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17 July 1979 Diffraction Gratings As Keys For Automatic Alignment In Proximity And Projection Printing
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Alignment keys in the form of diffraction gratings are described which can be used for automatic alignment in photolithography for the fabrication of integrated circuits. This technique is suitable for proximity printirg and for projection printing, 1:1 projection as well as reduction projection with step-and-repeat on the wafer. The system uses a small He-Ne laser, a chopper, a beam collimator and a number of silicon photodiodes. The signals from these photodiodes give a quantitative measure of the degree and direction of misalignment between mask and wafer. With suitable electronics these signals can be used for the control of servo motors in order to obtain automatic alignment. Our experiments with a 10:1 reduction projection set-up show that an alignment accuracy of 0.1 µm and alignment times of less than 1 sec are feasible. The alignment range is as large as ± 450 /µm.
© (1979) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Hans P. Kleinknecht "Diffraction Gratings As Keys For Automatic Alignment In Proximity And Projection Printing", Proc. SPIE 0174, Developments in Semiconductor Microlithography IV, (17 July 1979);

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