Accurate dimensional characterization of periodic structures by spectroscopic Mueller polarimetry

The potential of spectroscopic Mueller polarimetry for the dimensional characterization of periodic structures has already been discussed in several instances. With respect to standard scatterometry; the added value of the technique is related to the information contained in the 16 elements of the Mueller matrix, while usual scatterometry provides only two. The additional information can prove useful to decorrelate dimensional or optical parameters, and to assess the adequacy of the model describing the profiles to be reconstructed: if the model is adequate, the optimal values of the dimensional parameters must remain stable when the measurement conditions, and thus the input data, are varied. This issue has been addressed for a series of 1D gratings etched in bulk Si and characterized by a spectroscopic polarimeter operating in the visible (Horiba Jobin Yvon MM-16), as well as CD-SEM and state-of-the art CD-AFM. With the usual lamellar or trapezoidal models both the CD and thickness values exhibit up to 10 nm systematic variations with measurement conditions. In contrast, with an original model taking into account the non-flatness of the open areas between adjacent lines the parameters become consistent to within 2 nm, well below typical tool-to-tool offsets. The corresponding profiles are also compatible with the CD-AFM images.