Invited Paper PS-TuA3
Three Dimensional Modeling of Surface Profile Evolution During Plasma Etching (Plasma Prize Lecture)
Tuesday, October 21, 2008, 2:20 pm, Room 304
We have developed a profile simulator capable of modeling both feature scale evolution as well as roughening within the feature during plasma etching. As roughening is inherently a three dimensional phenomenon, we chose to extend our 2.5D Monte Carlo simulation with cellular surface position and composition representation to a full 3D simulation. The surface interaction is computed based on a local polynomial fitting of the surface cells and computing the surface kinetics based upon the particle interaction with this curved surface. An algorithm for addition and removal of cells was developed based upon a balance between adding cells which retain a smooth surface and the addition of cells which advance the surface in the direction of the local surface normal. The simulation was tested against a broad range of conditions and shown to satisfactorily model feature scale profile evolution. To model the surface kinetics, we used a moving mixed surface layer description in which the surface kinetics are based upon the composition in the cell(s) upon which the particle strikes as well and the incident. The kinetics included incident angle dependence with respect to the polynomial’s normal, the energy dependence of ion bombardment, and the etching yield dependence on surface curvature. Ion scattering with dispersion about the specular scattering angle of ions as well as dispersion of scattered neutrals and disperse emission of reaction products. Redeposition of reaction products was included as well. With this model, we have successfully simulated the roughening of Si surfaces under Ar ion bombardment demonstrating the creation of surface striations oriented transverse to the direction of ion bombardment at low off-normal angles, smooth surfaces at intermediate off-normal angles, and striations parallel with the ion bombardment at higher incident angles. We have also simulated the transition from transverse to parallel roughening which occurs with increased etching time. We have also successfully modeled oxide and low-K dielectric etching using surface kinetics developed for oxide etching with fluorocarbon discharges.