Patent Publication Number: US-2010117157-A1

Title: Semiconductor device

Description:
The application is based on Japanese patent application No. 2008-289187, the content of which is incorporated hereinto by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a semiconductor device which is small and in which an influence of a positional deviation between a gate interconnect and a contact on the characteristics of a circuit is reduced. 
     2. Related Art 
       FIG. 22  is a plan view explaining the configuration of a known semiconductor device. In this semiconductor device, a transistor is formed in an element region. The transistor has two diffusion layers  520 , which become a source and a drain, and a gate interconnect  540 . The element region is divided by an element isolation layer, and the gate interconnect  540  extends over the element region and the element isolation layer. A contact  570  is connected to each of the two diffusion layers  520 , and a contact  560  is connected to the gate interconnect  540 . The contact  560  is connected to the gate interconnect  540  over the element isolation layer. 
     As the size of a semiconductor device has decreased in recent years, the width of the gate interconnect  540  is becoming smaller than the diameter of the contact  560 . In this case, if the positional deviation occurs in the contacts  560  and  570 , the contact area between the contact  570  and the gate interconnect  540  is reduced and the contact resistance increases accordingly. In order to suppress this, it is necessary to make wide a contact region  544  of the gate interconnect  540  where the contact  560  is connected, compared with other portions. 
     In this case, however, the periphery  542  of the contact region  544  also becomes gradually wide in the form dragged to the contact region  544 . When the periphery  542  is positioned over the diffusion layer  520 , the characteristics of a circuit including the transistor are changed. In order to prevent this, it is necessary to ensure the distance between the transistor and the contact region  544  to be equal to or larger than a predetermined value. An example of such a technique is disclosed in Japanese Unexamined patent publication NO. 2007-208058. 
     In addition, Domestic Re-publication of PCT International Application JP A1, 2003/098698 discloses the following method of manufacturing a semiconductor device. First, a gate insulating layer is formed over a predetermined region of a semiconductor substrate, and a gate electrode is formed over the gate insulating layer. Then, a source region and a drain region are formed in portions of the predetermined region which are located at both sides of the gate electrode when seen in a plan view, respectively, and a contact which electrically connects the gate electrode with a body region, which is a region excluding the source and drain regions of the predetermined region, is formed. Here, a portion of the contact connected to the gate electrode is formed so as to cross the gate electrode when seen in a plan view. 
     As described above, when the contact region of the gate interconnect where the contact is connected is made wider than other portions, the periphery of the contact region also becomes gradually wider. For this reason, it is necessary to ensure the distance between the transistor and the contact region to be equal to or more than the predetermined value. Therefore, in order to make a semiconductor device small, it is preferable not to make the contact region wide so that the influence of the positional deviation of a contact on the circuit characteristics is reduced. 
     SUMMARY 
     In one embodiment, there is provided a semiconductor device including: a substrate; an element isolation layer provided on said substrate; an element region divided by said element isolation layer; a gate interconnect including a sidewall and extending over said element region and said element isolation layer; an insulating layer on said substrate; and a contact connected to said gate interconnect with an upper and a side surface of said gate interconnect located over said element isolation layer through said insulating layer. A film thickness of said sidewall on said element isolation layer on said substrate is substantially equal to a film thickness of said sidewall on said element region. 
     According to the embodiment of the present invention, when the diameter of the contact (plug) is larger than the width of the gate interconnect, the contact (plug) is in contact with the upper surface of the gate interconnect and at least the upper portion of the sidewall. Accordingly, the connection resistance between the contact (plug) and the gate interconnect can be reduced. In addition, when the diameter of the contact (plug) is equal to or less than the width of the gate interconnect, even if the positional deviation of the contact occurs, an increase in connection resistance between the contact (plug) and the gate interconnect can be suppressed because the region of at least the upper portion of the sidewall of the gate interconnect is in contact with the contact. Accordingly, it is not necessary to make thick a region of the gate interconnect in contact with the contact (plug), and it is suppressed that the connection resistance becomes larger than the reference value even if the positional deviation of the contact occurs. As a result, an influence of the positional deviation of the contact on the circuit characteristics can be reduced while making the semiconductor device small. 
     According to the embodiment of the present invention, it is not necessary to make thick a region of the gate interconnect in contact with the contact (plug), and it is suppressed that the connection resistance becomes larger than the reference value even if the positional deviation of the contact occurs. As a result, an influence of the positional deviation of the contact on the circuit characteristics can be reduced while making the semiconductor device small. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1A and 1B  are sectional views showing a semiconductor device according to a first embodiment; 
         FIG. 2  is a plan view showing the semiconductor device shown in  FIGS. 1A and 1B ; 
         FIGS. 3A and 3B  are sectional views explaining a method of manufacturing a semiconductor device; 
         FIGS. 4A and 4B  are sectional views explaining a method of manufacturing a semiconductor device; 
         FIGS. 5A and 5B  are sectional views explaining a method of manufacturing a semiconductor device; 
         FIGS. 6A and 6B  are sectional views showing the configuration of a semiconductor device according to a second embodiment; 
         FIGS. 7A and 7B  are sectional views explaining a method of manufacturing the semiconductor device shown in  FIGS. 6A and 6B ; 
         FIGS. 8A and 8B  are sectional views showing the configuration of a semiconductor device according to a third embodiment; 
         FIGS. 9A and 9B  are sectional views showing the configuration of a semiconductor device according to a fourth embodiment; 
         FIGS. 10A and 10B  are sectional views explaining a method of manufacturing the semiconductor device shown in  FIGS. 9A and 9B ; 
         FIG. 11  is a sectional view showing a semiconductor device according to a fifth embodiment; 
         FIG. 12  is a sectional view showing a semiconductor device according to a sixth embodiment; 
         FIG. 13  is a sectional view showing a semiconductor device according to a seventh embodiment; 
         FIG. 14  is a sectional view showing a semiconductor device according to an eighth embodiment; 
         FIGS. 15A and 15B  are sectional views showing a method of manufacturing the semiconductor device shown in  FIG. 14 ; 
         FIGS. 16A and 168  are sectional views showing a method of manufacturing the semiconductor device shown in  FIG. 14 ; 
         FIG. 17  is a plan view showing a semiconductor device according to a ninth embodiment; 
         FIG. 18  is a plan view showing a semiconductor device according to a tenth embodiment; 
         FIG. 19  is a plan view showing a semiconductor device according to an eleventh embodiment; 
         FIGS. 20A and 20B  are plan views showing main parts of a semiconductor device according to a twelfth embodiment; 
         FIG. 21  is a plan view showing a semiconductor device according to a thirteenth embodiment; 
         FIG. 22  is a plan view explaining the configuration of a known semiconductor device; 
         FIG. 23  is the process flow of the first embodiment; and 
         FIG. 24  is the process flow of the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposed. 
     Hereinafter, embodiments will be described with reference to the accompanying drawings. In addition, the same components are denoted by the same reference numerals in all drawings, and the explanation will not be repeated.  FIGS. 1A and 1B  are sectional views showing the configuration of a semiconductor device according to a first embodiment, and  FIG. 2  is a plan view showing the semiconductor device shown in  FIGS. 1A and 1B .  FIG. 1A  is a sectional view taken along the line A-A′ of  FIG. 2 , and  FIG. 1B  is a sectional view taken along the line B-B′ of  FIG. 2 . 
     This semiconductor device includes an element region  174 , an element isolation layer  20 , a gate interconnect  140 , a sidewall  150 , and a contact (plug)  200 . The element isolation layer  20  is provided in a semiconductor layer  10 . The element region  174  is divided by the element isolation layer  20 . The gate interconnect  140  extends over the element region  174  and the element isolation layer  20 . The sidewall  150  is formed at a sidewall of the gate interconnect  140 . The contact (plug)  200  is connected to a portion of the gate interconnect  140  located over the element isolation layer  20 . In addition, the gate interconnect  140  has a region  144 , which is not covered by the sidewall  150 , at an upper portion of a side surface (sidewall) of a portion connected to the contact (plug)  200 . Moreover, in the region  144 , the gate interconnect  140  is in contact with the contact (plug)  200 . 
     Accordingly, as shown in the drawings, when the diameter of the contact (plug)  200  is larger than the width of the gate interconnect  140  in a horizontal plane including an upper surface of the gate interconnect  140 , the contact (plug)  200  is in contact with the upper surface and region  144  of the gate interconnect  140 . In this case, since the contact area between the contact (plug)  200  and the gate interconnect  140  becomes large, the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be reduced. Accordingly, even if positional deviation of the contact (plug)  200  occurs, it is suppressed that the connection resistance becomes larger than the reference value. As a result, the influence of the positional deviation of the contact (plug)  200  on the circuit characteristics can be reduced. 
     In addition, even if the diameter of the contact (plug)  200  is equal to or less than the width of the gate interconnect  140 , the region  144  of the gate interconnect  140  and the contact (plug)  200  are in contact with each other when the contact (plug)  200  protrudes from the gate interconnect  140  due to the positional deviation. In this case, an increase in the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be suppressed. Accordingly, even if positional deviation of the contact (plug)  200  occurs, it is suppressed that the connection resistance becomes larger than the reference value. As a result, an influence of the positional deviation of the contact (plug)  200  on the circuit characteristics can be reduced. 
     For this reason, the gate interconnect  140  may be formed in a straight line so that the width of a portion of the gate interconnect  140  connected to the contact (plug)  200  becomes equal to the width of a portion of the gate interconnect  140  located over the element region  174 . Accordingly, the gap between the adjacent element regions  174  can be narrowed. As a result, the degree of integration of the device can be improved. 
     The height of the region  144  is preferably equal to or more than ⅕ of the height of the gate interconnect  140 . In addition, the height of the region  144  is preferably 10 nm or more. More preferably, the height of the region  144  is 20 nm or more. In addition, the height of the sidewall  150  is equal in all portions of the gate interconnect  140 . Specifically, the height of the sidewall  150  in a portion where the gate interconnect  140  is connected to the contact (plug)  200  is equal to the height of the sidewall  150  located over the element region  174 . 
     The gate interconnect  140  includes a polysilicon layer  146  and a silicide layer  142  provided over the polysilicon layer  146 . The silicide layer  142  is not covered by the sidewall  150  in the region  144  of a part of the side surface of the gate interconnect  140  and the upper surface of the gate interconnect  140 , and is connected to (in contact with) the contact (plug)  200  in each of the portions. In this way, the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be reduced further. Although it is preferable that the entire side surface of the silicide layer  142  is the region  144 , a part of the side surface of the silicide layer  142  may be the region  144 . 
     In addition, two impurity diffusion layers  170  which become a source and a drain of a transistor are formed in the semiconductor layer  10  located in the element region  174 . The two impurity diffusion layers  170  are located opposite each other with a region forming a channel of the semiconductor layer  10 , which is located below the gate interconnect  140 , interposed therebetween. A silicide layer  172  is formed at a surface layer of the impurity diffusion layer  170 . The impurity diffusion layer  170  is connected to a contact (plug)  210  through the silicide layer  172 . The sectional shapes of the contacts (plugs)  200  and  210  are approximately circular. 
     In addition, a gate insulating layer  130  is formed below the gate interconnect  140 . The gate insulating layer  130  may be a high dielectric constant layer formed of a material with a higher relative dielectric constant than silicon oxide, may be a silicon oxide layer, or may be a laminated structure in which a high dielectric constant layer is formed over a silicon oxide layer. For example, the high dielectric constant layer is a silicate layer, such as an HfSiON layer or a ZrSiON layer, which contains N (nitrogen) and one or two or more elements selected from the group consisting of Hf, Zr, and lanthanoids. 
     Next, a method of manufacturing the semiconductor device shown in  FIGS. 1A ,  1 B, and  2  will be described using  FIGS. 3A to 5B  and the sectional views of  FIGS. 1A and 13 . The process flow of the present embodiment is shown in  FIG. 23 .  FIGS. 3A ,  4 A, and  5 A correspond to the sectional view taken along the line A-A′ of  FIG. 2 , and  FIGS. 3B ,  4 B, and  5 B correspond to the sectional view taken along the line B-B′ of  FIG. 2 . 
     First, as shown in  FIGS. 3A and 3B , the element isolation layer  20  is formed in the semiconductor layer  10 . The semiconductor layer  10  may be a semiconductor substrate or may be a semiconductor layer of an SOI substrate. The element isolation layer  20  has a shallow trench structure, for example. 
     Then, the gate insulating layer  130  and the gate interconnect  140  are formed over the semiconductor layer  10 , and then the sidewall  150  is formed. In this state, the silicide layer  142  is not formed in the gate interconnect  140 . After forming the gate interconnect  140 , the extension regions of the source and drain are formed using an ion implantation method before forming the sidewall  150 . 
     Then, the entire surface for exposing the sidewall  150  is etched back as shown in  FIGS. 4A and 4B . As a result, the sidewall  150  becomes small, and the region  144  which is not covered by the sidewall  150  is formed in an upper portion of each of the two side surfaces of the gate interconnect  140 . This etchback process may be performed simultaneously with an etchback process for forming the sidewall. In addition, the etchback is performed by dry etching. However, for example, the etchback may be performed by wet etching. In the present embodiment, the film thickness of the sidewall  150  formed in the element region  174  is approximately equal to the film thickness of the sidewall  150  formed over the element isolation layer  20 . 
     Then, as shown in  FIGS. 5A and 5B , the impurity diffusion layer  170  is formed using the ion implantation method, for example, so as to be self-aligned. 
     Then, as shown in  FIGS. 1A and 1B , a region where silicide is not to be formed among a region where silicon is exposed is covered by a silicide block layer (not shown in the drawings), and then a metal layer using Ni, Co, or the like is formed by the gas phase method and is heat-treated. As a result, the silicide layers  142  and  172  using nickel silicide or cobalt silicide, for example, are formed. Then, the metal layer which is not a silicide and the silicide block layer are removed. 
     Then, an interlayer insulating layer (not shown in the drawings) and a connection hole are formed, and a conductive layer (for example, a tungsten layer) is embedded in the connection hole. As a result, the contacts (plugs)  200  and  210  are formed. 
     As described above, according to the first embodiment, the gate interconnect  140  has the region  144 , which is not covered by the sidewall  150 , at the upper portion of the side surface of the portion connected to the contact (plug)  200 . Accordingly, when the diameter of the contact (plug)  200  is larger than the width of the gate interconnect  140  in the horizontal plane including the upper surface of the gate interconnect  140 , the contact area between the contact (plug)  200  and the gate interconnect  140  becomes large. As a result, the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be reduced. Thus, the influence of the positional deviation of the contact (plug)  200  on the circuit characteristics can be reduced. 
     For this reason, the gate interconnect  140  may be formed in a straight line so that the width of a portion of the gate interconnect  140  connected to the contact (plug) becomes approximately equal to the width of a portion of the gate interconnect  140  located over the element region  174 . As a result, the gap between the adjacent element regions  174  can be narrowed. In this way, the semiconductor device can be made small. 
     In addition, the silicide layer  142  of the gate interconnect  140  is in contact with the contact (plug)  200  in at least a part of the region  144  of the side surface of the gate interconnect  140  and the upper surface of the gate interconnect  140 . Accordingly, the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be reduced further. 
       FIGS. 6A and 6B  are sectional views showing a semiconductor device according to a second embodiment.  FIGS. 6A and 6B  correspond to  FIGS. 1A and 1B  in the first embodiment.  FIG. 6A  corresponds to the sectional view taken along the line A-A′ of  FIG. 2  in the first embodiment, and  FIG. 6B  corresponds to the sectional view taken along the line B-B′ of  FIG. 2  in the first embodiment. This semiconductor device is the same as that according to the first embodiment except that the sidewall  150  located in the element region  174  is higher than the sidewall  150  in a region where the gate interconnect  140  and the contact (plug)  200  are connected to each other and covers approximately the entire side surface of the gate interconnect  140 . That is, the region  144  is not formed in the gate interconnect  140  located in the element region. 
       FIGS. 7A and 7B  are sectional views explaining the method of manufacturing the semiconductor device shown in  FIGS. 6A and 6B .  FIG. 7A  corresponds to the sectional view taken along the line A-A′ of  FIG. 2 , and  FIG. 7B  corresponds to a sectional view taken along the line B-B′ of  FIG. 2 . A method of manufacturing the semiconductor device is the same as the method described using  FIGS. 1A and 1B  and  3 A to  5 B in the first embodiment except that the sidewall  150  and the gate interconnect  140  located in the element region  174  are covered by a mask layer  50 , such as a resist, in the process of forming the region  144  by forming the sidewall  150  low. The explanation will not be repeated. 
     Also in the second embodiment, the same effects as in the first embodiment can be achieved. In addition, the sidewall  150  located in the element region is higher than the sidewall  150  in the region where the gate interconnect  140  and the contact (plug)  200  are connected to each other and has approximately the same shape as the case where the region  144  is not formed. Accordingly, even if the manufacturing conditions are not changed, the characteristics of a transistor can be made to be approximately equal to those in the case where the region  144  is not formed. 
       FIGS. 8A and 8B  are sectional views showing a semiconductor device according to a third embodiment.  FIGS. 8A and 8B  correspond to  FIGS. 6A and 6B  in the second embodiment. Specifically,  FIG. 8A  corresponds to the sectional view taken along the line A-A′ of  FIG. 2  in the first embodiment, and  FIG. 8B  corresponds to the sectional view taken along the line B-B′ of  FIG. 2  in the first embodiment. This semiconductor device is the same as that according to the second embodiment except that the sidewall  150  is removed in the region where the gate interconnect  140  and the contact (plug)  200  are connected to each other. In addition, a method of manufacturing the semiconductor device according to the third embodiment is approximately the same as the method of manufacturing the semiconductor device according to the second embodiment. 
     Also in the third embodiment, the same effects as in the second embodiment can be achieved. Moreover, since approximately the entire side surface of the gate interconnect  140  is in contact with the contact (plug), the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be reduced further. 
       FIGS. 9A and 9B  are sectional views showing a semiconductor device according to a fourth embodiment.  FIGS. 9A and 9B  correspond to  FIGS. 1A and 1B  in the first embodiment. Specifically,  FIG. 9A  corresponds to the sectional view taken along the line A-A′ of  FIG. 2 , and  FIG. 9B  corresponds to the sectional view taken along the line B-B′ of  FIG. 2 . This semiconductor device has the same configuration as that in the first embodiment except that the sidewall  150  is formed by a sidewall body  154  and a base layer  152 , the region  144  is formed by removing an upper portion of the base layer  152  without removing the sidewall body  154  and a notch shape, in which the contact (plug)  200  goes through the space where the base layer  152  is removed, is formed. The base layer  152  is located between the sidewall body  154  and the gate interconnect  140  and between the sidewall body  154  and the semiconductor layer  10  or the element isolation layer  20 . The thickness of the base layer  152  is equal to or more than 5 nm and equal to or less than 20 nm, for example. 
       FIGS. 10A and 10B  are sectional views explaining a method of manufacturing the semiconductor device shown in  FIGS. 9A and 9B .  FIGS. 10A and 10B  correspond to the sectional view taken along the line B-B′ of  FIG. 2  in the first embodiment. The process flow of the present embodiment is shown in  FIG. 24 . The gate interconnect  140  is formed, and the extension regions of the source and drain are formed by ion implantation as necessary. After forming the sidewall  150  formed by the base layer  152  and the sidewall body  154 , a process of performing etching of the sidewall  150  for gate sidewall exposure of a contact region is not performed. Then, the source and drain impurity diffusion layers  170  are formed by the ion implantation method and annealing. After forming a silicide block layer similar to the first embodiment, a metal layer for formation of silicide is formed and heat treatment or the like is performed to thereby form the silicide layers  142  and  172  over the source and drain impurity diffusion layers  170 . Then, the metal layer which is not silicided and the silicide block layer are removed. 
     Then, a stopper layer  300  and an interlayer insulating layer  310  are formed in this order over a transistor of the element region, the gate interconnect  140 , and the element isolation layer  20 . The stopper layer  300  is formed of a material whose etching selectivity is higher than that of the interlayer insulating layer  310  and is lower than that of the base layer  152 . For example, when the base layer  152  is formed of SiN and the interlayer insulating layer  310  is formed of SiO2, SiN which is the same material as the base layer  152  may be used for the stopper layer  300 . 
     Subsequently, as shown in  FIG. 10B , a mask pattern  52  is formed and then etching is performed using the stopper layer  300  as a stopper. As a result, a connection hole  200   a  is formed in the interlayer insulating layer  310 . Then, the stopper layer  300  is etched. As a result, the connection hole  200   a  passes through the stopper layer  300 . In etching of the stopper layer  300 , an upper portion of the base layer  152  is removed such that the notch shape is formed. As a result, the region  144  is formed. 
     Then, the mask pattern  52  is removed. Subsequently, a conductive layer is embedded in the connection hole  200   a.    
     As a result, the contact (plug)  200  is formed. Moreover, in the above process, the contact (plug)  210  shown in  FIG. 2  in the first embodiment is also formed. In the present embodiment, the film thickness of the sidewall  150  formed in the element region  174  is approximately equal to the film thickness of the sidewall  150  formed over the element isolation layer  20 . 
     Also in the fourth embodiment, the same effects as in the first embodiment can be achieved since the contact (plug)  200  goes through the space where the base layer  152  is removed. Here, in Japanese Unexamined Patent Publication NO. 2007-208058, a sidewall of a necessary place is removed using a mask after forming source and drain impurity diffusion layers. In this case, if this process is removed, the sidewall on the source and drain impurity diffusion layers  170  recedes. Then, since the bonding boundary position of the source and drain impurity diffusion layers  170  and the position of the silicide are brought close to each other, P/N bonding leakage occurs in this portion. In the present embodiment, the region  144  can be formed in the process of forming the connection hole  200   a  while reducing the mask process for removing the sidewall. Accordingly, the number of processes for manufacturing the semiconductor device is not increased, and the P/N bonding leakage does not occur. 
     Moreover, in the fourth embodiment, after forming the base layer  152  and the sidewall body  154 , the sidewall  150  may be etched back at least in the region where the gate interconnect  140  and the contact (plug)  200  are connected to each other before forming the stopper layer  300 , similar to the first or second embodiment. 
       FIG. 11  is a sectional view showing a semiconductor device according to a fifth embodiment.  FIG. 11  corresponds to the sectional view taken along the line B-B′of  FIG. 2  in the first embodiment. This semiconductor device is the same as the semiconductor device according to the first embodiment except that approximately the entire gate interconnect  140  is formed by the silicide layer  142 . A method of manufacturing the semiconductor device according to the fifth embodiment is the same as that in the first embodiment. Also in the fifth embodiment, the same effects as in the first embodiment can be achieved. 
       FIG. 12  is a sectional view showing a semiconductor device according to a sixth embodiment.  FIG. 12  corresponds to the sectional view taken along the line B-B′ of  FIG. 2  in the first embodiment. This semiconductor device is the same as the semiconductor device according to the first embodiment except that the gate interconnect  140  has a structure where a metal layer  145  for work function control, a polysilicon layer  146 , and a silicide layer  142  are laminated in this order. A method of manufacturing the semiconductor device according to the sixth embodiment is the same as that in the first embodiment that the metal layer  145  and the polysilicon layer  146  are laminated in this order and this laminated layer is selectively removed to thereby except form the gate interconnect  140 . The silicide layer  142  is formed by the same process as in the first embodiment. The metal layer  145  for work function control may be formed of La, for example, when a transistor in the element region is an N-channel MOSFET and may be formed of Al, for example, when a transistor in the element region is a P-channel MOSFET. Also in the sixth embodiment, the same effects as in the first embodiment can be achieved since the silicide layer  142  is in contact with the contact (plug)  200  in the region  144 . 
       FIG. 13  is a sectional view showing a semiconductor device according to a seventh embodiment.  FIG. 13  corresponds to the sectional view taken along the line B-B′ of  FIG. 2  in the first embodiment. This semiconductor device is the same as the semiconductor device according to the first embodiment except that the gate interconnect  140  has a structure where a metal layer  145  for work function control and a low resistance layer  148  are laminated in this order. The low resistance layer  148  is a metal layer, for example. However, the low resistance layer  148  may be a silicide layer. 
     A method of manufacturing the semiconductor device according to the seventh embodiment is the same as the method of manufacturing the semiconductor device according to the sixth embodiment when the low resistance layer  148  is a silicide layer. Moreover, the method of manufacturing the semiconductor device when the low resistance layer  148  is a metal layer is the same as that in the first embodiment except that the metal layer  145  and the low resistance layer  148  are laminated in this order and this laminated layer is selectively removed to thereby form the gate interconnect  140 . Also in the seventh embodiment, the same effects as in the first embodiment can be achieved since the region  144  is the low resistance layer  148  and the low resistance layer  148  is in contact with the contact (plug)  200 . 
       FIG. 14  is a sectional view showing a semiconductor device according to an eighth embodiment.  FIG. 14  corresponds to the sectional view taken along the line B-B′ of  FIG. 2  in the first embodiment. This semiconductor device is the same as the semiconductor device according to the first embodiment except that the metal layer  145  for work function control is provided at bottom and side surfaces of the gate interconnect  140  and the remaining portion of the gate interconnect  140  is formed by a metal layer  149 . 
       FIGS. 15A to 16B  are views showing a method of manufacturing the semiconductor device according to the eighth embodiment. In the drawings,  FIGS. 15A and 16A  correspond to the sectional view taken along the line A-A′ of  FIG. 2  in the first embodiment, and  FIGS. 158 and 168  correspond to the sectional view taken along the line B-B′ of  FIG. 2  in the first embodiment. First, as shown in  FIGS. 15A and 15B , a transistor having a dummy gate interconnect  180  instead of the gate interconnect  140  is formed. Although a material of the dummy gate interconnect  180  is not particularly limited, for example, polysilicon may be used. A method of forming the transistor is the same as the method of forming a transistor in the first embodiment. In this step, a region  182  which is not covered by the sidewall  150  is formed at the side surface of the dummy gate interconnect  180 . A method of forming the region  182  is the same as the method of forming the region  144  in the first embodiment. 
     Then, a stopper layer  300  and an interlayer insulating layer  310  are formed in this order over a transistor of the element region, the dummy gate interconnect  180 , and the element isolation layer  20 . Then, the interlayer insulating layer  310  and the stopper layer  300  are polished by the chemical mechanical polishing (CMP) method in order to expose an upper surface of the dummy gate interconnect  180 . 
     Then, as shown in  FIGS. 16A and 16B , the dummy gate interconnect  180  is removed by etching to thereby form a hole  185 . 
     Then, the metal layer  145  and the metal layer  149  are laminated in this order over the stopper layer  300  and the interlayer insulating layer  310  within the hole  185 , and the metal layers  145  and  149  over the stopper layer  300  and the interlayer insulating layer  310  are removed by the CMP method. As a result, the gate interconnect  140  shown in  FIG. 14  is formed. In the gate interconnect  140 , the region  144  is formed in a portion corresponding to the region  182  in the dummy gate interconnect  180 . In addition, the length of the region  144  in the height direction becomes shorter than that of the region  182  because the region  144  is processed by the CMP method. In the region  144 , the metal layer  145  is located at the surface. Then, an interlayer insulating layer is formed again and the contacts (plugs)  200  and  210  are embedded in the interlayer insulating layer. 
     Also in the eighth embodiment, the same effects as in the first embodiment can be achieved since the metal layer  145  is located at the surface in the region  144 . 
       FIG. 17  is a plan view showing a semiconductor device according to a ninth embodiment.  FIG. 17  is a view corresponding to  FIG. 2  in the first embodiment. This semiconductor device is the same as those according to the first to eighth embodiments except that the sectional shape of the contact (plug)  200  is elliptical and the long axis of the ellipse is inclined with respect to the width direction of the gate interconnect  140 . In addition, a method of manufacturing the semiconductor device according to the ninth embodiment is approximately the same as the method of manufacturing the semiconductor device according to any one of the first to eighth embodiments. It is preferable that the long axis of the contact (plug)  200  is parallel to the extending direction of the gate interconnect. 
     According to the ninth embodiment, the same effects as in the first to eighth embodiments can be achieved. In addition, since the long axis of the contact (plug)  200  is inclined with respect to the width direction of the gate interconnect  140 , the contact area between the contact (plug)  200  and the region  144  provided at the side surface of the gate interconnect  140  becomes large. Accordingly, the connection resistance between the contact  200  and the gate interconnect  140  can be reduced further. 
       FIG. 18  is a plan view showing a semiconductor device according to a tenth embodiment.  FIG. 18  is a view corresponding to  FIG. 2  in the first embodiment. This semiconductor device is the same as the semiconductor device according to the ninth embodiment except that the gate interconnect  140  is divided in a portion connected with the contact (plug)  200  and a divided portion  140   a  of the gate interconnect  140  is embedded by the contact (plug)  200 . The length L of the divided portion  140   a  of the gate interconnect  140  is smaller than the width W 1  of the gate interconnect  140 . The region  144  is also formed in the end surface of the divided portion  140   a  of the gate interconnect  140 . The gate interconnect  140  is in contact with the contact (plug)  200  in each region  144  of the upper surface, side surface, and end surface. A method of manufacturing the semiconductor device according to the tenth embodiment is the same as that in the ninth embodiment. Moreover, in  FIG. 18 , the contact (plug)  200  is shown by a dotted line for explanation. 
     Also in the tenth embodiment, the same effects as in the ninth embodiment can be achieved. In addition, since the division length L of the gate interconnect  140  is smaller than the width W of the gate interconnect  140 , the contact area between the gate interconnect  140  and the contact (plug)  200  becomes large compared with the case where the gate interconnect  140  is not divided. Accordingly, the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be reduced further. 
       FIG. 19  is a plan view showing a semiconductor device according to an eleventh embodiment.  FIG. 19  is a view corresponding to  FIG. 2  in the first embodiment. This semiconductor device is the same as that according to the ninth embodiment except from that the long axis of the contact (plug)  200  is parallel to the width direction of the gate interconnect  140 . A method of manufacturing the semiconductor device according to the eleventh embodiment is the same as that in the ninth embodiment. 
     Also in the eleventh embodiment, the same effects as in the first embodiment can be achieved. In addition, since the long axis of the contact (plug)  200  is parallel to the width direction of the gate interconnect  140 , an increase in connection resistance between the contact (plug)  200  and the gate interconnect  140  can be suppressed even when the position of the contact (plug)  200  deviates in the width direction of the gate interconnect  140 . 
       FIGS. 20A and 20B  are plan views showing the main parts of a semiconductor device according to a twelfth embodiment. The semiconductor device according to the twelfth embodiment is the same as those according to the first to eleventh embodiments except that the gate interconnect  140  has an auxiliary pattern  140   b  in a portion connected to the contact (plug)  200 . The auxiliary pattern  140   b  extends in a direction crossing the main body of the gate interconnect  140 . The width W 2  of the auxiliary pattern  140   b  is narrower than the diameter of the contact (plug)  200 . The configuration of the auxiliary pattern  140   b  is the same as that of the gate interconnect  140 , and has the region  144  at the side surface. Moreover, in  FIGS. 20A and 20B , the contact (plug)  200  is shown by a dotted line for explanation. 
     The auxiliary pattern  140   b  may extend from one side surface of the main body of the gate interconnect  140  as shown in  FIG. 20A  or may extend from each of two side surfaces of the main body of the gate interconnect  140  as shown in  FIG. 20B . For example, the auxiliary pattern  140   b  extends in a direction perpendicular to the gate interconnect  140 . A method of manufacturing the semiconductor device according to the twelfth embodiment is the same as the method of manufacturing the semiconductor device according to any one of the first to eleventh embodiments except that the auxiliary pattern  140   b  is formed when forming the main body of the gate interconnect  140 . 
     Also in the twelfth embodiment, the same effects as in the first to eleventh embodiments can be achieved. In addition, since the region  144  of the auxiliary pattern  140   b  is in contact with the contact (plug)  200 , the connection resistance between the contact (plug)  200  and the gate interconnect  140  can be reduced further. 
       FIG. 21  is a plan view showing the configuration of a semiconductor device according to a thirteenth embodiment.  FIG. 21  corresponds to  FIG. 2  in the first embodiment and is the same as the first embodiment except that the diameters of the contacts (plugs)  200  and  210  are equal to or less than the width of the gate interconnect  140 . Hereinafter, the same components as in the first embodiment are denoted by the reference numerals, and the explanation will not be repeated. 
     When the contact (plug)  200  protrudes from the gate interconnect  140 , the region  144  of the gate interconnect  140  and the contact (plug)  200  are in contact with each other. Accordingly, an increase in connection resistance between the contact (plug)  200  and the gate interconnect  140  can be suppressed. Thus, also in the thirteenth embodiment, even if the positional deviation of the contact occurs, it is suppressed that the connection resistance becomes larger than the reference value. As a result, an influence of the positional deviation of the contact on the circuit characteristics can be reduced. 
     In addition, if the diameters of the contacts (plugs)  200  and  210  are set to be equal to or less than the width of the gate interconnect  140  like the thirteenth embodiment in the semiconductor devices according to the second to seventh and ninth to twelfth embodiments, the same effects as in the thirteenth embodiment can be acquired. 
     While the first to thirteenth embodiments of the present invention have been described with reference to the drawings, these are only illustration of the present invention, and other various configurations may also be adopted. 
     For example, in the methods of manufacturing the semiconductor devices according to the first to seventh and ninth to thirteenth embodiments, the process of forming the region  144  by forming the sidewall  150  low may be performed after the process of forming the impurity diffusion layer  170 . 
     Moreover, in this case, after forming the impurity diffusion layer  170 , the process of forming the suicide block film described using  FIGS. 1A and 1B  may be performed before the process of forming the region  144 . In this case, after the silicide block film is formed, the region  144  is formed and then the silicide layers  142  and  172  are formed. 
     Moreover, in the methods of manufacturing the semiconductor devices according to the first to seventh and ninth to thirteenth embodiments, the process of forming the region  144  by forming the sidewall  150  to be low may be performed after the process of forming the suicide layers  142  and  172 . 
     In addition, the following invention is also disclosed in the above embodiments. That is, there is disclosed a semiconductor device including: an element isolation layer provided in a semiconductor layer; an element region divided by the element isolation layer; a gate interconnect which extends linearly over the element region and the element isolation layer; and a contact (plug) which is connected to the gate interconnect located over the element isolation layer and of which the diameter of a section is larger than the width of the gate interconnect. 
     It is apparent that the present invention is not limited to the above embodiment, but may be modified and changed without departing from the scope and spirit of the invention.