Ion-beam and dual-ion-beam sputter deposition of tantalum oxide films

Abstract

Ion-beam sputter deposition (IBS) and dual-ion-beam sputter deposition (DIBS) of tantalum oxide films was investigated at room temperature and compared with similar films prepared by e-gun deposition. The optical properties, i.e., refractive index and extinction coefficient, of IBS films were determined in the 250- to 1100-nm range by transmission spectrophotometry and at λ=632.8 nm by ellipsometry. They were found to be mainly sensitive to the partial pressure of oxygen used as a reactive gas in the deposition process. The maximum value of the refractive index of IBS deposited tantalum oxide films was n=2.15 at λ=550 nm and the extinction coefficient of order k=2×10 -4 . Films deposited by e-gun deposition had refractive index n=2.06 at λ=550 nm. Films deposited using DIBS, i.e., deposition assisted by low energy Ar and O 2 ions (E a =0 to 300 eV) and low current density (J i =0 to 40 μA/cm 2 ), showed no improvement in the optical properties of the films. Preferential sputtering occurred at E a (Ar)=300 eV and J i =20 μA/cm 2 and slightly oxygen deficient films were formed. Different bonding states in the tantalum-oxide films were determined by x-ray spectroscopy, whereas composition of the film and contaminants were determined by Rutherford backscattering spectroscopy (RBS). Tantalum oxide films formed by IBS contained relatively high Ar content (2.5%) originating from the reflected argon neutrals from the sputtering target whereas assisted deposition slightly increased the Ar content. Stress in the IBS-deposited films was measured by the bending technique. IBS-deposited films showed compressive stress with a typical value of s=3.2×10 9 dyn/cm 2 . Films deposited by concurrent ion bombardment showed an increase in the stress as a function of applied current density. The maximum was s5.6×10 9 dyn/cm 2 for E a =300 eV and J i =35 μA/cm 2 . All deposited films were amorphous as measured by the x-ray diffraction (XRD) method