Abstract:
A method for producing a semiconductor device includes forming a semiconductor-pillar on a substrate and forming a laminated-structure of at least two composite layers, each including a metal layer and a semiconductor layer in contact with the metal layer, the semiconductor layer containing donor or acceptor atoms, and two interlayer insulating layers sandwiching the composite layers, such that a side surface of at least one of the two interlayer insulating layers is separated from a side surface of the semiconductor pillar. The laminated-structure surrounds the semiconductor pillar. A first heat treatment causes a reaction between the metal layer and the semiconductor layer to form an alloy layer, and brings the alloy layer into contact with the side surface of the semiconductor pillar. A second heat treatment to expands the alloy layer into the semiconductor pillar and diffuses dopant atoms into the semiconductor pillar to form an impurity region therein.

Description:
CROSS REFERENCES TO RELATED APPLICATION 
       [0001]    This application is a divisional patent application of U.S. patent application Ser. No. 14/806,053, filed Jul. 22, 2015, which claims priority to PCT/JP2014/081455, filed Nov. 27, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method for producing a pillar-shaped semiconductor device. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, an SGT (Surrounding Gate MOS Transistor), a representative pillar-shaped semiconductor device, has been attracting attention as a semiconductor element providing a semiconductor device having a high integration degree. There has been a demand for a further increase in the integration degrees of semiconductor devices including SGTs. 
         [0006]    In a standard planar MOS transistor, the channel extends in a horizontal direction parallel to the upper surface of the semiconductor substrate. In contrast, the channel of an SGT extends in a direction perpendicular to the upper surface of the semiconductor substrate (for example, refer to Japanese Unexamined Patent Application Publication No. 2-188966 and Hiroshi Takato, Kazumasa Sunouchi, Naoko Okabe, Akihiro Nitayama, Katsuhiko Hieda, Fumio Horiguchi, and Fujio Masuoka: IEEE Transaction on Electron Devices, Vol. 38, No. 3, pp. 573-578 (1991)). For this reason, SGTs allow an increase in the density of semiconductor devices, compared with planar MOS transistors. 
         [0007]      FIG. 7  is a schematic structural view of an N channel SGT. A Si pillar  100  (hereafter, a silicon semiconductor pillar will be referred to as a “Si pillar”) of P or i (intrinsic) conductivity type has at its upper and lower positions N +  regions  101   a  and  101   b  (hereafter, a semiconductor region having a high concentration of donor impurity will be referred to as an “N +  region”) in which one of the N +  regions serves as a source and the other one serves as a drain. The Si pillar  100  between the N +  regions  101   a  and  101   b  serving as the source and the drain serves as a channel region  102 . A gate insulating layer  103  is formed so as to surround the channel region  102 . A gate conductor layer  104  is formed so as to surround the gate insulating layer  103 . In an SGT, the N +  regions  101   a  and  101   b  serving as the source and the drain, the channel region  102 , the gate insulating layer  103 , and the gate conductor layer  104  are formed within or on the single Si pillar  100 . The area of an SGT in plan view corresponds to the area of a single source or drain N +  region in a planar MOS transistor. As a result, compared with circuit chips including planar MOS transistors, further reduction in the size of chips can be achieved in circuit chips including SGTs. 
         [0008]    As illustrated in a schematic structural view in  FIG. 8 , for example, two SGTs  116   a  and  116   b  are formed at the upper and lower positions of a single Si pillar  115  to thereby achieve reduction in circuit area. 
         [0009]      FIG. 8  is a schematic structural view of a CMOS inverter circuit in which an N channel SGT  116   a  is formed in a lower portion of the Si pillar  115 , and a P channel SGT  116   b  is formed above this N channel SGT  116   a.  The Si pillar  115  is formed on an i-layer substrate  117  (hereafter, a semiconductor layer not containing a donor or acceptor impurity will be referred to as an “i layer”) with an N +  region  121   a  therebetween. A SiO 2  layer  118  is formed around the Si pillar  115  and on the i-layer substrate  117  and the N +  region  121   a.  In an intermediate portion of the Si pillar  115 , an N +  region  121   b  is formed. In the Si pillar  115 , a P +  region  122   a  (hereafter, a semiconductor region having a high concentration of an acceptor impurity will be referred to as a “P +  region”) is formed so as to be connected to the N +  region  121   b.  The top portion of the Si pillar  115  has a P +  region  122   b.  The N +  region  121   a  serves as a source of the N channel SGT  116   a . The N +  region  121   b  serves as a drain of the N channel SGT  116   a.  The Si pillar  115  between the N +  regions  121   a  and  121   b  serves as a channel region  123   a  of the N channel SGT  116   a.  The P +  region  122   b  serves as a source of the P channel SGT  116   b.  The P +  region  122   a  serves as a drain of the P channel SGT  116   b.  The Si pillar  115  between the P +  regions  122   a  and  122   b  serves as a channel region  123   b  of the P channel SGT  116   b.  A gate insulating layer  119   a  of the N channel SGT  116   a  is formed so as to surround the channel region  123   a.  A gate conductor layer  120   a  of the N channel SGT  116   a  is formed so as to surround the gate insulating layer  119   a.  Similarly, a gate insulating layer  119   b  of the P channel SGT  116   b  is formed so as to surround the channel region  123   b.  A gate conductor layer  120   b  of the P channel SGT  116   b  is formed so as to surround the gate insulating layer  119   b.  In a surface layer portion of the N +  region  121   a,  a nickel silicide layer (NiSi layer)  125   a  is formed. A NiSi layer  125   b  is formed around both of the N +  region  121   b  and the P +  region  122   a  positioned at a central portion of the Si pillar  115 . In an upper surface layer of the P +  region  122   b  in the top portion of the Si pillar  115 , a NiSi layer  125   c  is formed. A ground wiring metal layer  126   a  is formed on the NiSi layer  125   a.  This ground wiring metal layer  126   a  is connected to a ground terminal VSS. An output wiring metal layer  126   b  is formed on the NiSi layer  125   b.  This output wiring metal layer  126   b  is connected to an output terminal Vo. A power supply wiring metal layer  126   c  is formed on the NiSi layer  125   c.  This power supply wiring metal layer  126   c  is connected to a power supply terminal VDD. Input wiring metal layers  127   a  and  127   b  are respectively formed on the gate conductor layers  120   a  and  120   b.  These input wiring metal layers  127   a  and  127   b  are connected to an input terminal Vi. 
         [0010]    In  FIG. 8 , the NiSi layer  125   b,  which is connected to the N +  region  121   b  and the P +  region  122   a  in the central portion of the Si pillar  115 , is formed by forming a nickel (Ni) film on the circumferential surfaces of the N +  region  121   b  and the P +  region  122   a,  subsequently carrying out heat treatment at about 450° C., for example, and removing the remaining Ni film on the circumferential surfaces. As a result, the NiSi layer  125   b  is formed from the circumference to the inside of the N +  region  121   b  and the P +  region  122   a.  In a case where the Si pillar  115  has a diameter of 20 nm, for example, the NiSi layer  125   b  is desirably formed so as to have a thickness of about 5 to about 10 nm in the horizontal direction parallel to the semiconductor substrate. NiSi has a linear expansion coefficient of 12×10 −6 /K. Si has a linear expansion coefficient of 2.4×10 −6 /K. The linear expansion coefficient of NiSi is about five times that of Si. Because of this large difference in linear expansion coefficient, during production, for example, during heat treatment, the NiSi layer  125   b  causes high strain due to stress within the Si pillar  115 . This tends to result in defects such as bending and collapse of the Si pillar  115 . The probability of occurrence of such defects further increases as the diameter of a Si pillar is decreased for the purpose of an increase in the integration degree of circuits, for example. The N +  region  121   b  and the P +  region  122   a  need to be formed within the Si pillar  115  with high accuracy with respect to the positions of the gate conductor layers  120   a  and  120   b.  In addition, while such problems are considered, the N +  region  121   b  and the P +  region  122   a  need to be connected to the output wiring metal layer  126   b  with certainty. In addition, since processing in the side surface of the Si pillar  115  is carried out, a method of connecting the gate conductor layers  120   a  and  120   b  to the input wiring metal layers  127   a  and  127   b  with certainty is necessary. 
       SUMMARY 
       [0011]    As described above, in the pillar-shaped semiconductor device including SGTs in  FIG. 8 , there is a demand for a method that allows accurate and easy formation of the N +  region  121   b,  the P +  region  122   a,  the NiSi layer  125   b,  and the output wiring metal layer  126   b  in the central portion and in the side surface of the Si pillar  115  without causing bending or collapse of the Si pillar  115 . 
         [0012]    A pillar-shaped semiconductor device according to a first aspect of the present invention includes 
         [0013]    a semiconductor pillar that stands on a semiconductor substrate so as to be perpendicular to a surface of the semiconductor substrate; 
         [0014]    an impurity region formed within the semiconductor pillar and containing donor or acceptor atoms; 
         [0015]    an alloy layer formed so as to be in contact with a side surface of the impurity region, within the semiconductor pillar and around the semiconductor pillar; and 
         [0016]    two interlayer insulating layers sandwiching the alloy layer, 
         [0017]    wherein at least one of the two interlayer insulating layers is separated from a side surface of the semiconductor pillar, 
         [0018]    the alloy layer contains metal atoms and semiconductor atoms, and 
         [0019]    the metal atoms react with the semiconductor atoms upon heat treatment to form the alloy layer and, during formation of the alloy layer, the donor or acceptor atoms are pushed out from the alloy layer. 
         [0020]    The pillar-shaped semiconductor device preferably includes the semiconductor pillar that stands on the semiconductor substrate so as to be perpendicular to the surface of the semiconductor substrate; 
         [0021]    a gate insulating layer surrounding the semiconductor pillar; 
         [0022]    a gate conductor layer surrounding the gate insulating layer; 
         [0023]    a first interlayer insulating layer surrounding the gate conductor layer; 
         [0024]    a first impurity region formed under the semiconductor pillar and containing donor or acceptor atoms; 
         [0025]    a second impurity region positioned above the first impurity region and within the semiconductor pillar and being of the same conductivity type as the first impurity region; 
         [0026]    the impurity region, which is a third impurity region positioned on or above the second impurity region and within the semiconductor pillar and containing the donor or acceptor atoms; 
         [0027]    a fourth impurity region positioned above the third impurity region and within the semiconductor pillar and being of the same conductivity type as the third impurity region; 
         [0028]    a first alloy layer in contact with a side surface of the second impurity region; 
         [0029]    the alloy layer, which is a second alloy layer in contact with a side surface of the third impurity region; 
         [0030]    a second interlayer insulating layer that is one of the two interlayer insulating layers, is in contact with an upper surface of the first alloy layer and a lower surface of the second alloy layer, and is separated from the side surface of the semiconductor pillar; and 
         [0031]    a third interlayer insulating layer that is another one of the two interlayer insulating layers, is on an upper surface of the second alloy layer, and is in contact with a side surface of the first interlayer insulating layer, 
         [0032]    wherein a first SGT (Surrounding Gate MOS Transistor) is formed in which one of the first impurity region and the second impurity region functions as a source, another one of the first impurity region and the second impurity region functions as a drain, a portion of the semiconductor pillar between the first impurity region and the second impurity region functions as a channel, and the gate conductor layer functions as a gate, and 
         [0033]    a second SGT is formed in which one of the third impurity region and the fourth impurity region functions as a source, another one of the third impurity region and the fourth impurity region functions as a drain, a portion of the semiconductor pillar between the third impurity region and the fourth impurity region functions as a channel, and the gate conductor layer functions as a gate. 
         [0034]    The pillar-shaped semiconductor device preferably further includes 
         [0035]    a third alloy layer formed within the semiconductor pillar and connecting the second impurity region and the first alloy layer; and 
         [0036]    a fourth alloy layer formed within the semiconductor pillar and connecting the third impurity region and the second alloy layer. 
         [0037]    The third alloy layer and the fourth alloy layer are preferably mutually connected within the semiconductor pillar. 
         [0038]    The third alloy layer and the fourth alloy layer are preferably formed so as to extend to a center of the semiconductor pillar in plan view. 
         [0039]    The first alloy layer and the second alloy layer are preferably wiring conductor material layers. 
         [0040]    The first alloy layer and the second alloy layer are preferably connected via a contact hole extending through both of the first alloy layer and the second alloy layer, to a wiring metal layer formed above the contact hole. 
         [0041]    Stress directed downward from the fourth impurity region is preferably produced within the semiconductor pillar. 
         [0042]    A space is preferably formed among the first alloy layer, the second alloy layer, and the gate conductor layer. 
         [0043]    A method for producing a pillar-shaped semiconductor device according to a second aspect of the present invention includes 
         [0044]    a semiconductor-pillar formation step of forming a semiconductor pillar that stands on a semiconductor substrate so as to be perpendicular to a surface of the semiconductor substrate; 
         [0045]    a laminated-structure formation step of stacking at least two composite layers each including a metal layer and a semiconductor layer in contact with the metal layer, the semiconductor layer containing donor or acceptor atoms, and two interlayer insulating layers sandwiching the composite layers, in a direction perpendicular to the surface of the semiconductor substrate, such that a side surface of at least one of the two interlayer insulating layers is separated from a side surface of the semiconductor pillar, and the metal layer, the semiconductor layer, and the two interlayer insulating layers are formed so as to surround the semiconductor pillar; 
         [0046]    an alloy layer-semiconductor pillar side surface contact step of causing a reaction between the metal layer and the semiconductor layer by heat treatment to form an alloy layer, and making the alloy layer protrude toward the side surface of the semiconductor pillar by heat treatment to bring the alloy layer into contact with the side surface of the semiconductor pillar; and 
         [0047]    an intra-semiconductor pillar alloy layer-impurity region formation step of, after the alloy layer-semiconductor pillar side surface contact step, causing a reaction between metal atoms within the alloy layer and semiconductor atoms in the semiconductor pillar by heat treatment to expand the alloy layer into the semiconductor pillar and to diffuse the donor or acceptor atoms having been pushed out from the alloy layer into the semiconductor pillar to form an impurity region containing the donor or acceptor atoms within the semiconductor pillar. 
         [0048]    In the method for producing a pillar-shaped semiconductor device, preferably, 
         [0049]    after the semiconductor-pillar formation step, 
         [0050]    a gate insulating layer surrounding the semiconductor pillar is formed, 
         [0051]    a gate conductor layer surrounding the gate insulating layer is formed, 
         [0052]    a first interlayer insulating layer surrounding the gate conductor layer is formed, 
         [0053]    a first impurity region containing donor or acceptor atoms is formed under the semiconductor pillar; 
         [0054]    in the laminated-structure formation step, 
         [0055]    a second interlayer insulating layer is formed so as to surround the semiconductor pillar and have an upper surface positioned at an intermediate height of the semiconductor pillar in the perpendicular direction, 
         [0056]    portions of side surfaces of the first interlayer insulating layer, the gate conductor layer, and the gate insulating layer are removed from an intermediate height of the semiconductor pillar in the perpendicular direction to a lower end at the height of the upper surface of the second interlayer insulating layer, to expose the side surface of the semiconductor pillar, 
         [0057]    a third interlayer insulating layer is formed so as to cover a surface of the gate conductor layer exposed by the removal, 
         [0058]    a first metal layer, a first semiconductor layer containing first donor or acceptor atoms, a fourth interlayer insulating layer that is one of the two interlayer insulating layers, the metal layer, which is a second metal layer, the semiconductor layer, which is a second semiconductor layer containing second donor or acceptor atoms, and a fifth interlayer insulating layer that is another one of the two interlayer insulating layers are stacked on the second interlayer insulating layer by directing and depositing material atoms in a direction perpendicular to the surface of the semiconductor substrate such that the first metal layer and the first semiconductor layer are positioned between the second interlayer insulating layer and the fourth interlayer insulating layer, the second metal layer and the second semiconductor layer are positioned between the fourth interlayer insulating layer and the fifth interlayer insulating layer, and the first metal layer, the first semiconductor layer, the fourth interlayer insulating layer, the second metal layer, and the second semiconductor layer are formed so as to be separated from the exposed side surface of the semiconductor pillar; 
         [0059]    in the alloy layer-semiconductor pillar side surface contact step, 
         [0060]    heat treatment is carried out to form a first alloy layer formed from metal atoms of the first metal layer and semiconductor atoms of the first semiconductor layer, and a second alloy layer formed from metal atoms of the second metal layer and semiconductor atoms of the second semiconductor layer, to make the first alloy layer and the second alloy layer facing the exposed side surface of the semiconductor pillar protrude toward the exposed side surface of the semiconductor pillar such that a first protrusion formed at a protruding tip of the first alloy layer and having a high content of the first donor or acceptor atoms and a second protrusion formed at a protruding tip of the second alloy layer and having a high content of the second donor or acceptor atoms are brought into contact with the exposed side surface of the semiconductor pillar; 
         [0061]    in the intra-semiconductor pillar alloy layer-impurity region formation step, 
         [0062]    the first donor or acceptor atoms in the first protrusion are diffused into the semiconductor pillar to form a second impurity region positioned within the semiconductor pillar and above the first impurity region and being of the same conductivity type as the first impurity region, the second donor or acceptor atoms in the second protrusion are diffused into the semiconductor pillar to form the impurity region, which is a third impurity region on or above the second impurity region, the first alloy layer is expanded into the semiconductor pillar to form a third alloy layer, and the second alloy layer is expanded into the semiconductor pillar to form a fourth alloy layer, 
         [0063]    the method further includes a fourth-impurity-region formation step of forming a fourth impurity region positioned above the third impurity region and within the semiconductor pillar and being of the same conductivity type as the third impurity region, 
         [0064]    wherein a first SGT (Surrounding Gate MOS Transistor) is formed in which one of the first impurity region and the second impurity region functions as a source, another one of the first impurity region and the second impurity region functions as a drain, a portion of the semiconductor pillar between the first impurity region and the second impurity region functions as a channel, and the gate conductor layer functions as a gate, and 
         [0065]    a second SGT is formed in which one of the third impurity region and the fourth impurity region functions as a source, another one of the third impurity region and the fourth impurity region functions as a drain, a portion of the semiconductor pillar between the third impurity region and the fourth impurity region functions as a channel, and the gate conductor layer functions as a gate. 
         [0066]    In the intra-semiconductor pillar alloy layer-impurity region formation step, the third alloy layer and the fourth alloy layer are preferably formed so as to be mutually connected. 
         [0067]    In the intra-semiconductor pillar alloy layer-impurity region formation step, the third alloy layer and the fourth alloy layer are preferably formed so as to extend to a center of the semiconductor pillar in plan view. 
         [0068]    In the laminated-structure formation step, preferably, 
         [0069]    the first metal layer, a third semiconductor layer not containing donor or acceptor atoms, and the fourth interlayer insulating layer are stacked on the second interlayer insulating layer, 
         [0070]    ion implantation is carried out to implant the first donor or acceptor atoms into the third semiconductor layer to form the first semiconductor layer, 
         [0071]    the second metal layer, a fourth semiconductor layer not containing donor or acceptor atoms, and the fifth interlayer insulating layer are stacked on the fourth interlayer insulating layer, and 
         [0072]    ion implantation is carried out to implant the second donor or acceptor atoms into the fourth semiconductor layer to form the second semiconductor layer. 
         [0073]    In the laminated-structure formation step, preferably, 
         [0074]    the first metal layer, a third semiconductor layer containing the second donor or acceptor atoms, and the fourth interlayer insulating layer are stacked on the second interlayer insulating layer, 
         [0075]    the second metal layer and the second semiconductor layer are stacked in this order or a reversed order on the fourth interlayer insulating layer, 
         [0076]    the fifth interlayer insulating layer is stacked on a resultant product, and 
         [0077]    ion implantation is carried out to implant the first donor or acceptor atoms of a conductivity type opposite to that of the second donor or acceptor atoms, into the third semiconductor layer in an amount larger than an amount of the second donor or acceptor atoms in the third semiconductor layer to form the first semiconductor layer; or 
         [0078]    the first metal layer and the first semiconductor layer are stacked in this order or a reversed order on the second interlayer insulating layer, 
         [0079]    the fourth interlayer insulating layer is stacked on a resultant product, 
         [0080]    the second metal layer and a fourth semiconductor layer containing the first donor or acceptor atoms are stacked in this order or a reversed order on the fourth interlayer insulating layer, 
         [0081]    the fifth interlayer insulating layer is stacked on a resultant product, and 
         [0082]    ion implantation is carried out to implant the second donor or acceptor atoms of a conductivity type opposite to that of the first donor or acceptor atoms, into the fourth semiconductor layer in an amount larger than an amount of the first donor or acceptor atoms in the fourth semiconductor layer to form the second semiconductor layer. 
         [0083]    The method for producing a pillar-shaped semiconductor device preferably further includes 
         [0084]    a contact-hole formation step of forming a contact hole so as to extend through both of the first alloy layer and the second alloy layer, and 
         [0085]    a wiring-metal-layer formation step of forming a wiring metal layer electrically connected via the contact hole to the first alloy layer and the second alloy layer. 
         [0086]    The fourth impurity region is preferably formed so as to produce stress directed downward in the semiconductor pillar. 
         [0087]    A space is preferably formed among the first alloy layer, the second alloy layer, and the gate conductor layer. 
         [0088]    According to the present invention, in a semiconductor device including an SGT, a semiconductor region that serves as the source or drain of the SGT in the central portion of a semiconductor pillar can be formed with high accuracy with respect to the position of a gate conductor layer. According to the present invention, in a semiconductor device including an SGT, occurrence of bending or collapse of a semiconductor pillar is suppressed during formation of an alloy layer within a semiconductor region being present in the central portion of the semiconductor pillar and serving as the source or drain of the SGT, and the connection between the semiconductor region and a wiring metal layer connected to the alloy layer can be established with certainty. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0089]      FIGS. 1AA, 1AB, and 1AC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to a first embodiment of the present invention. 
           [0090]      FIGS. 1BA, 1BB, and 1BC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0091]      FIGS. 1CA, 1CB, and 1CC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0092]      FIGS. 1DA, 1DB, and 1DC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0093]      FIGS. 1EA, 1EB, and 1EC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0094]      FIGS. 1FA, 1FB, and 1FC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0095]      FIGS. 1GA, 1GB, 1GC, and 1GD  are respectively a plan view, sectional structural views, and an enlarged sectional view of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0096]      FIGS. 1HA, 1HB, 1HC, and 1HD  are respectively a plan view, sectional structural views, and an enlarged sectional view of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0097]      FIGS. 1IA, 1IB, and 1IC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0098]      FIGS. 1JA, 1JB, and 1JC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0099]      FIGS. 1KA, 1KB, and 1KC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0100]      FIGS. 1LA, 1LB, and 1LC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the first embodiment. 
           [0101]      FIGS. 2AA, 2AB, and 2AC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to a second embodiment of the present invention. 
           [0102]      FIG. 2B  is an enlarged sectional view of a dotted rectangle B in the sectional structural view of the CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the second embodiment in  FIG. 2AB . 
           [0103]      FIGS. 3AA, 3AB, and 3AC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to a third embodiment of the present invention. 
           [0104]      FIGS. 3BA, 3BB, and 3BC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the third embodiment. 
           [0105]      FIGS. 4A, 4B, and 4C  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to a fourth embodiment of the present invention. 
           [0106]      FIGS. 5A, 5B, and 5C  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a semiconductor device including an SGT according to a fifth embodiment of the present invention. 
           [0107]      FIGS. 6AA, 6AB, and 6AC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to a sixth embodiment of the present invention. 
           [0108]      FIGS. 6BA, 6BB, and 6BC  are respectively a plan view and sectional structural views of a CMOS inverter circuit for explanation of a method for producing a semiconductor device including an SGT according to the sixth embodiment. 
           [0109]      FIG. 7  is a schematic structural view illustrating an SGT as a conventional example. 
           [0110]      FIG. 8  is a schematic structural view of a CMOS inverter circuit as a conventional example in which an N channel SGT is formed in a lower portion of a single Si pillar and a P channel SGT is formed in an upper portion of the Si pillar. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0111]    Hereinafter, a method for producing a pillar-shaped semiconductor device including an SGT according to an embodiment of the present invention will be described with reference to drawings. 
       First Embodiment 
       [0112]    Hereinafter, a method for producing a CMOS inverter circuit including an SGT according to a first embodiment of the present invention will be described with reference to  FIG. 1AA  to  FIG. 1LC . 
         [0113]      FIGS. 1AA to 1AC  are a plan view and sectional views for explanation of a first production step of a CMOS inverter circuit including an SGT:  FIG. 1AA  is the plan view,  FIG. 1AB  is a sectional structural view taken along line X-X′ in  FIG. 1AA , and  FIG. 1AC  is a sectional structural view taken along line Y-Y′ in  FIG. 1AA . Regarding numbering of these drawings, the same relationship among the suffixes A, B, and C applies to other drawings that will be referred to below. 
         [0114]    As illustrated in  FIGS. 1AA to 1AC , a SiO 2  layer  5  is formed by thermal oxidation on an i-layer substrate  1 . 
         [0115]    Subsequently, as illustrated in  FIGS. 1BA to 1BC , the SiO 2  layer  5  is etched by lithography and RIE (Reactive Ion Etching) to thereby form a SiO 2  layer  5   a.  In addition, RIE using the SiO 2  layer  5   a  as a mask is carried out to etch the i-layer substrate  1  to thereby form a Si pillar  6  extending in a direction perpendicular to (up and down with respect to) the surface of the i-layer substrate  1 . The cross-sectional shape of the Si pillar  6  is, as illustrated in  FIG. 1BA , preferably circular. The side surface of the Si pillar  6  preferably forms substantially a right angle with the upper surface of the i-layer substrate  1 . 
         [0116]    Subsequently, as illustrated in  FIGS. 1CA  to ICC, an N +  region  7  is formed by ion implantation in a surface layer of the i-layer substrate  1  so as to surround the Si pillar  6 . Subsequently, a SiO 2  film (not shown) is deposited by CVD (Chemical Vapor Deposition). The upper surface of the SiO 2  film is planarized by MCP (Mechanical Chemical Polishing) and the SiO 2  film is subsequently etched by an etch back process. As a result, a SiO 2  layer  8  is left on the i-layer substrate  1  and the N +  region  7  so as to surround the Si pillar  6 . Subsequently, the Si pillar  6  and the SiO 2  layer  8  are entirely covered with a hafnium oxide (HfO 2 ) layer  9  by ALD (Atomic Layer Deposition) and further covered with titanium nitride (TiN) layer  10 . After that, the Si pillar  6  and the region surrounding the Si pillar  6  are entirely covered with a SiO 2  layer  11  by CVD. Finally, the HfO 2  layer  9  serves as a gate insulating layer of an SGT and the TiN layer  10  serves as a gate conductor layer of the SGT. 
         [0117]    Subsequently, while a resist layer formed by lithography is used as a mask, as illustrated in  FIGS. 1DA to 1DC , the SiO 2  layer  11  and the TiN layer  10  are etched by RIE, to thereby provide a SiO 2  layer  11   a  and a TiN layer  10   a,  which extend from the upper surface of the Si pillar  6  to the upper surface of the SiO 2  layer  8 . 
         [0118]    Subsequently, as illustrated in  FIGS. 1EA to 1EC , a silicon nitride (SiN) layer  12   a  is formed so as to surround the Si pillar  6 . Subsequently, a resist layer  13  is formed on the SiN layer  12   a.  The resist layer  13  is formed in the following manner: a resist material is applied to the whole upper surface of the i-layer substrate  1 ; a heat treatment at 200° C., for example, is subsequently carried out to increase the flowability of the resist material; and the resist material is left at rest on the SiN layer  12   a  surrounding the Si pillar  6  until the resist material forms a flat layer. Subsequently, hydrogen fluoride gas (hereafter, referred to as “HF gas”) is supplied to the whole structure. Subsequently, heating is carried out at 180° C., for example, to cause electrolytic dissociation of HF gas with moisture contained within the resist layer  13  to thereby form hydrogen fluoride ions (HF 2   + ) (hereafter, referred to as “HF ions”). These HF ions diffuse through the resist layer  13  and etch a portion of the SiO 2  layer  11   a  that is in contact with the resist layer  13  (regarding the mechanism of this etching, refer to Tadashi Shibata, Susumu Kohyama and Hisakazu lizuka: “A New Field Isolation Technology for High Density MOS LSI”, Japanese Journal of Applied Physics, Vol. 18, pp. 263-267 (1979)). On the other hand, a portion of the SiO 2  layer  11  a that is not in contact with the resist layer  13  is substantially left without being etched off. After that, the resist layer  13  is removed. 
         [0119]    As a result of this process, as illustrated in  FIGS. 1FA to 1FC , the SiO 2  layer  11   a  is divided into a SiO 2  layer  11   b,  which is a region covered with the SiN layer  12   a,  and a SiO 2  layer  11   c,  which is an upper region on the Si pillar  6 . Subsequently, while the SiO 2  layers  11   b  and  11   c  are used as masks, the TiN layer  10   a  is etched to thereby divide the TiN layer  10   a  into a TiN layer  10   b,  which is a lower region disposed on the Si pillar  6  and covered with the SiO 2  layer  11   b,  and a TiN layer  10   c,  which is an upper region disposed on the Si pillar  6  and covered with the SiO 2  layer  11   c.  Subsequently, while the SiO 2  layers  11   b  and  11   c  and the TiN layers  10   b  and  10   c  are used as masks, the HfO 2  layer  9  is etched to thereby divide the HfO 2  layer  9  into a HfO 2  layer  9   a,  which is a lower region disposed on the Si pillar  6  and partially covered with the TiN layer  10   b,  and a HfO 2  layer  9   b,  which is an upper region disposed on the Si pillar  6  and covered with the TiN layer  10   c.  As a result, an opening  30   a  is formed in the side surface of the Si pillar  6 . After that, exposed portions of the TiN layers  10   b  and  10   c  are oxidized to form TiO (titanium oxide) layers  14   a  and  14   b.    
         [0120]    Subsequently, as illustrated in  FIGS. 1GA to 1GC , As atoms in the N +  region  7  are diffused into the i-layer substrate by heat treatment to form an N +  region  7   a.  Subsequently, the following bias sputtering is carried out, for example: a substrate metal plate on which the i-layer substrate  1  is placed and a counter metal plate are prepared such that the counter metal plate is separated from the substrate metal plate; a direct voltage is applied to the substrate metal plate and a RF high-frequency voltage is applied to these two parallel metal plates to thereby sputter material atoms from the counter metal plate and to deposit the atoms onto the i-layer substrate  1 . In this way, Ni atoms are directed in a direction perpendicular to the upper surface of the i-layer substrate  1  to thereby form a Ni layer  15   a  on the SiN layer  12   a  and to form a Ni layer  15   c  on the Si pillar  6 . Subsequently, bias sputtering is carried out to form a poly-Si layer  16   a  containing arsenic (As) impurity on the Ni layer  15   a  and to form a poly-Si layer  16   c  containing arsenic (As) atoms serving as a donor impurity on the Ni layer  15   c.  Subsequently, bias sputtering is carried out to direct SiO 2  atoms in a direction perpendicular to the upper surface of the i-layer substrate  1  to thereby form a SiO 2  layer  17   a  on the poly-Si layer  16   a  and to form a SiO 2  layer  17   c  on the poly-Si layer  16   c.  The process used for forming the Ni layer  15   a,  the poly-Si layer  16   a,  and the SiO 2  layer  17   a  is similarly used to form a Ni layer  15   b,  a poly-Si layer  16   b  containing boron (B) atoms serving as an acceptor impurity, and a SiO 2  layer  17   b  on the SiO 2  layer  17   a  and to form a Ni layer  15   d,  a poly-Si layer  16   d  containing boron (B) atoms, and a SiO 2  layer  17   d  on the SiO 2  layer  17   c.    
         [0121]    The Ni atoms, the poly-Si atoms, and the SiO 2  atoms are directed in a direction perpendicular to the upper surface of the i-layer substrate  1 . As a result, a space  18  is generated between the circumferential side surface of the Si pillar  6  and the Ni layers  15   a  and  15   b,  the poly-Si layers  16   a  and  16   b,  and the SiO 2  layers  17   a  and  17   b.    
         [0122]      FIG. 1GD  is an enlarged view of a dotted rectangle A in  FIG. 1GB . The SiO 2  layer  17   b  is formed such that the upper surface thereof is positioned at a level higher than the upper end of the space  18 . The SiO 2  layer  17   b  is in contact with the SiO 2  layer  11   c.  Thus, the space  18  is formed as a closed space. 
         [0123]    Subsequently, as illustrated in  FIGS. 1HA to 1HC , a heat treatment at 550° C., for example, is carried out to diffuse Ni atoms in the Ni layers  15   a  and  15   b  into the poly-Si layers  16   a  and  16   b  to thereby form nickel silicide (NiSi) layers  20   a  and  20   b.  The NiSi layers  20   a  and  20   b  are expanded in volume relative to the poly-Si layers  16   a  and  16   b  (regarding this expansion in volume, refer to T. Morimoto, T. Ohguro, H. Sasaki, M. S. Momose, T. linuma, I. Kunishima, K. Suguro, I. Katakabe, H. Nakajima, M. Tsuchiaki, M. Ono, Y. Katsumata, and H. Iwai: “Self-Aligned Nickel-Mono-Silicide Technology for High-Speed Deep Submicrometer Logic CMOS ULSI” IEEE Transaction on Electron Devices, Vol. 42, No. 5, pp. 915-922 (1995)). The poly-Si layer  16   a  is sandwiched between the SiN layer  12   a  and the SiO 2  layer  17   a.  The poly-Si layer  16   b  is sandwiched between the SiO 2  layers  17   a  and  17   b.  Accordingly, the NiSi layers  20   a  and  20   b  mainly expand into the space  18 . As atoms contained in the poly-Si layer  16   a  and B atoms contained in the poly-Si layer  16   b  are pushed outside the NiSi layers  20   a  and  20   b  (regarding this push-out phenomenon, refer to T. Morimoto, T. Ohguro, H. Sasaki, M. S. Momose, T. linuma, I. Kunishima, K. Suguro, I. Katakabe, H. Nakajima, M. Tsuchiaki, M. Ono, Y. Katsumata, and H. Iwai: “Self-Aligned Nickel-Mono-Silicide Technology for High-Speed Deep Submicrometer Logic CMOS ULSI” IEEE Transaction on Electron Devices, Vol. 42, No. 5, pp. 915-922 (1995)). As a result of this impurity-atom push-out effect, during formation of the NiSi layers  20   a  and  20   b,  protrusions  21   a  and  21   b  containing large amounts of impurity atoms are formed in the surface layers of side surfaces of the NiSi layers  20   a  and  20   b  protruding into the space  18 ; and, finally, the side surfaces of the protrusions  21   a  and  21   b  come into contact with the surface of the Si pillar  6 . During the above-described process, NiSi layers  20   c  and  20   d  and their protrusions  21   c  and  21   d  are simultaneously formed on the Si pillar  6  from the Ni layers  15   c  and  15   d  and the poly-Si layers  16   c  and  16   d.  After that, the NiSi layers  20   c  and  20   d,  the protrusions  21   c  and  21   d,  and the SiO 2  layers  17   c  and  17   d  on the Si pillar  6  are removed. 
         [0124]      FIG. 1HD  is an enlarged view of a dotted rectangle A in  FIG. 1HB . The side surface of the protrusion  21   a  containing a large amount of As atoms serving as a donor impurity and the side surface of the protrusion  21   b  containing a large amount of B atoms serving as an acceptor impurity are in contact with the side surface of the Si pillar  6 . The SiO 2  layer  17   b  is formed such that the upper surface thereof is at a level higher than the upper end of the space  18 . Thus, the NiSi layer  20   a  is sandwiched between the SiN layer  12   a  and the SiO 2  layer  17   a;  and the NiSi layer  20   b  is sandwiched between the SiO 2  layers  17   a  and  17   b.    
         [0125]    Subsequently, as illustrated in  FIGS. 1IA to 1IC , heat treatment is carried out to promote silicide formation for the NiSi layers  20   a  and  20   b  and to cause diffusion of As atoms and B atoms from the protrusions  21   a  and  21   b  into the Si pillar due to the impurity push-out effect. In the surface layer of the side surface of the Si pillar  6  in contact with the NiSi layers  20   a  and  20   b,  NiSi layers  31   a  and  31   b  are formed and As atoms and B atoms are diffused into the Si pillar  6  by the impurity push-out effect. Thus, an N +  region  2   a  and a P +  region  3   a  are formed. 
         [0126]    Subsequently, as illustrated in  FIGS. 1JA to 1JC , the NiSi layers  20   a  and  20   b  and the SiO 2  layers  17   a  and  17   b  are patterned by lithography and RIE to thereby provide NiSi layers  20   aa  and  20   bb  and SiO 2  layers  17   aa  and  17   bb.    
         [0127]    Subsequently, as illustrated in  FIGS. 1KA to 1KC , the process used for forming the SiN layer  12   a  is similarly used to form a SiN layer  12   b  such that the upper surface thereof is at an intermediate level relative to the height of the TiN layer  10   c.  Subsequently, the process used for forming the opening  30   a  is similarly used to form an opening  30   b  around the TiN layer  10   c.  Subsequently, a NiSi layer  22  is formed so as to be in contact with the TiN layer  10   c. Subsequently, a SiO   2  film  12   c  is formed by CVD over the entire structure such that the upper surface thereof is at a level higher than the surface of the NiSi layer  22  and lower than the top of the Si pillar  6 . After that, while the SiO 2  layer  12   c  is used as a mask, the SiO 2  layer  11   c,  the TiN layer  10   c,  and the HfO 2  layer  9   b  are etched to thereby provide a SiO 2  layer  11   d,  a TiN layer  10   d,  and a HfO 2  layer  9   c.  Subsequently, while the SiO 2  layers  11   d  and  12   c,  the TiN layer  10   d,  and the HfO 2  layer  9   c  are used as masks, boron (B) ions are implanted to form a P +  region  24  at the top of the Si pillar  6 . 
         [0128]    Subsequently, as illustrated in  FIGS. 1LA to 1LC , a SiO 2  layer  12   d  is formed over the entire structure by CVD and MCP. Subsequently, lithography and RIE are used to form a contact hole  28   a  so as to extend through the NiSi layer  22  to the TiN layer  10   b,  to form a contact hole  28   b  so as to extend to the top of the Si pillar  6 , to form a contact hole  28   c  so as to extend through the SiO 2  layer  17   bb,  the NiSi layer  20   bb,  the SiO 2  layer  17   aa,  and the NiSi layer  20   aa,  and to form a contact hole  28   d  so as to extend to the N +  region  7   a.  Subsequently, an input wiring metal layer Vin is formed so as to be electrically connected via the contact hole  28   a  to the NiSi layer  22  and the TiN layer  10   b;  and a power supply wiring metal layer Vdd is formed so as to be electrically connected via the contact hole  28   b  to the P +  region  24  at the top of the Si pillar  6 . An output wiring metal layer Vout is formed so as to be electrically connected via the contact hole  28   c  to the NiSi layers  20   aa  and  20   bb;  and a ground wiring metal layer Vss is formed so as to be electrically connected via the contact hole  28   d  to the N +  region  7   b.    
         [0129]    The above-described production method provides a CMOS inverter circuit including an N channel SGT and a P channel SGT. The N channel SGT includes the i layer  1   a,  which is in a lower region of the Si pillar  6  and functions as a channel; the HfO 2  layer  9   a,  which surrounds the i layer  1   a  and functions as a gate insulating layer; the TiN layer  10   b,  which surrounds the HfO 2  layer  9   a  and functions as a gate conductor layer; the N +  region  7   a,  which is positioned under the i layer  1   a  and functions as source; and the N +  region  2   a,  which is positioned on the i layer  1   a  and functions as a drain. The P channel SGT includes the i layer  1   b,  which is in an upper region of the Si pillar  6  and functions as a channel; the HfO 2  layer  9   c,  which surrounds the i layer  1   b  and functions as a gate insulating layer; the TiN layer  10   d,  which surrounds the HfO 2  layer  9   c  and functions as a gate conductor layer; the P +  region  3   a,  which is positioned below the i layer  1   b  and functions as a drain; and the P +  region  24 , which is positioned on the i layer  1   b  and functions as a source. 
         [0130]    In the step illustrated in  FIGS. 1HA to 1HD , the NiSi layers  20   a  and  20   b  expand into the space  18  and the protrusions  21   a  and  21   b  containing large amounts of donor or acceptor impurity atoms are connected to the side surface of the Si pillar  6 . Alternatively, these expansion and connection may be performed in another step after the step in  FIGS. 1HA to 1HD  as long as the structure illustrated in  FIGS. 1KA to 1KC  is provided. For example, the expansion and connection may be performed in the step illustrated in  FIGS. 1IA to 1IC . 
         [0131]    As illustrated in  FIGS. 1LB and 1LC , the NiSi layers  20   aa  and  20   bb  are preferably separated from the TiO layers  14   a  and  14   b,  which are formed by oxidizing the exposed portions of the TiN layers  10   b  and  10   d.  In this case, the presence of spaces (air layers) between the NiSi layers  20   aa  and  20   bb  and the TiN layers  10   b  and  10   d  further enhances insulation between the NiSi layers  20   aa  and  20   bb  and the TiN layers  10   b  and  10   d.  The TiO layers  14   a  and  14   b  may be omitted. In this case, spaces (air layers) are preferably formed between the NiSi layers  20   aa  and  20   bb  and the TiN layers  10   b  and  10   d.    
         [0132]    In order to enhance insulation, additional insulating layers may be formed on the end surfaces of the TiN layers  10   b  and  10   d.  For example, in the step illustrated in  FIGS. 1FA to 1FC , after the opening  30   a  is formed in the side surface of the Si pillar  6 , the exposed portion in the side surface of the Si pillar  6  and the entire structure may be covered with an additional insulating layer, for example, with a SiN layer and a SiO 2  layer by ALD, and a process similar to that used for forming the opening  30   a  may be used to form an opening. In such a case where an additional insulating layer is formed, in the step illustrated in  FIGS. 1HA to 1HD , the SiO 2  layer  17   a  and the additional insulating layer sandwich the NiSi layer  20   a  therebetween; the SiO 2  layer  17   a  is separated from the side surface of the Si pillar  6 ; and the additional insulating layer is in contact with the side surface of the Si pillar  6 . 
         [0133]    In the step illustrated in  FIGS. 1IA to 11C , formation of the N +  region  2   a  and the P +  region  3   a  is achieved by a single heat treatment. Alternatively, instead of formation of the N +  region  2   a  and the P +  region  3   a  by a single heat treatment, in the steps illustrated in  FIG. 1IA  to  FIG. 1LC , a plurality of heat treatments may be carried out to form the N +  region  2   a  and the P +  region  3   a  by the final production step for SGTs. 
         [0134]    The method for producing a CMOS inverter circuit according to the first embodiment provides the following advantages. 
         [0135]    1. As illustrated in  FIGS. 1IB and 1IC , the N +  region  2   a  is formed with the NiSi layer  20   a  serving as a diffusion source of the donor impurity As atoms, the NiSi layer  20   a  having a lower end positioned at the upper end of the TiN layer  10   b  serving as the gate of the lower SGT. Thus, in the lower SGT, the drain N +  region  2   a  and the gate TiN layer  10   b  are formed by self alignment. Similarly, the P +  region  3   a  is formed with the NiSi layer  20   b  serving as a diffusion source of the acceptor impurity B atoms, the NiSi layer  20   b  having an upper surface positioned at the lower end of the TiN layer  10   c  serving as the gate of the upper SGT. Thus, in the upper SGT, the drain P +  region  3   a  and the gate TiN layer  10   c  are formed by self alignment. The two self-alignment formations of the drains N +  region  2   a  and P +  region  3   a  and the gates TiN layers  10   b  and  10   c  are simultaneously achieved. This leads to a decrease in the capacitance between the drain N+region  2   a  and the gate TiN layer  10   b  and between the drain P +  region  3   a  and the gate TiN layer  10   c  and reduction in variations in SGT characteristics. 
         [0136]    2. In the inverter circuit, the drain N +  region  2   a  and P +  region  3   a,  which are formed so as to be in contact with each other, are formed not separately but simultaneously. This leads to cost reduction in the production of ICs (Integrated Circuits) including an SGT inverter circuit. In addition, such formation of the drain N +  region  2   a  and P +  region  3   a  at accurate relative positions advantageously allows formation of inverter circuits having reduced variations in performance. 
         [0137]    3. The NiSi layers  20   a  and  20   b,  which are impurity diffusion sources for forming the drain N +  region  2   a  and P +  region  3   a,  themselves serve as lead wiring material layers for the drain N +  region  2   a  and P +  region  3   a.  This leads to cost reduction in the production of ICs including an SGT inverter circuit. 
         [0138]    4. The NiSi layers  20   a,    20   b,    20   aa,  and  20   bb  are present from the step of forming the NiSi layers  31   a  and  31   b  within the Si pillar  6  to subsequent steps and play the role of suppressing collapse or bending of the Si pillar  6 . 
         [0139]    5. The contact hole  28   c  is formed so as to extend through the NiSi layer  20   aa,  the SiO 2  layer  17   aa,  and the NiSi layer  20   bb.  The output wiring metal layer Vout is formed in the contact hole  28   c.  As a result, in plan view, the NiSi layers  20   aa  and  20   bb  are mutually connected via a single contact hole, the contact hole  28   c.  This leads to reduction in the area of IC chips on which SGT inverter circuits are mounted and reduction in the production cost. 
         [0140]    6. Spaces (air layers) are present between the NiSi layers  20   aa  and  20   bb  and the TiN layers  10   b  and  10   d.  This further enhances insulation between the NiSi layers  20   aa  and  20   bb  and the TiN layers  10   b  and  10   d.    
       Second Embodiment 
       [0141]    Hereinafter, referring to  FIG. 2AA  to  FIG. 2B , a method for producing a CMOS inverter circuit including an SGT according to a second embodiment of the present invention will be described. The CMOS inverter circuit according to the second embodiment is produced by the same steps as those illustrated in  FIG. 1AA  to  FIG. 1LC  in the first embodiment except for the following difference in the structure. 
         [0142]    In this embodiment, instead of the NiSi layers  31   a  and  31   b,  as illustrated in  FIGS. 2AB and 2AC , a NiSi layer  32  connected to the side surfaces of the NiSi layers  20   aa  and  20   bb  is formed in the side surface of the Si pillar  6 . A contact hole  28   e  is formed such that the bottom surface thereof is at the surface of the SiO 2  layer  17   aa.  The contact hole  28   e  is used to mutually connect the output wiring metal layer Vout and the NiSi layer  20   bb.    
         [0143]      FIG. 2B  is an enlarged view of a dotted rectangle B in  FIG. 2AB . The silicide formation from the NiSi layers  20   a  and  20   b  into the Si pillar  6  in  FIGS. 1IB and 1IC  is isotropically expanded in the surface layer of the side surface of the Si pillar  6 . For example, by changing the thickness of the SiO 2  layer  17   aa,  the NiSi layer  32  connected to the side surfaces of the NiSi layers  20   aa  and  20   bb  can be formed in the surface layer of the side surface of the Si pillar  6 . 
         [0144]    In this embodiment, the N +  region  2   a  and the P +  region  3   a  are mutually connected via the low-resistance NiSi layer  32 . Accordingly, the direct connection between the output wiring metal layer Vout and the NiSi layer  20   aa  is not necessary. For this reason, the contact hole  28   e  may be formed such that the bottom surface thereof is within the NiSi layer  20   bb  or within the NiSi layer  20   aa.  This facilitates the formation of the contact hole  28   e.    
       Third Embodiment 
       [0145]    Hereinafter, referring to  FIG. 3AA  to  FIG. 3BC , a method for producing a CMOS inverter circuit including an SGT according to a third embodiment of the present invention will be described. The CMOS inverter circuit according to the third embodiment is produced by the same steps as those illustrated in  FIG. 1AA  to  FIG. 1LC  in the first embodiment except for the following difference in the structure. 
         [0146]    After the same steps as in  FIG. 1AA  to  FIG. 1FC  are carried out, as illustrated in  FIGS. 3AB and 3AC , heat treatment is carried out to diffuse As atoms in the N +  region  7  into the i-layer substrate to thereby form an N +  region  7   a.  Subsequently, bias sputtering, for example, is carried out to direct Ni atoms in a direction perpendicular to the upper surface of the i-layer substrate  1 , to thereby form a Ni layer  15   a  on the SiN layer  12   a  and form a Ni layer  15   c  on the Si pillar  6 . Subsequently, bias sputtering is carried out to form a poly-Si layer  29   a  not containing impurity atoms and a SiO 2  layer  17   a  on the Ni layer  15   a,  and to form a poly-Si layer  29   c  not containing impurity atoms and SiO 2  layer  17   c  on the Ni layer  15   c.  Subsequently, ion implantation is carried out to implant donor impurity As ions into the poly-Si layers  29   a  and  29   c.    
         [0147]    Subsequently, as illustrated in  FIGS. 3BB and 3BC , bias sputtering, for example, is carried out to direct Ni atoms in a direction perpendicular to the upper surface of the i-layer substrate  1 , to thereby form a Ni layer  15   b  on the SiO 2  layer  17   a  and form a Ni layer  15   d  on the SiO 2  layer  17   c.  Subsequently, bias sputtering is carried out to form a poly-Si layer  29   b  not containing impurity atoms and a SiO 2  layer  17   b  on the Ni layer  15   b  and to form a poly-Si layer  29   d  not containing impurity atoms and a SiO 2  layer  17   d  on the SiO 2  layer  17   c.  Subsequently, ion implantation is carried out to implant acceptor impurity B ions into the poly-Si layers  29   b  and  29   d.    
         [0148]    In  FIG. 3AA  to  FIG. 3BC , donor impurity As ions are implanted after deposition of the Ni layer  15   a,  the poly-Si layer  29   a,  and the SiO 2  layer  17   a;  and subsequently, acceptor impurity B ions are implanted after deposition of the Ni layer  15   b,  the poly-Si layer  29   b,  and the SiO 2  layer  17   b.  Alternatively, donor impurity As ions and acceptor impurity B ions may be implanted after the Ni layer  15   a,  the poly-Si layer  29   a,  the SiO 2  layer  17   a,  the Ni layer  15   b,  the poly-Si layer  29   b,  and the SiO 2  layer  17   b  are successively deposited. The ion implantations are carried out in the following manner: at an increased ion implantation voltage, the maximum distribution of As atoms is positioned in a lower layer, the poly-Si layer  29   a;  and the ion implantation voltage is changed such that the maximum distribution of B atoms is positioned in an upper layer, the poly-Si layer  29   b.  Thus, the poly-Si layer  29   a  containing donor impurity As atoms and the poly-Si layer  29   b  containing acceptor impurity B atoms are formed. 
         [0149]    In the third embodiment, ion implantation is used to introduce donor impurity and acceptor impurity into the poly-Si layers  29   a  and  29   b.  In the formation of a circuit including a plurality of Si pillars  6 , the Si pillars  6  are individually covered with a resist layer or exposed through openings in the resist layer patterned by lithography, for example, and subsequently donor or acceptor impurity atom ions are implanted, so that upper and lower SGTs of the Si pillars  6  can be each formed as an N channel SGT or a P channel SGT depending on the design of the circuit. In this way, various types of circuits can be formed on a wafer. 
       Fourth Embodiment 
       [0150]    Hereinafter, referring to  FIGS. 4A to 4C , a CMOS inverter circuit including an SGT according to a fourth embodiment of the present invention will be described. 
         [0151]    As illustrated in  FIGS. 4B and 4C , NiSi layers  31   c  and  31   d  are respectively formed within the N +  region  2   a  and the P +  region  3   a  within the Si pillar  6 . In the NiSi layers  31   c  and  31   d,  silicide is formed in the region from the side surfaces of the NiSi layers  20   aa  and  20   bb  to the center in cross section of the Si pillar  6 . In this case, the NiSi layers  31   c  and  31   d  may be in contact with each other. 
         [0152]    In  FIGS. 1LB and 1LC , the NiSi layers  31   a  and  31   b  are formed in the surface layer of the side surface of the Si pillar  6 . In contrast, in the fourth embodiment, the NiSi layers  31   c  and  31   d  corresponding to the NiSi layers  31   a  and  31   b  are formed by formation of silicide to the center of cross section of the Si pillar  6 . 
         [0153]    In the fourth embodiment, collapse or bending of the Si pillar  6  due to the presence of the NiSi layers  31   c  and  31   d,  which have an expansion coefficient different from that of the Si pillar  6  and are formed over the whole cross sections and at intermediate heights, can be suppressed by the NiSi layers  20   aa  and  20   bb,  which are left without being removed around the NiSi layers  31   c  and  31   d.  This configuration is more effective in a case where the Si pillar  6  has a small cross-section diameter. 
       Fifth Embodiment 
       [0154]    Hereinafter, referring to  FIGS. 5A to 5C , a CMOS inverter circuit including an SGT according to a fifth embodiment of the present invention will be described. 
         [0155]    As illustrated in  FIGS. 5B and 5C , a Si 1-x Ge x  layer  33  (for example, x=0.17) containing acceptor atoms is formed at the top of the Si pillar  6 . The Si 1-x Ge x  layer  33  corresponds to the P+region  24  in  FIGS. 1LB and 1LC  and serves as a drain layer of a P channel SGT. The Si 1-x Ge x  layer  33  produces stress due to the difference in Si-atom interplanar spacing between the Si 1-x Ge x  layer  33  and the Si pillar  6 , the stress being directed from the Si 1-x Ge x  layer  33  downward in the Si pillar  6 . The P +  region  3   a  positioned at an intermediate height of the Si pillar  6  is subjected to compressive stress applied by the NiSi layers  20   aa  and  20   bb,  which protrude and are connected to the circumference of the Si pillar  6 . This compressive stress has a stress component directed from the P +  region  3   a  upward in the Si pillar  6 . 
         [0156]    In the fifth embodiment, the channel layer  1   b  of a P channel SGT in the Si pillar  6 , the channel layer  1   b  being sandwiched between the Si 1-x Ge x  layer  33  and the P +  region  3   a,  is subjected to compressive stress applied by the Si 1-x Ge x  layer  33  and the P +  region  3   a.  This results in an increase in hole mobility and enhancement of the current drive capability of the P channel SGT (regarding a phenomenon in which compressive stress increases the hole mobility of a P channel MOS transistor, refer to, for example, S. E. Thompson, G. Sun, Y. S. Choi, and T. Nishida: “Uniaxial-Process-Induced-Si: Exteding the COM Roadmap”, IEEE Transaction on Electron Devices, Vol. 53, No. 5, pp. 1010-1020 (1995)). 
       Sixth Embodiment 
       [0157]    Hereinafter, referring to  FIG. 6AA  to  FIG. 6BC , a method for producing a CMOS inverter circuit including an SGT according to a sixth embodiment of the present invention will be described. The CMOS inverter circuit according to the sixth embodiment is produced by the same steps as those illustrated in  FIG. 1AA  to  FIG. 1LC  in the first embodiment except for the following difference in the structure. 
         [0158]    In the step illustrated in  FIGS. 1GA to 1GD , as illustrated in  FIGS. 6AA to 6AC , bias sputtering is carried out to direct material atoms in a direction perpendicular to the upper surface of the i-layer substrate  1  to thereby form, on a SiN layer  12   a,  a Ni layer  15   a,  an N-type poly-Si layer  16   a  containing arsenic (As) impurity, a SiO 2  layer  17   a,  a Ni layer  15   b,  an N-type poly-Si layer  16   b  containing arsenic (As) impurity, and a SiO 2  layer  17   b.    
         [0159]    Subsequently, referring to  FIGS. 6BA to 6BC , ion implantation is carried out to implant acceptor impurity B atoms into the poly-Si layer  16   b  such that the resultant concentration of the acceptor impurity is higher than the concentration of donor impurity originally contained in the poly-Si layer  16   b.  As a result, a P-type poly-Si layer  16   b  is provided. After that, the steps in  FIG. 1IA  to  FIG. 1LC  are carried out. 
         [0160]    In the sixth embodiment, the number of ion implantation steps carried out in the third embodiment can be reduced by half. For example, in order to provide lower and upper SGTs of different channel types in a plurality of Si pillars  6 , two steps of implanting ions of donor or acceptor impurity atoms into poly-Si layers  16   a  and  16   b  are necessary. In contrast, a single ion implantation step will suffice in the sixth embodiment. 
         [0161]    In the first embodiment, material atoms are directed in a direction perpendicular to the upper surface of the i-layer substrate  1  by bias sputtering to thereby form the Ni layers  15   a  and  15   b,  the poly-Si layers  16   a  and  16   b,  and the SiO 2  layers  17   a  and  17   b.  Alternatively, a process other than bias sputtering may be used as long as material atoms can be directed in a direction perpendicular to the upper surface of the i-layer substrate  1 . The same can be applied to other embodiments according to the present invention. 
         [0162]    In the first embodiment, the poly-Si layers  16   a  and  16   b  are turned into silicide to cause protrusion of the NiSi layers  20   a  and  20   b  into the space  18 . Instead of the Ni layers  15   a  and  15   b,  other metal layers such as titanium (Ti) layers or cobalt (Co) layers may be used to cause protrusion of silicide layers into the space  18 . The same can be applied to other embodiments according to the present invention. 
         [0163]    In the first embodiment, the Ni layers  15   a  and  15   b  are formed as lower layers and the poly-Si layers  16   a  and  16   b  containing a donor or acceptor impurity are formed as upper layers. Alternatively, the Ni layers  15   a  and  15   b  may be formed as upper layers and the poly-Si layers  16   a  and  16   b  containing a donor or acceptor impurity may be formed as lower layers. The same can be applied to other embodiments according to the present invention. 
         [0164]    In the first embodiment, two layers of the Ni layer  15   a  and the poly-Si layer  16   a  are formed, and two layers of the Ni layer  15   b  and the poly-Si layer  16   b  are formed; and the former and the latter are subsequently subjected to heat treatment to respectively form the NiSi layers  20   a  and  20   b.  Alternatively, each of the NiSi layers  20   a  and  20   b  may be formed from a plurality of Ni layers and a plurality of poly-Si layers. Alternatively, a Ni layer and another metal layer may be used to form a silicide layer. In the first embodiment, the poly-Si layers  16   a  and  16   b  are entirely turned into silicide to form the NiSi layers  20   a  and  20   b.  Alternatively, after the heat treatment, portions of the poly-Si layers  16   a  and  16   b  may remain. These portions of the poly-Si layers  16   a  and  16   b  may remain even after the final step of producing SGTs. The same can be applied to other embodiments according to the present invention. 
         [0165]    In the first embodiment, the Si pillar  6  is formed such that the side surface thereof substantially forms a right angle (about 90°) with the upper surface of the i-layer substrate  1 ; and material atoms are directed in a direction perpendicular to the upper surface of the i-layer substrate  1  by bias sputtering to thereby form the Ni layers  15   a  and  15   b,  the poly-Si layers  16   a  and  16   b,  and the SiO 2  layers  17   a  and  17   b.  In this embodiment, the side surface of the Si pillar  6  is set to form substantially a right angle with the upper surface of the i-layer substrate  1 , to thereby suppress deposition of Ni, Si, and SiO 2  material atoms on the side surface of the SiO 2  layer  11   c  surrounding the Si pillar  6 . The angle of the side surface of the Si pillar  6  may be less than 90° as long as Ni, Si, and SiO 2  material atoms are not deposited on the side surface of the SiO 2  layer  11   c  surrounding the Si pillar  6 . In a case of bias sputtering, for example, a bias voltage applied between a substrate electrode plate on which the i-layer substrate  1  is placed and a counter electrode plate separated from the i-layer substrate  1 , is controlled to thereby suppress deposition of Ni, Si, SiO 2  material atoms on the side surface of the SiO 2  layer  11   c  (regarding a basic technique of this process, refer to C. Y. Ting, V. J. Vivalda, and H. G. Schaefer: “Study of planarized sputter-deposited SiO 2 ” J. Vac. Sci. Technol, 15(3), May/Jun (1978)). Ni, Si, and SiO 2  material atoms that have deposited on the side surface of the SiO 2  layer  11   c  but can be easily etched off by diluted hydrofluoric acid, for example, do not cause a problem. The same can be applied to other embodiments according to the present invention. 
         [0166]    In the first embodiment, heat treatments are carried out in  FIG. 1HA  to  FIG. 11C  to connect the side surface of the Si pillar  6  and the NiSi layers  20   a  and  20   b,  to form the NiSi layers  31   a  and  31   b  in the Si pillar  6 , and to form the N +  region  2   a  and the P +  region  3   a.  These connection between the side surface of the Si pillar  6  and the NiSi layers  20   a  and  20   b,  formation of the NiSi layers  31   a  and  31   b  in the Si pillar  6 , and formation of the N +  region  2   a  and the P +  region  3   a  may be performed in other steps as long as they are performed by the final step of producing SGTs. The NiSi layers  20   a  and  20   b  may undergo changes in the Ni—Si content ratios and may be present as layers such as NiSi 2  layers in the final step of producing SGTs. The same can be applied to other embodiments according to the present invention. 
         [0167]    In the first embodiment, the poly-Si layers  16   a  and  16   b  are used. Alternatively, amorphous layers may be used. The same can be applied to other embodiments according to the present invention. 
         [0168]    In the first embodiment, the SiN layers  12   a  and  12   b,  which are single-material layers, are used. Alternatively, a SiO 2  layer serving as a lower layer and a SiN layer serving as an upper layer may be used. Instead of the SiN layers  12   a  and  12   b,  insulating material layers having a low diffusion coefficient of HF ions may be used. The same can be applied to other embodiments according to the present invention. 
         [0169]    In the fourth embodiment, silicide is formed to the center of cross section of the Si pillar  6  to form the NiSi layers  31   c  and  31   d.  The same, which does not cause any problems in SGT operations in other embodiments according to the present invention, can be applied to other embodiments. 
         [0170]    In the above-described embodiments, semiconductor pillars that are Si (silicon) pillars are used as examples. The technical idea of the present invention is not limited to these embodiments and can be applied to semiconductor devices including SGTs including semiconductor pillars formed of semiconductor materials other than silicon. 
         [0171]    In the above-described embodiments, the methods for producing a semiconductor device including two SGTs in a single Si pillar are described. However, the technical idea of the present invention is not limited to these methods and can also be applied to a method for producing a semiconductor device including one SGT or three or more SGTs in a single semiconductor pillar. 
         [0172]    In the first embodiment, an N channel SGT is formed in a lower portion of the Si pillar  6  and a P channel SGT is formed in an upper portion of the Si pillar  6 . The technical idea of the present invention can also be applied to a circuit in which a P channel SGT is formed in a lower portion of the Si pillar  6  and an N channel SGT is formed in an upper portion of the Si pillar  6 . The technical idea of the present invention can also be applied to a circuit in which N channel SGTs or P channel SGTs are formed in both of upper and lower portions of the Si pillar  6 . The same can be applied to other embodiments according to the present invention. 
         [0173]    In the above-described embodiments, SGTs have a configuration in which the HfO 2  layer (gate insulating layer)  9   c  is formed around a semiconductor pillar such as the Si pillar  6  and the TiN layer (gate conductor layer)  10   d  is formed around the HfO 2  layer  9   c.  However, the technical idea of the present invention is not limited to this configuration and can also be applied to a nonvolatile memory element in which an electrically floating conductor layer or a charge storage layer such as a SiN layer is disposed between a gate insulating layer and a gate conductor layer because this nonvolatile memory element is one type of SGTs. In this case, instead of a HfO 2  layer, a SiO 2  layer is preferably used as a tunnel oxide film. 
         [0174]    In the above-described embodiments, the technical idea of the present invention is applied to CMOS inverter circuits. Alternatively, the technical idea of the present invention can also be applied to other semiconductor devices such as circuits, devices, and elements. 
         [0175]    In the first embodiment, the gate conductor layers are the TiN layers  10   b  and  10   d.  The present invention is not limited to this embodiment and the gate conductor layers may be formed of another metal material. The gate conductor layers may have a multilayer structure including a metal layer and a poly-Si layer, for example. The impurity region constituted by the N +  region  2   a  and the P +  region  3   a  may have this configuration of impurity layers of different conductivity types, or may have a configuration of impurity layers of the same conductivity type. In a case where an impurity region is constituted by two impurity layers of the same conductivity type, these two impurity layers constitute as a whole a single impurity region of the same conductivity type. On the other hand, in a case where an impurity region is constituted by two impurity layers of different conductivity types, these two impurity layers similarly constitute as a whole a single impurity region. Such configurations can also be applied to other embodiments according to the present invention. 
         [0176]    In the first embodiment, the gate insulating layer is a HfO 2  layer. However, the present invention is not limited to this embodiment and the gate insulating layer may be formed of another insulating material. 
         [0177]    In the first embodiment, in  FIGS. 1FA to 1FC , after the opening  30   a  is formed in the side surface of the Si pillar  6 , exposed portions of the TiN layers  10   b  and  10   c  are oxidized to form the insulating TiO layers  14   a  and  14   b.  Alternatively, instead of the insulating TiO layers  14   a  and  14   b,  other insulating layers such as SiO 2  layers may be formed. For example, in  FIGS. 1FA to 1FC , a SiO 2  film may be formed by ALD so as to cover the entirety of the Si pillar  6 ; and subsequently the same process used for forming the opening  30   a  in  FIGS. 1EA to 1EC  may be carried out to form an opening while exposed portions of the TiN layers  10   b  and  10   c  are covered with the SiO 2  layer. In a case where the exposed portions of the TiN layers  10   b  and  10   d  in  FIGS. 1LA to 1LC  are not in contact with the NiSi layers  20   aa  and  20   bb,  the insulating TiO layers  14   a  and  14   b  may be omitted. In this case, the spaces between the TiN layer  10   b  and the NiSi layer  20   aa  and between the TiN layer  10   d  and the NiSi layer  20   bb  serve as insulating layers. 
         [0178]    In the above-described embodiments, the i-layer substrate  1  may be replaced by an SOI (Silicon on Insulator) substrate. 
         [0179]    In the first embodiment, the N +  region  2   a  is in contact with the P +  region  3   a.  Alternatively, the technical idea of the present invention can also be applied to a case where an insulating layer is formed between the N +  region  2   a  and the P +  region  3   a.  The same applies to other embodiments of the present invention. 
         [0180]    In the fifth embodiment, the Si 1-x Ge x  layer  33  producing stress directed downward in the Si pillar  6  is formed at the top of the Si pillar  6 . Alternatively, another material layer may be used that produces stress directed downward in the Si pillar  6  and serves as a source or drain of a P channel SGT. 
         [0181]    The present invention encompasses various embodiments and modifications without departing from the broad spirit and scope of the present invention. The above-described embodiments are used for explaining embodiments of the present invention and do not limit the scope of the present invention. The above-described embodiments and modifications can be combined in a desired manner. Even in the cases where some features in the above-described embodiments are omitted, these cases are in the scope of the technical idea of the present invention. 
         [0182]    A method for producing a pillar-shaped semiconductor device according to an embodiment of the present invention can provide semiconductor devices having high integration degrees.