It is demonstrated that two kinds of soft X-ray spectroscopy are useful as nondestructive methods to investigate multilayer structures modified by interdiffusion or by chemical reaction of adjoining layers in depth direction. One is the total electron yield (TEY) spectroscopy involving angular dependence measurement. Using this method, it was found that in LiF/Si/LiF trilayers, the Si layers exhibited a characteristic similar to porous Si, and in CaF2/Si/CaF2 trilayers, it was found that CaF2 segregated through the Si layer. Moreover, it has been shown that the thickness of the top layer of a Mo/Si X-ray multilayer can be determined by analyzing TEY signals generated by the standing wave. The other is the soft X-ray emission spectroscopy involving spectral shape analysis. Using this method, it was found that in Mo/Si X-ray multilayers, the interdiffusion or chemical reaction giving rise to deterioration of reflectance character occurs in as-deposited samples as well as in heated samples. In antiferromagnetic Fe/Si multilayers, it was confirmed that there was no existence of pure Si layers, but insulating FeSi2 layers were present. This result suggests that the source of antiferromagnetic coupling is not conduction electrons but quantum wave interference.
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