Influence of capping layers on the crystallization of doped SbxTe fast-growth phase-change films

Isothermal crystallization of doped SbxTe fast-growth phase-change films, with and without capping layers, was investigated using transmission electron microscopy, which provided direct and quantitative information on nucleation and growth processes separately. Two types of amorphous dielectric layers, ZnS-SiO2 and GeCrN, were used for sandwiching the SbxTe films to form typical trilayer stacks, which are the active part in applications. The nucleation and growth parameters of SbxTe films were found to be influenced by the dielectric capping layers. The crystal growth rate is temperature dependent and it reduces when the film is sandwiched between the dielectric layers. The reduction in growth rate differs with the capping layer type. The capping layer influence on the growth rate is pronounced at lower temperatures similar to 160 degrees C, but tends to vanish at higher temperatures similar to 200 degrees C. The activation energy for crystal growth is 2.4 +/- 0.3 eV for an uncapped film and it increases similar to 40% when the capping layers, GeCrN or ZnS-SiO2, are added. A temperature and time dependent nucleation rate is found and it is accelerated similar to 1.7 times by GeCrN layers, whereas it is retarded similar to 5 times by ZnS-SiO2 layers. The activation energy for crystal nucleation is 6.1 +/- 0.4 eV for an uncapped film and it is not noticeably altered by the capping layers. These variations observed in the crystallization kinetics are attributed to variations in interface energy between the phase-change film and the capping layers or vacuum and the confinement effect by the capping layers on the phase-change film. (c) 2006 American Institute of Physics.