INTRODUCTION:
Contaminants present on the surface of silicon wafers at the start of processing, or accumulated during processing, have to be removed at specific processing steps in order to obtain high performance and high reliability semiconductor devices, and to prevent contamination of process equipment, especially the high temperature oxidation, diffusion, and deposition tubes. The RCA clean is the industry standard for removing contaminants from wafers. Werner Kern developed the basic procedure in 1965 while working for RCA (Radio Corporation of America) - hence the name.
The RCA cleaning procedure has three major steps used sequentially:
The RCA cleaning technique does not attack silicon, and only a very thin layer of
silicon dioxide is removed (in II) in the process. The procedure was also designed to
prevent replating of metal contaminants from solution back to the wafer's surface. When
finished, the polished side should be specular with no
residue.
SAFETY:
The chemicals used for RCA cleaning are all dangerous if you get in contact with them. They are not carcinogens. The MSDS sheets for all of these chemicals can be found in the yellow MSDS binder outside of Meyer 425. HF acid is very dangerous; 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 station. Lab coats, 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 the instructor or TA. 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. Exposure of the skin requires immediate removal of all contaminated clothing. Rinse under the shower for 15 minutes.
SOLUTION PREPARATION:
Each will be prepared made in 1000 ml polypropylene beakers.
A. Organic Clean solution of DIH2O:NH4OH:H2O2 (5:1:1)
*** Always add reactive compounds(acid/base) to water ***a.) 625mL DIH2O
b.) 125mL NH4OH
c.) 125mL H2O2
Stir solution with clean teflon rod. Place beaker into the temperature-controlled water bath and adjust the power to maintain the solution at 75 0C.
B. Oxide Strip solution of DIH2O:HF (50:1)
This solution will be prepared for you. Simply transfer the solution from the bottle to the 1000 ml beaker and place in water bath maintained at 25 0C.
C. Ionic Clean solution of DIH2O:HCl: H2O2 (6:1:1)
*** Always add reactive compounds(acid/base) to water ***
a.) 690mL of DIH2O
b.) 115mL of HCl
c.) 115mL of H2O2
Stir solution with clean teflon rod. Place beaker into the temperature-controlled water bath and adjust the power to maintain the solution at 75 0C.
D. Fill a 1000 ml beaker with DI water for rinsing.
PROCEDURE:
1. Place wafer(s) on teflon carriers.
2. Submerge the carrier with wafer in the Organic Clean solution for 10 minutes.
3. Remove carrier from the bath and rinse wafer in the DI water beaker for 1 minute.
4. Submerge the carrier with wafer in the Oxide Strip solution for 15 seconds.
5. Remove carrier from the bath and rinse wafer in the DI water beaker for 1 minute.
6. Submerge the carrier with wafer in the Ionic Clean solution for 10 minutes.
7. Remove carrier from the bath and rinse wafer in the DI water beaker for 1 minute.
8. Remove carrier from the DI water beaker and blow dry with nitrogen.
9. Take wafer to next processing step or place in a carrier box.
CLEAN UP:
1. Turn off water baths and allow to cool.
2. Dispose of Organic Clean in container marked 'Basic Waste'. Rinse beaker twice with DI water and dispose of similarly.
3. Return the Oxide Strip to the original container. Rinse beaker twice with DI water and dispose of in container marked 'Acid Waste'.
4. Dispose of Ionic Clean in container marked 'Acid Waste'. Rinse beaker twice with DI water and dispose of similarly.
5. Manually rinse the work area with DI water, wipe it with kimwipes, and rinse the rubber gloves that you have been wearing.
6. Remove the protective clothing.