Surface roughness and residual stress evolution in SiNx/SiO2 multilayer coatings deposited by reactive pulsed magnetron sputtering

The surface roughness and residual stress behavior in two types of SiNx/SiO2 dielectric quarter-wave stacks was investigated experimentally. A reactive pulsed magnetron sputtering system was used to prepare the SiNx/SiO2 multilayer thin films. The results show that SiNx/SiO2 quarter-wave stack with a buffer layer of MgF2 thin film can reduce the residual stress. The effect of aging on the residual stress in two quarter-wave stacks was also studied. We found that the residual stresses in both SiNx/SiO2 multilayer coatings are changed from a compressive state to a tensile stress state with increasing the aging time. The root mean square (RMS) surface roughness of MgF2/(SiNx/SiO2)22 and (SiNx/SiO2)22 quarter-wave stacks are 2.23 ± 0.22 nm and 2.08 ± 0.20 nm, respectively.