JP2018031714A - Physical quantity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical quantity sensor which can suppress increase of the pressure in the inside of a sensor to an atmospheric pressure side by water generated by passing-through an oxide film of a small angular velocity sensor manufactured by an MEMS process.SOLUTION: A water-permeable prevention film is formed immediately on an edge of a silicon oxide film around a penetration electrode part of an electrode substrate so as to directly contact with the silicon oxide film.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a structure of a physical quantity sensor used for measuring a physical quantity, and more particularly to an angular velocity sensor structure in which the inside of a sensor is sealed in a vacuum.

  In recent years, various sensors for measuring physical quantities such as acceleration and angular velocity using materials such as silicon and glass have been provided due to the development of miniaturization processing technology in MEMS technology.

  The physical quantity sensor using the MEMS technology has an advantage that a structure having a higher aspect ratio (ratio between the opening width and the processing depth) can be formed as compared with the semiconductor device. Also, by forming a three-dimensional structure and a movable structure made of silicon by dry etching method using RIE (Reactive Ion Etching) RIE (ICP) method that can process high aspect ratio grooves, machining and Various structures with excellent processing accuracy can be formed.

  As a physical quantity sensor using such MEMS technology, a composite sensor element described in JP-A-2015-11002 (Patent Document 1) is known. In this composite sensor element, a silicon direct bonding technique is applied to the assembly, and the planar vibration body of the angular velocity sensor and the movable body of the acceleration sensor are provided in a state of floating on the same substrate. Moreover, the upper side of the planar vibrating body and the movable body is covered with a lid member at an interval. The space portion composed of the substrate and the lid member is divided into an angular velocity sensor space portion and an acceleration sensor space portion by a partition wall portion. The angular velocity sensor space is hermetically sealed in a vacuum state of about 200 Pa, and the acceleration sensor space is hermetically sealed in a vacuum degree of about 10,000 to 50,000 Pa. Accordingly, the planar vibrating body can vibrate with a high frequency and a large amplitude, and the angular velocity detection sensitivity of the angular velocity sensor can be increased.

  A plurality of electrodes necessary for driving the device substrate on which the planar vibrating body is arranged are connected using the low resistance silicon material of the lid member as an electrode, and the periphery of the low resistance silicon electrode is insulated by an oxide film. A metal electrode is formed on the surface of the low-resistance silicon electrode portion of the lid member, and portions other than the metal electrode portion are protected by a protective film made of SiN and resin. For the protective film around the metal electrode, the same technology as the protective film of a general semiconductor circuit is applied. In other words, the entire portion other than the metal electrode portion is protected by the protective film of SiN and resin.

  Further, in the structure described in Patent Document 2, the MEMS element portion is held in the sealed space at a vacuum degree (pressure) when the metal film is sputtered. In order to improve reliability by suppressing fluctuation from the initial atmosphere, the inner wall in the sealed space is covered with a silicon nitride film and a silicon film. This structure suppresses the generation of gas from the inner wall of the space where the MEMS element is arranged. The manufacturing method protects the MEMS element with a sacrificial layer after forming the MEMS element, forms a polysilicon film, a silicon nitride film, and an interlayer insulating film, and then planarizes by applying CMP or an etch back technique, and forms a metal wiring and an interlayer insulating film. The above process is repeated to form an arbitrary metal wiring layer. Then, a space is formed around the MEMS element by removing the sacrificial layer using the metal film release hole. Finally, the release holes are blocked by applying a sputtering method. In the process, a part of the metal material enters the inside of the sealed space by the release hole sealing process. In this structure, a ring-shaped silicon nitride material is applied to the insulation around the metal electrode portion taken out to the outside. The ring-shaped silicon nitride film is formed along the slope of the polysilicon film, and an interlayer insulating film is formed on the top. The silicon nitride film is formed to protect the curved surface of the sealed space surrounding the MEMS element and the plurality of step portions.

  On the other hand, according to Non-Patent Document 1, it is generally known that moisture permeates a glass film. Moisture in the air exists as hydroxyl OH in the glass, and in most cases, penetration into the glass follows Fick's diffusion equation. The amount and depth of water penetrating into the glass is proportional to the square root of the product of time and diffusion coefficient at a constant temperature and humidity. Therefore, in a physical quantity sensor having a vacuum space as described above, the external pressure is generally atmospheric pressure, and moisture can permeate through the oxide film or the like from the viewpoint that the inside of the sensor is vacuum. Sex exists.

Japanese Patent Laid-Open No. 2015-11002 Japanese Patent Laid-Open No. 2015-145036

NEW GLASS Vol.21.No3 (2006)

  In the composite sensor element described in Patent Document 1, an oxide film is formed on a low-resistance silicon upper portion other than the metal electrode portion formed on the lid member, and is protected by a SiN and resin protective film thereon. It is described. And the protective film of SiN and resin is formed in the whole surface other than a metal electrode part. In the above structure, since the SiN film is formed on the oxide film, it is conceivable that moisture enters the vacuum space from the side surface of the oxide film on the side surface of the metal electrode portion.

  In Patent Document 2, since the release hole is sealed by a metal sputtering method in order to finally maintain the space of the MEMS element in a vacuum, metal powder is mixed inside. At the same time, the internal pressure can be sealed only by the pressure at the time of forming the metal powder by the metal sputtering method. That is, there is a possibility that arbitrary pressure adjustment cannot be performed.

  In general, in an angular velocity sensor, comb teeth of a movable electrode are formed facing a fixed electrode in a vacuum-sealed space, and the drive unit is driven at a constant resonance frequency at an arbitrary degree of vacuum. At this time, the driving unit is important because the weight of the driving mass determines the resonance frequency. In Patent Document 2, since the metal film enters the sealed space, it can be predicted that the metal powder adheres to the driving mass, and there is a problem that the weight of the driving mass is changed. Therefore, it is considered difficult to apply to the angular velocity sensor in the manufacturing process. In addition, it is predicted that the silicon nitride film is formed thick because the ring-shaped silicon nitride material is applied to the insulating portion around the metal electrode portion so as to cover the sloped polysilicon film. As a result, there is a possibility of cracking due to the difference in linear expansion coefficient.

  Since the sacrificial layer process is applied, the manufacturing process can be predicted to be complicated. In addition, the invention relates to a structure that suppresses outgas emission from the surface of the vacuum space inside the MEMS element, and is not an invention that takes into account moisture intrusion from the surroundings.

  An object of the present invention is to provide a structure in which a small angular velocity sensor manufactured by a MEMS process suppresses an increase in pressure inside the sensor to an atmospheric pressure side due to moisture that permeates an oxide film.

  According to the present invention, the sensing layer for measuring a physical quantity is composed of at least a three-layer structure of a substrate and an electrode substrate in which a fixed layer and a device layer are integrated or a fixed substrate, a device substrate, and an electrode substrate. The electrode substrate is a structure in which a plurality of through-electrodes made of low resistance silicon are individually insulated by a polygonal silicon oxide film, and the electrode substrate has a low resistance. A moisture permeation preventive film is formed directly on the edge of the polygonal silicon oxide film disposed around the through-electrode part made of silicon so as to cover the silicon oxide film peripheral part and directly adhere to it. It is good to apply the structure.

  According to the present invention, by directly adhering to the polygonal silicon oxide film, it is possible to directly prevent moisture from entering the sensing space consisting of vacuum, and to ensure a stable degree of vacuum in the sensing space. Since there is no step portion in the periphery of the silicon oxide film, it is possible to form a moisture permeation preventive film on the flat portion, so that the thickness of the moisture permeation preventive film can be reduced. Therefore, it is possible to stably maintain the degree of vacuum in the sensing space formed in the angular velocity sensor and to provide a physical quantity sensor with excellent reliability. Since the moisture permeation preventive film is disposed in close contact with the upper portion of the polygonal silicon oxide film, stress due to the moisture permeation preventive film can be reduced as compared with the case where the entire electrode substrate is protected. Further, by applying a structure in which an oxide film is formed in addition to the electrode pad portion, a protective film such as a resin is unnecessary.

Sectional drawing explaining the physical quantity sensor of this invention Plan view explaining the structure of the device substrate Plan view on the arrangement of moisture permeation prevention film Diagram explaining fluctuations in sensing space due to high humidity test Cross-sectional view of moisture penetration path in conventional structure Cross-sectional view explaining the aspect ratio of the oxide film Sectional drawing explaining the other physical quantity sensor of this invention Sectional view of a package on which the element of the present invention is mounted

  A structural example of a physical quantity sensor according to the present invention will be described with reference to FIG. FIG. 1 shows a cross-sectional view of a sensor for sensing angular velocity according to an example of the present invention. The substrate is composed of at least a three-layer structure of a fixed substrate 2, a device substrate 3, and an electrode substrate 1. A device substrate 3 is formed on the fixed substrate 2 by a silicon direct bonding method through a silicon oxide film 4b made of SiO2. Similarly, the upper part of the device substrate 3 and the lower part of the electrode substrate 1 have a structure in which silicon is directly bonded to silicon. The sensing space 5 for measuring the angular velocity in FIG. 1 is a space sealed by silicon and a silicon oxide film.

  The sensing space 5 for measuring the angular velocity of the device substrate 3 is a vacuum atmosphere with a pressure atmosphere of about 15 Pa in the space between the fixed substrate 2 and the electrode substrate 1 arranged above and below. The sensing space 5 includes a fixed electrode 7 and a movable electrode 8 formed on the device substrate 3. This has a plurality of comb teeth with a gap of several micrometers. An example of a plan view of the device substrate 3 is shown in FIG. A plurality of fixed electrode 7 comb teeth are arranged on the device substrate 3. The movable electrode 8 is integrally formed, and a spring beam 11 is formed inside, so that the displacement at the time of movement can be absorbed. This structure is for detecting the angular velocity in the in-plane direction. Note that the fixed electrode 7 and the movable electrode 8 in FIG. 2 are electrically connected to the electrode substrate 1 by a plurality of through electrodes 10a and 10b.

  In sensing the physical quantity of angular velocity, Coriolis force is generated when angular velocity is applied when a plurality of comb teeth are driven (vibrated) at a specific frequency. Due to this Coriolis force, the gap between the fixed electrode and the movable electrode changes. The angular velocity is detected by detecting the change amount of the gap between the electrodes due to the Coriolis force by the electrostatic force.

  Since the Coriolis force increases as the driving speed of the movable electrode vibrating body increases, it is necessary to vibrate the vibrating body at a high frequency and a large amplitude in order to improve the detection sensitivity of the angular velocity sensor. However, since the vibrator manufactured by the MEMS technology is formed with a small gap, when the vibration atmosphere is atmospheric pressure, the influence of the damping effect of air (sealing gas) becomes large. This damping effect adversely affects the vibration of the angular velocity sensor at a high frequency and a large amplitude, and decreases the detection sensitivity of the angular velocity sensor. Therefore, it is possible to obtain an angular velocity sensor having a high frequency and a large amplitude by sealing the sensing portion of the angular velocity sensor in a vacuum atmosphere, which is less affected by the damping effect. Further, the higher the vacuum, the smaller the influence of the damping effect.

  It is important to obtain a stable vacuum atmosphere in the space including the drive unit and the detection unit of the angular velocity sensor, and the detection sensitivity of the angular velocity sensor can be stabilized.

  The fixed electrode 7 of the device substrate 3 is planarly connected to the fixed electrode 3a, and is connected to the metal electrode 9 formed thereon through the through electrode 10a disposed inside the electrode substrate 1. Similarly, the movable electrode 8 is planarly connected to the movable electrode 3b of the device substrate, and is connected to the metal electrode 9 formed thereon through the through electrode 10b disposed inside the electrode substrate 1. It is. By connecting the metal electrode 9 with a gold wire or the like, the sensor can perform electrical exchange with the outside.

  The position of the metal electrode 9 can be arranged on the electrode pad 21 by the metal wiring 20 in a plan view as shown in FIG. Therefore, the electrode pad 21 can be routed to an arbitrary position on the surface of the electrode substrate. An oxide film is formed below the wiring material for electrical insulation.

  In addition, the material of the metal wiring 20 may be arranged such that chromium or titanium is disposed as a base film in consideration of adhesion, and gold is disposed thereon. Moreover, in order to improve thermal heat resistance, you may arrange | position platinum and nickel between chromium, titanium, and gold | metal | money. The wiring material is not limited to the above, and a wiring material such as aluminum may be applied.

  The through electrodes 10a and 10b formed inside the electrode substrate 1 are electrically insulated from each other by a silicon oxide film 4a such as SiO2. The metal electrode 9a of the electrode substrate is an electrode for electrically placing the electrode substrate on the ground.

  In the present invention, a structure that is movable in the in-plane direction is described. It can be applied as an angular velocity sensor.

  A moisture permeation preventive film 6 is disposed immediately above the silicon oxide film 4a disposed around the through electrode 10, and a silicon oxide film 4c is formed thereon.

  As shown in FIG. 3, the moisture permeation preventive film 6 includes a through electrode 10 (inside the inner dotted line) and a silicon oxide film 4a disposed on the outer periphery thereof (a portion covered with two dotted lines). It is arranged to cover. More specifically, it is preferable to cover the inside 6a of the through electrode 10 to the outside 6b of the silicon oxide film 4a in a ring shape by the moisture permeation preventive film 6. Depending on the shape of the through electrode 10 and the silicon oxide film 4a, a structure covered with a polygon may be used. The gist of the present invention is to directly form the moisture permeation preventive film 6 on the silicon oxide film 4a exposed on the surface of the electrode substrate 1.

  The moisture permeation preventive film 6 is preferably a silicon nitride film. This is because the effect of preventing moisture is high.

  In general, in order to reduce or protect the influence of moisture from the physical quantity sensor, a silicon nitride film is formed on the entire surface of the electrode substrate 1 other than the electrode pads 21. In some cases, a protective film made of a resin material is also formed on the surface. In the present invention, by partially forming the silicon nitride film, the stress of the film can be reduced as compared with the case where the silicon nitride film is formed over the entire surface. For example, when the thickness of the silicon nitride film is constant, the residual stress varies with the volume ratio. When the silicon nitride film is formed on the entire surface of the electrode substrate of the sensor, it can be estimated that the thickness is on the order of millimeters. Therefore, the stress acting on the entire sensor is extremely reduced.

  In addition, since the moisture permeation preventive film 6 formed in the present invention can be formed on the flat portion, there is no problem even if it is formed thinner than the case where it is formed on the step portion. When forming in a step part, since the coverage of a step part is required, it needs to form thickly.

  In the present invention, an SOI substrate can be applied to the fixed substrate 2, the device substrate 3, and the oxide film 4b made of SiO2. In general, an SOI wafer is composed of a fixed layer, a box layer, and a device layer. The box layer is removed after the device structure is formed to form the movable part. More specifically, the comb-like structure or the like can be floated hollow by removing the box layer after processing the structure such as the comb-teeth on the device layer by dry etching processing capable of processing with a high aspect ratio. Therefore, when the box layer is thickened, the etching rate in the depth direction and the etching rate in the planar direction are equal, and therefore, the portion for fixing the driving comb teeth or the like may be lost during removal. This is because the box layer is formed of an oxide film made of SiO2, and isotropically etched by a hydrofluoric acid aqueous solution or hydrofluoric acid vapor. For this reason, when the box layer is thickened, a portion for fixing the driving comb teeth and the like becomes large, so that it is difficult to reduce the size, and the box layer must be formed thin. As a result, the lower surface of the device layer, that is, the gap between the fixed substrate 2 and the lower surfaces of the fixed electrode 7 and the movable electrode 8 in the present invention is as small as several micrometers.

  An SOI wafer may be described as a single device substrate 3 in which a fixed layer and a device layer are integrated. Therefore, in the present invention, the moisture permeation preventive film 6 can be applied even in the case of the two-layer structure of the device substrate 3 and the electrode substrate 1.

  Maintaining the degree of vacuum in the sensing space is important from the viewpoint of improving reliability. In particular, the angular velocity sensor is used together with an acceleration sensor in a system for preventing a side slip for an automobile. Therefore, it can be assumed that the angular velocity sensor is applied in a harsh environment.

  FIG. 4 shows the results of the high-temperature and high-humidity test when the moisture permeation preventive film of the present invention is applied and when it is not applied. Since the sensing space has a small volume, the degree of vacuum cannot be measured directly. For this reason, the pressure in the sensing space on the vertical axis is represented by a Q value that is a resonance coefficient. When the high temperature and high humidity test time is increased on the horizontal axis, the Q value of the sensing space hardly fluctuates in the structure of the present invention, but the Q value of the sensing space gradually decreases when there is no moisture permeation prevention film. Go. This indicates that the pressure in the sensing space gradually increases to the atmospheric pressure side.

  A path through which moisture permeates through permeation will be described with reference to FIG. A silicon oxide film 4b is disposed between the fixed substrate 2 and the device substrate 3, and the electrode substrate 1 is disposed thereon. A MEMS element 15 is arranged on the device substrate 3, and a vacuum sensing space 5 sealed by three substrates is formed. A silicon oxide film 4a is disposed inside the electrode substrate 1. In the upper structure of the electrode substrate 1, a silicon oxide film 4c is formed around the metal electrode 9, a SiN film 12 is formed thereon, and a protective film 13 made of resin is formed thereon.

  The silicon oxide film 4c disposed on the electrode substrate 1 is formed for the purpose of insulation from the wiring material because the electrode substrate 1 uses a low-resistance silicon material.

  In terms of process, after the silicon oxide film 4c is formed on the entire surface, the pattern of the metal electrode portion and the electrode pad portion is formed by photolithography, and the silicon oxide film is removed by etching. Thereafter, a wiring structure is formed again by photolithography, a sputtering apparatus or a vapor deposition apparatus is applied to form a metal film, and then the resist is removed to form a metal electrode and a wiring structure at an arbitrary position. Alternatively, after forming a metal film on the entire surface, a pattern is formed by photolithography, and the metal film is etched using the resist as a mask, thereby forming a metal electrode and a wiring structure at an arbitrary position. Thereafter, the upper part of the wiring part and the periphery of the metal electrode 9 are protected by the silicon oxide film 4c. This is to prevent an electrical short when a foreign object is placed.

  Therefore, the silicon oxide film 4 c formed on the end portion of the metal electrode 9 is formed on the end portion of the metal electrode 9. That is, the side surface of the silicon oxide film 4c is exposed at the end of the metal electrode 9.

  As a result, moisture enters from the end of the silicon oxide film as shown by 14a. Thereafter, it penetrates the silicon oxide film 4a of the electrode substrate 1 and enters the sensing space 5.

  Generally, a sensor made of a wafer is finally cut by dicing. Therefore, the end face of the sensor chip was exposed, and the moisture intrusion path 14c was predicted.

In the above configuration, the ambient pressure of the sensor chip is about 100,000 Pa and the sensing space is 15 Pa. The atmospheric pressure is larger than the pressure in the sensing space. Therefore, it is in accordance with Fick's diffusion formula that moisture present in the atmosphere permeates the sensing space through the silicon oxide film. The infiltration diffusion coefficient D is expressed by equation (1). D ₀ : Diffusion coefficient, E is activation energy, k is Boltzmann constant, and t is absolute temperature.

D = D ₀ exp (-E / kT) (1)

  There are two paths that penetrate the silicon oxide film and enter the sensing space. Details are shown in FIG. One is a silicon oxide film 4b existing between the fixed substrate 2 and the device substrate 3, and the other is a silicon oxide film 4a formed in the electrode substrate 1 for insulation. Since the silicon oxide film 4b is a bonding surface and the side surface is processed by dicing as described above, the end surface is exposed. It is extremely difficult to prevent moisture entering from this portion. On the other hand, the silicon oxide film 4a formed for insulation in the electrode substrate 1 can prevent moisture from entering the sensing space by forming a moisture permeation preventive film on the top.

  In order to prevent moisture from entering, the dimensions of each silicon oxide film are important. The smaller the aspect ratio of the thickness and width dimension of the silicon oxide film, the easier it is for moisture to enter. This indicates that the cross-section with a small aspect ratio has a small width to length ratio, and assuming that the amount of moisture passing through per unit time is the same, the smaller the aspect ratio, This is because more moisture is permeated.

  Also, the surface area of the plurality of silicon oxide films formed on the electrode substrate in contact with the sensing space is compared with the surface area of the silicon oxide film 4b formed between the device substrate 3 and the fixed substrate 2, and the latter A structure with a smaller surface area is preferred. This is because the larger the surface area in contact with the sensing space 5, the more moisture enters.

  The ratio of the width 16b and the height 16a of the silicon oxide film 4a formed for insulation in the electrode substrate 1, that is, the aspect ratio 16a / 16b of the silicon oxide film 4a, and the thickness 17b of the silicon oxide film 4b When the ratio with the length 17a, that is, the aspect ratio 17a / 17b of the silicon oxide film 4b is compared, the aspect ratio of the silicon oxide film 4b is preferably large. Further, when the total surface area of the plurality of silicon oxide films 4a and the total surface area of the silicon oxide film 4b are in contact with the sensing space 5, the entire silicon oxide film 4b in contact with the sensing space 5 is compared. The surface area should be small.

  This is because when the aspect ratio of the silicon oxide film 4b is small and the entire surface area of the silicon oxide film 4b in contact with the sensing space 5 is large, even if the intrusion of moisture from the end of the silicon oxide film 4a is prevented, This is because moisture enters the sensing space 5 from the oxide film 4b.

  FIG. 7 shows a sectional view of a sensor for sensing angular velocity according to another example of the present invention. The substrate is composed of at least a three-layer structure of a fixed substrate 2, a device substrate 3, and an electrode substrate 1. A groove 19 is formed in the fixed substrate 2, and the device substrate 3 is formed by a silicon direct bonding method via a silicon oxide film 4b made of SiO2.

  Similarly, the upper part of the device layer and the lower part of the electrode substrate 1 have a structure in which silicon is directly bonded to silicon. The sensing space 5 for measuring the angular velocity in FIG. 7 is a space sealed by silicon and a silicon oxide film.

  The sensing space 5 for measuring the angular velocity of the device substrate 3 is a vacuum atmosphere having a pressure atmosphere of about 10 Pa in the space between the fixed substrate 2 and the electrode substrate 1 arranged above and below. A fixed electrode 7 and a movable electrode 8 are formed in the sensing space 5. This has a plurality of comb teeth formed with a gap of several microns.

  The electrical continuity between the fixed electrode 7 and the movable electrode 8 and the outside is the same as the example described in FIG.

  The periphery of the through electrode 10 made of low-resistance silicon formed inside the electrode substrate 1 has a structure in which a double-formed silicon oxide film 4a and polysilicon 18 are embedded therein. With this structure, the aspect ratio of the insulating portion can be increased, and the thickness of the electrode substrate 1 can be increased. Thereby, the pressure resistance performance of the electrode substrate is improved.

  Further, since the space volume of the angular velocity sensing part can be increased by forming the groove 19 in the fixed substrate 2, even if a minute gas (outgas) generated from the surface of the sensing space 5 is generated, Vacuum variation due to the generated gas can be suppressed.

  More specifically, although the angular velocity sensing space 5 is sealed in a vacuum, since it is held in a vacuum, a small amount of generated gas is generated in proportion to the passage of time from the viewpoint of long-term reliability. Can be predicted. As a result, it can be predicted that when the degree of vacuum is deteriorated, the resonance frequency of the movable electrode in the sensing space is changed and the performance is deteriorated. Therefore, it is important to suppress pressure fluctuations in the sensing space.

  Also, the sensing part of the substrate on which the device is formed often has many movable and detecting combs and beams formed in units of micrometers, and the sensing part is compared with the spatial volume of the sensing part. The surface area ratio is large. As a result, the rate at which minute gas components are generated increases. This is because the proportion of generation of minute gas components increases in proportion to the size of the surface area.

  On the other hand, since the groove space of the fixed substrate 1 has no structure inside, the ratio of the surface area to the volume is very small compared to the beam forming portion. For this reason, the rate at which minute gas components (outgas) are generated in the sensing space of the angular velocity sensor is reduced. Therefore, it can contribute to the stability of pressure.

  The gas pressure P decreases according to the equation (2) as the volume V increases. In other words, the pressure variation in the sensing space changes depending on the volume of the generated gas generated. Here, n is the amount of gas substance (number of moles), R is a gas constant, and T is the thermodynamic temperature of the gas.

PV = nRT (2)

  Therefore, in the structure of FIG. 7 of the present invention, even when a minute gas is generated in the angular velocity sensing space, the rate of change of the pressure P of the gas in the sensing space is small.

  Further, from the equation (2), when the volume is increased N times, the pressure is 1 / N. That is, as the volume increases, the pressure fluctuation in the sensing space can be suppressed.

  The direct bonding of silicon is applied to the bonding of the substrates applied to the present invention. In this method, a silicon wafer or a silicon wafer having an oxide film formed on the surface is subjected to a hydrophilization treatment and bonded together in the vicinity of room temperature. As a result, the two silicon wafers bonded together by hydrogen bonding or the like are bonded. Since the bonding strength is still weak in this state, heat treatment is performed at a temperature of 900 to 1150 degrees. Thereby, a siloxane bond state is created, and finally a strong bonding method is obtained in which a strong bond state between silicon and silicon is obtained.

  In the present invention, surface activated bonding using an argon ion beam may be applied. This bonding method has an effect that the thermal impossibility of the substrate is small.

  The silicon material applied to the electrode substrate 1 and the device substrate 3 is preferably a material having a resistance value of 0.01 to 0.05 Ωcm.

  The groove of the fixed substrate 2 and the groove of the electrode substrate 1 are preferably formed by dry etching processing capable of processing with a high aspect ratio. This is because the side surface of the groove can be processed vertically. This is because grooves having a curved shape in plan and a complicated rectangular shape can be formed by a dry etching method.

  FIG. 8 shows a practical assembly method of the physical quantity sensor of the present invention. A control LSI 24 is disposed on the lead frame 28 via a metal paste 27, and the angular velocity sensor 22 and the acceleration sensor 25 of the present invention are mounted on the control LSI 24 via an adhesive layer 26. A package state may be formed by applying molding resin 29 together with other components (not shown) such as a lead frame 28 and a capacitor, or may be mounted on a ceramic package. In order to detect a signal and supply electricity, the electrode pad 21b of a control LSI or the like and the electrode pads 21a of the angular velocity sensor 22 and the acceleration sensor 25 of the present invention are electrically connected by a gold wire 23.

  In the above package structure, the X-axis and Y-direction 2-axis acceleration sensor and the 1-axis angular velocity sensor, the X-direction and Z-direction acceleration sensor and the 1-axis angular velocity sensor, the 1-axis acceleration sensor and the 2-axis Various sensors such as an angular velocity sensor and a biaxial angular velocity sensor can be arranged, and the use of measuring physical quantities can be applied in various cases.

  In the present invention, the structure is configured to suppress moisture permeation, and the vacuum sensing space is surrounded only by the silicon material and the silicon oxide film material, so that the reliability is high. Therefore, the present invention can be applied even in a high humidity atmosphere and an atmosphere where a corrosive gas such as nitrogen oxide or oil vapor exists.

  In addition, the electrode substrate 1 has a structure in which a metal wiring portion is connected to an electrode pad portion from a part or all of the through electrode portions. All parts other than the electrode pad are covered with a silicon oxide film to protect the moisture permeation prevention film, preventing moisture permeation due to damage during the process or contact that occurs during assembly. The film can be prevented from being damaged, and a protective film such as a resin is not necessary.

In the physical quantity sensor described above, a silicon material is applied to the fixed substrate, a low resistance silicon material is applied to the device substrate and the electrode substrate, and a movable electrode portion and a fixed electrode portion are formed on the device substrate. The through electrode in which the silicon electrode is individually insulated by the silicon oxide film and the electrode substrate in which the groove is formed, and the movable electrode portion and the fixed electrode portion are in contact with the through electrode individually, and the physical quantity of the angular velocity is measured. It has a sensing unit, and is a capacitance type sensor, wherein the device substrate and the fixed substrate are bonded via an oxide film, and the device substrate and the electrode substrate are bonded by silicon. Thus, an angular velocity sensor excellent in reliability can be provided. The groove formed in the electrode substrate is preferably formed by a dry etching method capable of processing a high aspect ratio groove of silicon. This is because the side surface of the silicon processing groove can be made vertical.
It is preferable to apply direct silicon bonding as a method for bonding the fixed substrate, the device substrate, and the electrode substrate. By applying silicon direct bonding to the bonding of at least two of the three substrates, the groove with the vibrating body that is the movable electrode part of the angular velocity sensor is set to an arbitrary depth before bonding. Can do.

  The aspect ratio of the depth / width of the silicon oxide film formed on the electrode substrate is compared with the aspect ratio of the width / thickness of the silicon oxide film formed between the device substrate and the fixed substrate. By applying a structure having a larger aspect ratio, moisture permeation can be suppressed. This is because moisture permeation takes more time for the moisture to pass due to the smaller aspect ratio due to the relationship between the width and depth of the oxide film. This is because it is difficult to form a protective film that exists on the side surface of the sensor and suppresses moisture.

  In addition, the surface area of the silicon oxide film formed on the electrode substrate in contact with the sensing space is compared with the surface area of the silicon oxide film formed between the device substrate and the fixed substrate. A small structure is good.

  Furthermore, by applying a silicon nitride film as the moisture prevention film, the moisture intrusion suppression effect can be improved. Note that the same effect can be obtained by applying other materials as long as the insulating film is a film that can withstand the oxide film formation temperature.

  By disposing the angular velocity sensor described above and the acceleration sensor together with the control LSI in a package made of one ceramic material or resin material, a composite type physical quantity sensor having excellent reliability can be provided.

  Further, since the angular velocity sensor can be applied as a sensor for driving control of an automobile, it can be installed in a place with a high humidity atmosphere and a corrosive gas such as nitrogen oxide or oil vapor.

  Since the angular velocity sensor can be applied as an automobile sensor, it can be installed in a harsh environment of an automobile, for example, in an engine room.

  In the present invention, any sensor other than the angular velocity sensor can be applied as long as the sensing unit is a physical quantity sensor driven in a vacuum environment. For example, it can be applied to a pressure sensor.

  Although various structures of the present invention have been described, the present invention is not limited to the above-described examples, and it is easy for those skilled in the art to make various modifications within the scope of the invention described in the claims. Will be understood.

DESCRIPTION OF SYMBOLS 1 ... Electrode substrate, 2 ... Fixed substrate, 3 ... Device substrate, 4 ... Silicon oxide film, 5 ... Sensing space, 6 ... Moisture permeation prevention film, 7 ... Fixed electrode, 8 ... Movable electrode, 9 ... Metal electrode, 10 ... Through electrode,
11 ... Spring beam, 12 ... SiN film, 13 ... Protective film, 14 ... Moisture permeation path, 15 ... MEMS element,
16 ... length and width of silicon oxide film, 17 ... length and width of silicon oxide film at junction,
18 ... polysilicon, 19 ... groove, 20 ... wiring, 21 ... electrode pad, 22 ... angular velocity sensor,
23 ... Gold wire, 24 ... Control LSI, 25 ... Accelerometer, 26 ... Adhesive layer, 27 ... Metal paste,
28 ... Lead frame, 29 ... Mold resin

Claims (7)

In a physical quantity sensor having a two-layer structure of a substrate and an electrode substrate in which a fixed layer and a device layer are integrated, or at least a three-layer structure of a fixed substrate, device substrate, and electrode substrate
The electrode substrate includes a through electrode made of low-resistance silicon, and a silicon oxide film provided around the through electrode to insulate the through electrode from the surroundings,
A moisture permeation preventive film is formed directly on the opposite side of the electrode substrate on the side opposite to the device layer of the electrode substrate so as to cover the end and directly adhere to it. Physical quantity sensor. In the physical quantity sensor according to claim 1,
The electrode substrate has a structure in which a metal wiring is connected to the electrode pad portion from the through electrode on the surface thereof, and a surface on which the electrode pad portion is provided is entirely covered with a silicon oxide film except for the electrode pad portion. Physical quantity sensor characterized by the structure. The physical quantity sensor comprising at least a three-layer structure of the fixed substrate, the device substrate, and the electrode substrate according to claim 1 or 2,
Applying a silicon material to the fixed substrate;
Applying a low resistance silicon material to the device substrate and the electrode substrate,
The device substrate is formed with a movable electrode portion and a fixed electrode portion,
A plurality of the through electrodes are formed, and have a contact with the movable electrode part and a contact with the fixed electrode part,
The physical quantity sensor, wherein the device substrate and the fixed substrate are bonded via an oxide film, and the device substrate and the electrode substrate are bonded together by silicon. In the physical quantity sensor according to claim 3,
A depth / width aspect ratio of a silicon oxide film provided on the electrode substrate and formed around the through electrode; and
A physical quantity sensor characterized by comparing the aspect ratio of the width / thickness of a silicon oxide film formed between the device substrate and the fixed substrate, and the latter has a larger aspect ratio. In the physical quantity sensor according to claim 4,
Compare the surface area of multiple silicon oxide films formed on the electrode substrate in contact with the sensing space where the fixed electrode and the movable electrode are provided, and the surface area of the silicon oxide film formed between the device substrate and the fixed substrate. A physical quantity sensor characterized in that the latter has a smaller surface area.   6. The physical quantity sensor according to claim 1, wherein a silicon nitride film is applied to the moisture permeation preventive film.   7. The physical quantity sensor according to claim 1, wherein the physical quantity sensor is arranged in a package made of one ceramic material or resin material together with the control LSI together with the angular velocity sensor and the acceleration sensor.

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