PAC and PALS study in the HfO2+SiO2 system

C. Y. CHAIN; L. C. DAMONTE; S. FERRARI; E. L. MUÑOZ; A. F. PASQUEVICH; C. RODRIGUEZ TORRES

Buenos Aires, Argentina

Simposio; XV 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 make very important to study the solid state chemical interaction between both oxides.  Before beginning with a 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 mixing the oxides by ball milling. Sample preparation include pilling  and annealing at different temperatures. The  PAC technique requires the use of  specials radioactive isotopes. In this case the probe 181Ta was used.  This isotope results from the beta-decay of  181Hf.  This isotope was introduce in the samples  using HfO2 , where the 180Hf was activated by thermal neutron capture at the CNEA reactor.   On the other hand, the PALS measurements were carried out using 22Na as source of positrons and non active samples. Equal molar 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 annealing 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.