Cubic boron nitride (cBN) thin films were successfully deposited on fused silica substrates by low pressure inductively coupled radio frequency plasma chemical vapor deposition from B2H6 + N-2 + Ar gas mixtures. Ion bombardment was a necessary condition for the cubic phase growth. Glancing angle X-ray diffraction showed reflections of cBN up to 311 and confirmed the growth of the cubic phase. Lattice distortion in the films estimated from the X-ray diffraction data was about a half of that of films on silicon substrates. Adhesion to the silica substrates was better than to the silicon substrates. Auger and electron energy loss spectroscopy also confirmed the formation of cBN phase. Ultraviolet and visible spectra showed the films are transparent with an optical bandgap of similar to 5.4 eV.