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Impact of chuck flatness on wafer distortion and stepper overlay

: Simon, K.; Huber, H.-L.; Gabeli, F.; Scheunemann, H.U.

Patterson, D.O. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Electron-beam, X-ray, and ion-beam submicrometer lithographies for manufacturing III : 1-2 March 1993, San Jose, California
Bellingham/Wash.: SPIE, 1993 (SPIE Proceedings Series 1924)
ISBN: 0-8194-1158-2
Electron Beam, X-Ray, and Ion Beam Submicrometer Lithographies for Manufacturing Conference <3, 1993, San Jose/Calif.>
Conference Paper
Fraunhofer ISIT ()
integrated circuit technology; VLSI; X-ray lithography

Overlay accuracy is known as one of the most important subjects for ULSI device production. Significant contributions such as alignment accuracy and mask distortions are well known. By breaking the 100 nm range on overlay accuracy a number of influences have to take into account, which were usually be neglected for relaxed design rules. One of these influences to the overlay is directly related to wafer distortions induced by flatness deviations of wafer chucks. This impact was characterized by investigating the elastic behaviour of 4 wafers (525 mym thick), fixed on a wafer chuck. Induced elastical deformation due to flatness error of the chuck causes strains and elongations in the wafer surface and therefore wafer distortions. The results obtained by exposure experiments and calculations show that even a point size defect has a 30 mm spreading. Therefore the induced distortions arrives about 100 nm in case of a 3 mym flatness irregularity. The final result of the investigations induc es that the flatness differences between different wafer chucks or steppers should be smaller than 1 mym for design rules below quarter micron.