Side Wall Roughness Reduction in Deep Silicon Oxide Etching Using C₂F₆ Based ECR-RIBE

A process using multilayered mask, consisting of either novolak based resist or special type of light insensitive polymer and thin metal, is developed for improving the side wall smoothness of silicon oxide etching. Different techniques are used to reduce the side wall roughness of the mask prior to the underlying silicon oxide etching. The mask smoothness is reduced down to 25 nm using underlying thin metal layer which not only increases the adhesion of the upper resist/polymer with the silicon oxide, but also acts as the etch stopper during patterning of the upper resist/polymer. The side wall smoothness of underlying silicon oxide etching using the smooth polymer mask, is improved down to 60 nm which is better than conventional process where metal mask is used.