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Transient forebrain ischemia was induced in rats whose brain temperature was 31, 33, 35, 38, or 40°C. The development of regional injury was followed using magnetic resonance (MR) imaging, with the ultimate extent of neuronal injury quantified histopathologically. Animals in the hypothermic groups showed minimal changes in MR images over 4 days; normothermic animals snowed intensity enhancement attributed to progressive edema developing in the striatum and, later, in the hippocampus. Ischemia at 40°C resulted in widespread edema formation by I day post-ischemia; animals in this group did not survive beyond 30 hours. Histopathological analysis at 4 days (1 day for the hyperthermic group) post-ischemia showed that neuronal damage in the normothermic group was confined to the hippocampus and striatum. Minimal damage was found in the hypothermic groups; damage in the hyperthermic group was severe throughout the forebrain. There were no differences in the pre-ischemia 31P MR spectra for the different groups. During ischemia, the increase in intensity of the Pi peak and the fall in tissue pH increased with temperature in the order hypothermic < normothermic < hyperthermic group of animals. Post-ischemia energy recovery was similar in all groups, while pH recovered more rapidly in hypothermic animals.
Reducing specific contact resistivity of the silicide to silicon interface is advantageous to achieve high planar density and high drive current FET devices. Measuring the differential resistivities at different low voltage bias conditions of four terminal Kelvin test structures with a range of contact sizes has proven particularly effective in characterizing the linearity behavior and specific contact resistivity. This study shows that adding laser activation annealing for an n+ doped silicon contacted by a standard NiPt silicide is found to significantly improve the contact electrical properties. Initial results with only rapid thermal anneal activation show a size dependence of the contact resistivity with non-linear behavior exhibiting maximum resistance at zero bias, and contact resistivities ranging from 4×10-8 Ω-cm2 to 4×10-7 Ω-cm2. Adding laser anneal after the rapid thermal anneal gives ohmic behavior, for contact down to 50nm in size, with a specific contact resistivity of 1×10-8 Ω-cm2. The metal-to-silicide contact resistance was measured separately using a novel test structure and it was confirmed to be negligible. We describe our device structure, our experimental methodology, and the implications of our results for future devices.
The dose loss and transient enhanced diffusion of indium in silicon were studied as a function of dose. Indium was implanted into silicon through a 90 A oxide at 50 keV for doses ranging from 3x 1012 to 2x14 cm−2. These conditions provide peak concentrations that approximately range from 1x1018-1x1020 cm−3. After an RTA anneal at 1000°C for 5s, indium exhibits substantial motion at both the tail and peak regions for high doses. The enhanced diffusion is mostly over within 5s. There was not any observable enhanced diffusion in the tail region at the lowest dose although there was significant movement at the peak region. The dose loss correlates very well with the enhancement in the diffusivity. TEM images show that the amorphization dose lies between 3x1013 and 8x1013 cm−2. In spite of the amorphization, diffusion enhancement in the tail region still keeps increasing with dose, which is contrary to a model of “+1” interstitials and complete removal of interstitials in the regrown layer. The 550°C lh anneals show that the dose loss can partially be attributed to the sweeping of the dopant by the growing a/c interface. Previously, the solubility of indium has been estimated to be around 1–2×1018 cm−3. At high doses, significant movement is observed at the peak of the indium profile although the peak concentration exceeds the solubility level by at least an order of magnitude. This shows that indium is not precipitating into an immobile phase like antimony or boron.
Experiments have been caried out to form ultra-shallow (Xj <50nm) and abrupt (Xjs < 5nm/decade) P'junction for sub-50 nm CMOS devices using a combination of shallow implant, Ge preamorphization and high energy Si implant as an interstitial getter layer. Experimentally, it was observed that the Si getter layer, not only stopped the TED at the boron tail but also promoted enhanced diffusion close to the surface boron peak. These unique features have enabled the shallowest and sharpest box-like boron junction yet achieved by implant. With I kV BF2, Xj ∼ 23 nm, Xjs ∼ 48 A/decade, no Ge end of range damages and good dopant activation at the same time.The sheet resistance ρ − 1 kohm/sq is comparable to shallow BF2 + Ge and is better than the shallow BF 2 alone (ρ ∼ 2.38 kΩ/sq) or the shallow BF2 + Si implants (ρ ∼ 1.5 kohm/sq). Tests with device leakage test structures show that there is no additional junction leakage introduced by the Si getter layer.
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