A study of the oxidation of tantalum nitride by ellipsometry and auger electron spectroscopy

Abstract

Ellipsometry and Auger electron spectroscopy in conjunction with in-situ ion sputtering have been used to study the thermal and anodic oxidation of thin tantalum nitride (Ta 2N) resistor films which are used in microelectronic circuits. In addition, the effects of thermal oxidation on the resistor-conductor contact resistance and conductor adhesion have been investigated. Thermal oxide thickness and stoichometry were estimated by Auger electron spectroscopy. A more accurate determination of oxide thickness was obtained by using multiple angle-of incidence ellipsometry. The thermal oxide was found to demonstrate a parabolic growth rate, in agreement with other workers. It was determined that the contact resistance should not be adversely affected by oxidation of the tantalum nitride at room temperature for storage times of several months; no significant decrease in the conductor adhesion was observed for oxide thicknesses up to 8 nm. A significant difference in the stoichiometry and refractive index of the thermally and anodically oxidized films was found, however. Depletion of the nitrogen from the surface of the anodically oxidized Ta 2N films resulted in an increase in the refractive index of the anodic oxide layer to a value close to that of pure Ta 2O 5.