Diffusion Barrier Property of Sputtered Molybdenum Nitride Films for Dram Copper Metallization
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JONG-WAN PARK and JEONG-YOUB LEE Dep. of Metallurgical Engineering, Hanyang University, Seoul 133-791, KOREA
ABSTRACT Diffusion barrier property of sputtered molybdenum nitride films for DRAM copper metallization was investigated as a function of annealing temperature. Molybdenum nitride thin films on silicon remained stable upon annealing 650°C-30min, but h-MoSi 2 and t-MoSi 2 were formed after the heat treatment at 7001C and Mo 5 Si 3 phase was formed at 850°C. Increasing the annealing temperature decreased the stress of the r -Mo 2N/Si film down to about 0.8 X 10 '°dyne/cm 2 at 8001C due to the reduction of the intrinsic stress component. Copper films on silicon substrates separated by thin layers of molybdenum nitride remained stable during the heat treatment at 6001C, but they began to fail as a diffusion barrier after the heat treatment at 650 C, when molybdenum silicides and copper silicide were thought to be formed. On heating, Cu/! -Mo 2N/Si films were affected by thermal stress as due to the thermal expansion coefficient between copper and molybdenum nitride thin films. Furthermore, interlayer interactions between copper and silicon increased with increasing the annealing temperature. The interlayer reactions were investigated by Rutherford backscattering spectrometry, X-ray photoelectron spectrscopy and Nomarski microscopy.
INTRODUCTION Current semiconductor technology demands the use of low-resistivity metal layers for integrated circuit conduction lines and contact structures. In terms of device reliability, many studies have been concerned with preventing interaction between aluminum and silicon, but as alternative metallization schemes are explored, barriers to copper may become necessary[1,21. Transition metal nitrides are attractive candidates for copper diffusion barrier owing to their high conductivity, high stability and resistance to diffusion of foreign atoms[3,4]. Stoichiometric TiN and TaN have been extensively investigated and shown to be effective in this application[5,6]. More recently, molybdenum nitride films have been studied as hard coating[7,8], superconductor[9] and aluminum diffusion barrier[10] due to the above reasoning. However, up to date, characteristics of molybdenum nitride films as a copper diffusion 687 Mat. Res. Soc. Symp. Proc. Vol. 403 0 1996 Materials Research Society
barrier have not been established in the literature. Thus, in this study, diffusion barrier property of sputtered molybdenum nitride films was investigated. EXPERIMENTAL Molybdenum nitride films were deposited on p-type (100) single crystal silicon substrate by reactive dc magnetron sputtering using molybdenum metal target with 0.4 Nz/(Ar+N2) flow ratio at the substrate temperature of 4001C. The electrical and physical properties of the films were investigated so as to study thermal stability of molybdenum nitride films in variation with annealing temperature in the range of 600 -850'C for 30 min in N 2 ambient. In other to investigate the diffusion barrier behavior of the molybdenum nitride films, co
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