Abstract:
A method for manufacturing a semiconductor device wherein a contact hole formed in an interlayer insulating film on a semiconductor substrate is filled with a plug for electrically connecting an overlying conductor layer with an underlying conductor layer. The plug fills the contact hole, and comprised a tungsten film the upper end whereof is positioned below the upper surface of the interlayer insulating film, and a tungsten film which is filled on the tungsten film in the contact hole and the upper surface whereof is on substantially the same level as the upper surface of the interlayer insulating film.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method for manufacturing a semiconductor device, and specifically to a semiconductor device comprising a plug for connecting between an upper conductive layer and a lower conductive layer.  
           [0003]    2. Background Art  
           [0004]    In recent semiconductor devices, a plug made of tungsten (W) is frequently used as a plug structure for filling a contact hole or a via hole. Known methods for forming tungsten plugs include a method utilizing etch back, and a method utilizing CMP (chemical mechanical polishing).  
           [0005]    In the etch-back method, metal wiring must be embedded in the plug recess portion after forming a plug. On the other hand, in the plug forming method using CMP, since embedding of such metal wiring is not required, and the foreign matter formed in the formation of the tungsten film and the etch back of tungsten can be removed by CMP, short-circuiting between wirings can be reduced. Therefore, the plug forming method using CMP is becoming the main stream of plug forming.  
           [0006]    In the plug forming method using CMP, aiming at the removal of metal contamination and foreign matter after polishing, cleaning with hydrogen fluoride (HF), which is inexpensive and easy to handle, is frequently used.  
           [0007]    However, in the tungsten plug forming method using CMP, the degradation of electrical properties of wiring caused by voids, seams, or the like formed in the tungsten plug forming was unavoidable. Problems arisen in a conventional tungsten plug forming method will be described below referring to the drawings.  
           [0008]    [0008]FIGS. 7A and 7B are schematic sectional views showing a method for forming a tungsten plug using CMP. FIG. 7A shows the state where after forming an interlayer insulating film  102  on an underlying wiring layer  101  to form a contact hole, and sequentially forming a titanium film  103  and a titanium nitride film  104  so as to cover the internal wall of the contact hole, a tungsten film  105  is formed using the CVD method to fill the contact hole. Here, the underlying wiring layer  101  may be a semiconductor substrate. In the state where the contact hole has been filled with the tungsten film  105 , a seam portion  106  has been formed in the contact hole.  
           [0009]    [0009]FIG. 7B shows the state where the tungsten film  105  on the interlayer insulating film  102  has been removed by polishing using CMP after the state shown in FIG. 7A, and the product has been cleaned using a hydrogen fluoride (HF) solution. By the removal of the tungsten film  105  on the interlayer insulating film  102 , the tungsten film  105  fills only the inside of the contact hole  107 , and a tungsten plug consisting of the tungsten film  105  is formed.  
           [0010]    As FIG. 7B shows, since the hydrogen fluoride solution dissolves the titanium film  103  between the tungsten film  105  and the interlayer insulating film  102  rapidly in cleaning, the interlayer insulating film  102  positioned outside the contact hole moves back, and a gap  108  is formed.  
           [0011]    If the gap  108  reaches the underlying wiring layer (or semiconductor substrate)  101 , the underlying wiring layer (or semiconductor substrate)  101  is removed by hydrogen fluoride, and a void  109  as shown in FIG. 7B is formed.  
           [0012]    A problem of increase in via resistance and contact resistance has arisen by the formation of such a void  109 . Also, the void  109  has caused open defects to occur. Thereby, increase in the speed of semiconductor devices has been disturbed, and the reliability of semiconductor devices has been lowered.  
           [0013]    In the state after polishing shown in FIG. 7B, since the tungsten film  105  on the seam portion  106  is removed by polishing, the inside of the seam portion  106  is exposed upward. And the size of the seam portion  106  increases when hydrogen peroxide (aqueous solution of H 2 O 2 ) used in polishing permeates into the seam portion  106 . Therefore, a problem of decrease in the contact area of the tungsten film  105  with the overlying wiring has arisen.  
           [0014]    [0014]FIGS. 8A and 8B are plan views showing a decreased contact area of the tungsten film  105  with the overlying wiring, and shows the state where a metal wiring  110  consisting of, for example, aluminum on the tungsten film  105  has been formed from the state shown in FIG. 7B. Here, FIG. 8A shows an example wherein the metal wiring  110  is formed so as to overlap with the seam portion  106 , and FIG. 8B shows another example wherein the metal wiring  110  is formed beyond the seam portion  106 . In FIGS. 8A and 8B, the hatched areas show the regions where the metal wiring  110  contacts with the tungsten film  105 .  
           [0015]    As FIG. 8A shows, when the metal wiring  110  is formed so as to overlap with the seam portion  106 , the larger the size of the seam portion  106 , the smaller the contact area of the metal wiring  110  with the plug consisting of the tungsten film  105 . Thus, a problem that the decreased contact area of the metal wiring  110  with the tungsten film  105  lowers the reliability of semiconductor devices, such as EM resistance, has arisen.  
           [0016]    Also, as FIG. 8B shows, when the metal wiring  110  is formed beyond the seam portion  106 , the seam portion  106  is completely exposed upward. Therefore, when an aluminum alloy, which is a material of the metal wiring  110 , is subjected to dry etching, side etch occurs on the side of the metal wiring  110  along the contours of the seam portion  106 . Thereby, a problem that the reliability of semiconductor devices, such as EM resistance, is deteriorated by decrease in the contact area, has arisen.  
           [0017]    Furthermore, another problem that a wet solution permeates into the seam portion  106  corroding the plug has arisen when the tungsten film  105  is polished by CMP using hydrogen peroxide, when the tungsten film  105  is cleaned after polishing, or when a polymer is removed during etching for forming the overlying metal wiring. Therefore, a problem of the deterioration of electrical properties of the plug has arisen.  
           [0018]    In addition, when a tungsten plug is formed by polishing the tungsten film  105  using CMP, a problem of the deterioration of the accuracy of the alignment and superposition test marks for the photoengraving of the metal wirings, has arisen.  
           [0019]    [0019]FIGS. 9A and 9B are schematic sectional views showing the state where the accuracy of the alignment and superposition test marks has been deteriorated. Here, FIG. 9A shows the state immediately after the tungsten film  105  is formed, and FIG. 9B shows the state after polishing using CMP.  
           [0020]    In FIGS. 9A and 9B, a tungsten film  105  is formed through a barrier metal film  111  in an opening  112  formed in an interlayer insulating film  102 . Here, the barrier metal film  111  is a laminated film of a titanium film  103  and a titanium nitride film  104  shown in FIGS. 7A and 7B. As FIG. 9A shows, since the tungsten film  105  is formed along the internal wall of the opening  112 , a step  105   a  is formed on the center of the opening  112  in the state after polishing shown in FIG. 9B. The alignment and superposition for the photoengraving of the metal wirings is tested using this step  105   a.    
           [0021]    However, since the tungsten film  105  on the bottom of the opening  112  of the interlayer insulating film  102  in the test mark portion is not completely removed by polishing using CMP, a problem that the step  105   a  becomes small has arisen.  
           [0022]    Therefore, when a tungsten plug is formed using CMP, if the step  105   a  in the alignment and superposition test mark portion is formed together with the tungsten plug, the step  105   a  becomes shallow, and the detection of the step  105   a  in test becomes difficult. Therefore, a problem that the accuracy of alignment and superposition detection is lower than in the case of using the etch-back method, has arisen.  
         SUMMARY OF THE INVENTION  
         [0023]    The present invention aims at the solution of the above-described problems, and the object of the present invention is to improve the electrical properties and reliability of plugs in semiconductor devices, and to achieve the improvement of the accuracy of alignment and superposition tests.  
           [0024]    According to one aspect of the present invention, a method for manufacturing a semiconductor device comprises following steps. An insulating film is formed on a semiconductor substrate. An opening passing through the insulating film is formed by selectively removing the insulating film. A first adhering layer is formed so as to cover the internal wall and the bottom of the opening. A first conductive film is formed so as to fill the area on the insulating film and in the opening. A recess is formed by etching the first conductive film so that the first conductive layer is removed from the insulating film. And the upper surface of the first conductive film remaining in the opening is lower than the upper surface of the insulating film. A second conductive film is formed in the recess and on the insulating film. The recess is filled with the second conductive film by polishing the second conductive film until the insulating film is exposed.  
           [0025]    Since the conductor for filling the opening is made to be a two-stage structure consisting of a first conductive film and a second conductive film, the gap (seam portion) within the opening can be tightly sealed. Therefore, decrease in the contact area with the overlying wiring connected to the conductor by the gap can be inhibited. Thereby, the contact resistance with the overlying wiring can be reduced, and reliability such as EM resistance can be improved.  
           [0026]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIGS. 1A through 1D and  2 A through  2 D are schematic sectional views illustrating a method for manufacturing a semiconductor device according to First Embodiment in the order of process steps.  
         [0028]    [0028]FIGS. 2A through 2D are schematic sectional views showing the alignment mark portion and the superposition test mark portion for photoengraving formed in another region on the semiconductor substrate.  
         [0029]    [0029]FIGS. 3A through 3D are schematic sectional views illustrating a method for manufacturing a semiconductor device according to Second Embodiment in the order of process steps.  
         [0030]    [0030]FIG. 4 is a schematic sectional view illustrating a semiconductor device according to Third Embodiment.  
         [0031]    [0031]FIGS. 5A and 5B are schematic sectional views illustrating a method for manufacturing a semiconductor device according to Fourth Embodiment in the order of process steps.  
         [0032]    [0032]FIGS. 6A and 6B are schematic sectional views illustrating a method for manufacturing a semiconductor device according to Fifth Embodiment in the order of process steps.  
         [0033]    [0033]FIGS. 7A and 7B are schematic sectional views showing a method for forming a tungsten plug using CMP.  
         [0034]    [0034]FIGS. 8A and 8B are plan views showing a decreased contact area of the tungsten film  105  with the overlying wiring.  
         [0035]    [0035]FIGS. 9A and 9B are schematic sectional views showing the state where the accuracy of the alignment and superposition test marks has been deteriorated. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    Some embodiments of the present invention will be described below referring to the drawings.  
         [0037]    First Embodiment  
         [0038]    [0038]FIGS. 1A through 1D and  2 A through  2 D are schematic sectional views illustrating a method for manufacturing a semiconductor device according to First Embodiment in the order of process steps. The structure and the manufacturing method of a semiconductor device according to First Embodiment will be described below referring to FIGS. 1A through 1D and  2 A through  2 D.  
         [0039]    First, an interlayer insulating film  2  is formed on a conductive layer  1  so as to cover the conductive layer  1  with the interlayer insulating film  2 . Here, the conductive layer  1  is a semiconductor substrate or a wiring layer formed on a semiconductor substrate. Next, the interlayer insulating film  2  is selectively removed to form a contact hole  7  (opening) reaching the conductive layer  1 . Thereafter, a barrier metal film (first adhering layer) composing of a laminated film consisting of a titanium film  3  and a titanium nitride film  4  is formed on the internal wall of the contact hole  7  and on the interlayer insulating film  2 , and a tungsten film  5  (first conductive film) is formed on the barrier metal film to fill the contact hole  7 . At this time a seam portion  6  (gap) is formed in the tungsten film  5  in the contact hole  7 . This state is shown in FIG. 1A.  
         [0040]    Next, as FIG. 1B shows, etch back is performed using the titanium nitride film  4  as a stopper. Thereby, the tungsten film  5  is removed from the interlayer insulating film  2 , and a predetermined quantity of the tungsten film  5  in the contact hole  7  is removed. And as FIG. 1B shows, a recess  8  having a depth d 1  from the upper surface of the titanium nitride film  4  and a diameter D is formed. Thereby, the seam portion  6  formed in the contact hole  7  is exposed outward.  
         [0041]    Next, as FIG. 1C shows, a tungsten film  9  (second conductive film)is formed to fill the recess  8 . Thereby, the tungsten film  9  is laminated on the tungsten film  5  in the contact hole  7 , and the exposed seam portion  6  is sealed by the tungsten film  9 .  
         [0042]    Next, as FIG. 1D shows, the tungsten film  9  is polished using CMP. Here, since the recess  8  is a shallow hole, the coverage of the tungsten film  9  on the bottom of the recess  8  is substantially the same as the coverage on the side of the recess  8 . Therefore, when a tungsten film  9  is formed in the recess  8  in the process step shown in FIG. 1C, the tungsten film  9  is deposited upward from the bottom of the recess  8 , as well as in the lateral direction from the side of the recess  8 , and a seam portion  9   a  is also formed on the tungsten film  9 . As FIG. 1C shows, in the state where the seam portion  9   a  is adhered, since a tungsten film  9  of a thickness of D/2 is deposited from the side wall of the recess  8 , and the coverage is uniform, the lower end of the seam portion  9   a  is positioned above the bottom of the recess  8  by D/2. Therefore, if the recess  8  is formed in the state of FIG. 1B so as to be D/2&gt;d 1 , the lower end of the seam portion  9   a  is always above the upper surface of the titanium nitride film  4 , and the seam portion  9   a  is never exposed upward by polishing using CMP shown in FIG. 1D. Thus, if the shape of the recess  8  is established so as to be D/2&gt;d 1 , the presence of the remaining seam portion  9   a  on the tungsten film  9  in the state of FIG. 1D can be inhibited. Thus, a tungsten plug (conductor) of a two-stage structure consisting of tungsten films  5  and  9  can be formed in the contact hole  7  without leaving the seam portion  9   a  on the upper surface.  
         [0043]    Even if the condition of D/2&gt;d 1  is not satisfied, since the depth d 1  of the recess  8  is shallow, the recess  8  can be filled by the film thickness of the tungsten film  9 . Therefore, even if the diameter and depth of the recess  8  is not specified, the occurrence of the seam portion on the tungsten film  9  can be prevented because the plug has a two-stage structure.  
         [0044]    Since the tungsten plug can be made to have a two-stage structure, and the upward exposure of the seam portion  6  can be prevented, the contact area of the tungsten plug with the metal wiring can be secured sufficiently when the overlying metal wiring to be connected to the tungsten plug is formed. Therefore, the electrical resistance of the contact between the tungsten plug and the metal wiring can be lowered, and the reliability of the contact, such as EM resistance, can be improved. Also, by preventing the upward exposure of the seam portion  6 , the corrosion of the tungsten plug during polishing using CMP, or following cleaning or the like can be prevented.  
         [0045]    Next, the step for forming the alignment mark and the superposition test mark formed together with the tungsten plug of FIGS. 1A through 1D will be described below referring to FIGS. 2A through 2D. FIGS. 2A through 2D are schematic sectional views showing the alignment mark portion and the superposition test mark portion for photoengraving (hereafter referred to “mark portion”) formed in another region on the semiconductor substrate.  
         [0046]    First, as FIG. 2A shows, an interlayer insulating film  2  is formed on a conductive layer  1 , and by selectively removing the interlayer insulating film  2 , an opening  11  extending to the conductive layer  1  is formed. Thereafter, a barrier metal film  12  is formed on the internal wall of the opening  11  and on the interlayer insulating film  2 , and a tungsten film  5  is formed on the barrier metal film  12  to fill the opening  11 . Here the barrier metal film  12  is composed of a laminated film consisting of a titanium film  3  and a titanium nitride film  4  as FIGS. 1A through 1D show. This process step corresponds to the process step of FIG. 1A.  
         [0047]    Next, as FIG. 2B shows, etch back is performed using the barrier metal film  12  as a stopper. Thereby, the tungsten film  5  is removed from the interlayer insulating film  2  and the opening  11 , and the barrier metal film  12  on the bottom of the opening  11  is exposed. In the opening  11 , the tungsten film  5  remains on a part of the sidewall. This process step corresponds to the process step of FIG. 1B. Thus, in the mark portion, since the opening  11  of a width larger than the depth of the interlayer insulating film  2  is usually formed, after the etch back of the tungsten film  5 , the tungsten film  5  on the bottom of the opening  11  is completely etched back, and the underlying barrier metal film  12  is exposed as FIG. 2B shows.  
         [0048]    Next, as FIG. 2C shows, a tungsten film  9  is formed to cover the tungsten film  5  and the barrier metal film  12  in the opening  11 . This process step corresponds to the process step of FIG. 1C.  
         [0049]    Next, as FIG. 2D shows, the tungsten film  9  and the barrier metal film  12  on the interlayer insulating film  2  are removed by polishing using CMP. This process step corresponds to the process step of FIG. 1D. Thereby, the tungsten film  9  is left only in the opening  11 . In the process step shown in FIG. 2B, in order to etch back until the barrier metal film  12  in the opening  11  is exposed, a step  9   a  of a sufficient depth (=d 2 ) is formed on the surface of the tungsten film  9 , as FIG. 2D shows.  
         [0050]    In particular, since the tungsten film  9  is formed only for filling the recess  8  of the contact hole  7  shown in FIGS. 1A through 1D, it is sufficient to determine the film thickness of the tungsten film  9  to be the film thickness of the recess  8  or below. Thereby, as FIG. 2D shows, the step  9   a  on the surface of the tungsten film  9  can be deepened even after the tungsten film  9  has been polished. Therefore, it is ensured that the step  9   a  is formed in the mark portion, and the alignment and super position test for photoengraving can be performed at a high accuracy.  
         [0051]    According to First Embodiment, as described above, since the tungsten plug is made to be a two-stage structure consisting of a tungsten film  5  and a tungsten film  9 , the seam portion  6  in the contact hole  7  can be sealed tightly. Therefore, decrease in the contact area with the overlying wiring connected to the tungsten plug by the seam portion  6  can be prevented. Thereby, it can be ensured that the contact area of the tungsten plug with the overlying wiring is sufficiently widened, and decrease in electrical resistance in the contacting portion with the overlying wiring can be achieved. Also, since the contact area of the tungsten plug with the overlying wiring can be widened, reliability such as EM resistance can be improved. In addition, since the seam portion  6  is tightly sealed, the permeation of the polishing liquid used in CMP, the etching solution in the following process steps, and the cleaning solution into the seam portion  6  can be inhibited, and the corrosion of the tungsten plug can be prevented.  
         [0052]    Furthermore, in the alignment mark portion and the superposition test mark portion for photoengraving, since the tungsten film  5  is removed by etch back until the bottom of the opening  11  is exposed, and the tungsten film  9  of the thickness substantially the same as the depth of the recess  8  in the region to form the contact hole  7  is formed, the tungsten film  9  can be formed along the internal wall of the opening  11 . Therefore, the step  9   a  on the surface of the tungsten film  9  can be made sufficiently deep, it can be ensured that the step  9   a  is detected. Thereby, the accuracy of the alignment adjustment and the superposition test in photoengraving can be improved significantly.  
         [0053]    Second Embodiment  
         [0054]    [0054]FIGS. 3A through 3D are schematic sectional views illustrating a method for manufacturing a semiconductor device according to Second Embodiment in the order of process steps. The structure and the manufacturing method of a semiconductor device according to Second Embodiment will be described below referring to FIGS. 3A through 3D. In FIGS. 3A through 3D, the same reference numerals are used for the same constituting components as in First Embodiment.  
         [0055]    In the manufacturing process of Second Embodiment, the process step shown in FIG. 1A of First Embodiment is carried out in the same manner as in First Embodiment. FIG. 3A shows the state where the tungsten film  5  has been etched back after the process step shown in FIG. 1A of First Embodiment. Here, in Second Embodiment, the interlayer insulating film  2  is used as the stopper for etch back. Therefore, as shown in FIG. 3A, in the contact hole  7 , the titanium film  3  and the titanium nitride film  4  above the upper surface of the tungsten film  5  have been removed. Also, in the region other than the contact hole  7 , the titanium film  3  and the titanium nitride film  4  on the interlayer insulating film  2  have been removed, and the interlayer insulating film  2  has been exposed. In the state shown in FIG. 3A, a seam portion  6  is formed in the tungsten film  5  as in First Embodiment.  
         [0056]    After the process step shown in FIG. 3A, as FIG. 3B shows, a titanium film  13  and a titanium nitride film  14  are sequentially formed on the tungsten film  5  and the interlayer insulating film  2  in the contact hole  7 , and a barrier metal film (second adhering layer) consisting of the titanium film  13  and the titanium nitride film  14  is formed. Then, a tungsten film  15  (second conductive film) is formed again on the titanium nitride film  14 . Thereby, the seam portion  6  that has been exposed upward is tightly sealed.  
         [0057]    Next, as FIG. 3C shows, the tungsten film  15 , the titanium nitride film  14 , and the titanium film  13  are removed from the interlayer insulating film  2  are removed by polishing using CMP, and the interlayer insulating film  2  is exposed. Thereby, the tungsten plug of Second Embodiment is completed.  
         [0058]    In Second Embodiment, since the titanium film  13  and the titanium nitride film  14  are formed between the tungsten film  5  and the tungsten film  15 , the adhesion of the tungsten film  5  and the tungsten film  15  can be enhanced. Also, when the tungsten film  5  and the tungsten film  15  are substituted by two kinds of different conductive materials as the materials for the plug, ohmic properties between these different materials can be improved, and the diffusion of conductive materials to each other can be prevented.  
         [0059]    According to Second Embodiment, since the tungsten plug is made to be a two-stage structure consisting of a tungsten film  5  and a tungsten film  15 , the seam portion  6  formed in the tungsten film  5  can be tightly sealed. Therefore, as in First Embodiment, the contact area with the overlying wiring can be widened, decrease in electrical resistance and the improvement of reliability such as EM resistance can be achieved, and the corrosion of the tungsten plug can be prevented. Furthermore, by the etch back of the tungsten film  5 , the step of the mark portion can be deepened as in First Embodiment, and the accuracy of alignment and superposition test can be improved.  
         [0060]    Third Embodiment  
         [0061]    [0061]FIG. 4 is a schematic sectional view illustrating a semiconductor device according to Third Embodiment. A semiconductor device of Third Embodiment will be described below referring to FIG. 4. In FIG. 4, the same reference numerals are used for the same constituting components as in First and Second Embodiments.  
         [0062]    [0062]FIG. 4 shows the state where only a titanium nitride film  11  has been formed as a barrier metal film after a tungsten film  5  has been etched back in the process step shown in FIG. 3B of Second Embodiment. Other structures are identical to those of Second Embodiment.  
         [0063]    Thus, by forming the barrier metal film only from a titanium nitride film  11 , the dissolution of titanium in the barrier metal film can be prevented during cleaning with a hydrogen fluoride solution after polishing the tungsten film  15  using CMP.  
         [0064]    Since the tungsten plug is made to be a two-stage structure, as in First Embodiment, the contact area with the overlying wiring can be widened, decrease in electrical resistance and the improvement of reliability such as EM resistance can be achieved, and the corrosion of the tungsten plug can be prevented. Furthermore, the step of the mark portion can be deepened as in First Embodiment, and the accuracy of alignment and superposition test can be improved.  
         [0065]    Fourth Embodiment  
         [0066]    [0066]FIGS. 5A and 5B are schematic sectional views illustrating a method for manufacturing a semiconductor device according to Fourth Embodiment in the order of process steps. The structure and the manufacturing method of a semiconductor device according to Fourth Embodiment will be described below referring to FIGS. 5A and 5B. In FIGS. 5A and 5B, the same reference numerals are used for the same constituting components as in First and Second Embodiments.  
         [0067]    In the manufacturing process of Fourth Embodiment, the process step shown in FIG. 1A of First Embodiment is carried out in the same manner as in First Embodiment. FIG. 5A shows the state where the tungsten film  5  has been etched back after the process step shown in FIG. 1A of First Embodiment. Here, in Fourth Embodiment, the interlayer insulating film  2  is used as the stopper for etch back. Therefore, as shown in FIG. 5A, in the contact hole  7 , the titanium film  3  and the titanium nitride film  4  above the upper surface of the tungsten film  5  have been removed. Also, in the region other than the contact hole  7 , the titanium film  3  and the titanium nitride film  4  on the interlayer insulating film  2  have been removed, and the interlayer insulating film  2  has been exposed. As in First Embodiment, a seam portion  6  is formed in the tungsten film  5 .  
         [0068]    In Fourth Embodiment, after the tungsten film  5  has been etched back, the titanium film  10  on the sidewall of the contact hole  7  is oxidized by oxygen (O 2 ) plasma treatment, or by annealing in an oxygen atmosphere. Thereby, a titanium oxide (Ti x O y ) film  16  is formed on the titanium film  10 , and the upward exposure of the titanium film  10  is prevented.  
         [0069]    Thereafter, as FIG. 5B shows, a barrier metal film consisting of a titanium film  13  and a titanium nitride film  14  is formed as in Second Embodiment, and a tungsten film  15  is formed to seal the seam portion  6 . Then, the tungsten film  15  is polished using CMP, and cleaning with a hydrogen fluoride solution is performed.  
         [0070]    In cleaning with the hydrogen fluoride solution, the titanium film  13  exposed to the top is dissolved, and a gap  17  is formed. However, underneath the titanium film  13 , since a titanium oxide film  16  is formed along the internal wall of the contact hole  7 , the dissolution of titanium stops when the gap  17  reaches the titanium oxide film  16 . Therefore, the dissolution of the titanium film  3  under the titanium oxide film  16  in the hydrogen fluoride solution can be inhibited, and the reaching of the gap  17  to the underlying conductive layer  1  can be prevented.  
         [0071]    Since the tungsten plug is made to be a two-stage structure, as in First Embodiment, the contact area with the overlying wiring can be widened, decrease in electrical resistance and the improvement of reliability such as EM resistance can be achieved, and the corrosion of the tungsten plug can be prevented. Furthermore, the step of the mark portion can be deepened as in First Embodiment, and the accuracy of alignment and superposition test can be improved.  
         [0072]    Fifth Embodiment  
         [0073]    [0073]FIGS. 6A and 6B are schematic sectional views illustrating a method for manufacturing a semiconductor device according to Fifth Embodiment in the order of process steps. The structure and the manufacturing method of a semiconductor device according to Fifth Embodiment will be described below referring to FIGS. 6A and 6B. In FIGS. 6A and 6B, the same reference numerals are used for the same constituting components as in First Embodiment.  
         [0074]    In the manufacturing process of Fifth Embodiment, the process step shown in FIG. 1A of First Embodiment is carried out in the same manner as in First Embodiment. FIG. 6A shows the state where the tungsten film  5  has been etched back after the process step shown in FIG. 1A of First Embodiment. Here, in Fifth Embodiment, the interlayer insulating film  2  is used as the stopper for etch back. Therefore, as shown in FIG. 6A, in the contact hole  7 , the titanium film  3  and the titanium nitride film  4  above the upper surface of the tungsten film  5  have been removed. Also, in the region other than the contact hole  7 , the titanium film  3  and the titanium nitride film  4  on the interlayer insulating film  2  have been removed, and the interlayer insulating film  2  has been exposed. As in First Embodiment, a seam portion  6  is formed in the tungsten film  5 .  
         [0075]    In Fifth Embodiment, after the tungsten film  5  has been etched back, the titanium film  10  on the sidewall of the contact hole  7  is nitrogenized by nitrogen (N 2 ) plasma treatment, or by annealing in an nitrogen atmosphere at a temperature of 600° C. or above. Thereby, a titanium nitride (Ti x N y ) film  18  is formed on the titanium film  10 , and the upward exposure of the titanium film  10  is prevented.  
         [0076]    Thereafter, as FIG. 6B shows, a barrier metal film consisting of a titanium film  13  and a titanium nitride film  14  is formed as in Second Embodiment, and a tungsten film  15  is formed to seal the seam portion  6 . Then, the tungsten film  15  is polished using CMP, and cleaning with a hydrogen fluoride solution is performed.  
         [0077]    In cleaning with the hydrogen fluoride solution, the titanium film  13  exposed to the top is dissolved, and a gap  19  is formed. However, underneath the titanium film  13 , since a titanium nitride film  18  is formed along the internal wall of the contact hole  7 , the dissolution of titanium stops when the gap  19  reaches the titanium nitride film  18 . Therefore, the dissolution of the titanium film  3  under the titanium nitride film  18  in the hydrogen fluoride solution can be inhibited, and the reaching of the gap  19  to the underlying conductive layer  1  can be prevented.  
         [0078]    Since the tungsten plug is made to be a two-stage structure, as in First Embodiment, the contact area with the overlying wiring can be widened, decrease in electrical resistance and the improvement of reliability such as EM resistance can be achieved, and the corrosion of the tungsten plug can be prevented. Furthermore, the step of the mark portion can be deepened as in First Embodiment, and the accuracy of alignment and superposition test can be improved.  
         [0079]    In the above-described embodiments, although tungsten, which has favorable filling properties, is used as an example of a material for a plug, copper, which has lower resistance, can also be used in place of tungsten. Also, although a laminated film consisting of a titanium film and a titanium nitride film is used as an example of a barriar metal film, a laminated film consisting of a tantalum film and a tantalum nitride film, or a three-layer laminated film consisting of a tantalum film, a tantalum nitride film, and a tantalum film can also be used. Furthermore, a single layer tantalum film, or a single layer tantalum nitride film can also be used.  
         [0080]    Since the present invention is constituted as described above, the following effects can be obtained.  
         [0081]    Since the conductor for filling the opening is made to be a two-stage structure consisting of a first conductive film and a second conductive film, the gap (seam portion) within the opening can be tightly sealed. Therefore, decrease in the contact area with the overlying wiring connected to the conductor by the gap can be inhibited. Thereby, the contact resistance with the overlying wiring can be reduced, and reliability such as EM resistance can be improved.  
         [0082]    Since the diameter of the opening is made larger than the depth from the upper surface of the insulating film to the upper end of the first conductive film, the formation of a gap (seam portion) on the surface of the second conductive film can be inhibited.  
         [0083]    Since a first adhering layer is formed on the internal wall and the bottom of the opening, the adhesion of the conductor to the inside of the opening can be enhanced, and the diffusion of the conductive materials constituting the conductor to other layers can be inhibited.  
         [0084]    Since a second adhering layer is formed so as to cover the side and the lower surface of the second conductive film, the adhesion and ohmic properties of the first conductive film and the second conductive film can be improved, and the mutual diffusion of the conductive materials constituting the first conductive film and the second conductive film can be inhibited.  
         [0085]    Since the upper end portion of the titanium film of the first adhering layer in the upper portion of the internal wall of the opening is oxidized or nitrogenized, the dissolution of the underlying titanium film due to the following cleaning step, the etching step, and the like, can be inhibited, and the formation of voids in the further underlying conductive layer and semiconductor substrate can be prevented.  
         [0086]    Since the first conductive film is formed only on the circumferential portion along the internal wall of the opening, and the first conductive film is removed from a part of the bottom of the opening, a step can be formed on the upper surface in the vicinity of the center of the opening in formation of the second insulating film. Thereby on aligning, the step can be surely detected, and the adjustment of alignment and the accuracy of the superposition test in photoengraving can be significantly improved.  
         [0087]    Since tungsten films are used as the first and second conductive films, it is ensured that even an opening having a large aspect ratio is completely filled. Also, by using copper films as the first and second conductive films, decrease in the resistance of the conductor can be achieved.  
         [0088]    Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may by practiced otherwise than as specifically described.  
         [0089]    The entire disclosure of a Japanese Patent Application No. 2001-361243, filed on Nov. 27, 2001 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.