Abstract

X-ray reflectivity measurements are commonly used to characterize the structure and morphology of surfaces, thin films and multilayers.^1-3 In most reflectivity measurements the scattering vector q is much smaller than the characteristic length scale for diffraction =2n/d, where d is the crystal lattice spacing. Therefore, the reflectivity measurements are insensitive to the crystal structure of the layers; the scattered intensity for multilayers occurs predominantly from the interfaces. It is this sensitivity to the interfacial structure that makes reflectivity measurements complementary to diffraction⁴ for characterizing multilayers. Nb/Si multilayers provides an instructive case because extremely smooth, as will as conformal and cumulative roughness cases can be realized by adjusting the sputtering conditions.⁵ We will discuss the quantitative analysis of the specular reflectivity from a series of Nb/Si multilayers sputtered at various Ar pressures. The multilayers were grown by dc magnetron sputtering onto sapphire substrates at ambient temperatures. The target-substrate distance was fixed at 9 cm and the Argon sputtering pressure was varied from 3 to 15 mTorr. This spans the range from high kinetic energy to nearly thermalized deposited atoms. The expected pressure for thermalization is ≈9 mTorr.

© 1994 Optical Society of America