OP: Esther Kramer started her MSc project

Esther started her MSc Project on Classification of (an)isotropic sub-wavelength defects by optical scattering. Her supervisor is Paul Urbach

Short description of the project: In this MEP the optical response of (an)isotropic impunties (defects) on a flat silicon wafer is studied using both numerical optical models as well as experiments on a state-of-the-art optical particle scanner. A numerical model has been developed to calculate the far-field scatter distribution from a sub-wavelength defect on a substrate. After validation of this model with defects that have known analytical solutions for the far-field, it will be used to predict the far-field of defects with other shapes. This forward model (defect -> far-field) will be used to gain insight into the parameters ofthe defect having an influence on the far-field. Using this knowledge a reverse algonthm (farfield -> defect parameters) will be developed, allowing for the prediction of defect parameters from measured far-fields. To validate the algorithm, test wafers with programmed defects with different shapes, sizes and composition will be designed, fabricated and analyzed. To save time the student will only provide input on the design of the test wafers, while the production will be done by an experienced operator at TNG. The test wafer will be inspected on a dark-field particle detection tool (Rapid Nano 3). On this tool the defects can be illuminated from 9 different azimuth angles and their scattenng intensity recorded. Since this is a new operating mode of the tool it first needs to be characterized (e.g. relative intensities of the illuminadon arms). The measurements on the programmed defects will be processed with the developed algorithm to predict parameters o f t he defects (e.g. size, shape, aspect ratio). These predictions will be checked by re-detection of the programmed defects in high-resolution microscopes with strong analytical capabilities (e.g. SEM, AFM). The challenge is to identify quantifiable parameters from the optical response to the charactenstics of subwavelengthsized (an)isotropic defects. The student will develop measurement schemes, data processing algorithms and criteria to classify arbitrary defects based on the multi-angle opdcal response, and validate the classification scheme with nonoptical  high-resoludon techniques (e.g. AFM, SEM).