1. Basics E-beam lithography
Introduction of concepts
Pattern handling
Hardware issues
Miscellaneous

2. Main issues Introduction of concepts
Resist
Dose [µC/cm²]
Pattern
From design to beam stepping
Electron Beam Pattern Generator
Holder/substrate
Positioning
Beam
Exposure

3. Electron Beam Pattern Generator Introduction of concepts
Source Field Emission Gun
Beam column spot, scanning beam
Stage/holder  substrate, stepping, controls

4. Substrate holder Introduction of concepts
Beam current measurement
Calibrations
(spot size, focus)
Orientation reference (x,y)

5. E-beam definitions Introduction of concepts
Dose (material, kV) µC/cm²
Acceleration voltage kV
(20kV, 50kV, 100kV)
Spot size dspot
3 … 175 nm
Beam current Ispot (~dspot²)
300 pA … 317 nA
Beam step size BSS
Resolution Res
Beam step frequency BSF
500 Hz … 100MHz

6. From pattern to e-beam writing process pattern handling
Hardware
Stage movement
Beam deflection
Fracturing
Main field (scanfield, block)
Trapezium

7. Large structures pattern handling
pattern divided into main fields
substrate move for each next main field
main field exposure by beam deflection
each main field:
center main field
height compensation
deflection calibrated to stage movement
Writing order of main fields

8. Trapezium pattern handling
T = pixel exposure time
BSF (MHz) = 1/T(µs)
Ispot(nA)
= 0.1 * ~
Q(µC/cm²)*BSS²(µm²) dspot²

9. Trapezium-wise beam stepping in main field pattern handling
Each (xi,yi) is the start of a new trapezium

10. EBPG CHARACTERISTICS pattern handling
Trapezium resolution
0.08 nm ……… 0.5 nm
Main field resolution
0.16 nm ……… 1.0 nm
Main field deflection
º max field size = *main resolution (20bits)
º size range: … kV
Trapezium deflection
º BSF: 500 Hz – 100 MHz
º BSS = 1,2,3,4,5,…,16383 * trapezium resolution
º max field size = * trapezium resolution (14bits)
º size range: 1.31 … kV

11. Filling the pattern with spots pattern handling
e-beam is stepped
filling areas
use dspot=1.2–1.5*BSS
lines
use minimal 4-5 spots in linewidth
narrowest lines
º take smallest spot
º define linewidth of 1 BSS (often 1.25nm)

12. Intermezzo: dose considerations primary and secondary contributions
primary dose
º lateral range: spot diameter + little effect from forward scattering in resist
º gaussian distribution
º partial overlap of adjacent spots
secondary electrons
lateral range: 5 nm around primary electron path
backscattered electrons (proximity)
º lateral range: many µm
º on Si, at 100 kV typically 50 µm
… different dose settings for plane, line and spot

13. Intermezzo: dose considerations primary and secondary contributions

14. JOB TIME pattern handling
beam-on time
Q(µC/cm²)*A(mm²)
T(s) = 10* ~ ~
Ispot(nA) BSS² dspot²
to minimize beam-on
º split coarse and fine pattern layers, but keep small (e.g. 1 µm) overlap
º calibration per layer takes 3 to 5 minutes
overheads
º main settling 50µs/trapezium
º stage movements
º big pattern files (max 1GB!)

15. Software and computer overview pattern handling
Design Autocad/DesignCAD/LDM-file/L-Edit/Other
Output formats DXF/ GDSII/ CIF/ TXL/ other formats
Conversion LayoutBeamer  gpf pattern data
Gpf pattern data  exposure EBPG
 Cview inspection
Computer
Layout Beamer PG5000+
USER pegasus EPIC-ALFA
(design) (job)
pegasus.kavli.tudelft.nl epic-alfa.kavli.tudelft.nl
cad/&KN-lab
or PG5200
EPIC-BETA
epic-beta.kavli.tudelft.nl

16. Around the stage hardware issues
BSED: Back Scattered Electron Detector
locating marker
spot optimization and focussing
Laser: height measure-ment
 beam focus on substrate

17. Substrate holder hardware issues
Cup: current measurement, x-y reference
Markers: spot characteristics

18. Beam current measurement hardware issues
Faraday cup

19. Calibration markers hardware issues
spot optimisation (focussing)
spot size measurement
‘zero’ height reference
reference in (x,y) position
marker search

20. Spot size measurement hardware issues
dmeas² = dspot² + dedge²
dedge = 20nm for very good marker but often > 30nm; depends on marker edge itself and possible contamination
dmeas² = a.Ispot + b (small spots)

21. Spot size adjustment hardware issues
FEG: high brightness electron source
BSF too high  need for defocus
discrete steps of 20nm/bit in µm aperture
adds quadratically to initial spot
dadjust² = dmeas² + ddefocus²
unround spot if a few bits
real big spots: 4/3*measured size
defocus to dmeas or adjust by [+ -]<bits>

22. Height adjustment hardware issues
Beware:
Transparent substrate
Reflectivity topology
Flatness: 1µm/mm  height error ~ 1.5µm
 broadening of the beam with ~ 7.5nm
(at 400µm aperture)
Calibration marker at ‘zero’ height
Adjustment range; ± 100 µm

23. Height level hardware issues
final lens image of spot on substrate
Substrate NOT at constant height
should be < 1µm/mm
Height compensation during exposure:
spot size –FF
scaling
rotation
 Final aperture MUST be well aligned

24. E-beam threats miscellaneous
Charging
e-drain required  conductive layer*
Contamination
work clean!
handle holders carefully and with gloves
Vibrations
turbo: around 800Hz  writing strategy!*
don’t be around during writing
Thermal stability
Keep door closed
* In more detail in Advanced E-beam Litho

25. Limitations miscellaneous
Resist
shot noise: N ± √N
swelling
secondary electrons: 8nm extra
Position accuracy
laser interferometer: 0.6nm
marker location: 30nm
drift (0.1 µm/hr possible)
main field overlay
stitching: 60nm