Graphene Fabrication

Some trouble shooting tips about the 4“ furnace.

  1. Tips seals on the scroll pump which backs the turbo pump can degrade over time. The tip seals must be in excellent condition to pump H2. The scroll pump will detect problems and will slow down from 80,0000 rpm to much less (visible on the communications port of the Turbo pump unit). The pressure in the growth chamber will climb gradually when H2 flow is initiated - rather than holding steady over the 10 minute time scale.
  2. After a CNT growth run there will be alcohol vapor in the lines. Turn on the Ar line to purge for 10 minutes.

A note about PMMA:

“I found out that the poor acetone stripping of PMMA from graphene surfaces was a result of using an older batch of PMMA that I mixed up myself. I just realized I made this mistake recently. I don’t want to mislead you into thinking that the bake-off method is always much better. I don’t know if Grant and Pete tried the solution removal method, but in general it is highly regarded.

“For future reference I called Microchem awhile back and they told me that this difficulty with removal can be a result of poorly mixed solution. PMMA should be mixed for many hours on a magnetic stir plate. If someone is going to mix up their own in the future I recommend telling them to give Microchem a call and get exact directions.”

Transfer Procedure

After growth of graphene on copper foil spin on 950MW A8 PMMA @ 4000RPM for 60s (A2 will give better results but is much more difficult)

Float on Transene CE-200 copper etchant until copper is gone ~2 hours or until clean

Scoop graphene out into 6 sequential baths of DI water, soaking for two minutes in each bath.

Scoop graphene out onto final chip

N2 Dry blowing VERY GENTLY from center outward to flatten all wrinkles

Allow to air dry in fume hood for ~6 hours (don't use a hot plate to “speed” this up, this also varies based on PMMA thickness)

Soak in methylene chloride for 4 hours

Soak 10 min in acetone

Soak 10 min in IPA

N2 dry

Shaping procedure at Cornell

Prime with P-20 Primer @ 4000 RPM for 60

Spin on S1813 @ 4000 for 60 sec

Expose in autostep 0.6 sec +50 focus offset keys at 0,2.25 and 0,2.25 (make sure arrow is pointing down on left side)

develop in mif 300 for 75 sec

Rinse with DI H2O

Pre clean etching chamber for 10 min in O2 plasma

O2 plasma etch for 15 sec

Soak 1165 4+ hours

Rinse in 4 consecutive IPA baths

N2 Dry

Electrode patterning at Cornell

Expose 1.2 sec +50 focus offset on 5x stepper w/ image reversal mask

Image reversal oven

Flood exposure 78sec on ABM

MIF-321 90sec

Rinse in DI

Evaporate 1nm TI / 200nm Au

Liftoff in 1165 for 1 Hr

Rinse with 4 consecutive IPA baths

Spray with IPA bottle

N2 dry

Ta Da!

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