Ion Beam Figuring and Smoothing

Abstract

AbstractThe technologies, ion beam figuring (IBF) and ion beam-induced smoothing (IBS), are used to precisely remove imperfections or correct surface shape in a predetermined and controlled manner. The IBF method uses the computer-aided codes to realize the desired surface topography, where a spatially and temporally stable ion beam is passed vertically over the surface at a fixed distance in a high-vacuum environment. The main input variables of this approach, the ion beam removal function, the surface error function and the dwell time procedure, are presented. The various algorithms (Fourier transform algorithm, iterative dwell algorithm, matrix based algorithm, Bayesian algorithm) for determining the dwell time of the ion beam over each object point to be machined and the effect of temperature during the figuring procedure are discussed. The application of IBF technology for the correction of shape errors on surfaces to achieve depth accuracies in the nanometer and sub-nanometer range over the entire spectrum of the spatial surface wavelength is demonstrated with selected examples. Ion beam-induced smoothing (IBS) focuses on feature processing (spatial wavelength < a few microns and height amplitudes on the order of nanometers) with the aim of producing ultra-smooth surfaces. In addition to direct smoothing by low-energy ions, the technologies of smoothing with a planarization layer and smoothing by means of ions incident at a very oblique angle have also become established. Atomistic surface relaxation processes such as ion beam enhanced viscous flow, thermally activated surface diffusion, effective ion-induced diffusion, and ballistic mass redistribution can contribute to the smoothing process.