Improved corner rounding method for trenched MOSFET

This paper suggests an improved method to round off the concave corners of the deep trenches formed by plasma etch. The corner rounding technique, sacrificial oxidation (SACOX) before gate oxidation, has been practiced on the shallow trench isolation (STI) to improve the CMOS leakage performance. However, the direct implementation of the SACOX on the deep trenched MOSFET having less than 0.5 um trench width is insufficient to eliminate the oxide thinning at the concave corners. The experimental results including the scanning electron microscopy (SEM) images are presented to illustrate how the sharp corners vanish. The concave corners are encompassed by a smooth layer of silicon dioxide served as a gate oxide for vertical trenched MOSFET. Electrical measurement shows that the breakdown voltage was improved by eliminating the gate oxide weak spots.