Defects at electrode-oxide and electrode-silicon interfaces in VHSI device structures

The effect of impurities on the electrical properties of metal silicon interfaces has been investigated for Pt, Ta, Ti, Hf, and their silicides. These silicon-electrode systems are of critical importance in VHSIC and other VLSI systems. The impurities investigated include oxygen (as in SiO2 or metal oxides), carbon, and silicon dopants. In order to quantitatively determine the effect of these impurities on the electrical properties of the neutral silicon interface microanalysis measurements have been combined in situ with measurements of Schottky barrier height via internal photoemission. Using this combination of techniques, the interface chemical composition can be determined and related to the measured Schottky barrier height. With a few exceptions, we have found that reliable, reproducible, Schottky diodes on silicon can only be formed if the metal silicon structure is annealed above the silicide formation temperature, so that the silicide formation reaction can clean up the interface. In addition, we have determined the mechanism for the poor reproducibility in barrier height for a number of refractory metal silicon contacts which is related to thin oxides that may be present at the interface.