Oxynitridation of silicon with nitrogen plasma for flash memory applications characterized by high frequency capacitance-voltage measurements

Si(100) wafers were oxynitrided by nitrogen plasma exposure under different conditions and thermally oxidized in dry O₂ without the use of toxic or global warming gases. The atomic concentration ratio of N/Si was 0.075 at a plasma discharge power of 0.5 kW and an exposure time of 1 min and 0.176 at a plasma power of 2.0 kW and an exposure time of 3 min, as determined from X-ray photoelectron spectroscopy measurements. A progressive reduction in the oxidation rate with increasing N concentration, corresponding to an increase in N plasma power, was observed. The uniformity of film thickness over a 4-inch wafer was improved after nitrogen plasma exposure and rapid thermal oxidation, with a thickness variation of less than 2.6% compared with 13.2% for the N₂O thermal oxidation process. The advantages of exposing Si to N plasma for application in silicon devices was investigated by high-frequency capacitance-voltage measurements. A distortion in the capacitance-voltage curve was observed for samples that did not undergo nitridation, a distortion that was not observed in the nitrided samples. Capacitance-voltage curve distortion was found to be significantly reduced by Si nitridation under low plasma power.