This paper briefly reviews challenges and prospects for high-κ gate dielectric technology, mainly focusing on the fundamental material properties. First, we need to understand the origin of high dielectric constant of those materials, and then we can consider some material engineering such as the dielectric constant improvement as well as overcome drawbacks such as the fragile reliability, on the basis of mechanisms giving rise to the high dielectric constant. From the device performance point of view, the mobility and threshold voltage controls are necessarily required for employing high-κ materials in actual ULSIs. It is also discussed that the gate electrode selection is very important as well as the high-κ gate dielectrics in terms of the Fermi level pinning. Finally, it is emphasized that the material scalability applicable for a couple of technology nodes should be taken into account for the material selection.
Using 30Si-implanted 28SiO2 and natSiO2/28SiO2 structures, Si self-diffusion in SiO2 was studied as a function of temperature and SiO2 thickness (200−650 nm). Si self-diffusivity increased by about one order of magnitude with decreasing SiO2 thickness from 650 to 200 nm with a SiN layer, i.e., the shorter the distance between the 30Si diffusers and the Si/SiO2 interface became, the higher Si self-diffusivity became. The dependence of Si self-diffusion in SiO2 on the distance is caused by SiO generated at the Si/SiO2 interface and diffusing into SiO2. Si self-diffusion in SiO2 was modeled taking into account the effect of SiO molecules. The simulated results showed good agreement with the experimental profiles. Furthermore, the simulation predicts that the self-diffusivity would increase for a longer annealing time because more SiO molecules should be arriving from the interface. Such time-dependent diffusivity was indeed found in our follow-up experiments, and the experimental profiles were also fitted by the simulation using a single set of parameters.
Rare-earth oxides are promising high dielectric constant gate oxides to be used in metal-oxide-semiconductor devices in future. Properties of rare earth oxides are very different from those of the well-reported high dielectric constant materials such as HfO2. In this article, basic properties of rare-earth oxides are described comparing with La2O3 and Y2O3. These are typical rare earth oxides with a large and a middle ion radius, respectively. It is shown that interfacial silicate formation is an important character of rare-earth oxides on silicon substrates. To control silicate formation during thermal process, the addition of alumina into the rare-earth oxides is proposed. Physical and electrical properties of yttrium-aluminate films on silicon substrates are reported.
The reaction behavior of the Interfacial Layer (IL) in an HfAlOx/SiO2 and SiON structure during a post deposition annealing (PDA) in an N2-diluted oxygen ambient was examined. After a PDA at 1,050oC for 1 s, the 0.7 nm-thick IL was reduced if the O2 concentration was lower than 0.02%. The reduction of the IL led to the formation of defects and the Si migration to the HfAlOx surface, resulting in an increase in the C-V hysteresis. The amount of Si migrated to HfAlOx surface decreases with increasing the O2 concentrations during PDA and changing the interfacial layer from SiO2 to SiON. Even if SiON is used for interfacial layer, the decreasing of mobility was caused by nitrogen which stay in interface between SiON and substrate. Optimization of nitrogen in SiON interfacial layer is necessary. Electron and hole mobility of 75/77% of that for SiO2 were obtained for HfAlOx/SiON with EOT = 1.6 nm because of optimization of PDA O2 concentration and nitrogen profile in SiON.
Positron annihilation is an established technique for investigating defects in solids. Using this technique, thin Hf0.3Al0.7Ox films fabricated by an atomic-layer-deposition technique were characterized. It was found that positrons in the HfAlOx films annihilate from the trapped state by open spaces that exist intrinsically in their amorphous structure. The line-shape parameter S and the positron lifetime corresponding to the HfAlOx films decreased with increasing oxygen content in the annealing atmosphere. This fact was attributed to the shrinkage of the open spaces due to the change in the matrix structure of amorphous HfAlOx. A clear correlation between the mean size of the open spaces in HfAlOx and the suppression of transient leak current was observed.
Suppression of silicidation in poly-Si/high-κ insulators (ZrO2, HfO2)/SiO2/Si structure by the helium (He) through process that adds He gas during a poly-Si gate process was demonstrated. We found that the He through process of the low-temperature SiH4 flow diluted by He and high-pressure He post-annealing is the most effective means of suppressing not only the thermal degradation of high-κ insulator/SiO2/Si interface but also the silicidation of poly-Si/ultra-thin SiO2/high-κ insulator interface, whereas conventional N2 through process can suppress neither of them. From these results, it is supposed that high-concentration He atoms physically obstruct SiO creation through the quenching of atomic vibration at both SiO2/Si interfaces, thus impeding the first step of silicidation reaction.
Various kinds of oxygen-adsorbed configurations with oxygen coverages of up to two monolayers (ML) were studied through first-principles calculations to elucidate mechanisms of the layer-by-layer growth and of interfacial defect generation in initial oxidation processes. It was found that oxidation proceeds almost laterally. When the coverage reaches to around 1 ML, first-layer oxidation temporary saturates once, although there still remains oxidation sites in the first-layer. Partial second-layer oxidation opens again a channel of the first-layer oxidation. When the coverage exceeds 1.25 ML, oxygen atoms can be incorporated into a bridging site in the second layer, generating twofold-coordinated Si atoms in the third layer. Emission of such twofold-coordinated Si atoms leaves weakly bonded Si pairs in the fourth layer. When such pairs happen to be generated close to each other, they transform into a chain of Si trimers with one Pb0 center at each end. Pb0 centers appear initially in the fourth layer.
Tribology of the disk-head interface in hard-disk drives (HDDs) was reviewed in this article. The HDD has become a very popular device in our life, and been used for some consumer electronics. Tribology is an essential technology for the progress of HDDs. As the flying height of magnetic head has been reduced with increasing areal recording density, disk-head interference in case of contact is one of the greatest concerns for the reliability of HDDs. It is a very important subject of tribology for HDDs to develop the way to keep the head flying stable for avoiding the occasion of disk-head interference, or the way to allow contact without any troubles for recording operation. In future, development of a continuous contact recording system is expected to achieve ultimate magnetic spacing for endless demands to increase recording density.