MTL Fabrication

Photo-wet - Standard Operating Procedure

CORAL Name: photo-wet
Model Number: Semifab Model WPS 800 Wet Processing Station
Location: TRL
What it does: wet processing station
Introduction: The photo-wet station supports several processes with photoresist developing as the most prevalent process. A list of chemicals which can be used in the photo-wet station is compiled in the MATERIALS section. It is strongly advised that users read the MSDS (Material Safety Data Sheets) before Using these chemicals to become aware of the proper uses/handling/hazards of these chemicals. The MSDS sheets for these chemicals can be found in the copier room on the second floor of Building 39.

The photo-wet station has been approved for restricted processing with small amounts of solvents and for the developing of photoresist. No solvents are to be discarded through the water drain. Used solvents are collected into bottles for collection by the MIT-Safety Office. It is permissible to dispose of approved developers and "Semico" cleaners via the water drain.

The photo-wet is divided into 4 sections, two for metal lift-off processes, a rinse tank section, and a general use area. The first metal lift-off section is used for compound semiconductor processes, and for lift off of gold, tin, and silver. It contains a variable power ultrasonic tank with degassing control and time for automatic operation, two hot plates for solvent cleaning and degreasing, and a DI water gun.

The second metal lift-off section contains a similar ultrasonic tank, and is used for silicon based lift-off processes involving aluminum, platinum, and chromium.

The rinse tank area has dedicated DI rinse tanks, one for compound semiconductor processes, and the second for silicon processes.
The fourth area is used for general purpose rinses, etc.
The front control panel has the main power switch and reset switch, four timers, control switches for the cascade rinse tanks and the dump to resistivity tank, and the two ultrasonic controllers. A side control panel contains the two hot plate switches and temperature controllers.

Safety: All processing must be done below the lip-exhaust area to avoid inhalation of solvent vapors. Verify that the exhaust is working before beginning to use this station. Even though solvents handled in the photo-wet station are not corrosive, absorption through the skin or inhalation are potential safety hazards. Safety attire is mandatory when operating the photo-wet station, namely safety glasses/goggles and solvent gloves. If you have any questions regarding proper procedures, contact the area specialist.

Procedure: MATERIALS:
The following materials have been approved for use in this station.
Developers: (Tetramethyl Ammonium Hydroxide)
OCG 934 1:1 for developing of TRL standard resist OCG 825-34cs
AZ 422 MIF for developing of AZ 5214-E
AZ 440 MIF for developing of AZ 4620 Thick Resist

Acetone, Methanol, and 1,1,1-Trichloroethane
Cleaning Solution:
Semico (Ammonium Salt cleaning) - Used for Cleaning of
compound semiconductors PROCEDURE: (Immersion Developing)
  1. Check Equipment Reservations in CORAL to insure that you reserved the correct machine in the correct facility for the correct date. Another user may have reservations; it is your responsibility to honor them, if this is the case.
  2. Use the "Engage" command in CORAL for the equipment that you are about to use; use this command BEFORE you start the operation. Insure that the correct facility is set (TRL) and that your lot name is entered correctly.
    Note: The following procedure is for single wafer developing of the TRL standard photoresist, OCG 825-34cs.
  3. Choose the proper developer, in this case OCG 934 1:1.
  4. Rinse appropriate beaker with DI Water and fill with 100-200 cc of developer.
  5. Immerse wafer into beaker with photoresist side up and set timer on.
  6. Slowly move beaker in a "figure 8" pattern (forward/backward) to agitate liquid developer. You will see exposed resist dissolving in the developer by the color changes during developing.
  7. When large exposed pattern clears, add 10 more seconds developing time to allow small geometries to open.
  8. Dump developer into sink and fill beaker/wafer with DI water at least three times.
  9. Remove wafer from beaker, place it into a blue teflon carrier, and rinse wafer in cascade tank for 2 min.
  10. Transfer wafer in blue wafer carrier into the spin-dryer. Use 140 sec rinse, 240 sec dry time.
  11. Inspect wafer under microscope after drying.
  12. If you are only developing a single wafer, end "Operate Machine" in CAFE, and proceed to the clean up procedure described in 8 steps below:

Note: The following procedure is for batch developing of the TRL
standard photoresist, OCG 825-34cs.
  1. Place wafers in blue teflon wafer carrier.
  2. Rinse beaker with DI Water and place developer into polypropylene beaker, so that the developer level will comfortably cover the wafer carrier.
  3. Immerse wafer carrier/wafers into beaker and time process as determined by single wafer development above.
  4. After developing, immerse carrier/wafers into DI Water cascade tank and rinse for 2-3 min.
  5. After 2-3 min. rinse, transfer carrier/wafers into the spin-dryer.
    Use 140 sec rinse, 240 sec dry time.
  6. Inspect wafers under microscope after drying.
  7. "Disengage" in CORAL.
  8. Clean up photo-wet station...
    1. Rinse developing beaker at least 3 times and place it for storage/drying over the floating counter.

    2. Return bottles of developers and other chemicals used to the "pass-through".

    3. Return wafer carriers/holders to proper shelf.

Please follow the following rules for collecting/discarding waste solvents to avoid potential damage to wafers (and months of work to others) as well as to prevent the serious threat of gold or other contamination to MTL wafers/equipment.
  1. Take short plastic bottle marked as "WASTE SOLVENT".
  2. Place "SUBSTANCE IDENT" label on bottle
  3. Open plenum's cover and remove filled bottle, by swinging bottle and spout sideways. Alarm will sound and stay "on" until a new bottle is installed.
  4. Replace bottle with labeled/marked bottle by placing bottle into spout. Swing bottle/spout into bottle receptacle. Alarm will silence and solvent left in the line will start flowing again.
  5. Leave filled waste solvent bottle in the photo-wet's plenum. DO NOT return filled waste solvent bottles to the "pass-through" or leave them in any other place in the laboratory.

    Note: Lab staff are responsible for removing waste solvent bottles from the photo-wet plenum. If you have any questions, please contact the area specialist or technician for assistance.

Author: Octavio Hurtado 07/95