Polycrystalline sputtered Ta coatings on Si(100) substrates were thermally tested for I h at 585 degreesC, while their stress evolution and eventual delamination were observed in situ and in real-time using a recently developed synchrotron X-ray white beam technique. Films deposited at 'low' (0.26-0.67 Pa), 'intermediate' (0.80-0.93 Pa), and 'high' (1.06-2.00 Pa) Ar pressures exhibited severe, moderate, and no blistering, respectively. These results were explained by the attendant stress data, which indicated the development of high, moderate, and low maximum compressive stress in the low, intermediate, and high-pressure coatings, respectively. Additionally, the structure of the films was probed before and after thermal testing using X-ray diffraction in both grazing incidence and theta-2theta scanning geometries. It was determined that all coatings made a complete conversion to orthorhombic Ta2O5 after the 1 h thermal test, regardless of their deposition pressure. (C) 2003 Elsevier B.V All rights reserved.