The influence of LOCOS related oxide etch backs on thin oxide leakage in memory devices

The influence of oxide etch backs done in LOCOS based isolation technologies on the low level leakage and reliability of tunnel oxide capacitors has been studied. Tunnel oxide structures are part of nonvolatile memory devices such as Flash EEPROMs and are critical to their overall performance. LOCOS isolated, area and edge intensive capacitors with 94 A tunnel oxide have been manufactured and tested. Test results indicate that the extent of the etch back and the use of HF instead of buffered HF as etch chemical do not adversely affect the low level leakage of the tunnel capacitors. However, oxide endurance analysis based on constant current charge to breakdown tests shows a significant degradation if an aggressive pretunnel oxide etch back strategy is adopted.