Improved interface properties of yttrium oxide buffer layer on silicon substrate for ferroelectric random access memory applications

In this paper, we report upon an investigation into the feasibility of Y₂O₃ films as buffer layers for metal ferroelectric insulator semiconductor type capacitors. Buffer layers were prepared by a two-step process of low temperature film growth using the RF reactive magnetron sputtering method and subsequent rapid thermal annealing. By applying an yttrium metal seed layer of 4 nm, unwanted SiO₂ layer generation was successfully suppressed at the interface between the buffer layer and the Si substrate. Increasing the post-annealing temperature above 700 °C reduced the surface roughness of the Y₂O₃ films, and increasing the O₂ partial pressure from 10 to 20% increased the surface roughness from 4.0 to 15.1 nm. The Y₂O₃ films, prepared using an O₂ partial pressure of 20% and annealed at 900 °C, exhibited the best surface roughness characteristics of the samples studied. For a substrate temperature above 400 °C and an O₂ partial pressure of 20%, we observed that a cubic Y₂O₃ phase dominated the X-ray diffraction spectra. The lowest lattice mismatch achieved between the Y₂O₃ film and the Si substrate was 1.75%. By using a two-step process, we reduced the leakage current density of Y₂O₃ films by two orders of magnitude and the D_it to as low as 8.72×10¹⁰ cm^-2 eV^-1. A Y₂O₃ buffer layer grown at 400 °C in a 20% O₂ partial pressure and rapidly annealed at 900 °C in an oxygen enviroment exhibited the best overall properties for a single transistor ferroelectric random access memory.