Practical extracting method of PEB parameters by using rotating compensator spectroscopic ellipsometer

Abstract

It is important that more accurate process parameters are extracted to predict the results of each process by simulation. It is well known that both refractive index and absorption coefficient of photoresist (PR) are varied when the thickness of PR is changed during post exposure bake (PEB) process due to the de-protection of polymer and decrease of free volume. We applied fast scanning rotating compensator spectroscopic ellipsometry (RCSE) to PEB parameters extraction of chemically amplified resist (CAR). It is possible to analyze thin film properties such as refractive index with respect to each exposure wavelength. But we only used the obtained resist thickness change data of exposed CAR before and after PEB by using RCSE in order to find out the easiest way of extracting correct PEB parameters. The decreasing of PR thickness during PEB was measured. Exposure and PEB conditions were changed for various RCSE measurements and the differences of the optical and physical properties were used to extract the PEB parameters; kamp, kloss and activation energy of de-protection. This method can be easily adopted in a normal fab and lab so that one can easily determine the correct PEB parameters.