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Microscopy and Lithography

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The drive to create faster and lower power processors while reducing manufacturing costs requires that critical dimensions continue to shrink in size.  This in turn requires detailed investigations into how existing photolithography can be extended to ever-shorter wavelengths by using very high numerical aperture exposure tools, resolution enhancement techniques like optical proximity correction, phase shift masks, or some other technique.  All such approaches require detailed optical models of how exposure light interacts with sub-wavelength features either on mask, or on wafer.


Alternatively, ongoing research and development into nanolithography and next generation lithography including DUV, EUV, nanoimprint lithography, and surface plasmon resonant interference lithography may offer promise to fabricate nanoscale features beyond the diffraction limit.  Detailed investigation into such techniques often requires the use of advanced optical simulation techniques.  Lithography simulation can assist with improving device yields and reducing the number of reticle iterations, allowing a fabrication facility to ramp products faster and save substantially in production costs.


Simulating the lithographic process prior to manufacture can help ensure that severe proximity effects do not compromise the manufacturing process.  Ultimately, it is advantageous to employ semiconductor metrology techniques to ensure that the manufacturing process performed as expected.  Advanced optical critical dimension metrology offers a means by which high-throughput wafer inspection can be used to identify surface defects and manufacturing (e.g. bridging) imperfections.  Understanding the interplay of optical test conditions like polarization, incident angle, and wavelength and the specifics of the defect (size, orientation, etc) is a key capability of a rigorous optical simulation solution.


Simulating microscopy and lithograpy

FDTD uses the finite difference time domain technique to rigorously solve for the object fields at the mask or specimen plane, correctly accounting for all the phase delay and diffractive effects even for wavelength scale structures. All diffraction, refraction, interference, absorption and polarization effects are calculated in the near field without approximation. For lithography, one can calculate the aerial image at the wafer by post-processing the FDTD simulation data. For microscopy, one can calculate the equivalent bright field microscope image and the phase contrast image can be reconstructed at the image plane. In the case of the phase contrast microscope, the image can be calculated for an arbitrary phase delay due to the phase plate without having to re-simulate the fields at the specimen.


Compare results with experimental images obtained from a micrscope with an arbitrary numerical aperture.

Calculate the bright field and phase contrast image for an arbitrary phase delay due to the phase plate.

Rigorously calculate the aerial image printed on the wafer for a variety of illumination schemes as well as resolution enhancement techniques (RETs)

Lumerical’s conformal mesh technology can achieve sub-mesh cell accuracy for wavelength scale features.

Multi-coefficient materials (MCMs) can accurately model dispersive materials across wide wavelength ranges

Built-in parameter sweep and optimization algorithms make it easy to analyze and optimize parameterized designs

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