Bias sputtered Ta modified diffusion barrier in Cu/Ta( Vb)/Si(111) structures

Abstract

In this investigation, we have fabricated Ta( V b)/Si(111) and Cu/Ta( V b)/Si(111) systems using a DC bias sputtering technique at high Ar pressure (100 mTorr). For Ta/Si(111) system, tantalum layer was formed under various bias voltages ranging from 0 to −150 V. The films were characterized by Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM) and four-point probe sheet resistance measurements ( R s). From electrical resistivity and SEM data, a minimum resistivity (99 μΩ cm) and well surface morphology at an optimum bias voltage ( V b=−50 V) was obtained for the Ta( V b)/Si(111) system. The Ta films deposited under these conditions with 50 nm thickness are then used as a diffusion barrier in the Cu/Ta( V b)/Si(111) multilayer structure. According to our RBS, SEM and R s analysis, the Ta barrier layer formed under the controlled bias sputtering at high Ar pressure has demonstrated an improved Ta structure with excellent thermal stability up to 650°C for the Cu/Ta( V b)/Si(111) system annealed in N 2 environment for 30 min. Formation of TaSi 2 was observed at 700°C after the barrier failure using RBS spectra.