Optical Image Simulation

Brightfield Confocal and Coherence Probe Optical Microscopes

The model for these optical microscopes uses the same Maxwell solver as the stepper aerial image model. It supports both reflected and transmitted mode imaging. The line geometry is first specified using Metrologia's optical geometry editor, then a file is produced with this geometry encoded in it. Next a microscope is specified by giving it's numerical appertures and any illumination apodization if required. The user inputs the z range and z step for the simulation. An entry for the case run is entered into a batch file which can have as many entries as the user desires and which can be launced from within Metrologia.

The results may be viewed graphically and they are also stored in a text file for analysis.

These optical microscope models are useful for simulating overlay metrology tools, stepper alignment imaging, larger line structures, photomask lines for linewidth metrology, etc. Since it simulates only lines, it is not suitable for particle defect image simulation.

Stepper Aerial Image Modeling

The user first specifies a mask geometry. It must consist of a periodic line space pattern, but the chrome line may have complex sidewall geometry and may be covered with A/R coating. Certain types of phase shifting masks are also possible. Next the user specifies the stepper optics which includes magnification, wavelength, numerical aperture for illumination and imaging, and aperture shape apodization. Metrologia will then add lines to a batch file to run this case. Multiple cases can be added to the batch file and run all at once by launching the batch file from within Metrologia. Runtimes can vary from a few minutes to much longer depending on the complexity of the case being modeled.

Metrologia uses the analytical waveguide technique developed by Spectel over the last 6 years. This method of solving Maxwell's equations is a full vector solution. It is the fastest means known for solving Maxwell's eqautions. But the current implementation is limited to periodic line space pairs, and the lines must be symetrical under reflection about their center line.