Nano-scale modification of 2D surface structures exposed to 6keV carbon ions: Experiment and modeling

Abstract

In this work, a Si pitch grating with typical lateral dimensions of 200-250 nm was exposed to 6 keV C + ions at normal incidence and at an angle of 42° both parallel and perpendicular to the grating structure. In contrast to volatile and recycling ions (like Ar + or H + ), non-recycling ions are able to modify the surface not only due to sputtering, but also due to implantation of incident ions and the re-deposition of projectile atoms following sputtering or reflection. The targetprojectile combination used in this work is an example of such a system forming a mixed Si-C surface. The interaction between the ion beam and the surface has been studied both experimentally and numerically with the focus on validation of the numerical model of the newly developed SDTrimSP-2D code. SDTrimSP-2D is capable of following the evolution of the Si-C system including ion-surface interactions with 2D micro-and nano-structured surfaces. The SDTrimSP-2D code takes the interdependency of surface morphology, sputtering and implantation into account. The simulated surface morphology has been compared to crosssections of bombarded Si pitch grating obtained by SEM, revealing good agreement between experiment and simulation. The calculations also provide improved insight into the mechanisms of surface modification by sputtering, implantation and material transport by redeposition.Keywords: SDTrimSP-2D, sputtering, implantation, redeposition, surface morphology, local ion-surface interactions. IntroductionSputtering of a surface exposed to a flux of energetic ions is one of the most studied effects of ion-surface interactions [1]. However, the details of ion-surface interactions depend greatly on the target-projectile combination. In cases where the projectile is an ion of a volatile (recycling) element, sputtering is usually the dominant process and the surface is eroded. In such cases, experiments are well described theoretically, at least for relatively smooth surfaces. The sputtering yield is the main parameter, which has been used to validate theoretical models with experiments. Existing models like the TRIM code show good agreement with experiment for many target-projectile combinations.

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

“…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.…”

“…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.…”

Study of interaction of C+ ion beam with a Si pitch grating on a macro-scale level

“…This version allows to define a surface with variation not only as function of depth but also in one lateral dimension and model its evolution. A number of studies have been performed to validate this SDTrimSP-2D code comparing the simulation results with experiments from irradiation of a periodical Si pitch grating structure with Ar + [8], [9] and C + [10] ions. In these experiments a Si diffraction lattice has been used as a target.…”

“…Experimental data were compared to results of simulations with the SDTrimSP-2D code, which was used previously in [10] to follow the evolution of the surface morphology. In this work, SDTrimSP-2D with the same input parameters as in [10] has been used to simulate total areal densities of elements, total sputter yields and reflection coefficient.…”

“…In this work, SDTrimSP-2D with the same input parameters as in [10] has been used to simulate total areal densities of elements, total sputter yields and reflection coefficient. Further simulations show anisotropy effects, which could be observed also experimentally at irradiation of a 2D surface: irradiation of the pitch grating at inclined angle of incidence both parallel and perpendicular to the grating structure leads indeed to different fluence dependent dynamics of sputter yield, reflection and implantation.…”