Ultrathin oxide films deposited using electron cyclotron resonance sputter

Abstract

Ultrathin oxide films (SiO2, Al2O3,Ta2O5) with a minimum thickness of 2 nm have been deposited at low temperature by electron cyclotron resonance (ECR) sputter utilizing a plasma source coupled with a divided microwave beam. The uniformity of the film thickness was within ±2% over a 150 mm wafer. The surface roughness measured by atomic force microscopy was only 0.48 nm for a 100-nm-thick Al2O3 film. The fixed charge density of the Al/SiO2/Si metal oxide semiconductor capacitors decreased with increasing oxygen flow rate and substrate temperature during SiO2 deposition. A very low fixed charge density of about 5×1010 cm−2 was obtained without annealing the capacitor. The resistivities of SiO2, Al2O3, and Ta2O5 films with thicknesses from 2 to 40 nm were on the order of 1015 Ω cm. Under low electric fields the leakage current was a hopping current and under high electric fields it was a Poole–Frenkel current. The typical dielectric strength was 10 MV/cm for SiO2 and Al2O3 films. A high dielectric constant of 25 was obtained for Ta2O5 films. We think the low energy (10–20 eV) ion irradiation during ECR sputter contributed to the formation of smooth, high-quality oxide films.