Thermal stability of thin HfO2 films on plasma nitrided Si(100)

Thin dielectric films such as HfO2 grown on Si(100) are interesting for metal-oxide semiconductor MOS devices, because HfO2 has a high dielectric constant. Up to 750 C HfSi increases in the HfO2/Si layer stack, which creates unwanted conductive states. To avoid the formation of HfSi an amorphous Si3N4 diffusion barrier can be grown between the HfO2 film and the silicon substrate. The ultrathin Si3N4 films were grown on the Si(100) surface by nitrogen plasma which was provided from a special plasma source. Different thicknesses of Si3N4 interlayers were prepared in-situ and the HfO2 films were grown on top of the sample by electron beam evaporation. The film thicknesses were determined by ARXPS meassurements. The samples were flash heated for 1 minute at several temperatures. After each annealing step the chemical properties of the system HfO2/Si3N4/Si(100) were checked by photoelectron spectroscopy (PES). For temperatures up to 750 C the HfO2 layer remains unchanged. For higher temperatures a further signal could be observed in the spectra, due to the chemical shift in the Hf 4f signal to higher kinetic energies. This new component could be identified as Hfx1Six2Ox3Nx4. The Hfx1Six2Ox3Nx4 appears to be stable up to 850 C.