J. Mitard

Large-Scale Time Characterization and Analysis of PBTI In HFO2/Metal Gate Stacks

Many electrical properties of metal/high-k gate stack are dominated by defects. These defects play an important role in reliability issues in particular positive bias temperature instabilities (PBTI). In this paper, we investigate PBTI with a time resolved measurement technique allowing a large-scale time characterization. This technique allows us to separate different mechanisms, namely fast and slow trapping, newly slow stress-generated traps and finally positive charges. We clearly evidence which of them are or are not activated by temperature. We explain how to take into account these mechanisms for a precise lifetime extrapolation

Initial and PBTI-induced traps and charges in Hf-based oxides/TiN stacks.

Abstract Positive voltage instabilities are studied for Nmos transistors with hafnium-based high-κ gate stacks. Using an optimized dedicated fast measurement setup, dynamic transient measurements of drain current are performed over more than ten decades of time. The two main phenomena involved, a reversible one known as hysteresis and a nonreversible one known as PBTI are clearly experimentally separated and studied in detail. A physical model is presented, explaining the dynamic behaviour and leading to precise traps physical characteristics and profiles inside the HfO2 layer. PBTI defects in HfO2 are shown to be of a different nature than hysteresis traps. A turn-around effect is evidenced for PBTI above which physical mechanisms seem to change; it has important implications on lifetime determination methodology. Finally, HfSiON experiments are presented for both hysteresis and PBTI and they show that this material is much less critical than HfO2.

In Depth Analysis of VT Instabilities in HFO2 Technologies by Charge Pumping Measurements and Electrical Modeling

This paper investigates VT instabilities in HfO2 /TiN stacks from CP measurements and electrical modeling. CP measurements are well correlated to pulsed Idvg measurements and can be easily used to obtain the Vt instability over a large scale of time from 0.1mus to fews seconds. A complete modeling of the CP and the pulsed Id Vg measurements has been done to localize spatially and energetically the traps in HfO2. The main band of defects responsible for Vt instabilities was found at ~0.9eV from the HfO2 conduction band but deep energy levels were also identified. The impact of the detrapping phenomena on CP measurements has been finally investigated. No influence of detrapping of electrons into the gate was found. And the detrapping into the substrate during the half of the ac cycle at Vg=-1.5V is almost complete for the traps filled at low Vg

Reliability assessment of ultra-thin HfO/sub 2/ oxides with TiN gate and polysilicon-n/sup +/ gate

In this paper, we propose an extended study of the reliability of ultra-thin HfO/sub 2/ oxides (EOT<1.5 nm) with polysilicon and TiN gate. Breakdown of the dielectric stacks is shown to be well correlated to trapping in the oxide or to SILC measurements, depending on the stress polarity. Long-term reliability of these high-K dielectrics is also analyzed. At same EOT, HfO/sub 2/ generally demonstrates higher reliability than SiO/sub 2/. On high quality stacks, a typical variation of T/sub BD/ with EOT is also emphasized.

Reliable extraction of metal gate work function by combining two electrical characterization methods

In this paper, we extract the gate work function of metal/High-K stacks (WFM) with an internal photoemission (IPE) based method and a C(V) characterization method. We attempt to apply both of them on the same specially designed samples. We show that it leads to a better reliability of WFM and highlights new phenomena.

Work Function Investigation in Advanced Metal Gate-HfO2-SiO2 Systems with Bevel Structures

This paper presents for the first time the extraction of chemical vapor deposition (CVD)-TiN and poly-Si work functions on atomic layer deposition (ALD)-HfO2 and high temperature SiO2 (HTO) for a wide range of EOT values. The measurements were performed on bevel oxide structures. Our results reveal that the work functions of both TiN and poly-Si gates highly depend on the underlying dielectrics especially in the case of TiN on HTO films likewise lower leakage currents depending on dielectric stacks. It is notable that when TiN is formed on the HTO film, its work function has two distinct values depending on the HTO thickness; this indicates that Ti-Si bonds strongly affect the work function variation. Both TiN on HTO and poly-Si on HfO 2 show the work function shifts to about 4.3 eV, suggesting a pinning level on both structures

Impact of TiN/HfO 2 Integration on Carrier Mobility

We have investigated the impact of a metal gate (TiN) and high-k dielectric (HfO2) on the carrier mobility. We have shown that strong remote Coulomb scattering (RCS) due to charges in the HfO2 layer (either grown by ALD or MOCVD) mostly degrades the mobility at low/medium field. High amount of charges (>10cm) is needed to explain the 30% degradation observed in devices with a thin interface layer. These additional coulombic interactions are effective for bottom oxide up to 2nm. We have developed a RCS model to fully explain the experimental data. The influence of the metal gate is also evidenced. The latter has a significative impact on the Si/SiO2 interface roughness, and may induce some additional coulombic interactions.