Materials Science Reports最新文献

We review the properties of noble-metal layers deposited on silicon substrates. The microscopic properties of the interface are presented. The relevance of these results to macroscopic phenomena like diffusion, adherence of the metal layer and electrical properties of the junctions is discussed.

Methods for the preparation of amorphous phases by means of high pressures are reviewed briefly. The solid-state amorphization of various elements (carbon, germanium, silicon), compounds (H₂O, SiO₂, SnI₄, LiKSO₄, Gd₂(MoO₄)₃), and alloys (CdSb, ZnSb, GaSb, AlGe) is considered. The relationship between spontaneous solid-state amorphization induced by thermobaric treatment, and features of TCP phase diagrams of the materials amorphized is discussed. Liquit-to-amorphous state quenching under high presusres, and the influence of pressure on the properties of amorphous materials are also included.

This review presents an overview on the recent progress achieved in the epitaxial growth of Ni and Co silicides on Si(111) by UHV deposition techniques. While focusing on the disilicides NiSi₂ and CoSi₂, the discussion includes as well some less Si-rich intermediate phases which occur during the solid phase reaction of the metal with Si. They turn out to be especially important in the case of Ni. For both disilicides the merits of using two-step deposition processes are emphasized in which an ultrathin template is formed first by pure metal deposition or by codeposition in order to pin subsequent epitaxial growth. The defect structure and its dependence on the growth parameters are analysed in detail for CoSi₂, this being the technologically more important material due to the possibility to form structures buried in Si and even $\text{CoSi}{}_2\text{Si}$ superlattices. A substantial part of the review is devoted to the electrical properties of Ni and Co silicides and their relation to the structural parameters. In particular we discuss the Schottky barrier at type-A and type-B $\text{NiSi}{}_2\text{Si(111)}$ interfaces as well as interface scattering and magneto-transport in thin CoSi₂ films. Finally, one of the most promising applications is described, namely the permeable base transistor with a CoSi₂ gate embedded in Si.

An overview of atomic layer epitaxy (ALE) for III–V compounds using metalorganic and hydrbide sources had its possibilities for device fabrication are described. Surface reactions involving the adsorption and desorption processes of source molecules play an important role in the self-limiting growth which is at the very heart of ALE. Various types of ALEs have been developed using metalorganic sources mainly for GaAs growth. Different models have been proposed to explain the self-limiting growth process. Homoepitaxial layers of GaAs, InP, GaP, InAs and lattice-matched ternary alloys all grow in a self-limiting manner. On the other hand, deviations were observed for some lattice-mismatched heteroepitaxial systems, arising from the large strain energy at the heterointerface and the exchange reactions between epitaxial layer atoms and substrate atoms. The growth of (GaAs)_m(GaP)_n strained-layered superlattices has demonstrated the large potential of ALE in superlattice growth, including monolayer superlattices. The reduction of carbon contamination, which was a serious issue in GaAs ALE, has been achieved and carrier concentrations ranging from 10¹⁴ to 10²⁰ cm⁻³ for n-type GaAs and 10¹⁵ to 10²¹ cm⁻³ for p-type GaAs can now be obtained by control of growth conditions and doping levels. ALE offers unique possibilities for low-temperature growth, selective growth, side-wall growth and uniform-thickness growth. The ALE technique is now being applied to the growth of multilayers for high-speed and optoelectronic devices.

The technique of synthesizing buried epitaxial silicides by high-dose ion implantation and subsequent high-temperature annealing is reviewed. This technique, called mesotaxy, is at present the best way to produce high-quality buried epitaxial CoSi₂ in (100) Si and buried α- and β-FeSi₂ in (111) Si. In this report the experimental work of the first four years of mesotaxy is reviewed. The review begins with a brief introduction to epitaxial silicides, ion beam synthesis, and mesotaxy. This is followed by a discussion of the simulation of high-dose ion implantation. Next the microstructure during mesotaxial layer growth is described, including its dependence on implantation and annealing parameters. After the summary of the experimental results of the microstructure, particular emphasis is placed on discussing the growth process and developing a basic understanding of the mesotaxial process including nucleation and growth of precipitates during irradiation and coarsening, coalescence, and layer formation during annealing. Properties of buried CoSi₂ and NiSi₂ layers in (100) and (111) Si are reviewed and discussed. Results on the formation of buried NiSi₂, (Ni_1−xCo_x)Si₂, α- and β-FeSi₂, CrSi₂ and ErSi₂ layers are also summarized. The first device applications are reported in which ion beam synthesis provides significant advantages over other techniques.

Thin film interactions for ternary systems (metalmetalSi and metalGeSi) and quaternary systems (metalmetalGaAs and metalmetalGeSi) are reviewed in this paper. Interactions between silicon and metal alloys are classified into Sisolid solutions, Siamorphous phases and Siintermetallic compounds. Different reaction behaviors for these three categories and their respective applications are discussed. The outcomes of the reaction are analyzed using knowledge from binary silicide formation, solid solubilities of binary silicides and metalmetal interactions. For GaAs, emphasis is placed on thermal stabilities of different metallization schemes. Both amorphous alloys and intermetallic compounds are considered. The metalGeSi reactions are illustrated using specific examples and the results are explained based on data obtained from binary silicide and germanide formation. The energetically more favorable metalSi reaction than the metalGe reaction often causes composition changes in GeSi, thus thermally stable contacts are addressed.

Electromigration (EM) in thin-film interconnection lines is one of the major concerns for the development of ULSI devices, employing advanced design rules. Starting from the early sixties, several techniques have been used to characterize this phenomenon, producing a large, but frequently contradictory, amount of data. Different models have been proposed, but the complete comprehension of the basic physical mechanisms leading to EM is still unsatisfactory. In this work, well-established results and unsolved problems are reviewed. The physical model based on the general diffusion theory is used to describe the EM failure mechanism; the influence of the different stress parameters (temperature, current density, mechanical stress), of material properties (structural inhomogeneities, chemical composition) and line topography are taken into account. The accelerated methods employed to evaluate the EM resistance of the lines are classified into destructive and non-destructive, according to their effects on the samples under test. In the first group, a core position is occupied by the so-called median time to failure (MTF) technique, that has been extensively employed to gather results on many different materials and structures. Within the same group a survey is given of resistometric methods and faster techniques, based on a further acceleration of EM by means of high current densities and related Joule heating. The parameters extracted with these techniques are discussed in relation with the MTF results. The choice of a suitable statistical distribution, related to both the times to failure (TTFs) and the parameters used to estimate the EM performance with alternative methods, is also reviewed. More recently, an increasing importance has been achieved by non-destructive techniques able to give reliable information about the phenomenon without irreversibly damaging the samples. An important section of this work is devoted to the discussion of these techniques, which are mainly based on the accurate measurement of the resistance drift or low-frequency noise induced by the damage occurring at microscopic level. In the course of the discussion, particular emphasis is given to the comparison of the results obtained with the different techniques and to the improvement achievable by employing new materials and structures, including different aluminum alloys and Al/refractory metal sandwiches.

In this review paper, we first present an historical perspective of theoretical work and some early experimental work in the field of dislocations in strained-layer epitaxy. Equilibrium strained-layer theory is presented in a didactic fashion. Attempts at kinetic modifications of equilibrium theory are also discussed. Quantitative and qualitative experimental observations are summarized in view of theory and current understanding. The more important potential applications of mismatched semiconductor epitaxy and the materials processing necessary to reach these goals are presented.

The transport processes in transition metal oxides exposed to an oxygen potential gradient are analyzed as the prerequisite for an understanding of their degradation. For model systems, chemical diffusion, tracer self-diffusion and impurity tracer diffusion are studied, and both cation vacancies and cation interstitials are considered as defects in the oxide. The theoretical and experimental results for these transport processes in an applied oxygen potential gradient are reviewed. Using these results, two degradation processes in an oxygen potential gradient are investigated: demixing in doped oxides and morphological changes of the crystal during transport.