Thin Solid Films 424 (2003) 115–119 0040-6090/03/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII:S0040-6090 Ž 02 . 00909-4 A shaft-loaded blister test for elastic response and delamination behavior of thin film–substrate system Xiaojing Xu , Christopher Shearwood , Kin Liao * a b b, School of Materials Engineering, Nanyang Technological University, Singapore 639798, Singapore a School of Mechanical and Production Engineering, Nanyang Technological University, Singapore 639798, Singapore b Abstract The elastic response of a thin film of photoresist deposited on a silicon wafer is studied by using a shaft-loaded blister test method developed recently. Experiment data are compared with an analytical solution. Results demonstrated that under shaft loading, the thin film underwent a pure bending mode at small deformation and gradually transformed to a pure stretching mode at larger deformation. The effect of residual stress on elastic response is also studied. The delamination of thin film from substrate can be successfully measured under displacement control mode by the shaft-loaded blister test.  2002 Elsevier Science B.V. All rights reserved. Keywords: Mechanics of thin film; Shaft-loaded blister test; Thin film; Delamination 1. Introduction Thin-layered structures of dissimilar materials have found increasing applications in many advancing tech- nologies. For instance, polyimide and photoresist films are commonly used as dielectrics and sacrificial layers in electronic packaging and microelectromechanical sys- tem (MEMS). Reliability concerns, such as interfacial delamination and subsequent rupture and failure of devices utilizing film–substrate systems, demand a bet- ter understanding of the mechanical performance of thin film–substrate systems. The pressurized blister test, also referred to as the bulge test, is one of the testing methods widely used to measure mechanical properties of thin films. However, application of the pressurized blister test is limited because of the complicated fluid control system and the difficulty of simultaneously measuring both blister height and pressure. Recently, a more convenient method, namely, the shaft-loaded blis- ter test, has been proposed, in which a transverse load is applied to a thin film by a mechanical system where the load-shaft displacement data is easily obtainable experimentally. A constitutive equation that is capable of predicting film elastic response from a pure bending *Corresponding author. E-mail address: askliao@ntu.edu.sg (K. Liao). to a pure stretching mode under such a loading situation has also been proposed w1–4x. It has been known that residual stresses are present in most film–substrate systems. Although, Jensen et al. have studied the effect of residual stresses in the pres- surized blister and numerically obtained the energy release rate and mixed modes w5x, the effect of residual stress on thin film response has not been considered in the previously proposed analytical solution w1–4x. In this paper, the effect of residual stresses in thin films on the mechanical response is studied analytically and the modified constitutive equation is compared with exper- imental data obtained by testing a photoresist film- silicon wafer system under a transversely applied shaft load. Finally, delamination behavior between thin film and substrate under cyclic shaft loading is studied and results will be presented. 2. Theory The loading configuration of the flexible thin film– substrate system is illustrated in Fig. 1. A thin flexible film of elastic modulus, E, Poisson ratio, n, and thick- ness, h, is deposited onto a rigid substrate with a blister radius, a. A transverse central load, P, is applied onto the film via a shaft. Linear elasticity requires the overall blister profile, w(r), be governed by w6x