Self-cleaning reflective optical elements for use in X-ray optical systems, and optical systems and microlithography systems comprising same

An EUV-reflective mirror, comprising:

• a mirror substrate having a reflection surface;
• a multilayer film formed on the reflection surface so as to confer EUV-reflectivity to the mirror, the multilayer film having an upper surface and comprising alternating first and second layers laminated superposedly relative to each other, each first layer being formed of a high-Z material and each second layer being formed of a low-Z material, wherein the laminated first and second layers collectively form an interference coating;
• and
• a protective layer formed on the upper surface of the multilayer film, the protective layer comprising a material exhibiting an ability to photocatalyze, when irradiated by an energizing wavelength of light, molecules of an oxygen-containing gas so as to form oxygen free radicals that are reactive to carbon-containing compounds contacted by the free radicals.

A reflective reticle defining a pattern to be transferred from the reticle to a lithographic substrate by EUV lithography, the reticle comprising:

• a reticle substrate;
• a multilayer film formed on the reticle substrate so as to confer EUV-reflectivity to the reticle substrate, the multilayer film having an upper surface and comprising alternating first and second layers laminated superposedly relative to each other, each first layer being formed of a high-Z material and each second layer being formed of a low-Z material, wherein the laminated first and second layers collectively form an interference coating;
• a first protective layer formed on the upper surface of the multilayer film, the first protective layer comprising a material exhibiting a photocatalytic ability when irradiated by an energizing wavelength of light;
• a patterned absorbing-body layer formed on the first protective layer, the absorbing-body layer being segmented into individual absorbing bodies that, together with spaces between the individual absorbing bodies, define a reticle pattern;
• and
• a second protective layer formed on respective upper surfaces of the absorbing bodies, the second protective layer comprising a material exhibiting a photocatalytic ability when irradiated by an energizing wavelength of light.

A reflective reticle defining a pattern to be transferred from the reticle to a lithographic substrate by EUV lithography, the reticle comprising:

• a reticle substrate;
• a multilayer film formed on the reticle substrate so as to confer EUV-reflectivity to the reticle substrate, the multilayer film having an upper surface and comprising alternating first and second layers laminated superposedly relative to each other, each first layer being formed of a high-Z material and each second layer being formed of a low-Z material, wherein the laminated first and second layers collectively form an interference coating;
• an absorbing-body layer formed on the upper surface of the multilayer film, the absorbing-body layer being segmented into individual absorbing bodies that, together with areas of the upper surface located between the individual absorbing bodies, define a reticle pattern;
• and
• a protective layer coated over the absorbing bodies and over the regions of the upper surface situated between the absorbing bodies, the protective layer comprising a material exhibiting a photocatalytic ability when irradiated by an energizing wavelength of light.

An EUV lithography system, comprising:

• an EUV source that generates an illumination beam of EUV light;
• an illumination-optical system situated and configured to guide the illumination beam from the EUV source to an EUV-reflective reticle that defines a pattern to be transferred from the reticle to a lithographic substrate, wherein EUV light reflected from the reticle constitutes a patterned beam carrying an aerial image of a region of the reticle illuminated by the illumination beam;
• and
• a projection-optical system situated and configured to guide the patterned beam from the reticle to the lithographic substrate, thereby transferring the pattern from the reticle to the substrate, wherein at least one of the illumination-optical system, the reticle, and the projection-optical system includes at least one EUV-reflective optical element that comprises (1) a multilayer film comprising alternating first and second layers laminated superposedly relative to each other, each first layer being formed of a first substance exhibiting a relatively large difference between its refractive index for EUV light and a refractive index in a vacuum, and each second layer being formed of a second substance exhibiting a relatively small difference between its refractive index for EUV light and the refractive index of a vacuum;
• and (2) a protective layer situated superposedly relative to an uppermost layer of the multilayer film, the protective layer comprising a photocatalytic material;
• and
• means for introducing an oxygen-containing gas to a vicinity of the EUV-reflective optical element, wherein the photocatalytic material, when illuminated by an energizing wavelength of light, forms oxygen free radicals from the oxygen-containing gas, the oxygen free radicals being reactive to carbon-containing compounds contacted by the free radicals.

An X-ray lithography system, comprising:

• an X-ray source configured to produce an illumination beam;
• an illumination-optical system situated and configured to guide the illumination beam from the X-ray source to a selected region on a reflective reticle defining a lithographic pattern to be transferred to a sensitive substrate, wherein the illumination beam reflected from the reticle constitutes a patterned beam carrying an aerial image of the illuminated region;
• and
• a projection-optical system situated and configured to guide the patterned beam from the reticle to the sensitive substrate, so as to transfer the pattern from the reticle to the sensitive substrate,
• wherein the reflective reticle comprises a reticle substrate, an X-ray-reflective multilayer film formed on the reticle substrate and having an upper surface, an absorbing-body layer formed on the upper surface of the multilayer film, the absorbing-body layer being segmented into individual absorbing bodies separated from one another on the upper surface according to the pattern, and a protective layer comprising a photocatalytic material formed on the upper surface of the multilayer film and between the upper surface and the absorbing bodies.

An X-ray lithography system, comprising:

• an X-ray source configured to produce an illumination beam;
• an illumination-optical system situated and configured to guide the illumination beam from the X-ray source to a selected region on a reflective reticle defining a lithographic pattern to be transferred to a sensitive substrate, wherein the illumination beam reflected from the reticle constitutes a patterned beam carrying an aerial image of the illuminated region;
• and
• a projection-optical system situated and configured to guide the patterned beam from the reticle to the sensitive substrate, so as to transfer the pattern from the reticle to the sensitive substrate,
• wherein the reflective reticle comprises a reticle substrate, an X-ray-reflective multilayer film formed on the reticle substrate and having an upper surface, an absorbing-body layer formed on the upper surface of the multilayer film, the absorbing-body layer being segmented into individual absorbing bodies separated from one another on the upper surface according to the pattern, and a protective layer comprising a photocatalytic material coating the absorbing bodies as well as intervening regions of the upper surface.

In an EUV lithography system that includes an EUV-reflective optical element that includes a multilayer-film interference coating, a method for preventing accumulation of contaminants on a reflective surface of the optical element, the method comprising:

• applying a protective layer to the reflective surface, the protective layer comprising a photocatalytic material;
• in the presence of an oxygen-containing gas, directing light of a photocatalytically energizing wavelength to impinge on the protective layer so as to cause the photocatalytic layer to generate oxygen free radicals from the gas;
• and
• allowing the oxygen free radicals to react with the contaminants and form volatile by-products.

In an EUV lithography system that includes an illumination-optical system, a projection-optical system, and an EUV-reflective reticle that includes a multilayer-film interference coating and a patterned absorbing-body layer formed over the interference coating, the absorbing-body layer being segmented into individual absorbing bodies separated from one another on the interference coating according to a pattern, a method for preventing accumulation of contaminants on the reticle, the method comprising:

• applying a protective layer to the reticle in a manner such that the protective layer covers regions of the interference coating between the absorbing bodies as well as respective upper surfaces of the absorbing bodies, the protective layer comprising a photocatalytic material;
• in the presence of an oxygen-containing gas, directing light of a photocatalytically energizing wavelength to impinge on the protective layer so as to cause the photocatalytic layer to generate oxygen free radicals from the gas;
• and
• allowing the oxygen free radicals to react with the contaminants and form volatile by-products.