REMOVAL OF FLUOROCARBON RESIDUES ON CF4/H2 REACTIVE-ION-ETCHED SILICON SURFACES USING A HYDROGEN PLASMA

A cleaning procedure based on a hydrogen plasma is described which removes most of the fluorocarbon passivation layer remaining on silicon surfaces exposed to CF4/H2 reactive ion etching (RIE). Real time in situ ellipsometry performed during hydrogen plasma exposure of a reactive-ion-etched silicon surface showed removal of the bulk of this residue. The contamination layer thickness was reduced from 50-angstrom to less than 10-angstrom. X-ray photoelectron spectroscopy of hydrogen-plasma-cleaned silicon showed an 80% reduction in carbon contamination and a 95% reduction in fluorine without appreciable oxidation of the surface. The contamination left after cleaning is a 10-angstrom carbon film. Secondary ion mass spectrometry showed that hydrogen implantation into the silicon substrate during cleaning was negligible relative to the amount implanted during RIE. Continued exposure of the surface to the cleaning plasma resulted in a redeposition of contamination, the source of which is sputtered residue from the reactor walls that was deposited during RIE. Surface oxidation by residual water and oxygen desorbing from chamber surfaces may also take place during prolonged H-2 plasma cleaning.