Back-End-of-Line Compatible Low-Temperature Furnace Anneal for Ferroelectric Hafnium Zirconium Oxide Formation

The discovery of ferroelectricity in thin doped hafnium oxide films revived the interest in ferroelectric (FE) memory concepts. Zirconium-doped hafnium oxide (HZO) crystallizes at low temperatures (e.g., 400 degrees C), which makes this material interesting for the implementation of FE functionalities into the back end of line (BEoL). So far, the FE phase of prior amorphous HZO films is achieved by using a dedicated rapit thermal annealing (RTA) treatment. However, herein, it is shown that this dedicated anneal is not needed. A sole furnace treatment given by the thermal budget present during the interconnect formation is sufficient to functionalize even ultrathin 5 nm HZO films. This result helps to optimize the integration sequence of HZO films (e.g., involving a minimum number of BEoL process steps), which saves process time and fabrication costs. Herein, metal-FE-metal capacitors with Hf0.5Zr0.5O2 films of different thicknesses (5-20 nm) are fabricated annealed at 400 degrees C for various durations within different types of ovens (RTA and furnace). Structural and electrical characterization confirms that all furnace-annealed samples have similar X-ray diffraction patterns, remanent polarization, endurances, and thickness dependencies as RTA-annealed ones. With respect to remanent polarization, leakage current, and endurance, the HZO film of 10 nm thickness shows the most promising results for the integration into the BEoL.