ION-ASSISTED CRYSTALLIZATION IN SILICON - EPITAXY AND GRAIN-GROWTH

We report experimental investigations on the amorphous-to-crystal transition in silicon during ion bombardment. The transition was induced by 600 keV Kr irradiation of an amorphous layer in contact with a crystalline substrate. The growth rate depends on the substrate temperature, orientation and the logarithm of the dopant concentration. The crystallization was also stimulated in absence of a planar seed by irradiating an amorphous silicon layer deposited on a thick layer of SiO2. The presence of crystal seeds with radius of the order of a few nanometers in the as-deposited material has been observed. The growth of these seeds is controlled by the motion of [111] boundaries. The grain density is constant with the irradiation dose but it decreases with the substrate temperature. All of the data are discussed in terms of a phenomenological model based on the assumption that the same defects are responsible for the amorphous-to-crystal transition both in pure thermal and in ion-assisted processes.