Overview
Sample cleanliness is extremely important for achieving good results in nanofabrication (hence the need for a cleanroom). However, simply working in the cleanroom does not guarantee cleanliness, proper steps need to be taken at every processing step to ensure a clean result. While some processes have more stringent cleanliness needs than others, some general rules apply for all types of lithography:
- Handle substrates/wafers with cleaned tweezers, not hands.
- Substrates should not be left exposed. Although the cleanroom offers
Solvent Cleaning
Standard Process: TAI clean
- 5 min sonication in beaker of Toluene.
- 5 min sonication in beaker of Acetone.
- 5 min sonication in beaker of Isopropanol.
Background
Standard solvent cleaning is a three step process of ultrasonically agitating the substrate in subsequent solvent solutions to remove organic contamination. The first step is a nonpolar solvent (toluene) to remove any oils or grease present on the sample. The second step is a powerful polar solvent (acetone) to remove polar contaminants such as photoresist. The final step is a polar protic solvent (isopropanol).
Nonpolar Solvent Clean: Toluene
Toluene acts a nonpolar solvent to dissolve any grease or oil on the substrate. Nonpolar contaminants (especially fingerprints) will not be effectively removed by Acetone or IPA.
Polar Solvent Clean: Acetone
Acetone's high dipole moment leads to a powerful cleaning of polar residue (such as photoresist). However its quick evaporation leads to residue redepositing on the substrate if evaporation is allowed to occur.
Polar Solvent Clean: Isopropanol
IPA is used to remove fully wash away acetone from the substrate, and remove any remaining dissolved residue. As a result, IPA is not as much providing additional cleaning after Acetone as it is effectively removing the Acetone without residue.
IPA is prefered as a final step over methanol due to its significantly slower evaporation rate. Slower evaporation results in less residue, and the close dipole moments of the two chemicals (DIPA=1.66 vs. DMethanol=1.69) means the difference between the two is negligible. Additionally, unlike Methanol, IPA is nontoxic.
Piranha Clean
Questions & Troubleshooting
Process Library