IMEC has achieved promising
results in the race to scale CMOS to 22nm and below. The breakthroughs from
its transistor scaling programs include a successful integration of the laser-anneal
technique in a high-K/metal-gate first process and a step forward towards fabricating
aggressively scaled germanium-pFET transistors.
X-SEM picture of the Ge-in-STI structure
To scale CMOS technology to 22nm and below, high permittivity dielectrics and
metal gates (Hk/MG) are considered as one of the best options. One Hk/MG integration
scheme is metal inserted poly-silicon (MIPS). With a MIPS
CMOS process flow, IMEC has compared spike anneal and laser anneal. For the
first time, IMEC has shown functional ring oscillators with millisecond anneal-only
that show a similar performance as oscillators made using spike anneal.
The major advantage of using laser anneal over spike anneal is the reduced
thermal budget. This limits the diffusion of dopants in the Si during their
activation. Such a limited diffusion helps to keep short channel effects under
control as the physical dimensions of the transistors shrink. But laser anneal
is also challenging. IMEC’s results point to optimizations of the process
that limit the defects, maintain a low gate resistance, and show an excellent
effective work-function control using high-K capping layers. Capping layers
are dielectric layers that are deposited between the bulk dielectric and the
metal gate to tune the effective work function of the electrode to the desired
type (n- or p-).
Another scaling option that has attracted a lot of attention is using high-mobility
materials to boost the carrier mobility of the MOS transistors, as this can
lead to higher drive currents. This search has led to an interest in Germanium
MOSFETs: it has proved possible to make Ge pFET devices with a hole mobility
that is substantially above the hole mobility curve of silicon, and with conventional
processes. IMEC’s research now shows, for the first time, an STI module
(Shallow Trench Isolation) integrated in an advanced 70nm Ge-pFET technology
allowing EOT in inversion scaling down to 0.85nm. IMEC has also made an in-depth
analysis of the mechanisms that limit the hole mobility for sub-nm EOT Ge pFETs.
These results pave the way for further optimizations of Ge pFET devices, and
for their introduction in high-end high-performance ICs.
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. This work is further supported
by the European collaborative projects, especially DUALLOGIC.