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

• Al 2 O 3 films deposited by ALD (H 2 O, O 3 ) and magnetron sputtering studied. • H 2 O-based ALD layers show lower fixed charge than O 3 -based ones. • Fixed charge stable in annealed O 3 -based films but fluctuates in H 2 O-based ones. • Crystallization increases fixed charge and interface state density. • Hydrogen in alumina passivates defects or induces negative charge. This work investigates the origin and behavior of negative fixed charge in Al 2 O 3 layers deposited by atomic layer deposition (ALD) using H 2 O and O 3 as oxidants, and by magnetron sputtering (MS). The fixed charge density (C Fix ) and interface state density (D it ) 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 Al 2 O 3 , and lower in H 2 O-based ALD films compared to O 3 -based ones. Upon annealing, the fixed charge in H 2 O-based films fluctuated, while remaining relatively stable in O 3 -based layers. All annealed samples exhibited low interface state densities (<10 10 cm -2 eV -1 ) in amorphous Al 2 O 3 . Following crystallization at 800 °C, both C Fix and D it increased substantially, with H 2 O-based samples showing higher fixed charge and O 3 -based samples exhibiting higher D it . The results suggest that negative fixed charge in amorphous Al 2 O 3 cannot be fully explained by interfacial effects alone, and that hydrogen-related defects can play a significant role.