Photonic Band-gap Masks to Enhance Resolution and Depth of

Focus

John Nistler, Koby Duckworth,

Jiri Chaloupka, and Matt Brock

Proc. SPIE Vol. 6517, 65171F (Mar. 19, 2007)

By Marshal Miller

4/18/2007

Outline

• Background– Phase Shift Mask (PSM)– Finite Difference Time Domain (FDTD)– Photonic Crystals

• Simulation data

• Comparison of Photonic Bandgap Enhanced (PBE) masks to current PSM technology

Phase Shift Mask

• Alternating Aperture Phase Shift Mask (AAPSM)– Uses etch into quartz of

mask to produce 180o

phase difference– Destructive interference

allows printing of sub wavelength features

– Features of 65nm can be printed with 193nm illumination

Out of phase by 180 degrees

Finite Difference Time Domain

• Grid-based differential time-domain numerical method

• Maxwell’s differential equations converted to difference equations and discretized

• Simulation domain broken up into fixed size cells

• Equations solved in leapfrog manner

Photonic Crystals• Block of transparent material with tiny holes or nanotubes arranged

in a lattice pattern, abruptly changing permitivity and permeability• Ex: Silicon with tiny air holes• Creates confinement in one of the materials, allowing only certain

energy states, separated by a forbidden region, the band-gap• By adjusting the size of holes and contrast in refractive index can

tune properties of photonic crystals

2-D

periodic intwo directions

3-D

periodic inthree directions

1-D

periodic inone direction

Negative Refraction

[ Veselago, 1968negative , ] opposite of ordinary lens:

only images close objects

does not requirecurved lens can exceed classical

diffraction limit

Slide from SPIE short course on photonic crystals

Basic Simulation Geometry

• Quartz/glass opening on left etched to make the phase difference between the two openings 180 degrees

• Undercut and non-undercut etch tested• For 248nm phase trench: .2439um• For 193nm phase trench: .1721um

Simulation Results: All TE

AAPSM 248nm: 180nm line space pattern

PBE 248nm: 180nm line space pattern PBE 193nm 30nm line space pattern

PBE 248nm: 80nm line space pattern

Final Comparison

• Using 193nm TE illumination– Photonic Band Gap enhanced reticles show capability

of producing near field image with 25 nm features– Existing Phase Shift Technology can only produce

near field images down to 65nm• Authors claim manufacturable approach for

validating results is indicated, but not explained due to proprietary information about Photonic Bandgap materials

• Paper not specific about materials used or geometries simulated for PBE masks, only simulation results given

The End

Questions?

Extra

Properties of Bulk Crystalsby Bloch’s theorem

QuickTime™ and aGraphics decompressorare needed to see this picture. (cartoon)

cons

erve

d fr

eque

ncy

conserved wavevector k

photonic band gap

band diagram (dispersion relation)

d/dk 0: slow light(e.g. DFB lasers)

backwards slope:negative refraction

strong curvature:super-prisms, …

(+ negative refraction)

synthetic mediumfor propagation

Slide from SPIE short course on photonic crystals http://ab-initio.mit.edu/photons/tutorial/