Submicron Mask Repair Using Focused Ion Beam Technology

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Abstract
The establishment of the submicron device era brings out the problem of repairing advanced VLSI photomasks or reticles. Through recent advances in submicron focused ion beam (FIB) technology, a new method has been developed for repair of these photomasks. Using our specially designed FIB system, "opaque" repairs are performed by ion sputter etching. Repairing "clear" defects is carried out using the FIB to selectively deposit thin films using the "Ion Beam Induced Chemical Effect". Using these techniques, both "opaque" and "clear" repairs are carried out without damage to the glass substrate. "Clear" defects are repaired using carbon film deposition. The thickness of the film need only by about 200nm to have an optical density of 3 and resistance to scratch and cleaning damage equivalent to Cr. The carbon film is formed when gas molecules are continuously jetted onto the mask surface as the FIB repeat scans the defect area. Repairs to X-ray mask are carried out in the same way, using special gases containing a heavy metal. "Opaque" defects are removed by direct scanning of the FIB over the defect area. The sputter etching is automatically stopped, after the repairs are finished, by the etching monitor. Secondary ion emission is stimulated by the scanning FIB. These secondary ions are detected by a built-in mass spectrometer. The signal from the mass spectrometer can be used to image the sample surface and defect position on the CRT. This system is designed for high reliability and ease of use. Because of advanced design features, this system will smooth the transition between "micron" and "sub-micron" geometry design.

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