IMAGE POTENTIALS AND THE DRY ETCHING OF SUBMICRON TRENCHES WITH LOW-ENERGY IONS

The image potential between an ion and an etched sidewall is shown to be important in the dry etching of high-aspect ratio features. Low-energy ions are attracted to the walls of an etched trench, resulting in wall collisions which can lead to loss of etch directionality and slow vertical etch rates. Estimates are given for the depth at which one-half of the ion flux into an etched trench is lost to one of the etched walls, as a function of trench width and ion energy. The effect is particularly important in the etching of quarter-micron features and smaller using ion energies less than 200 eV.