| AVS 56th International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS1+EM-MoA |
| Session: | Semiconductor Surfaces and Interfaces I: Ge and III-V's |
| Presenter: | J.S. Lee, University of California, San Diego |
| Authors: | J.S. Lee, University of California, San Diego S.R. Bishop, University of California, San Diego A.C. Kummel, University of California, San Diego |
| Correspondent: | Click to Email |
Finding a good passivant for Ge surface is critical for fabricating a Ge-based MOSFET device. Recent studies have shown that GeON or GeO2 interfacial layers can partially passivate the Ge/high-k dielectric interface and improve the electrical properties of the device. Introducing N (GeOxNy or Ge3N4) suppresses the Ge outdiffusion from the passivation layer into the high-k oxide layer at elevated temperatures, thereby reducing the post annealing density of interface states between Ge and high-k gate oxide. To minimize the density of interface states, the GeOxNy or Ge3N4 must be formed with a minimal dangling bond density, which is challenging in a thermal oxidation or nitridation process. To investigate the bonding and electronic structures of Ge-N and Ge-O surface species, in-situ scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) experiments were performed after oxidation and nitridation. Direct nitridation was carried out on Ge(100) using an electron cyclotron resonance plasma source, both at room temperature and at 500oC. The nitridation at room temperature generated nitride sites, O sites (from trace water) and Ge adatoms which pin the surface Fermi level. The Ge adatoms are created because both O and N displace Ge surface atoms in order to bond at high coordination sites. These Ge adatoms can be removed by high temperature annealing. Nitridation at 500oC produced a highly ordered Ge-N structure on the surface without O sites or Ge adatoms, but the Fermi level of the n-type surface was still pinned near the valence band probably due to the surface defects caused by plasma damage. Oxidation of Ge(100) was studied using a differentially pumped H2O dosing system and the results were compared with our previous study on O2 dosing of Ge(100). The H2O dosed surface showed dark –OH adsorption sites with very few Ge adatoms, while the O2 dosed surface had the equal densities of Ge adatoms and O sites. Annealing the H2O/Ge(100) surface to 300oC induces formation of bright Ge oxide sites which are slightly taller than Ge adatoms. However, both H2O and O2 dosing form GeO sites which are observed in STS to pin the Fermi Level. DFT calculations are being performed to determine the ordered nitride structure. In addition, the e-beam or ALD deposition of Ge3N4 or GeO2 are being studied since they may form passivation layers without Ge displacement, plasma damage, and GeO, thereby unpinning the Fermi level.