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

Abstract

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 °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 °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.

Structural and Electrical Comparison of Si and Zr Doped Hafnium Oxide Thin Films and Integrated FeFETs Utilizing Transmission Kikuchi Diffraction

“…Since larger grains have been suggested to favor the monoclinic phase stronger as well as having a higher phase transition temperature for tetragonal to monoclinic [19], thus being less hindered by kinetic factors during this transition, a higher monoclinic phase fraction appears reasonable. The origin for larger grains in the HSO layer could be of interest for future research, as they are not expected due to the higher crystallization temperature of HSO [1,20].…”

“…The stronger pronounced texture in the case of HSO, while having the same processing parameters like HZO, can be attributed to differences of the thermal expansion coefficient and other material parameters due to the doping, as Si doping tends to favor shorter dopant-oxygen bonds [22]. Furthermore, the crystallization temperature for HSO (above 500 • C [1]) lies at higher temperatures than HZO, which crystallizes already at around 400 • C [20]. Therefore, nucleation and grain growth will occur at different temperatures for the two materials, which becomes also apparent in differences in the grain size and phase distribution discussed above.…”

Low‐Thermal‐Budget Fluorite‐Structure Ferroelectrics for Future Electronic Device Applications

“…In their previous report, the 400 °C furnace‐annealed HZO films had similar P r values, thickness dependencies, and endurance properties as the 400 °C RTA‐annealed HZO films. [ 42 ] However, unlike the HZO films annealed at 400 °C, the HZO films annealed at lower temperatures showed ferroelectric behaviors only when the annealing time sufficiently increased. In particular, the 300 °C RTA‐annealed HZO film behaved like a linear dielectric (consistent with Figure 3c and previous studies [ 2,4,7 ] ), whereas the HZO films that annealed for a long time in the furnace showed suitable 2 P r values.…”

On the Origin of Wake‐Up and Antiferroelectric‐Like Behavior in Ferroelectric Hafnium Oxide

“…AFE-like wake-up phenomena can be stabilized by increasing stress or doping. [1,26,29,36] The differences between classical, textured, and asymmetric wake-up can be explained by differences in the microstructure and layer stacking. Textured wake-up can be obtained by increasing the in-plane stress or using dopants whose ionic radii differ from hafnium, e.g., La (see Figure S1, Supporting Information) or Si.…”

“…Due to the symmetry and absence of parasitic capacitances or semiconductor‐based nonlinearities, MFM capacitors are generally used to characterize the ferroelectric behavior, directly paving the way to FeRAM and back‐end‐of‐line (BEoL) integration in FeFETs. [ 29,30 ] In contrast, MFIS stacks resemble the integration of hafnium oxide–based FeFETs in the front end of line (FEoL).…”