Abstract:
Provided is a method for manufacturing a semiconductor device which includes: providing a plurality of semiconductor substrates formed with through holes which penetrate between main surfaces of the substrates and are filled with porous conductors; stacking the plurality of semiconductor substrates while aligning the porous conductors filled in the through holes; introducing conductive ink containing particle-like conductors into the porous conductors of the plurality of stacked semiconductor substrates; and sintering the plurality of stacked semiconductor substrates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Japanese Patent Application No. 2011-74001, filed on Mar. 30, 2011 in the Japan Patent Office, the disclosure of which is incorporated herein in its entirety by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a method for manufacturing a semiconductor device. 
       BACKGROUND 
       [0003]    In recent years, high integration of semiconductor devices has progressed. However, when a plurality of highly-integrated semiconductor devices are placed on a horizontal plane and are connected by wirings for production, wiring length may be increased, which results in an increase in wiring resistance and wiring delay. 
         [0004]    To overcome this problem, there has been proposed a three dimensional integration technique for stacking semiconductor devices in three dimensions. In this three dimensional integration technique, a substrate incorporating integrated circuits is divided into chips, and chips verified as chips having low defects through a test for determining chips having low defects performed before the divided chips are selected and stacked on another substrate to form a three dimensional stack (stack chip). 
         [0005]    Such a stack chip is typically manufactured as follows. (1) A cohesive sheet such as a dicing tape or a backgrinding tape is attached to a substrate formed with semiconductor devices from a device-formed side in which the semiconductor devices are formed. (2) The substrate having the cohesive sheet attached to the device-formed side is grinded and thinned to a predetermined thickness from the opposite side to the device-formed side, that is, the back side of the substrate. (3) The thinned substrate is diced with the cohesive sheet attached to the substrate and is divided into individual chips, which are then detached from the cohesive sheet and are stacked. 
         [0006]    The chip stacking is realized by overlaying chips by forming a film by means of plating using Sn, Cu or the like on through electrodes formed on the chips or by arranging solder balls on the through electrodes, deoxidizing the chips by means of a flux or the like in a heating apparatus, and bonding the chips together by pressurization under the condition of a solder melting point or higher. 
         [0007]    The semiconductor device manufacturing method using such a three dimensional integration technique requires a high processing precision for the through electrodes arranged and interconnected on the chips. In addition, there is a need of processing of a flux used for soldering and an adhesive or a sticking agent for temporarily fixing the stacked chips. 
       SUMMARY 
       [0008]    According to one embodiment of the present disclosure, there is provided a method for manufacturing a semiconductor device, the method including: providing a plurality of semiconductor substrates formed with through holes which penetrate between main surfaces of the substrates and are filled with porous conductors; stacking the plurality of semiconductor substrates while aligning the porous conductors filled in the through holes; introducing conductive ink containing particle-like conductors into the porous conductors of the plurality of stacked semiconductor substrates; and sintering the plurality of stacked semiconductor substrates. 
         [0009]    According to another embodiment of the present disclosure, there is provided a method for manufacturing a semiconductor device, the method including: forming a plurality of chip areas on semiconductor substrates, each of the plurality of chip areas having through holes penetrating between main surfaces of the substrates; filling the through holes with porous conductors; cutting a plurality of chips from the plurality of chip areas; stacking the plurality of chips cut from the plurality of chip areas into a plurality of stacked chips while aligning the porous conductors; introducing conductive ink containing particle-like conductors into the porous conductors of the plurality of stacked chips; and sintering the plurality of stacked chips. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure. 
           [0011]      FIG. 1A  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0012]      FIG. 1B  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0013]      FIG. 1C  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0014]      FIG. 1D  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0015]      FIG. 1E  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0016]      FIG. 1F  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0017]      FIG. 1G  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0018]      FIG. 1H  is a sectional view of a semiconductor device in a process of a manufacturing method according to an embodiment. 
           [0019]      FIG. 2  is a flow chart showing a process of a manufacturing method according to an embodiment. 
           [0020]      FIG. 3A  is a sectional view of a semiconductor device in a process of forming a through via in a manufacturing method according to an embodiment. 
           [0021]      FIG. 3B  is a sectional view of a semiconductor device in a process of forming a through via in a manufacturing method according to an embodiment. 
           [0022]      FIG. 3C  is a sectional view of a semiconductor device in a process of forming a through via in a manufacturing method according to an embodiment. 
           [0023]      FIG. 3D  is a sectional view of a semiconductor device in a process of forming a through via in a manufacturing method according to an embodiment. 
           [0024]      FIG. 3E  is a sectional view of a semiconductor device in a process of forming a through via in a manufacturing method according to an embodiment. 
           [0025]      FIG. 3F  is a sectional view of a semiconductor device in a process of forming a through via in a manufacturing method according to an embodiment. 
           [0026]      FIG. 3G  is a sectional view of a semiconductor device in a process of forming a through via in a manufacturing method according to an embodiment. 
           [0027]      FIG. 4A  is a sectional view of a semiconductor device in a process of peeling off a support substrate in a manufacturing method according to an embodiment. 
           [0028]      FIG. 4B  is a sectional view of a semiconductor device in a process of peeling off a support substrate in a manufacturing method according to an embodiment. 
           [0029]      FIG. 4C  is a sectional view of a semiconductor device in a process of peeling off a support substrate in a manufacturing method according to an embodiment. 
           [0030]      FIG. 5A  is a sectional view of a semiconductor device in a process of filling porous metal material in a manufacturing method according to an embodiment. 
           [0031]      FIG. 5B  is a sectional view of a semiconductor device in a process of filling porous metal material in a manufacturing method according to an embodiment. 
           [0032]      FIG. 6A  is a sectional view of a semiconductor device in a deposition process in a manufacturing method according to an embodiment. 
           [0033]      FIG. 6B  is a sectional view of a semiconductor device in a deposition process in a manufacturing method according to an embodiment. 
           [0034]      FIG. 6C  is a sectional view of a semiconductor device in a deposition process in a manufacturing method according to an embodiment. 
           [0035]      FIG. 6D  is a sectional view of a semiconductor device in a deposition process in a manufacturing method according to an embodiment. 
           [0036]      FIG. 7  is a flow chart showing details of a process of a manufacturing method according to an embodiment. 
           [0037]      FIG. 8A  is a graph showing a relationship between a silver particle diameter and a sliver sintering temperature. 
           [0038]      FIG. 8B  is a sectional view of silver in a metal nano-particle paste. 
           [0039]      FIG. 8C  is a graph showing a relationship between a silver annealing temperature and a silver average particle diameter. 
           [0040]      FIG. 8D  is a graph showing a relationship between a silver sintering temperature and a silver specific resistance. 
           [0041]      FIG. 9A  is a graph showing a relationship between a gold particle diameter and a gold melting point. 
           [0042]      FIG. 9B  is a graph showing a relationship between a lead particle diameter and a lead melting point. 
           [0043]      FIG. 9C  is a graph showing a relationship between a copper particle diameter and a copper melting point. 
           [0044]      FIG. 9D  is a graph showing a relationship between a bismuth particle diameter and a bismuth melting point. 
           [0045]      FIG. 9E  is a graph showing a relationship between a silicon particle diameter and a silicon melting point. 
           [0046]      FIG. 9F  is a graph showing a relationship between an aluminum particle diameter and an aluminum melting point. 
           [0047]      FIG. 10A  is a view showing one example of a process of introducing metal nano-particle paste according to an embodiment. 
           [0048]      FIG. 10B  is a view showing one example of a process of introducing metal nano-particle paste according to an embodiment. 
           [0049]      FIG. 11A  is a view showing one example of a deposition process in a manufacturing method according to an embodiment. 
           [0050]      FIG. 11B  is a view showing one example of a deposition process in a manufacturing method according to an embodiment. 
           [0051]      FIG. 11C  is a view showing one example of a deposition process in a manufacturing method according to an embodiment. 
           [0052]      FIG. 11D  is a view showing one example of a deposition process in a manufacturing method according to an embodiment. 
           [0053]      FIG. 11E  is a view showing one example of a deposition process in a manufacturing method according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     Outline of Manufacturing Method of Embodiment 
       [0054]    An embodiment of the present disclosure will now be described in detail with reference to the drawings.  FIGS. 1A to 1H  are sectional views of a semiconductor device in a process of a manufacturing method according to an embodiment and  FIG. 2  is a flow chart showing the processes. The manufacturing method of this embodiment includes a through via forming process, a chip cutting process, a chip pickup process, a chip stacking process and a chip sintering process. 
       [Through Via Forming Process] 
       [0055]    First, a through via is formed in a device wafer  10  and a wafer  1  having a through via filled with porous metal material  54  is prepared (Step  100 , which is hereinafter referred to as “S 100 ,” which is equally applied to other steps). 
         [0056]    As shown in  FIG. 1A , an electrode pad  20  constituting a circuit is formed on one main surface of the device wafer  10  and a concave portion (or a through hole) corresponding to a position of the through via is formed in the electrode pad  20 . A through hole (through via) penetrating through the device wafer  10  is formed in the concave portion of the electrode pad  20 . An insulating layer  60  is formed on the other main surface of the device wafer  10 . The insulating layer  60  is also formed on an inner wall of the through via formed in the device wafer  10 . A dicing tape  80  is adhered to a portion of the main surface of the device wafer  10  on which the electrode pad  20  is formed. The metal nano-particle paste containing large-sized nano-metal particles is introduced into the through via and is temporarily sintered. 
         [0057]    With the above process, the wafer  1  having the through via filled with porous metal material  54  can be obtained. The metal nano-particle paste is prepared by making metal particles, such as silver or the like, having a particle diameter of, for example, about 100 nm or more in the form of a paste using a certain medium. The metal nano-particle paste is introduced into the through via, with its viscosity properly adjusted, and is temporarily sintered to provide a porous through conductor (porous metal material  54 ). 
       [Chip Cutting] 
       [0058]    Subsequently, the wafer  1  is cut into unit chips  2  having the through via filled with the porous metal material  54  (S 102 ). With the dicing tape  80  left in the wafer  1 , the device wafer  10  is diced to separate the unit chips  2  ( FIG. 1B ). 
       [Chip Pickup] 
       [0059]    When the dicing to cut the chip  2  is completed, the chips  2  are picked up from the wafer  1  (S 104 ). The chips  2  cut with the dicing tape  80  left is taken out by a pickup device ( FIG. 1C ). 
       [Chip Stacking] 
       [0060]    When the chips  2  are separated from the wafer  1 , the picked chips  2  are stacked and metal nano-particle ink is permeated into the porous metal  54  (S 106 ). 
         [0061]    As shown in  FIG. 1D , with the through via filled with the porous metal material  54  being aligned, the chips  2  are stacked to form a stack  3 . After the chips  2  are stacked, metal nano-particle ink  56  is injected into the porous metal  54  in the through via of the uppermost chip ( FIG. 1E ). The metal nano-particle ink  56  is prepared by making metal particles, such as silver or the like, having a particle diameter of, for example, several nm to 30 nm in the form of ink using a certain medium. The metal nano-particle ink  56  is prepared to have a viscosity smaller than that of the metal nano-particle paste filled in the through via. In addition, the metal nano-particle ink  56  injected into the porous metal material  54  is in some embodiments prepared using the same kind of metal as the porous metal  54  (metal nano-particle paste) filled in the through via. 
       [Sintering] 
       [0062]    After a suitable amount of the metal nano-particle ink  56  is injected into the porous metal material  54  in the through via, the stack  3  is sintered (S 108 ). The metal nano-particle paste and the metal nano-particle ink are melted by this sintering process to thereby achieve an integrated through conductor  59  ( FIG. 1F ). 
         [0063]    In the manufacturing method of the embodiment, since the porous metal material made by sintering the metal nano-particle paste is beforehand filled in the through via of the chips and the metal nano-particle ink is injected and sintered after the chips are stacked, a precision of stacking and processing is not required as compared to making a connection between through conductors of chips using welding. That is, a simple apparatus may be used to form through conductors of the stacked chips. This means that a finer through via structure (through conductor structure) can be formed as compared to when a stacked chip structure is formed using welding. In addition, since the through conductor is integrally formed by sintering without using a solder, a process using an adhesive, cohesive material or the like is not required. 
         [0064]    In addition, when the metal nano-particle paste (porous metal material) filled in the through via of the chips is formed of the same kind of metal as the metal nano-particle ink injected into the porous metal after the chips are stacked, resistance of the through conductor can be reduced. 
         [0065]    In addition, although the cut chips  2  are stacked in the method of the embodiment shown in  FIGS. 1A to 1F , the present disclosure is not limited thereto. As shown in  FIG. 1G , the chips  2  may be formed in the wafer  1  having chips  2  not cut (Chip On Wafer (COW)). In addition, as shown in  FIG. 1H , the wafer  1  having a through via filled with the porous metal material  54  may be stacked as it is without cutting the chips (Wafer On Wafer (WOW)). 
         [0066]    In addition, in the processes shown in  FIGS. 1B to 1D , the chips  2  are cut, and then, they are picked up and stacked with the dicing tape  80  left and the electrode pad  20  directed downward. However, the present disclosure is not limited thereto. For example, a separate tape may be attached to a surface (a surface with the insulating layer  60  formed thereon) other than a surface with the electrode pad  20  of the device wafer  10  formed thereon, and thereby, the dicing tape  80  may be separated and the chips  2  may be picked up and stacked with the separate tape left and with the electrode pad  20  formed surface directed upward. In this case, the electrode pad  20  is positioned on the top of the stack. 
       Details of Manufacturing Method of Embodiment 
       [0067]    Next, each process of through via forming and chip (wafer) stacking and sintering in the manufacturing method of the embodiment will be described in more detail with reference to  FIGS. 3A to 3G ,  FIGS. 4A to 4C ,  FIGS. 5A and 5B ,  FIGS. 6A to 6D  and  FIG. 7 .  FIGS. 3A to 3G  are sectional views showing sections of a semiconductor device in a process of forming a through via according to an embodiment.  FIGS. 4A to 4C  are sectional views of a semiconductor device in a process of peeling off a support substrate according to an embodiment.  FIGS. 5A and 5B  are sectional views of a semiconductor device in a process of filling porous metal material in a manufacturing method according to an embodiment.  FIGS. 6A to 6D  are sectional views of a semiconductor device in a stacking process according to an embodiment.  FIG. 7  is a flow chart showing details of a process of a manufacturing method according to an embodiment. In the following description, the same elements as those shown in  FIGS. 1A to 1H  are denoted by the same reference numerals and an explanation of which will not be repeated. In addition, in the following description, explanation of a dicing process of cutting chips out of a wafer will be omitted. 
       [Wafer Preparation and Through Via Forming] 
       [0068]    First, a wafer  1  is prepared and a through via is formed. As shown in  FIG. 3A , an electrode pad  20  constituting a circuit is formed on one main surface of a device wafer  10  (S 200 ). The device wafer  10  is formed of, for example, a silicon substrate or the like and the electrode pad  20  is made of conductive material such as, for example, copper, silver, aluminum, nickel, gold or the like. The electrode pad  20  is formed on the main surface of the device wafer  10  by, for example, plating or the like. As shown in  FIG. 3A , a concave portion or a through hole is formed in the central portion of the electrode pad  20  in a surface direction of the device wafer  10 . The concave portion or through hole is formed by etching or the like. 
         [0069]    Next, as shown in  FIG. 3B , a surface with the electrode pad  20  formed thereon of the device wafer  10  is directed to face and is adhered to a support substrate  40  by means of an adhesive  30  (S 202 ). The support substrate  40  acts as a base holding the device wafer  10 . The adhesive  30  may be, for example, a UV curable adhesive, a thermoplastic adhesive or the like and detachably bonds the device wafer  10  to the support substrate  40 . 
         [0070]    Subsequently, as shown in  FIG. 3C , a portion other than a portion of the main surface of the device wafer  10  where the support substrate  40  is adhered is ground, and the device wafer  10  is processed to be thinned (S 204 ). The device wafer  10  is adjusted to a thickness appropriate for stacking of chips (or wafers). 
         [0071]    When the device wafer  10  is thinned up to a predetermined thickness, a resist layer  50  is formed on the ground surface of the device wafer  10 . A resist opening corresponding to a position of forming the through hole is formed in the resist layer  50 . That is, the resist opening is formed at a position corresponding to the concave portion or through hole of the electrode pad  20  in the resist layer  50 . 
         [0072]    Subsequently, as shown in  FIG. 3E , a surface with the resist layer  50  formed thereon in the device wafer  10  is etched to form a through via  52  in the device wafer  10 . In addition, the resist layer  50  remaining after completion of the etching is removed. 
         [0073]    After the through via is formed in the device wafer  10 , an insulating layer  60  is formed on a through via opening surface (a surface other than the surface with the electrode pad  20  formed thereon) of the device wafer  10  (S 210 ). As shown in  FIG. 3F , the insulating layer  60  is formed in the inner wall or bottom of the through via  52  as well as the front surface of the device wafer  10 . 
         [0074]    Subsequently, as shown in  FIG. 3G , the insulating layer  60  in the bottom of the through via  52  of the device wafer  10  is removed using a laser or the like (S 212 ). The through via  52  of the device wafer  10  is completed by the processes from Step  200  to Step  212 . 
       [Support Substrate Peeling] 
       [0075]    After the through via  52  of the device wafer  10  is completely formed, as shown in  FIG. 4A , the device wafer  10  is separated from the support substrate  40  and is placed on a chuck  70 , while a surface with the insulating layer  60  formed thereon of the device wafer  10  (a surface other than the surface with the electrode pad  20  formed thereon) facing the chuck  70  (S 214 ). In addition, when the device wafer  10  is separated from the support substrate  40 , the residual adhesive  30  may be removed. 
         [0076]    Next, as shown in  FIG. 4B , the dicing tape  80  is attached to a surface with the electrode pad  20  formed thereon of the device wafer  10  (S 216 ), and as shown in  FIG. 4C , the chuck  70  is separated from the device wafer  10  while removing a corresponding portion of the through via  52  of the dicing tape  80  (S 218 ). The removal of the corresponding portion of the through via of the dicing tape  80  may be realized by laser light irradiation. The porous metal material is ready for filling by the processes from Step  214  to Step  218 . 
       [Porous Metal Material Filling] 
       [0077]    Subsequently, as shown in  FIG. 5A , while the surface of the device wafer  10  (the surface with the insulating layer  60  formed thereon) other than the surface with the dicing tape  80  attached thereto facing a porous material  90 , the device wafer  10  is disposed on the porous material  90 . After the device wafer  10  is disposed on the porous material  90 , the metal nano-particle paste  53  is introduced from an opening on a surface of the dicing tape  80  while making the internal pressure of the through via  52  negative through the porous material  90  using a suction device (not shown) (S 220 ). The metal nano-particle paste  53  may be prepared by making nano-silver particles having a diameter of, for example, about 100 nm in the form of a paste. The metal nano-particle paste  53  is in some embodiments introduced with its viscosity adjusted by a certain medium. The reason for making the internal pressure of the through via  52  negative through the porous material  90  is to facilitate introducing the metal nano-particle paste  53  into the through via. 
         [0078]    After the metal nano-particle paste  53  is introduced into the through via  52 , the device wafer  10  is temporarily sintered in its entirety (S 222 ). This temporary sintering allows the metal nano-particle paste  53  to be changed into porous material and the porous metal material  54  to be formed in the through via  52 . After the temporary sintering, the porous material  90  is separated from the device wafer  10  ( FIG. 5B ). The process described in Step  100  of  FIG. 2  is completed by the processes up to Step  222 . 
       [Stacking and Sintering] 
       [0079]    After the porous metal material  54  is formed in the through via  52 , the dicing tape  80  is separated from the device wafer  10 , and the device wafer  10  is stacked with the through via  52  being aligned (S 224 ). When manufacturing a stack of Chip On Chip or Chip on Wafer, the unit chips  2  may be stacked after being cut out of the device wafer  10  ( FIG. 6A ). That is, as shown in  FIG. 6A , device wafers  10   a  to  10   c  are stacked after porous metal  54   a  to  54   c  filled in the through vias of the device wafers  10   a  to  10   c  are aligned on the same axis. 
         [0080]    After the chips  2  (or the device wafer  10 ) are stacked into a stack  3 , as shown in  FIG. 6B , the metal nano-particle ink  56  is introduced from an opening on an insulating layer  60   a  of the device wafer  10   a  (or an opening of an electrode pad  20   c  of the device wafer  10   c ) (S 226 ). The metal nano-particle ink  56  is prepared to have a viscosity lower than that of the metal nano-particle paste  53  introduced into the through via so that the ink  56  can be widely spread into the porous metal  54   a  to  54   c , respectively. In addition, the metal nano-particle ink  56  and the metal nano-particle paste  53  are in some embodiments prepared using the same kind of metal. 
         [0081]    After a predetermined amount of metal nano-particle ink  56  is introduced into the porous metal  54   a  to  54   c  filled in the through via, the stack  3  is mainly sintered in its entirety (S 228 ). The main sintering is performed under the temperature environment where the metal nano-particle ink  56  and the metal nano-particle paste  53  are integrally melted. As a result, the metal nano-particle ink and the metal nano-particle paste are melted to complete an integrated through conductor  58  ( FIG. 6C ). 
         [0082]    In addition, although it is shown in  FIGS. 5B to 6A  that, after the porous metal material  54  is formed in the through via  52 , the dicing tape  80  is separated from the device wafer  10  and the device wafer  10  is stacked with the electrode pad  20  directed downward, the present disclosure is not limited thereto. For example, a separate tape may be attached to a surface other than the surface with the electrode pad  20  formed thereon of the device wafer  10 , and thereby, the dicing tape  80  may be separated and the device wafer  10  may be stacked while the surface with the electrode pad  20  formed thereon directed upward. In this case, the electrode pad  20  is positioned on the top of the stack  3   a , as shown in  FIG. 6D . 
         [0083]    In this manner, in the manufacturing method of the embodiment, while the through via being formed in the device wafer  10 , the through via is filled with the porous metal material, and the metal nano-particle ink is injected into the porous metal material after the device wafer  10  (or the chips  2 ) is stacked. This allows the through conductor to be integrally formed after the stacking. That is, it is possible to increase mechanical strength while decreasing electrical resistance as compared to conventional techniques where wafers or chips are stacked and soldered after a through conductor is buried in a through via. 
         [0084]    In addition, since the metal nano-particle paste is beforehand introduced in the through via of the wafer or chips before the stacking to form the porous metal material and the metal nano-particle ink having a viscosity lower than that of the metal nano-particle paste is injected into the porous metal material of the through via after the stacking, it is possible to prevent a metal solution from dropping from the through via in the manufacturing process. In addition, since the metal nano-particle ink is sintered to be integrated after it is injected into the porous metal material in the through via, it is possible to form a uniform through conductor. 
       (Metal Nano-Particle Paste and Metal Nano-Particle Ink) 
       [0085]    Subsequently, the metal nano-particle paste and the metal nano-particle ink used in the manufacturing method of the embodiment will be described with reference to  FIGS. 8A to 8D . 
         [0086]    In a three dimensional integration technique for stacking semiconductor devices in three dimensions, it is common that wafers and the like are stacked after semiconductor devices are formed and arranged on the wafers or chips. Therefore, if the wafers and the like are heated at a temperature (for example, 300 degrees C. or more) higher than a melting point of a solder, the semiconductor devices formed and arranged on the wafers or the like may be damaged. Accordingly, the wafers cannot be put under high temperature environments when the wafers are stacked. 
         [0087]    It has been known that a melting point of metal material used for the through conductor is generally high. For example, since the melting point of silver in a bulk state is 961 degrees C., it is difficult to use the bulk silver as a through conductor of stacked wafers or the like. The present inventors have paid attention to the effect that a sintering temperature of metal material decreases if a particle diameter of the metal material is miniaturized to a nanometer level (for example, see  FIG. 8C ). 
         [0088]      FIG. 8A  shows a relationship between a silver particle diameter and a sliver sintering temperature. In  FIG. 8A , a solid line denotes a relationship between a silver particle diameter and a sliver sintering temperature and a dashed line denotes a relationship between a silver particle diameter and a temperature at which a surface of silver particles begins to be melted. As shown in  FIG. 8A , when the silver particle diameter is decreased, the sintering temperature tends to decrease in case of the particle diameter of 100 nm or less. In addition, it can be seen that the sintering temperature is 300 degrees C. or less when the silver particle diameter is about 40 nm or less, which is equal to the melting point of a typical solder (for example, Sn—Ag—Cu or Sn—Pb). That is, when silver particles having a particle diameter of about 40 nm or less are used, it is possible to sinter the silver particles at the same degree of temperature as the solder. 
         [0089]    However, when a through conductor of stacked wafers is formed, metal material may be completely melted and flown out of the through via, which makes it difficult to manufacture it. In addition, if the porous metal material (metal nano-particle paste) and the metal nano-particle ink are not sintered at about the same temperature, the through conductor cannot be integrally formed. The present inventors have paid attention to the fact that a temperature at which a surface of metal particles begins to be melted becomes lower than a sintering temperature of the metal particles. That is, as shown in  FIG. 8A , when the silver particle diameter is decreased, it can be seen that a surface of the silver particles having a diameter of about 100 nm or less begins to be melted at a temperature of 300 degrees C. or so. 
         [0090]      FIG. 8B  shows a section where silver particles having a diameter of 100 nm is sintered at 300 degrees C. As shown in  FIG. 8B , when silver particles having a diameter of 100 nm is sintered under environments of 300 degrees C. or so, it can be seen that porous metal material can be formed. In addition, the same result can be expected for a mixture of silver particles having a diameter of 100 nm or less and silver particles having a diameter of 100 nm or more. 
         [0091]    In this manner, when the metal nano-particle paste is prepared using the silver having a particle diameter of 100 nm or so (or the mixture of silver having a particle diameter of 100 nm or less and silver having a particle diameter of 100 nm or more), it is possible to form the porous metal material under the temperature environments of 300 degrees C. or so. In addition, when the metal nano-particle ink is prepared using silver particles having the diameter of 40 nm or less, it is possible to melt the silver particles of the metal nano-particle ink while melting the surface of the silver particles of the porous metal material under the temperature environments of 300 degrees C. or less. This means that an integrated through conductor can be formed under the temperature environment of a melting point or so of a solder by preparing the metal nano-particle paste and the metal nano-particle ink using the silver particles. 
         [0092]    Subsequently, a specific resistance when a through conductor is formed using the metal nano-particle paste and the metal nano-particle ink composed of silver particles will be described.  FIG. 8D  is a view showing a relationship between a silver sintering temperature and a silver specific resistance. 
         [0093]    As shown in  FIG. 8D , the specific resistance of silver particles tend to change depending on their sintering temperature. With an example of a sintering temperature of 300 degrees C. appropriate when the porous metal material (metal nano-particle paste) and the metal nano-particle ink using the silver particles are mixed to form the through conductor, it can be seen that the same degree of specific resistance as a general solder can be obtained. That is, when the sintering temperature is set to 250 to 350 degrees C., in some embodiments 250 to 300 degrees C., the porous metal material and the metal nano-particle ink can be integrally sintered while providing the same degree of specific resistance as the conventional solder with an insignificant effect on semiconductor devices. 
         [0094]    For reference, a relationship between a particle diameter and a sintering temperature for each metal of gold (Au), lead (Pb), copper (Cu), bismuth (Bi), silicon (Si) and aluminum (Al) is shown in  FIGS. 9A to 9F . As shown in  FIGS. 9A to 9F , it can be seen that these metal particles have about two times or more the melting point of the general solder even if their diameter is decreased to 10 nm or so. That is, in the manufacturing method of the embodiment, it can be seen that the metal nano-particle paste and the metal nano-particle ink can be appropriately prepared using the silver particles. 
       Example of Introduction of Metal Nano-Particle Paste 
       [0095]    Next, an example of introducing a metal nano-particle paste into the through via  52  formed in the device wafer  10  will be described with reference to  FIGS. 10A and 10B .  FIG. 10A  shows an example of introducing the metal nano-particle paste  53  into the through via  52  using a squeegee and  FIG. 10B  shows an example of introducing the metal nano-particle paste  53  into the through via  52  using a supply nozzle. In the following description, the same elements as the wafer  10  shown in  FIGS. 3A to 3G ,  FIGS. 4A to 4C ,  FIGS. 5A and 5B , and  FIGS. 6A to 6D  are denoted by the same reference numeral, an explanation of which will not be repeated. 
         [0096]    In the process shown in  FIG. 5A , a suction portion  92  and a suction pump  94  are connected to a surface other than a surface with the device wafer  10  disposed thereon in porous material  90  ( FIG. 10A ). After the suction pump  94  is driven to allow the suction portion  92  to make the internal pressure of the through via  52  negative through the porous material  90 , the metal nano-particle paste  53  is applied on the dicing tape  80 . Then, a squeegee  96  is used to introduce the metal nano-particle paste  53  in the through via  52 . In the example shown in  FIG. 10A , since the squeegee  96  is used to introduce the metal nano-particle paste  53  in the through via  52 , it is possible to realize simple introduction of the metal nano-particle paste without requiring precision. 
         [0097]    In the example shown in  FIG. 10B , after the suction pump  94  is driven to allow the suction portion  92  to make the internal pressure of the through via  52  negative through the porous material  90 , a nozzle  98  is used to supply the metal nano-particle paste  53  into the through via  52 . In the example shown in  FIG. 10B , since a required amount of metal nano-particle paste  53  can be supplied through each via  52 , it is possible to form porous metal material with efficiency. 
         [0098]    Although in the examples shown in  FIGS. 10A and 10B , the metal nano-particle paste  53  is introduced from a side of the device wafer  10  at which the dicing tape  80  is formed, the present disclosure is not limited thereto. For example, the porous material  90  may be placed on the surface with the electrode pad  20  formed thereon and the metal nano-particle paste  53  may be introduced from the surface with the insulating layer  60  formed thereon. In addition, although in the examples shown in  FIGS. 10A and 10B , the metal nano-particle paste  53  is directly supplied and applied on a surface of the dicing tape  80  (or the insulating layer  60 ), the present disclosure is not limited thereto. For example, a mask may be beforehand formed and the metal nano-particle paste  53  may be introduced through an opening formed in the mask. Alternatively, the metal nano-particle paste  53  may be introduced using a dispenser, a transfer pin, a roller or the like instead of the squeegee  96  or the nozzle  98 . 
       Example of Chip Stacking 
       [0099]    Next, an example of stacking the device wafer  10  (or the chips  2 ) will be described with reference to  FIGS. 11A to 11E . Although in Step  224  of the embodiment, the device wafer  10  (or the chips  2 ) is stacked as it is, the device wafer  10  (or the chips  2 ) is temporarily fixed in the following example. 
         [0100]    For example, as shown in  FIG. 11A , a temporary fixing portion  55   a  is formed on a surface of an electrode pad  20   a  formed in the device wafer  10   a  using the same paste as the metal nano-particle paste  53 . The temporary fixing portion  55   a  is in some embodiments prepared using the same kind of metal particles as the metal nano-particle paste  53 . 
         [0101]    Subsequently, as shown in  FIG. 11B , the device wafers  10   a  and  10   b  are stacked with the temporary fixing portion  55   a  formed on the electrode pad  20   a  of the device wafer  10   a  facing porous metal material  54   b  at the surface of the device wafer  10   b  with an insulating layer  60   b  formed thereon. 
         [0102]    After the device wafers  10   a  and  10   b  are stacked, they are temporarily sintered ( FIG. 11C ). This temporary sintering allows the temporary fixing portion  55   a  to be changed into porous metal material  57   a . Then, the device wafers  10   a  and  10   b  are adhered together. 
         [0103]    Subsequently, a temporary fixing portion  55   b  is formed on an electrode pad  20   b  of the device wafer  10   b . The temporary fixing portion  55   b  may use the same paste used for the temporary fixing portion  55   a . After the temporary fixing portion  55   b  is formed on the electrode pad  20   b , the device wafers  10   a  and  10   b  and the device wafer  10   c  are stacked with the electrode pad  20   b  facing porous metal material  54   c  and insulating layer  60   c  of the device wafer  10   c  ( FIG. 11D ). 
         [0104]    After the device wafers  10   a  and  10   b  and the device wafer  10   c  are stacked, they are temporarily sintered ( FIG. 11E ). This temporary sintering allows the temporary fixing portion  55   b  to be changed into porous metal material  57   b . Then, the device wafers  10   b  and  10   c  are adhered together. 
         [0105]    For a stack  3   b  temporarily fixed by the temporary fixing portions  55   a  and  55   b , metal nano-particle ink is injected into the porous metal materials  54   a  to  54   c  and then the stack  3   b  is mainly sintered such that an integrated through conductor can be formed. 
         [0106]    In the examples shown in  FIGS. 11A to 11E , a precision of forming the through conductor can be increased since the porous temporary fixing portions  55   a  and  55   b  are used to align the device wafers  10  or the chips  2 . In addition, since the temporary fixing portions  55   a  and  55   b  are made of porous metal material, an integrated through conductor can be formed using metal nano-particle ink. 
         [0107]    Although in this example the metal nano-particle paste is temporarily sintered to form the temporary fixing portions, the present disclosure is not limited thereto. For example, porous metal material may be directly placed in the electrode pad  20  to form the temporary fixing portions. In this case, the temporary sintering is not required. In addition, although in this example the temporary fixing portions are formed on the electrode pad, the same effects can be obtained even when the temporary fixing portions are formed in an end portion of porous metal material exposed from the through via. In addition, although in this example the temporary fixing portions are formed on the electrode pad, the temporary fixing portions may be formed in an end portion of porous metal material at the surface with the insulating layer formed thereon of the device wafer. 
         [0108]    In this manner, according to the manufacturing method of the embodiment, even when the through conductor is formed in a fine through via, it is possible to realize a uniform through conductor with no void since there is no need for a large-scaled vacuum pressurizing apparatus or the like. 
         [0109]    In addition, according to the manufacturing method of the embodiment, the number of processes can be reduced since there is no need for a vacuum apparatus, a plating apparatus, a reduction apparatus, a resist application and so on. In particular, in the manufacturing method of the embodiment, processes can be simplified since the through conductor can be formed at a relatively low temperature, thereby requiring no sputter apparatus, CVD apparatus and plating apparatus. 
         [0110]    In addition, in the manufacturing method of the embodiment, resistance can be lowered since there is no need for solder and conductive adhesive for chip stacking and through via forming. 
         [0111]    According to some embodiments of the present disclosure, it is possible to provide a semiconductor device manufacturing method which is capable of easily realizing formation of through electrodes on chips and connection between the through electrodes. 
         [0112]    While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.