Abstract:
The present invention aims to relax stress induced by through-silicon via formed on semiconductor substrate in order to prevent property fluctuation of a transistor. A semiconductor device includes a semiconductor substrate, a through-silicon via formed in semiconductor substrate, an insulating film formed between the semiconductor substrate and the through-silicon via, and a transistor formed on the semiconductor substrate so as to be apart from the through-silicon via with a predetermined distance. The insulating film does not exist on a region close to a surface of the semiconductor substrate between the semiconductor substrate and the through-silicon via. A gap is formed to be surrounded by the semiconductor substrate, the through silicon via, and the insulating film under the region close to the surface of the semiconductor substrate.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a semiconductor device, and a method of manufacturing the same, and more particularly to a three-dimensional stacked semiconductor device having a through-silicon via, and a method of manufacturing the same. 
         [0003]    2. Background Art 
         [0004]    As an electronic device has a variety of functions and high performance in recent years, various developments have been made to realize a high-performance and highly integrated semiconductor device used for such an electronic device. Especially, a technique of three-dimensionally stacking semiconductor chips having a through-silicon via has been proposed, and this technique has been developed more actively. In the three-dimensional stacking technique, a through-silicon via penetrating through a semiconductor substrate and a bump connected to the through-silicon via are formed on one semiconductor chip, which is to be stacked, while a bump is also formed on the other semiconductor chip that is to be stacked. The chips are stacked by bonding both bumps. 
         [0005]      FIG. 8A  is a sectional view illustrating a stacked chip having a through-silicon via for a conventional three-dimensional stacking technique.  FIGS. 8B ,  9 A, and  9 B are sectional views illustrating a method of forming a stacked chip including a through-silicon via for a conventional three-dimensional stacking technique. 
         [0006]      FIG. 8A  illustrates a sectional view after a memory chip and a logic chip having a through-silicon via are stacked. The stacked semiconductor device includes memory chip  23 , logic chip  24 , through-silicon via  25 , microbump  26 , and filling material  27  between chips. 
         [0007]    The sectional view illustrating a process of manufacturing the chip involved with the through-silicon via and its surrounding region is illustrated next. 
         [0008]    As illustrated in  FIG. 8B , elements (not illustrated) such as a transistor or a resistor are formed on semiconductor substrate  11 , first interlayer insulating film  12  made of a silicon oxide film and including the elements and a wiring layer is formed, and then, contact plug  13  is formed in first interlayer insulating film  12 . 
         [0009]    Next, as illustrated in  FIG. 9A , through-silicon via hole  14  penetrating through first interlayer insulating film  12  and semiconductor substrate  11  is formed by using a lithography technique and a dry etching technique.  FIG. 9A  illustrates that through-silicon via  14  does not reach a back surface of the semiconductor substrate. Thereafter, insulating film  15  such as a silicon oxide film is formed on first interlayer insulating film  12  along an inner wall face of through-silicon via hole  14 , and then, a tantalum (Ta) film, for example, is formed as barrier film  16  that becomes a diffusion barrier of copper (Cu) that is a embedding material. Next, copper is filled in through-silicon via  14  as conductive film  17  for embedding the through-silicon via by using a plating technique, and then, an annealing process is carried out. 
         [0010]    Next, as illustrated in  FIG. 9B , conductive film  17  for embedding the through-silicon via, barrier film  16 , and insulating film  15  that remain on first interlayer insulating film  12  on semiconductor substrate  11  are removed by using a CMP (Chemical Mechanical Polishing) technique, in order to form through-silicon via  18 . A diameter of through-silicon via  18  generally ranges from several μm to a few dozen μm, and a depth thereof generally ranges from a few dozen μm to a few hundred μm. Finally, a bottom surface of semiconductor substrate  11  is etched or polished to expose the back surface of through-silicon via  18 , and a bump connected to through-silicon via  18  is formed, although this process is not illustrated. 
         [0011]    When the annealing process is carried out after through-silicon via  18  is formed, thick copper in through-silicon via  18  expands and contracts by the annealing process. In this case, stress is generated on semiconductor substrate  11  due to a difference in a thermal expansion coefficient between copper and silicon forming semiconductor substrate  11 , so that a problem that the stress varies a performance of a transistor close to through-silicon via  18  might arise (e.g., see A. Mercha et al., Comprehensive Analysis of the Impact of Single and Arrays of Through Silicon Vias Induced stress on High-k/Metal Gate CMOS performance, IEDM, 2010). 
         [0012]    Some proposals have been conventionally made in order to relax the stress caused by the through-silicon via. For example, there is a method (e.g., see Unexamined Japanese Patent Publication No. 11-163228) of forming a new layer between a metal in a through-silicon via and a semiconductor substrate for relaxing stress, as a method of relaxing stress to the semiconductor substrate due to the metal in the through-silicon via. There is another method (for example, see Unexamined Japanese Patent Publication No. 2008-085126) in which a metal in a through-silicon via is formed in two or more layers, and a heat treatment for relaxing stress is carried out after at least the first layer close to the semiconductor substrate is formed. 
       SUMMARY 
       [0013]    However, the methods of relaxing stress described above need an additional process of forming a relaxation layer or a metal layer, and this entails problems of a limitation in performance of a material to be added and complicated process. Therefore, a more simple method of relaxing stress has been demanded. 
         [0014]    The present invention is accomplished in view of the problems in the conventional technique, and aims to provide a highly reliable semiconductor device that relaxes stress to a semiconductor substrate induced by a through-silicon via in order to prevent property fluctuation of a transistor provided close to the through-silicon via, and a method of manufacturing the same. 
         [0015]    In order to solve the above-described problems, the semiconductor device according to the present invention includes a semiconductor substrate, a through-silicon via formed in the semiconductor substrate, an insulating film formed to be interposed between the semiconductor substrate and the through-silicon via, and a transistor formed on the semiconductor substrate so as to be apart from the through-silicon via with a predetermined distance. The insulating film does not exist on a region close to a surface of the semiconductor substrate between the semiconductor substrate and the through-silicon via. A gap is formed to be surrounded by the semiconductor substrate, the through silicon via, and the insulating film under the region close to the surface of the semiconductor substrate. 
         [0016]    It is preferable in the semiconductor device according to the present invention that the through-silicon via is formed to penetrate through a first interlayer insulating film formed on the semiconductor substrate, and the gap is also formed in the first interlayer insulating film. 
         [0017]    It is preferable in the semiconductor device according to the present invention that the predetermined distance and a depth of the gap from the surface of the semiconductor substrate are substantially equal to each other. 
         [0018]    It is preferable in the semiconductor device according to the present invention that a second interlayer insulating film is further formed on the through-silicon via, and a part of the gap is embedded with the second interlayer insulating film. 
         [0019]    It is preferable in the semiconductor device according to the present invention that the insulating film is made of a silicon nitride film. 
         [0020]    It is preferable in the semiconductor device according to the present invention that a stress liner film applying stress to the transistor is formed on the semiconductor substrate excluding a region on the through-silicon via and its surrounding region. 
         [0021]    It is preferable in the semiconductor device according to the present invention that the through-silicon via includes an outside barrier film and an inside conductive film. 
         [0022]    A method of manufacturing a semiconductor device according to the present invention includes a step (a) of forming a first interlayer insulating film including a transistor on a semiconductor substrate; a step (b) of forming a through-hole in the first interlayer insulating film and in the semiconductor substrate so as to be apart from the transistor with a predetermined distance; and a step (c) of forming an insulating film on an inner wall face of the through-hole. The method further includes a step (d) of forming a through-silicon via by embedding a conductive film in the through-hole after the step (c); and a step (e) of carrying out an annealing process to the semiconductor substrate after the step (d). The method also includes a step (f) of forming a gap between the semiconductor substrate and the through-silicon via on a region close to a surface of the semiconductor substrate by removing an upper part of the insulating film interposed between the first interlayer insulating film as well as the semiconductor substrate and the through-silicon via. 
         [0023]    It is preferable in the method of manufacturing a semiconductor device according to the present invention that the upper part of the insulating film is removed in order to allow the predetermined distance and a depth of the gap from the surface of the semiconductor substrate to be substantially equal to each other in the step (f). 
         [0024]    It is preferable that the method of manufacturing a semiconductor device according to the present invention further includes a step (g) of forming a second interlayer insulating film on a region on the first interlayer insulating film including a region on the through-silicon via after the step (f), wherein the second interlayer insulating film is embedded in a part of the gap in the step (g). 
         [0025]    It is preferable that the method of manufacturing a semiconductor device according to the present invention further includes, between the step (a) and the step (b), a step (i) of forming a stress liner film that applies stress to the transistor, and a step (j) of removing the stress liner film on a region on the through-silicon via and its surrounding region. 
         [0026]    It is preferable in the method of manufacturing a semiconductor device according to the present invention that the insulating film is made of a silicon nitride film. 
         [0027]    It is preferable in the method of manufacturing a semiconductor device according to the present invention that the through-silicon via includes an outside barrier film and an inside conductive film. 
         [0028]    According to the semiconductor device and the method of manufacturing a semiconductor device of the present invention, stress is released on the semiconductor substrate by the gap formed between the through-silicon via and the substrate, whereby the stress to the semiconductor substrate induced by the through-silicon via can be relaxed, and the property fluctuation of the transistor provided close to the through-silicon via can be prevented. Consequently, the present invention can provide a highly-reliable semiconductor device. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]      FIG. 1A  is a sectional view illustrating a process of a method of manufacturing a semiconductor device according to a first exemplary embodiment of the present invention. 
           [0030]      FIG. 1B  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the first exemplary embodiment of the present invention. 
           [0031]      FIG. 2A  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the first exemplary embodiment of the present invention. 
           [0032]      FIG. 2B  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the first exemplary embodiment of the present invention. 
           [0033]      FIG. 3  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the first exemplary embodiment of the present invention. 
           [0034]      FIG. 4  is a graph illustrating a relationship between a depth of a formed gap and an effect of reducing stress from a through-silicon via in a semiconductor device according to the first exemplary embodiment of the present invention. 
           [0035]      FIG. 5A  is a sectional view illustrating a process of a method of manufacturing a semiconductor device according to a second exemplary embodiment of the present invention. 
           [0036]      FIG. 5B  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the second exemplary embodiment of the present invention. 
           [0037]      FIG. 6A  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the second exemplary embodiment of the present invention. 
           [0038]      FIG. 6B  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the second exemplary embodiment of the present invention. 
           [0039]      FIG. 7  is a sectional view illustrating a process of the method of manufacturing a semiconductor device according to the second exemplary embodiment of the present invention. 
           [0040]      FIG. 8A  is a sectional view illustrating a conventional semiconductor device. 
           [0041]      FIG. 8B  is a sectional view illustrating a process of a conventional method of forming a through-silicon via. 
           [0042]      FIG. 9A  is a sectional view illustrating a process of a conventional method of forming a through-silicon via. 
           [0043]      FIG. 9B  is a sectional view illustrating a process of the conventional method of forming the through-silicon via. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0044]    Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. In the exemplary embodiments of the present invention, a formation of a through-silicon via by a via-middle process is supposed. However, the present invention is not limited thereto. 
       First Exemplary Embodiment 
       [0045]    A first exemplary embodiment of the present invention will be described below with reference to the drawings. 
         [0046]      FIGS. 1A to 3  are sectional views illustrating a process of a method of manufacturing a semiconductor device according to a first exemplary embodiment of the present invention. 
         [0047]    As illustrated in  FIG. 1A , elements (not illustrated) such as a transistor or a resistor are formed on semiconductor substrate  11 , first interlayer insulating film  12  made of a silicon oxide film and including the elements and a wiring layer is formed, and then, contact plug  13  is formed in first interlayer insulating film  12 . In this case, a thickness of first interlayer insulating film  12  is 500 nm, for example. 
         [0048]    Next, as illustrated in  FIG. 1B , through-silicon via hole  14  having a diameter of 5 μm and a depth of 50 μm is formed by using a lithography technique and a dry etching technique, and then, insulating film  15  made of a silicon nitride film having a thickness of 200 nm is formed, for example. Thereafter, barrier film  16  made of a tantalum (Ta) film having a thickness of 20 nm is formed, for example. Next, copper is filled in through-silicon via hole  14  as conductive film  17  for embedding the through-silicon via by using a plating technique, and then, an annealing process is carried out. 
         [0049]    Next, as illustrated in  FIG. 2A , conductive film  17  for embedding the through-silicon via, barrier film  16 , and insulating film  15  that remain on first interlayer insulating film  12  on semiconductor substrate  11  are removed by using a CMP (Chemical Mechanical Polishing) technique, in order to form through-silicon via  18 . When silicon is used as a material for semiconductor substrate  11 , a thermal expansion coefficient of silicon is about 3 ppm/° C., and a thermal expansion coefficient of copper (Cu) of the through-silicon via is about 17 ppm/° C. Therefore, stress is generated on semiconductor substrate  11  during the annealing process or cooling process due to mismatch in the thermal expansion coefficient between both of them. 
         [0050]    Next, as illustrated in  FIG. 2B , insulating film  15  made of the silicon nitride film and formed between conductive film  17  of through-silicon via  18  and surrounding first interlayer insulating film  12  as well as surrounding semiconductor substrate  11  is removed by a wet etching to a depth of 500 nm from the surface of semiconductor substrate  11 , for example. Thus, gap  19  is formed between a side face of through-silicon via  18  and surrounding semiconductor substrate  11 . The wet etching is carried out by using hot phosphoric acid. The wet etching is carried out to first interlayer insulating film  12  made of the silicon oxide film in order that only the silicon nitride film is selectively etched. In this case, the stress generated by insulating film  15  made of the silicon nitride film is released by the formation of gap  19 . 
         [0051]      FIG. 4  is a graph illustrating a relationship between the depth of the formed gap from semiconductor substrate  11  and an effect of reducing stress from the through-silicon via (1−stress during formation of gap/stress when gap is not formed×100).  FIG. 4  illustrates the effect of reducing stress on the transistors mounted on positions of 1, 2, and 5 μm from the through-silicon via respectively. 
         [0052]    For example, in the case of the transistor located on the position apart from the through-silicon via by 2 μm, the effect of reducing stress of about 60% is attained, if the depth of the formed gap is set to be 2 μm. 
         [0053]    Subsequently, as illustrated in  FIG. 3 , first wiring layer  20  and second interlayer insulating film  21  filling the surroundings of first wiring layer  20  are formed on through-silicon via  18  in first interlayer insulating film  12 . In this case, gap  19  may locally be filled with first wiring layer  20 . Finally, a bottom surface of semiconductor substrate  11  is etched or polished to expose the back surface of through-silicon via  18 , and a bump connected to through-silicon via  18  is formed, although this process is not illustrated. 
         [0054]    According to the configuration of the present exemplary embodiment, stress is released on the semiconductor substrate by the gap formed between the through-silicon via and the substrate, whereby the stress to the semiconductor substrate induced by the through-silicon via can be relaxed, and the property fluctuation of the transistor provided close to the through-silicon via can be prevented. 
         [0055]    In the present exemplary embodiment, after contact plug  13  is formed on first interlayer insulating film  12 , through-silicon via  18  is formed, and then, gap  19  is formed to relax the stress. However, the present invention is not limited to this process. It may be configured such that, after plural wiring layers are formed, through-silicon via  18  is formed, and then, gap  19  is formed to relax the stress. 
         [0056]    In the present exemplary embodiment, gap  19  is left after through-silicon via  18  is formed. However, if the stress is temporarily released by the formation of gap  19  between the side face of the through-silicon via and surrounding semiconductor substrate  11  after the annealing process, the property fluctuation of the element due to the stress can be prevented. Therefore, after the stress is temporarily released, another insulating material may be embedded in a part of gap  19 . 
       Second Exemplary Embodiment 
       [0057]    A second exemplary embodiment of the present invention will be described below with reference to the drawings. 
         [0058]      FIGS. 5A to 7  are sectional views illustrating a process of a method of manufacturing a semiconductor device according to a second exemplary embodiment of the present invention. 
         [0059]    As illustrated in  FIG. 5A , elements (not illustrated) such as a transistor or a resistor are formed on semiconductor substrate  11 , first interlayer insulating film  12  made of a silicon oxide film and including the elements and a wiring layer is formed, and then, contact plug  13  is formed in first interlayer insulating film  12 . In this case, a thickness of first interlayer insulating film  12  is 500 nm, for example. In the present exemplary embodiment, stress liner film  22 , which is mainly made of a silicon nitride film for applying stress to a channel of a transistor in order to enhance driving force, is formed in first interlayer insulating film on a position close to semiconductor substrate  11 . 
         [0060]    Stress liner film  22  formed on the region where through-silicon via  18  is formed by another process and its surrounding region is preliminarily removed by the lithography technique and the etching technique. When the present exemplary embodiment is applied to a dual stress liner film process for separately creating a stress liner film on a region where an Nch transistor is formed and a region where a Pch transistor is formed, the liner film formed on the region where through-silicon via  18  is formed and its surrounding region can simultaneously be removed upon forming the region where the Nch transistor is to be formed and the region where the Pch transistor is to be formed. Accordingly, the increase in the number of processes can be prevented. 
         [0061]    Next, as illustrated in  FIG. 5B , through-silicon via hole  14  having a diameter of 5 μm and a depth of 50 μm is formed by using a lithography technique and a dry etching technique, and then, insulating film  15  made of a silicon nitride film having a thickness of 200 nm is formed, for example. Thereafter, barrier film  16  made of a tantalum (Ta) film having a thickness of 20 nm is formed, for example. Next, copper is filled in through-silicon via hole  14  as conductive film  17  for embedding the through-silicon via by using a plating technique, and then, an annealing process is carried out. 
         [0062]    Next, as illustrated in  FIG. 6A , conductive film  17  for embedding the through-silicon via, barrier film  16 , and insulating film  15  that remain on first interlayer insulating film  12  on semiconductor substrate  11  are removed by using a CMP technique, in order to form through-silicon via  18 . When silicon is used as a material for semiconductor substrate  11 , a thermal expansion coefficient of silicon is about 3 ppm/° C., and a thermal expansion coefficient of copper (Cu) of the through-silicon via is about 17 ppm/° C. Therefore, stress is generated on semiconductor substrate  11  during the annealing process or cooling process due to mismatch in the thermal expansion coefficient between both of them. 
         [0063]    Next, as illustrated in  FIG. 6B , insulating film  15  made of the silicon nitride film and formed between conductive film  17  of through-silicon via  18  and surrounding first interlayer insulating film  12  as well as surrounding semiconductor substrate  11  is removed by a wet etching to a depth of 500 nm from the surface of semiconductor substrate  11 , for example. Thus, gap  19  is formed between a side face of the through-silicon via and surrounding semiconductor substrate  11 . The wet etching is carried out by using hot phosphoric acid. The wet etching is carried out to first interlayer insulating film  12  made of the silicon oxide film in order that only the silicon nitride film is selectively etched. In this case, the stress generated by insulating film  15  made of the silicon nitride film is released by the formation of gap  19 . 
         [0064]    In the present exemplary embodiment, stress liner film  22  formed on the region where through-silicon via  18  is formed by another process and its surrounding region is preliminarily removed by the lithography technique and the etching technique. Therefore, there is no chance that stress liner film  22  on the region needed to apply stress to the transistor is etched. Accordingly, only insulating film  15 , made of the silicon nitride film, between the side face of through-silicon via  18  and its surrounding semiconductor substrate  11  can selectively be removed by the wet etching. 
         [0065]    Subsequently, as illustrated in  FIG. 7 , first wiring layer  20  and second interlayer insulating film  21  filling the surroundings of first wiring layer  20  are formed on through-silicon via  18  in first interlayer insulating film  12 . In this case, gap  19  may locally be filled with first wiring layer  20 . Finally, a bottom surface of semiconductor substrate  11  is etched or polished to expose the back surface of through-silicon via  18 , and a bump connected to through-silicon via  18  is formed, although this process is not illustrated. 
         [0066]    According to the configuration of the present exemplary embodiment, stress is released on the semiconductor substrate by the gap formed between the through-silicon via and the substrate, whereby the stress to the semiconductor substrate induced by the through-silicon via can be relaxed, and the property fluctuation of the transistor provided close to the through-silicon via can be prevented. 
         [0067]    According to the configuration of the present exemplary embodiment, the stress liner film of through-silicon via  18  is selectively removed even in a semiconductor device including stress liner film  22  mainly made of the silicon nitride film. Accordingly, only insulating film  15 , made of the silicon nitride film, between the side face of through-silicon via  18  and its surrounding semiconductor substrate  11  can selectively be removed by a wet etching without giving damage to stress liner film  22  on the region required to apply stress to the transistor. 
         [0068]    In the present exemplary embodiment, after contact plug  13  is formed on first interlayer insulating film  12 , through-silicon via  18  is formed, and then, gap  19  is formed to relax the stress. However, the present invention is not limited to this process. It may be configured such that, after plural wiring layers are formed, through-silicon via  18  is formed, and then, gap  19  is formed to relax the stress. 
         [0069]    In the present exemplary embodiment, gap  19  is left after through-silicon via  18  is formed. However, if the stress is temporarily released by the formation of gap  19  between the side face of the through-silicon via and surrounding semiconductor substrate  11  after the annealing process, the property fluctuation of the element due to the stress can be prevented. Therefore, after the stress is temporarily released, another insulating material may be embedded in a part of gap  19 . 
         [0070]    The semiconductor device and the method of manufacturing the same can relax stress to a semiconductor substrate induced by a through-silicon via in order to prevent property fluctuation of a transistor provided close to the through-silicon via. The present invention is well useful to a three-dimensional stacked semiconductor device that has a through-silicon via and that is required to have microfabrication, high integration, high performance, and enhanced yield, and to a method of manufacturing the same.