L. Van den hove

Lymphocyte Subset Reference Ranges in Adult Caucasians

We report here the distributions of lymphocyte populations bearing the following antigens: CD3 (T cells), CD19 (B cells), CD4 (T helper/inducer cells), CD8 (T suppressor/cytotoxic and some NK cells), and CD3-, CD16+, and/or CD56+ (NK cells). At four sites, analyses were performed on healthy, normal subjects between the ages of 18 and 70, using identical flow cytometry systems and techniques. Reference ranges (unadjusted for sex differences and age variation) are CD3 (61 to 85%), CD19 (7 to 23%), NK (6 to 29%), CD4 (28 to 58%), and CD8 (19 to 48%). The lymphocyte subpopulation distributions for all antigens were found to be similar at all sites. By combining data from all sites, it has been possible to estimate age variation and sex differences for each of these subpopulations. Age and sex associated differences are substantial for some lymphocyte subsets (CD3, CD4, NK cells), and proper accounting of these effects is essential in evaluating the individual patient, if further disease-related variation is to be accurately and consistently assessed. It appears possible to recommend reference ranges for lymphocyte population parameters applicable across national and laboratory boundaries. These ranges provide a basis for comparing results from different institutions and for combining such results on subjects and patients from several institutions, provided the methodology and equipment are identical at all sites.

A self‐aligned cobalt silicide technology using rapid thermal processing

The feasibility of a self‐aligned silicide technology based upon cobalt has been investigated. Silicidation reactions were performed by means of rapid thermal processing. Phase sequence, layer morphology, and reaction kinetics were studied by XRD, SEM, RBS, AES, and TEM. Extremely smooth, highly conductive (16 μΩ cm) CoSi2 films were formed by direct reaction of Co on Si, without significant lateral silicide formation at oxide edges. Shallow arsenic junctions were successfully silicided and low contact resistances were obtained on n+ and p+ Si.

A self-aligned CoSi 2 interconnection and contact technology for VLSI applications

Cobalt silicide is investigated in view of possible application in a self-aligned technology. Extremely smooth, highly conductive CoSi2films are obtained using rapid thermal processing for silicide formation starting from deposited cobalt layers (on Si). The phase formation is studied by XRD and RBS. No lateral silicide formation is observed at contact edges. The influence of Si consumption and dopant behavior on diode performance is studied. Shallow arsenic (0.15 µm deep) and boron (0.3 µm deep) junctions are successfully silicided. Very low contact resistances are obtained between the silicide and n+ and p+ regions. MOS transistors were fabricated with CoSi2on the source, drain, and gate. An increase in current driving capability is noticed while no degradation of other electrical parameters due to the silicide processing steps is observed. At some critical points, comparison is made with the TiSi2process.

Observation of hot-hole injection in NMOS transistors using a modified floating-gate technique

A modified floating-gate technique for measuring small gate currents in MOSFETs with very high resolution (0.01 fA) is described. Using this technique, gate oxide currents due to hot-carrier injection are measured in n-channel MOSFETs. The conventional negative channel hot-electron gate oxide current is observed nearV_{g} = V_{d}and a small positive gate current occurs at low Vg. We argue that the dependencies of this small positive current on Vgand gate length, together with results from a separate floating-source experiment, are consistent only with hot-hole injection.

Stability of as-doped and b-doped si with respect to overlaying cosi2 and tisi2 thin-films

The thermodynamic equilibrium of structures consisting of a thin film silicide (TiSi2 or CoSi2) on doped Si (with As or B) is investigated. Isothermal sections of the ternary phase diagrams for Ti–Si–B, Co–Si–B, Ti–Si–As, and Co–Si–As have been evaluated, indicating the stability of high B concentrations in Si underneath a CoSi2 layer, the instability of high As concentrations in Si underneath a CoSi2 layer, and of B and As concentrations underneath a TiSi2 layer. The obtained thermodynamic predictions agree very well with experimental results (i) on the redistribution of dopants during silicide formation, (ii) on the diffusion of dopants from an ion implanted silicide, and (iii) on the stability of highly doped regions underneath the silicide, both for the case of TiSi2 and CoSi2. It is shown that even though the inaccuracy of reported thermodynamic data is substantial, thermodynamic calculations provide a useful guidance and are consistent with the experimental results.

Limitations of TiSi2 as a source for dopant diffusion

The application of TiSi2 as a dopant diffusion source for boron and arsenic was studied. The TiSi2 layers were formed by the usual salicide process and doped by ion implantation. Diffusion was carried out by various furnace and rapid thermal processing steps. Using secondary ion mass spectrometry, scanning electron microscopy, and x‐ray diffraction, clear evidence for compound formation between Ti and the two dopant species is found. This leads to low dopant concentrations at the silicide/silicon interface, very poor efficiency of the diffusion source, and unacceptably high contact resistivities.

WSi2 and CoSi2 as diffusion sources for shallow‐junction formation in silicon

The redistribution of B and As ions implanted into thin layers of WSi2 and CoSi2 on poly‐ or monocrystalline Si and the outdiffusion into the Si substrate during furnace annealing (FA) and rapid thermal processing (RTP) were investigated by several analytical techniques. Shallow junctions (depth xj < 100 nm) with interface concentrations Cint close to the solid solubility of the respective dopant in Si (Cint≳3×1020 cm−3 for As; (Cint ≳ 8 × 1019 cm−3 for B) were obtained with RTP. For FA above 800 °C, the diffusion of B from CoSi2 into Si results in a drop of Cint < 2 × 1019 cm−3 because of strong B segregation and probably reactive loss at the SiO2/CoSi2 interface. No evidence on metal‐dopant‐compound formation could be found. The dopant redistribution is demonstrated to be a superposition of lattice and grain‐boundary diffusion, solubility limits, layer inhomogeneities, dopant segregation at the interface and grain boundaries, and probably phase transformation of the dopants segregated at the SiO2/silici...

Recombinant human erythropoietin for the treatment of anemia in the myelodysplastic syndromes: A clinical and erythrokinetic assessment

SummaryThe clinical and ferrokinetic effects of escalating doses of subcutaneously administered recombinant human erythropoietin (rh-EPO) were studied in ten patients with myelodysplastic syndromes and severe transfusion-dependent anemia. Red blood cell transfusion requirements diminished in four patients, and one of the patients eventually became transfusion independent with an EPO-induced rise of Hb from 7.7 g/dl to 12.3 g/dl. Endogenous serum levels of EPO were significantly increased in all patients (100–5700 mU/ml), but three of four responders had a relatively low baseline level. The effective red cell iron turnover (RCIT) improved in two responding patients and even normalized in one patient. This increase in RCIT was accompanied with a decline in the ineffective red cell iron turnover (IIT). The other responding patients had a relatively preserved RCIT before EPO treatment. EPO therapy further increased the fraction of IIT in the latter patients. Red cell survival time did not increase during EPO therapy, even in the responding patients. One transient and one maintained increase in platelet count were observed. Disease progression with a sustained increase in blast cells in one patient and a transient elevation of blasts in another patient was seen. No other side effects of EPO therapy were observed. These results suggest that anemic MDS patients with low serum EPO levels and relatively spared effective erythropoiesis as measured by ferrokinetic studies may be the best candidates for treatment with recombinant human EPO.

Metal‐dopant‐compound formation in TiSi2 and TaSi2: Impact on dopant diffusion and contact resistance

The refractory metal disilicides TiSi2 and TaSi2 were investigated for their usefulness as dopant diffusion sources. During furnace annealing and rapid thermal processing, strong decomposition reactions occur between the dopants D (B or As) and the respective silicide (MSi2) to form MxDy compounds. With the help of special sample preparation methods and various analytical techniques, the compound phases TiB2, TiAs, TaB2, and TaAs were unambiguously detected. The fraction of freely diffusing B in TaSi2 is determined to be below 5% of the total dose; by far, the major part of the dopant is bound within the TaB2 phase detected. Careful sample preparation and analysis of secondary‐ion‐mass spectrometry profiles is necessary to avoid artifacts caused by these compound particles. The MxDy‐compound formation has detrimental consequences: The solubility of arsenic and even more of boron in TiSi2 and TaSi2 is limited to rather low‐concentration levels (e.g., B in TaSi2: 4 × 1018 B/cm3 < CB(900 °C) < 1.6 × 1019 B/c...

Aes and xps analysis of the interaction of ti with si and sio2 during rta

Abstract The interaction of Ti with Si and SiO2 is studied by means of Auger and X-ray photoelectron spectroscopy. The “peak-to-peak-minus-3-eV-height” method is used for the quantification with AES, while XPS is mainly used to characterize the oxide and nitride states. It will be shown that AES can successfully be applied for quantitative analysis of the resulting TiNx/TiOx/TiSix multilayers in the oxygen lean cases, while a small artifactal nitrogen signal occurs otherwise.