Study On Characteristics Of Solid State Reaction And Contact For Metal/Ge System

As the scaling of the minimum feature size of complementary metal-oxide-semiconductor field effect transistors (MOSFET) continues, silicon is approaching its physical limits. Ge is a promising candidate to replace Si for future very-large-scale integration (VLSI) technology due to its higher carrier mobility compared to Si. In this thesis, we study on nickel germanide used as source/drain contact on Ge substrate and characteristics of multiple metal/n-Ge Schottky contact.1) The study on solid state reaction in Ni/Ge system. Ni, Ni0.95Pt0.05and Ni0.85Pt0.15are deposited on Ge substrate respectively. Then samples are annealed with Rapid Thermal Annealing (RTA) method in different temperatures to form nickel germanide. By measuring the sheet resistance of the samples annealed in systematic temperatures and comparing the SEM photographs, we find that the incorporated Pt retards the agglomeration of NiGe, therefore enhance the thermal stability of NiGe films. During the whole RTA window, NiGe is the only phase of nickel germanide, which is shown by the X-ray diffraction (XRD) measurements. The XRD results also show that by incorporating Pt, the texture of NiGe is changed during the formation. Further study shows that Pt atoms are mainly distributed at the top and bottom regions of the NiGe and the Pt incorporation provides better interface morphology, which are shown by Energy Dispersive X-ray Spectroscopy (EDX) results and X-ray Transmission Electron Microscope (XTEM) photographs. No big difference is found when the percentage of Pt atoms in targets changes from5%to15%. We believe that the small quantity of incorporating Pt has enlarged NiGe crystal lattice so that the d-spacing of NiGe(211) matches to Ge(220), leading to the change of NiGe texture to axiotaxy, which is the reason why thermal stability of NiGe films is enhanced.2) Study on electrical characteristics of metal/n-Ge Schottky contact. Electrodes of different metals like Pt, Cu, Co etc. are deposited on Ge substrateThen electrical characteristics of multiple metals/n-Ge are detected by Ⅰ-Ⅴ measurements, and the Schottky barrier height (SBH) and ideality factor for different samples are extracted by thermal-emission theory. We find that the Schottky barrier is nearly independent from the metal work function, which demonstrates that there is strong Fermi-level pinning in metal/n-Ge contact fabricated by sputtering metal on Ge substrate. By further calculation, we find that the charge neutrality level (CNL) is only0.11eV above the valence band (VB) for Ge, which agrees with conclusions of metal/n-Ge contact fabricated in other conditions.