MTL Fabrication

Pre-metal - Standard Operating Procedure

CORAL Name: pre-metal
Model Number: Semifab Model WPS 400 Wet Process Station
Location: ICL
What it does: wet process station
Introduction: The pre-metal wet processing station is used primarily to support two processes, photoresist stripping, and cleaning of wafers prior to metallization. It is strongly recommended that users read the MSDS sheets for the chemicals used in these processes prior to Using them. The MSDS sheets can be found in the yellow MSDS binders in the copier room on the 2nd floor of Building 39.


Chemicals must be transported to and from the pre-metal station Using the chemical cart or single bottle plastic carrier. Handling chemical bottles, beakers, or any other vessel must always be done with dry gloved hands.

The chemicals used in the pre-metal station are all dangerous if you get in contact with them. They are not carcinogens. HF acid is very dangerous and HF burns are particularly hazardous. An insidious aspect of HF burns is that there may not be any discomfort until long after exposure. These burns are extremely serious and may result in tissue damage. If you contact HF, flush the area well and be sure to work under and around your finger nails. Finger nails and cuticles are the classic areas where people receive burns, having washed off the HF without washing under their nails. If washed off within a few minutes of exposure, HF may do no harm. Remember, HF may not produce any burning sensation until after it has already done damage. All HF burns should be looked at by a physician.

Acid protective gear MUST be worn when working at this sink. An acid-proof apron, sleeve guards, acid-proof gloves (atop the normal clean room gloves), and an acid face mask (with the face shield DOWN) worn over safety glasses, are all required. ALWAYS know the location of the nearest eye wash and safety shower.

In the case of chemical exposure, call for help to the person nearest you and tell them to call the ERT(dial 100). While you are speaking to the person nearest you, get to the nearest shower or eyewash as fast as possible. Exposure of the eyes requires flushing with water for at least 15 minutes. As a precaution, all exposures to the eye will require a visit to an emergency room for a check up. Contact a staff member as soon as possible for assistance or call 100. Exposure of the skin requires immediate removal of all contaminated clothing. Rinse under the shower for 15 minutes. Contact a staff member as soon as possible for assistance or call 100.


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 (ICL) and that your lot name is entered correctly.

3. Gown up with the proper acid garments...

a. acid apron - this garment is to be worn with the label
"front " facing out and tied securely to give maximum body protection.
b. oversleeves - these should be pulled as high on the arm as possible to give maximum arm protection.
c. acid gloves - gloves should be pulled up and cuffed.
d. face shield - face shield should be tightened on head to avoid slipping. View should be clear and unobstructed.
e. safety glasses - safety glasses are required before you enter the lab and must remain on at all times.
Note: If you notice any defect in the acid protective garments do not use them. Report the defect to the staff so that new garments can be issued to you.

4. Using the safety cart, transport chemicals from the "passthrough" to the wet station. Chemicals to be used are sulfuric acid and hydrogen peroxide.

5. Select the proper tank. Use the tank marked with the blue label for resist stripping, and the tank with the green label for pre-metal cleaning.

6. Photoresist stripping and premetal cleaning have the same ratios of sulfuric acid to hydrogen peroxide, 3 to 1.

a. pour hydrogen peroxide to the bottom of the teflon holder.

b. pour sulfuric acid into the bath to the top mark on the teflon holder.

7. Select the proper cassette. Cassettes are labeled as follows:
a. blue dot for photoresist removal
b. green dot for premetal cleaning
c. yellow dot for HF dip

8. Using a vacuum wand, place your wafers into the cassette.

9. Place the cassette with your wafers into the appropriate "Piranha" bath, blue for photoresist stripping, green for pre-metal cleaning, for 10 to 15 minutes.

10. After the "Piranha" bath step is complete, place the cassette with your wafers into the dump rinse tank directly in front of the bath that you have just used, and initiate the cycle.


11a. After the dump rinse cycle is completed, place your wafers into the spin rinse dryer for the final processing step.

12a. Proceed to step 14, below.


11b. After the dump rinse cycle is completed, place your wafers in the 50:1 HF bath for 1 minute; this removes approximately 100 A of silicon dioxide.
Note: The 50:1 HF step is optional. This step is intended to remove residual oxide from the contact areas before metallization, and generally results in lower contact resistance after

12b. Place the cassette with your wafers into the same dump rinse tank that you used in step 10, and initiate the cycle.

13. After dump rinse cycle is completed, place your wafers into the spin rinse dryer for the final processing step.
Note: After "Piranha" cleaning it is desirable to proceed directly to metalization with a minimum delay.

14. Rinse the deck of the wet station to insure that no residual chemicals are left.

15. Use the glove rinser (one cycle per glove) to rinse your gloves. Dry them with a clean room wipe.

16. Return all chemical containers(full, partially full, and empty) to the "passthrough" Using the transport cart. Be sure that all bottles are dry.

17. Return the transport cart to the wet station.

18. Rinse and dry your gloves again, as in step 15.

19. Remove your protective garments and return them to the proper storage place.

20. End "Operate Machine" in CORAL.


Author: Bob Hamilton (UCB) 03/94; Joe Walsh 07/95