Residual stress measurements of high spatial resolution

Residual stresses in semiconductor and MEMS devices superposing functional and environmental loading are one of the crucial reliability issues as they can add significant stress levels leading finally to component damage. Most of routinely used stress measurement methods today allow stress measurements with only limited spatial resolution. The authors present approaches under development, which are aiming at stress measurements on micro- and nanoscale devices with proven spatial resolution. After a brief review comparing different methods under development, they authors focus on local stress measurements tools applied in their labs. The first method bases on stress release due to local material removal by a focuses ion beam. SEM images before and after ion milling captured in a FIB equipment are compared to each other by cross correlation algorithms. As a result, residual stresses are evaluated from measured stress relief deformation. The second method refers to EBSD techniques. Displacements of Kikuchi diffraction patterns within a mono-crystalline material area are used to map incremental values of residual stress. Application capability of both stress measurement methods are demonstrated by principal experiments. Measurement resolution, limitations and potential application fields are considered. As far as residual stress measurements are extremely sensitive to underlying stress hypotheses and stress extraction algorithms, both issues are discussed in more detail. In this regard emphasis is made on stress analysis at multi-layer systems. Measurements by the mentioned stress release technique are used to illustrate importance of stress extraction approaches to determine stress values. Finite element simulations are included to evaluate stress extraction algorithms.