Integration of Cu with SiOCH Coral and SiC:H Low k Dielectric Films in a Dual Damascene Scheme

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Integration of Cu with SiOCH (Coral) and SiCH
Low kDielectric Films in a Dual Damascene Scheme
Tom Mountsier 1, Malcolm Grief 3, Chevan
Goonetilleke 1, Steve Lassig 2
1 Novellus Systems, San Jose, CA2 Lam Research,
Fremont, CA3 SpeedFam-IPEC, Chandler, AZ
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Dielectric DepositionAll dielectric films were
deposited at 400 C using conventional
PECVD techniques 3. To avoid poisoning of DUV
photoresist (discussed below) nitrogen and/or
nitrogen containing reactants were not included
in any of the processes. The density of Coral is
low compared to SiO2 due to -CH3 (methyl)
substitution for oxygen in Si-O-Si linkages.
Consequently, like other SiOCH films, Coral is
not as mechanically robust as SiO2 as is
reflected in the values for hardness and modulus.
Despite the reduction in mechanical strength, the
same CMP process conditions were successfully
used on both Cu/SiO2 and Cu/Coral samples.
Other unit processes such as etch and photoresist
strip were tailored to accommodate the presence
of carbon in the Coral film
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PhotolithographyPredominantly 248nm DUV imaging
with some I-line imaging was tested on the Coral
material. One of the key concerns associated with
integration of low k films is poisoning of DUV
photoresist 4, 5. Nitrogen contamination, as NHx,
originates during dielectric deposition processes
in which gases such as N2, N2O, and NH3 are used.
These species can diffuse rapidly through low
density materials such as PECVD OSG to neutralize
the photo-acid catalyst in DUV photoresist thus
preventing full post-exposure development. Resist
poisoning has been observed during trench
lithography in via-first integration schemes.
Removal of nitrogen containing gases from the
deposition processes eliminated the problem.
Figure 2 compares bond pads printed in DUV
resist over vias etched into Coral with and
without amine contamination.
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Dielectric Etch
5.5KA
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Resist Strip
Removal of photoresist from OSG films such as
Coral is complicated by the fact that the process
conditions used to strip away organic residues
will also extract carbon from the SiOCH film.
This can lead to moisture uptake and an
accompanying rise in k value. XPS carbon depth
profiles are shown in Figure 5 for Coral samples
exposed to two different strip processes
oxidizing and reducing (H2 - based) - along with
a control (non-treated) sample. Note that while
both treatments show some loss of carbon near the
exposed surface, the depletion in the case of the
oxygen-based strip is deeper and more severe. To
avoid such damage, the hydrogen- based strip
process is preferred. H2 -based processes tend to
have lower resist removal rates.
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CU/CORAL INTEGRATED STRUCTURES
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ELECTRICAL PERFORMANCE
Barrier a-SiCH
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Low k Dielectric PECVD Precursor Selection
and Film Integration Challenges
Gary W. Ray, Tom Mountsier, Patrick Van
Cleemput, Jen Shu, Paul Brunemeier, Ken
MacWilliams
Novellus Systems, Inc.4000 North First
StreetSan Jose, CA 95134
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Note that though all plots have parallel slopes,
the alkyl substituted silane films require
significantly larger carbon percentages to reach
the same k value reached at a lower carbon
content by the cyclic precursor. It should also
be noted that all three film families reach a
minimum k value after which further increases in
carbon content yield no improvement. Perhaps
further increases in the carbon percentage result
in the creation of dimethyl substituted silicon
atoms in the oxide matrix. This would further
weaken the film without reducing the
polarizability By making a careful precursor
choice, it is possible to obtain a desirable
dielectric constant and have a film that can be
successfully integrated. The ability to achieve
a desired k value at a lower carbon content is
also advantageous for etching and resist strip.
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Moisture absorption by state-of-the-art low k
materials is much improved over earlier films.
Nonetheless, a drift in k of 10 can be observed
after a few hours exposure to fab air.5 The
impact of absorbed moisture on via resistance and
morphology is well known.2 Care must be taken to
adequately out gas low k films before the
deposition of subsequent layers