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A practical approach, adopting a clever litho trim, to spacer double patterning is investigated in detail. In order to produce quarterpitch small lines of dense arrays ͑with pitch fragmentation techniques͒, state-of-the-art ArF photoresists can be used with a subsequent trim etch, to get the tiny line widths on desired target. Critical dimension ͑CD͒ control during the trim etch process plays a crucial role. Therefore, we investigated the application of a litho trim in order to reduce the trim etch close to zero bias. This approach has the further advantage to allow the printing of small spaces together with small lines, which reduces the k 1 and, therefore, the theoretical resolution. Applying CD trim by litho "overexposure," thin ArF bilayer system ͑silicon containing resist on spin-on carbon underlayer͒ showed basic suitability at k 1 = 0.146 at half pitch of 3xnm with a sufficient process window and a good CD uniformity after litho and after etch. ArF single-layer resists suffer from pattern collapse and resist thickness loss at defocus. For spacer deposition directly on resist, the control of profiles and film thicknesses is shown to be difficult using single-layer resists and more likely to be achieved with bilayer resists. It is also shown that spacer-based double patterning can generate good CD uniformity by use of bilayer resist and litho trim, both with an a-Si carrier and bilayer resist carrier ͑underlayer͒.

By assessment of options for the fabrication of small contact holes in DRAM devices the method of focus drilling was identified and investigated to overcome the depth of focus limitations. By use of ArF-dry lithography a practical shrink of the target CD by 15nm can be achieved both with a focus offset double exposure (FODEX) and with a tilted stage approach. This was optimized in simulation and demonstrated by CD measurement on wafer, as well as by electrical measurement on integrated lots. Application of dual lambda focus drilling is limited by the chromatic magnification error of the lens. The increase of hole-to-hole CD variations due to a lower dose latitude and to increased MEEF was characterized. As improvement option the use of a high transmission attPSM was identified.

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As design rules shrink, there is an increase in the complexity. OPC/RET have been facilitating unprecedented yield at k 1 factors, they increase the mask complexity and production cost, and can introduce yield-detracting errors. Currently OPC modeling techniques are based on extensive CD-SEM measurements which are limited to one dimensional structures or specific shape structures e.g. contact holes. As a result the measured information is not representing the whole spatial 2D change in the process. Therefore the most common errors are found in the OPC design itself and in the resulting patterning robustness across the process window. A new methodology for OPC model creation and verification is to extract contours from complex test structures which beside the CD values contain further information about e.g. various proximities.In this work we use 2D contour profiles extracted automatically by the CD-SEM over varying focus and exposure conditions. We will show that the measurement sensitivity and uncertainty of that algorithm through the whole process window fulfills the requirements of the ITRS with respect to CD-SEM metrology tools. This will be done on various test structures normally being used for OPC model generation and OPC stability monitoring. Furthermore a study on systematic influences on the quality of the extracted contours has been started. This study includes the evaluation of various parameters which are considered as possible contributors to the uncertainty of the edge contour extraction. As one of the parameters we identified the pixel size of the SEM images. Furthermore, a new metric for calculating repeatability and reproducibility determination for 2D contour extraction algorithms will be presented. By applying this contour extraction based methodology to different CD-SEM tool generations the influence of SEM beam resolution to the quality of the contours will be evaluated.