Patent Publication Number: US-2022216060-A1

Title: Conformal and smooth titanium nitride layers and methods of forming the same

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
     This application is a continuation in part of U.S. application Ser. No. 17/547,086, filed Dec. 9, 2021, entitled “CONFORMAL AND SMOOTH TITANIUM NITRIDE LAYERS AND METHODS OF FORMING THE SAME,” which is a continuation in part of U.S. application Ser. No. 16/595,945, filed Oct. 8, 2019, entitled “CONFORMAL AND SMOOTH TITANIUM NITRIDE LAYERS AND METHODS OF FORMING THE SAME.” The U.S. application Ser. No. 17/548,086 claims the priority benefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63/123,733, filed Dec. 10, 2020, entitled “CONFORMAL AND SMOOTH TITANIUM NITRIDE LAYERS AND METHODS OF FORMING THE SAME,” and this application claims the priority benefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63/164,219, filed Mar. 22, 2021, entitled “CONFORMAL AND SMOOTH TITANIUM NITRIDE LAYERS AND METHODS OF FORMING THE SAME.” The content of each of the above applications is hereby expressly incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The disclosed technology generally relates to forming a titanium nitride layer, and more particularly to a conformal and smooth titanium nitride layer. 
     Description of the Related Art 
     Titanium nitride (TiN) has been widely used in fabrication of various structures in integrated circuits (ICs). For example, TiN has been used in diffusion barriers, various electrodes and metallization structures. Such wide usage of TiN in IC fabrication can be attributed to its structural, thermal and electrical properties. As the dimensions of various IC structures shrink, TiN is formed on features having increasingly smaller dimensions and complex topologies. For example, as the technology node scales to 10 nm node and beyond, there is a need for TiN layers, e.g., as diffusion barriers, that can conformally line high aspect ratio trenches and vias having dimensions as small as few nanometers. While techniques such as physical vapor deposition (PVD) and chemical vapor deposition (CVD) have been used in the IC industry to form TiN for decades, the increased need for conformality of TiN films to be deposited in smaller trenches or vias may eventually limit their usage. On the other hand, while atomic layer deposition (ALD) has been demonstrated for conformal deposition of TiN films, some electrical properties (e.g., conductivity) and physical properties (e.g., surface roughness) of the film may be inferior compared to TiN films formed using other methods such as physical vapor deposition (PVD). Thus, there is a need for high yield atomic layer deposition methods for forming TiN-based films with superior surface smoothness and step coverage, while also having matching or superior electrical and physical properties, relative to TiN films formed by PVD and CVD, for use in IC fabrication. 
     SUMMARY 
     In some aspects, the techniques described herein relate to a method of depositing a thin film including titanium nitride (TiN) by cyclical vapor deposition, the method including: forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each including an exposure to a Ti precursor and an exposure to ammonia (NH 3 ) at a first NH 3  flow rate; and after forming the TiN thin film, subjecting the semiconductor substrate, without deposition of an additional TiN thin film on the thin film, to a post-deposition exposure to NH 3  at a second NH 3  flow rate, wherein the second NH 3  flow rate is lower than the first NH 3  flow rate by at least a factor of two. 
     In some embodiments, the techniques described herein relate to a method, wherein the method is carried out in a thin film deposition system wherein, relative to a thin TiN film deposited in the same thin film deposition system using the method except for subjecting the semiconductor substrate to the post deposition exposure to NH3, a number of particles on or embedded in the TiN thin film having a size greater than 0.1 μm is reduced by 50% or more. 
     In some embodiments, the techniques described herein relate to a method, wherein forming the TiN thin film and subjecting the semiconductor substrate to a post-deposition exposure are performed at the same semiconductor substrate temperature. In some embodiments, the techniques described herein relate to a method, wherein the first NH 3  flow rate is 1000-3000 sccm, and the second NH 3  flow rate is 200-1000 sccm. 
     In some embodiments, the techniques described herein relate to a method, wherein a ratio of the first NH3 flow rate to the Ti precursor flow rate is 3 to 100. In some embodiments, the techniques described herein relate to a method, wherein the Ti precursor flow rate is 100 sccm-5000 sccm and lower than the first NH 3  flow rate. In some embodiments, the techniques described herein relate to a method, wherein a duration of each of the one or more cyclic vapor deposition cycles is less than 2.0 sec. 
     In some aspects, the techniques described herein relate to a method of depositing a thin film including titanium nitride (TiN) by cyclical vapor deposition, the method including: forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each including an exposure to a Ti precursor and an exposure to ammonia (NH 3 ) for a first NH 3  exposure duration; and after forming the TiN thin film, subjecting the semiconductor substrate, without deposition of an additional TiN thin film, to a post-deposition exposure of NH 3  for a second NH 3  exposure duration, wherein the second NH 3  exposure duration is greater than the first NH 3  exposure duration by at least a factor of five. 
     In some embodiments, the techniques described herein relate to a method, wherein the method is carried out in a thin film deposition system wherein, relative to a TiN thin film deposited in the same thin film deposition system using the method except for subjecting the semiconductor substrate to the post deposition exposure to NH 3 , a number of particles on or embedded in the TiN thin film having a size greater than 0.1 μm is reduced by 50% or more. In some embodiments, the techniques described herein relate to a method, wherein forming the TiN thin film and subjecting the formed TiN thin film to a post-deposition exposure are performed at the same semiconductor substrate temperature. In some embodiments, the techniques described herein relate to a method, wherein the first NH 3  exposure duration is 0.1-0.6 sec., and the second NH 3  exposure duration exceeds 1 sec. 
     In some aspects, the techniques described herein relate to a method of depositing a thin film including titanium nitride (TiN) by cyclical vapor deposition process, the method including: subjecting a thin film deposition chamber without a substrate disposed therein to a pre-deposition chamber purge with ammonia (NH 3 ) at a first NH 3  purge flow rate; transferring a semiconductor substrate into the thin film deposition chamber; and forming on the semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each including an exposure to a Ti precursor and an exposure to NH 3 . 
     In some embodiments, the techniques described herein relate to a method, wherein the method is carried out in the thin film deposition system wherein, relative to a TiN thin film deposited in the same thin film deposition system using the method except for subjecting the thin film deposition chamber to the pre-deposition NH 3  purge, a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% or more. In some embodiments, the techniques described herein relate to a method, wherein the first NH 3  purge flow rate exceeds 200 sccm. In some embodiments, the techniques described herein relate to a method, wherein the pre-deposition chamber purge is performed for a duration exceeding 1 sec. In some embodiments, the techniques described herein relate to a method, wherein the method is carried out in a process station of a thin film deposition system, wherein the thin film deposition system includes a plurality of process stations each configured to carry out the method. 
     In some embodiments, the techniques described herein relate to a method, wherein forming the TiN thin film includes exposing the semiconductor substrate to NH 3  at a second NH 3  flow rate of 500-10,000 sccm. In some embodiments, the techniques described herein relate to a method, wherein the one or more cyclical vapor deposition cycles includes exposure to the Ti precursor at a Ti precursor flow rate and exposure to ammonia (NH 3 ) at a second NH 3  flow rate such that a flow rate ratio of the second NH 3  flow rate to the Ti precursor flow rate is 3 to 100. 
     In some embodiments, the techniques described herein relate to a method, wherein forming the TiN thin film includes exposing the semiconductor substrate to the Ti precursor at the Ti precursor flow rate of 100 sccm-5000 sccm and lower than the second NH 3  flow rate. In some embodiments, the techniques described herein relate to a method, wherein a duration each of the one or more cyclical vapor deposition cycles is less than 2.0 sec. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1D  schematically illustrate nucleation and growth mechanisms of thin films under different growth modes. 
         FIG. 2  is a cross-sectional transmission electron micrograph of a TiN layer grown on an oxide-coated silicon substrate by thermal atomic layer deposition. 
         FIG. 3A  is a flow chart schematically illustrating an atomic layer deposition method of forming a TiN layer by exposing a substrate to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. 
         FIG. 3B  schematically illustrates a cross-sectional view of a semiconductor structure comprising a TiN layer formed by an atomic layer deposition method in which a substrate is exposed to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. 
         FIG. 4  schematically illustrates pressure traces of different cycles of an atomic layer deposition method in which a substrate is exposed to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. 
         FIG. 5  schematically illustrates a cross-sectional view of a via lined with a TiN layer having different thicknesses at different portions of the via. 
         FIG. 6  is a graph showing experimentally measured surface roughness and step coverage trends as functions of thickness for TiN layers formed by an atomic layer deposition method in which a substrate is exposed to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. 
         FIG. 7A  is a cross-sectional transmission electron micrograph of high aspect ratio vias lined with a TiN layer formed by an atomic layer deposition method in which a substrate is exposed to ALD cycles performed at the same precursor exposure pressure. 
         FIG. 7B  is a cross-sectional transmission electron micrograph an upper region of the high aspect ratio vias shown in  FIG. 7A . 
         FIG. 7C  is a cross-sectional transmission electron micrograph of a lower region of the high aspect ratio vias shown in  FIG. 7A . 
         FIG. 8A  is a cross-sectional transmission electron micrograph of a TiN layer formed at an upper region of a high aspect ratio via similar to that shown in  FIG. 7A  by an atomic layer deposition method in which a substrate is exposed to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. 
         FIG. 8B  is a cross-sectional transmission electron micrograph of a TiN layer formed at a lower region of the high aspect ratio via trench shown in  FIG. 8A . 
         FIG. 9  is a graph showing statistical comparison of measured step coverages between a TiN layer formed by atomic layer deposition at a single exposure pressure and a TiN layer formed by atomic layer deposition at a plurality of exposure pressures, according to embodiments. 
         FIG. 10  schematically illustrates a cross-sectional view of a via lined with a TiN layer formed by an atomic layer deposition method in which a substrate is exposed to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. 
         FIG. 11  is a flow chart schematically illustrating an atomic layer deposition method of forming a TiN layer having high (111) crystalline texture by exposing a substrate to a relatively high N precursor flow rate, according to embodiments. 
         FIG. 12A  illustrates experimental X-ray diffraction spectra of TiN thin films having varying degrees of (111) crystalline texture, according to embodiments. 
         FIG. 12B  is a graph illustrating the experimental ratios of a peak height of an X-ray diffraction peak corresponding to a (111) crystal orientation of TiN to a peak height of an X-ray diffraction peak corresponding to a (200) crystal orientation of TiN obtained from the X-ray diffraction spectra of  FIG. 12A . 
         FIG. 13  is a graph of experimental thickness and resistivity measurements of TiN thin films having increased (111) crystalline texture, according to embodiments. 
         FIG. 14  is a graph of experimental hardness and modulus measurements of TiN thin films having increased (111) crystalline texture, according to embodiments. 
         FIG. 15  is a graph of experimental hardness measurements of TiN thin films having increased (111) crystalline texture, according to embodiments. 
         FIG. 16  illustrates experimental X-ray diffraction spectra of TiN thin films formed at different exposure pressures and having increased (111) crystalline texture, according to embodiments. 
         FIG. 17  illustrates chlorine concentration depth profiles of TiN thin films having increased (111) crystalline texture, according to embodiments. 
         FIG. 18  schematically illustrates a thin film deposition system including a thin film deposition chamber and a precursor delivery system, according to embodiments. 
         FIG. 19  shows a perspective view of a lid of a process chamber comprising multiple processing stations, according to embodiments. 
         FIG. 20  schematically illustrates a precursor delivery sequence for forming TiN thin films, according to embodiments. 
         FIG. 21  is a flow chart schematically illustrating a method of forming a TiN layer by cyclical vapor deposition process with reduced particle generation, according to some embodiments. 
         FIG. 22  shows an experimental measurement of the number of particles on a 300 mm wafer after forming a TiN layer using the method illustrated in  FIG. 21 . 
         FIG. 23  is a flow chart schematically illustrating a method of forming a TiN layer by cyclical vapor deposition process with reduced particle generation, according to some other embodiments. 
         FIG. 24A  shows an experimental measurement of the number of particles on a 300 mm wafer after forming a TiN layer using the method illustrated in  FIG. 23 . 
         FIG. 24B  shows an experimental measurement of the number of particles on a 300 mm wafer after forming a TiN layer using the method illustrated in  FIG. 23 . 
         FIG. 25  is a flow chart schematically illustrating a method of forming a TiN layer by cyclical vapor deposition process with reduced particle generation, according to some other embodiments. 
         FIG. 26  shows an experimental measurement of the number of particles on a 300 mm wafer after forming a TiN layer using the method illustrated in  FIG. 25 . 
     
    
    
     DETAILED DESCRIPTION 
     As described above, there is a need in the integrated circuit (IC) industry for smooth and conformal TiN films with superior electrical and physical properties, as well as methods of forming such films. To address these and other needs, disclosed herein is a smooth and conformal thin film comprising TiN and a cyclical vapor deposition method of forming the thin film, which displays the conformality characteristic of a film deposited by cyclical vapor deposition processes, while also having electrical and physical properties that are superior or matching those of TiN films formed by existing physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods. In particular, a method of forming a thin film comprising titanium nitride (TiN) comprises forming on a semiconductor substrate a first portion of the thin film by exposing the semiconductor substrate to one or more first cyclical vapor deposition cycles each comprising an exposure to a first Ti precursor and an exposure to a first N precursor. The method additionally comprises forming on the first portion of the thin film a second portion of the thin film by exposing the semiconductor substrate to one or more second cyclical vapor deposition cycles each comprising an exposure to a second Ti precursor and an exposure to a second N precursor. The exposures to one or both of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles are different compared to corresponding exposures to one or both of the first Ti precursor and the first N precursor during the one or more first cyclical vapor deposition cycles. The cyclical vapor deposition processes disclosed herein are sometimes referred to as atomic layer deposition (ALD). However, cyclical vapor deposition processes are not limited to atomic layer deposition processes. For example, the precursors may partly or substantially saturate a reaction surface in various embodiments described herein. 
     By exposing the substrate to the Ti and/or N precursors at relatively low pressures, e.g., less than 3 torr, during deposition of the first portion of the thin film, the initial film growth may proceed substantially in a layer-by-layer growth mode, which advantageously results in an average grain size that lower and a surface roughness that is lower relative to a comparable TiN film that is deposited by exposing the substrate to the Ti and/or N precursors at higher pressures, e.g., greater than 3 torr or 5 torr. On the other hand, by exposing the substrate to the Ti and/or N precursors at relatively high pressures, e.g., greater than 3 torr, during deposition of the second portion of the thin film, the latter portion of the film growth advantageously results in a degree of conformality or a step coverage that is higher relative to a comparable TiN film that is deposited by exposing the substrate to the Ti and/or N precursors at the relatively low pressures, e.g., less than 3 torr or less than 1 torr. 
     In addition, because the first portion of the TiN film grows in a layer-by-layer mode, the second portion of the thin film may continue to grow, using the first portion as a template, in a layer-by-layer mode compared to a comparable thin film grown starting with exposures to the Ti and/or N precursors at relatively higher pressures. 
     As a net result, when deposited on certain surfaces, e.g., a surface comprising a non-metallic surface, the thin film comprising the first and second portions deposited by depositing at two different corresponding exposure pressures for one or both of the Ti precursor and the N precursor according to methods disclosed herein advantageously has a combination of surface roughness and conformality that is superior relative to a thin film layer formed on the same surface using a single pressure. Alternatively, or in addition, in part owing to the improved smoothness and conformality, the thin film has a relatively low electrical resistivity compared to TiN layers formed by some existing methods. 
     As described herein, a compound referred to by its constituent elements without specific stoichiometric ratios thereof shall be understood to encompass all possible nonzero concentrations of each element unless explicitly limited. For example, titanium nitride (TiN) shall be understood to encompass all possible stoichiometric and nonstoichiometric compositions of titanium nitride that can be expressed by a general formula Ti x N, where x&gt;0, including TiN, Ti 3 N 4 , Ti 4 N 3 , Ti 6 N 5 , Ti 2 N and TiN 2  as well as other non-stoichiometric compositions of Ti and N. 
     As described above, titanium nitride (TiN) plays an important role in integrated circuit (IC) fabrication. While techniques such as physical vapor deposition (PVD) and chemical vapor deposition (CVD) have been used in the IC industry to deposit TiN, the need for deposition methods for forming TiN-based films having high conformality without significant compromise in electrical and physical properties has been increasing. 
     In addition, while plasma-enhanced processes such as plasma enhanced atomic layer deposition (PE-ALD) may be effective in forming conformal films on surfaces having relatively low aspect ratios, such processes may not be effective in depositing films inside vias and cavities having relative high aspect ratios. Without being limited by theory, one possible reason for this is that a plasma or its actives species may not reach deeper portions of high aspect ratio vias under some circumstances. In these circumstances, different portions of vias may be exposed to different amounts of the plasma or its active species, leading to undesirable structural effects of non-uniform deposition, such as thicker films being deposited near the opening of the via compared to deeper portions (sometimes called cusping or keyhole formation). For these reasons, thermal ALD may be more advantageous, because thermal ALD does not depend on the ability of the plasma or its active species to reach portions of the surface being deposited on. 
     However, while thermal ALD techniques may be suitable for forming relatively conformal TiN films on topography, particularly topography with relatively high aspect ratios (e.g., over 1:1), the inventors have recognized that TiN films formed by thermal ALD can be inferior to TiN films formed by PVD or CVD in some respects, e.g., film roughness and electrical resistivity. In this regard, the inventors have discovered that some electrical properties and/or physical properties of ALD-grown TiN-based films can be affected by the mode of growth. In particular, the inventors have discovered that, while it may be desirable to grow the TiN-based films in a two-dimensional layer-by-layer growth mode in ALD, such layer-by-layer growth mode may not be easily achieved under some circumstances. The inventors have further discovered that growing TiN-based films by ALD in a layer-by-layer growth mode poses a particular challenge in IC fabrication where the TiN-based films are formed on non-metal surfaces, such as insulating surfaces, such as oxide and nitride surfaces or semiconductor surfaces such as doped and undoped silicon surfaces. The inventors have recognized that the degree to which the TiN-based films may be grown in a layer-by-layer growth mode may in turn be dependent on the initial growth mode that is dependent on the type of surface, as described herein without being bound to any theory, in reference to  FIGS. 1A-1D . 
       FIG. 1A  schematically illustrates nucleation of a TiN layer and  FIGS. 1B-1D  illustrate different growth modes of the TiN layer on different surfaces. Referring  FIG. 1A , once precursor molecules  104  reach the surface of a substrate  100 , they become physically adsorbed thereon. Some of the adsorbed molecules  104  may diffuse along the surface of the substrate  100  until they reach an energetically favorable position to be chemisorbed. The surface diffusion is governed by, among other things, the substrate temperature, the substrate material and kinetic energy of the adsorbed molecules. When the size of a nuclei formed by chemisorbed molecules exceeds a certain size (sometimes referred to as “critical size”) determined by the trade-off between volume free energy and surface energy, the nuclei may become energetically stable, and start to grow in size. Thus formed layer  108  of stable nuclei continue to grow by incorporating additional precursor molecules  104 . Subsequent film growth can be classified according to different growth modes, schematically illustrated in  FIGS. 1B-1D . 
       FIG. 1B  schematically illustrates a three-dimensional island growth mode, sometimes referred to as Volmer-Weber growth mode, which results in the formation of a layer  112  of three-dimensional islands. Without being bound to any theory, the island growth mode can dominate when the net surface free energy associated with three-dimensional islands is positive, indicating that deposited atoms are more strongly bound to each other than to the substrate. It will be appreciated that the energetics of ALD growth of TiN layers can favor the island growth mode, e.g., when the metallic TiN layers are deposited on some semiconductor and/or insulating material surfaces. 
       FIG. 1C  illustrates a layer-by-layer growth mode, sometimes referred to as Frank-van der Merwe growth mode, which results in the formation of a relatively smooth two-dimensional layer  116 . Without being bound to any theory, the layer-by-layer growth mode can dominate when the deposited atoms are more strongly bound to the substrate than to each other, such that a stable two-dimensional layer  116  is energetically favored. The layer-by-layer growth mode can be sustained when there is a continuous decrease in bonding energy between the layers from the first monolayer to the bulk-crystal value of the TiN layer. 
     While  FIGS. 1B and 1C  are two different possible growth modes of thin films, it will be appreciated that, under some circumstances, a growth mode that is intermediate between a layer-by-layer growth mode and a three-dimensional growth mode is possible.  FIG. 1D  illustrates an example of an intermediate growth mode known as Stranski-Krastanov (SK) growth mode. Without being bound to any theory, the SK growth may occur in thin film growth that commences in a layer-by-layer mode. When layer-by-layer growth becomes unfavorable after the formation of one or more monolayers, an island growth mode starts to dominate over a layer-by-layer growth mode, resulting in thin film structure  120  in which three dimensional islands are formed on a two-dimensional initial layer. The SK growth mode can occur as a strain relaxation mechanism (strain-induced roughening). 
     In addition to the interaction between the deposit and the substrate, other factors such as the substrate temperature, reactor pressure and deposition rate can significantly affect the nucleation and early growth processes, which in turn affects the final nanostructure or microstructure of the resulting thin film. For example, deposition conditions that enhance surface diffusion, e.g., relatively high substrate temperatures, relatively low pressures and/or low deposition rates may promote the growth in a layer-by-layer mode. Hence, as disclosed herein, by enhancing surface diffusion during deposition of an initial portion of a TiN film by, e.g., lowering pressure and growth rate, the initial film growth according to embodiments may proceed substantially in a layer-by-layer growth mode. 
     It has been discovered that, when TiN is grown by ALD on various surfaces of interest in IC fabrication, such as dielectric and semiconductor surfaces, the ALD growth initializes in a three-dimensional island growth mode or a SK growth mode. For example, under some circumstances, ALD growth of TiN on substrate surfaces, including doped and undoped Si, SiO 2 , Si 3 N 4  and other high K or low K materials, may proceed in an island growth mode or the SK growth mode. The inventors have discovered that, in part owing to the initial growth mode of either an island or SK growth mode, subsequent growth of TiN by ALD often results in a film morphology that is undesirable for various applications of ultrathin conformal TiN for high aspect ratio structures, as illustrated in  FIG. 2 . 
       FIG. 2  is a cross-sectional transmission electron micrograph of a TiN layer grown by thermal ALD on a Si substrate coated with native oxide. After an initial film grown in either a three-dimensional island or SK growth mode, the ALD growth of TiN is often characterized by a competitive growth of adjacent crystals with different orientations, resulting, under some circumstances, in V-shaped grains close to the nucleation layer and culminating in a columnar morphology at higher film thicknesses. As illustrated in  FIG. 2 , the resulting film morphology includes facetted column tops that give rise to a significant surface roughness and column boundaries having lower density relative to the grains. It will be appreciated that the column boundaries can have significantly worse diffusion barrier properties relative to the grains themselves, and may serve as paths of least resistance for transportation of undesirable contaminant through the TiN layer. 
     The inventors have discovered that, when an initial portion of a TiN layer is formed on the non-metal surface by exposing the substrate to Ti and/or N precursors at relatively low pressures, e.g., less than 1 torr, an initial three-dimensional or SK growth mode can be suppressed and a layer-by-layer growth mode can be promoted in an initial stage, e.g., a nucleation stage, of the TiN deposition. Among other reasons, this may be because the local diffusion of adsorbed Ti and N precursor molecules have more time to locally diffuse and wet the substrate surface, especially a non-metal surface, with relatively low contact angles. The TiN layer grown at relatively low exposure pressures results in a layer that uniformly covers large areas of the non-metal surface without substantially forming islands, such that, the initial stages of growth tend more to favor a layer-by-layer growth mode on substrate surfaces on which ALD TiN would normally favor a three-dimensional island or SK growth mode as described above. Thus, by initiating ALD of TiN by exposing the substrate to the Ti and/or N precursors at relatively low precursor exposure pressures, e.g., less than 3 torr, the resulting initial layer may grow in a layer-by-layer mode, e.g., in the nucleation stage. A subsequent bulk stage of growth, which may proceed by exposing the substrate to the Ti and/or N precursors at the relatively high precursor exposure pressures, e.g., greater than 3 torr, may continue to proceed in a layer-by-layer mode. By employing the methods according to embodiments, some of the drawbacks of conventional ALD of TiN may be avoided, particularly when the TiN layer is formed by ALD directly on some semiconductor and/or insulating materials, particularly inorganic layers comprising Si, SiO 2  and/or Si 3 N 4 , which may ordinarily be associated with an initial growth characterized by an island or SK growth mode followed by a columnar growth as described above. 
       FIG. 3A  is a flow chart schematically illustrating an atomic layer deposition method  300  of forming a TiN layer by exposing a substrate to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. The resulting film may have at least two regions formed at different corresponding exposure pressures.  FIG. 3B  schematically illustrates a cross-sectional view of a semiconductor structure  350  comprising a TiN layer formed by an atomic layer deposition method in which a substrate is exposed to a plurality of cycles with different corresponding precursor exposure pressures, according to the method illustrated in  FIG. 3A . Referring to  FIG. 3A , the method  300  includes providing  310  a substrate comprising a non-metal surface in a reaction chamber configured for ALD, e.g., thermal ALD. The method  300  additionally comprises an initial stage, e.g., a nucleation stage, that includes forming  320  on the substrate a first portion of the thin film by exposing the semiconductor substrate to one or more first ALD cycles each comprising an exposure to a first Ti precursor and a first N precursor at first respective exposure pressures. The method  300  further comprises latter stage, e.g., a bulk deposition stage, including forming  330  on the first portion of the thin film a second portion of the thin film by exposing the semiconductor substrate to one or more second ALD cycles each comprising an exposure to a second Ti precursor and a second N precursor at second respective exposures. The exposures to one or both of the Ti precursor and the N precursor during the one or more second ALD cycles are at higher pressures relative to corresponding exposures to one or both of the Ti precursor and the N precursor during the one or more first ALD cycles. 
     Referring to  FIG. 3B , a cross-sectional view of a semiconductor thin film structure  350  comprising a substrate  360 , which in turn comprises a non-metal surface, e.g., a dielectric and/or a semiconductor surface. A first a first portion  370  of a thin film comprising TiN is formed on the substrate  360 , and a second portion  380  of the thin film is formed on the first portion  370 . The first and second portions  370 ,  380  are formed by an atomic layer deposition method illustrated in  FIG. 3A , in which the substrate  360  is exposed to first and second cycles with different corresponding precursor exposure pressures. Because the first portion  370  may be grown in a layer-by-layer growth mode in the initial stage, e.g., a nucleation stage as discussed above, at least the first portion  370  or both the first and second portions  370 ,  380  may be substantially free of adjacent crystals having different orientations characterized by columnar growth of V-shaped grains and the relatively high (e.g., 10% of the thickness) surface roughness. The resulting TiN layer has superior properties including one or more of relatively high conformality or step coverage, lower surface roughness, smaller average grain size, higher electrical conductivity and/or barrier characteristics relative to a comparable thin film layer formed at a single pressure during nucleation and bulk deposition stages. 
     As described herein and throughout the specification, it will be appreciated that the semiconductor substrate on which the TiN thin films according to embodiments can be implemented in a variety of substrates, including, but not limited to, a doped semiconductor substrate, which can be formed of an elemental Group IV material (e.g., Si, Ge, C or Sn) or an alloy formed of Group IV materials (e.g., SiGe, SiGeC, SiC, SiSn, SiSnC, GeSn, etc.); Group III-V compound semiconductor materials (e.g., GaAs, GaN, InAs, etc.) or an alloy formed of Group III-V materials; Group II-VI semiconductor materials (CdSe, CdS, ZnSe, etc.) or an alloy formed of Group II-VI materials. 
     According to certain embodiments, the substrate can also be implemented as a semiconductor on insulator, such as silicon on insulator (SOI), substrate. An SOI substrate typically includes a silicon-insulator-silicon structure in which the various structures described above are isolated from a support substrate using an insulator layer such as a buried SiO 2  layer. In addition, it will be appreciated that the various structures described herein can be at least partially formed in an epitaxial layer formed at or near a surface region. 
     Furthermore, the substrate can include a variety of structures formed thereon, e.g., diffusion regions, isolation regions, electrodes, vias and lines to name a few, on which any structure comprising the TiN layer according to embodiments may be formed, including topological features such as vias, cavities, holes or trenches having one or more semiconductor or dielectric surfaces. Thus, the non-metal surface on which the TiN layer according to embodiments is formed can include a semiconductor surface, e.g., a doped or undoped Si surface, and/or a dielectric surface, e.g., an interlayer dielectric (ILD) surface, a mask or a hard mask surface or a gate dielectric surface, to name a few, which can include an inorganic insulator, an oxide, a nitride, a high K dielectric, a low K dielectric, or carbon, to name a few dielectric materials. 
     As described herein and throughout the specification, a reactor chamber refers to any reaction chamber including a single wafer processing reaction chamber or a batch wafer processing reaction chamber that is suitably configured for thermal atomic layer deposition (ALD). In a thermal ALD reactor, the substrate may be placed on a suitable substrate holder, such as a susceptor or a carrier boat. The substrate may be directly heated by conduction through a heated susceptor, or indirectly heated by radiation from a radiation source such as a lamp or by convection through a heated chamber wall. 
     Generally in an ALD process, reactants or precursors, e.g., oxidizing and reducing reactants, are alternatingly introduced into a reaction chamber having disposed therein a substrate. The introduction of one or more reactants or precursors may be in turn be alternated with a purge and/or a pump out process for removing excess reactants or precursors from the reaction chamber. The reactants may be introduced into the reaction chamber under a condition over a suitable period of time such that the surface of the substrate becomes at least partly saturated with the precursors or reactants and/or a reaction product of the reactants. Excess or residual precursors or reactants may then be removed from the substrate, such as by being purged and/or pumped out of the reaction chamber. A pump out process may be performed by a suitable vacuum pumping process and a purge step may be performed by introducing a non-reactive or an inert gas, e.g., nitrogen or a noble gas, into the reaction chamber. In the context of layers formed by thermal ALD in examples hereinbelow, there are generally two categories of precursors or reactants, namely nitrogen (N) precursors and titanium (Ti) precursors. 
     In the following, with reference to  FIG. 4 , example implementations of the method  300  ( FIG. 3A ) of forming by ALD, e.g., thermal ALD, a thin film comprising TiN having at least two regions formed by exposing a substrate to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments. 
     Atomic Layer Deposition of TiN by Exposing Substrate to a Plurality of Cycles with Different Corresponding Precursor Exposure Pressures 
     Referring back to  FIG. 3A , after providing  310  the substrate (substrate  360  in  FIG. 3B ) comprising a non-metal surface in the reaction chamber, the method  300  proceeds to forming  320  by atomic layer deposition (ALD), e.g., thermal ALD, on the non-metal surface a first portion of the thin film by exposing the semiconductor substrate to one or more first ALD cycles, followed by a second portion of the thin film by exposing the semiconductor substrate to one or more second ALD cycles. In the following, exposure pressures applied during the first and second ALD cycles are described diagrammatically. 
       FIG. 4  diagrammatically illustrates pressure traces corresponding to exposures of the substrate to Ti and N precursors during a first cycle  400 A or stage, e.g., a nucleation stage, for forming the first portion  370  ( FIG. 3B ) of the thin film and the second cycle  400 B or stage, e.g., a bulk growth stage, for forming the second portion  380  ( FIG. 3B ) of the thin film, according to various embodiments. Referring to  FIG. 4 , a first portion of the thin film is formed by exposing the semiconductor substrate to one or more first ALD cycles  400 A each comprising one or more exposures  404  or exposure pulses to a partial pressure of a first Ti precursor and one or more exposures  408  or exposure pulses to a partial pressure of a first N precursor. A second portion of the thin film is formed by exposing the semiconductor substrate to one or more second ALD cycles  400 B each comprising one or more exposures  412  or exposure pulses to a partial pressure of a second Ti precursor and one or more exposures  416  or exposure pulses to a partial pressure of second N precursor. 
     As schematically depicted, each of the exposures  404  to a first Ti precursor,  408  to a first N precursor,  412  to a second Ti precursor and  416  to a second N precursor may have different partial pressure regimes, including a corresponding partial pressure rise regime  404 A,  408 A,  412 A and  416 A, a main exposure regime  404 B,  408 B,  412 B and  416 B, and a partial pressure fall regime  404 C,  408 C,  412 C and  416 C. Each of the partial pressure rise regimes  404 A,  408 A,  412 A and  416 A may correspond, for example, the respective precursor being introduced into the reaction chamber. Each of the main exposure regimes  404 B,  408 B,  412 B and  416 B may correspond to a period during which the amount of the respective precursor in the reaction chamber is relatively constant. The relative constant amount of the respective precursor may be maintained, e.g., using a pressure transducer or a throttle valve. Each of the partial pressure fall regime  404 C,  408 C,  412 C and  416 C may correspond, for example, to a regime when the respective precursor is being purged or pumped out of the reaction chamber. 
     Still referring to  FIG. 4 , it will be appreciated that, in some implementations, the precursors may be pumped out and/or purged out after each exposure. In some implementations where the precursor may be pumped out without being purged, the reaction chamber pressure may be substantially represented by the partial pressures of the respective precursors, and the pressures traces of the exposures  404 ,  408 ,  412  and  416  may substantially represent the reaction chamber pressures or the precursor partial pressures during the respective exposures. In some implementations where the precursor is purged out with an inert gas without being pumped out, the reaction chamber pressure may be represented by total reaction chamber pressures  404 P,  408 P,  412 P and  416 P corresponding to the exposures  404 ,  408 ,  412  and  416 , where the total reaction chamber pressures result from a mixture of the respective precursors and an inert gas. 
     In practice, a combination of pumping and purging may be used for higher throughput and improved film quality. In these implementations, the substrate may be subjected to partial pressures of the first Ti precursor, the first N precursor, the second Ti precursor and the second N precursor, while measuring total pressures  404 P,  408 P,  412 P and  416 P including during purging and pumping. In some embodiments, the total chamber pressure may be kept relatively constant throughout a given precursor exposure or exposure pulse while pumping power is adjusted using a pressure transducer and replacing the removed precursor with an inert gas. In these implementations, one or more first ALD  400 A cycles for forming the first portion ( 370  in  FIG. 3B ) may each comprise one or more exposures  404  to a partial pressure of a first Ti precursor (while the measured parameter may be a total reaction chamber pressure  404 P), and one or more exposures  408  to a partial pressure of a first N precursor (while measured parameter may be a total reaction chamber  408 P). Similarly, one or one or more second ALD cycles  400 B for forming the second portion ( 380  in  FIG. 3B ) may each comprise one or more exposures  412  to a partial pressure of a second Ti precursor (while the measured parameter may be a total pressure  412 P) and one or more exposures  416  to a partial pressure of a second N precursor (while the measured parameter may be a total pressure  416 P). 
     According to various embodiments, during an exposure to a precursor, the measured total reaction chamber pressure may be proportional to the partial pressure of the precursor. Thus, the total pressures  412 P and  416 P that are higher relative total pressures  404 P and  408 P, respectively, correspond to higher partial pressures of the second Ti precursor and the second N precursor relative to partial pressures of the first Ti precursor and the first N precursor, respectively. However, embodiments are not so limited and in other embodiments, the total pressures  412 P and  416 P that are higher relative total pressures  404 P and  408 P, respectively, may correspond to the same or lower partial pressures of the second Ti precursor and the second N precursor relative to partial pressures of the first Ti precursor and the first N precursor, respectively. 
     Referring back to the illustrated method  300  in  FIG. 3A , one or both of exposure pressures of the second Ti precursor and the second N precursor during one or more second ALD cycles of the latter, e.g., a bulk deposition phase are higher relative to corresponding one or both of exposure pressures of the first Ti precursor and the first N precursor during one or more first ALD cycles of the initial, e.g., a nucleation phase. In some embodiments, the exposure pressures may be partial pressures of the precursors or total pressures of the reaction chambers. Thus, in various embodiments, in reference to  FIG. 4 , one or both of the exposure  412  to the second Ti precursor and the exposure  416  to the second N precursor may be at higher partial pressures and/or a higher total reaction chamber pressures relative to the corresponding one or both of the exposure  404  to a the first Ti precursor and the exposure  408  to the first N precursor, respectively. 
     Still referring to  FIG. 4 , in various embodiments, the corresponding partial or total pressures between corresponding exposures to Ti and N precursors during the first and second cycles  400 A and  400 B may be corresponding partial or total pressures during any one of partial pressure rise regimes  404 A,  408 A,  412 A and  416 A, main exposure regimes  404 B,  408 B,  412 B and  416 B, and partial pressure fall regimes  404 C,  408 C,  412 C and  416 C. For example, the exposures  412 ,  416  to one or both of the second Ti precursor and the second N precursor during the main exposure regimes  412 B and  416 B, respectively, during the second ALD cycle  400 B, may be at higher total or partial pressures relative to the exposures  404 ,  408  to one or both of the first Ti precursor and the first N precursor during the main exposure regimes  404 B and  408 B, respectively, during the first ALD cycle  400 A. In various other embodiments, the corresponding partial or total pressures between corresponding exposures to Ti and N precursors during the first and second cycles  400 A and  400 B may be corresponding average, mean or peak partial or total pressures during the exposures  404 ,  408 ,  412  and  416 . 
     Still referring to  FIG. 4 , in the illustrated embodiment, the total and/or partial pressures during the exposure  404  to the first Ti precursor and the exposure  408  to the first N precursor are different, and the total and/or partial pressures during the exposure  412  to the second Ti precursor and the exposure  416  to the second N precursor are different. However, embodiments are not so limited, and in some embodiments, the total and/or partial pressures during the exposure  404  to the first Ti precursor and the exposure  408  to the first N precursor may be kept constant, and/or the total and/or partial pressures during the exposure  412  to the second Ti precursor and the exposure  416  to the second N precursor may be kept constant. 
     Still referring to  FIG. 4 , each of the total pressures during the exposure  404  to the first Ti precursor and the exposure  408  to the first N precursor, which may be the same or different, may be 0.01-0.2 torr, 0.2-0.4 torr, 0.4-0.6 torr, 0.6-0.8 torr, 0.8-1.0 torr, 1.0-1.5 torr, 1.5-2.0 torr, 2.0-2.5 torr, 2.5-3.0 torr, or a pressure in range defined by any of these values. Each of the total pressures during the exposure  412  to the second Ti precursor and the exposure  416  to the second N precursor, which may be the same or different, may be 3.0-4.0 torr, 4.0-5.0 torr, 5.0-6.0 torr, 6.0-7.0 torr, 7.0-8.0 torr, 8.0-9.0 torr, 9.0-10.0 torr, 10.0-11.0 torr, 11.0-12.0 torr, or a pressure in range defined by any of these values. A ratio of the total pressure (measured in torr) of the reaction chamber during the exposure  412  to the second Ti precursor and the exposure  404  to the first Ti precursor may be 2-5, 5-10, 10-20, 20-50, 50-100, or in a range defined by any of these values. Similarly. a ratio of the total pressure of the reaction chamber during the exposure  416  to the second N precursor and the exposure  408  to the first N precursor may be 2-5, 5-10, 10-20, 20-50, 50-100, or in a range defined by any of these values. In each of the exposures  404 ,  408 ,  412  and  416 , the respective Ti or N precursor can make up 1-2%, 2-5%, 5-10%, 10-20%, 20-50%, 50-100% of the total amount of gas molecules in the reaction chamber, or a percentage in a range defined by any of these values. 
     Still referring to  FIG. 4 , according to various embodiments, the total pressure or the partial pressure during the exposure  404  to the first Ti precursor and the exposure  408  to the first N precursor, in conjunction with the flow rates of the respective precursors and an inert gas and the pumping power of the reaction chamber, are controlled such that the deposition rate during the first cycle  400 A or stage is between 0.10-0.20 Å/cycle, 0.20-0.30 Å/cycle, 0.30-0.40 Å/cycle, 0.40-0.50 Å/cycle, 0.50-0.60 Å/cycle or a value in a range defined by any of these values, per cycle including an exposure  404  to the first Ti precursor and an exposure  408  to the first N precursor. The total pressure or the partial pressure during the exposure  412  to the second Ti precursor and the exposure  416  to the second N precursor, in conjunction with the flow rates of the respective precursors and an inert gas and the pumping power of the reaction chamber are controlled such that the deposition rate during the second cycle  400 B or stage is 0.20-0.30 Å/cycle, 0.30-0.40 Å/cycle, 0.40-0.50 Å/cycle, 0.50-0.60 Å/cycle, 0.60-0.70 Å/cycle, 0.60-0.70 Å/cycle, 0.70-0.80 Å/cycle or a value in a range defined by any of these values, per cycle including an exposure  404  to the first Ti precursor and an exposure  408  to the first N precursor. A ratio of the deposition rate per cycle during the second cycle  400 B to the deposition rate per cycle during the first cycle  400 A may be 1-1.5, 1.5-2.0, 2.5-3.0, or a ratio in a range defined by any of these values. 
     The inventors have found that various technical advantages of TiN thin films disclosed herein may be realized when each of forming  320  ( FIG. 3A ) the first portion  370  ( FIG. 3B ) and forming  330  ( FIG. 3A ) the second portion  380  ( FIG. 3B ) of the thin film comprising TiN comprises exposing a semiconductor substrate to 1-25 cycles, 26-50 cycles, 50-100 cycles, 100-200 cycles, 200-300 cycles, 300-400 cycles, 400-500 cycles, 500-600 cycles, or a value in a range defined by any of these values, of the first cycles  400 A ( FIG. 4 ) and second cycles  400 B ( FIG. 4 ), respectively. According to various embodiments, a ratio of the number of second cycles to the number of first cycles can be greater than 1, 2, 5 or 10 or a ratio in a range defined by any of these values, or smaller than 1, 0.5, 0.1 or 0.1 or a ratio in a range defined by any of these values. The overall thickness of the thin film comprising TiN including the first portion  370  ( FIG. 3B ) and the second portion  380  ( FIG. 3B ) can have a combined stack thickness that does not exceed about 25 nm, 20 nm, 15 nm, 10 nm, 7 nm, 4 nm, 2 nm, or having a value in a range defined by any of these values. A thickness ratio between the first portion  370  ( FIG. 3B ) and the second portion  380  ( FIG. 3B ) can be about 1:20-1:10, 1:10-1:5, 1:5-1:2, 1:2-1:1, 1:1-2:1, 2:1-5:1, 5:1-10:1, 10:1-20:1, or a ratio in a range defined by any of these values. It will be appreciated that in some embodiments, the first portion  370  ( FIG. 3B ) may be relatively thinner, e.g., when higher conformality may be more important compared to lower film roughness, while in other embodiments, the second portion  380  ( FIG. 3B ) may be relatively thinner, e.g., when lower film roughness may be more important compared to higher conformality. 
     Still referring to  FIG. 4 , each of the exposure  404  of the substrate to the first Ti precursor and the exposure  412  of the substrate to the second Ti precursor is such that the surface of the substrate is substantially or partly saturated with the first Ti precursor or the second Ti precursor, respectively. After each of the exposure  404  of the substrate to the first Ti precursor and the exposure  412  of the substrate to the second Ti precursor, excess or residual first and/or second Ti precursors or their reaction products that do not remain adsorbed or chemisorbed on the surface of the substrate may be pumped and/or purged out. 
     Similarly, each of the exposure  408  of the substrate to the first N precursor and the exposure  416  of the substrate to the second N precursor is such that the substrate is substantially or partly saturated with the first N precursor or the second N precursor, respectively. After each of the exposure  408  of the substrate to the first N precursor and the exposure  416  of the substrate to the second N precursor, excess or residual first and/or second N precursors or their reaction products that do not remain adsorbed or chemisorbed on the surface of the substrate may be pumped and/or purged out. Subjecting the substrate to one or more exposures to the first Ti precursor and one or more exposures to the first N precursor may form about a monolayer or less per cycle of TiN. Similarly, subjecting the substrate to one or more exposures to the second Ti precursor and one or more exposures to the second N precursor may form about a monolayer or less per cycle of TiN. 
     In some embodiments, the exposure  404  to the first Ti precursor, the exposure  408  to the first N precursor, the exposure  412  to the second Ti precursor and/or the exposure  416  to the second N precursor may be performed a plurality of times in sequence prior to introduction of the other precursor. For example, advantageously, under some circumstances, exposing the substrate to a Ti precursor and/or a N precursor more than once may result in a higher level of surface saturation e.g., when substantial stearic hindrance effect exists. 
     Still referring to  FIG. 4 , it will be appreciated that the relative order of exposures to a first Ti precursor and to a first N precursor may be selected depending on competing circumstances. In some implementations, the first Ti precursor may advantageously be the first precursor the substrate surface is exposed to. For example, one or more direct exposures of a Si surface to the first Ti precursor may lead to formation of one or more monolayers of TiSi and prevent formation of SiN, which may in turn be advantageous for lowering contact resistance between the underlying Si and the TiN layer formed thereover. However, in some other implementations, the first N precursor may advantageously be the first precursor the substrate is exposed to. For example, by directly exposing a Si surface to the first N precursor, one or more monolayers of SiN may be intentionally formed, which may be advantageous for improving barrier characteristics of the stack. 
     It will be appreciated that in various embodiments, the frequency and repetition of the exposures of the substrate to the first Ti reactant and/or the first N precursor in each of the first cycles  408 A, and to the second Ti reactant and/or the second N precursor in each of the second cycles  408 B may be varied to obtain a desired thickness and stoichiometry, based on various considerations including susceptibility to stearic hindrance effects of the precursors. 
     According to various embodiments, non-limiting examples of the first and second Ti precursors, which may be the same or different for forming first and second portions of a TiN layer according to embodiments, include titanium tetrachloride (TiCl 4 ), tetrakis(dimethylamino)titanium (TDMAT) or tetrakis(diethylamino)titanium (TDEAT). Having same precursors for the first and second portions of the TiN may be advantageous for, e.g., being lower in cost and/or easier for process design. However, having different precursors for the first and second portions of the TiN may be advantageous for, e.g., different deposition characteristics or film quality. 
     According to various embodiments, non-limiting examples of the first and second N precursors, which may be the same or different for forming first and second portions of a TiN layer according to embodiments, include ammonia (NH 3 ), hydrazine (N 2 H 4 ) or monomethylhydrazine (CH 3 (NH)NH 2 , “MMH”). Having same precursors for the first and second portions of the TiN may be advantageous for, e.g., being lower in cost and/or easier for process design. However, having different precursors for the first and second portions of the TiN may be advantageous for, e.g., different deposition characteristics or film quality. 
     According to various embodiments, non-limiting examples of the inert gas for purging may include nitrogen N 2  or a noble gas such as Ar or He. 
     Various technical advantages and benefits described herein can be realized when one or both of the first and second portions  370 ,  380  ( FIG. 3B ) of the thin film comprising TiN are formed at a substrate temperature of 350° C. to 800° C., 450° C. to 750° C., 500° C. to 700° C., 550° C. to 650° C., or in a range defined by any of these values, for instance about 600° C., according to embodiments. Keeping the temperature the same during growth of the first and second portions  370 ,  380  may be advantageous for throughput an ease of process control, as temperature adjustments during process may take long time. 
     In various embodiments, the exposure times or pulse times of each of the first and second Ti precursors and first and second N precursors can be in the range of about 0.1-1 sec., 1-10 sec., 10-30 sec., 30-60 sec., or a duration in a range defined by any of these values. 
     Advantageously, when the TiN layer is formed using an atomic layer deposition method in which a substrate is exposed to a plurality of cycles with different corresponding precursor exposure pressures according to various embodiments, one or both of the surface roughness and electrical resistivity can be substantially reduced to conventional TiN films including TiN films formed using other ALD processes with a single pressure setpoint. As deposited, the thin film comprising TiN formed at according the methods described herein and having the above-indicated thicknesses and thickness ratios between the first and second portions  370 ,  380  ( FIG. 3B ) can have a root mean square (RMS) surface roughness of 3%, 4%, 5%, 6%, 7%, 8%, and 9%, or a value in a range defined by any of these values, on the basis of an average thickness of the thin film. Alternatively, as-deposited, the thin film comprising TiN having the above-indicated thicknesses and thickness ratios between the first and second portions  370 ,  380  ( FIG. 3B ) can have an RMS surface roughness value that is less than 2.5 nm, 2 nm, 1.5 nm, 1.0 nm, 0.5 nm, or a value in a range defined by any of these values. 
     As deposited, the thin film comprising TiN formed according to the methods described herein and having the above-indicated thickness and thickness ratios between the first and second portions  370 ,  380  ( FIG. 3B ) can have an electrical resistivity of &lt;70 μΩ-cm, 70-100 μΩ-cm, 100-130 μΩ-cm, 130-160 μΩ-cm, 160-190 μΩ-cm, 190-220 μΩ-cm, 220-250 μΩ-cm, 250-280 μΩ-cm, 280-310 μΩ-cm, or greater than 310 μΩ-cm, or a value in a range defined by any of these values, for instance less than about 200 μΩ-cm. 
     In addition to reduced surface roughness and electrical resistivity, the thin film comprising TiN formed according to the methods disclosed herein has high conformality when deposited in high aspect ratio structures. One measure of conformality in the context of high aspect ratio structures is referred to herein as step coverage. A high aspect ratio structure may be, e.g., a via, a hole, a trench, a cavity or a similar structure. By way of an illustrative example,  FIG. 5  schematically illustrates a semiconductor structure  500  having an example high aspect ratio structure  516  formed therein, to illustrate some example metrics of defining and/or measuring conformality of thin films formed on high aspect ratio structures. The illustrated high aspect ratio structure  516  is lined with a TiN layer  512  having different thicknesses at different portions thereof. As described herein, a high aspect ratio structure has an aspect ratio, e.g., a ratio defined as a depth or height (H) divided by a width (W) at the opening region of the high aspect ratio structure  516 , that exceeds 1. In the illustrated example, the high aspect ratio structure  516  is a via formed through a dielectric layer  508 , e.g., an intermetal dielectric (ILD) layer, formed on a semiconductor substrate  504 , such that a bottom surface of the high aspect ratio structure  516  exposes the underlying semiconductor  504 . The TiN layer  512  can coat different surfaces of the high aspect ratio structure  516  with different thicknesses. As described herein, one metric for defining or measuring the conformality of a thin film formed in a high aspect ratio is referred to as step coverage. A step coverage may be defined as a ratio between a thickness of a thin film at a lower or bottom region of a high aspect ratio structure and a thickness of the thin film at an upper or top region of the high aspect ratio structure. The upper or top region may be a region of the high aspect ratio structure at a relatively small depth at, e.g., 0-10% or 0-25% of the H measured from the top of the opening. The lower or bottom region may be a region of the high aspect ratio structure at a relatively high depth at, e.g., 90-100% or 75-100% of the H measured from the top of the opening. In some high aspect ratio structures, a step coverage may be defined or measured by a ratio of thicknesses of the thin film  512 A formed at a bottom surface to the thin film  512 C formed at upper or top sidewall surfaces of the high aspect ratio structure. However, it will be appreciated that some high aspect ratio structures may not have a well-defined bottom surface or a bottom surface having small radius of curvature. In these structures, a step coverage may be more consistently defined or measured by a ratio of thicknesses of the thin film  512 B formed at a lower or bottom sidewall surface to the thin film  512 C formed at an upper or top sidewall surfaces of the high aspect ratio structure. 
     As described above, the thin film comprising TiN formed according to the methods disclosed herein results in a reduced surface roughness and electrical resistivity, while also providing high conformality in high aspect ratio structures. According to various embodiments, high aspect ratio structures having an aspect ratio exceeding 1, 2, 5, 10, 20, 50, 100, 200 or a value in a range defined by any of these values may be conformally coated with TiN films according to embodiments with a step coverage as defined herein that exceeds 70%, 80%, 90%, 95%, or has a value in a range defined by any of these values. 
     Physical Characterization of TiN Formed by Exposing Substrate to a Plurality of Cycles with Different Corresponding Precursor Exposure Pressures 
       FIG. 6  is a graph illustrating experimentally measured root mean square (RMS) surface roughness trend  604  and step coverage trend  608  as functions of the number of first cycles of exposures to Ti and N precursors at a relatively low chamber pressure of 0.5 torr, out of a total of 600 combined first cycles (e.g., nucleation stage) and second cycles (e.g., bulk deposition stage). The second cycles of exposures to Ti and N precursors were at a relatively high chamber pressure of 5 torr. Each experimental data point in  FIG. 6  was taken from a TiN film grown on a native SiO 2 -coated Si substrate for surface roughness measurements, and a TiN film grown in a via formed in SiO 2  and having about 40:1 aspect ratio. The measured deposition rates of the first and second cycles were 0.28 Å/cycle and 0.38 Å/cycle, respectively. The experimental data were measured on four different TiN films grown with 0 first cycles (0 Å)/600 second cycles (228 Å), 50 first cycles (14 Å)/550 second cycles (209 Å), 200 first cycles (56 Å)/400 second cycles (152 Å), and 600 first cycles (168 Å)/0 second cycles (0 Å). The four TiN films had total thicknesses of about 228 Å, 223 Å, 208 Å and 168 Å, respectively. As described above, the measured surface roughness values of the TiN films decrease with increasing relative number of first cycles including exposures at the relatively lower pressure. Without being bound to any theory, this may be because lower growth rate tends to allow for more surface diffusion which tends to reduce the surface roughness and promote layer-by-layer growth. The measured surface roughness values for thin films grown with 0 first cycles/600 second cycles, 50 first cycles/550 second cycles and 200 first cycles/400 second cycles were about 21 Å, 17.5 Å and 12.5 Å, respectively, corresponding to about 9%, 8% and 6% on the basis of the total thickness of the respective TiN films. In addition, as discussed above, the measured step coverage values of the TiN films were higher for the thin film grown with 0 first cycles/600 second cycles relative to the film grown with 600 first cycles/0 second cycles. Without being bound to any theory, this may be because higher pressure tends to allow for more precursors to reach the bottom of the high aspect ratio, which tends to improve step coverage. However, surprisingly, the inventors have found that, up to about 50 first cycles (8% of total number of cycles), the increasing number of first cycles actually improved the step coverage. Thus, according to some embodiments, forming the first portion of the TiN film comprises alternatingly exposing the semiconductor substrate to 1 to 50 cycles each comprising an exposure to a first Ti precursor and an exposure to a first N precursor at a relatively low exposure pressure of less than about 3 torr. 
       FIGS. 7A-9  illustrate further experimental comparisons between a TiN film grown by exposing a substrate to cycles with the same precursor exposure pressures and a TiN film grown by exposing a substrate to a plurality of cycles with different corresponding precursor exposure pressures, according to embodiments.  FIG. 7A  is a cross-sectional transmission electron micrograph of high aspect ratio vias lined with a TiN layer formed by an atomic layer deposition method in which a substrate is exposed to ALD cycles at the same precursor exposure pressure corresponding to second cycles.  FIGS. 7B and 7C  are transmission electron micrographs (TEMs) of a TiN film grown using only second cycles of exposures to Ti and N precursors at a relatively high chamber pressure of 5 torr. The TEMs are images of a via formed in SiO 2  having about 40:1 aspect ratio, taken at upper ( FIG. 7B ) and lower ( FIG. 7C ) regions of the via. In comparison,  FIGS. 8A and 8B  are transmission electron micrographs (TEMs) of a TiN film grown using a combination of first and second cycles of exposures to Ti and N precursors at a relatively low (0.5 torr) and high (5 torr) chamber pressures, according to embodiments. The TEMs are images of a via formed in SiO 2  having about 40:1 aspect ratio, taken at upper ( FIG. 8A ) and lower ( FIG. 8B ) regions of the via.  FIG. 9  is a graph illustrating an experimental statistical comparison between measured step coverages  904  measured from TEM micrographs shown in  FIGS. 7A-7C  and measured step coverages  908  measured from TEM micrographs shown in  FIGS. 8A-8B . The data points in  FIG. 9  represents a ratio taken from different locations within a lower region of the via and different locations within an upper region of the via. While not readily apparent from the TEM images, the statistical comparison in  FIG. 9  clearly illustrate a higher median step coverage of 93% for the TiN film deposited according to embodiments and 87% for the TiN film deposited using a single exposure pressure. In addition, the statistical spread of measured step coverage for the TiN film deposited according to embodiments is substantially smaller than that for the TiN film deposited using a single exposure pressure, indicating that the film roughness is significantly higher for the latter. 
     Atomic Layer Deposition of TiN Thin Films Having Increased (111) Crystalline Texture 
     TiN as disclosed herein have a face-centered cubic, NaCl-type lattice structure. As such, the surface atom density is highest when the surface has a (111) orientation, relative to (200) orientation. The fraction of the surface having a certain crystal orientation for TiN can be highly deposition condition-dependent. 
     For certain applications of TiN thin films, e.g., DRAM capacitor electrodes, to meet the increasing demands of aggressive scaling, the TiN films may need to be extremely thin, e.g., less than 30 nm, while simultaneously meeting a combination of stringent electrical and mechanical properties. For example, in addition to low electrical resistivity and high conformality as discussed above, there is a need for some TiN thin films to simultaneously meet a combination of stringent mechanical properties, e.g., relatively high density, hardness and modulus, in order to reduce the risk of integration failures. 
     A TiN film grown by atomic layer deposition can have grains that have different crystal orientations including (111) and (200) orientations at the surface, among other orientations. The inventors have discovered that TiN thin films that are textured to have certain crystalline texture can have superior mechanical properties, in addition to having a desirably low electrical resistivity and conformality as described above. In particular, ultrathin TiN films having relatively high (111) crystalline texture can have a relatively high density, hardness and modulus. In addition, the increased (111) crystalline texture can reduce columnar growth, thereby providing superior diffusion barrier properties. Without being bound to any theory, these advantageous properties of the TiN thin films having relatively high (111) crystalline texture may be associated with one of the highest surface atom packing density in a direction parallel to the growth surface, as well as grain boundary arrangements that favor the superior physical properties. The inventors have further discovered that the texture of TiN thin films can be controlled by controlling certain conditions of the cyclical vapor deposition cycles, as described herein. In particular, the inventors have discovered that cyclical vapor deposition cycles in which the substrate is subjected to a relatively high flow rate of the N precursor can cause a TiN thin film to grow with a relatively high (111) crystalline texture, as described herein. 
       FIG. 11  is a flow chart schematically illustrating an atomic layer deposition method  1100  of forming a TiN layer having a relatively high (111) crystalline texture by exposing a substrate to a relatively high N precursor flow rate, according to embodiments. The method  1100  includes providing  1110  a semiconductor substrate. The method  1100  additionally includes exposing  1120  the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to a N precursor at a N precursor flow rate. The method  1100  forms a TiN film having a relatively high (111) crystalline texture by exposing  1120  the semiconductor substrate to one or more cyclical vapor deposition cycles in which a ratio of the N precursor flow rate to the Ti precursor flow rate (N/Ti flow ratio) and/or the flow rate of the N precursor are substantially high compared to conventional methods. According to various embodiments, a ratio of the N precursor flow rate to the Ti precursor flow rate (N/Ti flow ratio) exceeds 3. According to various embodiments, the N precursor flow rate exceeds 500 sccm. It will be appreciated that the exposing  1120  and forming  1130  are not necessarily ordered as shown. Various implementations of the method  1100  are described herein. 
     Providing  1110  the semiconductor substrate can be similar to providing  310  a semiconductor substrate according to various examples described above with respect to  FIGS. 3A and 3B , the details of which are not repeated herein for brevity. For example, the substrate can be patterned or non-patterned, and can have one or both of insulating and conducting surfaces as described above. 
     Exposing  1120  the semiconductor substrate can be similar to exposing the semiconductor substrate to one or more first or second thermal ALD cycles as described above with respect to respect to  FIGS. 3A, 3B and 4 , the details of which is not repeated herein for brevity. For example, the exposure to a Ti precursor at a Ti precursor flow rate can be in accordance with the exposure  404  ( FIG. 4 ) to the first Ti precursor or the exposure  412  ( FIG. 4 ) to the second Ti precursor. Similarly, the exposure to a N precursor at a N precursor flow rate can be in accordance with the exposure  408  ( FIG. 4 ) to the first N precursor or the exposure  416  ( FIG. 4 ) to the second N precursor. The details of these processes are not repeated herein for brevity. According to various embodiments, exposing  1120  is such that a TiN thin film having a high (111) crystalline texture is formed, as described herein. 
     According to various embodiments, the Ti precursor and the N precursor can be any of the precursors described above. For example, the Ti precursor can be titanium tetrachloride (TiCl 4 ) and the N precursor can be ammonia (NH 3 ). 
     Various other process parameters including the substrate temperature, chamber pressure and exposure times, can be in accordance with various process parameters described above, the details of which are not repeated herein for brevity. 
     According to embodiments, exposing  1120  is such that a ratio of the N precursor flow rate to the Ti precursor flow rate (N/Ti flow ratio) exceeds 2. The ratio can exceed 2, 3, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or have a value in a range defined by any of these values. 
     According to embodiments, exposing  1120  is such that the N precursor flow rate exceeds 200 sccm. For example, the N precursor flow rate can exceed 200 sccm, 500 sccm, 1000 sccm, 2000 sccm, 3000 sccm. 4000 sccm, 5000 sccm, 6000 sccm, 7000 sccm, 8000 sccm, 9000 sccm, 10000 sccm, or have a value in a range defined by any of these values. 
     According to embodiments, exposing  1120  is such that the Ti precursor flow rate exceeds 100 sccm but does not exceed the flow rate of the N precursor, in accordance with the N/Ti flow ratio described above. For example, the Ti precursor flow rate can exceed 100 sccm, 200 sccm, 500 sccm, 1000 sccm, 2000 sccm, 3000 sccm. 4000 sccm, 5000 sccm, or have a value in a range defined by any of these values. 
       FIG. 12A  illustrates experimental X-ray diffraction spectra of the resulting TiN thin films having a relatively high (111) crystalline texture, according to embodiments. The X-ray diffraction spectra were taken on Examples 1-4 shown in TABLE 1 below.  FIG. 12B  is a graph illustrating the experimental ratios of a peak height of an X-ray diffraction peak corresponding to a (111) crystal orientation of TiN to a peak height of an X-ray diffraction peak corresponding to a (200) crystal orientation of TiN obtained from the X-ray diffraction spectra of  FIG. 12A . The illustrated TiN thin films are shown as examples only, and the embodiments are not so limited. According to embodiments, the N precursor flow rate range and the Ti precursor flow rate range are such that the TiN thin film has a relatively high (111) crystalline texture relative to a comparable thin film (e.g., a TiN having a similar thickness) formed by exposing the semiconductor substrate to cyclical vapor deposition cycles each comprising an exposure to a different Ti precursor flow rate range outside of the Ti precursor flow rate range described above and an exposure to a different N precursor flow rate range outside of the N precursor flow rate range described above. The degree of the increased (111) texture can be measured using, e.g., X-ray diffraction. For example, the relative intensities of different X-ray peaks can provide at least a semi-quantitative indication of the degree of texturing. The TiN thin films formed according to embodiments advantageously have a relatively high (111) crystalline texture such that an X-ray spectrum of the thin film has a ratio of a peak height or an intensity of an X-ray diffraction peak corresponding to (111) crystal orientation to a peak height or an intensity of an X-ray diffraction peak corresponding to (200) crystal orientation that exceeds 0.4. For example, this ratio can exceed 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, or a value in a range defined by any of these values. Selected experimental precursor flow conditions and the corresponding measurements of the ratios are summarized in TABLE 1. 
       FIG. 13  is a graph of experimental thickness and resistivity measurements of TiN thin films having relatively high (111) crystalline texture, according to embodiments. For Examples 1-4 listed in TABLE 1, increasing the N/Ti flow ratio decreases the thickness for the same number of cycles. Unexpectedly, unlike conventional methods, increasing the N/Ti flow ratio, which in turn decreases the thickness, decreases a resistivity of the TiN thin film. Prior to the present disclosure, decreasing thickness had been associated with increasing resistivity, which had been correlated to relatively higher amounts of chlorine in relatively thin TiN thin films formed with TiCl 4 . The illustrated TiN thin films are shown as examples only, and the embodiments are not so limited. Advantageously, the resistivity of the TiN films formed according to embodiments is less than about 200 μΩ-cm or any value described above. Selected experimental precursor flow conditions and the corresponding measurements of the thickness and resistivity are summarized in TABLE 1. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 TiCl 4   
                 NH 3   
                   
                   
                   
                   
                 (111) X-ray 
               
               
                   
                 Flow 
                 Flow 
                 NH 3 /TiCl 4   
                   
                   
                 Sheet 
                 Peak/(200) 
               
               
                   
                 Rate 
                 Rate 
                 Flow Rate 
                 Thickness 
                 Resistivity 
                 Resistance 
                 X-Ray Peak 
               
               
                 Example 
                 (sccm) 
                 (sccm) 
                 Ratio 
                 (Å) 
                 (μΩcm) 
                 (Ω/sq) 
                 Ratio 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 140 
                 500 
                 3.6 
                 268 
                 159 
                 59.3 
                 0.43 
               
               
                 2 
                 140 
                 1000 
                 7.1 
                 265 
                 145 
                 54.5 
                 0.56 
               
               
                 3 
                 140 
                 2000 
                 14.3 
                 261 
                 136 
                 52.2 
                 0.75 
               
               
                 4 
                 140 
                 4000 
                 28.6 
                 261 
                 129 
                 49.4 
                 1.39 
               
               
                   
               
            
           
         
       
     
       FIG. 14  is a graph of experimental hardness and modulus measurements of TiN thin films having substantially the same thicknesses and a preferential (111) crystalline texture, according to embodiments.  FIG. 15  is a graph of experimental hardness measurements of TiN thin films having a relatively high (111) crystalline texture for two different thicknesses, according to embodiments. According to embodiments, increasing the N/Ti flow ratio, which in turn decreases the thickness, increases a Young&#39;s modulus and a hardness of the TiN thin film. The illustrated TiN thin films are shown as examples only, and the embodiments are not so limited. Advantageously, the hardness of the TiN films formed according to embodiments exceeds 6 GPa. For example, the hardness can exceed 6 Gpa, 10 Gpa, 14 Gpa, 18 Gpa, 22 Gpa, 25 Gpa, or have a value in a range defined by any of these values. Advantageously, the elastic or Young&#39;s modulus of the TiN films formed according to embodiments exceeds 150 Gpa. For example, the Young&#39;s modulus can exceed 150 Gpa, 170 Gpa, 190 Gpa, 210 GPa, 230 GPa, 250 GPa, 270 GPa, 300 GPa, or have a value in a range defined by any of these values. 
     According to the methods described herein, decreasing a deposition pressure increases the ratio of the peak height or the intensity of the X-ray diffraction peak corresponding to the (111) crystal orientation of TiN to the peak height or the intensity of the X-ray diffraction peak corresponding to the (200) crystal orientation of TiN. This is illustrated in  FIG. 16 , which illustrates experimental X-ray spectra of TiN thin films formed at different exposure pressures and having a preferential (111) crystalline texture, according to embodiments. The illustrated TiN thin films are shown as examples only, and the embodiments are not so limited. In particular, the X-ray diffraction profiles were taken for TiN films having the same thickness but formed at two different exposure pressures, namely 5 torr and 3 torr. The results show that lower pressure can lead to further increase in the (111) crystalline texture. The inventors have recognized, however, that under some circumstances, lower exposure pressure can lead to compromised step coverage. Accordingly, in these circumstances, according to embodiments, after forming  1130  ( FIG. 11 ) the TiN thin film having a relatively high (111) crystalline texture, the method  1100  ( FIG. 11 ) can further include forming on the TiN thin film a second TiN thin film by exposing the semiconductor substrate to one or more second cyclical vapor deposition cycles each comprising an exposure to a second Ti precursor and an exposure to a second N precursor, wherein exposures to one or both of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles are at higher pressures relative to corresponding exposures to one or both of the Ti precursor and the N precursor during the one or more first cyclical vapor deposition cycles. Other exposure conditions corresponding to forming  1130  ( FIG. 11 ) the TiN thin film and forming the second TiN thin film can be according to any of the exposure conditions described above with respect to  FIGS. 3A, 3B and 4 . 
       FIG. 17  illustrates chlorine concentration depth profiles of TiN thin films having increased (111) crystalline texture, according to embodiments. The depth profiles are obtained using secondary ion mass spectrometry. The measured thin films correspond to Examples 1-4 listed in TABLE 1. As described above, increasing the N/Ti flow ratio decreases the thickness for the same number of cycles. Unexpectedly, unlike conventional methods, increasing the N/Ti flow ratio, which in turn decreases the thickness, decreases a resistivity of the TiN thin film.  FIG. 17  illustrates that this unexpected trend of decreasing resistivity with decreasing thickness correlates to decreasing chlorine concentration. For the range of N/Ti flow ratios covered by Examples 1-4, the amount of chlorine can decrease by more than 50%. For example, at about 10 nm, for Examples, 1-4, the chlorine concentration was measured to be 7.2×10 20 /cm 3 , 6.1×10 20 /cm 3 , 5.1×10 20 /cm 3  and 3.5×10 20 /cm 3 , respectively. Prior to the present disclosure, decreasing thickness had been associated with increasing chlorine content, which had been correlated to relatively higher resistivity. 
     Atomic Layer Deposition of Dual Layer TiN Thin Films Having Increased (111) Crystalline Texture 
     As described above, high N/Ti flow ratios, high N precursor flow rate and/or low deposition pressure may increase the (111) texture of the resulting TiN thin film. As further described above, high (111) texture may provide various advantages in a similar manner to low pressure-deposited (e.g., less than 5 torr) TiN thin films as described above. Such advantages include improvements in resistivity, hardness, modulus and roughness to name a few. However, the high N/Ti flow ratios may result in relatively low step coverage under some circumstances, in a similar manner as described above with respect to low pressure-deposited TiN thin films. To compensate, it may be desirable to have a dual or multiple layer process in which a second TiN thin film is grown on a first TiN thin film having a high (111) texture. 
     According to these embodiments, the method comprises forming on a semiconductor substrate a TiN thin film by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to a N precursor at a N precursor flow rate. The method additionally comprises forming on the TiN thin film a second TiN thin film by exposing the semiconductor substrate to one or more second cyclical vapor deposition cycles each comprising an exposure to a second Ti precursor at a second Ti precursor flow rate and an exposure to a second N precursor at a second N precursor flow rate. The method is such that one or both of the TiN thin film and the second TiN thin film have high (111) crystalline texture such that X-ray spectra of the one or both of the TiN thin film and the second TiN thin film have a ratio of a peak height or an intensity of an X-ray diffraction peak corresponding to a (111) crystal orientation of TiN to a peak height or an intensity of an X-ray diffraction peak corresponding to a (200) crystal orientation of TiN that exceeds 0.4. 
     According to some other embodiments, a method of forming a thin film comprising titanium nitride (TiN) by a cyclical vapor deposition process comprises forming on a semiconductor substrate a first TiN thin film at a first pressure by exposing the semiconductor substrate to one or more first cyclical vapor deposition cycles each comprising an exposure to a first Ti precursor at a first Ti precursor flow rate and an exposure to a first N precursor at a first N precursor flow rate. The first TiN thin film has a crystalline texture such that an X-ray spectrum of the TiN thin film has a ratio of a peak height or an intensity of an X-ray diffraction peak corresponding to a (111) crystal orientation of TiN to a peak height or an intensity of an X-ray diffraction peak corresponding to a (200) crystal orientation of TiN that exceeds 0.4. The method additionally comprises forming on the first TiN thin film a second TiN thin film at a second pressure higher than the first pressure by exposing the semiconductor substrate to one or more second cyclical vapor deposition cycles each comprising an exposure to a second Ti precursor at a second Ti precursor flow rate and an exposure to a second N precursor at a second N precursor flow rate. The second TiN thin film can be formed according to any first or second TiN thin film formed as part of a dual or multiple layer TiN thin film process described above, e.g., those described above with respect to  FIGS. 3A, 3B and 4 . 
     According to these embodiments, the resulting TiN thin film comprises a lower portion and an upper portion, where the lower and upper portions can have different crystalline textures. At least the lower portion of the thin film has a crystalline texture such that an X-ray diffraction profile of the thin film has a ratio of a peak height or an intensity of an X-ray diffraction peak corresponding to (111) crystal orientation to a peak height or an intensity of an X-ray diffraction peak corresponding to (200) crystal orientation exceeds 0.4. The upper portion can have similar or lower degree of (111) texture, depending on the deposition condition and the desired final film characteristics, as described herein. 
     Advantageously, the second TiN thin film grown on the TiN thin film can benefit from a high (111) texture of the underlying first TiN thin film. Under these circumstances, the second TiN thin film can also have relatively high (111) texture despite that fact that, if grown on another surface that does not have the high (111) TiN texture of the underlying first TiN thin film, the second TiN thin film may not have a relatively high (111) texture. For example, if grown on a different surface, e.g., a material other than TiN or TiN that does not have a relatively high (111) texture, such as an insulating film such as SiO 2 , Si or other materials, the second TiN thin film may not have a relatively high (111) texture. For example, if grown on another surface, the second TiN layer may have a crystalline texture such that an X-ray spectrum of the TiN thin film has a ratio of a peak height or an intensity of an X-ray diffraction peak corresponding to a (111) crystal orientation of TiN to a peak height or an intensity of an X-ray diffraction peak corresponding to a (200) crystal orientation of TiN that is substantially less than 0.4, e.g., 0.3, 0.2, 0.1 or a value in a range defined by any of these values. This is because the textured surface of the underlying TiN thin film can serve as a template for the second or subsequent TiN thin film. Because the second or subsequent TiN thin film is not necessarily formed under high (111) texturing condition, the second or subsequent TiN thin film can be formed under conditions that improve the overall performance of the combined TiN thin film. For example, the second or subsequent TiN thin film can be grown under conditions that increase the step coverage, e.g., at high pressure, as described above with respect to various two-step deposition processes. 
     For example, the second TiN thin film can be formed at a high pressure, e.g., greater than 3 or 5 torr, as described above, e.g., according to various two step processes described with respect to  FIGS. 3A and 3B , with or without the high N precursor flow rate and/or N/Ti precursor flow ratio. For example, by texturing the first TiN thin film to have a relatively high (111) orientation, the initial film growth may proceed substantially in a (111) texture-favorable mode, which advantageously results in improved mechanical properties and electrical resistivity as described above. On the other hand, by subsequently exposing the substrate to the Ti and/or N precursors at relatively high pressures, e.g., greater than 3 or 5 torr, during deposition of the second portion of the thin film, the latter portion of the thin film, or the second TiN thin film, can advantageously grow with a degree of conformality or a step coverage that is higher relative to a the first TiN thin film having a relatively high (111) texture, or relative to a TiN thin film that is deposited by exposing the substrate to the Ti and/or N precursors at the relatively low pressures, e.g., less than 3 torr or less than 1 torr. 
     In addition, because the first portion of the TiN thin film has a relatively high (111) texture, the second portion of the thin film, which may continue to grow in a layer by layer fashion, using the first portion as a template. The second TiN thin film can have a lower or comparable (111) texture relative the underlying first TiN thin film. 
     According to various embodiments, the thickness ratio between first and second TiN thin films can be 10%, 25%, 50%, 25%, 90% or a value in a range defined by any of these values, depending on the final film characteristics desired. For example, where higher degree of (111) texture is desired, the first TiN thin film may be 50% or greater in thickness relative to the overall thickness, whereas where higher degree of conformality is desired, the second TiN thin film may be 50% or greater in thickness. 
     The resulting TiN thin film can have (111) texture that is any fraction of the (111) texture value of the first TiN thin film, e.g., 10%, 25%, 50%, 25%, 90% or a value in a range defined by any of these values. The resulting Young&#39;s modulus and/or hardness can also have a value defined by these values. 
     The resulting TiN thin film can have a conformality value that is any fraction of the conformality value of the second TiN thin film without the underlying first TiN thin film, e.g., 10%, 25%, 50%, 25%, 90% or a value in a range defined by any of these values thereof. 
     As a net result, when deposited on certain surfaces, e.g., a surface comprising a non-metallic surface, the thin film comprising the first and second portions deposited by depositing a relatively highly (111) textured first TiN thin film followed by a second TiN thin film according to methods disclosed herein advantageously has a combination of surface roughness and conformality that is superior relative to a thin film layer formed on the same surface using a single step. Alternatively, or in addition, in part owing to the improved smoothness and conformality, the thin film has a relatively low electrical resistivity compared to TiN layers formed by some existing methods. 
     Thin Film Deposition System for Conformal and Smooth TiN Layers 
       FIG. 18  schematically illustrates a thin film deposition system including a thin film deposition chamber and a precursor delivery system configured for forming TiN layers according to embodiments. The illustrated thin film deposition chamber is configured to process a substrate on a support, e.g., a susceptor, under a process condition. The process chamber includes a gas distribution plate, also referred to as a showerhead, configured to diffuse the precursor(s) over a substrate on the susceptor. The thin film deposition system additionally includes a precursor delivery system configured to deliver a plurality of precursors from precursor sources and one or more purge gases, e.g., inert gases, from inert gas sources into the process chamber. Each of the precursors and purge gases is connected to the process chamber by a respective gas delivery line. The gas delivery lines additionally include mass flow controllers (MFCs) and respective precursor valves for introducing respective precursors into the thin film deposition chamber, which can be atomic layer deposition (ALD) valves. The gas delivery lines are connected to the thin film deposition chamber through a showerhead. By way of example only, the illustrated precursor delivery system is configured to deliver precursors including TiCl 4  and NH 3 , as a Ti precursor and a N precursor, respectively, into the process chamber from respective precursor sources through respective precursor delivery lines. The precursor delivery system is additionally configured to deliver Ar as a purge gas into the process chamber from Ar sources through purge gas delivery lines. The purge gas may be delivered as a continuous purge (CP) gas and/or a rapid purge (RP) gas. The illustrated precursor delivery system is configured to deliver Ar as both CP and RP gases into the process chamber from the Ar sources through respective gas delivery lines. While the illustrated thin film deposition system includes one process station for single wafer processing, embodiments are not so limited. In some embodiments, the thin film deposition system can advantageously include multiple processing stations for increased throughout among other advantages, as described below with respect to  FIG. 19 . 
       FIG. 19  shows a perspective view of a lid of a process chamber comprising multiple processing stations each configured to introduce precursors to a substrate for TiN deposition. Each of the multiple processing stations has a lid portion  112 - 1 ,  112 - 2 ,  112 - 3 ,  112 - 4  that is configured to introduce precursors through precursor delivery lines as shown in  FIG. 18 , according to embodiments. The lid illustrated in  FIG. 19  corresponds to a process chamber having four processing stations each configured to process a substrate on a support, e.g., a susceptor, under a process condition. Each of the processing stations is configured to independently process a substrate under a process condition, including a process temperature and a process pressure. The processing stations can be, e.g., single substrate processing stations each configured to deliver precursors through respective precursor delivery lines, as shown in  FIG. 18 . The illustrated lid portions  112 - 1 ,  112 - 2 ,  112 - 3  and  112 - 4  (not shown) are physically outside the process chamber. Inside the process chamber, the lid portion can include or be attached to a gas distribution plate (not shown), or a showerhead, configured to diffuse the precursor(s) over a substrate on the susceptor. 
     Each of the process chamber lids illustrated in  FIG. 19  is equipped with a precursor delivery system for delivering a plurality of precursors and one or more purge gases. Each of the precursors and purge gases is connected to the process chamber by a respective gas delivery line. Each of the delivery lines is connected to the respective gas source on the one end as described above with respect to the thin film deposition system illustrated in  FIG. 19 . On the other end, the delivery line is split into four local delivery lines connected to valve assembly blocks  250 - 1 ,  250 - 2 ,  250 - 3  and  250 - 4  (not shown) each including multiple ALD valves. The ALD valves are in turn connected to showerheads of each of the processing stations, in a similar manner as shown in  FIG. 18 . 
     Exemplary Gas Delivery Sequence for Forming Conformal and Smooth TiN Layers 
     Using a thin film deposition system similar to the ones described above, various advantageous methods of depositing a highly conformal thin film comprising TiN can be implemented. According to various embodiments, a method of depositing a thin film comprises alternatingly exposing a substrate in a thin film deposition chamber to a plurality of precursors. Exposing the substrate comprises introducing the precursors into the thin film deposition chamber through valves (e.g., atomic layer deposition (ALD) valves) each configured to supply one of the precursors. 
     It will be appreciated that each of the precursor valves can be configured as a three-port valve configured to simultaneously flow a carrier gas and a precursor gas. For example, a carrier gas, e.g., Ar or N 2 , enters through one port and exits through another. A precursor gas enters through a third port, which is a small, precise orifice that delivers a relatively small chemical volume. This three-port configuration can deliver a steady flow of carrier gas into the process station while pulsing a precursor gas, as shown. The carrier gas serves to facilitate the movement the precursor into the deposition chamber, and to control the overall process pressure during deposition. 
       FIG. 20  illustrates, by way of example only, an example precursor delivery sequence for delivering two precursors, according to some embodiments. A first precursor  2010  is delivered through a first precursor inlet connected to a first valve (e.g., an ALD valve) and a second precursor  2020  is delivered through a second precursor inlet connected to a second valve (e.g., an ALD valve). A deposition cycle  2006 , (e.g., an ALD cycle) comprises a first subcycle  2002  for exposing a substrate to the first precursor  2010 , e.g., a first one of Ti and N precursors, and a second subcycle  2004  for exposing the substrate to the second precursor  2020 , e.g., the other of the Ti and N precursors. Each of the precursor valves (e.g., ALD valves) can be configured as a three-port valve, and in some implementations, a continuous purge gas  2008 , e.g., an inert gas, may be provided through the valves while the substrate is exposed to the first precursor  2010  and/or the second precursor  2020 . In the illustrated embodiment, one or both of the first  2002  and second  2004  subcycles further comprise respective rapid purges  2012 ,  2022  using an inert gas following the exposures to one or both of the first  2010  and second  2020  precursors, respectively. The rapid purges  2012 ,  2022  may be performed using a purge valve. The rapid purge  2012  is higher in magnitude, e.g. has a higher flow rate, than the continuous purge  2008 . 
     Advantageously, one or both of the first  2010  and second  2020  precursors may be introduced into the thin film deposition chamber through respective valves. The first precursor  2010  can be, e.g., one of a Ti precursor such as TiCl 4  and a N precursor such as NH 3 , and the second precursor  2020  can be, e.g., the other of the Ti precursor and the N precursor. According to embodiments, the exposure time of one or both of the first  2010  and second  2020  precursors can be less than 1.0 sec., 0.8 sec., 0.6 sec, 0.4 sec, 0.2 sec., 0.1 sec., or a value in a ranged defined by any of these values. 
     The thin film deposition system is configured to introduce one or both of the first  2010  and second  2020  precursors through respective ones of the valves at respective flow rates such that a surface of the substrate substantially reaches a saturation level, e.g., a saturation level greater than 40%, 60%, 80% or a value in a range defined by any of these values, within the respective exposure times. 
     In embodiments where a rapid purge follows an exposure to a precursor as illustrated, durations of one or both of the first  2002  and second  2004  subcycles, including the precursor exposure and the rapid purge, can be less than 1.0 sec., 0.8 sec., 0.6 sec, 0.4 sec, 0.2 sec., 0.1 sec., or a value in a ranged defined by any of these values. By reducing the exposure times of one or both of the first  2010  and second  2020  precursors, the durations of one or both of the corresponding first  2002  and second  2004  subcycles may be reduced, thereby reducing the overall cycle  2006  time. According to embodiments, a duration of the overall cycle  2006  including the first  2002  and second  2004  subcycles may be less than 2.0 sec., 1.5 sec, 1.0 sec., 0.5 sec., or a value in a range defined by any of these values. 
     TiN Deposition Processes with Reduced Particle Generation 
     As described above, as the dimensions of various IC structures shrink, TiN is formed on features having increasingly smaller dimensions and complex topologies. The increasingly smaller dimensions are accompanied by an increasing difficulty of maintaining or improving yield and reducing defects in deposited films. Some defect in ICs can be attributed to particles produced during film deposition. Accordingly, the shrinking dimensions of the IC structures place an increasing demand on deposition processes to generate fewer particles. The inventors have discovered that NH 3 , when used as a nitrogen precursor or as a purge gas according to embodiments disclosed herein, can provide a significant reduction in particles that are deposited on a substrate directly or indirectly as a result of depositing the TiN layer. 
     The inventors have discovered that, when NH 3  is introduced as a precursor at relatively high flow rates and for relatively short durations according to embodiments, the resulting TiN thin film can be formed with a reduced number of particles on or embedded therein.  FIG. 21  is a flow chart schematically illustrating a method  2100  of forming a TiN layer by cyclical vapor deposition process with reduced particles generated therefrom, according to some embodiments. The method includes providing  2110  a semiconductor substrate and forming  2120  on the semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to NH 3  at a NH 3  flow rate. Exposing  2130  the semiconductor substrate includes subjecting the semiconductor substrate to one or more exposure conditions including: a ratio of the NH 3  flow rate to the Ti precursor flow rate exceeding 3; the NH 3  flow rate exceeding 300 sccm; and/or a NH 3  exposure duration of 0.1-0.6 sec. 
     Without limitation, the method  2100  can be implemented on a thin film deposition system similar to those described above with respect to  FIGS. 18 and 19 , and using a precursor delivery sequence similar to that described above with respect to  FIG. 20 . For example, referring to  FIG. 20 , the first precursor  2010  can be a Ti precursor, e.g., TiCl 4 , and the second precursor  2020  can be a N precursor, e.g., NH 3 , and the exposures to each of the first  2010  and second  2020  precursors can be followed by a rapid purge  2012 ,  2022  using, e.g., N 2  or Ar. The exposures to each of the first  2010  and second  2020  precursors can be accompanied by a continuous purge  2008  through a three-port ALD valve described above. 
     Various process parameters including the substrate temperature, chamber pressure and exposure times, can be, in accordance with various process parameters described above, the details of which are not repeated herein for brevity. 
     According to embodiments, subjecting  2130  the semiconductor substrate to one or more exposure conditions is such that a ratio of the NH 3  flow rate to the Ti precursor flow rate exceeds 2. The ratio can exceed 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or have a value in a range defined by any of these values. 
     According to embodiments, subjecting  2130  the semiconductor substrate to one or more exposure conditions is such that the NH 3  flow rate can exceed 200 sccm, 500 sccm, 1000 sccm, 2000 sccm, 3000 sccm. 4000 sccm, 5000 sccm, 6000 sccm, 7000 sccm, 8000 sccm, 9000 sccm, 10000 sccm, or have a value in a range defined by any of these values. 
     According to embodiments, subjecting  2130  the semiconductor substrate to one or more exposure conditions is such that the Ti precursor flow rate exceeds 100 sccm but does not exceed the flow rate of NH 3 . For example, the Ti precursor flow rate can exceed 100 sccm, 200 sccm, 500 sccm, 1000 sccm, 2000 sccm, 3000 sccm., 4000 sccm, 5000 sccm, or have a value in a range defined by any of these values. 
     It will be appreciated that, for multi-station systems such as the one described above with respect to  FIG. 19 , the flow rates disclosed herein can represent a flow rate per processing station, and one or more stations can be in operation at the same time. For example, for the multi-station system including four processing stations, the total flow rates described herein can be 1×, 2×, 3× or 4× depending on how many processing stations are operated at a given moment. 
     When implemented in a thin film deposition system such as described herein, relative to a TiN thin film deposited in the same thin film deposition system using a method having the same process parameters except for one or more of a ratio of the NH 3  flow rate to the Ti precursor flow rate exceeding 3, the NH 3  flow rate exceeding 300 sccm and/or a NH 3  exposure duration of 0.1 sec., 0.2 sec., 0.3 sec., 0.4 sec., 0.5 sec., 0.6 sec. or any range therebetween, a number of particles on or embedded in the thin film having a size greater than about 0.1 μm is reduced by 50% or more. 
       FIG. 22  shows an experimental measurement of the number of particles on a 300 mm wafer after forming TiN layers using the method illustrated in  FIG. 21 . The y-axis represents the total number of particles detected as having a size of about 0.100-0.700 μm, as measured using KLA-Tencor SP1/SP2. The x-axis represents the duration of the exposure of the substrate to NH 3  as part of the process that can be represented by the exposure sequence illustrated in  FIG. 20 . The number of particles was measured after subjecting a substrate to a plurality of cycles each including an exposure to TiCl 4  and an exposure to NH 3 , where the exposures to each of the precursors is followed by a rapid purge using Ar. In the illustrated experimental measurement, the TiCl 4  flow rate and NH 3  flow rate were 100 sccm and 2000 sccm, respectively, per processing station for each of the four processing stations as illustrated in  FIG. 19 , or a combined flow of 400 sccm and 8000 sccm, respectively. The TiCl 4  exposure duration, post-TiCl 4  exposure purge duration, NH 3  exposure duration and post-NH 3  exposure purge duration were 0.1 sec., 0.2 sec., 0.1-0.6 sec as shown and 0.3 sec., respectively. The chamber pressure during deposition was 5 Torr and the substrate temperature was about 550° C. during the deposition of the TiN layer. 
     As illustrated, the inventors have found that the NH 3  exposure duration less than 0.6 sec, or more particularly a duration of 0.1-0.6 sec., 0.1-0.2 sec, 0.2-0.3 sec., 0.3-0.4 sec., 0.4-0.5 sec, 0.5-0.6 sec., or 0.3-0.6 sec, can be critical in obtaining an expected reduction in the number of particles on or embedded in the thin film having a size greater than about 0.1 μm by 50% or more. 
     Without being bound to any theory, NH 3  may, alone or in combination of any of the chemical species present on the substrate or in the chamber, chemically or physically interact or react with some types of particles. The interaction may be, e.g., a chemical reaction that volatilizes the particles, thereby reducing the particles that may have formed on the substrate. The interaction may be, e.g., a physical interaction where the high relatively high flow rate physically removes the particles that may have formed on the substrate. 
     The inventors have discovered that beneficial NH 3  exposure conditions that lead to particle reduction are not limited to relatively high flow rate as part of reaction cycles. The inventors have further discovered that, when NH 3  is introduced as a post-deposition purge gas according to embodiments, the resulting TiN thin film can be formed with reduced number of particles on or embedded therein.  FIG. 23  is a flow chart schematically illustrating a method  2300  of forming a TiN layer by cyclical vapor deposition process with reduced particle generation, according to some other embodiments. Unlike the method  2100  described above with respect to  FIG. 21 , the method  2300  includes subjecting the semiconductor substrate to NH 3  after forming the TiN thin film. The method  2300  includes providing  2310  a semiconductor substrate and forming  2320  on the semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to NH 3  at a first NH 3  flow rate for a NH 3  exposure duration. The method  2300  additionally includes, after forming the TiN film, subjecting  2330  the semiconductor substrate, e.g., in situ and without further deposition of the TiN film to a post-deposition exposure to NH 3  under a condition including one or both of: a second NH 3  flow rate lower than the first NH 3  flow rate by at least a factor of two; and a second NH 3  exposure duration exceeding the NH 3  exposure duration by at least a factor of five. According to embodiments, the post-deposition exposure may be the last exposure step prior to removing the substrate from the chamber. 
     Without limitation, the method  2300  can be implemented in a thin film deposition system similar to those described above with respect to  FIGS. 18 and 19 . In addition, forming  2320  the TiN thin film can be implemented using a precursor delivery sequence similar to that described above with respect to  FIG. 20 . Various process parameters including the substrate temperature, chamber pressure, flow rates and exposure times during deposition, can be in accordance with various process parameters described above, the details of which are not repeated herein for brevity. However, unlike previously described embodiments, the illustrated method  2300  additionally includes, after forming the TiN thin film, subjecting  2330  the substrate having a TiN thin film formed thereon to a post-deposition exposure to NH 3 . 
     According to embodiments, subjecting  2330  the semiconductor substrate, without further depositing the TiN film, to a post-deposition exposure to NH 3  includes exposing the semiconductor substrate to a second NH 3  flow rate that is different, e.g., lower than the NH 3  flow rate during the deposition of the TiN by at least a factor of 2, 4, 6, 8, 10, or a value in a range defined by any of these values. For example, the second NH 3  flow rate can exceed 100 sccm, 250 sccm, 500 sccm, 1000 sccm, 1500 sccm, 2000 sccm, 2500 sccm, 3000 sccm, 3500 sccm, 4000 sccm, 4500 sccm, 5000 sccm, or have a value in a range defined by any of these values, for instance 500 sccm. 
     According to embodiments, subjecting  2330  the semiconductor substrate, without further depositing the TiN film, to a post-deposition exposure to NH 3  includes exposing the semiconductor substrate to a second NH 3  exposure for a duration exceeding the NH 3  exposure duration during the deposition of the TiN by at least a factor of 5, 10, 20, 50, 100, 200, 500 or a value in a range defined by any of these values. For example, the second NH 3  exposure duration can exceed 1 sec., 5 sec., 10 sec, 20 sec, 50 sec., 100 sec., 200 sec., 500 sec, 1000 sec., or have a value in a range defined by any of these values, for instance 120 sec. 
     According to some embodiments, subjecting  2330  the semiconductor substrate to a post deposition exposure can be performed at a first temperature. In some embodiments, subjecting  2330  the semiconductor substrate to a post deposition exposure can be performed at the same temperature as forming  2320  on the semiconductor substrate a TiN thin film without aid of plasma. In some other embodiments, subjecting  2330  the semiconductor substrate to a post deposition exposure can be performed at a different temperature than forming  2320  on the semiconductor substrate a TiN thin film without aid of plasma. 
     When implemented in a thin film deposition system such as described herein, relative to a TiN thin film deposited in the same thin film deposition system using a method having the same process parameters except for subjecting the substrate to the post deposition exposure to NH 3 , a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% or more. 
       FIGS. 24A and 24B  show experimental measurements of the number of particles on a 300 mm wafer after forming a TiN layer using the method illustrated in  FIG. 23 . In  FIG. 24A , the y-axis of the graph represents the total number of particles detected as having a size of about 0.100-0.700 μm, as measured using KLA-Tencor SP1/SP2. The x-axis of the graph shows two different post-deposition exposure times, namely 20 sec. (left bar graphs) and 120 sec. (right bar graphs), for exposing the substrate to NH 3 . For each exposure times, measurements were made on two different stations (Stn1, Stn4) in a multi-station chamber such that described above with respect to  FIG. 19 . The number of particles was measured after subjecting a substrate to a TiN deposition and to the post-deposition NH 3  purge, according to embodiments. The process condition for depositing the TiN thin film was the same as that described above with respect to  FIG. 22  with an NH 3  exposure time of 0.3 sec. After the TiN deposition including an inert gas purge, the NH 3  purge was performed at a flow rate of 500 sccm per processing station for each of the four processing stations as illustrated in  FIG. 19 , or a combined flow of 2000 sccm. The post-deposition NH 3  exposure durations for the two experimental conditions were 20 sec. and 120 sec. The chamber pressure during the TiN deposition and during the post-deposition NH 3  exposure was kept constant at 5 Torr and the substrate temperature was kept constant at about 550° C. during the TiN deposition and during the post-deposition NH 3  exposure. 
     The inventors have further discovered that the beneficial NH 3  exposure conditions that lead to particle reduction are not limited to relatively high flow rate as part of reaction cycles or post-deposition purge as described above. The inventors have further discovered that, when NH 3  is introduced as an idle purge gas between TiN depositions according to embodiments, e.g., without a substrate in a chamber, the substrates having formed thereon a TiN thin film after the idle purge can have reduced number of particles on or embedded therein.  FIG. 25  is a flow chart schematically illustrating a method  2500  of forming a TiN layer by cyclical vapor deposition process with reduced particle generation, according to some other embodiments. The method  2500  includes, prior to deposition, subjecting  2510  a thin film deposition chamber without a substrate disposed therein to a pre-deposition chamber purge under a NH 3  purge flow rate, which can be the same, higher or lower than a NH 3  flow rate during a TiN thin film deposition condition by at least a factor of two. Subsequently, the method  2500  includes transferring  2520  a semiconductor substrate into the thin film deposition chamber. Thereafter, the method  2500  additionally includes forming  2530  on the semiconductor substrate a TiN thin film under the thin film deposition condition in the thin film deposition chamber without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to ammonia (NH 3 ) at a NH 3  flow rate. 
     Without limitation, the method  2500  can be implemented in a thin film deposition system described above with respect to  FIGS. 18 and 19 . In addition, forming  2530  the TiN thin film can be implemented using a precursor delivery sequence similar to that described above with respect to  FIG. 20 . Various process parameters including the substrate temperature, chamber pressure, flow rates and exposure times during deposition, can be in accordance with various process parameters described above, the details of which are not repeated herein for brevity. However, unlike previously described embodiments, the illustrated method  2500  additionally includes, before and/or after forming the TiN thin film, subjecting  2530  the thin film deposition chamber without having a substrate disposed therein to an idle purge using NH 3 . 
     According to embodiments, subjecting  2510  the thin film deposition chamber to a NH 3  purge includes flowing NH 3  at a second NH 3  flow rate that can be the same or different compared to the NH 3  flow rate during the deposition of the TiN. For example, the NH 3  purge flow rate can exceed 200 sccm, 500 sccm, 1000 sccm, 2000 sccm, 3000 sccm, 4000 sccm, 5000 sccm, 6000 sccm, 7000 sccm, 8000 sccm, 9000 sccm, 10,000 sccm, or have a value in a range defined by any of these values, or have a value in a range defined by any of these values, for instance 2000 sccm. In some embodiments, the NH 3  purge can be accompanied by a nitrogen (N 2 ) purge at a flow rate similar to any of the above NH 3  flow rates. 
     According to embodiments, subjecting  2510  the thin film deposition chamber to a NH 3  purge includes flowing the NH 3  for a duration exceeding that of a deposition cycle duration. The purge duration can exceed 1 sec., 100 sec., 1000 sec., 10,000 sec., or have a value in a range defined by any of these values, for instance 2 hours. 
     When implemented in a thin film deposition system such as described herein, relative to a TiN thin film deposited in the same thin film deposition system using a method having the same process parameters except for subjecting the thin film deposition chamber to the pre-deposition NH 3  purge, a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% or more. 
       FIG. 26  shows experimental measurements of the number of particles on a 300 mm wafer after subjecting the thin film deposition to the pre-deposition chamber purge under a NH 3  purge according to the method illustrated in  FIG. 25 . In the upper graph, the y-axis represents the total number of particles detected as having a size of about 0.100-0.700 μm, as measured using KLA-Tencor SP1/SP2. The x-axis shows the conditions the chamber has been subjected to prior to inserting a virgin test wafer for particle detection, namely before the TiN deposition, after 5000 TiN deposition wafer cycles and after 2 hours of idle purge under NH 3 . The process condition for TiN deposition cycles was the same as that described above with respect to  FIG. 19B  with an NH 3  flow rate of 2,000 sccm and an NH 3  exposure time of 0.3 sec. After TiN deposition including an inert gas purge, the NH 3  purge was performed at a flow rate of 500 sccm per processing station for each of the four processing stations as illustrated in  FIG. 19 , or a combined flow of 2,000 sccm. For monitoring the effect of each of the process conditions the chamber has been subjected to, a virgin test wafer was mechanically inserted into the chamber, valves were operated without deposition gases, and the test wafer was taken out from the chamber for particle measurement. In the illustrated measurement, the experiment was performed for four different stations. N 2  at a flow rate of 5000 sccm was also flowed into the process chamber. 
     Applications 
     The thin films comprising TiN formed using different exposure pressures according to various embodiments disclosed herein can be used in a variety of applications, particularly where the substrate comprises a relatively high aspect ratio structure and/or a non-metal surface that can benefit from various advantageous characteristics of the TiN layer as disclosed herein. Example applications include deposition a via, a hole, a trench, a cavity or a similar structure having an aspect ratio, e.g., a ratio defined as a depth divided by a top width, that exceeds 1, 2, 5, 10, 20, 50, 100, 200 or a value in a range defined by any of these values. 
     By way of example,  FIG. 10  schematically illustrates an application in the context of a diffusion barrier for a contact structure, e.g., a source or drain contact, formed on an active semiconductor substrate region that may be heavily doped. A portion of a semiconductor device  1000  is illustrated, which includes a substrate  1004  on which a dielectric layer  1008 , e.g., an interlayer or intermetal dielectric (ILD) layer comprising a dielectric material such as an oxide or nitride is formed. In order to form contacts to various regions of the substrate  1004 , including various doped regions, e.g., source and drain regions, a via or a trench may be formed through the dielectric layer  1008 . The via or the trench may expose various non-metal surfaces, e.g., an exposed bottom surface comprising a substrate surface, e.g., a silicon substrate surface, as well as dielectric sidewalls of the vias. The bottom and side surfaces of the via can be conformally coated with a first portion (corresponding to the first portion  370  in  FIG. 3B ) of the TiN layer, followed by a second portion (corresponding to the second portion  380  in  FIG. 3B ) formed according to various embodiments described herein. A conformal first portion may first be formed directly on inner surfaces of the via, followed by formation of a conformal second TiN layer, according to various embodiments disclosed herein. Thereafter, the lined via may be filled with a metal, e.g., W, Al or Cu, to form a contact plug  1016 . For example, the via may be filled with tungsten by CVD using, e.g., WF 6 . 
     The barrier layer  1012  formed according to embodiments can be advantageous for various reasons. In particular, due to the conformal nature of the barrier layer  1012  formed by ALD, the propensity for a pinching off during the subsequent metal fill process may be substantially reduced. In addition, as described above, the barrier layer  1012  can provide effective hindrance of material transport thereacross, e.g., dopant (B, P) out-diffusion from the substrate  1004 , as well as in-diffusion of reactants, etchants and metals (e.g., F, Cl, W or Cu) from the contact plug formation process. The barrier effect may be enhanced by reduced surface roughness and increased step coverage. Furthermore, as described above, a layer-by-layer growth mode may reduce the overall contact resistance of the barrier layer  1012 . Furthermore, due to the reduced film roughness, a relatively thinner barrier layer  1012  may be formed while still accomplishing its desired barrier function, leading to further reduction in contact resistance. 
     Other applications of the TiN layers formed according to various embodiments disclosed herein include conductive structures formed in recessed substrates (e.g., buried electrodes or lines), electrodes (e.g., DRAM capacitor electrodes or gate electrodes), metallization barriers for higher metal levels (e.g., barriers in vias/trenches for Cu contacts/lines), high aspect ratio vertical rod electrodes or vias for three-dimensional memory and through-silicon vias (TSVs), to name a few. 
     Example Embodiments I 
     1. A method of forming a thin film comprising titanium nitride (TiN) by a cyclical vapor deposition process, the method comprising:
         forming on a semiconductor substrate a TiN thin film by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to a N precursor at a N precursor flow rate,   wherein a ratio of the N precursor flow rate to the Ti precursor flow rate exceeds 3.       

     2. A method of forming a thin film comprising titanium nitride (TiN) by a cyclical vapor deposition process, the method comprising:
         forming on a semiconductor substrate a TiN thin film by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to a first N precursor at a first N precursor flow rate,   wherein the N precursor flow rate exceeds 200 sccm.       

     3. A method of forming a thin film comprising titanium nitride (TiN) by a cyclical vapor deposition process, the method comprising:
         forming on a semiconductor substrate a TiN thin film by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate within a Ti precursor flow rate range and an exposure to a N precursor at a N precursor flow rate within a N precursor flow rate range,   wherein the N precursor flow range and the Ti precursor flow range are such that the TiN thin film has a preferential (111) crystalline texture relative to another TiN thin film formed by exposing the semiconductor substrate to cyclical vapor deposition cycles each comprising an exposure to the Ti precursor within a different Ti precursor flow rate range outside of the Ti precursor flow rate range and an exposure to the N precursor within a different N precursor flow rate range outside of the N precursor flow rate range.       

     4. The method of any of the above Embodiments, wherein the ratio of the N precursor flow rate to the Ti precursor flow rate is 2-100. 
     5. The method of any of the above Embodiments, wherein the N precursor flow rate is 200 sccm-10,000 sccm. 
     6. The method of any of the above Embodiments, wherein the Ti precursor flow rate is 100 sccm-5000 sccm. 
     7. The method of any of the above Embodiments, wherein the TiN thin film has a preferential (111) crystalline texture such that an X-ray spectrum of the TiN thin film has a ratio of a peak height or an intensity of an X-ray diffraction peak corresponding to (111) crystal orientation to peak height or an intensity of an X-ray diffraction peak corresponding to (200) crystal orientation exceeds 0.4. 
     8. The method of any of the above Embodiments, wherein the TiN thin film has a hardness exceeding 6 GPa. 
     9. The method of any of the above Embodiments, wherein the TiN thin film has a Young&#39;s modulus exceeding 150 GPa. 
     10. The method of any of the above Embodiments, further comprising:
         forming on the TiN thin film a second TiN thin film by exposing the semiconductor substrate to one or more second cyclical vapor deposition cycles each comprising an exposure to a second Ti precursor and an exposure to a second N precursor,   wherein exposures to one or both of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles are at higher pressures relative to corresponding exposures to one or both of the Ti precursor and the N precursor during the one or more cyclical vapor deposition cycles.       

     11. The method of Embodiment 10, wherein the exposures to one or both of the Ti precursor and the N precursor during the one or more cyclical vapor deposition cycles are at a reactor pressure of less than about 5 torr, and wherein the exposures to one or both of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles are at a reactor pressure greater than about 5 torr. 
     12. The method of Embodiments 10 or 11, wherein the exposure to each of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles is at a higher pressure relative to the corresponding exposure to each of the Ti precursor and the N precursor during the one or more cyclical vapor deposition cycles. 
     13. The method of any of Embodiments 10-12, wherein forming the TiN thin film comprises depositing at a first deposition rate less than 0.3 Å per one of the cyclical vapor deposition cycles comprising an exposure of the semiconductor substrate to the Ti precursor and an exposure to the N precursor, and wherein forming the second TiN thin film comprises depositing at a second deposition rate greater than 0.3 Å per one of the second cyclical vapor deposition cycles comprising an exposure of the semiconductor substrate to the second Ti precursor and an exposure to the second N precursor. 
     14. The method of any of the above Embodiments, wherein a root mean square surface roughness of the thin film is less than about 8% of a thickness of the thin film. 
     15. The method of any of Embodiments 10-14, wherein forming the TiN thin film and the second TiN thin film comprise depositing by thermal cyclical vapor deposition. 
     16. The method of any of Embodiments 10-15, wherein forming the TiN thin film comprises directly exposing one or both of a semiconductor surface and an insulator surface to the one or more cyclical vapor deposition cycles. 
     17. The method of any of Embodiments 10-16, wherein forming one or both of the TiN thin film and the second TiN thin film comprises growing in a layer-by-layer growth mode. 
     18. The method of any of Embodiments 10-17, wherein forming the TiN thin film comprises alternatingly exposing the semiconductor substrate to 1 to 50 the cyclical vapor deposition cycles. 
     19. The method of any of Embodiments 10-18, wherein forming the TiN thin film and the second TiN thin film comprises forming at a temperature between 400° C. and 600° C. 
     20. The method of any of the above Embodiments, wherein the semiconductor substrate comprises a trench or a via comprising an inner surface comprising a non-metallic sidewall surface in a trench or a via having an aspect ratio exceeding 1, and wherein forming the thin film comprises conformally lining the inner surface, wherein a ratio of thicknesses of the thin film formed on lower 25% of a height of the trench or the via and upper 25% of the height of the trench or the via exceeds 0.9. 
     21. The method of any of the above Embodiments, wherein an electrical resistivity of the thin film is less than about 200 μΩ-cm. 
     22. The method of any of Embodiments 10-21, wherein the Ti precursor is the same as the second Ti precursor and the N precursor is the same as the second N precursor. 
     23. The method of any of Embodiments 1-9, the method comprising:
         providing the semiconductor substrate comprising a trench or a via having an aspect ratio exceeding 1;   forming the thin film in the trench or the via by exposing the semiconductor substrate to the one or more cyclical vapor deposition to form the TiN thin film in the trench or the via; and   further exposing the semiconductor substrate to one or more second cyclical vapor deposition cycles each comprising an exposure to a second Ti precursor and an exposure to a second N precursor to form a second TiN thin film on the TiN thin film, wherein exposures to one or both of the Ti precursor and the N precursor during the one or more cyclical vapor deposition cycles are at different pressures relative to corresponding exposures to one or both of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles.       

     24. The method of Embodiment 23, wherein exposures to one or both of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles are at higher pressures relative to corresponding exposures to one or both of the Ti precursor and the N precursor during the one or more cyclical vapor deposition cycles. 
     25. The method of Embodiments 23 or 24, wherein exposures to one or both of the second Ti precursor and the second N precursor during the one or more second cyclical vapor deposition cycles are at higher pressures relative to corresponding exposures to one or both of the Ti precursor and the N precursor during the one or more cyclical vapor deposition cycles by a factor of 5 or greater. 
     26. The method of any of Embodiments 23-25, wherein forming the TiN thin film comprises alternatingly exposing the semiconductor substrate to 1 to 50 cyclical vapor deposition cycles. 
     27. The method of any of Embodiments 23-26, wherein forming the TiN thin film comprises exposing the semiconductor substrate to a first number of the one or more cyclical vapor deposition cycles, and wherein forming the second portion comprises exposing the semiconductor substrate to a second number of second cyclical vapor deposition cycles greater than twice the first number of the one or more cyclical vapor deposition cycles. 
     28. The method of any of Embodiments 23-27, wherein a root mean square surface roughness of the thin film is less than about 8% of a thickness of the thin film. 
     29. The method of any of Embodiments 23-28, wherein forming the TiN layer comprises forming by thermal cyclical vapor deposition at a temperature between 400° C. and 600° C. 
     30. The method of any of Embodiments 23-29, wherein the trench or the via has an aspect ratio exceeding 5 and an inner surface comprising a non-metallic sidewall surface, and wherein forming the thin film comprises conformally lining the inner surface, wherein a ratio of thicknesses of the thin film formed on lower 25% of a height of the trench or the via and upper 25% of the height of the trench or the via exceeds 0.9. 
     31. The method of any of Embodiments 23-29, wherein the Ti precursor is the same as the second Ti precursor and the N precursor is the same as the second N precursor. 
     32. A semiconductor structure, comprising:
         a semiconductor substrate comprising a non-metallic sidewall surface in a trench or a via having an aspect ratio exceeding 5; and   a thin film comprising TiN conformally lining the non-metallic sidewall surface,   wherein the thin film has a preferential (111) crystalline texture such that an X-ray spectrum of the thin film has a ratio of a peak height or an intensity of an X-ray diffraction peak corresponding to (111) crystal orientation to a peak height or an intensity of an X-ray diffraction peak corresponding to (200) crystal orientation exceeds 0.4.       

     33. The semiconductor structure of Embodiment 32, wherein the ratio exceeds 1.3. 
     34. The semiconductor structure of Embodiments 32 and 33, wherein the thin film has a hardness exceeding 6 GPa. 
     35. The semiconductor structure of any of Embodiments 32-34, wherein the thin film has a Young&#39;s modulus exceeding 150 GPa. 
     36. The semiconductor structure of any of Embodiments 32-35, wherein a ratio of thicknesses of the thin film formed on lower 25% of a height of the trench or the via and upper 25% of the height of the trench or the via exceeds 0.9. 
     37. The semiconductor structure of any of Embodiments 32-36, wherein the trench or the via has an aspect ratio exceeding 10. 
     38. The semiconductor structure of any of Embodiments 32-37, wherein a root mean square surface roughness of the thin film formed on the non-metallic surface is less than about 8% on the basis of an average thickness of the thin film. 
     39. The semiconductor structure of any of Embodiments 32-38, wherein the trench or the via has a dielectric sidewall. 
     40. The semiconductor structure of any of Embodiments 32-39, wherein the trench or the via has a bottom surface exposing a semiconductor material of the semiconductor substrate. 
     41. The semiconductor structure of any of Embodiments 32-40, wherein the thin film has an electrical resistivity less than about 200 μΩ-cm. 
     42. The semiconductor structure of any of Embodiments 32-41, wherein the trench or the via lined with the thin film is filled with a metal comprising tungsten. 
     Example Embodiments II 
     1. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition, the method comprising:
         forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to ammonia (NH 3 ) at a NH 3  flow rate exceeding 200 sccm,   wherein a NH 3  exposure duration is 0.1 to 0.6 sec.       

     2. The method of Embodiment 1, wherein the method is carried out in a thin film deposition system wherein, relative to a TiN thin film deposited in the same thin film deposition system using a method having the same process parameters except for one or both of the NH 3  flow rate and the NH 3  exposure duration, a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% of more. 
     3. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition, the method comprising:
         forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to ammonia (NH 3 ) at a NH 3  flow rate such that a flow rate ratio of the NH 3  flow rate to the Ti precursor flow rate exceeds 3,   wherein a NH 3  exposure duration is 0.1 to 0.6 sec.       

     4. The method of Embodiment 3, wherein the method is carried out in a thin film deposition system wherein, relative to a TiN thin film deposited in the same thin film deposition system using a method having the same process parameters except for one or both of the flow rate ratio and the NH 3  exposure duration, a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% of more. 
     5. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition, the method comprising:
         forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to ammonia (NH 3 ) at a NH 3  flow rate for a NH 3  exposure duration; and   after forming the TiN thin film, subjecting the semiconductor substrate without further deposition of the TiN thin film to a post-deposition exposure to NH 3  under a condition including a second NH 3  flow rate lower than the NH 3  flow rate by at least a factor of two.       

     6. The method of Embodiment 5, wherein the method is carried out in a thin film deposition system wherein, relative to a thin TiN film deposited in the same thin film deposition system using a method having the same process parameters except for subjecting the substrate to the post deposition exposure to NH 3 , a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% of more. 
     7. The method of Embodiments 5 or 6, wherein forming the TiN thin film and subjecting the TiN thin film to a post-deposition exposure are performed at the same substrate temperature. 
     8. The method of any one of Embodiments 5-7, wherein the NH 3  flow rate is 1000-3000 sccm, and the second NH 3  flow rate is 200-1000 sccm. 
     9. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition, the method comprising:
         forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor at a Ti precursor flow rate and an exposure to ammonia (NH 3 ) at a NH 3  flow rate for a NH 3  exposure duration; and   after forming the TiN thin film, subjecting the semiconductor substrate without further deposition of the TiN thin film to a post-deposition exposure to NH 3  under a condition including a second NH 3  exposure duration exceeding the NH 3  exposure duration by at least a factor of five.       

     10. The method of Embodiment 9, wherein the method is carried out in a thin film deposition system wherein, relative to a TiN thin film deposited in the same thin film deposition system using a method having the same process parameters except for subjecting the substrate to the post deposition exposure to NH 3 , a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% of more. 
     11. The method of Embodiments 9 or 10, wherein forming the TiN thin film and subjecting the TiN thin film to a post-deposition exposure are performed at the same substrate temperature. 
     12. The method of any one of Embodiments 9-11, wherein the NH 3  exposure duration is 0.1-0.6 sec., and the second NH 3  exposure duration exceeds 1 sec. 
     13. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition process, the method comprising:
         subjecting a thin film deposition chamber without a substrate disposed therein to a pre-deposition chamber purge with ammonia (NH 3 ) at a NH 3  purge flow rate;   transferring a semiconductor substrate into the thin film deposition chamber; and   forming on the semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor flow rate and an exposure to NH 3 .       

     14. The method of Embodiment 13, wherein the method is carried out in the thin film deposition system wherein, relative to a TiN thin film deposited in the same thin film deposition system using a method having the same process parameters except for subjecting the thin film deposition chamber to the pre-deposition NH 3  purge, a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% of more. 
     15. The method of Embodiments 13 or 14, wherein the NH 3  purge flow rate exceeds 200 sccm. 
     16. The method of any one of Embodiments 13-15, wherein the pre-deposition chamber purge is performed for a duration exceeding 1 sec. 
     17. The method of any of the above Embodiments, wherein the method is carried out in a process station of a thin film deposition system comprising a plurality of process stations each configured to carry out the method. 
     18. The method of any of the above Embodiments, wherein forming the TiN thin film comprises exposing the semiconductor substrate to NH 3  at a NH 3  flow rate of 500-10,000 sccm. 
     19. The method of any of the above Embodiments, wherein the one or more cyclical vapor deposition cycles comprises the exposure to the Ti precursor at a Ti precursor flow rate and the exposure to ammonia (NH 3 ) at a NH 3  flow rate such that a flow rate ratio of the NH 3  flow rate to the Ti precursor flow rate is 3-100. 
     20. The method of any of the above Embodiments, wherein forming the TiN thin film comprises exposing the semiconductor substrate to the Ti precursor at the Ti precursor flow rate of 100 sccm-5000 sccm and lower than the NH 3  flow rate. 
     21. The method of any of the above Embodiments, wherein forming the TiN thin comprises exposing the semiconductor substrate to the Ti precursor and NH 3  for respective durations such that a duration of a cycle of the cyclical vapor deposition cycles is less than 2.0 sec. 
     Example Embodiments III 
     1. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition, the method comprising:
         forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor and an exposure to ammonia (NH 3 ) at a first NH 3  flow rate; and   after forming the TiN thin film, subjecting the semiconductor substrate, without deposition of an additional TiN thin film on the TiN thin film, to a post-deposition exposure to NH 3  at a second NH 3  flow rate,   wherein the second NH 3  flow rate is lower than the first NH 3  flow rate by at least a factor of two.       

     2. The method of Embodiment 1, wherein the method is carried out in a thin film deposition system wherein, relative to a reference TiN thin film deposited in the same thin film deposition system using a reference method that is the same as the method of Claim  1  except for subjecting the semiconductor substrate to the post-deposition exposure to NH 3 , a number of particles on or embedded in the TiN thin film having a size greater than 0.1 μm is reduced by 50% or more. 
     3. The method of Embodiments 1 or 2, wherein forming the TiN thin film and subjecting the semiconductor substrate to the post-deposition exposure are performed at the same semiconductor substrate temperature. 
     4. The method of any one of Embodiments 1-3, wherein the first NH 3  flow rate is 1000-3000 sccm, and the second NH 3  flow rate is 200-1000 sccm. 
     5. The method of any one of Embodiments 1-4, wherein a ratio of the first NH 3  flow rate to the Ti precursor flow rate is 3 to 100. 
     6. The method of any one of Embodiments 1-5, wherein the exposure to the Ti precursor is performed at a Ti precursor flow rate of 100 sccm-5000 sccm that is lower than the first NH 3  flow rate. 
     7. The method of any one of Embodiments 1-6, wherein a duration of each of the one or more cyclic vapor deposition cycles is less than 2.0 sec. 
     8. The method of any one of Embodiments 1-7, wherein a flow rate ratio of the first NH 3  flow rate to a Ti precursor flow rate exceeds 3. 
     9. The method of any one of Embodiments 1-8, wherein the exposure to NH 3  is performed for a duration of 0.1 to 0.6 sec. 
     10. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition, the method comprising:
         forming on a semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor and an exposure to ammonia (NH 3 ) for a first NH 3  exposure duration; and   after forming the TiN thin film, subjecting the semiconductor substrate, without deposition of an additional TiN thin film on the TiN thin film, to a post-deposition exposure to NH 3  for a second NH 3  exposure duration,   wherein the second NH 3  exposure duration is greater than the first NH 3  exposure duration by at least a factor of five.       

     11. The method of Embodiment 10, wherein the method is carried out in a thin film deposition system wherein, relative to a reference TiN thin film deposited in the same thin film deposition system using reference a method that is the same as the method of Claim  10  except for subjecting the semiconductor substrate to the post-deposition exposure to NH 3 , a number of particles on or embedded in the TiN thin film having a size greater than 0.1 μm is reduced by 50% or more. 
     12. The method of Embodiments 10 or 11, wherein forming the TiN thin film and subjecting the TiN thin film to the post-deposition exposure are performed at the same semiconductor substrate temperature. 
     13. The method of any one of Embodiments 10-12, wherein the first NH 3  exposure duration is 0.1-0.6 sec., and the second NH 3  exposure duration exceeds 1 sec. 
     14. The method of any one of Embodiments 10-13, wherein a flow rate ratio of a first NH 3  flow rate to a Ti precursor flow rate exceeds 3. 
     15. The method of any one of Embodiments 10-14, wherein the exposure to NH 3  is performed for a duration of 0.1 to 0.6 sec. 
     16. A method of depositing a thin film comprising titanium nitride (TiN) by cyclical vapor deposition process, the method comprising:
         subjecting a thin film deposition chamber without a substrate disposed therein to a pre-deposition chamber purge with ammonia (NH 3 ) at a first NH 3  purge flow rate;   transferring a semiconductor substrate into the thin film deposition chamber; and   forming on the semiconductor substrate a TiN thin film without aid of plasma by exposing the semiconductor substrate to one or more cyclical vapor deposition cycles each comprising an exposure to a Ti precursor and an exposure to NH 3 .       

     17. The method of Embodiment 16, wherein the method is carried out in the thin film deposition system wherein, relative to a reference TiN thin film deposited in the same thin film deposition system using reference method that is the same as the method of Claim  16  except for subjecting the thin film deposition chamber to the pre-deposition chamber purge, a number of particles on or embedded in the TiN thin film having a size greater than about 0.1 μm is reduced by 50% or more. 
     18. The method of Embodiments 16 or 17, wherein the first NH 3  purge flow rate exceeds 200 sccm. 
     19. The method of any one of Embodiments 16-18, wherein the pre-deposition chamber purge is performed for a duration exceeding 1 sec. 
     20. The method of any one of Embodiments 16-19, wherein the method is carried out in a process station of a thin film deposition system, 
     wherein the thin film deposition system comprises a plurality of process stations each configured to carry out the method. 
     21. The method of any one of Embodiments 16-20, wherein forming the TiN thin film comprises exposing the semiconductor substrate to NH 3  at a second NH 3  flow rate of 500-10,000 sccm. 
     22. The method of any one of Embodiments 1-21, wherein the one or more cyclical vapor deposition cycles comprises the exposure to the Ti precursor at a Ti precursor flow rate and the exposure to ammonia (NH 3 ) at a second NH 3  flow rate such that a flow rate ratio of the second NH 3  flow rate to the Ti precursor flow rate is 3 to 100. 
     23. The method of any one of Embodiments 1-22, wherein forming the TiN thin film comprises exposing the semiconductor substrate to the Ti precursor at the Ti precursor flow rate of 100 sccm-5000 sccm and lower than the second NH 3  flow rate. 
     24. The method of any one of Embodiments 1-23, wherein a duration each of the one or more cyclical vapor deposition cycles is less than 2.0 sec. 
     Although the present invention has been described herein with reference to the specific embodiments, these embodiments do not serve to limit the invention and are set forth for illustrative purposes. It will be apparent to those skilled in the art that modifications and improvements can be made without departing from the spirit and scope of the invention. 
     Such simple modifications and improvements of the various embodiments disclosed herein are within the scope of the disclosed technology, and the specific scope of the disclosed technology will be additionally defined by the appended claims. 
     In the foregoing, it will be appreciated that any feature of any one of the embodiments can be combined or substituted with any other feature of any other one of the embodiments. 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” “include,” “including” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number, respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
     Moreover, conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. For example, while features are presented in a given arrangement, alternative embodiments may perform similar functionalities with different components and/or sensor topologies, and some features may be deleted, moved, added, subdivided, combined, and/or modified. Each of these features may be implemented in a variety of different ways. Any suitable combination of the elements and acts of the various embodiments described above can be combined to provide further embodiments. The various features and processes described above may be implemented independently of one another, or may be combined in various ways. All possible combinations and subcombinations of features of this disclosure are intended to fall within the scope of this disclosure.