Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

16B/2003G098

Depth profiling of interdiffused layers in Fe/Si multilayers
using standing-wave soft-X-ray fluorescence spectroscopy
Ryosuke HAMAMOTO, Masaki SUGAWARA, Shigeru ICHIKURA, Takeo EJIMAand Mihiro YANAGIHARA*
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Introduction
Fe/Si multilayers are widely studied from the aspect ofthe interlayer magnetic coupling. We have assigned themediating layer for the interlayer coupling to be an
amorphous FeSi2 layer of 0.7 nm thick resulted frominterdiffusion using soft-X-ray fluorescence (SXF)
spectroscopy [1]. However, if the interdiffused layers
have an asymmetric structure with respect to the Fe or Si
layer, the SXF technique provides an average of theequivalent silicide layers on both sides. For further
analysis of the interdiffusion layer the standing-wave
technique is promising as in the X-ray region. Antinodesof the standing wave generated in the multilayer under theBragg condition enhance the fluorescence locally, which
can differentiate a silicide layer from the equivalent one
on the opposite side.
Experimental
An Fe(3.0nm)/Si(1.9nm)/Fe(3.0nm) trilayer deposited
on a Mo(2.3nm)/B4C(2.7nm) multilayer of 20 bilayers
was prepared using a magnetron sputter system. Standing
wave is generated dominantly by the Mo/B4C multilayer,
while it is slightly modulated by the trilayer. Standing
wave was first confirmed to be present in the sample bymeasuring total photoelectron yield vs. incident photon
energy. The SXF experiment was carried out at BL-16B
using an SXF spectrometer of a flat-field focusing typeunder a resolution of about 0.4 eV at 100 eV.
Results
Figure 1 shows the Si L2,3 fluorescence spectra from theFe/Si/Fe trilayer at 136.1 eV for 22° and 28° angles ofincidence from the normal, where the latter angle was notunder the Bragg condition. A slight difference is foundbetween the two spectra in the shoulder region.
Differences between 22° and 28° in the fluorescenceintensity estimated by a curve fitting analysis for thesilicide layers are summarized in Table I. The signs ofFeSi2 and Si are different, whereas those of Fe3Si and Si
are the same. It is not reasonable because the FeSi2 layer
is closer to the Si layer than the Fe3Si layer. It must result
from the symmetric layer model. Figure 2 shows thedepth structure obtained from an analysis for the Si L2,3
fluorescence spectra measured for 20° at five photon
energies between 134 eV and 142 eV. The FeSi2 layer
above the Si layer is thinner than that below it, and viceversa for the Fe3Si layer. Therefore, it is ascertained thatthe interdiffused layer has an asymmetric structure. The

Table I. Relative changes in the SXF intensity for thesilicide layers between 22° and 28°.
Silicides
Change (%)

Fe3Si+13.5

FeSi2-17.6

a-Si+9.4

SiO2-4.6

origin of the asymmetric structure is though still underquestion, our result means that the standing wave SXF
technique is promising for interface analysis and thus
depth profiling.

Fig. 1. Si L2,3 SXF spectra from an Fe/Si/Fe trilayer for
22° and 28° angles of incidence at 136.1 eV.

Fig. 2. Depth structure of the Fe/Si/Fe trilayer. Standing
waves are also shown as absorbed energy for several E’s.
References[1] T. Imazono et al., Jpn. J. Appl. Phys. 43, 4327 (2004).
* m.yanagi@tagen.tohoku.ac.jp

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