A possible wafer heating during EUV exposure

Extreme ultraviolet (EUV) lithography is the most promising candidate for sub-1x nm pattering. CO2 laser irradiates to a Sn droplet and then, EUV radiation can be emitted. In this process, infrared radiation (IR) is simultaneously emitted 3 to 5 times more than EUV radiation. In order to suppress IR, spectral purity filter (SPF) [8] at collector mirror and dynamic gas lock (DGL) [4] are used. Nevertheless, some amount of IR still reaches to the wafer and it can lead to wafer heating issue, so that we investigated temperature and deformation of the wafer by using finite element method (FEM) simulation. Two different silicon wafer types are compared. There is a difference in temperature and deformation between single layered wafer with and without the bottom chuck. We also found that the temperature increased more with added stacks like hard mask or photoresist on the top of the wafer.