M.Sc Thesis

M.Sc StudentNormatov Alexander
SubjectNanoscale Surface Feature Evaluation by Structured Light
DepartmentDepartment of Electrical and Computer Engineering
Supervisors DR. Boris Spektor


Modern technologies (Nanotechnology, Semiconductor Technology, etc…) impose the need for high-speed & high sensitivity inspection systems. Conventional inspection methods are inadequate, either because of insufficient sensitivity (in the case of scattering and vision systems) or insufficient speed (Scanning Probe Microscopy methods). Interferometric approach that possesses both high sensitivity and high measurement speed has other significant limitations.

The objective of this research was a deeper study of a method that combines high speed (throughput) and at the same time high spatial sensitivity, as required by cutting-edge technologies. Our method is based on creating an optical singularity inside optical field, thus producing a "structured beam". Interaction between the structured beam and a surface object affects the scattered light distribution. Analysis of scattered light distribution and its changes reveal information about object features. In our work we show that these features can be evaluated with nanoscale sensitivity.

At the first stage of the research a general simulation was written assuming paraxial conditions. This assumption produced a limitation on the numerical aperture of the optical system. Analysis of the simulation results suggest that a system with signal to noise ratio of 30dB possesses sensitivity of a few nanometers, which matches the sensitivity of modern interferometric methods. At the second stage an experimental system was built, fully supported by simulations (adapted to the experimental setup). After adjustment of the experimental system parameters, a series of experiments followed, providing data for the analysis stage. Two different analysis approaches were developed. Both approaches use the excessive data, collected during experiments, for increasing the signal to noise ratio of the measurements. Finally, the results of both analysis approaches prove simulation predictions and show experimental sensitivity of 20nm.