Effect of Co,Pd and Pt ultra-thin films on the Ni-silicide formation: investigating the sandwich configuration

The effect of Co, Pd and Pt ultrathin films on the kinetics of the formation of Ni-silicide by reactive diffusion is investigated. 50 nm Ni/1 nm X/ 50 nm Ni (X?=?Co, Pd, Pt) deposited on Si(100) substrates are studied using in-situ and ex-situ measurements by X-ray diffraction (XRD). The presence of Co, Pd or Pt thin films in between the Ni layers delays the formation of the metal rich phase compared to the pure Ni/Si system and thus these films act as diffusion barriers. A simultaneous silicide formation (δ-Ni₂Si and NiSi phases) different from the classic sequential formation is found during the consumption of the top Ni layer for which Ni has to diffuse through the barrier. A model for the simultaneous growth in the presence of a barrier is developed, and simulation of the kinetics measured by XRD is used to determine the permeability of the different barriers. Atom probe tomography (APT) of the Ni/Pd/Ni system shows that the Pd layer is located between the Ni top layer and δ-Ni₂Si during the silicide growth, in accordance with a silicide formation controlled by Ni diffusion through the Pd layer. The effect of the barrier on the silicide formation and properties is discussed.

     

Nickel silicide formation on Si(100) and Poly-Si with a presilicide N2 + implantation

The key feature of this study is to incorporate N₂ ⁺ implant prior to Ni sputtering on the poly-Si gate and source/drain regions. The results show that the incorporation of the presilicide N₂ ⁺ implant is able to suppress agglomeration in the Ni silicide films up to 900°C and enhance the phase stability of NiSi on Si(100) up to 750°C. Stable and low sheet resistance was achieved on the silicided undoped poly-Si up to 700°C due to reduced layer inversion, which is driven by grain boundary energy and the surface energy of the poly-Si.     

Formation of C49-TiSi2 in flash memories: a nucleation controlled phenomenon?

The formation of Ti silicides has been examined in flash memories with 0.25 μm linewidth by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It has been observed that, after the first rapid thermal process and the selective metal etch, there is no silicide on the source and on a majority of drain contacts while C49-TiSi₂ is found on the gate. A pre-amorphisation implant increases drastically the formation of C49-TiSi₂ in the drain zone while modifications of annealing conditions have little impact. These results indicate that the formation of C49-TiSi₂ is most likely controlled by nucleation and that this nucleation is sensitive to both the width and the length of the reaction zone. The formation of a Ti rich silicide may play an important role in this nucleation by decreasing the driving force for the formation of C49-TiSi₂. Curiously enough, the formation of C49-TiSi₂ appears thus as a major concern for the salicide process in flash memories.     

Atom probe tomography of Ni silicides: First stages of reaction and redistribution of Pt

The silicide formation and the redistribution of Pt after deposition and after a heat treatment at 290 °C of Ni_1−xPt_x films on Si have been analysed by atom probe tomography assisted by femtosecond laser pulses. Two phases with different composition were found to form during deposition at room temperature: a NiSi layer with a relatively constant thickness of approximately 2 nm and a particle of Ni₂Si. The shape of the Ni₂Si particle is in accordance with nucleation followed by lateral growth formation. After heat treatment, two silicide phases Ni₂Si and NiSi were found together with the Ni_1−xPt_x solid solution. The redistribution of Pt at the Ni_1−xPt_x/Ni₂Si interface is a clear illustration of the snowplow effect. A segregation of Pt at the Ni₂Si/NiSi interface has been observed and is attributed to interfacial segregation. The effect of the redistribution of Pt on the silicide formation is discussed.     

New salicidation technology with Ni(Pt) alloy for MOSFETs

A novel salicide technology to improve the thermal stability of the conventional Ni silicide has been developed by employing Ni(Pt) alloy salicidation. This technique provides an effective avenue to overcome the low thermal budget (<700°C) of the conventional Ni salicidation by forming Ni(Pt)Si. The addition of Pt has enhanced the thermal stability of NiSi. Improved sheet resistance of the salicided narrow poly-Si and active lines was achieved up to 750°C and 700°C for as-deposited Ni(Pt) thickness of 30 nm and 15 nm, respectively. This successfully extends the rapid thermal processing (RTP) window by delaying the nucleation of NiSi₂ and agglomeration. Implementation of Ni(Pt) alloyed silicidation was demonstrated on PMOSFETs with high drive current and low junction leakage     

Improved NiSi salicide process using presilicide N/sub 2//sup +/ implant for MOSFETs

An improved Ni salicide process has been developed by incorporating nitrogen (N/sub 2//sup +/) implant prior to Ni deposition to widen the salicide processing temperature window. Salicided poly-Si gate and active regions of different linewidths show improved thermal stability with low sheet resistance up to a salicidation temperature of 700 and 750/spl deg/C, respectively. Nitrogen was found to be confined within the NiSi layer and reduced agglomeration of the silicide. Phase transformation to the undesirable high resistivity NiSi/sub 2/ phase was delayed, likely due to a change in the interfacial energy. The electrical results of N/sub 2//sup +/ implanted Ni-salicided PMOSFETs show higher drive current and lower junction leakage as compared to devices with no N/sub 2//sup +/ implant.     

In situ characterization of interface-microstructure dynamics in 3D-Directional Solidification of model transparent alloys

Microstructure plays a central role in determining properties of materials so that the fundamental understanding of the physics of microstructure selection is critical in the design of materials. Under terrestrial conditions fluid flow effects are dominant in bulk samples which preclude precise characterization of fundamental physics of microstructure selection. Experiments in thin samples, carried out to obtain diffusive growth, give microstructures that are neither 2D nor 3D. Rigorous theoretical models, using the phase-field method, have shown that the fundamental physics of pattern selection in 2D and 3D is significantly different. A benchmark experimental study is required in bulk samples under low gravity conditions. Also, the selection of microstructure occurs during the dynamical growth process so that in situ observations of spatio-temporal evolution of the interface shapes are required. Microgravity experiments on ISS are thus planned in a model transparent system by using a new Directional Solidification Insert (DSI), designed for use in the DECLIC facility of CNES and to be adapted to also fit ESA experiments. The critical aspects of hardware design, the key fundamental issues identified through 1g-experiments, the proposed experimental study on ISS, and the results of rigorous theoretical modeling are presented.     

Three-dimensional atom mapping of boron in implanted silicon

The redistribution of boron in highly implanted 〈1 0 0〉 silicon (10 keV; 5×10¹⁵ at/cm²) annealed at 600 °C for 1 h was studied using both laser-assisted wide-angle atom probe (LaWaTAP) and secondary ion mass spectrometry (SIMS). As expected, the concentration was found to increase steeply to 10²¹ boron atoms/cm³ at a distance close to 35 nm and to decrease slowly to 10¹⁹/cm³, a value close to the boron level of the silicon substrate. For depth under 75 nm, the implantation profile of boron as given by LaWaTAP was found very close to that given by SIMS investigations without any calibration of the LaWaTAP data. For larger depth, the LaWaTAP profile is observed above that of SIMS. Detection limits of LaWaTAP for low dopant concentrations are discussed. The contribution of the background noise in the spectrum and sampling errors are considered. Fine-scale fluctuations not detected in SIMS profile and related to clustering were evidenced in LaWaTAP maps and profiles. Numerous boron clusters lying on {0 0 1} planes parallel to the implanted surface, a few nanometer in size, were identified and interpreted as boron interstitial clusters (BICs), in agreement with Cristiano et al. observations. They contained between 50 and 300 atoms (Si and B). This is much higher than that generally assumed in particular in ab-initio modelling where a few atoms BICs are considered. These clusters contained 7 at% of boron in average.     

Influence of Forced/Natural Convection on Segregation During the Directional Solidification of Al-Based Binary Alloys

We analyzed the columnar solidification of a binary alloy under the influence of an electromagnetic forced convection of various types and investigated the influence of a rotating magnetic field on segregation during directional solidification of Al-Si alloy as well as the influence of a travelling magnetic field on segregation during solidification of Al-Ni alloy through directional solidification experiments and numerical modeling of macrosegregation. The numerical model is capable of predicting fluid flow, heat transfer, solute concentration field, and columnar solidification and takes into account the existence of a mushy zone. Fluid flows are created by both natural convection as well as electromagnetic body forces. Both the experiments and the numerical modeling, which were achieved in axisymmetric geometry, show that the forced-flow configuration changes the segregation pattern. The change is a result of the coupling between the liquid flow and the top of the mushy zone via the pressure distribution along the solidification front. In a forced flow, the pressure difference along the front drives a mush flow that transports the solute within the mushy region. The channel forms at the junction of two meridional vortices in the liquid zone where the fluid leaves the front. The latter phenomenon is observed for both the rotating magnetic field (RMF) and traveling magnetic field (TMF) cases. The liquid enrichment in the segregated channel is strong enough that the local solute concentration may reach the eutectic composition.