Time dependent preferential sputtering in the HfO2 layer on Si(100)

The time dependent preferential sputtering in the HfO2 layer on Si(100) has been investigated in-situ with X-ray photoelectron spectroscopy during Ar ion sputtering. Hf4f, O1s, and Si2p spectra show that three bonding environments (Hf0+ from the Hf metal, Hf2+ from HfO, and Hf4+ from HfO2) co-exist inside the HfO2 layer during sputtering. The Hf4+ doublet decreases with sputtering time in an exponential-like function. Both Hf0+ and Hf2+ doublets increase with sputtering time in opposite ways. Two concurrent sputtering mechanisms characterizing the formation of HfO and Hf due to preferential sputtering of oxygen within the HfO2 layer can well explain the detailed bond breaking and re-formation process. The Hf metal is the final product and the HfO is an intermediate product during sputtering under vacuum. The HfO cannot be removed and acts as a residual component in the HfO2 layer.