Evolution of the 2D surface structure of a silicon pitch grating under argon ion bombardment: Experiment and modeling

Abstract

This work aims at validation of the newly developed SDTrimSP-2D code by comparing experiment measurements and modeling of the evolution of a 2D surface structure under argon ion bombardment. SDTrimSP-2D allows for the simulation of ion-surface interactions with 2D micro-structured surfaces, where the first dimension is the depth and the second is parallel to the surface. The main advantage of the approach implemented in SDTrimSP-2D code is that the interdependency of surface morphology and sputtering is naturally taken into account. The code follows the evolution of surface morphology and provides a detailed nanoscale description of processes characterizing the ion-surface interactions. In this work, a Si pitch grating with typical dimensions of 200-250 nm, provides a well-characterized 2D system. This is bombarded with 6 keV Ar + ions at normal incidence angle as well as at an angle of 42° both parallel and perpendicular to the pitch grating structure. Cross-sections of the bombarded Si pitch grating were obtained by SEM and compared to the calculated surface profile revealing good agreement between experiment and simulation. The calculations also provide improved insight into the mechanisms of grating erosion and material transport by redeposition.

Macroscopic parameters of the interaction of an Ar+ ion beam with a Si pitch grating

“…At inclined angle perpendicular to the structure, the Si removal is suppressed by the stronger redeposition of the sputtered Si atoms on the walls of the structure. The stronger redeposition rate for the case of perpendicular bombardment has been confirmed in previous work [7], where the local sputtering and redeposition have been investigated.…”

“…These are somewhat different from the ones used in [7] One can notice the influence of 2D anisotropic structure on Si sputtering. The Si removal occurs faster, when the pitch grating is bombarded at inclined angle parallel to the structure.…”

“…The Si pitch grating sample has been taken from the same set of samples as the ones used in [7] and [8]. Its period is 500 nm and the height is 200 nm, the deviation from these values has been measured by scanning electron microscope and is within 5-20 nm.…”

“…The horizontal transport (parallel to the surface) is usually set smaller than the vertical one, because swelling or shrinking is primarily observed experimentally in the vertical direction. This anisotropy coefficient was calibrated in previous work [7]. Thus, the cells at the surface exposed to incident ions can change in two directions.…”

“…Recent investigations have been aimed on experimental validation of the 2D version of the code by comparing the surface cross-section profiles obtained by scanning electron microscope and by simulation [7], [8]. In these experiments a diffraction lattice with a period of 500 nm and a height of 200 nm has been used.…”