Transient and end silicide phase formation in thin film Ni/polycrystalline-Si reactions for fully silicided gate applications

Abstract

The Ni/polycrystalline-Si thin film reaction was monitored by in situ x-ray diffraction during ramp annealings, obtaining a detailed view of the formation and evolution of silicide phases in stacks of interest for fully silicided gate applications. Samples consisted of Ni (30–170nm)/polycrystalline-Si (100nm)∕SiO2 (10–30nm) stacks deposited on (100) Si. The dominant end phase (after full silicidation) was found to be well controlled by the deposited Ni to polycrystalline-Si thickness ratio (tNi∕tSi), with formation of NiSi2 (∼600°C), NiSi (∼400°C), Ni3Si2 (∼500°C), Ni2Si, Ni31Si12 (∼420°C), and Ni3Si (∼600°C) in stacks with tNi∕tSi of 0.3, 0.6, 0.9, 1.2, 1.4, and 1.7, respectively. NiSi and Ni31Si12 were observed to precede formation of NiSi2 and Ni3Si, respectively, as expected for the phase sequence conventionally reported. Formation of Ni2Si was observed at early stages of the reaction. These studies revealed, in addition, the formation of transient phases that appeared and disappeared in narrow temperature ranges, competing with formation of the phases expected in the conventional phase sequence. These included the transient formation of NiSi and Ni31Si12 in stacks in which these phases are not expected to form (e.g., tNi∕tSi of 1.7 and 0.9, respectively), at temperatures similar to those in which these phases normally grow.