Oxynitridation of silicon and postnitridation of thermal silicon oxide in N2O in a vertical furnace

Gate and tunnel oxides with nitrided interfaces processed in N2O ambient have been found to improve metal-oxide semiconductor device performance. The N2O process is determined by strongly temperature-dependent gas-phase decomposition chemistry, including endo- and exothermic reactions and heat-transfer effects. This can result in gas depletion and nonstationary equilibrium effects which are affecting the incorporation of nitrogen in silicon oxide. A process optimization of N2O nitrided oxides in a vertical furnace with a batch of 125 wafers is presented for the first time. Direct oxynitridation of silicon and postnitridation of pregrown thermal silicon oxides have been investigated. Reoxidation experiments have been used as a monitor for nitrogen incorporation. In general we found that the variation of the gas flow for a given process temperature and time is the most important variable affecting the process uniformity. Excellent uniformities for thickness (4.5+or-0.2 nm) and nitrogen i ncorporation were achieved by using low gas flow values. Furthermore, the nitrogen level [2.0 to 4.5 atom percent (a/o)] appeared to be roughly four times higher than the levels reported for conventional furnaces. The observed results are explained by thermokinetical considerations.