AVS 52nd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThM

Paper PS-ThM7
3-Dimensional Feature Scale Profile Simulation of Sidewall Roughening During Plasma Etching

Thursday, November 3, 2005, 10:20 am, Room 304

Session: Plasma-Surface Interactions II
Presenter: H. Kawai, Massachusetts Institute of Technology
Authors: H. Kawai, Massachusetts Institute of Technology
B. Bai, Massachusetts Institute of Technology
H.H. Sawin, Massachusetts Institute of Technology
Correspondent: Click to Email
Sidewall roughness or Line Edge Roughening (LER) is becoming an ever more significant issue as the line width of integrated circuits features shrink and the size of width variation caused by LER becomes comparable to the minimum feature dimension. Since roughening is inherently a three dimensional phenomenon, we have developed a 3-dimensional feature scale profile simulator to simulate the surface and sidewall roughening during the etching process of polysilicon and silicon dioxide. The simulator uses a dynamic Monte Carlo simulation to model the surface kinetics. The simulation domain is discretized into array of cubic cells with the side of 2.5 nm. The local surface conformation is determined by fitting the local region of the surface cells with a polynomial, which is used to compute the surface normal, scattering angle, and flux on the 3-D surface. Using the angular dependence of physical sputtering with a highest etching yield at 60 degrees off-normal incident angle, the initially smooth polysilicon surface is roughened with facets of approximately 60 degrees after the surface is sputter-etched at normal incident angle. Non-planar surfaces are etched and evolve to the same surface roughness as was found for the initially planar surface. However, using the angular dependence of ion (chlorine) etching yields where yield decreases monotonically with off-normal angle, an initially smooth polysilicon surface tends to stay smooth after it is etched at normal incident angle. The surface with small, shallow angle initial roughness also smoothes when it is etched at glancing incident angle, but the surface with large, steep features forms striations after it is etched due to the scattering of ions. Templating, also known as top LER, the most common mechanism of LER caused by mask edge roughening, has also been modeled. This LER is characterized by the transference of the mask spatial frequencies with reduced amplitude with distance from the mask.