X-ray diffraction and reflectivity characterization of SiGe superlattice structures

The authors demonstrate the effectiveness of both X-ray diffraction and X-ray reflectivity in the structural characterization of semiconductor structures. By combining information from both techniques the abruptness of the interfaces for Si1-xGex structures, with x=0.1-0.57, may be determined. For superlattice structures with x<0.3 both types of interface were found to have a root mean square (RMS) roughness of 0.5+or-0.3 nm. For a Si/Si0.45Ge0.55 superlattice structure the interfaces are found to have differing roughnesses. For the SiGe-on-Si interface the RMS roughness is found to be 0.5+or-0.2 nm; however, the Si-on-SiGe interface has a larger value of roughness, 1.0+or-0.3 nm. This roughness at the Si-on-SiGe interface is found to be dependent on the Ge content of the layer and it is shown by transmission electron microscopy analysis to be long ranged (about 70 nm) and wavy at the interface.