Importance of heat-up ramp rate for palladium-silicide fully-silicided-gate structure formation
Silicidation process for fully-silicided (FUSI) Pd2Si gate formation has been investigated. Two types of heating equipment was used for siliciding palladium deposited on a poly-Si/SiO2/Si MOS structure. One is lamp heating in a sputtering chamber and another is hot-plate heating. The former provide slower heat-up ramp because of relatively large thermal capacity. In this case, metal-rich phase was formed in the first stage of silicidation and it changed to Pd2 Si phase by additional heating after completion of silicidation reaction. FUSI utilizes impurity pre-doping to poly-Si to modulate workfunction. Pre-doping to poly-Si sometimes resulted in needle structure formation on a top of silicided film and voids at the interface between silicide and SiO2. These defects were reduced by silicidation with hot plate heating. In addition, Pd2 Si phase was obtained at the early stage of silicidation. Palladium and silicon reacts even at temperatures lower than 250degC. Therefore, in the case of the lamp heating, silicidation during heating is not negligible. These results are explainable considering change of major diffusion species during silicidation
Transmission electron microscopy and X-ray diffraction investigation of phase formation and transition between Pd2Si and PdSi in Pd thin films on (111)Si
Abstract Phase formation and transition between Pd 2 Si and PdSi in Pd thin films on (111)Si has been investigated by X-ray diffraction and transmission electron microscopy. In as-deposited and 200 °C/1 h annealed Pd(30nm)/(lll)Si samples, epitaxial Pd 2 Si was found to coexist with the unreacted Pd layer. In samples annealed at 250–800 °C, epitaxial Pd 2 Si is the only suicide phase present. PdSi was found to form along with Pd 2 Si in samples annealed at 850 °C. Pd 2 Si was found to be the predominant phase along with PdSi in samples annealed at 900–1000 °C. Pd 2 Si and PdSi were found to be the stable phases at 300–800 and 850–875 °C, respectively. The phase transition between Pd 2 Si and PdSi is reversible. In samples annealed at 900 °C, epitaxial Pd 2 Si is initially the only suicide phase present; then polycrystalline PdSi becomes the dominant phase. After annealing for more than 240 s, polycrystalline Pd 2 Si predominates over PdSi. The peculiar Pd 2 Si to PdSi, then back to Pd 2 Si phase transition behavior is correlated with the formation of PdSi islands, which is thought to alter the order of the total energy of the system.
Monte Carlo Study of the Effect of Backscatter Materail Thickness on 99 mTc Source Response in Single Photon Emission Computed Tomography
Introduction SPECT projections are contaminated by scatter radiation, resulting in reduced image contrast and quantitative errors. Backscatter constitutes a major part of the scatter contamination in lower energy windows. The current study is an evaluation of the effect of backscatter material on FWHM and image quality investigated by Monte Carlo simulation. Materials and Methods SIMIND program was used for simulation of a Siemen’s dual-head variable angle scintillation gamma camera. Planar and SPECT scanning of a 99m Tc source and a Jaszczak phantom for varying thicknesses of Perspex slabs, as a backscatter media, were analyzed using the photopeak and scatter windows. Simulated planar images and reconstructed tomographic images were evaluated qualitatively, by two nuclear medicine specialists, and quantitatively, by Structural Similarity (SSIM) Index. Results In the 99m Tc photopeak window, no significant change in total counts due to backscatter material was measured. In the scatter windows, scattering was overestimated compared with a simulated backscatter free SPECT system. For instance, at a thickness of 10 cm, total counts of a 99m Tc source detected in the 72 keV windows eventually doubled with increasing backscatter material, compared with the situation without backscatter material. The backscatter contribution plateaued when more than 7 cm of scatter material was placed but there were optimized results for a backscatter thickness of 4.5 cm. Better image quality for the thickness was confirmed by the results of eye interpretation and also by SSIM algorithm. Conclusion Backscatter should be taken into account, particularly in model-based scatter correction methods in SPECT for an accurate simulation system optimization.