Development of a Water-Film Chuck (2nd Report)

Abstract

A water-film chuck utilizing meniscus force has been developed to flatten highly warped concave wafers and to achieve high TTV (Total Thickness Variation) within 0.3 μm. This paper describes thinning methods of a water film, the spin conditions to form a water film of less than 100 nm and the experimental resuls of the wafer thinning by grinding with the water-film chuck. A water film was formed with the method in which the chuck is spun at high speed after interposing water between the chuck and a specimen. When the spinner rotation speed is 5000 min-1 and the rotation time is more than 300 s, the thickness of a water film becomes less than 100 nm over the entire surface of a 300 mm wafer. The thickness becomes thinner and more uniform with increasing the rotation speed and the rotation time. From the results of observation for two months, it was clarified that the thickness of a water film of less than 100 nm do not almost change and the uniformity of that is maintained. Furthermore, by using the water-film chuck, it was possible to thin a 300 mm silicon wafer from 725 to 30 μm with a TTV of less than 0.8 μm equivalent to that obtained using a porous vacuum chuck.