Smoothening of scalloped DRIE trench walls

Deep reactive ion etching (DRIE) is a popular technique used for etching through a silicon substrate to produce high aspect ratio trenches with vertical walls. However, an inherent problem associated with this technique is the resulting scalloping on the trench walls. Such rough trench walls can adversely influence subsequent process steps, e.g. trench filling with metal by electroplating, or the electrical behavior of devices which may incorporate and use these trenches. In this paper we report very significant roughness reduction of DRIE trench walls without optimizing the DRIE process parameters but only through the use of a post-DRIE processing technique involving successive thermal oxidation and oxide stripping steps. The scallop depth reduction is characterized in detail throughout the steps of this repetitive procedure and a quantitative analysis of the measured data illustrates the gradual improvement and smoothening of the trench walls.