Application of spectroscopic ellipsometer technology to titanium nitride process monitoring

Abstract

Titanium nitride (TiN) is increasingly used in multilevel metallization processing for a variety of applications: as an antireflective coating, an aluminum diffusion barrier layer and a tungsten interconnect and plug adhesion layer. Typical process control techniques are optical measurement of reflectivity of film thickness, or four-point probe measurements of sheet resistance monitor wafers. Reflectivity measurements of titanium nitride antireflective coatings at the stepper exposure wavelength are straightforward, but direct optical thickness measurements of TiN layers have been difficult to make. Spectroreflectometers rely on accurate values of refractive index dispersion (the change in RI as a function of wavelength) to calculate thickness. Single wavelength ellipsometers do not collect sufficient data to calculate thickness as well as the real and imaginary portions of the refractive index. Spectroscopic ellipsometry offers the ability to determine thickness and refractive index dispersion. This paper investigates possible correlation between the refractive index of TiN and its composition. Refractive index and thickness of TiN are determined by spectroscopic ellipsometry, and composition is determined by Rutherford backscatter spectrometry and Auger electron spectroscopy. If a correlation can be identified, the possibility exists for nondestructive process monitoring of TiN composition. A standard coherent sputtered TiN and two different CVD TiN processes will be examined.