Removal of copper and nickel contaminants from Si surface by use of cyanide solutions N. Fujiwara a,b , Y.-L. Liu a,b , T. Nakamura a,b , O. Maida a,b , M. Takahashi a,b , H. Kobayashi a,b,* a Institute of Scientific and Industrial Research, Osaka University, 8-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan b CREST, Japan Science and Technology Corporation, Japan Available online 2 July 2004 Abstract The cleaning method using cyanide solutions has been developed to remove heavy metals such as copper (Cu) and nickel (Ni) from Si surfaces. Immersion of Si wafers with both Cu and Ni contaminants in potassium cyanide (KCN) solutions of methanol at room temperature decreases these surface concentrations below the detection limit of total reflection X-ray fluorescence spectroscopy of 3  10 9 atoms/cm 2 . UV spectra of the KCN solutions after cleaning of the Cu-contaminated Si surface show that stable copper-cyanide complexes are formed in the solution, leading to the prevention of the re-adsorption of copper in the solutions. From the complex stability constants, it is concluded that the CuðCNÞ 4 3 is the most dominant species in the KCN solutions. # 2004 Elsevier B.V. All rights reserved. PACS: 81.65.C; 68.35.N; 68.43 Keywords: Cleaning; Silicon; Cyanide solutions; Copper; Defect passivation 1. Introduction Heavy metals such as copper (Cu) and nickel (Ni) on silicon (Si) materials cause an increase in the leakage current density [1], a decrease in the minority carrier lifetime [2], etc. for metal-oxide semiconduc- tor (MOS) devices. Copper contaminants on Si surfaces easily diffuse into the Si bulk during device fabrication processes [3], and then form deep levels in the Si-band gap, causing break-down of the pn-junction and decreasing the mobility [4]. There- fore, the decrease in the concentration of such heavy metal contaminants on the Si surfaces is one of the most important subjects for the current and future ULSI manufacturing processes. The RCA cleaning method, developed by Kern and Puotinen [5], is widely used to clean the surfaces of Si devices in ULSI manufacturing processes. This method consists of several cleaning steps which use ammonia hydroxide/hydrogen peroxide mixture (APM), diluted hydrofluoric acid (DHF), and hydro- chloride/hydrogen peroxide mixture (HPM). Concern- ing the removal of Cu, APM and DHF are not effective due to the re-adsorption of Cu onto Si surfaces [6,7]. Moreover, these methods cause etching of Si and SiO 2 , Applied Surface Science 235 (2004) 372–375 * Corresponding author. Tel.: þ81 6 6879 8450; fax: þ81 6 6879 8454. E-mail address: h.kobayashi@sanken.osaka-u.ac.jp (H. Kobayashi). 0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.05.109