X-ray photoelectron spectroscopy study of gate/ferroelectric interface chemistry in metal–ferroelectric–insulator–semiconductor stacks

Front-end-of-the-line thermal budgets used for complementary metal oxide semiconductor integration can strongly modify the gate/ferroelectric interface in metal–ferroelectric–insulator–semiconductor (MFIS) ferroelectric field-effect transistor (FeFET) stacks, yet the coupled evolution of interfacial chemistry, defect distribution, and band alignment remains difficult to access because the ferroelectric is buried under a metal gate. Here, we use x-ray photoelectron spectroscopy (XPS) combined with controlled, low-energy Ar+ thinning of the TiN gate to probe the near-gate region of the ferroelectric while avoiding sputter-induced artifacts. We show that FEoL annealing drives oxygen scavenging by TiN, producing a graded TiN/TiOxNy interfacial region. Angle-resolved XPS reveals a pronounced depth profile in oxygen vacancy (VO) concentration near the interface, with systematically higher VO at shallower probing depths. Increasing the anneal temperature from 750 to 1000 °C enhances the VO concentration across the probed depth range. Concomitantly, the Hf 4f core level exhibits an angle-independent shift of ∼0.25 eV toward higher binding energy after annealing at 1000°C, evidencing an anneal-induced modification of the local electrostatic potential. These results identify FEoL processing as a direct lever on defect redistribution and electrostatics at the TiN/ferroelectric interface, with implications for MFIS FeFET integration and reliability.