Essentials of Electron Beam Lithography

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?