Formation Of Amorphous Interlayer Research Articles

Solid state amorphization in metal/Si systems

The formation of amorphous interlayer (a-interlayer) by solid-state diffusion in diffusion couples has been one of the most challenging problems in condensed matter physics in recent years. The a-interlayer has been found to occur in all refractory metal/Si and a number of rare-earth (RE) metal and platinum group metal and crystalline silicon systems. A systematic survey and review of extensive studies on the subject in the past years showed that (1) a negative heat of mixing provides the driving force for the reaction and fast diffusion of one component in the other preempts the formation of crystalline compounds, (2) the growth follows a linear law at the initial stage with activation energy around 1–1.5 eV for refractory metal/Si systems and 0.5 eV for RE metal/Si systems, (3) the dominant diffusing species is Si, (4) the stability of amorphous interlayer depends on the composition, (5) simultaneous presence of multiphases in the initial stage of metal/Si interaction, and (6) good correlations between physical parameters and kinetic data. From the investigation of amorphous interlayers, mechanisms of roughing of epitaxial RE silicide/(0 0 1)Si interface, formation of stacking faults and pinholes in RE silicides have gained in basic understanding. The insight led to successful growth of pinhole-free epitaxial RE silicide layer on (1 1 1)Si. Furthermore, the enhanced formation of technologically important C54-TiSi 2 by high temperature sputtering, a thin interposing Mo layer and tensile stress can all be explained involving some aspects of the amorphous interlayers.

The determination of dominant diffusing species in the growth of amorphous interlayer between Gd and Si thin films by a Mo cluster marker experiment

The dominant diffusing species in the formation of amorphous interlayer between Gd and Si thin films have been determined by a Mo cluster marker experiment. Multilayered metal thin films were deposited on (001) Si in an ultrahigh vacuum electron beam evaporator. The positions of the Mo cluster markers relative to the Si substrate, before and after heat treatment, were determined by transmission electron microscopy and energy dispersive x-ray as well as autocorrelation function analysis. The displacement of the Mo cluster markers in the amorphous interlayer during the Gd–Si interdiffusion indicates that Si atoms constitute the dominant diffusing species during the growth of the amorphous interlayer.

Formation of amorphous interlayers by solid-state diffusion in Ti thin films on epitaxial Si–Ge layers on silicon and germanium

The formation of amorphous interlayers (a-interlayers) by solid-state diffusion in ultrahigh-vacuum-deposited polycrystalline Ti thin film on germanium and epitaxial Si1−xGex (x=0.3, 0.4, and 0.7) alloys grown on (001)Si has been investigated by transmission electron microscopy and Auger electron spectroscopy. Amorphous interlayers, less than 2 nm in thickness, were observed to form in all as-deposited samples. The growth of the a-interlayers was found to vary nonmonotonically with the composition of Si–Ge alloys in annealed samples. On the other hand, the formation temperature of crystalline phase was found to decrease with the Ge content. The results are compared with those of the Ti/Si system.

Formation of Amorphous Interlayers by Solid–State Diffusion in Ti Thin Films on Si–ge Layers on Silicon and Germanium

ABSTRACTThe formation of amorphous interlayers (a–interlayers) by solid–state diffusion in ultrahigh vacuum deposited polycrystalline Ti thin film on germanium and Sil-xGex alloys grown on (001)Si has been investigated by transmission electron microscopy and Auger electron spectroscopy.Amorphous interlayers, less than 2 nm in thickness, were observed to form in all as–deposited samples. The growth of a–interlayers was found to vary non–monotonically with the composition of Si–Ge alloys in annealed samples. On the other hand, the formation temperature of crystalline phase was found to decrease with the Ge content. The results are compared with that of the Ti/Si system. The formation mechanism are discussed in terms of thermodynamic and kinetic factors.

Formation of amorphous interlayers in ultrahigh vacuum deposited yttrium thin films on (111)Si

Formation of amorphous interlayers (a interlayers) has been observed in the interfacial reactions of ultrahigh vacuum deposited yttrium thin films on atomically clean (111)Si at low temperatures. The observation of the a interlayer in the Y/Si system represents the first report of solid-state amorphization for rare-earth metal/Si systems. The Y/Si system is also the only system found to date among all metal/Si systems in which the a interlayer can be grown to a thickness exceeding 10 nm during deposition at room temperature. A process involving significant diffusion of both Y and Si atoms is proposed to account for the dependence of amorphization on the thickness of deposited yttrium films.

Electrical and Microstructural Characteristics of Ti Contacts on (001)Si

ABSTRACTAn investigation of the electrical and microstructural characteristics of the Ti contact on silicon has been carried out. The presence of As in Ti/n+-Si samples was found to retard the formation of poly crystalline silicides compared with that in Ti/p+-Si samples with BF2+ implantation. The variations of Schottky barrier height, contact resistance and junction leakage current were correlated with microstrucxtural changes. The influences of the formation of amorphous interlayer between Ti and Si on the elctrical characteristics are discussed.

Formation of amorphous interlayers by solid-state diffusion in ultrahigh-vacuum-deposited polycrystalline Nb and Ta thin films on (111)Si

The formation of amorphous interlayers (a-interlayers) in ultrahigh-vacuum-deposited polycrystalline Nb and Ta thin films on (111)Si has been studied by cross-sectional transmission electron microscopy. The growth of a interlayers was found to follow a linear growth law initially in samples annealed at 450–500 °C and 550–625 °C for Nb/Si and Ta/Si, respectively. The growth then slows down and deviates from a linear growth behavior as a critical thickness of the a interlayer was reached. The a interlayer/crystalline Si interface was found to be rather smooth. The roughness of the interface between the Nb layer and a interlayer was observed to decrease with annealing temperature and time. The observation suggested that the growth of the a interlayer was interface reaction controlled initially.

Formation of amorphous interlayers by a solid-state diffusion in Zr and Hf thin films on silicon

The formation of amorphous interlayers (a interlayers) in polycrystalline Zr and Hf thin films on single-crystal (111)Si has been observed by cross-sectional transmission electron microscopy. The growth of a interlayers in group IVa metal thin films on silicon was found to exhibit similar behavior but was fundamentally different from those of metal-metal diffusion couples. The growth of a interlayers was found to follow a linear growth law initially then slowed down until a critical thickness was reached. Si was found to be the dominant diffusing species. Good correlation was found among the maximum thickness of the a interlayer, the difference in atomic size between metal and Si, the activation energy of the linear growth, and the largest heats of formation of the respective silicides.

Formation of Amorphous Interlayers by Solid-State Diffusion in Refractory Metal/Silicon Systems

AbstractFormation and growth of amorphous interlayers (a-interlayers) in nine refractroy metal and silicon systems by solid-state diffusion have been investigated by conventional and high resolution transmission electron microscopy. The amorphous interlayers were found to form in samples annealed at 350–650 °C. The growth was found to follow a linear growth law initially then slow down until a critical thicknees was reached. The interface structures were examined. The correlations among difference in atomic size between metal and Si atoms, growth rate and activation energy of the linear growth, critical and maximum a-interlayer thickness, the largest heat of formation energy for crystalline silicides, the calculated free energy difference in forming amorphous phase as well as atomic mobility in refractroy metal/silicon systems are discussed.

High Resolution Transmission Electron Microscope Study of UHV Deposited Titanium Thin Films on (001), (III) and (011)Si

AbstractHigh resolution transmission electron microscopy has been applied to study the formation of amorphous interlayers by solid-state diffusion in ultrahigh vacuum deposited Ti thin films on (001), (111) and (011)SiThe interface structures of as deposited and annealed samples were examined. The disordered regions at the a-interlayer/c-Si interfaces were found to be most and least extensive in (011) and (111) samples, respectively. Growth behaviors of a-interlayers are described. The amorphization appeared to be initiated at the grain boundaries of Ti thin films. Ti5 Si3 was identified to be the phase formed at the initial stage of the interfacial reactions by HREM in conjunction with the optical diffraction.

The formation of amorphous interlayers by solid-state interdiffusion between Pd-Er and Si

Interest has been maintained in the way silicides form between a deposited metal and silicon because the relationship between the contact potential and boundary reaction remains obscure. This is partially because the cleanliness as well as the vicinality of the silicon surface can change the temperature dependence and homogeneity of the reaction products and thus the presence of localised strains in the silicon. Chemical surface analysis and electrical measurements thus need careful correlation with microstructural examination and it was with this in mind, at the suggestion of K.N. Tu, that we followed up the work of his group on the behaviour of a rare earth-noble metal alloy pair on silicon (Pd-Er/Si) with a microscopical study. The more interesting results are summarised below.