Spectroscopic ellipsometric scatterometry: sources of errors in critical dimension control

This numerical study focused on the errors that can occur when ellipsometric spectroscopic scatterometry programs are used for critical dimension (CD) control and other significant geometrical parameters. The role of the number of wavelengths, the measurements noise and the spectral range is analyzed in terms of CD precision. Conversely, an important part is devoted to the effect of a bad shaping modelling of the lines (corner rounding, foot and notch effects ) and bad characterization of the index. We show that the scatterometry technique is very resistant to measurement noise, even for a small number of wavelengths, although the spectral range has an important role on the CD calculation. We also give quantitative data about the accuracy needed on refractive index of the diffracting material must. Excepted for profiles with additional feet, the CD found is very close to the original line without geometrical defects (corner rounding and notches).