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Applied Optics

Applied Optics


  • Editor: Joseph N. Mait
  • Vol. 48, Iss. 2 — Jan. 10, 2009
  • pp: 155–160

Microstructure of M o / S i multilayers with B 4 C diffusion barrier layers

Ileana Nedelcu, Robbert W. E. van de Kruijs, Andrey E. Yakshin, and Fred Bijkerk  »View Author Affiliations

Applied Optics, Vol. 48, Issue 2, pp. 155-160 (2009)

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The growth behavior of B 4 C interlayers deposited at the interfaces of Mo / Si multilayers was investigated using x-ray photoemission spectroscopy, x-ray reflectivity, and x-ray diffraction measurements. We report an asymmetry in the formation of B 4 C at the B 4 C -on-Mo interface compared to the B 4 C -on-Si interface. X-ray photoelectron spectroscopy (XPS) depth profiling shows that for B 4 C -on-Mo the formed stoichiometry is close to expectation ( 4 1 ratio), while for B 4 C -on-Si it is observed that carbon diffuses from the B 4 C interfaces into the multilayer, resulting in nonstochiometric growth ( > 4 1 ). As a result, there is a discrepancy in the optical response near 13.5 nm wavelength, where B 4 C -on-Mo behaves according to model simulations, while B 4 C -on-Si does not. The as-deposited off-stoichiometric B 4 C -on-Si interface also explains why these interfaces show poor barrier properties against temperature induced interdiffusion. We show that the stoichiometry of B 4 C at the Mo-Si interfaces is connected to the structure of the layers onto which B 4 C is grown. Because of enhanced diffusion into the amorphous Si surface, we suggest that deposited boron and carbon atoms form Si X B Y and Si X C Y compounds. The low formation enthalpy of Si X C Y ensures C depletion of any B X C Y interlayer. Only after a saturated interfacial layer is formed, does further deposition of boron and carbon atoms result in actual B 4 C formation. In contrast to the off-stoichiometric B 4 C growth on top of Si, B 4 C grown on top of Mo retains the correct stoichiometry because of the higher formation enthalpies for Mo X B Y and Mo X C Y formation and the limited diffusion depth into the (poly)-crystalline Mo surface.

© 2009 Optical Society of America

OCIS Codes
(230.4170) Optical devices : Multilayers
(340.7480) X-ray optics : X-rays, soft x-rays, extreme ultraviolet (EUV)
(310.4165) Thin films : Multilayer design

ToC Category:
Thin Films

Original Manuscript: August 11, 2008
Revised Manuscript: November 12, 2008
Manuscript Accepted: November 19, 2008
Published: January 7, 2009

Ileana Nedelcu, Robbert W. E. van de Kruijs, Andrey E. Yakshin, and Fred Bijkerk, "Microstructure of Mo/Si multilayers with B4C diffusion barrier layers," Appl. Opt. 48, 155-160 (2009)

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