Microtrench Formation in Polysilicon Plasma Etching over Thin Gate Oxide

Abstract

The formation of microtrenches in polysilicon plasma etching over thin gate oxides has been observed and modeled Microtrenches are small trenches formed in the bottom of etching features and are caused by the localized breakthrough of the gate oxide and subsequent rapid etching of the underlying silicon. In contrast to previous reports, the microtrenches were observed a small distance away from the sidewall. Their formation and position were functions of the thickness and angle of the photoresist and polysilicon sidewalls. Simulation of ion scattering from the sidewalls of the etching features indicated that the flux of ions at the bottom of the feature was peaked away from the sidewall under the process conditions of this study. The position of the peak ion flux predicted by the model and the experimentally observed trench varied in a similar fashion as a function of the topography of the etched feature.

Substrate bias effects in high-aspect-ratio SiO2 contact etching using an inductively coupled plasma reactor

“…Similar probability functions have been used previously. 9,11 Once again, the qualitative behavior of the computed ion flux was not critically dependent upon the precise choice of reflection probability function.…”

“…The structure of such a model has been described previously. 9 The major inputs required are the ion angular distribution ͑IAD͒ arriving from the plasma, the reflection probability as a function of incidence angle, and the feature geometry.…”

Roughening in Plasma Etch Fronts of Si(100)

“…Unlike the study of growth front roughening, such as in molecular beam epitaxy, very little work has been reported on plasma etch front roughening [3][4][5] despite the widespread use of this technique. Plasma etching is a major tool in thin film patterning, which is an important process for microelectronic fabrication.…”

Gas-Surface Dynamics and Profile Evolution during Etching of Silicon

“…Attempts to model etch profile evolution [3][4][5][6][7][8] have had limited success in identifying the origins of commonly observed profile phenomena. "Microtrenching" describes the appearance of a sharp groove near the foot of the etched feature [4,5] and has been attributed in models to reflection of ions from the sidewalls [4,5] and surface diffusion [8].…”

“…"Microtrenching" describes the appearance of a sharp groove near the foot of the etched feature [4,5] and has been attributed in models to reflection of ions from the sidewalls [4,5] and surface diffusion [8]. "Aspect ratio dependent etching" (ARDE) refers to the etch rate dependence on the relative spacing between features [1,6] and has been linked [6] to deposition of etch inhibitors, ion deflection, Knudsen transport of neutrals, ion and neutral shadowing effects, and surface diffusion.…”