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Essentials ofElectron Beam Lithography
Yuan Lu
Center for Nanoscale Systems
August 13, 2009
Flagship System: Elionix ELS-7000
Elionix 100kV system in LISE cleanroom
Workhorse: Raith 150
Raith 30kV system in LISE cleanroom
JOEL 7000F
JOEL 7000F 30KV system in LISE cleanroom
Outline
• Ebeam resists
• Substrate effects
• Pattern Design
• Electron Scattering—proximity effect
• Stage factors (laser height adjust)• Writing Hall of Fame – examples of great pictures!
Positive Electron Beam Resists
• ZEP520A
• 950 PMMA A2, A4, A7, A11
• MMA
• ZEP 520A Anisol 180C 3 min
• 1 0 500nm 5000rpm 300sec
• 1 1 200nm 2000rpm 70sec
• 1 2 100nm
• 1 3 60nm
Negative Electron Beam Resists
• XR‐1541 (HSQ, hydrogen silsequio xane)
• FOX 16, FOX 17 (less expensive alternative)–
What to Do?
• Process conditions
• Spin speed curves
• Dose
• Dose vs. curve, dose vs. different substrates
Example of a Useful Resist
Spin curve
Complication: Insulating Substrates
• Al, Cr, or Espacer ($1500/100ml)• Spin coat Espacer at 2000rpm, (2000 rpm/s) for 30 sec. No baking is necessary. This will create a uniform film of Espacer ‐200 angstroms in thickness
Pattern Design
• AutoCad, Design Cad, and LinkCad
• Examples (next slides)
Example: Starting with AutoCAD
Typical Alignment marker100 nm gap at vertices
Thermal Field Emission Gun
Filament
Emitter
Suppressor Cap
Base
Emitter: ZrO/W (Thermal type)
Acceleration Voltage
Forward scattering
Back scattering
- Low - - High - - Low - - High -
- Electron scattering behavior -
Less Forward Scattering
Smaller Beam DiameterHigher electron energy
Monte Carlo Simulation (1.5um thick resist on Si)
50kV 100kV
Electron Scattering – less is better!
- Electron scattering distribution -
Low acceleration voltage High acceleration voltage
Forward scattering
Back scattering
Forward scattering
Back scattering
Forward scattering: Narrow and high density of distribution
Back scattering: Broad and low density of distribution
At high acceleration voltage,
Acceleration Voltage
Enables finer line.
Reduces proximity effect.
100kV
30kV
100kV vs 30kV
(300nm line width, 600nm pitch, 1.5um thickness)
Stage moves up/down to keep the focus in constant.
1. Measure the height of specimen.
2. Moves the height of stage to keep the distance between EB gun and surface of
specimen
Stage
Visible (red)
Writing Performance
1:1 (30nm : 30nm)
1:2 (30nm : 60nm)
1:3 (30nm : 90nm)
1:10 (30nm : 300nm)
30nm Line
1:3 (10nm : 30nm)
1:4 (10nm : 40nm)
1:5 (10nm : 50nm)
1:10 (10nm : 100nm)
10nm Line
5nm Line
1:7 (5nm : 35nm) 1:11 (5nm : 55nm)
1:9 (5nm : 45nm) 1:21 (5nm : 105nm)
100nm L&S Cross section
500nm
250nm L&S Cross section
1.5μm
100nm
250nm
High aspect ratio
15nm
1.5μm
Line width: 15nm, Thickness: 1.5μm
Penetration
2μm
Pitch 70nm Dot Pattern
Cross Section (Pitch 600nm)
Dot patterns (2)
Honey Comb Structure
0.5μm
1μm
3D Structure (1)
Improved GDS file Pattern
Marcus group
Diameter : 10nmPitch : 100nm
Dot Pattern
Array of triangle :lateral dimension 100nm (Pitch 200nm)
200nm200nm
Lateral dimension:100nm
Array of doughnut pattern : Doughnut 85nm (Pitch 200nm)
doughnut φ85nm 200nm200nm
Array of dots :φ10nm (Pitch 80nm)
φ10nm
80nm
80nm
φ25nm
80nm
80nm
Array of dots :φ25nm (Pitch 80nm)
Questions?