Abstract:
A semiconductor device includes a semiconductor substrate, a lower wiring layer formed on the semiconductor substrate, a first interlayer insulating film formed on the lower wiring layer and including a first upper surface and a second upper surface, the first upper surface being higher than the second upper surface relative to a surface of the semiconductor substrate, a contact plug formed in the interlayer insulating film and including a first bottom surface contacting to the lower wiring layer, a third upper surface flush with the second upper surface and a fourth upper surface flush with the first upper surface, an upper wiring layer formed on the first and third upper surfaces and including a first side surface and a second side surface opposite to the first side surface, and a second interlayer insulating film formed on the second and fourth upper surfaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a division of and claims the benefit of priority under 35 U.S.C. §120 from U.S. Ser. No. 10/988,613, filed Nov. 16, 2004, and claims the benefit of priority under 35 U.S.C. §119 from Japanese Patent Application No. 2003-386526, the entire contents of each which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor device having a multilayer wiring structure. 
   2. Description of the Related Art 
   Semiconductor devices have been making progress in high integration year by year, and a reduction in the rules of circuit design has been introduced as the requirement for miniaturization. The reduction in the circuit design rules is directly related to a reduction in a circuit area. For example, in an integrated circuit having a multilayer wiring structure, a distance between adjacently formed via holes is reduced such that a distance between each via hole and metal wiring formed in an upper layer is also reduced at the same time. 
   Such a reduction in the distance between each via hole and the metal wiring further reduces a positioning margin in a lithography process, which renders the processing technique difficult. In addition, since a distance between adjacent wiring patterns is reduced, it becomes difficult to obtain a desired insulating property. When a sufficient distance of insulation is not obtained, there arises a problem of failure due to short circuit such as dielectric breakdown or direct short circuit or a problem of parasitic capacitance, resulting in a difficulty in achieving a stable device operation. 
     FIGS. 10A to 11B  illustrate an example of the foregoing circumstances.  FIG. 10A  shows an example of multilayer wiring structure having no occurrence of patterning misalignment, whereas  FIG. 10B  shows an example of multilayer wiring structure in which misalignment has resulted from the patterning. As shown in these figures, an Al—Cu layer  2  serving as a lower wiring layer is formed on a silicon substrate  1 . A titanium nitride (TiN) layer  3  serving as a barrier metal is formed on the Al—Cu layer  2 . An interlayer wiring layer  4  is formed on the TiN layer  3 . The interlayer wiring layer  4  has via holes each formed so as to extend vertically through a predetermined part of a dual tetraethyl orthosilane (d-TEOS) film  5 . Contact plugs  6   a  and  6   b  made from tungsten (W) or the like are formed in the via holes respectively. 
   Barrier metal layers  7   a  and  7   b  each serving as an upper wiring layer, Al—Cu layers  8   a  and  8   b  and barrier metal layers  9   a  and  9   b  are patterned on the top of the interlayer wiring layer  4  so as to correspond to the locations of the contact plugs  6   a  and  6   b . A distance d 0  between electrodes in the upper wiring layer is, for example, 80 nm. In the case of  FIG. 10B , there is an amount of misalignment A in the patterning of the upper wiring layer. 
     FIGS. 11A and 11B  are sectional views corresponding to parts of the fabrication process respectively. As shown in  FIG. 11A , the Al—Cu layer  2  and TiN film  3  of the lower wiring layer are formed, and the d-TEOS film  5  with a film thickness of 500 nm is formed on the TiN film  3 . Tungsten as a material for the contact plugs  6   a  and  6   b  is embedded in the via holes respectively. 
   In the state as shown in  FIG. 11A , the TiN film  7 , the Al—Cu film  8  of the upper wiring layer material and the TiN film  9  are formed on the d-TEOS film  5  serving as an interlayer insulating film, and resists  10   a  and  10   b  corresponding to a wiring circuit are patterned as shown in  FIG. 11B . Misalignment occurs during a lithography process and an amount of misalignment A is, for example, 50 nm. 
   The TiN film  9 , Al—Cu film  8  and TiN film  7  are etched by a reactive ion etching (RIE) process using a gas plasma such that the structure as shown in  FIG. 10B  is obtained. In this case, the TiN films  9   a  and  9   b , Al—Cu films  8   a  and  8   b , and TiN films  7   a  and  7   b  are electrically connected to the tungsten plugs  6   a  and  6   b  while misalignment has occurred by the misalignment amount A. 
   When the misalignment amount A is, for example, 30 nm as the result of occurrence of the foregoing misalignment, an insulation distance d 1  between the upper wiring layer of the TiN film  9   a , Al—Cu film  8   a  and TiN film  7   a  and the adjacent tungsten  6   b  becomes 50 nm. As a result, since a sufficient insulation distance can be ensured, no problem arises in the operation of the device. However, the insulation distance d 1  becomes 30 nm when the misalignment amount A is increased to 50 nm. Consequently, there is a possibility of occurrence of a short circuit or an increase in the parasitic capacitance. 
   As one of conventional countermeasures, the specification of positioning in the lithography process has been reconsidered and/or the diameters of the via holes have been reduced. However, the reduction in the circuit design rules makes it difficult to obtain an insulation distance and at the same time, it is quite difficult to carry out further reconsideration of the positioning specification in view of the device performance. Further, variations in the diameter of the via hole also make it difficult to obtain a stable distance between insulators. Still further, at the same time, even when the diameter of the via hole is reduced, such reduction directly results in reduction in a junction area. As a result, a desired operation of the device cannot be achieved. Thus, the foregoing problem needs to be overcome for future fabrication of semiconductor circuits. 
   Accordingly, securement of the insulation distance and prevention of failure due to short circuit or parasitic capacitance are particularly important in the fabrication of multilayer wiring circuits in order that a stable device operation may be obtained against miniaturization of the device. JP-A-2000-208615 and JP-A-2002-176098 disclose the foregoing countermeasures. 
   JP-A-2000-208615 discloses an interlayer connection structure connecting upper and lower wiring layers of a semiconductor substrate. In this case, even upon occurrence of misalignment during the lithography process, a sufficient distance of electrical insulation can be ensured between contact portions adjacent to each other, whereby a sufficient contact area can be secured. 
   Further, JP-A-2002-176098 discloses a semiconductor device employing a structure that a lower side contact plug is previously recessed in the formation of a multilayer wiring circuit of a borderless structure so that a contact pattern at an upper wiring layer is prevented from reaching a contact plug due to misalignment, thereby preventing short circuit. 
   In each of the foregoing references, however, a width of gap differs according to an amount of misalignment at the occasion of an etching process for recessing the contact plug, resulting in a problem of embeddability in the case where an interlayer insulating film is embedded in an upper layer. 
   BRIEF SUMMARY OF THE INVENTION 
   Therefore, an object of the present invention is to provide a semiconductor device in which a sufficient insulation distance can be ensured between the upper wiring layer and the adjacent contact plug in consideration of occurrence of misalignment in the lithography process, and a stable electric characteristic can be achieved and yet, a stable process can be provided so that embeddability of the interlayer insulating film stacked on the upper layer can be prevented from being reduced. 
   The present invention provides a semiconductor device comprising a semiconductor substrate, a lower wiring layer formed on the semiconductor substrate, a first interlayer insulating film formed on the lower wiring layer and including a first upper surface and a second upper surface, the first upper surface being higher than the second upper surface relative to a surface of the semiconductor substrate, a contact plug formed in the interlayer insulating film and including a first bottom surface contacting to the lower wiring layer, a third upper surface flush with the second upper surface and a fourth upper surface flush with the first upper surface, an upper wiring layer formed on the first and third upper surfaces and including a first side surface and a second side surface opposite to the first side surface, and a second interlayer insulating film formed on the second and fourth upper surfaces. 
   The invention also provides a method of fabricating a semiconductor device, comprising forming a lower wiring layer on a semiconductor substrate, forming an interlayer wiring layer on the lower wiring layer, forming a plurality of contact plugs in the interlayer insulating film so that the contact plugs are brought into electrical contact with the lower wiring layer, thereby forming an interlayer wiring layer, forming an upper wiring layer on the interlayer wiring layer so that the upper wiring layer is brought into electrical contact with the contact plugs, and patterning the upper wiring layer so that the upper wiring layer corresponds to the contact plugs, wherein in the patterning, after the upper wiring layer has been etched, both exposed interlayer insulating film and contact plugs are etched. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become clear upon reviewing the following description of the embodiments with reference to the accompanying drawings, in which: 
       FIGS. 1A and 1B  are typical longitudinal sections of the semiconductor device in accordance with a first embodiment of the present invention, showing a case where no misalignment has occurred and another case where misalignment has occurred respectively; 
       FIGS. 2A and 2B  are typical longitudinal sections of the semiconductor device at different stages of the fabrication process in the case where no misalignment has occurred; 
       FIG. 3  is a view similar to  FIG. 2B , showing the case where misalignment has occurred; 
       FIGS. 4A and 4B  are views similar to  FIGS. 1A and 1B , showing the semiconductor device in accordance with a second embodiment, respectively; 
       FIGS. 5A to 5C  are views similar to  FIGS. 2A and 2B , showing the longitudinal section of the semiconductor device; 
       FIGS. 6A and 6B  are view similar to  FIGS. 1A and 1B , showing the semiconductor device in accordance with a third embodiment, respectively; 
       FIGS. 7A and 7B  are views similar to  FIGS. 2A and 2B , respectively; 
       FIGS. 8A and 8B  are also views similar to  FIGS. 2A and 2B  respectively; 
       FIGS. 9A to 9C  are typical longitudinal sections of the semiconductor device at different stages of the fabrication process in the case where misalignment has occurred; 
       FIGS. 10A and 10B  are views similar to  FIGS. 1A and 1B , showing the conventional construction respectively; and 
       FIGS. 11A and 11B  are views similar to  FIGS. 9A to 9C , showing the conventional construction. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Several embodiments of the present invention will be described with reference to the accompanying drawings.  FIGS. 1A to 3  illustrate a first embodiment of the invention. Each figure shows a typical section of a part of the multilayer wiring structure. Dimensions do not sometimes agree to the actual dimensions for the sake of easiness in explanation. 
     FIGS. 1A and 1B  show one layer of the multilayer wiring structure in the first embodiment.  FIG. 1A  shows a case where no misalignment has occurred during the patterning.  FIG. 1B  shows a case where misalignment has occurred. Firstly, referring to  FIG. 1A , a silicon substrate  11  serving as a semiconductor substrate is formed with an Al—Cu layer  12  serving as a lower wiring layer. A TiN film  13  serving as a barrier metal layer is formed on the Al—Cu layer  12 . An interlayer wiring layer  14  is formed on the TiN film  13 . The interlayer wiring layer  14  has a plurality of via holes each vertically formed through predetermined portions of a d-TEOS film  15 . Tungsten plugs  16   a  and  16   b  serving as contact plugs are buried in the via holes respectively. 
   The tungsten plugs  16   a  and  16   b  are formed so as to protrude from the surfaces of the d-TEOS films  15  in the aforementioned construction. Although the d-TEOS film  15  is formed at the same level as the surfaces of the tungsten plugs  16   a  and  16   b , the plugs protrude relative to the surfaces of the d-TEOS films  15  when a recessed portion P has been formed. 
   On the interlayer wiring layer  14  are patterned TiN films  17   a  and  17   b  of barrier metal serving as an upper wiring layer, Al—Cu films  18   a  and  18   b  of the wiring layer, and TiN films  19   a  and  19   b  of the barrier metal. Subsequently, when a wiring layer is further formed as an upper layer, insulating films are formed on the upper surfaces of the TiN films  19   a  and  19   b  and thereafter, a multilayer wiring structure can be formed in the same manner as described above. In this state, upper layer side electrodes are separated by distance d 0 . Since no misalignment has occurred in the patterning during formation of the upper wiring layer in the aforementioned case, the portions of the tungsten plugs  16   a  and  16   b  protrude. 
   On the other hand, the following is a case where misalignment has occurred: that is, in  FIG. 1B , misalignment of a mask pattern amounting to distance A has occurred in the lithography process after stack of a TiN film  17 , an Al—Cu film  18  and a TiN film  19  all serving as an upper wiring layer. In this configuration, as the result of occurrence of misalignment, an interlayer wiring layer  14  is formed while the tungsten plugs  16   a  and  16   b  and d-TEOS film  15  is etched to be recessed. In this case, a pattern of the TiN film  17   a , Al—Cu film  18   a  and TiN film  19   a  of the left side upper wiring layer is located in the vicinity of the right side tungsten plug  16   b  and a distance d 1  is defined between the pattern and tungsten plug is as viewed in  FIG. 1B . 
   Even in the above-described case, a recessed portion P is formed such that there is a vertical difference of a predetermined distance between the underside of the TiN film  17   a  and the upper face of the adjacent contact plug  16   b . Accordingly, the distance d 1  is not defined between the tungsten plug  16   b  and the Al—Cu film  17   a  of the upper wiring layer but a distance in a straight line corresponding to a depth f of the recessed portion P can be ensured as a distance of insulation. Consequently, for example, even when a horizontal misalignment distance d 1  is almost 0, the insulation distance not less than a predetermined amount can be ensured since the recessing dimension f of the recessed portion P is ensured. 
   A fabricating process of the foregoing structure will be described with reference to  FIGS. 2A to 3 .  FIGS. 2A to 3  are sectional views corresponding to steps of the fabricating process respectively.  FIGS. 2A and 2B  show the case where no misalignment has occurred. As shown in  FIG. 2A , the d-TEOS film  15  having a film thickness of 500 nm, for example, and serving as the interlayer insulating film is formed on the Al—Cu film  12  of the lower wiring layer and the TiN film  13  serving as the material for the barrier metal layer. Further, a via-hole pattern in which each via hole has a diameter of 150 nm, for example is formed in the interlayer insulating film by a reactive ion etching (RIE). Subsequently, the tungsten plugs  16   a  and  16  serving as contact plugs are embedded in the via holes by the film-forming technique of the sputtering process respectively. In this case, films are formed on the tungsten plugs  16   a  and  16   b  embedded in the via holes by the sputtering and thereafter, a planarization process is carried out for the tungsten plugs as well as for the surface of the d-TEOS film  15 . Reference symbol d 0  in  FIG. 2A  designates a distance between the via holes adjacent to each other. In this case, the distance d 0  is 80 nm. 
     FIG. 2B  shows the TiN film  17  serving as the barrier metal, the Al—Cu film  18  serving as the upper layer wiring material and the TiN film  19  serving as the barrier metal. The TiN film  17  is formed on the d-TEOS film  15  serving as the interlayer insulating film in the state as shown in  FIG. 2A . The Al—Cu film  18  is formed on the TiN film  17 . Resists  20   a  and  20   b  are formed on the TiN film  19  by the lithography process into the pattern of a wiring circuit. Each resist has a width of 150 nm. Subsequently, an etching process is carried out so that the upper layer wiring layer is formed. The resists  20   a  and  20   b  are used as a mask for the etching. The TiN film  19 , Al—Cu film  18  serving as the upper layer wiring material and TiN film  17  serving as the barrier metal are etched by RIE process using a gas plasma comprising BCl 3 /Cl (the flow rate is set as BCl 3 /Cl=50/50 sccm, for example). 
   Successively, the etching process is further carried out to form the recessed portion P of the interlayer wiring layer  14 . Regarding the etching condition, a gas plasma comprising CF 4 /Ar (the flow rate is set to 30/50 sccm, for example) is used so that the case where the W plugs  16   a  and  16   b  are exposed can be coped with. Consequently, both W plugs  16   a  and  16   b  and d-TEOS film  15  serving as the interlayer insulating film can simultaneously be etched. Further, an amount of etching is determined so that the undersides of the TiN films  17   a  and  17   b  are downwardly recessed by a depth f. As a result, the recessed portion P is formed. Subsequently, the resists  20   a  and  20   b  are eliminated by an ashing process such that the semiconductor device as shown in  FIG. 1A  is obtained. 
   On the other hand, when misalignment occurs in the semiconductor device of  FIG. 2B  on which the resists  20   a  and  20   b  have been patterned,  FIG. 3  shows the semiconductor device under the aforesaid condition. In this case, when the TiN film  19 , Al—Cu film  18  and TiN film  17  each serving as an upper wiring layer are etched, the W plugs  16   a  and  16   b  are exposed at the surface of the interlayer wiring layer  14 . Accordingly, in a case where the interlayer wiring layer  14  is subsequently etched so as to be recessed, both W plugs  16   a  and  16   b  and d-TEOS film  15  are etched when the aforesaid etching condition is used. In this case, the TiN films  19   a  and  19   b , Al—Cu films  18   a  and  18   b , and TiN films  17   a  and  17   b  are affected by a misalignment amount A caused by the lithography process. As a result, these films are joined to the W plugs  16   a  and  16   b  formed in the via holes respectively under the occurrence of misalignment. 
   However, an insulation distance can be ensured since the following represents a distance between the upper wiring layer of TiN film  19   a , Al—Cu film  18   a  and TiN film  17   a  and the W plug  16   b  formed in the via hole adjacent to the wiring layer. That is, reference symbol d 0  designates a clearance in the case of occurrence of no misalignment. When a misalignment amount A has occurred, a two-dimensional clearance d 1  is obtained by subtracting the misalignment amount A from the aforesaid clearance d 0 , and additionally, the upper wiring layer is further spaced away from the W plug  16   b  by the misalignment amount f in the direction of the depth. Accordingly, for example, when the misalignment amount f is 20 nm, a clearance along the side is obtained by the sum of them (=d 1 +f). A distance in a straight line is obtained as a value of a square root of sum of square of d 1  and f (the Pythagorean proposition). 
   Consequently, a desired insulation distance is ensured and a stable device operation can be obtained. Accordingly, for example, when the recess amount f is set as a necessary insulation distance, the insulation distance can be ensured only by the recess amount f even if a misalignment amount A should become a maximum value of d 0 . 
   In the foregoing embodiment, when the upper wiring layer is patterned, the interlayer insulation layer  14  is also etched so as to be recessed, following the etching process for the TiN film  19 , Al—Cu film  18  and TiN film  17 . Consequently, even when a necessary horizontal insulation distance d 0  is not ensured, the recess amount f in the direction of the depth can be added to as the result of formation of the recessed portion P. As a result, even when a necessary margin cannot be obtained due to a misalignment amount in the lithography process or miniaturization in the circuit design rules, occurrence of a short circuit and an increase in the parasitic capacitance can be prevented. Moreover, an increase in the costs can be restrained since this can be achieved only by addition of the etching process without an increase in the number of times of lithography. 
     FIGS. 4A to 5C  illustrate a second embodiment of the invention. Only the difference of the second embodiment from the first one will be described.  FIGS. 4A and 4B  show one layer of the multilayer wiring structure.  FIG. 4A  shows the case where no misalignment has occurred. The construction as shown in  FIG. 4A  is apparently the same as the prior art as shown in  FIG. 10A . An interlayer wiring layer  22  employed instead of the interlayer  14  is formed so that a film thickness thereof becomes smaller by the recess amount f as the result of formation of the recessed portion P. 
   Further, when misalignment has occurred as shown in  FIG. 4B , lower layer portions of the TiN films  19   a  and  19   b , Al—Cu films  18   a  and  18   b  and TiN films  17   a  and  17   b  are located on the d-TEOS films  15  and raised so as to be formed into steps. 
   Thus, even when misalignment has occurred, the interlayer wiring layer  22   a  can be formed while the insulation distance is ensured as in the first embodiment. Consequently, an electrically stable semiconductor device can be realized with a sufficient processing time. Further, the number of added processes can be reduced and the number of steps of the lithography process can be prevented from being increased. 
   The process of fabricating the above semiconductor device will now be described with reference to  FIGS. 5A to 5C .  FIG. 5A  shows the condition where the interlayer wiring layer  22  has been formed in the same manner as in the first embodiment. Subsequently, as shown in  FIG. 5B , an etch back process is carried out for the W plugs  16   a  and  16   b  by RIE process.  FIG. 5B  shows the semiconductor device etched by gas plasma comprising NF 3 /O 2  (the flow rate is set as 30/50 sccm, for example) so that the W plugs  16   a  and  16   b  are located lower than a surface layer of the d-TEOS film  15 . Reference symbol f designates a recess amount by which the W plugs  16   a  and  16   b  have been recessed by the etch back process. In the shown case, f is set to 20 nm. 
   Subsequently, in the above-described state, a TiN film  17  serving as a barrier metal is formed on the W plugs  16   a  and  16   b  recessed by the etch back process and the d-TEOS film  15  serving as the interlayer insulating film. The Al—Cu film  18  serving as a material for the upper wiring layer is formed on the TiN film  17 . The TiN film  19  serving as the barrier metal material is then formed on the Al—Cu film  18 . The resists  20   a  and  20   b  corresponding to a wiring circuit are patterned on the TiN film  19  by the lithography process as shown in  FIG. 5C . Each resist has a width of 150 nm, for example. 
   When no misalignment due to the patterning has occurred, the construction as shown in  FIG. 4A  is obtained through the etching process. Further,  FIG. 4B  shows the construction obtained when misalignment has occurred. An amount of misalignment due to the lithography process is shown as the misalignment amount A, which is 50 nm, for example. 
   Subsequently, the etching process is carried out in the same manner as in the first embodiment such that the construction as shown in  FIG. 4A  or  4 B is obtained. Consequently, the same effect can be achieved from the second embodiment as from the first embodiment. 
     FIGS. 6A to 9C  illustrate a third embodiment of the invention. The following describes only the difference of the third embodiment from the first embodiment.  FIGS. 6A and 6B  show one layer of the multilayer wiring structure.  FIG. 6A  shows the case where no misalignment has occurred in the patterning, whereas  FIG. 6B  shows the case where misalignment has occurred. 
   The construction as shown in  FIG. 6A  is substantially the same as in the first embodiment as shown in  FIG. 1A . Describing the difference, the TiN films  17   a  and  17   b , Al—Cu films  18   a  and  18   b  and TiN films  19   a  and  19   b  serving as the upper wiring layer have the respective widths smaller than the W plugs  16   a  and  16   b.    
   In this construction, an interlayer wiring layer  23  differs from the interlayer wiring layer  14  employed in the first embodiment. Further, since etching conditions for tungsten plugs  16   a  and  16   b  in the third embodiment differ from those in the first embodiment, the depth of the recess exceeds the d-TEOS film  15  and a slight stepped portion is formed, as will be described with reference to  FIG. 6B  later. Further, since corners of the d-TEOS film  15  are etched so as to be actually rounded, no narrow gap is formed although not shown. 
   When misalignment due to the patterning has occurred as shown in  FIG. 6B , a recessed portion R is formed between the portion of TiN film  17   a , Al—Cu film  18   a  and TiN film  19   a  forming the left upper wiring layer and the W plug  16   b  serving as the right contact plug, whereupon a recess amount f is obtained between the left upper wiring layer and the right contact plug. As a result, an insulation distance can be ensured. 
   The process of fabricating the above semiconductor device will now be described.  FIG. 7A  shows the condition where the interlayer wiring layer  23  has been formed. The d-TEOS film  15  is then exposed to gas plasma comprising CHF 3 /Ar/O 2  so that an etch back process is carried out by RIE method, whereby the W plugs  16   a  and  16   b  are formed so as to protrude relative to the d-TEOS film  15  as shown in  FIG. 7B . The condition for the etch back process is shown as CHF 3 /Ar/O 2 =30/110/5 sccm and an etch-back amount is 20 nm. 
   The TiN film  17 , Al—Cu film  18  and TiN film  19  serving as an upper layer side Al wiring are formed. The wiring pattern forming resists  20   a  and  20   b  are patterned on the TiN film  17 , Al—Cu film  18  and TiN film  19  as shown in  FIG. 8A . For example, each of the resists  20   a  and  20   b  has a pattern width of 100 nm, and a distance between the patterns of resists  20   a  and  20   b  is 100 nm. Each of the W plugs  16   a  and  16   b  has a pattern width of 150 nm, and a distance between the patterns of W plugs  16   a  and  16   b  is 80 nm. Thus, the upper wiring layer is set so as to have a smaller width. A purpose of this setting is to increase the margin in the patterning. 
   The TiN film  19 , Al—Cu film  18  and TiN film  17  are etched and the d-TEOS film  15  is continuously etched so as to be recessed as shown in  FIG. 8B . Subsequently, an ashing process is carried out for the resists  20   a  and  20   b  so that the construction as shown in  FIG. 6A  is obtained. 
   Further, when misalignment has occurred in the process of patterning the upper wiring layer, the resists  20   a  and  20   b  are patterned through the state as shown in  FIG. 9A  into the state as shown in  FIG. 9B . When the etching process is carried out in the aforesaid state, the W plugs  16   a  and  16   b  are exposed as shown in  FIG. 9C . Subsequently, when the etching process is carried out on the condition that the plugs  16   a  and  16   b  and d-TEOS film  15  are etched, a shape as shown in  FIG. 6B  is obtained. 
   Consequently, substantially the same effect can be achieved from the third embodiment as from the first embodiment. Further, the margin in the patterning can be increased by reducing the width of the upper wiring layer. Still further, electrical contact with the W plugs  16   a  and  16   b  can be made on the side of the stepped portion upon occurrence of misalignment when the upper wiring layer is patterned. Consequently, an increase in the contact resistance can be reduced such that the wiring structure with a desired electrical characteristic can be obtained. 
   The invention should not be limited to the foregoing embodiments. Several modified forms of the foregoing embodiments will be described. The recess amount f is set to 20 nm in the foregoing embodiments. However, the recess amount f may take any value on the condition that the distance between insulators required for the operation of the device can be ensured. Consequently, occurrence of short circuit and parasitic capacitance can be reduced. 
   Further, the recess amount f may be set to a suitable value according to the misalignment amount A. When the misalignment amount A is small, the recess amount f is also reduced, whereupon the embeddability of the interlayer insulating film in a subsequent process can be increased. On the other hand, when the misalignment amount A is large, the recess amount f is also increased, whereupon a desired insulation distance can be ensured. 
   In the foregoing embodiments, the different types of gas plasmas are used between the etching of the TiN film  17 , Al—Cu film  18  and TiN film  19  serving as the upper wiring layer and the recessing of the W plugs  16   a  and  16   b . However, any gaseous condition may be employed if the W plugs  16   a  and  16   b  are located under the underside of the TiN film  17  serving as the barrier metal. Further, these two etching processes are successively executed in the same etching chamber. However, the etching processes may be separately executed on condition that the W plugs  16   a  and  16   b  are located under the underside of the TiN film  17  serving as the barrier metal. 
   In the foregoing embodiments, the d-TEOS film  15  constituting the interlayer wiring layer and the W plugs  16   a  and  16   b  are etched at respective selection ratios equal to each other (selection ratio=1). However, if the insulation distance is met with respect to the upper layer wiring material and the contact plug material, the similar effect is achieved from the etching characteristics of the upper layer wiring material and the contact plug material whatever values the selection ratios may take. For example, the process may have a condition that the W plugs  16   a  and  16   b  are etched deep or the d-TEOS film  15  is etched deep. 
   In the foregoing embodiments, tungsten, TiN and Al—Cu alloy are used as the contact plug material, barrier metal and wiring material respectively. However, the similar effect can be achieved irrespective of the types of the contact plug material and wiring material on condition that the contact plugs are recessed to a desired depth. Further, the same type film may be used. 
   Recessing the tungsten plugs  16   a  and  16   b  serving as contact plugs may be carried out by a chemical dry etching (CDE) or wet etching, instead of RIE in the foregoing embodiments. 
   The interlayer insulating film  15  comprises the d-TEOS film in the foregoing embodiments. However, the interlayer insulating film  15  may comprise a high density plasma (HDP)-TEOS film, low pressure (LP)-TEOS film, plasma (P)-SiH 4  film, boro-phospho-silicate-glass (BPSG) film, phosphor-silicate-glass (PSG) film, plasma (P)-SiN film or low pressure (LP)-SiN film. 
   Tungsten is employed as the contact plug material in the foregoing embodiments. However, Al, Al—Cu alloy, Al—Si—Cu alloy, TiN, Ti, doped poly-Si, Cu or WSi may be employed as the material, instead of tungsten. Similarly, although Al—Cu is employed as the materials for the lower and upper wiring layers in the foregoing embodiments, W, Al, Al—Si—Cu, TiN, Ti, doped-poly-Si, Cu or WSi may be employed, instead. 
   The interlayer insulating film and the contact plug material are etched vertically in the foregoing embodiment. However, if there is no problem in the operation of the semiconductor device, the same effect can be achieved whatever shape the recessed portion may take, for example, tapered, inverted tapered, isotropic shape. 
   In the foregoing embodiments, the d-TEOS film  15  of the interlayer insulating film and the W plugs  16   a  and  16   b  of the contact plug material are recessed together. However, the d-TEOS film may previously be formed so as to be thicker by the recess amount f. Consequently, a desired device operation can be obtained without losing the function of an insulating film. 
   An etching mask is used in the process of resists  20   a  and  20   b  in the foregoing embodiments. A hard mask material may be employed for the etching mask if a desired shape is obtained. 
   The recessing process is applied to the contact plugs formed in the respective via holes in the foregoing embodiments. However, the recessing process may be applied to a device circuit using embedded wiring formed with an interlayer insulating film, instead. In this case, too, the same effect can be achieved. 
   In the second embodiment, the etch back process for the W plugs  16   a  and  16   b  can be employed if an etching rate of the d-TEOS film  15  serving as the interlayer insulating film is lower than an etching rate of the W plugs  16   a  and  16   b . As a result, even when the d-TEOS film  15  has been etched, an etching amount at the W plug side can be rendered larger, the same effect can be achieved. 
   In the third embodiment, portions of the W plugs  16   a  and  16   b  exposed outside the upper wiring layer are removed without removal of the resists  20   a  and  20   b  after formation of the Al—Cu film  18  and TiN film  17 . However, even when the similar plasma process is carried out after removal of the resists  20   a  and  20   b , the similar shape can be obtained such that the same effect can be achieved. 
   The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.