NVLS), a leading provider of advanced process equipment for the global semiconductor
industry, has developed Dense ultra low dielectric constant (ULK) films that
provide more reliable device integration compared to porous ULK alternatives.
These films are deposited using a novel, single precursor that offers a five
percent lower effective dielectric constant (k-effective) when combined with
Novellus' diffusion barrier layers for typical 32nm device structures.
Comparison of etch profiles of Novellus Dense ULK and porous ULK showing relatively vertical etch profiles with dense ULK materials. Queue time effects manifesting as voids are also seen in the porous ULK materials.
The integration of ULK materials into a damascene interconnect scheme poses
numerous challenges associated with wet clean, chemical mechanical planarization
(CMP) and plasma etch. Conventional ULK films are porous in nature and are deposited
using two chemicals that include a porogen and a structure former. The porogen
is subsequently removed with an ultra-violet thermal processing (UVTP) step.
The matrix of interconnected pores created by the UVTP treatment results in
a lower dielectric constant, but causes the porous films to be highly susceptible
to solvent and moisture absorption. Extra integration steps, such as a thermal
bake-out or deposition of a capping layer, are required to retain the integrity
of the film. These additional process steps add manufacturing complexity and
cost. In contrast, UVTP of Dense ULK films results in increased mechanical strength
through the cross-linking of bonds.
Vertically etched structures can be easily obtained when patterning Novellus'
Dense ULK film - a direct result of the chemical homogeneity throughout the
layer. For the tight line-to-line spacing employed at 32nm, the improved patterning
capability translates into higher breakdown voltage and lower leakage currents.
Void formation in porous ULK, illustrates the need for control of the queue-time
between the CMP and dielectric diffusion barrier process steps. Strict queue-time
control is not required for Novellus' less-permeable, Dense ULK films.
"Novellus Dense ULK films enable five percent lower k-effective than porous
ULK films without adding complexity to the integration sequence," said
Andy Antonelli, technology manager at Novellus' PECVD business unit. "These
Dense ULK materials have been designed to enable a reliable, manufacturable
solution that is compatible with wet clean, CMP and etch modules."
Posted June 18th, 2009