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12 May 2005 CD control: Whose turn is it?
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Abstract
With the introduction of sub100nm nodes lithography faces drastically decreasing process windows and ever more demanding CD specifications at the same time. Inline process control usually allows only a few measurement sites per wafer due to throughput limitations at the CD metrology tool. The drawback is that these data do not show the real process capability with respect to CD control. Such a comparatively small number of measurement sites provides only limited information about systematic signatures of the investigated processes. However, during the setup of design rules it is assumed that CD deviations are purely statistical. Moreover, the CD budget is statistically divided into a certain ratio between the involved process steps (i.e. mask process, lithography and etch). As systematic effects cannot be taken into account in this procedure there arises the necessity to investigate the major signatures of all involved process steps and to minimize them as much as possible. This paper presents the recent CD uniformity analysis results of different critical low k1 lithography layers and the following etch process steps. In particular a line/space level and a contact hole level of a 90nm state of the art DRAM process in the 300mm line are investigated as part of the design rule verification. Inline sampling results and results from extensive intra field, intra wafer and wafer to wafer measurements are compared. Inline sampling gives a slightly different overall CD performance than the extensive measurements. This deviation can be explained by the strong systematic effects which dominate intra field and intra wafer CD uniformity after all process steps. Their major source is found to be at certain etch processes. As a consequence of these results the inline sampling plan must be adjusted and systematic effects with a focus on the etch processes have to be reduced as much as possible.
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Wolfram Koestler, Martin Rossiger, Stephan Wege, and Thomas Zell "CD control: Whose turn is it?", Proc. SPIE 5754, Optical Microlithography XVIII, (12 May 2005); https://doi.org/10.1117/12.598443
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