X-Ray Lithography Induced Radiation Effects In Deep Submicron Cmos Devices

Abstract

X-ray lithography introduces device radiation damage from the high energy photons during the lithography process. We have studied this effect on deep submicron n- and p-channel MOSFETs with gate dielectric thickness at 7 to 13 nm. After the x-ray irradiation the device characteristics are strongly affected by the generation of oxide charges, interface states and electron traps. These introduced damages cause the reduction of device transconductance, shift of the threshold voltages and increased leakage current. However, this degradation of device and circuit is lessened from technology scaling by thinning the gate oxide and lowering the supply voltage. The x-ray radiation damage, induces interface states and oxide charges which can be annealed out with a low temperature (400°C) forming gas (FG, 90% N₂, 10% H₂) annealing process. The device properties are essential unchanged after the annealing process. However, the residue damage is shown to enhance hot-carrier instability of p-channel devices if the remaining neutral traps act as electron or hole traps in the SiO₂. In this paper, we investigate the radiation effects on the n- and p-channel MOSFETS fabricated with deep submicron device processes with thinner gate oxides and compare the hot carrier reliability of these devices after the synchrotron x-ray irradiation and also after the post metal forming gas annealing. The results indicate the device hot carrier instability has no effect on the devices with thin gate oxide with thickness approaching the electron tunneling range.