Suppression of boron transport out of p+ polycrystalline silicon at polycrystalline silicon dielectric interfaces

The transport of B atoms out of p(+) polycrystalline silicon (poly-Si) gate electrodes through SiO2 gate oxides to the Si-SiO2 interface during dopant activation anneals degrades performance and reliability of hole-conducting (p-channel) field effect transistors. This article studies the suppression of B atom transport by using remote plasma processing to form ultrathin Si3N4 and silicon oxynitride diffusion barrier layers between p(+) poly-Si gate electrodes and SiO2 gate dielectrics. Suppression of B atom transport has been monitored through electrical measurements, demonstrating that similar to 0.8 nm of Si3N4, equivalent to a N areal density of similar to 4.5 x 10(15) atoms cm(-2) is sufficient to effectively suppress B out diffusion during aggressive anneals of similar to 1 min at 1000 degrees C. The suppression and transport mechanisms in nitrides, oxides, and oxynitrides have been studied by varying the N atom areal density by alloying. Quantum chemistry calculations suggest that B transport occurs through the formation of donor-acceptor pair bonds between B+ ions and nonbonding electron pairs on oxygen atoms with the transport process requiring a connected O atom percolation pathway. Donor-acceptor pair bonds with B+ ions are also formed with N atoms in nitrides and oxynitride alloys, but with a binding energy more than 1.5 eV higher than B+ ion O-atom bonds so that nitrides and oxynitride alloys effectively block B diffusion through the formation of a deep trapping site. (C) 1999 American Vacuum Society. [S0734-211X(99)05104-5].