Abstract:
Disclosed herein is a semiconductor device with improved electromigration durability and a method for producing the semiconductor device. A semiconductor device includes: an interlayer insulating film formed on a first metal wiring; a second metal wiring formed by embedding in the interlayer insulating film; a metal contact formed by embedding in the interlayer insulating film, for connecting between the first metal wiring and the second metal wiring; a first capping layer formed between the first metal wiring and the metal contact; and a barrier metal layer formed between the second metal wiring and the interlayer insulating film, for preventing metal diffusion in the second metal wiring. A method of producing a semiconductor device includes the steps of: forming an interlayer insulating film on a substrate having a first metal wiring formed thereon; forming in the interlayer insulating film a via hole reaching the first metal wiring; selectively forming a first capping layer only on the bottom of the via hole; forming a barrier metal layer on the inner wall of the via hole; and embedding a metal layer in the via hole.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present invention contains subject matter related to Japanese Patent Application JP 2005-018367 filed in the Japanese Patent Office on Jan. 26, 2005, the entire contents of which being incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a semiconductor device and a method for producing a semiconductor device, and more particularly, to a semiconductor device and a method for production thereof, which involve the groove wiring technology such as dual damascene or single damascene.  
         [0003]     The wiring material for LSI is being changed from aluminum alloy into copper because the latter has better electromigration durability and lower resistance than the former. Since copper usually encounters difficulties in dry etching, the copper wiring is formed by previously forming a wiring groove in the interlayer insulating layer and then filling the groove with the wiring material and finally removing the excess part of the wiring material by CMP (Chemical Mechanical Polishing).  
         [0004]     Incidentally, it is known that the copper wiring exhibits improved electromigration durability when it is covered with a capping layer of CoWP. (See Non-patent Document 1: T. Ishigami et al., “High Reliability Cu Interconnection Utilizing a Low Contamination CoWP Capping Layer”, IITC (International Interconnect Technology Conference), proceeding, p. 75-77 (2004))  
         [0005]     In the case of multi-layer interconnection, it is necessary to make via holes in the interlayer insulating layer for connection between the upper wiring and the lower wiring. The step of making via holes needs etching through a resist film on the interlayer insulating film, removal of resist by ashing, and wet cleaning to remove etching residues.  
       SUMMARY OF THE INVENTION  
       [0006]     The disadvantage of the above-mentioned conventional technology is that the capping layer formed on the low level wiring is partly or entirely lost from the via holes after etching, ashing, and wet etching. This makes the wiring vulnerable to electromigration that occurs when electrons flow from the upper level to the lower level.  
         [0007]     The present invention was completed in view of the foregoing. It is an object of the present invention to provide a semiconductor device with improved electron migration durability and a method for production thereof.  
         [0008]     The semiconductor device according to the present invention includes an interlayer insulating film formed on a first metal wiring, a second metal wiring embedded in said interlayer insulating film, a metal contact embedded in said interlayer insulating film for connection between said first metal wiring and said second metal wiring, a first capping layer formed between said first metal wiring and said metal contact for the prevention of electromigration in the metal wiring, and a barrier metal layer formed between said second metal wiring and said interlayer insulating film for the prevention of metal diffusion in said second metal wiring.  
         [0009]     The semiconductor device according to the present invention has the first capping layer which is formed between the first metal layer and the metal contact for the prevention of electromigration in the metal wire. Thus the first capping layer reinforces the region immediately under the contact from which electromigration starts when electrons flow from the second metal wiring in the upper level to the first metal wiring in the lower level.  
         [0010]     The method of producing the semiconductor device according to the present invention includes a step of forming an interlayer insulating film on a substrate having a first metal wiring formed thereon, a step of forming in said interlayer insulating film a via hole reaching said first metal wiring, a step of selectively forming a first capping layer only on the bottom of said via hole, a step of forming a barrier metal layer on the inner wall of said via hole, and a step of embedding a metal layer in said via hole.  
         [0011]     The method of producing the semiconductor device according to the present invention has the step of selectively forming the first capping layer only on the bottom of the via hole after a via hole reaching the first metal wiring has been formed. Thus the first capping layer reinforces the region immediately under the contact at which electromigration starts when electrons flow from the second metal wiring in the upper level to the first metal wiring in the lower level.  
         [0012]     The semiconductor device according to the present invention has improved electromigration durability. The method of producing the semiconductor device according to the present invention provides a semiconductor device having improved electromigration durability. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a sectional view showing one example of the semiconductor device pertaining to the present invention;  
         [0014]      FIGS. 2A and 2B  are sectional views showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0015]      FIGS. 3A and 3B  are sectional views showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0016]      FIGS. 4A and 4B  are sectional views showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0017]      FIGS. 5A and 5B  are sectional views showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0018]      FIGS. 6A and 6B  are sectional views showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0019]      FIGS. 7A and 7B  are sectional views showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0020]      FIGS. 8A and 8B  are sectional views showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0021]      FIG. 9  is a sectional view showing the process of fabricating the semiconductor device pertaining to the present invention;  
         [0022]      FIG. 10  is a sectional view showing another example of the semiconductor device pertaining to the present invention;  
         [0023]      FIG. 11  is a sectional view showing another example of the semiconductor device pertaining to the present invention;  
         [0024]      FIG. 12  is a sectional view showing another example of the semiconductor device pertaining to the present invention;  
         [0025]      FIG. 13  is a sectional view showing another example of the semiconductor device pertaining to the present invention; and  
         [0026]      FIG. 14  is a sectional view showing another example of the semiconductor device pertaining to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     The embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0028]      FIG. 1  is a sectional view showing one example of the semiconductor device pertaining to the present invention.  
         [0029]     There is shown a substrate  1  of semiconductor such as silicon. On the substrate  1  is an interlayer insulating film of silicon oxide. In the interlayer insulating film  2  is a contact  3  of tungsten. On the substrate  1  are transistors and other semiconductor elements to which the contact  3  is connected.  
         [0030]     On the interlayer insulating film  2  and the contact  3  is an interlayer insulating film  4 . In this embodiment, the interlayer insulating film  4  is composed of an organic insulating film  5  of polyarylene and a hard mask  6  of silicon oxide which has been used to form the insulating film  5 . Incidentally, the insulating film  5  may also be formed from SiCOH or may be replaced by so-called Low-k film.  
         [0031]     In the interlayer insulating film  4  is a wiring groove  4   a.  In the wiring groove  4   a  is a first metal wiring  8  of copper, with a barrier metal layer  7  interposed between the metal wiring  8  and the inner wall of the wiring groove  4   a.  The barrier metal layer  7  is formed between the first metal wiring  8  and the interlayer insulating film  4  in order to prevent the diffusion of copper in the case where the first metal wiring  8  is made of copper, because copper diffuses readily and rapidly into the surrounding insulating material. The barrier metal layer  7  may be a single layer of tantalum (Ta) or may be composed of layers of tantalum nitride (TaN) and tantalum (Ta).  
         [0032]     On the first metal wiring  8  is a capping layer  9  to protect the metal wiring against electromigration. (Electromigration is one kind of diffusion induced by mutual action of metal atoms (copper in this case) in the metal wiring and electrons flowing through the metal wiring. It is the movement of metal ions which is caused by an exchange of momentum between metal ions and electrons carrying electric current. It gives rise to local voids and hillocks.) The capping layer  9  on the first metal wiring  8  prevents the movement of metal ions.  
         [0033]     The capping layer  9  is composed of a first capping layer  9   b  and a second capping layer  9   a.  The former is formed on the top of the first metal wiring  8  in the via hole  10   a,  and the latter is formed on the top of the first metal wiring  8 , except for the region in the via hole  10   a.  The capping layer  9  is made of CoWP (cobalt-tungsten alloy containing phosphorus), for example. The capping layer  9  may also be made of other alloys than CoWP, such as CoWB (cobalt-tungsten alloy containing boron), NiWP (nickel-tungsten alloy containing phosphorus, and NiWB (nickel-tungsten alloy containing boron).  
         [0034]     On the capping layer  9  and the interlayer insulating film  4  is the interlayer insulating film  10 , which is composed of an etching stopper layer  11 , a first insulating film  12 , a second insulating film  13 , and a first hard mask  14 , which are sequentially deposited upward.  
         [0035]     The etching stopper layer  11  is made of silicon carbide (SiC), SiCN, or the like. The first insulating film  12  is made of SiOC or the like. The second insulating film  13  is an organic insulating film made of polyarylene or the like. The first hard mask  14  is made of silicon oxide or the like.  
         [0036]     In the etching stopper layer  11  (in the interlayer insulating film  10 ) and the first insulating film  12  is the via hole  10   a.  In the second insulating film  13  and the first hard mask  14  is the wiring groove  10   b  communicating with the via hole  10   a.    
         [0037]     In the via hole  10   a  and the wiring groove  10   b  is the metal layer  18  of copper, with the barrier metal layer  17  placed thereunder which covers the inner wall of the via hole  10   a  and the wiring groove  10   b.  The barrier metal layer  17  prevents the diffusion of copper in the metal layer  18 . The barrier metal layer  17  may be a single layer of tantalum (Ta) or may be composed of layers of tantalum nitride (TaN) and tantalum (Ta). The metal layer  18  embedded in the via hole  10   a  constitutes the metal contact  19  and the metal layer  18  embedded in the wiring groove  10   b  constitutes the second metal wiring  20 .  
         [0038]     The semiconductor device according to this embodiment has the capping layer  9   b  which is formed between the contact  19  and the first metal wiring  8 . Thus the capping layer  9   b  reinforces the region immediately under the contact  19  at which electromigration starts when electrons flow from the second metal wiring  20  in the upper level to the first metal wiring  8  in the lower level. This improves the electromigration durability, thereby eliminating voids due to electromigration, and improves the reliability of the wiring.  
         [0039]     In addition, the capping layer  9   a  is also formed on the top of the first metal wiring  8  (outside of the contact  19 ) for further improvement in electromigration durability.  
         [0040]     The semiconductor device pertaining to this embodiment is fabricated by the method which is described below with reference to FIGS.  2  to  8 .  
         [0041]     The initial steps (up to the formation of the first metal wiring  8  and the capping layer  9  in the lower level) will be described first. It is assumed that the first metal wiring  8  is formed by the single damascene process (to form a groove wiring).  
         [0042]     As shown in  FIG. 2A , the silicon wafer (substrate  1 ), on which transistors and other semiconductor elements have been formed, is covered with the interlayer insulating film  2  of silicon oxide. In the interlayer insulating film  2  is formed the contact  3  of tungsten for connection to transistors. On the interlayer insulating film  2  and the contact  3  is formed the interlayer insulating film  4  in two steps. First, the insulating film  5  (about 200 nm thick) is formed from polyarylene. Second, the hard mask  6  (about 200 nm thick) on the insulating film  5  is formed from silicon oxide by plasma CVD.  
         [0043]     As shown in  FIG. 2B , the hard mask  6  undergoes etching through a resist mask so that the pattern of the wiring groove  4   a  is formed. The organic insulating film  5  has a high etching selective ratio.  
         [0044]     As shown in  FIG. 3A , the insulating film  5  undergoes etching through the hard mask  6  as an etching mask. Thus the wiring groove  4   a  is formed in the interlayer insulating film  4 . When the insulating film  5  undergoes etching, the resist mask on the hard mask  6  also undergoes etching and hence it disappears.  
         [0045]     As shown in  FIG. 3B , in the wiring groove  4   a  of the interlayer insulating film  4  are formed the barrier metal layer  7  and the first metal wiring  8 . This step proceeds as follows. First, a Ta barrier metal layer (10 nm) and a Cu seed layer (80 nm) are formed by PVD (Physical Vapor Deposition). Second, copper is deposited (up to a thickness of 1000 nm) by electroplating process so that copper is embedded in the wiring groove  4   a.  Unnecessary copper on the interlayer insulating film  4  is removed by CMP process, and unnecessary thallium (as the barrier metal layer  7 ) is also removed by CMP process. The CMP process also shaves away (100 nm) the hard mask  6  on the insulating film  5 . Thus the barrier metal layer  7  of thallium and the first metal wiring  8  of copper are formed in the wiring groove  4   a.    
         [0046]     As shown in  FIG. 4A , the second capping layer  9   a  is selectively formed by electroless plating only on the top of the first metal wiring  8 . This step proceeds as follows. First, cleaning with an aqueous solution of an organic acid (such as citric acid and oxalic acid) is performed to remove the oxide film on the first metal wiring  8  and the anticorrosive compound for copper which has been formed on the surface of the first metal wiring  8  as the result of CMP process. (The anticorrosive compound is benzotriazole or a derivative thereof contained in the slurry for CMP process.) Second, the wafer is treated with an aqueous solution of palladium sulfate. (This step may be accomplished by dipping the wafer entirely in an aqueous solution of palladium sulfate, dropping an aqueous solution of palladium sulfate onto the wafer, or spraying the wafer with an aqueous solution of palladium sulfate.) This treatment permits the displacement plating of palladium only on the first metal wiring  8  through the chemical reaction represented by Pd 2+ +Cu→Pd+Cu 2+ , which takes place because palladium has a smaller ionization tendency than copper. Then, the wafer is treated with a plating solution of CoWP, so that CoWP film (10 to 20 nm thick) is formed on copper by selective plating which employs palladium as a catalyst. Thus the capping layer  9   a  of CoWP is formed only on the first metal wiring  9 .  
         [0047]     The plating of CoWP is carried out under the following conditions. The plating solution is composed of ammonium tungstate 10 g/L, cobalt chloride 30 g/L, ammonium hypophosphite (reducing agent) 20 g/L, ammonium oxalate 80 g/L, and surfactant. Also, the plating solution was kept at 90° C. and pH 8.5 to 10.5.  
         [0048]     The reducing agent mentioned above may be replaced by dimethylamineborane (DMAB) in the case where the capping layer  9   a  is formed from CoWB by electroless plating. Also, the cobalt chloride may be replaced by nickel chloride in the case where NiWP film is formed by electroless plating. Moreover, the cobalt chloride may be replaced by nickel chloride and the reducing agent may be replaced by dimethylamineborane (DMAB) in the case where NiWB film is formed by electroless plating.  
         [0049]     As shown in  FIG. 4B , on the capping layer  9   a  and the interlayer insulating film  4  is formed the etching stopper layer  11  of SiCN (50 nm thick) from trimethylsilane and NH 3 .  
         [0050]     The subsequent steps (up to the formation of the upper level wiring by dual damascene process (to form the groove wiring and contact simultaneously) will be described. Incidentally,  FIGS. 5 and 6  show only the upper layer (above the etching stopper layer  11 ) for the sake of brevity.  
         [0051]     As shown in  FIG. 5A , the interlayer insulating film  10  is formed in the following manner. First, an SiOC film (200 nm thick) is deposited from trimethylsilane by plasma CVD to form the first insulating film  12 . The first insulating film  12  is coated with a polyarylene film (200 nm thick) to form the second insulating film  13 . The second insulating film  13  is coated with SiO 2  film (200 nm thick) deposited from SiH 4  (silane) by plasma CVD, to form the first hard mask  14 . Thus the formation of the interlayer insulating film  10  is completed. Then, the first hard mask  14  is coated with the second hard mask  15  of SiN by plasma CVD, which is used to fabricate the wiring groove and the via hole. The third hard mask  16  of SiO 2  is formed by plasma CVD. A resist mask (not shown) is formed, and the third hard mask  16  (the uppermost layer) undergoes etching through the resist mask to form the pattern of the wiring groove.  
         [0052]     As shown in  FIG. 5B , a resist mask is formed again and the second hard mask  15  undergoes etching through the resist mask to form the pattern of the via hole in the second hard mask  15 .  
         [0053]     As shown in  FIG. 6A , the first hard mask  14  undergoes dry etching through the second hard mask  15  as an etching mask, and then the second insulating film  13  undergoes dry etching. Thus the via hole  10   a  is formed in the first hard mask  14  and the second insulating film  13 . At this time, the resist mask which has been used to fabricate the second hard mask  15  undergoes dry etching together with the second insulating film  13  which is organic.  
         [0054]     As shown in  FIG. 6B , dry etching is performed on the second hard mask  15  through the third hard mask  16  as an etching mask, thereby forming the pattern of the wiring groove in the second hard mask  15 . In this step, the first insulating film  12  of SiOC is partly etched, so that the via hole  10   a  extends to the intermediate depth of the first insulating film  12 .  
         [0055]     As shown in  FIG. 7A , dry etching is performed on the first hard mask  14  through the second hard mask  15  as an etching mask, thereby forming the wiring groove  10   b  in the first hard mask  14 . At this time, the first insulating film  12  also undergoes etching, which forms the via hole  10   a  reaching the etching stopper layer  11 .  
         [0056]     As shown in  FIG. 7B , dry etching is performed on the etching stopper layer  11  on the first metal wiring  8  together with the second hard mask  15  of SiN which is the uppermost layer. After that, wet cleaning is performed to remove etching residues from the via hole  10   a.  The dry etching mentioned above causes cobalt in the capping layer  9   a  to be oxidized by oxygen contained in the dry etching gas. The subsequent wet cleaning removes partly or entirely the capping layer  9   a  of CoWP in the via hole  10   a.  Incidentally,  FIG. 7B  illustrates the intermediate product, with the capping layer  9   a  in the via hole  10   a  entirely removed. The foregoing holds true with CoWB, NiWP, and NiWB.  
         [0057]     As shown in  FIG. 8A , the first capping layer  9   b  is formed only on that part of the first metal wiring  8  which is exposed at the bottom of the via hole  10   a.  This step is carried out in the following manner. First, the wafer is treated with an aqueous solution of palladium sulfate, so that displacement plating of Pd is performed only on Cu (or the bottom of the via hole  10   a ) in the same way as the above-mentioned displacement plating. Incidentally, treatment with palladium may be omitted because there is the possibility that palladium is not removed by wet cleaning. Then, the wafer is treated with a plating solution of CoWP, so that CoWP film (10 to 20 nm thick) is formed on copper by selective plating which employs palladium as a catalyst. In this way the capping layer  9   b  is formed. Plating is carried out under the same conditions as mentioned above. Also, the capping layer  9   b  may be any of CoWB film, NiWP film, and NiWB film.  
         [0058]     As shown in  FIG. 8B , the barrier metal layer  17  is formed on the inner wall of the via hole  10   a  and the wiring groove  10   b,  and the via hole  10   a  and the wiring groove  10   b  are filled with the metal layer  18 . Thus the contact  19  and the second metal wiring  20  are formed. This step is accomplished as follows. First, a tantalum film (10 nm thick) as the barrier metal layer  17  and a copper film (80 nm thick) as the seed layer for plating are formed by PVD. Second, copper is deposited (1000 nm thick) by electroplating so as to fill the via hole  10   a  and the wiring groove  10   b  with copper. Finally, unnecessary copper and tantalum which have been deposited on the interlayer insulating film  10  (except for the via hole  10   a  and the wiring groove  10   b ) are removed by CMP. This CMP shaves away the first hard mask  14  of silicon oxide as much as about 100 nm.  
         [0059]     The desired semiconductor device of multilevel wiring structure is obtained by repeating the steps shown in FIGS.  4  to  8 , viz. by repeating the steps of forming the capping layer, forming the interlayer insulating film, forming the wiring groove and via hole in the interlayer insulating film, selectively forming the capping layer on the bottom of the via hole, and embedding the metal layer.  
         [0060]     The advantage of the above-mentioned method for fabricating the semiconductor device according to this embodiment is that the capping layer  9   a  in the via hole  10   a  may be lost partly or entirely without any problem when the via hole  10   a  is made, because the capping layer  9   b  is selectively formed only on the bottom after the via hole  10   a  and the wiring groove  10   b  have been formed in the interlayer insulating film  10 .  
         [0061]     The capping layer  9   b  which has been selectively formed only on the bottom of the via hole  10   a  reinforces the region immediately under the contact  19  at which electromigration starts when electrons flow from the second metal wiring  20  in the upper level to the first metal wiring  8  in the lower level. Therefore, the resulting semiconductor device has improved electromigration durability and improved wiring reliability on account of the absence of voids due to electromigration.  
         [0062]     The electromigration durability is enhanced by the fact that the capping layer  9   a  is formed on the top of the first metal wiring  8  outside the contact  19 .  
         [0063]     It is not always necessary that the capping layer  9   a  and the capping layer  9   b  have the same thickness. That is, the capping layer  9   b  may be thinner than the capping layer  9   a  as shown in  FIG. 9 , or the capping layer  9   b  may be thicker than the capping layer  9   a  as shown in  FIG. 10 . The thickness of the capping layer  9   b  in the via hole  10   a  may be about 5 to 20 nm.  
         [0064]     The foregoing structure may be modified such that the capping layer  9   a  is omitted but only the capping layer  9   b  is formed on the bottom of the via hole  10   a,  as shown in  FIG. 11 . The modified structure shown in  FIG. 11  may be obtained by omitting the step of forming the capping layer  9   a  shown in  FIG. 4A .  
         [0065]     The structure may also be modified such that the capping layer  9   a  and the capping layer  9   b  are made from different materials. For example, the capping layer  9   a  may be a CuSi film. In this case, it is possible to selectively form a CuSi film on the first metal wiring  8  of Cu in the step of depositing SiCN from silane (SiH 4 ) gas to form the etching stopper layer  11  of SiCN.  
         [0066]     The embodiment illustrated above is characterized in that the capping layer  9   a  exposed in the via hole  10   a  is entirely removed when the via hole  10   a  is formed. However, the present invention may also be applied to the case in which the capping layer  9   a  in the via hole  10   a  is thinned as shown in  FIG. 14  or the case in which the capping layer  9   a  in the via hole  10   a  partly remains as shown in  FIG. 14 . The advantage of these cases is that the capping layer  9   b  formed in the via hole  10   a  has a film thickness necessary to improve electromigration durability as in the embodiment mentioned first.  
         [0067]     The foregoing embodiment is not intended to restrict the scope of the present invention. The structure of the interlayer insulating film  10  may be modified, and the composition of the plating solution (CoWP) may be modified, with cobalt chloride replaced by cobalt sulfate.  
         [0068]     Various changes and modifications may be made in the invention without departing from the sprit and scope thereof.