High-k Dielectrics And High Work Function Metals For Hybrid Floating Gate NAND Flash Applications

摘要

In this paper we will discuss the key materials issues involved in the successful fabrication of hybrid floating gate (HFG) devices, a solution to scale NAND flash below 20 nm node. In HFG a Simetal stack replaces the standard poly-Si FG. The metal is required to have a high work function (WF) in order to control the leakage through the inter-gate dielectric (IGD); a high k-value of the IGD is essential to increase the coupling factor of the memory cell. Our reference stack uses TiN(WF 4.7 eV) and Al_2O_3(k～9) IGD annealed at 1000 °C. The metal candidates are Ta_(1-x)Al_xN_y (WF>4.9eV) and Ru (WF>4.7eV). The high-k IGD of choice are Hfl-xAlxOy, Gd_xHf_(1-x)O_y, Gd_xSc_(1-x)O_y and Sc_(1-x)Al_(1-x)O_y. We will show that optimal memory performance is strongly linked to the IGD crystallinity and the thermal stability (inter-diffusion) of the metal-IGD system. The optimal material combination is found to be TiNHfAlO(k～19) annealed at 800 °C.