For 45nm Copper Interconnect And Copper Contact Technology, Ultra-thin Diffusion Barrier Layer Research

When the feature size of the integrated circuits(IC) comes to 45nm node and beyond, the RC delay in the Cu interconnects is growing rapidly due to the scaling-down rules and thus presenting a big challenge to threaten the high speed and reliability of the semiconductor devices. To seek the possible solutions, the semiconductor industry has developed various kinds of new processes and novel structures to prohibit the increase of RC delay, which are mainly divided into two genres: to reduce the series resistance by adopting interconnect metals of low resistivity such as copper instead of traditionally used aluminum, and to lower the capacitance through using low-k dielectric such as SiOC instead of SiO₂. In this thesis, we mainly focused on the description of two aspects in improving the RC delay from the angle of suppressing the series resistance.The growth of ruthenium films was investigated by atomic layer deposition (ALD). It is reported and verified in our experiments that to grow the ruthenium films by ALD on various kinds of substrates is difficult. We tried some pretreatments to the to-be-deposited substrates, like introducing the water vapor flowing along the surface of substrates, dipping the substrates in to a AuCl₂ diluted solution to give the surface some activation by Au²⁺, pre-depositing an ultra-thin PVD ruthenium seed onto the substrates hence lowering the nucleation barrier for the formation of ruthenium grains, and having the surface of the substrates undergone several minutes of bombardment by low-energy Argon ions, et.al, so as to improve the surface chemistry for absorption of precursors and thus enhancing the grain density. Among all kinds of pretreatments, the Ar⁺ bombardment is so far considered to be the most effective and after 400 cycles of ALD process with the Ar⁺ pretreatment, a continuous and uniform ruthenium films on TaN substrate was achieved which is attested by cross-sectional transmission electron microscopy (XTEM) and other characterization methods. The Ru/TaN bi-layer stack, with combination of well conductive, directly platable Ru films and TaN films, the preeminent currently used diffusion barrier and adhesion promoter for the dielectrics, will pave the way for the seedless copper interconnects processing.Two bi-layer diffusion barrier systems, i.e, Ta/TaN and Ru/TaN by physical vapor deposition (PVD) in a Cu/NiSi direct contact structure were studied. Four point probe(FPP), X-ray diffraction(XRD), Auger electron spectroscopy(AES), in-depth profiling X-ray photoelectron spectroscopy(XPS), scanning electron microscopy(SEM), and transmission electron microscopy(TEM) were carried out to depict the structural characteristics and the thermal stability of the specimen. A sensitive electrical characterization method of Schottky Barrier Characterization combining with Schottky Barrier Hight (SBH) fitting and inverse current testing was also introduced to indirectly perceive the influences of copper through the diffusion barrier and NiSi layer on the interfacial characteristics. So far, there're no reports about the application of Ru/TaN stack as the diffusion barrier in Cu contact. Both the Ta/TaN and the Ru/TaN system grown by PVD were found to show excellent diffusion barrier performance during the high temperature annealing with an endurance of half an hour. With the proper diffusion barrier system such as Ta/TaN and Ru/TaN, the direct Cu contact on NiSi source/drain substrates can be used as a candidate for the promising application of plug-free process instead of tungsten plug in the copper metallization in the near future.