Electrical characterization of doped and undoped PECVD TEOS oxides

It is shown that charge in plasma-enhanced chemical vapor deposition (PECVD) TEOS-based films is generated as a result of high-temperature annealing. This effect is dependent on oxide type and can be greatly reduced by the use of good-quality USG barrier layer or reduction of the anneal temperature. However, at very high temperatures the amount of generated charge is substantial. It was found that neither the use of TEOS as a precursor nor plasma processing is independently detrimental to the levels of charge in the oxides. The analytical data show some buildup of impurities at the Si-SiO₂ interface. Although impurity concentrations are comparable to those of the other oxides tested, this does not preclude the possibility of interactions of the plasma field with impurities to influence the fixed charge. The thermal energy of the postdeposition cycle above 875°C may be high enough to cause redistribution of ions and/or activation of species that are not detected electrically in as-deposited films. The charge observed is most likely localized close to the Si-SiO₂ interface and seems proportional to the length of plasma exposure