Separation and Recycling for Rare Earth Elements by Homogeneous Liquid-Liquid Extraction (HoLLE) Using a pH-Responsive Fluorine-Based Surfactant
A selective separation and recycling system for metal ions was developed by homogeneous liquid-liquid extraction (HoLLE) using a fluorosurfactant. Sixty-two different elemental ions (e.g., Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, In, Ir, La, Lu, Mg, Mn, Mo, Nb, Nd, Ni, Os, P, Pb, Pd, Pr, Pt, Re, Rh, Ru, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Te, Ti, Tl, Tm, V, W, Y, Yb, Zn, and Zr) were examined. By changing pH from a neutral or alkaline solution (pH ≥ 6.5) to that of an acidic solution (pH 90% efficiency into a sedimented Zonyl FSA® (CF3(CF2)n(CH2)2S(CH2)2COOH, n = 6–8) liquid phase. Moreover, all rare earth elements were obtained with superior extraction and stripping percentages. In the recycling of rare earth elements, the sedimented phase was maintained using a filter along with a mixed solution of THF and 1 M sodium hydroxide aqueous solution. The Zonyl FSA® was filtrated and the rare earth elements were recovered on the filter as a hydroxide. Furthermore, the filtrated Zonyl FSA was reusable by conditioning the subject pH.
Homogeneous liquid-liquid extraction using perfluorooctanesulfonic acid and calcium and its application to the separation and recovery of vitamin B12
A new phase separation phenomenon was observed in which the perfluorooctanesulfonate ion (PFOS−) and calcium ion form an ion-pair associator and the sedimented liquid phase occurs from the homogeneous aqueous solution. This phenomenon was observed in the neutral pH region at room temperature (25 °C). The optimum concentration conditions for the reagents were [PFOS−]T = 7 × 10−3 mol dm-3 and [Ca2+]T = 1.1 mol dm-3. When these findings were applied to the homogeneous liquid–liquid extraction of vitamin B12, the extraction percentage (E) was 83% and the concentration ratio (ie Va/Vs, where Va is the volume of the aqueous phase and Vs is the volume of the sedimented liquid phase) was a maximum of 149. The recovery of vitamin B12 was achieved by adding the propanol–acetone (20 : 80 v/v%) mixed solvent to the sedimented liquid phase; the vitamin B12 precipitated and was filtered. Both the PFOS− and Ca2+ were removed by dissolution in the mixed solvent. The recovery percentage of vitamin B12 was 78%. 
 
 
 
© 1999 Society of Chemical Industry
Bevel RIE application to reduce defectivity in copper BEOL processing
Bevel etch used during wafer fabrication for semiconductor devices is discussed. In this case, the bevel etch process was utilized in middle of the line processing (MOL) to reduce back end of line (BEOL) defectivity. Tungsten and titanium nitride films, from the formation of contacts to the transistors, extend into the bevel region of the wafer and have been shown to initiate arcing. This can spread foreign material defects on the front side of the wafer in various BEOL post processing steps including subsequent reactive ion etching, SEM metrology and film depositions. The bevel etch tool confines a plasma etch to the outer edge of the front side of the wafer (which can be individually adjusted) and can remove dielectric, organic and Ti/TiN/W films using a fluorine based chemistry.