Determination of interfacial roughness using X-ray scattering

Abstract

Crystal truncation rod (CTR) scattering is shown to be a powerful technique for determining interfacial roughness non-destructively. By measuring the decay of scattering away from a Bragg reflection in the surface direction an rms roughness of the surface or interface can be extracted. The authors obtain rms roughness values with an accuracy of {+-} 0.1 {angstrom}. Sensitivity to lateral length scale roughness ranges from the wavelength of the x-rays to between 1,000--10,000 {angstrom} depending on the instrument function and the specific truncation rod. The influence of different cleans, as well as the thermal oxidation process, on the Si-SiO{sub 2} interface is investigated. A hot water treatment prior to the thermal oxidation is shown to roughen the Si-SiO{sub 2} interface. CTR scattering results also show a smoothing of the interface as a result of the oxidation process even for as little as 60 {angstrom} of thermal oxidation. Comparison between AFM and CTR scattering gives a consistent picture of the relative roughness of the wafers, although the absolute numbers do not agree. The differences in the absolute values can be explained by the lateral roughness scale that the two techniques measure, indicating that it is at periodicities below {approx} 100 {angstrom} thatmore » the increased roughness observed by the x-ray is found. Crystal truncation rods are shown to be perpendicular to the surface and not along the crystallographic axes of a miscut crystal. It is shown that for a crystal terminated by a regular step array both an atomistic and a continuum description of CTR scattering give identical results. Furthermore, the atomistic approach is used to show that a diamond cubic surface with a miscut is inherently rough. Even for a small miscut the tilt of the CTR with respect to the crystallographic axes results in complications for measuring the rod intensity. The authors present schemes for determining the exact position of the CTR in reciprocal space and for measuring the miscut of a single crystal. These methods were applied to the measurement of CTR intensities of silicon(001) wafers with miscuts of 0.1 and 4 degrees.« less