The thermally induced solid-state reaction between a 10-nm-thick Ni film and a Si(001) substrate was investigated using in situ x-ray diffraction and ex situ pole figure analyses. The reaction begins with the appearance of orthorhombic Ni2Si grains characterized by a strong fiber texture. The formation of the metastable hexagonal θ phase—which inherits the fiber texture of Ni2Si—is then observed. This phase has been observed in every sample studied regardless of dopant, film thickness, deposition method, and anneal profile (>2000 conditions). Texture inheritance allows a reaction pathway with a lower activation energy than the expected formation through thermodynamically stable Ni silicide phases.

The thermally-induced reaction of thin Ni films with Si: Effect of the substrate orientationThe 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 ͑30-170 nm͒/polycrystalline-Si ͑100 nm͒ / SiO 2 ͑10-30 nm͒ stacks deposited on ͑100͒ Si. The dominant end phase ͑after full silicidation͒ was found to be well controlled by the deposited Ni to polycrystalline-Si thickness ratio ͑t Ni / t Si ͒, with formation of NiSi 2 ͑ϳ600°C͒, NiSi ͑ϳ400°C͒, Ni 3 Si 2 ͑ϳ500°C͒, Ni 2 Si, Ni 31 Si 12 ͑ϳ420°C͒, and Ni 3 Si ͑ϳ600°C͒ in stacks with t Ni / t Si of 0.3, 0.6, 0.9, 1.2, 1.4, and 1.7, respectively. NiSi and Ni 31 Si 12 were observed to precede formation of NiSi 2 and Ni 3 Si, respectively, as expected for the phase sequence conventionally reported. Formation of Ni 2 Si 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 Ni 31 Si 12 in stacks in which these phases are not expected to form ͑e.g., t Ni / t Si of 1.7 and 0.9, respectively͒, at temperatures similar to those in which these phases normally grow.

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