Abstract:
Processes are provided for selectively depositing a metal silicide material on a first H-terminated surface of a substrate relative to a second, different surface of the same substrate. In some aspects, methods of forming a metal silicide contact layer for use in integrated circuit fabrication are provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to U.S. Provisional Patent Application 62/200,502, filed Aug. 3, 2015 and entitled “SELECTIVE DEPOSITION ON METAL OR METALLIC SURFACES RELATIVE TO DIELECTRIC SURFACES” and U.S. Provisional Patent Application 62/281,593, filed Jan. 21, 2016 and entitled “SELECTIVE DEPOSITION ON METAL OR METALLIC SURFACES RELATIVE TO DIELECTRIC SURFACES,” the disclosures of which are hereby incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present application relates generally to the field of semiconductor device manufacturing. 
         [0004]    Description of the Related Art 
         [0005]    The continuous scaling of CMOS devices has increased process cost significantly, primarily due to the need for multiple patterning. To compensate for the rapid process cost increase and maintain a low cost per transistor, accelerated contact area scaling is required. This reduction in contact area raises an enormous challenge with respect to source/drain contact resistance in such devices, because contact resistance is inversely proportional to contact area. 
         [0006]    Currently for FinFET devices, the contact structure can include Ti deposited by physical vapor deposition (PVD) followed by TiN deposited by atomic layer deposition (ALD) and W deposited by ALD or chemical vapor deposition (CVD) to fill the contact trench. PVD processes typically have poor step coverage and only deposit on top of the source/drain, which has a very limited contact area. 
         [0007]    Metal silicides can be used as electrical contacts in integrated circuits. Typically silicides are formed by depositing a metal by a PVD process on top of silicon and annealing to induce a solid state reaction. Part of the silicon that is present in gate, source and/or drain structures can thus be converted into a low-resistivity metal silicide. However, the non-selective nature of this metal deposition process may require the addition of complicated patterning steps. This process is carried out to realize a conductive path with a low bulk resistivity on the one hand, and to ensure good contact resistance on the other hand. However, this reductive process can consume the source/drain substrate, leading to undesirable or degraded device performance, for example increased resistance due to a reduction in the contact area or device cross-section. 
       SUMMARY OF THE INVENTION 
       [0008]    In some aspects, processes for selectively depositing metal silicides are provided. According to some processes, a metal silicide is selectively deposited on a first H-terminated surface of a substrate relative to a second oxide, nitride, oxynitride, or carbide surface. The selective deposition process may comprise one or more deposition cycles comprising contacting the substrate with a first vapor phase precursor comprising silicon, removing the first vapor phase precursor and reaction byproducts, if any, from the substrate, contacting the substrate with a second vapor phase metal halide precursor comprising Ta, Nb, or Ti, and removing the second vapor phase precursor and reaction byproducts, if any, from the substrate. In some embodiments the metal silicide selectively deposited on the first surface of the substrate relative to the second surface of the same substrate comprises Ta, Nb, or Ti. 
         [0009]    In some embodiments H-terminations may be provided on the first surface of the substrate by treating at least the first surface prior to depositing the metal silicide. In some embodiments the H-terminations may be provided on the first surface of the substrate by contacting at least the first surface with HF. In some embodiments the second surface may be oxidized by treating at least the second surface prior to depositing the metal silicide. In some embodiments treating at least the second surface may comprise exposing the substrate to ambient conditions and/or moisture. In some embodiments the process may be an atomic layer deposition (ALD) process. 
         [0010]    In some embodiments the first surface may comprise silicon or germanium. In some embodiments the second surface may comprise silicon oxide, silicon nitride, germanium oxide, germanium nitride, titanium oxide, titanium nitride, hafnium oxide, or hafnium nitride. In some embodiments the metal silicide may be selectively deposited on the first surface of the substrate relative to the second surface of the substrate with a selectivity of at least 90%. In some embodiments the first vapor phase precursor comprising silicon may comprise a silane. In some embodiments the first vapor phase precursor comprising silicon may comprise disilane or trisilane. In some embodiments the second vapor phase metal halide precursor may comprise a chloride or fluoride. In some embodiments the second vapor phase metal halide precursor may comprise TaCl5 or TaF5. 
         [0011]    In some aspects processes for forming a contact structure on a substrate are provided. According to some embodiments, processes for forming a contact structure on a substrate may comprise providing a substrate comprising a first H-terminated surface and a second oxide, nitride, oxynitride, or carbide surface, and selectively depositing a metal silicide contact layer on the first H-terminated surface of the substrate relative to the second oxide, nitride, oxynitride, or carbide surface by an atomic layer deposition (ALD) process. In some embodiments the ALD process may comprise alternately and sequentially contacting the substrate with a silicon precursor and metal halide precursor. In some embodiments the metal of the metal halide precursor and the metal of the metal silicide contact layer may be one of Ta, Nb, and Ti. In some embodiments the process for forming a contact structure on a substrate may additionally comprise depositing a liner over the metal silicide contact layer; and depositing a low resistivity material over the metal silicide contact layer and the liner to thereby form a contact structure. 
         [0012]    In some embodiments selectively depositing a metal silicide contact layer may comprise selectively depositing until a metal silicide film of a desired thickness is formed. In some embodiments the process may further comprise treating at least the first surface of the substrate to provide H-terminations thereon. In some embodiments treating at least the first surface of the substrate may comprise contacting at least the first surface of the substrate with HF. In some embodiments the first surface of the substrate may comprise a source/drain region. In some embodiments the liner may comprise TiN and the low resistivity material may comprise W. In some embodiments the silicon precursor may comprise disilane or trisilane and the metal halide precursor may comprise TaCl5 or TaF5. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will be better understood from the detailed description and from the appended drawings, which are meant to illustrate and not to limit the invention, and wherein: 
           [0014]      FIG. 1  illustrates a deposition process flow for selectively depositing a metal silicide material on a first H-terminated surface of a substrate relative to a second, different surface of the same substrate; 
           [0015]      FIG. 2  illustrates a deposition process flow for selectively depositing a material comprising tantalum silicide on a first H-terminated surface of a substrate relative to a second, different surface of the same substrate; 
           [0016]      FIG. 3A  is an SEM image of a TaSi x  film deposited on substrate comprising an H-terminated surface by an ALD process as described herein. 
           [0017]      FIG. 3B  is an SEM image of a substrate comprising a 15 Å TiN surface on thermal oxide on silicon subsequent to an ALD process as described herein. 
           [0018]      FIG. 3C  is an SEM image of a substrate comprising a native silicon oxide surface subsequent to an ALD process as described herein. 
           [0019]      FIG. 3D  is an SEM image of a substrate comprising a thermal silicon oxide surface subsequent to an ALD process as described herein. 
           [0020]      FIG. 4  illustrates an exemplary process flow for forming a metal silicide contact layer. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In some situations it may be desirable to selectively form or deposit a metal silicide material on one surface of a substrate relative to a second, different surface of the same substrate. For example, selective deposition may be used to form a metal silicide contact layer in a FinFET device. In some embodiments a metal silicide material may be deposited or formed selectively on a first hydrogen-terminated surface of a substrate preferentially over a second, different surface, such as an oxide, nitride, oxynitride, or carbide surface of the same substrate. 
         [0022]    One or more surfaces may be treated in order to enhance deposition on one surface relative to one or more different surfaces. In some embodiments a first surface is treated, or activated, in order to enhance deposition on the first surface relative to a second surface. In some embodiments a second surface is treated, or deactivated, in order to decrease or inhibit deposition on the second surface relative to a first surface. In some embodiments a first surface may be treated to enhance deposition and a second surface may be treated to inhibit deposition, thereby increasing selective deposition on the first surface relative to the second surface. In some embodiments a deactivating treatment does not involve formation of a self-assembled monolayer (SAM). In some embodiments a deactivating treatment does not comprise treatment with an organic agent. 
         [0023]    For example, in some embodiments the first surface of a substrate may be treated to provide a H-terminated surface prior to or at the beginning of the metal silicide deposition process in order to increase or enhance deposition of the metal silicide on the first surface relative to the second, different surface. That is, selective deposition on the treated first, H-terminated surface is increased relative to the second, different surface. In some embodiments, for example, a native oxide present on a first surface may be removed in order to enhance deposition on the first surface relative to the second, different surface. In some embodiments where a native oxide may be present on a first surface the native oxide may be removed prior to or at the beginning of the selective deposition process. In some embodiments removal of a native oxide layer from a first surface may provide a H-terminated surface. In some embodiments, for example, a first surface may be contacted with HF, such as 0.5% HF, prior to or at the beginning of the metal silicide deposition process in order to increase or enhance deposition of the metal silicide on the first surface relative to the second, different surface. In some embodiments treatment of the first surface may comprise an optional in-situ or clustered native oxide removal process performed in the same reactor as the subsequent deposition, or in a separate reaction chamber from which the substrate can be transported to the deposition reactor without intermediate exposure to air, which could result in partial reoxidation or OH termination of the surface. The in-situ native oxide removal process which also provides a H-terminated surface may comprise, for example, exposure to HF vapor or H radicals. In some embodiments treatment of the first surface can include contacting the substrate with one of either the first or second precursors used in a subsequent deposition process prior to or at the beginning of the deposition process. 
         [0024]    In some embodiments a metal silicide material or thin film is deposited on a first H-terminated surface of a substrate relative to a second, different surface, and the second, different surface is oxidized prior to or at the beginning of the deposition process in order to decrease or inhibit deposition of the metal silicide on the second surface relative to the first, H-terminated surface. That is, selective deposition on the first, H-terminated surface is increased relative to the treated second, different surface. 
         [0025]    In some embodiments the first surface on which selective deposition of a metal silicide occurs comprises an H-terminated surface. In some embodiments the H-terminated first surface may comprise silicon and/or germanium. That is, the first surface may comprise H-terminated silicon and/or germanium. In some embodiments the first surface is formed by etching native oxide of silicon and/or germanium and the first surface comprises Si—H and/or Ge—H bonds. In some embodiments the first surface may be a —SiH, —SiH 2 , —SiH 3 , —GeH, —GeH 2 , or —GeH 3  surface. In some embodiments the first surface is a pure silicon and/or germanium surface. 
         [0026]    In some embodiments the second, different surface may comprise, for example, different surface terminations from the first surface, and/or a different material composition from the first surface. In some embodiments the second surface comprises an oxide, nitride, oxynitride, or carbide surface. In some embodiments the second surface may comprise, for example, silicon oxides, silicon nitrides, germanium oxides, germanium nitrides, titanium oxides, titanium nitrides, hafnium oxides, and/or hafnium nitrides. In some embodiments a second surface may be a native oxide surface, for example a native silicon oxide surface. In some embodiments the second surface may comprise a thermal oxide, for example a thermal silicon oxide surface. In some embodiments a second surface is oxidized prior to or at the beginning of the deposition process to provide an oxide, nitride, oxynitride, or carbide surface. For example, in some embodiments a TiN surface may be oxidized to provide a titanium oxide surface prior to or at the beginning of the deposition process. 
         [0027]    In some embodiments a metal silicide selectively formed or deposited on a first surface relative to a second, different surface may comprise, for example, tantalum silicide (TaSi x ), titanium silicide (TiSi x ), and/or niobium silicide (NbSi x ). In some embodiments the deposited metal silicide film or material may comprise a low resistivity film or material. 
         [0028]    In some embodiments the deposited metal silicide material may have low resistivity. In some embodiments the deposited metal silicide material may have a resistivity of between about 150 μΩcm to about 300 μΩcm, preferably from about 150 μΩcm to about 250 μΩcm. 
         [0029]    In some embodiments the selective deposition processes disclosed herein do not utilize plasma, such as direct plasma. In some instances, however, a selective formation process could utilize radicals made by plasma as a reactant. The radicals are preferably not too energetic and thus do not significantly destroy or degrade a surface of the substrate. Typically direct plasma can harm the second surface of the substrate too significantly to be useful, and thus is not used in some embodiments. 
         [0030]    In some embodiments deposition on the first surface of the substrate occurs selectively relative to deposition on the second surface of the substrate. In some embodiments selectivity may be measured in terms of, for example, the thickness or mass of material deposited on the first surface of a substrate relative to the second surface. In some embodiments selectivity may be measured in terms of, for example, the area of the first and second surfaces covered by deposited material. Unless indicated otherwise, selectivity is measured in terms of thickness of material deposited on the first surface of the substrate relative to the second surface. 
         [0031]    In some embodiments deposition on the first surface of the substrate relative to the second surface of the substrate is at least about 90% selective, at least about 95% selective, at least about 96%, 97%, 98% or 99% or greater selective. In some embodiments deposition only occurs on the first surface and does not occur on the second surface. In some embodiments deposition on the first surface of the substrate relative to the second surface of the substrate is at least about 80% selective, or about 70% selective, which may be selective enough for some particular applications. In some embodiments the deposition on the first surface of the substrate relative to the second surface of the substrate is at least about 50% selective, which may be selective enough for some particular applications. 
         [0032]    In some embodiments an etch step may be used subsequent to or in the course of deposition to remove material that is non-selectively deposited. Although addition of an etch step would typically add cost and complexity to the process, in some situations it may be commercially desirable, for example if it is less expensive overall than other options. In some embodiments the etch process may be a wet etch process or a dry etch process. 
         [0033]    In some embodiments deposition on the first surface of the substrate relative to the second surface of the substrate can be performed up to about 100 deposition cycles before losing the desired selectivity, or up to about 50 deposition cycles, or up to about 20 deposition cycles, or up to about 10 deposition cycles, or up to about 5 deposition cycles before losing selectivity. In some embodiments even deposition of 1 or 2 cycles before losing selectivity can be useful. 
         [0034]    A loss of selectivity can be understood to have occurred when the selectivities mentioned above are no longer met. Depending on the specific circumstances, a loss of selectivity may be considered to have occurred when deposition on the first surface of the substrate relative to the second surface of the substrate is less than about 50% selective, 70% selective, 80% selective, or 90% selective, less than about 95% selective, less than about 96%, 97%, 98% or 99% selective or greater. 
         [0035]    Although certain embodiments may have a lower selectivity than certain other embodiments, other processes, for example, an etch, may optionally be used to remove undesirably deposited material from at least the second surface in those relatively lower selectivity embodiments. 
         [0036]    In some embodiments deposition on the first surface of the substrate relative to the second surface of the substrate can be performed up to a thickness of about 50 nm before losing the desired selectivity, or up to about 15 nm, or up to 10 nm, or up to about 5 nm, or up to about 3 nm, or up to about 2 nm, or up to about 1 nm before losing the desired selectivity. In some embodiments even deposition of up to 3 Å or 5 Å before losing the desired selectivity can be useful. Depending on the specific circumstances, a loss of selectivity may be considered to have occurred when deposition on the first surface of the substrate relative to the second surface of the substrate is less than about 90% selective, less than about 95% selective, less than about 96%, 97%, 98% or 99% selective or greater. 
         [0037]    In some embodiments a metal silicide film or material is deposited according to a process described herein and the deposition process is not a selective deposition process. For example, in some embodiments a metal silicide film may be deposited on a first surface H-terminated of a substrate and a second oxide, nitride, oxynitride, or carbide surface of the same substrate. That is, in some embodiments deposition on a first surface is about 0% selective relative to a second, different surface. 
         [0038]    In some embodiments the selective deposition process is an atomic layer deposition (ALD) type process. In some embodiments the deposition process is a pure ALD process. In some embodiments the deposition process is a vapor deposition process comprising one or more deposition cycles in which a substrate is alternately and sequentially contacted with a first vapor phase reactant and a second vapor phase reactant. 
       ALD Type Processes 
       [0039]    ALD type processes are based on controlled, self-limiting surface reactions of precursor chemicals. Gas phase reactions are avoided by alternately and sequentially contacting the substrate with the precursors. Vapor phase reactants are separated from each other on the substrate surface, for example, by removing excess reactants and/or reactant byproducts from the reaction chamber between reactant pulses. 
         [0040]    Briefly, a substrate comprising at least a first surface and a second, different surface is heated to a suitable deposition temperature, generally at lowered pressure. Deposition temperatures are generally maintained below the thermal decomposition temperature of the reactants but at a high enough level to avoid condensation of reactants and to provide the activation energy for the desired surface reactions. Of course, the appropriate temperature window for any given ALD reaction will depend upon the surface terminations and reactant species involved. Here, the temperature may vary depending on the type of film being deposited and is preferably at or below about 500° C., more preferably at or below about 450° C. and most preferably from about 250° C. to about 400° C. 
         [0041]    The surface of the substrate is contacted with a vapor phase first reactant or precursor. In some embodiments a pulse of vapor phase first reactant is provided to a reaction space containing the substrate. In some embodiments the substrate is moved to a reaction space containing vapor phase first reactant. Conditions are preferably selected such that no more than about one monolayer of the first reactant is adsorbed on the substrate surface in a self-limiting manner. The appropriate contacting times can be readily determined by the skilled artisan based on the particular circumstances. Excess first reactant and reaction byproducts, if any, are removed from the substrate surface, such as by purging with an inert gas or by removing the substrate from the presence of the first reactant. 
         [0042]    Purging means that vapor phase precursors and/or vapor phase byproducts are removed from the substrate surface such as by evacuating a chamber with a vacuum pump and/or by replacing the gas inside a reactor with an inert gas such as argon or nitrogen. Typical purging times are from about 0.05 to 20 seconds, more preferably between about 1 and 10, and still more preferably between about 1 and 2 seconds. However, other purge times can be utilized if necessary, such as where highly conformal step coverage over extremely high aspect ratio structures or other structures with complex surface morphology is needed. 
         [0043]    The surface of the substrate is contacted with a vapor phase second gaseous reactant or precursor. In some embodiments a pulse of a second gaseous reactant is provided to a reaction space containing the substrate. In some embodiments the substrate is moved to a reaction space containing the vapor phase second reactant. Excess second reactant and gaseous byproducts of the surface reaction, if any, are removed from the substrate surface. The steps of contacting and removing are repeated until a thin film of the desired thickness has been selectively formed on the first surface of substrate, with each cycle leaving no more than a molecular monolayer. Additional phases comprising alternately and sequentially contacting the surface of a substrate with other reactants can be included to form more complicated materials, such as ternary materials. 
         [0044]    As mentioned above, each phase of each cycle is preferably self-limiting. An excess of reactant precursors is supplied in each phase to saturate the susceptible structure surfaces. Surface saturation ensures reactant occupation of all available reactive sites (subject, for example, to physical size or “steric hindrance” restraints) and thus ensures excellent step coverage. Typically, less than one molecular layer of material is deposited with each cycle, however, in some embodiments more than one molecular layer is deposited during the cycle. 
         [0045]    Removing excess reactants can include evacuating some of the contents of a reaction space and/or purging a reaction space with helium, nitrogen or another inert gas. In some embodiments purging can comprise turning off the flow of the reactive gas while continuing to flow an inert carrier gas to the reaction space. 
         [0046]    The precursors employed in the ALD type processes may be solid, liquid or gaseous materials under standard conditions (room temperature and atmospheric pressure), provided that the precursors are in vapor phase before they are contacted with the substrate surface. Contacting a substrate surface with a vaporized precursor means that the precursor vapor is in contact with the substrate surface for a limited period of time. Typically, the contacting time is from about 0.05 to 10 seconds, preferably between about 0.5 and 5 seconds. However, depending on the substrate type and its surface area, the contacting time may be even higher than 10 seconds. Contacting times can be on the order of minutes in some cases. The optimum contacting time can be determined by the skilled artisan based on the particular circumstances. 
         [0047]    The mass flow rate of the precursors can also be determined by the skilled artisan. In some embodiments the flow rate of metal precursors is preferably between about 1 and 1000 sccm without limitation, more preferably between about 100 and 500 sccm. 
         [0048]    The pressure in a reaction chamber is typically from about 0.01 to about 20 mbar, more preferably from about 1 to about 10 mbar. However, in some cases the pressure will be higher or lower than this range, as can be determined by the skilled artisan given the particular circumstances. 
         [0049]    Before starting the deposition of the film, the substrate is typically heated to a suitable growth temperature. The growth temperature varies depending on the type of thin film formed, physical properties of the precursors, etc. The growth temperatures are discussed in greater detail below in reference to each type of thin film formed. The growth temperature can be less than the crystallization temperature for the deposited materials such that an amorphous thin film is formed or it can be above the crystallization temperature such that a crystalline thin film is formed. The preferred deposition temperature may vary depending on a number of factors such as, and without limitation, the reactant precursors, the pressure, flow rate, the arrangement of the reactor, crystallization temperature of the deposited thin film, and the composition of the substrate including the nature of the material to be deposited on. The specific growth temperature may be selected by the skilled artisan. 
         [0050]    In some embodiments the growth rate of the metal silicide film on the first surface of the substrate may be greater than or equal to about 0.5 Å/cycle, greater than or equal to about 2 Å/cycle, greater than or equal to about 5 Å/cycle, and, in some embodiments, even greater than about 10 Å/cycle. 
         [0051]    In some embodiments the deposited metal silicide films are highly conformal. In some embodiments, the metal silicide film formed has step coverage of more than about 50%, more than about 80%, more than about 90%, or even more than about 95% on structures which have high aspect ratios. In some embodiments high aspect ratio structures have an aspect ratio that is more than about 3:1 when comparing the depth or height to the width of the feature. In some embodiments the structures have an aspect ratio of more than about 5:1, or even an aspect ratio of 10:1 or greater. 
         [0052]    In some embodiments the metal silicide film or material formed may be a relatively pure metal silicide film. In some embodiments, the metal silicide film comprises less than about 5-at % of any impurity other than hydrogen, preferably less than about 3-at % of any impurity other than hydrogen, and more preferably less than about 1-at % of any impurity other than hydrogen. In some embodiments a metal silicide film comprises less than about 5 at-% fluorine, less than about 3 at-% fluorine less than about 2 at-% fluorine or even less than about 1 at-% fluorine. In some embodiments, a metal silicide film comprises less than about 2-at % oxygen, preferably less than about 1-at % or less than about 0.5-at % and even less than about 0.25-at %. In some embodiments, a metal silicide film comprises less than about 2-at % hydrogen, preferably less than about 1-at % or less than about 0.5-at % and even less than about 0.25-at %. In some embodiments, a metal silicide film comprises less than about 1-at % carbon, preferably less than about 0.5-at % or less than about 0.25-at % and even less than about 0.1-at %. 
         [0053]    Examples of suitable reactors that may be used include commercially available ALD equipment such as the F-120® reactor, Eagle® XP8, Pulsar® reactor and Advance® 400 Series reactor, available from ASM America, Inc. of Phoenix, Ariz., ASM Japan KK, Tokyo, Japan and ASM Europe B.V., Almere, Netherlands. In addition to these ALD reactors, many other kinds of reactors capable of ALD growth of thin films, including CVD reactors equipped with appropriate equipment and means for pulsing the precursors can be employed. In some embodiments a flow type ALD reactor is used. Preferably, reactants are kept separate until reaching the reaction chamber, such that shared lines for the precursors are minimized. 
         [0054]    The growth processes can optionally be carried out in a reactor or reaction space connected to a cluster tool. In a cluster tool, because each reaction space is dedicated to one type of process, the temperature of the reaction space in each module can be kept constant, which improves the throughput compared to a reactor in which is the substrate is heated up to the process temperature before each run. For example, a substrate may be subjected to a native oxide removal process in a first module of a cluster tool and may be subjected to a deposition process in a different module of the same tool. 
         [0055]    A stand-alone reactor can be equipped with a load-lock. In that case, it is not necessary to cool down the reaction space between each run. 
         [0056]    Referring to  FIG. 1  and according to some embodiments a substrate comprising a first H-terminated surface as described above, such as H-terminated silicon, and a second oxide, nitride, oxynitride, or carbide surface is provided at step  120 . A metal silicide is selectively deposited on the first surface of the substrate by an ALD type deposition process  100  comprising at least one deposition cycle comprising: 
         [0057]    contacting the substrate with a vaporized first silicon precursor at step  130 . The first silicon precursor may comprise a silane, for example disilane or trisilane; 
         [0058]    removing excess first precursor and reaction byproducts, if any, from the substrate at step  140 ; 
         [0059]    contacting the substrate with a vaporized second metal precursor at step  150 . The second metal precursor may comprise a metal halide, for example a Ta, Nb, or Ti halide; 
         [0060]    removing excess second precursor and reaction byproducts, if any, from the substrate at step  160 ; 
         [0061]    optionally repeating the contacting and removing steps at step  170  until a thin film comprising the selectively deposited metal silicide of the desired thickness has been formed. 
         [0062]    As mentioned above, in some embodiments one or more surfaces of the substrate may be treated in order to enhance deposition on the first surface relative to one or more different surfaces prior to or at the beginning of deposition process  100 . In  FIG. 1  this is indicated by step  110  in which the first and/or second surface may optionally be treated. In some embodiments the first surface may be treated to provide H-terminations. For example, the first surface may be contacted with HF to provide a surface comprising H-terminations, for example a —SiH 3  terminations. In some embodiments the second surface may be treated to oxidize the second surface. For example, the second surface may be exposed to ambient conditions to thereby provide an oxidized surface, for example an oxidized TiN surface. 
         [0063]    Although the illustrated deposition cycle begins with contacting the surface of the substrate with the first silicon precursor, in other embodiments the deposition cycle begins with contacting the surface of the substrate with the second metal precursor. It will be understood by the skilled artisan that in general contacting the substrate surface with the first precursor and second precursor are interchangeable in the ALD cycle. 
         [0064]    In some embodiments, the reactants and reaction by-products can be removed from the substrate surface by stopping the flow of first precursor while continuing the flow of an inert carrier gas such as nitrogen or argon. 
         [0065]    In some embodiments, the precursor and reaction by-products can be removed from the substrate by stopping the flow of precursor while continuing the flow of an inert carrier gas. In some embodiments the substrate is moved such that different precursors alternately and sequentially contact the substrate in a desired sequence for a desired time. In some embodiments the removing steps,  140  and  160  are not performed. In some embodiments no precursor may be removed from the various parts of a chamber. In some embodiments the substrate is moved from a part of the chamber containing a first precursor to another part of the chamber containing the second precursor. In some embodiments the substrate is moved from a first reaction chamber to a second, different reaction chamber. 
         [0066]    In some embodiments each reaction is self-limiting and monolayer by monolayer growth is achieved. These may be referred to as “true ALD” reactions. In some such embodiments the first precursor (or other precursor as described herein) may adsorb on the first surface of the substrate in a self-limiting manner. A second precursor in turn will react with the adsorbed first precursor to form up to a monolayer of metal silicide on the first surface of the substrate. 
         [0067]    However, in some embodiments ALD-type reactions are provided, in which there may be some precursor decomposition, but the growth saturates. That is, in some embodiments although a certain amount of film growth may be caused by thermal decomposition of the first precursor (or second precursor as described herein) at some deposition temperatures, saturated growth is preferably achieved when the second precursor is utilized. Such a reaction is an example of an ALD-type reaction. In such ALD-type reactions, films with good uniformity and relatively few impurities can be deposited. 
         [0068]    In some embodiments the metal silicide is deposited to be a distinct layer from the substrate, meaning that no material from the substrate is consumed to form the metal silicide, except that some bonds may form between the substrate and the metal silicide. In some embodiments the selectively deposited material is not annealed in order to form a metal silicide material. 
         [0069]    In some embodiments a distinct metal silicide layer is formed on the substrate surface and the metal silicide layer may subsequently be annealed or subjected to an annealing process. An annealing process may result in some consumption of the substrate and/or the formation of bonds between the metal silicide layer and the substrate. In some embodiments bonds may be formed between the substrate and the metal silicide during the annealing process. In some embodiments an annealing process performed subsequent to the formation of a distinct metal silicide layer on the substrate surface may reduce the contact resistance between the metal silicide and the substrate. In some embodiments where some of the substrate may be consumed during an annealing process, the amount of substrate consumed may be limited such that it does not result in undesirable or degraded device performance, for example by reducing the contact area or device cross-section. In some embodiments where consumption of the substrate may occur during an annealing process the consumption can be limited by regulating the time and temperature of the annealing process as would be clear to one of skill in the art. In some embodiments the amount of substrate consumer by an annealing process may be limited by the amount of excess metal present in the deposited metal silicide film. In some embodiments the amount of excess metal in the metal silicide film may be controlled by adjusting the composition of the metal silicide film, as would be clear to one of skill in the art, for example by adjusting the flow rate of one or more of the vapor phase precursors in the metal silicide deposition process to provide a metal silicide film with the desired amount of excess metal. In some embodiments the amount of excess metal may be controlled by regulating the total thickness of the deposited metal silicide film, as would be clear to one of skill in the art. 
         [0070]    Referring to  FIG. 2  and according to some embodiments a substrate comprising a first H-terminated surface as described above, such as H-terminated silicon, and a second oxide, nitride, oxynitride, or carbide surface, such as TiN, is provided at step  220 . A material comprising tantalum silicide is selectively deposited on the first surface of the substrate by an ALD type deposition process  200  comprising at least one deposition cycle comprising: 
         [0071]    contacting the substrate with a vaporized first silicon precursor at step  230 . The first silicon precursor may comprise a silane, for example disilane or trisilane; 
         [0072]    removing excess first precursor and reaction byproducts, if any, from the substrate at step  240 ; 
         [0073]    contacting the substrate with a vaporized second tantalum precursor at step  250 . The second tantalum precursor may comprise a tantalum halide, for example TaCl 5  or TaF 5 ; 
         [0074]    removing excess second precursor and reaction byproducts, if any, from the substrate at step  260 ; 
         [0075]    optionally repeating the contacting and removing steps at step  270  until a thin film comprising the selectively deposited metal silicide of the desired thickness has been formed. 
         [0076]    As mentioned above, in some embodiments one or more surfaces of the substrate may be treated in order to enhance deposition on the first surface relative to one or more different surfaces prior to or at the beginning of deposition process  200 . In  FIG. 2  this is indicated by step  210  in which the first and/or second surface may optionally be treated. In some embodiments the first surface may be treated to provide H-terminations. For example, the first surface may be contacted with HF to provide a surface comprising H-terminations, for example a —SiH 3  terminations. In some embodiments the second surface may be treated to oxidize the second surface. For example, the second surface may be exposed to ambient conditions to thereby provide an oxidized surface, for example an oxidized TiN surface. 
         [0077]    According to some embodiments a substrate comprising a first H-terminated surface as described above, such as H-terminated silicon, and a second oxide, nitride, oxynitride, or carbide surface is provided. The substrate may then be pretreated with a vapor phase halide or silane precursor. In some embodiments the pretreatment may activate the first surface H-terminated surface in order to enhance deposition on the first surface relative to the second surface. A metal silicide is selectively deposited on the first surface of the substrate by an ALD type deposition process comprising at least one deposition cycle comprising: 
         [0078]    contacting the substrate with a vaporized first silicon precursor, wherein the first silicon precursor may comprise a silane, for example disilane or trisilane; 
         [0079]    removing excess first precursor and reaction byproducts, if any, from the substrate; 
         [0080]    contacting the substrate with a vaporized second metal precursor, wherein the second metal precursor may comprise a metal halide, for example a Ta, Nb, or Ti halide; 
         [0081]    removing excess second precursor and reaction byproducts, if any, from the substrate; 
         [0082]    optionally repeating the contacting and removing steps until a thin film comprising the selectively deposited metal silicide of the desired thickness has been formed. 
         [0083]    In some embodiments pretreating the substrate with a vapor phase halide or silane precursor may comprise contacting the substrate surface with vapor phase halide or silane precursor. In some embodiments the silane precursor may comprise disilane or trisilane. In some embodiments the halide precursor may comprise a metal halide precursor, for example the metal halide precursor used in the metal silicide deposition process. In some embodiments the halide precursor may comprise one of TaF 5 , TaCl 5 , NbF 5 , NbCl 5 , TiF 3 , TiBr 3 , and TiCl 3 . In some embodiments the pretreatment may activate the first surface in order to enhance deposition on the first surface relative to the second surface. In some embodiments pretreating the substrate may provide reactive sites on the first surface to react with the first vaporized precursor of the ALD process. In some embodiments the precursor used in the pretreatment step may be the same as a precursor used in the ALD process. In some embodiments the precursor used in the pretreatment step may not be the same as the first vapor phase precursor of the ALD process. 
       Silicon Precursors 
       [0084]    In some embodiments a silicon precursor is provided to the substrate such that a layer is formed on a first surface of the substrate relative to a second, different surface of the substrate. In some embodiments the silicon precursor is selected from the silane family Si n H 2n+2  (where n is equal to or greater than 1). In some embodiments the silicon precursor may comprise monosilane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), or tetrasilane (Si 4 H 10 ), preferably disilane or trisilane. In some embodiments the silicon precursor can be selected from silane compounds having the formula: SiH x L y , where L is a ligand selected from the groups including: alkyl, alkenyl, alkynyl, alkoxide, and amine. In some cases L is a ligand selected from the halide group: F, Cl, Br and I. In some embodiments the silicon precursor may comprise dichlorosilane (SiH 2 Cl 2 , or ‘DCS’). 
       Metal Precursors 
       [0085]    In some embodiments the metal precursor comprises a metal halide. In some embodiments the metal precursor preferably comprises fluorine. In some embodiments the metal of the metal precursor comprises Ta, Nb, or Ti. In some embodiments the metal precursor is selected from TaF 5  and TaCl 5 . In some embodiments the metal precursor is selected from NbF 5  and NbCl 5 . In some embodiments the metal precursor is selected from TiF 3 , TiBr 3 , and TiCl 3 . 
       EXAMPLE 
       [0086]    In this example tantalum silicide (TaSi x ) was selectively deposited on a first substrate comprising an H-terminated silicon surface relative to a substrate comprising a native silicon oxide surface, a substrate comprising a 1000 Å thick thermal oxide surface, and a substrate comprising a 15 Å TiN surface on thermal oxide on silicon. The substrate comprising a 15 Å TiN surface on thermal oxide on silicon was exposed to ambient conditions prior to the deposition process. The first substrate comprised an H-terminated silicon wafer, that is, the surface of the first substrate comprised Si—H terminations. 
         [0087]    TaSi x  was deposited on the first substrate by an ALD process as described herein in an EmerALD™ ALD tool. The deposition process included 30 deposition cycles carried out at a deposition temperature of about 300° C. The sample TaSi x  material was deposited using disilane as a silicon precursor and TaF 5  as a metal precursor. Each deposition cycle included a contacting time of about 0.6 seconds for the silicon precursor and a contacting time of about 2 seconds for the metal precursor. A second sample was also prepared using the above described deposition process and including 150 deposition cycles. 
         [0088]    A four point probe sheet resistance measurement was taken for both TaSi x  samples deposited on H-terminated silicon. The sheet resistance measurements showed low conductivity, about 30 ohm/sq for the TaSi x  sample deposited using 150 deposition cycles, and about 300 ohm/sq for the sample deposited using 30 deposition cycles, which was indicative of relatively uniform TaSi x  film deposition. X-ray spectroscopy was used to confirm deposition of a TaSix film on the H-terminated silicon substrates. The TaSi x  film was found to be about 16.9 nm thick for the sample formed by an ALD process comprising 30 deposition cycles. A scanning electron microscope (SEM) was also confirmed the presence of the TaSi x  film.  FIG. 3A  shows an SEM image of the TaSi x  film formed by an ALD process comprising 30 deposition cycles. 
         [0089]    The substrate comprising a native silicon oxide surface, the substrate comprising a thermal oxide surface, and the substrate comprising a 15 Å TiN surface on thermal oxide on silicon were likewise each subjected to an identical ALD process as used to deposit TaSi x  on H-terminated silicon and described above, the ALD process comprising 30 deposition cycles. A four point probe sheet resistance measurement was taken for each substrate subsequent to the deposition processes and no conductivity was measured. This result indicates that no TaSi x  film was deposited on the substrates. X-ray spectroscopy further confirmed that no film had been deposited.  FIG. 3B  shows an SEM image of the substrate comprising a 15 Å TiN surface on thermal oxide on silicon subsequent to the ALD process. No TaSi x  film can be seen.  FIG. 3C  shows an SEM image of the substrate comprising a native silicon oxide surface subsequent to the ALD process. TaSi x  island growth can be observed on the substrate, but no film is observed.  FIG. 3D  shows an SEM image of the substrate comprising a thermal oxide surface subsequent to the ALD process. TaSi x  island growth can be observed on the substrate, but no film is observed. 
       Integration 
       [0090]    The metal silicide films of the present disclosure may be used in a variety of semiconductor applications. In some embodiments a metal silicide material of the present disclosure may be advantageously used as, for example, a gate metal or an ohmic contact layer, such as an ohmic contact to source/drain electrodes. For example, metal silicide films may be particularly useful as a contact layer in a FinFET device. A metal silicide contact layer selectively deposited according to the processes described herein may allow for an increased contact area as compared to a contact layer formed by a different process, such as a reductive contact layer formation process. 
         [0091]    Referring to  FIG. 4 , an exemplary process flow  400  for the formation of a metal silicide contact layer in, for example, a FinFET device. In some embodiments the formation of a contact comprising a metal silicide contact layer proceeds as follows: 
         [0092]    a suitable substrate comprising a first surface, such as a silicon or germanium source/drain, and at least a second, different surface is provided at step  410 ; 
         [0093]    the substrate is optionally subjected to a treatment process or processes, either ex situ or in situ at step  420 ; 
         [0094]    a metal silicide film is selectively deposited on the first surface of the substrate provided at step  410 , said first surface comprising H-terminations, by an ALD process as described herein at step  430 ; 
         [0095]    a liner, for example a TiN liner is deposited over the metal silicide contact layer at step  440 , for example by a physical vapor deposition (PVD) process; 
         [0096]    a low resistivity material, for example W metal, is deposited over the liner at step  450  to thereby form a contact structure; and 
         [0097]    any further layers or processing as desired are formed on top of the contact structure in subsequent processing steps at step  460 . 
         [0098]    According to some embodiments a suitable substrate may comprise a semiconductor substrate comprising a first surface and a second, different surface. In some embodiments a first surface of the substrate provided at step  410  can comprise a source/drain region. In some embodiments the source/drain surface may be located in, for example, a contact trench on a substrate. The surface of the source/drain region may comprise silicon and/or germanium. 
         [0099]    In some embodiments the substrate can further include at least a second, different surface, for example a contact trench sidewall. In some embodiments a second, different surface may comprise an oxide, nitride, oxynitride, or carbide surface. In some embodiments the second surface may comprise, for example, silicon oxides, silicon nitrides, germanium oxides, germanium nitrides, titanium oxides, titanium nitrides, hafnium oxides, and/or hafnium nitrides. In some embodiments a second surface may be a native oxide surface, for example a native silicon oxide surface. In some embodiments the second surface may comprise a thermal oxide, for example a thermal silicon oxide surface. 
         [0100]      FIG. 4  illustrates an optional treatment process or processes at step  420 . A treatment process may be used for any number of reasons, including cleaning the substrate surface, removing native oxide, and/or providing desirable surface terminations on a surface or surfaces of the substrate. In some embodiments an optional treatment process  420  may comprise treating, or activating, the first surface in order to enhance deposition on the first surface relative to the second surface. In some embodiments an optional treatment process  420  may comprise treating, or deactivating, the second surface in order to decrease or inhibit deposition on the second surface relative to the first surface. In some embodiments an optional treatment process  420  may comprise treating the first surface to enhance deposition and treating the second surface to inhibit deposition, thereby increasing selective deposition on the first surface relative to the second surface. In some embodiments an optional treatment process  420  does not involve formation of a self-assembled monolayer (SAM). In some embodiments an optional treatment process  420  does not comprise treatment with an organic agent. 
         [0101]    For example, in some embodiments an optional treatment process  420  may comprise treating the first surface of the substrate to provide a H-terminated surface. In some embodiments, for example, an optional treatment process  420  can remove a native oxide layer present on the first surface. In some embodiments where a native oxide may be present on the first surface the optional treatment process  420  may comprise removing the native oxide by a clustered native oxide removal process. In some embodiments an optional treatment process  420  may remove a native oxide layer from the first surface and may also provide a H-terminated surface. In some embodiments, for example, an optional treatment process  420  may comprise contacting the first surface with HF, such as 0.5% HF in order to provide an H-terminated surface. In some embodiments an optional treatment process  420  may comprise contacting the substrate with one of either the first or second precursors of the metal silicide deposition process. In some embodiments an optional treatment process  420  may comprise oxidizing the second surface, for example by exposing the second surface to ambient conditions and/or moisture. 
         [0102]    Subsequent to any optional treatment process or processes  420 , a metal silicide contact layer is selectively formed on the first surface of the substrate relative to a second surface at step  430  by an ALD type process as described herein. In some embodiments a suitable metal silicide contact layer is one that comprises a metal silicide. Suitable metal silicides include those where the metal is selected from Ta, Nb, and Ti. Suitable metal silicides include, for example, those with a formula TaSi x , NbSi x , and TiSi x . In some embodiments the metal silicide contact layer is deposited to be a distinct layer from the substrate, meaning that no material from the substrate is consumed for the metal silicide contact layer, except that some bonds may form between the substrate and the metal silicide contact layer. 
         [0103]    In some embodiments step  430  may include subjecting the deposited metal silicide contact layer to an annealing process. An annealing process may result in some consumption of the substrate and/or the formation of bonds between the metal silicide contact layer and the substrate. In some embodiments bonds may be formed between the substrate and the metal silicide contact layer during the annealing process. In some embodiments an annealing process performed subsequent to the formation of a distinct metal silicide layer on the substrate surface may reduce the contact resistance between the metal silicide contact layer and the substrate. In some embodiments where some of the substrate may be consumed during an annealing process, the amount of substrate consumed may be limited such that it does not result in undesirable or degraded device performance, for example by reducing the contact area or device cross-section. 
         [0104]    In some embodiments, the metal silicide film is deposited to achieve a particular thickness. Suitable thicknesses may be greater than or equal to about 0.5 nm and less than or equal to about 10 nm. In some embodiments, the thickness will be between about 1 nm and about 5 nm. In to some embodiments, the suitable thickness will be one that achieves a complete layer over the substrate surface (i.e., one that leaves no gaps). Accordingly, the actual thickness that achieves a complete layer may depend on the type of metal silicide formed and the types of precursors used to achieve the metal silicide. 
         [0105]    The first surface comprises an H-terminated surface. In some embodiments the first surface may comprise a three-dimensional structure. In some embodiments the H-terminated first surface may comprise silicon and/or germanium. That is, the first surface may comprise H-terminated silicon and/or germanium. In some embodiments the first surface may be formed by etching native oxide of silicon and/or germanium, for example by an optional treatment process at step  420 , and the first surface comprises Si—H and/or Ge—H bonds. In some embodiments the first surface may be a —SiH, —SiH 2 , —SiH 3 , —GeH, —GeH 2 , or —GeH 3  surface. In some embodiments the first surface is a pure silicon and/or germanium surface. In some embodiments the first surface may comprise a source/drain structure. 
         [0106]    In some embodiments the deposited metal silicide films are highly conformal. In some embodiments, the metal silicide film formed has step coverage of more than about 50%, more than about 80%, more than about 90%, or even more than about 95% on structures which have high aspect ratios. In some embodiments high aspect ratio structures have an aspect ratio that is more than about 3:1 when comparing the depth or height to the width of the feature. In some embodiments the structures have an aspect ratio of more than about 5:1, or even an aspect ratio of 10:1 or greater. 
         [0107]    In some embodiments, subsequent to forming a metal silicide contact layer a liner, for example a TiN liner, is formed over the metal silicide contact layer at step  440 . In some embodiments the liner may be formed by a PVD process. In some embodiments the liner may be formed by other processes, such as ALD, CVD, or PEALD. A liner may be desirable in some embodiments, for example to prevent diffusion of metallic elements of a subsequently formed overlying layer into underlying layers and/or to decrease contact resistance to the metal silicide layer. In some embodiments a subsequently deposited or formed low resistivity material may serve as a liner. In some embodiments the liner may protect the metal silicide contact layer during transport or subsequent processing. 
         [0108]    In some embodiments a low resistivity material, for example a metal, such as W metal, may be deposited over the liner and metal silicide layer at step  450  to thereby form a contact structure. The low resistivity material may be deposited or formed according to any method known in the art or developed in the future. For example, W metal may be deposited over the metal silicide contact layer and liner by a PVD process. Other exemplary low resistivity materials may include, for example, metal silicides. 
         [0109]    In some embodiments, subsequent processing may occur at step  460  after the formation of the contact structure. For example, additional layers may be formed or patterning of the deposited layers may occur. In some embodiments, the process is used in the formation of semiconductor device, such as a FinFET device. 
         [0110]    In some embodiments, a process such as the one outlined above, is performed in situ or in a cluster tool. In some embodiments, only the metal silicide formation is performed in situ. In some cases, the substrate may be transferred between tools. 
         [0111]    It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. The described features, structures, characteristics and precursors can be combined in any suitable manner. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. All modifications and changes are intended to fall within the scope of the invention, as defined by the appended claims.