Abstract
In this study, the tantalum oxynitride-Ta(N,O) films were prepared by RF magnetron sputtering. By tuning the sputtering parameters, such as RF power, substrate temperatures, sputtering gas ratios such as like the N2/O2 flow ratio and the Ar fraction (Ar/(Ar+N2+O2)), the effects of microstructure on optical properties, thermal properties and mechanical properties were investigated. When the film was deposited at room temperature, it showed an amorphous phase, and remained amorphous after annealing at 700oC for one hour by using conventional furnace in Ar ambient, so as the rapid thermal annealing above 700oC for 5 min. The growth characteristic showed in the form of columnar, and the root mean square roughnesses of as-deposited films deposited at 25oC and 300oC, respectively, were 1.288±0.01 nm and 0.217±0.01 nm, and increased to 8.479±0.01 nm by RTA at 800oC for 5 min.When the N2/O2 flow ratio varied from 4, 1 to 0.25, the crystalline tantalum nitride particles embedded in a continuous, ring-like and granular amorphous matrix were observed and the particle size for both of the tantalum nitride and tantalum oxide phase grew gradually. In the wavelength ranging from 633nm to 780nm, the refractive index (n) of the tantalum oxynitride films deposited on silicon wafer decreased from 2.2 to 1.9 as increasing N2/O2 flow ratios. The reflectance (0.15 to 0.35) and the transmittance (0.73 to 0.90) of studied films deposited on glass substrate changed with sputtering parameters. The microcantilever beam method was used to study the residual stress and thermal expansion coefficient. All the as-deposited films showed a compressive state and the CTE values varied with different N2/O2 flow ratios from 12.5 to 0 MPa and 7.5 x 10–7 /oC to 7.5 x 10–6 /oC, respectively. Compared with the values of (ZnS)80(SiO2)20 films (4.78±0.29 GPa and 39.5±1.2Gpa), the hardness and the elastic constant of Ta(N,O) films were ranging from 6~39±0.5 GPa and 130~179±3.2 GPa, respectively. The harder Ta(N,O) film without sulfur inter-diffusion will be a more suitable candidate as the dielectric layer of optical recording disk.Keywords: RF sputter, tantalum oxynitride, columnar structure, microcantilever beam method, nanoindentation method, thermal traveling wave method, optical recording disk