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THE RCA CLEAN

This cleaning method is the industry standard way to clean wafers. Although every company has its own way of implementing the RCA clean and may have introduced their own proprietary improvements, they have all been significantly influenced by the work of Kern, a chemist at RCA. One of his articles is included at the end of this appendix in the printed version of the manual. Please read it. Below is the recipe for our particular implementation. We substitute sulfuric acid for hydrochloric acid as described in the other article at the end of this appendix. Sulfuric acid has a few safety advantages because its a solid in its pure form where as hydrochloric acid is a gas and the chlorine in hydrochloric acid may be harmful to the ozone layer. Ideally, if we had time, we would use this procedure before EVERY diffusion furnace operation.

Preliminary Clean

  1. Transfer the wafers to a teflon wafer carrier specifically reserved for the RCA clean.
  2. Securely mount the teflon wafer carrier handle, also reserved for the RCA clean.
  3. The wafers should be degreased before continuing. The SC-1 solution can be prepared during the degreasing procedure.
  4. Etch the wafers for 30 seconds in the 50:1 DI:HF etch.

Remove residual organics and certain metals using the RCA standard clean solution 1 (SC-1)

  1. Rinse the quartz tub, temperature sensor and thermometer under the SC-1 acid hood.
  2. Place the tub on the hotplate with the temperature sensor and thermometer inside.
  3. Add 900 ml of deionized water.
  4. Turn on the temperature controller. (actual temperature will be 75°C).

    5. NOTE: Whenever handling strong chemicals it is a very good idea to have DI slowly flowing from a faucet first. Not only will it help dilute accidental spills, but it allows you to rinse your gloves without getting the faucet valve contaminated! Always use neoprene gloves over the PVC gloves when handling strong chemicals and rinse them afterward!

  5. Slowly add 180 ml of hydrogen peroxide(30%).
  6. Slowly add 90 ml of ammonium hydroxide (58%). Be sure to rinse the neoprene gloves, the graduated cylinder, and the outside of the chemical containers with DI when finished.
  7. Slowly place the wafer carrier into the solution.
  8. Occasionally stir the solution by gently moving the wafer boat until the solution has been over 75°C for 10 minutes.

    9. NOTE: While waiting for the temperature to rise it is possible to begin preparation of the SC-2 solution. Do not forget to occaisionally stir and check the temperature of the SC-1 solution!

  9. Turn off the temperature controller after the SC-1 has been at 75-80°C for ten minutes.
  10. Carefully move the wafer carrier to SC-1 DI rinse tank for 20 seconds.
  11. Spray rinse the wafer carrier and as much of the handle as you can without getting your glove wet. At this point a drop of water from a relatively dirty glove could compromise the whole cleaning process.
  12. Move the wafer carrier to the cascade rinse tank for at least 2 minutes. Leave it there until the SC-2 solution is ready.

Prepare SC-2 solution

  1. Rinse the quartz tub, temperature sensor and thermometer under the SC-2 acid hood.
  2. Place the tub on the hotplate with the temperature sensor and thermometer inside.
  3. Add 960 ml of deionized water.
  4. Turn on the temperature controller. Actual temperature will be 75-80 °C.
  5. Slowly add 160 ml of hydrogen peroxide(30%).
  6. Slowly add 55 ml of sulfuric acid.
  7. Occasionally stir the solution with the temperature probe.
  8. When the solution has reached 75°C, continue.

Strip hydrous oxide

  1. Move the wafer carrier to the 50:1 DI:HF tank for 15 seconds.
  2. Agitate the carrier in the DI rinse tank for 20 to 30 seconds.

Desorb remaining contaminants

  1. Place the wafer carrier in the hot SC-2 solution for 10 minuites.
  2. Turn off the temperature controller.
  3. Carefully move the wafer carrier to SC-2 DI rinse tank for 20 seconds.
  4. Spray rinse the wafer carrier and as much of the handle as you can without getting your glove wet. Remember, at this point a drop of water from a relatively dirty glove could compromise the whole cleaning process.
  5. Move the wafer carrier to the cascade rinse tank for 5 minutes. Kern recommended 20 minutes.

Dry the wafers

  1. Verify that the rinser-dryer is set for:
    1. Rinse time = 120 seconds
    2. Dry time = 120 seconds
    3. Resistivity set point = 14 Megaohm-cm
  2. Rinse the special handle for lifting the wafer carrier from one end and switch it with the other handle.
  3. Load the wafer carrier into the rinser dryer and press start.
  4. Wait for the rinser dryer to stop by itself. Use the time wisely (e.g. prepare for the subsequent furnace operation).
  5. Return the wafer carrier to the rinser-dryer after removing the wafers.

Clean and reorganize the area.

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Processes/RCA.clean.html

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