Research On Multilayer Coating Of EUV Collector Mirror Of Laser Plasma Source

In an extreme ultraviolet lithography(EUVL)system,the mirror,which is a core component,has high requirements in the fabrication of Mo/Si multilayer coatings.The Mo/Si multilayer coating has a high reflectivity for EUV light because of the principle of Bragg diffraction,which makes it possible for the mass production of ultra-violet lithography machines.The reflectance of the Mo/Si multilayer coating is closely related to the surface roughness and the structure of the coating.We can predict and improve the coating process by building multilayer coating deposition model.Therefore,this dissertation introduced the working principles,fabrication and detection methods of EUV multilayer coatings;and was focused on the study of Mo/Si multilayer coatings,and the mainly work are as follows.1.We first studied on the coating defect of the EUVL source collector with grating structures.By simplifying the complete physical model of magnetron sputtering coating,according to the relative motion law between the target and the substrate,the shading algorithm of the grating to the depositing particles,and the geometric line tracing method,a Mo/Si multilayer coating model was built to simulate the deposition of the thin film on the large aperture curved grating.The contour of the Mo/Si multilayer coating deposited on the grating was obtained by the model,and the simulation results were therefore characterized.Moreover,grating structures with Mo/Si multilayer coating was fabricated by magnetron sputtering machine in the experiment and measured by transmission electron microscope(TEM)and focused ion beam(FIB).The results of the experiment agree well with that of the simulation,so it proves that the model is accurate.Finally,the evolution of the defect size of the coating was studied with the change of the distance between the grating and the center of the collecting mirror.It was found that the defect range of coating on the collection mirror accounted for 1.15% of the whole collector mirror range.2.In addition,a complete physical model of magnetron sputtering coating was established.The model was established by simulating the following physical processes: 1)The interaction between Ar ion with Mo and Si targets was studied by using binary collision model,and the initial angle and energy distribution of sputtering particles were calculated.2)Monte carlo method(MC)was employed to simulate the movement of the sputtering particles in the gas,and the angle and energy distribution of sputtering particles were obtained when incident on the substrate.3)By means of molecular dynamics(MD),the collision processes of high-energy physical deposition sputtering particles with substrate was studied,including four processes: reflection,resputtering,bias diffusion and kinetic energy assisted diffusion.4)The modified embedded atom method(MEAM)and nudged elastic band(NEB)methods were used to calculate the barrier energy when the atom jumps to another position.5)The physical process of thermal diffusion of depositing atoms at low energy was studied by kinetic monte carlo method(KMC).3.Furthermore,the variation of the incident angle and energy distribution of depositing Mo and Si atoms with the environment pressure and the target-substrate distance was investigated by the established model,and the evolution of the surface roughness and power spectral density with the environment pressure and targetsubstrate distance were studied by fabricating Mo/Si multilayer samples using a DC magnetron sputtering coating machine.It was found that: as the environment pressure increases,the surface roughness of the multilayers increases;the larger the targetsubstrate distance,the lower the high spatial frequency roughness.4.In the end,the surface roughness,the structure and the reflectivity of the Mo/Si multilayer coating were studied under different substrate inclination angles.A magnetron sputtering machine was used to fabricate the Mo/Si multilayer coating samples at the substrate inclination angles of 0°,20°,30°,40°,50°,60° and 70°.The surface roughness of the coating was measured and the exponential relationship between the surface roughness and the substrate inclination angles was obtained.The reflectivity of the Mo/Si multilayer coating at the substrate inclination angle of 0°,20°,40°,50° and 60° was measured by the extreme ultraviolet spectrometer.TEM was used to measure the structure of the Mo/Si multilayer coating at the substrate inclination angle of 0°,50° and 70°.Moreover,the established model was used to simulate the structure of the Mo/Si multilayer coating at the substrate inclination angle of 0°,20°,40°,50°,60° and 70°,and the surface roughness was then calculated.The results both in the experiment and simulation showed that the roughness on the surface and the interfaces of the multilayer coating increased with the increase of the substrate inclination angle.Besides,the simulation and experimental results are in good agreement,verifying the high applicability of the model.The above models can be used to study the physical process of Mo/Si multilayer coating deposition,which can predict the structure of Mo/Si multilayer coating and realize the research on the technology of Mo/Si multilayer coating.It provides a theoretical basis for the deposition of multilayer coating on the EUVL source collector.