Intra-field On-Product Overlay improvement by application of RegC and TWINSCAN corrections

摘要

The on product overlay specification and Advanced Process Control (APC) is getting extremely challenging particularly after the introduction of multi-patterning applications like Spacer Assisted Double Patterning (SADP) and multi-patterning techniques like N-repetitive Litho-Etch steps (LE~N, N ≥ 2). When the latter is considered, most of the intra-field overlay contributors drop out of the overlay budget. This is a direct consequence of the fact that the scanner settings (like dose, illumination settings, etc.) as well as the subsequent processing steps can be made very similar for two consecutive Litho-Etch layers. The major overlay contributor that may require additional attention is the Image Placement Error (IPE). When the inter-layer overlay is considered, controlling the intra-field overlay contribution gets more complicated. In addition to the IPE contribution, the TWINSCAN lens fingerprint in combination with the exposure settings is going to play a role as well. Generally speaking, two subsequent functional layers have different exposure settings. This results in a (non-reticle) additional overlay contribution. In this paper, we have studied the wafer overlay correction capability by RegC in addition to the TWINSCAN intra-field corrections to improve the on product overlay performance. RegC is a reticle intra-volume laser writing technique that causes a predictable deformation element (RegC deformation element) inside the quartz (Qz) material of a reticle. This technique enables to post-process an existing reticle to correct for instance for IPE. Alternatively, a pre-determined intra-field fingerprint can be added to the reticle such that it results in a straight field after exposure. This second application might be very powerful to correct for instance for (cold) lens fingerprints that cannot be corrected by the scanner itself. Another possible application is the intra-field processing fingerprint. One should realize that a RegC treatment of a reticle generally results in global distortion of the reticle. This is not a problem as long as these global distortions can be corrected by the TWINSCAN system (currently up to the third order). It is anticipated that the combination of the RegC and the TWINSCAN corrections act as complementary solutions. These solutions perfectly fit into the ASML Litho InSight (LIS) product in which feedforward and feedback corrections based on YieldStar overlay measurements are used to improve the on product overlay.