X-ray metrology by diffraction and reflectivity

X-ray methods can provide measurements that, for certain parameters of great technological importance, are the most accurate and sensitive available. High-resolution X-ray Diffraction (HRXRD) has become a vital tool in the silicon industry with the use of silicon-germanium epitaxial layers in the construction of HBT devices. Compositions and thicknesses of both uniform and compositionally-graded Si-Ge and Si cap layers may be rapidly and accurately derived from HRXRD. X-ray Reflectivity (XRR) is an important method for the metrology of thin films in the range 1nm to 1000 nm. it measures film thickness, roughness and electron density, and it is routinely applied to both high-k and low-k dielectrics, hetereoepitaxial layers and amorphous metallic films. It is of particular importance in the process development of thin gate oxides (and oxynitrides) for which optical constants are very uncertain. A metrological measurement should be traceable to a national standards laboratory, and be readily standardizable using different vendors' equipment. We show how X-ray methods fulfil this requirement, since they depend simply upon measurement of traceable quantities and upon sound theories with no uncertain material parameters to be fitted. The widespread adoption of traceable measurements should be expedited by the development of NIST standards for reference samples, diffractometer calibration software certification and analytical procedures.