Patent Publication Number: US-10770346-B2

Title: Selective cobalt removal for bottom up gapfill

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/349,460, filed Nov. 11, 2016, and which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The present technology relates to semiconductor processes and equipment. More specifically, the present technology relates to etching cobalt during gapfill operations. 
     BACKGROUND 
     Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers, or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process that etches one material faster than another facilitating, for example, a pattern transfer process. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits, and processes, etch processes have been developed with a selectivity towards a variety of materials. 
     Etch processes may be termed wet or dry based on the materials used in the process. A wet HF etch preferentially removes silicon oxide over other dielectrics and materials. However, wet processes may have difficulty penetrating some constrained trenches and also may sometimes deform the remaining material. Dry etches produced in local plasmas formed within the substrate processing region can penetrate more constrained trenches and exhibit less deformation of delicate remaining structures. However, local plasmas may damage the substrate through the production of electric arcs as they discharge. 
     Thus, there is a need for improved systems and methods that can be used to produce high quality devices and structures. These and other needs are addressed by the present technology. 
     SUMMARY 
     Exemplary methods for removing cobalt material may include flowing a chlorine-containing precursor into a processing region of a semiconductor processing chamber. The methods may include forming a plasma of the chlorine-containing precursor to produce plasma effluents. The methods may also include contacting an exposed region of cobalt with the plasma effluents. The exposed region of cobalt may include an overhang of cobalt on a trench defined on a substrate. The plasma effluents may produce cobalt chloride at the overhang of cobalt. The methods may include flowing a nitrogen-containing precursor into the processing region of the semiconductor processing chamber. The methods may further include contacting the cobalt chloride with the nitrogen-containing precursor. The methods may also include recessing the overhang of cobalt. 
     In exemplary methods a plasma power of the plasma formed from the chlorine-containing precursor may be less than about 100 W. A temperature of the substrate may be maintained between about 175° C. and about 250° C. during the etching method. A pressure within the semiconductor processing chamber may be maintained below about 5 Torr in embodiments. The etching methods may remove at least about 5 Å of cobalt during each removal or during the method operations. The methods may also include depositing additional cobalt in the trench, and producing a subsequent overhang. In some embodiments, the etching method may be repeated for at least two cycles. A total removal of cobalt after the at least 2 cycles may be at least about 20 Å. In some embodiments the method may further include, subsequent to recessing the overhang of cobalt, contacting the substrate with effluents of a hydrogen-containing plasma, and removing residue from exposed cobalt surfaces. The methods may remove less than 5% of material proximate a bottom region of the trench. The method may have a selectivity of cobalt to titanium nitride greater than or about 50:1. The method may also have a selectivity of cobalt to silicon nitride and silicon oxide greater than or about 100:1:1. In some embodiments, the processing region may be maintained plasma-free while contacting the cobalt chloride with the nitrogen-containing precursor. 
     The present technology may also include methods of producing a gap-free cobalt fill. The methods may include depositing a first amount of cobalt into a trench defined on a substrate. The deposition may form an overhang of cobalt at an opening of the trench. The methods may include flowing a chlorine-containing precursor into a processing region of a semiconductor processing chamber. A substrate may be housed within the processing region. The methods may also include forming a plasma of the chlorine-containing precursor to produce plasma effluents. The methods may include contacting the overhang of cobalt with the plasma effluents to produce cobalt chloride at the overhang of cobalt. The methods may include flowing a nitrogen-containing precursor into the processing region of the semiconductor processing chamber. The methods may further include contacting the cobalt chloride with the nitrogen-containing precursor. The methods may include recessing the overhang of cobalt. 
     In some embodiments the methods may further include depositing a second amount of cobalt into the trench. The deposition may form an additional overhang of cobalt at the opening of the trench. In some embodiments certain operations of the methods or the entire methods may be repeated at least twice. The first amount of cobalt may be at least 80% maintained in the trench while removing the overhang of cobalt. A plasma power of the plasma formed from the chlorine-containing precursor may be less than or about 60 W. In some embodiments, the methods may further include, subsequent to recessing the overhang of cobalt, contacting the substrate with effluents of a hydrogen-containing plasma, and removing residue from exposed cobalt surfaces. In some embodiments the cobalt may be deposited on a metallic nitride liner formed within the trench. 
     Such technology may provide numerous benefits over conventional systems and techniques. For example, the processes may remove an overhang portion of cobalt while substantially maintaining a portion of cobalt within the trench. Additionally, the removal operations of embodiments of the present technology may run an all-in-one process in a single chamber. These and other embodiments, along with many of their advantages and features, are described in more detail in conjunction with the below description and attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the nature and advantages of the disclosed technology may be realized by reference to the remaining portions of the specification and the drawings. 
         FIG. 1  shows a top plan view of one embodiment of an exemplary processing system according to embodiments of the present technology. 
         FIG. 2A  shows a schematic cross-sectional view of an exemplary processing chamber according to embodiments of the present technology. 
         FIG. 2B  shows a detailed view of a portion of the processing chamber illustrated in  FIG. 2A  according to embodiments of the present technology. 
         FIG. 3  shows a bottom plan view of an exemplary showerhead according to embodiments of the present technology. 
         FIG. 4  shows exemplary operations in a method according to embodiments of the present technology. 
         FIGS. 5A-5D  show cross-sectional views of substrates being processed according to embodiments of the present technology. 
     
    
    
     Several of the figures are included as schematics. It is to be understood that the figures are for illustrative purposes, and are not to be considered of scale unless specifically stated to be of scale. Additionally, as schematics, the figures are provided to aid comprehension and may not include all aspects or information compared to realistic representations, and may include exaggerated material for illustrative purposes. 
     In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a letter that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the letter. 
     DETAILED DESCRIPTION 
     As semiconductor device features continue to reduce in size, so do the interconnects between the features. For feature sizes in much of the current generation, copper interconnects have adequate resistivity, which may be less than cobalt. However, as features sizes continue to decrease below 20 nm, the effects may reverse, and cobalt may have reduced resistivity over copper. Tungsten is also a metal used in plugs and as a potential interconnect candidate. Similar to copper, though, as feature sizes continue to reduce, the resistivity of tungsten may be much larger than for cobalt. A semiconductor chip less than a couple centimeters in size may have dozens of miles of interconnect wiring running through the chip. Resistivity plays an important role in semiconductor performance, and the higher the resistivity, the more power the device may draw. Accordingly, by utilizing lower resistivity conductors, power management may be better controlled. 
     Because of the high aspect ratios of vias and trenches, many deposition techniques produce voids or keyholes when the top of a trench is sealed off during the deposition. One technique for handling this issue is to perform a dep-etch-dep process, which may include intermediate processes in which a portion of the deposited material is removed in order to expose the trench opening for better fill. Without complete fill, resistivity may increase, or the device may short circuit from these voids, which may render the device useless. Dep-etch-dep processes have been uncommon with cobalt because of the difficulty of cobalt removal. Many modified cobalt structures including cobalt fluoride, cobalt chloride, and cobalt bromide are non-volatile, and thus once formed may be difficult to remove. Conventional technologies have been unable to provide a cobalt etch with adequate queue times due to the multiple chambers, and multiple processes that may be used in an attempt to etch the cobalt. Additionally, the etching techniques used may also remove the cobalt within the trench or feature, which may further extend the formation operations, and reduce the overall quality of the cobalt formed. 
     The present technology overcomes these issues by performing an etch process that preferentially removes a top region of cobalt while maintaining cobalt within the trench features. Additionally, the removal operations may maintain a higher quality cobalt within the trench both by limiting the etchant contact with the cobalt, and also with optional operations that clean the cobalt surface. Finally, the entire removal process may be performed in a single chamber, unlike wet etch techniques that require transferring the processed substrate between multiple chambers to perform the wet etch and then dry the substrate. These processes may allow the formation of a high-quality cobalt fill in trenches and other features, and may improve queue times over conventional technologies. 
     Although the remaining disclosure will routinely identify specific etching processes utilizing the disclosed technology, it will be readily understood that the systems and methods are equally applicable to deposition and cleaning processes as may occur in the described chambers. Accordingly, the technology should not be considered to be so limited as for use with etching processes or chambers alone. Moreover, although an exemplary chamber is described to provide foundation for the present technology, it is to be understood that the present technology can be applied to virtually any semiconductor processing chamber that may allow the single-chamber operations described. 
       FIG. 1  shows a top plan view of one embodiment of a processing system  100  of deposition, etching, baking, and curing chambers according to embodiments. In the figure, a pair of front opening unified pods (FOUPs)  102  supply substrates of a variety of sizes that are received by robotic arms  104  and placed into a low pressure holding area  106  before being placed into one of the substrate processing chambers  108   a - f , positioned in tandem sections  109   a - c . A second robotic arm  110  may be used to transport the substrate wafers from the holding area  106  to the substrate processing chambers  108   a - f  and back. Each substrate processing chamber  108   a - f , can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation, and other substrate processes. 
     The substrate processing chambers  108   a - f  may include one or more system components for depositing, annealing, curing and/or etching a dielectric or metallic film on the substrate wafer. In one configuration, two pairs of the processing chambers, e.g.,  108   c - d  and  108   e - f , may be used to deposit material on the substrate, and the third pair of processing chambers, e.g.,  108   a - b , may be used to etch the deposited material. In another configuration, all three pairs of chambers, e.g.,  108   a - f , may be configured to etch a dielectric or metallic film on the substrate. Any one or more of the processes described may be carried out in chamber(s) separated from the fabrication system shown in different embodiments. It will be appreciated that additional configurations of deposition, etching, annealing, and curing chambers for dielectric films are contemplated by system  100 . 
       FIG. 2A  shows a cross-sectional view of an exemplary process chamber system  200  with partitioned plasma generation regions within the processing chamber. During film etching, e.g., titanium nitride, tantalum nitride, tungsten, copper, cobalt, silicon, polysilicon, silicon oxide, silicon nitride, silicon oxynitride, silicon oxycarbide, etc., a process gas may be flowed into the first plasma region  215  through a gas inlet assembly  205 . A remote plasma system (RPS)  201  may optionally be included in the system, and may process a first gas which then travels through gas inlet assembly  205 . The inlet assembly  205  may include two or more distinct gas supply channels where the second channel (not shown) may bypass the RPS  201 , if included. 
     A cooling plate  203 , faceplate  217 , ion suppressor  223 , showerhead  225 , and a substrate support  265 , having a substrate  255  disposed thereon, are shown and may each be included according to embodiments. The pedestal  265  may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate, which may be operated to heat and/or cool the substrate or wafer during processing operations. The wafer support platter of the pedestal  265 , which may comprise aluminum, ceramic, or a combination thereof, may also be resistively heated in order to achieve relatively high temperatures, such as from up to or about 100° C. to above or about 600° C., using an embedded resistive heater element. 
     The faceplate  217  may be pyramidal, conical, or of another similar structure with a narrow top portion expanding to a wide bottom portion. The faceplate  217  may additionally be flat as shown and include a plurality of through-channels used to distribute process gases. Plasma generating gases and/or plasma excited species, depending on use of the RPS  201 , may pass through a plurality of holes, shown in  FIG. 2B , in faceplate  217  for a more uniform delivery into the first plasma region  215 . 
     Exemplary configurations may include having the gas inlet assembly  205  open into a gas supply region  258  partitioned from the first plasma region  215  by faceplate  217  so that the gases/species flow through the holes in the faceplate  217  into the first plasma region  215 . Structural and operational features may be selected to prevent significant backflow of plasma from the first plasma region  215  back into the supply region  258 , gas inlet assembly  205 , and fluid supply system  210 . The faceplate  217 , or a conductive top portion of the chamber, and showerhead  225  are shown with an insulating ring  220  located between the features, which allows an AC potential to be applied to the faceplate  217  relative to showerhead  225  and/or ion suppressor  223 . The insulating ring  220  may be positioned between the faceplate  217  and the showerhead  225  and/or ion suppressor  223  enabling a capacitively coupled plasma (CCP) to be formed in the first plasma region. A baffle (not shown) may additionally be located in the first plasma region  215 , or otherwise coupled with gas inlet assembly  205 , to affect the flow of fluid into the region through gas inlet assembly  205 . 
     The ion suppressor  223  may comprise a plate or other geometry that defines a plurality of apertures throughout the structure that are configured to suppress the migration of ionically-charged species out of the first plasma region  215  while allowing uncharged neutral or radical species to pass through the ion suppressor  223  into an activated gas delivery region between the suppressor and the showerhead. In embodiments, the ion suppressor  223  may comprise a perforated plate with a variety of aperture configurations. These uncharged species may include highly reactive species that are transported with less reactive carrier gas through the apertures. As noted above, the migration of ionic species through the holes may be reduced, and in some instances completely suppressed. Controlling the amount of ionic species passing through the ion suppressor  223  may advantageously provide increased control over the gas mixture brought into contact with the underlying wafer substrate, which in turn may increase control of the deposition and/or etch characteristics of the gas mixture. For example, adjustments in the ion concentration of the gas mixture can significantly alter its etch selectivity, e.g., SiNx:SiOx etch ratios, Si:SiOx etch ratios, etc. In alternative embodiments in which deposition is performed, it can also shift the balance of conformal-to-flowable style depositions for dielectric materials. 
     The plurality of apertures in the ion suppressor  223  may be configured to control the passage of the activated gas, i.e., the ionic, radical, and/or neutral species, through the ion suppressor  223 . For example, the aspect ratio of the holes, or the hole diameter to length, and/or the geometry of the holes may be controlled so that the flow of ionically-charged species in the activated gas passing through the ion suppressor  223  is reduced. The holes in the ion suppressor  223  may include a tapered portion that faces the plasma excitation region  215 , and a cylindrical portion that faces the showerhead  225 . The cylindrical portion may be shaped and dimensioned to control the flow of ionic species passing to the showerhead  225 . An adjustable electrical bias may also be applied to the ion suppressor  223  as an additional means to control the flow of ionic species through the suppressor. 
     The ion suppressor  223  may function to reduce or eliminate the amount of ionically charged species traveling from the plasma generation region to the substrate. Uncharged neutral and radical species may still pass through the openings in the ion suppressor to react with the substrate. It should be noted that the complete elimination of ionically charged species in the reaction region surrounding the substrate may not be performed in embodiments. In certain instances, ionic species are intended to reach the substrate in order to perform the etch and/or deposition process. In these instances, the ion suppressor may help to control the concentration of ionic species in the reaction region at a level that assists the process. 
     Showerhead  225  in combination with ion suppressor  223  may allow a plasma present in first plasma region  215  to avoid directly exciting gases in substrate processing region  233 , while still allowing excited species to travel from chamber plasma region  215  into substrate processing region  233 . In this way, the chamber may be configured to prevent the plasma from contacting a substrate  255  being etched. This may advantageously protect a variety of intricate structures and films patterned on the substrate, which may be damaged, dislocated, or otherwise warped if directly contacted by a generated plasma. Additionally, when plasma is allowed to contact the substrate or approach the substrate level, the rate at which oxide species etch may increase. Accordingly, if an exposed region of material is oxide, this material may be further protected by maintaining the plasma remotely from the substrate. 
     The processing system may further include a power supply  240  electrically coupled with the processing chamber to provide electric power to the faceplate  217 , ion suppressor  223 , showerhead  225 , and/or pedestal  265  to generate a plasma in the first plasma region  215  or processing region  233 . The power supply may be configured to deliver an adjustable amount of power to the chamber depending on the process performed. Such a configuration may allow for a tunable plasma to be used in the processes being performed. Unlike a remote plasma unit, which is often presented with on or off functionality, a tunable plasma may be configured to deliver a specific amount of power to the plasma region  215 . This in turn may allow development of particular plasma characteristics such that precursors may be dissociated in specific ways to enhance the etching profiles produced by these precursors. 
     A plasma may be ignited either in chamber plasma region  215  above showerhead  225  or substrate processing region  233  below showerhead  225 . Plasma may be present in chamber plasma region  215  to produce the radical precursors from an inflow of, for example, a fluorine-containing precursor or other precursor. An AC voltage typically in the radio frequency (RF) range may be applied between the conductive top portion of the processing chamber, such as faceplate  217 , and showerhead  225  and/or ion suppressor  223  to ignite a plasma in chamber plasma region  215  during deposition. An RF power supply may generate a high RF frequency of 13.56 MHz but may also generate other frequencies alone or in combination with the 13.56 MHz frequency. 
       FIG. 2B  shows a detailed view  253  of the features affecting the processing gas distribution through faceplate  217 . As shown in  FIGS. 2A and 2B , faceplate  217 , cooling plate  203 , and gas inlet assembly  205  intersect to define a gas supply region  258  into which process gases may be delivered from gas inlet  205 . The gases may fill the gas supply region  258  and flow to first plasma region  215  through apertures  259  in faceplate  217 . The apertures  259  may be configured to direct flow in a substantially unidirectional manner such that process gases may flow into processing region  233 , but may be partially or fully prevented from backflow into the gas supply region  258  after traversing the faceplate  217 . 
     The gas distribution assemblies such as showerhead  225  for use in the processing chamber section  200  may be referred to as dual channel showerheads (DCSH) and are additionally detailed in the embodiments described in  FIG. 3 . The dual channel showerhead may provide for etching processes that allow for separation of etchants outside of the processing region  233  to provide limited interaction with chamber components and each other prior to being delivered into the processing region. 
     The showerhead  225  may comprise an upper plate  214  and a lower plate  216 . The plates may be coupled with one another to define a volume  218  between the plates. The coupling of the plates may be so as to provide first fluid channels  219  through the upper and lower plates, and second fluid channels  221  through the lower plate  216 . The formed channels may be configured to provide fluid access from the volume  218  through the lower plate  216  via second fluid channels  221  alone, and the first fluid channels  219  may be fluidly isolated from the volume  218  between the plates and the second fluid channels  221 . The volume  218  may be fluidly accessible through a side of the gas distribution assembly  225 . 
       FIG. 3  is a bottom view of a showerhead  325  for use with a processing chamber according to embodiments. Showerhead  325  may correspond with the showerhead  225  shown in  FIG. 2A . Through-holes  365 , which show a view of first fluid channels  219 , may have a plurality of shapes and configurations in order to control and affect the flow of precursors through the showerhead  225 . Small holes  375 , which show a view of second fluid channels  221 , may be distributed substantially evenly over the surface of the showerhead, even amongst the through-holes  365 , and may help to provide more even mixing of the precursors as they exit the showerhead than other configurations. 
     The chambers discussed previously may be used in performing exemplary methods including etching methods. Turning to  FIG. 4  is shown exemplary operations in a method  400  according to embodiments of the present technology. Prior to the first operation of the method, a substrate may be processed in one or more ways before being placed within a processing region of a chamber in which method  400  may be performed. For example, features may be produced, and vias or trenches may be formed or defined within the substrate. The vias or trenches may have an aspect ratio, or a ratio of their height to width, greater than or about 2, greater than or about 5, greater than or about 10, greater than or about 20, greater than or about 30, greater than or about 50, or more in embodiments. In some embodiments a liner material may be formed along the trench sidewalls to protect the substrate from metal diffusion. Additionally, an amount of cobalt may be deposited within a trench. For example, a first portion of cobalt may be deposited within a processing chamber positioned on a processing tool. 
     The chamber in which deposition is performed may be on the same tool as an etching chamber used in method  400 , or in embodiments may be on a different tool than the chamber used in method  400 . The deposition may include an overhang of cobalt extending past the sidewalls of the trench at an opening to the trench. This overhang of cobalt may constrict the trench width at the entrance to the trench, and in embodiments, the cobalt may completely pinch off or seal the trench from further deposition. Within the trench an amount of cobalt may be formed or deposited at the bottom of the trench and along the sidewalls. The trench may be only partially filled in embodiments before the trench opening is restricted or pinched off. The substrate may then be transferred to a chamber, such as chamber  200  described above, for method  400  to be performed. 
     Method  400  may include flowing a precursor into a processing region of a semiconductor processing chamber at operation  405 . The processing region may be region  233  of chamber  200  previously discussed, where the substrate including a portion of cobalt may be housed. The precursor may be or include a chlorine-containing precursor in embodiments. A plasma may be formed at operation  410  within the processing region of the chamber. The plasma may be formed from the chlorine-containing precursor to produce plasma effluents. The plasma may be formed by two electrodes within the processing chamber, which may include, for example, one or both of the showerhead  255  and support pedestal  265  previously described. The plasma may be a bias plasma formed within the chamber region that may direct plasma effluents to the substrate surface and provide low-energy ion bombardment to the substrate. 
     At operation  415 , an exposed region of cobalt may be contacted with the plasma effluents. The exposed region may include a portion of cobalt that is at least partially external to a trench defined on the substrate in embodiments, and may include the overhang region impinging on the trench or sealing access to the trench. The plasma effluents may include chlorine plasma effluents, which when contacting cobalt, may modify the cobalt, and may form cobalt chloride (CoCl x ) at the locations of contact. For example, the chlorine plasma effluents may contact cobalt preferentially outside of the trench, such as within a field region of the substrate, as well as cobalt within the trench. The chlorine may also at least initially contact cobalt external to the trench, which may have sealed or pinched off the entrance to the trench. 
     Subsequent the formation of cobalt chloride, the chlorine plasma may be halted, and the chamber may be purged with one or more inert precursors in some embodiments. A nitrogen-containing precursor may then be flowed into the processing region of the semiconductor processing chamber at operation  420 . The nitrogen-containing precursor may contact the substrate and modified cobalt at operation  425 . The modified cobalt may include the regions of cobalt chloride, and may interact with the cobalt chloride, while having little to no effect on unmodified regions of cobalt. The nitrogen-containing precursor may interact with the cobalt chloride to produce volatile substances, which may then be removed from the chamber. The overhang portion of cobalt may have been at least partially converted or modified into cobalt chloride, and when contacted with the nitrogen-containing precursor, the overhang of cobalt may be at least partially recessed at operation  430 . 
     The plasma formed in the processing region with the chlorine-containing precursor may be a low-power plasma in embodiments to limit the effect on cobalt. The plasma power may be maintained relatively low to provide slight directionality to the chlorine plasma effluents. However, by using a low power, the effluents may not extend deep into the trench. Additionally, the higher the plasma power the more likely to cause sputtering at the surfaces of materials being contacted. Accordingly, by maintaining the plasma power low, the underlying materials may remain unmodified while a surface-amount of cobalt may be modified. The plasma power may be below or about 300 W in embodiments, depending on the thickness of the desired modification. 
     Higher plasma power may provide additional modification and removal of the overhang to form a V-shape profile at the top opening or entrance to the trench during an operation cycle. However, a higher plasma power may allow more material within the trench to be modified and removed, which may increase the number of cycles that may be used to fill the trench, and may reduce the efficiency of the method. In embodiments, the plasma power may be below or about 250 W, below or about 200 W, below or about 150 W, below or about 100 W, below or about 50 W, between about 10 W and about 80 W, or between about 30 W and about 60 W. Utilizing a plasma power below 100 W may afford more control on the amount of cobalt modified at the bottom of the trench, and may allow increased control on the modification. 
     The chlorine-containing precursor flowing into the processing region may be provided in a low dose in embodiments to ensure an un-saturated reactant, such as chlorine, in this operation. This may limit the effect on cobalt formed at the bottom of the trench. The low-dose precursor plasma may modify a surface-amount of cobalt only or the overhang of cobalt more than cobalt formed at the bottom of the trench. By using a low-dose reactive precursor, the plasma effluents may not extend deep into the trench during the operations. Accordingly, by maintaining the low dose of chlorine-containing precursor flow and/or delivering the chlorine-containing precursor for a reduced time period, such as with a pulsed operation, the underlying materials may remain unmodified while a surface-amount of cobalt may be modified. 
     The flow rate of the chlorine-containing precursor may be less than or about 50 sccm in embodiments, and may be less than or about 45 sccm, less than or about 40 sccm, less than or about 35 sccm, less than or about 30 sccm, less than or about 25 sccm, less than or about 20 sccm, less than or about 15 sccm, less than or about 10 sccm, less than or about 5 sccm, or less. Additionally, the chlorine-containing precursor delivery may be pulsed for time periods of less than or about 40 seconds in embodiments, and may be pulsed for time periods of less than or about 35 seconds, less than or about 30 seconds, less than or about 25 seconds, less than or about 20 seconds, less than or about 15 seconds, less than or about 10 seconds, less than or about 5 seconds, or less. Additionally, the flow rate and pulsing may be combined for any of the listed numbers. For example, the chlorine-containing precursor flow rate may be below or about 10 sccm and may be delivered in pulses from about 5 to about 10 seconds in embodiments, depending on the thickness of the desired modification. Because only the modified regions of cobalt chloride may be subject to removal by the nitrogen-containing precursor, controlling the amount of material that is converted provides control over the material that is removed. 
     Other process conditions may impact the performance of the operations as well. A temperature within the processing chamber or at the substrate level may be maintained between about 50° C. and about 500° C. in embodiments. The temperature may be maintained below or about 500° C. in embodiments, and may be maintained below or about 450° C., below or about 400° C., below or about 350° C., below or about 300° C., below or about 250° C., below or about 200° C., below or about 150° C., below or about 100° C., or lower. The temperature may also be maintained between about 100° C. and about 300° C. in embodiments, and may be maintained between about 175° C. and about 250° C. during operations of the etching method  400 . In embodiments the temperature may be maintained within this range for all operations of method  400 . In some embodiments the temperature may be adjusted up or down between the two contacting operations  415  and  425 . 
     A higher processing temperature may allow the nitrogen-containing precursor to remove the cobalt chloride without further excitation in embodiments. For example, contacting the cobalt chloride with the precursor at operation  425  may be performed between about 175° C. and about 250° C. The nitrogen-containing precursor may interact with the cobalt chloride at this temperature producing volatile materials that may be expelled from the chamber. Additionally, the nitrogen-containing precursor may not interact or chemically react with unmodified portions of cobalt. Unlike plasma precursors which may sputter or otherwise etch materials on the substrate, the temperature based reaction of the nitrogen-containing precursor may be limited to the modified portions of cobalt, and may maintain the unmodified regions, including regions within the trench. Accordingly, in some embodiments, the processing region of the chamber may be maintained plasma-free during operation  425  of contacting the cobalt chloride with the nitrogen-containing precursor. 
     A pressure within the chamber may be maintained below or about 5 Torr in embodiments. A lower pressure may provide a more anisotropic process. The pressure may be maintained below or about 4 Torr in embodiments, and may be maintained below or about 3 Torr, below or about 2 Torr, below or about 1 Torr, below or about 100 mTorr, or lower. In embodiments the pressure may be maintained between about 500 mTorr and about 2 Torr. 
     As explained previously, the modification depth may affect the degree of cobalt removal during the etching method  400 . This may also impact the amount of cobalt material removed from within the trench, where a smaller amount of modification may reduce an amount of cobalt removed from within the trench. The low plasma power and/or low chlorine-containing precursor flow rate discussed previously may allow the removal to be limited to less than or about 5 nm of cobalt during the operation. Additionally, the low plasma treatment and/or low chlorine-containing precursor flow rate may provide a removal of less than or about 4 nm, less than or about 3 nm, less than or about 2 nm, less than or about 1 nm, less than or about 9 Å, less than or about 8 Å, less than or about 7 Å, less than or about 6 Å, less than or about 5 Å, less than or about 4 Å, less than or about 3 Å, less than or about 2 Å, or less in embodiments, down to a few molecules of cobalt. In some embodiments the removal may be at least about 5 Å, and may be between about 4 Å and about 2 nm of removal, or between about 5 Å and about 1 nm of removal. 
     Because of the reduced amount of cobalt removal in some embodiments, the process may involve cycling certain operations. Optional purge operations may be performed after each contacting operation to reduce the interaction of the plasma effluents of the chlorine-containing precursor and the nitrogen-containing precursor. Method  400  may represent one cycle of a process for recessing or removing cobalt from a substrate. In some embodiments, method  400  may be repeated for at least two cycles, and may be repeated for at least 3 cycles, at least 4 cycles, at least 5 cycles, at least 6 cycles, at least 7 cycles, at least 8 cycles, at least 9 cycles, or more. The number of cycles may be dependent on the amount of removal provided by each cycle. For example, a total amount of cobalt may be removed in a single cycle that is sufficient to provide adequate access to the trench for further deposition. 
     In some embodiments, each cycle may remove between about 5 Å and about 10 Å of cobalt, and a total amount of cobalt of a few nanometers may be performed with additional cycles. For example, the cycling of method  400  may remove at least about 10 Å of cobalt, and may remove at least about 15 Å, at least about 20 Å, at least about 25 Å, at least about 30 Å, at least about 40 Å, at least about 45 Å, at least about 50 Å, or more depending on the amount of cobalt deposited, and the amount sought for removal. The method may preferentially remove cobalt at the surface of the trench proximate the field region of the substrate. This may in part be from the overhang of cobalt that may both pinch off access to the trench for deposition, but may also protect cobalt within the trench from etching operations. Accordingly, during multiple cycles, the first cycle, two cycles, three cycles, or more may perform a recess exclusively on material pinching off access to the trench. Additional etching operations may further remove this material while removing a portion of material within the trench. As the access to the trench is increased, additional plasma effluents may access the trench and begin to modify the cobalt formed within the trench. The process may be halted when cobalt within the trench has been recessed, or may be continued until a certain threshold of cobalt has been removed either externally to the trench or within the trench. 
     The amount of cobalt that is modified and removed from within the trench may be less than the amount removed from the field region and from the access to the trench. For example, the amount of material removed from within the trench may be less than or about 90% of the total material within the trench or of the amount removed from the field region of the substrate. Additionally, the amount of material removed from within the trench may be less than or about 85%, less than or about 80%, less than or about 75%, less than or about 70%, less than or about 65%, less than or about 60%, less than or about 55%, less than or about 50%, less than or about 45%, less than or about 40%, less than or about 35%, less than or about 30%, less than or about 25%, less than or about 20%, less than or about 15%, less than or about 10%, less than or about 5%, less than or about 1%, or less of the total amount within the trench, proximate a bottom of the trench, or of the amount removed from the field region of the substrate. In some embodiments the cobalt material within the trench or formed at a bottom of the trench may be substantially or essentially maintained during method  400 . 
     The precursors used to form plasma may include a chlorine-containing precursor, or a halogen-containing precursor in embodiments. The precursor may include chlorine, bromine, fluorine, or other etchants that may interact with the cobalt under plasma conditions. A chlorine-containing precursor may include chlorine (CL 2 ), or may include a diatomic precursor including chlorine or a halogen. The nitrogen-containing precursor may include nitrogen, carbon, and/or hydrogen in any combination. For example, the nitrogen-containing precursor may include one or more methyl moieties coupled with nitrogen, or some other carbon based moiety. Exemplary nitrogen-containing precursors include amines, diamines, including aliphatic and aromatic diamines, including linear aliphatic diamines, branched aliphatic diamines, phenylenediamines, and other nitrogen-containing precursors. Exemplary precursors may include tetramethylethylenediamine (TMEDA) in embodiments. Either precursor may include additional carrier gases including chemically inert precursors including helium, argon, xenon, and other noble gases or precursors that may not chemically react with cobalt. 
     Method  400  may optionally include deposition operations that may occur on the same tool as the etching method, or on a different tool. In some embodiments in which the deposition and etching are performed on the same tool, a vacuum may be maintained between the operations, which may reduce contaminants, moisture, and other handling issues. The method may optionally include depositing additional cobalt in the trench. The deposition may additionally deposit on the field region as well, and in embodiments may produce a subsequent overhang of cobalt. In some embodiments the overhang may be produced in the additional deposition by design, which may protect additional cobalt deposited within the trench. The etching operations of method  400  may then be repeated in a subsequent set of cycles as previously explained. Within a certain number of iterations of deposition and removal, the trench may be filled with cobalt in a void-free and seam-free fill. Additional operations may be performed in between the iterations and cycles, including reflow in embodiments. 
     The methods may also optionally include a hydrogen treatment between recess or removal and deposition operations. Modification of the material to produce cobalt chloride and then removal of cobalt chloride may produce residue on the cobalt that may cause peeling of subsequently formed or deposited materials. By conducting a treatment with a hydrogen-containing precursor, residue materials may be removed to ensure a clean surface of the formed film. The hydrogen treatment may include contacting the substrate with effluents of a hydrogen-containing plasma at optional operation  435 . The plasma effluents may remove residue from exposed cobalt surfaces at optional operation  440 . The optional hydrogen treatment may be performed in the same chamber as the other operations of method  400  such that the entire method  400  is performed in a single chamber, such as chamber  200  as previously described. Additionally, in some embodiments one or more operations may be performed in a different chamber as other operations of method  400 . 
     The hydrogen treatment may include forming the plasma effluents remotely or at the substrate level. For example, the hydrogen-containing precursor may be flowed into a remote plasma region, such as a remote plasma unit, or a remote section of a processing chamber, such as region  215  discussed previously with respect to chamber  200 . Additionally, the hydrogen-containing precursor may be flowed into the processing region in which the substrate is housed, and a plasma may be formed. The hydrogen plasma effluents may interact with impurities and residue materials and remove them from exposed cobalt surfaces within the trench, including sidewalls and material along the bottom of the trench. Hydrogen formed by plasma processes may not interact with cobalt, and may not affect the cobalt on which the residue may be located. In this way, the cobalt surfaces may be cleared of residue material prior to additional deposition material or reflow, which may maintain a high quality cobalt fill. 
     The plasma process performed may interact with liner or barrier materials formed along the trench, and in embodiments may interact with materials within which the trenches are defined or formed. Based on the temperature and plasma characteristics used in the operations, the present technology may etch cobalt selectively over liner material and other substrate materials. For example, the liner may include one or more metals, including transition metals, as well as nitrides of metals. The metals may include, for example, titanium, titanium nitride, tantalum, tantalum nitride, ruthenium, and other materials and nitrides. The present technology may selectively etch cobalt over liner materials, such as titanium nitride, at an etch rate ratio greater than or about 20:1, and in embodiments may etch cobalt at an etch ratio greater than or about 30:1, greater than or about 40:1, greater than or about 50:1, greater than or about 60:1, greater than or about 70:1, or more in embodiments. 
     The present technology may also etch cobalt over silicon-containing materials, including silicon oxide and silicon nitride, at an etch rate ratio greater than or about 50:1. In embodiments, the present technology may etch cobalt at an etch rate ratio compared to silicon-containing materials greater than or about 60:1, greater than or about 70:1, greater than or about 80:1, greater than or about 90:1, greater than or about 100:1, greater than or about 110:1, greater than or about 120:1, greater than or about 150:1, or higher. 
     Turning to  FIGS. 5A-5D  are shown cross-sectional views of substrates on which the present technology may be performed.  FIG. 5A  illustrates a cross-sectional view of a substrate  505  on which a trench has been formed. A liner  510  may be formed within the trench and may produce a barrier on the sidewalls and the base. The liner may include titanium nitride, tantalum nitride, other transition metals or transition metal nitrides, and may protect the substrate  505  from metal diffusion. A first amount of cobalt  515  may be formed or deposited within the trench and on the liner material  510 . When deposited, the cobalt  515  may produce an overhang  516 , which may be a portion of cobalt that forms across the trench opening. Although illustrated as partially covering the trench opening, in some embodiments the overhang  516  may completely pinch off or seal the trench, which may prevent further deposition within the trench. 
       FIG. 5B  illustrates a plasma modification in which plasma effluents  520  of a chlorine-containing precursor are produced. The chlorine-containing precursor may be flowed into a substrate processing region where a plasma may be formed to produce the plasma effluents. The overhang  516  and field regions above the trench may be contacted with the plasma effluents  520  to produce a region of modified cobalt  517 . The modified cobalt  517  may be or include cobalt chloride. The degree to which the modified cobalt  517  extends into the trench may depend on the extent to which the overhang  516  seals the trench, the plasma power, and the processing conditions. It is to be understood that  FIG. 5B  is an example illustration to show a modified surface, and is not necessarily to scale or with an accurate amount of modification. 
     Subsequent the modification, a nitrogen-containing precursor may be flowed into the processing region. The nitrogen-containing precursor may contact the modified cobalt  517  to produce volatile materials, which may be extracted from the chamber. As illustrated in  FIG. 5C , after the nitrogen-containing precursor has contacted and removed the modified cobalt  517 , the overhang  516  may be recessed or removed, which may provide access to the trench. The modification and removal may be performed multiple times in order to provide adequate access to the trench. Additional operations may be performed, which may include reflow or a hydrogen-plasma treatment as previously discussed. 
     An additional amount or second amount of cobalt  525  may be deposited on the substrate as illustrated in  FIG. 5D . As shown, the second amount of cobalt  525  may further extend the fill within the trench, such as along the sidewalls and/or along or proximate the bottom of the trench. The second amount of cobalt  525  may be deposited to produce a second overhang  526  as illustrated. The second overhang  526  may also extend across the trench opening, and may completely seal or pinch off the trench opening, which may limit further deposition. The second overhang may similarly be produced purposefully to protect the cobalt deposited within the trench from excessive removal. As explained previously, an additional modification and removal may be performed, followed by additional deposition, removal, and deposition if required. In embodiments the deposition and removal may be repeated at least twice before a final deposition may fill the trench. By performing the modification and removal as explained throughout the disclosure, the present technology may provide a greater cobalt fill, and reduce cobalt removal from within the feature during the etching operations. This may reduce queue times for filling trenches, and may provide an improved quality of cobalt fill that may not suffer from peeling of additional or subsequent layers of material. 
     In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details. 
     Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the embodiments. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present technology. Accordingly, the above description should not be taken as limiting the scope of the technology. Additionally, methods or processes may be described as sequential or in steps, but it is to be understood that the operations may be performed concurrently, or in different orders than listed. 
     Where a range of values is provided, it is understood that each intervening value, to the smallest fraction of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Any narrower range between any stated values or unstated intervening values in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of those smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the technology, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included. 
     As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a precursor” includes a plurality of such precursors, and reference to “the layer” includes reference to one or more layers and equivalents thereof known to those skilled in the art, and so forth. 
     Also, the words “comprise(s)”, “comprising”, “contain(s)”, “containing”, “include(s)”, and “including”, when used in this specification and in the following claims, are intended to specify the presence of stated features, integers, components, or operations, but they do not preclude the presence or addition of one or more other features, integers, components, operations, acts, or groups.