Ru Gate Electrode Research Articles

The effects of (NH4)2Sx treatment on n-GaN MOS device with nano-laminated ALD HfAlOx and Ru gate stack

The effects of ammonium poly-sulfide, (NH4)2Sx, treatment on the surface of GaN metal oxide semiconductor (MOS) device with nano-laminated atomic layer deposition (ALD) HfAlOx gate dielectric and Ru gate electrode were investigated and compared with HCl pre-treatment. Compared with sample without sulfur (S) passivation, S-passivated sample shows improved surface roughness, increased capacitance, higher breakdown voltage, smaller frequency dependence, lower interface state density (Dit). It is found that (NH4)2Sx can remove native oxide and passivate the surface and interface states. Surface oxidation is suppressed due to higher strength in the NS bonds than that of the NO bonds. Further improvement is observed with increasing (NH4)2Sx treatment time.

Effect of Ti doping on Ta 2O 5 stacks with Ru and Al gates

The Ti-doped Ta 2O 5 thin films (<10 nm) obtained by rf sputtering are studied with respect to their composition, dielectric and electrical properties. The incorporation of Ti is performed by two methods – a surface doping, where a thin Ti layer is deposited on the top of Ta 2O 5 and a bulk doping where the Ti layer is sandwiched between two layers of Ta 2O 5. The effect of the process parameters (the method and level of doping) on the elemental distribution in-depth of the films is investigated by the time of flight secondary ion mass spectroscopy (ToF-SIMS). The Ti and Ta 2O 5 are intermixed throughout the whole thickness but the layers are very inhomogeneous. Two sub-layers exist in all the samples — a near interfacial region which is a mixture of Ta-, Ti-, Si-oxides as well as TaSiO, and an upper Ti-doped Ta 2O 5 sub-layer. For both methods of doping, Ti tends to pile-up at the Si interface. The electrical characterisation is performed on capacitors with Al- and Ru-gate electrodes. The two types of MIS structures exhibit distinctly different electrical behavior: the Ru gate provides higher dielectric permittivity while the stacks with Al electrode are better in terms of leakage currents. The specific metal-dielectric reactions and metal-induced electrically active defects for each metal electrode/high- k dielectric stack define its particular electrical behavior. It is demonstrated that the Ti doping of Ta 2O 5 is a way of remarkable improvement of leakage characteristics (the current reduction with more than four orders of magnitude as compared with undoped Ta 2O 5) of Ru-gated capacitors which originates from Ti induced suppression of the oxygen vacancy related defects.

Improvement in Fermi-Level Pinning of p-MOS Metal Gate Electrodes on HfSiON by Employing Ru Gate Electrodes

not Available.

Improvement in Fermi-Level Pinning of p-MOS Metal Gate Electrodes on HfSiON by Employing Ru Gate Electrodes

Methods of improving Fermi-level pinning of pure metal gate electrodes on Hf-based high-k dielectrics have been investigated. The pinning phenomenon is a crucial problem, resulting in an unintentional threshold voltage increase in p-MOSFETs when applying pure metal gate electrodes such as Ru and TiN in Hf-based high-k CMOS. After systematic investigation of the relation between oxygen vacancies in Hf-based high-k dielectrics and electrical characteristics, we concluded that the Fermi-level pinning is unavoidable in principle with a thin EOT, but is a stable phenomenon that should be intentionally utilized. It is necessary to modulate the stable pinning energy position of Hf-based high-k dielectrics in p-MOSFETs in order to obtain thin EOTs in the gate-first process.

The effect of oxygen in Ru gate electrode on effective work function of Ru/HfO 2 stack structure

Effective work function ( φ m,eff) values of Ru gate electrode on SiO 2 and HfO 2 MOS capacitors were carefully examined and discussed from the viewpoint of an effect of oxygen incorporation in Ru gate electrode on φ m,eff. Annealing at 400 °C in the reduction (3%H 2) and the oxidation (1%O 2) ambient resulted in similar changes in the φ m,eff of Ru/HfO 2/SiO 2 and Ru/SiO 2 MOS capacitors. Furthermore, the Ru gate MOS capacitor after annealing in the oxidation condition have shown almost the same φ m,eff value to that of RuO 2 gate MOS capacitors. The oxygen concentration in the Ru/HfO 2 interface after annealing in oxidizing atmosphere is approximately one order of magnitude higher than that after annealing in reducing atmosphere as confirmed by secondary ion mass spectroscopy analysis. Furthermore, the higher oxygen concentration at the Ru/dielectric interface leads to the higher φ m,eff value, regardless of SiO 2 or HfO 2 dielectrics. This indicates that φ m,eff of Ru gate MOS capacitor is dominantly determined by the oxygen concentration at the Ru/dielectric layer interface rather than the dipoles originated from the oxygen vacancy in HfO 2.

Electrical properties and thermal stability of MOCVD grown Ru gate electrodes for advanced CMOS technology

This paper presents an overview of electrical properties measured on advanced gate stacks consisting of a Ru electrode and Hf-based gate dielectrics. The gate stack is projected for application in the sub 45 nm complementary metal-oxide-semiconductor (CMOS) technology node. Ru films were grown by metal-organic chemical vapour deposition (MOCVD) on thin HfO 2, HfSiO x , HfSiON and SiO 2 (control sample) dielectrics. As-deposited and forming gas annealed (90% N 2 + 10% H 2) samples were characterized by means of capacitance–voltage ( C– V) and conductance–voltage ( G– V) measurements. We discuss variation in dielectric constant, interfacial layer thickness, effective metal work function ( Φ m,eff), oxide charge density and density of interface traps. Ru shows Φ m,eff of ∼5.1 eV for all Ru/Hf-based dielectrics gate stacks. We also investigated the thermal stability of the stacks upon rapid thermal annealing (RTA) in the temperature range 800–1000 °C for 10 s. Samples were analyzed by Rutheford backscattering spectroscopy. The results suggest a limited thermal stability of Ru/Hf-based dielectric gate stack during source/drain activation step.

Ruthenium gate electrodes on SiO2 and HfO2: Sensitivity to hydrogen and oxygen ambients

The incorporation of chemical species during annealing at the interface between the Ru gate electrode and the dielectric perturbs the electrostatic potential, thus affecting the effective work function of the metal. For both SiO2 and HfO2 gate dielectrics, O2 anneal at 550°C leads to Ru oxidation (i.e., to RuOx formation) at the Ru∕dielectric interface, resulting in a higher effective work function than that of metallic Ru. In turn, when RuOx is exposed to hydrogen, a work function reduction occurs, caused by either a reduction of RuOx into Ru or hydroxyl incorporation at the interface.

Thermal Stability of Ru Gate Electrode on HfSiO Dielectric

AbstractWe have investigated advanced MOS structures containing Ru gate electrode, HfxSi1-xOy dielectric film and Si substrate. The Ru gate electrode was grown by MOCVD at 300 °C. The MOS structures were annealed for 30 min in forming gas and nitrogen at temperatures up to 550 °C. Capacitance-voltage measurements showed important shift of the flat band voltage of the Ru/ HfxSi1-xOy/Si gate stack after treatment at 550 °C. X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), reflection electron energy loss spectroscopy (REELS) and secondary ion mass spectroscopy (SIMS) were used to analyze interface between ruthenium and high-k dielectric film. Based on the analysis we were able to build up energy-band alignement for the Ru/ HfxSi1-xOy interface. We observed that the energy-band structure of the Ru/HfxSi1-xOy interface remains stable upon annealing in forming gas up to 550 °C. Presence of hydrogen revealed by SIMS can account for compensation of negative charges in HfxSi1-xOy during thermal treatment.

Promising Gate Stacks with Ru &amp; RuO2 Gate Electrodes and Y-silicate Dielectrics

ABSTRACTIn this work, we studied the electrical and thermal stability of Ru and RuO2 electrode on Y-silicate dielectrics in contrast to ZrO2 and Al2O3 dielectrics. Very low resistivity Ru and rutile stoichiometric RuO2 films, deposited via reactive sputtering, were evaluated as gate electrodes on ultrathin Y-silicate, ZrO2 and Al2O3 films for Si-MOS devices. Thermal and chemical stability of the electrodes was studied at annealing temperatures up to 800°C in N2 and subsequently forming gas anneal. XRD and XPS were measured to study grain structure and interface reactions. The morphology of the films was tested by atomic force microscopy (AFM). Electrical properties were evaluated via MOS capacitors. The role of oxygen inside dielectrics was studied by comparing equivalent oxide thickness change as a function of annealing temperature for capacitors with Y-silicate, ZrO2and Al2O3 dielectrics. Good stability of Ru and RuO2 gate electrodes on all dielectrics studied was found. Flatband voltage and gate current as a function of annealing temperature was also studied. It was found that capacitors with Y-silicate after high-temperature anneal had less positive flatband voltage shift than ZrO2 and Al2O3. For capacitors with Ru gate electrode, the significant flatband voltage shift after high temperature anneal could be partially removed by a forming gas anneal.