Abstract:
A semiconductor device includes a substrate having first and second device regions separated from each other by a device isolation region, a first field effect transistor having a first polysilicon gate electrode and formed in the first device region, a second field effect transistor having a second polysilicon gate electrode and formed in the second device region, a polysilicon pattern extending over the device isolation region from the first polysilicon gate electrode to the second polysilicon gate electrode, and a silicide layer formed on a surface of the first polysilicon gate electrode, a surface of said the polysilicon gate electrode and a surface of the polysilicon pattern so as to extend on the polysilicon pattern from the first polysilicon gate electrode to the second polysilicon gate electrode, the silicide layer having a region of increased film thickness on the polysilicon pattern, wherein the silicide layer has a surface protruding upward in the region of increased film thickness.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on Japanese priority application No. 2004-178442 filed on Jun. 16, 2004, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to semiconductor devices and more particularly to a semiconductor device having polysilicon wiring. 
     A CMOS device is a semiconductor device comprising a p-channel MOS transistor and an n-channel MOS transistor formed on a common semiconductor substrate and has a construction in which respective polysilicon gate electrodes are connected with each other. 
     With the CMOS device of such a construction, the gate electrode of the p-channel MOS transistor and the gate electrode of the n-channel MOS transistor are formed respectively of p-type and n-type polysilicon having a generally equal work function, and thus, an advantageous feature of the p-channel MOS transistor and the n-channel MOS transistor having generally equal threshold characteristics is attained. 
     REFERENCES 
     
         
         (Patent Reference 1) Japanese Laid Open Patent Application 10-12745 official gazette 
         (Patent Reference 2) Japanese Laid Open Patent Application 10-74846 official gazette 
         (Patent Reference 3) Japanese Laid Open Patent Application 11-26767 official gazette 
       
    
     SUMMARY OF THE INVENTION 
     In recent high-speed or ultrahigh speed CMOS devices, the thickness of the gate insulation film is reduced to 2 nm or less according to the scaling low with miniaturization of the p-channel or n-channel MOS transistor constituting the CMOS device. 
     In such high-speed or ultrahigh speed CMOS devices, on the other hand, it is practiced to form a low-resistance silicide layer on the surface of the polysilicon gate electrode and on the surface of the source and drain regions in order to reduce the gate resistance and to reduce the contact resistance of the source and drain regions. It should be noted that such a silicide layer is formed also on the polysilicon pattern connecting the gate electrode of the p-channel MOS transistor and the gate electrode of the n-channel MOS transistor. Generally, such a silicide layer is formed by a so-called salicide process in which a metal film is deposited on the silicon substrate so as to cover the polysilicon gate electrode and the source and the drain regions and silicide is formed by causing the metal film thus deposited to react with the polysilicon pattern constituting the gate electrode and the part of the silicon substrate constituting the source and drain regions. 
       FIGS. 1A and 1B  show the construction of such a conventional CMOS device  10 , wherein  FIG. 1A  shows the CMOS device  10  in a plan view while  FIG. 1B  shows the same device in a cross-sectional view. 
     Referring to  FIGS. 1A and 1B , the CMOS device  10  is formed on a silicon substrate  11  wherein the silicon substrate  11  is formed with a device region  11 A for the p-channel MOS transistor  10 A and a device region  11 B for the n-channel MOS transistor  10 B separated from each other by a device isolation structure  12 . 
     It should be noted that the p-channel MOS transistor  10 A includes a gate electrode  14 A formed on the silicon substrate  11  via a gate insulation film  13 A in the device region  11 A, and a silicide layer  14   a  is formed on the gate electrode  14 A. Further, in the device region  11 A, p-type diffusion regions  11   a  and  11   b  are formed in the silicon substrate  11  at both lateral sides of the gate electrode  14 A, and silicide layers  11   c  and  11   d  are formed on the respective surfaces of the p-type diffusion regions  11   a  and  11   b.    
     Similarly, the n-channel MOS transistor  10 B includes, in the device region  11 B, a gate electrode  14 B formed on the silicon substrate  11  via a gate insulation film  13 B, and a silicide layer  14   b  is formed on the gate electrode  14 B. Further, in the device region  11 B, there are formed n-type diffusion regions  11   e  and  11   f  in the silicon substrate  11  at both lateral sides of the gate electrode  14 B, and silicide layers  11   g  and  11   h  are formed on the respective surfaces of the p-type diffusion regions  11   e  and  11   f.    
     As can be seen from the plan view of  FIG. 1A , the gate electrode  14 A and the gate electrode  14 B are connected with each other by a polysilicon pattern  14 C extending over the device isolation structure  12 , and a silicide layer  14   c  is formed on the polysilicon pattern  14 C in continuation with the silicide layers  14   a  and  14   b . Thereby, the gate electrode  14 A is doped to the p-type and the gate electrode  14 B is doped to the n-type, while the polysilicon pattern  14 C is undoped except of the parts connected to the gate electrode  14 A and the gate electrode  14 B. 
     In the cross-sectional diagram of  FIG. 1B , there is further formed an interlayer insulation film  15  on the substrate  11  so as to cover the gate electrodes  14 A and  14 B and further the polysilicon pattern  14 C, and contact plugs  16 A,  16 B,  16 C and  16 D are formed in the interlayer insulation film in contact with the diffusion regions  11   a ,  11   b ,  11   e  and  11   f  respectively, via respective silicide layers  11   c ,  11   d ,  11   g  and  11   h.    
     In such a CMOS device, on the other hand, there is a need of decreasing the thickness of the gate insulation films  13 A and  13 B in correspondence to the gate length thereof in the case the gate length of the p-channel MOS transistor  10 A or the n-channel MOS transistor  10 B is decreased for improvement of the operational speed. Associated with this, the thickness of the gate electrodes  13 A and  13 B, and hence the height thereof, is reduced, and as a result, there can occur the problem that the metal film deposited at the time of formation of the silicide layer  14   a  comes close the gate insulation film  13 A and the metal film deposited at the time of formation of the silicide layer  14   b  comes close to the gate insulation film  13 B. In such a case, there can occur diffusion of metal element from the metal film into the gate insulation film  13 A or  13 B, leading to formation of defects in the gate insulation film  13 A or  13 B. Further, associated with such formation of defects in the gate insulation film  13 A or  13 B, there arises a problem of increase of occurrence of so-called B-mode failure in which the lifetime of the semiconductor device is reduced with increase of the gate leakage current. 
     In order to avoid such B-mode failure, it is conceivable to reduce the thickness of the metal film deposited at the time of formation of the silicide layer in such a salicide process, while such an approach can lead to localized formation of region  14   x  lacking silicide as shown in  FIGS. 2A and 2B . In  FIGS. 2A and 2B , it should be noted that those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted. 
     When such a region  14   x  lacking silicide is formed on the polysilicon gate electrode  14 A or  14 B doped heavily to the p-type or n-type and thus having a sheet resistance of several ten Ω/□ or so, the electric current flowing therein avoids such a region  14   x  not formed with silicide and flows through the polysilicon pattern constituting the gate electrode  14 A or  14 B. Because of this, no particular problem such as disconnection or remarkable increase of resistance is caused. In the case the region  14   x  lacking silicide is formed on the non-doped polysilicon pattern  14 C extending over the device isolation region  12 , on the other hand, there is formed no alternative current path in view of the fact that the polysilicon layer underneath the silicide layer  14   c  has a very large sheet resistance of several MΩ/□, and there can be caused a serious problem such as disconnection or increase of resistance. 
     Contrary to this, Patent Reference 1 discloses the technology for avoiding the problem of  FIGS. 2A and 2B  by increasing the thickness of the silicide layer on the non-doped polysilicon pattern as compared with the silicide layer formed on the p-type or n-type pattern, by utilizing the phenomenon that the titanium silicide layer formed by a salicide process takes different thicknesses between the cases in which the silicide layer is formed on a non-doped polysilicon pattern and in which the silicide layer is formed on a doped polysilicon pattern doped to p-type or n-type. 
       FIG. 3  shows the construction of the polysilicon pattern according to the foregoing Patent Reference 1. 
     Referring to  FIG. 3 , there are formed device regions  1 A and  1 B on a silicon substrate  1  by an insulating device isolation film  2 , and a polysilicon pattern  3  is formed on the silicon substrate  1  via a gate insulation film not illustrated, such that the polysilicon pattern  3  extends over the device isolation film  2  from the device region  1 A to the device region  1 B. It should be noted that the polysilicon pattern  3  is doped to the p-type or n-type in the device region  1 A and to the opposite conductivity type in the device region  1 B. On the other hand, the polysilicon pattern  3  is not doped on the device isolation film  2 . 
     In the case a titanium silicide film  4  is formed on such a polysilicon pattern  3  by a salicide process, on the other hand, the titanium silicide film  4  is formed with an increased thickness in the region  4 A thereof because of the fact that the polysilicon pattern  3  is not doped on the device isolation film  2 , and it becomes possible to decrease the thickness of the metal titanium film deposited at the time of forming the titanium silicide film by a salicide process. 
     However, this conventional technology, utilizing the natural effect of doping of the underlying polysilicon pattern for the formation of silicide, can cause only the thickness change of several ten Angstroms (several nanometers) for the titanium silicide layer  4  in correspondence to the region  4 A. Obviously, the thickness change caused with this magnitude is insufficient at all for avoiding the discontinuity or disconnection of the silicide layer  4  on the device isolation film  2 . 
     In a first aspect of the present invention, there is provided a semiconductor device, comprising: 
     a substrate having first and second device regions separated from each other by a device isolation region; 
     a first field effect transistor having a first polysilicon gate electrode and formed in said first device region; 
     a second field effect transistor having a second polysilicon gate electrode and formed in said second device region; 
     a polysilicon pattern extending over said device isolation region from said first polysilicon gate electrode to said second polysilicon gate electrode; and 
     a silicide layer formed on a surface of said first polysilicon gate electrode, a surface of said second polysilicon gate electrode and a surface of said polysilicon pattern so as to extend on said polysilicon pattern from said first polysilicon gate electrode to said second polysilicon gate electrode, 
     said silicide layer having a region of increased film thickness on said polysilicon pattern, 
     wherein said silicide layer has a surface protruding upward in said region of increased film thickness. 
     In another aspect of the present invention, there is provided a semiconductor device, comprising: 
     a substrate having a device region defined by a device isolation region; 
     a field effect transistor having a polysilicon gate electrode and formed on said device region; 
     a polysilicon pattern extending out from said polysilicon gate electrode and extending over said device isolation region; and 
     a silicide layer formed on a surface of said polysilicon gate electrode and on a surface of said polysilicon pattern so as to extend over said polysilicon pattern from said polysilicon gate electrode, 
     said silicide layer including a region of increased film thickness on said polysilicon pattern, said silicide layer having a surface protruding upward in said region of increased film thickness. 
     Another object of the present invention is to provide a method of fabricating a semiconductor device, comprising the steps of: 
     forming, on a substrate including a device region device by a device isolation region, a field effect transistor in corresponding to said device region, such that a polysilicon pattern extends out from a polysilicon gate electrode of said field effect transistor, such that said polysilicon pattern extends over said device isolation region; 
     depositing a metal film on said substrate so as to cover said gate electrode and said polysilicon pattern; 
     forming a mask pattern on said metal film so as to cover a part of said polysilicon pattern existing on said device isolation region; 
     etching said metal film while using said mask pattern as a mask so as to reduce a thickness of said metal film in a part thereof not covered with said mask pattern; and 
     forming a silicide layer on a surface of said gate electrode and a surface of said polysilicon pattern by applying an annealing process after removing said mask pattern. 
     According to the present invention, the thickness of the silicide layer is increased in the polysilicon pattern extending from a polysilicon gate electrode even in the case the silicide layer itself is formed on the polysilicon gate electrode with an extremely small thickness by a salicide process, and it becomes possible to reduce the occurrence of B-mode failure drastically. Further, at the same time, it becomes possible to suppress the occurrence of the problem such as disconnection or increase of the resistance. Thus, according to the present invention, it becomes possible to miniaturize a semiconductor device such as a CMOS device such that the thickness of the gate insulation film of the MOS transistor is reduced to 2 nm or less and such that the gate length is reduced to 130 nm or less. 
     According to the present invention, in particular, it becomes possible to suppress the occurrence of the B-mode failure substantially to zero and simultaneously the occurrence of defective operation of the semiconductor device caused by failure of silicide formation also substantially to zero, by setting the thickness of the metal film on the gate electrode to 8 nm or less and by setting the thickness of the metal film on the polysilicon pattern extending out from the gate electrode to 10 nm or more at the time of formation of the silicide layer by a salicide process. 
     Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are diagrams showing the construction of a conventional CMOS device; 
         FIGS. 2A and 2B  are diagrams explaining the problems encountered when device miniaturization is made in the conventional CMOS device; 
         FIG. 3  is a diagram showing an example of a conventional polysilicon interconnection pattern; 
         FIG. 4  is a plan view diagram showing the construction of a CMOS device according to an embodiment of the present invention; 
         FIGS. 5A–5J  are diagrams showing the fabrication process of the CMOS device of  FIG. 4 ; 
         FIG. 6  is a diagram showing a part of  FIG. 5I  in an enlarged scale; and 
         FIG. 7  is a diagram showing the relationship between the thickness of the metal film in the salicide process, the occurrence of B-mode failure and the occurrence of defective operations. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 4  is a diagram showing a schematic construction of a CMOS device  20  according to a first embodiment of the present invention in a plan view. 
     Referring to  FIG. 4 , the CMOS device comprises a silicon substrate  21  formed with device regions  21 A and  21 B in such a manner that the device regions  21 A and  21 B are isolated from each other by an insulating device isolation film  22 , and a p-channel MOS transistor  20 A having a polysilicon gate electrode  24 A doped to the p-type and an n-channel MOS transistor  20 B having a polysilicon gate electrode  24 B doped to the n-type are formed respectively in the device region  21 A and in the device region  21 B, such that the gate electrodes  24 A and  24 B are connected by a polysilicon pattern  24 C extending over the device isolation film  22 . 
     Further, in the construction of  FIG. 4 , there is formed a thin cobalt silicide layer  24   a  on the polysilicon gate electrode  24 A, and a thin cobalt silicide layer  24   b  is formed on the polysilicon gate electrode  24 B. Further, a thin cobalt silicide layer  24   c  is formed on the polysilicon pattern  24 C in continuation with the cobalt silicide layer  24   a  and the cobalt silicide layer  24   b.    
     Further, there are formed silicide layers  24   e  and  24   f  in the device region  20 A at both lateral sides of the gate electrode  24 A respectively in correspondence to the source region and the drain region of the p-channel MOS transistor  20 A. In the device region  20 B, on the other hand, there are formed silicide layers  24   g  and  24   h  respectively in correspondence to the source region and the drain region of the n-channel MOS transistor  20 B. 
     Further, in the CMOS device  20  of the present embodiment, it should be noted that there is formed a region  24   d  of increased thickness in a part of the polysilicon pattern  24 C intermediate to the transistor  20 A and the transistor  20 B such that there occurs an increase of thickness of the silicide layer  24   c  in such a region  24   d  of increased thickness. 
     Hereinafter, the fabrication process of the CMOS device  20  of  FIG. 4  will be explained with reference to  FIGS. 5A–5J , wherein it should be noted that these drawings represent the cross-sectional diagrams taken along the lines A–A′, C–C′ and B–B′ of the plan view of  FIG. 4 . 
     Referring to  FIG. 5A , the device isolation film  22  forms an STI (shallow trench isolation) structure on the silicon substrate  21 , and gate insulation films  23 A and  23 B are formed in the step of  FIG. 5B  respectively on the device region  21 A and  21 B by an oxide film or an oxynitride film with a thickness of 2 nm or less. 
     In the step of  FIG. 5A , it should be noted that there is formed an n-type well (not shown) in the device region  21 A by introducing As+ or P+ with an impurity concentration level of 1×10 13  cm −3  by a ion implantation process. Similarly, there is formed a p-type well (not shown) in the device region  21 B by introducing B+ or BF 2 + with an impurity concentration level of 1×10 13  cm −3  by an ion implantation process. 
     Next, in the step of  FIG. 5B , a polysilicon film is deposited on the substrate  21  thus formed with the gate insulation films  23 A and  23 B, uniformly with the thickness of about 180 nm, and the gate electrodes  24 A and  24 B are formed respectively in the device regions  21 A and  21 B as a result of patterning of the polysilicon film. Further, as a result of the patterning of the polysilicon film, the polysilicon pattern  24 C is formed on the device isolation film  22  at the same time. In the present embodiment, it should be noted that the polysilicon film is patterned such that the p-channel MOS transistor  20 A and the n-channel MOS transistor  20 B have a gate length of 130 nm or less. 
     After the step of  FIG. 5B , an ion implantation process of B+ is conducted in the state that the device region  21 B is covered with the resist pattern with an impurity concentration level of 1×10 14  cm −3  while using the gate electrode  24 A as a self-aligned mask, and as a result, there are formed p-type LDD regions  21   a L and  21   b L in the device region  21 A at both lateral sides of the gate electrode  24 A. Further, by conducting an ion implantation process of As+ or P+ into the device region  21 B while using the gate electrode  24 B as a self-aligned mask in the state that the device region  21 A is covered with a resist pattern, there are formed n-type LDD regions  21   c L and  21   d L in the device region  21 B at both lateral sides of the gate electrode  24 B. 
     Next, in the step of  FIG. 5C , a sidewall insulation film is formed on both sidewall surfaces of the gate electrodes  24 A and  24 B, and a resist pattern R 1  having a resist window exposing the device region  21 A is formed on the substrate  21 . Further, ion implantation process of B+ is conducted into the device region  21 A with an impurity concentration level of 1×10 15  cm −3  while using the resist pattern R 1  as a mask. Thereby, there are formed p-type diffusion regions  21   a  and  21   b  in a partially overlapping relationship with the p-type LDD regions  21   a L and  21   b L formed previously, as the source region and the drain region of the p-channel MOS transistor  20 A. As a result of the process of  FIG. 5C , it should be noted that, although not illustrated, there is formed a similar sidewall insulation film also on both sidewall surfaces of the polysilicon pattern  24 C. 
     Next, in the step of  FIG. 5D , the resist pattern R 1  is removed and a resist pattern R 2  having a resist window exposing the device region  21 B is formed on the substrate  21 . Further, ion implantation of As+ or P+ is conducted into the device region  21 A with an impurity concentration level of 1×10 15  cm −3  while using the resist pattern R 2  as a mask, and there are formed n-type diffusion regions  21   c  and  21   d  in a partially overlapping relationship with the n-type LDD regions  21   c L and  21   d L as the source region and drain region of the n-channel MOS transistor  20 B. 
     With this ion implantation process of  FIGS. 5C and 5D , the part of the polysilicon pattern  24 C close to the gate electrode  24 A is doped to the p-type and the part of the polysilicon pattern  24 C close to the gate electrode  24 B is doped to the n-type. On the other hand, the intermediate part of the polysilicon pattern  24 C is not doped and maintains the undoped state. 
     Next, in the step of  FIG. 5E , the resist pattern R 2  is removed and a metallic cobalt film  25  is deposited on the substrate  21  by a sputtering process, and the like, uniformly with a thickness of about 10 nm, such that the cobalt film  25  covers the gate electrodes  24 A and  24 B. 
     Next, in the step of  FIG. 5F , a resist film is formed on the structure of  FIG. 5D , wherein the resist film is exposed by using an exposure mask used in the step of  FIG. 5C  for exposing the resist pattern R 1 . Further, by developing the resist film thus exposed, there is formed a resist pattern R 3  having a resist window R 3 A such that the resist window R 3 A exposes the device region  21 A. 
     Next, in the step of  FIG. 5G , the same resist pattern R 3  is exposed by using an exposure mask used at the time of exposing the resist pattern R 2  for use in the step of  FIG. 5D . After development, there is formed a resist window R 3 B exposing the device region  21 B in the resist pattern R 3 , in addition to the foregoing resist window R 3 A. Further, in the step of  FIG. 5G , the metallic cobalt film  25  is etched with a depth of about 2 nm for the part exposed by the resist openings R 3 A and R 3 B while using the resist pattern R 3  as a mask. 
     Because there occurs no etching in the metallic cobalt film  25  in this process for the part covered with the resist pattern R 3 , there is formed a structure shown in  FIG. 5H  when the resist pattern R 3  is removed, wherein it will be noted that there is formed a protruding part in the metallic cobalt film  25  in correspondence to the non-doped part of the polysilicon pattern such that the metallic cobalt film  25  has an increased thickness in the non-doped part. In the step of  FIG. 5H , it should be noted that the thickness of the metallic cobalt film  25  thus deposited is reduced to about 8 nm or less in the part covering the gate electrode  24 A or  24 B as a result of the etching conducted while using the resist pattern R 3  as a mask. On the other hand, the metallic cobalt film  25  maintains the initial thickness of 10 nm on the part covering the polysilicon pattern  24 C. 
     Thus, by applying an annealing process to the structure of  FIG. 5H  at the temperature of 850° C., the metallic cobalt film  25  causes a reaction with a silicon surface in the part where such a silicon surface is exposed underneath the metallic cobalt film  25 , and as a result, the silicide layers  21   e  and  21   f  are formed on the surface of the diffusion regions  21   a  and  21   b  and the silicide layers  21   g  and  21   h  are formed on the surface of the diffusion regions  21   c  and  21   d . Further, the silicide layers  24   a  and  24   b  are formed on the gate electrodes  24 A and  24 B and the silicide layer  24   c  is formed on the polysilicon pattern  24 C, wherein it will be noted that the silicide layer  24  thus formed includes the region  24   d  of increased thickness as shown in  FIG. 6  in correspondence to the region  25 A of increased thickness of the cobalt film  25 . 
     Referring to  FIG. 6 , it should be noted that the silicide layer  24   c  formed with such a process has a thickness t 1  smaller than 24 nm on the polysilicon pattern  24 C, while the thick region  24   d  of the silicide layer is formed with a thickness t 2  of 30 nm or more. Further, according to the present invention, the thick region  24   d  forms a protrusion having a step height Δ in correspondence to the protrusion  25 A of the metallic cobalt film  25 , wherein it should be noted that the thickness t 1  is equal to the thickness of the silicide film formed on the gate electrode  24 A or  24 B. 
     Further, in the step of  FIG. 5J , an interlayer insulation film  250  is formed on the structure of  FIG. 5I  and via-plugs  26 A and  26 B are formed in the interlayer insulation film  250  in contact with the diffusion regions  21   a  and  21   b  via the silicide layers  21   e  and  21   f . Further, in the interlayer insulation film  250 , there are formed via plugs  26 C and  26 D in contact with the diffusion regions  21   c  and  21   d  via the silicide layers  21   g  and  21   h.    
       FIG. 7  shows the occurrence of B-mode failure and occurrence of defective operation caused by failure of silicide formation for the CMOS device  10  explained previously with reference to  FIGS. 2A and 2B  for the case the thickness of the metallic film deposited in the step corresponding to the step of  FIG. 5E  for the formation of the silicide layer  14   a  is changed variously. 
     Referring to  FIG. 7 , it will be noted that the occurrence of the B-mode failure is decreased when the thickness of the metallic film is decreased, while there occurs an increase in the defective operation caused by the failure of silicide formation explained with reference to  FIGS. 2A and 2B  with such decrease of thickness of the metallic film. When the metallic film has a large thickness, on the other hand, the defective operation caused by failure of silicide formation is decreased, while it can be seen that there occurs increase of B-mode failure. 
     In the present embodiment, the thickness of the metallic cobalt film  25  formed on the gate electrodes  24 A and  24 B is reduced to 8 nm or less in the step of  FIG. 8H , and thus, the occurrence of the B-mode failure is reduced substantially to zero. Further, the occurrence of the defective operation of the CMOS device caused by the failure of silicide formation on the polysilicon pattern  24 C is also suppressed with the present invention to substantially zero by setting the thickness of the cobalt film in the region  25 A of increased thickness to 10 nm or more. 
     In the process of the Patent Reference 1 in which the titanium film is formed uniformly with the thickness of 300 Angstroms (30 nm) for the silicide formation reaction, on the other hand, formation of the B-mode failure is not suppressed in the case the process of the reference is applied to ultrafine semiconductor devices in which the thickness of the gate electrode is reduced. 
     While the foregoing embodiment has been explained for the case of formation of a cobalt silicide film, the present invention is not limited to such a specific material but is applicable also to the formation of other silicide films including a titanium silicide film, a nickel silicide film, a tungsten silicide film, a molybdenum silicide film, a zirconium silicide film, and the like. 
     In the present invention, there is formed a step in the metal film deposited for the silicide formation by conducting a patterning process prior to the silicide formation reaction, and thus, it becomes possible to secure a large difference of film thickness in the silicide layer between the region  24   d  of increased thickness and the region other than the foregoing region  24   d , and thus, it becomes possible to secure a sufficient film thickness for the silicide layer formed on the polysilicon pattern  24 C while simultaneously minimizing the thickness of the silicide layer on the gate electrodes  24 A and  24 B. 
     In relation to this, it should be noted that the present invention is particularly useful in the ultrafine semiconductor devices having a gate length of 130 nm or less and the thickness of the gate insulation film is 2 nm or less. 
     Further, it should be noted that the present invention is not limited to a CMOS device but also to semiconductor device in general as long as there is formed an extension of a polysilicon pattern from the polysilicon gate electrode of the p-channel MOS transistor or the n-channel MOS transistor. 
     Further, the present invention is not limited to the embodiments explained heretofore, but various variations and modifications may be made without deporting from the scope of the invention.