CRYSTALLIZATION OF SILICON IN ALUMINUM AMORPHOUS-SILICON MULTILAYERS

The crystallization of amorphous Si (a-Si) in Al/a-Si multilayer thin films has been investigated by ex situ and in situ transmission electron microscopy (TEM), X-ray diffraction and calorimetry. The a-Si crystallizes at about 200-degrees-C, a significantly lower temperature than for the pure elemental state, with a heat of crystallization of about 12 kJ(mol Si)-1. We show that crystalline Si(c-Si) nucleates within the Al layers and penetrates the Al as the c-Si grows. The speed of the growth of c-Si observed by in situ TEM was a few angstroms per second at 220-degrees-C. Al grains are separated and the layered structure is destroyed, while the Al(111) film texture is enhanced. The overall activation energy of the reaction, determined by calorimetry, is 1.2 +/- 0.1 eV. We propose a model in which diffusion of Si through the Al grains and rearrangement of the Al grains occur simultaneously.