Journal
ADVANCED ELECTRONIC MATERIALS
Volume 8, Issue 12, Pages -Publisher
WILEY
DOI: 10.1002/aelm.202200601
Keywords
biaxial stress; clamping effect; diffraction; ferroelectrics; hafnium zirconium oxide
Funding
- Semiconductor Research Corporation's (SRC) Global Research Collaboration Program [2875.001]
- Center for 3D Ferroelectric Microelectronics (3DFeM), an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0021118]
- National Science Foundation [CHE-2018870, DMR-1832829]
- National Science Foundation Major Research Instrumentation Award [162601]
- National Science Foundation Graduate Research Fellowship Program [DGE-1842490]
- U.S. Department of Energy's National Nuclear Security Administration [DE-NA0003525]
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The presence of the top electrode during thermal processing is shown to increase ferroelectric phase fraction and polarization response through larger tensile biaxial stress. Film chemistry, microstructure, and crystallization temperature are not affected. The top electrode inhibits out-of-plane expansion in HZO during crystallization, preventing equilibrium monoclinic phase formation and stabilizing the orthorhombic phase.
The presence of the top electrode on hafnium oxide-based thin films during processing has been shown to drive an increase in the amount of metastable ferroelectric orthorhombic phase and polarization performance. This Clamping Effect, also referred to as the Capping or Confinement Effect, is attributed to the mechanical stress and confinement from the top electrode layer. However, other contributions to orthorhombic phase stabilization have been experimentally reported, which may also be affected by the presence of a top electrode. In this study, it is shown that the presence of the top electrode during thermal processing results in larger tensile biaxial stress magnitudes and concomitant increases in ferroelectric phase fraction and polarization response, whereas film chemistry, microstructure, and crystallization temperature are not affected. Through etching experiments and measurement of stress evolution for each processing step, it is shown that the top electrode locally inhibits out-of-plane expansion in the HZO during crystallization, which prevents equilibrium monoclinic phase formation and stabilizes the orthorhombic phase. This study provides a mechanistic understanding of the clamping effect and orthorhombic phase formation in ferroelectric hafnium oxide-based thin films, which informs the future design of these materials to maximize ferroelectric phase purity and corresponding polarization behavior.
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