Cl4(PhCN)W(NPh) as a single-source MOCVD precursor for deposition of tungsten nitride (WNx) thin films

Article abstract of DOI:10.1016/S0022-328X(03)00769-1

The tungsten phenylimido complex Cl₄(PhCN)W(NPh) (2b) was tested as a single-source precursor for growth of tungsten nitride (WN_x) thin films, and results were compared to films previously deposited from the isopropylimido complexes Cl₄(RCN)W(NⁱPr) (1a, R=CH₃;1b, R=Ph). Films deposited from 2b exhibited growth rates ranging from 2 to 21 ? min^-1 over a temperature range of 475-750 °C, and the apparent activation energy for film growth in the kinetically controlled regime was 1.41±0.58 eV. Amorphous β-WN_x films were deposited below 500 °C, with minimum film resistivity and sheet resistance of 225 μΩ-cm and 75 Ω/□, respectively, observed for deposition at 475 °C. In contrast, films deposited from the isopropylimido complexes 1a, b exhibited higher growth rates and higher nitrogen content over a similar temperature range. These differences are attributed to the higher dissociation energy of the imido N-C bond in phenylimido complex 2b. Mass spectrometry fragmentation patterns are consistent with this behavior.

Full text of DOI:10.1016/S0022-328X(03)00769-1

Journal of Organometallic Chemistry 684 (2003) 338Á350
/
www.elsevier.com/locate/jorganchem
Cl4(PhCN)W(NPh) as a single-source MOCVD precursor for
deposition of tungsten nitride (WNx) thin films
Omar J. Bchir a, Kelly M. Green a, Mark S. Hlad a, Timothy J. Anderson a,*,
Benjamin C. Brooks b, Corey B. Wilder b, David H. Powell b, Lisa McElwee-White b,*
a Department of Chemical Engineering, University of Florida, Gainesville, FL 32611-6005, USA
b Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
Received 10 March 2003; received in revised form 3 June 2003; accepted 3 June 2003
Dedicated to Professor E.O. Fischer on the occasion of his 85th birthday
Abstract
The tungsten phenylimido complex Cl4(PhCN)W(NPh) (2b) was tested as a single-source precursor for growth of tungsten nitride
(WNx ) thin films, and results were compared to films previously deposited from the isopropylimido complexes Cl4(RCN)W(Ni Pr)
Ph). Films deposited from 2b exhibited growth rates ranging from 2 to 21 A minꢁ1 over a temperature range
˚
(1a, Rꢀ
/
CH3; 1b, Rꢀ
/
of 475Á
/
750 8C, and the apparent activation energy for film growth in the kinetically controlled regime was 1.4190.58 eV.
/
Amorphous b-WNx films were deposited below 500 8C, with minimum film resistivity and sheet resistance of 225 mV-cm and 75 V/
I, respectively, observed for deposition at 475 8C. In contrast, films deposited from the isopropylimido complexes 1a,b exhibited
higher growth rates and higher nitrogen content over a similar temperature range. These differences are attributed to the higher
dissociation energy of the imido NÃ/C bond in phenylimido complex 2b. Mass spectrometry fragmentation patterns are consistent
with this behavior.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Tungsten; Imido; Nitride; Chemical vapor deposition; Diffusion barrier
1. Introduction
in ICs should have amorphous film structure, low
resistivity, good conformality over different device
features, and low deposition temperature (5450 8C).
As feature sizes on integrated circuits (ICs) become
smaller, the need for a thin, effective barrier to prevent
intermixing of silicon and metallization layers becomes
more critical. Copper is being increasingly used as the
interconnect metallization for various levels on ICs due
to its lower bulk resistivity, greater resistance to
electromigration, and diminished contact resistance
relative to aluminum [1]. Unfortunately, copper has
much higher mass diffusivity in silicon than does
aluminum, making diffusion barrier performance even
more crucial [2]. Ideally, diffusion barrier materials used
/
Material selection is vital to a successful diffusion
barrier. Use of refractory metal thin films as diffusion
barriers failed due to the formation of grain boundaries,
which are facile pathways for Cu mFigration to the
underlying substrate [3]. Refractory metal nitrides, such
as tantalum nitride (TaN) and tungsten nitride (WNx),
however, are promising diffusion barrier materials for
Cu metallization [4]. Excess nitrogen in these films
accumulates at the grain boundaries during polycrystal
formation and is believed to hinder Cu diffusion.
Nitrogen atoms at the grain boundary significantly
reduce diffusion through a ‘‘stuffing’’ process, which
* Corresponding authors. Tel.: ꢂ
/
1-352-392-8768; fax: ꢂ
/
1-352-846-
involves repulsive CuÁN interactions [5,6]. Although
/
0296 (L.M.-W.); tel.:
(T.J.A.).
ꢂ
/
1-352-392-0946; fax: 1-352-392-9513
ꢂ/
TaN is currently used as a copper diffusion barrier
material for intermediate level wiring in IC applications
[7], WNx offers several advantages. These include
E-mail addresses: tim@nersp.nerdc.ufl.edu (T.J. Anderson),
lmwhite@chem.ufl.edu (L. McElwee-White).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00769-1

O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á
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339
superior adhesion to copper [8], more efficient subse-
quent processing (e.g. ease in use of chemical mechanical
polishing or CMP) [9], and potential use as an electrode
layer to enable seedless copper electrodeposition [10].
In addition to material selection, diffusion barrier
properties are heavily influenced by the choice of
technique and conditions used to deposit the film.
Chemical vapor deposition (CVD) operating in the
kinetically limited growth regime is a technique that is
well suited to deposit highly conformal films. Selection
of appropriate precursors for the CVD process may
enable deposition of amorphous films at low tempera-
ture. One variant of CVD depends on reduction of
halide precursors to deposit films. In another variant,
metal-organic chemical vapor deposition (MOCVD),
material is deposited on the substrate surface by
reaction of one or more carbon-containing vapor phase
precursor compounds. Both of these variants are often
operated at low pressure to increase mass transfer rates
to the extent that deposition is reaction limited, thus
producing more conformal films.
The typical strategies for CVD of multi-element
barrier materials involve the use of either single-source
or co-reactant precursors. Co-reactant deposition uses a
separate precursor for each element desired in the film;
hence, bonds between these elements must be formed by
intermolecular processes during deposition. In contrast,
a single-source precursor already has bonds established
between the elements that will comprise the film prior to
deposition. This approach is particularly useful when
the bond strengths in the individual precursor candi-
dates, and thus decomposition temperatures, are quite
different.
Unfortunately, the high temperatures required for reac-
tion of metal halides with NH3 (greater than 500 8C)
[19], along with the resulting reactive by-products (e.g.
hydrogen halides) [20,21], are two major drawbacks to
barrier deposition by co-reactant metal halide processes.
More recently, organometallic precursors have been
employed in co-reactant systems. Accordingly, W(CO)6
and NH3 have been used to deposit amorphous WNx
films below 275 8C [22]. In a similar study, deposition of
WNx from W(CO)5(C5H11NC) and NH3 was reported
in the temperature range 250Á400 8C [23]. In the sole
/
prior example of a single-source precursor for WNx
deposition, polycrystalline thin films were obtained by
pyrolyzing the bis(imido) bis(amido) complex
(tBuNH)2W(NtBu)2 in the temperature range 450Á
650 8C [24Á26].
/
/
Recently, we reported MOCVD of amorphous WNx
thin films from benzonitrile solutions of the single-
source imido precursor Cl4(CH3CN)W(NiPr) (1a) as a
mixture with its benzonitrile derivative 1b [27,28]. The
properties of these films were compared with those of
films deposited from the other reported tungsten imido
precursor, (tBuNH)2W(NtBu)2 [27,28]. Imido com-
plexes are attractive candidates for MOCVD of tungsten
nitride since the strong WÅ/N multiple bond is likely to
survive as other moieties dissociate during film deposi-
tion. Furthermore, the simple synthesis of 1a,b can
easily be adapted to produce a series of related
complexes containing different alkyl or aryl substituents
on the imido ligand. This feature allows variation of the
NÃ
this bond must be cleaved during the CVD process. The
NÃC (imido nitrogen to 28 alkyl) bond of 1a,b will be
relatively weak, compared to the NÃaryl bond of the
/C bond dissociation energy, which is important since
/
Previous examples of WNx deposited by CVD are
dominated by co-reactant systems using NH3 as the
nitrogen source (Scheme 1). Early examples employed
/
phenylimido complex Cl4(PhCN)W(NPh) (2b). We now
report the growth of WNx films from 2b, and discuss the
film deposition and the properties of the resulting
material. Comparison of material deposited from 1a,b
WF6, WCl6 or WO3 as the tungsten source [11Á18].
/
and 2b provides insight into the effect of the imido NÃ
/C
bond strength on the MOCVD process.
Scheme 1.

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/
2. Experimental
(X-SEM) on a JEOL JSM-6400, with growth rate
calculated by dividing film thickness by deposition time.
2.1. General (precursor synthesis)
3. Results and discussion
The complex Cl4(OEt2)W(NPh) (3) was synthesized as
previously described by Schrock et al. [29]. The benzo-
nitrile complex Cl4(PhCN)W(NPh) (2b) was not iso-
lated, but was produced in situ by the substitution of the
ether ligand of 3 with benzonitrile following solvation in
3.1. Mass spectrometry
As noted before, care must be taken in using mass
spectral data to predict CVD behavior since the latter is
thermal in nature [31]. Nevertheless, mass spectrometry
does provide insights into the relative fragmentation
characteristics of various precursors [32]. In order to
provide a direct comparison of mass spectral data for a
phenylimido complex and its isopropyl analogue, the
acetonitrile adduct Cl4(CH3CN)W(NPh) (2a) was pre-
pared as a model for 2b. Precedent for the modeling of
2a by 2b is provided by the virtually identical ion
fragmentation patterns for the isopropyl imido com-
plexes 1a and 1b [28]. Mass spectrometry results for 2a
could then be compared to our previously reported data
for the isopropyl imido complex Cl4(CH3CN)W(NiPr)
(1a) [28]. Accordingly, 2a was analyzed using both
positive ion electron-impact (EI) and NCI methods.
The EI and NCI mass spectra of 2a are depicted in
Fig. 1, and the relative abundances of the observed
peaks of the phenylimido and isopropylimido complexes
2a and 1a are summarized in Table 1. As observed in the
mass spectra of the isopropyl precursor, no molecular
ion was detected for 2a using either ionization method.
The base peak in the EI spectrum occurs at m/z 382, and
corresponds to the fragment [Cl3W(NPh)]ꢂ. The highest
mass peak observed in the EI spectrum was
[Cl4W(NPh)]ꢂ at m/z 417 (9% abundance). Interest-
ingly, although the high mass envelopes correspond to
fragments in which acetonitrile is lost, only a small
the 10:1 PhCNÁEt2O co-solvent utilized for the deposi-
/
tion experiments (vide infra). The acetonitrile complex
Cl4(CH3CN)W(NPh) (2a) was prepared as previously
reported by Nielson [30].
2.2. Mass spectrometry
All mass spectral analyses were performed using a
Finnigan MAT95Q hybrid sector mass spectrometer
(Thermo Finnigan, San Jose, CA). Electron ionization
(EI) was carried out in positive ion mode using electrons
of 70 eV potential and a source temperature of 200 8C.
Negative ion electron capture chemical ionization (NCI)
used methane as the bath gas at an indicate pressure of
2ꢃ
10ꢁ5 Torr, an electron energy of 100 V and a source
/
temperature of 120 8C. All samples were introduced via
a controlled temperature probe with heating and cooling
enabling temperature control down to 35 8C. The mass
resolving power (m/Dm) was 5000 full width-half
maximum (FWHM).
2.3. Film growth studies
The solid precursor was dissolved in 10:1 benzoni-
trile:ether at a concentration of 7.5 mg mlꢁ1, loaded
into a syringe and pumped into a nebulizer. Operation
of the nebulizer was described previously [28]. Experi-
ments were conducted in a custom-built vertical quartz
cold wall CVD reactor system. P-type boron doped Si
amount (Â
1% abundance) of the [CH3CN]ꢂ ion was
detected at m/z 41 in the EI spectrum of 2a. The
/
presence of the [Cl4W]ꢂ and [Cl3W]ꢂ fragments sug-
(100) substrates with resistivity of 1Á
/
2 V-cm were used
gests cleavage of the WÃ
Furthermore, observation of the [Ph]ꢂ fragment (m/z
77) indicates that the critical NÃPh bond is broken to
/
N bond occurs in the gas phase.
for the film growths. Growths were conducted for a
fixed time of 150 min at temperatures ranging from 450
to 800 8C. The system was maintained at vacuum by a
mechanical roughing pump, with the operating pressure
fixed at 350 Torr. Hydrogen (H2) carrier gas was used
for the depositions.
/
some extent under EI conditions; however, there is no
evidence of a metal nitrido fragment in the resulting
spectrum. Moreover, the base peak in the NCI spectrum
corresponds to [Cl4W(NPh)]ꢁ (m/z 417) while the mass
envelope of the nitride fragment [Cl4WN]ꢁ (m/z 340)
has a relative abundance of 4%. The presence of the
fragment [Cl5W(NPh)]ꢁ suggests that the nitrile ligand
of 2a is removed during the process of heating the
condensed phase sample to afford [W(NPh)Cl4]2 prior
to ionization.
Film structure was examined by X-ray diffraction
(XRD) on a Philips APD 3720, operating from 5 to 85
2u degrees with CuÁ
was determined by Auger electron spectroscopy (AES)
using a PerkinÁElmer PHI 660 Scanning Auger Multi-
probe, while XPS data were collected with a PerkinÁ
/
Ka radiation. Film composition
/
/
Elmer PHI 5100 ESCA System using an Mg anode X-
ray source. Film resistivity was measured with an Alessi
Industries four-point probe. Film thickness was esti-
mated by cross-sectional scanning electron microscopy
The mass spectral data for phenylimido complex 2a
and isopropylimido complex 1a show some similarities.
For both, the most prevalent ion on the high mass end
of the EI spectrum corresponds to [Cl3W(NR)]ꢂ,

O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á
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341
Table 1
Summary of relative abundances for positive ion EI and negative ion
NCI mass spectra of tungsten imido complexes Cl4(CH3CN)W(NPh)
(2a) and Cl4(CH3CN)W(Ni Pr) (1a)
Complex
EI fragments
NCI fragments m/ Abund-
ance a,b
z
Cl4(CH3CN)W(NPh) [Cl4W(NPh)]ꢂ
417
9
(2a)
[Cl3W(NPh)]ꢂ
[Cl4W]ꢂ
[Cl3W]ꢂ
[PhN]ꢂ
382 100
326
291 15
91
77 22
64
51 10
7
B/
1
[Ph]ꢂ
[C5H4]ꢂ
[C4H3]ꢂ
[CH3CN]ꢂ
[C3H2]ꢂ
1
41
38
1
1
[Cl5W(NPh)]ꢁ 452 23
[Cl4W(NPh)]ꢁ 417 100
[Cl4WN]ꢁ
340
348 100
4
Cl4(CH3CN)W(Ni Pr) [Cl3W(Ni Pr)]ꢂ
(1a)
[Cl4W]ꢂ
[Cl3WNH]ꢂ
[Cl3W]ꢂ
[CH3CN]ꢂ
326 26
306 78
291 30
41 24
[Cl4W(Ni Pr)]ꢁ 383 42
[Cl4WN]ꢁ
340 100
a
Relative abundances were adjusted by summing the observed
intensities for the predicted peaks of each mass envelope and normal-
izing the largest sum to 100%.
b
Values for 1a are from Ref. [28].
the small clusters of peaks centered at m/z 64, 51 and 38
[33]. Even more striking is the fact that the [Cl4WN]ꢁ
fragment is the base peak in the NCI spectrum of 1a, but
only accounts for 4% relative abundance in the pheny-
limido complex 2a.
Fig. 1. Positive ion electron-impact ionization (EI) and negative ion
electron capture chemical ionization (CI) mass spectra of 2a.
although 2a does also exhibit lower abundance peaks
from [Cl4W(NPh)]ꢂ. This, coupled with the lack of
molecular ion signals, is consistent with high lability of
the nitrile ligand in both complexes. Moreover, the
presence of the [Cl5W(NPh)]ꢁ fragment in the NCI
spectrum suggests that the lability of the nitrile ligand
results in partial conversion of 2a to the dimer
[W(NPh)Cl4]2 prior to ionization. The observation of
this chloride transfer process in 2a, but not 1a, is
consistent with the greater electron withdrawing nature
of the phenyl substituent, as compared to isopropyl.
The most notable difference in the spectra of 2a and
1a concerns the fragments [Cl3WNH]ꢂ and [Cl4WN]ꢁ.
In relation to the use of Cl4(PhCN)W(NPh) (2b) as a
precursor for tungsten nitride deposition, the mass
spectral data of 2a and 1a suggest that the NÃ
bond is more difficult to break than the NÃ
iPr bond.
This is consistent with the homolytic bond strength of
the two NÁ Ph bond cleavage were
/Ph
/
/
R moieties [34]. If NÃ
/
involved in the rate determining step, 2b would be
expected to require higher deposition temperatures
relative to the isopropyl system. The stronger NÃ
/Ph
bond may also affect growth rate and composition of
the deposited films. Additionally, these data suggest that
replacing the phenyl moiety with a group that will cleave
more readily (e.g. allyl) could decrease the deposition
temperature and improve the compositional character-
istics of the WNx films.
Since these ions are derived from cleavage of the NÃ
/R
bond of the imido moiety, they are critical to the CVD
process. As shown in Table 1, [Cl3WNH]ꢂ appears in
the EI spectrum of 1a with a relative abundance of 78%;
however, this fragment is not present in the spectrum of
the phenylimido complex 2a. Nevertheless, the presence
3.2. Volatilization of the precursor
of [Ph]ꢂ indicates the NÃ
extent under EI conditions. The ion [PhN]ꢂ (m/z 91)
was observed in very small relative abundance (B1%),
and its subsequent fragmentation may be responsible for
/
Ph bond is broken to a certain
Deposition of thin films by MOCVD requires trans-
port of the solid phenylimido precursor 2b to the reactor
in the vapor phase. Previous tests with similar complexes
in a solid source delivery system resulted in minimal
/

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/
precursor transport, due to the low vapor pressure of the
compounds. Transport difficulties were overcome by
using a nebulizer to generate an aerosol of the precursor/
solvent mixture, which is conveyed by carrier gas to the
reactor. Although benzonitrile is an appropriate solvent
for deposition from isopropylimido complexes 1a,b,
poor solubility of the phenylimido complexes in benzo-
nitrile necessitated a co-solvent mixture of 10:1 benzo-
nitrile:ether to achieve the same precursor concentration
previously used with 1a,b. To determine the impact, if
any, of the co-solvent on film composition, acetonitrile
was tested in place of ether. AES results indicated
similar film compositions regardless of the co-solvent
used.
istic b-WNx peaks. In contrast, the XRD spectrum
shown in Fig. 2b indicates polycrystalline film deposi-
tion at 750 8C. Four characteristic peaks are evident,
with relative peak intensities indicating that no preferred
crystal orientation exists. Although the relative peak
intensities in Fig. 2b are consistent with the pattern for
polycrystalline b-W2N, the 2u peak positions lie be-
tween the standard values for b-W2N and b-W2C, which
are shown in Fig. 2c.
Peak positions between these standard values suggest
that carbon is mixing with nitrogen and vacancies on
tungsten’s interstitial sublattice to form b-WNxCy
polycrystals. For the spectrum in Fig. 2b, primary
reflections at 37.13 and 43.08 2u degrees are consistent
with (111) and (200) b-WNxCy growth planes, while
additional reflections at 62.73 and 74.98 2u degrees
indicate (220) and (311) planes, respectively. No peaks
arising from the hexagonal WN or WC phases, or the
body centered cubic (BCC) a-W phase were evident for
any of the films.
Fig. 3 illustrates the evolution of film crystallinity
with deposition temperature for growth from 2b. The
trend of increasing crystallinity with deposition tem-
perature is similar to that observed for the isopropyl
imido precursor 1b [28]. At the lowest deposition
temperature (475 8C), the characteristic b-WNx peaks
are not observed, indicating that the film is amorphous.
As the temperature increases to 500 8C, peaks appear
at 23.48 (not shown) and 47.98 2u degrees, consistent
3.3. Film structure
The films typically had a smooth, shiny metallic
appearance with color varying from black to gold,
depending on the deposition conditions. The desired
WNx film structure and stoichiometry is face centered
cubic (FCC) b-W2N (b-WNx, xꢀ
/
0.5), since this phase
has the lowest resistivity. The XRD spectrum in Fig. 2a
is consistent with amorphous film deposition from 2b at
475 8C, as evidenced by a flat profile with no character-
with formation of tungsten oxide (WOx, x :3). Re-
/
peated attempts to deposit films at 500 8C resulted in
formation of tungsten oxide, while peaks consistent with
WNx are seen at all deposition temperatures above this.
Reproducible deposition of tungsten oxide at a single
temperature suggests that an air leak in the reactor
system is unlikely to be the source of oxygen. Micro-
structure dependent, post-growth oxygen incorporation
is a likely cause of oxide formation, especially for low
temperature, ‘‘clean’’ tungsten films with low carbon
Fig. 2. XRD spectra of WNx Cy grown from 2b on Si (100) in a H2
atmosphere at (a) 475 8C and (b) 750 8C; (c) shows standard powder
diffraction plots for b-W2N (solid lines) and b-W2C (dashed lines).
Fig. 3. Change in XRD pattern with deposition temperature for
WNx Cy grown from 2b on Si (100) in a H2 atmosphere.

O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á
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343
and nitrogen levels. This is due to lower contamination
levels, which make these films less resistant to oxygen in-
diffusion and reaction. The existence of a second oxygen
incorporation pathway involving the Et2O co-solvent,
however, cannot be ruled out. Diethyl ether is known to
undergo both homogeneous and heterogeneous decom-
position at temperatures near 500 8C [35,36]. Although
oxide formation still occurs for films grown at 500 8C
from Cl4(PhCN)W(NPh) (2b) in a benzonitrile/acetoni-
trile mixture (no Et2O present), the size of the oxide
crystallites is larger when the ether complex Cl4-
(Et2O)W(NPh) (3) was used to generate precursor or
when Et2O is the co-solvent. Even though the film is
amorphous at 475 8C, indicating that inadequate ther-
mal energy is available to produce oxide polycrystals,
the possibility of oxygen incorporation similar to that at
500 8C cannot be ruled out. High levels of oxygen in the
amorphous film, as demonstrated by AES data (vide
infra), support this possibility.
A broad peak near 38.03 2u degrees, which is above
the standard peak position for b-W2N (111), appears for
deposition at 525 8C, and indicates the presence of
nitrogen-deficient polycrystalline b-WNx (111). A broad
peak at 44.03 2u degrees for deposition at 550 8C
indicates the first appearance of b-WNx (200). As the
temperature increases to 600 8C, film peak positions
shift below the standard b-W2N positions, indicating
that b-WNxCy deposition is occurring. Broad peaks
emerge at 62.93 and 75.58 2u degrees for deposition at
700 8C, indicating b-WNxCy (220) and (311) growth.
The peaks sharpen further as the temperature increases
to 750 8C, due to polycrystalline grain growth. Peak
sharpness decreased somewhat for the film deposited at
800 8C (not shown), which is likely due to a decrease in
film thickness as measured by XSEM (vide infra).
Decreased film thickness may be caused by rapid
desorption of reactants from the film surface due to
high temperatures or by gas phase reactions, which
deplete the amount of reactant available at the film
surface. Some films deposited between 475 and 600 8C
displayed additional peaks at 32.98 and/or 61.68 2u
degrees, representing reflections from the underlying Si
consistent with Si (200) Ka and Si (400) Kb radiation,
respectively.
XPS, placing an upper limit of Â
/
1 at.% on Cl content.
HCl is the thermodynamically favored gas phase
chlorine-containing species, and was observed by resi-
dual gas analysis during deposition from 1a,b. It is
assumed that HCl is the dominant gas phase chlorine-
containing species for deposition from 2b as well.
Neither Cl2 nor chlorinated hydrocarbons were detected
in the reactor effluent, leading to the conclusion that
chlorine is lost from the precursor as HCl. From 475 to
500 8C, the carbon level is constant at approximately 3Á
/
5 at.%. The carbon content jumps from 5 to 14 at.%
between 500 and 525 8C. Although XRD indicates b-
WNx polycrystalline deposition at 525 8C, results for
growth rate and sheet resistance (vide infra) at this
temperature show strong deviation from the trends
evident between 550 and 750 8C. Given the proximity
in deposition temperature of the carbon spike (525 8C)
to the anomalous tungsten oxide formation seen in the
XRD (500 8C), the two phenomena may be related.
Above 550 8C, the carbon content rises steadily from 9
to 22 at.% at 750 8C. The increase in carbon content
from lowest to highest deposition temperature reflects
the increasing tendency of the hydrocarbon groups
present in the precursor ligands and the solvent to
deposit in the films at higher growth temperature.
The initial nitrogen content of films grown at 475 8C
was 1 at.%. The nitrogen content increased to a
maximum value of 3 at.% at 525 8C as a consequence
of decreased oxygen concentration through this range.
The nitrogen concentration then decreased with increas-
ing temperature, dropping below 1 at.% above 700 8C.
Although metal nitride barriers typically exhibit low
nitrogen content at higher deposition temperatures (due
to desorption of N2 gas), the films deposited from 2b
were nitrogen-deficient throughout the temperature
range studied. This nitrogen deficiency in the films
contrasts with XRD results in Fig. 3, which indicate b-
WNx polycrystal growth at lower temperatures. This
may indicate that b-WNxCy polycrystal formation
begins at temperatures below 600 8C, with carbon filling
the excess vacancies present in the polycrystals due to
nitrogen deficiency.
Although the value of y in b-WNxCy should be
relatively small at the lower deposition temperatures, it
may be sufficiently large to shift the XRD peak position
to lower values of 2u (and concomitantly increase the
lattice parameter, vide infra), even at the lower tem-
peratures. It should also be noted that preferential
incorporation of carbon and removal of nitrogen by
Arꢂ sputtering during AES analysis has been reported
to cause artificially high carbon and low nitrogen
concentration readings [37]. Since the AES data were
collected after 2.0 min of sputter, artificially high carbon
and low nitrogen compositions may have been observed.
In addition, the lack of a standard film sample for
calibration of elemental concentrations means that AES
At the highest deposition temperature, minimal
nitrogen and high carbon levels suggest that the
stoichiometry of the b-WNxCy polycrystals may be
approaching b-WCy deposition. A shift in the position
of the peaks toward b-W2C at higher deposition
temperature provides evidence of this trend.
3.4. Film composition
AES results for films deposited from the phenylimido
complex 2b indicate the presence of W, N, C and O (Fig.
4). No chlorine was detected in the films by AES or

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/
Fig. 4. Comparison of tungsten, nitrogen, carbon and oxygen content in the WNx Cy films grown from the 1b and 2b compounds. Data are from
AES measurements after 2.0 min sputter.
data may vary up to several atom percent from the
actual values. Despite the error bars on the concentra-
tions, the AES data serve to identify trends in film
composition with deposition temperature.
films are consistent with WO3, which has considerably
higher thermodynamic stability than b-WNx or b-WCx.
For example, values of the Gibbs energy of formation
(/
DGꢀf ) at 750 8C for the WO3, b-WN0.5 and b-WC0.5
phases are ꢁ 8.5
579 kJ molꢁ1, ꢂ21 kJ molꢁ1, and ꢁ
kJ molꢁ1, respectively [41Á
43]. The experimental ob-
The slight oxygen contamination in the film samples
deposited at higher temperatures likely resulted from
post-growth exposure of the film samples to air. The
higher oxygen levels in films deposited at and below
500 8C may be influenced by the presence of the Et2O
co-solvent during growth and exposure of the films to
air after growth. Incremental AES sputtering showed a
steady decrease in oxygen levels with increasing depth
into the WNx films. The oxygen concentration was
highest at 475 8C, reaching 15 at.%, and then decreased
slightly to 11 at.% at 500 8C. This behavior is consistent
with low density and high porosity in the amorphous
films deposited below 525 8C, which allow substantial
amounts of oxygen to penetrate into the film lattice.
/
/
/
/
servation of lower levels of oxygen at higher deposition
temperatures is consistent with post-growth oxygen
contamination. As the deposition temperature rises
from 500 to 525 8C, the oxygen content drops sharply
to 4 at.%. This behavior is consistent with the change in
crystallinity observed by XRD. As the film crystallizes,
it becomes more dense [44], thereby inhibiting post-
growth oxygen diffusion into the lattice and decreasing
the density of adsorption sites. As deposition tempera-
ture increases above 525 8C, the oxygen concentration
drops further, falling below 1 at.% above 700 8C. This
drop in oxygen levels likely results from film densifica-
tion (by polycrystal grain growth) and increased carbon
levels at higher deposition temperature stuffing the grain
boundaries. Porosity of amorphous films grown below
High oxygen concentrations (Â
exposure have been reported for porous TiN, TiC and
TiCN barriers [38Á40]. XPS results for oxygen in the
/
20%) attributed to air
/

O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á
/350
345
525 8C may be problematic for diffusion barrier appli-
cations, since defects in the film may degrade the
barrier’s resistance to Cu diffusion. A previous report,
however, indicates that diffusion barrier performance
depends more strongly on film microstructure than film
density [45]. In addition, impurities such as O, N and C
have been reported to enhance the stability of diffusion
barrier films [46].
WNxCy polycrystals may be forming even at the lower
temperatures, with carbon playing a role in the lattice
parameter increase at lower temperatures. While an
explicit relationship between x and y in b-WNxCy
cannot be determined from XRD and AES data, insight
into the relation between carbon and vacancies on the
interstitial sublattice is possible. Nitrogen prefers to
occupy interstitial lattice sites in the polycrystals, and
only resides at the grain boundary when its concentra-
tion in the film exceeds the b-W2N stoichiometry. Low
nitrogen levels in the 2b films imply that all nitrogen
resides at interstitial sites. Essentially constant, low
nitrogen levels (Fig. 4) indicate that changes in lattice
parameter will likely depend on the ratio of carbon to
vacancies on the interstitial sublattice.
3.5. Lattice parameter
The dependence of lattice parameter on deposition
temperature was determined by XRD using the 2u
position of the (111) b-WNxCy diffraction peak, with
peak position calibrated to the Si (400) diffraction peak
(Fig. 5). The standard b-W2N (111) and b-W2C (111)
peak positions are 37.735 and 36.977 2u degrees (Fig.
2c), respectively, and correspond to standard lattice
Values for lattice parameter in the films from 2b tend
to follow carbon content over the entire deposition
temperature range. This likely reflects an increase in the
ratio of carbon to vacancies on the interstitial sublattice
with deposition temperature. The lattice parameter for
˚
parameter values of 4.126 and 4.236 A. The position of
the (111) reflection peak can vary as a result of a change
in composition or a change in the film’s residual stress.
Assuming that compositional variation is responsible
for the peak shift and, thus, lattice parameter change,
trends in the relative concentrations of nitrogen, carbon,
and vacancies on the interstitial sublattice can be
suggested by coupling the peak shift with the composi-
tions measured by AES (Fig. 4). If the (111) peak
position is higher than 37.735 2u degrees, corresponding
˚
the films from 2b is 4.10 A for 525 8C deposition, drops
˚
˚
to 4.09 A for 550 8C, and then increases to 4.14 A for
600 8C. The carbon content follows the same trend (Fig.
4), decreasing from 525 to 550 8C, and then increasing
up to 600 8C. The lattice parameter increases only
˚
˚
slightly from a value of 4.14 A at 600 8C to 4.15 A at
650 8C, consistent with a small increase in carbon levels
as measured by AES. This behavior is consistent with a
decrease in compressive film stress, coupled with grain
growth. Above 650 8C, the lattice parameter again
˚
to a lattice parameter below 4.126 A, then minimal
carbon, a deficiency of nitrogen, and an excess number
of vacancies exist in the polycrystals. This is the case for
depositions between 525 and 575 8C. A peak position
between 37.735 and 36.977 2u degrees, which corre-
sponds to a lattice parameter between 4.126 and 4.236
˚
increases with carbon content, reaching 4.19 A at
750 8C.
3.6. Polycrystal grain size
˚
A, suggests mixing of nitrogen, carbon and vacancies on
the interstitial sublattice. This is the case for depositions
at and above 600 8C. As mentioned above, however, b-
Grain size (t) was estimated using the Scherrer
equation (Eq. (1)) [47,48]. The two main causes of
peak broadening in XRD thin film spectra are non-
uniform film stress and the presence of small crystal
grains. If we assume uniform film stress, the average
crystallite size (t) may be estimated using the Scherrer
equation:
0:9l
tꢀ
(1)
(B cos u)
˚
where l is the X-ray wavelength (1.5406 A for CuÁ
/
Ka),
B is the full width at half maximum (FWHM) for the
selected diffraction peak and u is the Bragg angle for
that peak.
The dominant (111) diffraction peak for the films was
used as the reference peak for FWHM determination.
As depicted in Fig. 6, grain size for the films from 2b
Fig. 5. Lattice parameters for films grown from 1b and 2b, based on
˚
the b-W2N (111) diffraction peak. The dashed line at 4.126 A
represents the standard lattice parameter value for b-W2N, while the
increased with deposition temperature, varying from 35
˚
˚
dashÁ
/
dot line at 4.236 A is that for b-W2C. Error bars indicate
˚
to 67 A over the 525Á
/
750 8C temperature range. Below
uncertainty in lattice parameter (9
/
0.002 A) due to X-ray Ka line
broadening.
525 8C, the films were X-ray amorphous, hence, the

346
O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á350
/
Fig. 6. Change in average grain size with deposition temperature for
polycrystalline films grown from 1b and 2b based on the FWHM of the
b-W2N (111) diffraction peak. Error bars reflect uncertainty in
FWHM measurements.
Fig. 8. Plot of WNx Cy film growth rate (G, A minꢁ1) from 2b on
Si(100) vs. inverse temperature. Error bars indicate uncertainty due to
˚
maximum grain size for amorphous films was below 35
˚
A. Interestingly, the grain size is essentially constant
deposition temperature variation (910 8C) and thickness measurement
from X-SEM photos. The line fit for the kinetic regime includes data
points for 450, 475 and 550 8C, and excludes points at 500 and 525 8C.
/
between 550 and 600 8C, which coincides with the
transition region between kinetic and diffusion con-
trolled growth. As the deposition temperature increases,
a competition likely exists between increased grain
growth due to higher surface diffusivity and decreased
grain growth due to increasing carbon concentration on
the film surface, which inhibits surface diffusion. Inter-
play between these phenomena causes grain growth in
regions with small shifts in carbon content and leveling
off of grain size in regions with larger shifts in carbon
content.
above 550 8C exhibits a weak dependence on tempera-
ture that is indicative of diffusion-controlled growth.
The region with a steep slope below 550 8C suggests that
growth is controlled by a kinetic process. In this regime,
the rate-determining step for film growth is presumably
reaction on the substrate surface. As observed in the
XRD and AES studies (vide supra), the growth rates for
films grown at 500 and 525 8C appear to be anomalous.
This may be due to a decrease in the film density causing
the measured thickness change to overestimate the
reaction rate. Excluding the data points at 500 and
525 8C, a fit of the data gives an apparent activation
energy for growth of films from 2b in the kinetic regime
3.7. Film growth rate
Growth rates were estimated by dividing the total film
thickness (from X-SEM or AES sputter profile for the
sample grown at 150 8C) by deposition time. Fig. 7
depicts X-SEM photos for films grown at the lowest and
highest growth temperature, corresponding to deposi-
as 1.4190.58 eV.
/
Depositions at 450 and 800 8C were done to establish
the temperature boundaries for film growth from the
phenylimido complex 2b. Films deposited at 450 8C
tion rates of 2 and 21 A minꢁ1. An Arrhenius plot using
˚
were not visible by X-SEM, but AES depth profiling
˚
100 A. This
the measured growth rates (Fig. 8) clearly delineates two
growth regimes. The region with the shallow slope
indicated a nominal film thickness of Â
/
Fig. 7. Cross-sectional SEM photo depicting thickness of WNx Cy film grown from 2b on a Si (100) substrate grown at (a) 475 8C and (b) 750 8C.

O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á
/350
347
thickness value (triangular symbol in Fig. 8) was used to
estimate the value of the apparent activation energy for
film growth in the kinetic regime. The growth rate at
Increased grain growth generally causes a resistivity
decrease, while increased carbon content and film
thickness are associated with increased resistivity.
ꢁ1
˚
800 8C dropped to 13 A min
(square symbol in Fig.
8), with a high degree of surface roughness visible on the
substrates after deposition. These results may be ex-
plained by either premature gas phase decomposition of
the precursor, due to upstream heating at the higher
temperature or by high desorption rate for a reactant
species.
3.9. Film sheet resistance
Film resistivities calculated with Eq. (2) depend on
both the sheet resistance and thickness of the analyzed
films. As deposition temperature increases above
550 8C, the film thickness also increases. To decouple
the impact of film thickness from the film’s electrical
properties, the sheet resistance was plotted as a function
of deposition temperature (Fig. 10). The sheet resistance
increases sharply with deposition temperature from 75
V/I at 475 8C to 1600 V/I at 500 8C, then rises further
to 2000 V/I at 525 8C. This increase in sheet resistance
for the less conductive films grown at 500 and 525 8C
indicates that these higher resistivity values (Fig. 9) are
not due solely to higher film thickness and is consistent
with oxide formation and the spike in carbon content
(vide supra) determined by AES (Fig. 4). As the
deposition temperature is increased to 550 8C, the sheet
resistance decreases to 279 V/I, concomitant with lower
oxygen and carbon content. The sheet resistance, like
the resistivity, fluctuates somewhat for deposition tem-
perature above 550 8C, but eventually reaches a constant
value near 210 V/I at 750 8C.
3.8. Film resistivity
Film resistivity was calculated as shown in Eq. (2),
where r is resistivity (V-cm),
rꢀRst
(2)
Rs is sheet resistance as measured by 4-point probe (V/
I), and t is film thickness determined by X-SEM (cm).
The variation of film resistivity with deposition tem-
perature is shown in Fig. 9. A deposition at 475 8C
produced films with the lowest resistivity value (225 mV-
cm) despite carbon and oxygen contamination levels of
3 and 15 at.%, respectively. This is lower than the 620
mV-cm
reported
for
films
grown
from
(tBuNH)2W(NtBu)2 at 650 8C [24,25], and also lower
than the 750 mV-cm value observed for films grown from
1b.
3.10. Comparison of films deposited from 1b and 2b
In the temperature range where anomalous growth
was observed, 500Á525 8C, the resistivity sharply in-
/
In terms of their decomposition chemistry, the most
significant difference between isopropylimido complex
1b and phenylimido complex 2b is the dissociation
creases, e.g. 73 000 mV-cm at 500 8C. This dramatic rise
is consistent with deposition of tungsten oxide at 500 8C
(vide supra). Interestingly, the resistivity climbs even
higher to 87 000 mV-cm for deposition at 525 8C, despite
XRD data consistent with polycrystalline b-WNx.
Moving to 550 8C, the film resistivity drops to 4750
mV-cm, then fluctuates somewhat with increasing
growth temperature. Changes in the film resistivity
above 550 8C occur due to the interplay of polycrystal
grain growth, carbon content and film thickness.
energy of the NÃ
/
C bond in the imido ligand. Based on
C bond of
data from organic model compounds, the NÃ
/
isopropylimido complex 1b is expected to be approxi-
mately 20 kcal molꢁ1 weaker than the analogous bond
in 2b [34]. Since cleavage of this bond is necessary for
deposition of WNx, one would expect there to be
Fig. 9. Variation of film resistivity with deposition temperature for
films deposited with 1b and 2b.
Fig. 10. Variation of film sheet resistance with deposition temperature
for films deposited from 1b and 2b.

348
O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á350
/
differences in film structure, film composition, and
lattice parameter between films grown from the two
precursors.
and Table 1 do not rule out loss of NPh as a major
heterogeneous process during deposition. Ideally, clea-
vage of the NÃ
should occur during CVD of WNx films. However, the
high NÃC dissociation energy would slow this process,
allowing cleavage of the WÃN bond to compete.
Isopropylimido complex 1b, with its weaker NÃ
/
C bond in 2b to release a phenyl group
Amorphous film growth occurs below 500 8C for 1b
and 2b. At 500 8C, a broad b-W2N (111) polycrystalline
peak appears for films from 1b, while polycrystalline
oxide peaks appear for the material from 2b. Evidence
of polycrystalline WNx deposition from 2b first appears
at 525 8C. The anomalous film characteristics of mate-
rial grown from 2b at 500 8C appear to be linked to the
presence of the Et2O co-solvent (necessary because the
solubilities of 1b and 2b differ). The maximum deposi-
tion temperature for films deposited from the isopropyl
complex was 700 8C. Above this temperature, black
particles were deposited on the substrate and susceptor,
which subsequently compromised film quality. In con-
trast, deposition from phenylimido complex 2b was
possible up to 750 8C. The higher temperature limit for
/
/
/C
bond, would be more likely to release the isopropyl
moiety and leave the imido nitrogen in the growing film.
For both precursors, oxygen levels were highest for
films deposited at the lower end of the temperature
range (5500 8C). AES indicated a decrease in oxygen
/
content with increasing sputter depth into the films;
hence, high oxygen levels were attributed to post-growth
exposure of the films to air. The low density and high
porosity of the amorphous structures grown at lower
temperatures allow more rapid diffusion of oxygen from
the air into the films and provide a large surface to
volume ratio for adsorption. High oxygen levels in the
films from 2b, however, may be due to a combination of
post-growth exposure to air and the presence of Et2O
during deposition. Increased carbon content in the films
grown at higher temperatures is believed to inhibit post-
growth oxygenation of the films by stuffing grain
boundaries.
2b could be due to the enhanced NÃ
/C bond strength in
its imido ligand.
Carbon levels in the films from 2b were considerably
lower than those from 1b throughout the temperature
range (Fig. 4). From 550 to 750 8C, films from both
precursors exhibited a gradual rise in carbon content,
with the isopropyl imido complex 1b affording a steeper
rise in carbon as growth temperature increased. Max-
imum nitrogen content for films from the two precursors
occurred near their respective crystallization tempera-
tures (500 8C for 1b and 525 8C for 2b). Throughout the
temperature range studied, the nitrogen content in films
deposited from 2b was significantly lower than those
grown from 1b. The fact that films from phenylimido
complex 2b contained lower levels of both nitrogen and
carbon than those from isopropylimido complex 1b
suggests that the phenylimido moiety is more likely to
dissociate intact than the isopropylimido ligand. This is
The lattice parameter shifts were also dependent on
the precursor. Fig. 5 shows the lattice parameter
increasing with temperature for films from both 1b
and 2b at temperatures up to 650 8C, with films from 1b
having higher lattice parameter values throughout this
range. This is expected, due to higher carbon content in
films from the isopropylimido complex 1b. Just above
675 8C, though, the lattice parameter in the films from
2b becomes larger than that of the films from 1b.
Polycrystalline films deposited from 1b have adequate
nitrogen, even at high temperatures, to be considered
primarily b-WNx into which carbon is incorporated to
form b-WNxCy. This b-WNx, although nitrogen-defi-
cient at higher temperatures, contains sufficient nitrogen
to prevent a shift from formation of b-WNxCy toward
b-WCy, and leads to an upper limit in lattice parameter
consistent with the higher NÃ
/C bond strength in the
phenylimido group.
Corroborating evidence for this effect can be found in
the mass spectra of 1a and 2a. Facile dissociation of the
isopropyl group from 1a is indicated by the observation
of [Cl3WNH]ꢂ at 78% abundance in the EI spectrum
and detection of [Cl4WN]ꢁ as the base peak in the NCI
trace. Loss of the phenyl moiety from 2a to yield the
same ions does not occur under EI conditions and the
NCI spectrum contains [Cl4WN]ꢁ at only 4% abun-
dance. Moderate amounts of [Cl4W]ꢂ and [Cl3W]ꢂ
were detected in the mass spectra of 2b under EI
˚
for films from 1b near 4.16 A. Thus, the decrease in
lattice parameter in films from 1b deposited above
650 8C was attributed to a solubility limit for carbon
in b-WNxCy polycrystals with excess carbon residing at
the grain boundaries above 675 8C.
The films from 2b, however, contain so little nitrogen
that tungsten is effectively left ‘‘bare’’ during deposition,
enabling formation of carbide by reaction with deposit-
ing carbon at high temperature. Minimal nitrogen
conditions, as well as fragments aÁd (Fig. 1), which
/
are consistent with what has previously been observed
upon generation of NPhꢂ from phenyl azide [33].
Although the mass spectral evidence for NPh loss
consists of low intensity mass envelopes, their presence
is significant. Because of the difference in conditions
between mass spectrometry (ion chemistry) and
MOCVD (thermal decomposition), the data in Fig. 1
coupled with Â20 at.% carbon above 675 8C may
/
mean that a shift away from deposition of b-WNxCy
toward b-WCy is occurring at high temperature with the
2b precursor. The lattice parameter of 4.19 A for films
˚
grown from 2b at 750 8C indicates that the composition
of the b-WNxCy polycrystals is nearing b-W2C (i.e. x is

O.J. Bchir et al. / Journal of Organometallic Chemistry 684 (2003) 338Á
/350
349
approaching zero and y is approaching 0.5), which has a
˚
lattice parameter of 4.236 A.
Although b-WNx films are reported to outperform b-
WCy for diffusion barrier applications, recent reports
growth from 2b in the kinetically controlled regime was
1.4190.58 eV, as compared to 0.84 eV for 1b and 0.9 eV
/
for (tBuNH)2W(NtBu)2 [24,25]. The higher activation
energy for 2b is consistent with cleavage of the stronger
indicate interest in b-WNxCy as a potential barrier
imido NÃ
/
C bond before or during the rate-determining
˚
material. Thin films (Â
/
250 A) of b-WNxCy have been
step of the deposition process. Interestingly, the Ea for
2b is above the typical activation energy range for CVD
growth in the kinetic regime, which is 0.5 to 1 eV [53].
With the exception of the anomalous results for
growth at 500 and 525 8C, comparison of the sheet
resistances, which negate the impact of film thickness on
electrical properties, shows that the films from 1b and 2b
have similar electrical properties when deposited at or
below 675 8C. Above 675 8C, 1b films have higher sheet
resistance than 2b films, consistent with the high carbon
levels in the 1b films, which scatter electrons flowing
through the material.
deposited by atomic layer CVD onto various substrates
(e.g. SiO2, Cu, SiC and SiLK) by sequential reaction of
WF6, NH3 and BEt3 [49,50]. Addition of carbon to b-
WNx was reported to lower film resistivity. In addition,
b-WNxCy with a composition ratio W:N:C:
/55:15:30
exhibited excellent adhesion to Cu. Hence, although
films deposited from 2b have low nitrogen content, this
precursor may be of interest for b-WNxCy deposition.
In addition, co-reactants could be used to raise the
nitrogen content in material deposited from 2b. We
recently reported use of this strategy to dramatically
increase the nitrogen content for films deposited from
1a,b in the presence of NH3 [51]. A similar approach
may enable control of the nitrogen levels of b-WNxCy
films from 2b.
3.11. Conclusions
The tungsten imido complex Cl4(CH3CN)W(NPh) 2b
was tested to determine its suitability as a single-source
precursor for low temperature growth of b-WNx thin
films. Comparison of the film growth properties of 2b to
those of its isopropylimido analogue 1b allows evalua-
Nitrogen levels in the films from 2b are much lower
than films from 1b at all temperatures. This trend in the
films grown from the phenylimido precursor can again
be attributed to the high NÃ/C bond dissociation energy
in the imido ligand of 2b, which causes less nitrogen
incorporation into the films, leaving open the possibility
of b-WCy formation. The XPS binding energy values for
C1s and W4f7/2 energy levels for films deposited from 2b
at 650 8C were 284.6 and 33.0 eV, respectively, while
those for deposition at 750 8C, were 283.6 and 32.1 eV.
These data are consistent with a shift toward formation
of the b-WCy phase for the film deposited from 2b at
750 8C [52]. The XPS results for films from 1b did not
indicate this shift. This suggests that adequate nitrogen
remained in the polycrystals to prevent a shift to carbide
formation, forcing additional carbon to deposit at the
grain boundaries.
tion of the effect of the imido NÃ
/
C bond dissociation
energy on film growth and properties. Films deposited
from 2b were deficient in nitrogen compared to those
from 1b, consistent with a tendency of the stronger
imido NÃ/C bond of 2b to result in dissociation of intact
NPh fragments during deposition. Since its films contain
more nitrogen and have lower amorphous deposition
temperatures and sheet resistances, the isopropyl imido
precursor 1b is superior to 2b for b-WNx barrier
deposition.
Acknowledgements
Grain growth behavior was similar for the two
precursors. Grain sizes for films grown from 1b and 2b
increased from lowest to highest deposition tempera-
ture, with those from 2b generally having smaller size
grains than those from 1b. Above 600 8C, where both
precursors are operating in the diffusion controlled
regime, the films from 2b required a temperature
The authors would like to thank the staff of the Major
Analytical Instrumentation Center (MAIC) at the Uni-
versity of Florida for assistance with film characteriza-
tion. Special thanks go to Eric Lambers for assistance
with AES and to Wayne Acree for assistance with X-
SEM. The Office of Naval Research provided support
under grant numbers N00014-95-1-0563 and N00014-
99-1-0841. Funding for the residual gas analyzer was
provided by the Air Force Office of Scientific Research.
increase of Â
their 1b counterparts. This observation can again be
traced to the difference in the strengths of imido NÃ
/
50 8C to deposit grains of similar size to
/C
bonds in the precursors, with the weaker isopropyl
imido bond affording higher growth rate and grain size
for a given deposition temperature.
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