Improvement of the Ferroelectric Response of La-Doped Hafnium Zirconium Oxide Employing Tungsten Oxide Interfacial Layer with Back-End-of-Line Compatibility

Abstract

In this work, the impact of a tungsten oxide (WO 3 ) seed and capping layer for ferroelectric La-doped (Hf, Zr)O 2 (La:HZO) based capacitors, designed with back-end-of-line (BEOL) compatibility, is systematically investigated. The WO 3 capping layer supplies oxygen to the La:HZO layer throughout the fabrication process and during device cycling. This facilitates the annihilation of oxygen vacancies (V o ) within the La:HZO layer, thereby stabilizing its ferroelectric orthorhombic phase and resulting in an increase of the remanent polarization (P r ) value in the capacitor. Moreover, the effectiveness of the WO 3 capping layer depends on the seed layer of the HZO film, suggesting that proper combination of the seed and capping layers should be employed to maximize the ferroelectric response. Finally, a TiN/ TiO 2 seed layer/La:HZO/WO 3 capping layer/TiN capacitor is successfully fabricated and optimized by a complete set of atomic layer deposition (ALD) processes, achieving a superior 2P r value and endurance value of more than 10 9 cycles at an electric field of 2.5 MV/cm. The WO 3 capping layer is anticipated to offer a viable solution for doped HZO capacitors with reduced thickness, addressing the challenge of elevated V o levels that favor the tetragonal phase and result in low 2P r values.