Schottky Barrier Inhomogeneities in Nickel Silicide Transrotational Contacts

Alberti, Alessandra; Roccaforte, Fabrizio; Libertino, Sebania; Bongiorno, Corrado; Magna, Antonino La

doi:10.1143/apex.4.115701

Cited by 7 publications

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References 21 publications

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“…The result obtained from this nanoscale analysis (scanning an area of 1 Â 1 lm 2 ) approaches the value of the density of patches (2.5 Â 10 9 cm À2 ) deduced from the macroscopic analysis of temperature dependent barrier height using the Tung's model. 11 On the basis of the local morphological and electrical analyses on the diode area, we are thus able to unequivocally associate the more conductive patches to the core regions of the transrotational domains. The core region is actually the domain central portion wherein a heteroepitaxial relationship between the NiSi and the Si lattices is established.…”

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“…6,10 The electrical behaviour of transrotational silicides is still under investigation. We have recently shown 11 that Schottky diodes, having as metallic contacts transrotational NiSi structures, exhibit an electrical behaviour vs temperature that can be reliably understood in the framework of Tung's model 12 for inhomogeneous barriers. In the model, it is discussed that structural inhomogeneities of a size comparable to the depletion region cannot be treated using a parallel conduction approach, in which the current of the diode is the sum of the contributions from the individual patches.…”

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“…If a classical TE model was applied, a SBH of $0.5 eV would be obtained by forcing a meaningless ideality factor close to 3. To go deep inside the electrical interfacial properties, I-V curves were collected by reducing the temperature during analyses from RT down to 80 K. 11 The diodes exhibited an electrical behaviour vs temperature that was interpreted in the framework of Tung's model for inhomogeneous barriers. Once Tung's model for a Gaussian distribution of patches (½r ¼ ½c ¼ ½ðDR 0 2 Þ 1=3 ) is applied, a value of r $2 Â 10 À4 eV 1/3 cm 2/3 is found, which is consistent with a distribution of patches having average values of the radius R 0 $ 10 nm and of the barrier reduction D $ 0.1 eV.…”

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Nanoscale study of the current transport through transrotational NiSi/n-Si contacts by conductive atomic force microscopy

Alberti

Giannazzo

2012

Applied Physics Letters

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The average electrical behaviour of transrotational NiSi layers used as contacts in diode structures on n-type Si was correlated to the local structure and conduction paths inside each domain by using conductive-atomic force microscopy. It was found that, independently of the domain orientation, the central portion of the domain (core $ 20 nm) possesses a Schottky barrier lower than in the rest of the structure. This was ascribed to an effect of the structural coupling between the NiSi lattice and the silicon substrate as realised at the interface in virtue of the pseudoepitaxial relationship established since the early stages of the reaction. V C 2012 American Institute of Physics.It is well assessed that the use of nickel silicide on source and drain contacts of microelectronic devices has a significant impact to reduce series and contact resistances. 1,2 The drastic scaling down of devices and also the recent interest to use plastic substrates, which have low critical temperatures (e.g., Tc polyimide 200 C), pose more and more the need to optimize the material properties, and particularly, the interfaces quality on the nanoscale. It is thus mandatory to know in more detail the process of silicide formation since the very early stages of the reaction process to control the structure and the stoichiometry of the silicide, especially on very thin layers.The pioneering studies on the very early stages of Ni-Si reaction date from 1980. It was observed that, on a perfectly cleaned Si surface, a Ni-Si precursor layer is formed even at room temperature (RT) after deposition of a very thin nickel layer (<2 nm). 3 The precursor layer (or diffusion layer) is formed once nickel atoms come in contact with silicon, and reasonably maintained also after subsequent reaction: its presence is thus adduced as the reason why all the Ni-silicide phases have comparable Schottky barrier height (e.g., 0.66 eV on n-type Si). 4 The precursor layer has a disordered structure with Ni atoms having the short range environment similar to that encountered in the NiSi 2 lattice 3 and originates from the diffusion process of Ni atoms into the Si lattice by means of tetrahedral interstitial sites. Due to the similarity of the diffusion layer structure to that of the NiSi 2 lattice, an epitaxial silicide layer is formed upsetting the usual sequence of phases encountered in thick layers, without significant transport of matter, 3 by annealing at relatively low temperature ($450 C). A different scenario is instead observed by depositing at RT a supply of Ni atoms on top of the interfacial diffusion layer. When a supply of Ni is then present, the role of the diffusion layer, as precursor to the reaction process, is shadowed by the fast diffusion of nickel atoms, and a conventional phase sequence is observed with NiSi 2 formed at the end, at the NiSi-Si interface. 1 We have recently 5 shown that the direct transition to NiSi 2 can be assured even in the presence of a nickel supply ($7 nm) by using a $2 nm-thick precursor layer and by reducing anneali...

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Nanoscale study of the current transport through transrotational NiSi/n-Si contacts by conductive atomic force microscopy

Alberti

Giannazzo

2012

Applied Physics Letters

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“…19,20,23,24,34 An inhomogeneous barrier along an interface due to a distribution of patches with lower U B n,eff than the rest of the interface can cause the measured U B n,eff to be lower than that of a reference without patches. 23 Indeed, our experimental results showed lower U B n,eff and higher I s than that of control contact devices. The reason for U B n,eff lowering is due to the modified carrier transport at the NiSi 2 /Si interfaces.…”

Section: Discussion On the Effect Of Pyramidal Nisi 2 On The Effementioning

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