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The use of multipass printing to reduce the magnitude of the registration and critical- dimension (CD) errors on photomasks through averaging has been demonstrated in laser- scanned reticle-writing systems, such as the ALTAR 3000 and the CORER family of products. In this paper, we discuss recent efforts to optimize the efficacy of the averaging in these tools. Key error sources in the systems are identified, and the degree to which multipass printing reduces their contributions to the total error budget is considered. Special consideration is given to the polygon and brush errors, which have been further reduced in the ALTA 3000 with a novel averaging technique employing uneven spacing of the beams in the brush. The tradeoff between throughput and printing precision is examined. Using modeling results, it is shown that the default number of passes for the CORE is optimal in maximizing the print quality. More passes yield diminishing returns due to the dominance of unaveraged systematic errors, whereas fewer passes do not allow the full benefits of the averaging to be obtained. Experimental data are presented which also support these conclusions. Comparing the two- and four-pass printing modes of a state-of-the-art CORE, the benefits of the latter are revealed primarily in CD control, where the intensity variations are the greatest error contributor.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
