A technique for projection x-ray lithography using computer-generated holograms

X-ray projection lithography has recently been explored as a method for the manufacture of <200 nm linewidth integrated circuits. A method is described whereby projected lithographic images can be formed with x rays by means of a transmission hologram. The form of the hologram is computed by an algorithm that eliminates the unwanted signals normally present as systematic errors in in-line holographic images. Example calculations are shown in which holograms are constructed to generate images of a given test pattern. The holographic images are shown to have excellent fidelity with respect to both resolution and contrast. Such an approach to projection x-ray lithography requires an x-ray beam with very little coherence and is thus compatible with high wafer throughput schemes; in addition, image fidelity remains high even when moderately small contaminant particles block the light from small regions of the hologram. Fabrication limits for the single optic involved are compatible with current technological limits. The approach is applicable over a large range of soft-x-ray wavelengths, indicating the feasibility of a 100 nm resolution system with 6 μm depth of field using a carbon mask system operating at 5 nm, or other materials at shorter wavelengths.