The Project

Motivation:

Dimensional metrology of small structures is a basic subject that is important for applications within a wide variety of areas mainly in the semiconductor and optical industries. The characterization of high-end laterally structured functional surfaces is a constant challenge due to the progressive minimization of structures combined with an increasing impact of feature details on the functionality of these surfaces. The development of sophisticated dimensional metrology of structures in the sub micrometere-range is therefore an important condition for the further development of technologies for optics and semiconductor industries.

Challenges:

For future technology nodes in the semiconductor industry, for example critical dimension (CD) metrology requirements are identified as an essential but unsolved problem [1]. For production measurements scatterometers and special scanning electron microscope systems (CD-SEMs) are key metrology tools. Although results of these different tools usually show a good correlation, systematic offsets are often observed. These offsets may be at least partly attributed to commonly used approximations and simplified models used for the data evaluation in scatterometry. Therefore, today scatterometry is generally used in the semiconductor industry only for relative measuring in-line metrology in process development and process control. Universal, product-related standards for the characterization and calibration of scatterometers are currently unavailable.

On the other hand, in the optics industry diffractive optics are becoming more and more important. The far field action of the diffractive optics can be characterized directly using scatterometry. Up to now only relatively slow and not in-line capable atomic force microscopy (AFM) or scanning electron microscopy (SEM) are in use to check the dimensions of structures. The characterization of curved structured surfaces is becoming increasingly important, since refractive-diffractive optics can replace multi-component products with a single component leading to  miniaturized products that can be used within a wide range of applications. However, a reliable and efficient metrology for the quality control of these optical elements is missing. Scatterometry is a promising candidate to fill this gap.

Approaches:

The limiting influences of common approximations will be quantified experimentally and theoretically and relevant contributions will be eliminated by the development of improved measurement and data evaluation methods.

To enhance the available information about the structures of interest and the sensitivity of scatterometry with respect to critical measurands, scatterometry will be extended methodically:

• extension to short wavelengths down to X-rays,

• a stringent exploitation of the polarization degree of freedom, and including phase information using
   coherent focused beam scatterometry

• development of improved or new concepts for modeling and data analysis

The detailed form and local deviations of the structures will be included in scatterometry analysis algorithms. To provide these structure detail information and to provide comparability to scatterometric measurements AFM and SEM methods will be expanded. Both an improved 3D capable AFM and a traceable AFM with a large sample area coupled to a silicon-based X-ray interferometer as a natural line scale will be developed for this purpose.

To exploit the synergy between metrology for semiconductor industry and for optics industry current scatterometry application fields will be extended towards diffractive and diffractive-refractive optics. The applicability of scatterometry as fast and reliable dimensional metrology both for flat and curved structured surfaces will be investigated and evaluated.

Development of sophisticated combined data analysis schemes and of more efficient and realistic rigorous modeling and data analysis methods for scatterometry.

Development of a scatterometry reference standard to face the tough specifications demanded especially by the semiconductor industry. As a first step towards a "golden reference standard" suitable for calibration of scatterometers as well as AFM and SEM metrology tools this standard will be designed and developed to be suitable also for testing of AFMs and SEMs, so that the matching of these different types of tools will be possible.

Objectives:

• Traceability of scatterometry and measurement uncertainty of the order of 1 nm

• Reduced systematic errors, improved matching also to AFM and SEM tools

• Improved modeling and combined data analysis

• 3D capability of scatterometry

• Methodical extensions to short wavelengths (EUV, X-ray), Mueller, Fourier and phase sensitive
   scatterometry

• Evaluation of scatterometry for characterization of diffractive-refractive optics

• Development of specially adapted AFM and SEM measurement tools and methods for reference

• Development of a scatterometry reference standard  (potentially extendable to a golden reference standard
   also for AFM, SEM calibration)


[1] www.itrs.net/Links/2009ITRS/2009Chapters_2009Tables/2009_Metrology.pdf