Development of thermal emissivity calculation method for transmissive multilayer nanomembranes

The power of EUVL (extreme ultraviolet lithography) scanner continues to increase, making the heat dissipation characteristics of EUV pellicles increasingly crucial. The thermal and chemical stability of the EUV pellicles, which have a multilayer thin film structure, relies on the capping layer, and the thermal stability of the capping layer is determined by its emissivity (ε). However, it is challenging to directly measure the ε of an ultrathin film, such as the capping layer of the EUV pellicle. Although a method to obtain the ε of a target material is employed which measure the ε of the whole layer with a target material on a support membrane having low ε, no approach has been proposed to exclude the measurement changes caused by the support membrane. In this study, a methodology for obtaining the ε of a multilayer nanomembrane is proposed. Ruthenium (Ru) with a high ε at nanoscale was deposited on SiN_x membranes to have varying thicknesses. The ε of SiN_x film and Ru deposited SiN_x film were precisely characterized by infrared spectroscopy according to Kirchhoff's law. Based on transfer matrix method (TMM), the ε of Ru layers was theoretically calculated, fitting by DrudeLorentz oscillator model. Finally, reliability was verified by comparing the measurement results through a free-standing membrane without a support. In this way, if the contribution of a single element to the ε of a multilayer or composite membrane can be derived, engineering for a high-emissive layer that combines various components will be possible and used as EUV pellicle and further application research.