Correlating biaxial stress to metastable phases in Hf0.5Zr0.5O2 on substrates with different coefficients of thermal expansion

Abstract

The effects of biaxial stress in hafnium zirconium oxide (HZO) thin films on the phase constitution and dielectric response are studied through the preparation of HZO films on substrates with coefficients of thermal expansion (CTE) ranging from 0.52 to 12.97 × 10−6 K−1. X-ray diffraction-based stress measurements revealed a systematic decrease in film biaxial tensile stress with increasing substrate CTE. Grazing incidence and attenuated total reflectance Fourier transform infrared spectroscopy revealed spectral energy shifts that scale with film stress, proving vibrational spectroscopy as an additional indicator of film stress. Ferroelectric responses are observed in HZO prepared on low CTE substrates, and antiferroelectric-like responses are observed in films on high CTE substrates. Results indicate that reducing substrate CTE increases tensile biaxial stress and results in higher fractions of the metastable polar orthorhombic phase. High substrate CTE values lead to low HZO stress values and spectroscopic and antiferroelectric responses consistent with the presence of the antipolar o-I phase.