Effects of Post Metal and Forming Gas Annealing on Characteristics of Ferroelectric FinFETs with HfZrOX Gate Dielectric

Abstract

Since excellent ferroelectric (FE) characteristics were demonstrated with a CMOS-process compatible thin hafnium-based material, FE field-effect-transistors (FETs) have attracted considerable attention as a promising candidate for next-generation nonvolatile memory, analog synaptic devices for neuromorphic systems, and steep slope devices called negative capacitance (NC) FETs, with low power consumption. Among various HfO2 thin film dopant materials suitable for FE operation, such as Si, Zr, Y, and Al, Zr is well-known as showing stable characteristics thanks to having almost identical chemical properties with Hf. HfZrOX (HZO) films consist of tetragonal, orthorhombic, and monoclinic phases. The orthorhombic phase is known to be responsible for the ferroelectricity of the thin film. Annealing after FE deposition, for example post metal annealing (PMA) or forming gas annealing (FGA), leads to crystallization which is a key factor in the final ferroelectric characteristics of the HZO thin film. Even though the effects of PMA and FGA on metal-ferroelectric-metal (MFM) capacitors have been investigated by several research groups, there has been no report on metal-ferroelectric-insulator-silicon (MFIS) structured FE FETs yet. In this work, the effects of PMA and FGA on characteristics of a highly-scaled FE FinFET with a 10 nm thick HZO film were carefully investigated. The effects of PMA at temperatures from 400 °C to 900 °C for 30 s were examined. An FGA split experiment was conducted with various temperatures and hydrogen (H2) gas content ratios. First, changes of orthorhombic phase peak were investigated by spectral measurements with the grazing incidence X-ray diffraction (GI-XRD), and changes in domain behavior were also investigated using piezoresponse force microscopy (PFM). MFM capacitors with a TiN top and a TiN bottom electrode exhibited different butterfly-like features in capacitance-voltage (C-V) characteristics and polarization-electric field (P-E) hysteresis loops by splitconditions. Finally, the electrical characteristics of the highly-scaled FE FinFETs were compared to those of the MFM capacitors for the first time under various conditions. The FE FinFETs were fabricated with a fin width of 50 nm, a fin height of 100 nm, and a gate length of 120 nm on bulk silicon wafers with gate last processes. The optimized PMA and FGA conditions determined in this experiment are expected to provide insights into the use of FE FETs as next-generation memory, synaptic devices for neuromorphic systems, and steep slope-based logic applications.