PAC and PALS study in the HfO2+ SiO2 system

CECILIA Y. CHAIN; LAURA C. DAMONTE; SERGIO FERRAI; EMILIANO MUÑOZ; CLAUDIA E. RODRIGUEZ TORRES; ALBERTO F. PASQUEVICH

Buenos Aires, Argentina

Simposio; 15th International Symposium on Metastable, Amorphous and Nanostructured Materials; 2008

A high-k HfO2/SiO2 gate stack is taking the place of SiO2 as a gate dielectric in field effect transistors. This fact makes the study of the solid-state reaction between these oxides very important. Before beginning with the study of the reactions between both oxides at the interface of thin films, we initiated Perturbed Angular Correlations (PAC) and Positron Lifetime Studies (PALS) of the solid state reactions using samples prepared by mixing the oxides by ball milling. Sample preparation includes pilling and annealing at different temperatures. The PAC technique requires the use of special radioactive isotopes. In this case the probe 181-Ta was used. This isotope results from the beta-decay of 181-Hf. This isotope was introduced in the sample using HfO2, where the 180-Hf was activated by thermal neutron capture at the CNEA reactor. On the other hand, the PALS measurements were carried out using 22-Na as source of positrons and non-active samples. Equimolar amounts of the oxides were milled during 2,4 and 8 hours. The samples were pilled under a pressure of 6 kN/m2. Room temperature PAC and PALS measurements were made after annealings under air at several temperatures. The results are compared with microstructure data existent in the literature of nanocrystalline ZrSiO4, synthesized by ball-milling and high-temperature annealing.