Patent Publication Number: US-2021167106-A1

Title: Solid-state imaging device and method for manufacturing the same

Description:
TECHNICAL FIELD 
     The present technology relates to a solid-state imaging device and a method for manufacturing the solid-state imaging device, and more particularly, to a solid-state imaging device capable of reducing bonding defects when two substrates are bonded to each other, and a method for manufacturing the solid-state imaging device. 
     BACKGROUND ART 
     Higher integration of semiconductor devices of two-dimensional structures has been realized through introduction of fine processing and enhancement of packaging density. However, there are physical limitations to higher integration of two-dimensional structures by these methods. Therefore, to further reduce the sizes of semiconductor devices and increase the pixel density, semiconductor devices having three-dimensional structures are being developed. 
     For example, Patent Document 1 discloses a stack semiconductor device in which two semiconductor devices are stacked. Patent Document 1 also discloses a technique of providing a buffer for adjusting the stress to be caused by a through electrode. Further, Patent Document 2 discloses a technique for reducing diffusion of copper (Cu) in a semiconductor device by preventing the main conductor film made of copper (Cu) from being brought into contact with the upper surface (CMP surface) of an insulating film. 
     CITATION LIST 
     Patent Documents 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2012-142414 
     Patent Document 2: Japanese Patent Application Laid-Open No. 2003-124311 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Meanwhile, in a solid-state imaging device as a semiconductor device having a three-dimensional structure, if a pumping phenomenon (Cu pumping) occurs due to the heat treatment after bonding when two substrates are stacked and bonded to each other, the wafer bonding become inadequate, and bonding defects might appear. Therefore, there has been a demand for a technique for reducing bonding defects when two substrates are laminated and bonded to each other. 
     The present technology has been made in view of such circumstances, and aims to reduce bonding defects when two substrates are bonded to each other. 
     Solutions to Problems 
     A solid-state imaging device according to one aspect of the present technology is a solid-state imaging device that includes: a first substrate including a first electrode formed with a metal; and a second substrate that is a substrate bonded to the first substrate, the second substrate including a second electrode formed with a metal, the second electrode being bonded to the first electrode. In at least one of the first substrate or the second substrate, a diffusion preventing layer of the metal is formed for a layer formed with the metal filling a hole portion, the metal forming the electrodes. 
     In the solid-state imaging device according to one aspect of the present technology, the diffusion preventing layer of the metal is formed for the layer in which the metal forming the electrodes is buried in the hole portion in at least one of the first substrate including the first electrode formed with a metal, or the second substrate that is the substrate bonded to the first substrate, the second substrate including the second electrode formed with the metal, the second electrode being bonded to the first electrode. 
     A manufacturing method according to one aspect of the present technology is a method for manufacturing a solid-state imaging device that includes: a first substrate including a first electrode formed with a metal; and a second substrate that is a substrate bonded to the first substrate, the second substrate including a second electrode formed with a metal, the second electrode being bonded to the first electrode. The method includes: forming a first layer in which the metal is buried in a first hole portion; forming a diffusion preventing layer of the metal, the diffusion preventing layer being stacked on the first layer; and forming a second layer in which the metal is buried in a second hole portion to form a connecting pad portion, the second layer being stacked on the first layer and the diffusion preventing layer, the first layer, the diffusion preventing layer, and the second layer being formed in at least one of the first substrate or the second substrate. 
     In the manufacturing method according to one aspect of the present technology, the first layer in which the metal is buried in the first hole portion is formed, the diffusion preventing layer of the metal is formed so as to be stacked on the first layer, and the second layer in which the metal is buried in the second hole portion to form the connecting pad portion is formed so as to be stacked on the first layer and the diffusion preventing layer. The first layer, the diffusion preventing layer, and the second layer are formed in at least one of the first substrate including the first electrode formed with the metal, or the second substrate bonded to the first substrate, the second substrate including the second electrode formed with the metal, the second electrode being bonded to the first electrode. 
     Effects of the Invention 
     According to one aspect of the present technology, bonding defects can be reduced when two substrates are bonded to each other. 
     Note that the effects of the present technology are not limited to the effect described herein, and may include any of the effects described in the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing the configuration of an embodiment of a solid-state imaging device to which the present technology is applied. 
         FIG. 2  is a cross-sectional diagram showing the state of the bonding portion when a pumping phenomenon occurs while two substrates are bonded to each other. 
         FIG. 3  is a cross-sectional view of relevant parts, showing the structure of a solid-state imaging device according to a first embodiment. 
         FIG. 4  is a diagram showing various example combinations of the upper surface shape of the via of a first layer and the upper surface shape of the via of a second layer. 
         FIG. 5  is a diagram showing example sizes of the upper surface and the lower surface of the via in the second layer. 
         FIG. 6  is a table showing the results of comparisons among the structures of A through C of  FIG. 5 . 
         FIG. 7  is a diagram showing the flow of a manufacturing process. 
         FIG. 8  is a diagram showing the flow of a manufacturing process. 
         FIG. 9  is a cross-sectional view of relevant parts, showing the structure of a solid-state imaging device according to a second embodiment. 
         FIG. 10  is a cross-sectional view of relevant parts, showing a first specific example of the structure of a solid-state imaging device to which the present technology is applied. 
         FIG. 11  is a cross-sectional view of relevant parts, showing a second specific example of the structure of a solid-state imaging device to which the present technology is applied. 
         FIG. 12  is a diagram showing an example configuration of an electronic apparatus using a solid-state imaging device to which the present technology is applied. 
         FIG. 13  is a diagram showing examples of use of a solid-state imaging device to which the present technology is applied. 
         FIG. 14  is a block diagram schematically showing an example configuration of an in-vivo information acquisition system. 
         FIG. 15  is a diagram schematically showing an example configuration of an endoscopic surgery system. 
         FIG. 16  is a block diagram showing an example of the functional configurations of a camera head and a CCU. 
         FIG. 17  is a block diagram schematically showing an example configuration of a vehicle control system. 
         FIG. 18  is an explanatory diagram showing an example of installation positions of external information detectors and imaging units. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     The following is a description of embodiments of the present technology, with reference to the drawings. Note that explanation will be made in the following order. 
     1. General Example Configuration of a Solid-State Imaging Device 
     2. First Embodiment 
     3. Second Embodiment 
     4. Specific Example Configurations of Solid-State Imaging Devices 
     5. Example Configuration of an Electronic Apparatus 
     6. Examples of Use of the Solid-State Imaging Device 
     7. Example Application to an In-Vivo Information Acquisition System 
     8. Example Application to an Endoscopic Surgery System 
     9. Example Applications to Moving Objects 
     1. General Example Configuration of a Solid-State Imaging Device 
       FIG. 1  is a diagram showing the configuration of an embodiment of a solid-state imaging device to which the present technology is applied. 
     In  FIG. 1 , a solid-state imaging device  1  is a semiconductor device having a three-dimensional structure that includes a first substrate  11  as a sensor substrate and a second substrate  21  as a circuit substrate bonded to the first substrate  11  in a stacked state. This solid-state imaging device  1  is designed as an image sensor, such as a complementary metal oxide semiconductor (CMOS) image sensor, for example. 
     In the solid-state imaging device  1 , the first substrate  11  has a pixel region  13  in which a plurality of pixels  12  including photoelectric conversion units is two-dimensionally arranged in a regular pattern. In this pixel region  13 , a plurality of pixel drive lines  14  is arranged in the row direction, and a plurality of vertical signal lines  15  is arranged in the column direction, so that each pixel  12  is connected to one pixel drive line  14  and one vertical signal line  15 . 
     Further, each pixel  12  includes a photoelectric conversion unit, a floating diffusion region (FD), and a pixel circuit formed with a plurality of pixel transistors and the like. Note that a plurality of the pixels  12  may share part of a pixel circuit in some cases. 
     On the other hand, peripheral circuits such as a vertical drive circuit  22 , a column signal processing circuit  23 , a horizontal drive circuit  24 , and a system control circuit  25  are formed in the second substrate  21 . 
     While the solid-state imaging device  1  is formed with the first substrate  11  and the second substrate  21  bonded to each other, it is known that a so-called pumping phenomenon (Cu pumping) occurs during a heat treatment (annealing treatment) after bonding those substrates, and the copper (Cu) used for the electrodes expands (bulges). Due to the local copper (Cu) bulging phenomenon caused by this heat treatment (or due to plastic deformation caused by thermal stress), the wafer bonding strength decreases, and the bonding becomes inadequate, which might lead to defective electrical connection or peeling. 
     (Bonding Portion at the Time of a Pumping Phenomenon) 
       FIG. 2  is a cross-sectional diagram showing the state of the bonding portion between electrodes when a pumping phenomenon occurs while two substrates are bonded to each other. 
     As shown in A of  FIG. 2 , a laminated film  900 - 1  in which an interlayer insulating film  901 - 1 , a liner insulating film  902 - 1 , and an interlayer insulating film  903 - 1  are stacked is formed in the upper substrate of the two substrates to be bonded. A metallic film  905 - 1  made of copper (Cu) is formed as an electrode in the laminated film  900 - 1 . Note that a metal seed film  904 - 1  is formed between the laminated film  900 - 1  and the metallic film  905 - 1 . 
     Meanwhile, in the lower substrate, copper (Cu) as a metallic film  905 - 2  is formed in a laminated film  900 - 2  in which an interlayer insulating film  901 - 2  through an interlayer insulating film  903 - 2  are stacked, in a similar manner as in the upper substrate. 
     B of  FIG. 2  shows the structure of the bonding portion between the two substrates after bonding. Then, a heat treatment is then performed in the state of the bonding portion shown in B of  FIG. 2 , so that the bonding portion enters a state shown in C of  FIG. 2 . That is, the heat treatment causes a pumping phenomenon, and the copper (Cu) as the metallic films  905 - 1  and  905 - 2  formed in the laminated films  900 - 1  and  900 - 2  of the upper and lower substrates expands ( 910 - 1  and  910 - 2  in the drawing). 
     As described above, when such a pumping phenomenon occurs, the wafer bonding strength decreases, and the bonding becomes inadequate, which might lead to defective electrical bonding. In view of the above, the present technology suggests a solution for reducing the bonding defects, to enable reduction of defects in the electrode bonding when two substrates are bonded to each other. 
     In the description below, such solutions will be described with reference to two embodiments: a first embodiment and a second embodiment. 
     2. First Embodiment 
     (Structure of the Bonding Portion) 
       FIG. 3  is a cross-sectional view of relevant parts, showing the structure of a solid-state imaging device  1  according to the first embodiment. In the description below, the configuration of the solid-state imaging device  1  according to the first embodiment is specifically described, with reference to the cross-sectional view of the relevant parts. 
     Note that, of the first substrate  11  and the second substrate  21  bonded in the solid-state imaging device  1 , the second substrate  21  will be described as a typical example with reference to  FIG. 3 , but the first substrate  11  may have a similar structure (the structure of the first embodiment). Further, the surface on the upper side in the drawing is a bonding surface  21 S of the second substrate  21  or a bonding surface  11 S of the first substrate  11 . 
     In  FIG. 3 , a laminated film  100  in which a first layer  100 - 1  and a second layer  100 - 2  are stacked is formed in the second substrate  21 . 
     The first layer  100 - 1  includes an interlayer insulating film  101  made of silicon oxide (SiO 2 ) or the like. Note that the coefficient of thermal expansion (CTE) of silicon oxide (SiO 2 ) is 0.5×10 −6 /K. 
     In the first layer  100 - 1 , a via  111  as a first hole portion is formed in the interlayer insulating film  101 , and a metallic film  105 - 1  is buried therein. Note that, in the case explained in the description below, copper (Cu) is used as the metallic film  105 - 1 . Copper (Cu) has a coefficient of thermal expansion of 16.5×10 −6 /K. 
     Further, in the first layer  100 - 1 , a metal seed film  104 - 1  as a barrier metal is formed between the side surface of the via  111  and the metallic film  105 - 1 . The metal seed film  104 - 1  may be a film formed with tantalum (Ta), titanium (Ti), or the like, for example. Note that the coefficient of thermal expansion of tantalum (Ta) is 6.3×10 −6 /K. Further, the coefficient of thermal expansion of titanium (Ti) is 8.6×10 −6 /K. 
     Meanwhile, the second layer  100 - 2  stacked as the upper layer on the first layer  100 - 1  as the lower layer includes an interlayer insulating film  103  made of silicon oxide (SiO 2 ) or the like. In the second layer  100 - 2 , a via  112  as a second hole portion is formed in the interlayer insulating film  103 , and a metallic film  105 - 2  made of copper (Cu) is buried therein. 
     That is, in the second layer  100 - 2 , the metallic film  105 - 2  is buried in the via  112 , so that a pad portion  121  made of copper (Cu) is formed on the side of the bonding surface  21 S. Note that, in the second layer  100 - 2 , a metal seed film  104 - 2  made of tantalum (Ta), titanium (Ti), or the like is also formed between the side surface of the via  112  and the metallic film  105 - 2 . 
     Here, in the laminated film  100 , a diffusion preventing layer  100 - 3  is formed between the first layer  100 - 1  and the second layer  100 - 2 . 
     The diffusion preventing layer  100 - 3  includes a diffusion preventing film  102 . The diffusion preventing film  102  is an insulating film, and is a film formed with a silicon compound such as silicon nitride (SiN), silicon carbonitride (SiCN), or silicon carbide (SiC), for example. Note that the coefficient of thermal expansion of silicon nitride (SiN) is 2.8×10 −6 /K. Further, the coefficient of thermal expansion of silicon carbide (SiC) is 3.7×10 −6 /K. 
     The diffusion preventing film  102  is formed under the interlayer insulating film  103  of the second layer  100 - 2  as the upper layer (under the region excluding the metal seed film  104 - 2  and the metallic film  105 - 2  formed in the via  112 ), so as to be in contact with the metal seed film  104 - 1  formed on the side surface of the via  111  of the first layer  100 - 1  as the lower layer and part of the metallic film  105 - 1 . 
     Note that, in the first layer  100 - 1 , a hard mask  106  is formed on the interlayer insulating film  101 , and is in contact with the diffusion preventing film  102  of the diffusion preventing layer  100 - 3 . However, the hard mask  106  is not necessarily formed. 
     Further, the metal seed film  104 - 2  is formed not only between the side surface of the via  112  and the metallic film  105 - 2 , but also in the region under the metallic film  105 - 2 . That is, the metal seed film  104 - 2  is also formed between the metallic film  105 - 2  buried in the via  112  of the second layer  100 - 2  and the metallic film  105 - 1  buried in the via  111  of the first layer  100 - 1 , and forms part of the diffusion preventing layer  100 - 3 . 
     As described above, in the second substrate  21 , the diffusion preventing layer  100 - 3  including the diffusion preventing film  102  and part of the metal seed film  104 - 2  is formed between the first layer  100 - 1  and the second layer  100 - 2 , and functions as a “support” that reduces volume expansion of the copper (Cu) serving as the metallic film  105 - 1  buried in the via  111  of the first layer  100 - 1  as the lower layer. 
     Then, the diffusion preventing layer  100 - 3  then reduces thermal expansion of the metallic film  105 - 1  of copper (Cu) during the heat treatment after the bonding of the bonding surfaces ( 11 S and  21 S) of the first substrate  11  and the second substrate  21 . As a result, it becomes possible to prevent a copper (Cu) pumping phenomenon (Cu pumping) from occurring in the bonding surface  21 S (or the bonding surface  11 S). 
     Further, as such a structure is adopted, the total volume of the copper (Cu) used as the metallic films  105 - 1  and  105 - 2  can also be reduced. That is, in contrast to the structure of the laminated film  900 - 1  or the laminated film  900 - 2  shown in  FIG. 2  described above, for example, the diffusion preventing film  102  is formed so that the diameter of the via  112  of the second layer  100 - 2  is smaller than the diameter of the via  111  of the first layer  100 - 1  in the structure of the laminated film  100  shown in  FIG. 3 . As a result, the total volume of the copper (Cu) can be made smaller. 
     Note that, in  FIG. 3 , the prevention of a pumping phenomenon is indicated by four arrows in the drawing. That is, in  FIG. 3 , the two arrows pointing to the upper side from the lower side in the drawing indicate thermal expansion of the copper (Cu) serving as the metallic film  105 - 1  buried in the via  111  of the first layer  100 - 1 . On the other hand, the two arrows that face those arrows and point to the lower side from the upper side in the drawing indicate that (the diffusion preventing film  102  of) the diffusion preventing layer  100 - 3  reduces thermal expansion of the copper (Cu) serving as the metallic film  105 - 1 . 
     As described above, in the structure of the solid-state imaging device  1  according to the first embodiment, the diffusion preventing layer  100 - 3  is formed between the first layer  100 - 1  and the second layer  100 - 2 , so that copper (Cu) bonding defects due to thermal expansion of the copper (Cu) during the heat treatment after the bonding can be reduced. 
     Particularly, in a case where the substrates to be stacked are connected by a through silicon electrode (through silicon via: TSV), the via of the through silicon electrode (TSV) has a great diameter and a great depth. Accordingly, the volume of the copper (Cu) buried therein is large. For example, in the above described structure shown in  FIG. 2  (a Cu wiring structure in which a wiring layer and a connecting hole layer are connected), the volume of the copper (Cu) becomes larger during the heat treatment after the bonding. Therefore, the amount of bulging at the time of a temperature rise becomes larger. As a result, bonding the pad portions (Cu—Cu bonding) becomes difficult. 
     In the structure of the present technology shown in  FIG. 3 , on the other hand, a “support” that restricts movement of the copper (Cu) buried in the lower layer is formed between the upper wiring layer (the second layer  100 - 2 ) and the lower connecting hole layer (the first layer  100 - 1 ), or the total volume of the copper (Cu) is reduced. Thus, it is possible to reduce copper (Cu) bonding defects due to thermal expansion of the copper (Cu) during the heat treatment after the bonding. 
     Note that, although the structure of the second substrate  21  has been described herein as mentioned above, the first substrate  11  can have a similar structure to reduce copper (Cu) bonding defects due to thermal expansion. Then, the first substrate  11  and the second substrate  21  are then bonded to each other, so that a through silicon electrode (TSV) is formed in the first substrate  11  and the second substrate  21 , which have been stacked. At that point of time, the pad portions can be bonded (Cu—Cu bonding) with precision. 
     However, the structure shown in  FIG. 3  can be adopted in at least one substrate between the first substrate  11  and the second substrate  21 . Even in a case where the structure shown in  FIG. 3  is adopted only in either the first substrate  11  or the second substrate  21 , copper (Cu) bonding defects due to thermal expansion can be reduced in at least one of the substrates. 
     Note that, in the structure shown in  FIG. 3 , the diffusion preventing layer  100 - 3  includes part of the metal seed film  104 - 2 , but the metal seed film  104 - 2  is not necessarily included therein. 
     (Various Example Combinations of Upper Surface Shapes of the Vias) 
       FIG. 4  is a diagram showing various example combinations of the upper surface shape of the via  111  of the first layer  100 - 1  and the upper surface shape of the via  112  of the second layer  100 - 2 . Note that  FIG. 4  shows the upper surface shapes of the vias in a case where the first layer  100 - 1  and the second layer  100 - 2  are viewed from the bonding surface  21 S (or the bonding surface  11 S) (or in a plan view). 
     Here, example combinations of the upper surface shape of the via  111  formed in the first layer  100 - 1  and the upper surface shape of the via  112  formed in the second layer  100 - 2  are shown in A through D of  FIG. 4 . 
     In A of  FIG. 4 , the upper surface of the via  111  formed in the first layer  100 - 1  has a square shape. On the other hand, the upper surface of the via  112  formed in the second layer  100 - 2  has a circular shape. Accordingly, the connecting pad portion  121  also has a circular shape. Here, the area of the upper surface of the via  112  (the area of a circle) is smaller than the area of the upper surface of the via  111  (the area of a square). 
     In B of  FIG. 4 , the upper surface of the via  111  formed in the first layer  100 - 1  has a square shape. Meanwhile, the shape of the pad portion  121  on the upper surface of the via  112  formed in the second layer  100 - 2  also has a square shape. Here, the area of the upper surface of the via  112  (the area of a square) is smaller than the area of the upper surface of the via  111  (the area of a square). 
     In C of  FIG. 4 , the upper surface of the via  111  formed in the first layer  100 - 1  has a circular shape. Meanwhile, the shape of the pad portion  121  on the upper surface of the via  112  formed in the second layer  100 - 2  also has a circular shape. Here, the area of the upper surface of the via  112  (the area of a circle) is smaller than the area of the upper surface of the via  111  (the area of a circle). 
     In D of  FIG. 4 , the upper surface of the via  111  formed in the first layer  100 - 1  has a circular shape. Meanwhile, the shape of the pad portion  121  on the upper surface of the via  112  formed in the second layer  100 - 2  has a square shape. Here, the area of the upper surface of the via  112  (the area of a square) is smaller than the area of the upper surface of the via  111  (the area of a circle). 
     As described above, various combinations of shapes can be adopted as the combination of the upper surface shape of the via  111  formed in the first layer  100 - 1  and the upper surface shape of the via  112  formed in the second layer  100 - 2 . However, the diameter of the via  112  in the second layer  100 - 2  is smaller than the diameter of the via  111  in the first layer  100 - 1 . 
     In other words, a result of comparison between the sizes of the longest portions of the upper surface shape of the via  111  and the upper surface shape of the via  112  shows that the Cu wiring line on the upper surface of the via  111  is longer than the Cu wiring line on the upper surface of the via  112 . 
     Note that the combinations of shapes shown in  FIG. 4  are merely examples, and any shape pattern that can be generated during the photolithography process may be adopted. That is, the diameter of the via  111  in the first layer  100 - 1  and the diameter of the via  112  in the second layer  100 - 2  may be the same or may be different. 
     (Example Sizes of the Upper Surface and the Lower Surface of the Via in the Second Layer) 
       FIG. 5  shows example sizes of the upper surface and the lower surface of the via  112  in the second layer  100 - 2 . Note that  FIG. 5  shows cross-sectional structures of laminated films  100  each including a first layer  100 - 1 , a second layer  100 - 2 , and a diffusion preventing layer  100 - 3 . 
     Here, examples sizes of the upper surface and the lower surface (dimensions of the upper and lower portions) of the via  112  in the second layer  100 - 2  are shown in A through C of  FIG. 5 . However, in A through C of  FIG. 5 , the size of the upper surface (the bonding surface) (the dimension of the upper portion) of the via  112  is fixed at a constant value (arrows pointing to the right and the left in the drawing), and the size of the lower surface (the surface on the opposite side from the bonding surface) (the dimension of the lower portion) of the via  112  is variable. Comparisons are made in cases where the size of the lower surface of the via  112  is varied. 
     In A of  FIG. 5 , the upper surface and the lower surface of the via  112  formed in the second layer  100 - 2  have the same size. Here, the two arrows pointing to the upper side from the lower side in the drawing indicate thermal expansion of the copper (Cu) serving as the metallic film  105 - 1  buried in the via  111  of the first layer  100 - 1 . On the other hand, the two arrows that face those arrows and point to the lower side from the upper side in the drawing indicate that (the diffusion preventing film  102  of) the diffusion preventing layer  100 - 3  reduces thermal expansion of the copper (Cu) serving as the metallic film  105 - 1 . 
     In B of  FIG. 5 , the size of the lower surface of the via  112  formed in the second layer  100 - 2  is smaller than the size of the upper surface thereof. In this case, as indicated by the arrows in the drawing, the arrows that face the two arrows indicating thermal expansion of the copper (Cu) (the arrows pointing to the upper side from the lower side in the drawing) are larger than the arrows shown in A of  FIG. 5 . 
     This is because, in the structure in B of  FIG. 5 , the size of the lower surface of the via  112  is smaller, so that the region of the diffusion preventing film  102  can be larger (can protrude more greatly) with respect to the metallic film  105 - 1  accordingly. Therefore, it is safe to say that the structure in B of  FIG. 5  is a structure superior to the structure in A of  FIG. 5  in reducing thermal expansion of the copper (Cu) serving as the metallic film  105 - 1 . 
     In C of  FIG. 5 , the size of the lower surface of the via  112  formed in the second layer  100 - 2  is larger than the size of the upper surface thereof. In this case, as indicated by the arrows in the drawing, the arrows that face the two arrows indicating thermal expansion of the copper (Cu) (the arrows pointing to the upper side from the lower side in the drawing) are smaller than the arrows shown in A of  FIG. 5 . 
     This is because, in the structure in C of  FIG. 5 , the size of the lower surface of the via  112  is larger, so that the region of the diffusion preventing film  102  can be narrower with respect to the metallic film  105 - 1  accordingly. Therefore, it is safe to say that the structure in C of  FIG. 5  is a structure inferior to the structure in A of  FIG. 5  in reducing thermal expansion of the copper (Cu) serving as the metallic film  105 - 1 . 
     The above facts can be summarized as shown in  FIG. 6 , for example. That is,  FIG. 6  shows the results of comparisons among the structures shown in A through C of  FIG. 5 : the top row shows the results of comparisons of the volume of the copper (Cu) serving as the metallic film  105 - 2  buried in the via  112  formed in the second layer  100 - 2  as the upper layer; and the bottom row shows the results of comparisons of the effect to reduce thermal expansion of the copper (Cu) serving as the metallic film  105 - 1  buried in the via  111  formed in the first layer  100 - 1  as the lower layer. 
     As shown in the top row in  FIG. 6 , the volume of the copper (Cu) in the upper layer is the smallest in the structure shown in B of  FIG. 5 , and is the second smallest in the structure shown in A of  FIG. 5 . Further, the volume of the copper (Cu) in the upper layer is the largest in the structure shown in C of  FIG. 5 . 
     Furthermore, as shown in the bottom row in  FIG. 6 , the effect to reduce thermal expansion of the copper (Cu) in the lower layer is the greatest in the structure shown in B of  FIG. 5 , and is the second greatest in the structure shown in A of  FIG. 5 . Further, the effect to reduce thermal expansion of the copper (Cu) in the lower layer is the smallest in the structure shown in C of  FIG. 5 . 
     From these comparison results, the diameter of the via  112  is made smaller in the surface on the opposite side from the bonding surface than in the bonding surface in the second layer  100 - 2 , so that the region of the diffusion preventing film  102  can be made wider (can protrude more greatly) with respect to the metallic film  105 - 1 . As such a structure shown in B of  FIG. 5  is adopted, the effects of the present technology can be further enhanced. 
     Note that, in the first substrate  11  and the second substrate  21  that are bonded to each other in the solid-state imaging device  1  of the first embodiment, the region corresponding to the above described bonding portion shown in  FIG. 3  is a particular peripheral region of the region surrounding the pixel region  13  in the first substrate  11 , for example. That is,  FIG. 3  shows the bonding portion between the peripheral region of the pixel region  13  in the first substrate  11  and the region corresponding to the peripheral region in the second substrate  21 , for example. 
     Further, as a process according to a method for manufacturing the solid-state imaging device  1  of the first embodiment, the process illustrated in  FIGS. 7 and 8  is performed on at least one substrate between the first substrate  11  and the second substrate  21 , for example. Note that, although not shown in the drawings, the diffusion preventing layer  100 - 3  and the second layer  100 - 2  are stacked on the first layer  100 - 1  prior to the process illustrated in  FIGS. 7 and 8  in this manufacturing process. 
     That is, after the metal seed film  104 - 1  is formed in the via  111  formed in the interlayer insulating film  101 , the metallic film  105 - 1  made of copper (Cu) is buried in the via  111 , to form the first layer  100 - 1 . Further, the diffusion preventing film  102  and the interlayer insulating film  103  are stacked on the first layer  100 - 1  (A of  FIG. 7 ). 
     After that, as shown in B of  FIG. 7 , a photolithography process is performed, and a photoresist  311  is applied onto the interlayer insulating film  103 , to generate a resist pattern for forming the via  112  (patterning). As shown in C of  FIG. 7 , an etching process is then performed, and dry etching is performed, with the mask being the resist pattern generated in the photolithography process. As a result, the via  112  is formed in the diffusion preventing film  102  and the interlayer insulating film  103 . 
     Next, as shown in D of  FIG. 7 , an asking/cleaning process is performed, so that the resist film of the photoresist  311  is removed, and wet cleaning is performed. As shown in E of  FIG. 8 , a first metallic film forming process is then performed, so that the metal seed film  104 - 2  is formed on the upper layer of the interlayer insulating film  103  and in the via  112  by sputtering. 
     Next, as shown in F of  FIG. 8 , a second metallic film forming process is performed, so that a Cu seed layer is formed by sputtering, and the metallic film  105 - 2  made of copper (Cu) is further buried in the via  112  by Cu plating. Then, as shown in G of  FIG. 8 , a polishing/planarizing process is then performed, so that the excess portion of the metallic film  105 - 2  and the metal seed film  104 - 2  on the interlayer insulating film  103  are removed by CMP (Chemical Mechanical Planarization). 
     As the above process is performed, the structure of the first substrate  11  or the second substrate  21  shown in  FIG. 3  and the like can be formed. 
     3. Second Embodiment 
     (Structure of the Bonding Portion) 
       FIG. 9  is a cross-sectional view of relevant parts, showing the structure of a solid-state imaging device according to a second embodiment. In the description below, the configuration of a solid-state imaging device  1  according to the second embodiment is specifically described, with reference to the cross-sectional view of the relevant parts. 
     Note that, of a first substrate  11  and a second substrate  21  bonded in the solid-state imaging device  1 , the second substrate  21  will be described as a typical example with reference to  FIG. 9 , but the first substrate  11  may have a similar structure (the structure of the second embodiment). 
     In  FIG. 9 , a laminated film  200  in which a first layer  200 - 1  and a second layer  200 - 2  are stacked is formed in the second substrate  21 . 
     In the first layer  200 - 1 , a via  211  is formed in an interlayer insulating film  201  made of silicon oxide (SiO 2 ) or the like, and a metallic film  205 - 1  made of copper (Cu) is buried therein. Note that, in the first layer  200 - 1 , a hard mask  206  is formed on the interlayer insulating film  201 . 
     Further, a metal seed film  204 - 1  as a barrier metal is formed between the side surface of the via  211  and the metallic film  205 - 1 . The metal seed film  204 - 1  may be a film formed with tantalum (Ta), titanium (Ti), or the like, for example. 
     On the other hand, in the second layer  200 - 2 , a via  212  is formed in an interlayer insulating film  203  made of silicon oxide (SiO 2 ) or the like, and a metallic film  205 - 2  made of copper (Cu) is buried therein. In the second layer  200 - 2 , the metallic film  205 - 2  is buried in the via  212 , so that a pad portion  221  made of copper (Cu) is formed on the side of the bonding surface  21 S. 
     In the second layer  200 - 2 , a metal seed film  204 - 2  is also formed between the side surface of the via  212  and the metallic film  205 - 2 . The metal seed film  204 - 2  may be a film using tantalum (Ta), tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN), tungsten (W), tungsten nitride (WN), a cobalt (Co)-containing alloy, manganese oxide (MnO), molybdenum (Mo), ruthenium (Ru), or the like, for example. 
     Here, in the laminated film  200 , a diffusion preventing layer  200 - 3  is formed between the first layer  200 - 1  and the second layer  200 - 2 . The diffusion preventing layer  200 - 3  includes part of the metal seed film  204 - 2 . 
     That is, the metal seed film  204 - 2  is formed not only between the side surface of the via  212  and the metallic film  205 - 2 , but also in the region under the metallic film  205 - 2 . Accordingly, the metal seed film  204 - 2  is also formed between the metallic film  205 - 2  buried in the via  212  of the second layer  200 - 2  and the metallic film  205 - 1  buried in the via  211  of the first layer  200 - 1 , and forms the diffusion preventing layer  100 - 3 . 
     As described above, in the second substrate  21 , the diffusion preventing layer  200 - 3  including part of the metal seed film  204 - 2  is formed between the first layer  200 - 1  and the second layer  200 - 2 , and functions as a “support” that reduces volume expansion of the copper (Cu) serving as the metallic film  205 - 1  buried in the via  211  of the first layer  200 - 1  as the lower layer. Thus, it is also possible to reduce thermal expansion of the metallic film  205 - 1  made of copper (Cu) during the heat treatment after bonding the bonding surfaces ( 11 S and  21 S) of the first substrate  11  and the second substrate  21 . 
     Note that, although a solid-state imaging device to which the present technology is applied has been described above as an example, the present technology can be applied not only to a solid-state imaging device but also to any semiconductor device in which substrates are bonded and stacked. 
     4. Specific Example Configurations of Solid-State Imaging Devices 
       FIG. 10  is a cross-sectional view of relevant parts, showing a first specific example of the structure of a solid-state imaging device to which the present technology is applied. 
     In  FIG. 10 , the first substrate  11  includes a semiconductor layer  411  made of silicon turned into a thin film. The pixel region  13  in which a plurality of pixels formed with photodiodes (PDs) to serve as photoelectric conversion units and a plurality of pixel transistors are two-dimensionally arranged in a regular manner is formed in the semiconductor layer  411 . 
     In the first substrate  11 , a wiring layer  412  is formed on the front surface side of the semiconductor layer  411 , and a light blocking film is formed on the back surface side of the semiconductor layer  411  including the upper portion of an optical black region  451 . Color filters (CFs) and on-chip lenses (OCLs) are further formed an effective pixel region  452 . 
     Also, in  FIG. 10 , a logic circuit  461  forming a peripheral circuit is formed in a predetermined region of a semiconductor layer  421  made of silicon in the second substrate  21 . In the second substrate  21 , a wiring layer  422  is formed on the front surface side of the semiconductor layer  421 . 
     In the first substrate  11  and the second substrate  21  having the above described structure, the bonding surface  11 S of the first substrate  11  and the bonding surface  21 S of the second substrate  21  are bonded to each other, and (the structure of a portion in the vicinity of the bonding surface of) at least one layer of the wiring layer  412  of the first substrate  11  and the wiring layer  422  of the second substrate  21  has the structure corresponding to the laminated film  100  shown in  FIG. 3  (including the diffusion preventing layer  100 - 3 ). 
     With this arrangement, thermal expansion of the metallic film (copper (Cu)) during the heat treatment after the bonding of the bonding surfaces ( 11 S and  21 S) of the first substrate  11  and the second substrate  21  can be reduced. As a result, it becomes possible to prevent a copper (Cu) pumping phenomenon (Cu pumping) from occurring in the bonding surface  11 S of the bonding surface  21 S. 
       FIG. 11  is a cross-sectional view of relevant parts, showing a second specific example of the structure of a solid-state imaging device to which the present technology is applied. 
     In  FIG. 11 , the first substrate  11  includes a semiconductor layer  511 , and a pixel region in which a plurality of pixels formed with photodiodes (PDs) and a plurality of pixel transistors are two-dimensionally arranged in a regular manner is formed in the semiconductor layer  511 . In the first substrate  11 , a wiring layer  512  is formed on the front surface side of the semiconductor layer  511 , and color filters (CFs) and on-chip lenses (OCLs) are formed above the respective photodiodes (PDs) on the back surface side of the semiconductor layer  511 . 
     Also, in  FIG. 11 , a peripheral circuit is formed in a predetermined region of a semiconductor layer  521  in the second substrate  21 . In the second substrate  21 , a wiring layer  522  is formed on the front surface side of the semiconductor layer  521 . 
     In the first substrate  11  and the second substrate  21  having the above described structure, the bonding surface  11 S and the bonding surface  21 S are bonded to each other, and (the structure of a portion in the vicinity of the bonding surface of) at least one layer of the wiring layer  512  of the first substrate  11  and the wiring layer  522  of the second substrate  21  has the structure corresponding to the laminated film  100  shown in  FIG. 3  (including the diffusion preventing layer  100 - 3 ). Thus, it is possible to prevent a copper (Cu) pumping phenomenon (Cu pumping) from occurring in the bonding surface  11 S or the bonding surface  21 S during the heat treatment. 
     5. Example Configuration of an Electronic Apparatus 
     The above described solid-state imaging device  1  as a semiconductor device can be applied to a camera system such as a digital camera or a video camera, for example, and can be further applied to an electronic apparatus such as a portable telephone having an imaging function or some other device having an imaging function. 
       FIG. 12  is a diagram showing an example configuration of an electronic apparatus using a solid-state imaging device to which the present technology is applied.  FIG. 12  shows, as an example of such an electronic apparatus, an example configuration of an imaging apparatus  1000  as a video camera capable of capturing a still image or a moving image. 
     In  FIG. 12 , the imaging apparatus  1000  includes: a solid-state imaging device  1001 ; an optical system  1002  that guides incident light to a light receiving sensor unit of the solid-state imaging device  1001 ; a shutter device  1003 ; a drive circuit  1004  that drives the solid-state imaging device  1001 ; and a signal processing circuit  1005  that processes an output signal of the solid-state imaging device  1001 . 
     The above described solid-state imaging device  1  ( FIG. 1 ) is used as the solid-state imaging device  1001 . The optical system (an optical lens)  1002  gathers image light (incident light) from an object, and forms an image on the imaging surface of the solid-state imaging device  1001 . With this, signal charges are stored in the solid-state imaging device  1001  for a certain period of time. Such an optical system  1002  may be an optical lens system including a plurality of optical lenses. 
     The shutter device  1003  controls the light exposure period and the light blocking period for the solid-state imaging device  1001 . The drive circuit  1004  supplies a drive signal to the solid-state imaging device  1001  and the shutter device  1003 . With the supplied drive signal (a timing signal), the drive circuit  1004  controls an operation to be performed by the solid-state imaging device  1001  to output a signal to the signal processing circuit  1005 , and controls a shutter operation of the shutter device  1003 . That is, by supplying the drive signal (timing signal), the drive circuit  1004  performs an operation to be performed by the solid-state imaging device  1001  to transfer a signal to the signal processing circuit  1005 . 
     The signal processing circuit  1005  performs various kinds of signal processing on signals transferred from the solid-state imaging device  1001 . A video signal obtained by this signal processing is stored into a storage medium such as a memory in a later stage, or is output to a monitor, for example. 
     In the electronic apparatus using a solid-state imaging device to which the present technology described above is applied, the solid-state imaging device  1  capable of reducing electrode bonding defects when two substrates are stacked and bonded to each other can be used as the solid-state imaging device  1001 . 
     6. Examples of Use of a Solid-State Imaging Device 
       FIG. 13  is a diagram showing examples of use of a solid-state imaging device to which the present technology is applied. 
     The solid-state imaging device  1  can be used in various cases where light such as visible light, infrared light, ultraviolet light, or an X-ray is sensed, as described below, for example. That is, as shown in  FIG. 13 , the solid-state imaging device  1  can be employed in an apparatus that is used not only in the appreciation activity field where images are taken and are used in appreciation activities, but also in the field of transportation, the field of home electric appliances, the fields of medicine and healthcare, the field of security, the field of beauty care, the field of sports, or the field of agriculture, for example. 
     Specifically, in the appreciation activity field, the solid-state imaging device  1  can be used in an apparatus (the imaging apparatus  1000  in  FIG. 12 , for example) for capturing images to be used in appreciation activities, such as a digital camera, a smartphone, or a portable telephone with a camera function, as described above. 
     In the field of transportation, the solid-state imaging device  1  can be used in apparatuses for transportation use, such as vehicle-mounted sensors configured to capture images of the front, the back, the surroundings, the inside of an automobile, and the like to perform safe driving such as an automatic stop and recognize a driver&#39;s condition or the like, surveillance cameras for monitoring running vehicles and roads, and ranging sensors or the like for measuring distances between vehicles, for example. 
     In the field of home electric appliances, the solid-state imaging device  1  can be used in an apparatus to be used as home electric appliances, such as a television set, a refrigerator, or an air conditioner, to capture images of gestures of users and operate the apparatus in accordance with the gestures, for example. Also, in the fields of medicine and healthcare, the solid-state imaging device  1  can be used in an apparatus for medical use or healthcare use, such as an endoscope or an apparatus for receiving infrared light for angiography, for example. 
     In the field of security, the solid-state imaging device  1  can be used in apparatuses for security use, such as surveillance cameras for crime prevention and cameras for personal authentication, for example. Further, in the field of beauty care, the solid-state imaging device  1  can be used in an apparatus for beauty care use, such as a skin measurement apparatus configured to image the skin or a microscope for imaging the scalp, for example. 
     In the field of sports, the solid-state imaging device  1  can be used in apparatuses for sporting use, such as action cameras and wearable cameras for sports, for example. Further, in the field of agriculture, the solid-state imaging device  1  can be used in apparatuses for agricultural use, such as cameras for monitoring conditions of fields and crops, for example. 
     7. Example Application to an In-Vivo Information Acquisition System 
     The technology (the present technology) according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system. 
       FIG. 14  is a block diagram schematically showing an example configuration of a patient&#39;s in-vivo information acquisition system using a capsule endoscope to which the technology (the present technology) according to the present disclosure may be applied. 
     An in-vivo information acquisition system  10001  includes a capsule endoscope  10100  and an external control device  10200 . 
     The capsule endoscope  10100  is swallowed by the patient at the time of examination. The capsule endoscope  10100  has an imaging function and a wireless communication function. Before naturally discharged from the patient, the capsule endoscope  10100  moves inside the internal organs such as the stomach and the intestines by peristaltic motion or the like, sequentially captures images of the inside of the internal organs (these images will be hereinafter also referred to as in-vivo images) at predetermined intervals, and sequentially transmits information about the in-vivo images to the external control device  10200  outside the body in a wireless manner. 
     Further, the external control device  10200  controls the overall operation of the in-vivo information acquisition system  10001 . The external control device  10200  also receives the information about the in-vivo images transmitted from the capsule endoscope  10100 , and, on the basis of the received in-vivo image information, generates image data for displaying the in-vivo images on a display device (not shown). 
     In this manner, the in-vivo information acquisition system  10001  can acquire in-vivo images showing the states of the inside of the body of the patient at any appropriate time until the swallowed capsule endoscope  10100  is discharged. 
     The configurations and the functions of the capsule endoscope  10100  and the external control device  10200  are now described in greater detail. 
     The capsule endoscope  10100  has a capsule-like housing  10101 , and the housing  10101  houses a light source unit  10111 , an imaging unit  10112 , an image processing unit  10113 , a wireless communication unit  10114 , a power feeder unit  10115 , a power supply unit  10116 , and a control unit  10117 . 
     The light source unit  10111  is formed with a light source such as a light emitting diode (LED), for example, and emits light onto the imaging field of view of the imaging unit  10112 . 
     The imaging unit  10112  is formed with an imaging device and an optical system including a plurality of lenses provided in front of the imaging device. Reflected light of light emitted to body tissue as the current observation target (this reflected light will be hereinafter referred to as the observation light) is collected by the optical system, and enters the imaging device. In the imaging unit  10112 , the observation light incident on the imaging device is photoelectrically converted, and an image signal corresponding to the observation light is generated. The image signal generated by the imaging unit  10112  is supplied to the image processing unit  10113 . 
     The image processing unit  10113  is formed with a processor such as a central processing unit (CPU) or a graphics processing unit (GPU), and performs various kinds of signal processing on the image signal generated by the imaging unit  10112 . The image processing unit  10113  supplies the image signal subjected to the signal processing as RAW data to the wireless communication unit  10114 . 
     Further, the wireless communication unit  10114  performs predetermined processing such as modulation processing on the image signal subjected to the signal processing by the image processing unit  10113 , and transmits the image signal to the external control device  10200  via an antenna  10114 A. The wireless communication unit  10114  also receives a control signal related to control of driving of the capsule endoscope  10100  from the external control device  10200  via the antenna  10114 A. The wireless communication unit  10114  supplies the control signal received from the external control device  10200  to the control unit  10117 . 
     The power feeder unit  10115  includes an antenna coil for power reception, a power regeneration circuit that regenerates electric power from the current generated in the antenna coil, a booster circuit, and the like. In the power feeder unit  10115 , electric power is generated according to a so-called non-contact charging principle. 
     The power supply unit  10116  is formed with a secondary battery, and stores the electric power generated by the power feeder unit  10115 . In  FIG. 14 , to avoid complication of the drawing, an arrow or the like indicating the destination of power supply from the power supply unit  10116  is not shown. However, the electric power stored in the power supply unit  10116  is supplied to the light source unit  10111 , the imaging unit  10112 , the image processing unit  10113 , the wireless communication unit  10114 , and the control unit  10117 , and can be used for driving these units. 
     The control unit  10117  is formed with a processor such as a CPU, and drives the light source unit  10111 , the imaging unit  10112 , the image processing unit  10113 , the wireless communication unit  10114 , and the power feeder unit  10115  unit as appropriate in accordance with a control signal transmitted from the external control device  10200 . 
     The external control device  10200  is formed with a processor such as a CPU or a GPU, or a microcomputer, a control board, or the like on which a processor and a storage element such as a memory are mounted together. The external control device  10200  controls operation of the capsule endoscope  10100  by transmitting a control signal to the control unit  10117  of the capsule endoscope  10100  via an antenna  10200 A. In the capsule endoscope  10100 , the conditions for emitting light to the current observation target in the light source unit  10111  can be changed in accordance with the control signal from the external control device  10200 , for example. Further, the imaging conditions (such as the frame rate and the exposure value in the imaging unit  10112 , for example) can also be changed in accordance with the control signal from the external control device  10200 . Further, the contents of the processing in the image processing unit  10113  and the conditions (such as the transmission intervals and the number of images to be transmitted, for example) for the wireless communication unit  10114  to transmit image signals may be changed in accordance with the control signal from the external control device  10200 . 
     Further, the external control device  10200  also performs various kinds of image processing on the image signal transmitted from the capsule endoscope  10100 , and generates image data for displaying a captured in-vivo image on the display device. Examples of the image processing include various kinds of signal processing, such as a development process (a demosaicing process), an image quality enhancement process (a band emphasizing process, a super-resolution process, a noise reduction (NR) process, a camera shake correction process, and/or the like), and/or an enlargement process (an electronic zooming process), for example. The external control device  10200  controls driving of the display device, to cause the display device to display an in-vivo image captured on the basis of the generated image data. Alternatively, the external control device  10200  may cause a recording device (not shown) to record the generated image data, or cause a printing device (not shown) to print out the generated image data. 
     An example of an in-vivo information acquisition system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to the imaging unit  10112  in the above described configuration. Specifically, the solid-state imaging device  1  in  FIG. 1  can be applied to the imaging unit  10112 . With this solid-state imaging device  1 , it is possible to reduce defects in electrode bonding when stacking and bonding two substrates. 
     8. Example Application to an Endoscopic Surgery System 
     The technology (the present technology) according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system. 
       FIG. 15  is a diagram schematically showing an example configuration of an endoscopic surgery system to which the technology (the present technology) according to the present disclosure may be applied. 
       FIG. 15  shows a situation where a surgeon (a physician)  11131  is performing surgery on a patient  11132  on a patient bed  11133 , using an endoscopic surgery system  11000 . As shown in the drawing, the endoscopic surgery system  11000  includes an endoscope  11100 , other surgical tools  11110  such as a pneumoperitoneum tube  11111  and an energy treatment tool  11112 , a support arm device  11120  that supports the endoscope  11100 , and a cart  11200  on which various kinds of devices for endoscopic surgery are mounted. 
     The endoscope  11100  includes a lens barrel  11101  that has a region of a predetermined length from the top end to be inserted into a body cavity of the patient  11132 , and a camera head  11102  connected to the base end of the lens barrel  11101 . In the example shown in the drawing, the endoscope  11100  is configured as a so-called rigid scope having a rigid lens barrel  11101 . However, the endoscope  11100  may be configured as a so-called flexible scope having a flexible lens barrel. 
     At the top end of the lens barrel  11101 , an opening into which an objective lens is inserted is provided. A light source device  11203  is connected to the endoscope  11100 , and the light generated by the light source device  11203  is guided to the top end of the lens barrel by a light guide extending inside the lens barrel  11101 , and is emitted toward the current observation target in the body cavity of the patient  11132  via the objective lens. Note that the endoscope  11100  may be a forward-viewing endoscope, an oblique-viewing endoscope, or a side-viewing endoscope. 
     An optical system and an imaging device are provided inside the camera head  11102 , and reflected light (observation light) from the current observation target is converged on the imaging device by the optical system. The observation light is photoelectrically converted by the imaging device, and an electrical signal corresponding to the observation light, or an image signal corresponding to the observation image, is generated. The image signal is transmitted as RAW data to a camera control unit (CCU)  11201 . 
     The CCU  11201  is formed with a central processing unit (CPU), a graphics processing unit (GPU), or the like, and collectively controls operations of the endoscope  11100  and a display device  11202 . Further, the CCU  11201  receives an image signal from the camera head  11102 , and subjects the image signal to various kinds of image processing, such as a development process (demosaicing process), for example, to display an image based on the image signal. 
     Under the control of the CCU  11201 , the display device  11202  displays an image based on the image signal subjected to the image processing by the CCU  11201 . 
     The light source device  11203  is formed with a light source such as a light emitting diode (LED), for example, and supplies the endoscope  11100  with illuminating light for imaging the surgical site or the like. 
     An input device  11204  is an input interface to the endoscopic surgery system  11000 . The user can input various kinds of information and instructions to the endoscopic surgery system  11000  via the input device  11204 . For example, the user inputs an instruction or the like to change imaging conditions (such as the type of illuminating light, the magnification, and the focal length) for the endoscope  11100 . 
     A treatment tool control device  11205  controls driving of the energy treatment tool  11112  for tissue cauterization, incision, blood vessel sealing, or the like. A pneumoperitoneum device  11206  injects a gas into a body cavity of the patient  11132  via the pneumoperitoneum tube  11111  to inflate the body cavity, for the purpose of securing the field of view of the endoscope  11100  and the working space of the surgeon. A recorder  11207  is a device capable of recording various kinds of information about the surgery. A printer  11208  is a device capable of printing various kinds of information relating to the surgery in various formats such as text, images, graphics, and the like. 
     Note that the light source device  11203  that supplies the endoscope  11100  with the illuminating light for imaging the surgical site can be formed with an LED, a laser light source, or a white light source that is a combination of an LED and a laser light source, for example. In a case where a white light source is formed with a combination of RGB laser light sources, the output intensity and the output timing of each color (each wavelength) can be controlled with high precision. Accordingly, the white balance of an image captured by the light source device  11203  can be adjusted. Alternatively, in this case, laser light from each of the RGB laser light sources may be emitted onto the current observation target in a time-division manner, and driving of the imaging device of the camera head  11102  may be controlled in synchronization with the timing of the light emission. Thus, images corresponding to the respective RGB colors can be captured in a time-division manner. According to the method, a color image can be obtained without any color filter provided in the imaging device. 
     Further, the driving of the light source device  11203  may also be controlled so that the intensity of light to be output is changed at predetermined time intervals. The driving of the imaging device of the camera head  11102  is controlled in synchronism with the timing of the change in the intensity of the light, and images are acquired in a time-division manner and are then combined. Thus, a high dynamic range image with no black portions and no white spots can be generated. 
     Further, the light source device  11203  may also be designed to be capable of supplying light of a predetermined wavelength band compatible with special light observation. In special light observation, light of a narrower band than the illuminating light (or white light) at the time of normal observation is emitted, with the wavelength dependence of light absorption in body tissue being taken advantage of, for example. As a result, so-called narrow band imaging is performed to image predetermined tissue such as a blood vessel in a mucosal surface layer or the like, with high contrast. Alternatively, in the special light observation, fluorescence observation for obtaining an image with fluorescence generated through emission of excitation light may be performed. In fluorescence observation, excitation light is emitted to body tissue so that the fluorescence from the body tissue can be observed (autofluorescence observation). Alternatively, a reagent such as indocyanine green (ICG) is locally injected into body tissue, and excitation light corresponding to the fluorescence wavelength of the reagent is emitted to the body tissue so that a fluorescent image can be obtained, for example. The light source device  11203  can be designed to be capable of suppling narrowband light and/or excitation light compatible with such special light observation. 
       FIG. 16  is a block diagram showing an example of the functional configurations of the camera head  11102  and the CCU  11201  shown in  FIG. 15 . 
     The camera head  11102  includes a lens unit  11401 , an imaging unit  11402 , a drive unit  11403 , a communication unit  11404 , and a camera head control unit  11405 . The CCU  11201  includes a communication unit  11411 , an image processing unit  11412 , and a control unit  11413 . The camera head  11102  and the CCU  11201  are communicably connected to each other by a transmission cable  11400 . 
     The lens unit  11401  is an optical system provided at the connecting portion with the lens barrel  11101 . Observation light captured from the top end of the lens barrel  11101  is guided to the camera head  11102 , and enters the lens unit  11401 . The lens unit  11401  is formed with a combination of a plurality of lenses including a zoom lens and a focus lens. 
     The imaging unit  11402  is formed with an imaging device. The imaging unit  11402  may be formed with one imaging device (a so-called single-plate type), or may be formed with a plurality of imaging devices (a so-called multiple-plate type). In a case where the imaging unit  11402  is of a multiple-plate type, for example, image signals corresponding to the respective RGB colors may be generated by the respective imaging devices, and be then combined to obtain a color image. Alternatively, the imaging unit  11402  may be designed to include a pair of imaging devices for acquiring right-eye and left-eye image signals compatible with three-dimensional (3D) display. As the 3D display is conducted, the surgeon  11131  can grasp more accurately the depth of the body tissue at the surgical site. Note that, in a case where the imaging unit  11402  is of a multiple-plate type, a plurality of lens units  11401  are provided for the respective imaging devices. 
     Further, the imaging unit  11402  is not necessarily provided in the camera head  11102 . For example, the imaging unit  11402  may be provided immediately behind the objective lens in the lens barrel  11101 . 
     The drive unit  11403  is formed with an actuator, and, under the control of the camera head control unit  11405 , moves the zoom lens and the focus lens of the lens unit  11401  by a predetermined distance along the optical axis. With this arrangement, the magnification and the focal point of the image captured by the imaging unit  11402  can be appropriately adjusted. 
     The communication unit  11404  is formed with a communication device for transmitting and receiving various kinds of information to and from the CCU  11201 . The communication unit  11404  transmits the image signal obtained as RAW data from the imaging unit  11402  to the CCU  11201  via the transmission cable  11400 . 
     Further, the communication unit  11404  also receives a control signal for controlling the driving of the camera head  11102  from the CCU  11201 , and supplies the control signal to the camera head control unit  11405 . The control signal includes information about imaging conditions, such as information for specifying the frame rate of captured images, information for specifying the exposure value at the time of imaging, and/or information for specifying the magnification and the focal point of captured images, for example. 
     Note that the above imaging conditions such as the frame rate, the exposure value, the magnification, and the focal point may be appropriately specified by the user, or may be automatically set by the control unit  11413  of the CCU  11201  on the basis of an acquired image signal. In the latter case, the endoscope  11100  has a so-called auto-exposure (AE) function, an auto-focus (AF) function, and an auto-white-balance (AWB) function. 
     The camera head control unit  11405  controls the driving of the camera head  11102 , on the basis of a control signal received from the CCU  11201  via the communication unit  11404 . 
     The communication unit  11411  is formed with a communication device for transmitting and receiving various kinds of information to and from the camera head  11102 . The communication unit  11411  receives an image signal transmitted from the camera head  11102  via the transmission cable  11400 . 
     Further, the communication unit  11411  also transmits a control signal for controlling the driving of the camera head  11102 , to the camera head  11102 . The image signal and the control signal can be transmitted through electrical communication, optical communication, or the like. 
     The image processing unit  11412  performs various kinds of image processing on an image signal that is RAW data transmitted from the camera head  11102 . 
     The control unit  11413  performs various kinds of control relating to display of an image of the surgical portion or the like captured by the endoscope  11100 , and a captured image obtained through imaging of the surgical site or the like. For example, the control unit  11413  generates a control signal for controlling the driving of the camera head  11102 . 
     Further, the control unit  11413  also causes the display device  11202  to display a captured image showing the surgical site or the like, on the basis of the image signal subjected to the image processing by the image processing unit  11412 . In doing so, the control unit  11413  may recognize the respective objects shown in the captured image, using various image recognition techniques. For example, the control unit  11413  can detect the shape, the color, and the like of the edges of an object shown in the captured image, to recognize the surgical tool such as forceps, a specific body site, bleeding, the mist at the time of use of the energy treatment tool  11112 , and the like. When causing the display device  11202  to display the captured image, the control unit  11413  may cause the display device  11202  to superimpose various kinds of surgery aid information on the image of the surgical site on the display, using the recognition result. As the surgery aid information is superimposed and displayed, and thus, is presented to the surgeon  11131 , it becomes possible to reduce the burden on the surgeon  11131 , and enable the surgeon  11131  to proceed with the surgery in a reliable manner. 
     The transmission cable  11400  connecting the camera head  11102  and the CCU  11201  is an electrical signal cable compatible with electric signal communication, an optical fiber compatible with optical communication, or a composite cable thereof. 
     Here, in the example shown in the drawing, communication is performed in a wired manner using the transmission cable  11400 . However, communication between the camera head  11102  and the CCU  11201  may be performed in a wireless manner. 
     An example of an endoscopic surgery system to which the technique according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to the imaging unit  11402  of the camera head  11102 . Specifically, the solid-state imaging device  1  in  FIG. 1  can be applied to the imaging unit  11402 . With this solid-state imaging device  1 , it is possible to reduce defects in electrode bonding when stacking and bonding two substrates. 
     9. Example Applications to Moving Objects 
     The technology (the present technology) according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be embodied as an apparatus mounted on any type of moving object, such as an automobile, an electrical vehicle, a hybrid electrical vehicle, a motorcycle, a bicycle, a personal mobility device, an airplane, a drone, a vessel, or a robot. 
       FIG. 17  is a block diagram schematically showing an example configuration of a vehicle control system that is an example of a moving object control system to which the technology according to the present disclosure may be applied. 
     The vehicle control system  12000  includes a plurality of electronic control units connected via a communication network  12001 . In the example shown in  FIG. 17 , the vehicle control system  12000  includes a drive system control unit  12010 , a body system control unit  12020 , an external information detection unit  12030 , an in-vehicle information detection unit  12040 , and an overall control unit  12050 . Further, a microcomputer  12051 , a sound/image output unit  12052 , and an in-vehicle network interface (I/F)  12053  are also shown as the functional components of the overall control unit  12050 . 
     The drive system control unit  12010  controls operations of the devices related to the drive system of the vehicle according to various programs. For example, the drive system control unit  12010  functions as control devices such as a driving force generation device for generating a driving force of the vehicle such as an internal combustion engine or a driving motor, a driving force transmission mechanism for transmitting the driving force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating a braking force of the vehicle. 
     The body system control unit  12020  controls operations of the various devices mounted on the vehicle body according to various programs. For example, the body system control unit  12020  functions as a keyless entry system, a smart key system, a power window device, or a control device for various lamps such as a headlamp, a backup lamp, a brake lamp, a turn signal lamp, a fog lamp, or the like. In this case, the body system control unit  12020  can receive radio waves transmitted from a portable device that substitutes for a key, or signals from various switches. The body system control unit  12020  receives inputs of these radio waves or signals, and controls the door lock device, the power window device, the lamps, and the like of the vehicle. 
     The external information detection unit  12030  detects information outside the vehicle equipped with the vehicle control system  12000 . For example, an imaging unit  12031  is connected to the external information detection unit  12030 . The external information detection unit  12030  causes the imaging unit  12031  to capture an image of the outside of the vehicle, and receives the captured image. On the basis of the received image, the external information detection unit  12030  may perform an object detection process for detecting a person, a vehicle, an obstacle, a sign, characters on the road surface, or the like, or perform a distance detection process. 
     The imaging unit  12031  is an optical sensor that receives light, and outputs an electrical signal corresponding to the amount of received light. The imaging unit  12031  can output an electrical signal as an image, or output an electrical signal as distance measurement information. Further, the light to be received by the imaging unit  12031  may be visible light, or may be invisible light such as infrared rays. 
     The in-vehicle information detection unit  12040  detects information about the inside of the vehicle. For example, a driver state detector  12041  that detects the state of the driver is connected to the in-vehicle information detection unit  12040 . The driver state detector  12041  includes a camera that captures an image of the driver, for example, and, on the basis of detected information input from the driver state detector  12041 , the in-vehicle information detection unit  12040  may calculate the degree of fatigue or the degree of concentration of the driver, or determine whether the driver is dozing off. 
     On the basis of the external/internal information acquired by the external information detection unit  12030  or the in-vehicle information detection unit  12040 , the microcomputer  12051  can calculate the control target value of the driving force generation device, the steering mechanism, or the braking device, and output a control command to the drive system control unit  12010 . For example, the microcomputer  12051  can perform cooperative control to achieve the functions of an advanced driver assistance system (ADAS), including vehicle collision avoidance or impact mitigation, follow-up running based on the distance between vehicles, vehicle speed maintenance running, vehicle collision warning, vehicle lane deviation warning, or the like. 
     Further, the microcomputer  12051  can also perform cooperative control to conduct automatic driving or the like for autonomously running not depending on the operation of the driver, by controlling the driving force generation device, the steering mechanism, the braking device, or the like on the basis of information about the surroundings of the vehicle, the information having being acquired by the external information detection unit  12030  or the in-vehicle information detection unit  12040 . 
     Further, the microcomputer  12051  can also output a control command to the body system control unit  12020 , on the basis of the external information acquired by the external information detection unit  12030 . For example, the microcomputer  12051  controls the headlamp in accordance with the position of the leading vehicle or the oncoming vehicle detected by the external information detection unit  12030 , and performs cooperative control to achieve an anti-glare effect by switching from a high beam to a low beam, or the like. 
     The sound/image output unit  12052  transmits an audio output signal and/or an image output signal to an output device that is capable of visually or audibly notifying the passenger(s) of the vehicle or the outside of the vehicle of information. In the example shown in  FIG. 17 , an audio speaker  12061 , a display unit  12062 , and an instrument panel  12063  are shown as output devices. The display unit  12062  may include an on-board display and/or a head-up display, for example. 
       FIG. 18  is a diagram showing an example of installation positions of imaging units  12031 . 
     In  FIG. 18 , a vehicle  12100  includes imaging units  12101 ,  12102 ,  12103 ,  12104 , and  12105  as the imaging units  12031 . 
     Imaging units  12101 ,  12102 ,  12103 ,  12104 , and  12105  are provided at the following positions: the front end edge of a vehicle  12100 , a side mirror, the rear bumper, a rear door, an upper portion, and the like of the front windshield inside the vehicle, for example. The imaging unit  12101  provided on the front end edge and the imaging unit  12105  provided on the upper portion of the front windshield inside the vehicle mainly capture images ahead of the vehicle  12100 . The imaging units  12102  and  12103  provided on the side mirrors mainly capture images on the sides of the vehicle  12100 . The imaging unit  12104  provided on the rear bumper or a rear door mainly captures images behind the vehicle  12100 . The front images acquired by the imaging units  12101  and  12105  are mainly used for detection of a vehicle running in front of the vehicle  12100 , a pedestrian, an obstacle, a traffic signal, a traffic sign, a lane, or the like. 
     Note that  FIG. 18  shows an example of the imaging ranges of the imaging units  12101  through  12104 . An imaging range  12111  indicates the imaging range of the imaging unit  12101  provided on the front end edge, imaging ranges  12112  and  12113  indicate the imaging ranges of the imaging units  12102  and  12103  provided on the respective side mirrors, and an imaging range  12114  indicates the imaging range of the imaging unit  12104  provided on the rear bumper or a rear door. For example, image data captured by the imaging units  12101  through  12104  are superimposed on one another, so that an overhead image of the vehicle  12100  viewed from above is obtained. 
     At least one of the imaging units  12101  through  12104  may have a function of acquiring distance information. For example, at least one of the imaging units  12101  through  12104  may be a stereo camera including a plurality of imaging devices, or may be an imaging device having pixels for phase difference detection. 
     For example, in accordance with distance information obtained from the imaging units  12101  through  12104 , the microcomputer  12051  calculates the distances to the respective three-dimensional objects within the imaging ranges  12111  through  12114 , and temporal changes in the distances (the speeds relative to the vehicle  12100 ). In this manner, the three-dimensional object that is the closest three-dimensional object on the traveling path of the vehicle  12100  and is traveling at a predetermined speed (0 km/h or higher, for example) in substantially the same direction as the vehicle  12100  can be extracted as the vehicle running in front of the vehicle  12100 . Further, the microcomputer  12051  can set beforehand an inter-vehicle distance to be maintained in front of the vehicle running in front of the vehicle  12100 , and can perform automatic brake control (including follow-up stop control), automatic acceleration control (including follow-up start control), and the like. In this manner, it is possible to perform cooperative control to conduct automatic driving or the like to autonomously travel not depending on the operation of the driver. 
     For example, in accordance with the distance information obtained from the imaging units  12101  through  12104 , the microcomputer  12051  can extract three-dimensional object data concerning three-dimensional objects under the categories of two-wheeled vehicles, regular vehicles, large vehicles, pedestrians, utility poles, and the like, and use the three-dimensional object data in automatically avoiding obstacles. For example, the microcomputer  12051  classifies the obstacles in the vicinity of the vehicle  12100  into obstacles visible to the driver of the vehicle  12100  and obstacles difficult to visually recognize. Then, the microcomputer  12051  then determines collision risks indicating the risks of collision with the respective obstacles. If a collision risk is equal to or higher than a set value, and there is a possibility of collision, the microcomputer  12051  can output a warning to the driver via the audio speaker  12061  and the display unit  12062 , or can perform driving support for avoiding collision by performing forced deceleration or avoiding steering via the drive system control unit  12010 . 
     At least one of the imaging units  12101  through  12104  may be an infrared camera that detects infrared rays. For example, the microcomputer  12051  can recognize a pedestrian by determining whether or not a pedestrian exists in images captured by the imaging units  12101  through  12104 . Such pedestrian recognition is carried out through a process of extracting feature points from the images captured by the imaging units  12101  through  12104  serving as infrared cameras, and a process of performing a pattern matching on the series of feature points indicating the outlines of objects and determining whether or not there is a pedestrian, for example. If the microcomputer  12051  determines that a pedestrian exists in the images captured by the imaging units  12101  through  12104 , and recognizes a pedestrian, the sound/image output unit  12052  controls the display unit  12062  to display a rectangular contour line for emphasizing the recognized pedestrian in a superimposed manner. Further, the sound/image output unit  12052  may also control the display unit  12062  to display an icon or the like indicating the pedestrian at a desired position. 
     An example of a vehicle control system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to the imaging unit  12031  in the above described configuration. Specifically, the solid-state imaging device  1  in  FIG. 1  can be applied to the imaging unit  12031 . With this solid-state imaging device  1 , it is possible to reduce defects in electrode bonding when stacking and bonding two substrates. 
     Note that the present technology may also be embodied in the configurations described below. 
     (1) 
     A solid-state imaging device including: 
     a first substrate including a first electrode formed with a metal; and 
     a second substrate that is a substrate bonded to the first substrate, the second substrate including a second electrode formed with a metal, the second electrode being bonded to the first electrode, 
     in which, in at least one of the first substrate or the second substrate, a diffusion preventing layer of the metal is formed for a layer formed with the metal filling a hole portion, the metal forming the electrodes. 
     (2) 
     The solid-state imaging device according to (1), in which 
     the diffusion preventing layer includes a diffusion preventing film formed between a first layer in which the metal is buried in a first hole portion, and a second layer in which the metal is buried in a second hole portion to form a connecting pad portion. 
     (3) 
     The solid-state imaging device according to (1) or (2), in which 
     the diffusion preventing layer includes a metal seed film formed between a first layer in which the metal is buried in a first hole portion, and a second layer in which the metal is buried in a second hole portion to form a connecting pad portion. 
     (4) 
     The solid-state imaging device according to (3), in which 
     the metal seed film is also formed between a side surface of the first hole portion and the metal, and between a side surface of the second hole portion and the metal. 
     (5) 
     The solid-state imaging device according to any one of (2) to (4), in which 
     a diameter of the second hole portion in the second layer is smaller than a diameter of the first hole portion in the first layer. 
     (6) 
     The solid-state imaging device according to (5), in which 
     the diameter of the first hole portion and the diameter of the second hole portion have the same shape or different shapes. 
     (7) 
     The solid-state imaging device according to any one of (2) to (6), in which, 
     in the second layer, a diameter of the second hole portion is smaller in a surface on the opposite side from a bonding surface than in the bonding surface. 
     (8) 
     The solid-state imaging device according to (2), in which the diffusion preventing film is an insulating film. 
     (9) 
     The solid-state imaging device according to (8), in which 
     the insulating film is a film using silicon nitride (SiN), silicon carbonitride (SiCN), or silicon carbide (SiC). 
     (10) 
     The solid-state imaging device according to (3) or (4), in which 
     the metal seed film is a film using tantalum (Ta) or titanium (Ti). 
     (11) 
     The solid-state imaging device according to any one of (1) to (10), in which 
     the metal forming the first electrode and the second electrode is copper (Cu). 
     (12) 
     The solid-state imaging device according to any one of (1) to (11), in which 
     the diffusion preventing layer is a layer for preventing diffusion of the metal at a time of heat treatment after bonding of bonding surfaces of the first substrate and the second substrate. 
     (13) 
     The solid-state imaging device according to any one of (1) to (12), in which 
     the first substrate is a sensor substrate having a pixel region in which a plurality of pixels including a photoelectric conversion unit are two-dimensionally arranged, and 
     the second substrate is a circuit substrate including a predetermined circuit. 
     (14) 
     A method for manufacturing a solid-state imaging device that includes: 
     a first substrate including a first electrode formed with a metal; and 
     a second substrate that is a substrate bonded to the first substrate, the second substrate including a second electrode formed with a metal, the second electrode being bonded to the first electrode, 
     the method including: 
     forming a first layer in which the metal is buried in a first hole portion; 
     forming a diffusion preventing layer of the metal, the diffusion preventing layer being stacked on the first layer; and 
     forming a second layer in which the metal is buried in a second hole portion to form a connecting pad portion, the second layer being stacked on the first layer and the diffusion preventing layer, 
     the first layer, the diffusion preventing layer, and the second layer being formed in at least one of the first substrate or the second substrate. 
     REFERENCE SIGNS LIST 
     
         
           1  Solid-state imaging device 
           11  First substrate 
           11 S Bonding surface 
           12  Pixel 
           13  Pixel region 
           14  Pixel drive line 
           15  Vertical signal line 
           21  Second substrate 
           21 S Bonding surface 
           22  Vertical drive circuit 
           23  Column signal processing circuit 
           24  Horizontal drive circuit 
           25  System control circuit 
           100  Laminated film 
           100 - 1  First layer 
           100 - 2  Second layer 
           100 - 3  Diffusion preventing layer 
           101  Interlayer insulating film 
           102  Diffusion preventing film 
           103  Interlayer insulating film 
           104 - 1 ,  104 - 2  Metal seed film 
           105 - 1 ,  105 - 2  Metallic film 
           111  Via 
           112  Via 
           121  Pad portion 
           1000  Imaging apparatus 
           1001  Solid-state imaging device 
           10112  Imaging unit 
           12031  Imaging unit