Multilayer-film mirrors, lithography systems comprising same, and methods for manufacturing same

#This disclosure relates to multilayer-film reflective mirrors in which a multilayer film is formed on a surface of a mirror substrate. The disclosure also relates to methods for manufacturing multilayer-film reflective mirrors, and to projection-exposure systems (notably, lithography systems) comprising at least one such multilayer-film reflective mirror.

#In recent years, with advances in miniaturization of semiconductor integrated circuits, projection-exposure systems have been developed that use, instead of the ultraviolet (UV) light utilized by older projection-exposure systems, extreme ultraviolet (“EUV”) light. EUV light has substantially shorter wavelengths (for example, approximately 11 to 14 nm) than the UV light used previously. The shorter wavelength of EUV light improves the resolving power of optical systems that had reached their diffraction limits with respect to UV light. See Japan Laid-open Patent Document No. 2003-14893.

#In configuring a projection-exposure system using EUV light (such a system is called an “EUV lithography” system, abbreviated “EUVL” system), there are no known materials that both transmit EUV light and exhibit sufficient refraction to such light to be useful as EUV lenses. Consequently, in an EUVL system, the constituent optical systems must be configured using EUV-reflective mirrors. But, in this wavelength range, the mirrors must be either oblique-incidence mirrors that utilize total reflection due to their refractive index being slightly smaller than 1, or multilayer-film mirrors in which the respective phases of multiple fronts of weakly reflected light at layer interfaces are superposed constructively in the reflected light to obtain high overall reflectance.

#FIG. 1 is an elevational sectional view of a portion of the multilayer-film reflective mirror according to the first embodiment.

#FIG. 2 is a flowchart depicting steps in a method for manufacturing a multilayer-film reflective mirror according to the first embodiment.

#FIG. 3 shows the configuration of a magnetron-sputtering device used for forming layers on a mirror substrate according to the first embodiment.

#The following description is set forth in the context of representative embodiments that are not intended to be limiting in any way.

#The following description and other portions of this disclosure, including the claims, may use terms such as “up,” “down,”, “upper,” “lower,” “top,” “bottom,” “left,” “right,” “vertical,” “horizontal,” and the like. These terms are used herein to facilitate understanding of the relationships of various components with respect to an exemplary orientation. But, these terms are not intended to be construed in any manner that limits the disclosure to the literal meanings of these words. For example, as a result of simply turning a thing over, a “top” surface becomes a “bottom” surface, but the thing itself is unchanged.

#A multilayer-film reflective mirror according to a first embodiment is explained referring to the drawings. The multilayer-film reflective mirror is used, for example, in an EUV exposure device or the like that uses extreme ultraviolet light (EUV light) as the exposure light. FIG. 1 is an elevational section schematically depicting a portion of the multilayer-film reflective mirror 2 of this embodiment. The multilayer-film reflective mirror 2 comprises a multilayer film 6, having a structure in which layers 6a comprising molybdenum (Mo) and layers 6b comprising silicon (Si) are deposited periodically in an alternating manner on the surface of a mirror substrate made of a low-thermal-expansion glass polished to a precise shape (figure profile). A Si single-layer film 7 is deposited on the multilayer film 6 as an oxidation-prevention film. A capping layer 8, comprising a ruthenium (Ru) layer, is deposited on the Si single-layer film 7 to prevent carbon contamination and oxidation of the Si single-layer film 7. The multilayer film 6 comprises multiple layer-pairs of Mo layers 6a and Si layers 6b. In FIG. 1, however, only four layer-pairs of Mo and Si are shown.