Refractive index measurements of photoresist and antireflective coatings with variable angle spectroscopic ellipsometry.

Lithography requires accurate knowledge of film thickness and refractive index (n and k) for photoresists (PR) and antireflective coatings. It is becoming increasingly necessary to track changes in refractive index over the process cycle. The refractive index can change by as much as 0.04 in both n and k simply by bleaching the film(1). These changes can be caused by changes in film chemistry by processing such as baking and bleaching by UV exposure(1,2). Thus, keeping track of changes in the refractive index is useful to both resist and antireflective coating manufacturers as well as the process engineer. This work uses Variable Angle Spectroscopic Ellipsometry (VASE(R)) to determine the refractive index of photoresist and antireflective coatings over the spectral range 190-1700 nm. Theory, hardware, and applications of Spectroscopic Ellipsometry are discussed along with procedures used to simultaneously extract the refractive index and film thickness of photoresist and antireflective coatings. Examples of commonly used films are presented.