(206g) Deposition of WnXCY Using Allylimido Complexes CL4(Rcn)W(Nc3H5): Effect of Nh3 on Film Properties

Abstract

  Tungsten nitride carbide (WN_xC_y)
is promising candidate for diffusion barrier application in copper
metallization. Previously, it has been demonstrated that tungsten allylimido
complexes Cl₄(RCN)W(NC₃H₅) (1a, R = CH₃;
1b, R = Ph) can be used as a single source precursor to deposit tungsten
nitride carbide thin films. In this study, we have used a mixture of the
tungsten allylimido complexes with ammonia as co-reactant to deposit tungsten
nitride carbide films.  The effect of ammonia on film composition,
crystallinity, lattice parameter, grain size, film growth rate and resistivity
was studied and compared with those for films deposited without ammonia. 
Thin films were deposited on Si (100) substrate in a CVD reactor.  The
lowest deposition temperature for 1a,b and ammonia was 450 °C. 
Film composition was determined by Auger electron spectroscopy.  Films
deposited between 450 and 750 °C had a varying concentration of tungsten (36
at. % to 61 at. %), nitrogen (8 ? 23 at. %), carbon (18 ? 54 at. %) and oxygen
(2 ? 5 at. %).  Films deposited with ammonia had significantly higher
carbon and nitrogen content and substantially lower oxygen content as compared
to films deposited without ammonia.  No chlorine was detected in the XPS
spectra over the entire deposition temperature range.  The films deposited
below 500 °C were amorphous whereas films deposited at or above 500 °C were
polycrystalline.  The peaks in the XRD spectra suggest that β-WN_0.5
and β-WC_0.6 coexist in the films.  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 lattice
parameter of WN_xC_y films decreased with increase in
deposition temperature for depositions with ammonia, with the highest lattice
parameter of 4.179 ± 0.002 Å observed at 450 °C deposition temperature and the
lowest lattice parameter of 4.112 ± 0.002 Å observed at 750 °C deposition
temperature.  The film growth rate varied from 4 Å/min for film deposited
at 450 °C to 17 Å/min for film deposited at 750 °C.  The activation energy
for the reaction of 1a,b with ammonia is estimated to be 0.33 eV, which
is significantly 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 1690
μΩ-cm obtained from growth at 550 °C.

From a diffusion barrier application standpoint,
it has been demonstrated that ammonia can be used with 1a,b to increase
film N content of WN_xC_y films.  A corresponding
increase in film resistivity is also seen and some optimization may be needed
to strike a balance between higher N content and lower film resistivity. 
In situ deposition of copper on the barrier films to test their diffusion
barrier properties is underway.