Abstract:
A method and apparatus for forming layers on a substrate comprising depositing a metal seed layer on a substrate surface having apertures, depositing a transition metal layer over the copper seed layer, and depositing a bulk metal layer over the transition metal layer. Also a method and apparatus for forming a via through a dielectric to reveal metal at the base of the via, depositing a transition metal layer, and depositing a first metal layer on the transition metal layer. Additionally, a method and apparatus for depositing a transition metal layer on an exposed metal surface, and depositing a layer thereover selected from the group consisting of a capping layer and a low dielectric constant layer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a metallization process for manufacturing semiconductor devices. More particularly, the present invention relates to preventing copper dewetting by depositing a transition metal that helps preserve the copper crystal structure and promote adhesion between copper and other materials.  
         [0003]     2. Description of the Related Art  
         [0004]     Copper is the current metal of choice for use in multilevel metallization processes that are crucial to semiconductor device manufacturing. The multilevel interconnects that drive the manufacturing processes require planarization of high aspect ratio apertures including contacts, vias, lines, and other features. Filling the features without creating voids or deforming the feature geometry is more difficult when the features have higher aspect ratios. Reliable formation of interconnects is also more difficult as manufacturers strive to increase circuit density and quality.  
         [0005]     As the use of copper has permeated the marketplace because of its relative low cost and processing properties, semiconductor manufacturers continue to look for ways to improve the boundary regions between copper and dielectric material by reducing copper diffusion and dewetting. Several processing methods have been developed to manufacture copper interconnects as feature sizes have decreased. Each processing method may increase the likelihood of errors such as copper diffusion across boundary regions, copper crystalline structure deformation, and dewetting. Physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), chemical mechanical polishing (CMP), electrochemical plating (ECP), electrochemical mechanical polishing (ECMP), and other methods of depositing and removing copper layers utilize mechanical, electrical, or chemical methods to manipulate the copper that forms the interconnects. Barrier and capping layers may be deposited to contain the copper.  
         [0006]     In the past, a layer of tantalum, tantalum nitride, or copper alloy with tin, aluminum, or magnesium was used to provide a barrier layer or an adhesion promoter between copper and other materials. These options are costly or only partially effective or both. As the copper atoms along the boundary regions experience changes in temperature, pressure, atmospheric conditions, or other process variables common during multiple step semiconductor processing, the copper may migrate along the boundary regions and become agglomerated copper. The copper may also be less uniformly dispersed along the boundary regions and become dewetted copper. These changes in the boundary region include stress migration and electromigration of the copper atoms. The stress migration and electromigration of copper across the dielectric layers or other structures increases the resistitivity of the resulting structures and reduces the reliability of the resulting devices.  
         [0007]     Preventing agglomeration of copper, especially when seed layers of copper are deposited on dielectric or other materials, is a research goal. Reducing deviation from ideal copper crystalline structure and discouraging copper dewetting is important. Finally, it is desirable to decrease the likelihood of diffusion of copper into dielectric, barrier, or other layers.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention generally provides a method and apparatus for forming a transition metal layer on a surface prior to metal deposition to minimize dewetting while maintaining the desired crystalline structure of the metal.  
         [0009]     The present invention also generally provides a method and apparatus for depositing layers on a substrate comprising forming a copper seed layer on a substrate surface having apertures, depositing a transition metal layer over the copper seed layer, and depositing a bulk copper layer over the transition metal layer.  
         [0010]     The invention also generally provides a method and apparatus for depositing layers on a substrate comprising forming a via through a dielectric to reveal a metal at the base of the via, depositing a transition metal layer on the metal at the base of the via, and depositing copper on the transition metal layer. A punch through step may optionally be performed.  
         [0011]     The present invention generally provides a method and apparatus for depositing layers on a substrate comprising depositing a transition metal layer on a bulk metal layer and optionally depositing an additional capping layer on the transition metal layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0013]      FIG. 1  is a schematic plan view of a processing platform.  
         [0014]      FIG. 2  is a schematic plan view of an alternative processing platform.  
         [0015]      FIG. 3  is a schematic cross-sectional view of a process chamber that may be used to perform a cyclical deposition process.  
         [0016]      FIG. 4  is a vertical, cross-sectional view of one embodiment of a chemical vapor deposition apparatus.  
         [0017]      FIGS. 5A  to  5 E are schematic diagrams of a metallized via.  
         [0018]      FIGS. 6A  to  6 E are schematic diagrams of an alternative embodiment of a metallized via.  
         [0019]      FIGS. 7A  to  7 B are schematic diagrams of an additional alternative embodiment of a metallized semiconductor substrate via.  
         [0020]      FIG. 8  is a schematic diagram of a surface of a substrate. 
     
    
     DETAILED DESCRIPTION  
       [0021]     The present invention uses a transition metal to prevent copper dewetting and to stabilize copper crystalline structure in interconnect boundary regions. The transition metal, for example, ruthenium, improves copper boundary region properties to promote adhesion, decrease diffusion and agglomeration, and encourage uniform roughness and wetting of the substrate surface during processing. Deposition of ruthenium to improve the dewetting of a copper seed layer before bulk fill copper deposition is presented. Deposition of ruthenium to help preserve the copper crystallinity in the base of a via is also presented. Deposition of ruthenium after copper has been deposited to fill a via before an optional additional capping layer is deposited is presented.  
         [0022]      FIG. 1  is a schematic top-view diagram of an exemplary multi-chamber processing system  900 . A similar multi-chamber processing system is disclosed in commonly assigned U.S. Pat. No. 5,186,718, entitled “Staged Vacuum Wafer Processing System and Method,” issued on Feb. 16, 1993, which is hereby incorporated by reference herein. The system  900  generally includes load lock chambers  902  and  904  for the transfer of substrates into and out of the system  900 . Because the system  900  is under vacuum, the load lock chambers  902  and  904  may “pump down” the substrates introduced into the system  900 . A first robot  910  transfers the substrates between the load lock chambers  902  and  904 , and one or more substrate processing chambers  912 ,  914 ,  916 , and  918  (four are shown). Each processing chamber  912 ,  914 ,  916 , and  918 , can be outfitted to perform a number of substrate processing operations such as ALD, CVD, PVD, etch, pre-clean, de-gas, orientation, and other processes. The first robot  910  also transfers substrates to and from one or more transfer chambers  922  and  924 .  
         [0023]     The transfer chambers  922  and  924  are used to maintain ultrahigh vacuum conditions while allowing substrates to be transferred within the system  900 . A second robot  930  may transfer the substrates between the transfer chambers  922  and  924  and one or more processing chambers  932 ,  934 ,  936 , and  938 . Similar to processing chambers  912 ,  914 ,  916 , and  918 , the processing chambers  932 ,  934 ,  936 , and  938  can be outfitted to perform a variety of substrate processing operations, such as ALD, CVD, PVD, etch, pre-clean, de-gas, and orientation, for example. Any of the substrate processing chambers  912 ,  914 ,  916 ,  918 ,  932 ,  934 ,  936 , and  938  may be removed from the system  900 .  
         [0024]     In one arrangement of an embodiment, processing chamber  916  and  918  may be an anneal chamber and each processing chamber  912  and  914  may be an ALD chamber, CVD chamber, or PVD chamber adapted to deposit a barrier layer.  
         [0025]     Processing chambers  932  and  938  may be an ALD chamber, CVD chamber, or PVD chamber adapted to deposit a copper layer. Further, processing chambers  934  and  936  may be an ALD chamber, CVD chamber, PVD chamber, or combinations thereof adapted to deposit a ruthenium layer. Processing chambers  934  and  936  may be an ALD/CVD hybrid chamber, such as disclosed in the co-assigned, pending U.S. patent application Ser. No. 10/712,690, filed Nov. 13, 2003, entitled, “Apparatus and Method for Hybrid Chemical Processing,” which is hereby incorporated by reference herein. Another process chamber configured to operate in both an ALD mode as well as a conventional CVD mode is described in commonly assigned U.S. patent application Ser. No. 10/016,300, filed on Dec. 12, 2001, entitled, “Lid Assembly for a Processing System to Facilitate Sequential Deposition Techniques,” which is incorporated by reference herein.  
         [0026]     In an additional embodiment, process chambers  916  and  918  may be pre-clean chambers and process chambers  912  and  914  may be de-gas chambers. Process chambers  932  and  938  may be configured for ALD or PVD barrier layer deposition. Additionally, process chambers  934  and  936  may be configured to deposit a seed layer by ALD, PVD, or CVD. Alternatively, process chambers  934  and  936  may be configured to deposit a liner layer by ALD or CVD. Any one particular arrangement of the system  900  is provided to illustrate the invention and should not be use to limit the scope of the invention.  
         [0027]      FIG. 2  is a schematic top-view diagram of an exemplary multi-chamber processing system  950 . The system  950  generally includes load lock chambers  952  and  954  for the transfer of substrates into and out from the system  950 . Typically, since the system  950  is under vacuum, the load lock chambers  952  and  954  may “pump down” the substrates introduced into the system  950 . A robot  960  may transfer the substrates between the load lock chambers  952  and  954 , and substrate processing chambers  962 ,  964 ,  966 ,  968 ,  970 , and  972 . Each processing chamber  962 ,  964 ,  966 ,  968 ,  970 , and  972  can be outfitted to perform a number of substrate processing operations such as ALD, CVD, PVD, etch, pre-clean, de-gas, heat, orientation, and other substrate processes. The robot  960  also transfers substrates to and from a transfer chamber  956 . Any of the substrate processing chambers  962 ,  964 ,  966 ,  968 ,  970 , and  972  may be removed from the system  950  if not necessary for a particular process to be performed by the system  950 .  
         [0028]      FIG. 3  is a schematic cross-sectional view of one embodiment of a process chamber  780  including a gas delivery apparatus  830  adapted for cyclic deposition, such as ALD. A detailed description for a process chamber  780  is described in commonly assigned U.S. patent application Ser. No. 10/032,284, entitled, “Gas Delivery Apparatus and Method for Atomic Layer Deposition,” filed Dec. 21, 2001, and commonly assigned U.S. patent application Ser. No. 10/281,079, entitled “Gas Delivery Apparatus for Atomic Layer Deposition,” filed Oct. 25, 2002, which are hereby incorporated by reference herein. The process chamber  780  may also be adapted for other deposition techniques.  
         [0029]     The process chamber  780  comprises a chamber body  782  having sidewalls  784  and a bottom  786 . A slit valve  788  in the process chamber  780 -provides access for a robot (not shown) to deliver and retrieve a substrate  790 , such as a semiconductor substrate with a diameter of 200 mm or 300 mm or a glass substrate, from the process chamber  780 .  
         [0030]     A substrate support  792  supports the substrate  790  on a substrate receiving surface  791  in the process chamber  780 . The substrate support  792  is mounted to a lift motor  814  to raise and lower the substrate support  792  and a substrate  790  disposed thereon. A lift plate  816  connected to a lift motor  818  is mounted in the process chamber  780  and raises and lowers pins  820  movably disposed through the substrate support  792 . The pins  820  raise and lower the substrate  790  over the surface of the substrate support  792 . The substrate support  792  may include a vacuum chuck, an electrostatic chuck, or a clamp ring for securing the substrate  790  to the substrate support  792  during processing.  
         [0031]     The substrate support  792  may be heated to increase the temperature of a substrate  790  disposed thereon. For example, the substrate support  792  may be heated using an embedded heating element, such as a resistive heater, or may be heated using radiant heat, such as heating lamps disposed above the substrate support  792 . A purge ring  822  may be disposed on the substrate support  792  to define a purge channel  824  which provides a purge gas to a peripheral portion of the substrate  790  to prevent deposition thereon.  
         [0032]     A gas delivery apparatus  830  is disposed at an upper portion of the chamber body  782  to provide a gas, such as a process gas or a purge gas, to the chamber  780 . A vacuum system  878  is in communication with a pumping channel  879  to evacuate any desired gases from the process chamber  780  and to help maintain a desired pressure or a desired pressure range inside a pumping zone  866  of the process chamber  780 .  
         [0033]     In one embodiment, the process chamber depicted by  FIG. 3  permits the process gas or purge gas to enter the process chamber  780  normal (i.e., 90°) with respect to the plane of the substrate  790  via the gas delivery apparatus  830 . Therefore, the surface of substrate  790  is symmetrically exposed to gases that allow uniform film formation on substrates. The process gas includes a first reagent during one pulse and includes a second reagent in another pulse.  
         [0034]     Process chamber  780 , depicted in  FIG. 3 , produces a uniform film and employs a short cycle time (as quick as tenths of a second pulse) to purge and short time to dose the substrate to saturation with precursors. The short dosing time is important because many of the ruthenium-containing compounds have the inherent characteristic of a low vapor pressure. The low vapor pressure correlates to less precursor saturating the carrier gas per time and temperature, therefore, more time is needed to saturate the surface of the substrate with ruthenium-containing precursor (e.g., bis(2,4-dimethylpentadienyl)ruthenium) than a traditional precursor with a higher vapor pressure (e.g., TiCl 4 ).  
         [0035]     In one embodiment, the gas delivery apparatus  830  comprises a chamber lid  832 . The chamber lid  832  includes an expanding channel  834  extending from a central portion of the chamber lid  832  and a bottom surface  860  extending from the expanding channel  834  to a peripheral portion of the chamber lid  832 . The bottom surface  860  is sized and shaped to substantially cover a substrate  790  on the substrate support  792 . The expanding channel  834  has gas inlets  836 A,  836 B to provide gas flows from two similar valves  842 A,  842 B. The gas flows from the valves  842 A,  842 B may be provided together or separately.  
         [0036]     In one configuration, valve  842 A and valve  842 B are coupled to separate reactant gas sources but are preferably coupled to the same purge gas source. For example, valve  842 A is coupled to reactant gas source  838  and valve  842 B is coupled to reactant gas source  839 , and both valves  842 A,  842 B are coupled to purge gas source  840 . Each valve  842 A,  842 B includes a delivery line  843 A,  843 B having a valve seat assembly  844 A,  844 B and includes a purge line  845 A,  845 B having a valve seat assembly  846 A,  846 B. The delivery line  843 A,  843 B connects with the reactant gas source  838 ,  839  and the gas inlet  836 A,  836 B of the expanding channel  834 . The valve seat assembly  844 A,  844 B of the delivery line  843 A,  843 B controls the flow of the reactant gas from the reactant gas source  838 ,  839  to the expanding channel  834 . The purge line  845 A,  845 B connects with the purge gas source  840  and intersects the delivery line  843 A,  843 B downstream of the valve seat assembly  844 A,  844 B of the delivery line  843 A,  843 B. The valve seat assembly  846 A,  846 B of the purge line  845 A,  845 B controls the flow of the purge gas from the purge gas source  840  to the delivery line  843 A,  843 B. If a carrier gas is used to deliver reactant gases from the reactant gas source  838 ,  839 , preferably the same gas is used as a carrier gas and a purge gas (i.e., an argon gas used as a carrier gas and a purge gas).  
         [0037]     Each valve seat assembly  844 A,  844 B,  846 A,  846 B may comprise a diaphragm and a valve seat. The diaphragm may be biased open or closed and may be actuated closed or open respectively. The diaphragms may be pneumatically actuated or may be electrically actuated. Examples of pneumatically actuated valves include pneumatically actuated valves available from Fujiken and Veriflow. Examples of electrically actuated valves include electrically actuated valves available from Fujiken. Programmable logic controllers  848 A,  848 B may be coupled to the valves  842 A,  842 B to control actuation of the diaphragms of the valve seat assemblies  844 A,  844 B,  846 A,  846 B of the valves  842 A,  842 B. Pneumatically actuated valves may provide pulses of gases in time periods as low as about 0.020 seconds. Electrically actuated valves may provide pulses of gases in time periods as low as about 0.005 seconds. An electrically actuated valve typically requires the use of a driver coupled between the valve and the programmable logic controller.  
         [0038]     Each valve  842 A,  842 B may be a zero dead volume valve to enable flushing of a reactant gas from the delivery line  843 A,  843 B when the valve seat assembly  844 A,  844 B of the valve is closed. For example, the purge line  845 A,  845 B may be positioned adjacent the valve seat assembly  844 A,  844 B of the delivery line  843 A,  843 B. When the valve seat assembly  844 A,  844 B is closed, the purge line  845 A;  845 B may provide a purge gas to flush the delivery line  843 A,  843 B. In the embodiment shown, the purge line  845 A,  845 B is positioned slightly spaced from the valve seat assembly  844 A,  844 B of the delivery line  843 A,  843 B so that a purge gas is not directly delivered into the valve seat assembly  844 A,  844 B when open. A zero dead volume valve as used herein is defined as a valve which has negligible dead volume (i.e., not necessary zero dead volume).  
         [0039]     Each valve  842 A,  842 B may be adapted to provide a combined gas flow and/or separate gas flows of the reactant gas  838 ,  839  and the purge gas  840 . One example of a combined gas flow of the reactant gas  838  and the purge gas  840  provided by valve  842 A comprises a continuous flow of a purge gas from the purge gas source  840  through purge line  845 A and pulses of a reactant gas from the reactant gas source  838  through delivery line  843 A. The continuous flow of the purge gas may be provided by leaving diaphragm of the valve seat assembly  846 A of the purge line  845 A open. The pulses of the reactant gas from the reactant gas source  838  may be provided by opening and closing the diaphragm of the valve seat assembly  844 A of the delivery line  843 A. One example of separate gas flows of the reactant gas  838  and the purge gas  840  provided by valve  842 A comprises pulses of a purge gas from the purge gas source  840  through purge line  845 A and pulses of a reactant gas from the reactant gas source  838  through delivery line  843 A. The pulses of the purge gas may be provided by opening and closing the diaphragm of the valve seat assembly  846 A of the purge line  845 A open. The pulses of the reactant gas from the reactant gas source  838  may be provided by opening and closing the diaphragm valve seat assembly  844 A of the delivery line  843 A.  
         [0040]     The delivery lines  843 A,  843 B of the valves  842 A,  842 B may be coupled to the gas inlets  836 A,  836 B through gas conduits  850 A,  850 B. The gas conduits  850 A,  850 B may be integrated or may be separate from the valves  842 A,  842 B. In one aspect, the valves  842 A,  842 B are coupled in close proximity to the expanding channel  834  to reduce any unnecessary volume of the delivery line  843 A,  843 B and the gas conduits  850 A,  850 B between the valves  842 A,  842 B and the gas inlets  836 A,  836 B.  
         [0041]     In  FIG. 3 , the expanding channel  834  comprises a channel which has an inner diameter which increases from an upper portion  837  to a lower portion  835  of the expanding channel  834  adjacent the bottom surface  860  of the chamber lid  832 .  
         [0042]     In one embodiment, the inner diameter of the expanding channel  834  for a chamber adapted to process  200  mm diameter substrates is between about 0.2 inches (0.51 cm) and about 1.0 inches (2.54 cm) at the upper portion  837  of the expanding channel  834  and between about 0.5 inches (1.27 cm) and about 3.0 inches (7.62 cm) at the lower portion  835  of the expanding channel  834 .  
         [0043]     In another specific embodiment, the inner diameter of the expanding channel  834  for a chamber adapted to process 300 mm diameter substrates is between about 0.2 inches (0.51 cm) and about 1.0 inches (2.54 cm) at the upper portion  837  of the expanding channel  134  and between about 0.5 inches (1.27 cm) and about 3.0 inches (7.62 cm) at the lower portion  835  of the expanding channel  834  for a 300 mm substrate. In general, the above dimensions apply to an expanding channel adapted to provide a total gas flow of between about 500 sccm and about 3,000 sccm.  
         [0044]     In other embodiments, the dimension may be altered to accommodate a certain gas flow. In general, a larger gas flow will require a larger diameter expanding channel. In one embodiment, the expanding channel  834  may be shaped as a truncated cone (including shapes resembling a truncated cone). Whether a gas is provided toward the walls of the expanding channel  834  or directly downward towards the substrate, the velocity of the gas flow decreases as the gas flow travels through the expanding channel  834  due to the expansion of the gas. The reduction of the velocity of the gas helps reduce the likelihood the gas will blow off reactants absorbed on the surface of the substrate  790 .  
         [0045]     The diameter of the expanding channel  834 , which is gradually increasing from the upper portion  837  to the lower portion  835  of the expanding channel, allows less of an adiabatic expansion of a gas through the expanding channel  834  which helps to control the temperature of the gas. For instance, a sudden adiabatic expansion of a gas delivered through the gas inlet  836 A,  836 B into the expanding channel  834  may result in a drop in the temperature of the gas which may cause condensation of the precursor vapor and formation of particles. Alternatively, a gradually expanding channel  834  according to embodiments of the present invention is believed to provide less of an adiabatic expansion of a gas. Therefore, more heat may be transferred to or from the gas, and, thus, the temperature of the gas may be more easily controlled by controlling the surrounding temperature of the gas or controlling the temperature of the chamber surfaces such as the chamber lid  832 . The gradually expanding channel may comprise one or more tapered inner surfaces, such as a tapered straight surface, a concave surface, a convex surface, or combinations thereof or may comprise sections of one or more tapered inner surfaces (i.e., a portion tapered and a portion non-tapered).  
         [0046]     In one embodiment, the gas inlets  836 A,  836 B are located adjacent the upper portion  837  of the expanding channel  834 . In other embodiments, one or more gas inlets may be located along the length of the expanding channel  834  between the upper portion  837  and the lower portion  835 .  
         [0047]     In  FIG. 3 , a control unit  880 , such as a programmed personal computer, work station computer, or the like, may be coupled to the process chamber  780  to control processing conditions. For example, the control unit  880  may be configured to control flow of various process gases and purge gases from gas sources  838 ,  839 ,  840  through the valves  842 A,  842 B during different stages of a substrate process sequence. Illustratively, the control unit  880  comprises a central processing unit (CPU)  882 , support circuitry  884 , and memory  886  containing associated control software  883 .  
         [0048]      FIG. 4  illustrates one embodiment of a parallel plate, cold-wall chemical vapor deposition system  10  having a vacuum chamber  12  in which the metal film according to the present invention can be deposited. CVD System  10  contains a gas distribution manifold  14  for dispersing deposition gases to a substrate  16  that rests on a resistively-heated susceptor  18 . Chamber  12  may be part of a vacuum processing system having multiple processing chambers connected to a central transfer chamber and serviced by a robot.  
         [0049]     Edge purge gases are flowed through purge guide  54  across the edge of substrate  16  to prevent deposition gases from contacting the edge and backside of the substrate. Purge gases are also flowed around heater/susceptor  18  to minimize deposition on and around the heater/susceptor. These purge gases are supplied from a purge line (not shown) and are also employed to protect stainless steel bellows  26  from damage by corrosive gases introduced into the chamber during processing.  
         [0050]     Deposition and carrier gases are supplied to a deposition zone of the chamber through gas lines  19  to manifold  14  in response to the control of valves  17 . During processing, gas supplied to manifold  14  is distributed uniformly across the surface of the substrate. Exhaust processing gases and by-product gases are evacuated from the chamber by means of exhaust system  36 . The rate at which gases are released through exhaust system  36  into an exhaust line is controlled by a throttle valve (not shown). During deposition, a second purge gas through gas channels in the susceptor (not shown) and purge guide  54  feeds purge gas against the edge of substrate  16 . An RF power supply  48  can be coupled to manifold  14  to provide for plasma-enhanced CVD (PECVD) cleaning of the chamber.  
         [0051]     The throttle valve, gas supply valves  17 , motor  20 , resistive heater coupled to susceptor  18 , RF power supply  48  and other aspects of CVD system  10  are-controlled by a system controller  42  over control lines  44  (only some of which are shown). System processor  42  operates under the control of a computer program stored in a computer-readable medium such as a memory  46 . The computer program dictates the temperature, chamber pressure, timing, mixture of gases, RF power levels, susceptor position, and other parameters of a particular process.  
         [0052]     A PVD chamber may be used to deposit ruthenium. Chambers that may be used include IMP™ chambers, ALPS™ chambers, and DURASOURCE™ chambers, all of which are available from Applied Materials, Inc., of Santa Clara, Calif. Other chambers that may be used include STANDARD™ and COHERENT™ chambers, available from Applied Materials, Inc., of Santa Clara, Calif. A layer of metal is deposited by PVD at a high power, such as between about 5 and about 60 kilowatts, e.g., about 10 kilowatts. The power density may be between about 0.04 and about 0.48 kilowatts per square inch, e.g., about 0.08 kilowatts per square inch. PVD chambers that may be used to deposit the metal layer include Standard and ALPS™ chambers. The chamber pressure during PVD may be between about 0.5 mTorr and 5 mTorr. The thickness of the deposited layer may increase or decrease depending on the size of the feature. Smaller features require less material and larger features require more material. The PVD may be performed without any backside gas or chucking. Therefore, while the temperature in the PVD chamber may be between about 400° C. and about 550° C., the substrate temperature may be between about 25° C. and about 300° C.  
         [0053]     The substrate may then be treated with another PVD step to deposit additional metal. The metal may be deposited by PVD at a high power, such as between about 5 and about 60 kilowatts, for example, about 10 kilowatts. The power density may be between about 0.04 and about 0.48 kilowatts per square inch, such as about 0.08 kilowatts per square inch. The metal may fill a via if the via was not previously filled or improve the surface morphology of the substrate. The PVD is performed at a high temperature, e.g., between about 400° C. and about 550° C. The temperature of both the PVD chamber and the substrate is preferably between about 400° C. and about 550° C. The high power of the PVD process contributes to a fast PVD step that increases the throughput of substrates during processing. Furthermore, it is believed that the high power used during PVD contributes to the deposition of more uniformly sized grains than a lower power and slower PVD process.  
         [0054]      FIGS. 5A  to  5 E illustrate a ruthenium layer between a copper seed layer and a bulk copper fill layer. It is believed that the presence of a ruthenium layer has a minimal effect on resistivity and decreases the likelihood of copper dewetting.  FIG. 5A  illustrates an interlayer dielectric layer  101  having a via  102  formed therein with a base  103  that reveals a metal feature  104  such as a copper feature deposited below the dielectric layer  101 .  FIG. 5B  shows an optional barrier layer  105  conformally deposited on the interlayer dielectric layer  101  such as by ALD. The optional barrier layer  105  may have a thickness of about 1 to about 20 Å. The optional barrier layer may be a tantalum/tantalum nitride layer deposited by ALD. The ALD may be performed by exposing the substrate to repetitions of alternating tantalum containing precursor and nitrogen containing precursor using an ALD deposition chamber such as the equipment illustrated by  FIG. 3 . The optional barrier layer  105  may also be deposited by PVD or CVD. The optional barrier layer  105  CVD process may be performed by using a CVD deposition chamber such as the equipment depicted by  FIG. 4 . If PVD is used as the deposition method for the optional barrier layer  105 , the tantalum nitride and tantalum layers may be deposited followed by an etching step, or a tantalum nitride layer may be deposited followed by an etching step followed by an additional tantalum deposition step. The subsequent etching step opens the bottom of the feature down to the metal feature  104 . Alternatively, ruthenium may be deposited as layer  105 . The ruthenium layer can be deposited by CVD or PVD.  
         [0055]      FIG. 5C  illustrates a copper seed layer  106  deposited on the optional barrier layer  105 . The copper can be deposited by ALD, PVD or CVD and has a thickness of about 50 Å to about 1500 Å. PVD is preferably the process used to deposit the copper seed layer  106 . Alternatively, the copper seed layer  106  may be deposited by alternating a copper containing precursor and a reducing agent using equipment as shown in  FIG. 3 .  
         [0056]     Next,  FIG. 5D  illustrates a transition metal layer, such as a ruthenium layer  107  deposited on the copper seed layer  106 . The transition metal layer  107  is intended to lock the grain boundaries of the copper seed layer to minimize agglomeration. Accordingly, it is believed that the transition metal layer  107  does not need to be continuous, but can be continuous. The ruthenium layer  107  may be deposited by thermal decomposition of a ruthenium containing precursor carried by an inert gas. The substrate may be heated to between about 100° C. to about 400° C. during a thermal decomposition process. Ruthenium precursors include Ru(Cp) 2 , Ru(EtCp) 2 , Ru(EtCp) 2,4, dimethyl pentadienyl, bis(2,4,dimethyl pentadienyl) ruthenium, Ru(EtCp)(MeCp), Ru(THD) 3 , and others. Ru(EtCp)(MeCp) is preferred. Alternatively, the ruthenium layer  107  may be deposited by exposing the substrate to a ruthenium containing precursor gas in an ALD or CVD process. The deposited ruthenium layer may be discontinuous. The ALD ruthenium may be deposited using the equipment shown in  FIG. 3 . ALD ruthenium is described in U.S. patent application Ser. No. 10/811,230 “Ruthenium Layer Formation for Copper Film Deposition,” filed on Mar. 26, 2004, which is hereby incorporated by reference herein. A ruthenium layer may be deposited by PVD, but the deposited film may be discontinuous or nonuniform, inconsistent thickness.  FIG. 5E  shows a bulk copper layer  108  deposited over the transition metal layer  107  by ECP. It is believed that the transition metal layers facilitate the ECP process when the seed layer is thin and/or discontinuous. The transition metal layer, e.g. ruthenium, provides a conductive bridge across the surface of the substrate to facilitate current distribution across the substrate and across areas where the seed layer may be discontinuous. The bulk copper layer  108  may also be deposited by PVD or other deposition method.  
         [0057]      FIGS. 6A  to  6 E illustrate an additional embodiment with a transition metal layer, such as a ruthenium layer deposited at the base of via  202 .  FIG. 6A  shows an interlayer dielectric  201  having a via  202  formed therein that reveals a copper layer  203  beneath the dielectric layer  201 .  FIG. 6B  illustrates a ruthenium layer  204  selectively deposited along the base of via  202 . The ruthenium layer  204  has a thickness of about 50 Å to about 1500 Å and may be deposited by the same processes as described for the ruthenium layer  107  in  FIG. 5D . The ruthenium layer  204  in the base of via  202  is believed to promote the stability of the copper layer at the base of via  202 .  FIG. 6C  has an optional tantalum nitride barrier layer  205  such as a tantalum/tantalum nitride barrier layer, conformally deposited over the surface of the via and the field of the substrate. The barrier layer may be deposited by ALD, PVD, or CVD. The ALD is performed by exposing the substrate to repetitions of alternating tantalum containing precursor and nitrogen containing precursor using the equipment shown in  FIG. 3 . CVD may be performed by using the equipment shown in  FIG. 4 .  
         [0058]      FIG. 6C  also shows a seed layer  206 , such as a copper layer deposited by PVD on top of the optional tantalum nitride layer  205  and ruthenium layer  204 . The copper layer  206  preferably has a thickness of about 5 Å to about 50 Å.  FIG. 6D  illustrates a ruthenium layer  207  deposited conformally on the copper layer  206 . The ruthenium layer  207  is deposited by the same processes as described for the ruthenium layer  107  in  FIG. 5D . Finally,  FIG. 6E  displays a bulk copper layer  208  that is deposited by ECP.  
         [0059]      FIGS. 7A and 7B  illustrate an additional embodiment utilizing a ruthenium layer in a capping layer application deposited on a metal feature such as copper.  FIG. 7A  illustrates a dielectric layer  301  with a ruthenium layer  302 , tantalum nitride layer  303 , and bulk copper fill  304  deposited in a feature formed therein. The ruthenium layer  302  is optional. The upper surface of the substrate has been chemically mechanically polished following copper deposition leaving the surface of the copper exposed. A ruthenium layer  305  is selectively deposited on the exposed copper surface. The ruthenium is preferably deposited on the exposed copper by thermal decomposition of a ruthenium containing precursor that may be combined with a carrier gas. Alternatively, ALD or CVD may be used to deposit the ruthenium. It is believed that the ruthenium layer  305  improves copper adhesion to subsequent capping layers formed thereon. The ruthenium layer  305  may act as a capping layer. Alternatively, a separate capping layer may be deposited on the ruthenium layer  305 . Optionally, a chemical treatment may be used to treat the ruthenium layer  305  before an additional capping layer is deposited. Chemical treatments include exposing the substrate surface to cleaning agents, complexing agents, or other chemicals and rinsing the substrate. As one example, a material such as cobalt tungsten or cobalt tungsten phosphorous may be deposited as the additional capping layer on the ruthenium layer.  FIG. 8B  illustrates a capping layer  306  deposited on top of the ruthenium layer  305 . The capping layer  306  may be deposited by an electroless process. In an electroless process, the substrate is exposed to a liquid containing the precursors for the capping layer. A similar ruthenium layer in combination with an additional material that acts as a capping layer is disclosed in commonly assigned U.S. patent application Ser. No. 10/965,099, entitled “Heterogeneous Activation Layers Formed by Ionic and Electroless Reactions Used for IC Interconnect Capping Layers,” filed on Oct. 15, 2004, which is hereby incorporated by reference herein.  
         [0060]     A low dielectric constant barrier layer such as a silicon carbide based layer and/or a silicon nitride layer may be deposited conformally on the ruthenium layer  305  or the capping layer  306 . An example of a suitable film is a silicon carbide based film formed using the chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD) processes such as the processes described in commonly owned U.S. Pat. No. 6,537,733, issued Sep. 25, 2003, U.S. patent application Ser. No. 10/196,498, filed on Jul. 15, 2002, and U.S. Pat. No. 6,790,788, issued Sep. 14, 2004, both of which are hereby incorporated by reference herein. It is believed that the ruthenium layer improves adhesion between subsequently deposited low dielectric constant film, such as a silicon and carbon containing low dielectric constant film, and capping layers. An additional dielectric deposition step may follow the silicon carbide and/or silicon nitride deposition.  
         [0061]     Several experiments were performed to show that the transition metal layer, e.g. ruthenium, prevented agglomeration of the metal layer, e.g. copper. For each of the experiments, the dewetting of copper was measured by SEM.  
         [0062]     First, a thin copper layer was deposited on top of an interlayer dielectric. A ruthenium layer was then deposited thereover and the stack was annealed. Specifically, 10 Å of TaN was deposited conformally over a dielectric layer with vias by sequentially flowing a tantalum containing precursor and a tantalum containing precursor in an ALD reaction. Then, 100 Å of copper was deposited using an ENCORE SIP™ chamber, which is commercially available from Applied Materials of Santa Clara, Calif. Next, a ruthenium precursor, Ru(EtCp) 2 , was used to deposit ruthenium at varied temperatures of 40 to 420° C. at 10 Torr for 15 minutes. To confirm a reduction in. dewetting and copper agglomeration, an anneal step was performed with nitrogen at 420° C. and 15 Torr for 15 minutes. The resulting film stack was, observed using an optical microscope and/or SEM.  
         [0063]     When the ruthenium deposition was performed between about 100° C. to about 420° C. no dewetting was observed. When the deposition was performed at 40° C., two thirds of the substrate closest to the edge  907  had no dewetting.  FIG. 8  is a schematic diagram of a surface of a substrate. Region  901  and region  903  represent two thirds of the substrate closest to the edge  907  of the substrate. The middle third of the substrate, region  905 , was observed to have dewetting. Thus, higher temperature ruthenium deposition is believed to decrease the likelihood of dewetting.  
         [0064]     A second experiment was performed in which tantalum nitride and copper were deposited with identical conditions as the first experiment. The ruthenium was deposited using Ru(EtCp) 2  heated to 80° C. with 200 sccm argon at a chamber pressure of 1.5 Torr. The substrate heater temperature was varied between 80° C. and 275° C. and the deposition time was varied at 5, 10, 15, 60, and 900 seconds. Annealing was performed with nitrogen at 380° C. for 15 minutes. When the substrate was heated to 275° C. during the ruthenium deposition for 5 or 15 seconds, no dewetting was observed. When the substrate was heated to 80° C. for 10 seconds, the entire substrate was observed to have dewetting. When the substrate was heated to 80° C. for 60 seconds, the entire substrate except the edge had dewetting. When the substrate was heated to 80° C. for 900 seconds, dewetting was observed only on a small portion of the center of the substrate. At lower temperatures, the longer the exposure time to the ruthenium containing precursor, the lower the likelihood that dewetting occured. This also is believed to indicate that with increased exposure time, a thicker layer of ruthenium is deposited which decreases the likelihood of copper dewetting.  
         [0065]     A third experiment was conducted in which silicon oxide and tantalum nitride were deposited with identical conditions as the first experiment. Then, 1200 Å of copper was deposited by PVD. Next, a ruthenium deposition was performed at the following conditions: a substrate support temperature of 275° C.; a a chamber pressure of 1.5 Torr; and 200 sccm argon through Ru(EtCp) 2  at 80° C. The deposition time was varied from 5 to 15 seconds. Additionally, 10 Å of tantalum nitride was deposited by alternating the flow of a tantalum containing precursor and a nitrogen containing precursor in an ALD process. Then, 100 Å copper was deposited by sputtering in a PVD process. Another layer of ruthenium was deposited at 275° C., a chamber pressure of 1.5 Torr, and 200 sccm argon through Ru(EtCp) 2  at 80° C. This structure is similar to the structure depicted in  FIG. 6E . Finally, the substrate was annealed in nitrogen at 380° C. for 15 minutes. The product of the 15 second ruthenium deposition step had no copper dewetting. The product of the 5 second ruthenium deposition step had copper dewetting at the center of the substrate only; no dewetting along the edge of the substrate was observed. These results indicate that with increased exposure time, a thicker layer of ruthenium is deposited. This also may indicate that pretreating the copper with a thicker layer of ruthenium before depositing the capping layer may decrease the likelihood of copper diffusion along the copper and capping layer boundary region.  
         [0066]     Generally, the experimental results indicate that depositing ruthenium on top- of copper seed layers stabilizes and prevents dewetting of the subsequent electroplated copper over a temperature range of about 0 to about 420° C. Additional testing was performed to examine capping layer adhesion and electrochemical plating chemistry requirements when ruthenium is deposited before an additional capping layer. Ruthenium deposition performed at higher temperatures provided a faster rate of ruthenium deposition and improved capping layer adhesion compared to lower temperature deposition. Another advantage of depositing ruthenium before an additional capping layer is that electrochemical plating chemistry can be used without modification. Finally, ruthenium deposition after chemical mechanical polishing before an additional capping layer is deposited capping layer adhesion to copper. The improvement in capping layer adhesion is based on XRF measurements of films with and without a ruthenium layer. The time for deposition of ruthenium is dependent on substrate temperature, chamber pressure, flow rate of the ruthenium containing precursor, and the flow rate of carrier and diluent gases.  
         [0067]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.