Quantitative Study of Charge‐to‐Breakdown of Thin Gate Oxide for a p+‐Poly‐Si Metal Oxide Semiconductor Capacitor

Abstract

The charge-to-breakdown (Q bd ) for p + -poly-Si MOS capacitors under positive and negative gate-bias stress was investigated. Among the various boron-implanted poly-Si samples, Q bd (+) increases with dopant concentration, but Q bd (-) decreases with the boron concentration. Meanw ile a large difference was found between the Q bd (+) and Q bd (-) values. Evidence for various degree of band bending of poly-Si was observed from C-V and Fowler-Nordheim tunneling measurements. From gate-voltage shift (ΔV g ) data after constant current stress, the centroid of the generated positive trapped charge can be determined. We modified the charge-trapping model to explain the above Q bd behavior. Hole trapping is the cause of oxide breakdown. The observed difference between gate-positive and gate-negative Q bd is due to a polarity-dependent critical trapped charge density which depends on the critical electrical field somehow related to the boron implantation. As the generated positive trapped charge reaches a critical value, part of the localized electric field near the anode disappears and the remaining part of the electric field (E) is enhanced. This critical E field triggers thermal runaway and oxide breakdown. Therefore, we determine that the amount of Q bd is related to the boron implantation.