Texture in thin film silicides and germanides : a review

Silicides and germanides are compounds consisting of a metal and silicon or germanium. In the microelectronics industry, silicides are the material of choice for contacting silicon based devices (over the years, CoSi2, C54-TiSi2, and NiSi have been adopted), while germanides are considered as a top candidate for contacting future germanium based electronics. Since also strain engineering through the use of Si1-xGex in the source/drain/gate regions of MOSFET devices is an important technique for improving device characteristics in modern Si-based microelectronics industry, a profound understanding of the formation of silicide/germanide contacts to silicon and germanium is of utmost importance. The crystallographic texture of these films, which is defined as the statistical distribution of the orientation of the grains in the film, has been the subject of scientific studies since the 1970s. Different types of texture like epitaxy, axiotaxy, fiber, or combinations thereof have been observed in such films. In recent years, it has become increasingly clear that film texture can have a profound influence on the formation and stability of silicide/germanide contacts, as it controls the type and orientation of grain boundaries (affecting diffusion and agglomeration) and the interface energy (affecting nucleation during the solid-state reaction). Furthermore, the texture also has an impact on the electrical characteristics of the contact, as the orientation and size of individual grains influences functional properties such as contact resistance and sheet resistance and will induce local variations in strain and Schottky barrier height. This review aims to give a comprehensive overview of the scientific work that has been published in the field of texture studies on thin film silicide/germanide contacts. Published by AIP Publishing

Development and fabrication of improved Schottky power diodes

Reproducible methods for the fabrication of silicon Schottky diodes have been developed for tungsten, aluminum, conventional platinum silicide, and low temperature platinum silicide. Barrier heights and barrier lowering under reverse bias have been measured, permitting the accurate prediction of forward and reverse diode characteristics. Processing procedures have been developed that permit the fabrication of large area (about 1 sq cm) mesageometry power Schottky diodes with forward and reverse characteristics that approach theoretical values. A theoretical analysis of the operation of bridge rectifier circuits has been performed, which indicates the ranges of frequency and voltage for which Schottky rectifiers are preferred to p-n junctions. Power Schottky rectifiers have been fabricated and tested for voltage ratings up to 140 volts

Development and Characterization of Next-Generation Contact Materials for Nanoelectromechanical Switches

Nanoelectromechanical (NEM) switches were identified by the semiconductor industry as a low-power beyond CMOS technology. However, the reliability of the contact interface currently limits the commercialization of NEM switches, as the electrical contact has to be able to physically open and close up to a quadrillion (10^15) times without failing due to adhesion (by sticking shut) or contamination (reducing switch conductivity). These failure mechanisms are not well understood, and materials that exhibit the needed performance have not been demonstrated. Thus, commercially viable NEM switches demand the development of novel contact materials along with efficient methods to evaluate the performance of these materials. To assess contact material candidates under NEM switch-like conditions, we developed a novel, high-throughput electrical contact screening method based on atomic force microscopy (AFM) that enables billions of contact cycles in laboratory timeframes. We compared the performance of self-mated and dissimilar single asperity Pt and PtxSi contacts under forces and environments representative of NEM switch operation and cycled up to 10 million times. The contact resistance increased by up to three decades due to cycling-induced growth of insulating tribopolymer in the case of Pt-Pt contacts whereas PtxSi exhibited reduced tribopolymer formation. We also pursued the development of novel contact material candidates that are highly conductive, minimally adhesive, chemically inert, mechanically robust, and amenable to CMOS fabrication processes. One promising candidate material is platinum silicide (PtxSi). The controlled diffusion of thin films of amorphous silicon and platinum allowed us to tune the chemical composition of PtxSi over a wide range (

Advanced source and drain contact engineering for multiple- gate transistors

Ph.DDOCTOR OF PHILOSOPH

High-purity Refractory Metals for Thin Film Metallization of VLSI

It is shown that cast targets of highly pure refractory metals like W, Mo, Ti, Ta, Co, etc. and their compounds can be produced by means of a set of vacuum-metallurgical techniques—by vacuum high-frequency levitation, EB floating zone melting, EB melting, and electric arc vacuum melting as well as chemical purifying by ion exchange and halides. The cast refractory metal targets are extremely pure and chemically homogeneous. For magnetron sputtering and laser ablation, the cast silicide targets are also produced. The study reveals the possibilities and conditions of depositing the silicides and titanium-tungsten barrier layers by both the laser evaporation and magnetron sputtering. The physical and structural parameters as well as a trace impurity composition of sputtered metals and deposited thin films are studied by grazing-beam incidence X-ray diffraction, Auger electron spectroscopy, Rutherford backscattering of helium ions, mass spectrometry with inductively coupled plasma, etc

Supported Mono And Bimetallic Platinum And Iron Nanoparticles Electronic, Structural, Catalytic, And Vibrational Properties

Catalysis technologies are among the most important in the modern world. They are instrumental in the realization of a variety of products and processes including chemicals, polymers, foods, pharmaceuticals, fuels, and fuel cells. As such, interest in the catalysts that drive these processes is ongoing, and basic research has led to significant advances in the field, including the production of more environmentally friendly catalysts that can be tuned at the molecular/atomic level. However, there are many factors which influence the performance of a catalyst and many unanswered questions still remain. The first part of this work is concerned with the factors that influence the catalytic properties (activity, selectivity, and stability) of supported Pt and Pt-M nanoparticles (NPs). These factors are a synergistic combination of size, composition, support, oxidation state, and reaction environment (i.e. adsorbates, temperature, pressure, etc.). To probe the catalytic properties of complex and dynamic NP systems we have used MeOH decomposition and oxidation reactions, each of which has significant environmental and economic potential. We have given some emphasis to the state of NP oxidation, and with the aid of X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), have followed the formation and temperature-dependent evolution of oxide species on Pt NPs. Further, we have explored how these species behave under the conditions of our probe reactions using a packed-bed mass flow reactor coupled to a quadrupole mass spectrometer (QMS). To carry out our investigations we exploit a NP synthesis method which is rather novel to nanocatalysis, micelle encapsulation. Since most available experimental techniques give information on ensemble averages, control over size distributions in NP samples is critical if unambiguous results are to be obtained. Micelle encapsulation allows us this control with several unique, inherent iv advantages. It is to this end that micelle encapsulation has allowed us to probe the detailed structure of small (~1 nm), supported, Pt NPs with extended X-ray absorption fine structure spectroscopy (EXAFS). Furthermore, we were able to explore experimentally, for the first time, the vibrational density of states (VDOS) of supported, isolated, monodispersed, mono and bimetallic NP systems via nuclear resonant inelastic X-ray scattering (NRIX). These synchrotron-based techniques (EXAFS, NRIXS) rely heavily on the monodispersity of the NP ensemble for reliable informatio

Growth and characterisation of thin film superconductors on oxides, silicon and silicides

Includes bibliographical references.High Tc thin film superconductors are of great interest because of their potential applications, particularly in the microelectronics field. A successful superconductor microelectronic technology depends both on the ability to grow good quality superconducting thin films, and the need to incorporate these films into multilayer semiconductor devices. In this work the growth and characterisation of high Tc Y₁Ba₂Cu₃O₇ films by inverted cylindrical magnetron sputtering and pulsed ruby laser ablation on oxides, silicon and silicides is investigated. The inverted cylindrical magnetron sputter system has been effectively used to counter the problem of negative ion re-sputtering found in sputter deposition of oxide films. The optimal growth conditions for both these techniques have been determined. Rutherford backscattering spectrometry is used to obtain thickness and stoichiometry information, while X-ray diffraction gave phase and orientational data. Ion channeling was used for structural analysis and Auger electron spectroscopy was used to determine the homogeneity of the films