Transcript ppt - Nanolithography

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
Devin K. Brown,
Georgia Tech
negative charge
accumulation
1
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
2
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
3
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
4
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
5
Charging causes pattern distortion
GOOD
(no charging)
BAD
(moderate charging)
Ti/Au/Ti under resist
ESpacer < 1 hour
front side Au
ESpacer > 24 hours
Devin K. Brown,
Georgia Tech
BAD
(severe charging)
no anti-charging layer
6
Charging causes pattern distortion & field stitch error
GOOD
(no charging)
Ti/Au/Ti under resist
ESpacer < 1 hour
front side Au
500um
field
boundary
BAD
(moderate charging)
BAD
(severe charging)
ESpacer > 24 hours
no anti-charging layer
field
stitch
error
also
pattern
distortion
Devin K. Brown,
Georgia Tech
7