Patent Publication Number: US-2021183661-A1

Title: Semiconductor device, manufacturing method, solid state image sensor, and electronic equipment

Description:
TECHNICAL FIELD 
     The present disclosure relates to a semiconductor device, a manufacturing method, a solid state image sensor, and electronic equipment, and more particularly to a semiconductor device, a manufacturing method, a solid state image sensor, and electronic equipment that can achieve further improvement in reliability. 
     BACKGROUND ART 
     Conventionally, a solid state image sensor, such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor, for example, is used in electronic equipment provided with an imaging function, such as a digital still camera or a digital video camera. The solid state image sensor has pixels in which photodiodes that perform photoelectric conversion and a plurality of transistors have been combined, and an image is constructed on the basis of pixel signals output from a plurality of pixels arranged on an image plane on which an image of a subject is produced. 
     Moreover, in recent years, in order to achieve size reduction and high performance of the solid state image sensor, a laminated-type solid state image sensor has been developed in which, on a sensor substrate on which pixels are formed, a signal processing substrate that performs signal processing on an image signal output from the sensor substrate has been laminated. In such a laminated-type solid state image sensor, composite bonding, such as physically connecting bonding surfaces of wafers and electrically connecting connection pads formed on the bonding surfaces is performed. 
     For example, Patent Literature 1 discloses a semiconductor device in which, by forming metal films entirely on bonding surfaces of two semiconductor substrates and performing a heating treatment in a state where the metal films are in contact with each other, portions of the metal films in contact with an interlayer insulation layer react to form an insulation film. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2013-168419A 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     Meanwhile, conventionally, a misalignment may occur when bonding wafers, which results in a structure in which part of a connection pad (Cu) of one of the wafers has been bonded to an insulation layer (SiO2) of the other wafer. In such a structure, barrier metal will not be provided at the interface between the connection pad and the insulation layer. This raises a concern that copper constituting the connection pad is diffused from the interface between the connection pad and the insulation layer into the insulation layer in a later process of applying heat (such as post bond anneal or ILD depo, for example) to cause leakage. 
     In addition, a low adhesion strength between the connection pad (Cu) and the insulation layer (SiO2) raises a concern for a reduction in the overall bonding strength (wafer bonding strength). Thus, a resistance to Electro Migration, a resistance to Stress Induced Voiding, and the like are reduced, which causes a reduction in reliability as a whole. 
     The present disclosure was made in view of these circumstances, and can achieve further improvement in reliability. 
     Solution to Problem 
     A semiconductor device of an aspect of the present disclosure includes: connection pads formed in interlayer films provided respectively in interconnection layers of a first semiconductor substrate and a second semiconductor substrate to make an electrical connection between the first semiconductor substrate and the second semiconductor substrate; and a metal oxide film formed between the interlayer films of the first semiconductor substrate and the second semiconductor substrate, between the connection pad formed on a side toward the first semiconductor substrate and the interlayer film on a side toward the second semiconductor substrate, and between the connection pad formed on the side toward the second semiconductor substrate and the interlayer film on the side toward the first semiconductor substrate. 
     In a method of manufacturing a semiconductor device of an aspect of the present disclosure, the semiconductor device includes connection pads formed in interlayer films provided respectively in interconnection layers of a first semiconductor substrate and a second semiconductor substrate to make an electrical connection between the first semiconductor substrate and the second semiconductor substrate, and a metal oxide film formed between the interlayer films of the first semiconductor substrate and the second semiconductor substrate, between the connection pad formed on a side toward the first semiconductor substrate and the interlayer film on a side toward the second semiconductor substrate, and between the connection pad formed on the side toward the second semiconductor substrate and the interlayer film on the side toward the first semiconductor substrate. The method includes the steps of: forming a metal film on at least one bonding surface of a bonding surface including the interlayer film on the side toward the first semiconductor substrate and the connection pad formed in the interlayer film and a bonding surface including the interlayer film on the side toward the second semiconductor substrate and the connection pad formed in the interlayer film; and by applying a heat treatment in a state where the first semiconductor substrate and the second semiconductor substrate are in close contact with each other with the metal film interposed between the first semiconductor substrate and the second semiconductor substrate, spontaneously forming the metal oxide film resulting from a reaction between the metal film and the interlayer films. 
     A solid state image sensor of an aspect of the present disclosure includes: connection pads formed in interlayer films provided respectively in interconnection layers of a sensor substrate on which a sensor surface having pixels is formed and a signal processing substrate configured to perform signal processing on the sensor substrate to make an electrical connection between the sensor substrate and the signal processing substrate; and a metal oxide film formed between the interlayer films of the sensor substrate and the signal processing substrate, between the connection pad formed on a side toward the sensor substrate and the interlayer film on a side toward the signal processing substrate, and between the connection pad formed on the side toward the signal processing substrate and the interlayer film on the side toward the sensor substrate. 
     Electronic equipment of an aspect of the present disclosure includes: a solid state image sensor including connection pads formed in interlayer films provided respectively in interconnection layers of a sensor substrate on which a sensor surface having pixels is formed and a signal processing substrate configured to perform signal processing on the sensor substrate to make an electrical connection between the sensor substrate and the signal processing substrate, and a metal oxide film formed between the interlayer films of the sensor substrate and the signal processing substrate, between the connection pad formed on a side toward the sensor substrate and the interlayer film on a side toward the signal processing substrate, and between the connection pad formed on the side toward the signal processing substrate and the interlayer film on the side toward the sensor substrate. 
     In an aspect of the present disclosure, connection pads are formed in interlayer films provided respectively in interconnection layers of a first semiconductor substrate (sensor substrate) and a second semiconductor substrate (signal processing substrate) to make an electrical connection between the first semiconductor substrate and the second semiconductor substrate. In addition, a metal oxide film is formed between the interlayer films of the first semiconductor substrate and the second semiconductor substrate, between the connection pad formed on a side toward the first semiconductor substrate and the interlayer film on a side toward the second semiconductor substrate, and between the connection pad formed on the side toward the second semiconductor substrate and the interlayer film on the side toward the first semiconductor substrate. 
     Advantageous Effects of Invention 
     According to an aspect of the present disclosure, it is possible to achieve further improvement in reliability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an illustration showing a configuration example of an embodiment of a solid state image sensor to which the present technology has been applied. 
         FIG. 2  is an illustration describing a method of manufacturing a solid state image sensor. 
         FIG. 3  is a block diagram showing a configuration example of an imaging device mounted on electronic equipment. 
         FIG. 4  is an illustration showing a usage example in which an image sensor is used. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     Hereinafter, a specific embodiment to which the present technology has been applied will be described in detail with reference to the drawings. 
       FIG. 1  is an illustration showing a configuration example of an embodiment of a solid state image sensor which is a semiconductor device to which the present technology has been applied. 
     In  FIG. 1 , a sectional configuration example of a solid state image sensor  11  and an enlarged portion thereof are shown. 
     As shown in  FIG. 1 , the solid state image sensor  11  is configured by laminating a sensor substrate  13  on which a sensor surface  12  arranged on an image plane on which an image of a subject is produced by an optical system not shown is formed and a signal processing substrate  14  attached in a manner as to support the sensor substrate  13 . 
     In the sensor surface  12 , photodiodes which are photoelectric changing units that receive light for conversion into electric charges are arranged in a matrix form, and imaging is performed when their pixels receive light. 
     The sensor substrate  13  is configured by laminating, for example, a silicon layer in which photodiodes, transistors, and the like constituting pixels are formed and an interconnection layer in which interconnect lines to be connected to pixels are formed, and outputs an image signal of an image imaged on the sensor surface  12 . For example, the interconnection layer is configured by forming a metal interconnect line having conductivity within an interlayer film  15  made of silicon dioxide (SiO2). 
     The signal processing substrate  14  carries out various types of signal processing on an image signal output from the sensor substrate  13 , and then, outputs the image signal to a later-stage image processing circuit. Moreover, the signal processing substrate  14  is provided with an interconnection layer in which an interconnect line for capturing the image signal output from the sensor substrate  13  is formed, and that interconnection layer is provided with an interlayer film  16  similarly to the interlayer film  15  of the sensor substrate  13 . 
     In this manner, the solid state image sensor  11  is configured by laminating the sensor substrate  13  and the signal processing substrate  14 , and the sensor substrate  13  and the signal processing substrate  14  are bonded physically and electrically. For example, on the right side of  FIG. 1 , a sectional configuration example in the vicinity of two bonding terminal portions  21 - 1  and  21 - 2  that make an electrical connection between the sensor substrate  13  and the signal processing substrate  14  is shown in an enlarged manner. 
     In the bonding surface between the sensor substrate  13  and the signal processing substrate  14 , a metal oxide film  22  is formed on the entire surface except for the positions where the bonding terminal portions  21 - 1  and  21 - 2  are formed. 
     Moreover, in the bonding terminal portion  21 - 1 , a connection pad  23 - 1  is formed in which a connection pad formed on the side toward the interlayer film  15  of the sensor substrate  13  and a connection pad formed on the side toward the interlayer film  16  of the signal processing substrate  14  have been bonded to be integral, and an electrical connection is made. The connection pad  23 - 1  is covered by a barrier metal  24   a - 1  on the side toward the interlayer film  15 , and the connection pad  23 - 1  is covered by a barrier metal  24   b - 1  on the side toward the interlayer film  16 . Similarly, as to a connection pad  23 - 2  formed in the bonding terminal portion  21 - 2 , the connection pad  23 - 2  is covered by a barrier metal  24   a - 2  on the side toward the interlayer film  15 , and the connection pad  23 - 2  is covered by a barrier metal  24   b - 2  on the side toward the interlayer film  16 . 
     Note that the bonding terminal portions  21 - 1  and  21 - 2  are configured similarly, and hereinafter, as necessary, in a case where it is not necessary to distinguish between the bonding terminal portions  21 - 1  and  21 - 2 , they will simply be referred to as a bonding terminal portion  21 . Similarly, the connection pads  23 - 1  and  23 - 1  will be referred to as a connection pad  23 , the barrier metals  24   a - 1  and  24   a - 2  will be referred to as a barrier metal  24   a , and the barrier metals  24   b - 1  and  24   b - 2  will be referred to as a barrier metal  24   b.    
     Here, when bonding the sensor substrate  13  and the signal processing substrate  14 , an adjustment for aligning the connection pad formed in the interlayer film  15  of the sensor substrate  13  and the connection pad formed in the interlayer film  16  of the signal processing substrate  14  is performed. If it is possible to fully match them in position at that time, the connection pad  23  can be covered by the barrier metals  24   a  and  24   b . However, a slight misalignment actually occurs. Therefore, as shown in  FIG. 1 , the connection pad  23  is formed into a shape in which portions on the side toward the interlayer film  15  and on the side toward the interlayer film  16  are misaligned. 
     The solid state image sensor  11  is configured such that, even if such a misalignment occurs, the connection pad  23  will not be brought into direct contact with the interlayer films  15  and  16  by forming the metal oxide film  22 . That is, in the solid state image sensor  11 , the metal oxide film  22  is formed between the interlayer film  15  of the sensor substrate  13  and the interlayer film  16  of the signal processing substrate  14 , between the connection pad  23  formed on the side toward the sensor substrate  13  and the interlayer film  16  of the signal processing substrate  14 , and between the connection pad  23  formed on the side toward the signal processing substrate  14  and the interlayer film  15  of the sensor substrate  13 . 
     Due to the fact that the metal oxide film  22  formed in this manner functions as a diffusion barrier, it is possible to prevent copper constituting the connection pad  23  from diffusing into the interlayer film  15  or  16 , and to suppress an occurrence of leakage (a short circuit between interconnect lines). 
     Moreover, it is known that an adhesion strength between copper constituting the connection pad  23  and SiO2 constituting the interlayer films  15  and  16  is low. In this respect, in the solid state image sensor  11 , it is possible to spontaneously form the metal oxide film  22  at the interface between the connection pad  23  and the interlayer films  15  and  16  as will be described later with reference to  FIG. 2 , and thus, an adhesion strength can be ensured. Accordingly, the solid state image sensor  11  can have a higher resistance to electromigration and a higher resistance to stress migration, and it is possible to attain more improved reliability than conventional. 
     Next, a step of bonding the sensor substrate  13  and the signal processing substrate  14  in a method of manufacturing the solid state image sensor  11  will be described with reference to  FIG. 2 . 
     First, before the step of bonding the sensor substrate  13  and the signal processing substrate  14  is performed, the connection pads  23   a  and  23   b  are formed in the sensor substrate  13  and the signal processing substrate  14 , respectively, through a damascene process. 
     Here, a step of forming the connection pad  23   a  in the interlayer film  15  of the sensor substrate  13  will be described. First, an interconnect line trench is formed in silicon dioxide (SiO2) to serve as the interlayer film  15  or an equivalent insulation film by lithography and dry etching, and the barrier metal  24   a  to serve as a diffusion barrier between the connection pad  23   a  and the interlayer film  15  is formed in that interconnect line trench. The barrier metal  24   a  can be formed by subjecting tantalum (Ta) to physical vapor deposition (PVD), for example. 
     Thereafter, a copper (copper alloy) seed layer to serve as an electrode in a plating process in a post process is formed by physical vapor deposition, for example, and then, copper is charged through the plating process, and excess copper is removed by chemical mechanical polishing (CMP) to fill the interconnect line trench with copper. By such a step, the connection pad  23   a  is formed. In addition, the connection pad  23   b  is formed in the interlayer film  16  of the signal processing substrate  14  by a similar step with the barrier metal  24   b  serving as a diffusion barrier. 
     Then, a metal film  31   a  is formed on the entire surface of the interlayer film  15  and the connection pad  23   a . Similarly, a metal film  31   b  is formed on the entire surface of the interlayer film  16  and the connection pad  23   b . At this time, the metal films  31   a  and  31   b  contain at least one or more elements among manganese (Mn), vanadium (V), aluminum (Al), magnesium (Mg), and zirconium (Zr), and is configured by depositing them with a thickness of about 0.1 to 10 nm. 
     As a metal employed as such metal films  31   a  and  31   b , a metal having a property of reacting with SiO2 constituting the interlayer films  15  and  16  in a later heat treatment to produce an oxide is selected, for example. Accordingly, it is possible to suppress leakage that would occur between the connection pads  23 . That is, it is desirable to use an oxide that has an insulation property that functions as a barrier for preventing copper diffusion and a property that is melted into copper constituting the connection pads  23  (which does not interfere with conduction of the interface of the connection pads  23 ). 
     Accordingly, in the sensor substrate  13 , the metal film  31   a  is formed on the entire surface of the interlayer film  15  and the connection pad  23   a , and in the signal processing substrate  14 , the metal film  31   b  is formed on the entire surface of the interlayer film  16  and the connection pad  23   b , as shown at the top of  FIG. 2 . Then, with the metal film  31   a  of the sensor substrate  13  and the metal film  31   b  of the signal processing substrate  14  facing each other, alignment is adjusted such that the connection pads  23   a  and  23   b  match in position. 
     Then, as shown in the middle of  FIG. 2 , a step of bringing the entire surface of the metal film  31   a  of the sensor substrate  13  and the entire surface of the metal film  31   b  of the signal processing substrate  14  into close contact and bonding them such that there are no regions provided where they are unbonded to each other is performed. At this time, bonding is performed with the metal film  31  formed on the entire surface of either one of the bonding surface of the sensor substrate  13  and the bonding surface of the signal processing substrate  14 , for example. Note that it is preferable to subject the metal film  31   a  and the metal film  31   b  to a pretreatment through use of liquid or gas containing hydrogen before this step is performed, in order to improve the bonding strength by hydrogen bonding. 
     Thereafter, a step of applying a heat load of 400 degrees or below is performed, for example, with the sensor substrate  13  and the signal processing substrate  14  remaining in close contact. 
     Accordingly, as shown at the bottom of  FIG. 2 , the metal films  31   a  and  31   b  are melted into copper constituting the connection pads  23   a  and  23   b , and the metal oxide film  22  resulting from a reaction between the metal and an oxide film is formed spontaneously. That is, as the final structure, the metal oxide film  22  is formed between the connection pad  23  and the interlayer films  15  and  16 , the connection pads  23   a  and  23   b  are integrated, and the metal film  31  does not exist at their interface. Note that it is generally known that many metals easily undergo oxidation, whilst in a case of using a metal to serve as a conventional diffusion barrier (tantalum, for example) for the metal films  31   a  and  31   b , the diffusion barrier function of tantalum will be lost through oxidation, and therefore, element selection is important. 
     Through the steps as described above, the sensor substrate  13  and the signal processing substrate  14  are bonded physically and electrically. 
     The solid state image sensor  11  manufactured by such a manufacturing method can suppress an occurrence of leakage between the connection pads  23  (a short circuit between interconnect lines) due to the fact that the metal oxide film  22  functions as a diffusion barrier. Moreover, since the adhesion strength can be ensured by spontaneously forming the metal oxide film  22 , it is possible to achieve further improvement in reliability. 
     Furthermore, the solid state image sensor  11  can obtain a favorable conduction property since the metal film  31  does not exist at the interface between the connection pads  23   a  and  23   b  as described above. In a case of using a metal element (titanium, for example) that causes the metal film  31  to remain at the interface between the connection pads  23   a  and  23   b  even after the heat treatment, for example, a resistance value will be increased. In contrast to this, in the solid state image sensor  11 , it is possible to avoid such an increase in resistance value. Note that the element constituting the metal film  31  having been present between the connection pads  23   a  and  23   b  is detected in the connection pad  23 . 
     In addition, the solid state image sensor  11  can favorably suppress an occurrence of leakage by making the metal films  31   a  and  31   b  have a thickness of about 0.1 to 10 nm to form the metal oxide film  22  thin. 
     Note that, as described with reference to  FIG. 2 , it is not necessary to form the metal film  31  on both of the interlayer film  15  of the sensor substrate  13  and the interlayer film  16  of the signal processing substrate  14 , but the metal film  31  should only be formed on at least one of them, and it should only be configured that the metal oxide film  22  is formed reliably. 
     Further, as an element that can be used for the metal film  31 , nickel (Ni), cobalt (Co), iron (Fe), zinc (Zn), or silver (Ag) can be used besides those described above. Although the Patent Literature 1, for example, discloses a configuration example in which titanium (Ti) is used for a metal film, titanium may easily undergo oxidation, and at the same time, is likely to form a passive state in which reactivity exhibited in a normal state has been lost, and therefore, a state in which the entire thin film cannot be oxidized will occur. It is not appropriate to use such a metal that is likely to form a passive state for the metal film  31  of the solid state image sensor  11 , but it is suitable to use a metal that does not form a passive state, such as manganese, for the metal film  31  of the solid state image sensor  11 . 
     Note that the present technology can be applied to various laminated-type semiconductor devices (a memory, for example) configured by bonding wafers, for example, besides the solid state image sensor  11  as described above. 
     Note that the solid state image sensor  11  of each embodiment as described above can be applied to various types of electronic equipment, such as an imaging system, such as a digital still camera or a digital video camera, a mobile phone having an imaging function, or other equipment having an imaging function, for example. 
       FIG. 3  is a block diagram showing a configuration example of an imaging device mounted on electronic equipment. 
     As shown in  FIG. 3 , an imaging device  101  includes an optical system  102 , an image sensor  103 , a signal processing circuit  104 , a monitor  105 , and a memory  106 , and is capable of capturing a still image and a moving image. 
     The optical system  102  has one or a plurality of lenses, and guides image light (incident light) from a subject to the image sensor  103  to produce an image on a light receiving surface (sensor portion) of the image sensor  103 . 
     As the image sensor  103 , the solid state image sensor  11  of the above-described embodiment is applied. In the image sensor  103 , electrons are accumulated for a certain period of time in accordance with an image produced on the light receiving surface via the optical system  102 . Then, a signal in accordance with electrons accumulated in the image sensor  103  is supplied to the signal processing circuit  104 . 
     The signal processing circuit  104  carries out various types of signal processing on a pixel signal output from the image sensor  103 . An image (image data) obtained by the signal processing circuit  104  carrying out signal processing is supplied to the monitor  105  for display, or supplied to the memory  106  for storage (recording). 
     The imaging device  101  configured in this manner can improve durability more and can perform imaging reliably, for example, by applying the solid state image sensor  11  of the above-described embodiment. 
       FIG. 4  is an illustration showing a usage example in which the above-described solid state image sensor  11  (image sensor) is used. 
     The above-described image sensor can be used for, for example, various cases in which light such as visible light, infrared light, ultraviolet light, or X-rays is detected as follows.
         Devices that take images used for viewing, such as a digital camera and a portable appliance with a camera function.   Devices used for traffic, such as an in-vehicle sensor that takes images of the front and the back of a car, surroundings, the inside of the car, and the like, a monitoring camera that monitors travelling vehicles and roads, and a distance sensor that measures distances between vehicles and the like, which are used for safe driving (e.g., automatic stop), recognition of the condition of a driver, and the like.   Devices used for home electrical appliances, such as a TV, a refrigerator, and an air conditioner, to takes images of a gesture of a user and perform appliance operation in accordance with the gesture.   Devices used for medical care and health care, such as an endoscope and a device that performs angiography by reception of infrared light.   Devices used for security, such as a monitoring camera for crime prevention and a camera for personal authentication.   Devices used for beauty care, such as skin measurement equipment that takes images of the skin and a microscope that takes images of the scalp.   Devices used for sports, such as an action camera and a wearable camera for sports and the like.   Devices used for agriculture, such as a camera for monitoring the condition of the field and crops.       

     Additionally, the present technology may also be configured as below. 
     (1) 
     A semiconductor device including: 
     connection pads formed in interlayer films provided respectively in interconnection layers of a first semiconductor substrate and a second semiconductor substrate to make an electrical connection between the first semiconductor substrate and the second semiconductor substrate; and 
     a metal oxide film formed between the interlayer films of the first semiconductor substrate and the second semiconductor substrate, between the connection pad formed on a side toward the first semiconductor substrate and the interlayer film on a side toward the second semiconductor substrate, and between the connection pad formed on the side toward the second semiconductor substrate and the interlayer film on the side toward the first semiconductor substrate. 
     (2) 
     The semiconductor device according to (1), in which 
     a metal film is formed on at least one bonding surface of a bonding surface including the interlayer film on the side toward the first semiconductor substrate and the connection pad formed in the interlayer film and a bonding surface including the interlayer film on the side toward the second semiconductor substrate and the connection pad formed in the interlayer film, and 
     by applying a heat treatment in a state where the first semiconductor substrate and the second semiconductor substrate are in close contact with each other with the metal film interposed between the first semiconductor substrate and the second semiconductor substrate, the metal oxide film resulting from a reaction between the metal film and the interlayer films is formed spontaneously. 
     (3) 
     The semiconductor device according to (2), in which 
     the metal film is composed of a metal having a property in which, in the heat treatment, a portion interposed between the connection pad formed on the side toward the first semiconductor substrate and the connection pad formed on the side toward the second semiconductor substrate is melted into the connection pads. 
     (4) 
     The semiconductor device according to (2) or (3), in which 
     the metal film is composed of a metal having a property of reacting with the interlayer films in the heat treatment to form an oxide having an insulation property. 
     (5) 
     The semiconductor device according to any one of (2) to (4), in which 
     the metal film contains at least one or more elements among manganese, vanadium, aluminum, magnesium, and zirconium. 
     (6) 
     The semiconductor device according to any one of (2) to (5), in which 
     the metal film is formed so as to have a thickness ranging from 0.1 nm to 10 nm. 
     (7) 
     The semiconductor device according to any one of (2) to (6), in which 
     a pretreatment through use of liquid or gas containing hydrogen is performed on the metal film in a state where the metal film has been formed on the entire surface of the interlayer films and the connection pads. 
     (8) 
     The semiconductor device according to any one of (2) to (7), in which 
     when bonding the first semiconductor substrate and the second semiconductor substrate, bonding is performed in a state where the metal film has been formed on the entire surface of at least one of the bonding surfaces. 
     (9) 
     A method of manufacturing a semiconductor device, in which 
     the semiconductor device includes
         connection pads formed in interlayer films provided respectively in interconnection layers of a first semiconductor substrate and a second semiconductor substrate to make an electrical connection between the first semiconductor substrate and the second semiconductor substrate, and   a metal oxide film formed between the interlayer films of the first semiconductor substrate and the second semiconductor substrate, between the connection pad formed on a side toward the first semiconductor substrate and the interlayer film on a side toward the second semiconductor substrate, and between the connection pad formed on the side toward the second semiconductor substrate and the interlayer film on the side toward the first semiconductor substrate,       

     the method including the steps of: 
     forming a metal film on at least one bonding surface of a bonding surface including the interlayer film on the side toward the first semiconductor substrate and the connection pad formed in the interlayer film and a bonding surface including the interlayer film on the side toward the second semiconductor substrate and the connection pad formed in the interlayer film; and 
     by applying a heat treatment in a state where the first semiconductor substrate and the second semiconductor substrate are in close contact with each other with the metal film interposed between the first semiconductor substrate and the second semiconductor substrate, spontaneously forming the metal oxide film resulting from a reaction between the metal film and the interlayer films. 
     (10) 
     A solid state image sensor including: 
     connection pads formed in interlayer films provided respectively in interconnection layers of a sensor substrate on which a sensor surface having pixels is formed and a signal processing substrate configured to perform signal processing on the sensor substrate to make an electrical connection between the sensor substrate and the signal processing substrate; and 
     a metal oxide film formed between the interlayer films of the sensor substrate and the signal processing substrate, between the connection pad formed on a side toward the sensor substrate and the interlayer film on a side toward the signal processing substrate, and between the connection pad formed on the side toward the signal processing substrate and the interlayer film on the side toward the sensor substrate. 
     (11) 
     Electronic equipment including: 
     a solid state image sensor including
         connection pads formed in interlayer films provided respectively in interconnection layers of a sensor substrate on which a sensor surface having pixels is formed and a signal processing substrate configured to perform signal processing on the sensor substrate to make an electrical connection between the sensor substrate and the signal processing substrate, and   a metal oxide film formed between the interlayer films of the sensor substrate and the signal processing substrate, between the connection pad formed on a side toward the sensor substrate and the interlayer film on a side toward the signal processing substrate, and between the connection pad formed on the side toward the signal processing substrate and the interlayer film on the side toward the sensor substrate.       

     In addition, embodiments of the present disclosure are not limited to the above-described embodiments, and various alterations may occur insofar as they are within the scope of the present disclosure. 
     REFERENCE SIGNS LIST 
     
         
           11  solid state image sensor 
           12  sensor surface 
           13  sensor substrate 
           14  signal processing substrate 
           15 ,  16  interlayer film 
           21  bonding terminal portion 
           22  metal oxide film 
           23  connection pad 
           24  barrier metal 
           31  metal film