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Step and Flash Imprint Lithography (S-FIL®) in conjunction with Sacrificial Imprint Materials (SIM)
shows promise as a cost effective solution to patterning sub 45nm features and is capable of
simultaneously patterning two levels of interconnect structures, which provides a high throughput
and low cost BEOL process. This paper describes the integration of S-FIL into an industry
standard Cu/low-k dual damascene process that is being practiced in the ATDF at Sematech in
Austin. The pattern transferring reactive ion etching (RIE) process is the most critical step and
was extensively explored in this study. In addition to successful process development, the results
provide useful insight into the optimal design of multilevel templates which must take into account
the characteristics of both the imaging material and the dielectric layer.
The template used in this study incorporates both the via and trench levels of an M2 (Metal 2) test
vehicle that incorporates via chains with varying via dimensions, Kelvin test structures,
serpentines, etc. The smallest vias on the template are 120nm vias with an aspect ratio of 2.0
and the smallest dense lines are 125nm/175nm with an aspect ratio of 2.9. Two inter-level
dielectrics (ILD), Coral® and Black Diamond® were studied. No trench etch stop was incorporated
in the ILD film stack. A multi-step, in-situ etching scheme was developed that achieves faithful
pattern transfer from the sacrificial imprint material (SIM) into the underlying low k ILD with
surprisingly wide process latitude. This multi-step scheme includes the following etch steps: a
residual layer open, a via etch, a trench descum, a trench etch, and an SIM removal ash. Among
these steps, the trench etch was found to be the most challenging to develop and it holds the key
to producing high aspect ratio dual damascene features. An etching chemistry based on two
fluorocarbon gases, CF4 and C4F8, was found to be very effective in delivering the desired etch
profiles with optimal sidewall angle, minimal facet formation. The optimized etch process can be
exploited to provide substantial size reduction and/or increased aspect ratio relative to the
template. In this way structures with final critical dimensions of 95nm in vias with aspect ratio of
3.0 and 67nm/233nm in dense lines with aspect ratio of 3.6 were demonstrated with wide process
latitude. This enables manufacturing of the template at larger dimensions, which simplifies both
fabrication and inspection.
The successful development of the dual damascene RIE process at the second metal (M2) level
was demonstrated in a mixed and matched build with an ATDF standard first layer metal (M1)
process. The M1 dielectric was TEOS and was patterned by 248nm lithography. The M2 and Via
levels used Coral as ILD and both levels were patterned simultaneously by S-FIL using Molecular
Imprint Imprio 55 and Imprio 100 imprint tools. This electrical test vehicle provided solid evidence
that S-FIL is fully compatible with industry standard dual damascene process.
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