Reaction of cyanide ions with copper on Si surfaces and its use for Si cleaning

摘要

A Si cleaning method has been developed by use of potassium cyanide (KCN) dissolved in methanol. When silicon dioxide (SiO_2)/ Si(100) specimens with 10~(14) atom/cm~2 order copper (Cu) contaminants are immersed in 0.1 M KCN solutions of methanol at 25℃, the Cu concentration is reduced to below the detection limit of total X-ray fluorescence spectrometer of ～3 x 10~9 atoms/cm~2. X-ray photo-electron spectra show that the thickness of the SiO_2 layers is unchanged after cleaning with the KCN solutions. 10~(14) cm~(-2) order Cu contaminants on the Si surface can also be removed below ～3 x 10~9 atoms/cm~2, without causing contamination by potassium ions. UV spectra show that Cu-cyano complex ions are formed in the KCN solutions after the cleaning. The main Cu species in the KCN solutions is Cu(CN)_4~(3-) ions with the concentration of [Cu(CN)_4~(3-)]:[Cu~+] = 1:1.6 x 10~(23). Even when the KCN solutions are contaminated with 64 ppm Cu~(2+) ions in the solutions, which form Cu(CN)_4~(3-) ions, the cleaning ability does not decrease, showing that Cu(CN)_4~(3-) ions are not re-adsorbed. The KCN solutions can also passivate defect states such as Si/SiO_2 interface states, leading to the improvement of characteristics of Si devices.