High-k gadolinium and aluminum scandates for hybrid floating gate NAND flash

Abstract

GdxSc1-xOy and Sc1-xAlxOy dielectrics are implemented in hybrid-FG flash devices.Large memory window and good retention is demonstrated for Sc1-xAlxOy (k-value~14).The low GdxSc1-xOy (k~21) breakdown field makes it unsuitable for our applications.The crystallinity of the films correlates well with the program memory performance.Retention is linked to the robustness of the IGD against Ti, N and Si diffusion. GdxSc1-xOy and Sc1-xAlxOy (0.2≤x≤0.5) were investigated as potential intergate dielectric (IGD) candidates for hybrid floating gate (HFG) applications. In HFG the poly-Si FG is replaced by a Si?TiN stack. An excellent program/erase window of ~14V and good retention performance are obtained for Sc1-xAlxOy, which has a k-value of ~14. GdxSc1-xOy displays a higher k of ~21, but its large leakage current and low breakdown field of less than 4MV/cm make this material incompatible with our applications. The main differences between both scandates concern to their crystallization and thermal stability. Indeed, for similar compositions and thermal treatments, as required by the fabrication process of the devices (800-1000?C), GdxSc1-xOy tend to be more crystalline and with an enhanced Ti, N and Si diffusion into the IGD as compared to Sc1-xAlxOy.