Immersion optical lithography system having protective optical coating

#The invention relates optical lithography systems and more particularly to the structure and processing of such systems for use in optical immersion lithography.

#One of the conditions necessary for the growth of the semiconductor industry is the ability to print ever smaller features on an integrated circuit (IC). However, recently, optical lithography is facing several challenges which may impede the further development of semiconductor technology. Investments have been made in techniques such as x-ray lithography and electron beam lithography as an alternative to traditional optical lithography. However, optical immersion lithography has garnered interest as potentially meeting the demands of improved semiconductor technology for printing smaller-sized features.

#The size W of the minimum feature that may be printed with an optical lithography system is determined by the following equation: W=k1λ/n sin α;  Eq. 1 where k1 is the resolution factor, λ the wavelength of the exposing radiation and nsinα is the numerical aperture (“NA”) of the interfacial medium through which the exposing radiation is transmitted at the interface to the feature being printed.

#FIG. 1 is a sectional view illustrating an immersion lithography system in accordance with an embodiment of the invention.

#FIG. 2 is a sectional view illustrating an immersion lithography system in accordance with another embodiment of the invention.

#FIG. 1 is a sectional view illustrating an exemplary immersion lithography system 100 in accordance with one embodiment of the invention. As shown in FIG. 1, the immersion lithography system 100 includes an optical imaging system 101 including an optical source 103, and an optical element 107. A photomask or “mask” 105 is mounted to a platform of the optical imaging system. The optical source 103 is used to produce light for projecting an image of a mask 105 (also sometimes referred to as a “reticle”) onto an article 150 such as a semiconductor wafer or other article having an exposed photolithographically imageable surface. Illustratively, the optical source produces light having a nominal wavelength of 248 nanometers, 193 nanometers or 157 nanometers. The optical element 107 is used to cast an image of the mask onto the article 150. Typically, the optical imaging system 100 includes a series of optical elements, e.g., focusing lenses, corrective lenses, collimators, filters, etc., which cooperate together in casting the image onto the article. Optical element 107 represents one such optical element at or near a lower extremity 110 of the optical imaging system 101. As illustrated in FIG. 1, imaging light directed towards the article 150 exits the optical imaging system 101 through a face 109 of the optical element 107. An exemplary optical element 107 takes a form of a convex lens. However, the face 109 of the optical element may have any of a flat, concave or convex shape. Alternatively, the face 109 may include one or more of a flat portion, a concave portion and/or a convex portion.

#FIG. 1 illustrates use of the immersion lithography system 100 to cast an image onto a photo-imageable surface 152 of an article 150, e.g., a semiconductor wafer or other lithographically patternable article. The immersion lithography system projects the image of the mask onto the article through a liquid 140 which occupies a space between the face 109 of the optical element 107 and the article 150. Illustratively, the liquid 140 entirely covers the surface 152 of the article 150. As illustrated in FIG. 1, the face 109 of the optical element 107 contacts the liquid. Preferably, the face is submerged within the liquid, i.e., fully contacted by the liquid such that the liquid is present over the entire face 109 and the liquid completely fills the space between the face 109 and the photo-imageable surface 152.

#FIG. 2 illustrates a variation of the immersion lithography system 100 in which the immersion liquid 140 does not cover the entire article but merely fills an interfacial region 145 between the face 109 of the optical element and the article 150. In such a system, water is dispensed by a supply tube 160 located just to the side of the optical imaging system 101. Movement of the article relative to the imaging system causes the interfacial region 145 between the optical imaging system and the article to remain filled with the liquid 140. Typically, the immersion lithography system 100 also includes a mechanism (not shown) which uses vacuum or other force to remove the liquid at an edge of the optical imaging system 101 opposite the edge of the imaging system to which the liquid is dispensed.