Far ultraviolet spectroscopic ellipsometry and its application

Spectroscopic ellipsometry is a very sensitive nondestructive optical characterization tool that measures the change in the polarization state of a light beam obliquely reflected from a sample surface. The typical information we obtain from the ellipsometry measurement includes the index of refraction, extinction coefficient of bulk materials and film thickness, void fraction, alloy fraction, interface and surface roughness of thin film structures. There are some types of materials requiring high-energy photon for the better characterization of the material properties such as wide bandgap materials and high-K dielectrics. In order to meet these requirements, we extended the spectral range of the spectroscopic ellipsometry up to 9 eV by building a far UV spectroscopic ellipsometry.; We applied it to the study of three 4H-SiC samples with different surface conditions: as-received and CMP processed bulk substrates as well as an epitaxial sample with macrosteps. The measurement results demonstrate the excellent surface sensitivity of far UV spectroscopic ellipsometry. It clearly distinguishes substrates with a few Å difference in surface roughness, and further indicates the existence of a damaged subsurface layer in as-received bulk substrate.; Next, we investigated high-K dielectric materials. As the device size shrinks, the use of SiO₂ in transistors is limited by tunneling-induced leakage current. High-K gate dielectrics are attractive since they can provide comparable device performance with a much thicker dielectric layer, thereby avoiding the tunneling-induced leakage current. We investigated the optical properties of four promising high-K dielectrics, LaAlO₃, HfO ₂, GdScO₃, and SmScO₃, in single crystalline form and obtained their dielectric functions and optical bandgap energies. Once we obtained the bulk dielectric response, we applied that knowledge to understand thin film properties. We investigated two thin HfO₂ films deposited on Si substrate by two different methods: e-beam deposition and jet-vapor deposition. The study showed the unintended growth of SiO₂ at the Si interface in the e-beam deposited HfO₂ film sample.; Finally, it is shown that far UV spectroscopic ellipsometry with extended spectral energy is a promising tool for studies of wide bandgap materials and high-K dielectric materials.