Characteristics of HfO₂ and SiO₂ on p-type silicon wafers using terahertz spectroscopy

The effect of high-κ dielectric HfO₂ films on 200 mm diameter p-type silicon substrates was investigated and compared with conventional dielectric material, SiO₂. We employed all-optical characterization methods using terahertz (THz) time-domain spectroscopy and visible cw pump/THz probe spectroscopy. Measurements were performed on two sets of samples, each set containing both HfO₂ and SiO₂ coated wafers with varying thickness of oxide layer. One set had a protective coating of either photoresist or Si₃N₄ deposition above the oxide layer which in turn was on a heavily doped p+ layer on p-type silicon. The samples exhibited similar linear transmission in the THz frequency range studied. However, when using an Ar+-ion laser as an optical pump source, differential measurements (with and without the pump source) showed that the transmission was far smaller for the high-κ dielectric HfO₂ films than its conventional dielectric SiO₂ counterparts, indicating the presence of large photo-generated carrier density in the p-type substrate.