Abstract:
In one embodiment, a method for forming a tungsten-containing material on a substrate is provided which includes positioning a substrate containing a metal nitride barrier layer within a process chamber and exposing the substrate to a reagent gas containing diborane to form a reagent layer on the metal nitride barrier layer. The method further provides exposing the substrate sequentially to a tungsten precursor and a reductant to form a nucleation layer during an atomic layer deposition (ALD) process and subsequently depositing a bulk layer over the nucleation layer. The bulk layer may contain copper, but generally contains tungsten deposited by a chemical vapor deposition (CVD) process. In some examples, the bulk layer may be used to fill apertures within the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. Ser. No. 11/130,515 (APPM/004349.C1), filed May 17, 2005, and issued as U.S. Pat. No. 7,238,552, which is a continuation of U.S. Ser. No. 10/196,514 (APPM/004349), filed Jul. 15, 2002, and issued as U.S. Pat. No. 6,936,538, which claims benefit of U.S. Ser. No. 60/305,765 (APPM/004349L), filed Jul. 16, 2001, which are herein incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the invention relate to the processing of semiconductor substrates. More particularly, embodiments of the invention relate to improvements in the process of depositing refractory metal layers on semiconductor substrates.  
         [0004]     2. Description of the Related Art  
         [0005]     The semiconductor processing industry continues to strive for larger production yields while increasing the uniformity of layers deposited on substrates having larger surface areas. These same factors in combination with new materials also provide higher density of circuits per unit area of the substrate. As circuit density increases, the need for greater uniformity and process control regarding layer thickness rises. As a result, various technologies have been developed to deposit layers on substrates in a cost-effective manner, while maintaining control over the characteristics of the layer. Chemical vapor deposition (CVD) is one of the most common deposition processes employed for depositing layers on a substrate. CVD is a flux-dependent deposition technique that requires precise control of the substrate temperature and precursors introduced into the processing chamber in order to produce a desired layer of uniform thickness. These requirements become more critical as substrate size increases (e.g., from 200 mm diameter substrates to 300 mm substrates), creating a need for more complexity in chamber design and gas flow technique to maintain adequate uniformity.  
         [0006]     A variant of CVD that demonstrates superior step coverage compared to CVD, is atomic layer deposition (ALD). ALD is based upon atomic layer epitaxy (ALE) that was employed originally to fabricate electroluminescent displays. ALD employs chemisorption to deposit a saturated monolayer of reactive precursor molecules on a substrate surface by alternating pulses of an appropriate reactive precursor into a deposition chamber. Each injection of a reactive precursor is separated by an inert gas purge to provide an adsorbed atomic layer to previously deposited layers to form a uniform layer on the substrate. The cycle is repeated to form the layer to a desired thickness. A drawback with ALD techniques is that the deposition rate is much lower than typical CVD techniques by at least one order of magnitude.  
         [0007]     Formation of film layers at a high deposition rate while providing adequate step coverage are conflicting characteristics often necessitating sacrificing one to obtain the other. This conflict is true particularly when refractory metal layers are deposited to cover apertures or vias during formation of contacts that interconnect adjacent metallic layers separated by dielectric layers. Historically, CVD techniques have been employed to deposit conductive material such as refractory metals in order to inexpensively and quickly fill vias. Due to the increasing density of semiconductor circuitry, tungsten has been used based upon superior step coverage to fill these high aspect ratio structures. As a result, deposition of tungsten employing CVD techniques enjoys wide application in semiconductor processing due to the high throughput of the process and good step coverage.  
         [0008]     Depositing tungsten by traditional CVD methods, however, is attendant with several disadvantages. For example, blanket deposition of a tungsten layer on a semiconductor wafer is time-consuming at temperatures below 400° C. The deposition rate of tungsten may be improved by increasing the deposition temperature between approximately 500° C. to 550° C. However, temperatures in this higher range may compromise the structural and operational integrity of the underlying portions of the integrated circuit being formed. Use of tungsten has also complicated photolithography steps during the manufacturing process as it results in a relatively rough surface having a reflectivity of 20% or less than that of a silicon substrate. Finally, tungsten has proven difficult to uniformly deposit on a substrate. Variance in film thickness of greater than 1% has been shown, thereby causing poor control of the resistivity of the layer. Several prior attempts to overcome the aforementioned drawbacks have been attempted.  
         [0009]     For example, in U.S. Pat. No. 5,028,565 to Chang et al., which is assigned to the assignee of the present invention, a method is disclosed to improve, inter alia, uniformity of tungsten layers by varying the deposition chemistry. The method includes, in pertinent part, formation of a nucleation layer over an intermediate barrier layer before depositing the tungsten layer via bulk deposition. The nucleation layer is formed from a gaseous mixture of tungsten hexafluoride, hydrogen, silane and argon. The nucleation layer is described as providing a layer of growth sites to promote uniform deposition of a tungsten layer thereon. The benefits provided by the nucleation layer are described as being dependent upon the barrier layer present. For example, the uniformity of a tungsten layer is improved by as much as 15% when formed on a titanium nitride barrier layer. The benefits provided by the nucleation layer are not as pronounced if the barrier layer formed from sputtered tungsten or sputtered titanium tungsten.  
         [0010]     A need exists, therefore, to provide techniques to improve the characteristics of refractory metal layers deposited on semiconductor substrates.  
       SUMMARY OF THE INVENTION  
       [0011]     A method and system to form a refractory metal layer over a substrate includes introduction of a reductant, such as PH 3  or B 2 H 6 , followed by introduction of a tungsten containing compound, such as WF 6 , to form a tungsten layer. It is believed that the reductant reduces the fluorine content of the tungsten layer while improving the step coverage and resistivity of the tungsten layer. It is believed that the improved characteristics of the tungsten film are attributable to the chemical affinity between the reductants and the tungsten containing compound. The chemical affinity provides better surface mobility of the adsorbed chemical species and better reduction of WF 6  at the nucleation stage of the tungsten layer.  
         [0012]     The method can further include sequentially introducing a reductant, such as PH 3  or B 2 H 6 , and a tungsten containing compound to deposit a tungsten layer. The formed tungsten layer can be used as a nucleation layer followed by bulk deposition of a tungsten layer utilizing standard CVD techniques. Alternatively, the formed tungsten layer can be used to fill an aperture. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of one embodiment of a semiconductor processing system in accordance with the present invention.  
         [0014]      FIG. 2  is a schematic cross-sectional view of one embodiment of the processing chambers shown above in  FIG. 1 .  
         [0015]      FIG. 3  is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a reductant over a substrate during sequential deposition.  
         [0016]      FIG. 4  is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a refractory metal containing compound over the substrate after introduction of the reductant.  
         [0017]      FIG. 5  is a graphical representation showing the concentration of gases present in a processing chamber, such as processing chamber as shown above in  FIG. 2 .  
         [0018]      FIG. 6  is a graphical representation showing the relationship between the number of ALD cycles and the thickness of a layer formed on a substrate employing sequential deposition techniques, in accordance with the present invention.  
         [0019]      FIG. 7  is a graphical representation showing the relationship between the number of sequential deposition cycles and the resistivity of a layer formed on a substrate employing sequential deposition techniques, in accordance with the present invention.  
         [0020]      FIG. 8  is a graphical representation showing the relationship between the deposition rate of a layer formed on a substrate employing sequential deposition techniques and the temperature of the substrate.  
         [0021]      FIG. 9  is a graphical representation showing the relationship between the resistivity of a layer formed on a substrate employing sequential deposition techniques and the temperature of the substrate, in accordance with the present invention.  
         [0022]      FIG. 10  is a schematic cross-sectional view of one embodiment of a patterned substrate having a nucleation layer formed thereon employing sequential deposition techniques, in accordance with the present invention.  
         [0023]      FIG. 11  is a schematic cross-sectional view of one embodiment of the substrate, shown above in  FIG. 10 , with a refractory metal layer formed atop of the nucleation layer employing CVD, in accordance with the present invention.  
         [0024]      FIG. 12  is a graphical representation showing the concentration of gases present in a processing chamber, such as the processing chamber as shown above in  FIG. 2 , in accordance with an alternative embodiment of the present invention.  
         [0025]      FIG. 13  is a graphical representation showing the concentration of gases present in a processing chamber, such as processing chamber as shown above in  FIG. 2 , in accordance with an alternative embodiment of the present invention.  
         [0026]      FIG. 14  is a graphical representation showing the fluorine content versus depth of a refractory metal layer formed on a substrate employing ALD, either Ar or N 2  being a carrier gas.  
         [0027]      FIG. 15  is a graphical representation showing the fluorine content versus depth of a refractory metal layer formed on a substrate employing ALD with H 2  being a carrier gas.  
         [0028]      FIG. 16  is a schematic cross-sectional view of one embodiment of a substrate shown above in  FIGS. 3 and 4  upon which a layer of either PH 3  or B 2 H 6  is disposed between a substrate and a tungsten layer, in accordance with one embodiment of the present invention.  
         [0029]      FIG. 17  is a graphical representation showing the concentration of gases present in a processing chamber, such as processing chamber as shown above in  FIG. 2 , in accordance with one embodiment of the present invention.  
         [0030]      FIG. 18  is a schematic cross-sectional view of one embodiment of a substrate shown above in  FIGS. 3 and 4  in which a titanium-containing layer is deposited between a substrate and a layer of either PH 3  or B 2 H 6 , in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0031]     Referring to  FIG. 1 , an exemplary wafer processing system includes one or more processing chambers  12  and  14  disposed in a common work area  16  surrounded by a wall  18 . Processing chambers  12  and  14  are in data communication with a controller  22  that is connected to one or more monitors, shown as  24  and  26 . The monitors typically display common information concerning the process associated with processing chambers  12  and  14 . One of the monitors  26  is mounted on wall  18 , with the remaining monitor  24  being disposed in work area  16 . Operational control of processing chambers  12  and  14  may be achieved by the use of a light pen, associated with one of the monitors  24  and  26 , to communicate with controller  22 . For example, light pen  28  is associated with monitor  24  and facilitates communication with controller  22  through monitor  24 . Light pen  39  facilitates communication with controller  22  through monitor  26 .  
         [0032]     Referring both to  FIGS. 1 and 2 , each of processing chambers  12  and  14  includes a housing  30  having a base wall  32 , a cover  34  disposed opposite to base wall  32 , and a sidewall  36  extending therebetween. Housing  30  defines a chamber  37 , and a pedestal  38  is disposed within processing chamber  37  to support a substrate  42 , such as a semiconductor wafer. Pedestal  38  may be mounted to move between cover  34  and base wall  32 , using a displacement mechanism (not shown), but the position thereof is typically fixed. Supplies of processing gases  39   a  ,  39   b  and  39   c  are in fluid communication with processing chamber  37  via a showerhead  40 . Regulation of the flow of gases from supplies  39   a  ,  39   b  and  39   c  is effectuated via flow valves  41 .  
         [0033]     Depending on the specific process, substrate  42  may be heated to a desired temperature prior to layer deposition via a heater embedded within pedestal  38 . For example, pedestal  38  may be resistively heated by applying an electric current from AC power supply  43  to heater element  44 . Substrate  42  is, in turn, heated by pedestal  38 , and can be maintained within a desired process temperature range of, for example, about 20° C. to about 750° C. A temperature sensor  46 , such as a thermocouple, is also embedded in wafer support pedestal  38  to monitor the temperature of pedestal  38  in a conventional manner. For example, the measured temperature may be used in a feedback loop to control the electrical current applied to heater element  44  by power supply  43  such that the substrate temperature can be maintained or controlled at a desired temperature that is suitable for the particular process application. Optionally, pedestal  38  may be heated using radiant heat (not shown). A vacuum pump  48  is used to evacuate processing chamber  37  and to help maintain the proper gas flows and pressure inside processing chamber  37 .  
         [0034]     Referring to  FIGS. 1 and 2 , one or both of processing chambers  12  and  14 , discussed above may operate to deposit refractory metal layers on the substrate employing sequential deposition techniques. One example of sequential deposition techniques in accordance with the present invention includes atomic layer deposition (ALD). The term “substrate” as used herein includes the substrate, such as semiconductor substrates and glass substrates, as well as layers formed thereover, such as dielectric layers (e.g., SiO 2 ) and barrier layers (e.g., titanium, titanium nitride and the like).  
         [0035]     Not wishing to be bound by theory,  FIG. 3  is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a reductant over a substrate during sequential deposition. The terms “adsorption” or “adsorb” as used herein are defined to include chemisorption, physisorption, or any attractive and/or bonding forces which may be at work and/or which may contribute to the bonding, reaction, adherence, or occupation of a portion of an exposed surface of a substrate structure. During the sequential deposition technique, in accordance with the present invention, a batch of a first processing gas, in this case “Aa x ,” results in a layer of “A” being deposited on substrate  42  having a surface of ligand “a” exposed to processing chamber  37 . Layer “A” may be a monolayer, more than a monolayer, or less than a monolayer. Thereafter, a purge gas enters processing chamber  37  to purge gas “Aa x ,” which has not been incorporated into the layer of A.  FIG. 4  is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a refractory metal containing compound over the substrate after introduction of the reductant. After purging gas “Aa x ” from processing chamber  37 , a second batch of processing gas, “Bb y ,” is introduced into processing chamber  37 . The “a” ligand present on the substrate surface reacts with the “b” ligand and “B” atom, releasing molecules, for example, “ab” and “aA,” which move away from substrate  42  and are subsequently pumped from processing chamber  37 . In this manner, a surface comprising a layer of B compound remains upon substrate  42  and exposed to processing chamber  37 , shown in  FIG. 4 . The composition of the layer of B compound may be a monolayer or less of atoms typically formed employing ALD techniques. In other embodiments, more than a monolayer of B compound may be formed during each cycle. Alternatively, the layer of compound B may include a layer of multiple atoms (i.e., other atoms besides atoms of B). In such a case, the first batch and/or the second batch of processing gases may include a mixture of process gases, each of which has atoms that would adhere to substrate  42 . The process proceeds cycle after cycle, until the desired thickness is achieved.  
         [0036]     Referring to both  FIGS. 3 and 4 , although any type of processing gas may be employed, in the present example, the reductant “Aa x ” may comprise B 2 H 6  or PH 3  and the refractory metal containing compound, Bb y , may comprise WF 6 . Some possible reactions are shown below in reference to chemical reaction (1) and chemical reaction (2). 
 
B 2 H 6 (g)+WF 6 (g)→W(s)+2BF 3 (g)   (1) 
 
PH 3 (g)+WF 6 (g)→W(s)+PF 3 (g)   (2) 
 
 Other by-products include but are not limited to H 2 , HF or F 2 . Other reactions are also possible, such as decomposition reactions. In other embodiments, other reductants may be used, such as SiH 4 . Similarly, in other embodiments, other tungsten containing gases may be used, such as W(CO) 6 . 
 
         [0037]     The purge gas includes Ar, He, N 2 , H 2 , other suitable gases, and combinations thereof. One or more purge gas may be used.  FIG. 5  is a graphical representation of one embodiment of gases present in a processing chamber utilizing two purge gases Ar and N 2 . Each of the processing gases was flowed into processing chamber  37  with a carrier gas, which in this example was one of the purge gases. WF 6  is introduced with Ar and B 2 H 6  is introduced with N 2 . It should be understood, however, that the purge gas may differ from the carrier gas, discussed more fully below. One cycle of the ALD technique in accordance with the present invention includes flowing the purge gas, N 2 , into processing chamber  37  during time t 1 , which is approximately about 0.01 seconds to about 15 seconds before B 2 H 6  is flowed into processing chamber  37 . During time t 2 , the processing gas B 2 H 6  is flowed into processing chamber  37  for a time in the range of about 0.01 seconds to about 15 seconds, along with a carrier gas, which in this example is N 2 . After about 0.01 seconds to about 15 seconds have lapsed, the flow of B 2 H 6  terminates and the flow of N 2  continues during time t 3  for an additional time in the range of about 0.01 seconds to about 15 seconds, purging the processing chamber of B 2 H 6 . During time t 4  which lasts approximately about 0 seconds to about 30 seconds, processing chamber  37  is pumped so as to remove most, if not all, gases. After pumping of process chamber  37 , the carrier gas Ar is introduced for a time in the range of about 0.01 seconds to about 15 seconds during time t 5 , after which time the process gas WF 6  is introduced into processing chamber  37 , along with the carrier gas Ar during time t 6 . The time t 6  lasts between about 0.01 seconds to about 15 seconds. The flow of the processing gas WF 6  into processing chamber  37  is terminated approximately about 0.01 seconds to about 15 seconds after it commenced. After the flow of WF 6  into processing chamber  37  terminates, the flow of Ar continues for an additional time in the range of 0.01 seconds to 15 seconds, during time t 7 . Thereafter, processing chamber  37  is pumped so as to remove most, if not all, gases therein, during time t 8 . As before, time t 8  lasts approximately about 0 seconds to about 30 seconds, thereby concluding one cycle of the sequential deposition technique, in accordance with the present invention. The cycle may be repeated to deposit a tungsten layer to a desired thickness.  
         [0038]     The benefits of employing the sequential deposition technique are many fold, including flux-independence of layer formation that provides uniformity of deposition independent of the size of a substrate. For example, the measured difference of the layer uniformity and thickness measured between a 200 mm substrate and a 300 mm substrate deposited in the same chamber is negligible. This is due to the self-limiting characteristics of the sequential deposition techniques. Further, this technique contributes to improved step coverage over complex topography.  
         [0039]     In addition, the thickness of the layer B, shown in  FIG. 4 , may be easily controlled while minimizing the resistance of the same by employing sequential deposition techniques. With reference to  FIG. 6 , it is seen in the slope of line  50  that the thickness of the tungsten layer B is proportional to the number of cycles employed to form the same. The resistivity of the tungsten layer, however, is relatively independent of the thickness of the layer, as shown by the slope of line  52  in  FIG. 7 . Thus, employing sequential deposition techniques, the thickness of a refractory metal layer maybe easily controlled as a function of the cycling of the process gases introduced into the processing chamber with a negligible effect on the resistivity.  
         [0040]      FIG. 8  is a graphical representation showing the relationship between the deposition rate of a layer formed on a substrate employing sequential deposition techniques and the temperature of the substrate. Control of the deposition rate was found to be dependent upon the temperature of substrate  42 . As shown by the slope of line  54 , increasing the temperature of substrate  42  increased the deposition rate of the tungsten layer B. The graph shows that less than a monolayer, a monolayer, or more than a monolayer of a tungsten layer may be formed depending on the substrate temperature utilized. For example, at  56 , the deposition rate is shown to be approximately 2 Å/cycle at 250° C. However at point  58  the deposition rate is approximately 5 Å/cycle at a temperature of 450° C. The resistivity of the tungsten layer, however, is virtually independent of the layer thickness, as shown by the slope of curve  59 , shown in  FIG. 9 . As a result, the deposition rate of the tungsten layer may be controlled as a function of temperature without compromising the resistivity of the same. However, it may be desirable to reduce the time necessary to deposit an entire layer of a refractory metal.  
         [0041]     To that end, a bulk deposition of the refractory metal layer may be included in the deposition process. Typically, the bulk deposition of the refractory metal occurs after the nucleation layer is formed in a common processing chamber. Specifically, in the present example, nucleation of a tungsten layer occurs in chamber  12  employing the sequential deposition techniques discussed above, with substrate  42  being heated in the range of about 200° C. to about 400° C., and processing chamber  37  being pressurized in the range of about 1 Torr to about 10 Torr. A nucleation layer  60  of approximately about 120 Å to about 200 Å is formed on a patterned substrate  42 , shown in  FIG. 10 . Nucleation layers of about 100 Å or less, about 50 Å or less, or about 25 Å or less have also been found to be effective in providing good step coverage over apertures having an aspect ratio of about 6:1 or greater. As shown, substrate  42  includes a barrier layer  61  and a patterned layer having a plurality of vias  63 . The nucleation layer is formed adjacent to the patterned layer covering vias  63 . As shown, forming nucleation layer  60  employing ALD techniques provides good step coverage. In another embodiment, sequential deposition techniques may be performed for both nucleation and bulk deposition. In still another embodiment, to decrease the time required to form a complete layer of tungsten, a bulk deposition of tungsten onto nucleation layer  60  occurs using CVD techniques, while substrate  42  is disposed in the same processing chamber  12 , shown in  FIG. 1 . The bulk deposition may be performed using recipes well known in the art. In this manner, a tungsten layer  65  providing a complete plug fill is achieved on the patterned layer with vias having aspect ratios of approximately 6:1, shown in  FIG. 11 .  
         [0042]     In an alternative embodiment, a bifurcated deposition process may be practiced in which nucleation of the refractory metal layer occurs in a chamber that is different from the chamber in which the remaining portion of the refractory metal layer is formed. Specifically, in the present example, nucleation of a tungsten layer occurs in chamber  12  employing the sequential deposition techniques, such as ALD, discussed above. To that end, substrate  42  is heated in the range of about 200° C. to about 400° C. and chamber  37  is pressurized in the range of about 1 Torr to about 10 Torr. A nucleation layer  60  of approximately 120 Å to 200 Å is formed on a patterned substrate  42 , shown in  FIG. 10 . Nucleation layers of about 100 Å or less, about 50 Å or less, or about 25 Å or less have also been found to be effective in providing good step coverage over apertures having an aspect ratio of about 6:1 or greater. As shown, substrate  42  includes a barrier layer  61  and a patterned layer having a plurality of vias  63 . The nucleation layer is formed adjacent to the patterned layer covering the vias  63 . As shown, forming the nucleation layer  60  employing sequential deposition techniques provides improved step coverage.  
         [0043]     In one embodiment, sequential deposition techniques are employed for bulk deposition of tungsten onto nucleation layer  60  occurs while substrate  42  is disposed in processing chamber  14 , shown in  FIG. 1 . The bulk deposition maybe performed using recipes disclosed herein. In another embodiment, CVD techniques are employed for bulk deposition of tungsten onto nucleation layer  60  occurs while substrate  42  is disposed in processing chamber  14 , shown in  FIG. 1 . The bulk deposition maybe performed using recipes well known in the art. Whether sequential deposition or CVD deposition techniques are employed, a tungsten layer  65  providing a complete plug fill is achieved on the patterned layer with vias having aspect ratios of approximately 6:1, shown in  FIG. 11 . Implementing the bifurcated deposition process discussed above may decrease the time required to form a tungsten layer having improved characteristics. Utilizing CVD deposition techniques for bulk deposition may further increase throughput.  
         [0044]     As mentioned above, in an alternate embodiment of the present invention, the carrier gas may differ from the purge gas, as shown in  FIG. 12 . The purge gas, which is introduced at time intervals t 1 , t 3 , t 5  and t 7 , comprises Ar. The carrier gas, which is introduced at time intervals t 2  and t 6 , comprises of N 2 . Thus, at time interval t 2  the gases introduced into the processing chamber include a mixture of B 2 H 6  and N 2 , and a time interval t 6 , the gas mixture includes WF 6  and N 2 . The pump process during time intervals t 4  and t 8  is identical to the pump process discussed above with respect to  FIG. 5 . In yet another embodiment, shown in  FIG. 13 , the carrier gas during time intervals t 2  and t 6  comprises H 2 , with the purge gas introduced at time intervals t 1 , t 3 , t 5  and t 7  comprises Ar. The pump processes at time intervals t 4  and t 8  are as discussed above. As a result, at time interval t 2  the gas mixture introduced into processing chamber  37  comprises of B 2 H 6  and H 2 , and WF 6 , and H 2  at time interval t 6 .  
         [0045]     An advantage realized by employing the H 2  carrier gas is that the stability of the tungsten layer B may be improved. Specifically, by comparing curve  66  in  FIG. 14  with curve  68  in  FIG. 15 , it is seen that the concentration of fluorine in the nucleation layer  60 , shown in  FIG. 10 , is much less when H 2  is employed as the carrier gas, as compared with use of N 2  or Ar as a carrier gas.  
         [0046]     Referring to both  FIGS. 14 and 15 , the apex and nadir of curve  66  show that the fluorine concentration reaches levels in excess of 1×10 21  atoms per cubic centimeter and only as low as just below 1×10 19  atoms per cubic centimeter. Curve  68 , however, shows that the fluorine concentration is well below 1×10 21  atoms per cubic centimeter at the apex and well below 1×10 17  atoms per cubic centimeter at the nadir. Thus, employing H 2  as the carrier gas provides a much more stable film, e.g., the probability of fluorine diffusing into the substrate, or adjacent layer is reduced. This also reduces the resistance of the refractory metal layer by avoiding the formation of a metal fluoride that may result from the increased fluorine concentration. Thus, the stability of the nucleation layer, as well as the resistivity of the same, may be controlled as a function of the carrier gas employed. This is also true when a refractory metal layer is deposited entirely employing ALD techniques, i.e., without using other deposition techniques, such as CVD.  
         [0047]     In addition, adsorbing a layer  70 , shown in  FIG. 16 , of either PH 3  or B 2 H 6  prior to introduction of the tungsten containing compound forms a tungsten layer  72  with reduced fluorine content, improved step coverage, and improved resistivity. This was found to be the case where the tungsten containing compound is introduced over a layer of PH 3  or B 2 H 6  employing sequential deposition techniques or employing standard CVD techniques using either tungsten hexafluoride (WF 6 ) and silane (SiH 4 ) or tungsten hexafluoride (WF 6 ) and molecular hydrogen (H 2 ) chemistries. The improved characteristics of the tungsten film are believed to be attributable to the chemical affinity between the PH 3  or B 2 H 6  layer and the WF 6  layer. This provides better surface mobility of the adsorbed chemical species and better reduction of WF 6  at the nucleation stage of the tungsten layer. This has proven beneficial when depositing a tungsten layer adjacent to a titanium containing adhesion layer formed from titanium (Ti) or titanium nitride (TiN). Layer  70  is preferably a monolayer, but in other embodiments may be less than or more than a monolayer. Layer  70  in the film stack, shown in  FIG. 16 , shows the formation of the tungsten layer  72 . It is understood that layer  70  may or may not be consumed during formation of the tungsten layer  72 . It is also understood that a plurality of layers  70  and tungsten layers  72  may be deposited to form a tungsten layer to a desired thickness. As shown, layer  70  is deposited on substrate  74  that includes a wafer  76  that may be formed from any material suitable for semiconductor processing, such as silicon. One or more layers, shown as layer  74 , may be present on wafer  76 . Layer  78  may be formed from any suitable material, included dielectric or conductive materials. Layer  78  includes a void  80 , exposing a region  82  of wafer  76 .  
         [0048]      FIG. 18  is a detailed cross-sectional view of a substrate in which a titanium-containing adhesion layer is formed between a substrate and a layer of either PH 3  or B 2 H 6  during the fabrication of a W layer adjacent to the titanium-containing adhesion layer. The titanium-containing adhesion layer may be formed employing standard CVD techniques. In one embodiment, the titanium-containing adhesion layer is formed employing sequential deposition techniques. To that end, processing gas Aa x  is selected from the group including H 2 , B 2 H 6 , SiH 4 , and NH 3 . Processing gas Bb y  is a titanium-containing gas selected from the group that includes TDMAT, TDEAT, and TiCl 4 . Also, Ar and N 2  purge gases are preferably employed, although other purge gas may be used.  
         [0049]     Referring to  FIGS. 2 and 17 , each of the processing gases is flowed into processing chamber  37  with a carrier gas, which in this example, is one of the purge gases. It should be understood, however, that the purge gas may differ from the carrier gas, discussed more fully below. One cycle of the sequential deposition technique, in accordance with the present invention, includes flowing a purge gas into processing chamber  37  during time t 1  before the titanium-containing gas is flowed into processing chamber  37 . During time t 2 , the titanium-containing processing gas is flowed into the processing chamber  37 , along with a carrier gas. After t 2  has lapsed, the flow of titanium-containing gas terminates and the flow of the carrier gas continues during time t 3 , purging the processing chamber of the titanium-containing processing gas. During time t 4 , the processing chamber  37  is pumped so as to remove all gases. After pumping of process chamber  37 , a carrier gas is introduced during time t 5 , after which time the reducing process gas is introduced into the processing chamber  37  along with the carrier gas, during time t 6 . The flow of the reducing process gas into processing chamber  37  is subsequently terminated. After the flow of reducing process gas into processing chamber  37  terminates, the flow of carrier gas continues, during time t 7 . Thereafter, processing chamber  37  is pumped so as to remove all gases therein, during time t 8 , thereby concluding one cycle of the sequential deposition technique in accordance with the present invention. The aforementioned cycle is repeated multiple times until titanium-containing layer reaches a desired thickness. For example, in reference to  FIG. 18 , after TiN layer  84  reaches a desired thickness, layer  86 , in this example formed from PH 3  or B 2 H 6 , is deposited adjacent thereto employing sequential deposition techniques, as discussed above. Thereafter, a layer of tungsten  88 , shown in  FIG. 18 , is disposed adjacent to layer  86  using the sequential deposition technique or standard CVD techniques, both of which are discussed above. Layer  86  is preferably a monolayer, but in other embodiments may be less than or more than a monolayer. Layer  86  in the film stack, shown in  FIG. 18 , shows the formation of the tungsten layer  88 . It is understood that layer  86  may or may not be consumed during formation of the tungsten layer  88 . It is also understood that a plurality of layers  86  and tungsten layers  88  may be deposited to form a tungsten layer to a desired thickness. If desired, a copper layer maybe deposited atop of tungsten layer  88 . In this manner, tungsten may function as a barrier layer.  
         [0050]     Referring again to  FIG. 2 , the process for depositing the tungsten layer may be controlled using a computer program product that is executed by controller  22 . To that end, controller  22  includes a central processing unit (CPU)  90 , a volatile memory, such as a random access memory (RAM)  92  and permanent storage media, such as a floppy disk drive for use with a floppy diskette or hard disk drive  94 . The computer program code can be written in any conventional computer readable programming language; for example, 68000 assembly language, C, C++, Pascal, FORTRAN and the like. Suitable program code is entered into a single file, or multiple files, using a conventional text editor and stored or embodied in a computer-readable medium, such as hard disk drive  94 . If the entered code text is in a high level language, the code is compiled and the resultant compiler code is then linked with an object code of precompiled WINDOWS® library routines. To execute the linked and compiled object code, the system user invokes the object code, causing the CPU  90  to load the code in RAM  92 . The CPU  90  then reads and executes the code to perform the tasks identified in the program.  
         [0051]     Although the invention has been described in terms of specific embodiments, one skilled in the art will recognize that various changes to the reaction conditions, e.g., temperature, pressure, film thickness and the like can be substituted and are meant to be included herein. Additionally, while the bifurcated deposition process has been described as occurring in a common system, the bulk deposition may occur in a processing chamber of a mainframe deposition system that is different from the mainframe deposition system in which the processing chamber is located that is employed to deposit the nucleation layer. Finally, other refractory metals may be deposited, in addition to tungsten, and other deposition techniques may be employed in lieu of CVD. For example, physical vapor deposition (PVD) techniques, or a combination of both CVD and PVD techniques may be employed. The scope of the invention should not be based upon the foregoing description. Rather, the scope of the invention should be determined based upon the claims recited herein, including the full scope of equivalents thereof.