RCA Clean

The RCA clean is the industry standard for removing contaminants from wafers. Werner K ern developed the basic procedure in 1965 while working for RCA (Radio Corporation of America) - hence the name. Two articles are presented at the end of the paper version of the Appendix for your review.

Over time many companies have tried to improve the effectiveness through variations in the original recipe. Our two step version is presented below.

SC-1 Clean:

Prepare the SC-1 cleaning solution.

1. Turn on the DI faucet with a latex gloved hand.
2. Put on the Nitrile gloves:
   • Only handle the nitrile gloves from the inside.
   • Assume anything that is wet is extremely caustic (pH > 9) in the SC-1 fume hood.
3. Rinse the quartz tub with DI water and place on the hotplate in the SC-1 fume hood.
4. Rinse the thermocouple connected to the digital temperature controller with DI water and place in the quartz tub.
5. Rinse the thermometer with DI water and place in the quartz tub.
6. Prepare the following solution in the quartz tub on the hotplate in the SC-1 fume hood:
   • 1800 mL H₂O (use the 500 ml graduated cylinder)
   • 360 mL H₂O₂ (use the 500 ml graduated cylinder)
   • 180 mL NH₄OH (use the 250 ml graduated cylinder)
     • The H₂O₂ and NH4OH are located beneath the SC-1 fume hood.
     • Only open the containers inside the fume hoods.
     • Make sure that you clean the graduated cylinders with DI water before measuring the chemicals.
     • When pouring chemicals, make sure that the mouth of the bottle does not contact the graduated cylinder. This will prevent contamination of the remaining chemicals in the bottle.
     • Slowly pour the measured amount of chemicals into the quartz tub. Splashing of chemicals should be avoided at all costs.
     • Rinse the outside of the chemical bottles with water before replacing in the storage area.
7. Remove the nitrile gloves (only handle them from the inside).
8. Turn on the temperature controller with latex gloved hands.
   • Check that it is set for 75°C by pressing the button with the star (*) on the digital temperature controller.

Preliminary Wafer Clean

1. Move the Teflon® wafer boat to the quartz plate in the SC-1 hood.
2. Remove the handle from the Teflon® wafer boat by squeezing the handle on the sides and lifting up.
3. Place the handle onto a quartz plate in the SC-1 hood.
4. Transfer the 4” silicon wafer container from the Inspection hood into the SC-1 hood.
5. Open the 4” silicon wafer container.
6. Transfer the 4” silicon wafers from the container to the TeflonÒ wafer boat using wafer tweezers.
7. After transferring the wafers, close the wafer container and place in the Inspection hood.
8. Replace the handle on the Teflon wafer carrier.
9. Transfer the boat to the Degreasing hood and degrease the boat and wafers using the following sequence:
   • Rinse with acetone
   • Rinse with IPA
   • Rinse with DI gun
10. Transfer the boat to the Etching hood and place on a quartz plate.
11. Turn on the DI water in the Etching hood with latex gloved hand.
12. Put on nitrile gloves.
13. Open the 50:1 DI:HF etch container, the HF Rinse container, and the Final Rinse container.
    • Open the containers from the front to the back and rest the lid on the back of Etch hood.
14. Etch for 30 seconds in the 50:1 DI:HF etch:
    • Place the wafer boat into the 50:1 etch, move back and forth slowly for uniform etching.
    • At the end of the etch time, slowly raise the boat and let drip for 1-2 seconds.
    • Transfer the boat to the HF Rinse container and rinse for 5-10 seconds.
    • At the end of the etch time, slowly raise the boat and let drip for 1-2 seconds.
    • Transfer the boat to the Final Rinse container and rinse for 10-20 seconds
    • At the end of the rinse time, slowly raise the boat and let drip for 1-2 seconds.
    • Transfer the boat over the sink.
    • Rinse your right glove under the flowing DI water.
    • Rinse the boat with the DI gun for 10-20 seconds.
    • Make sure to replace the covers on the acid and rinse containers and spray off the counter surface.

SC-1 Cleaning:

1. Transfer the boat to the SC-1 cleaning solution.
2. The wafers will remain in the SC-1 solution for 10 minutes at 75°.
   • When the temperature reaches 75°C, start timing.
   • Occasionally stir the solution with the thermometer.
   • Rinse and fill the DI Rinse container with DI water.
   • Start preparing the SC-2 solution while waiting for the completion of SC-1 cleaning.
3. After 10 minutes, turn off the digital temperature controller.
4. Open the DI Rinse container and rest the lid against the back of the SC-1 hood.
5. Open the Cascade Rinse container and rest the lid against the back of the SC-1 hood.
6. Transfer the wafer boat to the DI Rinse container and rinse for 20 seconds.
7. Rinse your right hand under the flowing DI water.
8. Transfer the wafer boat to the sink and rinse with the DI gun.
   • Be careful not to let a drop of water from your gloves land on your wafers
9. Transfer the wafer boat to the Cascade rinse.
   • The wafer boat should stay a minimum of 2 minutes in the cascade rinse.
   • Leave the boat in the Cascade rinse until the SC-2 solution is ready.

SC-2 Clean:

Prepare the SC-2 cleaning solution:

1. Turn on the DI faucet with a latex gloved hand.
2. Put on the Nitrile gloves:
   • Only handle the nitrile gloves from the inside.
   • Assume anything that is wet is extremely acidic (pH < 2) in the SC-2 fume hood.
3. Rinse the quartz tub with DI water and place on the hotplate in the SC-2 fume hood.
4. Rinse the temperature sensor connected to the analog temperature controller with DI water and place in the quartz tub.
5. Rinse the thermometer with DI water and place in the quartz tub.
6. Prepare the following solution in the quartz tub on the hotplate in the SC-2 fume hood:
   • 1820 mL H₂O (use the 500 ml graduated cylinder)
   • 320 mL H₂O₂ (use the 500 ml graduated cylinder)
   • 110 mL HCl (use the 250 ml graduated cylinder)
     • The H₂O₂ is located underneath the SC-1 fume hood.
     • The HCl is located in the plastic bottle beneath the counter of the SC-2 fume hood.
     • Only open the containers inside the fume hoods.
     • Make sure that you clean the graduated cylinders with DI water before measuring the chemicals.
     • Remember the AAA rule: Always Add Acid to water
     • If using Sulfuric acid rather than Hydrochloric acid, note that it reacts violently with water: add it very slowly, and only if the temperature of the water is below 30°C.
     • When pouring chemicals, make sure that the mouth of the bottle does not contact the graduated cylinder. This will prevent contamination of the remaining chemicals in the bottle.
     • Slowly pour the measured amount of chemicals into the quartz tub. Splashing of chemicals should be avoided at all costs
     • Rinse the outside of the chemical bottles with water before replacing.
7. Remove the nitrile gloves (only handle them from the inside).
8. Turn on the temperature controller with latex gloved hands.
   • Turn the knob until the set point indicator is above the actual temperature
   • Watch the thermometer
     • When 75°C is reached, turn the set point indicator so that it is right on top of the actual temperature indicator.
9. When the solution has reached 75°C, continue.

Strip hydrous oxide:

1. Transfer the boat to the Etching hood and place on a quartz plate.
2. Turn on the DI water in the Etching hood with latex gloved hand.
3. Put on nitrile gloves.
4. Open the 50:1 DI:HF etch container, the HF Rinse container, and the Final Rinse container.
5. Open the containers from the front to the back and rest the lid on the back of the Etch hood.
6. Etch for 15 seconds in the 50:1 DI:HF etch:
   • Place the wafer boat into the 50:1 etch, move back and forth slowly for uniform etching.
   • At the end of the etch time, slowly raise the boat and let drip for 1-2 seconds.
   • Transfer the boat to the HF Rinse container and rinse for 5-10 seconds
   • At the end of the etch time, slowly raise the boat and let drip for 1-2 seconds.
   • Transfer the boat to the Final Rinse container and rinse for 20-30 seconds.
   • At the end of the rinse time, slowly raise the boat and let drip for 1-2 seconds.
   • Transfer the boat over the sink.
   • Rinse your right glove under the flowing DI water.
   • Rinse the boat with the DI gun for 10-20 seconds.

SC-2 cleaning:

1. Transfer the boat to the SC-2 cleaning solution.
   • The wafers will remain in the SC-2 solution for 10 minutes at 75°.
     • When the wafers are placed in the SC-2 solution start timing.
     • Occasionally stir the solution with the thermometer.
     • Rinse and fill the DI Rinse container with DI water.
2. After 10 minutes, turn off the analog temperature controller.
3. Open the DI Rinse container and rest the lid against the back of the SC-2 hood.
4. Open the Cascade Rinse container and rest the lid against the back of the SC-2 hood.
5. Transfer the wafer boat to the DI Rinse container and rinse for 20 seconds.
6. Rinse your right hand under the flowing DI water.
7. Transfer the wafer boat to the sink and rinse with the DI gun.
   • Be careful not to let a drop of water from your gloves land on your wafers
8. Transfer the wafer boat to the Cascade rinse.
   • The wafer boat should stay in the cascade rinse for at least 5 minutes (Kern recommends 20 minutes).
9. Transfer the wafer boat to a clean quartz plate.
10. Remove the wafer boat handle by squeezing the sides – place the handle on a quartz plate.
11. Remove the nitrile gloves.
12. Remove the wafer from the boat with a clean pair of tweezers and blow dry with N2.
    • With the tweezers, hold the wafer at a steep angle (~75-80°) with your left hand.
    • With your right hand hold the N2 gun upside down.
    • Start drying from the top down.
    • Repeat for the backside.
      • There will be water droplets that move from the polished side to the backside and vice versa. Just repeat the steps until the wafer is dry
      • Make sure to dry beneath the tweezers.
      • When finished, the polished side should be specular with no residue.