Viktoryia’s photolithography procedure (April 2018):

• Substrate preparation:
  • Clean the substrate with sonication in Acetone (5 mins), rinse in IPA and blow dry with N2.
  • Dry the substrates, put them on hot plate at around 180C for 3 mins. Cool down the substrates, 1-2 mins. Note: if you cleaned the substrates beforehand, still put them on the hot plate right before the spincoating at 180C for couple of mins to remove any DI water molecules adsorbed from air. Let the samples cool
  • S1813 spincoat (recipe S1813-MRE), approximate polymer film thickness is 1.5um.
  • Clean the spincoater as quickly as you can
  • bake for 1 min at 115℃
• Photolithography:
  • Expose with UV light for 14s
  • Develop in positive developer (351:DI=1:5) for 40s, rinse in DI water for 20s, blow dry with N2
• Metal deposition:
  • RIE, Tongxin recipe for 1 min 70W and 40sccm
  • Blow with N2, Load the samples in deposition chamber using double sided tape
  • Deposit metals with Cr as an adhesion layer (2-5 nm is enough)
• Lift off:
  • use diamond scriber and scratch the sample edges, where no devices and structures are present;
  • put the substrate under angle in acetone (for sensitive devices), cover with Aluminium foil.
  • Quick lift off: put it on hot plate at 50C for 30mins-1h.
  • Gentle lift off: leave the substrate in acetone overnight (cover with parafilm, cover on top with aluminium foil)
  • Important: have enough Acetone, 1x1cm substrate use 20-30ml Acetone.
  • To remove the metal film, spray Acetone on the substrate, while the substrate is inside of Acetone. If the film doesn’t lift off, use sonication (3mins) only for substrates without 2D materials.
• NOTE: the photolithography masks are located in Martin's drawer. The CAD files of the patterns can be found in my folder on the desktop of the cleanroom computer.