Devin K. Brown, Georgia Tech

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

ma-N 2403

glass substrate

electron beam

electron beam

negative charge accumulation

Initial Condition Future Condition

repulsive electric potential lines

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)

Au

ma-N 2403

glass substrate

front side Au

e-beam exposure

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

ma-N 2403

glass substrate

Ti/Au/Ti under resist layer

e-beam exposure

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

Devin K. Brown, Georgia Tech

5

• ESpacer is spin coatable, no evaporation required• ESpacer is water soluble

– compatible with ma-N 2403

• Ebeam exposure must occur shortly after ESpacer application

ESpacer

ma-N 2403

glass substrate

front side ESpacer

e-beam exposure

ESpacer

Devin K. Brown, Georgia Tech

6

GOOD(no charging)

BAD (severe charging)

Ti/Au/Ti under resist

BAD(moderate charging)

no anti-charging layerESpacer > 24 hours

Charging causes pattern distortion

ESpacer < 1 hourfront side Au

Devin K. Brown, Georgia Tech

7

GOOD(no charging)

BAD(severe charging)

Ti/Au/Ti under resist

BAD(moderate charging)

no anti-charging layerESpacer > 24 hours

500umfield

boundary

fieldstitcherror

alsopattern

distortion

Charging causes pattern distortion & field stitch error

ESpacer < 1 hourfront side Au