Atsushi Horiuchi

Effect of Hf sources, oxidizing agents, and NH3/Ar plasma on the properties of HfAlOx films prepared by atomic layer deposition

The effect of Hf sources, oxidizing agents, and NH3/Ar plasma on the properties of HfO2 and HfAlOx films prepared by atomic layer deposition (ALD) have been investigated. The use of tetrakis(ethylmethylamino)hafnium: Hf(NEtMe)4 (TEMAHf) as a source of hafnium has avoided the problems associated with hafnium tetrachloride (HfCl4), such as poor throughput and the generation of a large number of particles. This source has also been effective in reducing the level of residual chlorine (Cl). However, the level of residual carbon (C) increased. Hydrolysis was found to be more effective than oxidation using O3 in removing ligands from the TEMAHf and/or trimethylaluminum (TMA); the film formed using O3 contained a higher level of C than that using H2O, resulting in the deterioration in field-effect transistor (FET) properties, such as the subthreshold swings and the mobilities. The total levels of residual impurities (C+Cl) were successfully reduced through the combination of TEMAHf and NH3/Ar plasma, leading to improvements in FET properties, particularly in the reduction of the gate leakage current.

Selective Dry Etching of HfO2 in CF4 and Cl2/HBr-Based Chemistries

We investigated HfO2 etching characteristics in conventional Si gate etching chemistries, namely, CF4 and Cl2/HBr/O2-based chemistries. We obtained an adequate etch rate of 2.0 nm/min for both chemistries and a selectivity of 1.9 over SiO2 for Cl2/HBr/O2-based chemistry. We examined the etch rate dependence on source power, bias power, O2 flow rate, and Cl2 flow rate in the Cl2/HBr/O2 chemistry. It was clarified that a physical component is dominant in HfO2 etching in this chemistry. The possibilities of achieving a higher HfO2/SiO2 selectivity and of controlling the anisotropic/isotropic component in HfO2 patterning were also discussed. Moreover, it was clarified that the surface portion of the damaged layer created by the dry-etching step can be removed by a subsequent wet etching. Based on these results, the sub-100 nm patterning of poly-Si/HfO2 gate stacks was successfully demonstrated.

Thermal Instability of Poly-Si Gate Al2O3 MOSFETs

The thermal stability of a SiO2/Al2O3 dielectric stack under high-temperature annealing after poly-Si gate deposition was examined. An interface reaction occurs when the activation temperature is higher than the post deposition annealing temperature, which results in the reduction of the interfacial oxide layer and hence silicate formation. As a result, the characteristics of metal oxide semiconductor field effect transistors (MOSFETs), such as mobility, reliability, and the distribution of capacitance are severely degraded. The formation of a SiON interfacial layer is found to be effective in suppressing the interface reaction.

Point defects in thin HfAlO x films probed by monoenergetic positron beams

Thin HfAlO x films grown on SiON(0.9 nm)/Si by atomic layer deposition technique were characterized by using monoenergetic positron beams. The lifetimes of positrons in the HfAlO x film after post-deposition annealing (PDA) ranged between 412–403 ps. Since these lifetimes were longer than the lifetime of positrons trapped by point defects in metal oxides, such as LaCoO 3 , PbTiO 3 , and BaTiO 3 , the positrons in HfAlO x films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. The line-shape parameter S of the Doppler broadening spectrum corresponding to the annihilation of positrons in HfAlO x films decreased by PDA, and the S value decreased with increasing an O 2 -content in an atmosphere during PDA (0.004–1%). The observed behavior of the S value was attributed to the shrinkage of the open spaces due to the change in the matrix structure of HfAlO x . After P + - and B + -implantation into poly-Si films grown on the HfAlO x films, the diffusion of positrons in the Si substrates toward the HfAlO x film was suppressed. This fact was attributed to positive charges introduced near the HfAlO x films.

Advanced Ti Salicide Technology for High Performance Quarter-Micron Logic LSIs

An advanced Ti salicide technology is proposed for high performance quater-micron logic LSIs. A new salici& pmcess nsned ESPAD @nhanced Silici.l,tion with Pre-Artorphization using Drect ion implantation) in combination with an optimum RTP (Rapid Thermal Promsing) and fumace annealing has been developed The fonired TiSi is able to maintain low sheet rcsistmce even in nanrow (0.2 4 m) S/D region to achieve minimuin basic cell size and low junction leakage cunent. High performance logic LSIs with low stand-by cunent are fabricated using this t€.hnology.