 12 and 12 are arranged so as to cover each side of the circular contour of the diaphragm 11.
  • the planar shape of the diaphragm 11 may be another shape such as a rectangle as long as it is distorted by pressure.
  • the cavity 13 is formed by removing a part of the second silicon substrate 10b and the first silicon substrate 10a from the second silicon substrate 10b side by a dry etching method.
  • the cavity 13 is formed as a cylindrical space, for example.
  • the cap substrate 20 is made of a silicon substrate and functions as a substrate that supports the sensor substrate 10 and covers the cavity 13.
  • the cap substrate 20 is bonded to the surface of the sensor substrate 10 on the side having the cavity 13, that is, the second silicon substrate 10b.
  • the second silicon substrate 10b of the sensor substrate 10 and the cap substrate 20 are bonded by a silicon (Si) -silicon (Si) bond in a non-oxide film state. That is, although the silicon wafer is made of silicon (Si), the surface is usually oxidized by leaving it in the atmosphere to form a silicon oxide film (SiO 2 ). However, when the cap substrate 20 and the second silicon substrate 10b of the sensor substrate 10 are joined with the silicon oxide film (SiO 2 ) formed, the cap substrate 20 and the sensor substrate are changed over time.
  • SiO 2 silicon oxide film
  • the cap substrate 20 and the second silicon substrate 10b are formed of a silicon (Si) -silicon (Si) junction in a non-oxide film state.
  • a low molecular weight gas such as helium (He) or hydrogen (H 2 ) from entering the cavity 13 from the bonding interface between the cap substrate 20 and the second silicon substrate 10b after bonding.
  • the cap substrate 20 and the second silicon substrate 10b can obtain a sufficient bonding strength by silicon (Si) -silicon (Si) bonding in a non-oxidized film state.
  • the inside of the cavity 13 is stably in a vacuum state for a long time.
  • the resistance values of the plurality of piezoresistors 12 and 12 change in accordance with the degree of distortion.
  • the midpoint potential of the bridge circuit constituted by the piezoresistors 12 and 12 is output as a sensor output to a known measuring device.
  • the measuring device is connected to the absolute pressure sensor 1 via each pad (not shown), and can measure the pressure based on the output (change in midpoint potential) of the absolute pressure sensor 1.
  • the thickness T2 of the cavity 13 is equal to or greater than the thickness T3 of the cap substrate 20. That is, Thickness T2 of cavity 13 ⁇ thickness T3 of cap substrate 20 It is said. The reason will be described in detail with reference to FIG. In the following analysis, it is assumed that the cavity 13 is circular.
  • the diaphragm 11 needs to bend due to a pressure change.
  • the cap substrate 20 supports the absolute pressure sensor 1, it is preferable that the cap substrate 20 be less bent.
  • a is a radius from the outer periphery to the center of the diaphragm 11.
  • the stress applied to the cap substrate and the diaphragm is The stress of the cap substrate thickness T3> 100 ⁇ the stress of the diaphragm thickness T1.
  • Cap substrate thickness T3> 10 ⁇ diaphragm thickness T1 If so, the cap substrate is less likely to bend about 100 times with respect to the stress, and it is considered that the effect of suppressing the influence of the stress is produced. For this reason, based on this concept, Cap substrate thickness T3> diaphragm thickness T1 I was trying.
  • the total thickness T of the absolute pressure sensor is limited by the thickness of the device in which the absolute pressure sensor is mounted.
  • the absolute pressure sensor length D is limited by the area of the device on which the absolute pressure sensor is mounted, and the cavity length D1 is limited by the influence of the adhesive strength between the sensor substrate and the cap substrate. Further, the diaphragm thickness T1 affects the sensitivity.
  • the thickness T3 of the cap substrate cannot be increased, so that the thickness T1 of the diaphragm is inevitably reduced.
  • the thickness T1 of the diaphragm needs to be determined in consideration of the variation in the diaphragm thickness, the tape application uniformity, and the variation in the wafer thickness. Accordingly, there is a limit to reducing the thickness T1 of the diaphragm.
  • the thickness T2 of the cavity is equal to or greater than the thickness T3 of the cap substrate.
  • the thickness T3 of the cap substrate 20 is reduced, it is not necessary to consider the variation in the thickness T1 of the diaphragm 11. Therefore, in the present embodiment, it is sufficient if the thickness T1 of the diaphragm is determined in consideration of two things, tape application uniformity and wafer thickness variation. Further, since it is not necessary to consider the variation in the thickness T1 of the diaphragm 11, the tape application uniformity may be low.
  • the overall thickness T of the absolute pressure sensor 1 can be easily made thinner than the conventional one.
  • the thickness (T1 + T2) of the sensor substrate is 25 ⁇ m and the thickness T3 of the cap substrate is 175 ⁇ m.
  • the total thickness T of the absolute pressure sensor is 200 ⁇ m.
  • the thickness (T1 + T2) of the sensor substrate 10 is 400 ⁇ m and the thickness T3 of the cap substrate 20 is 200 ⁇ m.
  • the thickness T can be 600 ⁇ m.
  • the thickness (T1 + T2) of the sensor substrate 10 is set to 300 ⁇ m
  • the thickness T3 of the cap substrate 20 is set to 200 ⁇ m. It can be 500 ⁇ m.
  • the thickness (T1 + T2) of the sensor substrate 10 is set to 100 ⁇ m and the thickness T3 of the cap substrate 20 is set to 100 ⁇ m so as to be built in an HDD (Hard disk drive).
  • the thickness is preferably 200 ⁇ m.
  • FIG. 2 is a cross-sectional view showing a piezoresistive forming process
  • FIG. 3 is a cross-sectional view showing a grinding process of a second silicon substrate
  • FIG. 4 is a cross-sectional view showing a cavity forming process
  • FIG. FIG. 6 is a cross-sectional view showing a process
  • FIG. 6 is a cross-sectional view showing a cap substrate grinding process.
  • piezoresistors 12 and 12 are formed on a sensor substrate 10 which is an SOI (silicon-on-insulator) substrate formed by bonding a first silicon substrate 10a and a second silicon substrate 10b.
  • a sensor substrate 10 which is an SOI (silicon-on-insulator) substrate formed by bonding a first silicon substrate 10a and a second silicon substrate 10b.
  • the thickness of the first silicon substrate 10a which is the thickness of the diaphragm T1
  • the total thickness of the first silicon substrate 10a and the second silicon substrate 10b is, for example, about 700 ⁇ m.
  • a grinding process of the second silicon substrate 10b in the sensor substrate 10 is performed.
  • the back surface of the second silicon substrate 10b is ground by BSG (backside grinding).
  • BSG backside grinding
  • a surface of the sensor substrate 10 opposite to the surface on which the piezoresistors 12 and 12 are formed is ground in a state where a double-sided tape is applied to the surface on which the piezoresistors 12 and 12 are formed and adhered to a stage (not shown).
  • grinding is performed until the total thickness of the first silicon substrate 10a and the second silicon substrate 10b becomes, for example, about 100 ⁇ m.
  • the ground surface is mirror-finished in a CMP (Chemical Mechanical Polishing) process.
  • CMP Chemical Mechanical Polishing
  • the ground surface is polished using a polishing liquid mixed with alumina abrasive grains.
  • the second silicon substrate 10 b and the silicon oxide film (SiO 2 ) 14 in the sensor substrate 10 are etched to form a recess that becomes the cavity 13, thereby forming the diaphragm 11 on the upper side.
  • the second silicon substrate 10b is etched by dry etching called Deep-RIE used in a MEMS (Micro Electro Mechanical Systems) process.
  • Deep-RIE Reactive Ion Etching
  • the second silicon substrate 10b is etched perpendicular to the surface of the second silicon substrate 10b.
  • the shape of the cavity 13 is a cylindrical shape of about 400 ⁇ m, for example. Accordingly, the cavity 13 has a circular horizontal cross section.
  • the shape of the horizontal section of the cavity 13 is not necessarily limited to this, and may be a polygon such as a square or a hexagon.
  • the sensor substrate 10 and the cap substrate 20 are bonded using a technique called room temperature bonding to form a vacuum cavity 13.
  • room temperature bonding first, in a high vacuum chamber in a bonding apparatus (not shown), the sensor substrate 10 is installed on the piston of the bonding apparatus, and the cap substrate 20 is installed on the stage of the bonding apparatus. And it hold
  • Ar argon
  • the sensor substrate 10 and the cap substrate 20 are joined by applying a load of about 2t in a state where the piston is lowered and the joining surface is brought into close contact therewith.
  • the sensor substrate 10 and the cap substrate 20 are bonded with silicon (Si) -silicon (Si) in a non-oxide film state.
  • the back surface of the cap substrate 20 is ground.
  • the back surface of the cap substrate 20 is ground by BSG (backside grinding) in the same manner as the grinding process of the second silicon substrate 10b in the sensor substrate 10 shown in FIG. To do.
  • BSG backside grinding
  • a double-sided tape is applied to the surface of the sensor substrate 10 on the side of the piezoresistors 12 and 12, and the surface opposite to the surface on which the piezoresistors 12 and 12 are formed is ground in a state of being bonded to a stage (not shown).
  • grinding is performed until the thickness T3 of the cap substrate 20 becomes about 100 ⁇ m, for example.
  • the absolute pressure sensor 1 shown in FIG. 1 is completed through the above steps.
  • a plurality of piezoresistors 12 and 12 are formed on the periphery of the diaphragm 11, and the cavity 13 is formed on the surface opposite to the surface on which the piezoresistors 12 and 12 are formed.
  • a cap substrate 20 is bonded to the formed sensor substrate 10 so as to close the cavity 13.
  • the thickness T2 of the cavity 13 is equal to or greater than the thickness T3 of the cap substrate 20.
  • the cap substrate 20 without the wiring pattern and the piezoresistors 12 and 12 may be ground, it is possible to easily grind the tape without applying the tape and considering the uniformity of the thickness of the diaphragm 11. As a result, the total thickness T of the absolute pressure sensor 1 can be made smaller than in the prior art.
  • the absolute pressure sensor 1 that can reduce the overall thickness T of the absolute pressure sensor 1.
  • the thickness T2 of the cavity 13 is equal to or greater than the thickness T3 of the cap substrate 20, the thickness T2 of the cavity 13 can be made larger than the thickness T2 of the conventional cavity.
  • the volume of the cavity 13 can be made larger than the volume of the cavity of the conventional product.
  • a low molecular weight gas such as helium (He) or hydrogen (H 2 ) 13 will be invaded.
  • the volume of the cavity 13 is larger than the volume of the conventional cavity. For this reason, even if a low molecular weight gas enters the cavity 13, there is an advantage that the pressure of the cavity 13 does not fluctuate greatly.
  • the sensor substrate 10 and the cap substrate 20 are both made of silicon (Si), and the sensor substrate 10 and the cap substrate 20 are in a non-oxide film state. Joined by a silicon (Si) -silicon (Si) junction.
  • the bonding interface between the sensor substrate 10 and the cap substrate 20 is completely sealed against a low molecular weight gas such as helium (He) or hydrogen (H 2 ). It is not possible. For this reason, when a low molecular weight gas leaks into the cavity 13 over time, the reference value as the absolute pressure varies. As a result, the measurement accuracy of the absolute pressure sensor 1 is lowered.
  • a low molecular weight gas such as helium (He) or hydrogen (H 2 ).
  • the sensor substrate 10 and the cap substrate 20 are bonded to each other by using a silicon (Si) -silicon (Si) bond in a non-oxide film state. It is in an oxide film state. For this reason, a low molecular weight gas such as helium (He) or hydrogen (H 2 ) does not enter from the bonding interface between the sensor substrate 10 and the cap substrate 20.
  • a low molecular weight gas such as helium (He) or hydrogen (H 2 ) does not enter from the bonding interface between the sensor substrate 10 and the cap substrate 20.
  • the absolute pressure sensor 1 since the reference value as the absolute pressure does not fluctuate, the measurement accuracy of the absolute pressure sensor 1 does not decrease. As a result, the absolute pressure sensor 1 having long-term quality stability can be provided.
  • the cavity 13 has a circular planar shape.
  • the sensor substrate and the cap substrate are both made of silicon (Si), and the sensor substrate and the cap substrate are made of silicon (non-oxide film state). Bonding is preferably performed by Si) -silicon (Si) bonding.
  • the cavity is initially in a vacuum, it cannot be completely sealed against a low molecular weight gas such as helium (He) or hydrogen (H 2 ) at the bonding interface between the sensor substrate and the cap substrate. .
  • a low molecular weight gas such as helium (He) or hydrogen (H 2 )
  • He helium
  • H 2 hydrogen
  • the sensor substrate and the cap substrate are brought into a non-oxide film state by forming a silicon (Si) -silicon (Si) bond between the sensor substrate and the cap substrate in a non-oxide film state. Therefore, helium from the bonding interface between the sensor substrate and the cap substrate (He) or hydrogen (H 2) of low molecular weight, such as gas never penetrates.
  • the cavity preferably has a circular planar shape.
  • Example 1 For the absolute pressure sensor 1 of the present embodiment, a comparative experiment with a conventional product was performed to confirm the effect of setting the thickness T2 of the cavity 13 to be equal to or greater than the thickness T3 of the cap substrate 20.
  • the absolute pressure sensor 1 was placed in an atmosphere of helium (He) at 2 atmospheres, and the change with time in the degree of vacuum in the cavity 13 was obtained.
  • the cavity 13 at this time has a circular planar shape, and the size of the cavity 13 is set to a radius of 0.4 mm. Further, the thickness T2 of the cavity 13 was set to 0.4 mm.
  • the shape of the cavity is a circular shape in a swing, and the cavity size is 0.4 mm in radius. Further, the thickness T2 of the cavity 13 was set to 0.2 mm.
  • the bonding between the sensor substrate 10 and the cap substrate 20 is a silicon (Si) -oxide film (SiO 2 ) -silicon (Si) bond through an oxide film.
  • the pressure fluctuation amount is 3321 (Pa)
  • the cavity 13 In the absolute pressure sensor 1 according to the present embodiment in which the thickness T2 is equal to or greater than the thickness T3 of the cap substrate 20, the pressure fluctuation amount is 1660 (Pa). Therefore, in the absolute pressure sensor 1 of this Embodiment, it has confirmed that the fluctuation amount of the vacuum degree in a cavity with time was 1/2 or less of a conventional product.
  • the amount of change in the degree of vacuum in the cavity 13 over time is smaller than that of the conventional product. Therefore, it was understood that the leakage of the low molecular gas with time is less affected by the offset fluctuation.
  • Example 2 the leak rate of helium (He) in the cavity 13 was confirmed when the sensor substrate 10 and the cap substrate 20 were in a silicon (Si) -silicon (Si) junction in a non-oxide film state.
  • the absolute pressure sensor of the silicon (Si) -oxide film (SiO 2 ) -silicon (Si) junction between the sensor substrate 10 and the cap substrate 20 via an oxide film is similarly treated with helium (He). The leak rate was confirmed.
  • the sensor substrate 10 and the cap substrate 20 are made of a silicon (Si) -oxide film (SiO 2 ) -silicon (Si) junction through an oxide film, thereby forming helium (He).
  • the leak rate was 6.8 ⁇ 10E-11 Pa ⁇ m 3 / s or less.
  • the leak rate of helium (He) is 1 ⁇ 10E-11 Pa ⁇ m 3 / s or less.
  • the leak rate of helium (He) is small in the silicon (Si) -silicon (Si) junction in the non-oxide film state.
  • the present invention can be applied to absolute pressure sensors such as a barometer, a water pressure gauge, and an altimeter.
  • the barometer, water pressure gauge, and altimeter using the absolute pressure sensor of the present invention are, for example, a tire pressure monitoring, a digital camera with a built-in barometer for underwater photography, a pedometer with a built-in altimeter that knows the altitude when climbing, Applicable to car navigation, wristwatches, etc.

Abstract

This absolute pressure sensor (1) is formed by joining a cap substrate (20) in a manner so as to close a cavity (13) to a sensor substrate (10) wherein a plurality of piezoresistors (12, 12) are formed at the rim of a diaphragm (11), and the cavity (13) is formed at the surface that is on the reverse side from the surface at which the piezoresistors (12, 12) are formed. The thickness (T2) of the cavity (13) is at least the thickness (T3) of the cap substrate (20). As a result, it is possible to provide an absolute pressure sensor that can have a reduced overall thickness of the absolute pressure sensor.

Description

絶対圧力センサAbsolute pressure sensor
　本発明は、ダイアフラム型の絶対圧力センサに関するものであり、特に、絶対圧力センサの全体厚みの薄型化及び長期品質安定性に関する。 The present invention relates to a diaphragm type absolute pressure sensor, and in particular, to a reduction in the overall thickness of the absolute pressure sensor and long-term quality stability.
　圧力センサは、気体や液体の圧力を、ダイアフラムを介して感圧素子にて計測し、電気信号に変換して出力する機器である。原理的には、ダイアフラムの表面に半導体ひずみゲージを形成し、外部からの力（圧力）によってダイアフラムが変形して発生するピエゾ抵抗効果による電気抵抗の変化を電気信号に変換している。 A pressure sensor is a device that measures the pressure of a gas or liquid with a pressure-sensitive element via a diaphragm, converts the pressure into an electrical signal, and outputs the electrical signal. In principle, a semiconductor strain gauge is formed on the surface of the diaphragm, and a change in electric resistance due to a piezoresistance effect generated by deformation of the diaphragm by an external force (pressure) is converted into an electric signal.
　上記圧力センサは、外部からの力（圧力）としてどのような圧力を使用するかによって、絶対真空を基準にして表した圧力を測定する絶対圧力センサと、大気圧等のある任意の比較する圧力（基準圧）に対して表した圧力を測定する差圧（相対圧）圧力センサとの２種類に大別される。 Depending on what pressure is used as the external force (pressure), the above pressure sensor measures absolute pressure based on the absolute vacuum, and any comparison pressure such as atmospheric pressure It is roughly classified into two types: a differential pressure (relative pressure) pressure sensor that measures a pressure expressed with respect to (reference pressure).
　上記の絶対圧力センサに関する従来技術として、例えば、特許文献１に開示された半導体圧力センサが知られている。特許文献１において従来技術として開示された半導体圧力センサ１００は、図８の（ａ）に示すように、ダイアフラム１０１の周縁に位置させて複数の圧力感応抵抗素子１０２・１０２を形成し、該圧力感応抵抗素子１０２・１０２の形成面とは反対側面にキャビティ１０３Ａを形成した半導体基板１１０Ａに、キャビティ１０３Ａを真空にして閉じるようにベース基板１２０を接合してなっている。上記キャビティ１０３Ａは側面壁が垂直となっている。 As a conventional technique related to the above absolute pressure sensor, for example, a semiconductor pressure sensor disclosed in Patent Document 1 is known. As shown in FIG. 8A, a semiconductor pressure sensor 100 disclosed as a prior art in Patent Document 1 is formed at a peripheral edge of a diaphragm 101 to form a plurality of pressure sensitive resistance elements 102 and 102, and the pressure A base substrate 120 is bonded to a semiconductor substrate 110A having a cavity 103A formed on the side surface opposite to the surface on which the sensitive resistance elements 102 and 102 are formed, so that the cavity 103A is closed in a vacuum. The cavity 103A has a vertical side wall.
　しかしながら、この側面壁が垂直となったキャビティ１０３Ａでは、半導体圧力センサ１００全体を小型化しようとする場合、ダイアフラムサイズを維持しつつチップサイズを小さくすると、半導体基板１１０Ａとベース基板１２０との接合面積が減少し、基板接合強度が弱くなってしまう。特に、半導体基板１１０Ａとベース基板１２０との接合によりキャビティ１０３Ａ内が真空状態で密閉される絶対圧センサの場合は、キャビティ１０３Ａの真空封止が不安定になり好ましくない。一方、半導体基板１１０Ａとベース基板１２０の接合面積を十分に確保してチップサイズを小さくすると、ダイアフラムサイズが小さくなり、感度が落ちてしまうという課題がある。 However, in the cavity 103A in which the side wall is vertical, when the entire semiconductor pressure sensor 100 is to be miniaturized, if the chip size is reduced while maintaining the diaphragm size, the bonding area between the semiconductor substrate 110A and the base substrate 120 is reduced. Decreases, and the substrate bonding strength becomes weak. In particular, in the case of an absolute pressure sensor in which the cavity 103A is sealed in a vacuum state by joining the semiconductor substrate 110A and the base substrate 120, the vacuum sealing of the cavity 103A becomes unstable, which is not preferable. On the other hand, there is a problem that if the bonding area between the semiconductor substrate 110A and the base substrate 120 is sufficiently secured and the chip size is reduced, the diaphragm size is reduced and the sensitivity is lowered.
　そこで、この課題を解決するために、特許文献１では、図８の（ｂ）に示すように、キャビティ１０３Ｂは、ベース基板１２０側から半導体基板１１０Ｂに向かって拡大する断面逆テーパ形状に形成され、ベース基板１２０との接合面における開口幅が隣り合う圧力感応抵抗素子１０２・１０２の素子間隔よりも小さく設定したものに改良されている。 Therefore, in order to solve this problem, in Patent Document 1, as shown in FIG. 8B, the cavity 103 </ b> B is formed in an inversely tapered cross section that expands from the base substrate 120 side toward the semiconductor substrate 110 </ b> B. The opening width at the joint surface with the base substrate 120 is improved to be set smaller than the element spacing between the pressure- sensitive resistance elements 102 and 102 adjacent to each other.
　これにより、ダイアフラムサイズを小さくすることなく半導体基板１１０Ｂとベース基板１２０との接合面積を確保でき、センサ感度を維持しつつ小型化に有利な半導体圧力センサ１００を得ることができるものとなっている。 As a result, the bonding area between the semiconductor substrate 110B and the base substrate 120 can be ensured without reducing the diaphragm size, and the semiconductor pressure sensor 100 advantageous for downsizing can be obtained while maintaining the sensor sensitivity. .
　また、他の従来技術としては、例えば、特許文献２に開示されたものが知られている。特許文献２に開示された圧力センサ２００は、図９の（ａ）（ｂ）に示すように、半導体基板２１０の内部における中央域αには、半導体基板表面２０１と略平行して広がるキャビティとしての第一空隙部２１１が設けられている。上記第一空隙部２１１の上側には、薄板化されたダイアフラム部２１２及び感圧素子２１３・２１３が備えられている。上記感圧素子２１３は、半導体基板表面２０１の外縁域βに設けられたバンプ２２０・２２０と電気的に接続されている。そして、この特許文献２に開示された圧力センサ２００には、半導体基板２１０の内部において外縁域βの少なくとも一部に、半導体基板表面２０１に対して閉じた第二空隙部２１４…がさらに配されている。 Further, as another conventional technique, for example, one disclosed in Patent Document 2 is known. As shown in FIGS. 9A and 9B, the pressure sensor 200 disclosed in Patent Document 2 has a cavity that extends substantially parallel to the semiconductor substrate surface 201 in the central region α inside the semiconductor substrate 210. The first gap 211 is provided. On the upper side of the first gap 211, a thinned diaphragm portion 212 and pressure sensitive elements 213 and 213 are provided. The pressure-sensitive element 213 is electrically connected to the bumps 220 and 220 provided in the outer edge region β of the semiconductor substrate surface 201. The pressure sensor 200 disclosed in Patent Document 2 is further provided with second gaps 214 closed to the semiconductor substrate surface 201 in at least a part of the outer edge region β inside the semiconductor substrate 210. ing.
　このように、半導体基板２１０の内部の外縁域βに第二空隙部２１４…を配することによって、バンプ２２０・２２０を介して伝わる被測定圧力以外の圧力変動をもたらす応力を該第二空隙部２１４…にて緩和することができる。したがって、特性変動の小さい圧力センサを提供するものとなっている。 As described above, by arranging the second gap portion 214... In the outer edge region β inside the semiconductor substrate 210, stress that causes pressure fluctuation other than the pressure to be measured transmitted through the bumps 220 and 220 is applied to the second gap portion. It can be mitigated at 214. Therefore, a pressure sensor with small characteristic fluctuation is provided.
　尚、被測定圧力以外の圧力変動として、例えば、（１）実装直後の残留応力によって圧力センサに生じる特性変動、（２）温度変化によって実装基板との間に生じる熱応力の影響によって圧力センサに生じる特性変動、（３）基板の変形・振動等の機械的な外部要因によって圧力センサに生じる特性変動を例示している。 Note that pressure fluctuations other than the pressure to be measured include, for example, (1) characteristic fluctuations that occur in the pressure sensor due to residual stress immediately after mounting, and (2) thermal stress that occurs between the mounting board due to temperature changes. Examples of characteristic fluctuations that occur and (3) characteristic fluctuations that occur in the pressure sensor due to mechanical external factors such as substrate deformation and vibration are shown.
日本国公開特許公報「特開２００９－２７６１５５号公報（２００９年１１月２６日公開）」Japanese Patent Publication “Japanese Patent Laid-Open No. 2009-276155 (published on November 26, 2009)” 日本国公開特許公報「特開２００９－２６４９０５号公報（２００９年１１月１２日公開）」Japanese Patent Publication “JP 2009-264905 A (published on November 12, 2009)”
　しかしながら、上記従来の絶対圧力センサでは、以下の問題点を有している。 However, the conventional absolute pressure sensor has the following problems.
　すなわち、上記特許文献１及び特許文献２のいずれにおいても、図１０に示すように、絶対圧力センサの基本構成として、キャビティの上側にダイアフラム及びピエゾ抵抗を有するセンサ基板とベース基板であるキャップ基板とを接合したものからなっている。そして、この構成においては、全体厚みＴ、ダイアフラム厚みＴ１、絶対圧力センサ長さＤ、及びキャビティ長さＤ１は、搭載装置のサイズ、感度、及びセンサ基板とキャップ基板との接着強度によって制約される。この制約下において、絶対圧力センサのチップサイズを小型にする場合には、ピエゾ抵抗へ外部応力が加わらないように、キャビティの下側に位置するキャップ基板の厚みＴ３をなるべく厚くしていた。 That is, in both Patent Document 1 and Patent Document 2, as shown in FIG. 10, as a basic configuration of an absolute pressure sensor, a sensor substrate having a diaphragm and a piezoresistor on the upper side of a cavity, and a cap substrate that is a base substrate It is made of what is joined. In this configuration, the total thickness T, the diaphragm thickness T1, the absolute pressure sensor length D, and the cavity length D1 are limited by the size and sensitivity of the mounting device and the adhesive strength between the sensor substrate and the cap substrate. . Under this restriction, when the chip size of the absolute pressure sensor is reduced, the thickness T3 of the cap substrate located below the cavity is made as thick as possible so that external stress is not applied to the piezoresistor.
　しかしながら、絶対圧力センサでは、ウエハプロセスにて製造することが主流であり、その際、センサ基板側はパターンニング等を行っているので、ウエハの反り及び凹凸が多い。したがって、グラインダー等を用いてウエハを薄型化する際、テープ貼り付けの平坦性が必要であり、かつ荷重に制限があるといった課題がある。この結果、絶対圧力センサの全体厚みを小さくすることができないという問題点を有している。 However, the absolute pressure sensor is mainly manufactured by a wafer process, and at this time, the sensor substrate side is subjected to patterning and the like, so that there are many wafer warps and irregularities. Therefore, when thinning a wafer using a grinder or the like, there is a problem that flatness of tape attachment is necessary and there is a limitation on the load. As a result, there is a problem that the entire thickness of the absolute pressure sensor cannot be reduced.
　本発明は、上記従来の問題点に鑑みなされたものであって、その目的は、絶対圧力センサの全体厚みを小さくし得る絶対圧力センサを提供することにある。 The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide an absolute pressure sensor capable of reducing the entire thickness of the absolute pressure sensor.
　本発明の絶対圧力センサは、上記課題を解決するために、ダイアフラムの周縁に複数の圧力感応抵抗素子を形成し、該圧力感応抵抗素子の形成面とは反対側の面にキャビティを形成したセンサ基板に、該キャビティを閉じるようにキャップ基板を接合してなる絶対圧力センサにおいて、上記キャビティの厚みは、キャップ基板の厚み以上となっていることを特徴としている。 In order to solve the above problems, the absolute pressure sensor of the present invention has a plurality of pressure sensitive resistance elements formed on the periphery of the diaphragm, and a cavity is formed on the surface opposite to the surface on which the pressure sensitive resistance elements are formed. In an absolute pressure sensor in which a cap substrate is bonded to a substrate so as to close the cavity, the thickness of the cavity is equal to or greater than the thickness of the cap substrate.
　すなわち、従来では、絶対圧力センサのチップサイズを小型にする場合、圧力感応抵抗素子へ外部応力が加わらないように、キャビティの下側に位置するキャップ基板の厚みをなるべく厚くしていた。この結果、従来では、キャビティの厚みは、キャップ基板の厚みよりも薄くなっていた。しかし、絶対圧力センサが搭載される装置においては、絶対圧力センサの全体厚みに制限が加えられることが多く、その制限に対応して感度を維持するためには、ダイアフラムを薄くする必要がある。しかし、ダイアフラムを薄くするにも限界があり、一定以上に薄くすることができないという問題があった。 That is, conventionally, when the chip size of the absolute pressure sensor is reduced, the cap substrate located below the cavity is made as thick as possible so that external stress is not applied to the pressure sensitive resistance element. As a result, conventionally, the thickness of the cavity is thinner than the thickness of the cap substrate. However, in an apparatus equipped with an absolute pressure sensor, a limit is often imposed on the total thickness of the absolute pressure sensor, and in order to maintain sensitivity corresponding to the limit, it is necessary to make the diaphragm thin. However, there is a limit to making the diaphragm thinner, and there is a problem that it cannot be made thinner than a certain level.
　具体的には、キャビティの厚みを薄くするときには、キャップ基板にテープを貼り付けて補強した上で、センサ基板におけるキャビティの上側を薄くすることになるが、そのときのテープを貼り付け均一性を高めることが困難であり、また、ダイアフラム厚みのバラつきも考慮する必要がある。 Specifically, when reducing the thickness of the cavity, a tape is applied to the cap substrate to reinforce it, and then the upper side of the cavity on the sensor substrate is made thinner. It is difficult to increase, and it is necessary to consider the variation in the thickness of the diaphragm.
　そこで、本発明では、キャビティの厚みは、キャップ基板の厚み以上となっているという構成を採用している。 Therefore, in the present invention, a configuration is adopted in which the thickness of the cavity is equal to or greater than the thickness of the cap substrate.
　これにより、配線パターン及び圧力感応抵抗素子のないキャップ基板を研削すればよいので、テープを貼り付け均一性及びダイアフラム厚みのバラつきを考慮することなく、容易に研削することができる。そして、結果的に、従来よりも絶対圧力センサの全体厚みを小さくすることができる。 Thus, it is only necessary to grind the cap substrate without the wiring pattern and the pressure sensitive resistance element, so that it is possible to grind easily without considering the uniformity of the tape and the variation in the diaphragm thickness. As a result, the entire thickness of the absolute pressure sensor can be made smaller than before.
　したがって、絶対圧力センサの全体厚みを小さくし得る絶対圧力センサを提供することができる。 Therefore, it is possible to provide an absolute pressure sensor that can reduce the entire thickness of the absolute pressure sensor.
　本発明の絶対圧力センサは、以上のように、キャビティの厚みは、キャップ基板の厚み以上となっているものである。 As described above, in the absolute pressure sensor of the present invention, the thickness of the cavity is equal to or greater than the thickness of the cap substrate.
　それゆえ、絶対圧力センサの全体厚みを小さくし得る絶対圧力センサを提供するという効果を奏する。 Therefore, there is an effect of providing an absolute pressure sensor that can reduce the entire thickness of the absolute pressure sensor.
本発明における絶対圧力センサの実施の一形態を示すものであって、絶対圧力センサの構成を示す断面図である。1 shows an embodiment of an absolute pressure sensor according to the present invention, and is a cross-sectional view showing a configuration of an absolute pressure sensor. 上記絶対圧力センサにおける製造方法を示すものであって、ピエゾ抵抗作成工程を示す断面図である。The manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a piezoresistance creation process. 上記絶対圧力センサにおける製造方法を示すものであって、第２シリコン基板の研削工程を示す断面図である。The manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows the grinding process of a 2nd silicon substrate. 上記絶対圧力センサにおける製造方法を示すものであって、キャビティ形成工程を示す断面図である。The manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a cavity formation process. 上記絶対圧力センサにおける製造方法を示すものであって、キャップ基板接合工程を示す断面図である。The manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a cap board | substrate joining process. 上記絶対圧力センサにおける製造方法を示すものであって、キャップ基板研削工程を示す断面図である。The manufacturing method in the said absolute pressure sensor is shown, Comprising: It is sectional drawing which shows a cap board | substrate grinding process. 上記絶対圧力センサにおけるヘリウム（Ｈｅ）雰囲気下でのキャビティ内真空度変動の経時変化を示すグラフである。It is a graph which shows a time-dependent change of the vacuum degree fluctuation | variety in a cavity under helium (He) atmosphere in the said absolute pressure sensor. （ａ）は従来の特許文献１に記載された従来技術の絶対圧力センサの構成を示す断面図であり、（ｂ）は従来の特許文献１に記載された絶対圧力センサの構成を示す断面図である。(A) is sectional drawing which shows the structure of the prior art absolute pressure sensor described in the conventional patent document 1, (b) is sectional drawing which shows the structure of the absolute pressure sensor described in the conventional patent document 1 It is. （ａ）は従来の他の絶対圧力センサの構成を示す断面図であり、（ｂ）はその平面図である。(A) is sectional drawing which shows the structure of the other conventional absolute pressure sensor, (b) is the top view. 従来の絶対圧力センサの基本構成を示す断面図である。It is sectional drawing which shows the basic composition of the conventional absolute pressure sensor.
　本発明の一実施形態について図１～図７に基づいて説明すれば、以下のとおりである。 An embodiment of the present invention will be described with reference to FIGS. 1 to 7 as follows.
　本実施の形態の絶対圧力センサ１は、図１に示すように、ダイアフラム１１の周縁に複数の圧力感応抵抗素子としてのピエゾ抵抗１２・１２とを形成し、該ピエゾ抵抗１２・１２の形成面とは反対側の面にキャビティ１３を形成したセンサ基板１０と、該キャビティ１３を閉じるキャップ基板２０とを接合してなっている。 As shown in FIG. 1, the absolute pressure sensor 1 of the present embodiment forms a plurality of piezoresistors 12 and 12 as pressure-sensitive resistance elements on the periphery of a diaphragm 11, and a surface on which the piezoresistors 12 and 12 are formed. The sensor substrate 10 in which the cavity 13 is formed on the opposite surface is joined to the cap substrate 20 that closes the cavity 13.
　詳細には、上記センサ基板１０は、シリコン酸化膜（ＳｉＯ２ ）１４を介して第１シリコン基板１０ａと第２シリコン基板１０ｂとを貼り合わせてなるＳＯＩ（シリコン・オン・インシュレータ）基板からなっている。すなわち、第１シリコン基板１０ａと第２シリコン基板１０ｂは、いずれもシリコン（Ｓｉ）からなっている。 Specifically, the sensor substrate 10 is composed of an SOI (silicon-on-insulator) substrate formed by bonding a first silicon substrate 10a and a second silicon substrate 10b with a silicon oxide film (SiO 2 ) 14 interposed therebetween. Yes. That is, the first silicon substrate 10a and the second silicon substrate 10b are both made of silicon (Si).
　第１シリコン基板１０ａは、複数の圧力感応抵抗素子であるピエゾ抵抗１２・１２を形成した回路形成面を有している。この回路形成面は、複数のピエゾ抵抗１２・１２の上方位置を除いて図示しないシリコン酸化膜にて覆われている。 The first silicon substrate 10a has a circuit forming surface on which piezoresistors 12 and 12 which are a plurality of pressure sensitive resistance elements are formed. The circuit formation surface is covered with a silicon oxide film (not shown) except for the upper positions of the plurality of piezoresistors 12 and 12.
　このセンサ基板１０には、第２シリコン基板１０ｂとシリコン酸化膜（ＳｉＯ２ ）１４の一部とを第２シリコン基板１０ｂ側から除去することによってキャビティ１３が形成され、このキャビティ１３の上面を構成する第１シリコン基板１０ａによってダイアフラム１１が形成されている。 A cavity 13 is formed in the sensor substrate 10 by removing the second silicon substrate 10b and a part of the silicon oxide film (SiO 2 ) 14 from the second silicon substrate 10b side, and the upper surface of the cavity 13 is configured. A diaphragm 11 is formed by the first silicon substrate 10a.
　上記ダイアフラム１１は、平面形状が例えば円形に形成されており、このダイアフラム１１の円形輪郭の各辺にかかるようにして複数のピエゾ抵抗１２・１２が配置されている。ただし、ダイアフラム１１の平面形状は、圧力を受けて歪む形状であれば、矩形等の他の形状でもよい。 The diaphragm 11 has a planar shape, for example, a circular shape, and a plurality of piezoresistors 12 and 12 are arranged so as to cover each side of the circular contour of the diaphragm 11. However, the planar shape of the diaphragm 11 may be another shape such as a rectangle as long as it is distorted by pressure.
　上記キャビティ１３は、上述したように、第２シリコン基板１０ｂと第１シリコン基板１０ａの一部を第２シリコン基板１０ｂ側からドライエッチング法により除去して形成されている。このキャビティ１３は、例えば、円筒形状の空間部として形成されている。 As described above, the cavity 13 is formed by removing a part of the second silicon substrate 10b and the first silicon substrate 10a from the second silicon substrate 10b side by a dry etching method. The cavity 13 is formed as a cylindrical space, for example.
　一方、キャップ基板２０は、シリコン基板からなり、センサ基板１０を支持し、キャビティ１３を覆う基板として機能している。このキャップ基板２０は、センサ基板１０のキャビティ１３を有する側の面、すなわち、第２シリコン基板１０ｂに接合されている。 On the other hand, the cap substrate 20 is made of a silicon substrate and functions as a substrate that supports the sensor substrate 10 and covers the cavity 13. The cap substrate 20 is bonded to the surface of the sensor substrate 10 on the side having the cavity 13, that is, the second silicon substrate 10b.
　ここで、本実施の形態では、センサ基板１０の第２シリコン基板１０ｂとキャップ基板２０との接合は、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合にて接合されている。すなわち、シリコンウエハはシリコン（Ｓｉ）からなっているが、通常、大気中に放置しておくことにより、その表面が酸化されシリコン酸化膜（ＳｉＯ２ ）が形成される。しかし、シリコン酸化膜（ＳｉＯ２ ）が形成された状態で、キャップ基板２０とセンサ基板１０の第２シリコン基板１０ｂとを接合した場合には、経時変化を経ることによって、キャップ基板２０とセンサ基板１０の第２シリコン基板１０ｂとの接合界面から、ヘリウム（Ｈｅ）又は水素（Ｈ２ ）等の低分子量の気体が真空状態としたキャビティ１３に侵入し、キャビティ１３内の真空状態が破られる。その結果、真の絶対圧力が測定できないことになる。そこで、本実施の形態では、これを防止するため、センサ基板１０の第２シリコン基板１０ｂとキャップ基板２０とを接合する前に、例えば、第２シリコン基板１０ｂの表面及びキャップ基板２０の表面をそれぞれプラズマ処理することにより、該キャップ基板２０の表面及び第２シリコン基板１０ｂの表面に形成されたシリコン酸化膜（ＳｉＯ２ ）を除去した後、キャップ基板２０と第２シリコン基板１０ｂとを接合している。これにより、キャップ基板２０と第２シリコン基板１０ｂとは、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合にてなっている。この結果、接合後にキャップ基板２０と第２シリコン基板１０ｂとの接合界面からヘリウム（Ｈｅ）又は水素（Ｈ２ ）等の低分子量の気体がキャビティ１３に侵入することを防止することができる。尚、キャップ基板２０と第２シリコン基板１０ｂとは、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合にて、充分な接合強度が得られるものとなっている。 Here, in the present embodiment, the second silicon substrate 10b of the sensor substrate 10 and the cap substrate 20 are bonded by a silicon (Si) -silicon (Si) bond in a non-oxide film state. That is, although the silicon wafer is made of silicon (Si), the surface is usually oxidized by leaving it in the atmosphere to form a silicon oxide film (SiO 2 ). However, when the cap substrate 20 and the second silicon substrate 10b of the sensor substrate 10 are joined with the silicon oxide film (SiO 2 ) formed, the cap substrate 20 and the sensor substrate are changed over time. A low-molecular-weight gas such as helium (He) or hydrogen (H 2 ) enters the vacuum cavity 13 from the bonding interface with the second silicon substrate 10b, and the vacuum state in the cavity 13 is broken. As a result, the true absolute pressure cannot be measured. Therefore, in the present embodiment, in order to prevent this, for example, the surface of the second silicon substrate 10b and the surface of the cap substrate 20 are bonded before the second silicon substrate 10b of the sensor substrate 10 and the cap substrate 20 are bonded. By removing the silicon oxide film (SiO 2 ) formed on the surface of the cap substrate 20 and the surface of the second silicon substrate 10b by performing plasma treatment, the cap substrate 20 and the second silicon substrate 10b are bonded to each other. ing. Thereby, the cap substrate 20 and the second silicon substrate 10b are formed of a silicon (Si) -silicon (Si) junction in a non-oxide film state. As a result, it is possible to prevent a low molecular weight gas such as helium (He) or hydrogen (H 2 ) from entering the cavity 13 from the bonding interface between the cap substrate 20 and the second silicon substrate 10b after bonding. Note that the cap substrate 20 and the second silicon substrate 10b can obtain a sufficient bonding strength by silicon (Si) -silicon (Si) bonding in a non-oxidized film state.
　上記の接合により、キャビティ１３内は長期間安定して真空状態となっている。その結果、上記構成の絶対圧力センサ１は、ダイアフラム１１が外面に付加される圧力に応じて歪むと、その歪み度合いに応じて複数のピエゾ抵抗１２・１２の抵抗値が変化し、この複数のピエゾ抵抗１２・１２にて構成されたブリッジ回路の中点電位がセンサ出力として公知の測定装置に出力される。測定装置は、図示しない各パッドを介して絶対圧力センサ１に接続され、この絶対圧力センサ１の出力（中点電位変化）に基づいて圧力が測定できるようになっている。 Due to the above-mentioned joining, the inside of the cavity 13 is stably in a vacuum state for a long time. As a result, in the absolute pressure sensor 1 configured as described above, when the diaphragm 11 is distorted in accordance with the pressure applied to the outer surface, the resistance values of the plurality of piezoresistors 12 and 12 change in accordance with the degree of distortion. The midpoint potential of the bridge circuit constituted by the piezoresistors 12 and 12 is output as a sensor output to a known measuring device. The measuring device is connected to the absolute pressure sensor 1 via each pad (not shown), and can measure the pressure based on the output (change in midpoint potential) of the absolute pressure sensor 1.
　ところで、本実施の形態では、キャビティ１３の厚みＴ２を、キャップ基板２０の厚みＴ３以上としている。すなわち、
　キャビティ１３の厚みＴ２≧キャップ基板２０の厚みＴ３
としている。その理由について、図１に基づいて詳述する。尚、以下の解析では、キャビティ１３が円形であるとしている。 By the way, in the present embodiment, the thickness T2 of the cavity 13 is equal to or greater than the thickness T3 of the cap substrate 20. That is,
Thickness T2 of cavity 13 ≧ thickness T3 of cap substrate 20
It is said. The reason will be described in detail with reference to FIG. In the following analysis, it is assumed that the cavity 13 is circular.
　すなわち、図１に示すように、ダイアフラム１１は圧力変化により撓む必要がある。一方、キャップ基板２０は、絶対圧力センサ１を支持するものであるので、撓みが少ない方がよい。ここで、絶対圧力センサ１について、ダイアフラム１１を梁と考えて、この梁であるダイアフラム１１に等分布荷重ｐが作用して撓むことを考えると、ダイアフラム１１の中心にかかる応力σは、
　　σ＝±３ｐａ２／４（Ｔ１）２
となる。尚、ａは、ダイアフラム１１の外周から中心までの半径である。 That is, as shown in FIG. 1, the diaphragm 11 needs to bend due to a pressure change. On the other hand, since the cap substrate 20 supports the absolute pressure sensor 1, it is preferable that the cap substrate 20 be less bent. Here, regarding the absolute pressure sensor 1, considering the diaphragm 11 as a beam and considering that the uniformly distributed load p acts on the diaphragm 11 which is the beam, the stress σ applied to the center of the diaphragm 11 is
σ = ± 3pa 2/4 ( T1) 2
It becomes. Note that a is a radius from the outer periphery to the center of the diaphragm 11.
　すなわち、撓みにより生じる応力は、ダイアフラム１１の厚みＴ１の２乗に反比例することが判る。 That is, it can be seen that the stress caused by the bending is inversely proportional to the square of the thickness T1 of the diaphragm 11.
　この結果、例えば、
　　キャップ基板の厚みＴ３＞１０×ダイアフラムの厚みＴ１
とした場合には、キャップ基板及びダイアフラムにかかる応力は、
　　キャップ基板の厚みＴ３の応力＞１００×ダイアフラムの厚みＴ１の応力
となる。 As a result, for example,
Cap substrate thickness T3> 10 × diaphragm thickness T1
In this case, the stress applied to the cap substrate and the diaphragm is
The stress of the cap substrate thickness T3> 100 × the stress of the diaphragm thickness T1.
　すなわち、
　　キャップ基板の厚みＴ３＞１０×ダイアフラムの厚みＴ１
とすれば、応力に対しては、キャップ基板が１００倍程度撓み難くなるので、応力による影響を抑制する効果が生じると考えられる。このため、従来では、この考え方に基づいて、
　　キャップ基板の厚みＴ３＞ダイアフラムの厚みＴ１
としていた。 That is,
Cap substrate thickness T3> 10 × diaphragm thickness T1
If so, the cap substrate is less likely to bend about 100 times with respect to the stress, and it is considered that the effect of suppressing the influence of the stress is produced. For this reason, based on this concept,
Cap substrate thickness T3> diaphragm thickness T1
I was trying.
　ところで、絶対圧力センサにおいては、図１０に示すように、絶対圧力センサの全体厚みＴは、絶対圧力センサが搭載される装置の厚さによって高さ制限を受ける。また、絶対圧力センサ長さＤは、絶対圧力センサが搭載される装置の面積によって制限を受け、キャビティ長さＤ１は、センサ基板とキャップ基板との接着強度の影響による制限を受ける。さらに、ダイアフラムの厚みＴ１は、感度に影響する。 Incidentally, in the absolute pressure sensor, as shown in FIG. 10, the total thickness T of the absolute pressure sensor is limited by the thickness of the device in which the absolute pressure sensor is mounted. The absolute pressure sensor length D is limited by the area of the device on which the absolute pressure sensor is mounted, and the cavity length D1 is limited by the influence of the adhesive strength between the sensor substrate and the cap substrate. Further, the diaphragm thickness T1 affects the sensitivity.
　そこで、従来では、絶対圧力センサの全体厚みＴに制限が課せられた場合には、キャップ基板の厚みＴ３を大きくすることができないので、必然的に、ダイアフラムの厚みＴ１を薄くしていた。 Therefore, conventionally, when a limit is imposed on the total thickness T of the absolute pressure sensor, the thickness T3 of the cap substrate cannot be increased, so that the thickness T1 of the diaphragm is inevitably reduced.
　しかしながら、ダイアフラムの厚みＴ１を薄くする場合には、キャップ基板のウエハにおける裏面にテープを貼り付けた後、センサ基板の表面を研削してウエハを薄くする。その場合、ダイアフラムの厚みＴ１は、ダイアフラム厚みバラツキとテープ貼り付け均一性とウエハ厚みバラツキとを考慮して決定する必要がある。したがって、ダイアフラムの厚みＴ１を薄くすることについては、限界があった。 However, in order to reduce the thickness T1 of the diaphragm, a tape is attached to the back surface of the cap substrate wafer, and then the surface of the sensor substrate is ground to thin the wafer. In that case, the thickness T1 of the diaphragm needs to be determined in consideration of the variation in the diaphragm thickness, the tape application uniformity, and the variation in the wafer thickness. Accordingly, there is a limit to reducing the thickness T1 of the diaphragm.
　そこで、本実施の形態では、この問題を解決するために、図１に示すように、キャビティの厚みＴ２は、キャップ基板の厚みＴ３以上となっている。この結果、本実施の形態では、キャップ基板２０の厚みＴ３を薄くするので、ダイアフラム１１の厚みＴ１のバラツキを考慮する必要がなくなる。そのため、本実施の形態においては、ダイアフラムの厚みＴ１は、テープ貼り付け均一性とウエハ厚みバラツキとの２つを考慮して決定すればそれで足りる。また、ダイアフラム１１の厚みＴ１のバラツキを考慮する必要がなくなるので、テープ貼り付け均一性が低くてもよい。 Therefore, in the present embodiment, in order to solve this problem, as shown in FIG. 1, the thickness T2 of the cavity is equal to or greater than the thickness T3 of the cap substrate. As a result, in the present embodiment, since the thickness T3 of the cap substrate 20 is reduced, it is not necessary to consider the variation in the thickness T1 of the diaphragm 11. Therefore, in the present embodiment, it is sufficient if the thickness T1 of the diaphragm is determined in consideration of two things, tape application uniformity and wafer thickness variation. Further, since it is not necessary to consider the variation in the thickness T1 of the diaphragm 11, the tape application uniformity may be low.
　すなわち、キャップ基板２０の厚みＴ３を薄くするよりも、テープ貼り付け均一性を上げる方が高める方が難しい。この結果、本実施の形態の絶対圧力センサ１では、従来のものよりも絶対圧力センサ１の全体厚みＴを容易に薄くできものとなっている。 That is, it is more difficult to increase the tape application uniformity than to reduce the thickness T3 of the cap substrate 20. As a result, in the absolute pressure sensor 1 of the present embodiment, the overall thickness T of the absolute pressure sensor 1 can be easily made thinner than the conventional one.
　具体的には、従来品では、センサ基板の厚み（Ｔ１＋Ｔ２）が２５μｍであり、かつキャップ基板の厚みＴ３が１７５μｍであり、その結果、絶対圧力センサの全体厚みＴが２００μｍとなっていた。これに対して、本実施の形態の絶対圧力センサ１では、センサ基板１０の厚み（Ｔ１＋Ｔ２）が４００μｍであり、かつキャップ基板２０の厚みＴ３が２００μｍであり、その結果、絶対圧力センサ１の全体厚みＴを６００μｍとすることができるものとなっている。尚、実用品として、例えば携帯電話に内蔵させるために、センサ基板１０の厚み（Ｔ１＋Ｔ２）を３００μｍとし、かつキャップ基板２０の厚みＴ３を２００μｍとし、その結果、絶対圧力センサ１の全体厚みＴを５００μｍとすることが可能である。さらに、例えばＨＤＤ（Hard disk drive）に内蔵させるために、センサ基板１０の厚み（Ｔ１＋Ｔ２）を１００μｍとし、かつキャップ基板２０の厚みＴ３を１００μｍとし、その結果、絶対圧力センサ１の全体厚みＴを２００μｍとすることが好ましい。 Specifically, in the conventional product, the thickness (T1 + T2) of the sensor substrate is 25 μm and the thickness T3 of the cap substrate is 175 μm. As a result, the total thickness T of the absolute pressure sensor is 200 μm. In contrast, in the absolute pressure sensor 1 of the present embodiment, the thickness (T1 + T2) of the sensor substrate 10 is 400 μm and the thickness T3 of the cap substrate 20 is 200 μm. The thickness T can be 600 μm. As a practical product, for example, to be built in a mobile phone, the thickness (T1 + T2) of the sensor substrate 10 is set to 300 μm, and the thickness T3 of the cap substrate 20 is set to 200 μm. It can be 500 μm. Further, for example, the thickness (T1 + T2) of the sensor substrate 10 is set to 100 μm and the thickness T3 of the cap substrate 20 is set to 100 μm so as to be built in an HDD (Hard disk drive). The thickness is preferably 200 μm.
　次に、上記構成の絶対圧力センサ１の製造方法について、図２～図６に基づいて説明する。図２はピエゾ抵抗作成工程を示す断面図であり、図３は第２シリコン基板の研削工程を示す断面図であり、図４はキャビティ形成工程を示す断面図であり、図５はキャップ基板接合工程を示す断面図であり、図６はキャップ基板研削工程を示す断面図である。 Next, a method for manufacturing the absolute pressure sensor 1 having the above configuration will be described with reference to FIGS. FIG. 2 is a cross-sectional view showing a piezoresistive forming process, FIG. 3 is a cross-sectional view showing a grinding process of a second silicon substrate, FIG. 4 is a cross-sectional view showing a cavity forming process, and FIG. FIG. 6 is a cross-sectional view showing a process, and FIG. 6 is a cross-sectional view showing a cap substrate grinding process.
　まず、図２に示すように、第１シリコン基板１０ａと第２シリコン基板１０ｂとを貼り合わせてなるＳＯＩ（シリコン・オン・インシュレータ）基板であるセンサ基板１０上に、ピエゾ抵抗１２・１２を作製する。このとき、本実施の形態では、ダイアフラムの厚みＴ１の厚さとなる第１シリコン基板１０ａの厚さは約５μｍとなっている。また、第１シリコン基板１０ａと第２シリコン基板１０ｂとの合計厚みは例えば約７００μｍとなっている。 First, as shown in FIG. 2, piezoresistors 12 and 12 are formed on a sensor substrate 10 which is an SOI (silicon-on-insulator) substrate formed by bonding a first silicon substrate 10a and a second silicon substrate 10b. To do. At this time, in the present embodiment, the thickness of the first silicon substrate 10a, which is the thickness of the diaphragm T1, is about 5 μm. The total thickness of the first silicon substrate 10a and the second silicon substrate 10b is, for example, about 700 μm.
　次に、図３に示すように、センサ基板１０における第２シリコン基板１０ｂの研削工程を行う。研削工程においては、ＢＳＧ（バックサイドグラインディング）にて、第２シリコン基板１０ｂの裏面を研削する。この場合、ピエゾ抵抗１２・１２を形成した面に両面テープを張り、図示しないステージに接着した状態で、センサ基板１０におけるピエゾ抵抗１２・１２の形成面とは反対側の面を研削する。このとき、第１シリコン基板１０ａと第２シリコン基板１０ｂとの合計厚みが例えば約１００μｍ程度になるまで研削する。その後、ＣＭＰ（ケミカルメカニカルポリッシング）工程にて、研削した面を鏡面仕上げする。ＣＭＰ（ケミカルメカニカルポリッシング）工程では、アルミナの砥粒が混入された研磨液を使って、研削面を磨く。 Next, as shown in FIG. 3, a grinding process of the second silicon substrate 10b in the sensor substrate 10 is performed. In the grinding step, the back surface of the second silicon substrate 10b is ground by BSG (backside grinding). In this case, a surface of the sensor substrate 10 opposite to the surface on which the piezoresistors 12 and 12 are formed is ground in a state where a double-sided tape is applied to the surface on which the piezoresistors 12 and 12 are formed and adhered to a stage (not shown). At this time, grinding is performed until the total thickness of the first silicon substrate 10a and the second silicon substrate 10b becomes, for example, about 100 μm. Thereafter, the ground surface is mirror-finished in a CMP (Chemical Mechanical Polishing) process. In the CMP (Chemical Mechanical Polishing) process, the ground surface is polished using a polishing liquid mixed with alumina abrasive grains.
　次いで、図４に示すように、センサ基板１０における第２シリコン基板１０ｂとシリコン酸化膜（ＳｉＯ２ ）１４とをエッチングし、キャビティ１３となる凹部を形成することにより、その上側にダイアフラム１１を形成する。具体的には、ＭＥＭＳ（Micro Electro Mechanical Systems）プロセスで使用されるＤｅｅｐ－ＲＩＥと称されるドライエッチングにより、第２シリコン基板１０ｂをエッチングする。このように、Ｄｅｅｐ－ＲＩＥ（Reactive Ion Etching：反応性イオンエッチング）と称される手法を利用することによって、第２シリコン基板１０ｂの表面に対して垂直に、第２シリコン基板１０ｂをエッチングすることができる。尚、キャビティ１３の形状は、例えば約４００μｍ程度の円柱形としている。したがって、キャビティ１３の形状は、水平断面が円形となる。ただし、必ずしもこれに限らず、キャビティ１３の水平断面の形状は、正方形又は六角形等の多角形でもよい。 Next, as shown in FIG. 4, the second silicon substrate 10 b and the silicon oxide film (SiO 2 ) 14 in the sensor substrate 10 are etched to form a recess that becomes the cavity 13, thereby forming the diaphragm 11 on the upper side. To do. Specifically, the second silicon substrate 10b is etched by dry etching called Deep-RIE used in a MEMS (Micro Electro Mechanical Systems) process. In this way, by using a technique called Deep-RIE (Reactive Ion Etching), the second silicon substrate 10b is etched perpendicular to the surface of the second silicon substrate 10b. Can do. The shape of the cavity 13 is a cylindrical shape of about 400 μm, for example. Accordingly, the cavity 13 has a circular horizontal cross section. However, the shape of the horizontal section of the cavity 13 is not necessarily limited to this, and may be a polygon such as a square or a hexagon.
　次に、図５に示すように、常温接合と称される手法を用いて、センサ基板１０とキャップ基板２０を接合し、真空のキャビティ１３を形成する。常温接合においては、まず、図示しない接合装置内の高真空チャンバ内において、接合装置のピストンにセンサ基板１０を設置すると共に、接合装置のステージにキャップ基板２０を設置する。そして、互いの接合面が対向した状態で保持する。続いて、センサ基板１０とキャップ基板２０とを１０ｃｍ程度離した状態で保持し、空間内にアルゴン（Ａｒ）イオンビームを照射し、センサ基板１０及びキャップ基板２０の各対向面上の自然酸化膜を除去する。アルゴン（Ａｒ）イオンビームを照射した後、ピストンを降下して接合面を密着させた状態で、２ｔ程度の荷重を加えることにより、センサ基板１０とキャップ基板２０とを接合する。これにより、センサ基板１０とキャップ基板２０とは、無酸化膜状態にてシリコン（Ｓｉ）－シリコン（Ｓｉ）接合される。 Next, as shown in FIG. 5, the sensor substrate 10 and the cap substrate 20 are bonded using a technique called room temperature bonding to form a vacuum cavity 13. In normal temperature bonding, first, in a high vacuum chamber in a bonding apparatus (not shown), the sensor substrate 10 is installed on the piston of the bonding apparatus, and the cap substrate 20 is installed on the stage of the bonding apparatus. And it hold | maintains in the state which the mutual joint surface opposes. Subsequently, the sensor substrate 10 and the cap substrate 20 are held in a state of being separated by about 10 cm, and an argon (Ar) ion beam is irradiated into the space, so that a natural oxide film on each facing surface of the sensor substrate 10 and the cap substrate 20 is obtained. Remove. After irradiating the argon (Ar) ion beam, the sensor substrate 10 and the cap substrate 20 are joined by applying a load of about 2t in a state where the piston is lowered and the joining surface is brought into close contact therewith. As a result, the sensor substrate 10 and the cap substrate 20 are bonded with silicon (Si) -silicon (Si) in a non-oxide film state.
　次に、図６に示すように、キャップ基板２０の裏面の研削を行う。キャップ基板２０の裏面の研削工程においては、前記図３に示すセンサ基板１０における第２シリコン基板１０ｂの研削工程と同様にして、ＢＳＧ（バックサイドグラインディング）にて、キャップ基板２０の裏面を研削する。このとき、センサ基板１０のピエゾ抵抗１２・１２側の面に両面テープを張り、図示しないステージに接着した状態で、ピエゾ抵抗１２・１２の形成面とは反対側の面を研削する。ここでは、例えば、キャップ基板２０の厚みＴ３が例えば１００μｍ程度になるまで研削する。 Next, as shown in FIG. 6, the back surface of the cap substrate 20 is ground. In the grinding process of the back surface of the cap substrate 20, the back surface of the cap substrate 20 is ground by BSG (backside grinding) in the same manner as the grinding process of the second silicon substrate 10b in the sensor substrate 10 shown in FIG. To do. At this time, a double-sided tape is applied to the surface of the sensor substrate 10 on the side of the piezoresistors 12 and 12, and the surface opposite to the surface on which the piezoresistors 12 and 12 are formed is ground in a state of being bonded to a stage (not shown). Here, for example, grinding is performed until the thickness T3 of the cap substrate 20 becomes about 100 μm, for example.
　以上の工程により、図１に示す絶対圧力センサ１が完成する。 The absolute pressure sensor 1 shown in FIG. 1 is completed through the above steps.
　このように、本実施の形態の絶対圧力センサ１では、ダイアフラム１１の周縁に複数のピエゾ抵抗１２・１２を形成し、該ピエゾ抵抗１２・１２の形成面とは反対側の面にキャビティ１３を形成したセンサ基板１０に、該キャビティ１３を閉じるようにキャップ基板２０を接合してなっている。そして、キャビティ１３の厚みＴ２は、キャップ基板２０の厚みＴ３以上となっている。 Thus, in the absolute pressure sensor 1 according to the present embodiment, a plurality of piezoresistors 12 and 12 are formed on the periphery of the diaphragm 11, and the cavity 13 is formed on the surface opposite to the surface on which the piezoresistors 12 and 12 are formed. A cap substrate 20 is bonded to the formed sensor substrate 10 so as to close the cavity 13. The thickness T2 of the cavity 13 is equal to or greater than the thickness T3 of the cap substrate 20.
　これにより、配線パターン及びピエゾ抵抗１２・１２のないキャップ基板２０を研削すればよいので、テープを貼り付け均一性及びダイアフラム１１の厚みのバラつきを考慮することなく、容易に研削することができる。そして、結果的に、従来よりも絶対圧力センサ１の全体厚みＴを小さくすることができる。 Thereby, since the cap substrate 20 without the wiring pattern and the piezoresistors 12 and 12 may be ground, it is possible to easily grind the tape without applying the tape and considering the uniformity of the thickness of the diaphragm 11. As a result, the total thickness T of the absolute pressure sensor 1 can be made smaller than in the prior art.
　したがって、絶対圧力センサ１の全体厚みＴを小さくし得る絶対圧力センサ１を提供することができる。 Therefore, it is possible to provide the absolute pressure sensor 1 that can reduce the overall thickness T of the absolute pressure sensor 1.
　また、本実施の形態では、キャビティ１３の厚みＴ２がキャップ基板２０の厚みＴ３以上となっていることによって、キャビティ１３の厚みＴ２を従来品のキャビティの厚みＴ２よりも大きくすることができる。このことは、キャビティ１３の容積を従来品のキャビティの容積よりも大きくすることができることを意味する。この結果、この結果、仮に、センサ基板１０とキャップ基板２０との接合が間に酸化膜を介した場合に、接合界面ではヘリウム（Ｈｅ）又は水素（Ｈ２ ）等の低分子量の気体がキャビティ１３に侵入することになる。しかし、本実施の形態では、キャビティ１３の容積が従来品のキャビティの容積よりも大きい。このため、低分子量の気体がキャビティ１３に侵入してもキャビティ１３の圧力が大きく変動しないというメリットがある。 In the present embodiment, since the thickness T2 of the cavity 13 is equal to or greater than the thickness T3 of the cap substrate 20, the thickness T2 of the cavity 13 can be made larger than the thickness T2 of the conventional cavity. This means that the volume of the cavity 13 can be made larger than the volume of the cavity of the conventional product. As a result, if the sensor substrate 10 and the cap substrate 20 are bonded via an oxide film, a low molecular weight gas such as helium (He) or hydrogen (H 2 ) 13 will be invaded. However, in the present embodiment, the volume of the cavity 13 is larger than the volume of the conventional cavity. For this reason, even if a low molecular weight gas enters the cavity 13, there is an advantage that the pressure of the cavity 13 does not fluctuate greatly.
　すなわち、気体の状態方程式である
　　ＰＶ＝ｎＲＴ
の関係から、ＰとＶとは反比例する。尚、Ｐは圧力、Ｖは体積、ｎは気体のモル数、Ｒはガス定数、Ｔは温度である。 That is, the equation of state of gas is PV = nRT
Therefore, P and V are inversely proportional. Note that P is pressure, V is volume, n is the number of moles of gas, R is a gas constant, and T is temperature.
　したがって、この気体の状態方程式により、Ｖが大きければ、低分子量の気体がキャビティ１３に侵入してもキャビティ１３の圧力Ｐは大きくは変動しないことが判る。 Therefore, it can be seen from this equation of state of the gas that if V is large, the pressure P of the cavity 13 does not fluctuate greatly even if a low molecular weight gas enters the cavity 13.
　また、本実施の形態の絶対圧力センサ１では、センサ基板１０及びキャップ基板２０は、いずれもシリコン（Ｓｉ）からなっており、かつセンサ基板１０とキャップ基板２０とは、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合にて接合されている。 In the absolute pressure sensor 1 of the present embodiment, the sensor substrate 10 and the cap substrate 20 are both made of silicon (Si), and the sensor substrate 10 and the cap substrate 20 are in a non-oxide film state. Joined by a silicon (Si) -silicon (Si) junction.
　すなわち、キャビティ１３は初期には真空になっているものの、センサ基板１０とキャップ基板２０との接合界面ではヘリウム（Ｈｅ）又は水素（Ｈ２ ）等の低分子量の気体に対しては完全密閉することはできない。このため、低分子量の気体が経時的にキャビティ１３内へリークしたときには、絶対圧としての基準値が変動する。この結果、絶対圧力センサ１の測定精度が低下することになる。 That is, although the cavity 13 is initially in a vacuum state, the bonding interface between the sensor substrate 10 and the cap substrate 20 is completely sealed against a low molecular weight gas such as helium (He) or hydrogen (H 2 ). It is not possible. For this reason, when a low molecular weight gas leaks into the cavity 13 over time, the reference value as the absolute pressure varies. As a result, the measurement accuracy of the absolute pressure sensor 1 is lowered.
　そこで、本実施の形態では、センサ基板１０とキャップ基板２０とを無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合とすることにより、センサ基板１０とキャップ基板２０との接合を無酸化膜状態としている。このため、センサ基板１０とキャップ基板２０との接合界面からヘリウム（Ｈｅ）又は水素（Ｈ２ ）等の低分子量の気体が侵入することがない。 Therefore, in the present embodiment, the sensor substrate 10 and the cap substrate 20 are bonded to each other by using a silicon (Si) -silicon (Si) bond in a non-oxide film state. It is in an oxide film state. For this reason, a low molecular weight gas such as helium (He) or hydrogen (H 2 ) does not enter from the bonding interface between the sensor substrate 10 and the cap substrate 20.
　したがって、絶対圧としての基準値が変動するがないので、絶対圧力センサ１の測定精度が低下することがない。この結果、長期間の品質安定性を有する絶対圧力センサ１を提供することができる。 Therefore, since the reference value as the absolute pressure does not fluctuate, the measurement accuracy of the absolute pressure sensor 1 does not decrease. As a result, the absolute pressure sensor 1 having long-term quality stability can be provided.
　また、本実施の形態の絶対圧力センサ１では、キャビティ１３は、平面形状が円形となっている。これにより、ウエハにて絶対圧力センサ１を複数個並べて製造する場合において個片化するときに、個片化し易くすることができる。 In the absolute pressure sensor 1 of the present embodiment, the cavity 13 has a circular planar shape. Thus, when a plurality of absolute pressure sensors 1 are manufactured on a wafer, they can be easily separated into individual pieces.
　以上のように、本発明の絶対圧力センサでは、前記センサ基板及びキャップ基板は、いずれもシリコン（Ｓｉ）からなっており、かつ上記センサ基板とキャップ基板とは、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合にて接合されていることが好ましい。 As described above, in the absolute pressure sensor of the present invention, the sensor substrate and the cap substrate are both made of silicon (Si), and the sensor substrate and the cap substrate are made of silicon (non-oxide film state). Bonding is preferably performed by Si) -silicon (Si) bonding.
　すなわち、キャビティは初期には真空になっているものの、センサ基板とキャップ基板との接合界面ではヘリウム（Ｈｅ）又は水素（Ｈ２ ）等の低分子量の気体に対しては完全密閉することはできない。このため、低分子量の気体が経時的にキャビティ内へリークしたときには、絶対圧としての基準値が変動する。この結果、絶対圧力センサの測定精度が低下することになる。 That is, although the cavity is initially in a vacuum, it cannot be completely sealed against a low molecular weight gas such as helium (He) or hydrogen (H 2 ) at the bonding interface between the sensor substrate and the cap substrate. . For this reason, when a low molecular weight gas leaks into the cavity over time, the reference value as an absolute pressure varies. As a result, the measurement accuracy of the absolute pressure sensor is lowered.
　そこで、本発明では、センサ基板とキャップ基板とを無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合とすることにより、センサ基板とキャップ基板との接合を無酸化膜状態としている。このため、センサ基板とキャップ基板との接合界面からヘリウム（Ｈｅ）又は水素（Ｈ２ ）等の低分子量の気体が侵入することがない。 Therefore, in the present invention, the sensor substrate and the cap substrate are brought into a non-oxide film state by forming a silicon (Si) -silicon (Si) bond between the sensor substrate and the cap substrate in a non-oxide film state. Therefore, helium from the bonding interface between the sensor substrate and the cap substrate (He) or hydrogen (H 2) of low molecular weight, such as gas never penetrates.
　したがって、絶対圧としての基準値が変動するがないので、絶対圧力センサの測定精度が低下することがない。この結果、長期間の品質安定性を有する絶対圧力センサを提供することができる。 Therefore, since the reference value as the absolute pressure does not fluctuate, the measurement accuracy of the absolute pressure sensor does not decrease. As a result, an absolute pressure sensor having long-term quality stability can be provided.
　本発明の絶対圧力センサでは、前記キャビティは、平面形状が円形であることが好ましい。 In the absolute pressure sensor of the present invention, the cavity preferably has a circular planar shape.
　これにより、ウエハにて絶対圧力センサを複数個並べて製造する場合において個片化するときに、個片化し易くすることができる。 Thus, when a plurality of absolute pressure sensors are manufactured side by side on a wafer, it can be easily separated into individual pieces.
　尚、本発明は、上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、本実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。 The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the invention can be obtained by appropriately combining the technical means disclosed in each of the embodiments. Such embodiments are also included in the technical scope of the present invention.
　　〔実施例１〕
　本実施の形態の絶対圧力センサ１について、キャビティ１３の厚みＴ２を、キャップ基板２０の厚みＴ３以上としたことの効果を確認すべく、従来品との比較実験を行った。 [Example 1]
For the absolute pressure sensor 1 of the present embodiment, a comparative experiment with a conventional product was performed to confirm the effect of setting the thickness T2 of the cavity 13 to be equal to or greater than the thickness T3 of the cap substrate 20.
　実験では、２気圧のヘリウム（Ｈｅ）の雰囲気下に絶対圧力センサ１を置き、キャビティ１３内の真空度の経時変化を求めた。このときのキャビティ１３は、平面形状が円形であり、キャビティ１３のサイズを半径０．４ｍｍとした。また、キャビティ１３の厚みＴ２を０．４ｍｍとした。一方、従来品は、キャビティの形状として、動揺に、平面形状円形とし、キャビティサイズを半径０．４ｍｍとした。また、キャビティ１３の厚みＴ２を０．２ｍｍとした。尚、両方とも、センサ基板１０とキャップ基板２０との接合は、酸化膜を介したシリコン（Ｓｉ）－酸化膜（ＳｉＯ２ ）－シリコン（Ｓｉ）接合とした。 In the experiment, the absolute pressure sensor 1 was placed in an atmosphere of helium (He) at 2 atmospheres, and the change with time in the degree of vacuum in the cavity 13 was obtained. The cavity 13 at this time has a circular planar shape, and the size of the cavity 13 is set to a radius of 0.4 mm. Further, the thickness T2 of the cavity 13 was set to 0.4 mm. On the other hand, in the conventional product, the shape of the cavity is a circular shape in a swing, and the cavity size is 0.4 mm in radius. Further, the thickness T2 of the cavity 13 was set to 0.2 mm. In both cases, the bonding between the sensor substrate 10 and the cap substrate 20 is a silicon (Si) -oxide film (SiO 2 ) -silicon (Si) bond through an oxide film.
　その結果、図７に示すように、両者とも放置日数により略直線的に圧力変動することが判った。具体的には、放置日数１０日において、キャビティの厚みＴ２がキャップ基板の厚みＴ３よりも小さい従来品の絶対圧力センサでは、圧力変動量が３３２１（Ｐａ）であったのに対して、キャビティ１３の厚みＴ２をキャップ基板２０の厚みＴ３以上とした本実施の形態の絶対圧力センサ１では、圧力変動量が１６６０（Ｐａ）であった。したがって、本実施の形態の絶対圧力センサ１では、経時的なキャビティ内真空度の変動量が従来品の１／２以下であることが確認できた。 As a result, as shown in FIG. 7, it was found that the pressure fluctuated substantially linearly depending on the number of days left. Specifically, in the conventional absolute pressure sensor in which the cavity thickness T2 is smaller than the cap substrate thickness T3 in 10 days, the pressure fluctuation amount is 3321 (Pa), whereas the cavity 13 In the absolute pressure sensor 1 according to the present embodiment in which the thickness T2 is equal to or greater than the thickness T3 of the cap substrate 20, the pressure fluctuation amount is 1660 (Pa). Therefore, in the absolute pressure sensor 1 of this Embodiment, it has confirmed that the fluctuation amount of the vacuum degree in a cavity with time was 1/2 or less of a conventional product.
　すなわち、本実施の形態では、従来品に対して経時的なキャビティ１３内真空度の変動量が小さくなる。したがって、低分子気体の経時的なリークに対し、オフセット変動の影響を受け難くなることが把握できた。 That is, in this embodiment, the amount of change in the degree of vacuum in the cavity 13 over time is smaller than that of the conventional product. Therefore, it was understood that the leakage of the low molecular gas with time is less affected by the offset fluctuation.
　　〔実施例２〕
　次に、センサ基板１０とキャップ基板２０とを無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合としたときのキャビティ１３内におけるヘリウム（Ｈｅ）のリークレートを確認した。また、比較として、センサ基板１０とキャップ基板２０とを酸化膜を介したシリコン（Ｓｉ）－酸化膜（ＳｉＯ２ ）－シリコン（Ｓｉ）接合の絶対圧力センサについても同様にしてヘリウム（Ｈｅ）のリークレートを確認した。 [Example 2]
Next, the leak rate of helium (He) in the cavity 13 was confirmed when the sensor substrate 10 and the cap substrate 20 were in a silicon (Si) -silicon (Si) junction in a non-oxide film state. For comparison, the absolute pressure sensor of the silicon (Si) -oxide film (SiO 2 ) -silicon (Si) junction between the sensor substrate 10 and the cap substrate 20 via an oxide film is similarly treated with helium (He). The leak rate was confirmed.
　その結果を、表１に示す。 The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　すなわち、表１に示すように、センサ基板１０とキャップ基板２０とを酸化膜を介したシリコン（Ｓｉ）－酸化膜（ＳｉＯ２ ）－シリコン（Ｓｉ）接合とすることにより、ヘリウム（Ｈｅ）のリークレートは、６．８×１０Ｅ－１１Ｐａ・ｍ３ ／ｓ以下であった。これに対して、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合では、ヘリウム（Ｈｅ）のリークレートは、１×１０Ｅ－１１Ｐａ・ｍ３ ／ｓ以下である。この結果、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合では、ヘリウム（Ｈｅ）のリークレートが小さいことが判った。 That is, as shown in Table 1, the sensor substrate 10 and the cap substrate 20 are made of a silicon (Si) -oxide film (SiO 2 ) -silicon (Si) junction through an oxide film, thereby forming helium (He). The leak rate was 6.8 × 10E-11 Pa · m 3 / s or less. On the other hand, in the silicon (Si) -silicon (Si) junction in the non-oxide film state, the leak rate of helium (He) is 1 × 10E-11 Pa · m 3 / s or less. As a result, it was found that the leak rate of helium (He) is small in the silicon (Si) -silicon (Si) junction in the non-oxide film state.
　本発明は、気圧計、水圧計、高度計等の絶対圧力センサに適用できる。また、本発明の絶対圧力センサを用いた気圧計、水圧計、高度計は、例えばタイヤの空気圧のモニタリング、水中撮影用等の気圧計内蔵のデジタルカメラ、山登りにおいて標高を知る高度計内蔵の歩数計、カーナビゲーション、腕時計等に適用可能である。 The present invention can be applied to absolute pressure sensors such as a barometer, a water pressure gauge, and an altimeter. The barometer, water pressure gauge, and altimeter using the absolute pressure sensor of the present invention are, for example, a tire pressure monitoring, a digital camera with a built-in barometer for underwater photography, a pedometer with a built-in altimeter that knows the altitude when climbing, Applicable to car navigation, wristwatches, etc.
　１　　　絶対圧力センサ
１０　　　センサ基板
１０ａ　　第１シリコン基板
１０ｂ　　第２シリコン基板
１１　　　ダイアフラム
１２　　　ピエゾ抵抗（圧力感応抵抗素子）
１３　　　キャビティ
１４　　　シリコン酸化膜（ＳｉＯ２ ）
２０　　　キャップ基板
Ｔ　　　　絶対圧力センサの全体厚み
Ｔ１　　　ダイアフラムの厚み
Ｔ２　　　キャビティの厚み
Ｔ３　　　キャップ基板の厚み DESCRIPTION OF SYMBOLS 1 Absolute pressure sensor 10 Sensor board | substrate 10a 1st silicon substrate 10b 2nd silicon substrate 11 Diaphragm 12 Piezoresistor (pressure sensitive resistance element)
13 Cavity 14 Silicon oxide film (SiO 2 )
20 Cap substrate T Total thickness of absolute pressure sensor T1 Diaphragm thickness T2 Cavity thickness T3 Cap substrate thickness

Claims (4)

  1. 　ダイアフラムの周縁に複数の圧力感応抵抗素子を形成し、該圧力感応抵抗素子の形成面とは反対側の面にキャビティを形成したセンサ基板に、該キャビティを閉じるようにキャップ基板を接合してなる絶対圧力センサにおいて、
    　上記キャビティの厚みは、キャップ基板の厚み以上となっていることを特徴とする絶対圧力センサ。     A plurality of pressure sensitive resistance elements are formed on the periphery of the diaphragm, and a cap substrate is joined to a sensor substrate having a cavity formed on the surface opposite to the surface on which the pressure sensitive resistance elements are formed so as to close the cavity. In absolute pressure sensor,
    The absolute pressure sensor according to claim 1, wherein the thickness of the cavity is equal to or greater than the thickness of the cap substrate.
  2. 　前記センサ基板及びキャップ基板は、いずれもシリコン（Ｓｉ）からなっており、かつ上記センサ基板とキャップ基板とは、無酸化膜状態でのシリコン（Ｓｉ）－シリコン（Ｓｉ）接合にて接合されていることを特徴とする請求項１記載の絶対圧力センサ。 The sensor substrate and the cap substrate are both made of silicon (Si), and the sensor substrate and the cap substrate are bonded by a silicon (Si) -silicon (Si) bond in a non-oxide film state. The absolute pressure sensor according to claim 1, wherein:
  3. 　前記キャビティは、平面形状が円形であることを特徴とする請求項１記載の絶対圧力センサ。 The absolute pressure sensor according to claim 1, wherein the cavity has a circular planar shape.
  4. 　前記キャビティは、平面形状が円形であることを特徴とする請求項２記載の絶対圧力センサ。 The absolute pressure sensor according to claim 2, wherein the cavity has a circular planar shape.
PCT/JP2012/054584 2011-03-10 2012-02-24 Absolute pressure sensor WO2012121030A1 (en)

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JP6230049B2 (en) * 2012-10-09 2017-11-15 国立大学法人 香川大学 Endoscope hood, endoscope and endoscope pressure sensor
JP6218330B2 (en) * 2014-07-04 2017-10-25 アルプス電気株式会社 Pressure sensor and manufacturing method thereof
JP6440488B2 (en) * 2014-12-24 2018-12-19 セイコーインスツル株式会社 Pulse wave measuring device and pulse wave measuring method
JP6474619B2 (en) * 2015-01-15 2019-02-27 国立大学法人 東京大学 Pressure measuring device and pressure measuring method
JP6300773B2 (en) * 2015-10-23 2018-03-28 三菱電機株式会社 Semiconductor pressure sensor

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JPH03112168A (en) * 1989-09-26 1991-05-13 Nippondenso Co Ltd Semiconductor piezosensor
JPH04328434A (en) * 1991-04-30 1992-11-17 Hitachi Ltd Composite sensor
JPH10160602A (en) * 1996-11-28 1998-06-19 Denso Corp Semiconductor type pressure sensor
WO2007058010A1 (en) * 2005-11-15 2007-05-24 Mitsubishi Electric Corporation Semiconductor pressure sensor and its fabrication method
JP2007147374A (en) * 2005-11-25 2007-06-14 Mitsubishi Electric Corp Pressure sensor

Patent Citations (5)

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Publication number Priority date Publication date Assignee Title
JPH03112168A (en) * 1989-09-26 1991-05-13 Nippondenso Co Ltd Semiconductor piezosensor
JPH04328434A (en) * 1991-04-30 1992-11-17 Hitachi Ltd Composite sensor
JPH10160602A (en) * 1996-11-28 1998-06-19 Denso Corp Semiconductor type pressure sensor
WO2007058010A1 (en) * 2005-11-15 2007-05-24 Mitsubishi Electric Corporation Semiconductor pressure sensor and its fabrication method
JP2007147374A (en) * 2005-11-25 2007-06-14 Mitsubishi Electric Corp Pressure sensor

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