James J. Chambers

Application of HfSiON as a gate dielectric material

Physical and electrical properties of HfSiON that make this material desirable as the gate dielectric in a standard metal–oxide–semiconductor flow are reported. Sputtering was used to deposit films with minimal low dielectric constant interface layers, equivalent oxide thicknesses below 13 A, and leakage current density at least two orders of magnitude lower than SiO2. The presence of nitrogen in the film enhances the thermal stability relative to HfSiO, and no crystallization was observed for anneals up to 1100 °C.

Advanced CMOS transistors with a novel HfSiON gate dielectric

We report for the first time on short channel transistors fabricated using HfSiON, a new high-k gate dielectric material. HfSiON has superior electrical characteristics such as low leakage current relative to SiO/sub 2/, low interfacial trap density, electron and hole carrier mobilities /spl sim/80% of the universal curve at E/sub eff/>0.8 MV/cm and scalability to equivalent oxide thicknesses of less than 10 /spl Aring/. This material is also thermally stable up to 1100/spl deg/C in contact with poly Si, and exhibits boron blocking significantly better than SiO/sub 2/ and SiON. The results indicate that this material is a promising high-k gate dielectric with good transistor characteristics.

Composition control of Hf1−xSixO2 films deposited on Si by chemical-vapor deposition using amide precursors

Hafnium silicate (Hf1−xSixO2) films were deposited by metalorganic chemical-vapor deposition with composition x ranging from 0 to 1 using amide precursors in an organic solvent. The liquid precursors, tetrakis(diethylamido)hafnium, Hf[N(C2H5)2]4, and tetrakis(dimethylamido)silicon, Si[N(CH3)2]4, are compatible when mixed in solution, have high elemental purity, and exhibit a low halogen content. Thin oxide films were deposited with these precursors over a range of wafer temperatures from 400 to 600 °C with very low carbon and nitrogen incorporation. Control of the film composition is attained by changing the ratio of silicon concentration to hafnium concentration in the precursor solution for specific deposition conditions. Composition and growth rate are reported as a function of process condition. Interfacial layers of less than 10 A were observed by high-resolution transmission electron microscopy.

Characteristics and mechanism of tunable work function gate electrodes using a bilayer metal structure on SiO/sub 2/ and HfO/sub 2/

In this letter, we investigate a method to adjust the gate work function of an MOS structure by stacking two metals with different work functions. This method can provide work function tunability of approximately 1 eV as the bottom metal layer thickness is increased from 0 to about 10 nm. This behavior is demonstrated with different metal combinations on both SiO/sub 2/ and HfO/sub 2/ gate dielectrics. We use capacitance-voltage (C-V) characteristics to investigate the effect of different annealing conditions and different metal/metal bilayer couples on the work function. By comparing the as-deposited and annealed films, and by comparing with metals that are relatively inert with each other, we deduce that the work function tuning behavior likely involves metal/metal interdiffusion.

Effect of N incorporation on boron penetration from p+ polycrystalline-Si through HfSixOy films

We demonstrate that incorporating N in Hf-silicate films reduces B penetration through the dielectric film. By modeling the B depth profiles, we calculated the B diffusivities through Hf-silicate (HfSixOy) to be ∼2× higher than the corresponding diffusivities for Hf-silicon oxynitride (HfSixOyNz). B diffusion through grain boundaries after HfSixOy crystallization is believed to be responsible for the enhanced B diffusivity observed. Suppression of crystallization observed in HfSixOyNz films is attributed to the lower Hf content in the films and the incorporation of N. The decreased B penetration observed in HfSixOyNz is a combination of absence of grain boundaries and the fact that N blocks B diffusion by occluding diffusion pathways. The minimum temperatures for B penetration are estimated to be approximately 950 and 1050 °C for HfSixOy and HfSixOyNz, respectively.

Characterization and comparison of the charge trapping in HfSiON and HfO/sub 2/ gate dielectrics

Charge trapping in HfSiON and HfO/sub 2/ gate dielectrics was studied using both DC and pulsed I/sub D/-V/sub G/ characterization techniques. The data shows a significant amount of hysteresis in HfO/sub 2/ but negligible instability in HfSiON. Constant voltage stress measurements of HfO/sub 2/ and HfSiON films show that the threshold voltage shift in HfO/sub 2/ films is as much as 10 times higher than that of HfSiON. Further, modeling of the time dependence of the threshold voltage shows that the trap capture cross section responsible for the instability of HfO/sub 2/ films is 10 times higher than the trap capture cross section of HfSiON. Our data indicate that amorphous HfSiON has better electrical stability than HfO/sub 2/.

Carrier mobility in MOSFETs fabricated with Hf-Si-O-N gate dielectric, polysilicon gate electrode, and self-aligned source and drain

A study of electron and hole mobilities for MOSFET devices fabricated with Hf-Si-O-N gate dielectric, polysilicon gate electrodes and self-aligned source and drain is presented. High effective electron and hole mobilities, 250 cm/sup 2//V/spl middot/s and 70 cm/sup 2//V/spl middot/s, respectively, were measured at high effective field (>0.5 MV/cm). The NMOSFETs have an equivalent oxide thickness (EOT) of 1.3 nm and the PMOSFETs have an EOT of 1.5 nm. The effect of interface engineering on the electron and hole mobilities is discussed.

A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors

Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that underlies lateral inhibition and establishes the antagonistic center-surround organization of the visual system. Cones transmit to HCs through an excitatory synapse and HCs feed back to cones through an inhibitory synapse. Here we report that HCs also transmit to cone terminals a positive feedback signal that elevates intracellular Ca2+ and accelerates neurotransmitter release. Positive and negative feedback are both initiated by AMPA receptors on HCs, but positive feedback appears to be mediated by a change in HC Ca2+, whereas negative feedback is mediated by a change in HC membrane potential. Local uncaging of AMPA receptor agonists suggests that positive feedback is spatially constrained to active HC-cone synapses, whereas the negative feedback signal spreads through HCs to affect release from surrounding cones. By locally offsetting the effects of negative feedback, positive feedback may amplify photoreceptor synaptic release without sacrificing HC-mediated contrast enhancement.

A homology-based model of the human 5-HT2A receptor derived from an in silico activated G-protein coupled receptor

A homology-based model of the 5-HT2A receptor was produced utilizing an activated form of the bovine rhodopsin (Rh) crystal structure [1,2]. In silico activation of the Rh structure was accomplished by isomerization of the 11-cis-retinal (1) chromophore, followed by constrained molecular dynamics to relax the resultant high energy structure. The activated form of Rh was then used as a structural template for development of a human 5-HT2A receptor model. Both the 5-HT2A receptor and Rh are members of the G-protein coupled receptor (GPCR) super-family. The resulting homology model of the receptor was then used for docking studies of compounds representing a cross-section of structural classes that activate the 5-HT2A receptor, including ergolines, tryptamines, and amphetamines. The ligand/receptor complexes that ensued were refined and the final binding orientations were observed to be compatible with much of the data acquired through both diversified ligand design and site directed mutagenesis.

Integrity of hafnium silicate/silicon dioxide ultrathin films on Si

Rapid thermal annealing at 1000 °C of (HfO2)1−x(SiO2)x pseudobinary alloy films deposited on Si were performed in N2 or O2 atmospheres. The effects on the atomic transport, structure, and composition were investigated using isotopic substitution of oxygen, high-resolution transmission electron microscopy, nuclear reaction analyses, narrow nuclear reaction resonance profiling, and grazing angle x-ray reflection.