Thermal Stability Study of Cu(MoN x ) Seed Layer on Barrierless Si

Abstract

This study reports the good thermal stability of a sputtered Cu(MoNx) seed layer on a barrierless Si substrate. A Cu film with a small amount of MoNx was deposited by reactive co-sputtering of Cu and Mo in an Ar/N2 gas mixture. After annealing at 560°C for 1 h, no copper silicide formation was observed at the interface of Cu and Si. Leakage current and resistivity evaluations reveal the good thermal reliability of Cu with a dilute amount of MoNx at temperatures up to 560°C, suggesting its potential application in advanced barrierless metallization. The thermal performance of Cu(MoNx) as a seed layer was evaluated when pure Cu is deposited on top. X-ray diffraction, focused ion beam microscopy, and transmission electron microscopy results confirm the presence of an ∼10-nm-thick reaction layer formed at the seed layer/Si interface after annealing at 630°C for 1 h. Although the exact composition and structure of this reaction layer could not be unambiguously identified due to trace amounts of Mo and N, this reaction layer protects Cu from a detrimental reaction with Si. The Cu(MoNx) seed layer is thus considered to act as a diffusion buffer with stability up to 630°C for the barrierless Si scheme. An electrical resistivity of 2.5 μΩ cm was obtained for the Cu/Cu(MoNx) scheme after annealing at 630°C.