Abstract
Nanoscale surface roughening and ripple formation in response to ion incidence angle has been investigated during inductively coupled plasma etching of Si in Cl2, using sheath control plates to achieve the off-normal ion incidence on blank substrate surfaces. The sheath control plate consisted of an array of inclined trenches, being set into place on the rf-biased electrode, where their widths and depths were chosen in such a way that the sheath edge was pushed out of the trenches. The distortion of potential distributions and the consequent deflection of ion trajectories above and in the trenches were then analyzed based on electrostatic particle-in-cell simulations of the plasma sheath, to evaluate the angular distributions of ion fluxes incident on substrates pasted on sidewalls and/or at the bottom of the trenches. Experiments showed well-defined periodic sawtooth-like ripples with their wave vector oriented parallel to the direction of ion incidence at intermediate off-normal angles, while relatively weak corrugations or ripplelike structures with the wave vector perpendicular to it at high off-normal angles. Possible mechanisms for the formation of surface ripples during plasma etching are discussed with the help of Monte Carlo simulations of plasma-surface interactions and feature profile evolution. The results indicate the possibility of providing an alternative to ion beam sputtering for self-organized formation of ordered surface nanostructures.
Highlights
A number of studies have been made of surface roughening during plasma etching,[5,6,7] including sidewall roughening in aPresent address: Sony Semiconductor Solutions Corporation, Device Development Division, Atsugi, Kanagawa 243-0014, Japan. bPresent address: Nippon Steel & Sumitomo Metal Corporation, Nagoya Works, Tokai, Aichi 476-8686, Japan. cPresent address: Nippon Steel & Sumitomo Metal Corporation, Kimitsu Works, Kisarazu, Chiba 299-1141, Japan. dPresent address: Toshiba Corporation Semiconductor & Storage Products Company, Center for Semiconductor Research & Development, Kawasaki, Kanagawa 212-8583, Japan. ePresent address: Division of Systems Research, Faculty of Engineering, Yokohama National University, Yokohama, Kanagawa 240-8501, Japan. fElectronic mail: ono.kouichi.63s@st.kyoto-u.ac.jp, ono@kuaero.kyoto-u.ac.jp, and ono@jwri.osaka-u.ac.jp
Little work has been concerned with surface roughening and rippling in response to ion incidence angle in plasma environments, except for a few plasma etching studies of Sawin et al using plasma beams[22,23] and Monte Carlo (MC) simulations[5,24] and a recent study of Chauhan et al.[25] using a reverse biased dc sputter magnetron source; the former showed the formation of nanoscale striations or ripplelike structures at off-normal angles of beam impingement, and the latter the formation of nanodot patterns at normal incidence of ions extracted from the so-called plasma fireball
The ion incidence angles onto substrates, set on sidewalls and/or at the bottom of inclined trenches of the plate, were evaluated based on 2D electrostatic particle-in-cell (PIC) simulations of the plasma sheath concerned
Summary
Atomic- or nanometer-scale roughness on etched feature surfaces has become an important issue to be resolved in the fabrication of nanoscale microelectronic devices.[1,2] The roughness formed on feature sidewalls and bottom surfaces during plasma etching is nowadays often comparable to the critical dimension of the feature and the thickness of the layer being etched and/or the layer underlying, leading to an increased variability in device performance.[3,4] A number of studies have been made of surface roughening during plasma etching,[5,6,7] including sidewall roughening in aPresent address: Sony Semiconductor Solutions Corporation, Device Development Division, Atsugi, Kanagawa 243-0014, Japan. bPresent address: Nippon Steel & Sumitomo Metal Corporation, Nagoya Works, Tokai, Aichi 476-8686, Japan. cPresent address: Nippon Steel & Sumitomo Metal Corporation, Kimitsu Works, Kisarazu, Chiba 299-1141, Japan. dPresent address: Toshiba Corporation Semiconductor & Storage Products Company, Center for Semiconductor Research. We have investigated surface roughening and rippling during Si etching in Cl-based plasmas, by developing a MC-based three-dimensional atomic-scale cellular model (ASCeM-3D) for plasmasurface interactions and feature profile evolution during plasma etching.[7,27,28] Simulations showed random roughness at normal incidence (θi = 0◦, relative to the substrate surface normal), while sawtooth-like ripples with their wave vector oriented parallel (crests/troughs elongated perpendicular) to the direction of ion incidence at intermediate off-normal angles (15◦ < θi < 60◦), and striations or ripplelike structures with the wave vector perpendicular (crests/troughs parallel) to it at high offnormal angles (70◦ < θi < 85◦). The formation of periodic nanoripples by inclined deposition of IBS-sputtered particles has recently been investigated for fabricating a multilayered blazed grating in extreme uv and soft-x ray applications,[51] where a triangular, sawtooth-shaped cross section would be indispensable
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