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

A Si cleaning method has been developed by use of potassium cyanide (KCN) dissolved in methanol. When silicon dioxide (SiO2)/Si(1 0 0) specimens with 1014 atom/cm2 order copper (Cu) contaminants are immersed in 0.1 M KCN solutions of methanol at 25 °C, the Cu concentration is reduced to below the detection limit of total X-ray fluorescence spectrometer of ∼3 × 109 atoms/cm2. X-ray photoelectron spectra show that the thickness of the SiO2 layers is unchanged after cleaning with the KCN solutions. 1014 cm−2 order Cu contaminants on the Si surface can also be removed below ∼3 × 109 atoms/cm2, 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 × 1023. Even when the KCN solutions are contaminated with 64 ppm Cu2+ 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/SiO2 interface states, leading to the improvement of characteristics of Si devices.