Oxynitridation of Si with nitrogen plasma for flash memory and its high frequency C-V characteristics

Si (100) substrates were oxynitrided with nitrogen plasma exposure, at different conditions, followed by thermal oxidation in dry O₂ without using any harmful or global warming gas. Atomic concentration of N to Si was 7.5% for plasma discharge power of 0.5kW and exposure time of 1 min. While, it was 17.6% for plasma power of 2.0kW and 3min, as depicted from X-ray photoelectron spectroscopy (XPS) measurements. A progressive reduction of the oxidation rate with the increase of N concentration associated with the increase of N plasma power was observed. Uniformity of film thickness across 4 inch wafer was improved with nitrogen plasma exposure followed by rapid thermal oxidation (RTO) with discrepancy less than 2.6% compared with 13.2% for N ₂O thermal oxidation process. High frequency C-V measurements investigated the advantage of using N plasma exposure to Si for device application. A distortion in the C-V curve was observed for samples without nitridation, which is not observed for nitrided samples. The distortion in C-V curves was found to be substantially reduced as a result of Si nitridation, under the condition of reduced plasma power.