Metallic impurities having a lower ionization tendency than Si, such as Cu, are adsorbed onto the surface of the silicon substrate in hydrofluoric acid (HF) chemicals and buffered hycirofluoric acid (BHF) and then degrade device characteristics. A new purification method using a granular polysilicon (poly-Si) as an adsorbent was designed to remove the metallic impurities. As an adsorbent, Au deposited poly-Si (Au-poly-Si) was developed to improve the Cu removal efficiency of the poly-Si, and Au removed Au-poly-Si (Au-R-poly-Si) was also developed to prevent Au contamination from the Au-poly-Si. These poly-Si were more promising for HF than for BHF because of the difference in the etching rate of the silicon. The purification system using the Au-R-poly-Si was investigated using a 36 day running test. This system shows sufficient performance and reliability for reprocessing HF in a wet station at point-of-use. This purification method makes it possible to lengthen HF lifetimes and decrease the amount of HF used in very large scale integration manufacturing.

The hydrogen bonding features of Si(100) surfaces treated with BHF (NH4F/HF/H2O) have been studied by Fourier transform infrared attenuated total reflection spectroscopy (FT-IR-ATR). The amount of residual silicon-fluorine bonds on Si(100) surfaces has been evaluated by X-ray photoelectron spectroscopy (XPS). It is found that Si-H3 bonds appears to be preferentially removed by OH ions so as to increase the surface SiH2 and SiH bonds. On the other hand, it is likely that fluorine-containing ionic species such as HF2 might attack the backbonds of surface hydrides to produce Si-H3 and Si-F bonds. ATR spectra have shown that a BHF treated Si(100) surface in 5∼10% NH4F with molar ratios of HF/NH4F=0.37∼0.56 (pH=3.7∼4.0) at a treatment time of 5 minutes is atomically flatter than that treated in BHF containing 15∼20% NH4F. This is because the amount of residual Si-F bonds on Si(100) increases with HF2 concentration in BHF and these Si-F bonds enhance attacking of silicon backbonds of Si-F bond by OH− and HF2− ions.

1997separation and purification methods, chromatography separation and purification methods, chromatography V 0200 -216New Method of Purification of HF Chemicals for Very Large Scale Integration (VLSI) Manufacturing.-Metallic impurities (e.g. Cu) in HF chemicals used in VLSI fabrication degrade the device characteristics. They can be removed by a new method using granular polysilicon (poly-Si) as adsorbent. The Cu removal efficiency of this adsorbent can be improved by an Au deposited poly-Si (Au-poly-Si) which, however, causes Au contamination of the HF. A new Au-removed Au-poly-Si adsorbent, prepared by immersion of Au-poly-Si in aqua regia at 60 • C, exhibits a Cu removal efficiency quite similar to that of Au-poly-Si. The new method, which is more promising for HF than for buffered HF, increases the HF lifetime and, therefore, reduces the amount of HF required for VLSI manufacturing. -(YAMAMOTO, K.; SHIMONO, T.; OKADA, T.; KAWAZAWA, Y.; TATSUNO, T.; J.