SiC is widely used in various mechanical applications as a protective film because of its strength, thermal stability and good mechanical hardness. Here, amorphous SiC thin films with AlN as a buffer layer were deposited on glass and Si substrates through RF magnetron sputtering at different RF powers. The influence of the AlN buffer layer thickness on the morphological and the mechanical properties of the composite films was investigated. Results demonstrate that the AlN buffer layer can effectively improve the adhesion strength of SiC thin films, which has increased gradually from 26.78 N to 37.66 N. The transmittance of SiC thin films was measured using a UV–Vis–NIR spectrophotometer over a spectral range of 300–1200 nm. The average transmittance of SiC films decreases with increasing RF power, and their optical band gap values have varied from 3.31 eV to 3.50 eV.