General Wet Processing

This document describes the standard operating procedure for the preparation of solutions involving the mixing and eventual disposing of different chemicals. Chemical solutions could be use for etching, cleaning or surface activation. It is important to note that reading this document IS NOT considered as a sufficient training for the use of chemicals and wet benches. Users must go through regular training with a member of the fab staff. Chemicals involved are toxic and dangerous. NEVER do something you are not absolutely sure of. ALWAYS ask in case of doubt.

Associated documents and references

  • Rules and safety regarding chemical use.
  • MSDS regarding the specific chemicals needed.

 

Equipment used

Wet chemical etchings must be done in the appropriate wet benches. The exhaust system ensures the evacuation of toxic fumes. When using non-HF acids and when the solutions must heated at a precise temperature, the experiment must be carried out using the hotplate.

Tool Location Process Capabilities
Non-HF wet bench Etch/Dep RCA nad Piranha cleaning, metal etching
HF wet bench Etch/Dep Oxide etching
Silicon Etch wet bench Etch/Dep Silicon bulk anisotropic etch with TMAH or KOH
Solvent wet bench Etch/Dep Substrate cleaning, resist strip, lift-off.
Lithography wet bench Lithography Work related to lithography: solvent clean and development

 

Chemical storage

  • All solvents and developers must be stored in yellow flammable cabinets. 
  • All acids and metal etchants must be stored inside the non-HF wet bench except nitric acid.
  • Nitric acid is stored in a dedicated white plastic cabinet.
  • All bases (KOH, TMAH, NH4OH) must be stored in the blue “Bases” cabinet.
  • Hydrogen Peroxide (H2O2) must be stored in the dedicated white tray in the blue “Bases” cabinet.

 

Maximum capacity at benches

Due to limited space, only one user is permitted at each wet bench at a time.

 

General rules

  • You MUST have received the wet bench training by a cleanroom staff member.
  • You MUST be aware of the MSDS data for each chemical that you are using before beginning your work.
  • Before mixing any chemical, you must be aware of the chemical reactions that may occur and their dangers.
  • You are NOT ALLOWED to bring new chemicals inside the cleanroom without approval.
  • Identify the chemical carefully when taking the bottle(s) from the cabinet.  
  • You MUST label any labware with the name of the chemical. A microscope slide can be used also. Slides with common chemical names are available on each wet bench. If you leave the wet bench unattended, indicate your name and the date as well.
  • DO NOT leave solutions unattended when strong reactions can occur (RCA and Piranha mixtures, Aqua Regia).
  • You MUST rinse the wafers/samples in between when using several incompatible chemicals during a process (e.g. solvents and acids, RCA-1 and HF).

  

Specific rules and procedures

Solvent and litho wet benches

  • ALWAYS wear safety glasses. 
  • ALWAYS use glass beakers or trays.
  • DO NOT use acids and bases.
  • DO NOT heat chemicals with low flow flash point (acetone, IPA, methanol).
  • DO NOT dump chemicals down the drain. Use the white waste containers.

Acid and base wet benches

  • DO NOT use solvents. IPA may be allowed for silicon etching but approval is needed. 
  • ALWAYS wear the protective personnal equipment (PPE) at all times: put on the chemical apron, then full face mask and lastly the tripolymer chemical resistant gloves.
  • DO NOT cross outside the green line with the chemical gloves and the PPE.
Warning: NEVER touch clothes, goggles, face shield or any surface outside the acid/base wet benches
while wearing the chemical gloves because abrasive chemicals might be left on the gloves and cause injuries.
Remove the complete PPE if you leave the wet bench area and use other device like computer, microscope, ...
  • ALWAYS use plasticware with HF and glassware with other acids and heated solutions. 
  • ALWAYS ADD ACID (AAA rule) to water. Always start pouring DIW and finish by adding acid. Pouring a large amount of water into acid or base might cause explosive reactions.
  • Rinse the chemical gloves regularly using the bottle rinser on the non-HF wet bench.

Hot plate usage

Non-HF and Silicon etch wet benches are equipped with a hot plate.

  • DO NOT use plasticware directly on the hot plate.
  • DO NOT use flammable or combustible materials.
  • The probe MUST be immerged in the solution for proper temperature regulation.
  • NEVER leave a heated solution unattended.
Warning: If the probe is not immerged in the liquid solution,  room temperature will be measured and
 the hot plate will keep on heating the solution way beyond the temperature wished.
This may lead to boiling and uncontrolled reaction.

  

Rinsing and drying

Each wet bench is equipped with a faucet, a water gun and a Nitrogen gun. Solvent and acid/base wet benches are equipped with a dump rinser.

6" wafers

  • Transfer the 6" wafers to a Teflon cassette.
  • Put the cassette in the dump rinser and run the automatic rinsing program.
  • Load the cassette into the Verteq dryer and run the automatic rinsing/drying program.

Small substrates/samples

  • Rinse the samples thoroughly with the water gun or the faucet.
  • Dry the surface with the nitrogen gun.

 

Disposal

Type of disposal Location Chemicals
Flammable waste container (white)

Drawer of the litho wet bench, litho room

Acetone

IPA

Methanol

Resists

Developers

Flammable cabinet, etch/dep room

Acetone

IPA

Methanol

Resists

Remover 1165

AZ resist stripper

Acid waste container (yellow) Drawer of the non-HF wet bench

Aluminum etchant

Chromium etchant

Gold etchant

HF waste bottles Inside the non-HF wet bench

HF 49%

BOE 6:1

Chemical drain Non-HF wet bench

Hydrochoric acid

Phosphoric acid

Nitric acid

Sulfuric acid

Nanostrip

RCA1/2

Si etch wet bench

KOH

TMAH


Warning: any hot chemical or mixture (e.g. TMAH, KOH, Piranha, RCA 1/2) must be cooled down (< 40°C) before disposing of it

 

Clean-up

  • Use the dump rinser or use the water gun/faucet to rinse all the labware and other equipment (tweezers, thermometers, etc) thoroughly.
  • Put the small beakers back on the drying rack. Large beaker and trays must be stored in the cabinet above the wet benches
  • Use 1 or 2 wipers to dry the working area. No droplet should remain.
  • Rinse the chemical resistant gloves and dry them with a wipe.

 

Empty bottles

  • Empty bottles of solvents must be rinsed thoroughly with DI water on the solvent or litho wet bench.
  • Empty bottles of acids, bases, metal etchants must be rinsed in the bottle rinser of the non-HF wet bench 3 times.
  • Dry the outside with the nitrogen gun and/or a cleanroom wipe.
  • Cross the label out with a permanent marker and write "Rinsed" on the bottle.
  • Leave the empty bottle in the pass-through or behind the double doors.
  • Contact the staff or make a comment in Coral to get a new bottle if there are no others in the cleanroom.