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Impact of chuck flatness on wafer distortion and stepper overlay - comparison of experimental and FEM results

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


Microelectronic engineering 23 (1994), No.1-4, pp.197-201
ISSN: 0167-9317
Journal Article
Fraunhofer ISIT ()
elastic deformation; elongation; finite element analysis; photolithography; VLSI; X-ray lithography

Overlay accuracy is one of the most important lithographic topics for ULSI device production. Significant contributions to the overlay like alignment accuracy and mask distortion are well known and subject of continuous investigations. Below an accuracy range of 100 nm additional influences must be taken into account, which were usually neglected for relaxed design rules. One of these influences is directly related to wafer distortions induced by flatness inaccuracies of wafer chucks used for instance in X-ray or optical steppers. This impact was characterised by investigating the elastic behaviour of 4" wafers, fixed on a wafer chuck. The resulting strains and elongations in the wafer surface were measured by exposure experiments and compared with additional FEM calculations. From these results we estimate that for design rules below quarter micron the flatness accuracy between different wafer chucks has to be smaller than 0.25 mu m.