Accuracy of thickness measurement for Ge epilayers grown on SiGe/Ge/Si(100) heterostructure by x-ray diffraction and reflectivity

Abstract

High-resolution x-ray diffraction rocking curve (RC), x-ray reflectivity (XRR), and transmission electron microscopy (TEM) were used to characterize strained Ge epilayers grown on relaxed SiGe/Ge/Si(100) virtual substrates by reduced pressure chemical vapor deposition. The investigation focused on the reliability and accuracy of thickness measurement by these different techniques. The authors found that both XRR and RC could give reliable values that agree well with TEM results over a wide range of Ge epilayer thicknesses. The best-fit thickness from both XRR and RC is within ±5% of the TEM measurement for a thickness in the range of 10–120 nm, with XRR producing more accurate values than RC. However, neither RC nor XRR could give reliable results for very thin Ge epilayers ( 122 nm) due to surface roughening caused by strain relaxation.