CHARACTERIZATION OF THE OXIDATION OF TANTALUM NITRIDE

Sputter-deposited non-stoichiometric tantalum nitride films are used f or laser-trimmed thin-film resistors owing to their stability and proc essability. The films are stabilized by heating in air to form a passi ve Ta2O5 film. This passive film can be destroyed if the resistors are exposed to aggressive thermal or chemical conditions. Thus we have st udied sputtered TaN films and resistors deposited on SiO2 and Al2O3 su bstrates and exposed to either KOH solutions or air at 250-500-degrees -C for various times. The oxidized films have been characterized with Auger electron spectroscopy (AES), x-ray photelectron spectroscopy (XP S), x-ray absorption near-edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS). Chemical shifts in the NOO Auger s pectrum have been used to show that the initial fraction of deposited TaN reacts with the SiO2 surface to form Ta2O5. X-ray photoelectron sp ectroscopy showed that although significant amounts of oxygen can be p resent in the sputtered films, little of the tantalum is fully oxidize d to Ta2O5. X-ray photoelectron spectroscopy was also used to show tha t the oxide layer slowly increases in thickness when heated in air. Fi nally, KTaO3 was identified by XANES on the surface of films exposed t o KOH. Once the passive Ta2O5 is converted to KTaO3, further oxidation of the underlying films occurs. The mechanism of oxidation of these f ilms and the unique advantages of each spectroscopic technique are dis cussed.