CHARACTERIZATION OF THE OPTICAL-PROPERTIES OF PECVD SINX, FILMS USINGELLIPSOMETRY AND REFLECTOMETRY

The optical properties of plasma-enhanced chemical vapor deposited (PE CVD) silicon nitride (a-SiNx) films are strongly dependent on the depo sition parameters. One of the important applications of a-SiNx is its use as an anti-reflection coating for submicron Deep UV (DUV) photolit hography, This application is primarily based on the ability to adjust the SiNx optical functions to the values optimal for the specific exp osure wavelength - 248 nm and, potentially, 193 nm - by changing the m aterial composition. Nitride films were deposited on Si wafers in a. p roduction PECVD reactor using dynamic deposition. Silane and ammonia g as flows were changed to create a matrix of wafers with changing compo sition, In this work we characterize the optical properties of the a-S iNx at 248 nm using a multiple wavelength and multiple angle of incide nce (MW-MAI) ellipsometer with a UV reflectometer. A new method is sug gested which combines the benefits of ellipsometry and reflectometry, and allows reliable measurement of film thickness (t), refractive inde x (n) and extinction coefficient (k) at the DUV exposure wavelength. T his method uses the effective medium approximation (EMA) to represent the optical properties of the SiNx. The limitations of the EMA interpr etation of strongly non-stoichiometric SIN, art: circumvented by corre cting the estimated value of the absorption of the material at exposur e wavelength using the measured reflectance. The results were found to be consistent with those obtained using research grade spectroscopic ellipsometry. The latter measurements were interpreted using the EMA a nd an effective dielectric function (EDF) approximation, The compositi on of the SiNx measured using the EMA model was found to correlate wel l with the deposition parameters and the results of Auger analysis of the material. (C) 1998 Elsevier Science S.A.