T. L. Lee

Evolution of vacancy ordering and defect structure in epitaxial YSi2−x thin films on (111)Si

The evolution of vacancy ordering and defect structure in epitaxial YSi2−x thin films on (111)Si have been studied by both conventional and high‐resolution transmission electron microscopy. Epitaxial YSi2−x with an ordered vacancy structure was grown on (111)Si by rapid thermal annealing. In samples annealed at 500 °C for 120 s epitaxial YSi2−x was found to form. After annealing at 600 °C for 15 s, the appearance of additional diffraction spots is attributed to the formation of an ordered vacancy superstructure in the epitaxial YSi2−x thin films. In samples annealed at 600 °C for longer time or higher temperatures, the splitting of extra diffraction spots is correlated to the formation of an out‐of‐step structure. Streaking of the split diffraction spots in the diffraction pattern is attributed to the presence of an out‐of‐step structure with a range of M values. The M was found to settle down to 2 after high‐temperature and/or long time annealing. Planar defects in YSi2−x films were analyzed to be stacki...

Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on (111)Si at low temperatures

Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on atomically clean (111)Si at low temperatures have been studied by both conventional and high‐resolution transmission electron microscopy, Auger electron spectroscopy, and x‐ray diffraction. A 10‐nm‐thick yttrium thin film, deposited onto (111)Si at room temperature, was found to completely intermix with Si to form an 11‐nm‐thick amorphous interlayer. Crystalline Y5Si3 and Si were observed to nucleate first within the amorphous interlayer in samples annealed at temperatures lower than 200 °C. Epitaxial YSi2−x was found to be the only phase formed at the interface of amorphous interlayer and crystalline Si in samples annealed at temperatures higher than 250 °C. In as deposited 20‐ to 60‐nm‐thick Y thin films on silicon samples, crystalline Y5Si3, Si, and YSi and a 2.5‐nm‐thick amorphous layer were found to be present simultaneously. Good correlations were found among difference in atomic size between metal and Si atoms, the calculated...

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.

Interfacial reactions in ultrahigh vacuum deposited Y‐Si multilayer thin films

Interfacial reactions of ultrahigh vacuum deposited Y‐Si multilayer thin films have been studied by both conventional and high‐resolution transmission electron microscopy, Auger electron spectroscopy, and x‐ray diffraction. An amorphous Y‐Si intermixing layer with a composition approximately equal to YSi2 was found to form in multilayer films with a composition ratio of 1Y:2Si at room temperature. Homogenization in atomic composition in the amorphous phase proceeded in samples annealed at 250–350 °C. In samples annealed at 400 °C for 30 min, the amorphous layer was completely transformed to crystalline YSi2. The formation of crystalline Y5Si3 and YSi was detected in as‐deposited samples with concentration ratios 1Y:1Si and 5Y:3Si as well as in samples prepared with excess Y. Y5Si3 was the only silicide phase present in 5Y:3Si films after 400 °C annealing. The results indicated that the phase formation and stability in Y‐Si multilayers depend critically on the composition. Based on the prediction of a grow...

High-resolution transmission electron microscopy investigation of interfaces in metal-silicon systems

Abstract High-resolution transmission electron microscopy (HRTEM) has been fruitfully applied to study metal/Si interfaces, formation and growth of amorphous interlayers, first nucleated phases, simultaneous occurence of multiphases, epitaxial silicide-Si interfaces, single-crystal silicide-silicon interfaces, twin boundaries and other defects in metal/Si systems. In this paper, examples are presented to highlight the contributions of HRTEM to the understanding of interfaces in metal/Si systems.

High resolution electron microscopy of amorphous interlayers between metal thin films and silicon.

High‐resolution electron microscopy of amorphous interlayers (a‐interlayer) formed by solid‐state diffusion between metal thin films and silicon is reviewed. In this paper, an overview of the development is presented. Pertinent data obtained on the growth kinetics and structure of a‐interlayers in polycrystalline metal thin films on single‐crystal silicon are reported.

NANOMETER THICK SI/SIGE STRAINED-LAYER SUPERLATTICES GROWN BY AN ULTRAHIGH-VACUUM CHEMICAL-VAPOR-DEPOSITION TECHNIQUE

High quality Si/Si1−xGex superlattices having layers as thin as 1.5 nm have been grown by an ultrahigh vacuum/chemical vapor deposition system. High‐resolution double‐crystal x‐ray diffraction, and conventional and high‐resolution cross‐sectional transmission electron microscopy were used to evaluate the crystalline quality of these superlattices. A dynamical x‐ray simulation program was employed to analyze the experimental rocking curves. Excellent matches between experimental rocking curves and simulated ones were obtained for all superlattices with various periodicity. A cross‐sectional transmission electron micrograph of an 80 period Si(4.2 nm)/Si0.878Ge0.122 (1.5 nm) superlattice, in which each individual layers was clearly resolved, demonstrated the capability of this growth technique for nanometer thick layer deposition.