Paper SS2+EM-MoM10
Formation of Titanium Sub-Oxide from TiO₂ ALD Films on Si and Ge Substrates after Vacuum Anneal

Monday, October 18, 2010, 11:20 am, Room Santa Ana

The formation of an oxide interlayer between a Si or Ge substrate and a metal oxide dielectric film has a direct influence on the physical and electrical properties of the field effect transistors made from these components. An oxide interlayer may form either during the deposition process or during a subsequent high temperature step. It is usually desirable to control or eliminate the formation of this oxide interlayer; one approach used is to create an oxide-free surface by chemically etching away the native oxide layer and adding a surface modifier such as hydrogen or halogens to inhibit further oxide formation.

In this work, we study the interlayer oxide formation on hydrogen-terminated silicon and halide-terminated germanium following TiO₂ atomic layer deposition (ALD). The surface analysis of TiO₂ films on silicon substrates is conducted immediately after the ALD process without exposure to ambient conditions by an integrated X-ray photoelectron spectroscopy (XPS)/ALD system. The results on hydrogen-terminated silicon show that no silicon oxide forms between the two materials during ALD at 100 ^oC. However, a silicon oxide interlayer is detected after annealing in ultrahigh vacuum. A concomitant depletion of oxygen in the TiO₂ films occurs, leading to generation of a Ti sub-oxide. The effect is shown to be correlated with both the annealing temperature and the thickness of the TiO₂ film. Control experiments carried out on TiO₂ film deposited by ALD on SiO₂-coated silicon show significantly less depletion of oxygen in the TiO₂ films. Our results indicate that TiO₂ is the source of O for Si oxidation, and that migration of oxygen to this interface is a driving force for oxygen depletion in the TiO₂ film. The TiO₂ films on Br- and Cl-terminated germanium substrates are deposited by ALD at temperatures in the range of 100-300 ^oC and analyzed using ex-situ synchrotron radiation photoemission spectroscopy (SR-PES). Formation of titanium germanate (TiGeO_x) was observed after annealing to 400 °C. Upon annealing to 700 °C, titanium sub-oxide formation is also observed for this system. However, this reduction was more pronounced in thinner TiO₂ films. The stability of these oxide structures upon annealing, and the prospect for eliminating the oxide interlayer in the TiO₂/Si and TiO₂/Ge systems will be discussed.