13 September 1982 Variable Magnification In A 1:1 Projection Lithography System
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A technique for varying the isotropic magnification of a scanning ring field projection mask aligner has been developed. This makes it possible to completely compensate for scale changes that occur as a consequence of the integrated circuit manufacturing process and temperature changes from one masking step to another. Since magnification errors are often a major source of overlay error in full field projection systems, correction of magnification errors on a wafer-by-wafer basis substantially improves the overlay accuracy. The Micralign Model 500 instrument contains a number of optically weak fused silica refractive components. The main purpose of these elements is to extend the degree of optical correction over a much wider annulus than could be obtained in an all-reflective design. An additional property of the design is that a pair of the refractive elements known as strong shells, which are symmetrically disposed about an intermediate image plane, can also provide correction for a variety of optical characteristics, one of which is magnification. Small motions of the strong shell elements in the same axial direction can readily provide magnification changes on the order of 25 parts per million. In order to produce an isotropic magnification change across the wafer, any departure from unity magnification must also be accompanied by a corresponding linear shift in the relative positions of the mask and wafer as they are scanned through the annular field of the projection system. This is provided by a precise, pneumatically-controlled micropositioning stage which also provides accurate registration control during alignment. Design characteristics of the shell adjustment mechanisms, the microstage, and the control algorithms are presented along with test data showing a +25 parts per million isotropic scale change.
© (1982) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
James J. Greed, James J. Greed, David A. Markle, David A. Markle, } "Variable Magnification In A 1:1 Projection Lithography System", Proc. SPIE 0334, Optical Microlithography I: Technology for the Mid-1980s, (13 September 1982); doi: 10.1117/12.933553; https://doi.org/10.1117/12.933553

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