A semiconductor device production process or the like utilizes a stepping or step-and-scan projection aligner that transfers the pattern of a reticle (photomask) to each shot area of a wafer via a projection optical system, a photoresist film being formed on the wafer. The resolution of the projection optical system included in the projection aligner increases as the exposure wavelength decreases and the numerical aperture of the projection optical system increases. Therefore, a shorter exposure wavelength has been used for the projection aligner along with miniaturization of integrated circuits, and the numerical aperture of the projection optical system has been increased.
The depth of focus is also important for exposure. The resolution R and the depth of focus δ are defined by the following expressions. The depth of focus δ increases while obtaining an identical resolution R when using radiation having a shorter wavelength.R=k1·λ/NA δ=k2·λ/NA2 where, λ is the exposure wavelength, NA is the numerical aperture of the projection optical system, and k1 and k2 are process coefficients.
A projection aligner has been normally designed so that the wafer placement space is filled with air or nitrogen. The resolution R and the depth of focus δ are shown by the following expressions when the space between the wafer and the lens of the projection aligner is filled with a medium having a refractive index of n.R=k1·(λ/n)/NA λ=k2·nλ/NA2 
For example, when using water as the medium of an ArF process (the refractive index n of light having a wavelength of 193 nm in water is 1.44), the resolution R is 69.4% and the depth of focus is 144% as compared with the case of using air or nitrogen as the medium. An exposure method that utilizes such a medium is referred to as liquid immersion lithography. Liquid immersion lithography makes it possible to transfer a finer pattern using radiation having a shorter wavelength (see Japanese Patent Application Publication (KOKAI) No. 11-176727).
When using water as the medium for liquid immersion lithography, water may permeate the photoresist film formed on the wafer when the photoresist film and the lens of the projection aligner come in contact with water, so that the resolution of the photoresist film may decrease. Moreover, the components of the photoresist composition may be eluted into water, and may contaminate the surface of the lens of the projection aligner.
Therefore, a liquid immersion lithography upper-layer film (protective film) may be formed on the photoresist film in order to isolate the photoresist film from the medium (e.g., water). It is normally desired that the liquid immersion lithography upper-layer film exhibits sufficient transmittance at the wavelength of radiation, can be formed on the photoresist film without being intermixed with the photoresist film, is not eluted into the medium (e.g., water) (i.e., is stable), and is not easily dissolved in the developer (e.g., alkaline solution) (see Japanese Patent Application Publication (KOKAI) No. 2005-264131, Japanese Patent Application Publication (KOKAI) No. 2006-64711, and Japanese Patent Application Publication (KOKAI) No. 2008-139789).
When using a scan-type liquid immersion lithography system, the immersion medium may not follow the movement of the lens, so that watermark defects (i.e., waterdrops remain on the exposed photoresist film) may occur. This may make it difficult to increase the scan speed, so that the production efficiency may decrease. A liquid immersion lithography upper-layer film-forming composition that contains a polymer that exhibits high water repellency (hydrophobicity) has been known (WO08/047,678). However, since a liquid immersion lithography upper-layer film that exhibits high hydrophobicity exhibits low solubility in the developer, bridge defects (i.e., the lines of a line-and-space pattern are connected in the top area) may occur due to undissolved residues of the liquid immersion lithography upper-layer film.
USPTO Backgrounds
USPTO Backgrounds