Ion beam smoothing of fused silica at atomic-scale assisted by damage recovery using inductively coupled plasma

For conventional optical manufacturing combining ion beam figuring (IBF) and abrasive finishing, it is difficult to achieve an atomic-scale smooth surface with microroughness below 0.1 nm. Because the abrasives inevitably damage the surface, and the damages are exposed during ion sputtering. To solve this problem, plasma-induced atom migration manufacturing (PAMM) and IBF were combined in this study. PAMM is a damage recovery process based on atom migration effect. In this study, PAMM was employed to recover the subsurface damage and then the damage-less surface was further processed by IBF to remove the form error as well as reduce the roughness to atomic level. Full spatial frequency error convergence was achieved via the combined process of PAMM and IBF. A good surface accuracy of 3.89 nm RMS and an atomically smooth surface with a roughness of 0.044 nm were obtained. The less damage characteristic of the hybrid process was also demonstrated by buffered oxide etching (BOE). This study proposed and verified a hybrid process combining PAMM for damage recovery and IBF for figuring and atomic-scale smoothing, which provided a novel process strategy for manufacturing ultra-precision optics with high quality.