RCA is a typical and widely used wet chemical cleaning method, which mainly includes the following cleaning solutions:
(1) SPM: H2SO4/H2O2120 ~150℃ SPM has a high oxidation capacity, which can dissolve metals in cleaning solution after oxidation, and can oxidize organic matter to produce CO 2 and H2O. Cleaning the silicon wafer with SPM can remove heavy organic pollution and some metals on the surface of the silicon wafer, but when the organic pollution is particularly serious, it will carbonize the organic matter and make it difficult to remove it.
(2) HF (DHF): At 20 ~ 25℃, DHF can remove the natural oxide film on the surface of silicon wafer, so the metal attached to the natural oxide film will be dissolved in the cleaning solution, and DHF can inhibit the formation of oxide film. Therefore, Al, Fe, Zn, Ni and other metals on the surface of silicon wafer can be easily removed, and DHF can also remove the metal hydroxide attached to the natural oxide film. When cleaning with DHF, when the natural oxide film is corroded, the silicon on the surface of the silicon wafer is hardly corroded.
(3) APM (SC-1): NH4OH/H2O 2/H2O2 30 ~ 80℃ Because of H2O2, there is a natural oxide film (SiO2) on the surface of the silicon wafer, which is hydrophilic, and the surface and particles of the silicon wafer can be soaked by cleaning solution. Because the natural oxide layer on the surface of the silicon wafer and the Si on the surface of the silicon wafer are corroded by NH 4OH, the particles attached to the surface of the silicon wafer fall into the cleaning solution, thus achieving the purpose of removing particles. While NH4OH corrodes the surface of silicon wafer, H2O 2 forms a new oxide film on the surface of oxidized silicon wafer.
(4) HPM (SC-2): HCl/H2O2/H2O2 65 ~ 85℃ is used to remove metal pollutants such as sodium, iron and magnesium on the surface of silicon wafer. HPM can remove iron and zinc at room temperature.
The general idea of cleaning is to remove organic pollutants on the surface of silicon wafer first, because organic substances will cover part of the surface of silicon wafer, which makes it difficult to remove oxide film and related pollutants; Then dissolve the oxide film, because the oxide layer is a "pollution trap", it will also introduce epitaxial defects; Finally, the pollution of particles and metals is removed and the surface of the silicon wafer is passivated.