NEW METHOD OF PURIFICATION OF HF CHEMICALS FOR VERY LARGE-SCALE INTEGRATION MANUFACTURING

Metallic impurities having a lower ionization tendency than Si, such a s Cu, are adsorbed onto the surface of the silicon substrate in hydrof luoric acid (HF) chemicals and buffered hydrofluoric acid (BHF) and th en degrade device characteristics. A new purification method using a g ranular polysilicon (poly-Si) as an adsorbent was designed to remove t he 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 preve nt Au contamination from the Au-poly-Si. These poly-Si were more promi sing 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 in vestigated using a 36 day running test. This system shows sufficient p erformance and reliability for reprocessing HF in a wet station at poi nt-of-use. This purification method makes it possible to lengthen HF L ifetimes and decrease the amount of HF used in very large scale integr ation manufacturing.