Patent number 8508718 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "The invention relates generally to semiconductor processing equipment. More particularly, the invention relates to methods and apparatus for enabling liquid in an immersion lithography system to effectively be contained between a surface of a lens and a plane that is moved relative to the lens.
"For precision instruments such as photolithography machines that are used in semiconductor processing, factors that affect the performance, e.g., accuracy, of the precision instrument generally must be dealt with and, insofar as possible, eliminated. When the performance of a precision instrument such as an immersion lithography exposure system is adversely affected, products formed using the precision instrument may be improperly formed and, hence, function improperly.
"In an immersion lithography system, a liquid is provided between a lens and the surface of a wafer in order to improve the imaging performance of the lens. The use of liquid allows a numerical aperture associated with the lens, i.e., an effective numerical aperture of the lens, to essentially be increased substantially without altering characteristics of the lens, since a liquid such as water generally has a refractive index that is greater than one. In general, a higher numerical aperture enables a sharper image to be formed on the wafer. As will be appreciated by those skilled in the art, a high refractive index liquid allows for a high numerical aperture of the lens because an effective numerical aperture of a lens system of an immersion lithography system is generally defined to be approximately equal to the sine of an angle of diffraction of light that passes through a lens and reflects off a surface multiplied by the refractive index of the liquid. Because the refractive index of the liquid is greater than one, the use of liquid allows the effective numerical aperture of the lens to be increased, thereby enabling the resolution associated with the lens to essentially be improved.
"Within most conventional lithography systems, air is present between a lens and a surface that passes under the lens, e.g., the surface of a wafer. In such systems, the numerical aperture associated with the lens is often in the range of approximately 0.8 to 0.9. Increasing the numerical aperture of a lens to achieve an improved resolution is generally impractical, because the diameter of a lens generally must be increased, which adds significant difficulty to a lens manufacturing process. In addition, the numerical aperture of a lens in air is theoretically limited to one, and, in practice, is limited to being somewhat less than one. Hence, immersion lithography systems enable the effective numerical aperture of a lens to be increased substantially beyond what is possible with a lens in air.
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