Ultrathin oxide films deposited using electron cyclotron resonance sputter

Ultrathin oxide films ( SiO 2 , Al 2 O 3 ,Ta 2 O 5 ) 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 Al 2 O 3 film. The fixed charge density of the Al/SiO 2 /Si metal oxide semiconductor capacitors decreased with increasing oxygen flow rate and substrate temperature during SiO 2 deposition. A very low fixed charge density of about 5×10 10 cm −2 was obtained without annealing the capacitor. The resistivities of SiO 2 , Al 2 O 3 , and Ta 2 O 5 films with thicknesses from 2 to 40 nm were on the order of 10 15 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 SiO 2 and Al 2 O 3 films. A high dielectric constant of 25 was obtained for Ta 2 O 5 films. We think the low energy (10–20 eV) ion irradiation during ECR sputter contributed to the formation of smooth, high-quality oxide films.