The RCA clean is a standard set of wafer cleaning steps which need to be performed before high-temperature processing steps (oxidation, diffusion, CVD) of silicon wafers in semiconductor manufacturing. The RCA cleaning process consists of a SC-1 clean step, an oxide strip step, and a SC-2 clean step.

SC1 Cleaning

Purpose: To remove residual organic contaminants and particles from samples (basic solution).

Location: General use fumehood

Chemicals: ammonium hydroxide, hydrogen peroxide, DI water

Supplies Needed: 2 quartz dishes, hotplate, plastic volumetric beakers or cylinders, TEFLON/PEEK tweezers, texwipe, nitrogen gun, chemical warning forms and PPE

Setup Procedures:

1. Find an available fumehood that is not currently being used for any processing. Make sure the area is free of other chemicals.
2. Fill out the chemical warning form (located at fumehood) with proper warning information (chemicals, contact information, process time and hazards).
3. Please notify the research users in the area that you are going to use heated base.
4. Using bottle carries, bring a bottle of ammonium hydroxide and a bottle of hydrogen peroxide to the fumehood.
5. Setup the hotplate, SC-1 solution dish, and put on your PPE gear.
6. Measure out amounts of NH₄OH, H₂O₂, and water in the volumetric beakers or cylinders in a 1:1:5 ratio, enough to cover your sample.
7. Place the quartz dish on the hotplate. Pour the water first, then ammonium hydroxide, then hydrogen peroxide into the SC-1 solution dish.
8. Turn the hotplate to 75-80ºC and allow the solution to come up to temperature (10-15 min).
9. Prepare a DI water rinse container while you wait. Fill out another chemical warning form. Triple rinse a clean quartz or plastic dish with DI water, then fill the dish with DI water. Set the dish off to the side. Before rinsing with DI water, turn on DI water and let water flow for 1 min to reach 18M ohm resistance.

Number of substrates: 1

Process Procedures:

1. Using TEFLON or peek tweezers, carefully place your sample into the SC-1 solution.
2. Return the chemical bottles to the chemical chase.
3. After 10-20 minutes, remove your sample from the SC-1 solution and place into the container with DI water.
4. Leave the SC-1 solution on the hotplate and turn the hotplate off.
5. Rinse your sample under running DI water (30 seconds).
6. Place your sample on a texwipe and blow dry with the nitrogen gun. Use a sweeping motion while working from one side of the sample to the opposite side (1 min).
7. Once the SC-1 solution is cool (after 1-2 hours), while wearing PPE gear, carefully pour it down the sink with plenty of running city water.
8. Rinse the SC-1 solution dish.

Time: approximately 45 minutes + cool down time

Comments:

• Be sure to rinse your tweezers off immediately after transferring your sample in or out of the solution.

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   Oxide Etch

Purpose: To remove the thin oxide layer

Location: General use fumehood

Chemicals: buffered oxide etch (BOE 6:1)

Supplies Needed: 2 plastic dishes, texwipe, tweezers, nitrogen gun, chemical warning forms, and PPE

Setup Procedures:

1. Find an available fumehood that is not currently being used for any processing. Make sure the area is free of other chemicals.
2. Fill out the chemical warning form (located at fumehood) with proper warning information (chemicals, contact information, process time, and hazards).
3. Please notify the research users in the area that you are going to use BOE.
4. Using a bottle carrier, bring a bottle of BOE to the fumehood.
5. Setup the BOE solution dish and put on your PPE gear.
6. Pour enough BOE into the plastic dish that will cover your sample.
7. Prepare a DI water rinse as well. Fill out another chemical warning form. Triple rinse a plastic dish with DI water, then fill the dish with DI water. Set the dish off to the side.

Number of substrates: 1

Process Procedures:

1. Place your sample into the BOE solution using plastic tweezers (30 seconds).
2. Remove your sample from the BOE solution and place into the DI water rinse container (30 seconds).
3. Rinse your sample under running DI water (30 seconds).
4. Place your sample on a texwipe and blow dry with the nitrogen gun. Use a sweeping motion while working from one side of the sample to the opposite side (1 min).
5. Carefully pour the BOE solution down the sink with plenty of running city water.
6. Rinse the plastic container.

Time: approximately 45 minutes + cool down time

Comments:

• BOE is hydrofluoric acid buffered in ammonium fluoride in a 1:6 ratio. The buffering agent allows for a more controlled etch of silicon dioxide.
• Approximate BOE etch rate: 20 A/sec
• Do not use metal tweezers as BOE may react with them.

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SC2 Cleaning

Purpose: To remove residual metal from samples

Location: general use fumehood or CMOS cleaning station

Chemicals: hydrochloric acid, hydrogen peroxide, DI water

Supplies Needed: 2 non-metal containing dishes (Pyrex contains metal), non-metal containing beakers or graduated cylinders, hotplate, tweezers, texwipe, nitrogen gun, chemical warning forms, and PPE

Setup Procedures:

1. Find an available fumehood that is not currently being used for solvent processing. Make sure the area is free of incompatible chemicals.
2. Fill out the chemical warning form (located at fumehood) with proper warning information (chemicals, contact information, process time and hazards).
3. Please notify the research users in the area that you are going to be using heated acid.
4. Using bottle carries, bring a bottle of hydrogen chloride and a bottle of hydrogen peroxide to the fumehood.
5. Setup the hotplate, SC-2 solution dish, and put on your PPE gear.
6. Measure out amounts of HCl, H₂O₂, and water in beakers or graduated cylinders in a 1:1:6 ratio, enough to cover your sample.
7. Pour the water first, then hydrochloric acid, then hydrogen peroxide into the SC-2 solution dish.
8. Turn the hotplate to 75-80ºC and place the SC-2 solution dish on the hotplate and allow it to come up to temperature (10-15 min).
9. Prepare a DI water rinse container while you wait. Fill out another chemical warning form. Triple rinse a non-metal containing dish with DI water, then fill the dish with DI water. Set the dish off to the side.

Number of substrates: 1

Process Procedures:

1. Using plastic tweezers, carefully place your sample into the SC-2 solution.
2. Return the chemical bottles to the chemical chase.
3. After 10-20 minutes, remove your sample from the SC-2 solution and place into a container of DI water.
4. Take the SC-2 solution off the hotplate and turn the hotplate off.
5. Rinse your sample under running DI water (30 seconds).
6. Place your sample on a texwipe and blow dry with the nitrogen gun. Use a sweeping motion while working from one side of the sample to the opposite side (1 min).
7. Once the SC-2 solution is cool (after 1-2 hours), while wearing PPE gear, carefully pour it down the sink with plenty of running city water.
8. Rinse the SC-2 solution dish.

Time: approximately 45 minutes + cool down time

Comments:

• Do not use metal tweezers as the SC-2 solution will dissolve them.
• Be sure to rinse your tweezers off immediately after transferring your sample in or out of the solution.

Verification:

• Particle level: can be observed under microscope with dark field, or measured accurately with Surfscan
• Hydrophobicity: can be measured with contact angle measurement tool

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