Y. Senzaki

Nucleation and growth study of atomic layer deposited HfO2 gate dielectrics resulting in improved scaling and electron mobility

HfO2 films have been grown with two atomic layer deposition (ALD) chemistries: (a) tetrakis(ethylmethylamino)hafnium (TEMAHf)+O3 and (b) HfCl4+H2O. The resulting films were studied as a function of ALD cycle number on Si(100) surfaces prepared with chemical oxide, HF last, and NH3 annealing. TEMAHf+O3 growth is independent of surface preparation, while HfCl4+H2O shows a surface dependence. Rutherford backscattering shows that HfCl4+H2O coverage per cycle is l3% of a monolayer on chemical oxide while TEMAHf+O3 coverage per cycle is 23% of a monolayer independent of surface. Low energy ion scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy were used to understand film continuity, density, and chemical bonding. TEMAHf+O3 ALD shows continuous films, density >9g∕cm3, and bulk Hf–O bonding after 15 cycles [physical thickness (Tphys)=1.2±0.2nm] even on H-terminated Si(100). Conversely, on H-terminated Si(100), HfCl4+H2O requires 50 cycles (Tphys∼3nm) for continuous films and bulk Hf–O bonding. ...

Effective work function modification of atomic-layer-deposited-TaN film by capping layer

We demonstrate that the metallic capping layer has a strong impact on the effective work function (EWF) of the metal gate. Specifically, the EWF of atomic-layer-deposited (ALD)-TaN could be increased from 4.5to4.8eV with chemical-vapor-deposited-TiN capping, which is sufficient amount of work function modification for silicon on insulator based devices. A strong interdiffusion of Ti atoms into the ALD-TaN film is observed and correlated well with the changes in the EWF change. Ti capping experiments confirm that the Ti interdiffusion can actually modify the EWF of Ti/ALD-TaN stack.

Composition dependence of the work function of Ta1−xAlxNy metal gates

It is shown that the work function of Ta1−xAlxNy depends on the electrode and gate dielectric compositions. Specifically, the work function of Ta1−xAlxNy increased with SiO2 content in the gate dielectric, reaching as high as 5.0eV on SiO2; the work function was nearly 400mV smaller on HfO2. In addition, the work function decreased with increasing nitrogen content in the Ta1−xAlxNy metal gate. Increasing Al concentration increased the work function up to about 15% Al, but the work function decreased for higher Al concentrations. Chemical analysis shows that Al–O bonding at the interface correlates with the observed work function values.

Thermal response of Ru electrodes in contact with SiO2 and Hf-based high-k gate dielectrics

A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with SiO2 and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the Ru∕SiO2, Ru∕HfO2, and Ru∕HfSiOx film systems were observed through cross-sectional high-resolution transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy with electron-energy-loss spectra, and energy dispersive x-ray spectra analysis. Ru interacted with SiO2, but remained stable on HfO2 at 1000°C. The onset of Ru∕SiO2 interfacial interactions is identified via silicon substrate pitting possibly from Ru diffusion into the dielectric in samples exposed to a 900°C∕10-s anneal. The dependence of capacitor device degradation with decreasing SiO2 thickness suggests Ru diffuses through SiO2, followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. ...

Evaluation and integration of metal gate electrodes for future generation dual metal CMOS

An overview of factors that contribute to the effective work function of metal gate electrodes are presented and reasons for disparity in reported values for effective work function of similar metals from different groups are discussed. Utilizing a standardized technique to accurately extract the effective work function of metal gates, the potential of amorphous metal gate materials and hafnium-based electrodes is presented. Also, the influence of metal gate materials and processing on the physical and electrical stability of the high-k metal gate stacks are discussed.

Evaluation of tantalum silicon alloy systems as gate electrodes

The effect of Si concentration on the effective work function of tantalum silicon (Ta–Si) alloy systems as gate electrodes in direct contact with SiO2 and HfSiOx gate dielectrics has been studied extensively. It was found that the Si concentration in the Ta–Si electrodes (⩾60at.% Si) has a strong effect on the effective work function, and three discrete composition-dependent phases (tantalum metal, tantalum silicide, and silicon) coexist in the films. The film resistivity and density also change dramatically as a function of Si concentration. Physical analysis shows that these Si-rich Ta–Si electrodes are amorphous at room temperature and crystallize with a 1000°C, 5-s anneal. Finally, an effective work function value of 3.98eV has been achieved by arsenic implantation of a capacitor electrode layer in Ta–Si∕HfSiOx film systems, thereby producing a potential n-type metal gate electrode in conjunction with high-k gate dielectrics.

Physical Characterization of Novel Metal Electrodes for Hf‐based Transistors

Metal electrode materials are being extensively evaluated as potential replacements for polysilicon in order to eliminate gate depletion, reduce gate resistance, overcome equivalent oxide thickness (EOT) scaling limitations and Fermi level pinning effects associated with the reaction between Hf‐based dielectric films and the polysilicon electrode. High‐angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) using X‐ray spectra and electron energy loss spectra (EELS) were used to produce elemental profiles of dielectric and metal electrode constituents with particular emphasis on interfacial interactions. High spatial resolution chemical scan profiles of silicon, oxygen, nitrogen, and hafnium from the dielectric components in conjunction with various transition metals including hafnium, tantalum, molybdenum and ruthenium have been acquired to characterize the extent of material intermixing and crystallization as a function of deposition parameters and anneal temperature. The influen...