| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 88 === Abstract
Cu is expected to be adopted in deep submicron ultra-large scale integration metallization due to its lower resistivity and better reliability than conventional Al alloys. Since copper diffuses fast in Si and introduce deep-level traps, a proper diffusion barrier is needed. The barrier should have high thermal stability, low resistivity, and good adhesion with Cu and substrate.
In this study, we investigate the diffusion barrier properties of TaN/Ti bilayers for Cu metallization in ULSI circuit device. The following structures are used:
SiNx /Cu(100nm) /TaN(10nm) /Ti(10nm) /SiO2(20nm) /Si
SiNx /TaN(50nm) /Ti(50nm) /SiO2(20nm) /Si
SiNx /TaN(20nm) /Ti(20nm) /SiO2(20nm) /Si
Copper and barriers were deposited by DC sputtering. Annealing was carried out in nitrogen at temperatures from 400 ℃ to 800 ℃ for 30 min. Sheet resistance was measured by a four-point probe method. Auger electron spectroscopy was used to evaluate the inter-diffusion across interfaces by the compositional depth profile. The phase identification of layers was performed by XRD . The microstructure was investigated by cross-sectional transmission electron microscopy with X-ray energy dispersive spectroscopy.
Sheet resistance measurement and microstructural characterization show that these structures have different behaviors after annealing. The barriers of Cu/TaN/Ti/SiO2/Si were failed after 650 ℃/30 min annealing as a result of barrier phase change. Sheet resistances of TaN(50nm) /Ti(50nm) /SiO2 /Si and TaN(20nm) /Ti(20nm) /SiO2 /Si increased after 450 ℃ and decreased after 500 ℃ to 800 ℃ annealing .
From these results, TaN(20 nm) is better than TaN(10nm) / Ti(10nm) on the thermal stability. Barrier was changed during annealing .It is suggested that nitrogen and oxygen elements play important roles on the thermal stability.
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