Youngjae Kwon

Silicidation behaviors of Co/Ti and Co/Hf bilayers on doped polycrystalline Si substrate

Abstract Silicide layer structures and morphological change of silicide/Si interface for Co/Ti and Co/Hf bilayers sputter-deposited on P-doped polycrystalline Si substrate and subjected to rapid thermal annealing were investigated and compared with those on single Si substrate. The CoSi-CoSi 2 phase transition temperature is lower and morphological degradation of the silicide layer occurs more severely for Co/refractory metal bilayer on P-doped polycrystalline Si substrate than on single Si substrate. Also, the final layer structure of the films after silicidation annealing was found to depend strongly upon the interlayer metals. In the Co/Ti/poly-Si system, Si atoms pile up at the surface of the silicide layer, while no Si pile-up is observed for the Co/Hf/poly-Si system.

Influence of ZnO encapsulation on the luminescence property of GeO2 nanowires

GeO2-core/ZnO-shell nanowires were synthesized on (100) Si substrates by thermal evaporation of Ge powders, followed by atomic layer deposition of ZnO. X-ray diffraction, scanning electron microscopy and transmission electron microscopy analyses showed that the mean diameter and lengths of the core‐shell nanowires were approximately 100nm and from a few tens to a few hundreds of micrometers, respectively. Photoluminescence measurements showed that pure GeO2 nanowires had a violet emission band centered at approximately 430nm. In contrast, GeO2-core/ZnO-shell nanowires had both a sharp near-band edge (NBE) emission band centered at approximately 380nm and a broad deep-level (DL) emission band centered at approximately 590nm, which is characteristic of ZnO. GeO2-core/ZnO-shell nanowires showed a higher intensity ratio of NBE emission to DL emission than either GeO2 or ZnO nanowires. In addition, the origin of the enhancement of luminescence in GeO2 nanowires by ZnO encapsulation is discussed. PACS numbers: 81.07. b, 61.10.Nz, 68.37.Hk (Some figures may appear in colour only in the online journal)

Thermal stability of Co/Hf and Co/Ti bilayers on SiO2

Abstract The Co/Ti bilayer silicidation technique is widely known as a method to obtain an epitaxial CoSi2. The Co/Hf bilayer also can be used for this purpose. During the silicidation the metal and the spacer SiO2 can react. Any residue of this reaction can degrade device performance by compromising the oxide integrity or by producing pattern bridging. In this paper the reaction of the Co/Hf bilayer with SiO2, as well as that of the Co/Ti bilayer with SiO2, during the silicidation annealing are reported. The collapse of the upper side of the SiO2 substrate occurred at 800°C in the Co/Ti/SiO2 sample and at 700°C in the Co/Hf/SiO2 sample. The sheet resistance of both the samples increased rapidly in the temperature range above 500°C. The rapid increase in the sheet resistance of Co/metal/SiO2 may be owing to the reaction between the metal layer and the SiO2 substrate, and the agglomeration of the Co layer on SiO2. Considering the temperature to get epitaxial CoSi2, along with the temperature from which the SiO2 substrate starts collapsing, we may conclude that optimum silicidation annealing temperatures for Co/Ti/Si and Co/Hf/Si are 700 and 600°C, respectively.

Prediction of Flow Curves and Micro-Structural Evolution in Strain Induced Dynamic Transformation of Low Carbon Steel

The relationships between flow stress curve and microstructure evolution in strain induced dynamic phase transformation (SIDT) of low carbon steel (0.22wt.%) were quantitatively investigated. The deformation was carried out at just above Ar3 temperature (710°C) as a function of strain rate (0.01-5/sec). The softening process of SIDT was well agreed with calculated result derived from Avrami’s and constitutive equation at higher strain rate than 0.5/sec. However, the calculated results differed from the experimental curve at strain rate of less than 0.2/sec. This is due to fact that the dynamic transformation from austenite to ferrite can not be completed owing to less stored energy during hot deformation.

Annealing of the Co/Hf bilayer on single Si, polycrystalline Si and SiO2

Silicidation of the Co/refractory metal/Si system in which the refractory metal is used as an epitaxy promoter for CoSi(2) has recently received much attention. Hf is one of the candidates for the epitaxy promoter of cobalt silicide like Ti. In this paper, we investigated the layer structures of the Co/Hf bilayer on various substrates like single (100)Si, polycrystalline Si and SiO(2) after rapid thermal annealing. Epitaxy of CoSi(2) was obtained on (100)Si by annealing Co/Hf/(100)Si. Co-Hf compounds seem to play an important role of barriers against the reaction between Co and Si during silicidation of Co/Hf/(100)Si. The existence of Co-Hf compounds is helpful in the formation of epitaxial CoSi(2) since they retard the diffusion of cobalt and silicon atoms. The transition temperatures of cobalt silicides in the Co/Hf/poly-Si system were found to be lower than those in the Co/Hf/(100)Si system. The reaction between the metal and the spacer SiO(2) during silicidation is a matter of concern since any conducting residue of this reaction could degrade oxide integrity or produce bridging. In the Co/Hf/SiO(2) system Hf oxides formed as a result of the reaction between Hf and SiO(2) but a conducting material like HfSi(2) was not found to form after annealing. Considering the temperature at which epitaxial CoSi(2) forms along with the one from which the SiO(2) substrate starts collapsing we may conclude that the optimum silicidation annealing temperature for Co/Hf/Si is 600 degrees C.