A Study of Immersion Processes of Activating Polished Crystalline Silicon for Autocatalytic Electroless Deposition of Palladium and Other Metals

TL;DR: In this paper, the authors study the effect of modifying the Pd-ammine complex and varying the substrate doping on Pd deposition during activation and Pd AED adhesion and find that the AED of Pd on polished crystalline Si is non-adherent using this activator solution.

Abstract: The solution in which Si is immersed for activation prior to autocatalytic electroless deposition (AED) of Ni, Cu, etc. is usually HF-PdCl 2 -HCl. However, we find that the AED of Pd on polished crystalline Si, which has important applications in modern planar integrated circuit technology, is nonadherent using this activator solution. Our study of the effects of modifying this solution and varying the substrate doping on the Pd deposition during activation and Pd AED adhesion reveals the following. The activation quality and hence AED adhesion depends not on the SiO 2 etch rate of the solution but on the composition of the solution Pd complex and the substrate hole concentration. In spite of the highest Pd deposition rate during immersion, the activation quality of n-Si with doping >10 19 /cm 3 is poor unless a hole-generating stimulus (e.g., illumination) is present. A change in substrate hole concentration influences AED adhesion by altering the substrate potential and/or density of nucleation sites during activation. Similarly, a change in the Pd complex affects AED adhesion by altering the solution Pd potential. Introduction of certain ammonium compounds into the HF-PdCl 2 -HCl bath creates a specific Pd-ammine complex, most probably Pd(NH 3 ) 2 Cl 2 , which gives Pd AED adhesions of ∼9 and 4 (3) × 10 6 N/m 2 on heavily doped p-Si and lightly doped p(n)-Si, respectively, using a low SiO 2 etch rate (∼90 A/min) and a low temperature (200°C) for Pd nuclei silicidation during activation. Our results regarding the activation mechanism are believed to apply generally to all AED on Si.