1. Anti-Charging Methods
when electron beam lithography must be performed on insulating substrates (e.g. Quartz, SiC, soda lime, etc.) negative charge buildup can occur on the substrate surface causing beam deflection, and thus pattern distortion
Initial Condition
Future Condition
electron beam
electron beam
repulsive electric potential lines
ma-N 2403
glass substrate
negative charge
accumulation
Devin K. Brown, Georgia Tech

2. Au on top of resist
Au can be coated on top of resist to dissipate charge
typically 100A is sufficient
Au must be deposited with Filament Evaporation
Electron beam evaporation will expose resist
Au must be stripped with Potassium Iodine prior to resist development
has worked well with ZEP520A on glass
has not worked well with ma-N 2403 on glass (see next slide)
front side Au
e-beam exposure Au
ma-N 2403
glass substrate
Devin K. Brown, Georgia Tech

3. Au incompatible with ma-N 2403
Au on top of ma-N 2403 on glass substrates has not worked well
Devin K. Brown, Georgia Tech

4. Ti/Au/Ti under resist layer
Ti/Au/Ti can be coated underneath resist to dissipate charge
typically 20/30/20A is sufficient
can use Electron beam evaporation since deposition occurs prior to resist coating
Ti/Au/Ti must remain after resist development, may not be compatible with process
Ti can help with resist adhesion issues to quartz
Ti/Au/Ti under resist layer
e-beam exposure
ma-N 2403
Ti/Au/Ti
glass substrate
Devin K. Brown, Georgia Tech

5. ESpacer ESpacer is spin coatable, no evaporation required
ESpacer is water soluble
compatible with ma-N 2403
Ebeam exposure must occur shortly after ESpacer application
front side ESpacer
e-beam exposure
ESpacer
ma-N 2403
glass substrate
Devin K. Brown, Georgia Tech

6. Charging causes pattern distortion
GOOD
(no charging)
BAD
(moderate charging)
BAD
(severe charging)
Ti/Au/Ti under resist
ESpacer < 1 hour
ESpacer > 24 hours
no anti-charging layer
front side Au
Devin K. Brown, Georgia Tech

7. Charging causes pattern distortion & field stitch error
GOOD
(no charging)
BAD
(moderate charging)
BAD
(severe charging)
Ti/Au/Ti under resist
ESpacer > 24 hours
no anti-charging layer
ESpacer < 1 hour
front side Au
500um
field
boundary
field
stitch
error
also
pattern
distortion
Devin K. Brown, Georgia Tech