X-ray mask fabrication using new membrane process techniques

A membrane process, in which the resist and the absorber are patterned after backetching, was developed to produce highly accurate X-ray masks. Two new techniques allow us to use the same equipment as that currently used in our wafer process. One is a one-point holder for electron beam writers that clamps, without causing any deformation, a small area of the wafer from both sides with just one pair of projections. The reproducibility of the pattern positioning obtainable with the new holder is below 36 nm (3σ) in both x and y directions. The other technique is an etching method that uses a heat sink to prevent temperature increases in the membrane during absorber etching. With the heat sink, there is no difference between the etch rate of the absorber film on the thinned membrane and that on the Si wafer. A comparison between the pattern placement accuracies of X-ray masks produced by the above membrane process and by the conventional wafer process confirms that highly accurate X-ray masks can be fabricated by the membrane process when there is extensive absorber coverage.