Characteristics of hafnium-aluminum-oxide thin films deposited by using atomic layer deposition with various aluminum compositions

Thin films of hafnium-aluminum-oxide [(HfO2)x(Al2O3)1-x] were investigated as a potential replacement for SiO2 gate dielectrics. Al2O3, HfO2, and hafnium-aluminum-oxide films were successfully deposited using the atomic layer deposition (ALD) method at 300 .deg. C. The Al2O3 films showed amorphous structures while the HfO2 films showed a randomly oriented polycrystalline structure with Hf-silicate and/or SiOx interfacial layers. Hafnium-aluminum-oxide films showed a much stronger resistance to oxygen diffusion than pure HfO2 films during annealing, and the crystallization temperature increased with further Al addition to the hafnium-aluminum-oxide film. The leakage current densities of the Al2O3, HfO2, and hafnium-aluminum-oxide films were measured at a gate bias voltage of |VG - VFB| = 2 V, yielding 2.7 X 10-8, 3.3 X 10-4, and 6.5 X 10-7A/cm2 (with a Al2O3 : HfO2 ratio of 1 : 1), respectively. The corresponding calculated equivalent oxide thickness (EOT) values were approximately 2.2, 1.8, and 1.6 nm, respectively. The hafnium-aluminum-oxide film had a higher dielectric constant and a lower EOT than the Al2O3 film and exhibited a lower leakage current and higher breakdown voltage than the HfO2 films. The dielectric constant, the leakage current, the flat band voltage, and the crystallinity of the hafnium-aluminum-oxide film exhibited a strong dependence on the Al-Hf composition ratio of the films.