Explosive crystallization processes in silicon

Abstract

This paper deals with selfsustaining crystallization processes, the so-called explosive crystallization, in silicon produced by short temperature pulses. By this, crystalline Si layers can be generated on amorphous substrates, e.g. on SiO₂, at which liquid and solid-state crystallization processes can take place.

Emphasis will be given to the liquid-phase explosive crystallization processes. Here, the transformation of amorphous into crystalline silicon occurs through two coupled laterally moving interfaces, amorphous-liquid and liquid-crystalline.

Using an experimental equipment existing of 3 synchronized lasers supplying the temperature pulse for the ignition, the spreading out and stopping of the laterally moving interfaces, in connection with time-resolved measurements of the reflectivity by a laser test beam, information about the characteristic parameters as the velocity of the process, the crystallized area and the course of the crystallization front will be obtained. The crystalline structure was investigated by optical and transmission-electron micrography.

The main results are: the crystallization fronts move radially from the ignition point with a velocity of about 15 m/s, crystalline laminae grow preferentially in 〈110〉 direction over a distance of more than 100 μm, areas of some millimeters in diameter can be crystallized and the quality of the crystallized layers essentially depends on the “amorphousness” of the virgin layer and the preparation method.

The experimental results are in good agreement with theoretical predictions.