SPECTRAL PURITY FILTER FOR MULTI-LAYER MIRROR, LITHOGRAPHIC APPARATUS INCLUDING SUCH MULTI-LAYER MIRROR, METHOD FOR ENLARGING THE RATIO OF DESIRED RADIATION AND UNDESIRED RADIATION, AND DEVICE MANUFACTURING METHOD

摘要

A multi-layer mirror includes a multi-layer stack. The multi-layer stack includes a plurality of alternating layers with a multi-layer stack top layer and a spectral filter top layer arranged on the multi-layer stack. The spectral filter top layer includes a first spectral purity enhancement layer that includes a first material m1 and has a first layer thickness d1, an intermediate layer that includes a second material m2 and has a second layer thickness d2. The intermediate layer is arranged on the multi-layer stack top layer. The first material is selected from SiN, Si3N4, SiO2, ZnS, Te, diamond, CsI, Se, SiC, amorphous carbon, MgF2, CaF2, TiO2, Ge, PbF2, ZrO2, BaTiO3, LiF or NaF. The second material includes a material different from the first material, and d1+d2 has a thickness between 1.5 and 40 nm.