Three-dimensional measurement and prediction of atomic-scale surface roughness on etched features become increasingly important for the analysis of line edge roughness (LER) and line width roughness (LWR) on feature sidewalls; however, the feature profiles are too small and/or too complex to measure the surface roughness on bottom surfaces and sidewalls of the etched features. To predict the surface roughness on atomic/nanometer scale, we have developed our own three-dimensional atomic-scale cellular model (ASCeM-3D) [1] and feature profile simulation. In this study, emphasis is placed on a better understanding of the formation mechanisms of nanoscale surface roughening and rippling during Si etching and sputtering under oblique ion incidence.

In the ASCeM-3D model, the simulation domain is divided into a number of small cubic cells of L = ρSi-1/3 = 2.7 Å, where ρSi = 5.0 x 1022 cm−3 is the atomic density of Si substrates. Ions and neutrals are injected from the top of the simulation domain, and etch and/or sputter products are taken to be desorbed from etching surfaces into microstructural features, where two-body elastic collision processes between incident ions and substrate atoms are also taken into account to analyze ion reflection on etched feature surfaces and penetration into substrates. The ASCeM-3D takes into account surface chemistries based on the Monte Carlo (MC) algorithm [2-4], including adsorption and reemission of neutrals, chemical etching, ion-enhanced etching, physical sputtering, and redeposition of etch and/or sputter products on feature surfaces. The etch yield of ion-enhanced etching and sputtering depending on ion incident energy and angle is taken from the empirical models.

Numerical results indicated that the ripple structures occur on etched surfaces, depending on incident angle of ions. The surfaces are randomly roughened in the case of Cl2 plasma etching for an ion incident angle θi = 0° or normal incidence of ions. For increased θi = 45°, the ripples are formed perpendicular to the direction of ion incidence, while parallel to that of ion incidence for further increased θi = 75°. These imply that the angular dependence of energy transfer processes from an incident ion to substrate atoms largely affects the evolution of feature profiles and surface roughness on atomic/nanometer scale.

[1] H. Tsuda et al., Jpn. J. Appl. Phys. 50 (2011) 08JE06.

[2] Y. Osano and K. Ono, J. Vac. Sci. Technol. B 26 (2008) 1425.

[3] H. Tsuda et al., Thin Solid Films 518 (2010) 3475.

[4] H. Tsuda et al., Jpn. J. Appl. Phys. 49 (2010) 08JE01.