The study of the birefringence as MoSi based materials for immersion lithography

Abstract

According to the semiconductor technology roadmap, immersion lithography is emerging for 32 nm and below technology. Therefore, immersion lithography requires new process parameters such as high refractive index fluid, stepper, resist, and birefringence. A lot of research for those items has been done, and the components and materials of thin film used blankmask have become more important. The birefringence of thin film is an especially essential issue for the development of advanced technology. Accordingly, we studied birefringence with thin film characteristics. Having a transmittance of 6% at 193 nm, six different kinds of molybdenum silicon-based thin films were prepared by DC magnetron sputter. The thin films were deposited on 6.3 mm thick quartz using O2, N2, CH4 and CO2 reactive gasses. We studied the effects of thin film composition, substrate, heat treatment, and dopant in this paper. First, we measured the birefringence as thin film composition and substrate by the 250AT Exicor system. We studied the effect of reactive gas flow rate and types on birefringence, and we selected thin film material adaptable to reduce the birefringence from the above results. Next, we doped the transition metal to the selected materials to decrease the birefringence. Then we did heat treatment to the thin films by using rapid thermal process (RTP) to further reduce the birefringence. According to the results, we confirmed that the birefringence was influenced by thin film composition and it was controlled by the tuning of thin film composition, dopants, and heat treatment. Next, we analyzed the intensity of crystal state and density of thin films by using x-ray diffractometer (XRD) and x-ray refractometer (XRR). Finally, we analyzed the thin film characteristics by using various analytic tools.