Paper PS1-MoM5
Ion Energy and Angular Distributions into Small Features in Plasma Etching Reactors: The Wafer- Focus Ring Gap¹

Monday, October 15, 2007, 9:20 am, Room 606

The termination of the edge of the wafer in reactive ion etching is important to obtaining uniform reactants across the entire substrate. This goal is often complicated by the necessary mechanical gap between the edge of the wafer and the terminating structures, such as the focus ring. Plasma penetration into the gap is of concern due to the likelihood of depositing particle forming materials and erosion. We previously showed that the ratio of the Debye length (or sheath thickness) to the width of the wafer-focus ring gap (WFG) is an important parameter: small ratios allow penetration of plasma species in the WFG.² As a result, orientation of the electric field, ion trajectories and ion energy and angular (IEAD) distributions are functions of this ratio as well as the details of the geometries and materials. In this talk, we extend that study with a computational investigation of ion energy and angular distributions into the WFG. The model used in this investigation is a 2-dimensional plasma hydrodynamics model utilizing an unstructured mesh to resolve the small structures of the WFG. A Monte Carlo simulation was added to the model to track the trajectories of the ions and neutrals while capturing their gas phase collisions and interactions with the surface. Electric potentials as a function of phase from the unstructured mesh are interpolated onto a fine rectilinear capable of resolving the WFG to facilitate a rapidly executing MCS. The consequences of voltage waveform, frequency and geometry of the WFG on IEADs inside the gap (e.g., incident on the lower edge of the wafer bevel) will be discussed for RIE plasmas sustained in fluorocarbon gas mixtures at tens of mTorr.

¹ Work supported by the Semiconductor Research Corp. and the National Science Foundation.
² N. Y. Babaeva and M. J. Kushner, "Penetration of Plasma into the Wafer-Focus Ring Gap in Capacitively Coupled Plasmas", to appear in J. Appl. Phys. (2007).