Surface morphology evolution during plasma etching of silicon: roughening, smoothing and ripple formation

Recent advances in the modeling and computer simulations of non-equilibrium plasma discharges

“…In this special issue, the paper by Ono et al [7] describes the modeling of nanoscale surface topology evolution using Monte Carlo and classical molecular dynamics. The fluence of plasma produced ions, their energy, and angle of impact at the process surface are shown to influence surface roughening and topological pattern formation such as ripples.…”

Origin of plasma-induced surface roughening and ripple formation during plasma etching: The crucial role of ion reflection

“…3,4 Surface roughening during plasma etching has been studied extensively, [5][6][7] including sidewall roughening in pattern transfer [8][9][10][11][12][13][14][15] and also maskless formation of organized nanostructures such as nanotextures and nanopillars. [16][17][18][19][20][21] Correspondingly, several mechanisms have been invoked in continuum models and Monte Carlo (MC) simulations to reproduce the experiments: 5,7,18,[22][23][24] stochastic roughening, 5,7,[22][23][24][25] geometrical shadowing, 22 reemission of neutrals, 23,24,26 micromasking by inhibitors, 18,27 and ion reflection. 5,7,25,[28][29][30] Longitudinal striations or ripplelike structures (called the line edge/width roughness) often formed on feature sidewalls [8][9][10]…”

“…[16][17][18][19][20][21] Correspondingly, several mechanisms have been invoked in continuum models and Monte Carlo (MC) simulations to reproduce the experiments: 5,7,18,[22][23][24] stochastic roughening, 5,7,[22][23][24][25] geometrical shadowing, 22 reemission of neutrals, 23,24,26 micromasking by inhibitors, 18,27 and ion reflection. 5,7,25,[28][29][30] Longitudinal striations or ripplelike structures (called the line edge/width roughness) often formed on feature sidewalls [8][9][10][11][12][13][14][15] are usually appreciated to arise extrinsically from pattern transfer of the mask edge roughness under the effects of ion shadowing; 12 in practice, they would also arise intrinsically or spontaneously from plasma-surface interactions themselves on feature sidewalls at high off-normal ion incidence, although little mechanistic work has been concerned with surface roughening and rippling in response to ion incidence angle during plasma etching. 5,7,25,[31]…”

“…5,7,25,[28][29][30] Longitudinal striations or ripplelike structures (called the line edge/width roughness) often formed on feature sidewalls [8][9][10][11][12][13][14][15] are usually appreciated to arise extrinsically from pattern transfer of the mask edge roughness under the effects of ion shadowing; 12 in practice, they would also arise intrinsically or spontaneously from plasma-surface interactions themselves on feature sidewalls at high off-normal ion incidence, although little mechanistic work has been concerned with surface roughening and rippling in response to ion incidence angle during plasma etching. 5,7,25,[31][32][33] The morphological evolution of solid material surfaces at atomistic scale has also been of interest during ion beam sputtering (IBS); in particular, spontaneous or self-organized formation of ordered nanostructures such as periodic dots and ripples in response to ion incidence angle onto surfaces has been extensively studied since decades, [34][35][36][37][38][39] as a promising approach to fabricate well-ordered nanostructures.…”

“…In this study, the "reflection coefficient r i (0 ≤ r i ≤ 1)" is further introduced in the model, representing the fraction of ions incident on surfaces with the reflection/penetration calculation scheme turned on; preliminary results for normal θ i = 0°were in part described previously. 7,74,75 A quantitative understanding, under what conditions the reduced ion reflection (r i < 1) results in surface smoothing/non-roughening and under what conditions it retains the roughening and rippling, would be of great technological as well as fundamental importance. Moreover, we discuss the ripple topography and dynamics (wavelength, amplitude, profile, and propagation velocity) at intermediate off-normal θ i = 45°depending on the degree of ion reflection.…”