Ion beam sputtering and dual ion beam sputtering of titanium oxide films

Abstract

Ion beam sputtering and dual ion beam sputtered films of titanium oxide were prepared and investigated at room temperature and compared with similar films prepared by e-beam (EB) gun deposition. Optical properties, i.e. Refractive index n and extinction coefficient k of films were determined by transmission spectrophotometry ( lambda =350-1100 nm) and at lambda =632.8 nm by ellipsometry. These were all found to be very dependent on deposition parameters (rate, substrate temperature and partial pressure of oxygen (PO2) in the case of EB deposition of TiO2). For ion beam sputtering (IBS) deposition the main controlling deposition parameter on the optical properties was PO2. The maximum refractive index achieved at 300 degrees C for EB deposited TiO2 films was n=2.35. Films deposited by IBS and dual ion beam sputtering (DIBS) at room temperature showed higher values of n(TiO2)=2.41-2.47 for lambda =550 nm. Values of extinction coefficient were similar and of the order of 10-4. X-ray diffraction (XRD) measurements revealed that all films deposited by IBS, DIBS and EB deposition were amorphous except for those films deposited by EB deposition at T>or=320 degrees C which were polycrystalline. DIBS of TiO2 with low-energy Ar and O2 ions (Ea=200-300 eV) and low currents (Ja=0-35 mu A cm-2) was not beneficial. Films bombarded with Ar+ were absorbing while films bombarded with O2+ showed no change in n or k. Different bonding states in IBS deposited TiO2 films were determined by x-ray spectroscopy (XPS) while the composition of films and contaminants were determined by Rutherford backscattering spectroscopy (RBS). TiO2 films formed by IBS contained approximately=0.4% Ar which originated from the reflected argon neutrals from the sputtering target while assisted deposition slightly increased argon content. Stress in the films deposited by IBS was measured and was compressive with a typical value of sigma =3.75-108 Pa.