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Currently the mask blanks used in extreme ultraviolet lithography cannot be fabricated free of defects. A rapid method of determining the optimum placement of mask patterns on the blank to avoid these defects is described. Using this method, the probability of fabricating defect-free masks, when the pattern is (1) randomly placed on the mask blank or (2) positioned optimally to avoid defects, is determined for a variety of integrated circuit designs, defect densities, and defect sizes. In addition to circular defects, oval and clusters of defects are also considered. Finally, simple analytical expressions for the probability of obtaining a defect-free mask in the case of random placement of the mask pattern is presented and compared to Monte Carlo simulations.

The status of x-ray mask inspection and repair at the IBM Advanced Mask Facility is presented. Defect classification and sources are presented along with some preliminary results from a defect printing study done at the Advanced Lithography Facility.

A model of focused ion beam deposition of materials is described. Decomposition of organometallic molecules by ion beams 50-300 nm in diameter allow localized deposition of a variety of metals. The large current density (approximately I A/cm2) and the inherent sputtering of a focused ion beam can result in no net deposition for a variety of process conditions. The major process parameters of current density, beam dwell time, and readsorption time are introduced. Experimental examples of gold depositions from dimethylgold hexafluoro acetylacetonate or DMG(hfac) are presented to illustrate the effect of the process parameters on size and shape of the depositions.

There are many material and processing options for building highly accurate defect-free X-ray masks that meet the 0.25-µ m and smaller lithography groundrules. IBM's path and rationale for reducing the key mask parameters of image size, image placement and defects is covered. For image size resolution and control, high voltage e-beam lithography (greater then 50 kV) is the preferred technique for X-ray masks. For tighter image placement control, special writing schemes that reduce the e-beam lithography systematic and random placement errors must be used. Special absorber electroplating conditions and thermal controls were implemented to control process-induced distortion. For tight defect control, identifying and eliminating sources of defect is key. Clearly, for IBM, most of the defect sources were process rather than foreign material related. Our defect reduction work has resulted in the fabrication of a fully functional 64-Mb DRAM (single chip) mask.