The solid-state reaction and agglomeration of thin nickel-silicide films was investigated from sputter deposited nickel films ͑1-10 nm͒ on silicon-on-insulator ͑100͒ substrates. For typical anneals at a ramp rate of 3°C / s, 5-10 nm Ni films react with silicon and form NiSi, which agglomerates at 550-650°C, whereas films with a thickness of 3.7 nm of less were found to form an epitaxylike nickel-silicide layer. The resulting films show an increased thermal stability with a low electrical resistivity up to 800°C. © 2010 American Institute of Physics. ͓doi:10.1063/1.3384997͔Nickel-silicides are currently used as contacting materials in state-of-the-art microelectronic devices.1,2 Feature size has shrunk to a few tens of nanometers, and for nickel monosilicide ͑NiSi͒ layers, this results in a particularly severe tendency to agglomerate, 3 leading to a large increase in the electrical resistance of the contact, and an increased mobility of the nickel as it starts to move on the defects, both resulting in a low yield. Since the agglomeration of thin films is driven by a minimization of interface energy, it is expected that thinner films will agglomerate faster ͑i.e., have a lower agglomeration temperature͒. 4 In this letter, we show that this holds true only for films with a thickness of at least 5 nm ͑as-deposited thickness of the nickel layer͒, while for thinner layers the resulting nickel-silicide layer is much more resistant to agglomeration.Nickel films with a thickness between 1 and 10 nm were sputter deposited onto lightly p-doped ͑ =14-22 ⍀ cm͒, Radio Corporation of America ͑RCA͒ cleaned, and HF dipped silicon-on-insulator substrates, with a top layer of 117 nm of Si ͑100͒. The deposition chamber was first evacuated to 10 −4 Pa during deposition, the samples were mounted on a rotating carousel to ensure a uniform deposition thickness. An argon pressure of 0.5 Pa and a sputtering power of 100 W were used, resulting in a deposition rate of 0.04 nm/s. After deposition, the samples were annealed in a high-purity He atmosphere, from 100 to 850°C at a rate of 3°C / s, and the surface roughness ͑using laser light scattering, recording the intensity of nonspecular reflection of the laser light͒, and the sheet resistance ͑using a four point probe͒ were recorded in situ. The thickness of both the as-deposited and annealed films was determined using x-ray reflectivity and cross section transmission electron microscopy, resulting in the reported thicknesses with a precision of Ϯ0.2 nm.An overview of the in situ sheet-resistance is shown in Fig. 1. All of the samples with more than 3.7 nm of nickel ͑6, 8, and 10 nm are shown͒, exhibit a sheet resistance qualitatively similar to what was previously reported 5 for 10 nm layers of nickel on Si ͑100͒; a complex phase sequence of high-resistive metal rich nickel-silicides at low temperatures, and the formation of the low-resistive NiSi phase at 400-450°C. This layer then agglomerates at 550-650°C, leading to the observed increase in sheet resistance. In contrast, for the thinn...