ELECTROMIGRATION IN THIN FILMS : THE EFFECT OF SOLUTE ATOMS ON GRAIN BOUNDARY DIFFUSION

Des études portant sur des conducteurs en couche mince d'Al, d'Au et de Cu ont montré que l'addition de certains éléments d'alliage réduit considérablement la vitesse d'électromigration aux joints de grains des atomes du solvant. Les résultats quantitatifs obtenus jusqu'à maintenant sont résumés. Pour l'Au ces résultats sont comparés à des expériences sur l'autodiffusion aux joints de grains faites au moyen de traceurs radioactifs. Deux conclusions sont établies. 1) En général la force (appelée charge effective) exercée par un courant continu sur des atomes placés dans les joints de grains n'est pas très différente de celle exercée sur un atome placé dans le réseau (à un facteur de 2 près). 2) Les résultats sur l'électromigration du Cu, du Mg et du Ni dans les joints de grains de l'Al suggèrent que l'adsorption de ces atomes sur les joints de grains est inversement proportionnelle aux différentes limites de solubilité.It has been shown that certain alloying additions are effective in reducing the rate of electromigration of the host element in thin film conductors of Al, Au and Cu. The quantitative results obtained up to now are summarized. For Au these results are correlated with grain boundary autodiffusion data obtained by means of radioactive tracers. Two conclusions are reached. 1) In most cases the force, usually called effective charge, excerted by a direct current on atoms within grain boundaries is not very different (within a factor of 2) from the force on atoms in the lattice. 2) The electromigration data for Cu, Mg and Ni atoms in Al grain boundaries suggest that the adsorption of these atoms on grain boundaries is inversely proportional to the respective solubility limits

Interfaces in Silicides

The role of interfaces with respect to the use of silicides in electronic technology is analyzed from two different points of view. To begin with interfaces of different nature, grain boundaries, stacking faults, etc... are examined in the perspective of their metallurgical properties as they affect silicide formation by solid state reaction, diffusion of silicon dopants, nucleation of the new phases.... While considering those metallurgical aspects, reference is made also to the integration of silicides in silicon device technology, and to the relations between metallurgical parameters and electrical properties, e.g. the density of stacking faults and the resistivity of WSi2. In a shorter second section the previous order is reversed : attention is focused on the electrical properties of silicide silicon interfaces in ohmic and rectifying contacts, and on the use of epitaxial silicides in metal base transistors, where one desires such perfect match between silicide layer and silicon as to allow the transfer of ballistic electrons across the layer

Diffusion - Reaction: The Oxidation of Silicides in Electronics and Elsewhere

The present article is a review of the up-to-date state of knowledge about the oxidation of silicide in film and “bulk" forms. The oxidation of silicides is analyzed with due respect to thermodynamics but the emphasis is placed on the kinetics of the process. A distinction is made between what occurs with silicide thin films used as conductors in the electronic industry, where the silicides are always in presence of excess silicon, and in the oxidation of “bulk" silicide structural parts where this condition is not encountered. Use is made of a graphical approach that was originally used to illustrate the oxidation of Si itself. The kinetic analysis provides at least a qualitative explanation of the conditions that must be met in the electronic industry to maintain the integrity of silicide layers in oxidizing atmospheres, and of the conditions that cause the occurrence of the “pest" phenomenon in structural parts. Although attention is directed mostly to silicides, it is clear that the approach and the model used are valid for other refractory compounds, so that allusions are made also to aluminides and beryllides, etc. Marker experiments to probe the motion of atoms in the silicides during oxidation are analyzed. It is suggested that the relation between electron concentrations and oxidation rates is related to the decomposition of oxygen molecules