The effective heat of formation (ΔH’) concept allows heats of formation to be calculated as a function of concentration. In this work the effective heat of formation rule is used to predict first phase formation in metal‐aluminum thin‐film systems and to predict subsequent phase sequence for thin metal films on thick aluminum or thin aluminum on thick metal substrates. The effective concentration at the growth interface is taken to be that of the lowest temperature eutectic (liquidus) for the binary system. Although the effective heat of formation rule may predict that formation of a certain phase would lead to the largest free energy change, this phase does not necessarily form at the moving reaction interface if it has difficulty to nucleate. By excluding phases with a large number of atoms per unit cell and which thus have difficulty to nucleate, the effective heat of formation rule successfully predicts first phase aluminide formation for all 15 metal‐aluminum binary systems for which experimental data could be found. It is also shown how the effective heat of formation rule can be used to predict formation and decomposition of aluminide phases in contact with each other or in contact with their component metals.

Prediction of phase formation sequence and phase stability in binary metal-aluminum thin-film systems using the effective heat of formation rule

A review of thin-film aluminide formation

This paper describes a method to improve the electromigration capacity of Al‐Cu or Al thin‐film interconnection metallurgy by incorporating a layer of intermetallic compounds of Al and transition metals. The improvement in lifetime can be 100 times greater than comparable Al‐Cu structures tested under the same conditions. Certain structural properties of the intermetallic compounds have been related qualitatively to the failure mode and electromigration lifetime. Results are discussed in an attempt to clarify the mechanisms by which an ordered phase (compound layer) can improve electromigration lifetime. Life‐test data obtained from the thin‐film metallurgy with Al–transition‐metal compound structures indicate that improvements can be achieved by one or a combination of the following factors: (a) blocking void propagation through the film, (b) reducing the rate of mass transport by electromigration, and (c) eliminating divergent damage sites by increasing the degree of preferred grain orientation. In many cases, the thickness of the intermetallic layer can be adjusted to yield a significant improvement in lifetime with only a small increase in stripe resistance.

Intermetallic compounds of Al and transitions metals: Effect of electromigration in 1-2-μm-wide lines

Thin film compound phase formation sequence: An effective heat of formation model

Aluminum alloys have virtually replaced aluminum thin films for interconnections in very large‐scale integration because of their improved reliability. Mechanical stress is a problem of growing importance in these interconnections. Stress as a function of temperature was measured for thin aluminum films on an oxidized silicon substrate and several aluminum alloys and layered films consisting of silicon, copper, titanium, tungsten, tantalum, vanadium, and TiSi2. Solid‐state reactions of the aluminum with the additives and with the ambient during thermal cycling will occur, and depending on what compounds have formed and at what temperature, this will determine the morphology and reliability of the metallization. The measurement technique, based on determination of wafer curvature with a laser scanning device, directly measures the total film stress and reflectivity in situ as a function of temperature during thermal cycling. Changes in stress were detected when film composition and structure varied and wer...

Mechanical stress as a function of temperature for aluminum alloy films

Intermetallic coumpound formation at metal–metal interfaces was observed for thin film couples of Al and transition metals such as Cr, Ti, Hf, Zr, Co, Ta, Pd, and Pt. The Al–Cr system was investigated in some detail using a conductance method and nuclear backscattering for reaction‐rate measurements. The compounds CrAl7 and Cr2Al11 were identified and their growth was found to be diffusion controlled. The temperature dependence of the rate constant for CrAl7 obeyed an Arrhenius plot from 300° to 450 °C with an activation energy of 1.91±0.1 eV. The Al‐rich phases of the remaining transition metals were investigated; the compounds either exhibited a planar interface with parabolic growth kinetics or an irregular interface with nonparabolic growth. An empirical relationship involving the melting point and stability of the compounds was proposed to explain the different growth kinetics.

Kinetics of compound formation in thin film couples of Al and transition metals

KINETICS OF COMPOUND FORMATION IN THIN FILM COUPLES OF Al AND TRANSITION METALS.

Anomalous growth of HfAl3 is observed on 400°C annealing of evaporated thin‐film samples consisting of 900 A aluminum, on 1000 A hafnium, 6000 A aluminum and SiO2 substrates A continuous layer of HfAl3 forms at the aluminum–hafnium interface nearer the surface, but not at the deeper interface The surface HfAl3 layer then continues to grow, fed by diffusion of underlying aluminum through the intervening hafnium layer Needlelike precipitates of HfAl3 are formed along the underlying aluminum grain boundaries Observations are made by nuclear backscattering, Auger electron spectroscopy, and transmission electron microscopy Similar behavior is observed in Al–Zr–Al layers

Anomalous growth of HfAl3 in thin films

Structure of Al-Hf Films

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Kinetics of compound formation in thin film couples of Al and transition metals

KINETICS OF COMPOUND FORMATION IN THIN FILM COUPLES OF Al AND TRANSITION METALS.

Anomalous growth of HfAl3 in thin films

Structure of Al-Hf Films