NOTCHING AS AN EXAMPLE OF CHARGING IN UNIFORM HIGH-DENSITY PLASMAS

Numerical simulation was used to study both surface charging and ion t rajectory distortion during submicron patterning in high density plasm a etching. The plasma was assumed uniform and the cause for the surfac e charging was the directionality difference between ions and electron s. The role of ion transit time effects on the ion energy distribution function was also considered, while the effect of discharging current s such as through insulators was not included. Using a Monte Carlo she ath simulator, a Poisson equation solver, and an ion/electron trajecto ry simulator, the steady state potential distribution and ion trajecto ries were calculated for various line-and-space structures and plasma conditions where notching, which is a local sidewall etching, has been observed after the overetching part of polysilicon etching processes. The results show significant positive charging at the bottom of high aspect ratio spaces which depends on the ion energy distribution funct ion. Notching at the bottom of an outermost polysilicon line before a wide space is the result of ion deflection toward the line which has t he lower potential from receiving more electrons from a side facing th e wide space. The simulator was validated using previously reported el ectron cyclotron resonance etcher notching results. It was found that the calculated potential difference between the bottom of a space and the adjacent line shows the same qualitative dependence on the wide sp ace width as experimental notch depth results show. In addition, these potential differences are large enough to substantially increase the ion flux at regions where notching occurs for the ion energy distribut ion function for the plasma conditions used. Thus this shows aspect ra tio dependent charging effects which are not dependent on initial plas ma nonuniformity. (C) 1996 American Vacuum Society.