Complete Removal of Copper Contaminants on Bare Silicon Surfaces by Use of HCN Aqueous Solutions

Due to the strong reactivity of CN - ions to form Cu-cyano complex ions and high stability of the ions in aqueous solutions, Cu contaminants on bare Si surfaces can be removed to less than ∼3 X 10 9 atoms/cm 2 by immersion in hydrocyanic acid (HCN) aqueous solutions, and cleaning can be performed with dilute (i.e., 0.027 - 0.0027 wt %) solutions at room temperature. Hydrofluoric acid plus hydrogen peroxide mixture can also completely remove Cu contaminants from the bare Si surfaces, but in this case, the Si surfaces become considerably rough due to etching. HCN solutions do not etch Si when pH is adjusted below 9, and consequently, the Si surface is not roughened at all. Cu contaminants are present on Si in the form of metallic islands and their size decreases with the HCN cleaning periods. Semi-log plots of the Cu concentration vs cleaning time consist of two linear lines for the initial fast and subsequent slow processes. The fast and slow processes are attributable to removal of Cu atoms bound to Cu atoms only and that of Cu atoms directly bound to Si, respectively. The rate constant for the fast and slow processes are determined to be 4.4 and 0.016/s, respectively.