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Spatially resolved Raman piezo‐spectroscopic stress analysis in CaMoO4 thin film grown on Si substrate

Confocal piezo‐spectroscopy was applied to analyze the residual stress distribution developed in a CaMoO4‐film/Si‐substrate system, based on the spectroscopic shift upon stress of the 879 cm–1 Ag Raman mode of CaMoO4. In the stress characterization, use was made of spectral line scans, as well as laser defocusing measurements. A preliminary spectroscopic calibration of the Raman band was performed with using a ball‐on‐ring flexural bending jig. As a result, a value of –1.4 cm–1/GPa was found for the biaxial piezo‐spectroscopic coefficient of the Ag Raman mode of CaMoO4. A probe deconvolution procedure was introduced in the effort to correct the convoluting effect due to the finite size of the laser probe, taking advantage of the measurement of the probe response function. A theoretical analysis of the edge‐stress effect was then carried out and, accordingly, the actual in‐depth stress distribution was deduced from the observed spectral variation. Compressive residual stresses appeared on the CaMoO4 film side, while tensile residual stress occurred in the silicon substrate, and both stress magnitudes pronouncedly decreased with increasing distance from the interface. The results indicated relief in lattice mismatch in the epilayer, and such a relaxation mechanism was discussed in the paper. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)