Abstract
A two-mirror projection Schwarzschild objective (reduction ratio ×5), formed by two aspheric mirrors and developed as part of upgrading a lithographic workbench with the operating wavelength of 13.4 nm, is proposed. The measurement procedure and results of correction of the shape of the aspheric mirrors and aberrations of the objective lens in the assembled version are described in detail. As a result of several corrections of local errors by an ion beam, a root-mean-square deviation of the shape of the primary mirror of 0.8 nm is achieved. The objective-lens aberrations were equal to 5.4 nm. Simulation of the resolving power of the objective lens, taking into account the measured aberrations, shows that 200-nm-wide strips are resolved with a contrast of 32%, 100 nm—23%, and 30 nm—15%. The reflectivities of the multilayer Mo/Si mirrors with an anti-stress Cr/Y sublayer were 63–65% depending on the coordinate on the mirror. The reasons why it was not able to correct the aberration of the objective lens to the level of 1 nm necessary for achievement of the diffraction limit of resolution are discussed.
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