Furnace annealed HfO2-Films for the Integration of Ferroelectric Functionalities into the BEoL

The discovery of ferroelectricity in thin films of doped hafnium oxide has led to a renaissance of ferroelectric (FE) memory concepts. Compared to all inspected dopants, zirconium doped hafnium oxide (HZO) crystallizes at the lowest temperatures. Thus, this material system is ideal for the implementation of FE functionalities into the back-end-of-line (BEoL). So far, the FE phase is achieved by rapid thermal annealing (RTA) of prior amorphous HZO films. Recently, it was shown that a sole furnace anneal at 400°C is sufficient to functionalize the films. Herein, a wide range of annealing conditions are compared in order to further reduce the thermal budget and the number of process steps. It is found that furnace-annealing at 300°C for 1 h crystallizes the HZO films in the FE phase. With respect to crystallinity, these films show no significant degradation compared to films annealed at 400°C. Nevertheless, the remanent polarization reduces slightly with temperature, but is still sufficient even at 300°C.