Pattern dependent distortion and temperature variation in EUV mask

Extreme ultraviolet lithography (EUVL) uses reflective optics due to the high absorption of EUV sources, and EUV masks consist of multiple layers of composites to increase reflectance. As repeated exposure proceeded, heat accumulation due to energy absorption and resulting heat deformation were observed in each layer constituting the EUV mask. In particular, the absorber is made of a material with high absorption rate, so the temperature accumulation and deformation are different depending on the part with and without the absorber. This means that thermal distortion can cause mask overlay and local critical dimension uniformity (LCDU) problems, resulting in lower process yields. In this paper, we will examine the temperature accumulation and heat deformation depending on the presence of absorber when electrostatic chuck (ESC) and hydrogen cooling are applied.