Alumina layers deposited with different precursors by atomic layer deposition and magnetron sputtering: negative charge and its origin

This work investigates the origin and behavior of negative fixed charge in Al2O3 layers deposited by atomic layer deposition (ALD) using H2O and O3 as oxidants, and by magnetron sputtering (MS). The fixed charge density (CFix) and interface state density (Dit) were evaluated through C-V and G-V measurements on MOS capacitors before and after annealing at various temperatures (400-800 °C). In as-deposited amorphous layers, the negative charge was consistently lower than in crystalline Al2O3, and lower in H2O-based ALD films compared to O3-based ones. Upon annealing, the fixed charge in H2O-based films fluctuated, while remaining relatively stable in O3-based layers. All annealed samples exhibited low interface state densities (<1010 cm-2eV-1) in amorphous Al2O3. Following crystallization at 800 °C, both CFix and Dit increased substantially, with H2O-based samples showing higher fixed charge and O3-based samples exhibiting higher Dit. The results suggest that negative fixed charge in amorphous Al2O3 cannot be fully explained by interfacial effects alone, and that hydrogen-related defects can play a significant role.