THE EFFECT OF AQUEOUS CHEMICAL CLEANING ON SI(100) DRY OXIDATION-KINETICS

The influence of aqueous chemical cleaning on the dry oxidation of Si (100) was studied for ten different preoxidation treatments at thicknesses ranging between 800 and 1200-degrees-C. The surface treatments included mixtures of acids or bases with hydrogen peroxide as well as HF:H2O. Below 1200-degrees-C, only the treatment with NH4OH:H2O2:H2O as a final step showed a deviation in oxidation kinetics compared to the other cleans. At 1200-degrees-C, variations in surface cleans had no affect on oxidation. A series of two-step oxidations with an intermediate treatment were performed to determine if the cleaning effect occurs at the Si/SiO2 interface, in the bulk of the oxide, or at the free surface of the oxide. The results indicate that the physical mechanisms associated with the surface cleans affected the outer surface of the thermal oxide. These experiments, and SIMS analysis of the surfaces, show that Al on the surface of the wafer is responsible for the retardation in kinetics. A mechanism is proposed where the surface Al, which causes the retardation, reduces the density of sites on the surface of the thermal oxide where the oxidant is incorporated into the bulk of the oxide.