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1 July 1991 Improvements in 0.5-micron production wafer steppers
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i-line wafer steppers have become the tool of choice for submicron production of advanced integrated circuits. These tools are now being extended to provide the required resolution, linewidth control, and overlay performance for devices with 16 Mb packing densities. To achieve this a manufacturing environment, suitable control procedures should be designed to minimize process and equipment variations. The primary goal of this paper is to characterize and quantify the ability of current generation steppers to meet or exceed the 100 nm AA (single machine) and the 175 nm BC (stepper to any other stepper in a production area) overlay requirements for half-micron production. For this, an overlay experiment using one reference and 12 randomly selected steppers was performed. Two Point through the lens alignment was used to reference wafer to reticle. Stages with three interferometrically controlled axes having both standard and enhanced resolution were used in the experiment. Features to improve stage positioning and overlay accuracy are discussed. To generate the required data, accurately calibrated reference wafers are used. The results were compared with a metrology model, which was used to optimize the matching of stepper lens and stage grid distortions so that optimum matching performance is achieved. The results then clearly predict whether all steppers meet the stringent overlay requirements for half-micron lithography in a production environment. In addition, experimental results show half-micron resolution performance with a number of commercially available i-line photoresists. Lens performance as affected by a phase-shifted reticle tooling are also examined to determine its potential benefit to 0.5 micron and sub-0.5 micron production.
© (1991) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Paul Frank Luehrmann Jr., Chris G. M. de Mol, Frits J. van Hout, Richard A. George, and Harrie B. van der Putten "Improvements in 0.5-micron production wafer steppers", Proc. SPIE 1463, Optical/Laser Microlithography IV, (1 July 1991);


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