Oxynitridation of Silicon and Postnitridation of Thermal Silicon Oxide in N O in a Vertical Furnace

Gate and tunnel oxides with nitrided interfaces processed in N,0 ambient have been found to improve metal-oxide semiconductor device performance. The N20 process is determined by strongly temperature-dependent gas-phase decom-position 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 opti-mization of N,O 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 0.2 nm) and nitrogen incorporation 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