portunity to make investigations with the STM, and to Dipl.-Phys. S. Br~uer for his help in recording the STM images and for helpful discussions about the results. We also thank the Stiftung Volkswagenwerk for financial support.
TEOS and O~ atmospheric pressure chemical vapor deposition has excellent conformality, film quality, and low particle generation; however, deposition rate obtained on thermal oxide is lower than that on silicon and the films have rough surface and higher etching rates if deposited with high ozone concentration. When deposited on silicon with a higher ozone concentration, films of sufficiently high quality are obtained. This drawback of the low film quality has been removed by doubleJayer deposition with two different ozone concentrations on thermal oxide, depositing the thin films at first with a low ozone concentration on thermal oxide and next with a high ozone concentration to the desired thickness. The film quality, namely, etch rate, depends on the thickness and ozone concentration for the first layer. The thicker the first film and the higher the ozone concentration, the better the film quality. By adjusting the first layer's thickness and ozone concentration, films can be obtained with quality that is sufficiently high for VLSI device applications.
Atmospheric pressure tetraethyloxysilicane (TEOS)/O3 chemically vapor deposited provides excellent step coverage for submicron device structures; however, the properties of the deposited films depend on the surface characteristics of the base materials being used. To illustrate this dependence, the deposition rate of nondoped silicon dioxide obtained on a thermal oxide surface is significantly lower than the deposition rate obtained on a bare silicon surface. A new method to eliminate this base material dependence involving plasma treatment has been investigated. The optimum treatment consists of exposing the base materials to a nitrogen plasma for 1 min while maintaining the base materials at 250~ Films deposited on thermal oxide base materials which have first been treated by this new method were found to have the same deposition rate, aqueous HF etch rate, and surface morphology as those films deposited on untreated bare silicon. In addition to a nitrogen plasma, oxygen and argon plasmas were studied and found to produce similar results when the base material temperature was raised to 350~ The elimination of base material dependence through the use of this new plasma treatment technique has resulted in higher integrity TEOS/O3 oxides and has also expanded the range of applications for this unique planarizing technology for very large scale integrated device fabrication. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.230.73.226 Downloaded on 2015-06-03 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.230.73.226 Downloaded on 2015-06-03 to IP
Borophosphosilicate glass (BPSG) films were deposited using tetraethoxysilane (TEOS), triethylborate (TEB), trimethylphosphate (TMOP), and ozone at atmospheric pressure. A uniform distribution of borate was obtained throughout the thickness of the film using TEB instead of trimethylborate (TMB). The deposition rates were characterized as functions of dopant gas flow rates, deposition temperature, and ozone concentration. Both dopants enhanced the deposition rates. The deposition rates did not show ozone concentration dependence. The typical deposition rate was as high as 0.2 μm/min. The borate and phosphate contents were characterized as functions of dopant gas flow rates, and deposition temperature. They ranged from 8 to 15 mole percent (m/o) for borate and from 3 to 8 m/o for phosphate. The film stress was as low as 1×109 normaldyn/cm2 (tensile) when deposited at 400°C with 4% ozone and relaxed to −0.7×109 normaldynsol;cm2 a week after deposition. The film shrinkage was minimum (5%) at 400°C, and decreased with increasing ozone concentration. The step‐coverage of an as‐deposited film was superior, hence, the film reflowed smoothly even after the low temperature (850°C) annealing.
a b s t r a c tLittle is known about the prevalence of hepatitis C virus (HCV) among healthcare workers (HCW) in Egypt, where the highest worldwide prevalence of HCV exists. The prevalence of HCV, hepatitis B virus and Schistosoma mansoni antibodies was examined in 842 HCWs at the National Liver Institute in the Nile Delta, where >85% of patients are HCV antibodypositive. The mean age of HCWs was 31.5 years and they reported an average of 0.6 ± 1.2 needlesticks/HCW/year. The prevalence of anti-HCV, hepatitis B surface antigen (HBsAg) and co-infection was 16.6%, 1.5% and 0.2%, respectively. HCV-RNA was present in 72.1% of anti-HCV-positive HCWs, and all but one subject were infected with HCV genotype 4. Schistosoma mansoni antibodies were present in 35.1%. The anti-HCV rate increased sharply with age and employment duration, but not among those with needlestick history. After adjusting for other risk factors, the anti-HCV rate was higher among older HCWs [P < 0.001; risk ratio (RR) = 1.086, 95% CI 1.063-1.11], males (P = 0.002; RR = 1.911, 95% CI 1.266-2.885) and those with rural residence (P < 0.001; RR = 2.876, 95% CI 1.830-4.52). Occupation (P = 0.133), duration of employment (P = 0.272) or schistosomal antibody positivity (P = 0.152) were not significant risk factors for anti-HCV positivity. In conclusion, although one in six HCWs had been infected with HCV, the infections were more likely to be community-acquired and not occupationally related.
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