Capping layer for EUV optical elements

A device manufacturing method using a lithographic apparatus, the method comprising:

• providing a mask containing a pattern to a first object table;
• providing a substrate at least partially covered by a layer of energy-sensitive material to a second object table;
• and
• irradiating said mask and imaging irradiated portions of said pattern onto said substrate;
• said irradiating comprising directing radiation onto a surface of an optical element, the surface having a capping layer formed of a relatively inert material,
• wherein said relatively inert material is selected from the group consisting of:
• diamond-like carbon, Ru, Rh, TiN, MgF2, LiF, C2F4 and compounds and alloys thereof.

A lithographic projection apparatus, comprising:

• an illumination system constructed and arranged to supply a projection beam of radiation;
• a first object table provided with a first object holder constructed and arranged to hold a mask;
• a second object table provided with a second object holder constructed and arranged to hold a substrate;
• a projection system constructed and arranged to utilize said radiation to image an irradiated portion of the mask onto a target portion of the substrate;
• and
• at least one of said illumination system and projection system having a sensor with a surface on which radiation is incident and a capping layer covering said surface, said capping layer being formed of a relatively inert material,
• wherein said relatively inert material is selected from the group consisting of:
• diamond-like carbon (C), Ru, Rh, Au, MgF2, LiF, C2F4, TiN and compounds and alloys thereof.

A lithographic projection apparatus, comprising:

• an illumination system constructed an arranged to supply a projection beam of radiation;
• a first object table provided with a first object holder constructed and arranged to hold a mask;
• a second object table provided with a second object holder constructed and arranged to hold a substrate;
• a projection system constructed and arranged to utilize said radiation to image an irradiated portion of the mask onto a target portion of the substrate;
• and
• at least one of said illumination system and projection system having an optical element with a surface on which radiation is incident and a capping layer covering said surface, said capping layer being formed of a relative inert material,
• wherein said optical element is a reflector having a multilayer reflective coating on which said capping layer is provided;
• and
• wherein said relative inert material is selected from the group consisting of:
• diamond-like carbon (C), boron-nitride (BN), boron carbide (B4C), silicon nitride (Si3N4), silicon carbide (SiC), B, Pd, Ru, Rh, Au, MgF2, LiF, C2F4, TiN and compounds and alloys thereof.

A lithographic projection apparatus, comprising:

• an illumination system constructed and arranged to supply a projection beam of radiation;
• a first object table provided with a first object holder constructed and arranged to hold a mask;
• a second object table provided with a second object holder constructed and arranged to hold a substrate;
• a projection system constructed and arranged to utilize said radiation to image an irradiated portion of the mask onto a target portion of the substrate;
• and
• at least one of said illumination system and projection system having an optical element with a surface on which radiation is incident and a capping layer covering said surface, said capping layer being formed of a relatively inert material,
• wherein said optical element comprises:
• a reflector having a multilayer reflective coating on said surface, said multilayer reflective coating comprising a plurality of layers of a first material having a relatively low refractive index at the wavelength of said projection beam;
• layers of a second material having a relatively high refractive index at said wavelength and alternating with said layers of said first material;
• and
• said capping layer comprises:
• a first sub-layer of said first material;
• a second sub-layer of a third material having a refractive index at said wavelength higher than said first material and being more inert than said second material;
• and
• a third sub-layer formed of a fourth material that is relatively inert, said first, second and third sub-layers being provided in that order with said third sub-layer outermost.