(Invited) 14nm FDSOI Technology for High-Speed and Energy-Efficient CMOS

As CMOS technology scales down, two paths are pursued by the industry to overcome the fundamental limits of traditional planar bulk transistors. One is the introduction of a Tri-Gate or FinFET transistor at the 22 and 16 nm nodes [1, 2]. These architectures provide impressive drive currents per footprint at low supply voltages because of the 3-D conduction channel and excellent electrostatic control. Conversely, they have high gate and parasitic capacitances, proportional to the 3-D effective W increase, which negatively impacts both the speed and active power consumption. Alternatively FDSOI provides an evolutionary path. First introduced at the 28nm node [3], FDSOI includes excellent mismatch properties, a simplified planar manufacturing process vs 3-D finFET technology and capitalization of existing design techniques. It also extends the possibility of back biasing and therefore offers unique “smart” solutions for dynamic power optimization [4]. The technology presented in this paper furthers the appeal of FDSOI to the 14nm node [5].

Compared to the 28nm technology, new Front-End process elements include a dual SOI/SiGeOI N/P channel, a dual workfunction gate-first HKMG integration scheme and a dual in-situ doped Si:CP/SiGeB N/P raised source-drain [5]. Additionally hybrid bulk areas, formed before Shallow Trench Isolation (STI), provide a space for passive devices and ESD FETs to be built [6]. The strained-SiGe channel (cSiGe) is realized before STI patterning to avoid SiGeOI over-thinning linked to the Ge condensation process at active edges [7] (Fig.1). As shown in Fig.1, strain into the channel has been experimentally measured by Nano-Beam Electron Diffraction (NBED) : 1% compressive strain in the 6nm thin SiGeOI channel (25%Ge) is demonstrated.

After gate patterning, a N/P dual spacer/dual epitaxy scheme is used, as illustrated in Fig.2.Since gate-to-drain capacitance (C_gd) is of high importance for the circuit speed and power, spacer, poly thickness and raised source-drain epitaxy (Fig.2) has been optimised to minimize C_gd down to ~0.3fF/µm for both n and pMOS devices. cSiGe and SiGeB source-drain implementation in 14nm FDSOI provides a large pMOS drive current enhancement when compared to FDSOI technology at the 28nm node.

As a result of low C_gd and large pMOS drive current, 14FDSOI technology demonstrated in [5] a -20% delay gain with the Fan-Out 3 (FO3) RO inverters at the same static leakage and a 100mV V_dd reduction (0.8V vs 0.9V) over the 28nm FDSOI technology (Fig.3). From this previous work, the transistor performance has further progressed and the delay boost is now established at -34% with -100mV V_dd operation, as shown in Fig.3. It means >50% speed frequency in 14FDSOI at 0.8V Vdd vs 28FDSOI at 0.9V Vdd.

These large performance enhancements over 28FDSOI make 14FDSOI as a leading edge technology for the 14nm node and a highly competitive technology for low voltage and energy efficient CMOS applications.

References:

[1] C.-H. Jan et al., IEDM Tech. Dig., 2012,

[2] S.-Y. Wu et al., IEDM Tech. Dig., 2013,

[3] N. Planes et al., VLSI Symposium Tech. Dig., 2012,

[4] F. Arnaud et al., IEDM Tech. Dig., 2012,

[5] O. Weber et al., VLSI Symposium Tech. Dig., 2014,

[6] D. Golanski et al., VLSI Symposium Tech. Dig., 2013,

[7] K. Cheng et al., IEDM Tech. Dig., 2012.