TiB2 and ZrB2 diffusion barriers in GaAs Ohmic contact technology

Abstract

The transition metal diboride compounds, ZrB2 and TiB2, interposed between Ni/Ge/Au Ohmic contact metallization on n-type GaAs wafers and an overlying thick Au contact layer, have been investigated to evaluate their effectiveness in stabilizing the Ohmic contact by limiting the in-diffusion of Au. All of the metal layers were e-beam deposited except the ZrB2 which was rf-diode sputtered. The barrier layer thicknesses were 50 and 100 nm for the TiB2 and the ZrB2, respectively. Postdeposition alloying of the contacts was performed at 400, 425, or 450 °C. Auger electron spectroscopy depth profiling of the resultant Ohmic contacts demonstrates that the barrier layers effectively preclude penetration of Au to the Ohmic contact structure. Specific contact resistivities for such contacts are in the low 10−7 Ω cm2 range; although some degradation of the contact resistivity is observed after long term annealing, the values of resistivities do not exceed 1.5×10−6 Ω cm2 after 92 h at 350 °C.