Current status and challenges of aggressive equivalent-oxide-thickness (EOT) scaling of high-κ gate dielectrics via higher-κ ( > 20) materials and interfacial layer (IL) scavenging techniques are reviewed. La-based higher-κ materials show aggressive EOT scaling (0.5-0.8 nm), but with effective workfunction (EWF) values suitable only for n-type field-effect-transistor (FET). Further exploration for p-type FET-compatible higher-κ materials is needed. Meanwhile, IL scavenging is a promising approach to extend Hf-based high-κ dielectrics to future nodes. Remote IL scavenging techniques enable EOT scaling below 0.5 nm. Mobility-EOT trends in the literature suggest that short-channel performance improvement is attainable with aggressive EOT scaling via IL scavenging or La-silicate formation. However, extreme IL scaling (e.g., zero-IL) is accompanied by loss of EWF control and with severe penalty in reliability. Therefore, highly precise IL thickness control in an ultra-thin IL regime ( < 0.5 nm) will be the key technology to satisfy both performance and reliability requirements for future CMOS devices.

Ultimate Scaling of High-κ Gate Dielectrics: Higher-κ or Interfacial Layer Scavenging?

Neuro-biology inspired Spiking Neural Network (SNN) enables efficient learning and recognition tasks. To achieve a large scale network akin to biology, a power and area efficient electronic neuron is essential. Earlier, we had demonstrated an LIF neuron by a novel 4-terminal impact ionization based n+/p/n+ with an extended gate (gated-INPN) device by physics simulation. Excellent improvement in area and power compared to conventional analog circuit implementations was observed. In this paper, we propose and experimentally demonstrate a compact conventional 3-terminal partially depleted (PD) SOI- MOSFET (100 nm gate length) to replace the 4-terminal gated-INPN device. Impact ionization (II) induced floating body effect in SOI-MOSFET is used to capture LIF neuron behavior to demonstrate spiking frequency dependence on input. MHz operation enables attractive hardware acceleration compared to biology. Overall, conventional PD-SOI-CMOS technology enables very-large-scale-integration (VLSI) which is essential for biology scale (~1011 neuron based) large neural networks.

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Leaky Integrate and Fire Neuron by Charge-Discharge Dynamics in Floating-Body MOSFET.

A 64Mb SRAM macro is fabricated in a 32nm high-k metal-gate (HKMG) SOI technology [1]. Figure 14.1.1 shows the 0.154μm2 bitcell (BC). A 2× size reduction from the previous 45nm design [2] is enabled by an equal 2× reduction in BC area. No corner rounding of BC gates allows tighter overlay of gate electrode and active area. The introduction of HKMG provides a significant reduction in the equivalent oxide thickness, thereby reducing the Vt mismatch. This reduction allows aggressive scaling of device dimensions needed to achieve the small area footprint. A 0.7V VDD MIN operation is enabled by three assist features. Stability is improved by a bitline (BL) regulation scheme. Enhancements to the write path include an increase of 40% of BL boost voltage. Finally, a BC-tracking delay circuit improves both performance and yield across the process space.

A 64 Mb SRAM in 32 nm High-k Metal-Gate SOI Technology With 0.7 V Operation Enabled by Stability, Write-Ability and Read-Ability Enhancements

Large scale BTI data was collected on discrete MG/HK devices to discuss modeling challenges related to BTI induced variability. A fast, parallel BTI testing procedure is introduced. This utilizes the PCI card characterization methodology to highlight a close link between BTI variability and RDF, and to discuss the impact of BTI recovery and wafer-to-wafer variation on the BTI statistics. We demonstrate a correlation between time-zero VT and ΔVT and illustrate the minor impact of BTI induced variability on post-stress VT distributions relevant for modeling the circuit aging.

Challenges in the characterization and modeling of BTI induced variability in metal gate / High-k CMOS technologies

Fully depleted SOI (FDSOI) has become a viable technology not only for continued CMOS scaling to 22 nm node and beyond but also for improving the performances of legacy technology when retrofitting to old technology nodes. In this paper, we provide an overview of FDSOI technology, including the benefits and challenges in FDSOI design, manufacturing, and ecosystem. We articulate that FDSOI is potential cornerstone for China to catch up and leapfrog in semiconductor technology% .

Fully depleted SOI (FDSOI) technology

This work presents a 32 nm SOI CMOS technology featuring high-k/metal gate and an SRAM cell size of 0.149 µm2. V min operation down to 0.6 V in a 16Mb SRAM array test vehicle has been demonstrated. Aggressive ground rules are achieved with 193 nm immersion lithography. High performance is enabled by hig-hk/metal gate plus innovation on strained silicon elements including embedded SiGe and dual stress liner (DSL). Gate lengths down to 25 nm have been demonstrated enabling performance without the power penalty from gate capacitance. AC drive currents of 1.55 mA/um and 1.22 mA/um have been achieved at an off-state of 100 nA/µm and V DD of 1 V for NFET and PFET, respectively. For the first time, we have also demonstrated that SOI maintains performance benefit over bulk silicon in high-k/metal gate and 32 nm ground rules.

Q. Liang

Papers

High performance 32nm SOI CMOS with high-k/metal gate and 0.149µm 2 SRAM and ultra low-k back end with eleven levels of copper