Effect of Thermal Annealing on Nonvolatile Memory Structures Containing a High-k La2O3 Charge-trapping Layer

摘要

We investigated the effect of thermal annealing on the memory properties of metal-oxide-highk-oxide-silicon (MOHOS)-type structures using high-k La2O3 as a charge-trapping layer. When a MOHOS memory capacitor underwent rapid thermal annealing (RTA), the memory window reached a maximum at an intermediate RTA temperature and then decreased with increasing annealing temperature. The oxide stack also broke down more easily with increasing RTA temperature. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that high-temperature annealing led to the diffusion of La and the formation of crystalline lanthanum silicate, resulting in a smaller breakdown field and an increased leakage current. Our experimental result indicates that the MOHOS memory can be optimized near an RTA temperature of ～600 °C. On the other hand, laser spike annealing (LSA), with its high peak temperature and fast heating/cooling led to a good memory property by suppressing silicate formation while creating high-density charge trapping defects in the La2O3 layer. Our results show that LSA can be an alternative choice for MOHOS memory devices when a high-temperature annealing process is needed for device applications.