Deposition of WNxCy Using the Allylimido Complexes Cl4„RCN...W„NC3H5...: Effect of NH3 on Film Properties

Deposition of WNxCy Using the Allylimido Complexes Cl4„RCN...W„NC3H5...: Effect of NH3 on Film Properties Hiral M. Ajmera,* Andrew T. Heitsch, Omar J. Bchir, David P. Norton,* Laurel L. Reitfort, Lisa McElwee-White, and Timothy J. Anderson* Department of Chemical Engineering, Department of Chemistry, and Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA

The introduction of copper interconnects and low-k dielectrics has presented several challenges to their integration into devices.A major issue is preventing Cu incorporation into the active device layer, where it can rapidly diffuse ͑atomic diffusivity of copper in silicon is ϳ2 ϫ 10 −5 cm 2 /s at 500°C͒. 1 Copper can generate energy levels within the bandgap of silicon that act as recombination centers that affect carrier relaxation, increase carrier leakage current, and decrease minority carrier lifetime. 2Thin-film diffusion barriers are thus incorporated to prevent copper incorporation. 3 In addition to low Cu permeation rates, the barrier film should have good adhesion to copper and the Si or dielectric layers as well as low electrical sheet resistance and good thermal and mechanical stability.
Refractory metal nitrides such as TiN, TaN, and WN x belong to a class of interstitial compounds that have been extensively investigated for diffusion-barrier applications due to their high density and melting temperature. 4Unfortunately, TiN typically shows a columnar microstructure, with columnar grain boundaries acting as rapid Cu transport pathways.In contrast, TaN barriers show dense microstructure and have been demonstrated to prevent Cu diffusion even after annealing at 650°C. 5 Industry has adopted a Ta/TaN bilayer as the preferred diffusion barrier for upper metal levels in integrated circuit devices.TaN has good barrier properties and excellent adhesion to SiO 2 , while Ta enables good adhesion to copper and fosters deposition of low-resistivity Cu͑111͒ in the copper seed and the subsequently electroplated film. 6One of the issues with using a Ta/TaN bilayer as a diffusion barrier is that it has a lower removal rate than Cu during chemical mechanical polishing ͑CMP͒.Because the rate of TaN removal is ϳ18 times slower than that of copper, industry often uses a two-step CMP process; 7 the first step removes copper, while the second removes TaN.Also, Ta/TaN is typically deposited by sputtering, which inherently gives poor step coverage.
Tungsten nitride ͑WN x ͒ is a viable alternative to TaN for diffusion-barrier application.In particular, WN x is chemically and thermodynamically stable with respect to copper and can be deposited in the amorphous state. 8Chemical-vapor-deposited ͑CVD͒ copper exhibits superior adhesion to WN x as compared to TaN. 9 Importantly, the removal rate of WN x during CMP is only ϳ2 times faster than that of copper, 10 thus eliminating the need for the two-step CMP process currently employed for TaN.If industry moves toward a seedless copper-deposition process, WN x would find wide accep-tance because of the higher nucleation density of copper on WN x . 11ue to the many advantages of WN x over TaN, development of a suitable process for WN x deposition is of interest.
Tungsten nitride has been deposited by a variety of techniques, including physical vapor deposition, [12][13][14][15] CVD, [16][17][18] and atomic layer deposition. 19,20The barrier properties are strongly dependent on film microstructure and stoichiometry, which depend on the deposition method and specific operating conditions.Sputtered films have shown low resistivity and can be deposited at low temperature.However, this method tends to afford poor step coverage due to the directional nature of the technique.21,22 Films deposited by CVD show good conformality and reasonable deposition rate.Halide-based reactants and their by-products, however, are corrosive and can react with the underlying Si surface.The use of metal-organic precursors in CVD is a good alternative to inorganic precursors, because the precursors typically thermally decompose at relatively low temperature and are less corrosive.3][34][35] Ternary refractory-metal materials like WN x C y have some advantage over binary compounds, because the addition of a third element to the transition-metal nitride disrupts the crystal lattice and forms amorphous ternary solid solutions that have a higher recrystallization temperature. 36Addition of C to WN x also lowers the film resistivity. 32ur group has previously reported growth of WN x C y thin films from Cl 4 ͑RCN͒W͑NC 3 H 5 ͒ ͑1a, R = CH 3 ; 1b, R = Ph͒. 37Films grown with 1a,b below 550°C were amorphous and had low resistivity at a lower deposition temperature ͑0.29 m⍀ cm at 450°C͒.Films deposited with 1a,b, however, had low N content even though the low N-C imido bond energy for 1a,b is expected to result in an increase in N content of the film.The film deposited with 1a,b at 450°C had only 4 atom % N, and the highest N concentration ͑11 atom %͒ was obtained for a film deposited at 550°C.A nitrogendeficient diffusion-barrier film is not desirable, because such films can easily form grain boundaries that act as pathways for copper diffusion.In addition to having low N content, films deposited with 1a,b also had high O content ͑16 atom % at 450°C and 11 atom % at 525°C͒.A previous report has shown that when ammonia is added to the H 2 carrier gas as a coreactant with the single source precursor Cl 4 ͑RCN͒W͑N i Pr͒ ͑2a,b͒, the N content increased from 8 to 24 atom % in WN x C y films deposited at 450°C. 38We now report the deposition of thin films with 1a,b and ammonia.The intent of this work is to increase the N content and decrease the O content so that films deposited with 1a,b are more suitable for diffusion barrier application.

Experimental
General (precursor synthesis).-Cl 4 ͑CH 3 CN͒W͑NC 3 H 5 ͒ ͑1a͒ was prepared as previously reported. 37The benzonitrile complex Cl 4 ͑PhCN͒W͑NC 3 H 5 ͒ ͑1b͒ was not isolated but was produced in situ by the substitution of the acetonitrile ligand of 1a with benzonitrile, which was utilized as the solvent for the deposition experiments ͑vide infra͒.Although we describe the precursor in benzonitrile solution as "1a,b" for rigor, the rapid rate of exchange of nitrile ligands in Cl 4 ͑CH 3 CN͒W͑NR͒ complexes ensures that the precursor is completely converted to 1b before deposition begins. 39lm growth studies.-Filmdeposition was done in a vertical quartz cold-wall CVD reactor.The solid precursor 1a,b was dissolved in benzonitrile at a concentration of 11.2 mg/mL, loaded into a 10 mL syringe, and pumped into a nebulizer at the rate of 4 mL/h.The nebulizer converted the dissolved precursor solution into an aerosol, which was then conveyed by hydrogen carrier gas into the reactor.The hydrogen flow rate was held constant at 1000 sccm.The H 2 -aerosol mixture was delivered to the horizontal heated substrate in a vertical glass tube fitted with a heated shower head.Ammonia was introduced into the surrounding glass reactor tube at a flow rate of 25 sccm.The secondary reactant was introduced approximately 10 cm upstream from the substrate, allowing partial mixing between NH 3 and 1a,b prior to reaching the substrate surface.The molar flow rates of H 2 , NH 3 , 1a,b, and solvent were 4.09 ϫ 10 −2 , 1.02 ϫ 10 −3 , 1.77 ϫ 10 −6 , and 6.47 ϫ 10 −4 mol/min, respectively.The duration of each deposition was 150 min.The reactor was pumped by a mechanical roughing pump, and pressure was maintained at 350 Torr using a throttle valve downstream of the reactor.Films were deposited on p-type boron-doped Si͑100͒ substrates with resistivity of 1-2 ⍀ cm.The substrate was placed on a graphite susceptor, which was heated using radio frequency induction coils.The deposition temperature was varied from 450 to 750°C.
The film crystallinity was examined by grazing-incidence X-ray diffraction ͑XRD͒ using a Phillips MRD X'Pert system.Cu K␣ radiation, generated at 45 kV and 40 mAmp ͑1.8 kW͒, was used for the XRD analysis.The angle of incidence for measurements was 2°, and the step size was 0.02°per step.The film composition was determined by Auger electron spectroscopy ͑AES͒ using a Perkin-Elmer PHI 660 scanning Auger multiprobe.A 5 kV acceleration voltage and 50 nanoamp beam current was used for the Auger analysis.The beam diameter was 1 m.The sample surface was cleaned by sputter etching for 30 s using Ar ions.The etch rate for the sputtering was calibrated at 100 Å/min using a tantalum oxide standard.X-ray photoelectron spectroscopy ͑XPS͒ measurements were taken using a Perkin Elmer PHI 5600 system.XPS spectra were taken using monochromatic Mg K␣ radiation with the X-ray source operating at 300 W ͑15 kV and 20 mA͒.The sample surface was sputter etched for 5 min using Ar ions to remove surface contaminants.The etch rate for the XPS system was calibrated at 10 Å/min using a tantalum oxide standard.Sheet resistance of the deposited films was measured using an Alessi Industries four-point probe.The film thickness was measured by cross-sectional scanning electron microscopy ͑X-SEM͒ on a JEOL JSM-6400.

Results and Discussion
Film appearance.-Filmsgrown with 1a,b and ammonia were generally smooth and had a shiny metallic surface finish.The film color varied from gray to metallic black.
Film composition.-Figure 1 shows the Auger results for films deposited in the presence ͑filled circle͒ and absence ͑open circle͒ of NH 3 at temperatures ranging from 450 to 750°C.For comparison, the elemental composition of films grown with ammonia using 2a,b 38 is also included ͑filled triangle͒.The Auger spectra for films deposited with ammonia indicate the presence of W, N, C, and O in all films.Note that the data were measured after 30 s of sputtering at conditions previously specified.Sputter etching can change the nearsurface composition of compounds due to preferential sputtering. 40n fact, tungsten nitride has been reported to undergo preferential erosion of nitrogen during sputter etching. 41Despite preferential sputtering, the film composition obtained from Auger measurements can be useful in comparative analysis of films deposited at different temperatures.
Comparing films grown from 1a,b with and without ammonia coreactant, the composition data shown in Fig. 1 show lower W and higher N concentration and, except for the growth at 700°C, higher C and lower O incorporation for films grown with ammonia.In the region of interest to barrier-film application ͑amorphous microstructure and Ͻ500°C growth temperature͒, the differences were largest.Thus, films deposited with ammonia at 450 and 475°C exhibited an N concentration of 23 and 17 atom %, respectively, which is considerably higher than growth without the addition of ammonia ͑e.g., 4 atom % N at 450°C͒.Films grown from 2a,b with ammonia at 450°C had the same N level ͑23 atom %͒.For films grown with a polycrystalline microstructure, the trends with increasing deposition temperature in the W, N, and O levels were decreasing, while that for C was increasing.The increased incorporation of C at higher deposition temperatures likely results from decomposition of the precursor ligands and the benzonitrile solvent.
Oxygen incorporation in the film remained below 6 atom % throughout the investigated temperature range.While the O concentration at the lower end ͑450-500°C͒ and higher end ͑650-750°C͒ of the temperature range was slightly higher than that at the center ͑525-600°C͒, the O concentration remained fairly constant over the range of deposition temperature.Oxygen is likely incorporated into the films either from residual gas in the reactor during growth or from atmospheric oxygen and water-vapor exposure postgrowth. 42he increase in N concentration for depositions with ammonia is quite dramatic in the low-temperature range, as exemplified by the effect for growth at 450°C, where the addition of ammonia raised the N concentration from 4 to 23 atom %.The increase in N concentration suggests that the ammonia reacts with 1a,b either in the gas phase or on the substrate, resulting in higher N incorporation in the film.Below 650°C, carbon incorporation for depositions with ammonia was higher than that for depositions without ammonia.Even at low temperature, when C deposition from the solvent was low, 42 the C content of films deposited with ammonia was higher than for films deposited without ammonia, again suggesting a reaction pathway change.
Due to the presence of chlorine in the precursor complex 1a, the possible incorporation of chlorine in the films was of interest.This analysis could not be carried out by AES, because the W NNN peak overlaps with the Cl LMM peak at 180 eV.Thus, XPS data were collected for films deposited at 450, 600, and 750°C ͑Fig.2͒ to ascertain if the films contained chlorine.No chlorine peaks were observed for either the Cl 2s or Cl 2p 3/2 at 270 and 199 eV, respectively, confirming that the chlorine level in the films was lower than the detection limit of ϳ1 atom %.The Fe 2p peaks at 723 and 711 eV in the XPS spectra are artifacts that arise from the sample holder ͑contains Fe͒ due to small sample sizes.
XRD of films.-Figure3a shows grazing-incidence XRD patterns for films deposited between 450 and 700°C.Figure 3b shows the peak position and relative peak intensities for standard powder diffraction of ␤-WN 0.5 and ␤-WC 0.6 .The peak intensities are normalized with respect to the highest-intensity peak for both ␤-WN 0.5 and ␤-WC 0.6 .Because thickness can affect the crystallinity of the film, the information of film thickness at different deposition temperature is shown in Fig. 3c.The film thickness increased as the growth temperature increased, with the film thickness varying between 60 and 250 nm for growth in the range of 450-750°C.
The XRD pattern of the film deposited at 450°C indicates that it is X-ray amorphous.At 500°C, three peaks emerge at 37.47, 43.49, and 63.71 2°.All three peaks lie between the standard diffraction peaks for ␤-WN 0.5 and ␤-WC 0.6 , suggesting the absence of the hexagonal phases and the presence of WN x C y solid solution or the existence of separate ␤-WN 0.5 or ␤-WC 0.6 phases.An attempt to deconvolute the most intense ͑111͒ peak could not resolve whether it contained two peaks corresponding to ␤-WN 0.5 and ␤-WC 0.6 or a single Gaussian peak representing ␤-WN x C y .Previous studies on WN x C y thin films have not been able to resolve whether the film is a binary mixture of ␤-WN 0.5 and ␤-WC 0.6 or a single solid solution of ␤-WN x C y . 43The relative peak intensities of the ͑111͒, ͑200͒, and ͑220͒ reflections ͑Fig.3b͒ as well as their positions, however, suggest that the crystalline material is predominantly ␤-WN 0.5 or a N-rich ␤-WN x C y alloy.As the deposition temperature is increased from 500 to 550°C, the same three peaks appear, although the intensity of these peaks is lower than that for films deposited at 500°C.In the same temperature range, the tungsten concentration changes from 59 to 49 atom %.A lower tungsten concentration would lead to a decrease in the amount of the WN 0.5 phase, WC 0.6 phase, or both, resulting in a decrease in the film crystallinity.The XRD pattern for film deposited at 600°C shows the highest level of crystallinity.As the deposition temperature is increased from 550 to 600°C, the nitrogen concentration decreases, while the carbon concentration increases.An increase in crystallinity would suggest an increase in the ␤-WC 0.6 phase.The peak intensity in XRD patterns for films deposited at 650, 700, and 750°C is less than that for the film grown at 600°C, suggesting a decrease in crystallinity with increasing deposition temperature.Lattice parameter values suggest that as the deposition temperature increases, the additional C deposited in the film is incorporated as amorphous C ͑vide infra͒.At higher temperature, an increase in amorphous C deposition could hinder the formation of crystallites, which is consistent with the decrease in film crystallinity at higher deposition temperature.Peaks at 650, 700, and 750°C are much broader, possibly due to increased residual strain.
It is interesting to compare the XRD patterns reported here for films deposited with 1a,b and ammonia with those grown without ammonia. 37The films deposited without ammonia are X-ray amorphous over a larger growth-temperature range ͑at and below 500°C͒ compared to those grown with ammonia ͑at and below 450°C͒.At higher growth temperature the films are polycrystalline, and the crystallinity of films grown without ammonia increases with deposition temperature, while those deposited with ammonia do not show this trend.In fact, for higher-temperature depositions with ammonia, the film crystallinity actually decreases.This observation reinforces the assertion that the ammonia coreactant alters the mechanism of film deposition.-Assuming that the ␤-WN x C y alloy phase is deposited in the polycrystalline films and that the alloy lattice parameter varies linearly with composition ͑Vegard's law͒, it is possible to estimate the alloy composition from the XRD peak posi-tions.Figure 4 shows the change in the calculated face-centered cubic lattice parameter for films deposited with and without ammonia using the most intense reflection ͓i.e., ␤-WN x C y ͑111͒ reflec-tion͔.
All films deposited with ammonia between 500 and 750°C have a lattice parameter between the standard lattice parameters for ␤-WN 0.5 ͑111͒ ͑4.126 Å͒ and ␤-WC 0.6 ͑111͒ ͑4.236 Å͒.The changes in lattice parameter with deposition temperature could result from uniform strain as well as compositional variation.Because the WN x C y films are not highly ordered, changes in the N and C content of the polycrystalline WN x C y rather than uniform strain is believed to be the primary factor affecting lattice parameter.Thus, the values plotted in Fig. 4 were calculated assuming there was no residual strain in the film.As shown in this figure, the lattice parameter decreases with an increase in deposition temperature for depositions with ammonia between 500 and 700°C.A decrease in lattice parameter can be produced by a decrease in N and/or C in the interstitial sublattice. 23Figure 1 shows, however, that the C concentration increases and N concentration decreases with deposition temperature for films deposited with ammonia.A possible explanation is that the added C with increasing temperature deposits as a second C phase ͑e.g., at the grain boundaries͒, and thus the variation in N concentration is primarily responsible for the lattice-parameter variation and the additional carbon deposited at higher temperature incorporates outside the WN x C y polycrystals.The conclusion that amorphous C incorporates at the grain boundary for films deposited at higher temperatures is based on the observation that even though the C content of the film significantly increases and the N level remains relatively constant with deposition temperature, the lattice parameter of the film decreases.In contrast, for films grown without ammonia the lattice constant increases with increased deposition temperature.
Polycrystal grain size.-Thegrain size ͑t͒ was estimated using the Scherrer equation 44 where is the wavelength of X-rays used for measurement, is the angle of incidence, and B is the broadening of the diffraction line measured as full width at half maximum ͑fwhm͒.The most intense ͑111͒ diffraction peak was used to determine fwhm.A plot of B cos vs sin using the measured intensities for ͑111͒, ͑200͒ and ͑220͒ reflection peaks for the films deposited at 500 and 700°C was horizontal, supporting the conclusion that the broadening was due to  grain size and not residual strain.Figure 5 shows the change in grain size with temperature for films deposited with and without ammonia.
The average grain-size calculation shows that films deposited with 1a,b and ammonia are nanocrystalline between 500 and 750°C deposition temperature, with the average grain size ranging from 37 to 60 Å.A previous study 32 has reported the growth of nanocrystalline WN x C y between deposition temperatures of 225 and 400°C.In the present work, we found that within the sensitivity limits of XRD, the films deposited with 1a,b and ammonia were amorphous at 450°C deposition temperature, and nanocrystalline growth is observed at deposition temperature of 500°C and higher.At a deposition temperature of 500°C, the average grain size of crystallites for film deposited with ammonia is 56 Å.The average grain size remains almost unchanged at 550°C.Between 550 and 700°C, the average grain size gradually decreases from 58 to 39 Å.As the deposition temperature increases, the excess C deposited from the solvent/precursor fragmentation could hinder the growth of polycrystals, resulting in a gradual decrease in grain size.
The comparison of grain size for experiments with and without ammonia shows that for deposition at temperature 600°C and below, the average grain size is higher for films deposited with ammonia than for those deposited without ammonia.This is consistent with the decrease in growth rate with ammonia addition or possible increase in the mobility of a limiting surface species.At 600°C, the grain size for film grown with ammonia is similar to that for film grown without ammonia within the margin of error.At 650°C, the grain size for film deposited with ammonia is slightly lower than the grain size for films deposited without ammonia.
Film growth rate (X-SEM).-Growthrates were estimated by dividing film thickness ͑measured from X-SEM͒ by deposition time.Figure 6 shows X-SEM images for films grown at 450 and 650°C.
The growth rate for 1a,b with ammonia ranged from ca. 4 Å/min at 450°C to ca. 17 Å/min at 750°C.For growth using 1a,b without ammonia, the concentration of 1a,b in benzonitrile was 7.5 mg/mL, whereas for growth using 1a,b with ammonia, the 1a,b concentration in benzonitrile was 11.2 mg/mL.Because the introduction of ammonia as coreactant reduces the film growth rate, a higher concentration of 1a,b was necessary to obtain films that were sufficiently thick for materials characterization.This trend is similar to that previously observed for growth from Cl 4 ͑RCN͒W͑N i Pr͒ ͑2a,b͒, where the use of ammonia as coreactant resulted in a decrease in growth rate in the diffusion-limited growth regime. 38Figure 7 shows Arrhenius plots of growth rates for deposition using 1a,b with ammonia, 1a,b without ammonia, and 2a,b with ammonia.The apparent activation energy ͑E a ͒ for film growth from 1a,b and ammonia was 0.34 eV, which is significantly higher than the 0.15 eV activation energy reported for depositions from 1a,b without ammonia.Activation energy for growth using 2a,b and ammonia was not reported, because the growth was in the diffusion-limited growth regime.A change of activation energy for film growth upon addition of ammonia is consistent with removal of the allylimido ligand of the precursor by transamination with ammonia to generate the parent imido ligand ͑NH͒ and free allylamine.This process has been calculated to be facile for 1a,b under CVD conditions. 45 where is film resistivity, R s is sheet resistance ͑measured by fourpoint probe͒, and t is film thickness ͑measured from X-SEM͒. Figure 8 shows film resistivity at different deposition temperature for films grown with and without ammonia.For depositions with ammonia, the resistivity is 5.8 m⍀ cm for 450°C and increases to 7.2 m⍀ cm for 500°C.Interestingly, the film resistivity has the lowest value of 1.7 m⍀ cm for growth at 550°C, although the film deposited at that temperature has lower W content and higher N content.This film also has the lowest degree of crystallinity for any   6 m⍀ cm at 600°C and continues to increase with increased deposition temperature until it reaches its highest value of 24.2 m⍀ cm at 700°C.The decrease in W concentration and concomitant increase in C concentration between 550 and 700°C is believed to be the reason for the increase in film resistivity.If the C in films exists as WC x , it would decrease the film resistivity.But an increase in resistivity with an increase in C content of film could result from the incorporation of additional C at the grain boundary ͑outside the WN x C y polycrystal͒ at higher deposition temperatures.The amorphous C present at grain boundaries increases electron scattering, thereby increasing the film resistivity. 38The film resistivity was considerably higher for films deposited with ammonia compared to films deposited without ammonia.This behavior is expected, because ammonia tends to increase N content in the films and higher N content leads to higher film resistivity.
Comparison of films deposited from 1a,b and ammonia with those deposited from 2a,b and ammonia.-Thecomparison of films deposited from 1a,b and ammonia with those deposited from 2a,b and ammonia 38 can provide insight into the effect of different ligands ͑C 3 H 5 and i Pr͒ on film properties.Films deposited at 450°C from 1a,b and ammonia have similar W and N content, higher C content, and lower O content as compared to films deposited with 2a,b and ammonia at the same temperature ͑Fig.1͒.At 500 and 600°C, films from 2a,b exhibit higher N content and lower C content as compared to films deposited with 1a,b and ammonia at the same temperature.The comparison of film crystallinity for films deposited with 1a,b and ammonia with those deposited with 2a,b and ammonia shows that while 1a,b results in crystalline films at and above 500°C, films deposited with 2a,b do not show crystallinity until 600°C and higher.This trend in crystallinity is possibly explained by the higher growth rate for films deposited with 2a,b and ammonia ͑17-23 Å/min͒ than with 1a,b and ammonia ͑4-17 Å/min, Fig. 7͒, especially at lower deposition temperature.Higher growth rate provides less time for species surface migration and thus growth of crystallites.
The comparison of film resistivity ͑Fig.8͒ shows that at 450 and 500°C, films grown with 1a,b and ammonia have a significantly lower resistivity than those grown with 2a,b and ammonia.Interestingly, films deposited with both precursors have the lowest resistivity at 550°C.Above 550°C, there is a dramatic increase in resistivity of films deposited with 1a,b and ammonia, while resistivity of films grown with 2a,b and ammonia levels off.
Evaluation of all films grown from 1a,b or 2a,b and ammonia shows that film deposited with 1a,b and ammonia at 450°C is the best candidate for diffusion-barrier application because of its high N content, low O content, low deposition temperature, amorphous microstructure, and lowest resistivity among amorphous films grown from 1a,b or 2a,b with ammonia.Diffusion-barrier testing is required to ascertain if this film is suitable for diffusion-barrier application.

Conclusions
Successful thin-film deposition of WN x C y by metallorganic CVD utilizing 1a,b, H 2 , and ammonia was demonstrated.When used as a coreactant with the allylimido complexes 1a,b, ammonia significantly alters the composition, crystallinity, resistivity, and apparent deposition mechanism of the resulting films as compared to films grown without NH 3 . 37Films deposited with ammonia had significantly higher tungsten, carbon, and nitrogen content and substantially lower oxygen content.No chlorine was detected in the XPS spectra of films grown over the entire deposition temperature range.It was observed that the addition of ammonia lowers the growth rate for T ഛ 550°C, consistent with a change in rate-determining step of the deposition upon removal of the allylimido ligand by transamination with ammonia.In the higher-temperature range T ജ 600°C the relative incorporation of N, C, and O modulates crystallinity.
While films grown without ammonia showed an increase in film crystallinity with increasing deposition temperature, those grown with ammonia exhibited more complex behavior, with crystallinity peaking for growth at 600°C.The activation energy for the film growth from 1a,b and ammonia is estimated to be 0.34 eV, which is higher than the activation energy of 0.15 eV reported for film growth from 1a,b without ammonia.Films deposited with ammonia have higher resistivity as compared to films deposited without ammonia because of a higher N and C concentration coupled with a lower W concentration.The lowest resistivity for films deposited with ammonia was the value of 1.7 m⍀ cm obtained from growth at 550°C.
Films deposited with 1a,b and ammonia have higher C content and lower O content as compared to those deposited from 2a,b and ammonia.The N content of film grown with 1a,b and ammonia is similar to that for film grown with 2a,b and ammonia at 450 and 700°C.Films grown with 2a,b and ammonia below 600°C were amorphous, whereas deposition from 1a,b and ammonia resulted in amorphous film below 500°C.At temperature below 550°C, films deposited with 1a,b and ammonia had a significantly lower resistivity as compared to films deposited with 2a,b and ammonia.But above 550°C, films deposited with 1a,b and ammonia had a much higher resistivity as compared to those deposited with 2a,b and ammonia.
From a diffusion-barrier-application standpoint, it has been demonstrated that ammonia can be used with 1a,b to significantly increase the N content of WN x C y films.

Figure 1 .
Figure 1.Composition of films deposited from 1a,b ͑with and without 37 ammonia͒ and 2a,b with ammonia 38 at different deposition temperature as determined by AES on Si͑100͒ substrate after 0.5 min of sputtering.

Figure 3 .
Figure 3. ͑a͒ Grazing-incidence XRD pattern for films deposited on Si͑100͒ substrate from 1a,b and ammonia.The solid and dashed vertical lines indicate the location of reference peaks for standard powder diffraction of ␤-WN 0.5 and ␤-WC 0.6 , respectively.͑b͒ Standard powder-diffraction patterns for ␤-WN 0.5 and ␤-WC 0.6 .I peak is the intensity of a particular peak and I max is the intensity of the most intense peak in the pattern.͑c͒ Thickness of film ͑obtained from X-SEM͒ at different deposition temperature for films deposited with 1a,b and ammonia on Si͑100͒ substrate.

Figure 4 .
Figure 4.Estimated lattice parameters for films grown from 1a,b on Si͑100͒ substrate with and without ammonia. 37The solid line at 4.126 Å corresponds to the standard lattice parameter for ␤-WN 0.5 .The dashed line at 4.236 Å corresponds to standard lattice parameter for ␤-WC 0.6 ͑111͒.Error bars indicate uncertainty in determination of the peak position.
Prior work has implicated homolytic cleavage of the N͑imido͒-C bond as the rate-determining step of film deposition from 1a,b and 2a,b.If transamination with ammonia removes the carbon-containing group prior to the rate-determining step of deposition from 1a,b, the rate of film deposition must necessarily be different in the presence of ammonia.Film resistivity.-Thefilm resistivity was calculated using = R s t ͓2͔

Figure 5 .
Figure 5. Average grain size at different deposition temperature for films grown from 1a,b with and without 37 ammonia on Si͑100͒ substrate.

Figure 6 .
Figure 6.X-SEM images for films grown from 1a,b with ammonia at ͑a͒ 450 and ͑b͒ 650°C.

Figure 7 .
Figure 7. Arrhenius plot for deposition from 1a,b ͑with and without 37 am-monia͒ and 2a,b with ammonia. 38Note that the precursor concentration was 7.5 mg/mL for 1a,b and 2a,b with NH 3 and 11.2 mg/mL without NH 3 .