Patent Publication Number: US-2021190617-A1

Title: Sensor element and method for manufacturing same, and sensor device

Description:
TECHNICAL FIELD 
     The present invention relates to a sensor element, a method for manufacturing the same, and a sensor device. 
     BACKGROUND ART 
     Conventionally, an invention relating to a physical quantity detection device for detecting a physical quantity of a gas is known (see PTL 1 below). PTL 1 discloses a physical quantity detection device that is mounted to an intake system of an internal combustion engine and detects a physical quantity of intake air. The physical quantity detection device includes a semiconductor substrate having a cavity, a support film made of an insulating material provided on the semiconductor substrate so as to cover the cavity, and a gauge resistor provided in a region on the support film that covers the cavity, and a humidity detecting element provided on the support film (see the same document, claim  1  and the like). 
     The semiconductor substrate is formed of single-crystal silicon, and the cavity is formed by a semiconductor microfabrication technique using photolithography and an anisotropic etching technique. The support film includes a single-layer insulating film or a plurality of stacked insulating films. As the insulating film, silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ) or the like is selected. 
     When manufacturing a sensor element as such a physical quantity detection device, for example, an SiO film or an SiN film is formed on the surface of the semiconductor substrate by a semiconductor microfabrication technique using the above-described photolithography, except for a portion that becomes a cavity of the semiconductor substrate. Then, the semiconductor substrate on which the mask has been formed is subjected to anisotropic etching using a potassium hydroxide solution or the like to form a cavity, thereby exposing the support film. 
     After that, the SiO film and the SiN film used as the mask are removed with a hydrofluoric acid, a hot phosphoric acid solution, or the like to expose a surface of the semiconductor substrate made of single-crystal silicon. Then, the semiconductor substrate from which the mask has been removed is bonded to a pedestal made of a base material such as glass by, for example, anodic bonding. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2016-11889 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     As described above, the hydrofluoric acid and hot phosphoric acid solutions used to remove the mask formed on the surface of the semiconductor substrate are highly dangerous, require careful handling, and waste liquid after use. Post-step such as waste liquid processing is required. 
     In addition, as described above, a multifunctional sensor element including a gauge resistor and a humidity detecting element on a support film may include an SiO film or an SiN film as a support film or a protective film formed thereon. In this case, the entirety of the semiconductor substrate having a mask formed on one surface and a support film and a protective film formed on the other surface is etched with hydrofluoric acid or a hot phosphoric acid solution to remove the mask. Then, the support film and the protective film are removed together with the mask. Therefore, it is necessary to etch only one surface of the semiconductor substrate, which complicates the manufacturing process. 
     The invention provides a sensor element that can be manufactured without using a hydrofluoric acid or hot phosphoric acid solution, a manufacturing method thereof, and a sensor device. 
     Solution to Problem 
     An aspect of the sensor element of the invention is a sensor element which includes a base material and a semiconductor chip bonded to the base material. The semiconductor chip includes a semiconductor substrate, a support film provided on a surface of the semiconductor substrate, a substrate chamber provided in a concave shape on the semiconductor substrate to form a cavity facing an element region of the support film, and an insulating layer provided in a rear surface of the semiconductor substrate, and a bonding layer provided between the insulating layer and the base material. The insulating layer includes at least one of a silicon oxynitride film and a silicon oxide film. The bonding layer includes a low-melting point glass. 
     An aspect of the sensor device according to the invention includes the sensor element. 
     An aspect of the method for manufacturing a sensor element of the invention is a method for manufacturing a sensor element including a base material and a semiconductor chip bonded to the base material. The method includes an arrangement step for arranging a semiconductor chip on a surface of the base material via a bonding agent containing a low-melting point glass in with the insulating layer facing the surface of the base material, wherein the semiconductor chip includes a semiconductor substrate, a support film provided on a surface of the semiconductor substrate, a substrate chamber provided in a concave shape in the semiconductor substrate to form a cavity facing an element region of the support film, and an insulating layer including at least one of a silicon oxynitride film and a silicon oxide film provided on a rear surface of the semiconductor substrate and a bonding step for heating the bonding agent to a heating temperature not lower than a softening point of the low-melting point glass and not higher than a heat-resistant temperature of the semiconductor chip, and bonding the semiconductor chip to the base material via the bonding layer. 
     Advantageous Effects of Invention 
     According to the above aspect of the invention, when the semiconductor substrate of the semiconductor chip is etched to form the substrate chamber, the insulating layer on the rear surface of the semiconductor substrate is used as a mask. Then, the semiconductor chip can be bonded to the base material without removing the insulating layer. Therefore, according to the above aspect of the invention, it is possible to provide a sensor element that can be manufactured without using hydrofluoric acid or hot phosphoric acid solution, a method for manufacturing the same, and a sensor device including the sensor element. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a sensor element according to one embodiment of the invention. 
         FIG. 2  is a plan view of the sensor element illustrated in  FIG. 1 . 
         FIG. 3  is a cross-sectional view illustrating a first modification of the sensor element illustrated in  FIG. 1 . 
         FIG. 4  is a cross-sectional view illustrating a second modification of the sensor element illustrated in  FIG. 1 . 
         FIG. 5  is a cross-sectional view illustrating a third modification of the sensor element illustrated in  FIG. 1 . 
         FIG. 6  is a graph illustrating an example of a DTA curve of glass. 
         FIG. 7  is a cross-sectional view illustrating a fourth modification of the sensor element illustrated in  FIG. 1 . 
         FIG. 8A  is a bottom view of a sensor device according to one embodiment of the invention. 
         FIG. 8B  is a cross-sectional view of the sensor device taken along line B-B illustrated in  FIG. 8A . 
         FIG. 9A  is a cross-sectional view illustrating an example of a mounting state of the sensor device illustrated in  FIG. 8B . 
         FIG. 9B  is a cross-sectional view illustrating another example of the mounting state of the sensor device illustrated in  FIG. 8B . 
         FIG. 10A  is a cross-sectional view illustrating a mounting state of the sensor device according to one embodiment of the invention. 
         FIG. 10B  is a cross-sectional view of the sensor device taken along line B-B of  FIG. 10A . 
         FIG. 11  is a STEM analysis result of a sensor element bonding interface according to a twelfth example of the invention. 
         FIG. 12  is a STEM analysis result of a sensor element bonding interface according to the twelfth example of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of a sensor element, a method for manufacturing the same, and a sensor device according to the invention will be described with reference to the drawings. 
     (Sensor Element and Manufacturing Method Thereof) 
       FIG. 1  is a schematic cross-sectional view of a sensor element  100  according to a first embodiment of the invention.  FIG. 2  is a schematic plan view of the sensor element  100  illustrated in  FIG. 1 . The sensor element  100  of this embodiment is used, for example, as a component of a sensor device such as a thermal humidity measuring device that measures the humidity of air passing through an intake pipe of an automobile or such as a multifunctional measuring device that measures both humidity and pressure. The most characteristic feature of the sensor element  100  of this embodiment is that it has the following configuration. 
     The sensor element  100  includes a base material  10  and a semiconductor chip  20  bonded to the base material  10 . The semiconductor chip  20  includes a semiconductor substrate  21 , a support film  22  provided on a surface  21   a  of the semiconductor substrate  21 , and a substrate chamber  23  provided in a concave shape on the semiconductor substrate  21  to form a cavity facing an element region  22 A of the support film  22 , an insulating layer  24  provided on a rear surface  21   b  of the semiconductor substrate  21 , and a bonding layer  25  provided between the insulating layer  24  and the base material  10 . The insulating layer  24  includes at least one of a silicon oxynitride film and a silicon oxide film. The bonding layer  25  includes a low-melting point glass. Further, in the sensor element  100  of this embodiment, the thickness of the semiconductor chip  20  is, for example, 10 μm or less. Hereinafter, the configuration of the sensor element  100  of this embodiment will be described in more detail. 
     The base material  10  is, for example, a plate-shaped member, and is bonded to the rear surface side of the semiconductor chip  20  via the bonding layer  25 . The material of the base material  10  is, for example, a semiconductor such as silicon (Si) or glass. As the glass, for example, borosilicate glass such as PYREX (registered trademark) or Tempax Float (registered trademark) can be used. Further, from the viewpoint of improving the bonding reliability between the base material  10  and the semiconductor chip  20 , it is preferable that the linear expansion coefficient of the base material  10  may be a value as close as possible to the linear expansion coefficient of the semiconductor substrate  21  of the semiconductor chip  20 . 
     The semiconductor substrate  21  is, for example, a single-crystal silicon substrate made of single-crystal silicon, and has the support film  22  on the surface  21   a  and the insulating layer  24  on the rear surface. In addition, the semiconductor substrate  21  has the concave substrate chamber  23  that opens at the opening of the insulating layer  24  on the rear surface  21   b.    
     The support film  22  is, for example, an insulator layer or film formed on the surface layer portion of the semiconductor substrate  21  or the surface  21   a  of the semiconductor substrate  21 . In the example illustrated in  FIG. 1 , the support film  22  has a multilayer structure including a protective film  22   a  formed on the outermost surface of the semiconductor substrate  21  and three insulating films  22   b ,  22   c , and  22   d  covered by the protective film  22   a . Further, the insulating films  22   b ,  22   c , and  22   d  forming the support film  22  are not limited to three layers, and may be, for example, a single layer, two layers, or four or more layers. The protective film  22   a  and the insulating films  22   b ,  22   c , and  22   d  forming the support film  22  are made of, for example, silicon oxide (SiO X ) or silicon nitride (SiN X ). The support film  22  includes, for example, the insulating film  22   d  made of such an oxide or nitride on the surface opposite to the substrate chamber  23 . 
     In the support film  22 , for example, at least one of a pressure measurement element  30  and a humidity measurement element  40  is formed in the element region  22 A facing the substrate chamber  23  forming a cavity in the semiconductor substrate  21 . The pressure measurement element  30  and the humidity measurement element  40  are covered with, for example, a protective film  22   a  forming the support film  22 . The element region  22 A of the support film  22  forms a diaphragm or a partition of the substrate chamber  23 . Among the insulating films  22   b ,  22   c , and  22   d  forming the support film  22 , the lowermost layer insulating film  22   d  facing the substrate chamber  23  is made of SiO X  or SiN X . 
     In the example illustrated in  FIGS. 1 and 2 , the support film  22  has two element regions  22 A, the pressure measurement element  30  is formed in one element region  22 A, and the humidity measurement element  40  is formed in the other element region  22 A. In other words, in the example illustrated in  FIGS. 1 and 2 , the pressure measurement element  30  and the humidity measurement element  40  are formed on the same support film  22 . The support film  22  supports the pressure measurement element  30  and the humidity measurement element  40  on a cavity formed by the substrate chamber  23 , respectively. 
     The substrate chamber  23  is provided in a concave shape on the rear surface  21   b  side of the semiconductor substrate  21  on which the insulating layer  24  is formed, on the side opposite to the surface  21   a  side of the semiconductor substrate  21  on which the support film  22  is formed, and forms a cavity facing the element region  22 A of the support film  22 . The semiconductor chip  20  of this embodiment has two substrate chambers  23 . At least one of the substrate chambers  23  is sealed between the semiconductor substrate  21  and the base material  10  and has a depressurized state lower than the atmospheric pressure. In the semiconductor chip  20  of this embodiment, the space between the semiconductor substrate  21  and the base material  10  is sealed in both of the two substrate chambers  23 , and the pressure is in a depressurized state lower than the atmospheric pressure. Further, the semiconductor chip  20  may have one substrate chamber  23 , or may have three or more substrate chambers  23 . 
       FIG. 3  is a cross-sectional view illustrating a first modification of the sensor element  100  illustrated in  FIG. 1 . In the example illustrated in  FIG. 3 , the sensor element  100  has a ventilation groove  11  formed in a concave shape on a surface  10   a  of the base material  10 . The ventilation groove  11  extends from the substrate chamber  23  facing the element region  22 A of the support film  22 , in which the humidity measurement element  40  is formed, along the surface of the base material  10  toward the side end of the base material  10 , and is open at the side end of the base material  10 . Thereby, the substrate chamber  23  facing the element region  22 A of the support film  22  in which the humidity measurement element  40  is formed communicates with the space around the sensor element  100  through the ventilation groove  11 , and has the same pressure as that of the surrounding space. 
       FIG. 4  is a cross-sectional view illustrating a second modification of the sensor element  100  illustrated in  FIG. 1 . In the example illustrated in  FIG. 4 , the sensor element  100  has a through hole  12  penetrating the base material  10  in the thickness direction. The through hole  12  extends in the thickness direction of the base material  10  from the substrate chamber  23  facing the element region  22 A of the support film  22  in which the humidity measurement element  40  is formed, and opens at the bottom surface of the base material  10 . Thereby, the substrate chamber  23  facing the element region  22 A of the support film  22  on which the humidity measurement element  40  is formed communicates with the space around the sensor element  100  through the through hole  12 , and has the same pressure as the pressure in the surrounding space. 
     In any case, it is desirable that the substrate chamber  23  facing the element region  22 A of the support film  22  on which the pressure measurement element  30  is formed in the depressurized state. The reason is that the internal pressure of the substrate chamber  23  adjacent to the pressure measurement element  30  becomes a reference pressure at the time of pressure measurement by the pressure measurement element  30 , and an absolute pressure can be measured. For this purpose, the depressurized state of the substrate chamber  23  is not only a state in which the internal pressure of the substrate chamber  23  is reduced than the atmospheric pressure, but also, for example, it is preferable that the internal pressure of the substrate chamber  23  is a medium vacuum of 100 Pa or less. More preferably, the internal pressure of the substrate chamber  23  is 20 Pa or less. 
     The pressure measurement element  30  includes, for example, a gauge resistor  31  formed in the element region  22 A of the support film  22 , a reference resistor  32  formed outside the element region  22 A of the support film  22 , and a plurality of electrodes  33  connected to the gauge resistor  31  and the reference resistor  32  for transmitting and receiving voltage and current. The gauge resistor  31  and the reference resistor  32  are made of a material having a high temperature coefficient of resistance such as, for example, platinum (Pt), tantalum (Ta), molybdenum (Mo), and polycrystalline silicon (Si) doped with impurities. Molybdenum (Mo) has excellent heat resistance, but the gauge factor of a Mo film is relatively small about 0.4 to 1.5, but the measurement accuracy can be improved by optimizing the shape and structure of the pressure measurement element  30 . 
     In the pressure measurement element  30 , the number of the gauge resistors  31  and the number of the reference resistors  32  may be respectively singular, but it is preferable that the number is each plural from the viewpoint of improving the gauge factor and the measurement accuracy. In addition, from the viewpoint of improving the measurement accuracy of the pressure measurement element  30 , the thickness of the support film  22  is desirably, for example, a thin film of several tens μm or less. In the examples illustrated in  FIGS. 1, 3 and 4 , a portion made of single-crystal silicon of the semiconductor substrate  21  adjacent to the element region  22 A of the support film  22  is removed to form a cavity substrate chamber  23 , and the support film  22  is exposed in the substrate chamber  23 . Therefore, by making the support film  22  thin film as described above, the deflection of the support film  22  due to the pressure acting on the support film  22  increases, and the measurement accuracy of the pressure measurement element  30  can be improved. 
     The humidity measurement element  40  includes, for example, a first heating element  41 , a second heating element  42 , and a plurality of electrodes  43  connected to these heating elements  41  and  42  for transmitting and receiving voltage and current. The heating elements  41  and  42  are made of, for example, the same material as the gauge resistor  31  of the pressure measurement element  30 . From the viewpoint of improving the measurement accuracy of the humidity measurement element  40 , the material forming the heating elements  41  and  42  is preferably a material having a temperature coefficient of resistance of 1000 [ppm/° C.] or more and a heat-resistant temperature of 400 [° C.] or more. 
     In a case where polycrystalline silicon doped with impurities is used as the material of the heating elements  41  and  42  of the humidity measurement element  40  and the gauge resistor  31  and the reference resistor  32  of the pressure measurement element  30 , the heat-resistant temperature of these elements is, for example, about 200 [° C.]. Therefore, the material of the humidity measurement element  40  has a problem in reliability for a long period of time. However, the gauge factor of polycrystalline silicon is relatively large, for example, about 3 to 14, and the measurement accuracy of the pressure measurement element  30  can be improved. 
     Therefore, in a sensor device that is not assumed to be used for a long period of time, materials doped with impurities are effective for the heating elements  41  and  42  of the humidity measurement element  40  of the sensor element  100  and the gauge resistor  31  and the reference resistor  32  of the pressure measurement element  30 . However, in the sensor element  100  used for a vehicle-mounted sensor device that is assumed to be used for a long period of time, it is desirable to use a high heat-resistant material such as molybdenum as a material for the heating elements  41  and  42  of the humidity measurement element  40  and the gauge resistor  31  and the reference resistor  32  of the pressure measurement element  30  are used. 
     The electrodes  33  and  43  of the pressure measurement element  30  and the humidity measurement element  40  are electrically connected, for example, to a drive circuit (not illustrated) via a gold bonding wire or a lead frame. As a material of the electrodes  33  and  43 , for example, aluminum (Al) can be used. 
     The humidity measurement element  40  can measure the humidity as described below, for example. First, the first heating element  41  is controlled to be heated, for example, to a temperature of about 400° C. to 500° C. 
     In addition, the second heating element  42  is an auxiliary heating element, and is controlled to be heated, for example, to a temperature of about 200° C. to 300° C. 
     When the humidity of the air changes, the thermal conductivity of the air changes, and the amount of heat radiated from the first heating element  41  to the air changes. The absolute humidity can be measured by detecting the change in the heat release amount. 
     The second heating element  42  is an auxiliary heating element for maintaining the periphery of the first heating element  41  at a constant temperature. With the second heating element  42 , even when the environmental temperature at which the sensor element  100  is installed changes, the vicinity of the first heating element  41  can be maintained at a constant temperature, and the temperature characteristics in humidity measurement can be improved. In this embodiment, the humidity measurement element  40  has the second heating element  42 , but the humidity can be measured without the second heating element  42 . In a case where the humidity measurement element  40  does not have the second heating element  42 , it is necessary to compensate for a measurement error due to a change in air temperature using a temperature sensor or the like as needed. 
     Further, one factor that causes a measurement error in the humidity measurement element  40  is an error in a case where a high-speed pressure fluctuation occurs. In the example illustrated in  FIGS. 3 and 4 , the substrate chamber  23  facing the element region  22 A of the support film  22  on which the humidity measurement element  40  is formed communicates with the space around the sensor element  100 . In this case, the deflection of the support film  22  in the element region  22 A where the humidity measurement element  40  is formed can be reduced. Therefore, it is possible to improve the correction accuracy of humidity measured under high-speed pressure and temperature change conditions, and to perform accurate pressure correction even under high-speed pressure fluctuation conditions (transient conditions). In addition, it is possible to suppress a decrease in the correction accuracy of the measured humidity due to a variation at the time of manufacturing. 
     The pressure measurement element  30  can measure the pressure as follows, for example. Due to the pressure of the gas around the sensor element  100 , the element region  22 A of the support film  22  facing the cavity formed by the substrate chamber  23  bends, and the resistance of the gauge resistor  31  changes. In other words, since the substrate chamber  23  facing the element region  22 A of the support film  22  provided with the pressure measurement element  30  is tightly sealed, the element region  22 A of the support film  22  bends due to the pressure of the surrounding gas, and the resistance of the gauge resistor  31  changes. By measuring the resistance change of the gauge resistor  31 , the pressure of the gas around the sensor element  100  can be measured. 
     In addition, in the sensor element  100  of this embodiment, the humidity measurement element  40  and the pressure measurement element  30  are provided on the support film  22  of the semiconductor chip  20 . In this case, even if the temperature of the environment around the sensor element  100  changes, the temperature change of the humidity measurement element  40  and the pressure measurement element  30  can be suppressed by the heating elements  41  and  42  of the humidity measurement element  40 . Therefore, the influence on the measurement of humidity and the measurement of pressure can be suppressed even under a situation where the temperature changes at high speed. 
     The insulating layer  24  formed on the rear surface of the semiconductor substrate  21  is at least partially made of, for example, silicon oxide (SiO X ) or silicon nitride (SiN X ). In the insulating layer  24 , for example, in a manufacturing process of the semiconductor chip  20 , a pattern having an opening at a position corresponding to the substrate chamber  23  is formed by photolithography. At least a part of the insulating layer  24  is used as a resist when the substrate chamber  23  is formed in the semiconductor substrate  21  by, for example, anisotropic etching from the rear surface of the semiconductor substrate  21  using potassium hydroxide (KOH). At least a part of the insulating layer  24  functioning as a resist may be formed simultaneously with the support film  22  on the surface of the semiconductor substrate  21 . 
     In addition, the insulating layer  24  includes, for example, at least one of a silicon oxynitride film and a silicon oxide film. In other words, the insulating layer  24  may include a multilayer film in which, for example, a single-layer or multi-layer silicon oxynitride film, a single-layer or multi-layer silicon oxide film, or a silicon oxynitride film and a silicon oxynitride film in addition to the portion formed by SiO X  or SiN X  are laminated. At least one of the silicon oxynitride film and the silicon oxide film is generated, for example, in the process of manufacturing the sensor element  100  when the base material  10  and the semiconductor substrate  21  are bonded via the bonding layer  25 , and is a thin film having a thickness of approximately 100 nm or less. Further, in the example illustrated in  FIG. 1 , the insulating layer  24  is made of only a silicon oxide film. 
       FIG. 5  is a cross-sectional view illustrating a third modification of the sensor element  100  illustrated in  FIG. 1 . In the example illustrated in  FIG. 5 , the insulating layer  24  has a two-layer structure including an insulating film  24   a  made of SiN X  and an insulating film  24   b  made of SiO X  from the bonding layer  25  toward the surface  21   a  of the semiconductor substrate  21 . In addition, the support film  22  has a four-layer structure which includes the protective film  22   a  made of SiO X  on the outermost surface, the insulating film  22   b  made of SiO X  in the lower layer thereof, the insulating film  22   c  made of SiN X  in the lower layer thereof, and the insulating film  22   d  made of SiO X  in the lowermost layer. 
     The bonding layer  25  is a layer containing low-melting point glass. The low-melting point glass forming the bonding layer  25  contains, for example, vanadium. In addition, the low-melting point glass forming the bonding layer  25  has, for example, a linear expansion coefficient of 30×10 −7  [1/° C.] or more and 70×10 −7  [1/° C.] or less. The bonding layer  25  is provided between the base material  10  and the insulating layer  24  provided on the rear surface  21   b  of the semiconductor substrate  21  forming the semiconductor chip  20 , and bonds the semiconductor chip  20  and the base material  10 . 
       FIG. 6  is a graph illustrating an example of a differential thermal analysis (DTA) curve of glass. Here, the low-melting point glass is a glass having a softening point of 600° C. or lower, where the second endothermic peak is a softening point (Ts), as illustrated in  FIG. 6 . The low-melting point glass is selected, for example, from those capable of joining the semiconductor chip  20  and the base material  10  at or below the heat-resistant temperature of the semiconductor chip  20 . Examples of the low-melting point glass include Bi 2 O 3  containing bismuth, SnO containing tin, and V 2 O 5  containing vanadium. 
     In the sensor element  100  of this embodiment, as the low-melting point glass included in the bonding layer  25 , for example, V 2 O 5  containing vanadium is used, and one containing substantially no lead is used. As a result, it is possible to provide the sensor element  100  compliant with the European Parliament and Council Directive (hereinafter, referred to as the RoHS Directive) on the restriction on the use of specific harmful substances contained in electric and electronic devices. Further, substances banned under the RoHS Directive shall be subject to the Hazardous Substances Regulations enforced by the EU (European Union) on Jul. 1, 2006, and it is acceptable that banned substances are contained within the range specified by the regulations. 
     Further, in a case where the substrate chamber  23  of the semiconductor chip  20  is in a depressurized state, it is desirable to select SnO-based or V 2 O 5 -based as the low-melting point glass contained in the bonding layer  25 . This is because in a case where the Bi 2 O 3 -based glass is heated under a depressurized state, the reliability of the bonding layer  25  decreases due to the reduction and precipitation of Bi. 
     In addition, in a case where the insulating layer  24  is a nitride such as a silicon nitride film, for example, the low-melting point glass contained in the bonding layer  25  is preferably a SnO-based or V 2 O 5 -based glass. When a Bi 2 O 3 -based low-melting point glass is converted into a silicon oxide film by a reaction, it reacts with the silicon nitride film to release nitrogen gas and generate bubbles. On the other hand, SnO-based or V 2 O 5 -based low-melting point glass has low reactivity with the silicon nitride film, suppresses generation of bubbles, and can improve the reliability of the bonding layer  25 . In other words, by using the bonding layer  25  containing a SnO-based or V 2 O 5 -based low-melting point glass, the reaction with the silicon nitride film can be suppressed, and the reaction can be suppressed up to the silicon oxynitride film instead of the silicon oxide film. Thereby, the release of the nitrogen gas can be reduced, and the reliability of the bonding layer can be improved. 
     The bonding layer  25  can include a filler or the like for adjusting the thermal expansion coefficient, in addition to the low-melting point glass. Examples of the filler may include zircon, zirconia, quartz glass, ß-spondumene, cordierite, mullite, ß-eucryptite, ß-quartz, zirconium phosphate, zirconium phosphate tungstate (ZWP), zirconium tungstate and these solid solutions, and the like. These can be used alone or in combination of two or more. It is desirable that the content of the filler in the bonding layer  25  be 50% by volume or less. If the content is larger than this value, the softening fluidity of the material when forming the bonding layer  25  may be reduced, and the reliability of bonding may be reduced. 
     The thermal expansion coefficient of the bonding layer  25  is preferably in the range of 30×10 −7  [1/° C.] or more and 70×10 −7  [1/° C.] or less from the viewpoint of bonding reliability. Thereby, the difference in the thermal expansion coefficient from the base material  10  made of, for example, silicon or glass can be reduced, and the bonding reliability can be improved. Here, the thermal expansion coefficient refers to a linear thermal expansion coefficient value measured in a temperature range of 50° C. or more and 250° C. or less. 
     The most preferable low-melting point glass contained in the bonding layer  25  is a V 2 O 5 -based low-melting point glass. The V 2 O 5 -based low-melting point glass has a lower softening point than other low-melting point glasses, and has a linear expansion coefficient that is easier to match with the base material  10  made of silicon or the like. Therefore, a thermal stress when joining the semiconductor chip  20  and the base material  10  via the bonding layer  25  can be reduced. It is desirable that the composition of the V 2 O 5 -based low-melting point glass further contains 10% by weight or more of Fe 2 O 3  in terms of oxidation. By containing 10% by weight or more of Fe 2 O 3 , it becomes possible to lower the softening point of the glass while lowering the thermal expansion coefficient of the glass composition containing V 2 O 5  as a main component. 
     As a range of the glass composition that can form a good bonding layer  25 , for example, in terms of oxidation, V 2 O 5  is 45 to 50% by weight, TeO 2  is 20 to 30% by weight, Fe 2 O 3  is 10 to 15% by weight, P 2 O 5  is 5 to 16% by weight, and WO 3  is 0 to 10% by weight. The glass composition is easily crystallized when Fe 2 O 3  is contained in an amount of 10% by weight or more, but the crystallization can be suppressed by containing WO 3  in the range of 0 to 10% by weight. 
     In addition, the low-melting point glass may contain an alkaline earth metal element in its composition from the viewpoint of thermal stability, but it is desirable to contain the element in a range of less than 10 mol % in terms of oxide. If the range exceeds, the thermal expansion coefficient will increase. The content of the alkali metal element in the low-melting point glass is more preferably 5 mol % or less, more preferably 3.4 mol % or less in terms of oxide. 
       FIG. 7  is a cross-sectional view illustrating a fourth modification of the sensor element  100  illustrated in  FIG. 1 . The sensor element  100  illustrated in  FIG. 7  mainly includes the support film  22  formed by the insulating film  22   b , which is an oxide film formed on the surface of the semiconductor substrate  21 , and a part of the surface side of the semiconductor substrate  21 , and differs from the sensor element  100  illustrated in  FIG. 1  in that the humidity measurement element  40  is not included. 
     In the example illustrated in  FIG. 7 , the sensor element  100  has the pressure measurement element  30  in the element region  22 A of the support film  22  facing the substrate chamber  23  of the semiconductor substrate  21 . The insulating film  22   b  forming a part of the support film  22  is an oxide film formed on the surface of the semiconductor substrate  21 , and a region for forming the gauge resistor  31  is opened and removed by photolithography technology. The gauge resistor  31  is formed in a portion of the surface of the semiconductor substrate  21  where the insulating film  22   b  is opened, for example, by thermal diffusion. The electrode  33  of the pressure measurement element  30  is, for example, an Al electrode formed in a contact hole provided in the insulating film  22   b  by an oxidation process or a photographic technique. 
     On the rear surface  21   b  of the semiconductor substrate  21 , the insulating layer  24 , which is a SiN X  film, is formed. The insulating layer  24  is patterned by a photolithography technique, and has an opening in a portion corresponding to the substrate chamber  23 . The substrate chamber  23  is formed by etching the semiconductor substrate  21  with, for example, KOH using the insulating layer  24  as a resist. In the semiconductor chip  20 , the rear surface of the semiconductor substrate  21  on which the insulating layer  24  is formed is bonded to the base material  10  via the bonding layer  25 . The insulating layer  24  includes at least one of a silicon oxynitride film and a silicon oxide film formed when the insulating layer  24  is bonded to the base material  10  via the bonding layer  25 . 
     Hereinafter, an embodiment of a method for manufacturing a sensor element according to the invention will be described, and an operation of the sensor element  100  according to the above-described embodiment will be described. 
     The method for manufacturing the sensor element  100  according to this embodiment is a method for manufacturing the sensor element  100  including the above-described base material  10  and the semiconductor chip  20  bonded to the base material  10 . The method for manufacturing the sensor element  100  according to this embodiment includes the following arranging step and joining step. 
     The arranging step is a step of arranging the semiconductor chip  20  via a bonding agent containing low-melting point glass with the insulating layer  24  facing the surface of the base material  10 . Here, as described above, the semiconductor chip  20  includes the semiconductor substrate  21 , the support film  22  provided on the surface of the semiconductor substrate  21 , the substrate chamber  23  forming a cavity facing the element region  22 A of the support film  22  provided in a concave shape on the semiconductor substrate  21 , and the insulating layer  24  provided on the rear surface of the semiconductor substrate  21  and including at least one of a silicon oxynitride film and a silicon oxide film. 
     The semiconductor chip  20  can be manufactured, for example, by the following procedure. First, an insulating film forming the support film  22  and the insulating layer  24  is formed on the front and rear surfaces of the semiconductor substrate  21  by, for example, thermal oxidation or chemical vapor deposition (CVD). In addition, the humidity measurement element  40  and the pressure measurement element  30  are formed on the support film  22  by a CVD method or a photolithography technique. In addition, the insulating layer  24  formed on the rear surface of the semiconductor substrate  21  is patterned by photolithography to remove the insulating film forming the insulating layer  24  in the region where the substrate chamber  23  is formed. 
     Next, using the insulating layer  24  formed on the rear surface of the semiconductor substrate  21  as a resist, the substrate chamber  23  is formed in the semiconductor substrate  21  by anisotropic etching from the rear surface of the semiconductor substrate  21  using potassium hydroxide (KOH). Thus, even in a case where the semiconductor chip  20  has a plurality of substrate chambers  23 , the plurality of substrate chambers  23  can be formed collectively. For example, in a case where the semiconductor substrate  21  is made of silicon (Si), the etching is stopped by the difference in etching rate between the semiconductor substrate  21  made of Si and the insulating film made of SiO X  forming the support film  22 , and the substrate chamber  23  can be easily formed. Further, the insulating film for stopping the etching may be an insulating film made of SiN X . If there is a difference in the etching rate from the semiconductor substrate  21 , stable etching can be performed. 
     The bonding agent is, for example, a paste-like material for forming the bonding layer  25 . The bonding agent can be prepared, for example, by kneading the powder of the low-melting point glass, which is an adhesive component, the above-mentioned filler material, a solvent, and a binder. As the solvent, for example, butyl carbitol acetate, α-terpineol, or the like can be used. As the binder, for example, ethyl cellulose, nitrocellulose, or the like can be used. 
     For example, a low-melting point glass is prepared by mixing and mixing various oxides as raw materials in a platinum crucible, and heated from  800  [° C.] to about 1100 [° C.] using an electric furnace at a heating rate of about 5° C./min to 10° C./min, and manufactured by maintaining the heating temperature for several hours. As long as the heating temperature is maintained, it is desirable to stir the heated and molten material in order to obtain a uniform glass. When removing the crucible from the electric furnace, in order to prevent moisture from adsorbing to the glass surface, it is desirable to pour the melted material onto a graphite mold or stainless steel plate that has been heated to a temperature of about 100° C. to 150° C. in advance. 
     In the arranging step, first, a paste-like bonding agent is applied to the surface of the base material  10  by a method such as screen printing and dried. Then, the semiconductor chip  20  is arranged on the bonding agent applied to the surface of the base material  10 . In order to reduce the pressure in the substrate chamber  23  of the semiconductor chip  20  to a depressurized state lower than the atmospheric pressure, a desired depressurized state is set in a state in which the semiconductor chip  20  is arranged on the surface of the base material  10  via a bonding agent. 
     The bonding step is a step in which the bonding agent is heated to a heating temperature equal to or higher than the softening point of the low-melting point glass and equal to or lower than the heat-resistant temperature of the semiconductor chip  20  to form the bonding layer  25 , and the semiconductor chip  20  is bonded to the base material  10  via the bonding layer  25 . In this bonding step, the bonding layer  25  can be formed by performing the binder removal process and the preliminary firing at once. The heating temperature of the bonding agent is preferably, for example, 400° C. or less. 
     As described above, the sensor element  100  manufactured by the manufacturing method according to this embodiment including the arranging step and the bonding step has the above-described configuration. In other words, the sensor element  100  includes the base material  10  and the semiconductor chip  20  bonded to the base material  10 . The semiconductor chip  20  includes a semiconductor substrate  21 , a support film  22  provided on the surface of the semiconductor substrate  21 , and a substrate chamber  23  provided in a concave shape on the semiconductor substrate  21  to form a cavity facing an element region  22 A of the support film  22 , an insulating layer  24  provided on the rear surface of the semiconductor substrate  21 , and a bonding layer  25  provided between the insulating layer  24  and the base material  10 . The insulating layer  24  includes at least one of a silicon oxynitride film and a silicon oxide film. The bonding layer  25  includes a low-melting point glass. 
     Therefore, according to the sensor element  100  and the method for manufacturing the same of this embodiment, when the semiconductor substrate  21  of the semiconductor chip  20  is etched to form the substrate chamber  23 , the insulating film on the rear surface of the semiconductor substrate  21  is used as a mask. Then, the semiconductor chip  20  can be bonded to the base material  10  without removing the insulating film. Therefore, according to this embodiment, it is possible to provide the sensor element  100  that can be manufactured without using a hydrofluoric acid or a hot phosphoric acid solution and a manufacturing method thereof. 
     In addition, in the sensor element  100  of this embodiment, the semiconductor chip  20  has a plurality of substrate chambers  23  as described above. At least one of the substrate chambers  23  is sealed between the semiconductor substrate  21  and the base material  10  and is in a depressurized state lower than the atmospheric pressure. Accordingly, as described above, the internal pressure of the substrate chamber  23  adjacent to the pressure measurement element  30  becomes the reference pressure at the time of pressure measurement by the pressure measurement element  30  by reducing the substrate chamber  23  facing the element region  22 A of the support film  22  in which the pressure measurement element  30  is formed to the depressurized state, so that the absolute pressure can be measured. 
     In addition, in the sensor element  100  of this embodiment, in a case where the low-melting point glass contained in the bonding layer  25  includes vanadium, as described above, it is possible to comply with the RoHS directive and improve the reliability of the bonding layer  25 . Further, the reliability of the sensor element  100  can be improved. Further, in a case where the substrate chamber  23  is in the depressurized state, the reliability of the bonding layer  25  is particularly important in order to maintain the depressurized state in the substrate chamber  23 . 
     In addition, in the sensor element  100  of this embodiment, the support film  22  has a film made of oxide or nitride on the surface on the side opposite to the substrate chamber  23 . Therefore, for example, in the etching for forming the substrate chamber  23  in the semiconductor substrate  21 , the surface of the semiconductor substrate  21  opposite to the substrate chamber  23  can be protected. 
     In addition, in the sensor element  100  of this embodiment, in a case where the material of the base material  10  is silicon or glass, the substrate chamber  23  can be formed by etching, and the insulating film can be formed by thermal oxidation. 
     In addition, in the sensor element  100  of this embodiment, in a case where the insulating layer  24  formed on the rear surface side of the semiconductor substrate  21  includes a silicon nitride film, this silicon nitride film can be used as a resist when the semiconductor substrate  21  is etched to form the substrate chamber  23 . In addition, in the sensor element  100  of this embodiment, the semiconductor chip  20  can be bonded to the base material  10  via the bonding layer  25  without removing the silicon nitride film. 
     In addition, in the sensor element  100  of this embodiment, the insulating layer  24  may include at least one of the silicon oxynitride film and the silicon oxide film between the silicon nitride film and the bonding layer  25  as described above. As described above, these films are thin films having a thickness of about 100 nm or less, which are generated when the base material  10  and the semiconductor substrate  21  are bonded via the bonding layer  25 . Therefore, even in this case, the sensor element  100  of this embodiment can bond the semiconductor chip  20  to the base material  10  via the bonding layer  25  without removing the silicon nitride film. 
     In addition, in the sensor element  100  of this embodiment, as described above, the insulating layer  24  may be formed only of the silicon oxide film. Even in this case, when the semiconductor substrate  21  is etched to form the substrate chamber  23 , this silicon oxide film can be used as a resist. In addition, in the sensor element  100  of this embodiment, the semiconductor chip  20  can be bonded to the base material  10  via the bonding layer  25  without removing the silicon oxide film. 
     In addition, in the sensor element  100  of this embodiment, as described above, the insulating layer  24  may include a silicon oxynitride film having a thickness of 100 nm or less. As described above, this silicon oxynitride film is a thin film formed when the base material  10  and the semiconductor substrate  21  are bonded via the bonding layer  25 . Therefore, even in this case, the sensor element  100  of this embodiment can bond the semiconductor chip  20  to the base material  10  via the bonding layer  25  without removing the silicon oxynitride film or the silicon oxide film included in the insulating layer  24 . 
     In addition, in the sensor element  100  of this embodiment, the semiconductor chip  20  has a thickness of 10 μm or less. Thereby, the sensor element  100  can be reduced in size, and the sensor device including the sensor element  100  can be reduced in size. 
     In addition, in the sensor element  100  of this embodiment, the low-melting point glass contained in the bonding layer  25  has a linear expansion coefficient of 30×10 −7  [1/° C.] or more and 70×10 −7  [1/° C.] or less. Accordingly, as described above, in a case where the base material  10  is silicon or glass, the difference in the thermal expansion coefficient between the base material  10  and the bonding layer  25  is reduced, and the bonding reliability between the semiconductor chip  20  and the base material  10  can be improved. 
     In addition, in the sensor element  100  of this embodiment, at least one of the pressure measurement element  30  and the humidity measurement element  40  is formed in the element region  22 A of the support film  22 . Thereby, the sensor element  100  capable of measuring at least one of the pressure and the humidity can be obtained. In addition, in a case where the sensor element  100  includes both the pressure measurement element  30  and the humidity measurement element  40  in the plurality of element regions  22 A of the support film  22 , as described above, the influence on the measurement of the humidity and the measurement of the pressure can be suppressed even under a condition where the temperature changes at high speed. 
     In addition, in the method for manufacturing the sensor element  100  of this embodiment, in a case where the heating temperature in the bonding step is 400° C. or lower, the semiconductor chip  20  and the base material  10  can be bonded at a temperature equal to or lower than the heat-resistant temperature of the semiconductor chip  20 , so that the reliability of the sensor element  100  can be improved. 
     (Sensor Device) 
     Hereinafter, an embodiment of a sensor device according to the invention will be described with reference to  FIGS. 8A and 8B ,  FIGS. 9A and 9B , and  FIGS. 10A and 10B . 
       FIG. 8A  is a bottom view of the sensor device  200  according to an embodiment of the invention.  FIG. 8B  is a cross-sectional view of the sensor device taken along line B-B illustrated in  FIG. 8A . 
     The sensor device  200  of this embodiment is a thermal humidity detection device including the above-described sensor element  100  illustrated in  FIGS. 1 to 5 , for example. The sensor device  200  includes a housing  210  that stores the sensor element  100 . The housing  210  has a measurement chamber  211  in which the sensor element  100  is arranged, a gas introduction pipe  212  for introducing gas into the measurement chamber  211 , and a wiring connector  213  connected to a terminal of an external wiring. 
     A plate-shaped gas guide  220  is provided in the gas introduction pipe  212  of the housing  210 . The gas guide  220  is disposed in the gas introduction pipe  212  and extends along the gas introduction pipe  212 . One end of the gas guide  220  protrudes from a gas inlet/outlet  212   a  of the gas introduction pipe  212 , and the other end of the gas guide  220  reaches the measurement chamber  211 . As illustrated in  FIG. 8A , one end of the gas guide  220  has a gap between the gas guide  220  and the gas inlet/outlet  212   a  of the gas introduction pipe  212 . 
       FIG. 9A  is a cross-sectional view illustrating an example of a mounting state of the sensor device  200  illustrated in  FIG. 8B . In the example illustrated in  FIG. 9A , the sensor device  200  is mounted to, for example, an intake passage AI of an automobile. One end of the gas guide  220  of the sensor device  200  protrudes from the gas inlet/outlet  212   a  of the gas introduction pipe  212  toward the center line of the intake passage AI. Therefore, when a gas such as air A flowing through the intake passage AI hits one end of the gas guide  220 , a differential pressure is generated between the upstream side and the downstream side of the gas guide  220 , and the gas flows through the gas introduction pipe  212 . 
     More specifically, the gas on the upstream side of the gas guide  220  is introduced into the gas introduction pipe  212  from the gas inlet/outlet  212   a  of the gas introduction pipe  212 , flows through the gas introduction pipe  212  along the gas guide  220 , and reaches the measurement chamber  211 . The gas that has reached the measurement chamber  211  flows through the gas introduction pipe  212  from the measurement chamber  211  along the gas guide  220 , reaches the gas inlet/outlet  212   a , and is discharged from the gas inlet/outlet  212   a  to the downstream side of the gas guide  220 . Thereby, the gas flowing through the intake passage AI is introduced around the sensor element  100 , and the responsiveness of the sensor device  200  can be improved. 
     As described above, in the sensor device  200  of this embodiment, one end of the gas guide  220  has a gap between the one end of the gas guide  220  and the gas inlet/outlet  212   a  of the gas introduction pipe  212 . Accordingly, a gas passage is secured all around the gas inlet/outlet  212   a  around the gas guide  220 , and the gas can be actively introduced to the gas inlet/outlet  212   a  of the gas introduction pipe  212  by the gas guide  220  regardless of the flowing direction of the gas. With this configuration, the responsiveness of the sensor device  200  to a change in the humidity of the gas can be improved. 
       FIG. 9B  is a cross-sectional view illustrating another example of the mounting state of the sensor device  200  illustrated in  FIG. 8B . The sensor device  200  illustrated in  FIG. 9B  is mounted to, for example, the intake passage AI of an automobile in a state where the sensor device  200  illustrated in  FIG. 9A  is rotated by 90°, similarly to the sensor device  200  illustrated in  FIG. 9A . The other end of the gas guide  220  protruding from the gas inlet/outlet  212   a  opposite to the one end of the gas introduction pipe  212  is fixed to the gas introduction pipe  212  via a support  221  extending in the radial direction of the gas introduction pipe  212 . 
     As described above, when the gas flowing in the intake passage AI hits one end of the gas guide  220 , a differential pressure occurs between the upstream side and the downstream side of the gas guide  220 , and the gas flows through the gas introduction pipe  212 . Here, in the sensor device  200  of this embodiment, one end of the gas guide  220  has a space between the gas guide  220  and the gas inlet/outlet  212   a  of the gas introduction pipe  212 . Therefore, similarly to the sensor device  200  illustrated in  FIG. 9A , the gas on the upstream side of the gas guide  220  is introduced into the gas introduction pipe  212  from the gas inlet/outlet  212   a  of the gas introduction pipe  212 , and the gas flows through the gas introduction pipe  212  along the gas guide  220  and reaches the measurement chamber  211 . The gas that has reached the measurement chamber  211  flows through the gas introduction pipe  212  from the measurement chamber  211  along the gas guide  220 , reaches the gas inlet/outlet  212   a , and is discharged from the gas inlet/outlet  212   a  to the downstream side of the gas guide  220 . Thereby, the gas flowing through the intake passage AI is introduced around the sensor element  100 , and the responsiveness of the sensor device  200  can be improved. 
     Therefore, according to the sensor device  200  of this embodiment, a high-speed response to a change in humidity can be realized regardless of the mounting direction of the sensor device  200  with respect to the flow of gas. Here, the high-speed response is, for example, a response that is shorter than the response time of the humidity-sensitive film type humidity sensor. For example, the output of the sensor device  200  follows a change in humidity of a step shape according to a transition of time within one second. In addition, since the mounting direction of the sensor device  200  is not limited, various layouts can be supported. 
     In addition, according to the sensor device  200  of this embodiment, it is possible to measure the humidity even in a place where the flowing direction of the gas is not uniform, such as the intake passage AI of an automobile. In other words, it is possible to mount the sensor device  200  even in a place such as an intake manifold where gas flows randomly in many directions instead of one direction, and it is possible to measure humidity near the engine, which was conventionally impossible. 
     In particular, the intake manifold has more pollutants such as moisture and dust than the intake passage AI. However, since the sensor element  100  of the sensor device  200  is heated to a high temperature, deterioration of the sensor element  100  over time due to contaminants can be suppressed, and measurement of humidity in the intake manifold can be performed. In addition, the sensor device  200  of this embodiment can measure the humidity by the sensor element  100  also in the intake manifold, and thus can measure the humidity at a location closer to the engine. Therefore, the sensor device  200  of this embodiment can contribute to more accurate engine control. 
     Further, since the sensor element  100  of the sensor device  200  dissipates heat by the flow of gas, a measurement error of humidity may occur due to the flow of gas. Therefore, as a more preferable example, by arranging the sensor element  100  in a place not exposed to the main flow of gas, it is possible to suppress an error in detection of humidity due to the flow of gas. Specifically, as illustrated in  FIG. 9A , the sensor element  100  may be arranged at a position hidden from the opening of the gas introduction pipe  121 , that is, a position radially outside the gas introduction pipe  212  from the gas introduction pipe  212  in the measurement chamber  211  of the housing  210 . 
       FIG. 10A  is a cross-sectional view illustrating a mounting state of the sensor device  300  according to an embodiment of the invention.  FIG. 10B  is a cross-sectional view taken along line B-B of  FIG. 10A . The sensor device  300  of this embodiment includes the above-described sensor element  100  illustrated in  FIGS. 1 to 5 , for example. The sensor device  300  of this embodiment is a multifunctional measuring device in which a humidity sensor, an airflow sensor, and a pressure sensor are integrated. 
     The sensor device  300  of this embodiment is mounted, for example, to an insertion port PI of an air passage component P forming a main air passage AP. The sensor device  300  includes, for example, a housing  310  and the sensor element  100  housed inside the housing  310 . The housing  310  includes a housing component  311 , a base member  312 , a cover member  313 , and an auxiliary air passage forming member  314 . 
     An electronic circuit board  320  is fixed inside the base member  312 . The housing component  311  has a flange-like shape mounted to the insertion port PI of the air passage component P, and the space between the housing component  311  and the insertion port PI is sealed by a seal member S. In addition, a part of the housing component  311  is a connector portion connected to a terminal of an external wiring, and a connector terminal  330  is insert-molded. The connector terminal  330  is connected to a circuit of the electronic circuit board  320  via a bonding member  340 . 
     The electronic circuit board  320  is provided with the sensor element  100 , a heat generating resistor  350 , a temperature compensating resistor  360 , and an intake air temperature sensor  370 . The electrodes  33  and  43  of the pressure measurement element  30  and the humidity measurement element  40  of the sensor element  100  are connected to the circuit of the electronic circuit board  320 . The heat generating resistor  350 , the temperature compensating resistor  360 , and the intake air temperature sensor  370  are respectively connected to the circuit of the electronic circuit board  320  via the bonding member  340 , and are disposed in an auxiliary air passage  380  which is formed by the auxiliary air passage forming member  314 . 
     The connector terminal  330  is connected to the sensor element  100 , the heat generating resistor  350 , the temperature compensating resistor  360 , and the intake air temperature sensor  370  via the bonding member  340  and the circuit of the electronic circuit board  320 , and inputs and outputs signals and supplies power. The space around the sensor element  100  is defined by members forming the housing  310  and communicates with the auxiliary air passage  380 . With this configuration, the humidity can be accurately measured, and the sensor element  100  contained in the gas to be measured can be isolated from the polluting substances and water droplets. 
     As described above, the embodiment of the invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the invention, which are also included in the invention. 
     EXAMPLES 
     Hereinafter, examples of the sensor element according to the invention will be described. 
     First, a low-melting point glass contained in a bonding layer for bonding the semiconductor chip and the base material is manufactured. In addition, two types of commercially available SnO—P 2 O 5 -based low-melting point glasses are prepared. Table 1 illustrates the compositions and softening points Ts of the 13 types of manufactured low-melting point glasses (glass Nos. G1 to G13) and the softening point Ts of commercially available low-melting point glass (glass No. G14). Further, in the manufactured low-melting point glasses Nos. G1 to G13, lead is not substantially contained in consideration of environment and safety. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Glass 
                 Glass Composition [% by Weight] 
                 Ts 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 No. 
                 V 2 O 5   
                 TeO 2   
                 Fe 2 O 3   
                 P 2 O 5   
                 WO 3   
                 BaO 
                 Nb 2 O 5   
                 K 2 O 
                 Bi 2 O 3   
                 B 2 O 3   
                 ZnO 
                 CuO 
                 [° C.] 
               
               
                   
               
               
                 G1  
                 50 
                 20 
                 10 
                 15 
                  5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 357 
               
               
                 G2  
                 50 
                 25 
                 10 
                 15 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 362 
               
               
                 G3  
                 47 
                 30 
                 10 
                 13 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 364 
               
               
                 G4  
                 47 
                 20 
                 10 
                 13 
                 10 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 367 
               
               
                 G5  
                 47 
                 25 
                 10 
                 13 
                  5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 356 
               
               
                 G6  
                 47 
                 20 
                 10 
                 15 
                  8 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 367 
               
               
                 G7  
                 45 
                 22 
                 12 
                 16 
                  5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 372 
               
               
                 G8  
                 45 
                 30 
                 15 
                 10 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 377 
               
               
                 G9  
                 45 
                 25 
                 — 
                 10 
                 10 
                 10 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 364 
               
               
                 G10 
                 45 
                   29.5 
                  5 
                 10 
                  5 
                  5 
                 0.5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 355 
               
               
                 G11 
                 40 
                 30 
                 — 
                  5 
                 10 
                 15 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 357 
               
               
                 G12 
                 47 
                 30 
                  7 
                 10 
                  5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 1 
                 — 
                 353 
               
               
                 G13 
                 — 
                 — 
                   0.4 
                 — 
                 — 
                   3.4 
                 — 
                 — 
                 76.8 
                 8.1 
                   6.3 
                 5 
                 450 
               
            
           
           
               
               
               
            
               
                 G14 
                 Commercial Product (SnO-P 2 O 5 -based) 
                 398 
               
               
                 G15 
                 Commercial Product (SnO-P 2 O 5 -based) 
                 — 
               
               
                   
               
            
           
         
       
     
     The production of the low-melting point glass is performed according to the following procedure. First, the raw material compounds are blended and mixed so as to have the composition illustrated in Table 1. As the raw material compounds, vanadium pentoxide, tellurium oxide, ferric oxide, phosphorus pentoxide, tungsten oxide, barium oxide, niobium oxide, potassium oxide, bismuth oxide, boron oxide, zinc oxide, and copper oxide are used. 
     Next, 1 kg of the mixed raw material compounds is put in a platinum crucible, and heated to 1,000° C. at a heating rate of 5 to 10 [° C./min] by an electric furnace, and the heating temperature is maintained for 2 hours. While maintaining the heating temperature, the molten raw material compound is stirred to obtain a uniform glass. Next, the platinum crucible is taken out of the electric furnace, and poured onto a stainless steel plate which has been heated to 100° C. in advance to obtain a low-melting point glass. 
     The obtained glasses Nos. G1 to G13 low-melting point glass and the commercially available glass No. G14 low-melting point glass are pulverized until the average particle diameter (D50) becomes less than 20 μm, and the softening point Ts is measured by performing differential thermal analysis (DTA) at a heating rate of 5° C./min. Further, alumina powder is used as a standard sample. In the DTA curve, the softening point is the temperature of the second endothermic peak. 
     Next, a paste-like bonding agent for forming a bonding layer for bonding the semiconductor chip and the base material is prepared. Specifically, low-melting point glasses Nos. G1 to G15 are first pulverized using a jet mill until the average particle diameter (D50) became about 3 μm. In addition, a predetermined amount of Zr 2  (WO 4 ) (PO 4 ) 2  (hereinafter, referred to as ZWP) is added to glass as a filler having an average particle diameter (D50) of about 3 μm. Ethyl cellulose as a binder resin and butyl carbitol acetate as a solvent are added to the mixture and kneaded to prepare a paste-like bonding agent. 
     Next, a semiconductor substrate made of silicon is prepared, and the semiconductor chip  20  having the configuration illustrated in  FIG. 5  described in the above embodiment is manufactured by thermal oxidation, CVD, etching using photolithography, or the like. Further, the protective film  22   a  and the insulating films  22   b  and  22   d  forming the support film  22 , and the insulating films  24   a  and  24   b  forming the insulating layer  24  are silicon oxide films (SiO X  films), and the insulating film  22   c  forming the support film  22  is a silicon nitride film (SiN X  film). Molybdenum (Mo) is used for the gauge resistor  31  and the reference resistor  32  of the pressure measurement element  30 , and aluminum (Al) is used for the electrode  33 . 
     Next, using Pyrex (registered trademark) as a base material, a paste-like bonding agent prepared on the substrate is applied by screen printing, and dried at a temperature of 150° C. for several minutes. Thereafter, calcination is performed in a temperature range of 30° C. to 50° C. higher than the softening point Ts of the low-melting point glass contained in the bonding agent. After that, a semiconductor chip is arranged on the base material via the temporarily baked bonding agent, and the surrounding atmosphere is reduced to a depressurized state of 20 Pa or less. In this state, the bonding agent is heated at a predetermined heating temperature for 10 minutes to form a bonding layer, and the semiconductor chip and the base material are bonded via the bonding layer. 
     Through the above procedure, the sensor elements of the first to sixteenth examples are manufactured. In addition, a sensor element of a first comparative example is manufactured by applying an anode voltage of 500 [V] at a temperature of 400 [° C.] and applying a voltage of 500 [V] so as to anodic-bond the semiconductor chip and the base material without using a bonding agent. Table 2 below illustrates the configuration of the bonding agent, the thermal expansion coefficient of the bonding layer, the bonding conditions, and the bonding atmosphere used in the sensor element of each example. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                   
                 Configuration of Bonding Agent 
                 Thermal 
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Content 
                   
                 Content 
                 Expansion 
                   
                   
               
               
                   
                 Glass 
                 [% by 
                   
                 [% by 
                 Coefficient 
                 Bonding 
                 Bonding 
               
               
                   
                 No. 
                 Volume] 
                 Filler 
                 Volume] 
                 [x10 −7 /° C.] 
                 Condition 
                 Atmosphere 
               
               
                   
               
               
                 First 
                 G1  
                 70 
                 ZWP 
                 30 
                 50 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Second 
                 G2  
                 70 
                 ZWP 
                 30 
                 58 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Third 
                 G3  
                 70 
                 ZWP 
                 30 
                 60 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fourth 
                 G4  
                 70 
                 ZWP 
                 30 
                 44 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fifth 
                 G5  
                 70 
                 ZWP 
                 30 
                 52 
                 390° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Sixth 
                 G6  
                 70 
                 ZWP 
                 30 
                 49 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Seventh 
                 G7  
                 70 
                 ZWP 
                 30 
                 47 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Eighth 
                 G8  
                 70 
                 ZWP 
                 30 
                 54 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Ninth 
                 G9  
                 70 
                 ZWP 
                 30 
                 76 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Tenth 
                 G10 
                 70 
                 ZWP 
                 30 
                 62 
                 390° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Eleventh 
                 G11 
                 70 
                 ZWP 
                 30 
                 86 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Twelfth 
                 G12 
                 60 
                 ZWP 
                 40 
                 37 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Thirteenth 
                 G13 
                 70 
                 ZWP 
                 30 
                 66 
                 500° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fourteenth 
                 G4  
                 60 
                 ZWP 
                 40 
                 32 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Fifteenth 
                 Commercial Product  
                 70 
                 430° C.-10 min 
                 Vacuum 
               
               
                 Example 
                 (SnO-P 2 O 5 -based) 
                   
                   
                   
               
               
                 Sixteenth 
                 Commercial Product  
                 52 
                 430° C.-10 min 
                 Vacuum 
               
               
                 Example 
                 (SnO-P 2 O 5 -based) 
                   
                   
                   
               
               
                 First 
                 Anodic Bonding 
                 — 
                 400° C.-500 V 
                 Vacuum 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 
               
               
                   
               
            
           
         
       
     
     With respect to the manufactured sensor elements of the first to sixteenth examples and the first comparative example, the bonding state of the semiconductor chip and the base material, the presence or absence of metal particles, the generation state of bubbles, and the operation are confirmed and evaluated. 
     Regarding the bonding state of the semiconductor chip and the base material, the semiconductor chip and the base material are integrally bonded, the substrate chamber is in a depressurized state, and the support film is dented in a concave shape, which is determined as “good”. It is determined that the bonding cannot be performed as “impossible”. In addition, when a plurality of sensor elements are manufactured, most of the bonding states are “good”, but those in which “impossible” is present is determined to be “possible”. 
     The presence or absence of metal particles and the generation state of bubbles are evaluated by observing the cross section of the sensor element by SEM. Then, it is determined as “good” in a case where the number of bubbles of 10 μm or more is 20 or less in the bonding portion including the bonding layer, “possible” in the case of 20 or more and 100 or less, and “impossible” in the case of 100 or more. 
     Regarding the operation of the sensor element, the electrodes of the pressure measurement element and the humidity measurement element are wire-bonded to the circuit board, and it is confirmed whether the output voltage value is within a normal value range. In a case where all were normal, it is determined as “good”. In a case where a plurality of sensor elements are manufactured, and not only normal ones, but also ones that output abnormal values or caused communication failure, it is determined as “possible”, and others are determined as “impossible”. The results are illustrated in Table 3 below. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 Precipitation of 
                   
                   
               
               
                   
                 Bonding State 
                 Metal Particles 
                 Bubbles 
                 Operation 
               
               
                   
               
             
            
               
                 First 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Second 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Third 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Fourth 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Fifth 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Sixth 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Seventh 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Eighth 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Ninth 
                 Possible 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Tenth 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Eleventh 
                 Possible 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Twelfth 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Thirteenth 
                 Good 
                 Present 
                 Possible 
                 Possible 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Fourteenth 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Fifteenth 
                 Good 
                 None 
                 Good 
                 Possible 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 Sixteenth 
                 Good 
                 None 
                 Good 
                 Possible 
               
               
                 Example 
                   
                   
                   
                   
               
               
                 First 
                 Impossible 
                 — 
                 — 
                 — 
               
               
                 Comparative 
                   
                   
                   
                   
               
               
                 Example 
               
               
                   
               
            
           
         
       
     
     From the above results, the semiconductor chips of the sensor elements of the first to sixteenth example are successfully bonded to the base material without being subjected to an etching step of removing the insulating layer even in a case where the sensor layer has an insulating layer on the rear surface of the semiconductor substrate because the bonding layer contains low-melting point glass. On the other hand, in the sensor element of the first comparative example in which anodic bonding is performed, the semiconductor chip having the insulating layer on the rear surface of the semiconductor substrate and the base material cannot be bonded. 
     In addition, it has been found out that the absolute pressure can be measured by the pressure measurement element of the sensor element by setting the substrate chamber of the semiconductor chip to a depressurized state lower than the atmospheric pressure. At this time, a desirable range for the thermal expansion coefficient of the bonding layer is a region of 70×10 −7 /° C. or less. In addition, from the viewpoints of precipitation of metal particles and bubbles, V 2 O 5 -based and SnO-based low-melting point glass are desirable as the low-melting point glass contained in the bonding layer. Further, considering the operation of the sensor element, the most desirable is a V 2 O 5 -based low-melting point glass. This is because the bonding temperature between the semiconductor chip and the base material can be reduced to 400° C. or less. 
     In addition,  FIGS. 11 and 12  illustrates the results of STEM analysis of the bonding interface between the insulating layer  24  and the bonding layer  25  of the sensor element of the twelfth example. As a result, it has been found out that the low-melting point glass and the silicon nitride film reacted at the bonding interface between the insulating layer  24  and the bonding layer  25  to form a silicon oxynitride film of about 2 nm. In the sensor element of the twelfth example, the number of bubbles is small at the interface between the insulating layer  24  and the bonding layer  25 , presumably because the reactivity between the low-melting point glass and the silicon nitride film is low. 
     Next, the sensor elements of seventeenth to nineteenth examples are manufactured in the same manner as in the first to sixteenth examples except that the insulating layer  24  is a single-layer silicon oxide film. As the low-melting point glass contained in the bonding layers of the sensor elements of the seventeenth, eighteenth, and nineteenth examples, those used in the twelfth, thirteenth, and fifteenth examples, respectively, are used. Table 4 below illustrates the configuration of the bonding agent used in the sensor element of each example, the thermal expansion coefficient of the bonding layer, the bonding conditions, and the bonding atmosphere. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                   
                 Configuration of Bonding Agent 
                 Thermal 
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Content 
                   
                 Content 
                 Expansion 
                   
                   
               
               
                   
                 Glass 
                 [% by 
                   
                 [% by 
                 Coefficient 
                 Bonding 
                 Bonding 
               
               
                   
                 No. 
                 Volume] 
                 Filler 
                 Volume] 
                 [x10 −7 /° C.] 
                 Condition 
                 Atmosphere 
               
               
                   
               
               
                 Seventeenth 
                 G12 
                 60 
                 ZWP 
                 40 
                 37 
                 400° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Eighteenth 
                 G13 
                 70 
                 ZWP 
                 30 
                 66 
                 500° C.-10 min 
                 Vacuum 
               
               
                 Example 
                   
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Nineteenth 
                 Commercial Product  
                 70 
                 430° C.-10 min 
                 Vacuum 
               
               
                 Example 
                 (SnO-P 2 O 5 -based) 
                   
                   
                   
               
               
                 First 
                 Anodic Bonding 
                 — 
                 400° C.-500 V 
                 Vacuum 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 
               
               
                   
               
            
           
         
       
     
     In addition, the evaluation of the sensor elements of the seventeenth to nineteenth examples is performed in the same manner as in the first to sixteenth examples. Table 5 below illustrates the evaluation results of the sensor elements of the seventeenth to nineteenth examples together with the evaluation results of the sensor element of the first comparative example described above. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                 Precipitation  
                   
                   
               
               
                   
                 Bonding 
                 Bonding 
                 of Metal  
                   
                 Opera- 
               
               
                   
                 Atmosphere 
                 Possibility 
                 Particles 
                 Bubbles 
                 tion 
               
               
                   
               
             
            
               
                 Seventeenth 
                 Vacuum 
                 Good 
                 None 
                 Good 
                 Good 
               
               
                 Example 
                   
                   
                   
                   
                   
               
               
                 Eighteenth 
                 Vacuum 
                 Good 
                 Present 
                 Good 
                 Possible 
               
               
                 Example 
                   
                   
                   
                   
                   
               
               
                 Example 19 
                 Vacuum 
                 Good 
                 None 
                 Good 
                 Possible 
               
               
                 Comparative 
                 Vacuum 
                 Impossible 
                 — 
                 — 
                 — 
               
               
                 Example 1 
               
               
                   
               
            
           
         
       
     
     From the above results, it is confirmed that, in the sensor elements of the seventeenth to nineteenth examples in which the insulating layer formed on the rear surface of the semiconductor chip is a silicon oxide film, the same results as those of the sensor elements of the first to sixteenth examples are obtained. 
     REFERENCE SIGNS LIST 
     
         
           10  base material 
           20  semiconductor chip 
           21  semiconductor substrate 
           21   a  surface 
           21   b  rear surface 
           22  support film 
           22 A element region 
           23  substrate chamber 
           24  insulating layer 
           25  bonding layer 
           30  pressure measurement element 
           40  humidity measurement element 
           100  sensor element 
           200  sensor device 
           300  sensor device