Molecular orbital theory examination into improved gate oxide integrity through the incorporation of nitrogen and fluorine

Molecular orbital theory was used to examine the improved gate oxide integr ity of MOS (metal-oxide-semiconductor) devices against hot-hole injection; this improvement is associated with the incorporation of a nitrogen atom an d subsequent incorporation of a fluorine atom. The bond dissociation energi es of eight cluster models containing representative chemical bond environm ents in a modified oxide film - -Si-O-Si-, N(-Si-O-)-(3), Si-N(-Si)-O-Si, S i-N(-O-Si)(2), Si-N(-Si)-H, Si-F, Si-O-F, Si-N(-Si)-F - were extensively ev aluated for both the neutral state and the hole-trapped state since the bon d dissociation energy change is thought to be a relevant measure of bond du rability against hot holes. A semiempirical molecular orbital program packa ge, MOPAC, was used because of its short computational time. The applicabil ity of MOPAC to the hole-trapped state was confirmed by comparing the MOPAC results with those obtained by first-principle calculations. The calculate d changes in bond dissociation energy upon hole trapping imply that the imp rovement stems from the chemical bond formation of a silicon-nitride-like s tructure, N(-Si-O-)-3, in oxide bulk, and a =Si-F structure in the Si/SiO2 interfacial region. The synergetic effect of nitrogen and fluorine incorpor ation is most likely brought about by the formation of a Si-2=N-F structure in both the oxide and the interfacial region. (C) 1999 Elsevier Science B. V. All rights reserved.