Effect of in situ plasma oxidation of TiN diffusion barrier for AlSiCu/TiN/Ti metallization structure of integrated circuits

An oxygen plasma treatment of the TiN diffusion barrier prior to Al deposit ion of an AlSiCu/TiN/Ti structure is studied and compared to an air break p rocess in order to determine the reactions occurring at the Al/TiN interfac e as well as the mechanisms responsible for the improved barrier performanc e using an ex situ and an in situ oxygen plasma, respectively. Various expe rimental techniques such as grazing angle x-ray diffraction, elastic recoil detection and field emission scanning electron microscopy were used. The t ernary and quaternary phase diagrams were used to predict the phases formed . It is first observed that an oxygen plasma increases the oxygen concentra tion at the Al/TiN interface as well as in the TiN barrier. It is conjectur ed that first the oxygen reacts with Ti in order to form Ti oxides in the T IN grain boundaries and on the TiN surface. The Al film then reacts with th is Ti oxide layer in order to form an Al2O3 layer upon sintering which in t urn acts as an additional diffusion barrier at the Al/TiN interface. It is also determined that the Al2O3 phase formation is increased after an oxygen plasma treatment of the TiN diffusion barrier. This Al oxide layer as well as the Ti oxides in the TiN grain boundaries could;reduce the Al and Ti in termixing as observed by the reduction in the formation of TiAl3. The reduc ed Al diffusion in the barrier would then stop Si outdiffusion from the sub strate. In addition, the penetration of Si would also be blocked at the Al/ TiN interface by the Al2O3 layer. The decreased Si penetration in the upper layers in addition to the lower TiAl3 formation are the mechanisms propose d to explain the decreased formation of Ti(7)A(5)Si(12) after an in situ ox ygen plasma treatment of the TiN diffusion barrier. It is concluded that an oxygen plasma-treated TiN barrier is more efficient than an air-exposed Ti N one due to the lower degree of Ti7Al5Si12 formation which also explains t he reduced risks of junction spiking. The advantage of the in situ oxygen p lasma treatment is therefore related to better process control in addition to higher throughput. (C) 1999 American Vacuum Society. [S0734-211X(99)0430 2-4].