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

摘要

The discovery of ferroelectricity in thin doped hafnium oxide films revived theinterest in ferroelectric (FE) memory concepts. Zirconium-doped hafnium oxide(HZO) crystallizes at low temperatures (e.g., 400 ℃), which makes this materialinteresting 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 adedicated rapid thermal annealing (RTA) treatment. However, herein, it is shownthat this dedicated anneal is not needed. A sole furnace treatment given bythe thermal budget present during the interconnect formation is sufficientto functionalize even ultrathin 5 nm HZO films. This result helps to optimizethe integration sequence of HZO films (e.g., involving a minimum number ofBEoL process steps), which saves process time and fabrication costs. Herein,metal–FE–metal capacitors with Hf_(0.5)Zr_(0.5)O_2 films of different thicknesses(5–20 nm) are fabricated annealed at 400 ℃ for various durations within differenttypes of ovens (RTA and furnace). Structural and electrical characterizationconfirms that all furnace-annealed samples have similar X-ray diffraction patterns,remanent polarization, endurances, and thickness dependencies as RTA-annealedones. With respect to remanent polarization, leakage current, and endurance, theHZO film of 10 nm thickness shows the most promising results for the integrationinto the BEoL.