INFRARED REFLECTION-ABSORPTION SPECTROSCOPY OF PHOTORESIST FILMS ON SILICON-WAFERS - MEASURING FILM THICKNESS AND REMOVING INTERFERENCE-FRINGES

Infrared reflection absorption spectroscopy (IRRAS) of thin films produces IR spectra in sampling situations where transmission spectroscopy would be impossible, such as in situ spectroscopy of films on thick substrates, and it is also more sensitive because the path length is more than doubled. Unfortunately, interpretation of IRRAS data can be complicated by the existence of interference fringes which prevent the accurate determination of peak heights and areas. A method has been devised to use the information provided by these fringes to obtain the thickness and complex refractive index of the film in regions of little or no absorption. This information potentially could be used to calculate the fringe-free optical constant spectra by use of a Kramers-Kronig transformation. We also confirm that the interference effects can be eliminated to a large extent by incorporating a mirror behind a high-resistivity double-polished silicon wafer during IRRAS data collection.