Simultaneous optical measurement of Ge-content and carbon doping in strained epitaxial SiGe films

We use a novel analytical technique, previously shown to be able to decouple germanium and boron contents, to measure simultaneously the germanium and carbon contents of a set of carbon-doped epitaxial SiGe films. The method is based on the use of ‘‘perturbation functions’’ to account empirically for the effects that the dopant has upon the fundamental dielectric functions of the material. To demonstrate the technique, a matrix of 10 wafers having variation in both germanium and carbon contents was analyzed. Neglecting the presence of carbon led to large errors in germanium content, whether measured optically or by X-ray diffraction (XRD). However, using the new method the thickness, germanium and carbon contents could be derived together and very good agreement was obtained between measurements on a production-grade optical metrology tool and measurements by secondary ion mass spectrometry (SIMS). To verify the production-worthiness of the approach used, results from two different production metrology tools (i.e. two Therma-Wave Opti-Probe 5220 tools) were compared and some repeatability testing was also performed. The method holds great promise for improving run-to-run process control for advanced epitaxy processes