Thermal Stability of ALD Lanthanum Aluminate Thin Films on Si (100)

The thermal stability of high-κ dielectrics on Si is critical in avoiding the malfunction of metal oxide field effect transistors (MOSFET) in devices. Series of annealing experiments have been performed to investigate the thermal stability of atomic layer deposited (ALD) lanthanum aluminate (LAO) thin films, a promising amorphous high-κ candidate. The abrupt interface between LAO and Si remains intact at temperatures below 600 °C. Above this temperature, a SiO2-rich interfacial layer begins to appear and thickens at higher temperatures. At 900 °C, the interface is roughened due to the formation of nano sized crystal nuclei above the interfacial layer, which indicates the interfacial reactions with the Si substrate. The thermal stability of ALD Al2O3 thin films on Si have also been studied under similar conditions. The Al2O3/Si interface retains its smoothness even after full crystallization. This comparison suggests that the rare earth element may catalyze the interfacial reactions. Further annealing experiments on LAO films with different thickness and with a capping layer show that the oxygen source of the interfacial layer mainly comes from the ALD oxide films.