The contamination of cleaned silicon wafer surfaces by metal ions is a significant problem. The RCA cleaning process developed by Kern and Puotinen 1 has been very successful at reducing metal contamination to low levels; however, we now are attempting to produce surfaces cleaner than anything dreamed of 30 years ago. Various cleaning recipes have been established to produce very clean surfaces. These are generally made up from a few treatments that include ammonia and hydrogen peroxide, hydrochloric acid (usually with hydrogen peroxide), and hydrofluoric acid. No matter which treatments are included in a cleaning process sequence, the final step is normally a rinse in deionized (DI) water, although several alternatives have been described. Miyamoto and co-workers have described using low concentrations of HF in the water. 2 Shiramizu and co-workers have described the use of electrolysis-ionized water containing NH 4 Cl to keep the pH low and remove and keep off metallic impurities. 3 Lampert and Fabry have suggested the addition of CO 2 to water. 4 Loewenstein and Mertens have described the use of HNO 3 in preventing metal deposition. 5 These approaches arise out of a growing understanding that DI water can itself contribute to contamination of the silicon wafer, and that low pH in the rinse water can significantly reduce the metallic contamination on the surfaces of treated wafers.The nature of the adsorbing species has also been an area of study in the literature. Ohmi and co-workers used the segregation of metallic impurities across the surface of a silicon wafer to make inferences regarding adsorbing species. 6 The approach of drying a puddle of water containing dissolved metal ions is difficult to interpret, however, as metal ion concentrations, wafer and solution temperatures, and possibly even the nature of the surface are changing over the 3 h spent drying the puddle. Mouche and co-workers have investigated the mechanism of metal ion adsorption onto silicon. 7 Their work concentration on adsorption from industrially important solutions (SC1, SC2, Caro's acid, dilute HF, and H 2 O) for cleaning silicon wafers. As such, their work lacked a systematic control of pH. Several investigators have used thermodynamic analyses. Helms and co-workers consider the formation of metal silicates, 8 and the phase diagrams of the ternary metal-oxide-silicon systems thus involved. While informative, metal silicates often need temperatures of 800ЊC or higher to form, 9 and so are not accessible at the low temperatures involved in aqueous processing. Building on the work of Pourbaix, 10 Mori and co-workers have concentrated on the changes in the metal species present in solution as the pH changes, combining this with calculations of the free energy change of adsorption for different species. 11 Mori concluded that neutral metal hydroxides are the main adsorption species in SC1 solutions. Loewenstein and Mertens, on the other hand, found that cations are the adsorbing species in acidic solution. 12 All of these studies lack a...

No abstract

No abstract

The HTR pebble fuel experiment HFR EU1bis was irradiated in the High Flux Reactor, Petten, The Netherlands, in 2004 and 2005. It consisted of five fuel pebbles from the German HTR program (GLE4 type, UO2 fuel, 16.75% enrichment) and six minisamples (UO2 fuel, 9.75% enrichment). Its instrumentation included three flux monitor sets. The experiment was loaded in a REFA-170 rig, surrounded by a strongly moderating filler element. The central fuel temperature was held at 1250°C during the irradiation. In the framework of the European RAPHAEL project, Post Irradiation Examination (PIE) has been done at NRG in Petten, The Netherlands and at JRC ITU in Karlsruhe, Germany. In Petten, flux monitor analysis has been done, whereas in Karlsruhe, a quantitative evaluation of γ-emitters was used to make a burn-up determination.\ud A benchmark description based on this experiment has been written by NRG. Until now, five RAPHAEL project participants have modeled the experiment, each with their own neutronics code system. Participating codes are three versions of MONTEBURNS (MCNP with ORIGEN), MURE/MCNP and OCTOPUS (MCNP with FISPACT).\ud The pebble burnup and isotopic inventories (Bq/gram initial HM) of selected fission products and actinides in the fuel pebble samples are both calculated and determined by gamma spectrometry, mass spectrometry and ion chromatography by JRC-ITU. Additionally, two participants calculated the flux monitor activities that were measured by NRG.\ud A burnup measurement of 11.0 %FIMA by gamma\ud spectrometry could be confirmed by calculation. Differences\ud between the various modeling approaches and the experimental\ud burn-up determination will be discussed