Development of holistic measurement concepts for highly resolved measurement of micro structures based on scanning and imaging optical techniques

Due to a continuous down-scaling of technical components, the demand for measurement technology used for quality control increases. Optical 3D topography measurement instruments enable a fast and contactless measurement of 2D height profiles.

Caused by the wave characteristics of light, systematic deviations between optically measured and real surface topographies occur, which reduce the reliability of optical measurement technology significantly. These deviations depend on various measurement parameters, the state of the surface as well as the used measurement method.

In this project, we develop numerical simulation models, which enable to predict these deviations reliably for different optical profilers (see Figs. 1-3). The models are used to investigate physical dependencies of the systematics deviations, recognize the discrepancies and eliminate them directly in the measurement chain and find the most accurate measurement instrument with regard to certain applications.

Figure 1: Finite element method (FEM) based simulation and measurement of a rectangular grating (period length 6μm, height 190nm) with a Linnik interferometer (100x NA=0.9) utilizing a red LED. The simulations are performed using a time-efficient 2D approximation (a,d,g) and a full 3D modeling (b,e,h). The envelope evaluation is displayed with blue lines and the phase evaluation in red lines.
Figure 2: FEM based simulation (a,c) and measurement (b) results of a sinusoidal standard with a period length of 2.5μm and a peak to valley amplitude of 120nm obtained by a Mirau interferometer (50x, NA=0.55) using red LED illumination. (a) shows simulation results assuming an ideal sinusoidal measurement object, in (c) an atomic force microscope (AFM) measurement result is used as surface under investigation in the simulation. The envelope evaluation result is depicted in blue, the phase evaluation in red, the uwrapped phase evaluation in green and the AFM result in black.
Figure 3: Simulation (a,b) and measurement (c) results of a rectangular grating (period length 400nm, height 140nm) measured by a confocal microscope (100x, NA=0.95) using a cyan LED. The red lines display the structure obtained with a realistic pixel size. The blue curves show results simulated assuming a smaller pixel size. Two different rigorous methods are applied to simulate the light-surface interaction, the FEM (a) and the rigorous coupled-wave analysis (RCWA) (b).

 
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M.Sc. Tobias Pahl