Characterization and Modeling of a Highly Reliable ONO Antifuse for High-Performance FPGA and PROM

The characteristics and reliability of ONO (oxide-nitride-oxide) anti-fuse devices prepared basing on 0.6µm SOI CMOS process have been studied experimentally and theoretically. The intrinsic principles of ONO dielectric breakdown were investigated with tunneling and emission models. It has been found that the conduction mechanisms of ONO dielectrics under high electric field (>10MV/cm) mainly obeys Fowler-Nordheim (F-N) tunneling and Poole-Frenkel (P-F) emission and Ohmic transport models. Meanwhile, the nitrogen depth distribution and the composition of the ONO stack films have been accurately determined using SIMS and EDX, respectively. The results indicate that the nitrogen concentration of interface between tunneling oxide and N+ sub-silicon is higher than that of interface between top oxide and N+ poly-silicon, which can contribute to prove the difference of top and bottom electrode interface barriers according to energy band diagrams of ONO anti-fuse devices. Besides, it is also found that the average breakdown voltage of ONO anti-fuse arrays and that of distribution decrease with increasing the number of anti-fuse cells, and the result is attributed to traps density of various areas. Moreover, the programming resistance of ONO anti-fuse cells and programming circuits decreases with increasing programming current, and the programming resistance of ONO anti-fuse cells can reach less than 200 ohm/cont when programming current is above 5mA. And the life of unprogrammed ONO anti-fuse devices can reach more than 40 years under an electric stress of 5.5v at the temperature from 25°C to 125°C. So, it can be concluded that the characteristics and reliability of the proposed ONO anti-fuse elements are suitable for applications in FPGA and PROM.