Impact of MoSi2 crystal structure on nano-membrane emissivity

As the EUV pellicle becomes more widely applied in the semiconductor industry, efforts are carried out to develop an EUV pellicle with a transmittance of over 90% and a heat emission efficiency that can withstand the increasing EUV source power. A metal silicide applied to such a pellicle can form crystal structures exhibiting different thermal properties depending on it. In this paper, the rapid thermal annealing process was performed to crystallize the MoSi₂ pellicle composite and subsequent thermal property evaluation confirmed the change in heat emission efficiency depending on the crystal structure. On the SiNx membrane fabricated through KOH wet etching, MoSi₂ and SiNx were deposited through co-sputtering and reactive sputtering, respectively. The composite films were annealed at various temperatures and time conditions through a rapid thermal annealing process. The crystallinity and resistivity of the films were analyzed using XRD and 4-point probe. Heat load tester was introduced to evaluate heat emission efficiency. The temperature of the pellicle surface was measured by optical pyrometer under 808 nm laser irradiation conditions, emulating the EUV exposure process. It was confirmed that the hexagonal and tetragonal structures of MoSi₂ were formed in the pellicle according to the annealing temperature. Structural change due to the heat treatment alters the band structure, which leads to a change in free-electron density. According to the Drude model, these variations in free electron density can affect the thermal emissivity of nano-membrane structures. For the heat load test, the tetragonal structured MoSi₂ pellicle with low resistivity reached lower temperature at the same thermal load, thereby confirming the higher heat emission efficiency compared to that of the hexagonal structure.