Effects of Moisture Exposure and Total Dose Irradiation on MOS Low Frequency Noise

Abstract

We have studied the effects of moisture exposure and total dose irradiation on MOS low frequency noise. We compare the effects of moisture on the 1/f noise of nMOS and pMOS devices and how the noise changes for each with irradiation. We also investigate the gate-voltage and frequency dependences of the 1/f noise of these devices, and their changes with total dose irradiation. Large increases in low frequency noise were observed in pMOS devices exposed to moisture, before and after irradiation, while the noise for moisture-exposed nMOS devices was comparable to that of non-exposed nMOS devices. It has been suggested that these differences may be related to the inhibited diffusion of moisture to the gate oxides in nMOS devices due to phosphorus incorporation in the field oxide regions that are adjacent to and/or overlie the sources and drains. Phosphorus inhibits moisture diffusion; in contrast, boron can enhance moisture diffusion in the gate oxides of pMOS devices. Significant changes in the gate-voltage dependence of the 1/f noise were also observed for the pMOS devices after irradiation, while for the nMOS devices the gate-voltage dependence changed relatively little. These changes suggest that irradiation has altered the defect energy distribution in our pMOS devices, resulting in a more uniform distribution after irradiation. We conclude that these results can be explained by a simple trapping model, and that frequency and gate-voltage dependences of the noise can be a valuable means in revealing trap energy distributions in MOSFET devices before and after irradiation.