Mask Haze Measurement by Spectroscopic Ellipsometry

Haze formation on a reticle continues to be a major problem for the semiconductor industry. Haze can be formed on the outside pellicle and on the quartz backside of the reticle. The major component of haze is known to be ammonium sulfate that comes from the reticle cleaning process. Reticle materials, exposure wavelength, the roughness of a photomask and haze affect resolution and process latitude. Thus, haze on a mask surface needs to be studied. We need to know the usable lifetime of the reticle in terms of haze formation and how to prolong reticle lifetime by removing haze, if possible. In this paper, we introduce the haze measurement method by spectroscopic ellipsometry. The quantity of haze including the roughness of the reticle can be accurately measured by spectroscopic ellipsometry. Spectroscopic data shows an increase in the measured ellipsometry value with energy dose given to the reticle. We confirm that this signal increase is a direct result of the increase in haze quantity with exposed dose.