Depth profiling of ZrO 2/SiO 2/Si stacks—a TOF-SIMS and computer simulation study

Abstract

This study is dedicated to a better understanding of the processes occurring under ion bombardment of ultra-thin ZrO 2/SiO 2/Si gate dielectric stacks. Complex-shaped depth profiles were obtained by using TOF-SIMS with dual beam (500 eV for sputtering and 10 keV for analysis) Ar + ions. The SIMS intensities of all the elements depend critically on the amount of oxygen at any moment of the sputtering process. Increased intensity is observed at the surface and at the ZrO 2/SiO 2 interface. A long tail of the Zr signal is present in the Si substrate, even after the second (SiO 2/Si) interface, and a double bump structure in the 90 Zr and ZrO dimer is observed, which is more pronounced with increasing thickness of the interfacial SiO 2 layer. Computer simulations using the dynamic Monte Carlo code (TRIDYN) are performed in order to distinguish the ion-bombardment-induced effects from changes in the ionization degree. The original code is extended with simple models for the ionization mechanism and for the molecular yield during sputtering. Oxygen preferential sputtering at the surface and ballistic transport of Zr towards and through the interface are clearly demonstrated, but there is also evidence that due to recoil implantation oxygen gets piled-up near the ZrO 2/SiO 2 interface.