| Metallic diborides TiB2, ZrB2 and HfB2 were used for the formation of contacts integrated with ultra shallow junctions required in deep submicron devices in integrated circuits. The films were deposited by electron-beam evaporation on an oxide free surface of both p- and n-type Si. Rapid thermal processing (RTP) in N2 ambient was performed using temperatures up to 1100°°C and time up to 30s. Electrical characterization of the films was done using sheet resistance measurements, which show decreasing resistance with increasing thermal budget of the annealing processes. Test structures on p-type Si were fabricated to determine contact resistance before and after the annealing processes. The borides form ohmic contacts on p-type Si after deposition and improve their ohmic behavior after annealing; specific contact resistivity decreases with temperature. On n-type Si, the formation of Schottky diodes was determined by current-voltage (I-V) and capacitance-voltage (C-V) measurements for as deposited and annealed structures. A set of complementary material testing including x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS), cross-section transmission electron microscopy (TEM), and Rutherford Backscattering (RBS) was done to determine stoichiometry, composition, and crystallographic structure of the processed films. All boride films showed recrystallization, which increases with thermal budget of the annealing processes, as identified by XRD and by TEM with electron diffraction. Material studies show very high thermal stability of the diborides if their composition is stoichiometric. However, this stability deteriorates in nonstoichiometric layers, which leads to larger than desired B outdiffusion clearly detected by SIMS results. |
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