Influence of Cu on the native oxide growth of Si

The influence of Cu on the native oxide growth on Si wafers was investigated by means of x-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy (HREELS). The Cu coverage on the Si wafers was varied from 1012 cm−2 to about half a monolayer by adding Cu to aqueous HF in the ppm range. Immediately after the HF treatment no SiO2−x component (chemical shift ≳3.4 eV) can be measured by XPS. The chemical surface composition as characterized by HREELS is practically the same as for noncontaminated HF. A short additional water rinse of 2 min changes the chemical surface state of the Si wafers significantly. For Cu coverages more than about 1% of a monolayer, a pronounced initial oxide growth was noticed already after a 2-min water rinse with the oxide thickness depending on the amount of Cu coverage present on the Si surface. The oxide growth kinetics after storage of Cu-contaminated Si surfaces in air was studied for storage times up to 1 year. With almost no change in the chemical surface state visible directly after the HF treatment, however, an enhanced roughness of the Si wafer was noticed. The copper-induced enhancement of the oxidation of the silicon surface in combination with the oxide removal of the HF leads to an etching of the Si wafer.