Improvement of gate dielectric reliability for p+ poly MOS devices using remote PECVD top nitride deposition on thin gate oxides

Dual layer dielectrics have been formed by remote PECVD deposition of ultra-thin (0.4 similar to 1.2 nn) nitrides onto thin thermal oxides grown on n-type Si(100) substrates. Activation of boron-implanted p+ polycrystalline silicon gate electrodes was accomplished by a high temperature anneal, 1 similar to 4 minutes at 1000 degrees C. Boron penetration through the dielectric film to the n-type substrate was investigated by performing a quasi-static C-V analysis and monitoring the flatband voltage shift. Boron penetration was effectively stopped by a 0.8 nm nitride film, and partially stopped by a 0.4 nm nitride film. In addition, the charge to breakdown as monitored by the Q(bd) value to 50% cumulative failure was highest for the device with the 0.8 nm top nitride, and decreased significantly in the thermal oxide. However there were essentially no differences in the mid-gap interface state densities, D-it, between oxide and nitride/oxide gate dielectric structures with Al gate. It is concluded that the 0.8 nm of plasma nitride was sufficient to block boron atom out diffusion from a heavily implanted p+ poly-Si gate electrode under the conditions of an aggressive implant activation anneal to improve the dielectric reliability.