Gate Engineering to Improve Effective Resistance of 28-nm High- $k$ Metal Gate CMOS Devices

In this paper, we report the development of a high-
$k$
/metal gate stacking process to reduce the effective gate resistance, and circuit level validation results in 28-nm gate first integrated high-
$k$
/metal gate CMOS devices. To achieve this, millisecond annealing was adopted and the silicon (Si) gate and TiN gate electrode thicknesses were controlled. The recrystallized poly-Si gate by millisecond annealing improved the performance of the ring oscillator (RO) by 15% and the minimum operating voltage (
$V_{\min }$
) of the high-frequency test pattern (HFTP) by 34 mV. The poly-Si gate improved the uniformity of the boron concentration and suppressed localized low doping area at the bottom of the gate. When the Si gate thickness was reduced by 10 Å with respect to the reference (POR) value, the performance of the RO improved by 5% and
$V_{\min }$
of HFTP improved by 20 mV due to the shorter boron diffusion distance. A 10- Å thicker TiN gate electrode improved
$V_{\min }$
of HFTP by 30 mV, since the thicker TiN reduced the TiN/Si gate interface resistance.