Investigation and validation of pulsed ion extraction in reactive ion beam etching for ultra-precision surface processing

Reactive ion beam etching enables ultra-precise transfer of micro- and nanostructured features (e.g., diffractive optical elements) from a mask to a substrate while preserving sub-nanometer surface roughness, with broadly tunable selectivity and high dimensional accuracy. Scaling the process to large optical components requires sophisticated motion algorithms. Tight constraints on base removal and limitations of the motion system make homogeneous pattern transfer particularly challenging. Pulsed ion extraction adds an additional degree of freedom and allows local control of the removal rate during complex motion sequences. We investigate the influence of duty cycle on the etching mechanism of the SiO 2 /photoresist material system using a radio-frequency broad-beam ion source with a CHF 3 / O 2 feed gas mixture and Ar as a reference. We measure removal rates and surface roughness for both materials under continuous and pulsed extraction. From these data, we derive spatially resolved selectivity across the sample. We observe a material-dependent correlation between duty cycle and removal rate. The results indicate that chemical etching proceeds during the pulse-off time and significantly influences the overall process. We discuss the implications for achieving large-area homogeneous pattern transfer in pulsed reactive ion beam etching.