Nitrogen incorporation during N2O- and NO-oxidation of silicon at temperatures down to 600 degrees C

The preferred incorporation of nitrogen in the SiOx transient layer near the SiO2/Si interface was investigated using N2O- and NO-oxidation at temperatures from 1200 degrees C down to 600 degrees C and 20 s to 135 min process time. The peak nitrogen content, measured by AES and SIMS depth profiling, was accumulated with a high starting rate during N2O-oxidation. This leads to a temperature-dependent concentration level of nitrogen of 4.5 at.% down to 0.25 at.% at the lowest temperature. An exponential fit of the peak nitrogen concentration (N-peak) against reciprocal temperature gives an apparent activation energy of about 0.45 eV under the conditions used here at rapid thermal and at conventional furnace oxidation. After longer process time, e.g. 270 s to 800 s, a further low rate nitrogen accumulation at the SiO2/Si interface was measured. This also holds at reduced temperatures down to 600 degrees C, independent of the type of preoxide grown by dry O-2-oxidation or by chemical vapor deposition (CVD). The NO-oxidation leads to a more than three times higher peak nitrogen level, dependent on temperature and time. A low thermal budget gate oxide preparation with nitrogen stabilization of the interface seems to be possible at 800 degrees C with not more than 30 s to 40 s process time using a CVD preoxide and diluted NO. Copyright (C) 1996 Elsevier Science Ltd.