Sidewall angle measurements using CD SEM

Measurement of the sidewall angles of features (line, trench or contact hole) is important for focus exposure matrix (FEM) wafers and shallow trench isolation (STI) fillings. Cross section SEM (scanning electron microscope), tilted stage inspection SEM and AFM (atomic force microscope) are common tools to obtain information on sidewall angles. However, sidewall angles are not routinely determined using in-line metrology tools like CD (critical dimension) SEM. In this study, we use CD SEM to measure feature edge widths (EW) in both FEM and STI wafers. The sidewall angle is estimated from known feature height (resist thickness or etched trench depth) with a linear slope assumption. A flared tip AFM (Veeco SXM) or a cross section SEM (X-SEM) is used as a reference to check CD SEM performance on sidewall angle measurements. We find that for sidewall angles less than 88°, CD SEM measurements match reference tool measurements on sidewall angle well. The limitations of CD SEM on sidewall angle measurement are also discussed