Etch-induced damage in single crystal Si trench etching by planar inductively coupled Cl₂/N₂ and Cl₂/HBr plasmas

In this study, 0.3-0.5 μm deep and 0.3 μm wide silicon trenches were etched using Cl₂/10%-N₂ and Cl₂/50%-HBr inductively coupled plasmas, the physical and electrical defects remaining on the etched silicon trench surfaces and the effects of various annealing and oxidation on the removal of the defects were studied. High resolution transmission electron microscopy and capacitance-voltage techniques were used to investigate the physical and electrical defects, respectively. Physical defects were found on the silicon trench surfaces etched in both Cl₂/10%-N₂ and Cl₂/50%-HBr. The most dense defects were found near the trench bottom edge, lesser dense defects were found at the trench bottom, and the least dense defects were found at the trench sidewall. The silicon etched in Cl₂/50%-HBr showed more physical defects compared to that etched in Cl₂/10%-N₂. Thermal oxidation of 20 nm at temperatures up to 1100°C alone appears not to remove the defects formed on the etched silicon trenches for both of the etch conditions. To remove the defects, an annealing at temperatures higher than 1000°C in N₂ for 30 min appears to be required.