Deposition of hafnium zirconium oxide (HfZrO2) ferroelectric layers can be achieved through hybrid techniques combining atomic layer deposition (ALD) and sputtering. These methods enable precise control over stoichiometry, crystallinity, and interfacial properties, which are critical for achieving robust ferroelectric polarization switching and memory endurance. The interplay between deposition parameters and ferroelectric performance is a key focus in optimizing these films for non-volatile memory applications.

HfZrO2 exhibits ferroelectricity when stabilized in the orthorhombic phase, which depends on composition, thickness, and thermal treatment. A hybrid ALD-sputtering approach leverages the conformality and atomic-level control of ALD with the tunable stoichiometry and higher deposition rates of sputtering. This combination allows for fine-tuning of the Hf:Zr ratio, oxygen vacancy concentration, and grain structure, all of which influence polarization switching characteristics.

In a typical hybrid process, an ALD base layer is first deposited to ensure uniform coverage and interface quality. ALD precursors such as tetrakis(dimethylamido)hafnium (TDMAHf) and tetrakis(dimethylamido)zirconium (TDMAZr) are used with ozone or water as oxidants. The ALD cycle ratio between HfO2 and ZrO2 is adjusted to achieve the desired HfZrO2 composition. Following this, reactive sputtering is employed to deposit an additional HfZrO2 layer, where the Hf:Zr ratio is controlled via target composition and sputtering power. Argon and oxygen gas mixtures regulate oxygen stoichiometry, which is crucial for minimizing defects that degrade ferroelectric performance.

Post-deposition annealing is essential to induce the ferroelectric orthorhombic phase. Rapid thermal annealing at temperatures between 400°C and 600°C in an inert or oxygen-containing atmosphere promotes crystallization. Excessive temperatures or prolonged annealing can lead to monoclinic phase formation, which is non-ferroelectric, while insufficient annealing results in amorphous or defective films with poor polarization response.

Polarization switching in HfZrO2 is influenced by film thickness, composition, and interfacial layers. Thinner films (below 20 nm) typically exhibit higher coercive fields due to increased depolarization effects, while thicker films may suffer from increased leakage and reduced endurance. A Zr content of around 50% is often optimal for maximizing remanent polarization, with values ranging between 10-30 µC/cm² depending on processing conditions. Wake-up effects, where the ferroelectric response improves with electric field cycling, are commonly observed and attributed to defect reconfiguration and phase stabilization.

Endurance is a critical metric for ferroelectric memory applications, defined as the number of polarization switching cycles a film can endure before significant degradation. HfZrO2 films deposited via hybrid ALD-sputtering typically demonstrate endurance exceeding 10^10 cycles, though this depends on interface engineering and electrode materials. TiN electrodes are widely used due to their compatibility and ability to sustain high cycling stresses. Oxygen scavenging at the electrode interface can lead to vacancy accumulation, increasing leakage and eventual breakdown. Insertion of thin interfacial layers such as Al2O3 or SiO2 can mitigate this effect, improving endurance.

Fatigue mechanisms in HfZrO2 include charge trapping at grain boundaries and interfaces, phase degradation, and electrode reactions. Optimizing the deposition process to minimize defects and control grain size is crucial. Films with smaller, uniform grains tend to exhibit better endurance due to reduced percolation paths for defect migration. Additionally, field cycling conditions play a role; higher switching voltages accelerate degradation, while moderate fields promote stable operation.

Comparative studies between pure ALD and hybrid ALD-sputtering approaches reveal trade-offs. Pure ALD films often show better conformality and interface control but may suffer from lower crystallinity and higher impurity levels. Hybrid films benefit from the sputtering step’s ability to enhance crystallinity and adjust composition dynamically, but they require careful optimization to avoid interfacial defects. The hybrid approach is particularly advantageous for thicker films or when integrating HfZrO2 with complex geometries where ALD alone may be insufficient.

Temperature stability is another consideration for memory applications. HfZrO2 retains ferroelectric properties up to temperatures around 200-250°C, beyond which phase instability and increased leakage become problematic. The hybrid deposition method can improve thermal resilience by enabling better control of oxygen vacancies and grain structure, though excessive temperatures during operation or processing remain detrimental.

Scalability is a key advantage of the hybrid ALD-sputtering technique. Both methods are compatible with industrial semiconductor manufacturing, allowing for seamless integration into existing fabrication lines. The ability to tune composition and structure at various deposition stages makes the hybrid approach versatile for optimizing ferroelectric performance across different device architectures.

Future developments in hybrid deposition may focus on further reducing defect densities, improving interface engineering, and exploring novel electrode materials. Advances in in-situ characterization during deposition could enable real-time optimization of film properties, enhancing reproducibility and performance. Additionally, combining hybrid deposition with advanced patterning techniques may open new possibilities for three-dimensional ferroelectric memory architectures.

In summary, the hybrid ALD-sputtering approach for HfZrO2 ferroelectric layers offers a balanced solution for achieving high polarization switching performance and endurance. By leveraging the strengths of both deposition methods, it is possible to tailor film properties to meet the demanding requirements of next-generation non-volatile memory technologies. Continued refinement of process parameters and a deeper understanding of degradation mechanisms will be essential for further improving reliability and scalability.