Transient annealing as a tool for the investigation of thin-film–substrate solid-phase reactions

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Abstract
The solid‐phase reaction of a thin film and a substrate induced by a transient annealing in the solid phase is analyzed in detail. The technique is based on the scanning of a line‐shaped energy beam. At a given point on the sample the transient process can be considered equivalent to an isothermal one at an effective temperature for an effective time. Whatever the assumed reaction process is, it has an exponential dependence on the temperature; moreover, the real annealing time of the transient treatment is quite short so that the effective temperature can be chosen equal to the maximum value reached and the effective time can be computed by solving the heat equation numerically. The beam scanning induces a temperature gradient on the sample along the scanning direction so that each irradiated point is annealed at slightly different effective temperatures. In the present work the annealing temperatures range from 600 °C up to 1100 °C and the effective times from 0.7 to 1.5 sec, owing to the different experimental conditions. Such ranges make the transient annealing a powerful tool for the investigation of reaction processes on a time scale which is not accessible in a furnace treatment. As an application, the early stages of the reaction between a clean titanium film and a silicon substrate are described in the temperature range 700–900 °C. In this temperature range, the kinetics are first dominated by diffusion through the Ti‐rich silicides which are formed. This process, with presumably high activation energy and large preexponential factor, cannot be observed in standard furnace annealing where a continuous TiSi2 layer is formed at the interface during the temperature rise time and the silicon supply is limited by the diffusion through this layer.