CHARACTERIZATION OF GRADED REFRACTIVE-INDEX SILICON OXYNITRIDE THIN-FILMS BY SPECTROSCOPIC ELLIPSOMETRY

Lavers with a continuous variation in the optical index with thickness were characterized by spectroscopic ellipsometry. These oxynitride fi lms were grown by electron cyclotron resonance plasma-enhanced chemica l vapor deposition using silane as a silicon precursor and oxygen and nitrogen as plasma gases. Specific linear and parabolic index profiles were fabricated by computer-controlled gas flow. Reduction of ellipso metry data measured ex situ on these films was performed with polynomi al analysis. The validity of this approach was checked by a depth anal ysis via chemical etching. An investigation of the limits of the metho d is presented. (C) 1998 Elsevier Science S.A.