Mechanical and electrical properties of plasma and thermal atomic layer deposited Al2O3 films on GaAs and Si

Mechanical and electrical properties of Al2O3 films are compared for plasma-assisted atomic layer deposition (ALD) and thermal ALD on two substrates, GaAs and Si, of different thermal expansion coefficient. Films with stable chemical structure and mechanical residual stress could be produced by both techniques without inducing any damage to sensitive multiquantum-well structures. However, the as-deposited residual stress in the plasma ALD Al2O3 films is lower and decreases, while that in the thermal ALD films increases with the deposition temperature. Moreover, the stress hysteresis observed upon thermal cycles is much lower for the plasma ALD films compared to that for the thermal ALD films. The biaxial elastic modulus (BEM or stiffness parameter) increases with the deposition temperature for both ALD films, being higher for the plasma ALD than that for the thermal ALD at a given temperature. The higher BEM is reflected in better electrical properties of the films. Thu s, the leakage current of metal-oxide-semiconductor capacitors with the plasma ALD-Al2O3 film is three orders of magnitude lower and the breakdown voltage 20% higher than that of the capacitors with the thermal ALD film.