Isolation dependence of gate oxide quality at the LOCOS edge using an in-situ HCl-based pre-gate Pyroclean

The in-situ furnace HCl-based Pyroclean has been shown to remove metallics from silicon surfaces with dramatic efficiency. This paper demonstrates for the first time that, while the Pyroclean effectively reduces initial gate oxide shorts, it can degrade the gate oxide charge-to-breakdown of isolation modules which have not been properly optimized. A comparison of three LOCOS isolation schemes suggests that the Pyroclean preferentially attacks stressed previously roughened silicon. Optimizing the isolation edge to reduce stress and roughness is shown to eliminate deleterious Pyrocleaning effects.