====== RECIPE FOR NANOTUBE DEVICES ON 170-m FUSED SILICA WAFERS ======

//Lisa Larrimore – June 2006//

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=== General Information and Tips ===
  * Order wafers from Mark Optics (http://markoptics.com, 714-545-6684). I used wafers straight out of the box (cleaning with acetone and IPA on the spinners), though doing some initial cleaning step might be better. The Craighead folks (John, Jose, Elizabeth) had some suggestions. These wafers are extremely thin, but if you are careful you won’t break any.
When manipulating whole wafers, I try to lift with the edge of a wafer tweezers and then hold by the edges with my hand (I've been told that clamping with tweezers can cause fractures), but I'll use rounded tweezers for pieces.
When drying whole wafers, I lay it on a Beta Wipe, trap it with my hand, and blow from the top, then move it to a dry section of the wipe and repeat. I then gently blow of small drops on the backside. When drying pieces, I brace one end against a Beta Wipe, hold the edges with my fingers, and dry from the other edge.

  * Keep track of which side of the wafer you’re working on! As soon as I start with a new wafer, I scribe a distinctive mark on the left side, and after I dice the wafers (but before I remove the blue sticky paper), I write a number in the upper left corner of each chip.

  * 5x Stepper: Put wafers or pieces on top of the 90 mm Whatman filter paper circles that are in the stepper room, and don't forget to check the Transparent/Opaque switch! You can't adjust the focus beyond 50 in your file, so you need to set it to 77 after executing each file. I haven't optimized the exposure times – the ones here work, but doing a focus/exposure matrix (with the EXPO command) would be good.

  * P10 Profilometer: You can't use an interferometer, so this is important for measuring etch rates. But it is only set up to measure substrates taller than ~400 um, so to measure 170-um thick wafers, you need to but a Beta Wipe underneath (the measurement will be noisier, but it still works).

=== GCA Keys ===

Clean wafer on spinner with acetone + IPA
Spin P20 (wait 10 s) and S1813 with program 4
Bake 115 C for 90 s (lift with edge of wafer tweezers, then grab with hand)
Cool on heat sink

5x Stepper: exposure=0.6-0.7 s, focus=77
Develop in MIF300 for 60-75 s, transfer to water, rinse, blow dry
Oxford 80 Etcher
5 min O2 clean with no wafer
Load wafer
30 s O2 descum
35 minute CHF3/O2 oxide etch (25-30 nm/min)
P10 Profilometer: ~1900 nm from bottom of gate to top of PR
Etch remaining PR with O2 (~13 minutes)
P10 Profilometer: gate pads ~850 nm deep (they don’t need to be quite this deep, but these show up very well)

Dicing with the Wafer Saw
Spin protective photoresist coating
Load wafer upside down onto metal rim with blue sticky paper
For Xinjian's mask, set angle 0 index to 32 mm (cut between every other row) and angle 90 index to 18 mm (cut between every column)
Before removing diced pieces, scratch numbers into upper left corner of each chip
Dissolve blue stuff with acetone (don't try to pull off pieces directly, or they will break!)
Wash each piece with acetone & IPA; blow dry


=== Catalyst Pads ===

Spinner: P20 (wait 10 s) and S1830 with program 4, bake 115 C 90 s
5x Stepper: cat pad mask, exp=0.6-0.7 s, focus=77
Develop in MIF300 for 60-75 s, transfer to water, rinse, blow dry
Oxford 80 Etcher
5 min O2 clean with no wafer
Etch PR with O2 to level you want (2-3.5 min, for 1000-600nm remaining, as measured with P10 Profilometer)
Take chips back to Clark (yay, a day not in a bunny suit!)


=== Catalyst Deposition (pick one) ===

(Note: I don't know which of these is better, but in general the growth seems more inconsistent than on silcon wafers. Some of my chips have tons and tons of NTs, while others from the same wafer have very few, and Zhaohui has found the same thing.)
  * Ken's catalyst:
Mix Ken's nanoparticles 1:100 in hexanes (be sure to wrap up the container back up very tightly when you are finished!)
Drop catalyst (~200 uL) onto chips
Air dry
Heat on 90 C hotplate for 10 minutes
Liftoff in 1 M NaOH (30-60 s) or acetone (5 min), rinse in DI, blow dry

  * Standard catalyst in water:
If catalyst isn't already made, mix:
60 mg Fe(NO3)9H2O
15 mg MoO2(acac)2 (note: previously I was told 3 mg!)
45 mg Al2O3
45 mL DI water
Sonicate several hours when first made
Sonicate catalyst 30-60 min, stir until ready to use
Add catalyst to chips in large mound, wait 2-10 minutes, rinse with water
Liftoff in acetone (5 min) + IPA, dry with N2

=== "Flying Catalyst" Nanotube Growth ===
Reserve furnace at www.calsnet.com/mcfur, sign log book
Clean tube for front furnace (rinse, bake out in air at 800 C)
Start with tube far to the right, insert chips so they are in the center, and make a mark on the furnace tube just outside the furnace on the left edge
Start with chips outside (sliding tube to left), or, if reducing in H2:
Start with chips inside furnace
Heat to 700 C in 0.8 SLM Ar (~4 min)
Add 0.2 SLM H2, wait 15 min, turn H2 off
Push tube out so chips are outside the furnace
Heat to 1040 C in 0.8 SLM Ar, with or without 0.2 SLM H2 (5-6 min)
Add 0.2 SLM H2, 0.8 SLM CH4, 5.5 SCCM C2H2, wait 2 min
Turn off Ar, set T to 915 C, pull in tube so chips are in center, grow for 10 min
Cool in 0.8 SLM Ar (~30 min): open furnace at 500 C, remove chips at 100 C


=== Electrodes: ===

Spinner: P20 and S1813 with program 2, bake 115 C 90 s
5x Stepper: electrode mask, exp=0.55s, focus=77
Check with microscope (should see faint outline of electrodes)
YES Image Reversal Oven
HTG Contact Aligner: flood expose 30 s
Develop in MIF321 for 60-75 s, transfer to water, rinse, blow dry
Note: can't do a plasma descum here – will kill NTs!
Evaporator: 40 nm Pd at 1 A/s
Liftoff: 1165 for 3-8 hours, rinse w/ acetone & IPA, blow dry

Alternative method: Grow NTs on top of Electrodes
(This is much easier, since you can do the electrodes on a whole wafer, but you also seem to get much noisier devices.)
Evaporate 2 nm Ti + 40 nm Pt before catalyst pads (remember to do 30 s oxygen descum first to clean extra photoresist)
Dice wafer
Define catalyst pads with PR on top of electrodes
