Proceedings Article | 30 October 2007
Proc. SPIE. 6730, Photomask Technology 2007
KEYWORDS: Lithography, Reticles, Metrology, Image registration, Photomasks, Extreme ultraviolet lithography, Double patterning technology, Critical dimension metrology, Semiconducting wafers, Overlay metrology
Double patterning (DPT) lithography is seen industry-wide as an intermediate solution for the 32nm node if high index
immersion as well as extreme ultraviolet lithography are not ready for a timely release for production. Apart from the
obvious drawbacks of additional exposure, processing steps and the resulting reduced throughput, DPT possesses a
number of additional technical challenges. This relates to, e.g., exposure tool capability, the actual applied process in the
wafer fab but also to mask performance and metrology. In this paper we will address the mask performance.
To characterize the mask performance in an actual DPT process, conventional parameters need to be re-evaluated.
Furthermore new parameters might be more suitable to describe mask capability. This refers to, e.g., reticle to reticle
overlay but also to CD differences between masks of a DPT reticle set. A DPT target of reticle to reticle induced overlay
of 6nm, 3σ at mask level was proposed recently for the 32nm node. The results show that this target can be met.
Besides that, local CD variations and local displacement become critical. Finally, the actual mask metrology for
determination of these parameters might not be trivial and needs to be set up and characterized properly. In this paper
we report on the performance of two-reticle sets based on a design developed to study the impact of mask global and
local placement errors on a DPT dual line process.
In a first step we focus on reticle to reticle overlay. The overlay between two masks evaluated for different wafer
overlay targets is compared with measurements on actual resolution structures. In a second step, mask to mask CD
variations are addressed. Off-target CD differences as well as variations of CD signatures on both reticles of a set are
investigated. Finally, local CD variations and local displacements are examined. To this aim, local variations of adjacent
structures on the reticle are characterized. The contribution of local effects to the overall CD and registration budget is
estimated.
