Abstract:
In a method of manufacturing a semiconductor device, a semiconductor substrate including an insulating layer is provided. A groove is formed on the insulating layer. An additive-containing barrier layer is formed on the insulating layer. A metal seed layer and a metal layer are formed on the barrier layer. Then, the metal layer is subjected to a first heat treatment at a first temperature that is capable of promoting grain growth of the metal seed layer and the metal layer. The barrier layer, the metal seed layer and the metal layer are partially removed so that a conductive layer including the metal seed layer and the metal layer is formed in the groove. Finally, the conductive layer is subjected to a second heat treatment at a second temperature that is higher than the first temperature and allows an additive element in the barrier layer to diffuse into the metal layer.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method of forming a metal layer (for instance, a buried copper (Cu) layer). 
     In order to improve the electro-migration (EM) resistance of a copper layer in a semiconductor element, a countermeasure to diffuse an impurity element in the copper layer is known. As a method of forming such copper layer, there is a method in which a Cu alloy seed layer is formed on an inner surface of a groove by use of sputtering apparatus, subsequently a copper plating layer is formed by use plating apparatus, thereafter by applying heat treatment, an additive element (that is, an impurity element) in the Cu alloy seed layer is allowed to diffuse into the Cu plating layer. 
     However, in the above-mentioned method of forming a metal layer, a sample (wafer) thereon the Cu alloy seed layer is formed in the sputtering apparatus is transferred through air exposure to the plating apparatus and there the Cu plating is performed. Accordingly, because of oxidation of the additive element of the Cu alloy seed layer, on a surface of the Cu alloy seed layer an oxidation layer is formed. As a result, there are concerns about deterioration of the adhesion between the Cu alloy seed layer and the Cu plating layer. 
     Furthermore, the impurity element diffused into the Cu plating layer can work on one hand so as to improve the EM resistance of the Cu plating layer but on the other hand also works so as to suppress grains of the Cu plating layer from growing. Accordingly, since in the Cu plating layer after the heat treatment, there are fine crystallites, there is a problem in that the fine crystallites deteriorate the EM resistance. 
     SUMMARY OF THE INVENTION 
     The invention may overcome the problems of the existing technology such as mentioned above and may intend to provide a method of forming a metal layer that allows forming a metal layer excellent in the adhesion and the EM resistance. 
     In a method of manufacturing a semiconductor device according to the present invention, a semiconductor substrate including an insulating layer is provided. A groove is formed on the insulating layer. An additive-containing barrier layer is formed on the insulating layer. A metal seed layer and a metal layer are formed on the barrier layer. Then, the metal layer is subjected to a first heat treatment at a first temperature that is capable of promoting grain growth of the metal seed layer and the metal layer. The barrier layer, the metal seed layer and the metal layer are partially removed so that a conductive layer including the metal seed layer and the metal layer is formed in the groove. Finally, the conductive layer is subjected to a second heat treatment at a second temperature that is higher than the first temperature and allows an additive element in the barrier layer to diffuse into the metal layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A through 1G are process explanatory diagrams showing a method of forming a metal layer according to a first embodiment of the invention. 
     FIGS. 2A through 2G are process explanatory diagrams showing a method of forming a metal layer according to a second embodiment of the invention. 
     FIGS. 3A through 3J are process explanatory diagrams showing a method of forming a metal layer according to a third embodiment of the invention. 
     FIGS. 4A through 4J are process explanatory diagrams showing a method of forming a metal layer according to a fourth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     FIGS. 1A through 1G are process explanatory diagrams showing a method of forming a metal layer according to a first embodiment of the invention. 
     In a method of forming a metal layer according to the first embodiment, firstly, as shown in FIG. 1A, an insulating layer  102  is formed on a semiconductor substrate  101 . The semiconductor substrate  101  is constituted of, for instance, silicon. Furthermore, the insulating layer  102  is constituted of, for instance, silicon oxide and so on. However, constituent materials are not restricted to particular ones. 
     In the next place, as shown in FIG. 1B, by use of known photolithography technology and etching technology, a groove  103  is formed in the insulating layer  102 . The groove  103  is formed in a region corresponding to a layer pattern formed in the insulating layer  102 . A depth of the groove  103  is, for instance, 0.3 μm, and a width of the groove  103  is, for instance, 0.3 μm. A shape of the groove  103  and the number thereof are not restricted to ones shown in the drawing. Furthermore, dimensions of the groove  103  are neither restricted to ones cited above. 
     Next, as shown in FIG. 1C, on the insulating layer  102  therein the groove  103  is formed, an additive-containing barrier layer  104  and a Cu seed layer  105  are sequentially formed. The additive-containing barrier layer  104  functions as a diffusion stop layer that inhibits a constituent metal of a layer formed thereon from diffusing into the insulating layer  102 . The additive-containing barrier layer  104  is, for instance, a TaMgN layer obtained by adding Mg to TaN. A thickness of the additive-containing barrier layer  104  is, for instance, 40 nm. A thickness of the Cu seed layer  105  is, for instance, 100 nm. However, the dimensions of the respective layers are not restricted to the cited ones. 
     The additive-containing barrier layer  104  and the Cu seed layer  105  are sequentially formed in the sputtering apparatus (not shown in the drawing) by use of a sputtering method in which the directional characteristics are enhanced. The TaMgN layer as the additive-containing barrier layer  104  is formed, with an Ar/N 2  mixture gas introducing into evacuated sputtering apparatus, by use of a TaMg target. The Cu seed layer  105  is formed, with Ar gas introducing into evacuated sputtering apparatus, by use of a Cu target. When thus the Cu seed layer  105  is sequentially formed on the additive-containing barrier layer  104  that is disposed in the evacuated sputtering apparatus, the additive element in the additive-containing barrier layer  104  can be inhibited from being exposed to air and thereby from being oxidized. As the additive element of the additive-containing barrier layer  104 , at least one or more of Ag, Ca, Zn, Cd, Au, Be, Mg, Sn, Zr, B, Pd, Al, Hg, In, Ni and Ga can be used. A content (% by weight) of the additive in the additive-containing barrier layer  104  is in the range of 0.05 to 10% by weight. As other examples of the constituent materials of the additive-containing barrier layer  104 , TaN, TaCN, TaSiN, TaSiCN, WN, WCN, WSiN, WSiCN, TiN, TiCN, TiSiN, TiSiCN, ZrN, ZrCN, ZrSiN, and ZrSiCN can be cited. As the method of forming the additive-containing barrier layer  104  and the Cu seed layer  105 , without restricting to the sputtering method, other methods such as the CVD method can be adopted. 
     Subsequently, the sample (wafer) thereon the Cu seed layer  105  is formed is taken out of the sputtering apparatus, and while exposing to air, transferred to the plating apparatus (not shown in the drawing). Then, as shown in FIG. 1D, on the Cu seed layer  105 , a Cu plating layer  106  is formed by use of an electroplating method. The Cu plating layer  106  is formed so that the groove  103  may be completely buried. 
     In the next place, in order to stabilize layer qualities such as the hardness, the crystallinity and the specific resistance of the Cu plating layer  106 , heat treatment is applied at a first temperature (for instance, 100 to 350 degree centigrade) for 1 min to 5 hr in nitrogen atmosphere. However, the most preferable heat treatment temperature is different depending on various kinds of factors such as a width of the layer and so on. In the first embodiment, in order to make the diffusion of the additive element from the additive-containing barrier layer  104  to the Cu seed layer  105  and the Cu plating layer  106  as small as possible, the heat treatment is carried out at a relatively low temperature, and in order to grow Cu grains of the Cu seed layer  105  and the Cu plating layer  106  the heat treatment is performed for a relatively longer time period. According to the heat treatment, as shown in FIG. 1E, the Cu seed layer  105  and the Cu plating layer  106  are promoted in integrating. 
     Subsequently, as shown in FIG. 1F, the respective layers on the insulating layer  102 , that is, the additive-containing barrier layer  104 , the Cu seed layer  105  and the Cu plating layer  106  are partially removed until a top portion of the insulating layer  102  is exposed. The removing is performed according to a CMP polishing method by use of CMP (chemical-mechanical polishing) apparatus (not shown in the drawing). According to the process, a conductive layer  107  (constituted of part of the Cu seed layer  105  and part of the Cu plating layer  106 ) is left in the groove  103 . The conductive layer  107  becomes a metal layer of a semiconductor element. 
     Slurry used in the CMP method is silica-based one and mixed with H 2 O 2  as an oxidant. Respective down forces of a carrier (a system that holds a wafer to be polished) and a retainer ring (a member that surrounds an outer periphery of the wafer held by the carrier) of the CMP apparatus are, for instance, 4 psi and 5 psi. Furthermore, respective rotation speeds of the carrier and a platen (polishing cloth for polishing a sample held by the carrier) of the CMP apparatus are, for instance, 80 rpm and 80 rpm. 
     The polishing process of the CMP method comprises two steps. In the first polishing step, the Cu plating layer  106  and the Cu seed layer  105  are polished and the additive-containing barrier layer  104  on the insulating layer  102  is left. In the subsequent second polishing step, by use of a different silica-based slurry, the additive-containing barrier layer  104  disposed on a top portion of the insulating layer  102  is completely removed. When a polishing speed of the Cu plating layer  106  is set at, for instance, one tenth that of the additive-containing barrier layer  104 , the conductive layer  107  can be suppressed from dishing. At this time, the down forces of the carrier and the retainer ring of the CMP apparatus are, for instance, 4 psi and 5 psi, respectively. Furthermore, the rotation speeds of the carrier and the platen of the CMP apparatus are, for instance, 50 rpm and 50 rpm, respectively. 
     In the next place, as shown in FIG. 1G, heat treatment is carried out at a second temperature (for instance, in the neighborhood of 400 degree centigrade) for 0.5 to 5 hr in a mixture atmosphere of nitrogen and hydrogen. In the heat treatment, the additive element in the additive-containing barrier layer  104  is diffused into the conductive layer  107  and thereby an additive-containing conductive layer  108  is formed. Accordingly, the second temperature is higher than the first temperature. Furthermore, the second temperature, without restricting to the neighborhood of 400 degree centigrade, can be a temperature in the range of 250 to 450 degree centigrade. Owing to the heat treatment, the additive element in the additive-containing barrier layer  104  is allowed diffusing into the conductive layer  107 , and thereby the additive-containing conductive layer  108  is formed. In the above, the formation of the Cu layer in the semiconductor element comes to completion. 
     As mentioned above, according to the method of forming a metal layer according to the first embodiment, after the Cu seed layer  105  is formed in the sputtering apparatus, the sample is transferred through air to the plating apparatus. Accordingly, the additive-containing barrier layer  104  is not exposed to air. As a result, the additive element of the additive-containing barrier layer  104  is not oxidized with the air, and thereby the Cu plating layer  106  can be inhibited from deteriorating in the adhesion. 
     Furthermore, according to the method of forming a metal layer according to the first embodiment, in order to promote grain growth of the Cu seed layer  105  and the Cu plating layer  106 , the heat treatment is carried out at the first temperature that is relatively low, and thereafter at the relatively higher second temperature that enables the additive element to diffuse from the additive-containing barrier layer  104  to the conductive layer  107 , the heat treatment is implemented. Thus, according to the method of forming a metal layer according to the first embodiment, since the grain growth and the diffusion of the additive element that are two countermeasure for improving the EM resistance can be implemented, the Cu layer excellent in the EM resistance can be formed. 
     In the above explanation, the method of forming a Cu layer to a semiconductor element is explained. However, the invention can be applied also to a method of forming a metal layer other than the Cu layer. 
     Second Embodiment 
     FIGS. 2A through 2G are process explanatory diagrams showing a method of forming a metal layer according to the second embodiment of the invention. The method of forming a metal layer according to the second embodiment is different from that according to the first embodiment in that a barrier layer  204  is provided between an insulating layer  202  and an additive-containing barrier layer  205 . Here, the barrier layer  204  is either a barrier layer that does not contain an additive or a barrier layer whose additive content is smaller than that of the additive-containing barrier layer  205 . 
     In a method of forming a metal layer according to the second embodiment, firstly, as shown in FIG. 2A, an insulating layer  202  is formed on a semiconductor substrate  201 . The semiconductor substrate  201  is constituted of, for instance, silicon. Furthermore, the insulating layer  202  is constituted of, for instance, silicon oxide and so on. However, the constituent materials are not restricted to particular ones. 
     In the next place, as shown in FIG. 2B, by use of known photolithography technology and etching technology, a groove  203  is formed in the insulating layer  202 . The groove  203  is formed in a region corresponding to a layer pattern formed in the insulating layer  202 . A depth of the groove  203  is, for instance, 0.3 μm, and a width of the groove  203  is, for instance, 0.3 μm. A shape of the groove  203  and the number thereof are not restricted to ones shown in the drawing. Furthermore, dimensions of the groove  203  are neither restricted to one cited above. 
     Next, as shown in FIG. 2C, on the insulating layer  202  therein the groove  203  is formed, a barrier layer  204 , a additive-containing barrier layer  205  and a Cu seed layer  206  are sequentially formed. The barrier layer  204  and the additive-containing barrier layer  205  work as a diffusion stop layer that inhibits a constituent metal of a layer formed thereon from diffusing into the insulating layer  202 . The barrier layer  204  is formed by use of one material selected from a group of TaN, TaCN, TaSiN, TaSiCN, WN, WCN, WSiN, WSiCN, TiN, TiCN, TiSiN, TiSiCN, ZrN, ZrCN, ZrSiN and ZrSiCN. The additive-containing barrier layer  205  is formed by use of a material in which one material selected from a group of TaN, TaCN, TaSiN, TaSiCN, WN, WCN, WSiN, WSiCN, TiN, TiCN, TiSiN, TiSiCN, ZrN, ZrCN, ZrSiN and ZrSiCN is mixed with at least one or more additive elements selected from Ag, Ca, Zn, Cd, Au, Be, Mg, Sn, Zr, B, Pd, Al, Hg, In, Ni and Ga. 
     The barrier layer  204 , the additive-containing barrier layer  205  and the Cu seed layer  206  are sequentially formed in the sputtering apparatus by use of a sputtering method in which the directional characteristics are enhanced. As the method of depositing the barrier layer  204 , the additive-containing barrier layer  205  and the Cu seed layer  206 , without restricting to the sputtering method, other methods such as the CVD method can be adopted. 
     Subsequently, the sample (wafer) thereon the Cu seed layer  206  is formed is taken out of the sputtering apparatus, while exposing to air, transferred to the plating apparatus (not shown in the drawing). Then, as shown in FIG. 2D, on the Cu seed layer  206 , a Cu plating layer  207  is formed by use of an electroplating method. The Cu plating layer  207  is formed so that the groove  203  may be completely buried. 
     In the next place, with an intension of stabilizing layer qualities such as the hardness, the crystallinity and the specific resistance of the Cu plating layer  207 , the heat treatment is carried out at a first temperature (for instance, 100 to 350 degree centigrade) for 1 min to 5 hr in nitrogen atmosphere. Owing to the heat treatment, as shown in FIG. 2E, the Cu seed layer  206  and the Cu plating layer  207  are promoted in integrating. 
     Subsequently, as shown in FIG. 2F, the respective layers on the insulating layer  202 , that is, the barrier layer  204 , the additive-containing barrier layer  205 , the Cu seed layer  206  and the Cu plating layer  207  are partially removed until a top portion of the insulating layer  202  is exposed. The removing is performed according to a CMP polishing method. According to the process, a conductive layer  208  (constituted of part of the Cu seed layer  206  and part of the Cu plating layer  207 ) is left in the groove  203 . The conductive layer  208  is used as a metal layer of a semiconductor element. 
     In the next place, as shown in FIG. 2G, heat treatment is carried out at a second temperature (for instance, in the neighborhood of 400 degree centigrade) for 0.5 to 5 hr in a mixture atmosphere of nitrogen and hydrogen. In the heat treatment, the additive element in the additive-containing barrier layer  205  is diffused into the conductive layer  208  and thereby an additive-containing conductive layer  209  is formed. Accordingly, the second temperature is set higher than the first temperature. Furthermore, the second temperature, without restricting to the neighborhood of 400 degree centigrade, can be a temperature in the range of 250 to 450 degree centigrade. Owing to the heat treatment, the additive element in the additive-containing barrier layer  205  is allowed to diffuse into the conductive layer  208 , and thereby the additive-containing conductive layer  209  is formed. In the above, the formation of the Cu layer in the semiconductor element comes to completion. 
     As mentioned above, according to the method of forming a metal layer according to the second embodiment, after the Cu seed layer  206  is formed in the sputtering apparatus, the sample is transferred through air to the plating apparatus. Accordingly, the additive-containing barrier layer  205  is not exposed to the air. As a result, the additive element of the additive-containing barrier layer  205  is not oxidized with the air, and the Cu plating layer  207  can be inhibited from deteriorating in the adhesion and from generating voids when the Cu plating layer  207  is formed. 
     Furthermore, according to the method of forming a metal layer according to the second embodiment, in order to promote growing grains of the Cu seed layer  206  and the Cu plating layer  207 , the heat treatment is carried out at the first temperature that is relatively low, and thereafter at the relatively higher second temperature that enables the additive element to diffuse from the additive-containing barrier layer  205  to the conductive layer  208 , the heat treatment is implemented. Thus, according to the method of forming a metal layer according to the second embodiment, since the grain growth and the diffusion of the additive element that are two countermeasure for improving the EM resistance can be implemented, the Cu layer excellent in the EM resistance can be formed. 
     Furthermore, in the method of forming the metal layer according to the second embodiment, as an under layer of the additive-containing barrier layer  205 , the barrier layer  204  is provided. Accordingly, an effect that inhibits the Cu element from diffusing into the insulating layer  202  can be furthermore enhanced. 
     Except for the above, the second embodiment is the same as the first embodiment. 
     Third Embodiment 
     FIGS. 3A through 3J are process explanatory diagrams showing a method of forming a metal layer according to a third embodiment of the invention. 
     A method of forming a metal layer according to the third embodiment is one in which a metal layer is formed on a sample (wafer) provided with a conductive layer  308  such as shown in FIG.  3 A. In FIG. 3A, reference numerals  301 ,  302  and  304  denote a semiconductor substrate, an insulating layer and a barrier layer, respectively. The sample shown in FIG. 3A may be whatever samples provided with a metal layer. Furthermore, the sample shown in FIG. 3A may be one that is formed according to the first or second embodiment. 
     In the method of forming a metal layer according to the third embodiment, as shown in FIG. 3B, on the insulating layer  302  provided with the conductive layer  308 , a SiN layer  311  as a cap layer, an insulating layer  312 , a SiN layer  313  as an etch stop layer, and an insulating layer  314  are sequentially formed. The insulating layer  312  and the insulating layer  314  are formed of, for instance, silicon oxide. The SiN layer  311  has a function of inhibiting the insulating layer  312  from oxidizing the conductive layer  308 . However, constituent materials are not restricted to these. 
     Subsequently, as shown in FIG. 3C, by use of known photolithography technology and etching technology, a groove  315  is formed in the insulating layer  314 , and at a lower portion of the groove  315 , a via  316  that penetrates through the SiN layer  313 , the insulating layer  312 , and the cap layer  311  and thereby exposes the conductive layer  308  is formed. The groove  315  is divided into regions corresponding to layer patterns formed in the insulating layer  312 . A depth of the groove  315  is, for instance, 0.3 μm, and a width of the groove  315  is, for instance, 0.3 μm. Furthermore, a depth of the via  316  is, for instance, 0.8 μm, and a diameter of the via  316  is, for instance, 0.3 μm. Shapes of the groove  315  and the via  316  and the numbers thereof are not restricted to ones shown in the drawing. Furthermore, dimensions of the groove  315  and the via  316  are neither restricted to ones cited above. 
     Next, as shown in FIG. 3D, on a side surface of the groove  315  of the insulating layer  314  as well as on a side surface and a bottom surface of the via  316 , an additive-containing barrier layer  317  is formed. The additive-containing barrier layer  317  functions as a diffusion stop layer that inhibits a constituent metal of a layer formed thereon from diffusing into the insulating layers  312  and  314 . The additive-containing barrier layer  317  is, for instance, a TaMgN layer obtained by adding Mg to TaN. A thickness of the additive-containing barrier layer  317  is, for instance, 80 nm (a thickness of a deposition layer above the insulating layer  314 ). However, the dimensions are not restricted to the cited ones. 
     The additive-containing barrier layer  317  is formed in the sputtering apparatus (not shown in the drawing) by use of a sputtering method in which the directional characteristics are enhanced. The TaMgN layer as the additive-containing barrier layer  317  is formed, with an Ar/N 2  mixture gas introducing into evacuated sputtering apparatus, by use of a TaMg target. As the additive element of the additive-containing barrier layer  317 , at least one or more of Ag, Ca, Zn, Cd, Au, Be, Mg, Sn, Zr, B, Pd, Al, Hg, In, Ni and Ga can be used. A content (% by weight) of the additive in the additive-containing barrier layer  317  is in the range of 0.05 to 10% by weight. As other examples of the constituent materials of the additive-containing barrier layer  317 , TaN, TaCN, TaSiN, TaSiCN, WN, WCN, WSiN, WSiCN, TiN, TiCN, TiSiN, TiSiCN, ZrN, ZrCN, ZrSiN, and ZrSiCN can be cited. As the method of depositing the additive-containing barrier layer  317 , without restricting to the sputtering method, other methods such as the CVD method can be adopted. 
     Subsequently, as shown in FIG. 3E, the additive-containing barrier layer  317  on the bottom surface of the via  316 , without exposing the sample to the air, is removed by use of anisotropic etching. For instance, when the additive-containing barrier layer  317  is deposited by 80 nm, a layer thickness at a bottom portion of the via  316  is substantially 15 nm, and a film thickness of a sidewall portion of the via  316  is substantially 4 nm. Accordingly, when the additive-containing barrier layer  317  on the bottom portion of the via  316  is removed, the additive-containing barrier layer  317  on the sidewall portion of the via  316  and an external portion of the groove  315  (a top portion of the insulating layer  314 ) can be left. 
     In the next place, after the additive-containing barrier layer  317  on the bottom portion of the via  316  is removed, without exposing the sample to the air, as shown in FIG. 3F, a Cu seed layer  318  is formed. Since the additive-containing barrier layer  317  on the bottom portion of the via  316  is removed, the Cu seed layer  318  is directly connected to the conductive layer  308  that is a lower layer. 
     Subsequently, the wafer thereon the Cu seed layer  318  is formed is taken out of the sputtering apparatus, and while exposing to air, transferred to the plating apparatus. Then, as shown in FIG. 3G, on the Cu seed layer  318 , a Cu plating layer  319  is formed by use of an electroplating method. The Cu plating layer  319  is formed so that the via  316  and the groove  315  may be completely buried. 
     In the next place, in order to stabilize layer qualities such as the hardness, the crystallinity and the specific resistance of the Cu plating layer  319 , heat treatment is carried out at a first temperature (for instance, 100 to 350 degree centigrade) for 1 min to 5 hr in nitrogen atmosphere. However, the most preferable heat treatment temperature is different depending on a width of the layer. Furthermore, the most preferable heat treatment time period is different depending on a width of the layer. In the third embodiment, in order to make the diffusion of the additive element from the additive-containing barrier layer  317  to the Cu seed layer  318  and the Cu plating layer  319  as small as possible, the heat treatment is carried out at a relatively low temperature, and in order to grow Cu grains of the Cu seed layer  318  and the Cu plating layer  319  the heat treatment is performed for a relatively longer time period. According to the heat treatment, as shown in FIG. 3H, the Cu seed layer  318  and the Cu plating layer  319  are promoted in integrating. 
     Subsequently, as shown in FIG. 3I, the respective layers on the insulating layer  314 , that is, the additive-containing barrier layer  317 , the Cu seed layer  318 , and the Cu plating layer  319  are partially removed until a top portion of the insulating layer  314  is exposed. The removing is performed according to the CMP polishing method. According to the process, a conductive layer  320  (constituted of part of the Cu seed layer  318  and part of the Cu plating layer  319 ) is left in the groove  315  and the via  316 . The conductive layer  320  is used as a metal layer of a semiconductor element. The CMP method is similar to one in the first embodiment. 
     In the next place, as shown in FIG. 3J, heat treatment is carried out at a second temperature (for instance, in the neighborhood of 400 degree centigrade) for 0.5 to 5 hr in an atmosphere of a mixture gas of nitrogen and hydrogen. In the heat treatment, the additive element in the additive-containing barrier layer  317  is diffused into the conductive layer  320  and thereby an additive-containing conductive layer  321  is formed. Accordingly, the second temperature is set higher than the first temperature. Furthermore, the second temperature, without restricting to the neighborhood of 400 degree centigrade, can be a temperature in the range of 250 to 450 degree centigrade. Owing to the heat treatment, the additive element in the additive-containing barrier layer  317  is allowed to diffuse into the conductive layer  320 , and thereby the additive-containing conductive layer  321  is formed. In the above, the formation of the Cu layer in the semiconductor element comes to completion. 
     As mentioned above, according to the method of forming a metal layer according to the third embodiment, after the Cu seed layer  318  is formed in the sputtering apparatus, the wafer is transferred through air to the plating apparatus. Accordingly, the additive-containing barrier layer  317  is not exposed to air. As a result, the additive element of the additive-containing barrier layer  317  is not oxidized with the air and the Cu plating layer  319  can be inhibited from deteriorating in the adhesion. 
     Furthermore, according to the method of forming a metal layer according to the third embodiment, in order to promote grain growth in the Cu seed layer  318  and the Cu plating layer  319 , the heat treatment is carried out at the first temperature that is relatively low, and thereafter at the relatively higher second temperature that enables the additive element to diffuse from the additive-containing barrier layer  317  to the conductive layer  320 , the heat treatment is implemented. Thus, according to the method of forming a metal layer according to the third embodiment, since the grain growth and the diffusion of the additive element that are two countermeasure for improving the EM resistance can be implemented, the Cu layer excellent in the EM resistance can be formed. 
     Furthermore, since the conductive layer  308  that is a first conductive layer and a second conductive layer  321  are directly connected through the via  316 , the layer low in the resistance can be formed, that is, a layer configuration preferable for improving an operation speed of the semiconductor element is obtained. 
     Still furthermore, in the above explanation, the method of forming a Cu layer to a semiconductor element is explained. However, the invention can be applied also to a method of forming the metal layer other than the Cu layer. 
     Fourth Embodiment 
     FIGS. 4A through 4J are process explanatory diagrams showing a method of forming a metal layer according to the fourth embodiment of the invention. The method of forming a metal layer according to the fourth embodiment is different from that according to the third embodiment in that a barrier layer  417  is provided between insulating layers  412 ,  414  and an additive-containing barrier layer  418 . Here, the barrier layer  417  is either a barrier layer that does not contain an additive or a barrier layer whose additive content is smaller than that of the additive-containing barrier layer  418 . 
     A method of forming a metal layer according to the fourth embodiment is one in which a metal layer is formed on a sample (wafer) provided with a conductive layer  408  such as shown in FIG.  4 A. In FIG. 4A, reference numerals  401 ,  402  and  404  denote a semiconductor substrate, an insulating layer, and a barrier layer, respectively. The sample shown in FIG. 4A may be any one of samples that are provided with a metal layer. Furthermore, the sample shown in FIG. 4A may be either one that is formed according to the first embodiment or one that is formed according to the second embodiment. 
     In the method of forming a metal layer according to the fourth embodiment, as shown in FIG. 4B, on the insulating layer  402  provided with the conductive layer  408 , a SiN layer  411  as a cap layer, the insulating layer  412 , a SiN layer  413  as an etch stop layer, and an insulating layer  414  are sequentially formed. The insulating layers  412  and  414  are constituted of, for instance, silicon oxide. The SiN layer  411  has a function of inhibiting the insulating layer  412  from oxidizing the conductive layer  408 . However, constituent materials are not restricted to these. 
     In the next place, as shown in FIG. 4C, by use of known photolithography technology and etching technology, a groove  415  is formed in the insulating layer  414 , and at a lower portion of the groove  415  a via  416  that penetrates through the SiN layer  413 , the insulating layer  412 , and the cap layer  411  and thereby exposes the conductive layer  408  is formed. Shapes and the sizes of the groove  415  and the via  416  are the same as that of the third embodiment. 
     Next, as shown in FIG. 4D, on a side surface of the groove  415  of the insulating layer  414 , as well as on a side surface and on a bottom surface of the via  416 , the barrier layer  417  and the additive-containing barrier layer  418  are sequentially formed. The barrier layer  417  and the additive-containing barrier layer  418  work as a diffusion stop layer that inhibits a constituent metal of a layer formed thereon from diffusing into the insulating layers  412  and  414 . The barrier layer  417  is formed by use of one material selected from a group of, for instance, TaN, TaCN, TaSiN, TaSiCN, WN, WCN, WSiN, WSiCN, TiN, TiCN, TiSiN, TiSiCN, ZrN, ZrCN, ZrSiN, and ZrSiCN. The additive-containing barrier layer  418  is formed by use of a material in which one material selected from a group of TaN, TaCN, TaSiN, TaSiCN, WN, WCN, WSiN, WSiCN, TiN, TiCN, TiSiN, TiSiCN, ZrN, ZrCN, ZrSiN and ZrSiCN is mixed with at least one or more additive elements selected from Ag, Ca, Zn, Cd, Au, Be, Mg, Sn, Zr, B, Pd, Al, Hg, In, Ni and Ga. 
     In the next place, as shown in FIG. 4E, the barrier layer  417  and the additive-containing barrier layer  418  on the bottom surface of the via  416 , without exposing the sample to air, are removed by means of the anisotropic etching. 
     Next, after the barrier layer  417  and the additive-containing barrier layer  418  on the bottom surface of the via  416  are removed, without exposing the sample to air, as shown in FIG. 4F, a Cu seed layer  419  is formed. Since the barrier layer  417  and the additive-containing barrier layer  418  on the bottom surface of the via  416  have been removed, the Cu seed layer  419  is directly connected to the conductive layer  408  that is a lower layer. 
     Subsequently, the wafer thereon the Cu seed layer  419  is formed is taken out of the sputtering apparatus, and while exposing to air, transferred to the plating apparatus. Then, as shown in FIG. 4G, on the Cu seed layer  419 , a Cu plating layer  420  is formed by use of the electroplating method. The Cu plating layer  420  is formed so that the via  416  and the groove  415  may be completely buried. 
     In the next place, in order to stabilize layer qualities such as the hardness, the crystallinity and the specific resistance of the Cu plating layer  420 , the heat treatment is carried out at a first temperature (for instance, 100 to 350 degree centigrade) for 1 to 5 hr in an atmosphere of a gas mixture of nitrogen and hydrogen. The most preferable heat treatment temperature differs depending on a width of the layer. Furthermore, the most preferable heat treatment time period differs depending on a width of the layer. In the fourth embodiment, in order to make the diffusion of the additive element from the additive-containing barrier layer  418  to the Cu seed layer  419  and the Cu plating layer  420  as small as possible, the heat treatment is performed at a relatively low temperature, and in order to grow Cu grains of the Cu seed layer  419  and the Cu plating layer  420 , the heat treatment is performed for a relatively long time. According to the heat treatment, as shown in FIG. 4H, the Cu seed layer  419  and the Cu plating layer  420  are promoted in integrating. 
     Subsequently, as shown in FIG. 4J, the respective layers on the insulating layer  414 , that is, the barrier layer  417 , the additive-containing barrier layer  418 , the Cu seed layer  419  and the Cu plating layer  420  are partially removed until a top portion of the insulating layer  414  is exposed. The removing is performed according to a CMP polishing method. According to the process, a conductive layer  421  (constituted of part of the Cu seed layer  419  and part of the Cu plating layer  420 ) is left in the groove  415  and the via  416 . The conductive layer  421  is used as a metal layer of a semiconductor element. 
     In the next place, as shown in FIG. 4J, heat treatment is carried out at a second temperature (for instance, in the neighborhood of 400 degree centigrade) for 0.5 min to 5 hr in nitrogen atmosphere. In the heat treatment, the additive element in the additive-containing barrier layer  418  is diffused into the conductive layer  421  and thereby an additive-containing conductive layer  422  is formed. Accordingly, the second temperature is set higher than the first temperature. Furthermore, the second temperature, without restricting to the neighborhood of 400 degree centigrade, can be a temperature in the range of 250 to 450 degree centigrade. According to the heat treatment, the additive element in the additive-containing barrier layer  418  is allowed to diffuse into the conductive layer  421 , and thereby the additive-containing conductive layer  422  is formed. In the above, the formation of the Cu layer in the semiconductor element comes to completion. 
     As mentioned above, according to the method of forming a metal layer according to the fourth embodiment, after the Cu seed layer  419  is formed in the sputtering apparatus, the wafer is transferred through air to the plating apparatus. Accordingly, the additive-containing barrier layer  418  is not exposed to the air. As a result, the additive element in the additive-containing barrier layer  418  is not oxidized with the air, and the Cu plating layer  420  can be inhibited from deteriorating in the adhesion and from generating voids when the Cu plating layer  420  is formed. 
     Furthermore, according to the method of forming a metal layer according to the fourth embodiment, in order to promote grain growth of the Cu seed layer  419  and the Cu plating layer  420 , the heat treatment is carried out at the first temperature that is relatively low, and thereafter at the relatively higher second temperature that enables the additive element to diffuse from the additive-containing barrier layer  418  to the conductive layer  421 , the heat treatment is implemented. Thus, according to the method of forming a metal layer according to the fourth embodiment, since the grain growth and the diffusion of the additive element that are two countermeasure for improving the EM resistance can be implemented, the Cu layer excellent in the EM resistance can be formed. 
     Furthermore, since the conductive layer  408  that is a first conductive layer and a second conductive layer  422  are directly connected through the via  416 , the layer low in the resistance can be formed, that is, a layer configuration preferable for improving an operation speed of the semiconductor element is obtained. 
     Still furthermore, in the method of forming the metal layer according to the fourth embodiment, as a under layer of the additive-containing barrier layer  418 , the barrier layer  417  is provided. Accordingly, an effect that inhibits the Cu element from diffusing into the insulating layers  412  and  414  can be furthermore enhanced. 
     Except for the above points, the fourth embodiment is the same as the third embodiment. 
     As explained above, according to the method of forming a metal layer according to the invention, in order to promote grain growth of a metal seed layer and a metal layer, the heat treatment is carried out at a first temperature that is relatively low, and thereafter at a relatively higher second temperature that enables an additive element to diffuse from an additive-containing barrier layer to a metal layer, the heat treatment is implemented. Thus, according to the methods of forming a metal layer set forth in claims 1 through 9, since the grain growth and the diffusion of the additive element that are two countermeasure for improving the EM resistance can be implemented, there is an effect that a Cu layer excellent in the EM resistance can be formed.