During the deposition of a Ni film on a Si substrate, an intermixed layer usually forms at the Ni/Si interface. In this work, the influence of Pt incorporation in this intermixed layer on the phase formation sequence and especially on the first phase formation is studied by in situ-XRD measurements and atom probe tomography (APT). Four different samples were elaborated where the intermixed layer was modified by deposition of a 3 nm of Ni or Ni(10 at% Pt) on the Si substrate prior to the deposition of Ni(10 at%Pt) or Ni film respectively. These results show that the formation of the first phase changes between delta-Ni2Si and theta-Ni2Si depending on the Pt concentration integrated in the intermixed layer. Using this selection method to control the formation of the first phase, can impact the self-aligned silicide process used by the industry. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.