Analytical electron microscopy of Al/TiN contacts on silicon for applications to very large scale integrated devices

Abstract

Aluminum contacts on silicon have been realized for very large scale integration applications by interposing a titanium nitride diffusion barrier. The TiN films have been prepared by implanting nitrogen ions on silicon wafers coated with titanium layers of different thicknesses (60,80, and 100 nm); by a subsequent annealing in vacuum, films ofTiSi 2 , from ° up to 75 nm thick, grow at the nitride/silicon interface. The AI/TiN/Si and AI/TiN/TiSi 2 /Si structures have been annealed at 600 ·C for 30 and 10 min, which in some cases results in barrier degradation, due to AI/Si interdiffusion. Cross-sectioned specimens of these contacts have been studied by analytical transmission electron microscopy (AEM) employing a Philips EM 400T microscope, equipped with a field emission gun. It has been found that, contrary to previous suggestions, the TiN film does not dissolve during the failure process, but retains its morphology and a sharp interface with the neighboring layers. Unlike scanning electron microscopy experiments, where the Al film must be removed after the barrier degradation to investigate the pits formed by the massive migration of Si into AI, AEM on cross sections allowed us to make an accurate structural and compositional characterization of the material filling these pits. In addition, when the anneaiing treatment does not result in the barrier failure, the migration of AI, Ti, and Si throughout the structure can be easily detected and analyzed.

A study of the failure mechanism of a titanium nitride diffusion barrier

“…8,9 These results indicate that TiN remains stable upon annealing but that the interdiffusion between Al and Si is dominant through shortcircuit paths in TiN such as grain boundaries or microcracks. [8][9][10][11]13 Another failure mechanism that has been suggested is that Si diffuses through TiN and forms eutectic liquid with Al. 12,13 However, one should note that the analysis around the spikes themselves has been very limited because it is impossible to perform chemical characterization in those local areas by using conventional, broad-beam analysis tools such as RBS or AES.…”

“…6 Although this provides a reasonable chemical consideration, several researchers also reported that the decomposition reaction does not proceed any further after the thin reaction layer forms, which implies that the decomposition reaction cannot be an immediate cause of spiking. [7][8][9] Armigliato et al showed that a TiN film retains its morphology after annealing at 600°C from a transmission electron microscopy ͑TEM͒ study, and Kotte et al inferred from the depth profiles of Auger electron spectroscopy ͑AES͒ that TiN barriers remain chemically intact throughout annealing and that Al, Si, and Ti diffuse, probably along grain boundaries, without interacting chemically. 8,9 These results indicate that TiN remains stable upon annealing but that the interdiffusion between Al and Si is dominant through shortcircuit paths in TiN such as grain boundaries or microcracks.…”

“…[7][8][9] Armigliato et al showed that a TiN film retains its morphology after annealing at 600°C from a transmission electron microscopy ͑TEM͒ study, and Kotte et al inferred from the depth profiles of Auger electron spectroscopy ͑AES͒ that TiN barriers remain chemically intact throughout annealing and that Al, Si, and Ti diffuse, probably along grain boundaries, without interacting chemically. 8,9 These results indicate that TiN remains stable upon annealing but that the interdiffusion between Al and Si is dominant through shortcircuit paths in TiN such as grain boundaries or microcracks. [8][9][10][11]13 Another failure mechanism that has been suggested is that Si diffuses through TiN and forms eutectic liquid with Al.…”

Nondestructive Method for Mapping Metal Contact Diffusion in In2O3 Thin-Film Transistors

“…24 One of the major drawbacks in using Al contacts is the formation of the native oxide and Al diffusion into the semiconductor material which can affect the contact reliability. 24−26 …”

Failure mechanism of a multilayer (TiN/Al/TiN) diffusion barrier between copper and silicon

“…One can intimately observe and study the condition of the interface, the formation of new phases via interfacial reaction, and can even estimate the concentration of the species diffusing through the interfaces at different depths. [19][20][21][22][23][24] …”