Using an ammonia treatment to improve the floating-gate spacing in split-gate flash memory

In the split-gate flash memory process, during poly oxidation, the bird's beak encroaches under the SiN film, especially along the poly grain boundary, and that will cause nonuniform floating-gate (FG) spacing, even bridging, which is an obstacle to cell shrinkage. We show that employing an ammonia treatment on the poly can nitridize the poly surface, thereby avoiding bird's beak bridging. After the ammonia treatment, FG spacing is quite uniform and can be improved from 0.09 to 0.03 μm. The XPS analysis on the ammonia treated poly shows the oxynitride thickness is less than 5 nm.