Substrate defects affecting gate oxide integrity

During the past 20 years, there have been several breakthroughs regarding t he research on grown-in defects in Czochralski silicon (CZ-Si) for commerci al use. The presence of oxide defects originating in CZ-Si was first report ed in 1979. and it was soon proposed that they could be eliminated by sacri ficial oxidation, as well as by nitrogen annealing or hydrogen annealing. I n 1990, crystal-originated particles were reported, but the origin of the d efects remained unclear. Octahedral void defects were found under oxide def ects in 1995, and in 1996, octahedral void defects were also found in bulk CZ-Si. A series of these discoveries lead some manufacturers of Si metal-ox ide-semiconductor large-scale integrated circuits to widely recognize that the octahedral void defects are closely related to the failures of the actu al dynamic random access memories they manufactured. The principal factor f or the generation of gate-oxide defects may be oxide thinning at the corner s and/or edges of the voids (as a geometrical effect). Another factor may b e due to some impurities in the voids reducing the dielectric strength of g ate oxides, even though the presence of impurities that may have accumulate d in the void has not been directly observed, However, we have found two ki nds of thin marks located around the void defects after oxidation, and we a ssume that the marks are closely related to the impurities originating in t he void defects. (C) 2000 Elsevier Science S.A. All rights reserved.