This example shows how to create the FDTD model of the surface plasmon resonant nanolithography contact mask. A 2D cross-section through the quartz substrate (blue), silver contact mask (grey), photoresist (pink) and silicon wafer (red) is shown here in the FDTD layout editor, along with the sources and monitors used in the simulation.
To reproduce the following results, open and run the simulation file. Use the script file to create the following plots.
A plot of the near field intensity in cross-section through the silver mask layer (y = 0 to 60 nm) and the photoresist layer (y = -50 to 0 nm) is shown on a logarithmic scale. Surface plasmon modes are clearly seen at the silver mask/photoresist interface. The periodic structure allows the normal incidence beam to couple to counter-propagating surface plasmon waves, which gives rise to subwavelength variation in the nearfield intensity inside the photoresist layer.
The nearfield optical intensity in the middle of the photoresist layer, 30 nm below the contact mask, is plotted as a function of position. The high contrast ratio shown allows for patterns with minimum size about 80 nm to be transferred to the photoresist. This sub-wavelength result achieved with surface plasmons is well below the diffraction limit for a 436 nm source and is therefore amenable to nanolithography applications.
Simplified Microscopic Imaging
Photolithographic projection to photoresist