In Situ Two‐Dimensional Residual Stress Characterization of Thin Films
Wai Jue Tan, Wadwan Singhapong, Arindam Majhi, Chris Bowen, Alexander J.G. Lunt, Hongchang Wang, Kawal SawhneyABSTRACT
The precise exploitation and efficient control of residual stresses are crucial for the development of high‐performance thin‐film optics. Multi‐beam optical sensors (MOS) have been widely used for in situ residual stress measurements; however, this only provides information on the average residual stress at a single position. To overcome this limitation, speckle‐based curvature optical metrology (SCOM) has been implemented at the multilayer deposition system (MDS) at Diamond Light Source. SCOM delivers two‐dimensional curvature mapping, which has enabled direct visualization of the variation of spatial residual stress and substrate deformation for the first time. Benchmarking of SCOM measurements against MOS reveals excellent agreement in the extracted curvature for a deformable mirror. Importantly, SCOM offers a significantly larger dynamic range, allowing accurate measurements under the extreme curvature conditions that are frequently encountered in thick, high‐residual stress films. This approach was also used to evaluate the residual stress evolution of a range of important materials, including Mo, Si and WSi 2 , which have been systematically investigated across varying deposition thicknesses and working pressures.