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device_making [2012/05/15 13:52]
landon [Vacuum Anneal]
device_making [2018/01/17 15:16] (current)
carly
Line 131: Line 131:
   *Metal evaporation,​ $60 per 2 hour session + $0.80 per nm of gold deposited   *Metal evaporation,​ $60 per 2 hour session + $0.80 per nm of gold deposited
   *Reactive Ion Etching, $30 per hour, need about a 30 minute session to do 500 nm etch.   *Reactive Ion Etching, $30 per hour, need about a 30 minute session to do 500 nm etch.
 +
 +======Device Fabrication:​ Updated January 2017======
 +
 +==Overview of GFET Fabrication==
 +
 +(I) On SiO2 substrate
 +(0) -Expose alignment marks on wafer (see: Photolithography Procedures).
 +-Deposit Chromium using E-beam procedures (about 30 nm).
 +-Place sample in PG-remover on hotplate at 65 C to remove photochemicals and excess metal. Leave for about 15 minutes. Using pipette to gently remove as much metal as possible while in solution. Transfer to fresh PG bath on hotplate. Leave overnight. Rinse with IPA and DI water, then dry with N2 to store.
 +(1) Add prepared graphene to chip. (see Preparation of Graphene). Let dry overnight in covered dish. Soak in acetone overnight to remove PMMA. Rinse with IPA and DI water, dry with N2.
 +(2) Spin-coat chip, expose device contacts using photolithography and develop (see: Photolithography Procedures).
 +(3) Dep. Cr or Ti (1 nm) and Au (50 nm) using E-beam.
 +(4) Place sample in PG-remover on hotplate at 60 C to remove photochemicals and excess metal. Leave for about 15 minutes. Using pipette to gently remove as much metal as possible while in solution. Transfer to fresh PG bath on hotplate. Leave overnight. Rinse with IPA and DI water, then dry with N2 to store.
 +(5) Spin-coat chip, expose graphene using photolithography and develop (see: Photolithography Procedures). ​
 +(6) Plasma-etch to remove excess graphene (see: Plasma Etch Procedures)
 +(7) [optional:​ to isolate leads] Dep. SiO2 (50-100 nm) everywhere apart from contact regions. Place in PG-remover, following same procedure as for metal deposition.
 +
 +(II) On glass cover slip
 +(0) [optional:​ for releasable devices] Use chip with AlO3 already deposited.
 +(1) Add prepared graphene to cover slip. (see: Preparation of Graphene). Let dry overnight in covered dish. Soak in acetone overnight to remove PMMA. Rinse with IPA and DI water, dry with N2.
 +(2) Expose device contacts using lithography and develop (see: Photolithography Procedures).
 +(3) Deposit Cr or Ti (1 nm) and Au (50 nm) using E-beam.
 +(4) Place sample in PG-remover on hotplate at 60 C to remove photochemicals and excess metal. Leave for about 15 minutes. Using pipette to gently remove as much metal as possible while in solution. Transfer to fresh PG bath. Leave overnight. Rinse with IPA and DI water, then dry with N2 to store.
 +(5) Expose graphene using photolithography and develop (see: Photolithography Procedures). ​
 +(6) Plasma-etch to remove excess graphene (see: Plasma Etch Procedures).
 +
 + 
 +==Preparation of Graphene==
 +(1) Cut graphene on copper (Cu) foil to desired size (the side with the graphene on it should be marked).
 +(2) [Oksana’s lab] Spin PMMA (use 2% PMMA in anisole) onto graphene side. 
 +a. Turn on air and lights in fume hood; sign in for instrument use.
 +b. Set spin coater to 3000 rpm for 60 s. Use chuck with small holes in top (not o-ring).
 +c. Set Cu sample on chuck, with graphene side facing up, ensuring all holes are covered. Put chuck onto spin coater.
 +d. Open PMMA in fume hood. Cleanly pipette several drops onto graphene. Press “vacuum”;​ close lid and begin spin coat.
 +e. Carefully remove coated sample and store.
 +(3) [Ethan’s lab] Hard-bake @ 90 C for 60 s.
 +(4) Float in CE200, copper-side down, for about 8 hours.
 +(5) Remove from solution using tongs and plate, and put into water bath (“water PMMA” label) for about 15 minutes.
 +(6) Transfer to fresh DI water bath. Leave for at least 15 minutes (longer is acceptable). Repeat twice more. 
 +(7) Store graphene floating in water bath. (now the graphene still has a layer of PMMA on it => once graphene has dried overnight on substrate, remove PMMA by soaking in acetone overnight, followed with IPA and H2O rinse).
 +
 +
 +==Photolithography Procedures (in OSU cleanroom)==
 +(I) Spin-coating
 +-For bilayer processing (metal deposition) complete all steps below
 +-For single layer processing (graphene) skip steps 3 – 5
 +(1) Place chip on hotplate at 115 C for about 3 minutes to remove any residual water. Cool chip on cooling plate for 1 minute.
 +(2) Set spinner to 4000 RPM (ramp rate = 1000 R/s).
 +(3) Cleanly pipette P20 and drop onto chip; wait about 30 s. for solution to spread. Spin for 45 s.
 +(4) Cleanly pipette LOR onto center of chip. Immediately spin for 45 s.
 +(5) Place chip on hotplate at 190 C for 4 minutes (hard bake). Cool for 1 minute.
 +(6) Cleanly pipette S1813 onto center of chip. Immediately spin for 30 s.
 +(7) Place chip on hotplate at 115 C for 90 s (hard bake). Cool for 1 minute.
 +(II) Exposure
 +-Using ECE418 aligner
 +(1) Check N2 and compressed air pressure (gauges near door; expect about 40 psi and 80 psi, respectively). ​
 +(2) Turn on N2, compressed air, and bulb. Set power to 350 W, constant power. Let bulb warm up for 15 minutes. Note: warning light will blink for about 1 minute. If it blinks longer the bulb needs to be replaced. ​
 +(3) Carefully insert mask, with purple (chrome) side facing sample. Add chip and align properly. Exposure time is 3 – 4 s.
 +(4) After exposure, remove mask. Turn off bulb but leave N2 on until system is cool (30 minutes). If necessary, clean mask with acetone/​IPA.  ​
 +(III) Development
 +-Note S1813 is a positive photo-resist so exposure breaks bonds, allowing it to be washed away with developer
 +(1) Place chip in AZ300 bath for 90 s., constantly agitating. ​
 +(2) Remove from developer bath and put into water for 60 s, agitating.
 +(3) Dry with N2. 
 +
 +==Plasma-etch Procedures==
 +(last edit: 1/2/18 by Carly)
 +(1) Place samples inside chamber.
 +(2) Turn on plama-etcher (switch on back).
 +(3) Press ​           twice (starts power)
 +(4) Toggle left or right to Setup menu, press                           
 +Use settings:
 +a. Vacuum set point 201.1
 +b. Atmospheric Vent 00:15
 +c. Purge Vent 00
 +d. Gas Stabilize 59
 +e. Vacuum Alarm 5:00 minutes **Important! If the vacuum is not reached by this time limit, system shuts down.**
 +f. Plasma Time: 3:00 minutes
 +(5) Press up to return to main menu. Select Commands. Select Plasma to begin process. ​
 +(6) After timer runs out, go back to Commands menu, and select Off.
 +(7) Remove samples from chamber.
 +

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