Structured surface metrology
Main objectives are to develop knowledge on
- Inverse scattering (reconstruction) algorithms that take “end-effects” of gratings into account
- EM-solvers that can deal with non-periodic scattering structures
- Optimum sensor design and data acquisition methods that provide sufficient information for the reconstruction algorithms;
- The impact of LER on measurement accuracy for large measurement spots
- The influence of spot size on LER sensitivity;
- Using single-resolved scatterometry to measure LER and correct for LER-induced errors.
In order to maintain control over CD and overlay performance, new technologies will have to be developed. In the recent past an angle resolved scatterometer has been developed, which does not fully comply with the industry’s needs. There is a very strong drive towards measurements on very small “in-die” test patterns that have some inherent Line Edge Roughness (LER). These measurements are further complicated by other factors such as the absence of nanometer positioning accuracy, patterns below the resist test pattern, surface roughness or micro grains on the product layers or internal scattering on the sensor as well.
In order to tackle these challenges, existing hardware and associated modeling technology need conceptual improvement. This asks for strict research conditions: (1) reduced measurement area, (2) arbitrary substructures below the feature, (3) a vibration sensitive environment, (4) measurement of the line-edge roughness, (5) new light sources and (6) imperfect optics needs. For line-edge roughness (LER), first a modeling method will be developed to paste near-field wave-fronts from separate diffraction lines together. Further, scatterometry measurements of LER parameters with an extended spot will be evaluated. Next, with simulations, the effect of using a coherent laser beam will be studied.
Separation of “vertical” surface roughness from the “horizontal” line-edge roughness will also be investigated.
Further, the project aims at the measurement and characterization of Contact Hole Roughness (CHR) using top-down CD-SEM images of the contact holes. Among others, it will supply algorithms for modeling CHR, which can be used as input in scatterometry simulations and possibly 2D CD-reconstruction on contact holes.
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