IMEC presents innovations
in dielectrics and metallization technologies as well as in their integration
approaches. Great progress has been obtained in the metallization of 22nm interconnects,
in Cu/low-k reliability assessment and in the suppression of low-k integration
damage. The results contribute to deliver the interconnect performance and reliability
beyond the 32nm node.
Cross-section TEM inspection of a 22nm interconnect line.
IMEC researchers have investigated RuTa metallization as a promising scheme
for achieving good metallization of 22nm features. It could likely replace the
traditional Ta physical vapor deposition (PVD), which, for decreasing feature
sizes, looses its ability to achieve uniform Cu seed. Four different metallization
schemes (i.e., TaN/Ta, RuTa, TaN + Co and MnOx) were evaluated in terms of Cu
fill, electrical performance and compatibility with chemical mechanical polishing
(CMP) slurries. (Figure 1)
Barrier and dielectric reliability assessment
IMEC developed a model that for the first time describes the link between line
edge roughness (LER) and time dependent dielectric breakdown (TDDB) lifetime.
The model was validated on 50nm half pitch Cu damascene lines embedded into
a k=2.5 low-k material, indicating that LER significantly contributes to the
integrated dielectric reliability margin degradation. For older technology nodes,
the reliability is mainly determined by dielectric deposition, patterning (lithography,
etch/ash), barrier deposition, CMP and cap deposition, while for the 22nm and
beyond the LER impact is expected to increase.
IMEC researchers also studied the stress of Cu interconnects inlayed into porous
low-k and airgap structures. As a main trend, high porosity materials result
in Cu with a lower stress, an effect which is less significant for narrow lines.
Air gap structures show the lowest stress. This work is useful for interpreting
reliability failure mechanisms and calibrating finite element models to predict
stress in devices of future technology nodes.
IMEC demonstrated a unique test vehicle for assessing intrinsic reliability
aspects of copper low-k interconnects and successfully used it for ranking different
technology options. The test structure is also suited for studying the barrier/low-k
interface, low-k plasma treatments, cleans, etc. It is expected that by using
this test vehicle significant contribution will be made to the entire interconnect
community by identifying and describing the fundamental reliability limits of
Plasma induced low-k damage reduction
IMEC proposes a non-contact dielectric constant metrology based on a near-field
scanning probe microwave microscope to evaluate the dielectric properties after
each processing step. The technique has been used to study the effect of plasma
ash chemistry for removal of the photoresist mask and is shown to be a good
method for non-invasive real-time in-line monitoring of patterned low-k structures
at every step during interconnect integration. Plasma damage is the main cause
of dielectric reliability loss in low-k materials during Cu/low-k integration.
The introduction of porous low-k materials has increased the dielectrics sensitivity
to plasma damage.
IMEC has also made good progress in developing alternative non-plasma routes
for photo resist removal without attacking the low-k material. A particularly
attractive approach is “all wet removal” since it mitigates the
damage caused by dry ash. Among the methods, UV pretreatments followed by O3
and solvent treatments have resulted in full removal of post metal-hard-mask
etch photoresist. Besides, radical anion based followed by O3 and gas expanded
liquid processes show promising post-etch residue removal.
These results were obtained in cooperation with IMEC’s key parners in
its core programs: Intel, Micron, Panasonic, Samsung, TSMC, Elpida, Hynix, Powerchip,
Infineon, NXP, Qualcomm, Sony, ST Microelectronics.