A method of fabricating an LFCC device includes forming a first trench in a substrate that extends vertically from an upper surface to a depth within the substrate, the first trench having first sidewalls, a first bottom, and a pattern formed on the first sidewalls near the first bottom of the trench, and forming an oxide layer on the first sidewalls and first bottom of the first trench that leaves a second trench located within the first trench and is separated from the first trench by the oxide layer. The second trench has second sidewalls that are substantially vertical without showing the pattern and a second bottom that is substantially flat. The pattern compensates for the difference in oxidation rates between the bottom of the first trench and the first sidewalls. The LFCC structure includes a first trench with the pattern.