Crystallization behavior of Hf-rich aluminates and influence on film dielectric properties

In this study, the investigation of crystallization behaviour of Hf-rich aluminate is presented. Different alloys were deposited by ALCVD(TM) with composition ranging between 16 and 47 Al2O3 mol%. Post-deposition annealings were carried out in single or sequential mode using purified N-2 at atmospheric pressure. Process temperature and time were varied from 700degreesC to 900degreesC and from 1' to 30' respectively. Upon these conditions, film thermal evolution was observed without any relevant increasing of in interface layer and any change in material composition. Measurements on 20 Al2O3 mol% films evidenced that thermal treatments up to 800degreesC promoted initial shrinking in thickness and material densification. Above 900degreesC, all considered aluminates were found to crystallize in orthorhombic phase maintaining original alloy composition. The higher the alumina content, the lower the grain size, the higher the crystallites density. Stability of orthorhombic crystalline structure was demonstrated upon single prolonged annealing up to 30' and upon sequential processes. In correspondence with film crystallization, enhancement of dielectric constant was detected with an increasing trend upon hafnia content. For 20 Al2O3 mol% aluminate, change in k form 19 to 40-45 was observed together with limited degradation in conduction and breakdown characteristics.