ASMLNeed for accuracy, precision, speed and sophistication in metrology has increased tremendously over the past few years. Lithography performance will increasingly depend on post patterning metrology and this dependency will be heavily accelerated by technology shrinkage. These requirements will soon become so stringent that the current metrology capabilities may not be sufficient to support these near future needs. Accuracy and precision requirements approaching well into sub-nanometer range while the demand for increase in sampling also continues, triggering the need for a new technology in this area.In this technical presentation the authors would like to evaluate such technology, a new scatterometry based platform under development at ASML, that has the potential to support the future needs. Extensive data collection and tests are ongoing for both CD and overlay. Data on scatterometry based overlay shows unprecedented measurement precision. The levels of precision are so high that for evaluation special methods have been developed and tested. In this paper overlay measurement results from this new system will be discussed, as well as applicability for future nodes and novel lithography techniques. CD data (from the same evaluation system) will be reported in the future technical publications.

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A brand new CD metrology technique that can address the need for accuracy, precision and speed in near future lithography is probably one of the most challenging items. CDSEMs have served this need for a long time, however, a change of or an addition to this traditional approach is inevitable as the increase in the need for better precision (tight CDU budget) and speed (driven by the demand for increase in sampling) continues to drive the need for advanced nodes.The success of CD measurement with scatterometry remains in the capability to model the resist grating, such as, CD and shape (side wall angle), as well as the under-lying layers (thickness and material property). Things are relatively easier for the cases with isotropic under-lying layers (that consists of single refractive or absorption indices). However, a real challenge to such a technique becomes evident when one or more of the under-lying layers are anisotropic.In this technical presentation the authors would like to evaluate such CD reconstruction technology, a new scatterometry based platform under development at ASML, which can handle bi-refringent non-patterned layers with uniaxial anisotropy in the underlying stack. In the RCWA code for the bi-refringent case, the elegant formalism of the enhanced transmittance matrix can still be used. In this paper, measurement methods and data will be discussed from several complex production stacks (layers). With inclusion of the bi-refringent modeling, the in-plane and perpendicular n and k values can be treated as floating parameters for the bi-refringent layer, so that very robust CD-reconstruction is achieved with low reconstruction residuals. As a function of position over the wafer, significant variations of the perpendicular n and k values are observed, with a typical radial fingerprint on the wafer, whereas the variations in the in-plane n and k values are seen to be considerably lower. BACKGROUNDAmorphous carbon is now widely being used in the industry as anti-refractive coating (ARC) and barrier layer [1]. Some of these layers show no problem in CD reconstruction using scatterometry based technology with regular RCWA methods; however a few different flavors of such material exists where a straight forward CD reconstruction model does not work. The root cause for this particular case is due to a phenomena called birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as certain amorphous carbon films.This effect occurs when the structure of the material is anisotropic, showing a different propagation speed depending on the direction. Those anisotropic materials can present one or two axes of anisotropy, thus being named, respectively, uniaxial and biaxial birefringent materials.Metrology, Inspection, and Process Control for Microlithography XXIII, edited

Advanced lithography is becoming increasingly demanding when speed and sophistication in communication between litho and metrology (feedback control) are most crucial. Overall requirements are so extreme that all measures must be taken in order to meet them. This is directly driving the metrology resolution, precision and matching needs in to deep sub-nanometer level [4].Keeping the above in mind, a new scatterometry-based platform is under development at ASML. Authors have already published results of a thorough investigation of this promising new metrology technique which showed excellent results on resolution, precision and matching for overlay, as well as basic and advanced capabilities for CD [1], [2], [3]. In this technical presentation the authors will report the newest results from this ASML platform. This new work was divided in two sections: monitor wafer applications (scanner control -overlay, CD and focus) and product wafer applications. BACKGROUNDPrevious publications on this scatterometry platform showed notable performances as follows [1]:Accuracy: Perfect match between programmed and measured overlay Resolution (Sensitivity) < 0.25 nm TMU < 0.25 nm (including matching) TIS < 0.05nm and TIS 3σ < 0.15nm (no need for extra TIS calibration) Tool-to-tool overlay (mean) matching < 0.2nm (all five layers) Feedback to scanner (via GridMapper) -basic capability proven 2-in-1 configuration (overlay and CD with one tool) for cycle time advantageThe results (overlay results as shown above) were in the atomic level performance (<0.3nm) and were very encouraging in light of the ITRS roadmap for advanced node requirements.Further work on overlay showed good capabilities with small overlay targets of 30um x 60um scatterometry-based targets [2]. Also complex production stack CD reconstruction revealed anisotropic modeling capabilities [3]. MOTIVATIONExtreme low focus, CDU and overlay budget in lithography driving metrology requirements into deep subnanometer level. Existing metrology solutions are reaching the limit. Image-based overlay shows limited precision, tool matching and high tool-induced-shift or TIS. In advanced node applications, CDSEM shows limited signal to noise, low speed, and no shape / sidewall angle / profile information.