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

Abstract In this investigation, we have fabricated Ta(Vb)/Si(111) and Cu/Ta(Vb)/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 (Rs). From electrical resistivity and SEM data, a minimum resistivity (99 μΩ cm) and well surface morphology at an optimum bias voltage (Vb=−50 V) was obtained for the Ta(Vb)/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(Vb)/Si(111) multilayer structure. According to our RBS, SEM and Rs 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(Vb)/Si(111) system annealed in N2 environment for 30 min. Formation of TaSi2 was observed at 700°C after the barrier failure using RBS spectra.