Patent Publication Number: US-7217631-B2

Title: Semiconductor device and method for fabricating the device

Description:
This application is a Divisional of application Ser. No. 09/898,082, filed Jul. 5, 2001, now U.S. Pat. No. 7,078,811 the entire content of which is incorporated herein by reference in this application. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor device that has a plurality of substrates and a method for fabricating the device. 
     Lately, the present inventor has proposed this kind of semiconductor device obtained by laminating a conductive layer and an insulating layer on a first semiconductor substrate, polishing its surface by chemical mechanical polishing (hereinafter abbreviated to CMP) for the formation of a flat first bonding surface on which a silicon nitride film that serves as an insulating layer and copper that is a through hole conductor for plugging a through hole of the silicon nitride film are exposed, laminating a conductive layer and an insulating layer on a second semiconductor substrate, subjecting its surface to CMP for the formation of a flat second bonding surface on which a silicon nitride film and copper that is a through hole conductor are exposed, further applying pressure welding loads to the first semiconductor substrate and the second semiconductor substrate for the achievement of the solid state bonding of the first bonding surface to the second bonding surface and electrically connecting the through hole conductors to each other. It is to be noted that this semiconductor device is mentioned for the sake of explaining the present invention, and this means that the device has not vet been made public and is not the prior art. 
     This semiconductor device has the advantages that it can simply prevent electromagnetic radiation noises because of the provision of the conductive layer on the first and second substrates and that the interconnections can be made short and easy because the through hole conductors are bonded together in the solid state bonding manner. 
     However, the aforementioned semiconductor device, in which the through hole conductors that are made of copper and provided inside the through holes of the silicon nitride films have a hardness lower than that of the silicon nitride films that are the insulating layers. Therefore, when the first bonding surface and the second bonding surface are subjected to CMP, then dishing (a dish-shaped hollow) occurs on the surface of the through hole conductors, and this possibly leads to a fail in directly bonding the through hole conductors to each other. That is, the electrical connection of the through hole conductors has no reliability. 
     SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to provide a semiconductor device and a method for fabricating the device capable of achieving reliable electrical connection by securely directly bonding conductors to each other even though their bonding surfaces are subjected to CMP and solid state bonding. 
     In order to achieve the aforementioned object, the present invention provides a semiconductor device comprising: 
     a first portion having a first substrate, a conductive layer and an insulating layer laminated on the first substrate and a bonding surface that is chemically mechanically polished and exposes a conductive region and an insulating region; 
     a second portion having a second substrate, a conductive layer and an insulating layer laminated on the second substrate and a bonding surface that is chemically mechanically polished and exposes at least a conductive region; and wherein 
     the bonding surface of the first portion and the bonding surface of the second portion are solid-state-bonded to each other and 
     at least one of the bonding surface of the first portion and the bonding surface of the second portion has the insulating region lowered with respect to the conductive region. 
     In the semiconductor device of the aforementioned construction, the bonding surfaces of the first and second portions are chemically mechanically polished, and therefore, dishing portions occur in the conductive regions adjacent to the insulating regions. However, the insulating region is lowered with respect to the conductive region on at least one of the bonding surface of the first portion and the bonding surface of the second portion, and therefore, the conductive region is protruding. Accordingly, the conductive regions are securely directly bonded to each other even though the dishing portions exist. Therefore, a high-reliability electrical connection of the conductive regions can be obtained. 
     In one embodiment, dishing portions of the conductive regions are bonded to each other. 
     In one embodiment, the conductive region of the first portion and the conductive region of the second portion are solid-state-bonded to each other, and the insulating region of the first portion and the insulating region of the second portion face each other with interposition of a clearance. 
     In one embodiment, the insulating region that surrounds the conductive region of the first portion and the insulating region that surrounds the conductive region of the second portion face each other with interposition of a clearance. 
     In one embodiment, the conductive region of the first portion and the conductive region of the second portion are solid-state-bonded to each other, and the insulating region of the first portion and the insulating region of the second portion are put in contact with or solid-state-bonded to each other. 
     In one embodiment, the insulating region that surrounds the conductive region of the first portion and the insulating region that surrounds the conductive region of the second portion are put in contact with or solid-state-bonded to each other. 
     In one embodiment, the conductive regions are end surfaces of through hole conductors and the insulating regions are end surfaces of through hole insulators that surround the respective through hole conductors. 
     In one embodiment, the first substrate or the second substrate is any one of a semiconductor substrate, an inorganic substrate and an organic substrate. 
     According to the present invention, there is provided a semiconductor device fabricating method comprising the steps of: 
     forming a first portion having a first substrate, a conductive layer and an insulating layer laminated on the first substrate and a bonding surface that is chemically mechanically polished and exposes a conductive region and an insulating region; 
     forming a second portion having a second substrate, a conductive layer and an insulating layer laminated on the second substrate and a bonding surface that is chemically mechanically polished and exposes at least a conductive region; 
     selectively etching the insulating region of at least one of the bonding surface of the first portion and the bonding surface of the second portion, thereby lowering the surface of the insulating region with respect to the surface of the conductive region; and 
     applying pressure welding loads to the first portion and the second portion for achievement of solid state bonding of the bonding surface of the first portion to the bonding surface of the second portion and for achievement of electrical connection of the conductive region of the first portion with the conductive region of the second portion. 
     According to the semiconductor device fabricating method of the above construction, the bonding surfaces of the first and second portions are chemically mechanically polished, and therefore, dishing portions occur in the conductive regions adjacent to the insulating regions. However, the surface of the insulating region is lowered with respect to the surface of the conductive region by selectively etching the insulating region on at least one of the bonding surface of the first portion and the bonding surface of the second portion, and therefore, the surface of the conductive region is protruding from the surface of the insulating region. Accordingly, the conductive regions are securely directly bonded to each other even though the dishing portions exist in the conductive regions. Therefore, a high-reliability electrical connection of the conductive regions can be obtained. 
     In one embodiment, the surface of the insulating region is lowered by reactive ion etching. 
     In one embodiment, etching is performed so that a height of a bottom of a dishing portion of the conductive region and a height of the insulating region become approximately equal to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIGS,  1 A,  1 B,  1 C,  1 D and  1 E are views for explaining a semiconductor device fabricating method according to a first embodiment of the present invention; 
         FIGS. 2A ,  2 B and  2 C are views for explaining an etching process of the first embodiment; 
         FIG. 3  is a view for explaining a state immediately before the execution of the solid state bonding of the first embodiment; 
         FIG. 4  is a sectional view of the semiconductor device of the first embodiment; 
         FIGS. 5A ,  5 B,  5 C,  5 D and  5 E are views for explaining a semiconductor device fabricating method according to a second embodiment of the present invention; 
         FIGS. 6A ,  6 B and  6 C are views for explaining an etching process of the second embodiment; 
         FIG. 7  is a view for explaining a state immediately before the execution of the solid state bonding of the second embodiment; and 
         FIG. 8  is a sectional view of the semiconductor device of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in detail below on the basis of the embodiments shown in the drawings. 
       FIGS. 1A through 1E ,  2 A through  2 C,  3  and  4  show a semiconductor device fabricating method of the first embodiment. First, as shown in  FIG. 1A , a wiring layer  3  is provided as an example of a conductive layer on a semiconductor substrate  1  that serves as an example of a first substrate. Further, as shown in  FIG. 1B , an insulating layer  7  is laminated on the semiconductor substrate  1  and the wiring layer  3 . The wiring layer  3  is made of a metal of, for example, copper, an aluminum alloy or the like, a polysilicon doped with an impurity, a silicide or the like, while the insulating layer  7  is made of, for example, silicon nitride. 
     Next, as shown in  FIG. 1C , a through hole  13  that reaches the wiring layer  3  is formed through the insulating layer  7 , and a grounding wiring groove  8  is formed on the insulating layer  7  by the techniques of photolithography and dry etching. A portion of the insulating layer  7  that is left between the through hole  13  and the grounding wiring groove  8  becomes a through hole insulator  11  that forms a wall surface of the through hole  13 . 
     Next, as shown in  FIG. 1D , a conductive layer  9  made of, for example, copper is formed on the insulating layer  7  so as to entirely cover the insulating layer  7  and fill up the through hole  13  and the grounding wiring groove  8 . 
     Next, as shown in  FIG. 1E , the conductive layer  9  is flattened by polishing according to the CMP method until the through hole insulator  11  is exposed. As described above, by performing polishing according to the CMP method until the through hole insulator  11  is exposed, the conductive layer  9  is separated into a through hole conductor  5  that is made of copper and fills up the through hole  13  and a grounding wiring layer  6  that buries the grounding wiring groove  8 . The surfaces of the through hole conductor  5 , the through hole insulator  11  and the grounding wiring layer  6  form a bonding surface  12  of an approximately same height. It is to be noted that the through hole conductor  5  and the grounding wiring layer  6 , which are made of copper, have a hardness lower than that of the through hole insulator  11 . Therefore, as shown in  FIG. 1E  and  FIG. 2A , the surfaces of the through hole conductor  5  and the grounding wiring layer  6  become concave in a dish-like shape and lowered with respect to the surface of the through hole insulator  11  by the CMP. That is, a dishing portion  17  that is concave in a dish-like shape occurs on the surface of the through hole conductor  5 . 
     Next, as shown in  FIGS. 2B and 2C , by the reactive ion etching (RIE) method, the through hole insulator  11  is selectively etched until the through hole insulator  11  comes to have a height equal to the height of the bottom portion  19  of the dishing portion  17  of the through hole conductor  5 . This reactive ion etching has selectivity and anisotropy, and therefore, the through hole insulator  11  can be finely processed to make the through hole insulator  11  have a height approximately equal to the height of the bottom portion  19  of the dishing portion  17 . On the whole, the height of the surface of the through hole insulator  11  is lowered with respect to the height of the surface of the through hole conductor  5 . That is, the through hole conductor  5  is protruding from the surface of the through hole insulator  11 . 
     As shown in  FIG. 3 , a first portion  100  constructed of the semiconductor substrate  1 , the wiring layer  3 , the insulating layer  7 , the through hole insulator  11 , the through hole conductor  5  and the grounding wiring layer  6  is thus formed. Although not shown, semiconductor elements such as transistors, capacitors and so on are built in the first portion  100 . 
     By performing quite the same processes as the fabricating processes of the first portion  100 , a second portion  200  as shown in  FIG. 3  is formed. This second portion  200  is constructed of a semiconductor substrate  20  that serves as a second substrate, a wiring layer  23  that serves as a conductive layer, an insulating layer  27 , a grounding wiring layer  26  that serves as a conductive layer, a through hole insulator  21  and a through hole conductor  25 . A bonding surface  22  of this second portion  200  is flattened by polishing according to the CMP method, and therefore, a dishing portion is formed on the through hole conductor  25  and the grounding wiring layer  26 , which serve as conductive regions. However, the through hole insulator  21  is selectively etched by reactive ion etching so that the bottom portion of the dishing portion  29  of the through hole conductor  25  and the through hole insulator  21  come to have an approximately equal height. It is to be noted that a reference numeral  28  denotes a through hole. 
     Although not shown, semiconductor elements such as transistors, capacitors and so on are built in the second portion  200 , similarly to the first portion. 
     Next, the bonding surfaces  12  and  22  of the first portion  100  and the second portion  200  are subjected to a cleaning process in a vacuum to become clean surfaces. In other words, the bonding surfaces  12  and  22  are activated. Subsequently, in a vacuum or an inert gas atmosphere, the bonding surface  12  of the first portion  100  and the bonding surface  22  of the second portion  200  are made to face each other in a manner that the through hole conductors  5  and  25  are aligned with each other and the grounding wiring layers  6  and  26  are aligned with each other, respectively. Then, as shown in  FIG. 4 , by applying pressure welding loads F and F to the semiconductor substrate  1  of the first portion  100  and the semiconductor substrate  20  of the second portion  200 , the through hole conductors  5  and  25  are solid-state-bonded or bonded at a room temperature (room temperature bonding) to each other, and the grounding wiring layers  6  and  26  are solid-state-bonded to each other. Then, the height of the bottom portions of the dishing portions  17  and  29  of the through hole conductors  5  and  25  becomes approximately equal to the height of the through hole insulators  11  and  21 . As a whole, the through hole conductors  5  and  25  and the grounding wiring layers  6  and  26  are convex with respect to the surfaces of the through hole insulators  11  and  21 . Therefore, the through hole conductor  5  and the grounding wiring layer  6  are securely solid-state-bonded to the through hole conductor  25  and the grounding wiring layer  26 , respectively. With this arrangement, the electrical connection of the through hole conductors  5  and  25  and the electrical connection of the grounding wiring layers  6  and  26  can be improved in terms of reliability. 
     A clearance  30  occurs in a portion located between the through hole insulators  11  and  21  and around the through hole conductors  5  and  25  that have been solid-state-bonded (i.e., in a surface activated bonding manner). As described above, by providing the clearance  30  between the through hole insulators  11  and  21 , the through hole conductors  5  and  25  and the grounding wiring layers  6  and  26  can be more securely solid-state-bonded to each other, respectively, enabling the achievement of more secure mechanical and electrical bonding. It is also acceptable to put the through hole insulators  11  and  21  in light contact or make them solid-state-bonded without providing the clearance  30 . As described above, when the through hole insulators  11  and  21  are solid-state-bonded to each other, the bonding of the first portion  100  to the second portion  200  is made more firm. 
     In the aforementioned embodiment, the surfaces of the through hole insulators  11  and  21  are lowered with respect to the surfaces of the through hole conductors  5  and  25  on both the bonding surface  12  of the first portion  100  and the bonding surface  22  of the second portion  200 . However, it is acceptable to perform etching so that the through hole insulator is much lowered with respect to the surface of the through hole conductor on one bonding surface and to make the entire surface of the dishing portion of the through hole conductor lower than the surface of the through hole insulator without performing the etching for adjusting the height of the through hole insulator on the other bonding surface. Even with this arrangement, by increasing the quantity of etching of one through hole insulator, the through hole conductors can be securely electrically connected to each other even through the dishing portions exist. 
       FIGS. 5A through 5E ,  6 A through  6 C,  7  and  8  are views for explaining the semiconductor device fabricating method of the second embodiment. As clearly shown in  FIGS. 7 and 8 , a first portion  100  has the same construction as that of the first portion  100  of the first embodiment and is fabricated through the same processes. Therefore, no description is provided for the first portion  100 , and the same reference numerals as those used in the first embodiment are used. 
     A second portion  300  is fabricated through the processes shown in  FIGS. 5A through 5E  and  6 A through  6 C. First, as shown in  FIG. 5A , a wiring layer  33  is provided as an example of the conductive layer on a semiconductor substrate  31  that serves as an example of the second substrate. Further, as shown in  FIG. 5B , an insulating layer  37  is laminated on the semiconductor substrate  31  and the wiring layer  33 . The wiring layer  33  is made of a polysilicon doped with an impurity, copper, an aluminum alloy or the like, while the insulating layer  37  is made of, for example, silicon nitride, silicon oxide or the like. 
     Next, as shown in  FIG. 5C , a through hole  43  that reaches the wiring layer  33  is formed through the insulating layer  37  by the techniques of photolithography and dry etching. 
     Next, as shown in  FIG. 5D , a conductive layer  39  made of, for example, polysilicon is formed on the insulator  37  and the wiring layer  33  located at the bottom of the through hole  43  so as to fill up the through hole  43 . 
     Next, as shown in  FIG. 5E , the conductive layer  39  and the insulating layer  37  are flattened by polishing according to the CMP method. By performing polishing according to the CMP method, the surfaces of the through hole conductor  35  positioned inside the through hole  43  and the insulating layer  37  form a bonding surface  42  having an approximately equal height. It is to be noted that the through hole conductor  35  made of polysilicon has a hardness lower than that of the insulating layer  37  made of silicon nitride. Therefore, as shown in  FIG. 5E  and  FIG. 6A , the surface of the through hole conductor  35  becomes concave in a dish-like shape and lowered with respect to the surface of the insulating layer  37  by the CMP. That is, a dishing portion  47  that is concave in a dish-like shape occurs on the surface of the through hole conductor  35 . 
     Next, as shown in  FIGS. 6B and 6C , by the reactive ion etching method, the insulating layer  37  is selectively etched until the insulating layer  37  comes to have a height equal to the height of the bottom portion  49  of the dishing portion  47  of the through hole conductor  35 . On the whole, the height of the surface of the insulating layer  37  is lowered with respect to the height of the surface of the through hole conductor  35 . That is, the through hole conductor  35  is protruding from the surface of the insulating layer  37 . 
     As shown in  FIG. 7 , the second portion  300  constructed of the semiconductor substrate  31 , the wiring layer  33 , the insulating layer  37  and the through hole conductor  35  is thus formed. 
     Next, the bonding surfaces  12  and  42  of the first portion  100  and the second portion  300  are subjected to a cleaning process in a vacuum to become clean surfaces. In other words, the bonding surfaces  12  and  42  are activated. Subsequently, in a vacuum or an inert gas atmosphere, the bonding surface  12  of the first portion  100  and the bonding surface  42  of the second portion  300  are made to face each other in a manner that the through hole conductors  5  and  35  are aligned with each other. Then, as shown in  FIG. 8 , by applying pressure forces, i.e., pressure welding loads F and F to the semiconductor substrate  1  of the first portion  100  and the semiconductor substrate  31  of the second portion  300 , the through hole conductors  5  and  35  are solid-state-bonded to each other, and the grounding wiring layer  6  and the insulating layer  37  are solid-state-bonded to each other. Then, the height of the bottom portion of the dishing portion  17  of the through hole conductor  5  becomes approximately equal to the height of the through hole insulator  11 . The through hole conductor  5  and the grounding wiring layer  6  are totally convex with respect to the through hole insulator  11 . In addition, the height of the bottom portion of the dishing portion  47  of the through hole conductor  35  is approximately equal to the height of the insulating layer  37 , and the through hole conductor  35  is convex with respect to the insulating layer  37 . Therefore, the through hole conductor  5  and the through hole conductor  35  are securely solid-state-bonded to each other, while the grounding wiring layer  6  and the insulating layer  37  are securely solid-state-bonded to each other. With this arrangement, the mechanical connection and electrical connection of the through hole conductors  5  and  35  as well as the mechanical connection of the grounding wiring layer  6  and the insulating layer  37  can be improved in terms of reliability. 
     A clearance  40  occurs between the through hole insulator  11  and the insulating layer  37  and around the through hole conductors  5  and  35  that have been solid-state-bonded. As described above, by providing the clearance  40  between the through hole insulator  11  and the insulating layer  37 , the solid state bonding of the through hole conductor  5  to the through hole conductor  35  and the solid state bonding of the grounding wiring layer  6  to the insulating layer  37  can be further secured for the achievement of more secure mechanical and electrical bonding. It is also acceptable to put the through hole insulator  11  and the insulating layer  37  in light contact or make them solid-state-bonded without providing, the clearance  40 . As described above, when the through hole insulator  11  and the insulating layer  37  are solid-state-bonded to each other, the bonding of the first portion  100  to the second portion  300  is made more firm. 
     In the aforementioned first or second embodiment, the insulating regions (through hole insulators and insulating layer)  11 ,  21  and  37  surround the conductive regions (through hole conductors)  5 ,  25  and  35  on the bonding surfaces  12 ,  22  and  42 . However, the insulating regions are not required to surround the respective conductive regions, and it is only required to provide the conductive regions and the insulating regions. It is also acceptable that one bonding surface has the conductive region and the insulating region while the other bonding surface has only the conductive region. According to the present invention, the insulating region is etched so that the dishing portion in the conductive region protrudes above the insulating region on the bonding surface polished by the CMP method. Therefore, the present invention can be applicable if at least one bonding surface has the conductive region and the insulating region. 
     According to the first or second embodiment, the through hole conductor  5  is solid-state-bonded to the through hole conductor  25  or  35 , and the grounding wiring layer  6  is solid-state-bonded to the grounding wiring layer  26  or the insulating layer  37 . However, the present invention is, of course, not limited to this. For example, it is acceptable to solid-state-bond an insulating layer to an insulating layer or solid-state-bond a plurality of wiring layers and through hole conductors to a power supply layer that serves as a conductive layer. It is also acceptable to solid-state-bond a plurality of wiring layers to one another. 
     Although the conductive layer is made of copper or polysilicon in the aforementioned embodiments, the conductive layer may be formed of, for example, silicide, an aluminum alloy or the like, while the insulating layer may be formed of silicon oxide besides the silicon nitride. 
     Although the semiconductor substrate is employed as a substrate in the aforementioned embodiments, it is acceptable to employ an inorganic substrate such as a glass substrate and a ceramic substrate or an organic substrate made of an organic compound. 
     Although the aforementioned embodiments uses reactive ion etching as etching, it is acceptable to use other dry etching such as reactive sputtering etching, plasma etching, ion beam etching and photoetching or wet etching. 
     As is apparent from the above, according to the semiconductor device of the present invention, the insulating region is lowered with respect to the conductive region on at least one of the two bonding surfaces that are to be polished by the CMP method and then solid-state-bonded. Therefore, the conductive regions can be securely subjected to solid state bonding and securely electrically connected to each other. 
     Furthermore, according to the semiconductor device fabricating method of the present invention, the insulating region is selectively etched so that the surface of the insulating region is lowered with respect to the surface of the conductive region on at least one of the two bonding surfaces that have been polished by the CMP method. Therefore, the conductive regions can be securely subjected to solid state bonding and securely electrically connected to each other even though a dishing portion exists on the conductive region. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.