Radiation Effects Introduced by X-Ray Lithography in MOS Devices

Abstract

The effects of low energy ionizing irradiation on MOS structures, with doses typical of those encountered in x-ray lithography, were studied in capacitors and transistors. The capacitor studies indicated the irradiations induced a slow trapping instability and an increase in surface state density. This surface state density increase was partially annealed at 450C in N2 after 1/2 hour. Transistor threshold shifts were largely annealed away under these conditions. However, a shift of 250 mV was observed in 1000 Å oxides which was not annealed away. In the 250 Å case, 50 mV remained after anneal. Even in the thinnest oxides studied (250 Å oxides) increases in subthreshold swing as large as 35% were encountered. This degradation was only partially annealed away under the conditions listed above. No channel length dependence to the effect was uncovered (down to 1 μm channel length).