THERMAL STABILITY OF Cu/Ta/ULTRA LOW k POROUS POLYMER STRUCTURES FOR MULTILEVEL INTERCONNECTS

Abstract

This paper reports a detailed study of the thermal stability of Cu (150 nm )/ Ta (25 nm )/ porous polymer (600 nm )/ Si structures for multilevel interconnects of the new generation integrated circuits. The samples were annealed at 400°C for different time periods and we then characterized using sheet resistance measurement, X-ray diffraction (XRD), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS) and cross-section transmission electron microscopy (TEM). It is found that the abrupt increase of the sheet resistance of the Cu film takes place after annealing at 400°C for 150 min. An accumulation of oxygen was observed near the Ta /dielectric interface and both oxygen and Ta were significantly diffused into the Cu films as well as the dielectric. It is revealed that the strain between Cu and Ta accelerates Ta diffusion into the pores of the porous polymer and the Ta diffusion coefficient was 0.05±0.001 nm 2/ s which is more than double of that obtained from the structure without Cu deposited (0.023±0.001 nm 2/ s ).