Low refraction properties of F-doped SiOC:H thin films prepared by PECVD

Low refractive index materials which F-doped SiOC:H films were deposited on Si wafer and glass substrate by low temperature plasma enhanced chemical vapor deposition (PECVD) method as a function of rf powers, substrate temperatures, gas flow ratios (SiH₄, CF₄ and N₂O). The refractive index of the F-doped SiOC:H film continuously decreased with increasing deposition temperature and rf power. As the N₂O gas flow rate decreases, the refractive index of the deposited films decreased down to 1.378, reaching a minimum value at an rf power of 180 W and 100 °C without flowing N₂O gas. The fluorine content of F-doped SiOC:H film increased from 1.9 at.% to 2.4 at.% as the rf power was increased from 60 W to 180 W, which is consistent with the decreasing trend of refractive index. The rms (root-mean-square) surface roughness significantly decreased to 0.6 nm with the optimized process condition without flowing N₂O gas.