SETs Procedure
Alvar Rodríguez, Simranjeet Singh
UCF, 2015
Developing of Single-Electron Transistors in Dr. Enrique del Barco Lab, using the clean
room of the Department of Physics of UCF.
1.
Chemicals
a. Rinse pipettes, beakers, IPA, ethanol and acetone.
b. Vials of resists.
c. CD-26 and DI water beaker.
2.
Wafer preparation.
a. Cut 3 inch Si-SiO2 into a 1.8 inch square using diamond cutter pen.
b. Clean wafer with Acetone, Ethanol, and IPA (in that order) then blow dry with
Nitrogen gas.
c. Spin on LOR resist then bake on hotplate for 5 minutes at 175°C.
d. Spin on Shipley resist then back on hotplate for 2 minutes at 120°C.
LOR 3A (B)
2s at 500rpm / 30s at 3000rpm / 2s at 0rpm
3.
Shipley S1813 (A)
2s at 500rpm / 30s at 5000rpm / 2s at 0rpm
Alignment
a. Clean Mask with Acetone, Ethanol, IPA and then sonication in DI water for at
least 5 minutes.
b. Place wafer on mask aligner using cut away plastic to ensure sample vacuum.
Turn on sample vacuum (Read guide lines of Mask Aligner).
c. With your eyes align wafer piece to the sample pattern on the mask.
d. Using contact vacuum raise wafer also you can use the dial.
e. Use micrometers to align layers.
f. Once it is aligned, check the intensity of the UV-light in order to choose the time
𝐦𝐉
of exposition correctly. The exposing relation must be ~ 𝟏𝟐𝟔 𝐜𝐦𝟐 .
g. Slide chuck gently all the way to the left and look away from the lamp.
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4.
Development
a. Place wafer in beaker of CD-26 for 45 seconds, then quickly in DI water.
b. Spray wafer with DI water then Nitrogen blow dry.
c. Check patterning with microscope, if the etches and color is good and uniform;
place the sample at 130° C for 5 minutes, then 1 minute in CD-26 followed by DI
water and Nitrogen blow dry.
d. It is very recommendable to use new CD-26 in every development. Also, Change
DI water every time that it has been used.
5.
Evaporate
a. Carefully place sample on sample holder and mount in chamber. The
evaporations should take place at <5E-6 Torr.
b. Before these 3 evaporations clean the wafer right before introducing it into the
chamber with O2 plasma.
SCCM
12
Power
50 W
Layer 1:
Time
10 s
5 nm Ti followed by 10 nm Pd
Density
Z-ratio
Tooling Factor
Deposition Rate
Thickness
Current
Layer 2:
Pressure
200 mTorr
Ti
4.5 g/cm3
0.628
170 %
1 Å/s
5 nm
~30 mA
Pd
12 g/cm3
0.357
170 %
0.4 Å/s
10 nm
~40 mA
10 nm Ti followed by 70 nm Pd
Density
Z-ratio
Tooling Factor
Deposition Rate
Thickness
Current
Ti
4.5 g/cm3
0.628
170 %
1 Å/s
10 nm
~30 mA
Pd
12 g/cm3
0.357
170 %
1.4 Å/s
70 nm
~45 mA
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Layer 3:
35 nm Al.
Density
Z-ratio
Tooling Factor
Deposition Rate
Thickness
Current
Al
2.7 g/cm3
1.08
160 %
0.6 Å/s
35 nm
~200 mA
Evaporate 10nm before opening the shutter in order to remove the Al2O3 first.
Oxidation in Chamber:
a. For the Al layer oxidation inside the chamber will be used.
b. Use the manual Instructions to be followed by user during introduction of
oxygen to the Evaporator Chamber. This manual is next to the chamber in the
clean room.
c. Please be careful it might be dangerous!
d. First open the oxygen valve and then add oxygen “slowly” to the chamber with
the two wheels valve (This valve is very sensitive and both wheels have to be
moved at the same time)
e. Stop at 250 mTorr
f. Close valve of oxygen and the two wheels valve
g. Leave it in 250 mTorr for 40 min
h. Then, pump with dry pump for 15s and then roughing pump around 20 min
(until pressure in the chamber is very low)
i. Then turn off roughing and dry pump
j. Vent chamber
6.
Lift off
a. Place sample in fresh PG Remover for 1 hour in the 1st and 2nd layer
b. Spray with PG to help the lift-off then clean it with DI water.
c. For the Al layer place the sample in Acetone at Room Temperature for about 1
hour checking periodically, spray with acetone for helping the lift off, followed
by 5 min in PG and then DI water.
7.
Oxidation Gates - Al layer
a. After lifted off leave the sample for 24 hours at atmosphere conditions. Also it
might be useful to oxidize the gates even more with O2 plasma Oxidation.
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SCCM
12
Power
50 W
Pressure
100 mTorr
Time
10 min
b. Then check with meter or probe station the resistance of the gates. They should
be around ~ 400 Ω. In case of not conduction between the gate it is possible to
have to make the next point with the gates.

If they don’t work: in Probe Station measure the gate’s resistance on top
of gate’s ends (sometimes you will need to scratch them a little bit) and
suddenly it will start measuring resistance.
Although, If the step of cleaning the wafer with O2 plasma after the Al
evaporation should solve this problem of connection between the gates and rest
of the circuit.
8.
E-beam Lithography
a. Spin on MMA resist then bake for 5 minutes at 175°C.
b. Spin on PMMA resist then bake for 5 minutes at 175°C.
c. Take it to CREOL & follow E.beam CREOL instructions.
MMA (8.5) EL 6 (E)
2s at 500 rpm / 60s at 4000 rpm / 2s at 0 rpm
9.
950 PMMA C 2 (F)
2s at 500 rpm / 60s at 6000 rpm / 2s at 0 rpm
Nano-Wire Developing
a. Develop sample in 3 IPA : 1 MIBK for 45 seconds.
b. Rinse with IPA and blow dry.
c. Check patterning under microscope if necessary develop a bit more.
10.
Nano-wire Evaporation
a. Mount the sample in chamber.
Layer 1:
17~20 nm Au.
Density
Z-ratio
Tooling Factor
Deposition Rate
Thickness
Current
Au
19.3 g/cm3
0.381
175 %
1.5 Å/s
17 nm
~ 50 mA
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Layer 2:
50 nm Au or Pd
Density
Z-ratio
Tooling Factor
Deposition Rate
Thickness
Current
Au
19.3 g/cm3
0.381
175 %
1.5 Å/s
50 nm
~ 50 mA
This evaporation is divided in two steps of 25 nm where the current is driven to
zero in between the steps. This layer needs to be 5 to 10 nm thicker than the Gate.
11.
Nano-wire Lift-off
a. Place sample in Acetone at Room Temperature for about 1 hour checking
periodically.
b. Don’t rush in these layers or the nano-wires will be gone!
c. If it still doesn’t come off try spraying gently with Acetone.
d. Blow dry with a very light stream of Nitrogen gas.
12.
Does it work?
a. Check that the gates are still conducting
b. Check that there are indeed wires there (~100 Ω) by measuring with probe
station.
c. Check if there is a leak between the sources (drain) and gates with probe station.
d. If there is a leak check ALL chips, if all of them leak then you just wasted lots of
time and money.
13.
Getting ready for Measuring and Measuring
Use manual SETs Getting ready for Measuring.
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