An in-situ FTIR Study on Palladium Displacement Reaction for Autocatalytic Electroless Copper Deposition

Abstract

We have investigated on the mechanism of palladium autocatalytic displacement reaction on the Si substrate in PdCl₂-HCl-HF-NH₄OH bath, which occurs in the Pd activation step in electroless Cu deposition process. It has been monitored that Pd(NH₃)₄Cl₂ in the electrolyte is reduced to Pd particles by displacement reaction with substrate silicon and NH₄⁺ complex are generated during the Pd activation. In the in-situ FTIR analysis, N-H vibration peaks in Pd(NH₃)₄Cl₂ of electrolyte are shifted to N-H peaks in NH₄⁺ complex. The IR peaks of SiF₆^2-and N-H bonds of NH₄⁺ are also evident during the Pd activation on the Si surface. It reveals that palladium in Pd(NH₃)₄Cl₂ has been reduced to metallic Pd particles on Si substrate and (NH₄)₂SiF₆ compound has been produced. Also, in our presentation, we will discuss on the autocatalytic reaction between formaldehyde contained copper electrolyte and Pd activated Si surface at various conditions using the in-situ and ex-situ ATR-FTIR and XPS analysis. We could find 1583cm^-1 (υ_as(HCOO-)), 1380cm^-1 (δ(C-H)), and 1356cm^-1 (υ_s(HCOO-)) in the experiment of Cu ELD on the Pd activated silicon wafer. The growth of these peaks means HCOO-, which is oxidized from CH₂(OH)O- in electrolyte, is attached on the Pd as reaction.