Metal/semiconductor interfaces studied by transmitted X-ray reflectivity

Buried metal/Si interfaces were studied by X-ray reflectivity (XR) for samples which have macroscopically thick metal overlayers with rough surfaces. XR under transmission geometry (transmitted X-ray reflectivity (TXR)) was conducted so as to avoid the troublesome effects caused by the thick and rough overlayers. A 40-mum-sized X-ray beam of short wavelength (lambda = 0.06nm) emitted from an undulator in a synchrotron radiation facility was used effectively. TXR of a [Au layer consisting of An fine particles]/Si interface indicates a sharp contrast to the conventional XR scattered from the Au layer surface: The former (TXR) shows a distinct specular reflectivity from the interface. However, the latter (XR) indicates very weak specular reflectivity above the critical angle due to the microscopic surface roughness of the overlayer. Quantitative analysis of diffuse scattering in TXR profiles yielded a precise electron density at the interface. Both the specular and diffuse TXR from a [liquid Ga]/Si interface support an intermediate layer of approximately 2nm thick. By considering the average electron density, it is most likely that Ga is sorbed to a large extent in the native oxide at unexpectedly low temperatures (<400 K).