Thermal stability and nitrogen redistribution in the 〈Si〉/Ti/W–N/Al metallization scheme

Abstract

Backscattering spectrometry, Auger electron spectroscopy, and x-ray diffraction have been used to monitor the thin-film reactions and nitrogen redistribution in the (Si)/Ti!W-N/Al metallization system. It is found that nitrogen in the W-N layer redistributes into Ti after annealing at temperatures above 500 oc. As a consequence of this redistribution of nitrogen, a significant amount ofinterdiffusion between AI and the underlayers is observed after annealing at 550 oc. This result contrasts markedly with that for the (Si)/W-N/ AI system, where no interdiffusion can be detected after the same thermal treatment. We attribute this redistribution of nitrogen to the stronger affinity ofTi for nitrogen than W. If the Ti layer is replaced by a sputtered TiSi 2 3 film, no redistribution of nitrogen or reactions can be detected after annealing at 550 oc for 30min.

Amorphous Mo–N and Mo–Si–N films in microelectromechanical systems

“…The crystallization temperature depends on the alloy used, the elements and the composition, the impurities originating from the deposition process and the media in contact with the film. Sometimes crystallization starts when one of the film constituents (such as nitrogen) diffuses into an adjacent layer or evaporates out of the film 17,18 . We have not measured the crystallization temperature for Mo–N, but according to the literature it seems to behave very similarly to the more widely studied W–N 5,19 .…”

“…Sometimes crystallization starts when one of the film constituents (such as nitrogen) diffuses into an adjacent layer or evaporates out of the film. 17,18 We have not measured the crystallization temperature for Mo-N, but according to the literature it seems to behave very similarly to the more widely studied W-N. 5,19 Mo-N can be amorphous, either being nitrogen deficient 19 or nitrogen rich 20 with respect to Mo 2 N. If the original film composition is very close to Mo 2 N, the crystallization temperature appears to be about 480 • C, otherwise approaching or exceeding 700 • C. [19][20][21] Near 800 • C, unprotected Mo-N film starts to deliver nitrogen to the ambient. The same applies to W-N. 5 Mo-Si-N crystallizes at even higher temperatures, 11,18,22 at least when protected from oxidation or nitrogen loss during annealing, allowing extensive post-processing without significant structural or electrical changes.…”