A new vacuum pin chuck for ArF laser lithography
To meet the demands of next-generation ArF excimer laser lithographya site flatness better than 0.03 ?m in a 30-mm square fielda new vacuum pin chuck was developed. A 2-mm wide static-pressure seal, which extends beyond the wafer edge, makes it possible to almost completely flatten the wafer periphery. Since the wafer back-surface contacts only the tips of the pins, the chuck can significantly reduce the influence of dust. In addition, conductive pore-free ceramics and a coating of SiC, as well as round pin corners and small roughness on the pin tops, prevent dust adhesion. It was found experimentally and theoretically that the flattening ability of the new chuck around the wafer periphery is several times higher than that of an ordinary ring-seal chuck. Such superior flattening was achieved by expanding the vacuum region by the wafer edge. Calculations showed that the new chuck can flatten an 8-inch concave wafer with a bow of 200 ?m to a residual bow of less than 0.03 ?m.
pin chuck arf laser lithography flattening ability chucking accuracy wafer flatness