Abstract:
Embodiments described herein relate to depositing a cobalt-containing layer by a cyclical deposition process while forming interconnects on a substrate. In one embodiment, a method for forming an interconnect structure is provided which includes depositing a tungsten-containing barrier layer over an exposed contact metal surface within an aperture formed in an insulating material disposed on a substrate, forming a cobalt-containing layer on the tungsten-containing barrier layer using a cyclical deposition process by sequentially exposing the substrate to a cobalt precursor gas and a silicon reducing gas, wherein the cobalt precursor gas contains a cobalt precursor having a cyclopentadienyl ligand, and depositing a copper material on the cobalt-containing layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Ser. No. 10/443,648 (APPM/005975), filed May 22, 2003 now U.S. Pat. No. 7,404,985, which claims benefit of U.S. Ser. No. 60/385,499 (APPM/005975L), filed Jun. 4, 2002, which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to a method of noble metal layer formation and, more particularly to a method of noble metal layer formation for copper film deposition. 
     2. Description of the Related Art 
     Sub-quarter micron, multi-level metallization is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) semiconductor devices. The multilevel interconnects that lie at the heart of this technology require the filling of contacts, vias, lines, and other features formed in high aspect ratio apertures. Reliable formation of these features is very important to the success of both VLSI and ULSI as well as to the continued effort to increase client density and quality on individual substrates and die. 
     As circuit densities increase, the widths of contacts, vias, lines and other features, as well as the dielectric materials between them may decrease to less than about 250 nm (nanometers), whereas the thickness of the dielectric layers remains substantially constant with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Many conventional deposition processes have difficulty filling structures where the aspect ratio exceeds 6:1, and particularly where the aspect ratio exceeds 10:1. As such, there is a great amount of ongoing effort being directed at the formation of void-free, nanometer-sized structures having aspect ratios wherein the ratio of feature height to feature width can be 6:1 or higher. 
     Additionally, as the feature widths decrease, the device current typically remains constant or increases, which results in an increased current density for such feature. Elemental aluminum and its alloys have been the traditional metals used to form vias and lines in semiconductor devices because of aluminum&#39;s perceived low electrical resistivity, its superior adhesion to most dielectric materials, its ease of patterning, and the ability to obtain it in a highly pure form. However, aluminum has a higher electrical resistivity than other more conductive metals such as copper, and aluminum can also suffer from electromigration leading to the formation of voids in the conductor. 
     Copper and its alloys have lower resistivities than aluminum, as well as a significantly higher electromigration resistance compared to aluminum. These characteristics are important for supporting the higher current densities experienced at high levels of integration and increased device speed. Copper also has good thermal conductivity. Therefore, copper is becoming a choice metal for filling sub-quarter micron, high aspect ratio interconnect features on semiconductor substrates. 
     A thin film of a noble metal such as, for example, palladium, platinum, cobalt, nickel, and rhodium, among others may be used as an underlayer for the copper vias and lines. Such noble metals, which are resistant to corrosion and oxidation, may provide a smooth surface upon which a copper seed layer is subsequently deposited using for example, an electrochemical plating (ECP) process. 
     The noble metal is typically deposited using a chemical vapor deposition (CVD) process or a physical vapor deposition (PVD) process. Unfortunately, noble metals deposited on high aspect ratio interconnect features using CVD and/or PVD processes generally have poor step coverage (e.g., deposition of a non-continuous material layer). The poor step coverage for the noble metal material layer may cause the subsequent copper seed layer deposition using an ECP process to be non-uniform. 
     Therefore, a need exists in the art for a method of depositing noble metals in high aspect ratio interconnect features having good step coverage. 
     SUMMARY OF THE INVENTION 
     A method of noble metal layer formation for high aspect ratio interconnect features is described. The noble metal layer is formed using a cyclical deposition process. The cyclical deposition process comprises alternately adsorbing a noble metal-containing precursor and a reducing gas on a substrate structure. The adsorbed noble metal-containing precursor reacts with the adsorbed reducing gas to form the noble metal layer on the substrate. Suitable noble metals may include, for example, palladium, platinum, cobalt, nickel, and rhodium, among others. 
     The noble metal layer formation is compatible with integrated circuit fabrication processes. In one integrated circuit fabrication process, the noble metal layer may be used as an underlayer for a copper seed layer in a copper interconnect. For such an embodiment, a preferred process sequence includes providing a substrate having an interconnect pattern defined in one or more dielectric layers formed thereon. The interconnect pattern includes a barrier layer conformably deposited thereon. A noble metal layer is conformably deposited on the barrier layer. The noble metal layer is deposited using a cyclical deposition process by alternately adsorbing a noble metal-containing layer and a reducing gas on the substrate. Thereafter, the copper interconnect is completed by depositing a copper seed layer on the noble metal layer and than filling the interconnects with bulk copper metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof 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. 
         FIG. 1  depicts a schematic cross-sectional view of a process chamber that can be used to perform a cyclical deposition process described herein; 
         FIG. 2  illustrates a process sequence for noble metal layer formation using cyclical deposition techniques according to one embodiment described herein; 
         FIG. 3  illustrates a process sequence for noble metal layer formation using cyclical deposition techniques according to an alternate embodiment described herein; and 
         FIGS. 4A-4C  illustrate schematic cross-sectional views of an integrated circuit fabrication sequence. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a schematic cross-sectional view of a process chamber  10  that can be used to perform integrated circuit fabrication in accordance with embodiments described herein. The process chamber  10  generally houses a substrate support pedestal  48 , which is used to support a substrate (not shown). The substrate support pedestal  48  is movable in a vertical direction inside the process chamber  10  using a displacement mechanism  48   a.    
     Depending on the specific process, the substrate can be heated to some desired temperature prior to or during deposition. For example, the substrate support pedestal  48  may be heated using an embedded heater element  52   a . The substrate support pedestal  48  may be resistively heated by applying an electric current from an AC power supply  52  to the heater element  52   a . The substrate (not shown) is, in turn, heated by the pedestal  48 . Alternatively, the substrate support pedestal  48  may be heated using radiant heaters such as, for example, lamps (not shown). 
     A temperature sensor  50   a , such as a thermocouple, is also embedded in the substrate support pedestal  48  to monitor the temperature of the pedestal  48  in a conventional manner. The measured temperature is used in a feedback loop to control the AC power supply  52  for the heating element  52   a , such that the substrate temperature can be maintained or controlled at a desired temperature which is suitable for the particular process application. 
     A vacuum pump  18  is used to evacuate the process chamber  10  and to maintain the pressure inside the process chamber  10 . A gas manifold  34 , through which process gases are introduced into the process chamber  10 , is located above the substrate support pedestal  48 . The gas manifold  34  is connected to a gas panel (not shown), which controls and supplies various process gases to the process chamber  10 . 
     Proper control and regulation of the gas flows to the gas manifold  34  are performed by mass flow controllers (not shown) and a microprocessor controller,  70 . The gas manifold  34  allows process gases to be introduced and uniformly distributed in the process chamber  10 . Additionally, the gas manifold  34  may optionally be heated to prevent condensation of any reactive gases within the manifold. 
     The gas manifold  34  includes a plurality of electronic control valves (not shown). The electronic control valves as used herein refer to any control valve capable of providing rapid and precise gas flow to the process chamber  10  with valve open and close cycles of less than about 1-2 seconds, and more preferably less than about 0.1 second. 
     The microprocessor controller  70  may be one of any form of general purpose computer processor (CPU) that can be used in an industrial setting for controlling various chambers and sub-processors. The computer may use any suitable memory, such as random access memory, read only memory, floppy disk drive, hard disk, or any other form of digital storage, local or remote. Various support circuits may be coupled to the CPU for supporting the processor in a conventional manner. Software routines as required, may be stored in the memory or executed by a second CPU that is remotely located. 
     The software routines are executed to initiate process recipes or sequences. The software routines, when executed, transform the general purpose computer into a specific process computer that controls the chamber operation so that a chamber process is performed. For example, software routines may be used to precisely control the activation of the electronic control valves for the execution of process sequences according to the present invention. Alternatively, the software routines may be performed in hardware, as an application specific integrated circuit or other type of hardware implementation, or a combination of software or hardware. 
     Noble Metal Layer Formation 
     A method of noble metal layer formation for high aspect ratio interconnect features is described. The noble metal layer is deposited using a cyclical deposition process. The cyclical deposition process comprises alternately adsorbing a noble metal-containing precursor and a reducing gas on a substrate structure. The noble metal-containing precursor and the reducing gas undergo a reaction to form the noble metal layer on the substrate. Suitable noble metals may include for example, palladium, platinum, cobalt, nickel, and rhodium, among others. 
       FIG. 2  illustrates a process sequence  100  detailing the various steps used for the deposition of the silicon layer. These steps may be performed in a process chamber similar to that described above with reference to  FIG. 1 . As shown in step  102 , a substrate is provided to the process chamber. The substrate may be for example, a silicon substrate having an interconnect pattern defined in one or more dielectric material layers formed thereon. The process chamber conditions such as, for example, the temperature and pressure are adjusted to enhance the adsorption of the process gases on the substrate so as to facilitate the reaction of the noble-metal-containing precursor and the reducing gas. In general, for noble metal layer deposition, the substrate should be maintained at a temperature less than about 300° C. at a process chamber pressure of between about 1 Torr to about 10 Torr. 
     In one embodiment where a constant carrier gas flow is desired, a carrier gas stream is established within the process chamber as indicated in step  104 . Carrier gases may be selected so as to also act as a purge gas for the removal of volatile reactants and/or by-products from the process chamber. Carrier gases such as, for example, helium and argon, and combinations thereof, among others may be used. 
     Referring to step  106 , after the carrier gas stream is established within the process chamber, a pulse of a noble metal-containing precursor is added to the carrier gas stream. The term pulse as used herein refers to a dose of material injected into the process chamber or into the carrier gas stream. The pulse of the noble metal-containing precursor lasts for a predetermined time interval. 
     The noble metal-containing precursor may comprise, for example, noble metals such as palladium, platinum, cobalt, nickel, and rhodium, among others. Suitable palladium-containing precursors include bis(allyl) palladium, bis(2-methylallyl) palladium, and cyclopentadienyl (allyl) palladium, among others. Suitable platinum-containing precursors include trimethyl (cyclopentadienyl) platinum, trimethyl (methylcyclopentadienyl) platinum, cyclopentadienyl (allyl) platinum, dimethyl (cyclooctadiene) platinum, methyl carbonyl cyclopentadienyl platinum, trimethyl (acetylacetonato) platinum, and bis(acetylacetonato) platinum, among others. Suitable cobalt-containing precursors include cyclopentadienyl cyclohexadienyl cobalt, cyclobutadienyl cyclopentadienyl cobalt, bis(cyclopentadienyl) cobalt, bis(methylcyclopentadienyl) cobalt, cyclopentadienyl (1,3-hexadienyl) cobalt, cyclopentadienyl (5-methylcyclopentadienyl) cobalt, and bis(ethylene) (pentamethylcyclopentadienyl) cobalt, among others. A suitable nickel-containing precursor includes bis(methylcyclopentadienyl) nickel, among others. Suitable rhodium-containing precursors include bis(propylene) rhodium, bis(carbonyl) (cyclopentadienyl) rhodium, bis(carbonyl) (methylcyclopentadienyl) rhodium, and bis(carbonyl) (ethylcyclopentadienyl) rhodium, among others. 
     The time interval for the pulse of the noble metal-containing precursor is variable depending upon a number of factors such as, for example, the volume capacity of the process chamber employed, the vacuum system coupled thereto and the volatility/reactivity of the reactants used. For example, (1) a large-volume process chamber may lead to a longer time to stabilize the process conditions such as, for example, carrier/purge gas flow and temperature, requiring a longer pulse time; (2) a lower flow rate for the process gas may also lead to a longer time to stabilize the process conditions requiring a longer pulse time; and (3) a lower chamber pressure means that the process gas is evacuated from the process chamber more quickly requiring a longer pulse time. In general, the process conditions are advantageously selected so that a pulse of the noble metal-containing precursor provides a sufficient amount of precursor so that at least a monolayer of the noble metal-containing precursor is adsorbed on the substrate. Thereafter, excess noble metal-containing precursor remaining in the chamber may be removed from the process chamber by the constant carrier gas stream in combination with the vacuum system. 
     In step  108 , after the excess noble metal-containing precursor has been flushed from the process chamber by the carrier gas stream, a pulse of a reducing gas is added to the carrier gas stream. The pulse of the reducing gas also lasts for a predetermined time interval. In general, the time interval for the pulse of the reducing gas should be long enough for adsorption of at least a monolayer of the reducing gas on the noble metal-containing precursor. Thereafter, excess reducing gas is flushed from the process chamber by the carrier gas stream. Suitable reducing gases may include, for example, silane (SiH 4 ), disilane (Si 2 H 6 ), dimethylsilane (SiC 2 H 8 ), methyl silane (SiCH 6 ), ethylsilane (SiC 2 H 8 ), borane (BH 3 ), diborane (B 2 H 6 ), triborane, tetraborane, pentaborane, hexaborane, heptaborane, octaborane, nonaborane, and decaborane, among others. 
     Steps  104  through  108  comprise one embodiment of a deposition cycle for a noble metal layer. For such an embodiment, a constant flow of carrier gas is provided to the process chamber modulated by alternating periods of pulsing and non-pulsing where the periods of pulsing alternate between the noble metal-containing precursor and the reducing gas along with the carrier gas stream, while the periods of non-pulsing include only the carrier gas stream. 
     The time interval for each of the pulses of the noble metal-containing precursor and the reducing gas may have the same duration. That is, the duration of the pulse of the noble metal-containing precursor may be identical to the duration of the pulse of the reducing gas. For such an embodiment, a time interval (T 1 ) for the pulse of the noble metal-containing precursor is equal to a time interval (T 2 ) for the pulse of the reducing gas. 
     Alternatively, the time interval for each of the pulses of the noble metal-containing precursor and the reducing gas may have different durations. That is, the duration of the pulse of the noble metal-containing precursor may be shorter or longer than the duration of the pulse of the reducing gas. For such an embodiment, a time interval (T 1 ) for the pulse of the noble metal-containing precursor is different than the time interval (T 2 ) for the pulse of the reducing gas. 
     In addition, the periods of non-pulsing between each of the pulses of the noble metal-containing precursor and the reducing gas may have the same duration. That is, the duration of the period of non-pulsing between each pulse of the noble metal-containing precursor and each pulse of the reducing gas is identical. For such an embodiment, a time interval (T 3 ) of non-pulsing between the pulse of the noble metal-containing precursor and the pulse of the reducing gas is equal to a time interval (T 4 ) of non-pulsing between the pulse of the reducing gas and the pulse of the noble metal-containing precursor. During the time periods of non-pulsing only the constant carrier gas stream is provided to the process chamber. 
     Alternatively, the periods of non-pulsing between each of the pulses of the noble metal-containing precursor and the reducing gas may have different duration. That is, the duration of the period of non-pulsing between each pulse of the noble metal-containing precursor and each pulse of the reducing gas may be shorter or longer than the duration of the period of non-pulsing between each pulse of the reducing gas and the noble metal-containing precursor. For such an embodiment, a time interval (T 3 ) of non-pulsing between the pulse of the noble metal-containing precursor and the pulse of the reducing gas is different from a time interval (T 4 ) of non-pulsing between the pulse of the reducing gas and the pulse of noble metal-containing precursor. During the time periods of non-pulsing only the constant carrier gas stream is provided to the process chamber. 
     Additionally, the time intervals for each pulse of the noble metal-containing precursor, the reducing gas and the periods of non-pulsing therebetween for each deposition cycle may have the same duration. For such an embodiment, a time interval (T 1 ) for the noble metal-containing precursor, a time interval (T 2 ) for the reducing gas, a time interval (T 3 ) of non-pulsing between the pulse of the noble metal-containing precursor and the pulse of the reducing gas and a time interval (T 4 ) of non-pulsing between the pulse of the reducing gas and the pulse of the noble metal-containing precursor each have the same value for each deposition cycle. For example, in a first deposition cycle (C 1 ), a time interval (T 1 ) for the pulse of the noble metal-containing precursor has the same duration as the time interval (T 1 ) for the pulse of the noble metal-containing precursor in subsequent deposition cycles (C 2  . . . C N ). Similarly, the duration of each pulse of the reducing gas and the periods of non-pulsing between the pulse of the noble metal-containing precursor and the reducing gas in the first deposition cycle (C 1 ) is the same as the duration of each pulse of the reducing gas and the periods of non-pulsing between the pulse of the noble metal-containing precursor and the reducing gas in subsequent deposition cycles (C 2  . . . C N ), respectively. 
     Alternatively, the time intervals for at least one pulse of the noble metal-containing precursor, the reducing gas and the periods of non-pulsing therebetween for one or more of the deposition cycles of the noble metal layer deposition process may have different durations. For such an embodiment, one or more of the time intervals (T 1 ) for the pulses of the noble metal-containing precursor, the time intervals (T 2 ) for the pulses of the reducing gas, the time intervals (T 3 ) of non-pulsing between the pulse of the noble metal-containing precursor and the reducing gas and the time intervals (T 4 ) of non-pulsing between the pulses of the reducing gas and the noble metal-containing precursor may have different values for one or more deposition cycles of the cyclical deposition process. For example, in a first deposition cycle (C 1 ), the time interval (T 1 ) for the pulse of the noble metal-containing precursor may be longer or shorter than one or more time interval (T 1 ) for the pulse of the noble metal-containing precursor in subsequent deposition cycles (C 2  . . . C N ). Similarly, the durations of the pulses of the reducing gas and the periods of non-pulsing between the pulse of the noble metal-containing precursor and the reducing gas in the first deposition cycle (C 1 ) may be the same or different than the duration of each pulse of the reducing gas and the periods of non-pulsing between the pulse of the noble metal-containing precursor and the reducing gas in subsequent deposition cycles (C 2  . . . C N ). 
     Referring to step  110 , after each deposition cycle (steps  104  through  108 ) a thickness of the noble metal will be formed on the substrate. Depending on specific device requirements, subsequent deposition cycles may be needed to achieve a desired thickness. As such” steps  104  through  108  are repeated until the desired thickness for the noble metal layer is achieved. Thereafter, when the desired thickness for the noble metal layer is achieved the process is stopped as indicated by step  112 . 
     In an alternate process sequence described with respect to  FIG. 3 , the noble metal layer deposition cycle comprises separate pulses for each of the noble metal-containing precursor, the reducing gas and a purge gas. For such an embodiment, the noble metal layer deposition sequence  200  includes providing a substrate to the process chamber (step  202 ), providing a first pulse of a purge gas to the process chamber (step  204 ), providing a pulse of a noble metal-containing precursor to the process chamber (step  206 ), providing a second pulse of the purge gas to the process chamber (step  208 ), providing a pulse of a reducing gas to the process chamber (step  210 ), and then repeating steps  204  through  210 , or stopping the deposition process (step  214 ) depending on whether a desired thickness for the noble metal layer has been achieved (step  212 ). 
     The time intervals for each of the pulses of the noble metal-containing precursor, the reducing gas and the purge gas may have the same or different durations as discussed above with respect to  FIG. 2 . Alternatively, corresponding time intervals for one or more pulses of the noble metal-containing precursor, the reducing gas and the purge gas in one or more of the deposition cycles of the noble metal layer deposition process may have different durations. 
     In  FIGS. 2-3 , the noble metal layer deposition cycle is depicted as beginning with a pulse of the noble metal-containing precursor followed by a pulse of the reducing gas. Alternatively, the noble metal layer deposition cycle may start with a pulse of the reducing gas followed by a pulse of the noble metal-containing precursor. 
     One exemplary process of depositing a noble metal layer comprises sequentially providing pulses of (cyclopentadienyl)(allyl)palladium and pulses of diborane (B 2 H 6 ). The (cyclopentadienyl)(allyl)palladium may be provided to an appropriate flow control valve, for example, an electronic control valve, at a flow rate between about 0.01 sccm (standard cubic centimeters per minute) to about 5 sccm, preferably between about 0.1 sccm to about 1 sccm, and thereafter pulsed for about 5 seconds or less, preferably about 1 second or less. The diborane (B 2 H 6 ) may be provided to an appropriate flow control valve, for example, an electronic flow control valve at a flow rate between about 1 sccm to about 80 sccm, preferably between about 10 sccm to about 50 seem, and thereafter pulsed for about 10 seconds or less, preferably about 2 seconds or less. The substrate may be maintained at a temperature less than about 250° C., preferably about 180° C. at a chamber pressure between about 1 Torr to about 10 Torr, preferably about 4 Torr. 
     Formation of Copper Interconnects 
       FIGS. 4A-4C  illustrate cross-sectional views of a substrate at different stages of a copper interconnect fabrication sequence incorporating the noble metal layer of the present invention.  FIG. 4A , for example, illustrates a cross-sectional view of a substrate  300  having metal contacts  304  and a dielectric layer  302  formed thereon. The substrate  300  may comprise a semiconductor material such as, for example, silicon, germanium, or gallium arsenide. The dielectric layer  302  may comprise an insulating material such as, for example, silicon oxide or silicon nitride, among others. The metal contacts  304  may comprise for example, copper, among others. Apertures  304 H may be defined in the dielectric layer  302  to provide openings over the metal contacts  304 . The apertures  304 H may be defined in the dielectric layer  302  using conventional lithography and etching techniques. 
     A barrier layer  306  may be formed in the apertures  304 H defined in the dielectric layer  302 . The barrier layer  306  may include one or more refractory metal-containing layers such as, for example, titanium, titanium nitride, tantalum, tantalum nitride, tungsten, and tungsten nitride, among others. The barrier layer  306  may be formed using a suitable deposition process. For example, titanium nitride may be deposited using a chemical vapor deposition process wherein titanium tetrachloride and ammonia are reacted. 
     Referring to  FIG. 4B  a noble metal layer  308  is formed on the barrier layer. The noble metal layer is formed using the cyclical deposition techniques described above with reference to  FIGS. 2-3 . The thickness for the noble metal layer is variable depending on the device structure to be fabricated. Typically, the thickness for the noble metal layer is less than about 100 Å, preferably between about 25 Å to about 60 Å. 
     Thereafter, referring to  FIG. 4C , the apertures  304 H may be filled with copper  310  to complete the copper interconnect. The copper  310  may be formed using one or more suitable deposition processes. For example, a copper seed layer may be formed on the noble metal layer using an electrochemical plating (ECP) process followed by deposition of bulk copper to fill the interconnects using a chemical vapor deposition (CVD) process. 
     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.