Instability study of high-κ Inter-Gate Dielectric stacks on hybrid floating gate flash memory

Abstract

Scaling of floating gate NAND flash will require switching from conventional control gate wrap-around cells to fully planar memory cells. Due to the low coupling ratio of these cells, a high work function metal on top of Si, together with a high-k Inter-Gate Dielectric (IGD) are required. In this work we study the performance and instability of high-κ IGD, in combination with or without Al₂O₃ in hybrid floating gate stack for future application in NAND flash memory and compare it to a single Al₂O₃ IGD. We use Post-Program and Erase discharge to study the program/erase transients as well as the instability. Results show that by replacing single Al₂O₃ IGD by a low thermal budget HfAlO or by a multilayer IGD combining low-κ / high-κ / low-κ where high-κ is HfO₂ and low-κ is Al₂O₃ show strong improvement in term of program/erase level and instability, thus a good IGD/CG interface control.