Nitric oxide rapid thermal nitridation for Flash memory applications

Rapid thermal annealing in nitric oxide (RTNO) has long been used for the formation of ultrathin silicon oxynitride gate dielectrics. Nitric oxide (NO) furnace anneals are used in the formation of floating gate Flash memory transistor tunnel oxides. Nitrogen is thus, incorporated to improve the oxide reliability during program/erase cycling endurance and data retention. We present here a study of rapid thermal annealing and oxide growth in nitric oxide using Applied Materials single-wafer rapid thermal process (RTP) that enables the RTNO anneal to operate at higher temperatures compared to furnace, thereby allowing two times greater incorporation of nitrogen at the silicon/silicon dioxide interface. At 1200°C, a greater than 11% peak interface nitrogen concentration as measured by secondary ion mass spectroscopy (SIMS) in a 75 Angstrom SiON film is achieved. Reliability testing using a floating gate flash memory capacitor with minority carrier source (implants) test vehicle shows that this increase in the peak interface nitrogen results in an improvement in the tunnel oxide's program/erase cycling endurance and data retention. For future memory devices, for example 3D memory devices, the use of direct RTNO oxide growth for dielectric formations is possible. In this case, higher temperatures allow the growth of thicker oxides in pure NO at 1200°C, with greater nitrogen incorporation.