Abstract:
A method in which a base layer is deposited in a contact hole region under a protective gas, where base layer contains a nitride as main constituent. After the deposition of the base layer, a covering layer is deposited under gaseous nitrogen. An adhesion promoting layer results which is simple to produce and has good electrical properties.

Description:
RELATED APPLICATIONS 
     The present patent document is a divisional of application Ser. No. 10/511,851 filed Aug. 25, 2005, now U.S. Pat. No. 7,390,737 which is an application that is a U.S. nationalization of PCT Application No. PCT/DE2003/00861, filed Mar. 17, 2003, and claims priority to German Patent Application No. 102 19 115.8, filed Apr. 29, 2002. 
    
    
     TECHNICAL FIELD 
     The invention relates to a method for filling a contact hole, in which a covering layer is deposited in the contact hole, which covering layer contains a nitride as main constituent. 
     The contact hole lies between two metal layers. Such contact holes are also referred to as vias. 
     The covering layer is part of a so-called liner layer which serves as a mechanical adhesion promoting layer between a metal to be contact-connected and the contact hole filling. Titanium nitride or tantalum nitride, for example, is used as material for the adhesion promoting layer in order, for example in the case of a line section made of aluminium or an aluminium alloy and lying below the contact hole, to fill the contact hole with tungsten or a tungsten compound. Adhesion promoting layers which contain a nitride have good adhesion promoting properties and can be produced comparatively simply by sputtering under nitrogen. 
     SUMMARY 
     In the case of the method according to the invention, a base layer is deposited in the contact hole under a protective gas, which base layer contains a nitride as main constituent. It is only after the deposition of the base layer that the covering layer is then deposited under gaseous nitrogen. 
     By virtue of the fact that firstly the base layer is deposited under a protective gas, no disturbing nitride compounds between the metal at the bottom of the contact hole and nitrogen contained in a reactive gas form on the metal at the bottom of the contact hole in the case of the method according to the invention. A metal nitride layer is nevertheless formed directly on the metal in the case of the method according to the invention, in order e.g. to form a good electrical contact and to avoid or to reduce undesirable effects or compounds between a pure metal and the metal at the bottom of the contact hole, Thus, e.g. TiA 1   3  would be disturbing because it has a density which deviates considerably from the density of the materials surrounding it. Moreover, TiA 1   3  is granular and has a non-uniform structure which fosters electromigration 
     During the subsequent deposition of the covering layer and a gaseous nitrogen, on account of the base layer that has already been deposited, the nitrogen can no longer penetrate as far as the metal at the bottom of the contact hole in order to form a disturbing nitride there. Therefore, the covering layer can be produced by a simple method for deposition, namely that using a nitrogen atmosphere. 
     In one development of the method according to the invention, the base layer and the covering layer are deposited by directional sputtering. Whereas non-directional sputtering methods are well suited to the deposition of material on a planar area, directional sputtering affords the possibility of depositing sufficient material of the base layer and of the covering layer even in the narrow contact hole, and in particular on the bottom of the contact hole, without resulting in excessively large differences in the thickness of the base layer and of the covering layer inside and outside the contact hole. Since such differences are avoided or considerably reduced by directional sputtering, the method in accordance with the development can be incorporated in a simple manner into the overall process for producing an integrated circuit arrangement. 
     In a next development of the method according to the invention, an intermediate layer is deposited in the contact hole after the deposition of the base layer but before the deposition of the covering layer. The deposition of the intermediate layer affords the possibility of effecting continuous transition from the method for depositing the base layer to the method for depositing the covering layer. By way of example, process gases can be exchanged in this time. Moreover, incorporating an intermediate layer with a material which differs from the material of the base layer and from the material of the covering layer, because it is nitride-free, results in a degree of freedom for producing a layer stack with improved mechanical adhesion properties and/or with improved electrical contact properties and/or with improved other properties, e.g. with regard to the prevention of diffusion or electromigration. Thus, it is possible to considerably improve the adhesion properties of the contact hole filling that is to be introduced later, in the contact hole itself, by means of an intermediate layer which contains titanium as main constituent, i.e. which comprises e.g. titanium or in which at least 80% of the atoms are titanium atoms. 
     In other developments, the surface of a sputtering target is firstly nitrided under a nitrogen atmosphere. The nitrided surface is then removed during the production of the base layer. The intermediate layer is then removed from an essentially nitride-free surface of the sputtering target, the protective gas remaining unchanged. The conditions for producing the covering layer are then prescribed by the change to a different atmosphere. These measures form a simple but effective method for prescribing the process conditions during the production of the layer stack for filling the contact hole. In particular, the entire method can be carried out without changing the process chamber. 
     In a next development, the contact hole is introduced into a dielectric carrier material as far as an electrically conductive connecting section which contains, as main constituent, aluminium, an aluminium alloy or a different metal, e.g. copper or a copper alloy. Such a deeply penetrating contact hole, too, can be filled well by the method according to the invention, in particular because no gaseous nitrogen reaches the bottom of the contact hole. Thus, by way of example, the formation of disturbing aluminium nitride, as explained above, is avoided by other measures, namely in particular by the production of the base layer under a protective atmosphere. 
     In a next development, a multiplicity of contact holes are etched simultaneously during the processing of a semiconductor wafer. The semiconductor wafer has a diameter of 150 to 300 mm, for example. This size means that the etching conditions are not identical at all locations of the semiconductor wafer. By way of example, etching takes place more rapidly at the edge of the semiconductor wafer than in the centre of the semiconductor wafer. The thickness of the dielectric layer outside contact holes also varies at different locations of the semiconductor wafer. By virtue of the method according to the invention, it is possible that, in the case of the development, although an auxiliary layer lying between the dielectric layer and a metal layer is prescribed as a desired point for an etching stop, the auxiliary layer is nonetheless permitted to be etched through, in particular in a partial region of the semiconductor wafer. All of the contact holes subsequently have good electrical properties despite the different etching conditions and thickness conditions. In particular in the case of a low etching selectivity between the dielectric layer and the auxiliary layer, the measures mentioned enable a large process window during the etching. The thickness of the auxiliary layer can also be reduced. 
     The auxiliary layer has properties, for example, which make it possible to avoid or reduce electromigration. Even if the auxiliary layer is etched through, this is not disturbing because later a liner layer is applied which has similar properties to the auxiliary layer with regard to avoiding electromigration. The similar properties result e.g. from the use of identical materials and layer sequences in the auxiliary layer and the liner layer. 
     In another development, a contact hole filling is deposited after the deposition of the covering layer in the contact hole, which contact hole filling contains tungsten as main constituent. Even when the intermediate layer is composed of titanium, the formation of disturbing titanium fluoride during the introduction of the tungsten can be avoided or considerably reduced because the intermediate layer is embedded between the base layer and the covering layer and, moreover, can be made so that it is only thin, e.g. thinner than 10 mm. 
     In a next development, the thickness of the covering layer is less than about 20 nm. Such a small thickness is not disturbing even when the contact hole is filled with tungsten. The formation of titanium fluoride and the resultant lifting-off of the layer stack from the contact hole need no longer be feared. Therefore, the layer thickness, in particular of the covering layer, which is otherwise enlarged in order to avoid the lifting-off can also be reduced again, for example to the size mentioned. 
     In one development, the contact hole has a diameter of less than 1 .mu.m. The depth of the contact hole is greater than 500 nm. Given a diameter of about 500 nm and a depth of 1 .mu.m, the aspect ratio is two. However, even with aspect ratios of up to about three, the method according to the invention can still be carried out reliably because, particularly in the case of a directional sputtering method, the difference in thickness of the layers inside and outside a contact hole remains within tenable limits. 
     In a next development, one or more of the materials titanium nitride or tantalum nitride is used as material for the base layer and/or the covering layer. In these cases, titanium or tantalum is suitable as material for the intermediate layer. 
     The invention additionally relates to an integrated circuit arrangement which contains the filled contact hole, in particular including the base layer and the covering layer. In one development, the circuit arrangement is produced by the method according to the invention or one of its developments. Thus, the effects mentioned above also apply to the circuit arrangement and the development thereof. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The invention is explained below with reference to the accompanying figures, in which: 
         FIG. 1  shows a dielectric layer of an integrated circuit arrangement, 
         FIG. 2  shows a contact hole etched into the dielectric layer, 
         FIG. 3  shows an adhesion promoting layer to be arranged in the contact hole, in accordance with one variant, 
         FIG. 4  shows partial layers of an adhesion promoting layer introduced into the contact hole, 
         FIG. 5  shows a sputtering chamber used for introducing the adhesion promoting layer, and 
         FIG. 6  shows method steps carried out during the production of the adhesion promoting layer. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an integrated circuit arrangement  10  during production. In a semiconductor substrate (not illustrated) of the integrated circuit arrangement  10 , a multiplicity of electrical components such as transistors have already been fabricated, e.g. in accordance with CMOS technology, in accordance with BICMOS technology or in accordance with a technology for power switching elements (power devices). The production was then continued until the application of a metal layer  12 . 
     The metal layer  12  contains a connecting section  14  made of an aluminium-copper alloy containing e.g. 0.5% copper. An antireflection layer  16  comprising titanium nitride, for example, or containing at least one titanium nitride layer was sputtered onto the metal layer  12 . The antireflection layer  16  was required for patterning the metal layer  12  in a photolithographic process during which the connecting section  14  was also patterned. 
     After the deposition of the antireflection layer  16 , a dielectric layer  18  was deposited with a thickness of 600 nm, for example, e.g. with the aid of a CVD method (Chemical Vapour Deposition). The dielectric layer comprises silicon dioxide, for example, and serves for electrical insulation between the metal layer  12  and a metal layer that is still to be arranged in the dielectric layer  18 . 
       FIG. 2  shows the circuit arrangement  10  after the etching of a contact hole  20 , which extends through the dielectric layer  18  and the antireflection layer  16  right into the connecting section  14 . Between a lower surface  22  and a contact hole bottom  24  of the contact hole  20  there is a distance A 1  of 10 nm, for example. The diameter of the contact hole is 0.5 .mu.m, for example. 
     The etching process for etching the contact hole  20  is conducted such that, for a large part of contact holes of the circuit arrangement  10 , the bottom  26  of the contact hole lies in the centre of the antireflection layer  16 . Between the bottom  26  of the contact hole and the lower surface  22  of the antireflection layer  16  there is then a distance A 2  of a few nanometres. In this process implementation, there are no contact holes in which the bottom  28  of the contact hole lies above the antireflection layer  16 . Between the bottom  28  of the contact hole and the lower surface  22  there would then be a distance A 3  which is greater than the distance A 2  and also greater than the thickness of the antireflection layer  16 . The contact hole  20  has a central region  30 , which is shown in enlarged illustration in  FIGS. 3 and 4 . 
     After the etching of the contact hole  20 , an adhesion promoting layer  32  is deposited, the construction of which is explained in more detail below with reference to  FIG. 4 . 
       FIG. 3  shows a titanium nitride layer  40  which could be deposited in the contact hole  20  as adhesion promoting layer. If this were done under a reactive nitrogen atmosphere, then an aluminium nitride layer  42  would form between the titanium nitride layer  40  and the connecting section  14 , which aluminium nitride layer considerably increases the contact resistance. 
     By contrast,  FIG. 4  shows the construction of the adhesion promoting layer  32  actually deposited in the contact hole  20 , the said adhesion promoting layer containing a base layer  50  made of titanium nitride, an intermediate layer  52  and a covering layer  54  made of titanium nitride. The base layer  50 , the intermediate layer  52  and the covering layer  54  were sputtered in the order mentioned by a method which is explained in more detail below with reference to  FIG. 6 . 
     The intermediate layer  52  comprises a mixture of titanium nitride and titanium in lower regions B 1  and B 2 , the proportion of titanium increasing in the regions B 1  and B 2 , starting from the base layer  50 , and reaching 100% in a region B 3  adjoining the region B 2 . Equally, the proportion of titanium nitride decreases from 100% to 0%. The proportion of titanium in the centre of the region B 1  and of the region B 2  is, for example, 60% and 90%, respectively. The proportion of titanium is also 100% in a region B 4  lying above the region B 3 . The regions B 1  to B 2  have identical thicknesses D 1  of 0.5 nm, for example, so that a total thickness D 2  of the intermediate layer  52  is 2 nm. A thickness D 3  of the base layer  50  is 3 nm in the exemplary embodiment. A thickness D 4  of the covering layer is 10 nm. The thicknesses D 1  to D 4  relate to the extent of the layers in a stack direction R, in which the layers  50  to  54  are stacked one above the other and which lies at right angles to the surface of the semiconductor substrate. 
       FIG. 5  shows a sputtering chamber  100  used for introducing the adhesion promoting layer  32 . A receptacle  102  has a gas inlet  104  and a gas outlet  106 . The receptacle additionally contains a sputtering target  108  made of titanium, which serves as cathode  107  and a wafer holder  11   0 , which serves as anode  109 . The wafer holder  110  carries a wafer  112 , e.g. an 8 inch wafer (1 inch=25.4 mm). The sputtering target  108  has e.g. the same diameter as the wafer. 
     The sputtering chamber  100  is suitable for directional sputtering because a distance A between sputter target  108  and wafer  112  has been considerably increased in comparison with a sputtering chamber for non-directional sputtering, for example by a factor of four to five. Thus, the distance A is about 25 cm in the exemplary embodiment. Between the connecting line from a point P in the centre of the wafer  112  toward the edge of the sputtering target  108  and the normal N to the main surface of the wafer  112  there is an angle W, which is less than 45.degree., in particular less than 30.degree., in the case of directional sputtering. 
     However, directional sputtering can also be achieved or enhanced by measures other than a large distance A, e.g. by reducing the pressure within the sputtering chamber  100 , e.g. to only 1 to 2 millitorr, or by suitable bias voltages during sputtering. Other methods also lead to directional sputtering, e.g.: the use of an IMP method (Ionized Metal Plasma) from the company Applied Materials, the use of an SIP method (Self Ionized Plasma) from the company Applied Materials, the use of the Advanced High Fill method from the company Trikon, the use of the Ultra High Fill method from the company Trikon, or the use of older sputtering with a collimator. 
     Thus, directional sputtering can be differentiated from non-directional sputtering by an angle W of less than 45.degree. or less than 30.degree. or else by other measures which lead to the same effect as a small angle W with regard to the ratio of the layer thicknesses inside and outside a contact hole  20 . 
       FIG. 6  shows method steps carried out during the production of the adhesion promoting layer  32 . The method begins in a method step  150 . In a method step  152 , the sputtering target  108  is inserted into the sputtering chamber  100  in order to utilize it for a multiplicity of sputtering processes. The sputtering target  108  contains a titanium layer  153  made of pure titanium. 
     In a subsequent method step  154 , nitrogen gas is introduced into the sputtering chamber  100 . The nitrogen brings about a nitriding of the reactive titanium layer  153 . A thin titanium nitride layer  157  is therefore produced at the surface of the titanium layer  153 . 
     After the nitriding, in a method step  158 , the supply of nitrogen is interrupted and the nitrogen contained in the sputtering chamber  100  is extracted by suction. In a next method step  106 , the wafer  112  is fixed on the wafer holder  110  in the sputtering chamber. 
     In a method step  162 , a protective gas, for example argon, is introduced into the sputtering chamber  100 . Under the argon atmosphere that forms, sputtering is begun in a method step  164 , the base layer  50  being deposited on the wafer  112 . If the last parts of the titanium nitride layer  157  and then parts of the titanium layer  153  are sputtered away, then the intermediate layer  52  is likewise formed under the argon atmosphere. 
     After the deposition of the intermediate layer  52 , in a method step  166 , nitrogen is introduced into the sputtering chamber  100  in addition to the protective gas or instead of the protective gas. The sputtering can be interrupted in this case in order to produce reproducible layers. In a method step  168 , the sputtering is continued by reigniting the plasma, the covering layer  54  being formed. In a method step  170 , the method is ended if the covering layer  54  and thus also the adhesion promoting layer  32  have reached their predetermined thickness. 
     Without changing the sputtering target  108 , the method explained is carried out a number of times in succession. 
     Later, in a different chamber, tungsten is introduced into the contact hole that has already been lined with the adhesion promoting layer  32 . Afterwards, still further metal layers of the integrated circuit arrangement  10  are produced.