Notching as an example of charging in uniform high density plasmas

Abstract

Design of notched gate processes in high density plasmasOn the origin of the notching effect during etching in uniform high density plasmas Numerical simulation was used to study both surface charging and ion trajectory distortion during submicron patterning in high density plasma etching. The plasma was assumed uniform and the cause for the surface charging was the directionality difference between ions and electrons. The role of ion transit time effects on the ion energy distribution function was also considered, while the effect of discharging currents such as through insulators was not included. Using a Monte Carlo sheath simulator, a Poisson equation solver, and an ion/electron trajectory simulator, the steady state potential distribution and ion trajectories 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 function. Notching at the bottom of an outermost polysilicon line before a wide space is the result of ion deflection toward the line which has the lower potential from receiving more electrons from a side facing the wide space. The simulator was validated using previously reported electron 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 space 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 distribution function for the plasma conditions used. Thus this shows aspect ratio dependent charging effects which are not dependent on initial plasma nonuniformity.

In situ electrical characterization of dielectric thin films directly exposed to plasma vacuum-ultraviolet radiation

“…The enhanced conductivity can also have beneficial effects on the etching properties of SiO 2 such as reduction of notching, sidewall bowing, and trenching. 17 FIG. 7.…”

Top down nano technologies in surface modification of materials

“…This effect leads to a number serious plasma process induced damage problems such as bowing, trenching, reactive ion etching lag, and notching [48]. Surface charging has been a subject of numerous papers [49][50][51] including charging induced damage in [52][53][54][55][56]. Since the finite difference method is not useful when the geometry of the problem is irregular, the finite elements method has been used for solving Poisson equation describing the electric field in the feature.…”

The influence of surface currents on pattern-dependent charging and notching

“…1 The prevailing cause of the notching effect is believed to be the charging of the exposed SiO 2 surface at the bottom of cleared trenches between gate electrodes, which can lead to ion trajectory bending and lateral sidewall etching. 4,5 When SiO 2 surface charging is reduced, e.g., by decreasing the thickness of the gate oxide so that electron tunneling becomes important, notching is eliminated. 2,6 Surface charging could also be reduced by surface conduction.…”