Comparison of charge trapping in undoped oxides made by low- and high-temperature deposition techniques

Charge trapping has been studied in a series of undoped low-pressure deposited oxides made using either silane and oxygen in a low-temperature oxidation (LTO) process or pure tetraethylorthosilicate (TEOS) in a high-temperature process. The extent of charge trapping was determined by measuring the flatband voltage shift ΔV_fb, resulting from injection of either holes or electrons separately (using photo-assisted injection techniques) or from exposure to 10 keV X-rays, in which holes and electrons are simultaneously created in the oxide. It is found that hole trapping is similar in identically annealed LTO and TEOS oxides, but that electron trapping is much larger in the TEOS oxides. Electron trapping in TEOS oxides is also found to depend inversely on the electric field. These results are used to explain the observation that X-ray exposure results in much smaller changes in ΔV_fb in TEOS oxides than in LTO oxides at low applied fields, but to equivalent changes in ΔV _fb at high applied fields. O₂ anneals, but not N ₂ anneals, are found to decrease the extent of electron trapping in the TEOS oxides, supporting previous suggestions that the electron traps result from carbon in the TEOS gas