Optical objective for operation in EUV spectral region

A catoptric system having a reference axis and operable to form an image of a pattern-source, the system comprising:

• first, second, and third reflectors situated on the reference axis and a reflective element, situated on the reference axis between the second reflector and the third reflector, the first reflector including the pattern-source;
• and
• a combination of the second and third reflectors configured to form the image with a reduction factor N>1, of a substantially one-dimensional (1D) diffractive structure of the pattern-source in extreme UV light provided by only two diffracted beams of light, in a plane that is optically-conjugate to the first reflector, wherein the only two diffracted beams of light originate at the first reflector as a result of irradiation of the first reflector with an illumination beam of light, and
• wherein the only two diffracted beams of light do not include a beam of light that represents a specular reflection of the illumination beam of light at the first reflector,
• the second reflector includes a convex reflector unit defining a first opening therein,
• the third reflector includes a concave reflector unit defining a second opening therein,
• the reflective element is situated to reflect the illumination beam of light to the pattern-source,
• the system configured to:
• receive, at a surface of the convex reflector unit, the two diffracted beams of light delivered thereto through the second opening defined in the third reflector,
• receive, at the concave reflector unit, the two diffracted beams of light from the surface of the convex reflector unit and reflect the two diffracted beams of light through the first opening defined in the second reflector to form the image of the pattern-source at an image plane;
• wherein the two diffracted beams of light are generated at the pattern-source in response to the irradiating with the illumination beam received from the reflective element, and wherein the reflective element is situated to block light from the pattern-source and passing between the two diffracted beams of radiation produced at the pattern-source.

A catoptric system having a reference axis and comprising:

• a first pair of reflector elements that are symmetric to one another about the reference axis, each surface of the first pair of reflectors having a convex surface;
• a second pair of reflector elements that are symmetric to one another about the reference axis, each surface of the second pair of reflectors having a concave surface, wherein reflecting surfaces of the reflector elements from the first pair and face reflecting surfaces of the reflector elements from the second pair;
• and
• an illumination element disposed on the reference axis between the first pair of reflector elements and the second pair of reflector elements,
• the catoptric system configured to:
• receive, at the surfaces of the first pair of reflectors, optical radiation in a form of two diffracted beams of radiation delivered thereto from between the second pair of reflector elements, and
• form an image of an object by irradiating an image plane with optical radiation after the optical radiation has been reflected from the surfaces of the second pair of reflectors and after the optical radiation has passed between the first pair of reflectors,
• wherein the illumination element is situated to reflect an illumination radiation to the object, the two diffracted beams of radiation are generated at a substantially one-dimensional (1D) diffractive structure defined by the object in response to the illumination radiation received from the illumination element, and the illumination element is situated to block light passing between the two diffracted beams of radiation originating at the object.

A catoptric system having a reference axis and comprising:

• a primary mirror unit made of a first material and having a first area centered on the reference axis, the first area being devoid of the first material;
• a secondary mirror unit made of a second material and having a second area centered on the reference axis, the second area being devoid of the second material;
• and
• a reflective illumination element situated on the reference axis between the primary mirror unit and the secondary mirror unit,
• the catoptric system having a length defined by distance separating the primary mirror unit and the secondary mirror unit, the length equal to approximately 0.3 m,
• the catoptric system configured to image a substantially one-dimensional (1D) diffractive structure through the first and second areas onto an image plane in extreme UV light with a reduction ratio between 4 and 6,
• wherein the substantially 1D diffractive structure is characterized by a pattern period between 40 nm and 60 nm and is associated with a curved surface of an object, and
• wherein the image plane is separated from the primary mirror unit by about 25 mm and is separated from the secondary mirror unit by the primary mirror unit,
• the primary mirror unit having a concave reflecting surface,
• the secondary mirror unit having a convex reflecting surface,
• the system configured to:
• receive, at the convex reflecting surface of the secondary mirror unit, optical radiation in a form of two diffracted beams of radiation delivered thereto through the first area of the primary mirror unit, and
• form an image of an object by irradiating an image plane with the optical radiation after the optical radiation has been reflected from the concave reflecting surface of the primary mirror unit and after the optical radiation has passed through the second area of the secondary mirror unit,
• wherein the reflective illumination element is situated to reflect illumination radiation to the object, the two diffracted beams of radiation being generated at the object in response to the illumination radiation received from the reflective illumination element, and to block light propagating from the object between the two diffracted beams of radiation.