An expanding plasma process for thin metal films nitriding: reactivity and

structure of the surface correlated to MICROWAVE plasma parameters

 

I. Jauberteau1*, P. Goudeau2, J. L. Jauberteau1, B. Soulestin1,

M. Marteau2, M. Cahoreau2, J. Aubreton1

1UMR 6638 CNRS, SPCTS, Faculté des Sciences et des Techniques, F-87060 Limoges cedex, France

2UMR 6630 CNRS, SP2MI, UFR des Sciences, Bd3, Téléport 2, BP 179, F-86960 Futuroscope, France

* Corresponding author.

Received: 31 March 2006; revised version accepted: 02 July 2006

Abstract

The reactivity of molybdenum surface heated at temperatures as low as 673 K and exposed to (Ar-N2-H2) expanded microwave plasma is explained by the formation of a large amount of defects where nitrogen species pile up before diffusing in the metal. This effect is caused by the impact of the impinging active gaseous species such as ions and simple radicals on the molybdenum surface. Moreover, in contrast to binary gas mixtures, the plasma is stable and expands to long distance in ternary gas mixture containing large concentration of N2 and H2.

Investigation means such as secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron spectroscopy (TEM) are carried out to determine the composition, the crystallographic and morphologic structure of the molybdenum films after nitriding. (Ar-25%N2-30%H2) and (Ar-8%N2-10%H2) plasma exposures of thin molybdenum films up to 600 nm thick and heated at 873 K lead to nitrogen diffusion into the whole film thickness. A nitride compound of tetragonal-like bMo2N structure has formed whereas a low amount of pure bcc Mo phase is detected. The film consists of small columnar grains ranging in size from 20 nm to 30 nm in the growth direction.

Keywords: metal nitriding; surface reactivity; microwave plasma processes; molybdenum nitride.

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