ASPECT RATIO INDEPENDENT ETCHING - FACT OR FANTASY

The scaling of anisotropic plasma etch rates with feature dimensions i s an important issue when fabricating microelectronic and photonic dev ices. For a wide rage of conditions, etch rates are found to scale pri marily with the feature depth/width or aspect ratio. Features with lar ge aspect ratios etch more Slowly than those with low aspect ratios re gardless of feature width. However, in the presence of etch inhibitors , the scaling of etching rates with feature dimensions becomes more co mplicated. Smaller aspect ratio features may etch more slowly than lar ger aspect ratio features suggesting that etch-inhibiting chemistry co uld be exploited in achieving the here-to-fore elusive goal of aspect ratio independent etching (ARIE). Using a well-established etching mod el, based on Langmuir adsorption kinetics, we derive the etch inhibito r flux and surface adsorption parameters required to achieve ARIE. Alt hough the required parameters are non-physical when the range of aspec t ratios is unconstrained, it is possible to achieve ARIE over a restr icted range of aspect ratios. However, the balance required between io n, etchant, and inhibitor fluxes is a fragile one. The best approach t o minimizing the variation in etching rate with aspect ratio is to ope rate a high density plasma at low pressure with high neutral how rates .