One of the largest challenges faced in the semiconductor manufacturing industry is the surface contamination of silicon wafers. Most commonly, silicon wafers become contaminated simply from exposure to the air, which contains a high degree of organic particle contaminants. These contaminants strongly bond to the silicon wafer surface due to a strong electrostatic force, creating a lot of headache for those in the semiconductor manufacturing industry.
In order to function properly, silicon wafers must be completely free of any contaminants. Removing these contaminants is not the simplest of tasks, however, as silicon wafers are very fragile. For this reason, semiconductor manufacturing businesses must adhere to a carefully formulated cleaning plan that ensures the wafer surfaces are returned to a clean state while maintaining minimal risk of damage.
To most effectively clean silicon wafers, manufacturers of silicones recommend the following list of cleaning steps:
Step One: Solvent Clean
Semiconductor manufacturing businesses use solvents to successfully remove oils and organic residues from the surface of silicon wafers. While solvents do remove these contaminants, solvents themselves actually leave residue on the surface of wafers as well. For this reason, a two-solvent method is implemented to ensure that the wafer is returned to a contaminant free state. The solvent cleaning method is outlined below:
- Prepare two baths, one glass container with acetone and another with methanol.
- Place the acetone container on a hot plate to heat the acetone to a temperature of no more than 55°C.
- Once warm, soak the silicon wafer in the acetone bath for 10 minutes.
- After the acetone bath is complete, remove the silicon wafer and place it into the methanol container for 5 minutes.
- Once time is up, remove the wafer from the methanol and rinse in DI water.
- Blow dry the silicon wafer with nitrogen.
Step Two: RCA-1 Clean
Those in the semiconductor manufacturing industry then use an RCA clean to remove organic residue. The RCA clean oxidizes the silicon and provides a thin protective layer of oxide to the surface of the wafer. The RCA-1 cleaning method is outlined below:
- Begin preparation of an RCA bath by combining 5 parts DI water and 1 part ammonium hydroxide (27%).
- Place the RCA container on a hot plate to heat the solution to a temperature of approximately 70°C.
- Once this temperature has been reached, remove the container from the hot plate and add 1 part hydrogen peroxide (30%). The solution will bubble after a minute or two.
- Once the solution begins to bubble, soak the silicon wafer for approximately 15 minutes.
- When time is up, remove the wafer from the RCA bath and place it into a container with DI water, changing the water multiple times to completely rinse the solution.
- After this process, remove the wafer from the container under flowing water to ensure that no residue from the water surface sticks to the wafer.
Step Three: Hydrofluoric Acid (HF) Dip
Semiconductor manufacturing businesses then implement the final step, an HF dip, to remove silicon dioxide from the silicon wafer surface. It is important to note that HF is a dangerous chemical, so manufacturers of silicones recommend that protective gear, such as heavy gloves and eye wear, be worn at all times during this step. The HF Dip process is outlined below:
- Create an HF dip container by combining 480 ml water with 20 ml HF. Always use a polypropylene beaker as opposed to a glass beaker as HF is known to react dangerously when coming into contact with any glass material.
- After creating the solution, soak the silicon wafer for 2 minutes.
- Once time is up, remove the wafer and rinse under running DI water.
- Perform a wettability test by pouring DI water on the wafer surface. If the water turns into little beads and rolls off, you will know that the surface is hydrophobic and free of oxides.
- Blow dry the silicon wafer with nitrogen.
Performing the above steps recommended by manufacturers of silicones will help those businesses in the semiconductor manufacturing industry to overcome the challenges of contamination to silicon wafers.
If you are interested in high quality silicon wafers for your semiconductor manufacturing operations, the professionals at Shin-Etsu MicroSi can help. As a semiconductor manufacturing leader, Shin-Etsu Microsi stays on top of the latest in semiconductor manufacturing technology, and can provide you with silicon wafers that will work well in your operations when paired with the cleaning steps listed above. To learn more about semiconductor manufacturing products or semiconductor repair services, call Shin-Etsu MicroSi at (480) 893-8898 or contact us online.